Ultrasonic temperature imaging for the guidance of thermal ablation therapies: in vitro results

Ultrasonic estimation of heat-induced echo strain has been suggested as a technique for the guidance of thermal ablation tumour therapies by predicting the location of the thermal lesion before it is formed. Preliminary investigations of this method were carried out using in vitro bovine liver starting at a baseline temperature of 24°C. Three non-ablative temperature rises (∼10, 20 and 30°C respectively) were induced using a focused ultrasound surgery system. In each case, a strain (temperature) image was generated by processing ultrasound images acquired before and after tissue heating. The final step was to induce an ablative temperature rise (∼40°C) so as to produce a thermal lesion. The temperature images for all three non-ablative temperature rises possessed excellent spatial and contrast resolution. The technique demonstrated good repeatability within and between tissue samples. The position of the hot spot in the temperature images correlated well with the region of echo enhancement seen in B-mode images after ablation. We conclude that the proposed technique is feasible in the liver, although additional sources of error that will arise in vivo may require correction.