Direct Digital Radiography System Research Articles

Evaluation of the detector linearity response of the DR system in different x-ray bean filters

In the recent past, at Brazilian radiology services, direct digital radiography (DR) systems are replacing Computed Radiography (CR). This situation provides several significant advantages such as improving digital image quality, patient effective dose reduction, and improved speed of examinations performed. To evaluate DR systems, various organizations have published protocols with guidelines concerning quality assurance and acceptance tests for DRs. In these protocols, there are methodologies for evaluating several parameters, such as the detector linearity response (DLR). To test the DLR, different methodologies are proposed by the organizations, such as the application of different additional filters on the X-ray beams spectrum to promote the X-ray doses suitable to produce the latent image in the DR. The objective of this work was to evaluate the results of different protocol methodologies for carrying out the DLR test of a DR flat panel. An analogic radiology equipment, a primary ionization chamber, a DR system and images unprocessed were used in this study. As indicated by the protocols, the spectra of the X-rays were modified by additional filters of copper (Cu) with aluminum (Al); Al; Cu; and polymethylmethacrylate (PMMA). The spectra of the X-rays were modified to achieve the exposure range of 0.1 to 7 mR. The results showed that the DLR curves adjustment were R²>0.99, for a logarithmic equation, type y=a.ln(x)+b. For the filters of 0.5 mmCu with 1.0 mmAl; 11.5 mmAl; 1.0 mmCu; 21 mmAl the mean pixel values showed 0.9% of the coefficient of variation (COV), while for 10 cm PMMA filters, the COV increased to 2.7%. The study showed that methodologies using Al, Cu and Al with Cu filters DLR have similar responses while using PMMA, the response was slightly different.

Is digital mammography reducing radiation doses to women?

This study aims to investigate the impact of national quality programs in mammography and technological advances in digital mammography units on the radiation doses delivered to women in Brazil. Radiation dose assessments in mammography units were conducted through a mail-based dosimetric system. For each unit of facilities that applied to one of the two national quality programs, a postal dosimetric system is dispatched, comprising an optically stimulated luminescent dosimeter (OSL) attached to the surface of a 4.0 cm thick polymethyl methacrylate (PMMA) phantom, simulating a compressed breast with 4.5 cm thickness. Testing instructions to expose the dosimetric phantom for assessing the mean glandular dose (MGD) are provided. Between 2012 and 2023, the programs evaluated the MGD in 1,687 mammography units of computed radiography (CR) and direct digital radiography (DR) technologies from 1,399 facilities located in all Brazilian regions. A total of 1,660 (70.5%) evaluations were carried out on CR technology mammography units and 696 (29.5%) on DR units, totaling 2,356 MGD evaluations. The overall average MGD was 1.60 ± 0.80 mGy, with 1.68 ± 0.83 mGy for CR technology and 1.42 ± 0.68 mGy for DR technology. A comparison of average MGD between the periods 2012 - 2018 and from 2019 onwards shows a dose reduction of 8.6% for CR systems and of 26.0% for DR systems (p = 0.000). As CR systems use analog mammography units, which did not undergo technological advances between the two periods, the reduction in doses observed is due to the actions of national quality certification programs and by using image plates for dual-sided reading or needle-based image plates. The reduction observed in DR systems is due to both national quality programs and technological advances in mammography units, especially the use of radiation beams generated by X-ray tubes with tungsten targets.

Proposed Institutional Diagnostic Reference Levels in Computed and Direct Digital Radiography Examinations in Two Teaching Hospitals

Background: The detectors of both computed radiography (CR) and direct digital radiography (DR) have a wide dynamic range that could tolerate high values of exposure factors without an adverse effect on image quality. Therefore, this study aims to assess patient radiation dose and proposes institutional diagnostic reference levels (DRLs) for two teaching hospitals in Ghana.Materials and Methods: CR and DR systems were utilized in this study from two teaching hospitals. The CR system was manufactured by Philips Medical Systems DMC GmbH, while the DR system was manufactured by General Electric. The entrance skin doses (ESDs) were calculated using the standard equation and the tube output measurements. Free-in-air kerma (μGy) was measured using a calibrated radiation dosimeter. The proposed institutional DRLs were estimated using 75<sup>th</sup> percentiles values of the estimated ESDs for nine radiographic projections.Results and Discussion: The calculated DRLs were 0.4, 1.6, 3.4, 0.5, 0.4, 1.1, 1.0, 1.2, and 1.7 mGy for chest posteroanterior (PA), lumbar spine anteroposterior (AP), lumbar spine lateral (LAT), cervical spine AP, cervical spine LAT, skull PA, pelvis AP, and abdomen AP, respectively in CR system. In the DR system, the values were 0.3, 1.6, 3.1, 0.4, 0.3, 0.7, 0.6, 0.9, and 1.3 for chest PA, lumbar spine AP, lumbar spine LAT, cervical spine AP, cervical spine LAT, skull PA, pelvis AP, and abdomen AP, respectively.Conclusion: Institutional DRLs in nine radiographic projections have been proposed for two teaching hospitals in Ghana for the first time. The proposed DRLs will serve as baseline data for establishing local DRLs in the hospitals and will be a valuable tool in optimizing patient doses.

