Schizophrenia: A Handbook For Families

Table of Contents

Appendix III

Types of Brain Imaging Techniques

Note: The following techniques can also be used for other parts of the body.

Techniques that Measure Structure

These allow for the study of brain anatomy and possible structural abnormalities.

Computerized Tomography (CT)

Developed in the early 1970s, this is one of the earliest imaging techniques. Basically, CT emits a beam of X-rays that rotates around the patient. Detectors placed on the other side of the patient's body pick up the radiation. The computer aspect of CT then translates the pattern of radiation into images of detailed, cross-sectional slices.

CT has proven useful in spotting brain abnormalities that may be connected with different types of mental illness, including schizophrenia, depression, and bipolar disorder. Additionally, it is a painless procedure that requires no special preparation.

One of the more consistent findings using CT is an indication that schizophrenia patients appear to have larger ventricular sections of the brain when compared to other individuals. The ventricles are cavities in the brain filled with fluid, and it is thought that an enlargement in this area occurs at the expense of other brain tissue.

Magnetic Resonance Imaging (MRI)

Also known as NMR (nuclear magnetic resonance), MRI is a relatively new technique that has become widely available over the last four years. Unlike CT, it can image brain regions in different directions and uses a magnetic field as opposed to radiation. It can also produce an accurate reconstruction of brain structures, thus leading to improved visualization, particularly of areas not easily picked up by CT. Because MRI does not use ionizing radiation, it poses a minimum risk for the patient.

Unfortunately, because of its newness, more research needs to be conducted on its potential range of applicability. Several studies done with MRI, however, appear to support the observation of several abnormalities in people with schizophrenia, including enlarged ventricles.

Techniques that Measure Function

These enable the study of the brain at work, through the measurement of metabolic activity and neurotransmitter systems.

Regional Cerebral Blood Flow (RCBF)

This method involves the measurement of the blood flow using what is known as tracers. A tracer is a substance that carries or emits electromagnetic radiation. The most common is the use of a safe radioactive gas called xenon 133 in which its rate of disappearance is measured after the patient has inhaled it. One study using this method has indicated that there is an abnormality in the blood flow of schizophrenic patients.

By having the individual perform various tests or "challenges," RCBF can be used to map patterns of metabolic activity in the brain. For example, one study has demonstrated that patients with schizophrenia appear to have a reduced ability to use the parts of the brain known as the frontal lobes. This finding is consistent with the general hypothesis or premise that schizophrenic individuals suffer from frontal lobe dysfunction. Additionally, there have been some abnormalities observed with the left hemisphere. that is the left half of the brain, of schizophrenic patients. This seems consistent with the language and auditory abnormalities noticed in schizophrenia.

Single Photo Emissions Computed Tomography (SPECT)

This scanning technique uses the method of both CT and MRI in combination with the detection of radioactive particles (photons), which are emitted through an externally administered tracer. Xenon can sometimes be used as a tracer but its low energy makes it impractical for detection. At present, tracers exist for dopamine receptors.

Tracers appropriate for imaging entire neurotransmitter systems are currently being developed, and may make it possible to use SPECT to monitor the effects of treatment and mechanisms of drug action. This method has already proven particularly fruitful in its application to Alzheimer's disease.

SPECT is less expensive to use than PET and although its resolution is not as good as that of PET, it may prove useful in a variety of applications. For example, further development of this technique may make it feasible for use in smaller university centres and community hospitals. Additionally, for research purposes. both SPECT and PET have the advantage of being able to evaluate a large group of samples rapidly.

Positron Emission Tomography (PET)

Unlike RCBF and SPECT studies, which rely on the detection of single photons, PET detects two photons, thus allowing for better, clearer imaging.

Although PET is the most flexible and sensitive of all techniques, it unfortunately requires specialized equipment and considerable expertise to run it, thus making the purchase and operation of PET expensive.

PET research appears especially promising in the area of neurotransmitter systems in the brain. An example is the study of nerve receptors using the neurotransmitter dopamine, and in particular their relation with schizophrenia. Furthermore, with PET, one can examine the effects that various medications have on different receptors. This could have great significance for the understanding of side effects such as tardive dyskinesia, and could lead to the development of better effective treatments for schizophrenia.