Patient exposure in medical X-ray imaging in Europe

Patients are exposed to X rays when undergoing medical examinations in diagnostic radiology. Exposure data acquired and assessed in Germany for the year 1997 resulted in a mean annual effective dose of 2 +/- 0.5 mSv per head of the population, thereby reaching or exceeding the average level of environmental radiation in many cases. The underlying frequency of medical X-ray examinations was approximately 136 million, i.e. approximately 1.7 examinations annually per head of the population. For comparison, corresponding data of other countries were extracted from the UNSCEAR 2000 report or originate from the literature. Data analysis shows significant differences in national radiological practices and a very uneven distribution of patient doses amongst the world population. The mean annual effective dose per head of the population varies by up to a factor of 60 between health care level I and IV countries, and still by a factor of approximately 6 within health care level I countries. While projection radiography has succeeded in reducing dose consumption, computed tomography and radiological interventions have given rise to a significant growth of patient exposure, and interventional radiology can even exceed thresholds for deterministic radiation effects. Patient exposure is further shown to result from misadministration and retakes of X-ray examinations, usually not registered, as well as from technical failures of X-ray facilities, which can cause significantly enhanced exposure times. Corresponding data are presented and comments are made on the international situation of non-harmonised data collection on patient exposure as well as of parameters affecting the assessment of exposure and risk.     

Dose optimisation in computed radiography

After the installation of computed radiography (CR) systems in three hospitals in Luxembourg a patient dose survey was carried out for three radiographic examinations, thorax, pelvis and lumbar spine. It was found that the patient doses had changed in comparison with the patient doses measured for conventional radiography in the same three hospitals. A close collaboration between the manufacturers of the X-ray installations, the CR imaging systems and the medical physicists led to the discovery that the speed class with which each radiographic examination was to be performed, had been ignored, during installation of the digital imaging systems. A number of procedures were carried out in order to calibrate and program the X-ray installations in conjunction with the CR systems. Following this optimisation procedure, a new patient dose survey was carried out for the three radiographic examinations. It was found that patient doses for the three hospitals were reduced.     

A framework for optimising the radiographic technique in digital X-ray imaging

The transition to digital radiology has provided new opportunities for improved image quality, made possible by the superior detective quantum efficiency and post-processing capabilities of new imaging systems, and advanced imaging applications, made possible by rapid digital image acquisition. However, this transition has taken place largely without optimising the radiographic technique used to acquire the images. This paper proposes a framework for optimising the acquisition of digital X-ray images. The proposed approach is based on the signal and noise characteristics of the digital images and the applied exposure. Signal is defined, based on the clinical task involved in an imaging application, as the difference between the detector signal with and without a target present against a representative background. Noise is determined from the noise properties of uniformly acquired images of the background, taking into consideration the absorption properties of the detector. Incident exposure is estimated or otherwise measured free in air, and converted to dose. The main figure of merit (FOM) for optimisation is defined as the signal-difference-to-noise ratio (SdNR) squared per unit exposure or (more preferably) dose. This paper highlights three specific technique optimisation studies that used this approach to optimise the radiographic technique for digital chest and breast applications. In the first study, which was focused on chest radiography with a CsI flat-panel detector, a range of kV(p) (50-150) and filtration (Z = 13-82) were examined in terms of their associated FOM as well as soft tissue to bone contrast, a factor of importance in digital chest radiography. The results indicated that additive Cu filtration can improve image quality. A second study in digital mammography using a selenium direct flat-panel detector indicated improved SdNR per unit exposure with the use of a tungsten target and a rhodium filter than conventional molybdenum target/molybdenum filter techniques. Finally, a third study focusing on cone-beam computed tomography of the breast using a CsI flat-panel detector indicated that high Z filtration of a tungsten target X-ray beam can notably improve the signal and noise characteristics of the image. The general findings highlight the fact that the techniques that are conventionally assumed to be optimum may need to be revisited for digital radiography.     

