Simultaneous 3D‐TOF angiography and 4D‐flow MRI with enhanced flow signal using multiple overlapping thin slab acquisition and magnetization transfer

Abstract

Purpose: To investigate the fusion of 3D time-of-flight principles into 4D-flow MRI to enhance vessel contrast and signal without an exogenous contrast agent, enabling simultaneous in-flow based angiograms. Methods: A 4D-flow MRI technique was developed consisting of multiple overlapping slabs with intermittent magnetization transfer preparation. The scan time penalty associated with multiple slab acquisitions was mitigated by using undersampled distributed spiral trajectories and compressed sensing reconstruction. A flow phantom was used to characterize in-flow enhancement, velocity noise improvement, and flow rate measurements against the single-slab 4D-flow MRI. In a patient-volunteer cohort (n = 15), magnitude-based angiograms were radiologically evaluated against 3D time-of-flight, and velocity measurements were compared pixel-wise against single-slab and contrast-enhanced 4D-flow MRI.Results: Multiple-slab acquisitions, together with magnetization transfer preparation, substantially improved vessel signal, contrast, and vessel conspicuity in magnitude angiograms. Both clinical 3D time-of-flight and the proposed technique produced equivalent vessel depictions with no statistically significant difference (p < .1). Both techniques also produced clear depictions of brain aneurysms in all patients; however, very small vessels tended to show reduced conspicuity in the proposed technique. Velocity measurements agreed with contrast-enhanced and single-slab scans with high correlations (R 2 = 0.941-0.974) and agreements (slopes = 0.994-1.071). Slab boundary and magnetization transfer-related artifacts were not observed in velocity measurements, and velocity noise was reduced with in-flow enhancement over single-slab scans (phantom). Conclusion:The vessel signal and contrast can be improved in 4D-flow MRI without exogenous contrast agents by utilizing in-flow enhancement, efficient sampling, and compressed sensing. The in-flow enhancement also enables simultaneous 3D time-of-flight angiograms useful for flow quantification and diagnosis.

Systematic review of reconstruction techniques for accelerated quantitative MRI

“…Different transform operators 𝜙 and priors have been proposed to find a sparse representation of the images. This includes the wavelet transform, 27,[47][48][49][50][51][52] the total variation transform, 26,50,[52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68] group sparsity where images are divided into multiple sparse regions, 69 weighted quadratic prior that aims to suppress the noise and reconstruction artifacts based on the intensity differences between neighboring voxels, 56 gradient across the contrast dimension, 53,[70][71][72][73][74] second-order discrete derivative in the contrast dimension, 75,76 principal component analysis-based transform, 75,[77][78][79][80] image ratio constraints, where the ratio between a low-resolution image and the reconstructed image is used as a constraint, 50 and learned sparsifying transform 𝜙 from the measurements. 81 Apart from these, alternative ways to use regularizers and transform domains have been proposed.…”

Editorial for “Multidelay MR Arterial Spin Labeling Perfusion Map for the Prediction of Cerebral Hyperperfusion After Carotid Endarterectomy”

“…Emerging MR angiographic methods that efficiently portray neurovascular anatomy and provide quantitative hemodynamic information may therefore be another practical area of future investigation. [8][9][10] In closing, the work of Fan et al is notable in that it probes the potential of multidelay ASL perfusion MRI to predict postoperative radiographic cerebral hyperperfusion and presents a practical image-based scoring system to help identify a subgroup of patients who may progress to symptomatic CHS. Further study will be needed to determine whether the presented approach can accurately predict symptomatic CHS, alter clinical decision-making, and improve patient outcomes.…”

“…Consequently, further work is needed to refine and standardize ASL perfusion MRI as well as more generally develop MRI‐based methods that safely, efficiently, and reliably evaluate both neurovascular anatomy and hemodynamics. Emerging MR angiographic methods that efficiently portray neurovascular anatomy and provide quantitative hemodynamic information may therefore be another practical area of future investigation 8–10 …”

Editorial for “Does the Internal Carotid Artery Attenuate Blood‐Flow Pulsatility in Small Vessel Disease? A 7T 4D‐Flow MRI Study”

“…Recent advances include schemes that combine inflow enhancement, efficient sampling, and compressed sensing to produce improve flow signal, vessel contrast 4D flow, and simultaneous three-dimensional time of flight. 2 Moreover, clever velocity encoding schemes have been proposed to alleviate dynamic range issues. 3 Another approach toward increased spatiotemporal resolution is imaging at higher B0 field strengths.…”

“…Thus, development of techniques to reduce neurovascular 4D flow scan times has been a subject of research. Recent advances include schemes that combine in‐flow enhancement, efficient sampling, and compressed sensing to produce improve flow signal, vessel contrast 4D flow, and simultaneous three‐dimensional time of flight 2 . Moreover, clever velocity encoding schemes have been proposed to alleviate dynamic range issues 3 .…”