CT screening--whole-body and targeted.

At present, the Australasian College of Physical Scientists and Engineers in Medicine does not support the practice of self-referred whole-body CT screening of asymptomatic patients because: The procedure involves a non-trivial radiation dose, which assumes even greater significance in the context of an ongoing screening programme; There is a high likelihood of false positives requiring further intervention with its attendant risks; and There is no proven evidence to date that early detection of life-threatening disease by CT has a significant positive effect on patient outcome. The ACPSEM will continue to monitor scientific studies concerning this procedure.

Estimation of effective dose to the patient during medical x-ray examinations from measurements of the dose-area product.

Effective dose is likely to be used as a dose index for patient exposures in diagnostic radiology. Calculation of effective dose requires estimates of doses to many organs. In the absence of such dose data it would be useful to be able to directly estimate effective dose from a quantity that can be easily measured in the x-ray room. Relationships between effective dose and each of entrance surface dose, entrance air kerma and dose-area product were studied for common radiographic projections using the organ dose data from Monte Carlo modelling performed at the National Radiological Protection Board, UK. Dose-area product proved to be the best quantity for estimating effective dose and these data are presented. For typical peak generating potentials, estimates of effective dose can be made from dose-area product using a small number of conversion coefficients. For cervical spine, chest, kidneys, abdomen, lumbar spine and pelvis AP projections, the conversion coefficient 0.21 mSv per Gy cm2 will estimate effective dose within 30% of the value obtained using specific organ doses. Conversion coefficients for lateral and PA projections of the trunk are approximately half this value. These coefficients allow the direct estimation of effective dose with sufficient accuracy for most purposes.

The distribution of medical X-ray doses amongst individuals in the British population.

This study has estimated the distribution of diagnostic X-ray doses amongst individuals in the British population by sampling the records kept by general practitioners (GPs) on their patients and the records held by the radiology department of a district general hospital. Deceased patients were chosen in the former case in order to evaluate the dose acquired over a complete lifetime. In each case, several hundred records were sampled. The GP data obtained have enabled an estimate to be made of the likelihood of reaching various dose levels in a lifetime. It is estimated that about 1% of the population has received a lifetime effective dose-equivalent of more than 100 mSv. The largest cumulative dose revealed by the samples of GP and radiology department records was about 200 mSv. The GP data have also shown that the last year of life sees a four-fold increase in the number of X-ray examinations experienced compared with the previous 9 years. The hospital data have allowed an estimate to be made of current rates of dose acquisition amongst the population of a District Health Authority.

Radiographic quality and radiation protection in general medical practice and small hospitals.

Radiation protection and image quality were assessed in a survey of 22 general medical practices and the 24 smallest hospitals with x-ray facilities. Limited radiography, usually of extremities for trauma, was being performed in these facilities since access to regular radiology services was restricted, mainly for geographic reasons. An anthropomorphic ankle phantom with simulated fractures was presented at each facility for radiography, and the resulting films assessed for radiographic technique and basic diagnostic usefulness. While the standard of radiographic techniques was lower than in regular x-ray departments, most films of the phantom ankle were still diagnostically useful and only 4 were rejected entirely. The principal deficiency in general practice x-ray was in darkrooms and x-ray film processing. Generally, the x-ray equipment was adequate for the range of procedures performed and complied with the National Radiation Laboratory Code of Safe Practice for the Use of X-rays in Diagnosis (Medical). Radiation doses to the ankle phantom ranged widely for effectively the same procedure although none was excessive. Improved x-ray film processing, and tighter x-ray beam collimation, would result in a narrower range of doses to patients. Personnel exposures to radiation were satisfactorily low and special shieldings are not required in general practice.

Performance assessment of X-ray image intensified television fluoroscopy systems in New Zealand.

The protocol for image intensifier (II) quality assurance recommended by the UK Hospital Physicists' Association (HPA) and the UK Department of Health and Social Security has been adapted for use in New Zealand for assessment of such systems. Test objects were constructed at the National Radiation Laboratory to match the specifications of those recommended by the HPA. Over 100 individual surveys have been made and, in a few cases, machines have been surveyed several times. Results are summarized in terms of key parameters: II input dose rate, low-contrast detectability, contrast-detail performance and limiting resolution. These are given as mean and standard deviation, and also as good, average or poor. Video waveforms, conversion factors and modulation transfer functions have also been determined on a number of systems. In several cases, video voltages were found to be seriously maladjusted.

Measurement of x-ray image intensifier sharpness in the x-ray department.

A method is presented for determining the modulation transfer function (MTF) of an image intensifier as it is found in the x-ray department. The image of an edge input into the image intensifier tube is photographed at the television camera port with a high quality camera and the photographic image scanned with a microdensitometer. Densitometric conversion enables the determination of the edge spread function and further calculation produces the line spread function and the MTF. A correction is made for the camera/lens/film/developer response function. Results from the use of the technique on over 25 x-ray image intensifiers in New Zealand hospital x-ray departments are presented and discussed. Most of the image intensifiers had been in use for more than 7 years. The low-frequency drop values were similar to reported values with an average value of 22%, but modulation values at 1 cycle/mm (the average value was 29%) were generally lower than values previously reported, indicating that the sharpness performance in the clinical environment is inferior to claims for new or state-of-the-art intensifiers.