Accelerated dual‐venc 4D flow MRI with variable high‐venc spatial resolution for neurovascular applications

Abstract

Purpose: Dual-velocity encoded (dual-venc or DV) 4D flow MRI achieves wide velocity dynamic range and velocity-to-noise ratio (VNR), enabling accurate neurovascular flow characterization. To reduce scan time, we present interleaved dual-venc 4D Flow with independently prescribed, prospectively undersampled spatial resolution of the high-venc (HV) acquisition: Variable Spatial Resolution Dual Venc (VSRDV).Methods: A prototype VSRDV sequence was developed based on a Cartesian acquisition with eight-point phase encoding, combining PEAK-GRAPPA acceleration with zero-filling in phase and partition directions for HV. The VSRDV approach was optimized by varying z, the zero-filling fraction of HV relative to low-venc, between 0%-80% in vitro (realistic neurovascular model with pulsatile flow) and in vivo (n = 10 volunteers). Antialiasing precision, mean and peak velocity quantification accuracy, and test-retest reproducibility were assessed relative to reference images with equal-resolution HV and low venc (z = 0%). Results:In vitro results for all z demonstrated an antialiasing true positive rate at least 95% for R PEAK−GRAPPA = 2 and 5, with no linear relationship to z (p = 0.62 and 0.13, respectively). Bland-Altman analysis for z = 20%, 40%, 60%, or 80% versus z = 0% in vitro and in vivo demonstrated no bias >1% of venc in mean or peak velocity values at any R ZF . In vitro mean and peak velocity, and in vivo peak velocity, had limits of agreement within 15%. Conclusion:VSRDV allows up to 34.8% scan time reduction compared to PEAK-GRAPPA accelerated DV 4D Flow MRI, enabling large spatial coverage and dynamic range while maintaining VNR and velocity measurement accuracy.

Four‐dimensional flow MRI for quantitative assessment of cerebrospinal fluid dynamics: Status and opportunities

“…Neurovascular 4D flow requires high spatiotemporal resolution to detect blood flow in smaller structures 76,77 . Advances in neurovascular 4D flow acquisition, 76–79 reconstruction, 80,81 and the development of postprocessing 82–85 tools have turned 4D flow MRI into a versatile technique for the assessment of CBF dynamics. This includes derivation of a large number of hemodynamic biomarkers (reviewed elsewhere) 67,68,80,84,86–92 .…”

“…A 12.5% scan time reduction can be achieved by sharing a reference scan between the high and low V enc acquisitions 77 . More recently, ~35% scan time reductions in neurovascular dual‐V enc 4D flow scans were demonstrated by undersampling of the high V enc acquisition while preserving the dynamic range and VNRs of dual‐V enc 78 . Other studies have demonstrated the feasibility of accelerating neurovascular 4D flow acquisitions by 25% using machine learning and a convolutional neural network (CNN) that produces three directional velocities from three flow encodings, without requiring a fourth reference scan measuring background phase 81 .…”