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Biomedical subjects

B R Pullan

Publications and source records attributed to B R Pullan.

At least 37 records · Page 2Linked to original sources
PubMed1978

Bone mineral measurement using an EMI scanner and standard methods: a comparative study.

The established techniques of scanning photon densitometry and radiographic microdenstiometry for the analysis of bone mineral content are compared with results obtained using a modified EMI brain scanner. The EMI method shows significantly greater sensitivity to changes in bone density than either of the other two methods. This latter method also has the added advantage of being able to visualize and measure the density of trabecular bone, which is a very sensitive indicator of bone mineral changes.

Absorptiometry, Photon↗
PubMed1977

Electron density and atomic number determination by computed tomography. Part I: Methods and limitations. Part II: A study of colloid cysts.

The feasibility of extracting electron density and effective atomic number from measurements of tissue in vitro and in vivo has previously been reported. The method requires scans to be obtained at two different beam energies. Optimization of these energies at 40 keV and 80 keV could enable a variation of 1 part in 400 of effective atomic number to be detected. The method is subject to certain limitations related to accuracy and sensitivity. The effect of varying the concentrations of certain atoms has been modelled demonstrating the limits below which variation in effective atomic number is unlikely to be detectable at acceptable radiation doses. A series of 12 patients with colloid cysts has been considered. All were treated by bilateral ventriculo-cisternostomy from one to 23 years ago. Nine of these patients, and the colloid cyst of one patient who died before treatment could be instituted, have been subjected to double energy scanning. The results suggest that the high attenuation values observed in colloid cysts are due to increased electron density and not to any increase in high atomic number elements. The cysts do not appear to change in size or content over long periods.

Adult↗
PubMed1977

Computer tomography of the spinal canal using metrizamide.

Eleven patients have been examined by whole body CT employing the EMI CT 5000 following lumbar injection of 10 ml of metrizamide (Amipaque) 170 mg I/ml. The distribution, flow and dilution of the contrast medium have been investigated. The results suggest that whilst metrizamide is necessary in the spinal canal to demonstrate the neural axis and pathologic processes affecting it, it appears to enter the extracellular space of the spinal cord during the first hour and achieves an equilibrium in the subarachnoid space and spinal cord from 3 to 6 hours. The medium may concentrate in a second compartment, possibly intracellular, from 3 to 6 hours. The effect of spectral filtering by metrizamide on the attenuation values of the spinal cord has been modelled and shown not to be significant at the anticipated dilution of the medium in the cerebrospinal fluid space and the spinal canal.

Humans↗
PubMed1976

Bone-mineral estimation by computer-assisted transverse axial tomography.

The technique of computer-assisted transverse axial tomography has been exploited by minor modification of an E.M.I. brain scanner to determine measurements of bone-mineral content in distal radius and ulna. Such measurements are possible independent of adipose tissue subcutaneously or within the bone and irrespective of bony contour. Preliminary studies suggest that the accuracy and precision justify further longitudinal studies in the exploration of trabecular bone within vertebral bodies by whole-body computer-assisted tomography.

Adult↗
PubMed1976

Calibration and response of an EMI scanner.

Computed tomography provides a measurement of the linear absorption coefficient of material in vivo. The precision and accuracy of the measurements of this parameter made by the EMI scanner have been investigated at all three recommended voltage settings of the machine. The relationship between the EMI number and the linear absorption coefficient was found to be linear despite the polychromatic nature of the X-ray beam. The spatial resolution of the machine and the response to materials at different depths within the section have also been investigated.

Computers↗
PubMed1976

Measurement of effective atomic number and electron density using an EMI scanner.

Computed tomography, employing an EMI scanner at two beam energies, can be used to obtain information about the electron density and the effective atomic number of materials. The theory which is discussed has been verified experimentally and then applied in the investigation of some brain tumours in vivo. It is anticipated that, as techniques improve, the ability to carry out chemical and physical analysis of pathological processes in vivo will be an important application of computed tomography.

Brain Chemistry↗
PubMed1976

X-ray energies for effective atomic number determination.