The IAEA remote and automated quality control methodology for radiography and mammography.

Radiography remains the most widely used imaging modality throughout the world. Additionally, while it has been demonstrated that a quality control (QC) program, especially in mammography, improves image quality, weekly technologist QC testing might be lacking even where there is clinical qualified medical physicist (CQMP) support. Therefore, the International Atomic Energy Agency (IAEA) developed simple QC phantoms that can easily be used on a regular basis (daily/weekly) for radiography and mammography. These are simple in design and use materials that are easily accessible in most parts of the world. A software application is also developed that automatically analyzes images and Digital Imaging and Communications in Medicine (DICOM) header information. It exports data to a comma‐separated values (CSV) file that is read by a Microsoft Excel® spreadsheet for documentation and graphical analysis. The phantom and the software were tested in four institutions (in Costa Rica and the United States of America) both on computed radiography and direct digital mammography and radiography systems. Data were collected over a 3‐year period. No corrective actions were taken on the data, but service was performed on two of the units. Results demonstrated noise that could be attributed to suboptimal placement of the phantom and incorrect data being put into the DICOM header. Preliminary evaluation of the IAEA methodology has demonstrated that it can provide meaningful QC data that are sensitive to changes in the imaging systems. Care must be taken at implementation to properly train personnel and ensure that the image data, including the DICOM header, are being correctly transmitted. The methodology gives the opportunity for a single CQMP to provide QC services even to remote sites where travel is prohibitive, and it is feasible and easy to implement.

Comparison of two digital intraoral radiography imaging systems as a function of contrast resolution and exposure time.

To compare the image quality of two different digital imaging systems; one photostimulable phosphor plate system (PSP) and a direct digital radiography system with CMOS imaging sensor; via evaluating contrast resolution among four different exposure times. Endodontically treated incisor teeth embedded in paraffin blocks are aligned next to a 99.5% Al wedge and exposed for 0.8, 0.1,0.125 and 0.16 seconds using both the CMOS and PSP systems. Using ImageJ software, 5 isometric and isogridded ROI from each root filling area and isometric ROI from the Al stepwedge were calculated. Evaluation of the total of 120 images displayed that PSP system produced significantly higher contrast resolution (P<0.05) in regard to pixel values than the CMOS. The CMOS system was non- responsive to increasing dose (P=0.000). Regarding the EqAl values, no significant difference was determined between groups (P>0.05). The contrast resolution was higher using the PSP system. It can be estimated that, filling material will be more obvious under lower doses using PSP.

Optimisation of the lateral lumbar spine projection using an air-gap technique

IntroductionLumbar spine radiography is considered as having a high radiation dose compared to other planar radiography examinations. The aim of this study was to investigate the feasibility of replacing an antiscatter grid with an air gap technique to achieve dose reduction for lateral lumbar spine radiography while maintaining image quality on a direct digital radiography (DDR) system. MethodsIn phase 1, an experimental study using an anthropomorphic phantom identified the optimal airgap technique. In phase 2, lateral projections of the lumbar spine were performed on 50 patients randomly assigned equally into a control group (using the antiscatter grid) and an experimental group (using the airgap technique). The dose area product (DAP) was recorded, keeping other variables constant. Image quality evaluation was performed by 5 radiologists performing Absolute Visual Grading Analysis (VGA) using an image quality score tool, with resultant scores analysed using Visual Grading Characteristics (VGC). ResultsA 10 cm airgap in conjunction with a source to image distance (SID) of 121 cm was found as the optimal airgap technique. The clinical application of this technique resulted in a statistically significant (p < 0.05) reduction in DAP of 72%. Image quality scores were higher for the antiscatter grid but variation between the two techniques was not significant (p > 0.05). ConclusionReplacing the antiscatter grid with an airgap technique in lateral lumbar spine digital radiography, provides a significant dose reduction whilst still maintaining diagnostic image quality. Implications for practiceThe airgap technique is a simple and easy technique to implement and radiographers should find no difficulties in applying it, as It involves no additional cost and no additional equipment.

