Automated OTMS Raghav Malik

Background Tissue thickness measurements Several methods already exist Biomechanics applications Dealing with soft tissue Useful for determining tensile strength Applications in Finite Element Analysis Several methods already exist Calipers/Thickness Gauge LVDT Probe Electrical Resistance Gauge

Challenges/Motivations Caliper/Thickness Gauge Easy to setup and use Requires physical contact Induces deformation Artificially low measurements Electrical Resistance Gauge No contact deformation Sensitive to temperature Requires extensive calibration Expensive LVDT Probes and Laser Displacement Probes High precision Extremely sensitive to temperature Relies on voltage measurements Artificially high readings

Premise of AutoOTMS Works on high resolution medical images of tissue No contact so no deformation Precision bounded only by resolution of image Computation carried out by software No inconsistency associated with human application Streamlines the data collection process Quick and inexpensive Deals entirely with physical units No extra calibration steps necessary Insensitive to nature of the tissue Operates separately from the tissue Insensitive to environmental factors

Specifications Image to be analyzed Tissue sample Caliber of known thickness in the same plane as tissue Placed on high-contrast table (easily identify bottom edge) Display average pixel heights of tissue and caliber Display standard deviation of pixel heights Display actual average thickness of tissue (based on proportion) Option to output analysis results to an XML file with marked up image

Edge Detection Analyze column by column Reduce 3D RGB signal to 1D intensity signal Transform into differential domain "High" spike in derivative = edge Relative image clustering

Edge Detection Visualization

Error Detection Need to remove false edges from image Edge with error Need to remove false edges from image Transform detected edge into derivative Detect spikes (p < 0.01) Spikes come in pairs: Cancel positive and negative Accumulate the net Accumulate the derivative Error removed from edge Derivative of edge Spike detected and removed

Sample Output

XML Caching Save the results of a scan Easy to read Provide overview No need to repeat the scan Format of XML Image file information Calibration units Scan information Statistics Image files Save original image Save marked up image

Complete Workflow Start program Python 3.x Run graphics.py script Load image From file From camera Specify parameters Left and right of tissue Left and right of caliber Calibrate Thickness of caliber in physical units Review Statistics Average pixels Average mm Standard Deviation Save results Cache scans to XML file Save original and marked up images

Technologies Self-contained python script Cross-platform compatible Good for scientific measurements Maintains open-source paradigm Relies on widely used python libraries Tkinter for graphics: native NumPy for numerical manipulation PIL for image manipulation Basic XML writer to "cache" the results Store original and marked up image Information about scan locations and frequency: reproducible

Results Sample Name AutoOTMS Trial 1 AutoOTMS Trial 2 AutoOTMS Trial 3 Manual OTMS oks00TR1-FMC-MCXX 2.030 mm 2.027 mm 2.028 mm 1.952 mm oks00TR1-MNS-LCuX 1.013 mm 0.996 mm 1.088 mm 0.854 mm Sample Name AutoOTMS Mean Manual OTMS Mean Difference % Error oxs00TR1-FMC-MCXX 2.0276 mm 1.952 mm 0.076 mm 3.9% oks00TR1-MNS-LCuX 1.0323 mm 0.854 mm 0.178 mm 20.1 % Sample Name AutoOTMS Stdev AutoOTMS CV Manual Stdev Manual CV CV Ratio FMC-MCXX 0.00153 mm 0.00075 0.08525 mm 0.04367 58.23x MNS-LCuX 0.04895 mm 0.04742 0.05910 mm 0.06920 1.46x

Conclusions Delivers consistent results AutoOTMS Standard Deviations lower than Manual OTMS Standard Deviations Coefficient of Variation smaller than 1 for both tissues AutoOTMS Coefficient of Variation lower than Manual OTMS Coefficient of Variation oks00TR1-FMC-MCXX AutoOTMS very close to Manual OTMS results (3.9% difference) Slightly higher oks00TR1-MNS-LCuX AutoOTMS differs significantly from Manual OTMS results (20.1% difference) Significantly higher Conclusion: Results are precise; accuracy should be verified by a third method of measurement

Acknowledgements Cleveland Clinic Dr. Erdemir and the rest of the Open Knee(s) team The Open Knee(s) project Mentor High School