Investigation of Patellar Deep Tendon Reflex Using Millimeter-Wave Radar and Motion Capture Technologies

Physicians typically measure deep tendon reflexes visually, leading to ambiguity and disagreement over exact reflex classification. Millimeter-wave radar addresses this problem by providing an accurate, unambiguous measurement of reflex limb motion and features noncontact sensing for convenience and patient comfort. Radar spectrograms closely match optical motion capture results, supporting radar’s viability as a clinical assessment tool. This study analyzes data from 60 radar and motion capture measurement trials across four subjects. Six reflex characteristics are defined and extracted. The extracted parameters show a high level of agreement between the two different techniques, with a mean relative error of only 10.39%. Additionally, a positive correlation was observed between hammer tap speed and reflex response speed, with maximum leg velocities showing a slope of 0.4. This study also quantifies and discusses the effects of hammer tap speed and leg length. An analytical model is derived to describe the patellar DTR system dynamics. In the future, physicians may use a specialized radar system to assess reflex performance quickly, accurately, and comfortably for a patient under test.