Imaginal desensitization see Exposure treatment

Imaginal exposure see Exposure treatment

Imaging studies

Definition

Imaging studies are tests performed with a variety of techniques that produce pictures of the inside of a patient's body.

Description

Imaging tests are performed using sound waves, radioactive particles, magnetic fields, or x rays that are detected and converted into images after passing through body tissues. Dyes are sometimes used as contrasting agents with x-ray tests so that organs or tissues not seen with conventional x rays can be enhanced. The operating principle of the various techniques is based on the fact that rays and particles interact differently with various types of tissues, especially when abnormalities are present. In this way, the interior of the body can be visualized and pictures are provided of normal structure and function as well as of abnormalities. In the fields pertaining to mental health including psychology and psychiatry, imaging is often used to help rule out other health problems that could be causing symptoms (such as brain tumors), and imaging studies are often used in research. Once a person's diagnosis has been established, various imaging techniques may help to confirm the diagnosis, and also serve as a way to study the disorder. The imaging techniques may shed new light on the way the disorder affects the brain, so that new treatment methods can be discovered.

Major imaging techniques in mental health

Computed tomography scan (CT scan)

Computed tomography , or computed axial tomography (CAT), scans show a cross-section of a part of the body, such as the brain. In this technique, a thin x-ray beam is used to produce a series of exposures detected at different angles. The exposures are fed into a computer which overlaps them, yielding a single image analogous to a slice of the organ or body part being scanned. A dye is often injected into the patient so as to improve contrast and obtain images that are clearer than images obtained with regular x rays.

Magnetic resonance imaging (MRI)

Magnetic resonance imaging also produces cross-sectional images of the body, but MRI uses powerful magnetic fields instead of radiation. MRI uses a cylinder housing a magnet that will induce the required magnetic field. The patient lies on a platform inside the scanner. The magnetic field aligns the hydrogen atoms present in the tissue being scanned in a given direction. Following a burst of radio-frequency radiation, the atoms flip back to their original orientation while emitting signals that are fed into a computer for conversion into a two- or three-dimensional image. Dyes can also be injected into patients to produce clearer images.

Positron emission tomography (PET)

Positron emission tomography uses a form of sugar that contains a radioactive atom which emits particles called positrons. The positrons are absorbed to a different extent by cells varying in their metabolic rate. PET scans are especially useful for brain imaging studies and are used to illustrate the differences between brains of people without mental disorders and brains of people with mental disorders. For example, because PET scans can detect brain activity, PET scans of the brains of depressed and non-depressed persons can show researchers where brain activity is decreased in depressed patients. Similar scans have been taken of brains affected by schizophrenia or Alzheimer's disease . Such research can help scientists discover new ways to treat these disorders.

Single photon emission computerized tomography (SPECT)

Single photon emission computerized tomography is used in research, and in diagnosing brain disorders such as Alzheimer's and Parkinson's diseases. As of 2002, research for Parkinson's disease at Harvard, for example, in the Division of Neurochemistry is focused on the diagnosis of the disease before motor control is compromised signalling the advancing degeneration. It uses a radio-labeled compound that targets key proteins responsible for regulating brain dopamine levels to determine neural changes before problems with motor symptoms begin to occur. This research is also being used to improve PET imaging in the diagnosis and consequent treatment of these neurological disorders.

Resources

BOOKS

Seeram, E. Computed Tomography: Physical Principles, Clinical Applications and Quality Control. Philadelphia: W. B. Saunders and Co., 2001.

von Schulthess, G. K., ed. Clinical Positron Emission Tomography. Philadelphia: Lippincott, Williams and Wilkins, 1999.

Westbrook, C. Handbook of MRI Techniques. Malden, MA: Blackwell Science, 1999.

OTHER

Alzheimer Society of British Columbia. "What is Alzheimer Disease?" (cited June 2002) <http://www.alzheimerbc.org/> .

Harvard Medical School, Harvard University, ldquo;Parkinson's Disease.rdquo; (cited June 2002) <http://www.hms.harvard.edu/nerprc/parkinson/> .

Monique Laberge, Ph.D.



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