Increasing the public awareness of justification.

One of the requirements of the UK Ionising Radiation (Medical Exposure) Regulations 2017 is that all medical exposures must be justified before the exposure can proceed. One of the main elements of justification is a determination that the medical benefits from the exposure will exceed the associated radiation detriment. The field of medical exposure to ionising radiation is in the rare position of having this explicit legal requirement for net benefit. In this article it is argued that, although separate information on benefit and detriment is also required for implied or explicit informed consent prior to exposure, justification comes first, is simple to explain, and is easily related to the commonly understood basis of medical ethics. It seems reasonable, therefore, to make patients and the public more aware of the protection that UK law already provides for them. A proposal for a single-sentence general statement on justification is made.

Comparing benefit and detriment from medical diagnostic radiation exposure using disability-adjusted life years: towards quantitative justification.

Justification of medical radiation exposure is one of the main elements of radiation protection for patients. For a medical exposure to proceed, the benefit from the procedure must have been determined to be greater than the detriment. It is rare, however, that justification can be stated quantitatively as a ratio of benefit to detriment, or as a net benefit, and this is particularly true for medical diagnostic exposures associated with non-fatal diseases where survival statistics do not apply. The concept of the disability-adjusted life year (DALY) is well established as a measure of disease severity in public health, and there have been calls to revise the international system of radiation protection dosimetry to employ the DALY as a measure of radiation detriment. This paper looks at possible routes to quantify the benefit and detriment aspects of justification based on initial published results for the use of the DALY as a measure of radiation detriment, together with established values of DALY for a range of diseases. Although spreadsheet-style solutions for the calculation of a justification factor based on statistical life tables can be devised, these will be shown to have some limitations. A justification factor based on the rate of change of benefit divided by the rate of change of detriment following medical exposure is proposed. This factor is simple to calculate, is age independent, can apply to non-fatal diseases and is argued to have logical and ethical advantages for the explanation of the relative benefits and detriments of radiological procedures to patients.

Application of ALARP cost-benefit analysis to hospital-based radiation protection.

The UK Ionising Radiations Regulations 2017 require employers to restrict radiation doses to their employees and the public to be as low as reasonably practicable (ALARP). This article looks at the boundary between what might be considered to be reasonable and unreasonable in protecting staff and the general public in the field of hospital-based diagnostic radiology. Guidance on cost-benefit analysis in support of ALARP has been used to formulate relationships for the estimation of the cost at which a radiation protection intervention is no longer ALARP. These relationships allow for a direct link between a reduction in radiation exposure and the maximum reasonable ALARP cost of intervention. Application of the approach to hospital-based radiation protection situations show that the ALARP cost limits for protecting radiation workers against the residual risks in the hospital environment are relatively low. Conversely, the ALARP limit to investment in public dose reduction by means of reducing patient doses can be very high.

Duty of Candour and Clinically Significant Accidental or Unintended Exposures: revisiting the definition of moderate harm for patient safety incidents involving ionising radiation.

OBJECTIVE: To explore a quantitative interpretation of the term 'moderate harm' as applied to the triggering of the Duty of Candour associated with Clinically Significant Accidental and Unintended Exposures of ionising radiation. METHODS: Current definitions of 'moderate harm' were matched to the lay descriptions of disease and injury states used in the calculation of detriment as disability-adjusted life years (DALY) by the World Health Organisation, to obtain a value of detriment associated with 'moderate harm'. Published conversion factors between effective dose and DALY were used to calculate the effective dose associated with the same detriment. RESULTS: The DALY loss associated with a moderate harm incident is estimated as 0.0216 years. This corresponds to the detriment resulting from an exposure to ionising radiation of 21 mSv. An effective dose of 21 mSv relates to a probability of induced cancer of 0.0012. CONCLUSION: The results obtained closely match existing guidance although the method used is completely different. It is concluded that there is no evidence to change the existing guidance on the triggering of DoC in radiation incidents. ADVANCES IN KNOWLEDGE: An alternative approach to linking 'moderate harm' and radiation detriment has reinforced existing guidance.

Short communication: an investigation of search pattern extent in the threshold contrast detection task.

