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Design of a solid tank prototype optical computed tomography scanner

University of British Columbia

Purpose: The objective of this work is to design a new prototype fan-beam optical computed tomography (OCT) scanner for three-dimensional radiation dosimetry. Primary distinctions are a solid acrylic tank and the inclusion of iterative reconstruction techniques (IR) into the scanning methods. This scanner attempts to address artifacts related to color and index matching baths that are often found with OCT for gel dosimeters. As a result of the solid tank design there is lensing that the fan-beam experiences while passing through a gel dosimeter, this lensing makes filtered back projection (FBP) less suitable than IR for image reconstruction. Methods: The two distinct features of this scanner are the use of a solid tank as an alternative to refractive index (RI) matching baths, and the inclusion of IR rather than FBP for image reconstruction. A polished acrylic block functions as a solid tank that is used to reduce the effects of material RI mismatch. Five arrays of 64 photodiode detectors (0.8mm x 0.7mm) were run in series to collect optical projection data. The detectors sat flush against the acrylic. A gel rotates inside a hole in the acrylic block and each projection is taken at 0.5 degree steps for 360 degrees before and after irradiation. The scanner properties were evaluated by imaging radiochromic silicon gel dosimeters. Results: Spatial frequency was measured using the modulation transfer function found from the edge spread function of a cylindrical attenuating object. The average spatial frequency measured was 3.111 cycles/mm. Image geometry was measured by placing opaque objects of known geometry inside of a gel and comparing the ratio of their pixel distances to their ratio geometric distances. The pixel ratio found with this system was 2.63px/mm. Conclusion: This work provides an alternative to traditional matching bath methods of addressing color and index matching for OCT of gel dosimeters. The inclusion of iterative reconstruction provides an alternative to filtered back projection. The system is capable of scanning 0.8mm slices of cylindrical volumes in under 3 minutes.

Text

2018-10-02

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/67304

Medical Physics

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/