Effectiveness of adjusting radiographic technique parameters on image quality in direct digital radiography: a systematic review protocol.

The purpose of this review is to investigate the effectiveness of adjusting radiographic technique parameters on image quality of projectional radiographs acquired on a direct digital radiography system. Projectional radiography performed with direct digital detectors is now commonplace in many medical imaging departments across the world. While the acquisition technology has advanced, it appears that many sites have not optimized their radiographic technique factors for this new technology. The aim of this review is to uncover evidence to support the continued use of these traditional technique parameters or to suggest changes in clinical practice that would produce optimized results. The review will consider studies that include projectional radiographs acquired on a direct digital radiography system of the axial and appendicular skeleton. Only studies that investigate a human subject (living or post-mortem), or an anthropomorphic phantom will be included. Studies that directly investigate the effect of changing a technique parameter on the resultant image quality and the effect on patient dose will be included. A comprehensive search of both published and unpublished literature will be performed to uncover studies meeting the inclusion criteria. Studies will be screened for inclusion by two reviewers and disagreements resolved through discussion or with a third reviewer. Studies included in final analysis will be critically appraised for methodological quality. Data will be extracted by a single reviewer and checked by the author team for accuracy. Statistical meta-analysis and subgroup analyses will be performed as appropriate, and a Summary of Findings created. PROSPERO CRD42019137806.

Optimization of simulated cranial, thorax, and abdominal examination in paediatric digital radiography

This study was aimed to obtain optimum parameter combination in simulated cranial, thorax, and abdominal examinations using computed radiography (CR) and direct digital radiography (DDR) systems. Optimization was performed using in-house phantom with contrast objects on Siemens Luminos Agile Max DDR and Siemens Axiom Luminos TF CR. Paediatric patients were separated into four age groups; 0-1 year (group A), 1-5 years (group B), 5-10 years (group C), and 10-15 years (group D). Slab phantoms with different total thickness were used to simulate patients belonging to each age group for different anatomical region (cranial, thorax, and abdomen). Optimization were performed in three steps; first kVp, followed by mAs, and then additional filter optimization. All the steps of optimization were performed based on FOM (figure of merit) values calculated as ratio of squared SDNR (signal difference to noise ratio) and entrance surface dose with the highest FOM representing the optimum condition. The results of this optimization were evaluated based on the highest FOM generated from each exposure. For both CR and DDR, optimum parameters (i.e. highest FOM) are different for each age group and anatomical region. Even with different X-Ray units, the CR device had slightly similar optimized parameters.

Estimation of Mean Estimation of Mean Glandular Dose in Mammography Examination in some of Radiology Centers in Tehran city

Introduction: the objectives of this research were determination of Mean Glandular Dose in film- screen and digital mammography examinations, estimation of accumulated effective dose in some of mammography centers in Tehran city and estimating cancer risk due to these examinations. Materials and Methods: the clinical data were collected from the 1318 mammograms taken from 333 women who were referred to 4 mammography centers in Tehran. The mammography instruments in this study were one film-screen system, one DDR system and two CR system. An RTI dosimeter, piranha system version 3.1, was used for measurement of ESAK and HVL. Compressed breast thickness determined by the mammography systems which was calibrated by a millimeteric ruler. Dgn conversion factor was determined from a program written in C by Bouzarjomehri and et al. Height and weight patients were also measured. Results: The mean ±SD results of MGD per film and per woman were respectively 2.04±0.75 mGy and 8.12 ± 2.75 mGy. The mean effective dose ± SD of patient was 0.4±0.13 m Sv. the number of patients referring to these four mammography centers estimated 8352 per year, so accumulated dose was 3.34 ±1.08 man. Sv With considering of 8% per Sv cancer risk, according to BEIR VII report, the carcinogenic risk of the mammography examinations in these centers will be 0.26 women per year. The MGD results showed a relatively linear correlation with CBT, but age, weight, BMI of the patients haven’t a correlation with MGD, r2<0.3. Conclusion: The average MGD per mammogram of this study was higher than other references, which may be due to the higher average breast thickness of these women relative of the other references but the mean MGD of this study was lower than the RLs values reported by ICRP (3 mGy). The average MGD resulted in this study for the analogue mammography device was lower than the computed radiography (CR) and the direct digital radiography (DDR) devices of.

