6F-3 A Regularized Real-Time Motion Tracking Algorithm Using Dynamic Programming for Ultrasonic Strain Imaging

This study developed a robust algorithm for realtime ultrasonic strain imaging that employs dynamic programming techniques. Since tissue motion under external mechanical stimuli should be highly continuous, the speckle tracking problem fits well within the general framework of the hidden Markov model and can be solved as an optimization problem. A cost function combining correlation and motion continuity was used to regularize motion tracking. We found that the new algorithm provides more accurate displacement estimates than our previous algorithm for in vivo clinical data. In particular, the new algorithm is capable of tracking larger frame-average tissue deformation (1-2%) and increasing strain image consistency in a sequence of images. The new algorithm can also tolerate larger local strain (approx. 10%). Preliminary results also suggest that a significantly longer sequence of high contrast strain images (e.g. 45 vs. 15 in one cancer dataset) could be obtained with the new algorithm compared to the previous algorithm. We also achieved more than 10 frames/second with a 3 cm by 3 cm region of interest, which is sufficient to provide real-time feedback during in vivo elasticity imaging