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Optimization of CBCT image quality in implant dentistry Alawaji, Yasmine 2018

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  Optimization of CBCT Image Quality in Implant Dentistry by  Yasmine Alawaji  BDS, King Saud University, 2011  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF  Master of Science in THE FACULTY OF GRADUATE AND POSTDOCTORAL STUDIES (Craniofacial Science)  THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver)   March 2018  ÓYasmine Alawaji, 2018  ii Abstract Objectives: This study was conducted to optimize the CBCT image quality in implant dentistry using both clinical and quantitative image quality evaluation with measurement of the radiation dose. Materials and methods: A natural bone human skull phantom and an image quality phantom were used to evaluate the images produced after changing the exposure parameters (kVp and mA). A 10x5 cm2 FOV was selected for average adult. Five scans were taken with varying kVp (70 kVp, 75 kVp, 80 kVp, 85 kVp, 90 kVp) first at fixed 4 mA. After assessment of the scans and selecting the best kVp, nine scans were taken with varying mA (2 mA, 2.5 mA, 3.2 mA, 4 mA, 5 mA, 6.3 mA, 10 mA, 12 mA) and the optimal kVp was fixed. A dosimetry index phantom was used to measure the absorbed dose for each scan setting. Quantitative image quality was assessed for noise, uniformity, artifact added value, contrast-to-noise ratio, spatial resolution and geometrical distortion. A clinical assessment of implant related anatomical landmarks was done in random order by two blinded examiners. Results: The absorbed dose was reduced with reduction of exposure settings. The quantitative image quality values were acceptable at variable exposure settings. The anatomical landmarks of the maxilla had good quality at all different kVp settings. To produce good image quality, the mandibular landmarks demanded higher exposure parameters than maxilla. Conclusion: Changing the exposure parameters does not necessarily produce higher image quality outcomes but does affect the radiation dose to the patient. The image quality could be optimized for implant treatment planning at lower exposure settings and dose than the default settings.   iii Lay Summary The study was done to enhance the quality of the scans of the cone beam computed tomography (CBCT) machine to be used for dental implants. The scans were taken at different radiation exposure parameters, the peak kilovoltage (kVp) and the milliampere (mA). The corresponding absorbed dose was measured for each scan. Three types of phantoms were used: image quality phantom, dosimetry phantom and real human skull. The scans were evaluated for clinical value of important structures used for dental implant treatment planning. Several physical parameters were used to evaluate the quantitative image quality, including the noise, uniformity, contrast, resolution, artifacts and distortion. High quality scans could be achieved at low radiation dose and exposure parameters.   iv Preface This research was done and written by the author under the supervision of Dr. Nancy Ford. The clinical assessment of the images was done by research committee members: Dr. David MacDonald and Dr. George Giannelis. The positioning of image quality and dosimetry index phantoms was done with some help from Ms. Celina Li.  The assessment of the quantitative image quality was done by the author. The analysis of the point spread function (PSF) and the geometrical distortion were done by Dr. Nancy Ford and the author using MATLAB. The scripts were written by Elham Abouei and Dr. Nancy Ford. The second chapter of this dissertation is planned to be submitted for publication.   v Table of Contents  Abstract ............................................................................................................................................................. ii Lay Summary ................................................................................................................................................... iii Preface .............................................................................................................................................................. iv Table of Contents............................................................................................................................................... v List of Tables .................................................................................................................................................. viii List of Figures ................................................................................................................................................... ix List of Abbreviations ...................................................................................................................................... xiv Glossary .......................................................................................................................................................... xvi Acknowledgements ........................................................................................................................................ xvii Dedication ..................................................................................................................................................... xviii Chapter 1: Introduction .................................................................................................................................... 1 1.1 Cone Beam Computed Tomography (CBCT) use in Dentistry ............................................................. 1 1.2 Dosimetry ........................................................................................................................................... 1 1.2.1 CBCT dose as compared to conventional radiography ..................................................................... 2 1.2.2 Dose measurement in dental CBCT ................................................................................................ 3 1.2.2.1 Dose measurement using SEDENTEXCT Dosimetry index (DI) phantom .............................. 4 1.3 Quantitative image quality .................................................................................................................. 5 1.3.1 Noise and uniformity ...................................................................................................................... 6 1.3.2 Artifact added value (AAV) ............................................................................................................ 7 1.3.2.1 Extinction artifact ................................................................................................................... 7 1.3.2.2 Beam hardening artifact.......................................................................................................... 7  vi 1.3.3 Contrast-to-noise ratio (CNR) ......................................................................................................... 8 1.3.4 Geometrical distortion .................................................................................................................... 8 1.3.5 Spatial resolution ............................................................................................................................ 8 1.3.5.1.1 Polymer line chart inserts, line pairs/mm (lp/mm) .............................................................. 9 1.3.5.1.2 Point Spread Function (PSF) ............................................................................................. 9 1.3.5.1.3 Modulation transfer function (MTF) .................................................................................. 9 1.4 Other artifacts ................................................................................................................................... 10 1.4.1.1 Ring artifact ......................................................................................................................... 10 1.4.1.2 Misalignment artifacts .......................................................................................................... 10 1.4.1.3 Motion artifact ..................................................................................................................... 10 1.5 CBCT in Implant dentistry ................................................................................................................ 10 1.6 Clinical image quality ....................................................................................................................... 12 1.6.1 Standard reference images ............................................................................................................ 13 1.6.2 Reject analysis .............................................................................................................................. 13 1.6.3 Systematic audit using established clinical image criteria .............................................................. 13 1.7 Research objectives........................................................................................................................... 13 Chapter 2: Experimental Methods and Results.............................................................................................. 15 2.1 Materials and methods ...................................................................................................................... 15 2.1.1 CBCT machine ............................................................................................................................. 15 2.1.2 Data acquisition protocol .............................................................................................................. 15 2.1.3 Dosimetry ..................................................................................................................................... 16 2.1.4 Quantitative image quality ............................................................................................................ 17 2.1.5 Clinical image quality ................................................................................................................... 22 2.2 Results .............................................................................................................................................. 24 2.2.1 Dose measurement ........................................................................................................................ 24  vii 2.2.2 Quantitative image quality assessment .......................................................................................... 24 2.2.3 Clinical Image Quality Assessment ............................................................................................... 25 Chapter 3: Discussion ...................................................................................................................................... 36 3.1 Conclusion........................................................................................................................................ 43 3.2 Future research ................................................................................................................................. 43 Bibliography .................................................................................................................................................... 45 Appendix A Figures ...................................................................................................................................... 49 A.1 Maxillary anatomical Landmarks at different kVp......................................................................... 49 A.2 Mandibular anatomical landmarks at different kVp ....................................................................... 52 A.3 Maxillary anatomical landmarks at different mA settings: ............................................................. 55 A.4 Mandibular anatomical landmarks at different mA settings: .......................................................... 57   viii List of Tables  Table 1-1: Effective dose for dental radiography, SEDENTEXCT 2011 (10) .......................................... 3 Table 1-2: ICRP 103, 2007 recommended for tissue weighting factors in head and neck region (4) ........ 