No abstract available

[en] This article reviews the basis of PET imaging and current applications to cardiology. Included is a discussion of physical principles, detectors, quantitative estimation of regional radioactivity concentrations, radiopharmaceuticals, and application to flow and metabolism measurements in the myocardium

[en] A method of computing tomographic images from single photon radionuclide emission data is presented. The method takes into account attenuation of gamma rays inside the source and makes use of an iterative technique, based on the difference between the projection data obtained from the source and computed projections, called reprojections, from successive reconstructions of the sources. The method has been tested both by computer simulations and reconstruction of plastic phantoms imaged with /sup 99m/Tc radionuclides. Substantial improvement in reconstruction accuracy over algorithms uncorrected for internal attenuation is demonstrated. Since the technique is iterative, it can be used with a variety of reconstruction algorithms or combined with other first approximation techniques of attenuation correction

[en] The problem of naturally occurring 222-radon contamination has received a great deal of public and scientific attention over the past several years, and has become a major public health issue worldwide. The purpose of the work reported in this document was to provide information about the behavior of ingested 222-radon in the digestive system and other organs of the human body. 133-Xenon, an element which behaves in the same manner as 222-radon in tissue and differs only in tissue solubility, was used in studies on human subjects. The tissue solubility differences were accounted for by using the tissue/blood partition coefficients of the two gases

[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%

No abstract available

No abstract available

[en] Some sources of error in the equilibrium inhalation method for the measurement of oxygen extraction fraction and CMRO₂ by positron emission computed tomography scanning have been evaluated by computer simulation. Emphasis has been placed on errors that have not been thoroughly studied in past work. These include effects of random statistical errors, systematic errors in arterial blood radioactivity concentrations, and errors due to perturbations of the equilibrium state, to tissue inhomogeneity, and to subject motion

[en] The various adaptations of the Kety model used to estimate local CBF from PET data impose a fundamental limitation on the accuracy of measurements. Because of the finite spatial resolution of PET, measurements on tissue volumes contain an unknown admixture of tissue types which leads to systematic errors in the estimation of CBF and partition coefficients when compartmental assumptions are made. The physiological parameters of the author's model are E and F, the unidirectional extraction fraction and blood flow respectively. Clearance of the tracer is described by two residence probability functions: R/sub E/(t) for extracted tracer and R/sub V/(t) for non-extracted tracer, which depend on details of the capillary exchange process. IN the GFM the tracer concentration is given by C(t)=F[(1-E)R/sub V/(t)+ER/sub E/(t)]C/sub A/(t), where denotes convolution and C/sub A/ represents arterial concentration. Analysis of the GFM has shown that for highly diffusible tracers (i.e. E≅1) that F can be estimated without a detailed knowledge R/sub E/. Unless there is apriori knowledge of the correct functional form of R/sub E/ it is not possible to estimate the partition coefficient from bolus studies and PET. The finding indicate that the GFM may be used in estimating CBF with PET and that the result will be virtually independent of the model assumptions about the capillary exchange process

[en] The simple models used to compute the physiological parameters from the equilibrium inhalation method require that the arterial level of radioactivity be kept constant during the breathup and imaging periods. Drifts in the input of labeled gas or in breathing dynamics can cause drifts in these input concentrations. In order to characterize the effects of such drifts the authors have carried out a computer simulation study under the following assumptions: 1. drifts are such that the various arterial blood concentrations have the form: C(t)=C/sub o/+mt. This is the first term of a Taylor expansion in t and hence is representative of all slowly varying drifts; 2. drift begins after initial equilibrium is established and continues to the end of the study. Studies were carried out for three different cases: 1. effects of drift on flow measurements; 2. Effects on OEF and CMRO/sub 2/ of a drift in flow measurement, and 3. Effects on OEF and CMRO/sub 2/ of a drift in O/sub 2/ measurement. Systematic errors in flow tend to be minimum at zero flow and increase slowly with flow. Systematic errors in OEF and CMRO/sub 2/ increase rapidly as these parameters become small and tend to level off to constant values as they increase. For very large drift rates (10%/min), errors in flow vary from 3-30% depending on duration of drift. For more moderate drift rates (eg. 2%/min) errors range up to 7% for the longest drift times. For relatively stable operation errors in OEF and CMRO/sub 2/ are less than 15% for E> 0.2 and increase rapidly for lower values of E