Ventricular morphology and function: study of cardiomyopathies

Abstract

The high resolution of magnetic resonance using the spin echo technique allows the acquisition of images of the left ventricle on which it is possible to determine the wall thickness and the chamber diameters. This is due to both the notable spontaneous contrast between the myocardium and the intracavitary flow without the need for contrast agents as well as the possibility it offers of obtaining planes on any orientation. In order to take standard and reproducible measurements, it is important to follow an acquisition strategy which enables a ventricular slice to be obtained on a longitudinal true anatomical plane and during the diastolic phase of the cardiac cycle. Since the long ventricular axis is not generally aligned within any of the natural planes which are systematically used in MRI (axial, coronal and sagittal), it will be necessary to perform a series of angulations: first, it is recommended that an estimate of the orientation of the base and the apex of the left ventricle be taken on one of the axial planes (Figure 2.1); on this plane we will plan a single slice, synchronized with the R wave of the electrocardiogram, that will give an oblique sagittal image which will depict the ventricle along its long axis, including the anterior wall, the ventricular apex and the inferior wall (Figure 2.2). Although this plane already includes the long axis of the left ventricle, a certain amount of artifacts frequently blur the contour of the inferior wall due to movements of the diaphram that is adjacent to it. Therefore, a third sequence is recommended, once again aligning the slice along an imaginary line that includes the apex and the mid point of the mitral plane. This will give us a new longitudinal plane of the left ventricle orthogonal to the previous one, along with the septal and lateral free wall, including the right ventricle and both atria, similar to the echocardiographic four- chamber plane (Figure 2.3). With this slice we can determine the thickness of the left ventricular wall and its transverse diameter. Obviously, these measurements will show good correlation with the corresponding ones obtained by echocardiography¹.