The measurement of the effective atomic number of a piece of material in vivo can be achieved using computed tomography. The precision of measurement of this parameter depends on the precision of measurement of the X-ray absorption coefficient at two energies and the separation of these energies. With the assumption of a fixed photon flux, it is shown that two optimum energies exist for the measurement of effective atomic number. The analysis indicates that if energies of 40 keV and 80 keV are employed, a precision of at least 1 part in 400 in the measurement of effective atomic number may be achieved.

Absorption↗
PubMed1976

Effect of fasting on mucosal blood flow in antrum and corpus of the stomach.

Gastric mucosal blood flow in the rat was determined by the indicator fractionation technique 86RbCl. Antral and corpus flow rates were determined after increasing periods of fasting, and the effect of vagotomy was assessed. The physiological stimulus of food in the stomach markedly increased antral as well as corpus blood flow, and after vagotomy lower flow rates were recorded in all parts of the stomach. With progressive starvation, the antral:corpus flow ratio decreased. The findings suggest that the antrum plays an active role in response to a physiological stimulus and may, as has been suggested by others, contribute to the control of parietal cell blood flow and secretion.

Animals↗
PubMed1975

Observations of gastric mucosal blood flow using 99Tcm in rat and man.

The 99Tcm clearance technique is shown to be a useful method of assessing gastric function. It is easily carried out and is relatively non-toxic--the dose of isotope could be reduced to 100 muCi or less without sacrificing the accuracy of the investigation. Although the results are preliminary and the number of cases investigated so far is small, they suggest that the measurement of pertechnetate clearance is directly related to gastric mucosal blood flow; it is a useful parameter of gastric function and may well prove to be a more accurate discriminant in cases of peptic ulceration than the conventional measurement of gastric acid secretion.

Aminopyrine↗
PubMed1975

Evaluation of a proposed index of myocardial blood flow in dogs.

An index of myocardial blood flow developed from studies with a computer and a mechanical circulatory model has been investigated in 18 dogs. An intravenous injection of 131I is used with external scintillation detection over the left ventricle and the lung. The index is given by the ratio of the half time of the downslope of the curve recorded from the left ventricle to that of the curve recorded from the lung. This index has been compared with that suggested by Mena et al in which the left ventricular half time is compared with the half time of the brain curve. The effect on these indices and on the clearance of 133Xe of clamping the anterior descending branch of the left coronary artery has been observed. Statistically significant differences in both indices and in Xenon clearance were seen to be induced by coronary artery clamping but there was overlap between the clamped and unclamped values. The method used for coronary clamping also affected the results.

Animals↗
PubMed1975

A computer model and a mechanical model of the circulation and their use in the evaluation of indices of myocardial blood flow.

Computer and mechanical models of the circulation have been made to study isotopic techniques of determining indices of myocardial blood flow. Parameters in the program and dimensions in the mechanical model have been scaled to represent the human circulation. Single rapid injections of 131I labelled human serum albumen were given into the venous line of the mechanical model and records obtained from collimated scintillation detectors positioned over the heart, lung and brain. Similar injections and recordings were simulated in the computer model. Two indices of myocardial flow have been studied. The first, described by Mena et al. is the ratio of the half time of the downslope of the left ventricular curve to the half time of the downslope of the brain curve. This index distinguished myocardial flows of 0,5% and 10% of total cardiac output but was also affected by changes in cerebral flow. A new index is proposed in which the half time of the left ventricular curve downslope is related to the half time of the downslope of the lung curve. This index can distinguish myocardial flows of 0,5% and 10% total flow but is not affected by changes in cerebral flow.

Blood Circulation↗
PubMed1972

Radioactive bromide partition test in differential diagnosis of tuberculous meningitis.

In 19 cases of lymphocytic meningitis, the radioactive bromide partition test showed that four were tuberculous and 15 viral in origin. In all the tuberculous cases the serum/cerebrospinal fluid bromide ratio was below a critical value of 1.6, and in all the cases of viral meningitis the ratio was above this value. The test may be particularly helpful when diagnosis is difficult. The test may prove to be a valuable and justified additional procedure in the early diagnosis of tuberculous meningitis.

Adolescent↗