4 Table 2-1: Selected anatomical landmarks commonly used for pre-surgical implant planning ............... 23 Table 2-2: Quantitative image quality values at different kVp............................................................... 29 Table 2-3: Quantitative image quality values at different mA ............................................................... 29 Table 3-1: Recommended kVp specific to the task in implant treatment planning ................................. 42   ix List of Figures  Figure 1: Flow Chart illustrates the sequence of assessment and optimization of the image quality ....... 16 Figure 2: a) D1 phantom and thimble ionization chamber, b) IQ phantom, c) PAN DXTTR positioned in the FOV to scan the maxillary arch ....................................................................................................... 17 Figure 3: a) Lower segment of PMMA cylinder with uniform density, b) Five ROIs used to measure the noise and uniformity ............................................................................................................................. 18 Figure 4: Different inserts to measure CNR, a) Air, b) Al, c) PTFE, d) POM, e) LDPE ........................ 19 Figure 5: a) Lower segment of PMMA with a slice with 2.0 mm x 3.0 mm gaps uniformly distributed, b) two line profiles were plotted to measure the geometrical distortion ..................................................... 20 Figure 6: a) and b) two rectangular ROIs were used to measure the AAV around the insert’s rods ........ 21 Figure 7: a) Spatial resolution bar patterns with voxel spacing, b) PSF insert: metal wire suspended in air ............................................................................................................................................................. 22 Figure 8: Dose measurements at different kVp ..................................................................................... 26 Figure 9: Dose measurements at different mA. ..................................................................................... 26 Figure 10: CNR at different kVp .......................................................................................................... 27 Figure 11: CNR at different mA ........................................................................................................... 27 Figure 12: Resolution (0.26 mm) at 10% MTF ..................................................................................... 28 Figure 13: Maxillary assessment at different kVp ................................................................................. 30 Figure 14: Mandibular landmark assessment at different kVp ............................................................... 31 Figure 15: Nasopalatine canal and nasal spine at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ................................................................................................................... 32 Figure 16: Superior and inferior lingual foramina at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ................................................................................................................... 32  x Figure 17: Maxillary landmarks assessment at different mA ................................................................. 33 Figure 18:  Mandibular landmarks assessment at different mA ............................................................. 34 Figure 19: Nasopalatine and nasal spine at different mA settings, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3, g) 8 mA, h) 10 mA, i) 12 mA ............................................................................... 35 Figure 20: Superior and inferior lingual foramina, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA .................................................................................................. 35 Figure 21: Maxillary sinus septum at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ..................................................................................................................................... 49 Figure 22: Arterial anastomosis at the right sinus wall at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp .............................................................................................................. 49 Figure 23: Arterial anastomosis at the left sinus wall at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp .............................................................................................................. 50 Figure 24: Interproximal bone between teeth #13, 14 at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp .............................................................................................................. 50 Figure 25: Buccal plate thickness at tooth #23 at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ................................................................................................................... 50 Figure 26: Buccal plate thickness at midpoint apicocoronally of tooth #22 at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ................................................................................ 51 Figure 27: Buccal plate thickness at the crest of tooth #21 at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp .................................................................................................. 51 Figure 28: Nasal spine and incisive canal at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ................................................................................................................................ 51  xi Figure 29: Inferior alveolar canal (right side) at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ............................................................................................................................ 52 Figure 30: Mental foramen (Left side) at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ..................................................................................................................................... 52 Figure 31: Buccal plate thickness at the crest of tooth #43 settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ................................................................................................................................ 52 Figure 32: Buccal plate thickness of tooth #42 at midpoint apicocoronally at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ................................................................................ 53 Figure 33: Buccal plate thickness of tooth #41 apically at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp .......................................................................................................... 53 Figure 34: Interproximal bone between #33, 32 at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ................................................................................................................... 53 Figure 35: Superior and inferior lingual foramina at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ................................................................................................................... 54 Figure 36: Interalveolar medial foramen (left side) at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp ................................................................................................................... 54 Figure 37: Interalveolar lateral foramen (right side) at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp .............................................................................................................. 54 Figure 38: Maxillary sinus septum, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA ...................................................................................................................... 55 Figure 39: Arterial anastomosis at the right sinus wall, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA ....................................................................................... 55  xii Figure 40: Arterial anastomosis at the left sinus wall, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA .............................................................................................. 55 Figure 41: Interproximal bone between teeth #13, 14, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA .............................................................................................. 55 Figure 42: Buccal plate thickness at tooth #23, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA ........................................................................................................ 56 Figure 43: Buccal plate thickness at midpoint apicocoronally of tooth #22, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA.......................................................... 56 Figure 44: Buccal plate thickness at the crest of tooth #21, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA ....................................................................................... 56 Figure 45: Nasal spine and incisive canal, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA ............................................................................................................... 56 Figure 46: Inferior alveolar canal (right side), a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA ........................................................................................................ 57 Figure 47: Mental foramen (Left side), a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA.................................................................................................................... 57 Figure 48: Buccal plate thickness at the crest of tooth #43, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA ....................................................................................... 57 Figure 49: Buccal plate thickness of tooth #42 at midpoint apicocoronally, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA.......................................................... 58 Figure 50: Buccal plate thickness of tooth #41 apically, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA ....................................................................................... 58  xiii Figure 51: Interproximal bone between #33, 32, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA .................................................................................................. 58 Figure 52: Superior and inferior lingual foramina, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA .................................................................................................. 58 Figure 53: Interalveolar medial foramen (left side), a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA .................................................................................................. 59 Figure 54: Interalveolar lateral foramen (right side), a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA .............................................................................................. 