Three-dimensional echo decorrelation imaging of percutaneous microwave ablation in liver tumors

Abstract

In a pilot clinical study, patients underwent standard-of-care percutaneous microwave ablation (MWA) of liver tumors with monitoring by three-dimensional (3D) ultrasound echo decorrelation imaging. An MWA needle (Amica) was inserted into each tumor, guided by x-ray computed tomography (CT) and ultrasound imaging. A matrix ultrasound array (4Z1c array with Acuson SC2000 scanner, Siemens) was positioned on patients’ skin near the MWA needle insertion point. Paired sequential complex in-phase/quadrature (IQ) echo volumes (inter-frame time 5–20 ms) were acquired throughout ablation at 10–20 s intervals, then processed to form 3D echo decorrelation images. Respiratory motion was estimated and compensated using a theoretical model that separates motion- and heat-induced echo decorrelation. Volumetric B-mode images constructed from the same IQ data were rigidly registered to follow-up contrast-enhanced magnetic resonance (MR) image volumes, recorded within 4 days after MWA. Specified registration transformations were then applied to cumulative 3D echo decorrelation maps, which were compared voxel-wise to ablation zones segmented from MR images. Receiver operator characteristic (ROC) curve analysis indicated effective prediction of local ablation by motion-compensated echo decorrelation imaging. Comparison with subsequent follow-up MR images tested the ability of 3D echo decorrelation imaging to predict any incomplete treatment or recurrence of treated tumors.