Radiation protection in interventional radiology.
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Health Personnel↗
Biomedical subjects
K Faulkner
Publications and source records attributed to K Faulkner.
Film viewing conditions in mammography.
A requirement for a minimum viewing box brightness of 3000 cd m-2 for reading mammograms has been widely advocated. Some recent work has challenged that opinion by reporting no significant variation in visibility of low contrast and fine detail objects over a wide range of brightness levels. This paper provides further experimental evidence to support the latter conclusion, at least over the range 1340-4190 cd m-2, and suggests that the currently recommended minimum viewing box brightness levels need to be revised. The importance of reducing room lighting levels is fully confirmed.
Breast Neoplasms↗
The impact of cardiology on the collective effective dose in the North of England.
Two cardiology X-ray rooms were monitored with dose-area product meters as part of a Regional Patient Dosimetry Programme. Dose-area product measurements on over 2000 patients undergoing examinations in the cardiology rooms are presented. The data have been corrected according to patient size where possible. In room A mean dose-area product values for coronary angiography, coronary angioplasty, radiofrequency ablation and mitral valvuloplasty were found to be 47.7, 72.2, 91.1 and 161.9 Gy cm2 respectively. In room B mean dose-area product values for coronary angiography and coronary angioplasty were found to be 23.4 and 51.6 Gy cm2 respectively. Observational studies were used to deduce the typical projections and technique factors. This typical examination was used to simulate an angiogram from which it was possible to derive factors to convert measured dose-area product values into estimates of effective dose. In room A, the effective doses were estimated to be 9.4, 14.2, 17.3 and 29.3 mSv for coronary angiography, coronary angioplasty, radiofrequency ablation and mitral valvuloplasty, respectively. The effective doses during coronary angiography and coronary angioplasty, performed in room B, were found to be 4.6 and 10.2 mSv, respectively. A regional survey of the frequency of these cardiac procedures was performed. It was deduced that the annual collective effective dose from these cardiac procedures in the North of England, the former Northern Region, was 45.7 manSv.
Angioplasty↗
Standing conference on health and safety in the nuclear age. Report on a conference organized by Directorate General XI of the European Commission, held in Luxembourg, 26-27 November 1996.
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Environmental Exposure↗
Androgen supplementation in eugonadal men with osteoporosis-effects of 6 months of treatment on bone mineral density and cardiovascular risk factors.
This open, prospective therapeutic trial studied the effects of regular moderate androgen supplementation on bone mineral density in eugonadal men with established osteoporosis, and collected data on the safety of androgen therapy used in this setting. 23 men, aged 34-73 years, with vertebral crush fractures and back pain, in whom secondary causes of osteoporosis had been excluded, were treated with fortnightly intramuscular injections of 250 mg testosterone esters (Sustanon 250(R)) for 6 months. Blood pressure was recorded monthly; fasting lipids, glucose, haematocrit, plasma viscosity, and testosterone levels were measured every 3 months. Psychological effects were assessed using the Hospital Anxiety and Depression Scale (HADS) and General Health Questionnaire (GHQ), together with questioning on libido changes. Principal outcomes measured were changes in bone mineral density at the hip and spine by dual-energy X-ray absorptiometry (DEXA) over the treatment period. 21 men completed the study period. Mean bone mineral density at the lumbar spine increased from 0.799 g/cm(2) to 0.839 g/cm(2) during treatment (p < 0. 001), a rise of 5% in 6 months. Bone mineral density at the hip did not change. There were significant, favorable changes in diastolic blood pressure (-4.7 mmHg, p < 0.01), serum triglyceride levels (-0.405 mmol/L,p < 0.01), and total cholesterol (-0.27 mmol/L, p < 0.05). Adverse changes included a fall in HDL cholesterol (-0.087 mmol/L, p < 0.05) and a rise in plasma viscosity which was significant at 3 months but not at 6 months. The expected rises in hematocrit (0.434 to 0.456) and FAI (0.504 to 0.887) occurred. We conclude that testosterone supplementation significantly increased bone mineral density in this heterogeneous group of men with idiopathic primary osteoporosis, without an overall adverse effect on cardiovascular risk factors. This treatment warrants further evaluation in a randomized, controlled trial.
Absorptiometry, Photon↗
The use of electrochemistry for the synthesis of 17 alpha-hydroxyprogesterone by a fusion protein containing P450c17.