59      xiv List of Abbreviations AAOMR The American Academy of Oral and Maxillofacial Radiology AAE AAV American Academy of Endodontics Artifact Added Value Al Aluminum ALARA As Low As Reasonably Achievable CBCT Cone beam Computed Tomography CNR Contrast-to-Noise Ratio CT Computed Tomography DAP Dose Area Product DI Dosimetry Index DRLs Diagnostic Reference Levels EAO The European Association for Osseointegration  FDA Food and Drug Administration  FFT Fast Fourier Transform  FOV Field Of View FWHM Full Width at Half Maximum Gy Gray ICRP International Commission on Radiological Protection  IQ Image Quality kVp Peak Kilovoltage LDPE Low Density Polyethylene  xv lp Line Pair LSF Line Spread Function mA MilliAmpere MGV Mean Gray Value MSCT Multi-Slice Computed Tomography MTF Modulation Transfer Factor PMMA Poly Methyl Methacrylate POM Polyoxymethylene or Delrin PSF Point Spread Function  PTFE Polytetrafluoroethylene  ROI Region Of Interest Sv Sievert TLDs Thermoluminescent Dosimeters WT Tissue Weighting factor  xvi Glossary Alveoantral anastomosis Anastomosis between the infraorbital and posterior superior alveolar arteries at the lateral wall of maxillary sinus Deterministic effects The effects from the x-rays where is no effect occurs below a certain threshold and the severity of the effect depends on the received dose (1) Inferior lingual foramina Foramina located at posterior side of symphysis. Inferior foramina located below genial tubercle (2) kVp The maximum voltage applied across the electrodes of an x-ray tube during exposure (1) Lateral interalveolar foramina Foramina located between the mandibular lateral incisor and canine (2) Medial interalveolar foramina Foramina located between the mandibular central and lateral incisors (2) Superior lingual foramina Foramina located at posterior side of symphysis. Superior lingual foramina are located above genial tubercle (2) Stochastic effects Probability of effect occurrence as result from radiation dose regardless the specific threshold of dose (1)     xvii Acknowledgements I have been honored to be supervised by Dr. Nancy Ford. I am very grateful for the continuous guidance and being approachable whenever I needed throughout this research conduction. I appreciate the smooth conduction of the study with the right pace that worked for my combined program with clinical degree in periodontics.   I would like to thank my committee members Dr. David MacDonald and Dr. George Giannelis for the cooperation, for all the valued comments and guidance.    I owe particular thanks for Ms. Celina Li for assistance in positioning the image quality and dosimetry phantoms during the scans of CBCT. The funding for this project was through a University of British Columbia Faculty of Dentistry Research Equipment grant.   Lastly but not least, I’d like to thank my loving parents and family for their endless support, guidance and encouragement   xviii Dedication   This thesis is dedicated to each person who seeks implant therapy and wondered:  “Is the x-ray you’re taking harmless? or is it going to affect me?” 1 Chapter 1: Introduction 1.1 Cone Beam Computed Tomography (CBCT) use in Dentistry CBCT is a three-dimensional imaging modality that was approved by the Food and Drug Administration (FDA) for dental use in 2001 (3). The use of CBCT in dentistry has increased over the last few years due to the increased use of implants. The CBCT can be taken at different fields of views (FOV). Large FOV could cover the entire maxillofacial or craniofacial regions that are required for maxillofacial trauma, pathology, and orthodontic use. Medium size FOV can be used for implant treatment planning. Small FOV are mostly used in endodontics. The use of CBCT as compared to conventional 2-dimensional imaging modalities has several advantages as it allows cross-sectional assessment in three dimensions, and the dimensional accuracy is superior to conventional imaging modalities. The main disadvantage as compared to intraoral radiography and panoramic radiographs is the increased radiation dose (3). The three fundamental principles of the International Commission of Radiological Protection (ICRP) are: justification, optimization and application of dose limits. These principles can be achieved by optimization of CBCT specifically to the clinical task to obtain a diagnostic image quality at the lowest possible dose. The optimization of CBCT image quality was done in literature for both clinical and quantitative image qualities. The optimization can also include the measurement and monitoring of the dose to achieve the lowest possible dose.    1.2 Dosimetry Dosimetry means the monitoring, measurement, device and method of quantifying the radiation dose. Ionizing radiation is always associated with risk as there is not a dose that is considered absolutely safe for humans. The adverse effect from radiation could be either “deterministic effects” caused by direct killing or affected function of cells or “stochastic effects” caused by mutation that could lead to cancer or heritable issues. A threshold of 100 mGy absorbed dose is considered to be too low to cause clinical  2 functional impairment of tissues as concluded from clinical and biological data (4,5). This includes both single dose and annual accumulation. There are several types of dose measurements that can be defined as follows: Absorbed dose: “is the energy absorbed from ionizing radiation per unit of mass of any type of matter”. The quantity of absorbed dose is averaged over the volume of tissue to correlate it with stochastic effects to that specific tissue. The unit of measurement is Gray (Gy).  D=!∈!#, where D is the absorbed dose, d∈ is the energy from ionizing radiation, dm is the mass.  Effective dose: represents the stochastic health effect of the whole body as it sums the tissue weighted equivalent dose in all body tissues and organs. The effective dose is measured in units of Sievert (Sv). It is considered as the best estimate of the radiation risk. 𝐸 = ∑ 𝑊𝜏	𝑋	𝐻𝜏, , where E is the effective dose, W𝜏:	weighting factor for each tissue, H𝜏 is the equivalent dose. Equivalent dose is the absorbed dose in the volume of specific tissue or organ (4) Dose Area Product (DAP): is the product of the beam area and the absorbed dose. It can be measured using ionization chamber over a large area (1). This measurement is related to the x-ray tube output and not related to patient dose as opposed to the absorbed dose and effective dose which are related to patient dose. This dose was included as it is the most applicable and routinely used dose measurement in the dental practice. It can be used to monitor the radiation dose level of the imaging modality as compared to national or international diagnostic reference level (DRL).  1.2.1 CBCT dose as compared to conventional radiography Some studies in the literature attempted to quantify the effective dose form the CBCT using tissue weighting factors published in either ICRP 2007 or ICRP 1999. The contribution to the effective dose from different organs are mostly from the salivary gland, thyroid gland, red bone marrow and remainder organs (6).  The average worldwide annual normal background radiation is 2.4 mSv per person (5). The  3 introral radiograph has effective dose that ranges from 0.66 to 18.47 µSv depending on the film speed, x-ray tube and the exposure settings (5,7). The dose increased with use of dental CBCT as an imaging modality in dentistry (Table 1-1) (5). The dose of CBCT has wide range among different machines and different FOV. The effective dose of CBCT for an average adult ranges from 84 µSv	for small FOV to 212	µSv in large FOV (8). The selection of the smallest possible FOV and the optimization of the dose based on the task is required (9). The radiographs are indicated only after thorough clinical examination and attaining a complete medical and dental history of the patient. Optimization and limiting of the dose should be done by quality control of equipment, adjustment of dose parameters, limit the exposure to unnecessary organs by use of lead apron and thyroid collar. Also, digital radiography reduces the dose as compared to conventional films (5).  Table 1-1: Effective dose for dental radiography, SEDENTEXCT 2011 (10)           1.2.2 Dose measurement in dental CBCT Radiation dose should be kept As Low As Reasonably Achievable (ALARA) as a principle concept in medical imaging. The dose measurement in dental radiography can be done using DAP. It gives an indication of the dose level in x-ray beam as well as the irradiated area. Most CBCT provide DAP Dental radiographic modality Effective dose, 𝜇Sv Intraoral Radiograph <1.5 Panoramic Radiograph 2.7-24.3 Cephalometric radiograph <6 CBCT (Dentoalveolar) 11-674 CBCT (Craniofacial) 30-1073 MSCT maxilla-mandibular region 280-1410  4 automatically after exposing the radiation. If not provided, the dentist is responsible to coordinate with a medical physicist to monitor the dose used. The effective dose, although considered as the best dose to estimate the radiation risk, cannot be measured directly and has to be calculated from other easily measureable doses. Effective dose can be measured by multiplying the absorbed dose by the weighting factor of tissues/organs. The Tissue Weighting (WT) factors in the head and neck region are listed in (Table 1-2) (4,10) Table 1-2: ICRP 103, 2007 recommended for tissue weighting factors in head and neck region (4)  Tissue or organ ICRP 103 WT red bone marrow 0.08 thyroid 0.04 skin 0.01 bone surface 0.01 salivary gland 0.01 brain 0.01 oral mucosa 0.0086 muscle 0.0086  1.2.2.1 Dose measurement using SEDENTEXCT Dosimetry index (DI) phantom The Dosimetry Index (DI) phantom was developed by the European Union medical exposures directive as part of the safety and efficacy of a new and emerging dental x-ray modality (SEDENTEXCT) project and is commercially available (SEDENTEXCT DI; Leeds Test Objects, Boroughbridge, UK). It consists of six stacks of poly methyl methacrylate (PMMA) slices. The density of the PMMA is close to the density of water (1.20 ± 0.01g/cm3) to simulate the human tissue density, which is mostly composed of  5 water. The DI phantom has an average adult head size (diameter: 160 mm x height: 176 mm). It was designed to accommodate different types of detector systems that include ionization chamber, Thermoluminescent detectors (TLDs), or Gafchromic film. Four ionization chamber plates are located at different levels in the phantom. The dimensions of two chamber plates are (diameter: 160 mm x height: 22 mm) and two plates are (diameter: 160 mm x height: 44 mm). The plates have 5 holes to insert the ionization chambers. Blank PMMA fillers can fill unused holes in the ionization chamber plates.  The dose can be measured using an ionization chamber or TLDs as described by SEDENTEXCT project. Two indices were proposed to measure the dose. In index 1, the dose can be measured along the diameter of SENDENTEXCT phantom and the mean of measurements is calculated. For index 2, the dose is measured at the center and periphery of the phantom to calculate the on-axis as well as off-axis exposures (1). 1.3 Quantitative image quality  A quality control program was developed by the SEDENTEXCT European Union Medical Exposures directive to standardize the use of dental CBCT. It ensures that the dental CBCT is used for images with proper diagnostic value and protects the patient from unneeded radiation exposure. The program includes testing of the equipment, control of patient dose, quantitative image quality assessment and performance of the display screen. The program aims to produce diagnostic image quality at the lowest possible dose. The SEDENTEXCT developed phantoms to perform various measurements specific to dental CBCT. Some of the measurements are considered essential to be tested by the medical physicist while other measurements are recommended (10). The SEDENTEXCT image quality (IQ) phantom was manufactured by (SEDENTEXCT IQ; Leeds Test Objects Ltd, Boroughbridge, UK). The phantom consists of cylindrical PMMA. The size of the phantom approximates an average adult size (diameter: 160 mm x height: 176 mm). The density of the PMMA is (1.20 ± 0.01 g/cm3). The upper section of the  6 phantom is composed of seven cylindrical columns, each with a diameter of 35 mm and height of 131 mm. Six columns are located around the periphery of the phantom and one column is in the center. Different test inserts for measuring image quality (diameter: 35 mm x height: 20 mm) are positioned inside the PMMA columns at different positions and levels to allow scanning of all of the different test inserts. The lower section of the phantom (diameter: 160 mm x height: 45 mm) is composed of a PMMA slab with uniform density. 1.3.1 Noise and uniformity Noise can be defined as random fluctuations in the image intensity. Noise represents either inconsistent reduction or increase in gray values of the image. It can be quantified as the standard deviation from the mean gray value. There are several types of noise in the reconstructed image. Noise could be due to round-off errors (electrical noise), quantum noise (photon count noise), or scintillator structures (detector electronics). The noise in dental CBCT images is higher than computed tomography (CT) due to lower mA. The increase in the mA means an increase in quantity of radiation, which overcomes the fluctuation in the image intensity and results in smoother images (10,11). Another source of noise is the scattered radiation. Scatter is caused by photons that deviate from original path between the source and detector after the interaction with matter. The scatter correlates with the size of the detectors as the larger the detector, the higher the probability of detection the scattered radiation. This scatter results in a reduction of contrast of soft tissue and affects the gray values of other tissues (11). Uniformity is the difference in the mean gray value (MGV) between the center of the image and the peripheries. Noise and uniformity can be measured at the lower part of image quality cylinder where density is uniform (1.20 ± 1.00 %). (10).  