Highly Accelerated Compressed‐Sensing 4D Flow for Intracardiac Flow Assessment

Abstract

BackgroundFour‐dimensional (4D) flow MRI allows for the quantification of complex flow patterns; however, its clinical use is limited by its inherently long acquisition time. Compressed sensing (CS) is an acceleration technique that provides substantial reduction in acquisition time.PurposeTo compare intracardiac flow measurements between conventional and CS‐based highly accelerated 4D flow acquisitions.Study TypeProspective.SubjectsFifty healthy volunteers (28.0 ± 7.1 years, 24 males).Field Strength/SequenceWhole heart time‐resolved 3D gradient echo with three‐directional velocity encoding (4D flow) with conventional parallel imaging (factor 3) as well as CS (factor 7.7) acceleration at 3 T.Assessment4D flow MRI data were postprocessed by applying a valve tracking algorithm. Acquisition times, flow volumes (mL/cycle) and diastolic function parameters (ratio of early to late diastolic left ventricular peak velocities [E/A] and ratio of early mitral inflow velocity to mitral annular early diastolic velocity [E/e′]) were quantified by two readers.Statistical TestsPaired‐samples t‐test and Wilcoxon rank sum test to compare measurements. Pearson correlation coefficient (r), Bland–Altman‐analysis (BA) and intraclass correlation coefficient (ICC) to evaluate agreement between techniques and readers. A P value < 0.05 was considered statistically significant.ResultsA significant improvement in acquisition time was observed using CS vs. conventional accelerated acquisition (6.7 ± 1.3 vs. 12.0 ± 1.3 min). Net forward flow measurements for all valves showed good correlation (r > 0.81) and agreement (ICCs > 0.89) between conventional and CS acceleration, with 3.3%–8.3% underestimation by the CS technique. Evaluation of diastolic function showed 3.2%–17.6% error: E/A 2.2 [1.9–2.4] (conventional) vs. 2.3 [2.0–2.6] (CS), BA bias 0.08 [−0.81–0.96], ICC 0.82; and E/e′ 4.6 [3.9–5.4] (conventional) vs. 3.8 [3.4–4.3] (CS), BA bias −0.90 [−2.31–0.50], ICC 0.89.Data ConclusionAnalysis of intracardiac flow patterns and evaluation of diastolic function using a highly accelerated 4D flow sequence prototype is feasible, but it shows underestimation of flow measurements by approximately 10%.Evidence Level2Technical EfficacyStage 1

Quantitative 4D flow MRI-derived thoracic aortic normal values of 2D flow MRI parameters in healthy volunteers

“…Ad-ditionally, head-to-head comparisons between the used kt-GRAP-PA 4 D flow MRI sequence and 2 D flow MRI has been published already in a phantom study and in vivo as well, without significant differences between both techniques [8,9] in pulsatile and nonpulsatile flow. Another limitation is the rather long acquisition time of the used 4 D flow MRI sequence, while there are other sequences with more advanced acceleration techniques that allow for scanning of the whole aorta within < 5 minutes [36]. This is because the aim of this study was to generate normal values using a commercially available and widely accessible 4 D flow MRI sequence.…”

Editorial for “Highly Accelerated Compressed Sensing 4D Flow for Intracardiac Flow Assessment”

“…The current study sheds light on the fact that optimal image acceleration is selected on the basis of a balance between scan time clinical feasibility and ideal data quality 7 . The CS‐based acceleration method is efficient in 4D flow imaging, considering its high‐dimensional characteristics 6,7 .…”

“…3 In this issue of Journal of Magnetic Resonance Imaging, Emrich et al studied the highly accelerated CS-based image acquisition in 4D flow imaging and validated it in comparison to the conventional technique of PI-based GeneRalized Autocalibrating Partial Parallel Acquisition (GRAPPA) for intra-cardiac valve flow assessment in 50 healthy volunteers in a prospective study. 7 CS 4D flow data were undersampled using a spiral phyllotaxis subsampling pattern and the acceleration factors were set in 3 for GRAPPA and 7.7 for CS. All four intra-cardiac valve flow measurements and the diastolic function assessment of E/A and E/e' were included in the validation effort.…”

“…The current study sheds light on the fact that optimal image acceleration is selected on the basis of a balance between scan time clinical feasibility and ideal data quality. 7 The CS-based acceleration method is efficient in 4D flow imaging, considering its high-dimensional characteristics. 6,7 Meanwhile, the possible underestimation associated with the highly accelerated image acquisition is a concern as presented in the current study.…”

“…7 The CS-based acceleration method is efficient in 4D flow imaging, considering its high-dimensional characteristics. 6,7 Meanwhile, the possible underestimation associated with the highly accelerated image acquisition is a concern as presented in the current study. When utilizing a CS-based high acceleration rate of 7.7, the aortic 4D flow image scan time can be shortened substantially up to 2 min with the trade-off being the underestimation of peak velocities and peak flow generally within 13% when compared with the conventional PI-based methods.…”