Effects of coordinate system choice on measured regional myocardial function in short axis cine electron-beam tomography

Following myocardial infarction, the size of the infarcted region and the systolic functioning of the non-infarcted region are commonly assessed by various cross-sectional imaging techniques. For the assessment of patterns of ventricular contraction, images are commonly acquired of ventricular cross-sections normal to the long axis of the heart and parallel to the mitral valve plane. The endocardial and epicardial surfaces of the myocardium are identified. Then the ventricle is divided into sectors and the volumes of blood and myocardium within each sector at multiple phases of the cardiac cycle are measured. Regional function parameters are derived from these measurements. This generally mandates the use of a polar or cylindrical coordinate system. Various algorithms have been used to select the origin of this coordinate system. These include the centroid of the endocardial surface, the epicardial surface, or of a polygon whose vertices lie midway between the epicardial and endocardial surfaces of the myocardium (centerline method). Another algorithm has been developed in the laboratory. This uses the centroid (or center of mass) of the myocardium exclusive of the ventricular cavity.Each of these choices for origin of coordinate system can be derived from the end-diastolic image or from the end-systolic image. Alternately, new coordinate system can be selected for each phase of the cardiac cycle. These are referred to as floating coordinate systems. A series of computer models have been developed in the laboratory to study the effects of each of these choices on the regional function parameters of normal ventricles and how these choices effect the quantification of regional abnormalities after myocardial infarction