Image quality and dose management in digital radiography: a new paradigm for optimisation

The advent of digital imaging in radiology, combined with the explosive growth of technology, has dramatically improved imaging techniques. This has led to the expansion of diagnostic capabilities, both in terms of the number of procedures and their scope. Throughout the world, film/screen radiography systems are being rapidly replaced with digital systems. Many progressive medical institutions have acquired, or are considering the purchase of computed radiography systems with storage phosphor plates or direct digital radiography systems with flat panel detectors. However, unknown to some users, these devices offer a new paradigm of opportunity and challenges. Images can be obtained at a lower dose owing to the higher detective quantum efficiency (DQE). These fundamental differences in comparison to conventional film/screens necessitate the development of new strategies for dose and quality optimizations. A set of referral criteria based upon three dose levels is proposed.     

Comparative reject analysis in conventional film-screen and digital storage phosphor radiography

The purpose of this work was to gather information about the benefits in patient care caused by the introduction of digital radiography. In particular, the possibility of reducing the number of image repeats and thus unnecessary patient radiation was sought. Waste films of conventional radiography were collected--in digital radiography each image delete command at the post-processing workstation was documented. Rejected images were analysed retrospectively. The overall reject rate was 27.6% in the conventional and 2.3% in the digital department. While in the conventional department the main reason for rejection was 'exposure' and 'others' (i.e. problems related to film handling), the main reason in the digital environment was 'positioning'. Reject analysis yields representative data about the current performance of a radiology department. A marked reduction of repeated X rays and consequently reduced radiation exposure of the patient was clearly shown in this study comparing two differently working radiology departments. This is one of several benefits of digital radiography in patient care.     

An assessment of annual whole-body occupational radiation exposure in Ireland (1996-2005)

Whole-body occupational exposure to artificial radiation sources in Ireland for the years 1996-2005 has been reviewed. Dose data have been extracted from the database of the Radiological Protection Institute of Ireland, which contains data on >95% of monitored workers. The data have been divided into three sectors: medical, industrial and education/research. Data on exposure to radon in underground mines and show caves for the years 2001-05 are also presented. There has been a continuous increase in the number of exposed workers from 5980 in 1996 to 9892 in 2005. Over the same time period, the number of exposed workers receiving measurable doses has decreased from 676 in 1996 to 189 in 2005 and the collective dose has also decreased from 227.1 to 110.3 man millisievert (man mSv). The collective dose to workers in the medical sector has consistently declined over the 10-y period of the study while that attributable to the industrial sector has remained reasonably static. In the education/research sector, the collective dose typically represents 5% or less of the total collective dose from all practices. Over the 10 y of the study, a total of 77 914 annual dose records have been accumulated, but only 4040 (<6%) of these represent measurable radiation doses in any given year. Over the same time period, there were 283 instances in which exposed workers received individual annual doses >1 mSv and 21 of these exceeded 5 mSv. Most of the doses >1 mSv were received by individuals working in diagnostic radiology (which also includes interventional radiology) in hospitals and site industrial radiography. There has been only one instance of a dose above the annual dose limit of 20 mSv. Evaluating the data for the period 2001-05 separately, the average annual collective dose from the medical, industrial and educational/research sectors are approximately 60, 70 and 2 man mSv with the average dose per exposed worker who received a measurable dose being 0.32, 0.79 and 0.24 mSv, respectively. Diagnostic radiology and site industrial radiography each represents >60% of the collective dose in their respective sectors. Available data on radon exposure in one underground mine and in three show caves indicate an annual collective dose of 75 man mSv from these work activities. By comparison, previous estimates of exposure of Irish air crew to cosmic radiation have given rise to an estimated collective dose of 12 000 man mSv. It can be concluded therefore that the natural radioactivity sources account for well >90% of all occupational exposure in Ireland. This evaluation does not include an estimate of exposure to radon in above-ground workplaces-these data are currently being evaluated and their inclusion will increase both the total occupational collective dose as well as the percentage of that dose due to natural radiation.     