7 1.3.2 Artifact added value (AAV) The artifact can be defined as a visualized structure in the image that does not exist in the investigated object. It often appears in the image as streaks, shadows or line structures along the projection lines (11). There are several sorts of artifacts in the image: 1.3.2.1 Extinction artifact  Extinction artifact is also called “missing value artifact”. It results from highly absorbing objects, such as prosthetic crowns or implants as compared to the surrounding tissues. The surrounding tissues in direct contact with the prosthetic crowns or implants would suffer missing values in the reconstruction process. These highly absorbing objects affects the signals in the detector and record values of adjacent structures close to or equal to zero. The thicker the object or presence of multiple objects would lead to more severe artifact (11,12).  1.3.2.2 Beam hardening artifact The low energy rays of the polychromatic spectrum emitted by an x-ray source is subjected to considerable absorption after passing through an object. The x-ray beam becomes harder and contains higher energy making the gray value darker as compared to less dense structures. In three-dimensional reconstructions, the hardening of the x-ray beam is back-projected and results in dark streaks, i.e. beam hardening artifact. Titanium, although considered a light metal, results in substantial beam hardening at the standard kilovoltage range of CBCT (11,12).  In the SEDNETEXCT IQ phantom, two inserts are used to measure the metal artifact added value. Each insert has three 5.0 mm diameter rods made of titanium, that are embedded in PMMA forming a line (10). The selection of titanium as material to test the AAV in the SEDENTEXCT phantom was due to the increased use of implants in dentistry (13).  8 1.3.3 Contrast-to-noise ratio (CNR) Contrast is the ability to distinguish between different gray values of various objects in the image. Five inserts in the IQ phantom are used to measure the contrast made of five materials with different densities: Polytetrafluoroethylene (PTFE), Polyoxymethylene (POM) or Delrin, low density polyethylene (LDPE), Aluminum (Al), and air. Each insert has five rods with different diameters: 1.0, 2.0, 3.0, 4.0, and 5.0 mm (10). The gray values of the rods can be compared to the PMMA background. The aluminum and air have the highest contrast and are easily distinguishable. Other materials, POM, LDPE, and PTFE have a lower range of contrast. The use of a range of inserts with variable contrast in assessment of image quality replicates the use of dental materials with variable CNR including bone grafts, membranes, crowns, etc.  1.3.4 Geometrical distortion The CBCT three-dimensional reconstructed images are isotropic as the imaged objects have the same value when measured from different directions. The CBCT dimensional accuracy was tested in many studies reported in the literature. The dimensional difference between the produced image and the actual object was found to be not clinically significant (14,45). In the image quality phantom, the lower section of PMMA cylinder has a slice with 2.0 mm x 3.0 mm depth gaps, distributed uniformly. The distance between the gaps is 10 mm. Any deviation from the known distance between the gaps indicates dimensional distortion of the image (10). 1.3.5 Spatial resolution The spatial resolution is the ability of the imaging modality to differentiate two small objects with high contrast in the image. It can be measured in the image quality phantom by qualitative and quantitative methods using the polymer line chart insert and point spread function respectively. Spatial resolution is an essential parameter in the quality assurance program (10). Spatial resolution is among the most  9 important parameters of image quality especially in the dental field where fine details are meaningful. The spatial resolution in CBCT images are influenced by the two-dimensional detector, three-dimensional reconstruction, patient movement, as well as exposure settings (15). 1.3.5.1.1 Polymer line chart inserts, line pairs/mm (lp/mm) Visual assessment of the lp/mm is used to qualitatively assess the spatial resolution (15). In the IQ phantom, two inserts are along the Z-direction and in the XY plane. Each insert consists of alternating discs of Al and polymer. The spacing between the line pairs are: 1.0, 1.7, 2.0, 2.5, 2.8, 4.0 and 5.0 lp/mm (10). The line pairs can be counted for the visible pairs per mm. Different devices were compared for the visible pairs and found to be visible in less than (3 lp/mm  ) in all dataset (16). An alternative approach suggested by Pauwels et al., is to evaluate the inserts using a (0-5) score based on the identification of adjacent pairs, geometrical appearance of the lines, and the sharpness of the lines (16).  1.3.5.1.2 Point Spread Function (PSF) The PSF can be measured using a 0.25 mm diameter wire made of stainless steel and suspended in air with high contrast. The pixel values across the cross-section of the image of the wire can be plotted. The resulting distribution can be used to calculate the Full Width at Half Maximum (FWHM) (1,10). 1.3.5.1.3 Modulation transfer function (MTF) MTF is the spatial frequency of the imaging system and considered the essential metric to measure the limiting spatial resolution in objective or quantitative manner (1,15). It can be calculated using either PSF or line spread function (LSF). It can be calculated as the modulus of the Fourier transform of either PSF or LSF. The MTF values quoted are at frequencies of 50% or 10% of modulation initial value (1). The spatial frequency at 10% of modulation initial value is most commonly used as it is the limiting resolution for the human naked eye. MTF values reported in literature using different devices and FOV ranges from 0.5-2.3 cycles per mm (15).   10 1.4 Other artifacts Other kinds of artifacts that could affect the image quality and alter the interpretation of the images include ring artifacts, motion artifacts and misalignment artifacts. These types of artifacts are not measured as part of the image quality assessment as they are difficult to reproduce and measure. They are not included as measurements in the quality assurance program by SEDNETEXCT. 1.4.1.1 Ring artifact Concentric rings can be detected around the axis of rotation. They result from a defect or uncalibrated detector elements (11).  1.4.1.2 Misalignment artifacts This artifact results from misalignment of either source, object or detector causing inconsistency in the backprojection operation (11). 1.4.1.3 Motion artifact Motion artifacts could result from either movement or misalignment of the object (patient). The movement could be small that results in blurring, or could be large that results in a double image or ghost image. The resolution of CBCT is high and any motion could affect the image quality detrimentally (17). 1.5 CBCT in Implant dentistry The indication of cross-sectional imaging modalities, such as CBCT, in implant dentistry was subject to controversy among different organizations around the world. The European Association for Osseointegration (EAO) stated that CBCT use in implant dentistry is indicated only if the site cannot be adequately evaluated using conventional radiography (5). On the other hand, the American Academy of Oral and Maxillofacial Radiology (AAOMR) stated that CBCT should be used in implant treatment planning (9). The selection of imaging modalities is divided into three steps according to AAOMR:  11 initial assessment, pre-operative and post-operative imaging. Initial assessment includes overall assessment of the remaining dentition, abnormalities and pathologies. Panoramic radiograph is recommended for the overall assessment supplemented with intraoral radiographs. CBCT or other cross-sectional modalities are not indicated for initial assessment. Pre-operative assessment is done at the stage of pre-surgical implant planning. It includes assessment of the morphology, orientation, local anatomy, pathology and plan to match prosthetic needs. The use of conventional radiographs during pre-operative assessment is often inadequate to achieve most of these needs. Cross-sectional imaging is indicated in this stage of implant planning to match the needs. CBCT usually has lower cost and dose as compared to other cross-sectional modalities as CT. These factors make CBCT the modality of choice for implant planning. CBCT is also indicated for implant site development as in block grafts, bone augmentations, and maxillary sinus augmentation, in addition to assessment of healing of bone grafts prior to implant placement. In post-operative assessment, the assessment of implants after placement is required to confirm the position and for follow up treatment evaluations. If no signs or symptoms of complications are present, the intraoral radiographs should be adequate for the task. The use of CBCT is indicated only if altered sensation, or implant mobility is present. If implant retrieval is indicated after thorough assessment and diagnosis of implant failure, CBCT should be considered prior to retrieval of the implant (18).  The involvement of some anatomical landmarks during implant treatment could lead to serious or even life-threatening complications. Hemorrhage in the floor of the mouth is considered to be a life threatening complication due to airway obstructions (19). Involvement of the anteroalveolar vessels at the lateral wall of maxillary sinus could lead to hemorrhage if the operator failed to identify the vessels pre-operatively and planned to avoid or manage the hemorrhage (20). Iatrogenic injuries to neurosensory disturbances at variable degrees were reported to be associated with implant placement. Intraoral  12 imaging was associated with 30% of neurosensory disturbances, panoramic radiographs with 50%, long cone periapical radiographs 48%, while CBCT was associated with the least disturbances equal to 10%. It is important to note that the use of CBCT has helped to reduce, but has not eliminated, iatrogenic complications (21). Limitation of the FOV as small as necessary is required. This would limit the radiation dose to the patient and avoid unnecessary radiation risk (5). In addition, interpretation of the entire volume is required when using CBCT, so the larger the volume, the higher the responsibility of the clinician, who should be knowledgeable in interpreting any possible pathology included in the volume (18). 1.6 Clinical image quality The assessment of clinical image quality is a subjective task required in optimization, comparison of different imaging systems or dose reduction studies. This assessment of clinical image quality is necessary to ensure the production of images with adequate diagnostic quality and should be a part of the quality assurance program. The assessment can be done by assessing each image individually which is called “absolute visual grading analysis”, or by comparing two images, known as “relative visual grading analysis”. Metric assessment of the images can be done using an ordinal scale, such as Likert’s scale, a commonly used method in medical imaging. This scale could be labeled or not labelled. It can be also used with or without a reference image. It can be used with three-point scale, five-point scale, etc. (22). A five point Likert’s scale is the most commonly used scale in medical imaging. A score of three or above often represents a positive result (23,24). Three methods of assessment of clinical image quality, as suggested by the SEDENTEXCT project are the use of standard reference images with high quality for comparison, reject analysis from unacceptable CBCT images, or systematic audit of CBCT images as compared to certain clinical image quality criteria.  