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Biomedical subjects

T J Spinks

Publications and source records attributed to T J Spinks.

At least 37 records · Page 2Linked to original sources
PubMed1988

Abnormalities in myocardial metabolism in patients with unstable angina as assessed by positron emission tomography.

Regional myocardial perfusion and glucose metabolism were assessed in six normal volunteers and 29 patients with coronary heart disease and stable or unstable angina using rubidium-82 (Rb-82) and F-18 fluoro 2-deoxy-D-glucose (FDG) with positron emission tomography. All normals and patients were studied following overnight fasting, at rest, with no angina or electrocardiographic signs of acute myocardial ischemia or necrosis. Rb-82 myocardial cross-sectional images were obtained employing the continuous infusion technique, while dynamic FDG imaging was employed after intravenous tracer bolus injection. Regional Rb-82 and FDG myocardial concentrations were then calculated by drawing regions of interest over the interventricular septum, anterior and lateral wall of the left ventricle. The mean Rb-82 uptake for each left ventricular region analyzed was found to be similar between both groups of patients and normal volunteers. The mean myocardial glucose utilization was found to be similar in normal volunteers and patients with stable angina (0.023 +/- 0.032 vs. 0.012 +/- 0.008 microns ml/min p less than 0.42). However, myocardial glucose utilization was found to be significantly higher in patients with unstable angina compared with both normals and patients with stable angina (0.048 +/- 0.047 microM/ml/min p less than 0.001 for both comparisons). Thus, in patients with severe coronary artery disease and unstable angina, myocardial glucose utilization was enhanced in spite of the absence of clinical, electrocardiographic, or detectable perfusion evidence of acute ischemia.

Adult↗
PubMed1988

Regional myocardial glucose metabolism in angina pectoris obtained from positron emission tomography.

This article presents a review of studies carried out with positron tomography on myocardial blood flow and glucose metabolism in patients with coronary artery disease and either stable (SA) or unstable angina (UA) pectoris. Regional blood flow was assessed with rubidium 82, an analogue of potassium, and glucose metabolism both with fluorine 18-labeled fluorodeoxyglucose (FDG) and carbon 11-labeled glucose (CG). There were no clear differences in regional myocardial blood flow between SA and UA patients and a group of normal volunteers. FDG uptake was low and homogeneous in both SA patients and normals. In contrast, all UA patients showed abnormally high FDG uptake in at least one left ventricular region at rest in the absence of symptoms or signs of acute ischemia. In the recovery from a period of exercise-induced angina, FDG uptake in SA patients was observed to be higher in previously ischemic regions than in nonischemic regions (as defined by 82Rb). It is postulated that higher FDG uptake in the postischemic myocardium of SA patients is due to repletion of glycogen stores. It remains unclear whether the high uptake in UA patients is due to a recent ischemic episode or is a reflection of a chronic adaptation to repeated stress.

Angina Pectoris↗
PubMed1988

Performance characteristics of a whole-body positron tomograph.

This paper describes an investigation of some of the important physical characteristics of a whole-body positron tomograph consisting of two rings of bismuth germanate detectors of dimensions 5.6 mm X 30 mm X 30 mm (512/ring). The resolution applicable to in vivo imaging is six mm or more, depending on radionuclide and reconstruction filter and is very uniform over the field of view normally used. Axial resolution can be varied by moving side collimation (maximum approximately 16 mm FWHM with interplane septa). A simple scheme has been devised to correct for loss of true coincidence events with varying count rate based on the total random and multiple coincidence rates. It is concluded that correction for scattered radiation should be implemented for reliable quantitation.

Humans↗
PubMed1987

Effect of nifedipine on myocardial metabolism in patients with unstable angina.

Myocardial glucose metabolism was assessed using 18F-fluorodeoxyglucose and positron emission tomography in 6 normal volunteers, 7 patients with coronary artery disease and stable angina and 15 patients with unstable angina. All studies were carried out on resting, fasting patients. The patients were off treatment and had no evidence of acute myocardial necrosis or ischaemia. A second study investigated the myocardial glucose metabolism of 5 of the patients with unstable angina after treatment with oral nifedipine. In the first study, the metabolic rate for glucose (MRG) was found to be similar in patients with stable angina and normal volunteers (0.023 +/- 0.032 vs 0.012 +/- 0.008 mumol ml-1 min-1, P less than 0.42), whereas the MRG was significantly higher in patients with unstable angina compared with both that of normal volunteers and patients with stable angina (0.084 +/- 0.047 mumol ml-1 min-1, P less than 0.001). In the second study, the MRG of all of the 5 patients with unstable angina studied after the administration of nifedipine was significantly reduced (P less than 0.05), but was still higher than that of the normal controls. The possibility of spontaneous metabolic changes cannot be excluded, but the consistent reduction of the MRG in all 5 patients after the administration of nifedipine suggests that nifedipine has a beneficial effect on myocardial metabolism that could be related to either an increase in myocardial blood flow or to a direct metabolic effect of nifedipine.

