From2Dto4DPhase‐ContrastMRIin the Neurovascular System: Will It Be a Quantum Jump or a Fancy Decoration?

Abstract

Considering the crosstalk between the flow and vessel wall, hemodynamic assessment of the neurovascular system may offer a well-integrated solution for both diagnosis and management by adding prognostic significance to the standard CT/MR angiography. 4D flow MRI or time-resolved 3D velocity-encoded phase-contrast MRI has long been promising for the hemodynamic evaluation of the great vessels, but challenged in clinical studies for assessing intracranial vessels with small diameter due to long scan times and low spatiotemporal resolution. Current accelerated MRI techniques, including parallel imaging with compressed sensing and radial k-space undersampling acquisitions, have decreased scan times dramatically while preserving spatial resolution. 4D flow MRI visualized and measured 3D complex flow of neurovascular diseases such as aneurysm, arteriovenous shunts, and atherosclerotic stenosis using parameters including flow volume, velocity vector, pressure gradients, and wall shear stress. In addition to the noninvasiveness of the phase contrast technique and retrospective flow measurement through the wanted windows of the analysis plane, 4D flow MRI has shown several advantages over Doppler ultrasound or computational fluid dynamics. The evaluation of the flow status and vessel wall can be performed simultaneously in the same imaging modality. This article is an overview of the recent advances in neurovascular 4D flow MRI techniques and their potential clinical applications in neurovascular disease. Level of Evidence: 5 Technical Efficacy Stage: 3

Noninvasive quantification of cerebrovascular pressure changes using 4D Flow MRI

“…Time-resolved four-dimensional phase-contrast magnetic resonance imaging (4D Flow MRI) enables full-field flow quantification through multidirectional velocity encoding. 24,25 Several studies have highlighted the applicability of 4D Flow MRI for cerebrovascular assessment, 26,27 including mapping non-diseased flow characteristics, 28,29 identifying flow features in cerebrovascular atherosclerosis, 9,18 evaluating arteriovenous malformations, [30][31][32] or assessing hemodynamic changes in neurodegenerative disorders. 33,34 When it comes to using 4D Flow MRI to map relative pressure in the cerebrovasculature, a few examples exist largely building on methods used in other cardiovascular domains.…”

Imaging Modalities for Intracranial Aneurysm: More Than Meets the Eye

“…This 2D phasecontrast MRI has evolved to 3D time-resolved phase-contrast MRI, also called 4D-MRI. This flow imaging quantifies direct blood flow velocity in 3D, allowing flow pattern modeling and quantification of WSS, OSI and vorticity (55)(56)(57)(58). In 2020, two complete state-of-the-art reviews on the 4D-MRI's ability to study IA hemodynamics have been published (56,58).…”

“…This flow imaging quantifies direct blood flow velocity in 3D, allowing flow pattern modeling and quantification of WSS, OSI and vorticity (55)(56)(57)(58). In 2020, two complete state-of-the-art reviews on the 4D-MRI's ability to study IA hemodynamics have been published (56,58). To summarize, 4D-MRI, mostly compared to CFD, reliably depicts intra-aneurysmal flow pattern in different IA morphologies.…”

“…To summarize, 4D-MRI, mostly compared to CFD, reliably depicts intra-aneurysmal flow pattern in different IA morphologies. However, this 4D-imaging still has great limitations, in particular in terms of spatial and temporal resolution which has consequences on the calculation of hemodynamic parameters (depending on magnetic field and acquisition protocol, 4D-MRI = ranging from 0.43 × 0.43 × 0.43 to 1 × 1 × 1.6 mm 3 voxels vs. CFD = 0.1-mm voxels) ( 56 , 58 ). For instance, the WSS values had a lower magnitude when derived from 4D-MRI even if the localization of these WSS are similar ( 59 ).…”

Evaluation of the Role of Angiography in Diagnosis and Management of Brain Aneurysm

“…Recent advances in rendering have shown promising evidence of 4D magnetic resonance imaging and 3D contrast-MRI in the diagnostic accuracy and subsequent follow-up of management of cerebral aneurysms and vascular abnormalities. [16] While CT angiography is the initial test for ruptured aneurysms, MR angiography can be used to confirm the diagnosis in late presentations. While CT angiography is suitable as initial imaging for ruptured aneurysms, it would not be as useful in patients who developed diffuse subarachnoid hemorrhage.…”