Cryoablation temperature monitoring with dense ultrasonic speed-of-sound shift imaging

Accurate temperature monitoring during cryoablation, a minimally invasive technique that destroys tissue locally by forming an ice ball around an inserted cryoprobe, is vital for achieving complete ablation while protecting surrounding tissue. We present a dense slowness-shift imaging method that estimates local speed-of-sound changes from ultrasound B-mode images using optical flow. This single-transducer, image-based approach enables mapping of spatial temperature change without requiring additional hardware. Cryoablation experiments in a tissue-mimicking phantom and ex vivo turkey breast demonstrated that slowness deviation increases with decreasing temperature. In the phantom, the dependence was linear (a = -20.70 s{middle dot}m-1C{degrees}-1), while in turkey breast it presented an exponential relationship (t = 34.04xexp(0.075(-{Delta}T)) s{middle dot}m-1C{degrees}-1). The algorithm detected sub-degree temperature variations and accurately tracked cooling down to -39.4 {+/-} 5.6 {degrees}C. This work demonstrates the feasibility of ultrasound-based, noninvasive temperature monitoring during cryoablation, providing a scalable, real-time alternative to existing invasive or high-cost thermal assessment techniques.