A method has been developed for the commercial application of the unique oxygen chemistry catalyzed by various cytochrome P450s. This is illustrated here for the synthesis of hydroxylated steroids. This method requires the preparation of large amounts of enzymatically functional P450 proteins that can serve as catalysts and a technique for providing electrons at an economically acceptable cost. To generate large amounts of enzymatically active recombinant P450s we have engineered the cDNAs for various P450s, including bovine adrenal P450c17, by linking them to a modified cDNA for rat NADPH-P450 reductase and placing them in the plasmid pCWori+. Transformation of E. coli results in the high level expression of an enzymatically active protein that can be easily purified by affinity chromatography. Incubation of the purified enzyme with steroid in a reaction vessel containing a platinum electrode and a Ag/AgCl electrode couple poised at -650 mV, together with the electromotively active redox mediator, cobalt sepulchrate, results in the 17 alpha-hydroxylation of progesterone at rates as high as 25 nmoles of progesterone hydroxylated/min/nmole of P450. Thus, high concentrations of hydroxylated steroids can be produced with incubation conditions of hours duration without the use of costly NADPH. Similar experiments have been carried out for the generation of the 6 beta-hydroxylation product of testosterone (using a fusion protein containing human P450 3A4). It is apparent that this method is applicable to many other P450 catalyzed reactions for the synthesis of large amounts of hydroxylated steroid metabolites. The electrochemical system is also applicable to drug discovery studies for the characterization of drug metabolites.
17-alpha-Hydroxyprogesterone↗
Assessment of effective dose to staff in brachytherapy.
The aim of this paper is to investigate the problem of monitoring effective dose to hospital staff who are involved in the treatment of tumors using sealed sources placed inside the body (brachytherapy). In addition, the use of an unsealed source to treat the thyroid was also considered. Radiation distributions produced by both sealed sources commonly used in brachytherapy (192I, 137Cs, 226Ra) and an unsealed source used in the treatment of the thyroid (131I) were used to irradiate a Rando phantom. The brachytherapy treatments of esophageal and gynecological carcinoma were simulated. The Rando phantom was loaded with lithium fluoride thermoluminescent dosimeters at positions corresponding to a number of radiosensitive organs. Film badges and electronic personal dosimeters were attached to the Rando phantom at various anatomical sites. The Rando phantom was positioned adjacent to the patient at an angle of 90 degrees to the longitudinal axis of the patient. Irradiations were performed with and without a portable lead screen used on the radiotherapy wards. Effective dose was estimated for each simulated radiotherapy treatment and compared with the personal monitor readings. The data were used as a basis for the provision of advice on the wearing of the film badge dosimeters and the design of portable lead screens. The data also permitted a comparison between the two types of dosimeter when used for personal monitoring in brachytherapy.
Brachytherapy↗
Measured scattered x-ray energy spectra for simulated irradiation geometries in diagnostic radiology.
In this study, scattered x-ray distributions were produced by irradiating an anthropomorphic pelvis phantom under fluoroscopic conditions using incident beams generated at tube potentials between 61 kVp and 112 kVp. Both overcouch and undercouch x-ray tube orientations were used when irradiating the phantom. The energy spectrum of the scattered x rays was measured with a germanium x-ray detector. Two measurement geometries were employed: (i) the detector placed at 90 degrees to the incident x-ray beam to determine the energy spectra incident on the trunk region of staff and (ii) the detector placed at 45 degrees to the x-ray beam, measuring spectra incident on the head and neck region. The effect of irradiation area on the scattered spectra was also investigated. Spectral distributions, along with mean energy and half-value layer (HVL) in mm Al, are presented for each spectrum. Energy spectra measured at 90 degrees to the incident x-ray beam were found to have HVLs approximately 10%-15% greater than the corresponding primary incident spectrum, for both overcouch and undercouch irradiations. The magnitude of the irradiation area had negligible effect on the mean energy and HVL of the spectra.
Biophysical Phenomena↗
An experimental investigation of the effect of light-box luminance on the detection of low contrast objects in mammography.
