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Specific Aim

Design a new apparatus for measuring the cross-sectional area of mouse patellar tendons and other small, soft connective tissues. This is important for calculating mechanical properties, stress, and elastic modulus, as well as indicating scar tissue formation. The current methods have limitations in accuracy and non-contact measurement.

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Specific Aim

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Presentation Transcript

  1. Specific Aim • Design a new apparatus for measuring the cross-sectional area of mouse patellar tendons and other small, soft connective tissues Why is this important? …

  2. Cross-Sectional Area • Indicator of scar tissue formation • Important for calculation of mechanical properties • Stress • Elastic modulus • Area of mouse patellar tendon challenging to measure • Small • Easily compressed • Can dry out somewhat rapidly

  3. tendon tibia patella stain lines Mouse Tendon Prepared for Testing • Tendon dissected with tibia and patella • Stamped in standard dumbbell shape • Stain lines placed on surface for optical strain measurement • Tendons typically ~1 mm wide and <1 mm thick mm

  4. Indenter probe Previous Area Measurement Method • Our previous technique: • Thickness measured with indenter probe attached to LVDT • Width obtained optically from digital images • Cross-sectional area = thickness x width Limitations: • Not non-contact compression of tissue • Rectangle is not true representation of cross-sectional shape

  5. Existing Non-Contact Methods • Non-contact area measurement techniques: • Shadow amplitude method (Ellis, 1968) • Rotating microscope (Gupta, 1971) • Collimated laser beams (Lee, 1988) • Limitation: Unable to detect concavities  overestimation of area

  6. Existing Non-Contact Methods • Other techniques: • Replica molding (Race, 1996; Goodship, 2005) • Ultrasound (Noguchi, 2002; Ying, 2003) • MRI (Magnusson, 2003) • Costly and labor-intensive • Need for a new approach still exists …

  7. Specimen Laser Reflectance • Charge-coupled device (CCD) laser reflectance system • Laser transmitter projects light spot onto surface below • Light is reflected off surface and focused onto receiving element Laser transmitter Receiving element x

  8. Specimen thickness Specimen Laser Reflectance • Charge-coupled device (CCD) laser reflectance system • When specimen introduced, position of projected spot on receiving element changes • Changes in spot position output as changes in voltage proportional to thickness of specimen Laser transmitter Receiving element x x

  9. Specimen thickness Specimen Laser Reflectance • Charge-coupled device (CCD) laser reflectance system • Can detect surface concavities • Newer lasers offer improved accuracy and resolution • Suitable for small specimens Laser transmitter Receiving element x x

  10. Laser sensor New Device – Configuration • Specimen placed on moveable stage • Laser measures thickness • Two LVDTs measure stage motion • Data output to LabVIEW Stage Two LVDTs

  11. New Device – User Interface

  12. Custom fixture Setup for Mouse Patellar Tendon

  13. Custom fixture Setup for Mouse Patellar Tendon Tibia Patella Patellar tendon

  14. Start data collection Measurement Protocol • Fixture placed on stage • Tendon translates beneath laser • Five passes (“slices”) • <1 minute To tibia Stain line Stain line Patella

  15. Average area Cross-Sectional Area Calculation • Software plots “slices” • Creates interpolated mesh to reconstruct volume • Calculates area of all slices in mesh and returns average • Validation …

  16. Validation – Range of Thicknesses • Measured thickness of 4 strip gauges of varying sizes • Measured each 10 times with laser • Accuracy: Compared to digital caliper measurements • Repeatability: Coefficient of variation (COV)

  17. Validation – Range of Thicknesses • Measured thickness of 4 strip gauges of varying sizes • Measured each 10 times with laser • Accuracy: Compared to digital caliper measurements • Repeatability: Coefficient of variation (COV) Strip Gauge 1 Strip Gauge 2 Strip Gauge 3 Strip Gauge 4 (mm) (mm) (mm) (mm) Mean Laser Measurement 0.46 0.81 2.16 3.18 Standard Deviation 0.01 0.01 0.01 0.01 COV(%) 1.60 0.87 0.33 0.33 Caliper Measurement (mm) 0.46 0.79 2.16 3.15 Percent Difference (%) 0.15 2.69 0.05 0.87

  18. Validation – Range of Thicknesses • Measured thickness of 4 strip gauges of varying sizes • Measured each 10 times with laser • Accuracy: Compared to digital caliper measurements • Repeatability: Coefficient of variation (COV) Strip Gauge 1 Strip Gauge 2 Strip Gauge 3 Strip Gauge 4 (mm) (mm) (mm) (mm) Mean Laser Measurement 0.46 0.81 2.16 3.18 Standard Deviation 0.01 0.01 0.01 0.01 COV(%) 1.60 0.87 0.33 0.33 Caliper Measurement (mm) 0.46 0.79 2.16 3.15 Percent Difference (%) 0.15 2.69 0.05 0.87

  19. Validation – Area of Known Geometry • Measured cross-sectional area of thin metal strip 10 times with laser system • Accuracy: Compared to digital caliper measurements (height x width) • Differed by 3.4% • Repeatability: COV = 2.4%

  20. Final Validation – Mouse Tendon • Measured cross-sectional area of same mouse patellar tendon 10 times with laser system • Repeatable results (COV = 4.1%) • Unable to test accuracy in this tissue • No “gold standard” for comparison

  21. Comparison with Old Method • Measured area of 10 mouse patellar tendons using both methods and compared results • Average was 0.41±0.11 mm when measured with the laser system and 0.08±0.02 when measured using previous method • Non-contact vs. contact method • Repeatability of previous method • Assessed by taking 10 consecutive measurements at same location on a single specimen using probe • COV = 8.9% • Less repeatable than laser system (4.1%)

  22. www.uphs.upenn.edu/orl McKay Orthopaedic Research Laboratory

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