First-pass myocardial perfusion MRI: artifacts and advances

Abstract

Magnetic resonance imaging of myocardial perfusion during the first-pass of a contrast agent has been proved valuable for the detection of coronary artery disease. During contrast enhancement, transient dark rim artifacts are sometimes visible in the subendocardium, mimicking real perfusion defects and complicating diagnosis. This thesis studied several different mechanisms behind dark rim artifacts with the aim of exploring possible solutions to minimise them and potentially improve the accuracy of perfusion methods. An in-depth review of current myocardial perfusion imaging techniques is presented. This is followed by a comprehensive study of dark rim artifacts, with realistic phantom and numerical simulations, and in vivo measurements. Simulations for the most common perfusion sequences are made, showing that Gibbs, myocardial radial-motion, and frequency-offsets are capable of creating endocardial signal-loss, although dependent on many sequence parameters. Frequency-offsets during first-pass of contrast agentwere measured in vivo; results show negligible intra-voxel signal dephasing, although careful frequency adjustments need to be considered for the b-SSFP and h-EPI sequences. The investigations on dark rim artifacts lead to the development of an ultrafast but robust sequence suitable for first-pass myocardial perfusion imaging, and the assessment of its in vivo performance. The sequence was a multi-slice single-shot spin-echo EPI sequence accelerated by a reduced phase-encode FOV (zonal excitation), and parallel imaging R=2. When tested in clinical volunteers with CA at rest, the sequence yielded a reasonable CNR with a very short acquisition time, although spatial resolution needs to be improved