Method for assessing cardiac function using magnetic resonance imaging

The authors sought to define a method to use magnetic resonance (MR) to assess cardiac function by obtaining short-axis images of the left ventricle (LV) in humans. Sagittal and axial scout1H MR images were used in the protocol. The long axis of the LV was defined in both planes using the mitral valve and left ventricular apex as references. Based on this double angulation, the acquisition planes were created for a series of parallel short-axis images extending from the base to the apex of the left ventricular cavity. Cardiac images acquired with a fast-field echo technique, six slices with 16-20 phases per RR interval, were analyzed, representing the initial 75-80% of the cardiac cycle. For each slice, the endocardial border of the left ventricular chamber was manually traced. Using Simpson's rule, the total LV volume at a given phase was determined, considering the traced area, thickness, and position in three-dimensional space of each of the six constituent slices. The calculated volumes were plotted against time, and the stroke volume, ejection fraction, and cardiac output were determined. These parameters are clinically significant indices of cardiac function. Accurate and useful estimates of LV function can be obtained using MRI according to this protocol.