Experimental investigation of 2D myocardial strain imaging

Abnormal regional wall-motion often appears in the early stages of ischemic heart disease such as angina pectoris and cardiac infarction. Therefore, it is very important to accurately estimate multi-dimensional displacements in order to precisely diagnose ischemic heart disease. There are various estimation methods for measuring tissue displacement, but most of them estimate only the component of the 3-D displacement vector along the beam direction, making it difficult to correctly assess the abnormality of regional myocardial contraction using these conventional methods. We have proposed a Weighted-Phase Gradient Method (WPGM) for measuring 3-D displacement vectors regardless of the direction of movement. We obtained a strain tensor from the displacement vector and subsequently investigated 2- D and 3-D myocardial strain imaging by displaying parameters for regional myocardial contraction derived from components of the strain tensor. First, the validity of the 2-D and 3-D myocardial strain imaging was confirmed by numerical simulation using normal and ischemic myocardial models. Next, we evaluated the feasibility of 2-D myocardial strain imaging through phantom experiments. A phantom of the left ventricle was made from cylindrical konnyaku with a hollow. A balloon was inserted and controlled by a hydraulic pump in order to expand the ventricle. Echo data from the phantom corresponding to the short-axis cross section was received by a linear-array probe with a center frequency of 5MHz, using a 64-channel amplifier to control each element individually. Received echoes were processed into a 2-D displacement vector and strain or parameters for regional myocardial contraction using the proposed method. As a result, a 2-D displacement vector and strain images corresponding to the predicted deformation were obtained. These results validated the feasibility of the proposed method.