Search

Internationally agreed standards for radiation measurements applied to medicine underpin the application of scientific methods to both therapeutic and diagnostic radiological practices. Equally it is recommended that these standards should underpin radiation measurements within the fields of nuclear energy and industrial applications of ionizing radiations. Such measurements should also apply to all exposed groups: patients, workers and members of the general public. It would appear that the underlying philosophy as well as measurement methods, including units, employed in the therapeutic and diagnostic domains have developed separately and independently over the past 30 years. Similarly, although radiological imaging methods are fundamental to both domains, a similar situation appears to apply to the assessment of image quality. This letter attempts to highlight the present situation regarding the role and relevance of dosimetric methods applied in both therapeutic and diagnostic radiological practices. In particular the present situation is discussed in relation to the primary objectives of the International Commission on Radiological Units and Measurements (ICRU). Scope for harmonization and unification of scientific methods applied in therapy and diagnosis is highlighted.

Preliminary images produced by a prototype digital radiographic imaging system are presented. These images indicate the potential of this technique and also highlight the interplay between hardware and software developments in digital imaging. The existing imaging performance, approximately 1% large area threshold contrast and 2 lp/mm resolution, compares quite favourably with screen/film performance for the same total absorbed X-ray energy. At present the resolution limit is set by the electrometer probe and ionographic. chamber design. It seems quite probable that systems can be designed with resolutions exceeding the limit. However, other factors will then begin to play a more noticeable role, for instance:—(i) The accuracy with which the heads can be incremented at the end of each scan line;(ii) The foil-to-probe separation;(iii) Factors inherent in the ionography.Similarly, for large image fields the interplay between resolution, the rate of data collection, image memory size, display characteristics, and image processing facilities will all need to be considered. Nevertheless it appears that digital radiographic systems with large field sizes, satisfactory digital image characteristics and radiographic factors can be produced with existing technology.

Lithium fluoride (LiF) thermoluminescent dosemeters (TLD) have been employed to measure the radiation dose distribution within a phantom and the central axis dose in air. Results are presented for seven (four EMI CT1010, one EMI CT5005, one EMI CT7070 and one Siemens DR2) different machines. Organ doses for four different computed tomography (CT) investigations (head, lung, liver and pelvis) have been estimated from previously published tables and the central axis dose in air in 3 CT units. These estimated organ doses were used in turn to deduce the somatic and genetic risks for the four types of CT examination. These calculations indicate that for an ‘average’ male patient undergoing a CT examination corresponding to the average conditions encountered, the total somatic risks are 3.15 10-4, 1.98 10-4, 2.31 10-4, and 1.38 10-4for head, lung, liver and pelvis scans, respectively. The corresponding figures for female patients are 3.39 10-4, 3.95 10-4, 2.73 10-4, and 1.60 10-4. The risk from head scanning is approximately 250 times that of a dental pantomograph. Somatic and genetic risks will be approximately twice as high for contrast examinations.

Measurements of scattered radiation were made on two fluoroscopic installations, one with an overcouch tube and one with an undercouch tube. The annual doses to staff involved in a fluoroscopic procedure undertaken on both types of unit were estimated using measured dose rates and weighting factors referred to in ICRP 26.Environmental monitoring at the protective barrier was performed for various room layouts to determine the effect of both equipment and room design on the annual dose received by staff at the control panel. In all circumstances the annual dose to staff inside the control cubicle was negligible.

In order to investigate the levels of radiation exposure resulting from fluoroscopic examinations, area–exposure product measurements were performed on 6532 patients whilst undergoing a variety of examinations at a large district general hospital. Results for both the same and different types of examinations, performed in two different X-ray rooms by a number of different radiologists, are compared in order to highlight some of the factors which influence the wide variations in patient exposure which frequently occur in radiological examinations. Variations in exposure of patients of different weights are also presented.

Radiation dose levels in xeromammography were measured both on entry and exit surfaces of the breast. The mean skin dose in the upper inner quadrant was 2.4 rad for a complete examination. The addition of 1 mm aluminium filtration reduced this dose to 1.6 rad. The mean dose to the breast tissues is, however, a more meaningful indication of potential hazard from mammographic investigations and entrance and exit dose measurements enable this to be assessed.

A number of image-processing techniques have been applied to a digital ionographic chest image in order to evaluate their possible effects on this type of image. In order to quantify any effect, a simulated lesion was superimposed on the image at a variety of locations representing different types of structural detail. Visualization of these lesions was evaluated by a number of observers both pre- and post-processing operations. The operations employed included grey-scale transformations, histogram operations, edge-enhancement and smoothing functions. The resulting effects of these operations on the visualization of the simulated lesions are discussed.

A test phantom containing simulated micro-calcifications was constructed. This was imaged by seven systems suitable for use in mammography, firstly in scatter-free conditions and secondly with the addition of tissue-equivalent scattering material. The ability of the systems to resolve micro-particles of known size was assessed using the techniques of signal detection theory. The resultant receiver operating characteristic curves separated the systems into three major groups. Firstly, high resolution systems requiring high radiation dose techniques; secondly at the other extreme, a mediocre imaging system producing its results at low radiation levels; and thirdly a larger middle group producing intermediate resolution of fine particles at similar, acceptable dose levels. The ability to image small particles does not increase linearly with the radiation dose. Scatter did not affect all of the systems to the same extent.

Eye dose measurements have been performed when using medium speed conventional and rare-earth screen-film combinations during tomography of the para-nasal sinuses. The measurements show that using conventional intensifying screens with the A.P. view a total eye dose of about 20 rad may be given during an examination. This eye dose can be reduced by 98% using the P.A. position. If rare-earth screen/film combinations are employed the eye dose measured in the A.P. view was reduced by 75% of that obtained with conventional screens without detectable loss of image quality. A total eye dose reduction of about 99·5% was measured in the P.A. view with the rare-earth systems.