In vivo ultrasound electrode displacement strain imaging

Abstract

The incidence of primary and secondary liver tumors has increased significantly over the last two decades. Due to poor liver function and/or distribution of lesions, surgery is often not an option for affected patients. An alternative to surgical resection, percutaneous radiofrequency ablation is often used to thermally destroy the tumor in situ. Radiofrequency ablation is evolving into one of the more popular minimally-invasive treatments for hepatic tumors. Monitoring the treated region is an important factor in the success of radiofrequency ablation, and ultrasound elastography could become a convenient, cost-effective means to delineate the thermal lesion boundaries for clinical personnel during the procedure. This study assesses “electrode displacement” strain imaging for monitoring abdominal radiofrequency ablation procedures. We present results utilizing a novel approach of displacing the ablation electrode itself to introduce the mechanical stimuli required for strain imaging. Utilizing a Siemens Antares clinical ultrasound scanner equipped with a research interface, ultrasound radiofrequency data were acquired immediately following radiofrequency ablation of porcine liver. The porcine liver was excised following the procedure, and the dimensions of the thermal lesion in the imaging plane measured by slicing though the lesion. Strain images of the lesions were produced offline using axial guidance based block-matching and multi-level motion tracking algorithms. The area of the lesion on the strain image was compared to the area of the lesion in pathology images obtained from eight separate lesions. The estimated linear correlation coefficient between the pathology image and the strain image was r = 0.961 (p ≪ .001) for manual segmentation using 4 observers. The area of the lesion in the strain image slightly underestimates the area of the lesion in the pathology image for all slices, agreeing with earlier ex-vivo experiments.