Optimization of MR phase-contrast-based flow velocimetry and shear stress measurements

From 2D to 4D Phase-Contrast MRI in the Neurovascular System: Will It Be a Quantum Jump or a Fancy Decoration?

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.

Image-Based Evaluation of Vascular Function and Hemodynamics

The noticeable characteristics of the blood vascular structure are the inconsistent viscosity of blood and the stiffness of the vascular wall. If we can control these two factors, we can solve more problems related to hemodynamics and vascular wall function. Understanding the properties of hemodynamics and vascular wall function may provide more information applicable to clinical practice for cardiovascular disease. The bedside techniques evaluating vascular function usually measure indirect parameters. In contrast, some medical imaging techniques provide clear and direct depictions of functional cardiovascular characteristics. In this review, image-based evaluation of hemodynamic and vascular wall functions is discussed from the perspective of blood flow velocity, flow volume, flow pattern, peripheral vascular resistance, intraluminal pressure, vascular wall stress, and wall stiffness.

Screening for subclinical atherosclerosis by noninvasive methods in asymptomatic patients with risk factors

Atherosclerosis is a leading cause of cardiovascular death due to the increasing prevalence of the disease and the impact of risk factors such as diabetes, obesity or smoking. Sudden cardiac death is the primary consequence of coronary artery disease in 50% of men and 64% of women. Currently the only available strategy to reduce mortality in the at-risk population is primary prevention; the target population must receive screening for atherosclerosis. The value of screening for subclinical atherosclerosis is still relevant, it has become standard clinical practice with the emergence of new noninvasive techniques (radio frequency [RF] measurement of intima-media thickness [RFQIMT] and arterial stiffness [RFQAS], and flow-mediated vasodilatation [FMV]), which have been used by our team since 2007 and are based on detection marker integrators which reflect the deleterious effect of risk factors on arterial remodeling before the onset of clinical events. These techniques allow the study of values according to age and diagnosis of the pathological value, the thickness of the intima media (RFQIMT), the speed of the pulse wave (RFQAS), and the degree of endothelial dysfunction (FMV). This screening is justified in asymptomatic patients with cardiovascular risk factors (hypertension, diabetes, obesity, dyslipidemia, and tobacco smoking). Studies conducted by RF coupled with two-dimensional echo since 2007 have led to a more detailed analysis of the state of the arterial wall. The various examinations allow an assessment of the degree of subclinical atherosclerosis and its impact on arterial remodeling and endothelial function. The use of noninvasive imaging in screening and early detection of subclinical atherosclerosis is reliable and reproducible and allows us to assess the susceptibility of our patients with risk factors and ensures better monitoring of atherosclerosis, thus reducing the occurrence of cardiovascular events in the long term.