Recent progress in radiofrequency-tagged left ventricular function studies.

Magnetic resonance imaging (MRI) is the optimal tool for the evaluation of ventricular function due to improved contrast, spatial resolution, and signal-to-noise performance over other imaging modalities. The ability to select oblique tomographic planes allows longand shortaxis views of the heart to be obtained from any patient. With the advent of multiphase (cine), electrocardiogramgated cardiac imaging, i t became possible to evaluate the overall function of the ventricle. The desire for quantitative regional contractile performance information has led to the development of means to automatically encode the motion of the myocardium. These methods fall into two classes: phase velocity mapping and radiofrequency (RF) tagging methods. In RF-tagged ventricular function studies, the myocardium receives a selective saturation excitation immediately on the R-wave trigger. This excitation, an example of which is shown in Fig. 1, produces a series of parallel saturation bands in the field of view (FOV) that appear as parallel dark lines. The direction of the lines is determined by the direction of the applied tagging gradient. Delivering two such excitations (each using one of the in-plane gradients) will produce a tag grid (1-6). For the grid tag excitation, the second set of RF pulses is phase