Abstract
The study of the chemical events that regulate the function of the human brain is particularly difficult. The introduction by Hounsfield, in 1973, of a tomographic technique based on the attenuation of X-rays by tissues has proved invaluable in the study of the morphology of the brain. An extension of this technique, employing the concepts of computerised tomography in combination with the use of specific molecules labelled with positron emitters, is now making the direct regional measurement of metabolic rates during life possible. Although some positron tomography systems are available commercially, they do not necessarily fulfil the specific needs of all researchers. Faced with the problem of quantitating the regional distribution of the essential neurotransmitter, dopamine, in the human brain a positron tomography system, which forms the basis of this work, was designed and built based on a series of experiments aimed at optimizing spatial resolution and detection efficiency. The performance of the tomograph has been evaluated through a series of phantom studies; and the system has been used to measure the local cerebral metabolic rate of glucose and the local distribution of dopamine in the healthy and diseased brain. It is felt that the ability of this tomograph to resolve metabolic structures in the brain as small as 10[3] mm[3] will only be surpassed at the cost of unduly increasing the radiation dose to the subject. The results of positron tomographic studies performed using different positron labelled molecules and those obtained using X-ray computerized tomographic techniques and magnetic resonance techniques in the same subject have been compared. The results have been found to be complementary, each technique providing a clue to the proper understanding of the functioning of the brain.