Editorial for “Does the Internal Carotid Artery Attenuate Blood‐Flow Pulsatility in Small Vessel Disease? A 7T 4D‐Flow MRI Study”

Editorial for “Does the Internal Carotid Artery Attenuate Blood-Flow Pulsatility in Small Vessel Disease? A 7T 4D-Flow MRI Study” Over the last decade four-dimensional (4D) flow magnetic resonance imaging (MRI) have steadily continued to march toward routine clinical implementation. Clinical adoption has been driven by radiologists championing the utilization of 4D flow. They have realized the potential of 4D flow to aid in decision-making of clinical diagnoses and prognoses. This has been made possible by technological advances in system hardware, data acquisition strategies, and reconstruction algorithms that have reduced 4D flow scan times. To date, most 4D flow applications have focused on body imaging. In these regions, hemodynamic parameters, including blood flow rates, pulse wave velocity, wall shear stress, pressure gradients and others, are used to characterize the health of the heart and large arteries such as the aorta. Yet, head/neck and neurovascular 4D flow has been underutilized compared to body applications, despite the fact that it appears to be a natural fit for 4D flow. The brain receives roughly 15–20% of the cardiac output. High perfusion levels make the brain susceptible to cardiovascular disease and, thus, a suitable target of 4D flow for hemodynamic characterization. Importantly, transand intracranial 4D flow spatiotemporal resolution needs are different from body imaging. For example, neurovascular 4D flow typically requires large volumetric coverage to include various tortuous vessels of interest, in contrast to tailored geometries of aortic and heart imaging. While respiratory gating is not necessary, high spatiotemporal resolution is needed to characterize small vessels. Moreover, the diversity of the neurovascular landscape can lead to a wide dynamic range of velocities. These neuroimaging requirements translate in longer scan times hindering 4D flow clinical adoption beyond body imaging. Thus, development of techniques to reduce neurovascular 4D flow scan times has been a subject of research. Recent advances include schemes that combine inflow enhancement, efficient sampling, and compressed sensing to produce improve flow signal, vessel contrast 4D flow, and simultaneous three-dimensional time of flight. Moreover, clever velocity encoding schemes have been proposed to alleviate dynamic range issues. Another approach toward increased spatiotemporal resolution is imaging at higher B0 field strengths. Neuroimaging applications at ultrahigh field (UHF) systems are becoming popular. This is due to increased availability of UHF scanners and neuroimaging robustness against common UHF technical challenges. For example, accelerated 4D flow brain imaging at 7T has been successfully implemented for the characterization of intracranial aneurysms. Nonetheless, there is a lack of 4D flow studies at 7T, with just a handful reported in the scientific literature. In the current issue of JMRI, van Tuijl et al contributed to unexplored territories and leveraged 7T imaging for high spatiotemporal resolution neurovascular 4D flow. The study showcased the ability of 4D flow to identify neurovascular modifications in the presence of cerebral small vessel disease (cSVD). The investigators characterized velocity pulsatility index (vPI), vPI attenuation, and vessel distensibility along the C1–C7 segments of the internal carotid artery (ICA) in a group of patients diagnosed with cSVD and in age/sex matched controls. In addition, the association of these hemodynamic markers with intracranial ICA calcification (iICAC) volumes determined from computed tomography angiography was examined in a subset of subjects. In this context, cSVD was defined by the presence of lacunar infarcts and deep intracerebral hemorrhage. Analysis of their data revealed intriguing results, including higher vPI, lower distensibility, and reduced vPI attenuation along the carotid siphon in cSVD patients compared to controls. Moreover, iICAC volumes were associated with increased vPI and decreased distensibility. These vascular markers indicate decreased ICA compliance and ability to attenuate the cardiac pulse wave. If we speculate on the physiological implications of such vascular alterations, it is not hard to imagine a scenario where the undampened energy of the cardiac pulse wave would ultimately be deposited in the micro-circulation and tissue. This