Real-time spatial compounding with warping

Abstract

Spatial compound imaging via beam-steering aims to improve image quality through signal averaging. However, compounding techniques are vulnerable to speed-of-sound and refraction distortions in non-homogeneous tissue. We have developed a system to perform image-based non-rigid registration in real time. The goal is to increase image quality by improving the alignment of the ultrasound frames before compounding. Frames are acquired by a PC-based ultrasound machine (Ultrasonix Medical Corp, Vancouver, Canada), and transmitted to a Windowsbased workstation through a high-speed network. Robust image-to-image registration (warping) is performed using block-based estimation of local shifts and thin-plate spline interpolation of shift vectors. Compound images are computed as a rolling average of the nine most recent warped frames. The process runs at 20 frames per second on a dual-processor Xeon workstation, demonstrating the feasibility of sophisticated real-time image processing on a standard PC platform. High speed is achieved through algorithm refinements, approximations in speed-critical sections, and low-level optimizations. The result is a fully-automatic real-time spatial compounding system with a demonstrated improvement in image quality. Tests of registration accuracy were performed on simulated data with realistic speckle patterns, using a 10% speed-of-sound variation and an 8 • beam-steering angle. The average misalignment across the image was reduced by 70%, from 0.22 mm to 0.07 mm; in the deepest parts of the image, alignment was improved by 91%. Improved quality is demonstrated on images of a human forearm, which show visibly improved edge sharpness. This work is one of a series of projects demonstrating the ability of a new open-architecture ultrasound system.

Clinical Evaluation of Combined Spatial Compounding and Adaptive Imaging in Breast Tissue

“…In a sim i lar study, spa tial com pound ing was com bined with im age reg is tra tion to com pensate for the dis tor tion ef fects of ab er ra tion. 27 In this study, reg is tra tion be tween subap er ture im ages is ap plied af ter beamforming to com pen sate for ab er ra tion ef fects.…”