The on-line monitoring of continuously withdrawn arterial blood during PET studies using a single BGO/photomultiplier assembly and non-stick tubing.

A robust, highly sensitive system is described for monitoring the concentration of positron emitting radioisotopes contained within arterial blood continuously withdrawn during PET studies of the brain. Utilizing a specially designed flow-through bismuth germanate detector, gammas are more effectively counted, replacing the less efficient method of positron detection with plastic detectors. A polytetrafluoroethylene flow path system has been developed to overcome the problem of highly cohesive tracers adhering to the tubing material. Blood is drawn through the system from the radial artery by a medically approved peristaltic pump. Syringe samples of blood are extracted periodically downstream of the detector, for calibrations, plasma assays, metabolic analysis and physiological measurements. The complete system, including efficient heavy lead shielding is contained on a bedside trolley. Blood activity is continuously recorded throughout the PET investigations, and stored directly by the scanning computer, and additionally backed up on disc by a P.C.

Measurement of total body nitrogen and oxygen by irradiation with cyclotron neutrons and 'delayed' gamma ray counting.

Measurement of total body nitrogen is assuming increasing importance in the nutritional evaluation of seriously ill patients. Nitrogen has been previously measured either by counting (i) the annihilation radiation from 13N immediately after neutron irradiation with 14 MeV neutrons or (ii) the 'prompt' gamma rays from thermal neutron capture by 14N during irradiation with 14 MeV neutrons or with those produced by isotopic sources or a cyclotron. The present work describes studies into the feasibility of measuring 13N produced by irradiation with a neutron beam from the MRC Cyclotron. A complication of this method is that 13N is also produced in a reaction with 16O. Direct measurement of oxygen by use of the reactions 16O(n, p)16N or 16O(n, 2n)15O enables this interference to be estimated. The former reaction is possible with both 14 meV and cyclotron-produced neutrons but the 7.1 s half-life of 16N requires detectors to be placed in or very close to the irradiation site. In our particular circumstances this is not possible but the more energetic cyclotron neutron spectrum allows the production of 15O which has a half-life of 2.05 min and can be measured in a remote whole-body counter. A disadvantage with the cyclotron beam, in comparison with 14 MeV neutrons, is that a higher dose is required for similar accuracy. A reproducibility of about 4% is obtained with a dose equivalent of 0.01 Sv.

Total body calcium mass in primary hyperparathyroidism and long-term changes.

The total body calcium mass of patients with primary hyperparathyroidism was measured by whole-body neutron activation analysis. Among 14 untreated patients, the calcium mass was significantly subnormal in 2. Long-term follow-up in 4 unoperated patients showed that the calcium mass remained unchanged in 3; in the 4th patient, parathyroidectomy was carried out after the 18th month of follow-up. Her total body calcium fell by 16% before operation, but was nearly regained in the following 3 years. In 1 patient followed for 32 months after parathyroidectomy, the calcium mass remained unchanged. After a follow-up in 4 additional patients for an average of 15 months, the calcium mass remained unchanged in 3, whereas the 4th showed a significant decrease 12 months after the first measurement.

Positron emission tomography in venous ulceration and liposclerosis: study of regional tissue function.

Oxygen-15 administered by continuous inhalation and emission computed tomography were used to study regional tissue oxygen utilisation and blood flow in the limbs of 11 patients with venous ulceration and five patients with liposclerosis due to venous insufficiency. The results showed increased blood flow and appreciably reduced fractional oxygen extraction in the diseased tissues. These findings indicated a local, functional shunting of blood through the abnormal microcirculation of the skin and subcutaneous tissues. This may be an important factor in the aetiology of the skin changes seen in patients with calf muscle pump failure.

Long-term measurement of skeletal and lean body mass in Paget's disease of bone treated with synthetic human calcitonin.

Total body calcium (an index of skeletal mass), ulnar bone density, and total body potassium (lean body mass) were followed for up to 5 years in 38 patients with Paget's disease during treatment with synthetic human calcitonin. Calcium was measured by neutron activation, ulnar density by X-ray photodensitometry, and potassium by counting its natural 40K radioactivity. There was a significant rise in total skeletal mass in a group of 8 patients in the 12 months following the start of therapy, but overall, total bone mass and ulnar density remained constant during treatment. Small mean losses of body potassium were observed (approximately 4%) after several years elapsed on treatment. Over an average period of 12 months after discontinuation of therapy in 21 patients there was no significant mean change in calcium or potassium. The means of the ratios of total body calcium divided by predicted normal calcium (over the whole period of measurement) were 1.08 (males) and 0.99 (females) and were not significantly different. Comparison of the ulnar densities of patients and normal subjects gave similar results. The average ratio of measured to predicted normal potassium was 1.13 (both males and females). Thus there was no indication of depletion in skeletal mass below normal either in the untreated disease or resulting from treatment.

Metabolic activity of sodium, measured by neutron activation, in the hands of patients suffering from bone diseases: concise communication.

Turnover of sodium in the human hand was studied by neutron activation. Patients suffering from various metabolic abnormalities affecting the skeleton, who were undergoing routine neutron activation for the measurement of calcium, were investigated along with a group of healthy volunteers. Neutron activation labels the sodium atoms simultaneously and with equal probability regardless of the turnover time of individual body compartments. The loss of sodium can be described either by a sum of two exponentials or by a single power function. Distinctions between patients and normal subjects were not apparent from the exponential model but were brought out by the power function. The exponent of time in the latter is a measure of clearance rate. The mean values of this parameter in (a) a group of patients suffering from acromegaly: (b) a group including Paget's disease, osteoporosis, Cushing's disease, and hyperparathyroidism; and (c) a group of healthy subjects, were found to be significantly different from each other.

Neutron-activation measurement of metabolic activity of sodium in the human hand.

Turnover of sodium in the human hand was studied by neutron activation. One hand of each subject was irradiated with a 1.5-rad dose of partially thermalized fast neutrons. The activity of 24Na was measured at intervals from 3 min to 48 hr after irradiation. The loss of sodium from the hand during this period can be described either by two exponentials or by a single power function. The latter description involves only two disposable factors compared with four in the former. The rate of loss of sodium was found, on the average, to be greater in patients suffering from bone disease than in normal subjects. Neutron activation is a powerful method for studying sodium turnover because the sodium atoms are labeled simultaneously and with equal probability, regardless of the turnover time of individual bodily compartments.