Measurement of rapid variation in ultrasound backscattering during change in thickness of tissue phantom

The cyclic variation in ultrasound integrated backscatter (IB) during one cardiac cycle offers potential for evaluation of myocardial contractility. Since there is large motion due to the heartbeat in the heart wall, in the conventional method, the position of the region of interest (ROI) for calculating the IB is manually set for each timing during one heartbeat. Moreover, change in the size of the ROI during contraction and relaxation of the myocardium is not considered. In this paper, a new method is proposed for automatic tracking of the position and the size of the ROI. Rapid components, which are detected by increasing the spatial and time resolutions to 1 mm and 200 μs, respectively, highly depend on the instantaneous velocity of the ROI. These components are the result of interference between the waves reflected by the ROI and those reflected by scatterers other than the ROI. By separately estimating the bias component, these interfering components which cause interference are eliminated. By applying the proposed method to a sponge phantom, which was cyclically depressed in a water tank, and to the posterior wall of the heart of a healthy subject, the interference components were sufficiently suppressed and the IB signals were obtained with high spatial and time resolution.