13 1.6.1 Standard reference images The image quality is compared to high quality standard images in this method. It is an established method of monitoring the shift from an optimal image quality. It was suggested by the European Union to have standard images specific to each machine to compare with. The optimal reference image quality could be different however from an adequate image quality to the diagnostic task. For this reason, it is suggested that the reference clinical image should match the diagnostic task.  1.6.2 Reject analysis This method could be done either prospectively or retrospectively using the scans that have unacceptable image quality and attempting to identify the reason. Rejected images can be calculated as a percentage of the overall images. The European guidelines on radiation protection in dental radiology in 2004 suggested that rejected images be classified according to ability of interpretation into “Excellent”, “Acceptable” and “Unacceptable” categories. The UK health protection agency in 2010 recommended a minimal target of ≤5% of “unacceptable images”.   1.6.3 Systematic audit using established clinical image criteria The visual assessment of anatomical characteristics is well established in assessment of CT but their relevance to dental CBCT is scarce. Some studies have attempted to establish several anatomical landmarks for assessment of clinical image quality. However, there is no well-established criteria to compare with to date (10).  1.7 Research objectives The motivation of this thesis is to: 1) Apply ALARA principle and optimize CBCT images in implant treatment and pre-surgical planning at the lowest possible dose.   14 2) Obtain a diagnostic image quality at the lowest possible dose using comprehensive evaluation that includes clinical and quantitative image quality assessments. 3) Obtain the lowest possible dose for the full arch CBCT scans that is mostly required in routine as well as in the fully guided digital implant planning.  15 Chapter 2: Experimental Methods and Results 2.1 Materials and methods 2.1.1 CBCT machine A dental CBCT scanner (CS 9300, Carestream Health, Inc., Rochester, NY, USA) at the Faculty of Dentistry, University of British Columbia was used for the scans. A 10x5 cm2 FOV was selected in this study as it is a commonly used FOV in implant planning. The default setting for this FOV for an average adult patient is 90 peak kilovoltage (kVp), 4.0 milliampere (mA), 6.20 sec and a voxel size of 180 µm.  2.1.2 Data acquisition protocol Three types of phantoms were used in this study for three types of assessments: clinical image quality assessment, physical image quality assessment and dosimetry. The CBCT scans were taken at five different tube potentials, 90 kVp, 85 kVp, 80 kVp, 75 kVp, and 70 kVp. Other parameters were fixed at 4.0 mA, 6.20 sec and a voxel size of 180 µm. The scans were taken using each phantom separately following the same protocol of exposure settings. A comprehensive analysis of dosimetry, quantitative and clinical image quality of the images was done to select scans with good image quality at the lowest possible kVp and dose. After selection of the optimal kVp, scans were taken at 9 different tube currents, 2 mA, 2.5 mA, 3.2 mA, 4 mA, 6.3 mA, 8 mA, 10 mA, and 12 mA at fixed kVp, voxel size and time. All scans were evaluated for the dosimetry, quantitative image quality and clinical image quality to select the good quality images at the lowest possible mA and dose. The sequence of the protocol to optimize the image quality is illustrated in (Figure 1).  16  Figure 1: Flow Chart illustrates the sequence of assessment and optimization of the image quality  2.1.3 Dosimetry  The absorbed dose was measured at the five different kVp settings, 70 kVp, 75 kVp, 80 kVp, 85 kVp, and 90 kVp. Other parameters were fixed at 4 mA, 6.20 sec, and a voxel size of 180 µm. After selection of the kVp of choice, the dose was measured at nine different mA settings 2 mA, 2.5 mA, 3.2 mA, 4 mA, 5 mA, 6.3 mA, 8 mA, 10 mA and 12 mA. The kVp setting was fixed at the selected kVp. The DI phantom was used (SEDENTEXCT DI, Boroughbridge, UK) (Figure 2a). The phantom is composed of six stacks of PMMA plates that simulate human tissue density (1.20±0.01g/cm3). The cylinder size was of head size (160 mm diameter and 176 mm height). The dose measurement method was done according to the SEDENTEXCT project (1). Five different regions along the phantom diameter were selected to measure the dose. The FOV was at the level of the center slice of the DI phantom. A thimble ionization Scans at different mA(2-12 mA)Scans at different kVp(70-90 kVp)Default exposure settings CBCT imageDosimetry assessmentQuantitative image quality assessment Optimized image kVpDosimetry assessment Quantitative image  quality assessmentOptimized ImageClinical Image quality  assessmentClinical Image quality Assessment  17 chamber was placed into a hollow column at each of selected five regions at the level of the center slice of the phantom. Two measurements of the dose using the thimble ionization chamber were taken at five different regions along gradient of dose profile. Each of the selected regions were positioned at the center of 10x5 cm2. The average of measurements was used to calculate the absorbed dose (Eq. 1). Eq. 1: DI1=∑ 𝐃𝐢𝟓𝐢;𝟏𝟓   Figure 2: a) D1 phantom and thimble ionization chamber, b) IQ phantom, c) PAN DXTTR positioned in the FOV to scan the maxillary arch  2.1.4 Quantitative image quality  The IQ phantom was manufactured by Leeds Test Objects Ltd. (SEDENTEXCT, Boroughbridge, UK). The phantom is composed of a cylinder made of PMMA with density close to human tissues (1.20	±	0.01	g/cm3). The phantom represents the head size of an average adult (160 mm diameter x 176 mm height). The phantom contains different test objects located at different heights to allow scanning them simultaneously (Figure 2b). Five essential physical image quality parameters were used in the assessment of physical image quality of each scan, including noise/uniformity, CNR, AAV, geometrical distortion, and spatial resolution. The analysis was done using Image J software (NIH Inc, Bethesda, Maryland, USA).  18  Noise/Uniformity: the standard deviation was measured in 5 circular Regions Of Interest (ROIs) of the lower segment of the PMMA cylinder where the density is uniform (1.20 ± 1.00 %). The mean of the five standard deviations were used as the value of the noise (Figure 3). The uniformity was measured by subtracting the four peripheral ROIs from the central circular ROI using (Eq. 2). Eq. 2: Uniformity==1 − ?@ABCDEFDG	–	@ABIDGJKLDGMN@ABIOOP ?Q × 100,	  Figure 3: a) Lower segment of PMMA cylinder with uniform density, b) Five ROIs used to measure the noise and uniformity   CNR: five different materials with different contrasts were arranged in 5 circular rods. Insert rods are made of Al, PTFE, POM or Delrin, LDPE, and Air at five different diameters ranging from 1 to 5 mm (Figure 4). The contrast was measured for each material as compared to MGV of the PMMA background using (Eq. 3). Eq. 3: CNR=|@ABOMFDGJMNU@ABIOOP|V/X(Z[OMFDGJMN\Z[IOOP)  19  Figure 4: Different inserts to measure CNR, a) Air, b) Al, c) PTFE, d) POM, e) LDPE   Geometrical distortion: the lower segment of PMMA cylinder contains a slice with 2.0 x 3.0 mm depth gaps distributed uniformly. Two line profiles perpendicular to each other were plotted to measure the geometrical distortion using MATLAB software (Mathworks, Natick, Massachusetts). The actual distance between voids was 10 mm. Any deviation in the measurements between the voids from the actual distance is considered geometrical distortion (Figure 5).  20  Figure 5: a) Lower segment of PMMA with a slice with 2.0 mm x 3.0 mm gaps uniformly distributed, b) two line profiles were plotted to measure the geometrical distortion  AAV: two metal inserts with three 5-mm diameter rods made of titanium and located perpendicular to each other were used (Figure 6). Two rectangular ROIs adjacent to the rods were measured to calculate the metal artifact value as compared to the MGV of background using (Eq. 4). Eq. 4: AAV= MGVabcdefgc − MGVh@@a  21  Figure 6: a) and b) two rectangular ROIs were used to measure the AAV around the insert’s rods   Spatial Resolution: The spatial resolution was measured using both quantitative and qualitative methods. The qualitative method was done using two polymer line chart inserts located along the Z-direction and XY-plane. The spacing of the line pairs are: 1.0, 1.7, 2.0, 2.5, 2.8, 4.0, and 5.0 lp/mm (Figure 7a). The line pairs clearly seen at a certain spacing were considered the qualitative measurement. The spatial resolution was calculated quantitatively using the PSF following the method described by Abouei (45). The PSF insert contains a 0.25 mm diameter wire made of stainless steel and suspended in air (Figure 7, b). A square ROI was placed around the wire and the resulting distribution was plotted using MATLAB software. The FWHM was calculated. The PSF was used to calculate MTF using the fast Fourier transform (FTT). The spatial resolution was calculated using the frequency at 10% of MTF (Eq. 5).  Eq. 5: Resolution= 𝟏𝟐∗𝐋𝐏𝟏𝟎%𝐌𝐓𝐅   22  Figure 7: a) Spatial resolution bar patterns with voxel spacing, b) PSF insert: metal wire suspended in air  2.1.5 Clinical image quality A PAN DXTTRâ natural manikin (Dentsply Rinn, York, Pennsylvania, USA) with a dry human skull embedded into resin was used (Figure 2c). The phantom is mounted on a metal tripod with wheel base adjustable up to 5’6” height. The extraoral landmarks of the phantom are accurate to position the skull using the Frankfort and midsagittal planes. The clinical image quality assessment was done through evaluation of selected essential anatomical landmarks that involves vital structures in both maxilla and mandible. Nine maxillary and ten mandibular structures were selected based on the anatomy of the skull phantom, and are listed in (Table 2-1). These structures are required to be assessed at pre-surgical implant planning to avoid complications and to select the proper surgical technique.       23 Five images were taken of each arch at five different kVps (70 kVp, 75 kVp, 80 kVp, 85 kVp, and 90 kVp). Two examiners evaluated the clinical image quality in a random order using a 5-point Likert scale (22) (Excellent, Good, Adequate, Poor, Undetectable). The examiners who performed the assessment were blinded to the parameters of the scans and are an experienced oral and maxillofacial radiologist and an experienced periodontist. Randomized order of the images was generated using MATLAB software, version 2014 (Mathworks Inc., Natick, Massachusetts, USA). Excellent, good and adequate scores of detecting and tracing the anatomical landmark in three-dimensional assessment were considered as high image quality. Each examiner did the examination separately using the same monitor and under the same lighting conditions. The assessment of different kVp was done twice by each examiner and they were given the choice of changing the brightness and contrast of the images.  