Tackling the commissioning of a digital radiography AEC system

AEC devices aim to maintain a consistent level of clinical image quality despite variations in patient body habitus and imaging method. The assessment of AEC performance has undergone significant revision with the advent of digital radiography and challenges still remain. Verification of manufacturers’ target detector air kerma (DAK) values with differing AEC testing protocols can be problematic, particularly when the system has been configured with integrated direct digital radiography (DDR) detectors. In addition, there is a need for comparative dose information from current DDR technology to be made available to the wider Medical Physics community. AEC testing was performed on 4 recently-installed Carestream DRX Evolution Plus digital radiographic systems as part of their commissioning tests. AEC calibration was assessed using 3 IPEM-recommended parameters; DAK, image pixel value and detector dose indicator (DDI). Testing was performed with both free and scatter-free configurations and with and without antiscatter grid. A mixture of exit dose and in-bucky measurements were performed with the assistance of a field service engineer (FSE) for both free and integrated detectors. Results from the AEC testing of the four Carestream digital radiographic systems are presented for different testing conditions along with hints and tips on assessing the AEC dose levels when commissioning the systems. DAK results are compared to the manufacturers target values and to Bowden et al.’s (2011) published results on other DDR systems. These results could be used as initial AEC reference values against which others can compare their results when commissioning comparable systems.

Diagnostic accuracy of a charge-coupled device and a photostimulable phosphor plate in detection of non-cavitated proximal caries

Objective: The aim of this study was to compare the diagnostic accuracy of two direct digital radiography systems: the charge-coupled device (CCD) XIOS XG Sirona® and the photostimulable storage phosphor (PSP) VistaScan DürrDental®, in the detection of non-cavitated proximal caries lesions. Materials and methods: in this experimental and cross-sectional study 112 proximal surfaces from 27 molars and 31 premolars with or without proximal caries lesions were evaluated and randomly allocated in a study unit. Bitewing radiographs were acquired with a CCD XIOS XG and with the PSP VistaScan. A single X-ray unit was used for both systems. Radiographic images were assessed independently by two calibrated radiologists. Histological evaluation on a stereomicroscope was used as gold standard. Results: Sensitivity values were found to be 0.35 for CCD and 0.31 for PSP. Specificity values were found to be similar for both systems (0.867). Az values showed a low diagnostic accuracy for both sensors: 0.61 for CCD and 0.59 for PSP, no statistical difference was found between these two values (p=0.78). Conclusion: Both digital radiology systems have a high diagnostic accuracy to detect sound surfaces but low diagnostic accuracy to detect proximal carious lesions.

Dependence of low contrast detail on exposure dose and tube voltage in digital flat-panel detector radiography—a pre-clinical phantom study

Purpose. Pre-clinical determination of reasonable simplified examination protocols before clinical application to assess the performance of a direct digital radiography (DDR) system. Material and methods. The experimental setup consists of a DDR system with fixed flat-panel detector (CsI). A phantom with low-contrast structures (LCS) was examined in two settings in order to simulate standard radiographs: (1) small peripheral joints like the wrist (no patient phantom, no anti-scatter grid) and (2) big proximal joints like the hip (20 cm water tank patient simulation and with an anti-scatter grid). Setup (1) was manually exposed at 55 kV/2 mAs, 60 k V/1.6 mAs and 65 k V/1.25 mAs. Setup (2) was automatically exposed at 1.6, 2.5, 4 and 6 μGy per kV-setting (80 ± 5 kV). Contrast-detail curves (CDC) were generated by analyzer software. Results. Exposures of setup (1) showed similar CDC (p = 0.99) with a decreasing curve with larger diameter of LCS. In all exposures of setup (2) CDC were similar for all kV-settings (p > 0.93) with a decreasing curve with larger LCS diameter. CDC insignificantly decrease with increasing exposure dose (p > 0.38). Conclusion. Low-contrast detectability was independent of kV and marginally dependent on the dose, both within a certain range. This could be used to further reduce radiation dose and simplify examination protocols to be tested in a further clinical study.

