Editorial for “MR Assessment of Acute Changes of Cerebral Perfusion, Metabolism, and Blood–Brain Barrier Permeability in Response to Aerobic Exercise”

The long-term positive impact of aerobic physical activity on cerebrovascular health and its protective role in the presence of disease or during healthy aging is supported by a large body of scientific evidence.1, 2 While many studies understandably investigate the long-term effects of regular aerobic activity, some literature also investigates the acute effects of exercise, notably on cerebral blood flow (CBF).3 Importantly, medical imaging, and specifically magnetic resonance imaging, can play a pivotal role in the assessment of the impact of both long-term and short-term aerobic physical activity on important cerebrovascular measures. In this issue of the Journal of Magnetic Resonance Imaging, Lin et al4 present an investigation of the short-term effects of a single session of aerobic exercise on different measures of brain perfusion and metabolism. One key innovation of this new study is that recent and complementary quantitative magnetic resonance imaging techniques are used to paint a clearer picture of the various cerebrovascular effects involved and to study their temporal evolution immediately following physical activity. The first of the quantitative techniques employs phase-contrast imaging to measure blood flow at the level of the main feeding arteries of the brain and thus provides an estimate of whole-brain CBF.5 While this technique lacks the spatial specificity of other techniques employed to measure CBF, such as arterial spin labeling, it benefits from a high accuracy and short acquisition time.5 In addition, a whole-brain estimate of venous oxygenation is provided by the T2 Relaxation Under Spin Tagging (TRUST) approach.6 This technique performs T2 mapping of venous blood in the sagittal sinus, using a spin-labeling technique to isolate the signal from blood. Blood T2 values are then converted to blood oxygenation using an external calibration. The combined information about whole-brain CBF and venous blood oxygenation can then be used to estimate the global cerebral metabolic rate of oxygen (CMRO2), a key metric of brain metabolism.7 Finally, it is also hypothesized that acute aerobic activity can influence the blood–brain barrier (BBB). While measuring BBB permeability noninvasively using MRI remains an area of technical development, this study leverages the Water Extraction with Phase Contrast Arterial Spin. Tagging (WEPCAST) technique.8 This approach tracks arterially labeled spins that make it to the venous system, isolating the signal from blood from the signal from other static tissues using a phase-contrast mechanism. The work presented in Lin et al4 represents a proof-of-concept study performed on a relatively small cohort of young and healthy volunteers, but it demonstrates that these quantitative imaging techniques can be used to dynamically track the impact of acute aerobic activity on various cerebrovascular measures. It opens the door to larger studies leveraging the same techniques, that will hopefully be able to investigate the physiological mechanisms of these effects on larger cohorts, in the presence of disease or during healthy aging.