[Image courtesy of UC Berkeley]
The technology, known as a displacement spectrum (DiSpect) MRI, tags hydrogen spins in blood water molecules, lets them travel for several seconds, and then reads those tags when the blood reaches larger veins.
“We can tag information onto spins in the blood, knowing that they store that information for three, four, five seconds, or so,” said Michael Lustig, professor of electrical engineering and computer sciences and the study’s principal investigator. “In that time, the tagged blood will have traveled, draining from the brain’s capillaries and smaller veins into larger veins. And when we image it at the larger veins, we can decode the information to determine where it came from.”
DiSpect mapped each vein’s territory and captured blood-flow changes. The scan spotted whole-brain shifts after caffeine and local shifts during simple hand-squeezing tasks.
“This is an occurrence that has been widely hypothesized but difficult to directly observe using conventional MRI methods, like functional MRI [fMRI],” said lead author Ekin Karasan, a postdoctoral researcher in electrical engineering and computer sciences. “DiSpect could potentially help us gain a deeper understanding of blood flow redistribution as it relates to brain activity — a phenomenon known as arterial blood stealing.”
How the technology works
DiSpect uses the body’s own blood water as a built-in tracer. Researchers first tag the hydrogen spins in water molecules at a known location. Because these spins hold their magnetic memory for several seconds, the tagged blood can move from tiny capillaries into larger veins before the team captures an image. By decoding the preserved spin information at the larger veins, the scan reveals exactly where the blood originated, effectively mapping brain perfusion in reverse.
“When it comes to detecting brain activity, our method can help us determine whether the neurons are driving signal changes, or whether they are being driven by local perfusion of blood movement,” said Chunlei Liu, a professor in electrical engineering and computer sciences and the Helen Wills Neuroscience Institute. “Unlike other MRI methods, DiSpect allows you to pin down where the local perfusion changes are happening, which could help advance our understanding of these mechanisms.”
Karasan and the team suggest that DiSpect could help physicians assess arteriovenous malformations without contrast agents or catheterization.
“Starting at the veins that are draining this malformation, we could use reverse imaging to identify which artery the blood is coming from — [and] then figure out whether intervention is required,” Karasan said.
