Validation and reproducibility of cardiovascular 4D-flow MRI from two vendors using 2 × 2 parallel imaging acceleration in pulsatile flow phantom and in vivo with and without respiratory gating

Abstract

Background: 4D-flow magnetic resonance imaging (MRI) is increasingly used.

Purpose: To validate 4D-flow sequences in phantom and in vivo, comparing volume flow and kinetic energy (KE) head-to-head, with and without respiratory gating.

Material and methods: Achieva dStream (Philips Healthcare) and MAGNETOM Aera (Siemens Healthcare) 1.5-T scanners were used. Phantom validation measured pulsatile, three-dimensional flow with 4D-flow MRI and laser particle imaging velocimetry (PIV) as reference standard. Ten healthy participants underwent three cardiac MRI examinations each, consisting of cine-imaging, 2D-flow (aorta, pulmonary artery), and 2 × 2 accelerated 4D-flow with (Resp+) and without (Resp-) respiratory gating. Examinations were acquired consecutively on both scanners and one examination repeated within two weeks. Volume flow in the great vessels was compared between 2D- and 4D-flow. KE were calculated for all time phases and voxels in the left ventricle.

Results: Phantom results showed high accuracy and precision for both scanners. In vivo, higher accuracy and precision ( P < 0.001) was found for volume flow for the Aera prototype with Resp+ (-3.7 ± 10.4 mL, r = 0.89) compared to the Achieva product sequence (-17.8 ± 18.6 mL, r = 0.56). 4D-flow Resp- on Aera had somewhat larger bias (-9.3 ± 9.6 mL, r = 0.90) compared to Resp+ ( P = 0.005). KE measurements showed larger differences between scanners on the same day compared to the same scanner at different days.

Conclusion: Sequence-specific in vivo validation of 4D-flow is needed before clinical use. 4D-flow with the Aera prototype sequence with a clinically acceptable acquisition time (<10 min) showed acceptable bias in healthy controls to be considered for clinical use. Intra-individual KE comparisons should use the same sequence.

Keywords: 4D-flow; cardiac output; heart failure; valvular regurgitation.

Fig. 1.

Validation setup and results. (a) Phantom geometry. A custom-built pump was used to produce a pulsatile flow through a nozzle, generating vortex rings downstream from the nozzle orifice. MR 4D-flow was acquired and compared to laser PIV data. (b) Validation of KE for both scanners. Good agreement was shown for Aera and a small underestimation for Achieva. (c, d) Validation of velocity in individual voxels in the sagittal centerline of the flow phantom for (c) Aera and (d) Achieva.

Fig. 2.

Image quality assessment of 4D-flow data. Grading scale: 0 = excellent image quality to 3 = inadequate image quality. Lines show median image quality. **P < 0.01.

Fig. 3.

Pulmonary artery flow curves from 2D-flow and 4D-flow with (Resp+) and without (Resp−) respiratory gating on the two scanners at the same day, same participant.

Fig. 4.

Correlation between SV from 4D-flow and 2D-flow acquisitions. Line of identity is shown by dashed line and line of regression with solid line.

Fig. 5.

Bland–Altman analysis of 4D-flow vs. 2D-flow volumes.

Fig. 6.

Correlation between SV from 4D-flow and 2D-flow acquisitions from Achieva when excluding acquisitions with suboptimal image quality. Line of identity is shown by dashed line and line of regression with solid line.