What is neuroimaging?

Indications and Procedures

Images of the living brain or other part of the central nervous system are indicated for any disorder anywhere in the body that may have neurological involvement or complications. Psychiatrists may also order neurological images for their patients whose mental disorders may have physical causes. Typical indications for neuroradiologic diagnosis include cancer, stroke, and head trauma, especially closed head injury.

Depending on what tissue is involved and what condition is suspected, the physician may order any of dozens of neuroimaging methods. The most common in the early twenty-first century are computed tomography (CT),
magnetic resonance imaging (MRI), positron emission tomography (PET), single photon emission computed tomography (SPECT), and magnetoencephalography (MEG). Additional methods include Electroencephalography (EEG), near infrared spectroscopy (NIRS), diffuse optical imaging (DOI), and other techniques.

Uses and Complications

Besides clinical uses in diagnosing disease in individual patients, neuroimaging is also valuable as a research tool for studying Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, epilepsy, and other degenerative and acute conditions that affect the central nervous system. It can also increase the understanding of drug effects on the brain, natural aging processes, brain function localization, autism, psychiatric disorders, and many other kinds of physiological events. Well-funded initiatives exist for “brain mapping” to create precise, molecular-level, function-specific atlases of the human brain, as well as the brains of mice, rats, and many other animals. The Laboratory of Neuro Imaging (LONI) at the University of California, Los Angeles (UCLA) is the world leader in this kind of research.

Risks are minimal for patients undergoing brain scans. Usually the worst that can happen is that the scan may provide inadequate diagnosis. The physical dangers are generally the same as for CT or MRI scans on other parts of the body. Occasionally, CT brain scans trigger seizures, especially in children. The chance of these inadvertent seizures is much less with MRI. Another safety advantage of MRI over CT is that MRI does not use radioactive materials. On the other hand, MRIs can be harmful if there is metal inside the body, such as from bone or joint repair, or a pacemaker; doctors must be notified of this ahead of time.

Perspective and Prospects

Neuroimaging began almost immediately after German physicist Wilhelm Conrad Röntgen discovered x-rays in 1895. The limits of using plain film x-rays to diagnose nervous system diseases and other soft tissue disorders soon became apparent. Nevertheless, because of its simplicity and thanks to the pioneering work of Austrian neurologist Artur Schüller and Swedish radiologist Erik Lysholm, physicians until the early 1970s generally preferred plain film to the three other methods available for intracranial and spinal diagnosis: pneumography, radiopaque myelography, and cerebral angiography. These other three all involved using contrast media to improve the detail in the x-ray.

American physician Walter Dandy invented pneumography at Johns Hopkins University in 1918. After observing that x-rays show air as black, soft tissue as gray, and bone as white, Dandy developed techniques to inject air into the central nervous system to serve as a contrast medium. The resulting x-rays clearly highlighted abnormalities such as tumors, but the technique was very dangerous. French scientists Jean Athanase Sicard and Jacques Forestier developed radiopaque myelography, the use of contrast media in spinal x-rays, in the early 1920s.

In the 1920s, Portuguese physician António Egas Moniz developed cerebral angiography, a technique in which a rapid series of skull x-rays were taken immediately after injecting a radioactive contrast medium into both carotid arteries. This proved to be an excellent method of showing abnormalities and displacements caused by tumors, but was disfavored because of its significant danger to the patient and the ugly surgical scars left on the patient’s neck.

British physicist Godfrey Newbold Hounsfield and his team of radiologists built the first practical clinical CT scanning machine in 1971. Between 1971 and 1977, several scientists developed practical MRI from facts about the magnetic properties of atomic nuclei that had been known since the 1950s. These two methods soon superseded both plain film and cerebral angiography as the preferred methods of neuroimaging. Today, there are a great variety of specialized MRI techniques geared toward different kinds of body imaging and diagnosis; an especially important one for brain imaging is functional MRI (fMRI), which can measure neural activity.

Bibliography

Cabeza, Roberto, and Alan Kingstone, eds. Handbook of Functional Neuroimaging of Cognition. 2d ed. Cambridge, Mass.: MIT Press, 2006.

Carter, Rita, and Christopher D. Frith. Mapping the Mind. Rev. ed. Berkeley: University of California Press, 2010.

Clarke, Edwin, and Kenneth Dewhurst. An Illustrated History of Brain Function: Imaging the Brain from Antiquity to the Present. 2d rev. ed. San Francisco: Norman, 1996.

Damasio, Hanna. Human Brain Anatomy in Computerized Images. 2d ed. New York: Oxford University Press, 2005.

D’Esposito, Mark. Functional MRI: Applications in Clinical Neurology and Psychiatry. Boca Raton, Fla.: Taylor & Francis, 2006.

Dumit, Joseph. Picturing Personhood: Brain Scans and Biomedical Identity. Princeton, N.J.: Princeton University Press, 2004.

Mori, Susumu, et al. MRI Atlas of Human White Matter. Boston: Elsevier, 2005.

"Neuroimaging and Mental Illness: A Window into the Brain." National Institutes of Mental Health, 2013.

"Neurological Imaging." National Institutes of Health, March 29, 2013.

Taveras, Juan M. “Diamond Jubilee Lecture: Neuroradiology—Past, Present, and Future.” Radiology 175 (1990): 593–602.

Toga, Arthur W., and John C. Mazziotta, eds. Brain Mapping: The Methods. 2d ed. Boston: Academic Press, 2002.

Toga, Arthur W., and John C. Mazziotta, eds. Brain Mapping: The Systems. San Diego, Calif.: Academic Press, 2000.

Toga, Arthur W., John C. Mazziotta, and Richard S. J. Frackowiak, eds. Brain Mapping: The Disorders. San Diego, Calif.: Academic Press, 2000.

Van Bruggen, Nick, and Timothy P. L. Roberts, eds. Biomedical Imaging in Experimental Neuroscience. Boca Raton, Fla.: CRC Press, 2003.