In magnetic resonance imaging (MRI), a magnetic field generated by a large magnet sends protons in the brain spinning. Specially constructed coils of wire in the machine detect changes in the spin, which differ in different tissue types, as the magnetic field changes. Computer algorithms then use measurements from different parts of the brain to create the anatomical picture.
MRI machines in medical centers typically have up to 12 coils, but the new devices under development have up to 96 coils arrayed in a dense field over the scalp. "A small detector up close is more efficient," says Lawrence Wald, a biophysicist at Boston's Massachusetts General Hospital (MGH), whose team has developed the devices in collaboration with Siemens. "But it only captures a small part of the brain, so you need lots of small detectors spread out over the scalp." Each coil measures a small but highly accurate spin signal from the chunk of brain tissue beneath it. The images are then computationally stitched together to create a high-resolution picture of the brain.
These multichannel devices have already helped some epilepsy patients. In a study using an early prototype, neurologists found abnormalities in about two-thirds of epileptic patients whose previous brain scans had been declared normal, making these patients better candidates for neurosurgery.
Scientists are now using a newer prototype to study Alzheimer's patients. "In diseases like Alzheimer's, where there is not a basic diagnosis based on imaging, we hope that being able to look at smaller alternations in the brain would yield some additional diagnostic information and perhaps allow you to monitor medication," says Wald.
Patients suspected of having Alzheimer's may get an MRI to rule out other neurological causes for their symptoms. But recent studies suggest that subtle neurological changes increase risk for the disease; these changes can include shrinkage of the hippocampus, a crucial memory area, and of parts of the cortex important for memory and higher cognitive function. Detecting these changes requires lengthy scanning sessions to generate high-quality data, making such scans unfeasible in routine clinical practice. "This technology has the potential to change that," says Brad Dickerson, a neurologist at Harvard Medical School, in Boston. While he cautions that routine clinical use is still years off, he says that "we are rapidly moving into a new era where we can use this kind of data to identify abnormalities that are consistent with Alzheimer's."
Siemens is now working on a commercial version of the 32-channel array developed at MGH, which is expected to be on the market later this year. The imaging device, now being tested by some of Siemens's customers, "increases spatial or temporal resolution," says Jeffrey Bundy, vice president of the MR division at Siemens Medical Solutions, headquartered in Malvern, PA.
The device is likely to have important applications in functional magnetic resonance imaging (fMRI), a variation of standard MRI that tracks blood flow in the brain as an indirect measure of activity. The technique is often used to locate the parts of the brain that control specific functions, such as speech and movement. The first clinical application for the device will likely be fMRI for neurosurgery planning, says Bundy. "Surgeons want to know where speech and motor areas are when they take a tumor out--the more precise, the better."
The instrument could also impact our basic understanding of the brain. "The spatial resolution of fMRI is somewhat limited," says Gabrieli. "We've hit the wall on a lot of scientific questions." With higher-resolution images, scientists could try to determine neurological basis of various aspects of cognitive function. Gabrieli, for example, says that he'd like to figure out if different parts of the amygdala--a small structure deep in the brain that plays a key role in emotion--regulate different emotions, such as fear and joy.
While Siemens is putting the finishing touches on the 32-channel array, Wald and his colleague Graham Wiggins, also at MGH, are already developing new scanners with even more channels, including 96-channel and 128-channel arrays. "These are the highest-resolution brain images being taken today," says Wald. (source) By Emily Singer.