Self-gated golden-angle spiral 4D flow MRI

PurposeThe acquisition of 4D flow magnetic resonance imaging (MRI) in cardiovascular applications has recently made large progress toward clinical feasibility. The need for simultaneous compensation of cardiac and breathing motion still poses a challenge for widespread clinical use. Especially, breathing motion, addressed by gating approaches, can lead to unpredictable and long scan times. The current work proposes a time-efficient self-gated 4D flow sequence that exploits up to 100% of the acquired data and operates at a predictable scan time. MethodsA self-gated golden-angle spiral 4D flow sequence was implemented and tested in 10 volunteers. Data were retrospectively binned into respiratory and cardiac states and reconstructed using a conjugate-gradient sensitivity encoding reconstruction. Net flow curves, stroke volumes, and peak flow in the aorta were evaluated and compared to a conventional Cartesian 4D flow sequence. Additionally, flow quantities reconstructed from 50% to 100% of the self-gated 4D flow data were compared. ResultsSelf-gating signals for respiratory and cardiac motion were extracted for all volunteers. Flow quantities were in agreement with the standard Cartesian scan. Mean differences in stroke volumes and peak flow of 7.611.5 and 4.0 +/- 79.9mL/s were obtained, respectively. By retrospectively increasing breathing navigator efficiency while decreasing acquisition times (15:06-07:33 minutes), 50% of the acquired data were sufficient to measure stroke volumes with errors under 9.6mL. ConclusionThe feasibility to acquire respiratory and cardiac self-gated 4D flow data at a predictable scan time was demonstrated. Magn Reson Med 80:904-913, 2018. (c) 2018 International Society for Magnetic Resonance in Medicine

Accelerated aortic 4D flow cardiovascular magnetic resonance using compressed sensing: applicability, validation and clinical integration

Background Three-dimensional time-resolved phase-contrast cardiovascular magnetic resonance (4D flow CMR) enables the quantification and visualisation of blood flow, but its clinical applicability remains hampered by its long scan time. The aim of this study was to evaluate the use of compressed sensing (CS) with on-line reconstruction to accelerate the acquisition and reconstruction of 4D flow CMR of the thoracic aorta. Methods 4D flow CMR of the thoracic aorta was acquired in 20 healthy subjects using CS with acceleration factors ranging from 4 to 10. As a reference, conventional parallel imaging (SENSE) with acceleration factor 2 was used. Flow curves, net flows, peak flows and peak velocities were extracted from six contours along the aorta. To measure internal data consistency, a quantitative particle trace analysis was performed. Additionally, scan-rescan, inter- and intraobserver reproducibility were assessed. Subsequently, 4D flow CMR with CS factor 6 was acquired in 3 patients with differing aortopathies. The flow patterns resulting from particle trace visualisation were qualitatively analysed. Results All collected data were successfully acquired and reconstructed on-line. The average acquisition time including respiratory navigator efficiency with CS factor 6 was 5:02 +/- 2:23 min while reconstruction took approximately 9 min. For CS factors of 8 or less, mean differences in net flow, peak flow and peak velocity as compared to SENSE were below 2.2 +/- 7.8 ml/cycle, 4.6 +/- 25.2 ml/s and - 7.9 +/- 13.0 cm/s, respectively. For a CS factor of 10 differences reached 5.4 +/- 8.0 ml/cycle, 14.4 +/- 28.3 ml/s and - 4.0 +/- 12.2 cm/s. Scan-rescan analysis yielded mean differences in net flow of - 0.7 +/- 4.9 ml/cycle for SENSE and - 0.2 +/- 8.5 ml/cycle for CS factor of 6. Conclusions A six- to eightfold acceleration of 4D flow CMR using CS is feasible. Up to a CS acceleration rate of 6, no statistically significant differences in measured flow parameters could be observed with respect to the reference technique. Acquisitions in patients with aortopathies confirm the potential to integrate the proposed method in a clinical routine setting, whereby its main benefits are scan-time savings and direct on-line reconstruction

Respiratory motion corrected 4D flow using golden radial phase encoding

Purpose To minimize respiratory motion artifacts while achieving predictable scan times with 100% scan efficiency for thoracic 4D flow MRI. Methods A 4D flow sequence with golden radial phase encoding (GRPE) was acquired in 9 healthy volunteers covering the heart, aorta, and venae cavae. Scan time was 15 min, and data were acquired without motion gating during acquisition. Data were retrospectively re-binned into respiratory and cardiac phases based on respiratory self-navigation and the electrocardiograph signals, respectively. Nonrigid respiratory motion fields were extracted and corrected for during the k-t SENSE reconstruction. A respiratory-motion corrected (GRPE-MOCO) and a free-breathing (GRPE-UNCORR) 4D flow dataset was reconstructed using 100% of the acquired data. For comparison, a respiratory gated Cartesian 4D flow acquisition (CART-REF) covering the aorta was acquired. Stroke volumes and peak flows were compared. Additionally, an internal flow validation based on mass conservation was performed on the GRPE-MOCO and GRPE-UNCORR. Statistically significant differences were analyzed using a paired Wilcoxon test. Results Stroke volumes and peak flows in the aorta between GRPE-MOCO and the CART-REF showed a mean difference of -1.5 +/- 10.3 mL (P > 0.05) and 25.2 +/- 55.9 mL/s (P > 0.05), respectively. Peak flow in the GRPE-UNCORR data was significantly different compared with CART-REF (P < 0.05). GRPE-MOCO showed higher accuracy for internal consistency analysis than GRPE-UNCORR. Conclusion The proposed 4D flow sequence allows a straight-forward planning by covering the entire thorax and ensures a predictable scan time independent of cardiac cycle variations and breathing patterns