Number of X-ray examinations performed on paediatric and geriatric patients compared with adult patients

The age of the patient is of prime importance when assessing the radiological risk to patients due to medical X-ray exposures and the total detriment to the population due to radiodiagnostics. In order to take into account the age-specific radiosensitivity, three age groups are considered: children, adults and the elderly. In this work, the relative number of examinations carried out on paediatric and geriatric patients is established, compared with adult patients, for radiodiagnostics as a whole, for dental and medical radiology, for 8 radiological modalities as well as for 40 types of X-ray examinations. The relative numbers of X-ray examinations are determined based on the corresponding age distributions of patients and that of the general population. Two broad groups of X-ray examinations may be defined. Group A comprises conventional radiography, fluoroscopy and computed tomography; for this group a paediatric patient undergoes half the number of examinations as that of an adult, and a geriatric patient undergoes 2.5 times more. Group B comprises angiography and interventional procedures; for this group a paediatric patient undergoes a one-fourth of the number of examinations carried out on an adult, and a geriatric patient undergoes five times more.     

Equipment requirements and specification for digital and interventional radiology

During the past decade there has been a substantial growth in digital and interventional radiology. Equipment requirements and specification for digital (interventional) radiology are necessary to facilitate the purchase of proper installations for specific purposes. Inappropriate equipment might lead to increased dose to patients and staff, insufficient image quality and, for interventional radiology, to inefficient procedures and the potential for deterministic effects to occur. The equipment requirements and specifications are of various types. Requirements for dose displays and dose record keeping are dealt with in a separate contribution to this workshop. Detailed information is presented in this contribution on requirements and specifications in relation to ergonomic, dosimetric and image quality aspects.     

Status and prospects of digital detector technology for CR and DR

Projection radiography is in the middle of the transition from conventional screen-film imaging to digital image acquisition modalities, mainly based on imaging plates (computed radiography, CR) and flat-panel detectors (direct radiography, DR). Cassette-based CR has been available for the past 20 y, and constitutes the major part of direct radiography installations in hospitals today. direct radiography systems based on large-area amorphous silicon active matrix arrays are commercially available for the last 5 y and exist basically in two different types: with scintillators or photoconductors as X-ray conversion material ('indirect' or 'direct' type). direct radiography systems allow for improved image quality and/or dose reduction due to their high detective quantum efficiency and enable faster workflow because of instant image availability. However, new technology developments are improving the performance for CR systems as well, rendering it competitive to direct radiography in many practical aspects. Therefore, it is assumed that the CR and direct radiography systems will coexist for many years to come. This paper reviews the digital detector technologies and the possible future directions of development.     

Patient doses and image quality in digital chest radiology

Chest X-ray examination is one of the most frequently required procedures used in clinical practice. For studying the image quality of different X-ray digital systems and for the control of patient doses during chest radiological examinations, the standard anthropomorphic lung/chest phantom RSD 330 has been used and exposed in different digital modalities available in Slovakia. To compare different techniques of chest examination, a special software has been developed that enables researchers to compare digital imaging and communications in medicine header images from different digital modalities, using a special viewer. In this paper, this special software has been used for an anonymous correspondent audit for testing image quality evaluation by comparing various parameters of chest imaging, evaluated by 84 Slovak radiologists. The results of the comparison have shown that the majority of the participating radiologists felt that the highest image quality is reached with a flat panel, assessed by the entrance surface dose value, which is approximately 75% lower than the diagnostic reference level of chest examination given in the Slovak legislation. Besides the results of the audit, the possibilities of using the software for optimisation, education and training of medical students, radiological assistants, physicists and radiologists in the field of digital radiology will be described.     