The threshold contrast-detail diameter test is used as a semi-quantitative measure of image quality in radiology. This observation task is called "signal known exactly/background known exactly" because the signals are usually low contrast disks in known positions, and the background is uniform except for noise fluctuations. The performance of the observer undertaking this task can to some extent be predicted from knowledge of the noise power in the image background, and adoption of the assumption that the noise is sampled through an aperture of the same area as the test feature being observed. In order to extend this approach to optimization of clinical images, the effect of the cluttered anatomical background on the detection task must be quantified. To study the effect on detection of nearby structure, a series of contrast-detail tests was carried out using a progressively restricted background area of Gaussian noise, and a range of object diameters. It was found that the observer's ability to detect low contrast objects is progressively reduced as the area of the search area is reduced, the difficulty of the task increasing rapidly as the diameter of the restricted search area falls to less than twice that of the target disk. The results suggest the presence of a search pattern that scales in proportion with the size of the test feature.

Trends in image quality in high magnification digital specimen cabinet radiography.

Advances in microfocus X-ray tube design together with the availability of high resolution charge coupled device (CCD) detectors have led to the introduction of high magnification digital specimen cabinets for the examination of tissue samples. This paper explores the effect that the high magnification geometry permitted by such units has upon image quality in terms of phase contrast edge enhancement, spatial resolution and the appearance of test phantom images. Phase contrast effects and spatial resolution were studied using a previously established method (using edge profiles) and by computing the system spatial frequency response at various geometries. It was demonstrated that the magnitude of the phase contrast enhancement effect reaches a stable maximum at a magnification of x 4. It has also been shown that a continual increase in both the spatial resolution together with an improved signal to noise ratio occurs up to the maximum permissible magnification geometry, with effects of focal spot blur being negligible. In practice, the limited size of the digital detector and the difficulty of object alignment can constrain the use of the very high magnification option.

Suppression of the low spatial frequency effects of scattered radiation in digital radiography.

One of the deleterious effects of scattered radiation in the digital radiograph is to add a slowly varying background to the image. This can reduce the ability of the observer to discern low contrast signals if the background gradient over a signal feature prevents the use of a small enough display window to make the signal visible. This paper presents an image processing scheme for suppressing the low spatial frequency effects of scattered radiation in digital radiography and demonstrates it on a range of clinical and phantom images. The approach relies on the approximate separation of high atomic number bony features from the low atomic number soft tissue background, and the use of forward convolution with a scatter kernel to produce an estimate of the scatter distribution arising from the soft tissue background. This is then scaled by an estimate of the soft tissue scatter fraction and subtracted from the original image to produce the final scatter-suppressed image. The implementation employs many approximations in order to make use of information that is readily available in the image headers of current x-ray imaging systems. The performance of the image processing scheme is demonstrated on phantom and clinical images. It is argued that clinical application of the approach could employ a user-controlled scatter subtraction step that would reduce any risk of misinterpretation of the processed image.

Short communication: A printed image quality test phantom for mammography.

This communication describes a novel design for a mammographic image quality test phantom, the final design of which was produced as a radiographer weekly quality assurance phantom for breast screening and symptomatic mammography. The phantom is based on low contrast test features which are built up by superimposing sheets of Mylar overhead projector transparency, on which the test features are printed using a standard LaserJet printer. The required radiation contrast at mammographic energies is produced by the approximately 50% by weight component of iron oxide (Fe(3)O(4)) present in the toner. An easily replicated design of mammographic image quality phantom based on LaserJet printed test features is described. Approximately 40 of these phantoms were constructed, and these have been used successfully for 5 years in both breast screening and symptomatic mammography. The phantom design offers a performance similar to much more expensive mammographic contrast-detail phantoms, but suffers from the disadvantage that high contrast resolution bar patterns cannot be produced using the standard printing process.

Pilot study into optimisation of viewing conditions for electronically displayed images.

The increased use of soft-copy reporting introduces new concerns over the effect of viewing conditions on the observer's ability to report images. Owing to their lower luminance, electronic display screens may be more susceptible to poor viewing conditions than conventional viewing boxes and there is the potential for images to be displayed in locations not optimised for viewing radiographs. In the present work, the effects of sub-optimal viewing conditions on the observer's performance for images on an electronic display device are investigated. A test object was used to produce a computed radiography image containing a wide range of grey levels. The image was scored under quasi-ideal and sub-optimal conditions and the effect of changing the viewing conditions on the observer's performance determined. Basic photometric quantities were used to characterise the viewing conditions and the degradation in observer performance related to these quantities. The presence of structured reflection had a significant effect on the observer's ability to discern low-contrast objects. The study demonstrates the need for adequate viewing conditions especially when images are displayed on low luminance devices in sub-optimal conditions.