Table 2-1: Selected anatomical landmarks commonly used for pre-surgical implant planning Maxillary anatomical landmarks Mandibular anatomical landmarks Nasal spine Interalveolar lateral foramen (right side) Incisive canal  Interalveolar medial foramen (left side) Buccal plate thickness at tooth #21 at the crest  Inferior lingual foramen Buccal plate thickness at tooth #22 at midpoint apico-coronally Superior lingual foramen Buccal plate thickness at tooth #23 apically Interproximal bone height between teeth #33, 32 Interproximal bone height between teeth #13 and 14 Buccal plate thickness of tooth #41 apically Antroalveolar anastomosis at lateral maxillary sinus wall (left side) Buccal plate thickness of tooth #42 midpoint apico-coronally Antroalveolar anastomosis at lateral maxillary sinus wall (right side) Buccal plate thickness of tooth #43 crestally  Mental foramen left side Sinus septum Tracing of the Mandibular canal (Right)  24 The images at different kVp were evaluated for the best clinical and quantitative image quality at lowest possible dose. Then, nine images of each arch were taken at nine different mA settings, 2 mA, 2.5 mA, 3.2 mA, 4 mA, 5 mA, 6.3 mA, 8 mA, 10 mA and 12 mA. The images were assessed for the clinical, quantitative image quality following the same protocol used to assess images at different kVp.   2.2 Results 2.2.1 Dose measurement The radiation absorbed dose increased with increase in peak kilovoltage and tube current settings. The dose measurements at the five selected regions along the phantom profile at all exposure settings are represented in (Figure 8) and (Figure 9). The exposure settings of choice were selected based on the lowest possible dose that have good clinical as well as quantitative image quality. The default settings of 90 kVp and 4 mA had a dose equal to 1.9 ± 0.3 mGy. Thus, the average dose of the selected settings of 85 kVp and 3.2 mA was 1.2 ± 0.6 mGy. This resulted in reduction of dose by around 0.7 mGy. 2.2.2 Quantitative image quality assessment The noise as measured by the standard deviation from the mean gray value increased with decrease in both kVp and mA. The uniformity had the best value at 70 kVp among different kVp settings. When uniformity was measured at different mA, it had the best value at 4 mA. AAV had the best result with lowest value at 90 kVp. After assessment of AAV at different mA settings, the best value was found at 4 mA. CNR had the best values at 85 kVp for Al, PTFE, and Air. 80 kVp had the best value for materials with low contrast, the LDPE and POM. CNR had the vest value at 12 mA for all materials except Air as it had the best value at 8 mA (Figure 10, Figure 11). Spatial resolution and geometrical distortion did not differ with variable exposure settings (Figure 12). Quantitative image quality values of different kVp settings are listed in (Table 2-2) and at different mA settings in (Table 2-3).  25 2.2.3 Clinical Image Quality Assessment The landmarks that had a score of 3 or more were considered to have good image quality. The viewers evaluated the anatomical structures for the clarity of identification as well as tracing the structures in all three-dimensional cross-sections. The evaluated maxillary landmarks had good quality at all different kVp settings from highest kVp at 90 kVp to lowest at 70 kVp. The overall subjective evaluation of mandibular landmarks had good quality at 85 and 90 kVp. The inferior alveolar canal was clearly seen at three different cross-sections. However, the tracing of the landmark continuously in any plane was impossible at all settings. The 85 kVp was selected as the optimal kVp as it is the lowest possible kVp that worked for the maxillary and mandibular landmarks. The clinical assessment of both maxillary and mandibular landmarks at different kVp are shown at (Figure 13, Figure 14). Sample images are shown at different kVp settings (Figure 15, Figure 16). After changing the mA at fixed 85 kVp setting, the clinical assessment of maxillary landmarks had good quality at different mA from 3.2 mA and above. The inferior alveolar canal was still not possible to trace continuously for all different mA settings. The buccal thickness of lower right canine had poor visibility at 6.3, 2.5 and 2 mA. The clinical assessment of maxillary and mandibular landmarks at mA are illustrated in (Figure 17, Figure 18). A sample of clinical images at different mA settings are shown (Figure 19, Figure 20). The optimal mA setting was 3.2 mA where all maxillary and mandibular landmarks had good quality. Thus, 85 kVp and 3.2 mA were the finally selected settings based on the clinical assessment of image quality. All the study images of anatomical landmarks are listed in appendix A.  26  Figure 8: Dose measurements at different kVp   Figure 9: Dose measurements at different mA.   27  Figure 10: CNR at different kVp   Figure 11: CNR at different mA   28   Figure 12: Resolution (0.26 mm) at 10% MTF   29  Table 2-3: Quantitative image quality values at different mA mA 2 2.5 3.2 4 5 6.3 8 10 12 Noise (SD) 157.5 140.3 121.7 97.1 98.4 95.1 79.6 70.7 65.8 Uniformity -35.9 -54.7 26.8 84.9 79.5 52.3 34.9 -18.4 -27.5 Geometrical Distortion 1st line ±𝐒𝐃 10.0 ±0.3 10.1 ±0.3 10.1 ±0.4 10.0 ±0.3 10.1 ±0.4 10.1 ±0.2 10.1 ±0.1 10.0 ±0.4 10.0 ±0.1 2nd line ±𝐒𝐃 10.0 ±0.5 10.0 ±0.4 10.0 ±0.4 10.0 ±0.5 10.0 ±0.4 10.0 ±0.5 10.0 ±0.4 10.0 ±0.4 10.0 ±0.3 Artifact 1 243.6 379.1 417.8 397.9 521.9 412.2 441.0 356.3 422.0 Artifact 2 288.8 249.6 227.4 298.8 282.7 265.9 276.4 297.1 177.0 LPP/mm 1.8 1.8 1.8 1.9 1.8 1.9 1.9 1.9 1.9 Resolution(mm) 0.28 0.27 0.28 0.27 0.28 0.27 0.27 0.27 0.26  Table 2-2: Quantitative image quality values at different kVp kVp 90 kVp 85 kVp 80 kVp 75 kVp 70 kVp Noise (SD) 88.1 97.1 115.3 131.9 152.7 Uniformity 81.5 84.9 80.7 82.9 85.6 Geometrical Distortion 1st line±𝐒𝐃 10.0±0.5 9.9±0.4 10.0±0.3 9.9±0.3 10.0±0.3 2nd line±𝐒𝐃 10.0±0.4 10.0±0.4 10.0±0.4 10.0±0.5 10.1±0.3 Artifact 1 331.0 397.9 370.6 452.9 457.8 Artifact 2 164.2 168.1 192.7 227.3 282.4 LPP/mm 1.7 1.8 1.8 1.9 1.9 Resolution (mm) 0.29 0.27 0.28 0.27 0.27   30  Figure 13: Maxillary assessment at different kVp   31   Figure 14: Mandibular landmark assessment at different kVp   32  Figure 15: Nasopalatine canal and nasal spine at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 16: Superior and inferior lingual foramina at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp  33  Figure 17: Maxillary landmarks assessment at different mA   34       Figure 18:  Mandibular landmarks assessment at different mA   35  Figure 19: Nasopalatine and nasal spine at different mA settings, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3, g) 8 mA, h) 10 mA, i) 12 mA   Figure 20: Superior and inferior lingual foramina, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA    36 Chapter 3: Discussion The three fundamental principles of ICRP regarding the use of medical radiation exposure include the justification, optimization and the application of the dose limit as there is no radiation dose considered to be harmless (4). The effective dose of CBCT as compared to intraoral radiography is increased by around 600 times (4). This makes the justification for CBCT use over conventional radiographic modalities necessary. The AAOMR recommended using the CBCT only after obtaining the complete dental history, examination and using the conventional radiographs during screening and initial examination. The CBCT use is indicated mainly during the pre-surgical planning. Few indications are recommended for the use of CBCT post-implant treatment such as to confirm the violation of anatomical structures, or to assess the site prior to implant removal, etc. (18). The use of CBCT in pre-surgical implant treatment planning includes selecting the suitable implant size, direction of the implants, and identifying the need for site preparation (bone augmentation, maxillary sinus augmentation, etc.). The local anatomy requires careful examination and identification of local vital structures. The prosthetically-driven planned implant position, however, can be highly critical in dimensions and proximity to vital structures with minimum safety zone that necessitates high accuracy in implant position. Methods used to plan implant locations utilizing the CBCT scans includes conventional implant guides, or digital implant guides. The conventional implant guides require wax-up of missing teeth or duplication of the denture. A radiopaque radiographic marker can be used to indicate the planned implant location and/or direction in the guide to be used during CBCT scan and utilized during implant placement. The digital implant planning can be either partially or fully guided planning. It requires merging of the CBCT scan with an intraoral digital scan of the teeth, if present, as well as the oral soft tissues or the scan of a denture in fully edentulous arch. The shift to use fully guided implant planning has increased in the past few years (25). The accuracy of fully guided implant placement over  37 conventional or free-hand placement had controversial results across different studies but mostly reported to be similar or superior to free-hand placement (25,26). The additional advantages of digitally planned guided surgeries are to facilitate the pre-surgical planning for extraction of remaining teeth, bone reduction, implant placement as well as immediate loading. The smile line can also be incorporated to dictate the amount of bone reduction needed for prosthetic reasons (27,28). Cross-arch FOVs are required for the digital implant planning to achieve accurate merging of the CBCT scan with an intraoral scan or denture scan. The indication of this large FOV as compared to single site FOV, however, is controversial due to the increased dose to the patient that may not be justified for the need (29,30). If the CBCT images could be optimized at lower doses, then the ethical reason could be justified for this indication. However, the interpretation of larger scans will still be necessary for medicolegal concerns (31).  The reduction of CBCT dose can be done by modifying several factors such as the selection of a limited FOV to the site of concern, reduction of exposure parameters kVp and/or mA, or the use of half scan mode instead of full scan to achieve the lowest possible dose (32). This study was conducted to optimize the diagnostic value of the CBCT images in the field of implant dentistry as well as the application of the dose limit. The 10x5 cm2 FOV for average adult was selected as it is the most commonly used FOV and patient parameter in implant treatment planning. The measurement of the dose with changes in kVp and mA was an important approach to control the applicability of the results as the radiation must comply with the ALARA principle (4). The effective dose provides an estimation of the biological harm from radiation; however, it can’t be measured directly and could be inferred from other ways of measuring the dose. The measurement of dose in this study was done using the methods recommended by SEDENTEXCT Dose Index 1 (1). The DI phantom was used to measure the absorbed dose at five different points along the midaxial slice. The absorbed dose found to be highest at the back of the  38 phantom and decreased gradually approaching the front part of the phantom. This dose distribution was consistent in all absorbed dose measurements obtained at variable exposure settings and confirmed the results from a study conducted by Abouei et al. (45). This pattern of dose distribution can be explained by the half rotation of the CBCT machine during the scan around the patient head instead of a full rotation. The average absorbed dose was used to report the dose of each exposure settings. The optimal settings selected were at 85 kVp among different kVp. The 3.2 mA was selected as the optimal mA setting among variable mA. The optimization resulted in considerable amount of dose reduction as compared to the default settings. The changes in mA had slightly more impact over the dose as compared to kVp changes. The kVp however, had more impact on image quality than the change in mA. This was consistent with conclusion from study conducted by Pauwels, et al. (33). The optimization of image quality was done and both SEDENTEXCT IQ and DI phantoms were used.  