MRI: A Window on the Brain
Page 3 of 7
Indeed, despite years of work, neuroscientists still do not know what causes bipolar disorder, or exactly which parts of the brain are involved. That lack of knowledge has severely hampered the search for safer and more effective ways to treat the disease. The principal drugs for bipolar disorder, lithium and Depakote, have been around for decades.
Both were discovered by accident, when researchers trying to do something else noticed that the drugs eased the symptoms of patients with bipolar disorder. And though the drugs can be reasonably effective in some people, doctors have no idea how they work or which patients are most likely to benefit. In order to find better pharmaceuticals, researchers need to be able to target the exact mechanisms or structures involved in bipolar disorder.
Pinpointing the mechanisms could also lead to more accurate evaluation of the disorder. Often, diagnosis in psychiatry is done by a kind of trial and error, in which a psychiatrist makes an educated guess based on the behavior or self-reported symptoms of a patient, prescribes a medication, and sees whether or not it helps. If it doesn’t, the psychiatrist considers a different diagnosis and a different medication, until something begins to work.
“What psychiatrists need is some test that will give them the answer: this patient has the disease or doesn’t,” says Port. He and other researchers hope MRI scanners will offer the definitive diagnosis. And for those in the mental-health profession, that would change everything. “I’m dedicating the rest of my career to coming up with an imaging test that will help psychiatrists diagnose” bipolar disorder and other illnesses, Port says.
Port is one of many researchers now experimenting with MRI spectroscopy, in which software produces an image of the brain based on a spectroscopic scan. The image is made up of individual data points called voxels, cubes analogous to the pixels in a 2-D computer image. Each corresponds to a volume about the size of a kidney bean. For each voxel, Port gets a reading on the presence or absence of certain chemicals that are indicators of brain function.
To understand how MRI spectroscopy works, it’s necessary to understand a bit about how magnetic resonance imaging works more generally. MRI scanners pick up extremely faint electromagnetic signals coming from protons in the atoms of molecules that make up the body’s tissues – in this case, brain tissue.
“Think of it like listening for a pin drop in a thunderstorm,” Port says. Each proton has a magnetic field that points in a certain direction, as the earth’s does. When the MRI is turned on, its magnet aligns the protons’ magnetic fields in the same direction. Bursts of radio frequency energy temporarily knock some of the protons out of alignment. When the protons snap back into place, they release energy, generating a minuscule signal that the MRI’s detectors can pick up. By flipping the protons different ways and measuring various properties of those flips, including the time they take, researchers can identify various tissues and chemicals in the brain.
2 comments. Share your thoughts » 0 comments about this story. Start the discussion »