Development and application of programs to measure modulation transfer function, noise power spectrum and detective quantum efficiency.

This project aimed to produce programs to calculate the modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) of digital X-ray systems, given a suitable digital image. The MTF was calculated using the edge technique and the NPS was calculated from a flat field image. Both programs require a suitably edited DICOM image as input. The DQE was then calculated from the output of MTF and NPS programs. This required data external to the DQE program to estimate the number of quanta per mm2 in the beam which formed the NPS image. All three programs run independent of each other on a PC and require no special software to be installed. Results for MTF, NPS and DQE for a Philips AC3 CR system are presented. In addition, the results for MTF from a Siemens Duo CT scanner with a specially designed PTFE edge are also shown.

The influence of patient size on patient doses in cardiology.

In cardiology and interventional radiology, areas that contribute large components to medical radiation exposure, a major source of variation in patient dose is the variation in complexity between cases for nominally identical procedures. In patient dose surveys, this variation tends to mask that due to patient size. The effect of applying a previously defined size correction to cardiology patient dose-area product (DAP) records was investigated. The correction method uses the experimentally determined relationship between patient diameter and DAP to derive a factor to convert DAP to that which would be expected had the patient been similar in size to ICRP Reference Man. The size correction was found to greatly reduce the residual correlation of DAP with patient weight. An implication of this finding is that data collection for the setting of diagnostic reference levels in cardiology can be performed for all patients rather than just 'standard-sized' patients.

Quantification of motion unsharpness in digital fluoroscopy.

The objectives of this work were first to develop a convenient method to quantify persistence in digital fluoroscopy systems, then to quantify the effect of variable temporal averaging on the detection of moving low-contrast test details within digital fluoroscopic and pulsed fluoroscopic images. The results were analysed to clarify the relationship between the optimum persistence required to see the lowest contrast for circular test details for a range of diameters and their speed of movement. The optimum persistence values obtained are compared with the limited data available on speeds of movement of patient organs during fluoroscopy. It is tentatively concluded that for imaging the abdomen, the optimum imaging system persistence time constant is approximately 0.15 s. For the much greater speeds associated with cardiac motion, no additional frame averaging is necessary, i.e. just the persistence provided by the observer's visual system appears to be optimal for small objects.

Reference levels in PTCA as a function of procedure complexity.

The multicentre assessment of a procedure complexity index (CI) for the introduction of reference levels (RLs) in percutaneous transluminal coronary angioplasties (PTCA) is presented here. PTCAs were investigated based on methodology proposed by Bernardi et al. Multiple linear stepwise regression analysis, including clinical, anatomical and technical factors, was performed to obtain fluoroscopy time predictors. Based on these regression coefficients, a scoring system was defined and CI obtained. CI was used to classify dose values into three groups: low, medium and high complexity procedures, since there was good correlation (r = 0.41; P < 0.001) between dose-area product (DAP) and CI. CI groups were determined by an ANOVA test, and the resulting DAP and fluoroscopy time third quartiles suggested as preliminary RLs in PTCA, as a function of procedure complexity. PTCA preliminary RLs for DAP are 54, 76 and 127 Gy cm2, and 12, 20 and 27 min for fluoroscopy time, for the three CI groups.

A micro-computer based CT and digital fluorography system for radiotherapy simulators.

A low cost system designed to produce low resolution CT images from a radiotherapy treatment simulator is described. The system is based upon a standard micro-computer and operates using the simulator's image intensifier as the CT detector. The resulting images are intended to supply cross-sectional anatomical information appropriate for the application of inhomogeneity corrections to treatment plans for megavoltage radiotherapy of the thorax. Options for digital fluorography and hold-last-frame fluoroscopy are also described. Examples of clinical images are presented.

Estimation of mean glandular dose for mammography of augmented breasts.

The standard quantity used to relate breast surface exposure to radiation risk is the mean dose received by the radiation sensitive tissue contained within the female breast, the mean glandular dose (MGD). At present, little is known about the MGD received by women with breast implants as there is no technique available to facilitate its calculation. The present work has involved modification of the conventional method for MGD estimation to make it applicable to women with augmented breasts. The technique was used to calculate MGDs for a cohort of 80 women with breast implants, which were compared with similar data calculated for a total of 1258 non-augmented women. Little difference was found in median MGD at low compressed breast thickness. At high breast thickness, however, the MGDs received by women with augmented breasts were found to be considerably lower than those relating to their non-augmented counterparts.