The dose was reduced greatly by reducing mA with minor loss of image quality (33). The quantitative image quality parameters added value to the optimization by making it more objective as clinical image quality assessment alone is subjective in nature. The noise of the image is a measure of random deviation from the MGV of the image. It affects the smoothness of the image. The higher the noise in the image, the more difficult is the identification of structures’ outline. The noise was increased as the exposure parameters decreased as higher quantity of radiation is needed to overcome the scattered radiation. The quantitative measurement of noise was consistent with clinical image quality as images taken at low exposure parameters appears more granular and could affect the interpretation of anatomical structures. Uniformity is the difference in mean gray value between the centre and periphery of the image. This could affect the interpretation of the images that requires comparison of the mean gray area at one region over the other. High quality uniform images should have a value close to 100%. The alteration of mA settings had more impact on uniformity than the kVp. AAV was measured using  39 two inserts, each containing three titanium rods. This insert measures the beam hardening artifact as well as the extinction or missing value artifact (11,12). Titanium caused significant artifacts in the CBCT scans. The use of the titanium inserts has direct applicability to clinical scenarios as it replicates the presence of highly absorbing objects such as implants or metal crowns. The AAV measurement was a significant factor to consider how it can be minimized if possible. The best measurement for AAV is the lowest possible measurement. In this study, the lowest AAV was at 90 kVp among different kVp settings. The best AAV value among different mA settings was at 4 mA. The geometrical distortion is one of the essential parameters to be evaluated in CBCT by a medical physicist as recommended by the SEDENTEXCT project. This parameter is highly significant in implant treatment planning as the measurements on the CBCT scan in all planes should be accurate for implant placement to avoid invading anatomical structures. The CBCT is isotropic where measurements in all planes should not be different after 3-dimensional reconstruction. This study confirmed that the geometrical distortion does not differ by changing the exposure settings. Spatial resolution is a measurement of details in a high contrast situation. High resolution could be required for the diagnosis of root fractures, accessory root canal, or pathological lesions. In implant treatment planning the resolution is not required to be high to achieve the diagnosis and treatment planning.  In this study, resolution did not differ significantly at different settings. This suggest that lower exposure parameters could still obtain adequate image resolution (29,34–37).  The optimization of image quality was tested using different machines in the literature. The results of image quality were found to be affected by the exposure settings, FOV and the type of machine. Different machines have different results and the image quality outcome from this study may not apply to other machines or different FOVs. However, most studies that attempted optimization of CBCT machines confirmed the possibility of optimizing the dose by reducing exposure parameters without  40 major effect on image quality (13,36,38). The optimization of image quality quantitatively using SEDENTEXCT IQ and DI phantoms were tested in a few studies (33,36). This is considered an emerging concept in optimization and standard results have not been established for each machine and FOV to compare with.  The clinical images of the maxillary arch had high quality at low kVp settings. All landmarks were produced at high image quality. When mA was altered, the images had high quality at 3.2 mA and above. This indicates that high diagnostic image quality can be produced at much lower dose by decreasing the mA and kVp without compromising the interpretation of implant anatomical landmarks. When scans were taken at variable kVp for the mandible, the anatomical landmarks had high quality at 85 and 90 kVp only. When scans were taken at different mA for mandible, the anatomical landmarks had high quality at 3.2 mA and above. Thus, the increase in exposure settings did not necessarily improved the quality of images but increased the corresponding radiation dose. These results are consistent with Lofthag-Hansen’s study (35), where maxillary landmarks needed much lower exposure settings than the mandible. This could be explained by the highly dense cortical bone in the mandible that requires higher radiation than the less cortical bone in the maxilla to produce adequate image quality. The tracing of the mandibular canal is one of the essential anatomical landmarks in pre-surgical implant planning. In this study, the tracing of the mandibular canal was not possible as the canal was visible only at three different cross-sections. In a study by Miles et al. (39), the mandibular canal was evaluated at different sites and found to be visible at 56% of sites only. When they attempted to correlate different factors, they found that age, gender and location affects the visibility. The younger age group (47-56 years) had lower visibility of the mandibular canal than the older group. Females had lower visibility than males. In older subjects, the mandibular canal had higher visibility at the premolar region as compared to the molar region. In female subjects, the premolar region had lower visibility than the  41 molar region (39). On the contrary, in a study by Motghare et al. (40), the level of decortication of the mandibular canal was studied and found that older age (50+) was associated with lower visibility. This was especially true for older females than males. In a study by Oliveira-Santos, et al. (41), the mandibular canal was visible in 53% of CBCT cross-sections only. The difficulty in visualization of the mandibular canal increased close to the mental foramen. In our study, the age and gender of the skull phantom are unknown and cannot be correlated. The assessment of the buccal plate pre-surgically is one of the factors that aids in making the decision of immediate versus delayed implant placement. In this study, the buccal plate thickness at the crest part of mandibular canine was difficult to visualize. It was reported in the literature that the buccal plate thickness of a lower canine has the least thickness at the crest as compared to other anterior teeth (42). In a study by Timock et al. (43), the reliability and accuracy of buccal plate height and thickness measurements were tested using cone beam CT. They found that the bone thickness has lower reliability as compared to the height (43). This is consistent with the results of this study as the thin buccal plate with high contrast situation made it difficult to identify this anatomical structure. Other anatomical landmarks in general had adequate visibility in our study even for the smaller structures, such as the antroalveolar intraosseous anastomosis at lateral walls of the sinuses as well as the superior and inferior lingual foramina. The results from the maxillary landmarks indicates that the exposure settings resulted in good image quality at all kVp settings. The 70 kVp could be selected to reduce the dose. When we evaluated the different tube current settings, the images had good quality at 3.2 mA and above. The selection of 3.2 mA would be ideal as the dose would be reduced substantially. However, the anatomical landmarks of mandible required higher dose and exposure settings. The selection of certain exposure settings of the maxilla different than the mandible in the same FOV would be an intuitive approach. However, the settings of the machine do not allow to pre-set the settings specifically to each arch. For this reason, the settings 85 kVp and 3.2 mA were selected as the  42 optimal settings for the clinical image quality assessment that works for both arches. A suggested exposure settings specific to the anatomical sites are listed in (Table 3-1) as different maxillary and mandibular landmarks required different exposure settings.  Table 3-1: Recommended kVp specific to the task in implant treatment planning  Anatomical site Recommended kVp Maxillary anterior 70 kVp Maxillary posterior 70 kVp Maxillary sinus 70 kVp Mandibular anterior 85 kVp Mandibular posterior 85 kVp  The optimization of CBCT images should be done in task specific manner to match the need. In implant dentistry, cross-arch and large FOVs with low spatial resolution are often required. On the contrary, in endodontics, limited size FOV is adequate confined to the size of the tooth with limited surrounding anatomy around the apical region. High resolution FOV in endodontics are always preferred as details needs to be clearly visualised. Limited FOV was recommended in endodontics in the American Academy of Endodontics (AAE) and AAOMR joint position statement due to lower dose, higher resolution and smaller volumes that require interpretation (44). The spatial resolution is required to be higher in endodontics to identify fine structures such as calcified canals, extra canals, inconclusive vertical root fractures, root resorption, complex morphology, and pathological lesions (18,25,44). In orthodontics, the FOV differ depending on the task as small FOV could be required for impacted teeth and to examine associated pathology. The presence of pathology usually requires high resolution to examine the details. Large FOV, such as craniofacial FOV, are indicated for tracing specific craniofacial landmarks. The resolution requirement is usually low. Each dental speciality has different indications for  43 CBCT with different requirements in terms of FOV and resolution. For the abovementioned reasons, optimisation should be done specifically to dental discipline and for the tasks (3).   3.1 Conclusion  This study included a comprehensive method to optimize CBCT image quality by using dose measurements, clinical image assessment, and quantitative image quality assessments. The optimal exposure settings recommended for the CBCT scanner (CS 9300, Carestream Health, Inc., Rochester, NY, USA) for the average adult, 10x5 cm2 FOV are 85 kVp, 3.2 mA, at 6.20 sec and voxel size of 180 𝜇m. Although this optimization was specific to the FOV, machine and task used, it can be concluded that optimization of the image quality may be obtained at a lower dose by reducing the exposure settings as compared to default settings. The optimization of the images is affected by the dose and should be measured together to obtain adequate diagnostic value of images at lowest possible dose complying with ALARA principle. The optimization should be task specific as different tasks may require different FOVs and exposure settings to produce the required diagnostic value. The assessment of clinical as well as quantitative image quality are required to ensure that adequate diagnostic value is obtained. 3.2 Future research Future research should focus on the optimization of CBCT image quality in a task specific manner that includes all dental specialties depending on the need for fine details, etc. Each dental discipline has their own requirements in terms of size and amount of details needed to be examined.  The images should be examined for all required anatomical landmarks and features and evaluated by a specialist from the same dental discipline.  The image quality of CBCT machines could be monitored by retrospective assessment of the patient’s scans for each FOV specific to the intended diagnostic task. This would highlight the limitations of the obtained clinical image quality. The images can be compared for the diagnostic value to a standard  44 image after specifying anatomical landmarks. This method may help further identification of applicability of optimization to the patients.    45 Bibliography 1.  European Commission, Directorate-General for Energy and Transport, Directorate H NS and S. European guidelines on radiation protection in dental radiology: the safe use of radiographs in dental practice. Luxembourg: Office for Official Publications of the European Communities; 2004.  2.  Christos D. R. Kalpidis, Reza M. Setayesh. Hemorrhaging Associated with endosseous implant placement in the anterior mandible: A review of the literature. J Periodontol. 2004;75(5):631–45.  3.  Patil S, Prasad BSK, Shashikala K. Cone beam computed tomography: Adding three dimensions to endodontics. Int Dent Med J Adv Res - Vol 2015. 2015;1(1):1–6.  4.  ICRP. The 2007 Recommendations of the International Commission on Radiological Protection. Ann ICRP. 2007;37(2.4):1–332.  5.  Harris D, Horner K, Gröndahl K, Jacobs R, Helmrot E, Benic GI, et al. E.A.O. guidelines for the use of diagnostic imaging in implant dentistry 2011. A consensus workshop organized by the European Association for Osseointegration at the Medical University of Warsaw. Clin Oral Implants Res. 2012 Nov;23(11):1243–53.  6.  Theodorakou C, Walker A, Horner K, Pauwels R, Bogaerts R, Jacobs Dds R, et al. Estimation of paediatric organ and effective doses from dental cone beam CT using anthropomorphic phantoms. Br J Radiol. 2012 Feb;85(1010):153–60.  7.  Okano T, Sur J. Radiation dose and protection in dentistry. Jpn Dent Sci Rev. 2010 Aug;46(2):112–21.  