An in vivo technique was developed for measuring the absolute myocardial blood flow with H2`50 and dynamic positron-emission tomography. This technique was based on a new model involving the concept of the tissue fraction, which was defined as the fraction of the tissue mass in the volume of the region of interest. The myocardium was imaged dynamically by positron-emission tomography, starting at the time of intravenous bolus injection of 1212O. The arterial input function was measured continuously with a beta-ray detector. A separate image after C`50 inhalation was also obtained for correction of the H2"5O radioactivity in the blood.The absolute myocardial blood flow and the tissue fraction were calculated for 15 subjects with a kinetic technique under region-of-interest analysis. These results seem consistent with their coronary angiographic findings. The mean value of the measured absolute myocardial blood flows in normal subjects was 0.95 0.09 ml/min/g. This technique detected a diffuse decrease of myocardial blood flow in patients with triple-vessel disease. (Circulation 1988;78:104-115) W ith the use of suitable tracers and appropriate mathematical models, positronemission tomography (PET) has the capability ofproviding noninvasive quantitative measurements of physiological functions in organs. However, in the field of cardiac PET, relatively few measurements have been made of the absolute value of the myocardial blood flow (MBF) and metabolism.1,2 The main reason for this concerns the so-called partial volume effect (PVE), 1-6 that is, the spillover effect in radioactivity measurement due to the relatively thin-walled myocardium compared with the spatial resolution of PET,7 and the wall motion of the myocardium. The PVE problem

To investigate changes in cerebral circulation and oxygen metabolism during aging, regional cerebral blood flow (rCBF), regional oxygen extraction fraction (rOEF), regional cerebral metabolic rate of oxygen (rCMRO2) and regional cerebral blood volume (rCBV) were measured using the 15O labelled gas inhalation technique and a multi-slice positron emission tomograph (PET) in 22 healthy volunteers, aged from 26 to 64 years old. The measurements were performed with subjects at rest, without sensory deprivation. The values of rCBF, rOEF, rCMRO2 and rCBV in more than 40 anatomical structures of the brain were evaluated by studying a large series of scans in each region of interest after the functional PET image had been anatomically identified using x-ray computed tomographic images corresponding to the PET. In mean gray values, only CMRO2 showed significant reduction with age. rCMRO2 significantly decreased with age only in the supratentrium, and much more in the left hemisphere. Especially remarkable was rCMRO2 reduction in the left caudate region. Both CBF and OEF were variable and less age-dependent. It was concluded that CMRO2 could be reflecting healthy brain aging most properly.

The tracer appearance time relative to the radial artery-sampling site has been evaluated in six brain locations in five human subjects using dynamic positron emission tomography (PET) following the bolus injection of H2(15)O. There was a maximum difference of +/- 2 s from the average in each location. To globally adjust the timing difference between the measured arterial curve and the PET scan, a correction method was developed based on a nonlinear least-squares fitting procedure. This new technique determined the global time delay with an accuracy of +/- 0.5 s. On the other hand, the linear backward extrapolation method resulted in a systematic error of 4 s.

The authors examined 50 patients with cerebral glioma with use of positron emission tomography (PET) and L-[methyl]-[11C]methionine to assess the grade of malignancy and the extent of cerebral glioma. Carbon-11 methionine was highly accumulated in the lesion in 31 of 32 patients with high-grade glioma and 11 of 18 patients with low-grade glioma. The rate of uptake of C-11 methionine in high-grade glioma was significantly higher than in low-grade glioma (P < .001). However, in individual cases it was difficult to evaluate the grade of malignancy only from the degree of C-11 methionine accumulation. In most cases, the area of increased accumulation of C-11 methionine did not correspond to the abnormalities seen at computed tomography (CT). Surgical intervention confirmed that methionine PET delineated the extent of cerebral glioma more clearly than did CT. The authors concluded that methionine PET has greater utility in assessing the extent rather than the grade of malignancy of cerebral glioma.

Early computed tomographic (CT) findings (scans obtained within 6 hours of the onset of stroke) were retrospectively analyzed in 25 patients with embolic cerebral infarction of the middle cerebral artery or internal carotid artery distribution, including the lentiform nucleus, diagnosed on the basis of findings at sequential CT. CT scans were analyzed for the following: (a) an obscured outline or partial disappearance of the lentiform nucleus, (b) a slight decrease in tissue density, or (c) effacement of the cortical sulci. One or more of these findings was recognized in 23 of 25 patients (92%). The first finding was noted most frequently, and it appeared earliest. Obscuration of the lentiform nucleus was thought to be an important early sign of cerebral infarction, including the lentiform nucleus.