Radiation dosimetry for diagnostic medical exposures

The number and complexity of medical procedures using X rays or radioactive materials are both steadily increasing. As a result, the dose from medical exposures now makes up the largest component of the radiation dose to the population in some developed countries. Key developments include the change from film to digital radiography, the increasing sophistication of interventional radiology allowing more complex procedures and the speed and facilities available with multi-slice computed tomography scanners that have extended the range of applications. It is crucial to have accurate dosimetry to monitor the impact of these developments, to ensure that techniques are optimised, and to provide information on health risk that clinicians can consider when justifying exposures. There are two aspects to dosimetry in radiology, assessment of doses to patients and measurement of equipment performance. The techniques that are used will be described, factors that influence doses and that must be considered when making measurements will be discussed, and future developments will be considered.     

Relevant training issues for introduction of digital radiology: results of a survey

Council Directive 97/43/Euratom establishes the need for adequate training of radiology staff. The transition to digital radiology implies changes in various imaging aspects, which are not sufficiently covered by current institutional training programmes. This work aimed to assess how professionals, experienced in digital imaging, acquired their expertise and hence, what form institutional training should take. Within DIMOND III, a survey on training and resources was performed among radiology professionals. A lack of institutional education for digital radiology was found. In the transition to digital radiology, 30-35% train on the job and another 23-28% receive training from digital equipment vendors. A general agreement exists on the need for new quality criteria and strategies for dose management. Issues relevant for conventional/digital transition are only sparsely covered in EC training programmes. Based on these results, a set of training issues was produced, to be included in future European guidelines.     

Review of image quality standards to control digital X-ray systems

A literature review was carried out on quality criteria for the evaluation of image quality for interventional radiology, digital subtraction angiography, computed radiography and direct digital radiography systems. Existing national and international standards were also reviewed. Recommendations for image quality standards for digital X-ray systems are proposed.     

Digital radiographic equipment in the Belgian dental office

A survey was performed among Belgian dentists to evaluate the use and management of digital radiographic equipment. The majority of respondents work as general dental practitioners. One out of eight sets of equipment for extraoral exposures is digital. For intraoral radiography, 30% of the equipment is digital. While exposure time is reduced by about 50% for digital intraoral radiography compared with conventional radiography, no differences can be found between different conventional film speed classes. Appropriate collimation of the radiation beam is only sparingly used. Beam aiming devices to hold the film and position the radiation beam are not used by the majority of dentists. While 25% of the respondents stand behind a protective wall during exposure, 8% of dentists remain next to the patient during exposure while assisting in holding the film inside the mouth. A minority of the latter practitioners wear lead aprons.     

Review of acceptability criteria for X ray systems relevant for digital radiology

The Medical Exposure Directive (97/43/EURATOM) states that competent authorities shall adopt specific criteria of acceptability for equipment in order to indicate when remedial action is necessary. To assist the competent authorities of the European Union Member states, the EC has prepared a document on criteria of acceptability for radiological (including radiotherapy) and nuclear medicine installations. The purpose of the document was to specify minimum standards of performance. Specific criteria for digital equipment are not given in the EC document. In the guidelines for quality control of equipment used in diagnostic radiology in the Netherlands limiting values as well as measurement methods are included. However, guidelines specific for digital imaging equipment are lacking. At present, Report 77 of the Institute of Physics and Engineering in Medicine is the most comprehensive document within Europe for quality control of diagnostic X ray imaging systems. It covers digital fluoroscopy systems and includes or refers to test methods. It contains test frequencies, levels of expertise required, priority of tests and remedial and suspension levels. In the present contribution the available criteria of acceptability for equipment relevant for digital radiology are summarised.     