Adult↗
PubMed1987

Regional and total skeletal measurements in the early postmenopause.

In a cross-sectional study of 70 early postmenopausal women, regional bone measurements were compared with total body calcium (TBCa). Spinal and forearm trabecular bone were mainly related to age and time since menopause. In contrast, TBCa and forearm integral (cortical and trabecular) and cortical bone were unrelated to age, although the time since menopause also had some influence. Forearm integral and cortical bone measurements were quite well correlated with TBCa (r = 0.84 and 0.73, respectively, P less than 0.001). The correlation between spinal bone measurements and any of the forearm measurements, even purely trabecular bone, was weak (r less than 0.52, P less than 0.001). Our results show quite clearly that forearm bone measurements cannot be used to predict bone density in the vertebrae. Loss of ovarian function affects bone in general, and trabecular bone in particular. Bone measurements at specific anatomical sites are clearly necessary for studies of metabolic bone diseases and their response to treatment.

Adult↗
PubMed1986

Total body calcium measurements using neutron-activation analysis in Cushing's syndrome.

Total body calcium content (TBCa) was estimated by in vivo neutron activation analysis in 16 patients (14 female, 2 male) with active Cushing's syndrome, pituitary driven in all but two cases. Apart from being nonreproductive, patients were unselected. TBCa was below the predicted young normal value in all patients (mean +/- SD, 85.2 +/- 5.8% of predicted, P less than 0.01 vs. predicted) and in 13 of the 16 patients, was also below the predicted value when allowance was made for expected postmenopausal skeletal losses (mean +/- SD, 92.7 +/- 12.5% of predicted, P less than 0.02). However, individual values of TBCa were significantly lower (P less than or equal to 0.05) than the predicted normal range, corrected for postmenopausal losses, in only 3 patients (19% of the group). Initial TBCa apparently was not related to duration of the disease or to current urinary-free cortisol levels. At presentation, radiographic signs of significant osteoporosis (multiple vertebral and/or rib fractures) were present in four patients, three of whom had subnormal or borderline TBCa compared with the young normal predicted range. TBCa measurements were repeated in 9 patients 1-10 years after successful treatment, and were generally unchanged. During this period, only one vertebral fracture (consistent with simple postmenopausal osteoporosis) appeared in these patients. We conclude that bone mass tends to be low in newly diagnosed Cushing's syndrome, but that significant reduction beyond expected postmenopausal losses is relatively uncommon.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenalectomy↗
PubMed1984

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.

Adult↗
PubMed1984

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.

Body Composition↗
PubMed1983

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.

Humans↗
PubMed1982

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.

Absorptiometry, Photon↗
PubMed1982

Regional bone density measurements compared to total body calcium in osteoporosis.

In 21 women with crush fracture osteoporosis quantities related to trabecular bone density in lumbar vertebrae and in the distal radius were significantly correlated (r = 0.50, P less than 0.05). When the group was enlarged to include data from other patients without osteoporosis, a higher coefficient of correlation was obtained (r = 0.69, P less than 0.001). Total body calcium, measured by in vivo neutron activation analysis, was significantly correlated to quantities related to cortical bone mass in the radius and femur. Thus, these quantities could be used to make estimates of total body calcium in osteoporotic patients. There was no significant correlation between total body calcium and quantities related to trabecular bone density, measured by computed tomography, in vertebrae or in the distal radius.

Bone and Bones↗
PubMed1980

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.

Activation Analysis↗
PubMed1979

Effect of size and composition of the body on absolute measurement of calcium in vivo.

The effect of size and composition of the body on the measurement of total calcium in absolute units by neutron activation analysis is described. The neutron beam, produced from a cyclotron, was of mean energy 7.5 MeV. Counting of the activities induced in a patient was carried out with a multidetector whole body counter. Calibration of the system was achieved by using two phantoms of different sizes containing known quantities of calcium. The dimensions of various phantom sections were varied to determine the effect on efficiency of activation, an approximately linear relationship with body thickness being found. The influence of body habitus on counting efficiency was assessed by counting different patients who had been given known quantities of 42K. The effects of (a) the non-uniform distribution of calcium and (b) the variation in density of different tissues on both activation and counting efficiency are discussed. It is estimated that the 68% confidence limits on the measurement of 49Ca count rate per unit neutron fluence is +/- 3.0% and on the measurement of calcium in grams +/- 8.2%.

Body Composition↗