Digital detector quality assurance testing in Ireland

As Direct Digital Radiography (DDR) systems are replacing older imaging systems in hospitals, it is essential to ensure that Medical Physicists are performing the most appropriate testing on this newer modality. Specifically, quality control testing on the Digital Detector is central to ensuring adequate image quality to allow clinical diagnosis and treatment. There are a number of different guidelines [ [1] , [2] , [3] , [4] ] available on testing for digital systems, however it is unclear what practical approaches are being undertaken in Ireland. A short survey of DR testing practice in Ireland was performed to establish common practice and assist in developing recommendations for progression of this type of testing in conjunction with the Ionising Imaging Special Interest Group (II SIG) of the IAPM. This poster aims to discuss the findings of the survey.

Technique for Performing Lumbar Puncture in Microgravity Using Portable Radiography.

Visual Impairment and Intracranial Pressure Syndrome (VIIP) has caused symptomatology during and after long duration missions on the International Space Station (ISS). Only indirect measurements of intracranial pressure (ICP), such as ultrasound, have been performed on ISS. Discussion and interest has happened at NASA about performing lumbar puncture (LP) in microgravity. Only the "blind" palpation approach and the ultrasound-assisted approach have been discussed. This article, as proof of concept, discusses the possibility of portable radiography to assist lumbar punctures in microgravity. An anthropomorphic radiological phantom of an adult lumbar spine was made containing a fluid-filled space in the spinal canal with a latex membrane which simulated the dural sac and cerebrospinal fluid. A portable direct-digital radiography system with wireless transmitting image receptor and screen was used to perform image-guided lumbar puncture. Using the same equipment and technique, this procedure was then performed on a cadaver for final proof of concept. Technical success was achieved in all approaches on the first try without needle redirection. There was no difference between the cadaver model and the phantom model in terms of difficulty in reaching the fluid space or visually confirming needle location. Portable radiography via proof of concept has the potential to guide lumbar puncture while minimizing volume and mass of equipment. This could be ideal for assisting in performing lumbar puncture in microgravity, as this is the standard of care on Earth for difficult or failed "blind" lumbar punctures. Lerner DJ, Parmet AJ, Don S, Shimony JS, Goyal MS. Technique for performing lumbar puncture in microgravity using portable radiography. Aerosp Med Hum Perform. 2016; 87(8):745-747.

Technical innovation in equine radiology: what's changed?

THE transition from analogue (film-to-screen) radiographic imaging to digital radiographic imaging has improved the quality of radiographic studies in veterinary medicine. The potential advantages of digital imaging over conventional imaging...

Radiation doses received in the United Kingdom breast screening programme in 2010 to 2012.

To review the radiation doses received by women attending the UK breast-screening programme between 2010 and 2012. To compare doses with previous years and to quantify the impact on dose of changing from analogue to digital imaging and to analyse doses by type of imaging system. Measurements of doses to samples of about 50-100 women attending for screening were collected across the whole of the UK breast-screening programme. Data were collected for 87,122 exposures, using 449 X-ray sets, for 25,408 women. The average mean glandular dose (MGD) was 1.79 mGy for mediolateral oblique images and 1.58 mGy for craniocaudal images. The average MGD per two-view examination was 4.01 mGy for film-screen imaging and 3.03 mGy for direct digital radiography (DR) and 4.69 mGy for computed radiography. The MGD to women attending breast screening has been reduced on average by about 25% where DR systems have replaced film-screen systems. The dose reduction was greatest for breasts with the largest compressed thickness. There are large variations in dose between the different models of DR system provided by different manufacturers. There should be further work to ensure that all DR systems are operated at the optimal dose level to ensure the best cancer detection while balancing the detriment caused by using radiation. Changes in the radiation dose in breast screening over time have been determined. Specifically, the impact on radiation dose of introducing different types of DR and computed radiography system into breast screening has been quantified.

Analysis of the reproducibility of the gray values and noise of a direct digital radiography system

The aim of this study was to evaluate the reproducibility of the gray values and noise of a direct digital radiography system (Visualix eHD) for various exposure times and analyzed regions. To obtain radiographic images in a standardized manner, the digital sensor of the system and a stepwedge were positioned in a phantom at a focus-film distance of 30 cm in a dental device at 70 kV, 7 mA and 2.2 mm filtration. Ten consecutive repetitions of X-ray imaging were performed at each exposure time (0.05, 0.07, 0.09 and 0.13 s). Gray values were analyzed using ImageJ software in five regions of interest (ROIs): alveolar bone (AB), soft tissue (ST) and three steps of the stepwedge (S1, S2 and S3). The results showed that both the variability of the gray values and the noise were statistically greater (p < 0.05) in the most radiolucent region (ST). Only the noise was affected by the exposure time. In conclusion, the reproducibility of the gray values and the noise of the Visualix eHD system can vary in specific areas with different radiolucency.