It has been hypothesized that light-box luminance is an important factor in the detection of objects on radiographs. In this work, existing psychophysical data relating to the measurement of visual thresholds at various scene luminance levels are applied to the problem of the observation of radiographs on a light-box. These data suggest that for a given stimulus size, the threshold contrast varies little over several orders of magnitude of scene luminance. In a series of contrast detail experiments performed over a wide range of light-box luminances it has been demonstrated that the detection of low contrast objects on mammographic film is dominated by external noise, that is noise on the film, rather than the internal visual noise of the observer. It is therefore suggested that in mammography it is inappropriate to base recommendations for optimal values of light-box luminance on psychophysical studies of visual noise. It has been shown that commonly used light-box luminances are suitable for viewing mammograms at the higher average optical densities now being recommended, provided that precautions are taken to avoid glare and reflection.
Contrast Sensitivity↗
A hepatic ectopic pregnancy treated with direct methotrexate injection.
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Abortifacient Agents, Nonsteroidal↗
Technical note: perspex blocks for estimation of dose to a standard breast--effect of variation in block thickness.
Mean glandular dose in mammography may be deduced from measurements made using Perspex blocks. This method is almost universally used in the National Health Service Breast Screening Programme. The effect on the estimated mean glandular dose of variations in the measured thickness of Perspex from a nominal thickness of 40 mm was investigated. Results are presented from three UK Regions. Variations in measured Perspex thicknesses ranged from almost 8% below to about 2% above the 40 mm nominal, causing errors in dose estimation, if uncorrected, of about +20% to -6.5%. A means of correcting dose estimates for measured differences in block thickness is presented. An alternative method of ensuring consistent dosimetry would be to use accurately machined Perspex blocks.
Breast↗
The use of a contrast-detail test object in the optimization of optical density in mammography.
In mammography, it is important that the maximum amount of diagnostic information is obtained from each radiograph. One of the factors influencing image quality is the optical density of the film. In this study, a contrast-detail test object was used to establish the optimum optical density value on the basis of signal-to-noise ratio (SNR) for two mammographic film-screen combinations under particular processing conditions. The optimum optical density, taken as being the point at which the threshold contrast is a minimum varied little with detail size. The optimum optical density for the Fuji film-screen combination with Photosol chemistry was found to be higher than that for the Kodak film-screen combination and Kodak processing conditions studied. Although the actual values of optical density are specific to the fixed processing conditions encountered, the technique has more general applicability.
Breast Neoplasms↗
Patient and staff dosimetry in neuroradiological procedures.
Cerebral angiography provides valuable information for use in the clinical management of patients but can result in relatively high radiation doses to patients and staff due to the extended fluoroscopy time and number of images acquired during an examination. In this study, extremity doses to radiologists and scrub nurses working in a neuroradiological centre were monitored during a 3 month period using thermoluminescent dosemeters (TLDs). Electronic personal dosemeters were also used to monitor doses above the lead apron at chest height to the radiologists, radiographers and the scrub nurses. Patient doses were recorded using a dose-area product meter whilst patient thyroid dose was measured using TLDs. Two types of examination were studied: cerebral angiography and arterial embolization. It was deduced from the results of the study that the radiologist may expect to receive a mean dose above the lead apron at chest height of 11 microSv and 25 microSv per examination when performing cerebral angiography and arterial embolization, respectively. A radiologist mean hand dose of 19.3 microSv per examination was found, whilst the average eye dose for both radiologist and scrub nurse was 13.4 microSv per examination. The patient dosimetry results revealed a mean thyroid dose of 1.7 mSv and a dose-area product of 48.5 Gy cm2 for cerebral angiography. Average dose-area product for arterial embolization was 122.2 Gy cm2 along with a mean patient thyroid dose of 3.3 mSv. More detailed patient dosimetry was also performed using a Rando anthropomorphic phantom loaded with TLDs to measure organ doses and hence estimate effective dose. A typical four vessel angiogram was found to result in a patient effective dose of 3.6 mSv.
Cerebral Angiography↗
Assessment of mean glandular dose in mammography.
The routine assessment of patient dose in the National Health Service Breast Screening Programme is performed as part of the quality assurance protocol recommended by the Institute of Physical Sciences in Medicine. The mean glandular dose to a standard breast is deduced from measurement of the air kerma at the entrance surface of a 4 cm Perspex phantom by applying a series of conversion factors. The exposure factors for this measurement are those used clinically. The measured mean glandular dose is then compared with nationally accepted action levels. In some centres the assessment of mean glandular dose using Perspex is supplemented by patient dose surveys. The mean glandular dose to a series of patients attending a breast screening unit may be estimated from a knowledge of the exposure factors and compressed breast thickness, using a knowledge of the X-ray tube output. Measurements made on units in the Northern Region of England and in Scotland using both methods are presented. The implication of these measurements with regard to patient dose surveys in mammography and quality assurance programmes are discussed. An analysis of the uncertainties associated with the measurement techniques is presented.
