Comparison of fast acquisition strategies in whole‐heart four‐dimensional flow cardiac MR: Two‐center, 1.5 Tesla, phantom and in vivo validation study

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.

High-Frame-Rate Contrast-enhanced US Particle Image Velocimetry in the Abdominal Aorta: First Human Results

“…Subsequently, a three-dimensional acquisition was performed with freebreathing retrospective vectorcardiography-gated gradientecho and echo planar imaging readout (repetition time msec/ echo time msec, 8.9/4.6; echo planar imaging factor, 5; flip angle, 10°). Standard four-point three-directional velocity encoding was used with V enc (maximum velocity encoding) of 150 cm/sec (12). The acquisition volume captured the aortoiliac bifurcation, including renal and external iliac arter- Comparison of Echo PIV and Phase-contrast MRI Quantitative comparisons of echo PIV and phase-contrast MRI velocity data were performed.…”

Assessment of mitral valve regurgitation by cardiovascular magnetic resonance imaging

“…4D-flow CMR allows for visualization of 2D velocity vectors in any plane, facilitating a comprehensive assessment of the blood flow dynamics in the left atrium 32,33 . MR jets are dynamic and can change directions during systole depending on mitral leaflet adaptations.…”

“…This approach overcomes the limitations of the third method described above, but acquisition times and postprocessing can be challenging 27 . In retrospective valve tracking, a dynamic reformatted 2D phase-contrast plane is reconstructed by tracking the mitral annulus over the whole cardiac cycle 28,32,38 . MR jets are quantified by defining a systolic reformatted plane perpendicular to the single jet or individually for multiple jets.…”

Automated Cardiac Valve Tracking for Flow Quantification with Four-dimensional Flow MRI

“…(both with over 20 years of experience in cardiac MRI) using 1.5-T or 3.0-T MRI systems (Philips Healthcare, Best, the Netherlands). Two validated 4D flow MRI acquisition approaches were followed: a whole-heart protocol covering all four chambers of the heart (16) or a cardiac basal volume acquisition (planned parallel to the basal plane of the heart, encompassing all heart valves) (9,12). Four-dimensional flow MRI was supplemented with 2D steady-state freeprecession cine acquisitions of left and right ventricular two-and four-chamber views and left and right ventricular outflow tract in such a way that for each valve, two orthogonal cine views were available for valve tracking during postprocessing.…”