Broad-beam transmission data in lead for scattered radiation produced at diagnostic energies.
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Humans↗
Biomedical subjects
R M Harrison
Publications and source records attributed to R M Harrison.
Memorandum from the Institute of Physical Sciences in Medicine. Back-scatter and F-factors for low- and medium-energy X-ray beams in radiotherapy. Working Party of the Institute of Physical Sciences in Medicine.
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Humans↗
Exogenous progesterone recycling and early detection of pregnancy in rhesus monkeys.
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Animals↗
The impact of local emissions on the formation of secondary pollutants in urban plumes.
The results of modelling studies are reported together with a further analysis of an existing field measurement dataset. Emphasis is on the maximum ozone concentrations occurring in the urban plume from London, UK, on days of photochemical activity. Nitrogen oxide and volatile organic compound emissions from automotive exhausts are expected to be a large proportion of the total emission of these species, and the effect of their distinct diurnal variation is apparent in the field data. Factorial sensitivity studies on an expanding box model of the urban plume also show the dominance of urban emissions in the determination of plume maxima 100km downwind of the upwind urban boundary. These effects are not additive and depend strongly on the level of other variables.
Air Pollution↗
Automated quality assurance and patient dosimetry in diagnostic radiology.
It has been generally considered that improved methods of quality assurance would reduce the population dose from diagnostic radiology. This paper describes the development of a computerized method of automatically monitoring tube and generator parameters to perform on-line quality assurance, whilst undertaking various patient dosimetry measurements and calculations for each exposure. The method involves interfacing a microcomputer to a microprocessor controlled X-ray generator. Details of the various interfacing methods and modifications to the X-ray unit are given. The instrument enables quality assurance to be performed for every exposure by comparing tube and generator parameters against nominal settings. The software automatically warns the operator of any deviations from accepted limiting values. When a patient is examined, details of the examination and projection are entered into a database. The exposure area product and field size are monitored for each exposure. This data, together with information on tube potential and examination/projection is used to deduce patient entrance skin dose and energy imparted. Doses to individual organs are estimated using normalized organ dose data and a knowledge of tube potential and field size.
Equipment Design↗
Measurement of backscatter factors for low energy radiotherapy (0.1-2.0 mm Al HVL) using thermoluminescence dosimetry.
Significant discrepancies of up to 10% exist between backscatter factors (BSF) recommended in a recent IAEA dosimetry Code of Practice (1987) compared with those published in Br. J. Radiol. Supplement 17 (1983), for the x-ray quality range 0.1-2.0 mm Al HVL. In an attempt to resolve this discrepancy, BSFs have been measured using thermoluminescence dosimetry (TLD) with small lithium borate chips, in order to minimise displacement effects associated with the use of larger volume ionisation chambers. Although subject to uncertainties inherent in the TLD calibration and readout process, the results indicate that the BJR (1983) data overestimate BSFs in this quality range. Broad agreement with the IAEA data is indicated, for the limited number of x-ray qualities and field sizes used.
Humans↗
An investigation into the performance of an automated quality assurance and dosimetry system in diagnostic radiology.
A system has been developed to undertake automatic quality assurance and dosimetry for diagnostic radiology examinations. The accuracy and reproducibility of the measurements and calculations made by the system have been investigated in a laboratory study and compared with concurrent measurements of exposure parameters made using standard techniques. In a later set of experiments, doses measured using a RANDO phantom and thermoluminescent dosimeters were compared with those calculated by the automated system. Assessment was carried out over a wide range of exposure factors and for a number of different radiological examinations. It is deduced from the results that exposure parameters can be measured with comparable accuracy to standard techniques, and that the automated system is suitable for performing on-line dosimetry.
Humans↗
Testicular temperatures measured by thermistor probe and contact thermography.
The results of this study indicate that contact scrotal thermography provides a means for detecting relative differences in temperatures within the testes, but absolute temperatures, as determined by thermistor probes, are about 5% lower. The data do not indicate that this difference is constant, and a simple correction factor cannot be used to equilibrate the two methods of determining the intratesticular temperature. The data also indicate that elevated intratesticular temperatures are associated with surgically induced varicoceles in monkeys.
Animals↗
The assessment of air and soil as contributors of some trace metals to vegetable plants. I. Use of a filtered air growth cabinet.
