Delineation of microwave ablated hepatocellular carcinomass using electrode displacement elastography

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 cm 2 , when compared to 7.7 ± 3.2 cm 2 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 <0.001). This study showed that thermally ablated regions were delineated in EDE strain images with enhanced detectability. Potential application of EDE for real-time monitoring of the MWA procedure may improve the treatment outcome.