8.  Ludlow JB, Timothy R, Walker C, Hunter R, Benavides E, Samuelson DB, et al. Effective dose of dental CBCT—a meta analysis of published data and additional data for nine CBCT units. Dentomaxillofacial Radiol. 2015 Jan;44(1):20140197.  9.  Bornstein M, Scarfe W, Vaughn V, Jacobs R. Cone Beam Computed Tomography in Implant Dentistry: A Systematic Review Focusing on Guidelines, Indications, and Radiation Dose Risks. Int J Oral Maxillofac Implants. 2014 Jan;29(Supplement):55–77.  10.  Directive C. Council Directive 96/29/Euratom of 13 May 1996 laying down basic safety standards for the protection of the health of workers and the general public against the dangers arising from ionizing radiation. Off J Eur Communities. 1996;39(L159):1–114.  11.  Schulze R, Heil U, Groβ D, Bruellmann D, Dranischnikow E, Schwanecke U, et al. Artefacts in CBCT: a review. Dentomaxillofacial Radiol. 2011 Jul;40(5):265–73.  12.  Schulze RKW, Berndt D, D’Hoedt B. On cone-beam computed tomography artifacts induced by titanium implants: Titanium artifacts in CBCT. Clin Oral Implants Res. 2010 Jan;21(1):100–7.   46 13.  Bamba J, Araki K, Endo A, Okano T. Image quality assessment of three cone beam CT machines using the SEDENTEXCT CT phantom. Dentomaxillofacial Radiol. 2013 Aug;42(8):20120445.  14.  Lagravère MO, Carey J, Toogood RW, Major PW. Three-dimensional accuracy of measurements made with software on cone-beam computed tomography images. Am J Orthod Dentofacial Orthop. 2008 Jul;134(1):112–6.  15.  Brüllmann D, Schulze RKW. Spatial resolution in CBCT machines for dental/maxillofacial applications—what do we know today? Dentomaxillofacial Radiol. 2015 Jan;44(1):20140204.  16.  Pauwels R, Beinsberger J, Stamatakis H, Tsiklakis K, Walker A, Bosmans H, et al. Comparison of spatial and contrast resolution for cone-beam computed tomography scanners. Oral Surg Oral Med Oral Pathol Oral Radiol. 2012 Jul;114(1):127–35.  17.  Lee RD. Common image artifacts in cone beam CT. AADMRT Newsl. 2008;1–7.  18.  Tyndall DA, Price JB, Tetradis S, Ganz SD, Hildebolt C, Scarfe WC. Position statement of the American Academy of Oral and Maxillofacial Radiology on selection criteria for the use of radiology in dental implantology with emphasis on cone beam computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol. 2012 Jun;113(6):817–26.  19.  Jacobs R, Quirynen M, Bornstein MM. Neurovascular disturbances after implant surgery. Periodontol 2000. 2014;66(1):188–202.  20.  Zijderveld SA, van den Bergh JPA, Schulten EAJM, ten Bruggenkate CM. Anatomical and Surgical Findings and Complications in 100 Consecutive Maxillary Sinus Floor Elevation Procedures. J Oral Maxillofac Surg. 2008 Jul;66(7):1426–38.  21.  Renton T, Dawood A, Shah A, Searson L, Yilmaz Z. Post-implant neuropathy of the trigeminal nerve. A case series. BDJ. 2012 Jun 8;212(11):E17–E17.  22.  Keeble C, Baxter PD, Gislason-Lee AJ, Treadgold LA, Davies AG. Methods for the analysis of ordinal response data in medical image quality assessment. Br J Radiol. 2016 Jul;89(1063):20160094.  23.  Harada T, Abe T, Kato F, Matsumoto R, Fujita H, Murai S, et al. Five-point Likert scaling on MRI predicts clinically significant prostate carcinoma. BMC Urol [Internet]. 2015 Dec [cited 2017 Sep 27];15(1). Available from: http://bmcurol.biomedcentral.com/articles/10.1186/s12894-015-0087-5 24.  Renard-Penna R, Mozer P, Cornud F, Barry-Delongchamps N, Bruguière E, Portalez D, et al. Prostate imaging reporting and data system and Likert scoring system: multiparametric MR imaging validation study to screen patients for initial biopsy. Radiology. 2015;275(2):458–68.   47 25.  D’haese J, Ackhurst J, Wismeijer D, De Bruyn H, Tahmaseb A. Current state of the art of computer-guided implant surgery. Periodontol 2000. 2017;73(1):121–33.  26.  D’haese J, Van De Velde T, Komiyama A, Hultin M, De Bruyn H. Accuracy and Complications Using Computer-Designed Stereolithographic Surgical Guides for Oral Rehabilitation by Means of Dental Implants: A Review of the Literature: Stereolithographic Guided Surgery: A Review. Clin Implant Dent Relat Res. 2012 Jun;14(3):321–35.  27.  Demurashvili G, Davarpanah K, Szmukler-Moncler S, Davarpanah M, Raux D, Capelle-Ouadah N, et al. Technique to Obtain a Predictable Aesthetic Result through Appropriate Placement of the Prosthesis/Soft Tissue Junction in the Edentulous Patient with a Gingival Smile: Predictable Aesthetics for the Gingival Smile. Clin Implant Dent Relat Res. 2015 Oct;17(5):923–31.  28.  Bidra AS, Agar JR, Parel SM. Management of patients with excessive gingival display for maxillary complete arch fixed implant-supported prostheses. J Prosthet Dent. 2012;108(5):324–31.  29.  Benavides E, Rios HF, Ganz SD, An C-H, Resnik R, Reardon GT, et al. Use of Cone Beam Computed Tomography in Implant Dentistry: The International Congress of Oral Implantologists Consensus Report. Implant Dent. 2012 Apr;21(2):78–86.  30.  Mora MA, Chenin DL, Arce RM. Software Tools and Surgical Guides in Dental-Implant-Guided Surgery. Dent Clin North Am. 2014 Jul;58(3):597–626.  31.  Carter L, Farman AG, Geist J, Scarfe WC, Angelopoulos C, Nair MK, et al. American Academy of Oral and Maxillofacial Radiology executive opinion statement on performing and interpreting diagnostic cone beam computed tomography. 2008;  32.  Sur J, Seki K, Koizumi H, Nakajima K, Okano T. Effects of tube current on cone-beam computerized tomography image quality for presurgical implant planning in vitro. Oral Surg Oral Med Oral Pathol Oral Radiol Endodontology. 2010 Sep;110(3):e29–33.  33.  Pauwels R, Silkosessak O, Jacobs R, Bogaerts R, Bosmans H, Panmekiate S. A pragmatic approach to determine the optimal kVp in cone beam CT: balancing contrast-to-noise ratio and radiation dose. Dentomaxillofacial Radiol. 2014 Jul;43(5):20140059.  34.  Pauwels R, Stamatakis H, Manousaridis G, Walker A, Michielsen K, Bosmans H, et al. Development and applicability of a quality control phantom for dental cone-beam CT. J Appl Clin Med Phys. 2011;12(4):245–60.  35.  Lofthag-Hansen S, Thilander-Klang A, Gröndahl K. Evaluation of subjective image quality in relation to diagnostic task for cone beam computed tomography with different fields of view. Eur J Radiol. 2011 Nov;80(2):483–8.  36.  Pauwels R, Seynaeve L, Henriques JCG, de Oliveira-Santos C, Souza PC, Westphalen FH, et al. Optimization of dental CBCT exposures through mAs reduction. Dentomaxillofacial Radiol. 2015;44(9):20150108.   48 38.  Kwong JC, Palomo JM, Landers MA, Figueroa A, Hans MG. Image quality produced by different cone-beam computed tomography settings. Am J Orthod Dentofacial Orthop. 2008 Feb;133(2):317–27.  39.  Miles MS, Parks ET, Eckert GJ, Blanchard SB. Comparative evaluation of mandibular canal visibility on cross-sectional cone-beam CT images: a retrospective study. Dentomaxillofacial Radiol. 2016 Feb;45(2):20150296.  40.  Motghare D, Mishra I, Kapoor R, Tambawala S. Decortication of Inferior Alveolar Canal in Elderly Population: A Cone Beam Computed Tomography Study. [cited 2017 Aug 15]; Available from: http://ijhsr.org/IJHSR_Vol.6_Issue.9_Sep2016/36.pdf 41.  Oliveira-Santos C, Capelozza ALÁ, Dezzoti MSG, Fischer CM, Poleti ML, Rubira-Bullen IRF. Visibility of the mandibular canal on CBCT crosssectional images. J Appl Oral Sci. 2011;19(3):240–3.  42.  Sadeghian S, Yahyapour F, Ghafari R, Jafari S. Anthropometric Analysis of the Mandibular Anterior Buccal and Lingual Bone in Iranian Adult Population by CBCT. Iran J Orthod [Internet]. 2016 [cited 2017 Aug 15];(In Press). Available from: http://cdn.neoscriber.org/cdn/serve/83/f8/83f8f413caeb22fad303543e82a01dcde29eea90/ijo-inpress-inpress-7591.pdf 43.  Timock AM, Cook V, McDonald T, Leo MC, Crowe J, Benninger BL, et al. Accuracy and reliability of buccal bone height and thickness measurements from cone-beam computed tomography imaging. Am J Orthod Dentofacial Orthop. 2011 Nov;140(5):734–44.  44.  Fayad MI, Nair M, Levin MD, Benavides E, Rubinstein RA, Barghan S, et al. AAE and AAOMR joint position statement: use of cone beam computed tomography in endodontics 2015 update. Oral Surg Oral Med Oral Pathol Oral Radiol. 2015;120(4):508–12.  45.  Abouei E, Lee S, Ford NL. Quantitative performance characterization of image quality and radiation dose for a CS 9300 dental cone beam computed tomography machine. J Med Imaging. 2015;2(4):044002–044002.   49 Appendix A  Figures A.1 Maxillary anatomical Landmarks at different kVp  Figure 21: Maxillary sinus septum at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 22: Arterial anastomosis at the right sinus wall at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   50  Figure 23: Arterial anastomosis at the left sinus wall at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 24: Interproximal bone between teeth #13, 14 at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 25: Buccal plate thickness at tooth #23 at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   51  Figure 26: Buccal plate thickness at midpoint apicocoronally of tooth #22 at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 27: Buccal plate thickness at the crest of tooth #21 at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 28: Nasal spine and incisive canal at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp       52 A.2 Mandibular anatomical landmarks at different kVp   Figure 29: Inferior alveolar canal (right side) at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 30: Mental foramen (Left side) at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 31: Buccal plate thickness at the crest of tooth #43 settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   53  Figure 32: Buccal plate thickness of tooth #42 at midpoint apicocoronally at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 33: Buccal plate thickness of tooth #41 apically at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 34: Interproximal bone between #33, 32 at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   54  Figure 35: Superior and inferior lingual foramina at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 36: Interalveolar medial foramen (left side) at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp   Figure 37: Interalveolar lateral foramen (right side) at different kVp settings, a) 70 kVp, b) 75 kVp, c) 80 kVp, d) 85 kVp, e) 90 kVp    55 A.3 Maxillary anatomical landmarks at different mA settings:  Figure 38: Maxillary sinus septum, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 39: Arterial anastomosis at the right sinus wall, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 40: Arterial anastomosis at the left sinus wall, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 41: Interproximal bone between teeth #13, 14, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   56  Figure 42: Buccal plate thickness at tooth #23, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 43: Buccal plate thickness at midpoint apicocoronally of tooth #22, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 44: Buccal plate thickness at the crest of tooth #21, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 45: Nasal spine and incisive canal, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA     57 A.4 Mandibular anatomical landmarks at different mA settings:  Figure 46: Inferior alveolar canal (right side), a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 47: Mental foramen (Left side), a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 48: Buccal plate thickness at the crest of tooth #43, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   58  Figure 49: Buccal plate thickness of tooth #42 at midpoint apicocoronally, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 50: Buccal plate thickness of tooth #41 apically, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 51: Interproximal bone between #33, 32, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 52: Superior and inferior lingual foramina, a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   59  Figure 53: Interalveolar medial foramen (left side), a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA   Figure 54: Interalveolar lateral foramen (right side), a) 2 mA, b) 2.5 mA, c) 3.2 mA, d) 4 mA, e) 5 mA, f) 6.3 mA, g) 8 mA, h) 10 mA, i) 12 mA    

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