The sources of heavy metals in a number of consumer crops were investigated in the laboratory by growing plants in a dual growth cabinet supplied with both clean and ambient air. Under these conditions, plants were exposed separately to filtered and normal ambient air to assess the influences of soil and atmosphere on the accumulation of Cd, Pb, Zn, Cr and Ni. Radish, carrot, pea, spinach and lettuce plants were successfully grown in the cabinet. Analysis of the metals in the plant tissues showed that the foliar route is potentially of similar importance to the soil-root pathway as a route of transport to the exposed parts of the plants. Whilst the exposed parts showed the highest metal accumulation from the air, the levels of metals in fruits and storage roots resulting from foliar translocation of the airborne component appeared to be low generally. The metal which achieved highest translocation from foliar deposition was Pb. The effect of spraying plants with rain-water was to enhance slightly the total content of all trace metals analysed.
Air Pollutants↗
The assessment of air and soil as contributors of some trace metals to vegetable plants. II. Translocation of atmospheric and laboratory-generated cadmium aerosols to and within vegetable plants.
Radish, spinach and lettuce were grown in the field on 109Cd-labelled soil. Efficient transfer to the plant was observed with concentration factors [Cd concn. in plant (dry wt) divided by Cd concn. in soil (dry wt)] of between 0.30 and 2.00. Soil uptake of Cd accounted for only 69-64% of Cd in the plants, the remainder arising from atmospheric deposition. By fumigating radish, lettuce and carrot with Cd aerosol in a wind tunnel and harvesting and analysis subsequent to further growth, translocation of Cd to non-exposed parts of plants was demonstrated. The percentage of deposited Cd which is translocated in the wind-tunnel-fumigated plants is small (0.6-4%), but is larger in plants grown in the field (28-36%) or in a laboratory growth cabinet (12-35%).
Aerosols↗
The assessment of air and soil as contributors of some trace metals to vegetable plants. III. Experiments with field-grown plants.
Plants have been grown on common soils at a number of field sites with differing air metal concentrations. Moss bags were co-located with the plants to evaluate atmospheric deposition. Values of the concentration factor (CF) have been estimated (soil-derived metal in plant divided by soil metal concentration) and are generally found to be in the order Zn greater than Cd greater than Ni greater than Cr greater than Pb (sometimes Cd greater than Zn), with values for Pb comparable with earlier studies in which the atmospheric contribution was subtracted. Values of the air accumulation factor (AAF) (air-derived metal in plant divided by air metal concentration) showed values of 15-30 m3g-1 for Cd and Pb for the exposed parts of plants, and lower values for non-exposed parts. Values of both CF and AAF are comparable with those determined in Part I, using a laboratory growth chamber.
Air Pollutants↗
Estimation of effective dose equivalent to staff in diagnostic radiology.
The irradiation of staff in diagnostic radiology was simulated for conditions commonly encountered in fluoroscopy. Scattered radiation distributions were produced from diagnostic x-ray beams generated at tube potentials in the range 60-120 kVp, using the abdomen sections of a Rando phantom. Doses to a number of organs in the head and neck were measured using a Rando phantom loaded with lithium fluoride thermoluminescent dosemeters. The torso sections were placed on a water phantom on top of a stand, with film badge dosemeters positioned on the surface of the phantom at the forehead, neck, chest and waist, and the phantom was placed in the radiation field. Doses to organs in the torso were calculated from the waist-level film badge dosemeter reading using normalised organ dose data. Radiation doses to organs below a lead apron, when worn, were estimated from the unshielded dose values using a transmission factor appropriate to the quality of the scattered radiation. The effective dose equivalent (EDE) to the phantom was calculated for various x-ray beam qualities and lead apron thicknesses and compared with the film badge doses. The results indicate that a dosemeter worn at the waist/chest level under a lead apron generally underestimates the EDE. Conversely, dosemeters worn at the forehead/neck tend to overestimate the EDE. It is recommended that a dosemeter is positioned under a lead apron, if worn.
Female↗
Digital radiography.
