By Paul Gabrielsen
NOTE: This is an overview of an article, which appeared on Stanford University’s website.
Click here to view the entire article.
An interdisciplinary Stanford team has recently developed a new method for quantitatively measuring human brain tissue using magnetic resonance imaging (MRI). Formerly, MRI provided mostly qualitative information, such as “bright” or”dark.” Previous attempts at quantitative MRI required uncomfortably long scan times.
This article describes how team members at Stanford measured the number of large molecules (macromolecules) within each cubic millimeter of the brain, which may change the way doctors diagnose and treat neurological disorders such as multiple sclerosis. Aviv Mezer, Stanford postdoctoral scholar in psychology, and psychology professor Brain Wandell discovered a faster scanning technique, although it is noted for its lack of consistency.
“Now we’ve found a way to make the fast method reliable,” Mezer said. Mezer and Wandell worked with neuroscientists, radiologists, and chemical engineers, calibrated their method with a physical model – a radiological “phantom” – filled with agar gel and cholesterol to mimic brain tissue in MRI scans.
MRI images of the brain are made up of many “voxels,” or three-dimensional elements. Each voxel represents the signal from a small volume of the brain. The fraction of each voxel filled with brain tissue (as opposed to water) is called the macromolecular tissue volume, or MTV. Mezer found that his MRI method produced MTV values that were in harmony with measurements that, until now, could only come from post-mortem brain specimens.
The team applied its method to a group of multiple sclerosis patients. MS attacks a layer of cells called the myelin sheath, which protects neurons the same way insulation protects a wire. Myelin comprises most of the volume of the brain’s “white matter.” The team found that the MTV of the white matter changes as MS erodes myelin. As they had predicted, the MTV tissue volumes were significantly lower than those of healthy volunteers.
Mezer and his Stanford colleagues are now following up with the patients to evaluate the effect of MS drug therapies. Mezer and Wandell are currently collaborating to use MRI measurements to monitor brain development in children, particularly as the children learn to read.
“You can compare whether the circuits are developing within specified limits for typical children,” Wandell said, “or whether there are circuits that are wildly out of spec, and we ought to look into other ways to help the child learn to read.” According to the team, tracking MTV can help doctors compare patients’ brains with those of the general population, therefore providing an opportunity to act on a problem before it’s too late.
The full article provides a link to the detailed study results, reported in Nature.
ABOUT THE AUTHOR
Paul Gabrielsen is an intern at Stanford News Service.