3D cardiac motion estimation using RF signal decorrelation

Mouse cardiac ultrasound imaging is generally acquired as sets of 2D B-mode video or RF data. The high signal bandwidth and frame rate (>100 Hz) required for real-time 3D mouse heart scanning presents a major challenge making it unlikely that direct capture of finely sampled real-time 3D data will be achieved in the near future. Collecting and registering image sets from intersecting orthogonal 2D scan planes enables the estimation of 3D motion, but only at points along lines of intersection between acquired image frames. We propose the use of RF signal decorrelation to estimate elevational motion from 2D data at points other than the lines of intersection. RF data was collected and processed using a 30 MHz VisualSonics Vevo 770 scanner. A mouse heart was scanned along short and long axis imaging planes, producing RF data throughout the entire cardiac cycle. RF decorrelations were computed along all A-lines. Orthogonal displacement measurements were used to compute functions which map decorrelation to displacement at lines of intersection between planes. Combining in-plane speckle tracked estimates and out of plane decorrelation based displacement estimates yielded a full 3D displacement data set for the entire cardiac cycle. Displacements estimated using RF decorrelation were highly correlated with independent (orthogonal) speckle-tracked estimates. Out-of-plane decorrelation provides a method for computing 3D displacements from 2D scan-planes of in vivo mouse heart RF data. 3D displacement vectors may be used to compute 3D strain that may be useful when analyzing ischemic, normal and ldquoborder zonerdquo regions post myocardial infarct.