|
Ultrasound speckle tracking has the potential to quantify shear strain in patients with myofascial pain, leading to previous clinical conclusions (derived from a cross-correlation-based, windowed-search speckle tracking method) that shear strain is altered in patients with myofascial pain when compared to healthy individuals. However, differences in speckle-tracking techniques are known to impact the accuracy of estimated displacement fields, which has the potential to alter clinical conclusions. Therefore, this work aims to assess the reliability of two displacement estimation algorithms in the context of muscle lateral shear strain measurements, specifically Search and a Search-initialized Second-Order Ultrasound eLastography that we name SOUL-Search. Search utilizes a window-based displacement tracking method that determines the optimal displacement based on maximum signal correlation, whereas SOUL-Search fine-tunes the Search initial estimates by optimizing a cost function comprising data and regularization terms. A simulation study was implemented to provide controlled in silico assessments, followed by initial comparisons with in vivo data from the shoulder muscles of three research participants with myofascial post-stroke shoulder pain, acquired with a robot-held ultrasound probe with passive muscle motion induced by a bimanual arm trainer. SOUL-Search improved the in silico root-mean-square error, mean absolute error, and mean structural similarity of lateral displacement estimates by 64%, 43%, and 34%, respectively, relative to Search. When applied to the in vivo data, both Search and SOUL-Search agree with a novel clinical hypothesis that painful paretic shoulders exhibit altered muscle shear strain when compared to each participant’s non-paretic shoulder. However, SOUL-Search produced less-noisy lateral displacement images (enabling better qualitative assessments of clinical observations) and provided a smoother progression of lateral shear strain over time when compared to Search (which aligns with expectations based on the controlled in vivo environment). Results are promising for the creation and validation of new clinical hypotheses surrounding the identification and management of myofascial pain.
|