A quantitative comparison of the digital techniques reviewed in section 4.1-4.7 is difficult, for two reasons. Firstly, various authors have used slightly different techniques for assessing aspects of imaging performance (e.g. a variety of test objects for, and definitions of, spatial resolution). Secondly, with all imaging systems there exists an inter-relationship between spatial resolution, image acquisition time, image noise and dose. Some authors have chosen to emphasise one feature at the expense of others. Arnold (1982), in an overview of digital radiographic technology at that time, also noted the lack of standardisation of measurement techniques and exposure conditions, but nevertheless attempted a quantitative comparison of some aspects of digital radiographic systems with screen-film radiography and CT. The continuing developments in the field since then make a brief quantitative intercomparison of dubious value. Nevertheless, a qualitative summary of point, line and area exposure techniques is given in table 2 which incorporates many of the comments made by Arnold et al (1986) in a similar summary of digital radiographic systems.
Humans↗
Fluoroscopic peroperative cholangiography: technique and associated radiation hazards.
The techniques specific to peroperative fluorocholangiography are discussed based on an experience of 632 cholangiograms and an estimation has been made of the associated radiation doses to staff and patients. Rapid and accurate information can be obtained during fluorocholangiography using appropriate techniques with acceptably low radiation hazards.
Bile Duct Diseases↗
Noise and threshold contrast characteristics of a digital fluorographic system.
The noise and threshold contrast characteristics of a Picker DAS 211 digital fluorography system are described. Leeds test objects were used to measure contrast-detail-dose relationships for digital fluorography and the results compared with similar measurements using screen-film radiography and 100 mm photofluorography. Noise and spread function measurements were made and from them threshold contrast (CT) values were calculated using the theory of signal detection developed by Hay and Chesters. Comparison with the results of visual assessment of images indicated generally good agreement between theory and practice depending upon the value taken for the threshold signal-to-noise ratio. It is concluded that calculations of CT can provide a means of summarising system performance based only upon objective measurements. This would be of value in quality assurance and performance assessment but should be used in addition to, not instead of, the traditional visual methods since these are important in maintaining a link with clinical practice.
Fluoroscopy↗
Doses to patients from routine diagnostic X-ray examinations in England.
A collaborative survey between the National Radiological Protection Board and the Hospital Physicists' Association has been conducted to ascertain current levels of exposure for patients undergoing 10 routine types of X-ray examination in England. The main part of this study consisted of measurements on nearly 3200 patients attending 20 randomly selected English hospitals. The energy imparted to each patient was determined from a measurement of the total exposure-area product for the examination. In addition, thermoluminescent dosemeters were attached to the patient's skin to enable the derivation of doses to the major radiosensitive organs, either directly or using appropriate conversion factors calculated for a mathematical phantom by a Monte Carlo technique. Histograms are presented showing the wide distributions often observed in the doses for each type of examination. Mean values of exposure-area product, energy imparted to the patient, entrance skin dose per film and organ dose are reported, together with coefficients of variation. Comparison of the results with those from similar surveys in the UK and abroad is complicated by inconsistencies in the reporting of such data, but substantial differences are sometimes apparent, particularly for the estimates of organ doses. The present measurements will provide a useful baseline for future measurements and will be used to evaluate the collective dose to the population from medical exposures and the radiation risks from the various radiological procedures.
Humans↗
Pathophysiology of varicocele in nonhuman primates: long-term seminal and testicular changes.
Varicocele was surgically induced in monkeys to study the long-term effects of the condition on seminal and testicular parameters. Sperm motility was depressed but improved after varicocelectomy. Sperm concentration was less affected, but sperm morphology showed long-term degenerative changes, i.e., for more than 2 years. Testicular blood flow was depressed acutely but returned to normal after 2 years. Electron microscopy showed changes in the basal lamina and spermatogonia that persisted throughout the study. Left adrenalectomy, at the time of varicocele induction, did not alter the development of varicocele-related changes. The sequence of changes suggests that the effects of this experimental varicocele may be reversed in the monkey model through changes in collateral and ancillary revascularization.
Animals↗
An assessment of the contribution from paint flakes to the lead content of some street and household dusts.
A method has been developed for estimating crudely the quantity of lead in dusts derived from paint flakes. This involves an assessment of the paint mass in the dust: gravimetrically in the coarse fractions, and by microscopic measurement in the fine fractions. Some street and house dust samples were examined. The street dusts contained up to 20% of lead from paint, and the house dusts up to 15%. However, it was the least lead-polluted dusts that contained the highest proportions of lead from paint. In the samples examined the paint flakes contained only low to moderate amounts of lead (0.07-4.21% w/w) and in the case of high lead paints the contribution from this source could be considerably greater.
Air Pollutants↗