Decreases in myocardial motion caused by changes in tissue stiffness often appear in the early stage of ischemic heart disease. Since the myocardium exhibits complex 3-D motion, 3-D assessmentof the stiffness distribution is required for accurate diagnosis. However, conventional tissue Doppler and strain-rate imagingtechniques cannot meet the above requirement completely because they are angle-dependent, use in-plane (2-D) processing, and suffer from aliasing in the case of large myocardial motion. In order to overcome these problems, we propose novel methods to trackthe 3-D motion by using a 2-D phased array with a small apertureand to assess myocardial malfunction based on full strain tensors obtained by 3-D motion analysis. As a new method of 3-Dmyocardial motion tracking, we incorporated our phase-gradient method, which is capable of real-time 3-D displacement vector measurement using a 2-D phased array, and our combined autocorrelation method, which accurately measures large phase shifts at each element without aliasing. As a new method of assessing a myocardial ischemic region, the full strain tensor invariant obtained by the measured 3-D vectors is visualized as a 3-D myocardial strain image. We evaluated the feasibility of the proposed methods by numerically simulating left ventricle short-axis imaging of a 3-D elliptic myocardial model including infarction. RF signals received at each element on the 2-D array probe were faithfully simulated. When the simulated echoes were processed by the proposed methods, the invariant image obtained by the full strain tensor clearly depicted the hard infarction area where conventional imaging could not. The proposed methods were also modified for systems with an ordinary 1-D array probe. Finally, a phantom experiment was conducted by using the basic system based on the 1-D arrayprobe. These results validated the feasibility of the proposed methods.
- array probe
- myocardial local contraction
- strain tensor
- three-dimensional myocardial strain imaging
ASJC Scopus subject areas
- Radiology Nuclear Medicine and imaging