[en] Positron computed tomography allows for the in vivo measurement of the regional tissue concentration of positron-emitting radionuclides such as ¹⁵O, ¹¹C, ¹³N, and ¹⁸F. By using different tracers, a variety of metabolic processes can be quantitated. These include blood flow, oxygen utilization, glucose utilization, amino acid transport, blood volume, cation exchange, pH, and others. This review will contain three sections. First, the principles of positron computed tomography and the progress in instrumentation will be discussed. Second, tracer models will be analyzed. These models are vital in the extraction of physiological data from the measurements of activity. Finally, clinical studies will be evaluated in terms of new pathophysiological information obtained. 271 references

[en] The short-lived isotopes ¹¹C, ¹³N, ¹⁴O and ¹⁵O are ideal for the in vivo examination of tissue functions and, together with positron emission tomography, enable absolute activity measurements in all parts of the body. The procedure is described. A model that describes the uptake of the radionuclide in the body and especially in the organ to be studied, is presented. Using this model a desired physiological parameter (such as the cerebral blood flow) can be calculated from the activity measurement. This technique is described and the limitations and accuracy considered. The activity measurements and physiological parameters have accuracies of 4-5% and 10-15% respectively. (C.F.)

[en] There is a growing interest in the tomographic measurement of regional cerebral blood flow and oxygen utilisation using continuous inhalation of C15O2 and 15O2. This paper examines the influence of certain assumptions in the underlying steady-state model. Estimations are made for possible errors in the actual measurement of these quantities in grey and white matter

[en] By external detection, the influence of arterial blood pressure (BP), osmolarity, and cold-induced blood-brain barrier damage was assessed on the extraction of water labeled with oxygen 15 during single-capillary transit in the rat. There was an inverse relation between arterial BP and extraction that was attributable to the influence of arterial BP on cerebral blood flow (CBF) and the relation between CBF and extraction. Neither arterial BP nor osmolarity of the injected bolus had any direct effect on extraction of water 15O, signifying that the diffusional exchange component (determined by blood flow) of extraction greatly surpasses the convection flow contribution by hydrostatic or osmotic forces. Damage to the blood-brain barrier did not change its permeability to water

[en] Results are discussed briefly of quantitative PET measurements of blood flow, blood volume, oxygen and glucose metabolism in studies of the normal brain, brain disorders as dementia, cerebrovascular diseases and movement disorders, and in the investigation of the myocardium and tumours. 5 refs.; 1 table

[en] Stability of arterial whole blood and plasma concentrations is a basic requirement in the application of the oxygen-15 (¹⁵O₂) steady-state inhalation technique for measuring regional cerebral blood flow and oxygen use. The level of stability obtainable in practice is reported in the form of retrospectively analysed blood data from 626 consecutive studies in patients with a range of clinical conditions. Serial arterial whole blood and plasma concentrations were measured during both C¹⁵O₂ and ¹⁵O₂ inhalations, and coefficients of variation were calculated. In addition, these concentrations were compared with the corresponding values recorded at the start of each study and maximum variations were calculated. For all four concentrations, mean and median coefficients of variation were around 5 and 4%, respectively. Mean and median maximum variations were around 9 and 7%, respectively. The effects of these variations on the calculations of regional cerebral blood flow, oxygen extraction, and oxygen use were estimated. Mean expected errors were found to be between 4 and 9%, and median expected errors between 3 and 6%. Inherent blood sampling errors were assessed from blood volume studies using ¹¹CO-labeled red cells. These errors were found to be less than 3%

[en] The oxygen-15 steady-state technique to measure the regional cerebral metabolic rate for oxygen requires a correction for the nonextracted intravascular molecular oxygen-15. To perform this correction, an additional procedure is carried out using RBCs labeled with ¹¹CO or C¹⁵O. The previously reported correction method, however, required knowledge of the regional cerebral to large vessel hematocrit ratio. A closer examination of the underlying model eliminated this ratio. Both molecular oxygen and carbon monoxide are carried by RBCs and are therefore similarly affected by a change in hematocrit

[en] To increase our understanding of cancer and to improve cancer treatment on a rational basis we need to identify qualitative and quantitative differences between normal and neoplastic tissue. The lack of selectivity of existing anticancer treatment testifies to the elusive nature of such exploitable differences. The multimodality approach to cancer therapy today includes surgery, radiotherapy, chemotherapy, immunotherapy, and more recently, hyperthermia. The resurgence of hyperthermia was partly based on the fact that heart treatment will effectively deal with those cells thought to be most radioresistant. It follows, then, that hyperthermia should ideally be given in conjunction with a course of radiotherapy. Apart from surgery and ''immunotherapy,'' there is little specificity in these forms of treatment. We turn, therefore, to PET to provide information on the anomalous behavior of tumor tissue. This review first defines briefly what is known about the pathophysiology of human tumors and then goes on to discuss present and future projects

[en] Intravenous administration of L-(¹⁸F)-fluorodopa (fluorodopa) to normal subjects gives a characteristic and well contrasted signal in the caudate nucleus and putamen. The signal arising principally from the synthesis and slow turnover of the corresponding (¹⁸F) - labeled dopamine, reflects dopaminergic innervation in these regions. Pathological lesions of the nigrostriatal pathway, notably as in Parkinsons desease, are associated with a marked decrease in this signal. In this paper the quantification and interpretation of the cerebral signal following administration of fluorodopa is considered, and how it relates to the endogenous process of dopa and dopamine synthesis and turnover. (author). 7 refs.; 4 figs

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