Myocardial suppression in vivo by spin locking with composite pulses.

Improved myocardium-blood contrast by myocardial suppression resulting from T 1 ρ-weighting in contrast-enhanced, gradient-echo, bright-blood cine images, acquired at 1.5T, is shown. In the standard images, blood has twice the intensity of muscle. In similar T 1 ρ-weighted images, it has 3-4 times the intensity of muscle. A composite spin-lock pulse before each observation pulse provides T 1 ρ-weighting. A typical pulse was : 90y-135x-360x-135x-90(-y) with element durations : 0.84, 1.26, 8.12, 1.26, and 0.84 ms. The tolerance of this composite pulse to shimming and frequency errors allows spin locking with comparatively weak RF and therefore low specific absorption rate (SAR). Initial clinical evaluation on patients with poor ventricular function demonstrates both a qualitative and quantitative improvement in delineation of myocardial borders.