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The use of brain hemodynamics is important in the assessment of numerous pathophysiologic conditions. The measurement of perfusion or delivery of blood to tissues by MR imaging is essential for neuroradiologists to understand and appropriately apply to clinical practice. Several different approaches are used. DSC and dynamic contrast-enhanced MR imaging study the signal change (according to T2* and T1, respectively) induced by an exogenous contrast agent, allowing the measurement of CBF, CBV, and time-related parameters. Blood oxygen level--dependent (BOLD) MR imaging measures the T2* signal changes induced by the paramagnetic molecule deoxyhemoglobin. BOLD MR imaging provides complex measurements because the signal varies not only with changes in CBF but also with several other parameters such as tissular oxygen uptake and brain activation. Arterial spin-labeling MR imaging is a technique relying on labeled endogenous water as a tracer. By measuring the signal difference between 2 sets of acquisitions (labeling and control), arterial spin-labeling MR imaging calculates cerebral perfusion in a quantitative manner. This article aims to review the fundamentals of perfusion MR imaging techniques essential to any neuroradiology practice along with their advantages, disadvantages, and applications to research and clinical care. [ABSTRACT FROM AUTHOR]

Purpose: Endovascular treatment of unruptured intracranial aneurysms with stent-assisted coiling or flow diverter stents requires a prophylactic antiplatelet premedication to avoid thrombo-embolic complications. Guidelines for optimal antiplatelet regimens are poorly defined. The aim of this study is to report our experience using a high dosage antiplatelet premedication regimen for patients with unruptured intracranial aneurysms undergoing endovascular treatment by stent-assisted coiling or flow diverter stents. Methods: From a retrospective analysis of a prospectively maintained database, we collected clinical and angiographic data of 400 procedures in 362 patients treated by stent-assisted coiling or flow diverter stents for 419 unruptured intracranial aneurysms. Descriptive and analytic statistics were performed to report morbidity, mortality, and complication rates and to demonstrate associations between variables and outcomes. Logistic multivariable regression was performed to rule out confounding factors between subgroups. Results: Thrombo-embolic complications occurred in 23/400 procedures (5.75%) and hemorrhagic complications in 19/400 procedures (4.75%). The majority of complications were minor and transient with overall procedure-related morbidity and mortality rates of 1.75% (n = 7/400) and 1.25% (n = 5/400) respectively. The co-existence of multiple cardiovascular risk factors among smoking, hypertension, dyslipidemia, and age > 65 years old was significantly associated with permanent procedure-related morbidity (p = 0.006) and thrombo-embolic complications occurrence (p = 0.034). Age alone was associated with higher permanent morbidity (p = 0.029) and was the only variable associated with higher hemorrhagic complication (p = 0.024). Conclusion: In this study, the use of a high dosage antiplatelet premedication was safe and effective for the treatment of unruptured intracranial aneurysms with stent-assisted coiling or flow diverter stents. Mortality and morbidity rates compare favorably with the current literature. The thrombo-embolic complications rate is low and most of them were clinically silent. However, the hemorrhagic complications rate was substantial and a significant proportion of them were associated with mortality. [ABSTRACT FROM AUTHOR]

Neurovascular 4D-Flow MRI enables non-invasive evaluation of cerebral hemodynamics including measures of cerebral blood flow (CBF), vessel pulsatility index (PI), and cerebral pulse wave velocity (PWV). 4D-Flow measures have been linked to various neurovascular disorders including small vessel disease and Alzheimer’s disease; however, physiological and technical sources of variability are not well established. Here, we characterized sources of diurnal physiological and technical variability in cerebral hemodynamics using 4D-Flow in a retrospective study of cognitively unimpaired older adults (N = 750) and a prospective study of younger adults (N = 10). Younger participants underwent repeated MRI sessions at 7am, 4 pm, and 10 pm. In the older cohort, having an MRI earlier on the day was significantly associated with higher CBF and lower PI. In prospective experiments, time of day significantly explained variability in CBF and PI; however, not in PWV. Test-retest experiments showed high CBF intra-session repeatability (repeatability coefficient (RPC) =7.2%), compared to lower diurnal repeatability (RPC = 40%). PI and PWV displayed similar intra-session and diurnal variability (PI intra-session RPC = 22%, RPC = 24% 7am vs 4 pm; PWV intra-session RPC = 17%, RPC = 21% 7am vs 4 pm). Overall, CBF measures showed low technical variability, supporting diurnal variability is from physiology. PI and PWV showed higher technical variability but less diurnal variability. [ABSTRACT FROM AUTHOR]