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Biomedical subjects

B F Wall

Publications and source records attributed to B F Wall.

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

A comparison of diagnostic radiology practice and patient exposure in Britain, France and Italy.

Surveys have been conducted in Britain, France and Italy, using essentially the same techniques, to establish the level of provision of diagnostic radiology services, the frequency of X-ray examinations and examples of the radiation doses delivered to patients in each country. Different national strategies for conducting some types of X-ray examination and marked differences in the general availability of this aspect of health care indicate that the justification and optimization of medical exposures is not interpreted in the same way in these countries.

Age Factors↗
PubMed1986

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↗
PubMed1985

Nuclear medicine activity in the United Kingdom.

A survey of the extent of diagnostic and therapeutic nuclear medicine procedures in the UK has been conducted, and information collected on the types of imaging equipment employed and the typical activities of radiopharmaceuticals administered to patients. A total of 380,000 administrations took place in 1982, corresponding to approximately 6.8 per thousand head of population. 84% were imaging investigations, 13% were non-imaging diagnostic procedures and about 3% were for therapy. Bone scans accounted for 25% of all procedures and 99Tcm was the radionuclide of choice for 75% of investigations. Gamma cameras are superseding rectilinear scanners and most are being purchased together with dedicated image processing computers. Their average annual workload is 922 patients per year. There was considerable variation between the typical administered activities reported by different hospitals for the same procedure, and in some cases the figures reported exceeded the maximum usual activities recommended by the Administration of Radioactive Substances Advisory Committee.

Humans↗
PubMed1984

The measurement of energy imparted to patients during diagnostic x-ray examinations using the Diamentor exposure-area product meter.

The mean energy imparted to the patient has been proposed as a practical quantity which may be useful for assessing somatic risk in X-ray diagnostic radiology. A technique is described for estimating energy imparted during most common X-ray examinations of the trunk or complete head from a measurement of exposure-area product conveniently provided by the Diamentor transmission ionisation chamber. The necessary energy imparted calibration for the Diamentor has been deduced from consideration of incident spectral energy fluence and Monte Carlo calculations of the fraction of total beam energy imparted to mathematical phantoms representing the patient. The relationship between energy imparted and exposure-area product depends primarily on the applied potential and total filtration of the X-ray beam, and to a lesser extent on voltage waveform and X-ray target angle. Direct measurements of energy imparted to an Alderson Rando phantom for a range of irradiation conditions provided an excellent verification of the technique developed. Using the energy imparted per exposure-area product factors presented, overall uncertainties of less than +/- 15% and +/- 20% should be possible for measurements of energy imparted during examinations of the trunk and head respectively using the Diamentor.

Adult↗
PubMed1983

Dental X-rays.

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Humans↗
PubMed1983

Collective doses and risks from dental radiology in Great Britain.

The continued expansion of dental radiology in Britain up to the end of 1981 is demonstrated, with a rate of increase much in excess of that seen for general medical radiography. Of the total of 7.8 X 10(6) dental X-ray examinations undertaken in 1981 approximately 6.7 X 10(6) were intra-oral, 1.5 X 10(5) were extra-oral and 9.1 X 10(5) were pantomographic. Weighted dose equivalents for typical examinations in each of these categories were calculated using specific weighting factors for the important "remainder" organs. Values of 20 muSv, 30 muSv and 80 muSv were obtained for intra-oral, extra-oral and pantomographic techniques, respectively, corresponding to risks of fatal malignancy of 0.33, 0.5 and 1.3 per million. The estimated collective weighted dose equivalent of 212 man Sv to the population of Britain from the current level of dental radiology is predicted to result in no more than about three extra cases of fatal cancer when the age- and sex-related opportunity for manifestation of radiation-induced cancers is taken into account.

Age Factors↗
PubMed1982

The suitability of different preparations of thermoluminescent lithium borate for medical dosimetry.

The thermoluminescence properties of three different preparations of lithium borate have been studied with specific reference to their use in medical dosimetry. The properties of lithium borate powder doped with copper make it more attractive for low dose measurements than the more conventional phosphor doped with manganese. However, the energy response of the copper-doped material was not quite so suitable as that of the manganese-doped material for measuring doses to tissue at photon energies below 100 keV. It also exhibited appreciable light induced fading.

Borates↗
PubMed1981

A reappraisal of the genetic consequences of diagnostic radiology in Great Britain.

