Date Published: February 11, 2019
Publisher: Public Library of Science
Author(s): Ye Tian, Jason Mendes, Apoorva Pedgaonkar, Mark Ibrahim, Leif Jensen, Joyce D. Schroeder, Brent Wilson, Edward V. R. DiBella, Ganesh Adluru, Dalin Tang.
Dynamic contrast enhanced MRI of the heart typically acquires 2–4 short-axis (SA) slices to detect and characterize coronary artery disease. This acquisition scheme is limited by incomplete coverage of the left ventricle. We studied the feasibility of using radial simultaneous multi-slice (SMS) technique to achieve SA, 2-chamber and/or 4-chamber long-axis (2CH LA and/or 4CH LA) coverage with and without electrocardiography (ECG) gating using a motion-robust reconstruction framework.
12 subjects were scanned at rest and/or stress, free breathing, with or without ECG gating. Multiple sets of radial SMS k-space were acquired within each cardiac cycle, and each SMS set sampled 3 parallel slices that were either SA, 2CH LA, or 4CH LA slices. The radial data was interpolated onto Cartesian space using an SMS GRAPPA operator gridding method. Self-gating and respiratory states binning of the data were done. The binning information as well as a pixel tracking spatiotemporal constrained reconstruction method were applied to obtain motion-robust image reconstructions. Reconstructions with and without the pixel tracking method were compared for signal-to-noise ratio and contrast-to-noise ratio.
Full coverage of the heart (at least 3 SA and 3 LA slices) during the first pass of contrast at every heartbeat was achieved by using the radial SMS acquisition. The proposed pixel tracking reconstruction improves the average SNR and CNR by 21% and 30% respectively, and reduces temporal blurring for both gated and ungated acquisitions.
Acquiring simultaneous multi-slice SA, 2CH LA and/or 4CH LA myocardial perfusion images in every heartbeat is feasible in both gated and ungated acquisitions. This can add confidence when detecting and characterizing coronary artery disease by revealing ischemia in different views, and by providing apical coverage that is improved relative to SA slices alone. The proposed pixel tracking framework improves the reconstruction while adding little computational cost.
Dynamic contrast enhanced MRI of the heart is becoming a more widespread tool to detect and characterize coronary artery disease. A standard protocol acquires 2–4 SA slices every heartbeat during the first pass of contrast agent, under stress and at rest. ECG gating and breath-holding are commonly employed to suppress motion. However, this acquisition suffers from limited coverage of the left ventricle myocardium, which can limit the sensitivity and confidence of detecting and quantifying ischemic regions. And when the ECG signal is poor, for example in patients with arrhythmias or patients who cannot hold their breath, the scans can be non-diagnostic.
In this study we tested the feasibility of acquiring different views of myocardium perfusion by using radial SMS. We were able to achieve full coverage of 17 myocardial segments suggested by American Heart Association  during first-pass perfusion including the apical segment typically missed by traditional 3 SA slices coverage. Compared with previous studies on acquiring LA slices that acquired 3 SA slices and 0–2 LA slices at a spatial resolution 2.7 x 3.6 mm to 3.1 x 4.1 mm , or acquired 4–7 LA slices at a spatial resolution 3.5 x 1.9 mm , the unique acquisition framework proposed here is able to achieve high resolution (1.8 x 1.8 mm) multi-view coverage in patients with high heartrate (up to 120 bpm) and also in patients with poor ECG gating, where both SA and LA slices at systolic and diastolic phases are guaranteed by ungated acquisitions. These advantages can increase the confidence when reading the scans. As well, the acquired LA views were matched with other acquisitions like cine, T1 maps and LGE images during the same scan, which collectively can provide a more confident detection of cardiac diseases.
Our results suggest that acquiring SA, 2CH LA and/or 4CH LA perfusion images using radial SMS technique is feasible in both gated and ungated myocardial perfusion dynamic contrast enhanced imaging. Combined SA and LA coverage may add confidence when detecting and characterizing coronary artery disease by revealing perfusion deficits in different views, and providing apical coverage that is improved relative to short axis slices alone. The self-gating and respiratory binning methods can separate acquired time frames into near-systolic and near-diastolic phases and different respiratory states. The proposed reconstruction framework using SMS GROG pre-interpolation and a motion robust iterative PT-STCR reconstruction improves the reconstruction of undersampled cardiac perfusion MRI while adding little computational cost.