Breast↗
The impact of digital imaging on patient doses during barium studies.
Barium studies performed on 10 digital and four non-digital fluoroscopic systems were monitored with dose-area product meters as part of a Regional Patient Dosimetry Audit programme. The data have been collected using a computer to read and reset the dose-area product meter and also to collect patient and examination details. A comparison of dose-area product measurements from digital and non-digital fluoroscopy units on over 10,000 barium studies is presented. The data have been corrected according to patient size. The mean size corrected dose-area product for a barium meal examination was found to be 7.62 Gy cm2 for a digital set compared with 15.45 Gy cm2 for a non-digital set with 2462 and 1308 patients included in each measurement series, respectively. Dose-area products were also a factor of approximately two lower for barium enema, barium swallow and barium follow-through examinations performed on digital systems.
Barium Sulfate↗
A phantom based method for deriving typical patient doses from measurements of dose-area product on populations of patients.
One of the chief sources of uncertainty in the comparison of patient dosimetry data is the influence of patient size on dose. Dose has been shown to relate closely to the equivalent diameter of the patient. This concept has been used to derive a prospective, phantom based method for determining size correction factors for measurements of dose-area product. The derivation of the size correction factor has been demonstrated mathematically, and the appropriate factor determined for a number of different X-ray sets. The use of phantom measurements enables the effect of patient size to be isolated from other factors influencing patient dose. The derived factors agree well with those determined retrospectively from patient dose survey data. Size correction factors have been applied to the results of a large scale patient dose survey, and this approach has been compared with the method of selecting patients according to their weight. For large samples of data, mean dose-area product values are independent of the analysis method used. The chief advantage of using size correction factors is that it allows all patient data to be included in a survey, whereas patient selection has been shown to exclude approximately half of all patients. Reduction of the size of the data set may lead to mean dose-area product values that are less reliable indicators of typical practice. The use of size correction factors will be of particular benefit in the analysis of paediatric dosimetry data, where a wide range of sizes exist, even within accepted age bands.
Body Constitution↗
The contrast-detail behaviour of a photostimulable phosphor based computed radiography system.
Contrast-detail measurements were performed on a computed radiography imaging system as a function of detector entrance air kerma over the dose range from 0.743 microGy (0.085 mR) to 277 microGy (31.8 mR). A theoretical model of contrast-detail behaviour for a photostimulable phosphor computed radiography system has been derived, which is based on a modified version of the Rose theory of threshold detection. Included in the model are both system and x-ray quantum noise terms, as well as the response of the eye. The zero-frequency noise power of the computed film images was measured with a double-beam scanning microdensitometer. For a given detector dose, good agreement was found between the predicted and measured data when this measurement of system noise was included in the model. The contrast-detail results obtained for the computed radiography system were also compared with contrast-detail results for an image intensifier-TV based digital imaging system and a conventional film-screen system.
Air↗
A comparison of mammographic phantoms.
It is important to establish and maintain high standards of image quality in mammography in order to detect breast cancer at an early stage. A commonly used method of assessing image quality in mammography is to use test phantoms. This paper reports a comparison of seven mammographic phantoms. These are the Ackermann (DuPont, Stevenage), Barts (White and Tucker), CIRS XI (Computerized Imaging Reference Systems, USA), Leeds TOR(MAX) and Leeds TOR(MAM) (Faxil, Leeds), Newcastle, and RMI 152 (Gammex RMI, Nottingham). These phantoms were assessed on the detectability of the various details and bar patterns contained in each. Step wedges and simulated anatomical features were not assessed. The effect on phantom images of changes in contrast, caused by changing tube potential from 25 kV to 35 kV, and of changes in resolution, caused by different focal spot sizes and by different magnifications, were investigated. It was deduced from the results of this study that there was no single phantom which was clearly superior to all the others. The three phantoms which had the greatest sensitivity to changes in imaging parameters were the Leeds TOR(MAM), the Newcastle and the Ackermann (DuPont) phantoms.
Breast Neoplasms↗