Improved delineation rate of thermally ablated liver tumors with electrode displacement elastography compared to commercial acoustic radiation force impulse imaging

Ultrasound elastography is an effective modality for the delineation of thermally ablated regions after liver tumor treatments. Image contrast in elasticity imaging is based on differences in the Young's modulus of local tissue. In this work, we compare our previously introduced electrode displacement elastography (EDE) with a commercially available acoustic radiation force impulse imaging (ARFI) technique, for delineating the post ablation regions. Forty-seven patients diagnosed with either hepatocellular carcinoma (HCC) or metastases underwent microwave ablation (MWA) procedures with a typical setting of 65 W for 5 minutes. EDE and ARFI images were acquired with a Siemens Acuson S2000 system and 6C1 HD transducer. EDE images were generated from a continuous loop of ultrasound radiofrequency (RF) data using a 2D cross-correlation algorithm. ARFI images were obtained using the `Virtual Touch' function available on the Siemens Acuson S2000 system. Delineation of the ablated region was performed by two observers. Imaging depth dependence of EDE and ARFI was evaluated using tissue mimicking (TM) phantoms with the inclusion positioned at different depths. Delineation results from the two observers indicate that the ablated region in ARFI images was recognizable on an average of 19 patients, while delineable ablation boundaries could be generated on an average of 4 patients. With EDE strain images, delineable ablation boundaries were generated on an average of 39 patients, without obvious imaging depth dependence. The TM phantom studies show that differences in inclusion dimensions measured with EDE and ARFI images were within 8%, while image contrast and contrast to noise ratio (CNR) with EDE was 2-3 times higher than that obtained with ARFI. This study showed that monitoring MWA in terms of the delineation rate and CNR was higher with EDE when compared to the commercially available ARFI approach. EDE could therefore become an alternative imaging modality for monitoring MWA procedures for liver tumor treatments in the ablation suite. EDE is also feasible for deeper tumor locations beyond the evaluated imaging depth for ARFI.