Comparison of the perceived image quality between two digital imaging systems for neonatal bedside radiography – A case study

BackgroundChest X-rays are performed daily in the neonatal intensive care and high care units. The skill of the radiographer is critical for obtaining the best image quality and limiting the patient's radiation exposure. The literature states that indirect flat panel detectors produce images of superior quality in comparison to computed radiography systems. At Steve Biko Academic Hospital a decision was made to revert from the direct digital radiography (DR) system to the computed radiography (CR) system, due to poor image quality experienced. MethodThe case study objective was to conduct a comparative analysis describing key technical factors contributing to image quality. The analysis entailed retrospectively comparing the images obtained during 2010 and 2011. An image analysis form was utilised in evaluating the technical aspects of the image. A total of 160 images were viewed by 16 participants sampled from the radiography, radiology and paediatric departments. The participants were asked to re-evaluate two of their allotted images after five days to determine their reliability. ResultsFindings were that the DR system provides significantly better image quality than the CR system (p < 0.05) for all the technical factors evaluated. However technical improvements are recommended. A wide variance in intra-observer reliability was also found. ConclusionThis case study demonstrated that DR images were considered to be superior to CR images. Recommendations include: a standardised technique for imaging the neonates; optimisation of the imaging software for the digital detectors, improved feedback systems in terms of exposure index values, and the training of radiographers and referring physicians in technical image analysis.

Latin American dose survey results in mammography studies under IAEA programme: radiological protection of patients in medical exposures (TSA3).

Latin American countries (Argentina, Brazil, Chile, Costa Rica, Cuba, Ecuador, El Salvador, Guatemala, Mexico, Nicaragua, Paraguay, Uruguay and Venezuela) working under the International Atomic Energy Agency (IAEA) Technical Cooperation Programme: TSA3 Radiological Protection of Patients in Medical Exposures have joined efforts in the optimisation of radiation protection in mammography practice. Through surveys of patient doses, the region has a unique database of diagnostic reference levels for analogue and digital equipment that will direct future optimisation activities towards the early detection of breast cancer among asymptomatic women. During RLA9/057 (2007-09) 24 institutions participated with analogue equipment in a dose survey. Regional training on methodology and measurement equipment was addressed in May 2007. The mean glandular dose (DG) was estimated using the incident kerma in air and relevant conversion coefficients for both projections craneo caudal and mediolateral oblique (CC and MLO). For Phase 2, RLA9/067 (2010-11), it was decided to include also digital systems in order to see their impact in future dose optimisation activities. Any new country that joined the project received training in the activities through IAEA expert missions. Twenty-nine new institutions participated (9 analogue and 20 digital equipment). A total of 2262 patient doses were collected during this study and from them D(G) (mGy) for both projections were estimated for each institution and country. Regional results (75 percentile in mGy) show for CC and MLO views, respectively: RLA9/057 (analogue) 2.63 and 3.17; RLA/067: 2.57 and 3.15 (analogue) and 2.69 and 2.90 (digital). Regarding only digital equipment for CC and MLO, respectively, computed radiography systems showed 2.59 and 2.78 and direct digital radiography (DDR) systems 2.78 and 3.04. Based on the IAEA Basic Safety Standard (BSS) reference dose (3 mGy), it can be observed that there is enough room to start optimisation processes in Latin America (LA); several countries or even particular institutions have values much higher than the 3 mGy. The main issues to address are lack of well-established quality assurance programmes for mammography, not enough medical physicists with training in mammography, an increase in patient doses with the introduction of digital equipment and to create awareness on radiation risk and optimisation strategies.

Study on construction of a medical x-ray direct digital radiography system and hybrid preprocessing methods.

We construct a medical X-ray direct digital radiography (DDR) system based on a CCD (charge-coupled devices) camera. For the original images captured from X-ray exposure, computer first executes image flat-field correction and image gamma correction, and then carries out image contrast enhancement. A hybrid image contrast enhancement algorithm which is based on sharp frequency localization-contourlet transform (SFL-CT) and contrast limited adaptive histogram equalization (CLAHE), is proposed and verified by the clinical DDR images. Experimental results show that, for the medical X-ray DDR images, the proposed comprehensive preprocessing algorithm can not only greatly enhance the contrast and detail information, but also improve the resolution capability of DDR system.