High-speed STEAM MRI of the human heart

High-speed STEAM MR images of the normal human heart were obtained from single cardiac cycles using a 2.0-T whole-body system equipped with conventional 10 mT m-1 gradients. The single-shot 90 degrees-TE/2-90 degrees-TM-(alpha-TE/2-Acq)n pulse sequence acquires n differently phase-encoded stimulated echoes. Measuring times of 127-254 ms were achieved using a "repetition time" of 3.96 ms in conjunction with data matrices of 32-64 x 128 pixels covering a field-of-view of 250-350 mm. The sequence provides easy access to anatomical short-axis and long-axis views of the heart by single and double oblique rotation of the image orientation. STEAM images resemble the features of spin-echo images with respect to chemical shifts, susceptibilities, and flow. Thus, no additional techniques are required for the suppression of blood signals. EKG-triggered acquisitions demonstrate that slice-selective STEAM sequences using short TM intervals allow an unambiguous delineation of those parts of the myocardium that remain stationary within the selected plane throughout the entire imaging process. Neither spins leaving nor entering the slice defined by the initial 90 degrees RF pulses give rise to a stimulated echo and therefore do not contribute to the resulting image.