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Minimally invasive procedures such as microwave ablation (MWA) are growing in popularity as a substitute for surgical resection of hepatocellular carcinomas. Ultrasound electrode displacement elastography (EDE) has demonstrated the potential to provide a feasible non-ionizing approach for monitoring the region of thermal necrosis. We present results on a comparison of the contrast, signal-to-noise (SNR) and contrast-to-noise (CNR) ratios for two displacement estimation algorithms; namely the Quality-Guided Displacement Tracking (QGDT) and the Coupled Subsample Displacement Estimation (CSDE) methods. Twenty patients with EDE strain images estimated from the same radiofrequency frame pair using both algorithms are presented. CSDE depicts well delineated ablated regions, while QGDT in many instances depicts noisy boundaries. Quantitatively, the SNR, contrast, and CNR obtained using CSDE were higher than those obtained with QGDT. The axial SNR, contrast, and CNR for QGDT were found to be 34.6 ± 11.9 dB, 7.8 ± 4.2 dB, and 2.7 ± 6.4 dB, while the CSDE presented with values of 56.9 ± 20.4 dB, 22.5 ± 12.3, and 3.8 ± 2.5 dB, respectively. This study indicates that EDE using CSDE provides improved strain images however, both approaches produced reproducible results.

An effective imaging modality to delineate the ablated region after microwave ablation (MWA) therapy is crucial to yield promising treatment outcomes. Ultrasound B mode imaging is widely used to guide the ablation needle. However, the image quality suffers from relatively low imaging contrast due to the similar echogenicity between the ablated and surrounding liver tissue. In this study, we applied a quasi-static ultrasound elastography technique, referred to as electrode displacement elastography (EDE), to delineate the thermally ablated regions for patients diagnosed with hepatocellular carcinoma (HCC) treated with MWA procedures.

An effective imaging modality to delineate ablated regions after microwave ablation (MWA) therapy is crucial to yield successful treatment outcomes. Ultrasound B-mode imaging is widely used to guide the ablation antenna placement. However, the image quality suffers from relatively low imaging contrast due to the similar echogenicity between the ablated and surrounding tissue. In this study, we applied a quasi-static ultrasound elastography technique, referred to as electrode displacement elastography (EDE), to delineate the thermally ablated regions for patients diagnosed with hepatocellular carcinoma (HCC) and treated with minimally invasive MWA procedures. Under our approved institutional review board (IRB) protocol, EDE was used for monitoring MWA on fifty-one patients. MWA was performed using a NeuWave Certus 140 system, with a typical setting of 65 W and 5 minutes. Ultrasound B-mode and radiofrequency (RF) data loops for EDE were acquired using a Siemens Acuson S2000 system and a 6C1 HD transducer. RF data loops were acquired simultaneously with a manual perturbation of the ablation antenna performed by a physician. EDE strain images were generated with a 2D cross-correlation based displacement tracking algorithm with a kernel size of 1.35 mm × 3.29 mm along the axial and lateral direction. Ablation area, contrast and contrast to noise ratio (CNR) of EDE strain and ultrasound B-mode images were compared. Delineable ablation regions were obtained using EDE for 45 patients, with a success rate of 88.2%. The area of the ablation region in EDE images was 13.3 ± 5.0 cm2, when compared to 7.7 ± 3.2 cm2 with B-mode images. Contrast and CNR obtained with EDE was on the order of 236% and 102%, respectively, significantly higher than values measured in B-mode images (p

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.