Comparing Volumetric Speckle Tracking Performance of Common Parallel-Acquisition Sequences using a Matrix Probe for Respiratory-Induced Liver Motion

Intensity Modulated Radiotherapy (IMRT) is a cancer treatment modality that is often used to treat malignant liver lesions while minimizing damage to healthy tissues. Liver motion poses a challenge during IMRT, potentially compromising the dose to cancer cells and sparing of healthy liver. To manage liver motion during treatment, real-time tissue motion estimation with high accuracy and precision is required. This paper explores the use of a 1024-element 2D matrix probe with a 256 channel Verasonics ultrasound system for B-mode motion tracking in three-dimensions. This study compared image quality and tracking performance for ‘step and shoot’ motion of three common imaging sequences, single diverging wave (SDW), compounded plane wave-1D (CPW-1D), and compounded diverging wave (CDW) at a fixed frame rate (10 Hz) and field of view. The CDW method demonstrated superior overall imaging performance. CPW-1D and SDW exhibited less favorable results in both lateral and elevational directions. Tracking accuracy, based on the mean absolute difference between measured and true displacements, in the axial direction deteriorated with displacement for all imaging methods, and both CPW-1D and CDW demonstrated favorable lateral tracking. Further investigation is needed to understand the good elevational tracking performance SDW. Of the three sequences evaluated, we found CDW to display the best overall performance for tissue motion tracking. Matrix array probes offer promising performance for reliable motion tracking in radiotherapy.