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Design and characterisation of an improved spinal canal occlusion transducer

University of British Columbia

The spinal canal occlusion transducer (SCOT) is a sensor used to detect changes in geometry of the cervical spinal canal. A constant current field is created in saline filling the SCOT casing. Radial compression of the SCOT casing results in a change in cross sectional area and an increased resistance to current flow. Sensing elements along the SCOT are used to detect the change in potential difference along the length of the probe and quantify the change in area of the SCOT casing. Shortfalls of the existing SCOT iteration were identified for improvement. These included long term durability and stability of the signal. A new design for the SCOT probe was sought with the aim of addressing these shortfalls. Six prototype SCOT probes were designed, manufactured and tested. Prototypes considered sensing elements, the casing materials used, input signal conditions and the method used to construct the SCOT probe. Signal to noise ratio and stability of signal were used to compare the prototypes against the original SCOT. The design chosen consisted of a heat shrink casing, 3.97 mm diameter SS ball bearings for ground and excitation elements, and 3.18 mm diameter SS ball bearings for sensing elements. Electrical connections were soldered. A sinusoidal input with frequency of 3 kHz and peak to peak amplitude of 1.5 V was used. The minimum measurable total canal area was 107.6 ± 1.2 mm². The signal to noise ratio of the new SCOT was 74.3 dB and the variation of unoccluded SCOT signal was found to be 1.4 ± 2.5 mVRMS compared to 74.4 dB and 2.3 mVRMS for the previous iteration. The new SCOT was used in a flexibility study of cervical spine segments. Specimens were loaded in flexion-extension, left-right lateral bending and axial rotation up to 4 Nm at 2 ˚/s. Mean maximum percent decreases in total canal area were 5.8%, 15.9%, 5.1%, 4.6%, 4.6% and 4.2% for flexion, extension, left axial rotation, right axial rotation, left lateral bending, and right lateral bending, respectively. Only extension consistently demonstrated mean maximum decreases that exceeded the mean error of the SCOT (5.3 ± 1.3 mm²).

Text

2016-01-06

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/56216

Mechanical Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/