The methods described earlier for the evaluation of the left ventricular function are based on the analysis of changes in the shape of the ventricular cavity. There is, however, a need to evaluate the myocardial function more directly by analyzing the rate and extent of contraction and relaxation of the
Tlma celer ink
Param&Ln c Imsges
FIGURE 7 Phase analysis of dynamic cine-MRI images. See also Plate 54.
Jrnplitudt myocardial muscle. Echocardiography is the preferred imaging modality for the evaluation of myocardial wall thickening and measurement of regional myocardial contraction. Differences between diastolic and systolic wall thickness as well as the rate of contraction and relaxation of the myocardial muscle can be directly measured from the dynamic images. Most analysis techniques rely on manual identification of the endocardial and epicardial borders for measurement of myocardial thickness at any point in time during the cardiac cycle.
With the rapid development of cardiac MRI and fast CT imaging techniques, it is nowadays possible to obtain highresolution dynamic images of the heart with excellent quality allowing the clear delineation of endocardial and epicardial contours. This is particularly attractive with MRI imaging modality allowing images to be acquired in multiple oblique planes more suitable for alignments along the axis of the heart and the orientation of the ventricular cavities (see Fig. 8). Using dynamic cardiac MRI images in multiple planes it is possible to evaluate myocardial wall thickening in all segments of the left and right ventricle. Furthermore, with recent MR imaging techniques, the contrast ratio between the myocardium and the ventricular cavity and the surrounding structures is such that automatic edge detection techniques can reliably be
applied to the images for automatic assessment of regional wall motion .
Several studies have demonstrated that fast cine-MRI sequences provide means for reliable and accurate measurement of ejection fraction and ventricular function. Dark blood sequences also allow measurement of regional wall thickening. In an attempt to provide a better temporal analysis of regional wall motion abnormalities, Fourier analysis of regional wall motion can also be used. Similar to the "phase" analysis technique used in radionuclide angiography studies, Fourier analysis of regional wall motion from cine MRI images can depict subtle asynchronies in wall motion that are undetectable through visual analysis before they can affect the global ventricular function .
Dynamic MR imaging techniques provide very attractive and promising means for evaluation of global and regional cardiac wall motion and function. Special tagging techniques allow the myocardium to be physically marked with a geometric pattern that can be followed during the cardiac cycle to identify regional abnormality in myocardial contraction. This technique is described in Chapter 24.
Was this article helpful?