Cerebrovascular MRI: a review of state‐of‐the‐art approaches, methods and techniques

Abstract

Cerebrovascular imaging is of great interest in the understanding of neurological disease. MRI is a non-invasive technology that can visualize and provide information on: (i) the structure of major blood vessels; (ii) the blood flow velocity in these vessels; and (iii) the microcirculation, including the assessment of brain perfusion. Although other medical imaging modalities can also interrogate the cerebrovascular system, MR provides a comprehensive assessment, as it can acquire many different structural and functional image contrasts whilst maintaining a high level of patient comfort and acceptance. The extent of examination is limited only by the practicalities of patient tolerance or clinical scheduling limitations. Currently, MRI methods can provide a range of metrics related to the cerebral vasculature, including: (i) major vessel anatomy via time-of-flight and contrast-enhanced imaging; (ii) blood flow velocity via phase contrast imaging; (iii) major vessel anatomy and tissue perfusion via arterial spin labeling and dynamic bolus passage approaches; and (iv) venography via susceptibility-based imaging. When designing an MRI protocol for patients with suspected cerebral vascular abnormalities, it is appropriate to have a complete understanding of when to use each of the available techniques in the 'MR angiography toolkit'. In this review article, we: (i) overview the relevant anatomy, common pathologies and alternative imaging modalities; (ii) describe the physical principles and implementations of the above listed methods; (iii) provide guidance on the selection of acquisition parameters; and (iv) describe the existing and potential applications of MRI to the cerebral vasculature and diseases. The focus of this review is on obtaining an understanding through the application of advanced MRI methodology of both normal and abnormal blood flow in the cerebrovascular arteries, capillaries and veins.

Comparison of extracranial artery stenosis and cerebral blood flow, assessed by quantitative magnetic resonance, using digital subtraction angiography as the reference standard

“…MRI is a nonradioactive detection technique capable of detecting acute ischemic lesions and providing morphological and hemodynamic information. [30] Because of this, an increasing number of medical doctors prefer it to QMR when examining patients with extracranial artery stenosis. PWI is an important MRI for detecting cerebral hemodynamics changes, and it has been widely used in clinical practice.…”

What Have We Learned from Perfusion MRI in Multiple Sclerosis?

“…In DSC, an intravenous paramagnetic contrast agent is administered, and the brain is scanned with a rapid imaging technique, typically T2*-weighted single-shot gradient-echo-planar imaging 9 or a T2-weighted spin-echo-planar scan. When the contrast agent reaches the tissue vasculature, it makes the vessels more paramagnetic, creating field inhomogeneities around the vessels.…”

“…This function can be converted into maps of cerebral blood flow, cerebral blood volume, and temporal parameters such as mean transit time. 9 However, this step requires a deconvolution with the concentration function in a feeding artery, the arterial input function, which has its limitations. Deconvolution is an inherently ill-posed mathematic operation, and accurate measurement of the arterial input function is hampered by partial volume effects.…”

“…Furthermore, the ill-posed deconvolution and the selection of the arterial input function required in DSC make serial studies particularly difficult to perform. 9 Second, analysis of perfusion imaging requires many technical steps that are each susceptible to measurement error. Imaging protocols and techniques are also heterogeneous, with most studies using DSC-MR imaging but some using ASL.…”

Hyperpolarized 13C MR Angiography

“…The most frequently applied angiographic techniques are ultrasound imaging (US), computed tomography (CT), and nuclear medicine imaging such as PET [1]. US is non-invasive, but has its limitations in imaging of the cerebrovascular system, where cranium and tissue-bone interfaces cause attenuation and disturbance of the signal.…”