Brain Imaging Progress
From MRI to PET to diffusion spectrum imaging, as our technology to capture images of the brain improves, so does our understanding of it.
Thanks to Dr. Jack Belliveau, Dr. Bruce Rosen, and Dr. Mark Cohen
1991 Functional Magnetic Resonance Imaging
Conventional MRI and fMRI both use a strong magnet and radio waves to create images of the brain of a person lying in a scanner. But fMRI, which was developed at MGH, for the first time let researchers observe which areas of the brain were activated when the person in the scanner performed a task or received stimuli. Oxygenated blood contains iron, and when it rushes into an active brain region, it perturbs the scanner’s magnetic field and “lights up” that part of the brain. Being able to watch the way the brain thinks has fundamentally changed psychological research.
Courtesy of Steve Stufflebeam
1993 Whole-Head Magnetoencephalography
MEG, developed at the University of Illinois and MIT, also maps the brain in action, but it delivers images at millisecond intervals, as compared with fMRI’s relatively static images, which occur every one to six seconds. Resembling an old-fashioned helmetlike hair dryer, the MEG scanner contains sensors that plug into electrodes placed on the head. Recording the magnetic fields that form as activated neurons generate electrical currents, it can detect rapid brain changes, such as the abnormal activity that triggers epileptic seizures, and provide brain images of small children and claustrophobic adults who can’t lie still in an fMRI scanner.
Courtesy of Dr. David Boas
1995 Diffuse Optical tomography
This noninvasive technique uses a near-infrared light that penetrates the skull, permeates the surface of the brain and bounces back to small detectors on the scalp. The patterns of light reaching the detectors are reconstructed into a brain image that can reveal changes in blood volume and oxygenation that occur when a brain region is active or has suffered a stroke. Radiologists use DOT to scan the brains of newborns—avoiding the general anesthesia babies would need to have an MRI—and because it’s portable, it’s ideal for patients who can’t be moved from intensive care. Someday it could be used in ambulances and on battlefields.
2008 Transcranial Magnetic Stimulation
An electromagnetic coil attached to the scalp creates pulses of electrical current that stimulate or inhibit the firing of neurons in a focused location. Although TMS is not itself an imaging technology, radiologists use MRI with TMS to guide where to place the electrical pulse in the brain and to see the location and dynamics of spontaneous neural activity. Used mostly in research, such as for studying language development, TMS was also approved by the Food and Drug Administration in 2008 to treat depression and migraines.
Courtesy of Ciprian Catana
2008 Integrated PET/MRI
The first human scanner to combine positron emission technology and MRI, both developed in the 1970s, was built by Siemens, which installed one of the first prototypes at MGH. A PET scanner detects the accumulation of a radioactive tracer in tissue and is used to assess changes in physiology and metabolism, often because of disease. MRI can pinpoint abnormal metabolic activity, a job otherwise done by simultaneous computed tomography. MRI delivers superior tissue contrast—and without a CT scan’s radiation—but it took advances in material science, photon detector technology and engineering to shrink PET scanners to fit inside an MRI and to get PET to work in an MRI’s magnetic field.
Courtesy of Randy Buckner and Koene Van Dijk
2011 Diffusion Spectrum Imaging
In another improvement on standard MRI, this technology, developed at MGH, greatly increases the power of conventional scanners and uses mega-magnets to map the way water molecules move in gray matter, delineating in real time which neurons are activated and in which direction they are sending impulses. The whole-brain images created, of normal young adults, reveal in ultrahigh resolution the neural fibers, or white matter tracts, which crisscross the brain and connect its regions, while the colors allow scientists to track the fibers’ multiple pathways. By depicting less than 1% of the dense neural pathways, the images also show the brain’s underlying structure.