The National Radiological Protection Board has recently carried out a reappraisal of the annual genetically significant dose (GSD) to the population of Great Britain arising from the practice of diagnostic radiology. The current value of 120 muGy (12 mrad) is indistinguishable from the value determined 20 years ago despite a 48% increase in the number of X-ray examinations performed per head of the population. This is mostly due to a large decrease in the contribution from obstetric radiology and to a marked reduction in the gonadal doses delivered to children for nearly all types of examination. The GSD and the frequency of X-ray examinations in Great Britain would appear to be considerably lower than those found in other industrialized countries and seem unlikely to result in more than 100 cases of serious hereditary ill-health per year at genetic equilibrium. On the other hand, diagnostic radiology is responsible for 87% of the GSD from all man-made sources of population exposure in Great Britain and there is evidence from the data collected for this reappraisal that radiological protection measures could be improved so as to reduce significantly this large contribution without detriment to patient care.

Adolescent↗
PubMed1979

The radiation dose to patients from EMI brain and body scanners.

Absorbed doses throughout the head of a Rando standard man phantom have been measured during simulated neurological examination with the EMI Mk I brain scanner and the second generation CT 1010 brain scanner. Similar measurements have been made with the CT 5005 whole-body scanner which have also included scans through thoracic and abdominal sections of the phantom. Lithium borate thermoluminescent dosimeters placed at regular intervals throughout, and on either side of the scanned volume, have enabled estimates to be made of the total energy imparted to the phantom by each scanner as well as the absorbed dose at various locations including organs of interest in health physics such as the lens of the eye, thyroid and gonads. Isodose curves have been plotted for the central transverse section of each simulated examination. Results are reported for both the standard and high accuracy scan speed options on the two scanners where this choice is available. It would appear that all three machines when operated at their standard scan speeds impart no more energy to the phantom than that associated with a few conventional radiographs of the same part of the body. Maximum skin doses vary from 30 to 56 mGy (3.0 to 5.6 rad) being highest for the CT 1010 scanner. Use of the high accuracy scan option increases the energy imparted and the maximum skin doses by a factor of about five, while providing much enhanced tissue density discrimination. In the case of the body scanner this higher value of energy imparted becomes comparable to that associated with lengthy fluoroscopic examinations like barium enemas. Recent work by EMI involving further refinements to the collimation system has reduced the dose levels by typically 50%. Some preliminary results with this new system are included to indicate the likely degree of improvement, but a detailed account will be the subject of a separate paper.

Brain↗
PubMed1979

Doses to patients from pantomographic and conventional dental radiography.

The increasing popularity of pantographic dental radiography and particularly its recent use for routine screening of asymptomatic patients have prompted the NRPB to compare the risks to patients from this technique with those from more conventional dental diagnostic procedures. Pantographic equipment from seven manufacturers have been investigated along with five procedures for obtaining similar information using conventional dental X-ray sets. Lithium borate thermoluminescent dosimeters located at 141 sites in the head and neck of a Rando phantom have been used to measure the mean absorbed dose to organs of interest as well as the total energy imparted to the phantom. Relative values of the energy imparted by the various techniques provide an estimate of their relative somatic risk to the patient. Pantomographic techniques were generally found to impart less than half the energy to the phantom than that given by a conventional full-mouth periapical series conducted at 45 kV, and a similar amount of energy to four bitewing intra-oral films. The restriction of the frequency of pantomographic examinations to no more than once per year during adolescence and once per three to five years during adulthood has been shown to involve only a minimal increase in the risk of somatic injury to the patient.

Absorption↗
PubMed1976

A TLD system based on lithium borate for the measurement of doses to patients undergoing medical irradiation.

A dosimetry system has been developed which is especially suited to the measurement of doses to patients undergoing irradiation for medical purposes. It is a TLD system based on lithium borate which has been used both in powder form and made up into solid discs by incorporation within PTFE. The predominant advantages of this material over other more widely used TLD materials are its closer approximation to soft tissue, its simple glow curve which eliminates the need for complicated annealing procedures and its low cost. The luminescence from the lithium borate is measured with a specially designed reader which uses radiofrequency heating. At present, using lithium borate powder, the system is capable of measuring doses down to 10 mrad and using lithium borate/PTFE discs it can measure down to 50 mrad with adequate precision. Preliminary measurements on solid glassy discs of lithium borate suggest that this form of the material may in some respects be superior for patient dosimetry.

Borates↗