Real-time control of radiofrequency ablation by three-dimensional echo decorrelation imaging

Feasibility for real-time control of radiofrequency ablation (RFA) by three-dimensional (3-D) echo decorrelation imaging, with potential application to liver cancer treatment, is investigated. Ex vivo bovine liver is treated using a clinical RFA system (RITA 1500X generator with StarBurst probe, Angiodynamics). During ablation, pairs of echo volumes from a Siemens SC2000 scanner with a 4Z1c matrix array probe (inter-frame time 18 ms) are recorded as in-phase and quadrature (IQ) data. 3-D echo decorrelation maps are computed from these volume pairs every 11 s. Cumulative echo decorrelation, defined as the temporal maximum decorrelation for each voxel, is spatially averaged within a spherical region of interest (ROI) centered at the RF needle tip. Once the spatially averaged cumulative decorrelation within the spherical ROI exceeds a predefined threshold, ablation is halted by communication with the RF generator via a pneumatic switch connected to a microcontroller circuit. The control threshold and ROI were determined by empirically evaluating predictive performance of decorrelation in preliminary uncontrolled ablation trials. Controlled and uncontrolled ablation are compared based on correspondence of sectioned tissue histology to targeted ablation zones, receiver operating characteristic curve analysis of local ablation prediction by echo decorrelation, treatment duration, and ablation rate.