Noncontrast Magnetic Resonance Angiography in the Era of Nephrogenic Systemic Fibrosis and Gadolinium Deposition

Iodinated contrast media shortage: Insights and guidance from two major public hospitals

Global shortage of iodinated contrast medium (ICM) is the latest health care ripple-effect from the COVID-19 pandemic. Some public hospitals in Australia have less than a week's supply. Strategies are, therefore, urgently needed to conserve ICM for those diagnostic tests and interventions, which are time-critical, and without which patients would suffer death or significant morbidity. A plan is also required to continue providing best possible care to patients in the worst-case scenario of exhausted ICM supplies. This document, by representatives from two major public hospitals, will provide some guidance that is tailored to the Australian context.

Cerebral white matter vasculature: still uncharted?

White matter vasculature plays a major role in the pathophysiology of permanent neurological deficits following a stroke or progressive cognitive alteration related to small vessel disease. Thus, knowledge of the complex vascularization and functional aspects of the deep white matter territories is paramount to comprehend clinical manifestations of brain ischemia. This review provides a structured presentation of the existing knowledge of the vascularization of the human cerebral white matter from seminal historical studies to the current literature. First, we revisit the highlights of prenatal development of the endoparenchymal telencephalic vascular system that are crucial for the understanding of vessel organization in the adult. Second, we reveal the tangled history of debates on the existence, clinical significance, and physiological role of leptomeningeal anastomoses. Then, we present how conceptions on white matter vascularization transitioned from the mixed ventriculopetal/ventriculofugal theory, in which a low-flow area was interposed in between concurrent arterial flows, to the purely ventriculopetal theory. The latter model explains variable white matter sensitivity to ischemia by various organizations of ventriculopetal vessel terminals having different origin/length properties and interconnection patterns. Next, arteries supplying primarily the white matter are described according to their length and overall structure. Furthermore, the known distribution territories, to date, are studied in relation to primary anatomical structures of the human cerebral white matter, emphasizing the sparsity of the "ground-truth" data available in the literature. Finally, the implications for both large vessel occlusion and chronic small vessel disease are discussed, as well as the insights from neuroimaging. All things considered, we identify the need for further research on deep white matter vascularization, especially regarding the arterial supply of white matter fiber tracts.

MR Angiography Series: Fundamentals of Non-Contrast-enhanced MR Angiography

Unlike CT angiography, which requires the use of contrast medium, MR angiography (MRA) can be performed without the use of contrast agents. This subfield of MRA is referred to as non-contrast-enhanced MRA (NC-MRA). While NC-MRA can be performed in many patients, it is especially useful in the imaging of pediatric and pregnant patients, as well as in patients with renal impairment. NC-MRA can also provide unique functional and hemodynamic information that is not obtainable with CT angiography or contrast-enhanced MRA. This module gives an overview of the predominant NC-MRA techniques that are currently available on modern clinical MRI systems, while also discussing some new and emerging topics in the field. This module is the second in a series created on behalf of the Society for Magnetic Resonance Angiography (SMRA), a group of researchers and clinicians who are passionate about the benefits of MRA but understand its challenges. The full digital presentation is available online. ^©RSNA, 2021.