Cardiac Function

90 Cardiac Function

Case 89 demonstrated that MRI is capable of acquiring high-quality structural (morphologic) information of the heart, with good tissue contrast and spatial resolution, while suppressing the artifacts associated with motion as well as the signal from blood. However, a more complete analysis of the heart with MRI requires that information regarding the efficiency of cardiac function be obtained as well. A full assessment of cardiac function, like structure, requires specially adapted sequences and postprocessing software.

In morphologic imaging, a certain number of echoes associated with lines of k space are split into small segments and are acquired during the diastolic phase of several cardiac cycles until a complete image is obtained. Imaging of cardiac function is accomplished in a similar fashion except the individual segments are smaller and spread across the entire cardiac cycle. In this way, small snapshots of information are gathered about each phase of the complete cardiac cycle in every heartbeat until a complete image of each phase is acquired. After reconstruction, the individual images are combined and viewed in a cine loop giving the appearance of a beating heart. Figure 90.1 presents five such images representing different phases of the cardiac cycle. The data necessary to complete this set of images was collected within one breath-hold covering 30 heartbeats.

To the trained eye, images of cardiac function alone provide valuable information about contractile uniformity and myocardial efficiency. The acquisition of additional data combined with postprocessing tools offers quantitative assessments similar to that obtained with other imaging modalities (e.g., nuclear medicine). Following the methods described above, a set of slices covering the entire left ventricle is acquired (Fig. 90.2

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