Strain Imaging for Arterial Wall with Translational Motion Compensation and Center Frequency Estimation

Abstract

Atherosclerotic change of the arterial wall leads to a significant change in its elasticity. For assessment of elasticity, measurement of arterial wall deformation is required. For motion estimation, correlation techniques are widely used, and we have developed a phase-sensitive correlation-based method, namely, the phased-tracking method, to measure the regional strain of the arterial wall due to the heartbeat. Although phase-sensitive methods require less computation in comparison with the correlation between RF signals, the displacements estimated by such phase-sensitive methods are biased when the center frequency of RF echo varies. One of reasons for the change in the center frequency is the interference of echoes from scatterers within the wall. The artery-wall displacement includes both the component due to the radial translation of the arterial wall and that contributing to strain. In the case of the arterial wall, the displacement due to radial translation is larger than that contributing to strain by a factor of 10, and, thus, the error resulting from the translational motion often becomes larger than the small displacement contributing to strain. To reduce this error, in this study, a method is proposed in which the global translational motion is compensated before correlating echoes in two different frames to estimate the displacement distribution contributing to strain. Using this procedure, the significant error due to the large translational motion can be suppressed in comparison with the simultaneous estimation of the displacements due to translational motion and strain in the conventional methods. In this study, the accuracy improvement by the proposed method was validated using phantoms. The error from the theoretical strain profile and standard deviation in strain estimated by the proposed method was 12.0% and 14.1%, respectively, significantly smaller than that (23.7% and 46.2%) obtained by the conventional method.