Abstract
PurposeTo validate three widely‐used acceleration methods in four‐dimensional (4D) flow cardiac MR; segmented 4D‐spoiled‐gradient‐echo (4D‐SPGR), 4D‐echo‐planar‐imaging (4D‐EPI), and 4D‐k‐t Broad‐use Linear Acquisition Speed‐up Technique (4D‐k‐t BLAST).Materials and MethodsAcceleration methods were investigated in static/pulsatile phantoms and 25 volunteers on 1.5 Tesla MR systems. In phantoms, flow was quantified by 2D phase‐contrast (PC), the three 4D flow methods and the time‐beaker flow measurements. The later was used as the reference method. Peak velocity and flow assessment was done by means of all sequences. For peak velocity assessment 2D PC was used as the reference method. For flow assessment, consistency between mitral inflow and aortic outflow was investigated for all pulse‐sequences. Visual grading of image quality/artifacts was performed on a four‐point‐scale (0 = no artifacts; 3 = nonevaluable).ResultsFor the pulsatile phantom experiments, the mean error for 2D PC = 1.0 ± 1.1%, 4D‐SPGR = 4.9 ± 1.3%, 4D‐EPI = 7.6 ± 1.3% and 4D‐k‐t BLAST = 4.4 ± 1.9%. In vivo, acquisition time was shortest for 4D‐EPI (4D‐EPI = 8 ± 2 min versus 4D‐SPGR = 9 ± 3 min, P < 0.05 and 4D‐k‐t BLAST = 9 ± 3 min, P = 0.29). 4D‐EPI and 4D‐k‐t BLAST had minimal artifacts, while for 4D‐SPGR, 40% of aortic valve/mitral valve (AV/MV) assessments scored 3 (nonevaluable). Peak velocity assessment using 4D‐EPI demonstrated best correlation to 2D PC (AV:r = 0.78, P < 0.001; MV:r = 0.71, P < 0.001). Coefficient of variability (CV) for net forward flow (NFF) volume was least for 4D‐EPI (7%) (2D PC:11%, 4D‐SPGR: 29%, 4D‐k‐t BLAST: 30%, respectively).ConclusionIn phantom, all 4D flow techniques demonstrated mean error of less than 8%. 4D‐EPI demonstrated the least susceptibility to artifacts, good image quality, modest agreement with the current reference standard for peak intra‐cardiac velocities and the highest consistency of intra‐cardiac flow quantifications. Level of Evidence: 1 Technical Efficacy: Stage 2J. Magn. Reson. Imaging 2018;47:272–281.
Highlights
To validate three widely-used acceleration methods in four-dimensional (4D) flow cardiac MR; segmented 4D-spoiled-gradient-echo (4D-SPGR), 4D-echo-planar-imaging (4D-echo-planar imaging (EPI)), and 4D-k-t Broad-use Linear Acquisition Speedup Technique (4D-k-t Broad-use Linear Acquisition Speed-up Technique (BLAST))
Four-dimensional flow cardiac MR (4D flow cardiac MR) is increasingly used in clinical and research applications for complex aortic and intra-cardiac flow assessment. 4D flow cardiac MR is a 3D phase-contrast magnetic resonance imaging (PC MRI) method with 3D velocity encoding allowing post hoc time-resolved 3D visualization and retrospective quantification of blood flow at any location in a 3D volume. 4D flow cardiac MR enables a wide variety of options for visualization and quantification of intra-cardiac flow, ranging from basic aspects such as flow volume and peak velocity to more complex analyses such as the estimation of hemodynamic effects at the vessel wall and myocardium, as well as visualization of flow pathways in the heart and great vessels.[1]
Comprehensive information on the details of pulse-sequences and corrections for all the 2D and 4D flow acceleration methods are included in the online Supplementary Document S1, which is available online
Summary
To validate three widely-used acceleration methods in four-dimensional (4D) flow cardiac MR; segmented 4D-spoiled-gradient-echo (4D-SPGR), 4D-echo-planar-imaging (4D-EPI), and 4D-k-t Broad-use Linear Acquisition Speedup Technique (4D-k-t BLAST). 4D-EPI demonstrated the least susceptibility to artifacts, good image quality, modest agreement with the current reference standard for peak intra-cardiac velocities and the highest consistency of intra-cardiac flow quantifications. Several data acceleration methods have been used to shorten scan times in 4D flow cardiac MR, including radial under-sampling, parallel imaging, k-t Broad-use Linear Acquisition Speed-up Technique (BLAST), k-t Sensitivity encoding (SENSE), generalized auto-calibrating partially parallel acquisitions (GRAPPA), echo-planar imaging (EPI), Iterative self-consistent parallel imaging reconstruction (L1-SPIRiT), and 5-point PC-vastly undersampled isotropic voxel radial projection imaging (VIPR).[2,3,4,5,6,7,8,9]
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