Measurement and correction of the effects of lag on contrast-detail test results in fluoroscopy.

Persistence of the video signal between TV frames, an effect also known as image lag, can lead to anomalously good contrast-detail test results for fluoroscopy systems. In this practical paper, a simple method is described which quantifies lag in fluoroscopy systems and corrects for its effect on threshold contrast. A digital framestore was used to acquire temporally contiguous fluoroscopy images. Correlation of the variance between an initial base TV frame and successive later frames was then measured via the correlation coefficient. Plotted against time, this function defines a time constant which characterizes the rate at which the initial variance pattern is replaced by incoming quantum noise. A survey of seven fluoroscopy units incorporating vacuum TV camera tubes found a mean time constant of 0.06 s. The relative change in contrast-detail performance was then measured as a function of applied digital frame averaging for two separate fluoroscopy units. A time constant was found for each frame averaging mode using the correlation of variance between frames. These measurements were used to derive a function which corrects contrast-detail results obtained for a unit with a measured nominal time constant to the typical vacuum camera tube time constant of 0.06 s. The correction is shown to significantly reduce the spread of contrast-detail results obtained over a range of temporal filtration settings.

Assessment of the effects of pixel loss on image quality in direct digital radiography.

Modern digital radiographic 'flat panel' detectors can exhibit a progressive form of image degradation arising from non-functioning pixels. The effect of these 'dead pixels' on the quantitive image quality measures of modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) is investigated by a simulated degradation of images obtained from an Hologic EPEX system. The effects on the semi-quantitive measures obtained from contrast threshold test objects and resolution gratings are also investigated. Results suggest that the contrast-detail tests often employed in quality assurance measures are not sufficient to reveal the presence of dead pixels until well beyond the recommended replacement point for the flat panel detector. However, measurements of spatial resolution using a line pairs phantom were found to be more sensitive to pixel loss. Measurement of the MTF, NPS and DQE can reveal small changes in image quality with increasing pixel loss, with a distinctive pattern in the trend of the NPS.

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.

Dosimetric implications of age related glandular changes in screening mammography.

The UK National Health Service Breast Screening Programme is currently organized to routinely screen women between the ages of 50 and 64, with screening for older women available on request. The lower end of this age range closely matches the median age for the menopause (51 years), during which significant changes in the composition of the breast are known to occur. In order to quantify the dosimetric effect of these changes, radiographic factors and compressed breast thickness data for a cohort of 1258 women aged between 35 and 79 undergoing breast screening mammography have been used to derive estimates of breast glandularity and mean glandular dose (MGD), and examine their variation with age. The variation of mean radiographic exposure factors with age is also investigated. The presence of a significant number of age trial women within the cohort allowed an extended age range to be studied. Estimates of MGD including corrections for breast glandularity based on compressed breast thickness only, compressed breast thickness and age and for each individual woman are compared with the MGD based on the conventional assumption of a 50:50 adipose/glandular composition. It has been found that the use of the conventional 50:50 assumption leads to overestimates of MGD of up to 13% over the age range considered. By using compressed breast thickness to estimate breast glandularity, this error range can be reduced to 8%, whilst age and compressed breast thickness based glandularity estimates result in an error range of 1%.

Phase contrast enhancement of x-ray mammography: a design study.

This paper explores the application to mammography of phase contrast produced by variations in x-ray refractive index. As a spatially coherent x-ray beam propagates through an x-ray transparent medium, the phase of the incident wavefront becomes modified in a manner related to the electron density of the medium. The resulting phase gradient across the wavefront is equivalent to a small change in direction of the propagation of the wave. For a general object, the change in propagation direction will vary from point to point depending on the structures within the object. The net effect can be recorded in a radiographic image using an appropriate geometry to produce the visual appearance of edge enhancement at interfaces between materials with differing x-ray refractive indices. Normally these materials will also have differences in attenuation coefficient, so the overall effect is to increase the visibility of interfaces between materials. It is proposed that mammographic images can be subtly enhanced by the use of phase contrast information to overcome some of the known limitations of the imaging process whilst leaving the gross radiological appearance of the images substantially unchanged. The design trade-offs required to utilize phase contrast information were investigated using a conventional mammographic x-ray generator and film-screen system. The Leeds TORMAM mammographic image quality test object was then used to demonstrate a considerable improvement in image quality for the phase contrast enhanced images over those produced in the conventional geometry with no increase in radiation dose to the patient. The results are discussed in terms of their possible practical application.