Dose level of occupational exposure in China

This paper discusses the dose level of Chinese occupational exposures during 1986-2000. Data on occupational exposures from the main categories in nuclear fuel cycle (uranium enrichment and conversion, fuel fabrication, reactor operation, waste management and research activity, except for uranium mining and milling because of the lack of data), medical uses of radiation (diagnostic radiation, nuclear medicine and radiotherapy) and industrial uses of radiation (industrial radiography and radioisotope production) are presented and summarised in detail. These are the main components of occupational exposures in China. In general, the average annual effective doses show a steady decreasing trend over periods: from 2.16 to 1.16 mSv in medical uses of radiation during 1990-2000; from 1.92 to 1.18 mSv in industrial radiography during 1990-2000; from 8.79 to 2.05 mSv in radioisotope production during the period 1980-2000. Almost all the average annual effective doses in discussed occupations were lower than 5 mSv in recent years (except for well-logging: 6.86 mSv in 1999) and no monitored workers were found to have received the occupational exposure exceeding 50 mSv in a single year or 100 mSv in a five-year period. So the Chinese protection status of occupation exposure has been improved in recent years. However, the average annual effective doses in some occupations, such as diagnostic radiology and coal mining, were still much higher than that of the whole world. There are still needs for further improvement and careful monitoring of occupational exposure to protect every worker from excessive occupational exposure, especially for the workers who were neglected before.     

Evolution of diagnostic reference levels in Spanish intraoral radiology

A total of 16 175 official reports of quality assurance on dental radiodiagnostic surgeries from 16 Spanish autonomous regions compiled during 2002-09 were studied to determine the evolution of diagnostic reference levels (DRLs) for obtaining a diagnostic image in the normal conditions of clinical practice in Spanish dental clinics. A DRL of 3.1 mGy was set in 2009, which represents a 35.4 % decrease compared with the dose determined in 2002 (4.8 mGy). During the same period, the mean dose fell by only 17.2 %. The DRL recommended by the European Union in 2004 for intraoral radiology is 4 mGy, and this study shows that 83.4 % of the installations used a dose below this. Of the installations using indirect or direct digital systems 1.1 and 1.2 %, respectively, used doses higher than those recommended, while 14.2 % of those using radiographic film exceeded this limit.     

Quality control of equipment used in digital and interventional radiology

Digital and interventional radiology are increasingly important areas of radiology. Quality control (QC) of such equipment is of particular importance to avoid unnecessary high doses and to help to achieve good image quality. Within the DIMOND III project, equipment requirements and specifications for digital and interventional radiology have been formulated. A protocol for QC tests has been drafted based on various national and international recommendations. Tests are included for various parts of the imaging chain, i.e. X-ray tube and generator, X-ray tube control system, laser printer and display station, and image quality and patient dose. Preliminary tolerance levels have been set for the various tests, after initial measurements. To check the suitability of QC tests and stated tolerance levels, measurements were made at the University Hospital Gasthuisberg in Leuven for equipment used for paediatric radiology and a unit used for chest examinations. The results of the various tests are reported.     

Radiation doses to neonates during X ray computed tomography examinations

As the survival rate of newborns has increased, the number of X ray computed tomography (CT) examinations performed on neonates has been increasing. The exposure doses from CT examinations are known to be higher than those from conventional radiography. Although radiation sensitivity of neonates is higher than that of adults, there are few reports on dose estimates of neonates in CT examinations. Four cylindrical phantoms and one neonatal phantom have been developed to estimate doses to neonates during CT examinations. Using these phantoms and glass dosemeters, absorbed doses were measured. Estimated exposure doses to neonates were higher than those to adults, and our results suggest a need to optimise carefully CT examinations in newborns.     

Evaluation and testing of computed radiography systems

The implementation of film replacement digital radiographic imaging systems throughout Europe is now gathering momentum. Such systems create the foundations for totally digital departments of radiology, since radiographic examinations constitute the most prevalent modality. Although this type of development will lead to improvements in the delivery and management of radiological service, such widespread implementation of new technology must be carefully monitored. The implementation of effective QA tests on installation, at periodic intervals and as part of a routine programme will aid this process. This paper presents the results of commissioning tests undertaken on a number of computed radiography imaging systems provided by different manufacturers. The aim of these tests was not only to provide baseline performance measurements against which subsequent measurements can be compared but also to explore any differences in performance, which might exist between different units. Results of measurements will be presented for (1) monitor and laser printer set-up; (2) imaging plates, including sensitivity, consistency and uniformity; (3) resolution and contrast detectability; and (4) signal and noise performance. Results from the latter are analysed in relationship with both system and quantum noise components.