Tracking Oscillations in Brain Scans Could Reveal Vascular Disorders
Technique uses functional MRI signals to noninvasively assess abnormalities in circulation time.
Functional MRI experiments typically measure neuronal activity in the brain indirectly based on the blood oxygen level-dependent (BOLD) signal. Intriguingly, this signal also consists of systemic low-frequency oscillations (sLFOs), which are widely distributed throughout the brain and likely do not originate from neuronal activity. sLFOs have also been recorded in finger tips and toes, suggesting that these oscillations might originate outside the brain.
In support of this idea, a study published earlier this year in the Journal of Cerebral Blood Flow & Metabolism provides evidence that the sLFO appears in the arteries before entering the brain, and travels with the blood throughout the brain from large arteries to large veins. Using the publicly available MyConnectome dataset, the researchers analyzed sLFOs from 90 imaging scans collected on a single participant over a two-year period. Specifically, they looked for sLFO BOLD signals in the internal carotid arteries, and compared them both to the global signal, which primarily reflects the capillary and venous blood, and to the signals found in prominent veins such as the superior sagittal sinus and the internal jugular vein.
There were consistent time delays between the sLFO signals from the internal carotid arteries, the global signal and the veins, coinciding with the blood transit time through the cerebral vascular tree. The sLFO BOLD signal appears in the arteries prior to any location in the brain. From there, it passes through arterioles, capillaries, and venules, and finally drains out through the veins. According to the authors, this is the first study to follow a particular physiological component of the BOLD signal throughout the entire cerebral vasculature.
According to the authors, the study offers a novel and simple way for using fMRI to assess cerebral circulation time, thereby detecting and monitoring vascular disorders and injuries, without using exogenous contrast agents.