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.

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.

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.

Phase-contrast and magnification radiography at diagnostic X-ray energies using a pseudo-microfocus X-ray source.

OBJECTIVE: To investigate the use of conventional diagnostic X-ray tubes for applications in which specialist microfocus sources are normally required. METHODS: A conventional diagnostic X-ray tube was used in conjunction with a range of apertures to investigate improvements in spatial resolution using a line-pairs test object. Phase-contrast effects were investigated by varying source-to-object and object-to-receptor distances using a 2-French catheter as a clinically realistic test object. RESULTS: For magnification radiography using a computed radiography receptor and conventional X-ray tube with a 1-mm nominal focus size, the limiting spatial resolution was improved from 3.55 line-pairs per millimetre, for a conventional contact image, to 5.6 line-pairs per millimetre, for a ×2 magnified view with a 250-µm aperture. For inline phase-contrast radiography, phase contrast enhancement of a 2-French catheter was demonstrated, and the expected trends with variations in source-to-object and object-to-receptor distances were found. Images of a neonatal phantom demonstrated a subtle improvement in visibility of a superimposed 1-French catheter simulating a percutaneously inserted central catheter for no increase in patient radiation dose. CONCLUSION: Spatial resolution improvement and visible phase contrast can be produced in clinically relevant objects using a pseudo-microfocus geometry at X-ray energies in the normal diagnostic range, using conventional diagnostic X-ray tubes and image receptors. The disadvantages of the proposal are the large distances required to produce phase contrast and limitations imposed by the resulting tube loading. ADVANCES IN KNOWLEDGE: It is possible to use conventional diagnostic X-ray equipment in applications that normally require microfocus X-ray sources. This presents some possibilities for clinical applications.

Statistical analysis of mammographic breast composition measurements: towards a quantitative measure of relative breast cancer risk.

OBJECTIVE: A number of studies have identified the relationship between the visual appearance of high breast density at mammography and an increased risk of breast cancer. With the advent of digital mammography and the promise of routine measurements of parameters associated with breast composition, the possibility arises of using breast composition in a quantitative manner to predict relative breast cancer risk. Previous measurements have shown that the average proportion of glandular and adipose tissue within the breast varies with both age and breast size. In order to be able to identify individual women with an unusually high volume of glandular tissue, it will therefore be necessary to make comparisons with a disease-free population matched for age and breast size. METHODS: A large number of breast glandular thickness measurements were analysed to investigate the statistics of breast composition across a disease-free population as a test of a suitable methodology for relative risk estimation. The large data set is also used to revisit the trends in breast composition used in the current UK method of breast radiation dosimetry. RESULTS: It is demonstrated that a non-linear transformation can be used to produce normal statistical distributions, suitable for producing a standardised "Z-score" for breast composition. CONCLUSION: A standard "Z-score" approach to identify women with unusually glandular breasts is recommended and so provide a basis for cancer risk estimations.

X-ray absorptiometry of the breast using mammographic exposure factors: application to units featuring automatic beam quality selection.

A number of studies have identified the relationship between the visual appearance of high breast density at mammography and an increased risk of breast cancer. Approaches to quantify the amount of glandular tissue within the breast from mammography have so far concentrated on image-based methods. Here, it is proposed that the X-ray parameters automatically selected by the mammography unit can be used to estimate the thickness of glandular tissue overlying the automatic exposure sensor area, provided that the unit can be appropriately calibrated. This is a non-trivial task for modern mammography units that feature automatic beam quality selection, as the number of tube potential and X-ray target/filter combinations used to cover the range of breast sizes and compositions can be large, leading to a potentially unworkable number of curve fits and interpolations. Using appropriate models for the attenuation of the glandular breast in conjunction with a constrained set of physical phantom measurements, it is demonstrated that calibration for X-ray absorptiometry can be achieved despite the large number of possible exposure factor combinations employed by modern mammography units. The main source of error on the estimated glandular tissue thickness using this method is shown to be uncertainty in the measured compressed breast thickness. An additional correction for this source of error is investigated and applied. Initial surveys of glandular thickness for a cohort of women undergoing breast screening are presented.

Trends in compressed breast thickness and radiation dose in breast screening mammography.

An analysis was performed of the compressed breast thickness recorded in 146 mammographic patient dose surveys each consisting of 50 or more women carried out between 1993 and 2004. The results show a steady and statistically significant increase in compressed breast thickness with time, which is also present when individual independent screening centres and equipment manufacturers are compared. This increase seems most likely to be associated with an increase in the proportion of women in the breast screening age range classified as overweight and obese, which has occurred over the same time period. The associated trends in mean glandular dose per image were calculated for the mammography units used at the time of the surveys, using the most recently published conversion factors. The increase in average radiation dose that might have been expected as a result of the increase in average compressed breast thickness was not actually found in practice, possibly because of advances in equipment design and dose optimization strategies made during the 11-year period. Other implications of an increasing average compressed breast thickness are discussed.

Patient and staff radiation doses from early radiological examinations (1899-1902).

A source of data on radiographic and fluoroscopic examinations, including radiographic technique factors, was used in conjunction with information about cold-cathode X-ray apparatus to estimate patient and staff radiation doses for the years 1899 to 1902 at the Forth Banks Infirmary, Newcastle-upon-Tyne. Physical evidence from representative apparatus of the period was used with a beam spectral simulation program to characterize the X-ray beam, and information about the electrical supply waveform was produced by experimental operation of a contemporary induction coil. Results are given in terms of skin entrance dose, and these are compared with modern values. An estimate of the annual dose received by the radiographer known to have carried out all of the examinations within this period is also given.

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.

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.

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.

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.

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.