The use and applications of single-photon emission computerised tomography in dementia

Article Abstract:

In single-photon emission computerized tomography (SPECT), minute variations in brain-tissue density are measured by an X-ray source and opposing detectors placed around the head. A related diagnostic imaging procedure - positron-emission tomography (PET) - measures differences in cerebral blood flow (CBF) and glucose metabolism of different brain regions. SPECT combines the PET and computerized tomography (CT) techniques. PET studies of regional CBF in relation to aging processes have yielded inconsistent and inconclusive results. A review of functional imaging studies in dementia also demonstrates many inconsistent findings, which are attributed to three research problems: (1) normal variations between and within individuals in CBF; (2) diagnostic difficulties in, for example, differentiating between Alzheimer's disease (AD) and multi-infarct dementia (MID); and (3) difficulties in distinguishing the effects of normal aging from pathological changes. Nevertheless, several studies have found that when compared with non-demented individuals, demented patients demonstrate lower average CBF. PET studies in AD have consistently shown that reductions in average CBF, oxygen levels and glucose metabolism are significantly related to degree of dementia. SPECT has been used to study dementia since the mid-1980s. Several SPECT studies found that patients with probable AD diagnoses had significantly more blood flow deficits than patients diagnosed with MID. PET studies of patients in the early stages of AD have also shown that cortical reductions in glucose metabolism are often present before cognitive deficits become apparent. Because they measure cerebral function, SPECT and PET studies can demonstrate cerebral abnormalities that other imaging techniques - such as computerized tomography and magnetic resonance imaging (which measure cerebral structure) - have not been able to detect. (Consumer Summary produced by Reliance Medical Information, Inc.)

PET imaging, Positron emission tomography

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Cranial computerised tomography in dementia of the Alzheimer type

Article Abstract:

The non-invasive technique of computerized tomography (CT) allows clinicians to examine serial sections of the brain. Computerized calculation of tissue density not only can identify an abnormal structure, but can indicate its exact nature (e.g., differentiate abnormalities consisting of air from those made of blood or bone). The main use of CT is the detection of intracranial mass lesions, and CT head scans are essential for investigating dementia syndromes. CT scans have shown white-matter changes in both demented patients and normal elderly patients, suggesting that such changes are related to cognitive decline and motor abnormalities. CT has also shown cortical atrophy and ventricular enlargement in chronic alcoholism and in Huntington's disease. There is a great deal of evidence that cortical atrophy in dementia of the Alzheimer's type (DAT) is greater than atrophy related to the normal aging process. CT has shown that DAT patients have significantly larger ventricles than age-matched normal controls. In particular, the third ventricle in male DAT patients has been found to be larger than that of female DAT patients, and significantly larger than the third ventricles of age-matched normal individuals of either gender. Mortality in DAT patients has been associated with decreased tissue density in both the parietal and occipital lobes. Although CT is an invaluable tool for aiding in making differential diagnoses, there is often a considerable overlap between the scans of normal and demented geriatric patients. Therefore, CT scans alone cannot provide a definitive diagnosis. (Consumer Summary produced by Reliance Medical Information, Inc.)

Analysis, CT imaging, CAT scans

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A study of depression in old age using single-photon emission computerised tomography

Article Abstract:

Research demonstrates that there are many biochemical changes inherent in aging which are similar to biochemical changes found in depression and dementia. In single-photon emission computerized tomography (SPECT), minute variations in the density of brain tissue are measured by an X-ray source and opposing detectors placed around the head. A related procedure - positron-emission tomography (PET) - measures differences in cerebral blood flow (CBF) and glucose metabolism in different brain regions. Most SPECT studies of depression have been done with young patients. To demonstrate CBF changes in dementia, and to assess CBF differences among elderly demented and depressed patients, SPECT techniques were used to study three groups: 14 geriatric patients with AD; 12 age-matched healthy people (controls); and 18 elderly patients with major depressive disorder (MDD). All MDD patients were being treated with tricyclic antidepressants or electroconvulsive shock therapy (ECT). SPECT was performed on MDD patients before they received any ECT. Results demonstrated that CBF was more impaired in elderly MDD and AD patients than in controls. The reduction in CBF in MDD was similar in magnitude to the reduction in AD patients. Reduced CBF levels did not reach statistical significance, but instead demonstrated a strong trend. The cause of CBF deficits in MDD and AD remains unknown. The implications of these findings will only be understood when long-term, prospective studies have been carried out. (Consumer Summary produced by Reliance Medical Information, Inc.)

Abnormalities, Cerebral circulation, Depression, Mental

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