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.

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.

Vertical gastric plication: an operation for gastro-oesophageal reflux.

An operation has been devised to prevent gastro-oesophageal reflux in which a vertical partition is made parallel to the proximal gastric lesser curvature. The technique, which can be simply, safely and rapidly performed, prevents reflux in the following ways: 1. Increasing the effective length of the 'intra-abdominal oesophagus'; 2. Increasing the crural sling and mucosal flap valve effect; 3. Sharpening the angle of entry into the gastric reservoir; 4. Creating a flutter valve and markedly reducing the gastric cross-sectional area along which reflux can occur. The stomach is neither opened nor divided. The efficacy of the operation was investigated in six dogs which had their lower oesophageal sphincter excised by circular myomectomy before vertical gastric plication. Pre- and postoperative manometric and oesophageal pH studies were performed. Vertical gastric plication prevented the oesophagitis produced by circular myomectomy alone. The operation has been performed in 26 patients over a 2-year period. Assessment has been by clinical methods, ambulatory 24 h pH studies and endoscopy. Twenty-one patients were classified in Visick grades I and II and ambulatory pH recordings showed a marked reduction in reflux in 13 of 14 patients. The operation is technically simple, quick and safe to perform, being accurately and scientifically reproducible.

A technique for simultaneous dual energy scanning.

A method of deriving simultaneous dual energy scans on a conventional EMI CT5005 scanner is described. The only change that has to be made to the scanner involves the detector collimator where alternate slits are covered by a thin metal foil. The detector readings from the covered and uncovered slits are separated by software before picture processing to give two pictures from one scan--one at the usual X-ray energy and the other at a higher X-ray energy due to the beam hardening produced by the foil. A procedure is then outlined for converting these into pictures showing the effective electron density and the effective atomic number for the whole scan field.

A method for the determination of microvascular volume in tissue samples.

An estimate of the volume of the microvascular bed in injected tissue specimens of human bowel has been made by measuring the concentration of injected contrast material using X-ray fluorescent analysis. The contrast medium used was barium sulphate and this completely fills the microvasculature in excised specimens. The concentration of barium in excised tissue samples has been determined by measuring the ratio of gamma-ray induced X-ray fluorescence in the barium to the 90 degree Compton scattered 140 keV gamma rays from a collimated 99Tcm source. Barium concentration was estimated in tissue samples from 45 specimens of normal bowel and 11 specimens of radiation damaged bowel. The radiation group showed a highly significant reduction (p less than 0.001) in barium concentration and therefore vascular volume. The mean percentage error for barium concentration measured on two separate occasions in 45 randomly selected tissue samples was 5%.

Microvascular studies in non-specific inflammatory bowel disease.

The microvasculature was investigated in the normal bowel and in ulcerative colitis and Crohn's disease. Tissue samples from postoperative colectomy specimens in which the microvasculature had been perfused with barium sulphate suspension were examined. Microradiography was used to study intramural vascular pattern which was abnormal in both disease states. A recently described radiograph fluorescence system was used to estimate barium concentration and hence microvascular volume in tissue samples. Highly significant negative correlations were demonstrated between barium concentration and age in normal bowel (n = 44; r = -0.669; p less than 0.001) and in segmental Crohn's disease (n = 11; r = -0.698; p = 0.017). Barium concentration was significantly reduced (p less than 0.05) in segmental Crohn's disease (n = 11) but remained normal in diffuse Crohn's disease of the colon (n = 6) and ulcerative colitis (n = 7). It is postulated that ischaemia may be a factor in the pathogenesis of segmental Crohn's disease in older patients.

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.

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.

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.

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.

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.

Radiation dose in neuroradiological procedures.

Radiation dose is cumulative in the radiosensitive organs. In neuroradiology the organ of particular interest is the eye. There is an immutable physical relationship between spatial resolution, signal-to-noise ratio (i.e., density discrimination), and dose: Dose alpha (formula: see text). Optimal imaging conditions require a compromise between these three factors. The factors concerned in the effective utilisation of dose are discussed and the various compromises considered. Radiation dose measurements are given for a wide variety of neuroradiological procedures, including CT employing the EMI CT1010 and CT5005.

Tissue characterization by an analysis of the distribution of attenuation values in computed tomography scans: a preliminary report.

Attenuation values as measured by a computed tomography scanner are distributed in both magnitude and space. The distribution in magnitude can be described by the mean, standard deviation, and skewness of histograms of attenuation values. The distribution in space can be characterized by auto-correlation functions or histograms of gradients. Using these measures of scan structure, it has been shown that the spatial distribution of attenuation values can be influenced by tissue. Also, there are some indications that changes in tissue structure corresponding to disease can be detected.

Urethral lumen cross-sectional shape: its radiological determination and relationship to function.

This report shows that the urethral lumen cross-sectional shape is complex but slit-like and it is suggested that this shape is related to function. A radiological method for determining urethral shape during micturition has been developed and compared with histological studies. The lumen is markedly non-circular even during micturition. Simple theoretical analysis of preliminary shapes shows that current concepts of urethral flow are incomplete and urethral pressure profile measurements require re-evaluation. The function of accepted sphincter mechanisms requires a slit-like lumen. Lumen shape is a fundamental property of the urethra, the clinical importance of which has yet to be explored.