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Monitoring clinical exposure and deviation indices for dose optimization based on national diagnostic reference level: Focusing on general radiography of extremities
Abstract
Background:
The International Electrotechnical Commission established the concept of the exposure index (EI), target exposure index (EIT) and deviation index (DI). Some studies have conducted to utilize the EI as a patient dose monitoring tool in the digital radiography (DR) system.
Objective:
To establish the appropriate clinical EIT, this study aims to introduce the diagnostic reference level (DRL) for general radiography and confirm the usefulness of clinical EI and DI.
Methods:
The relationship between entrance surface dose (ESD) and clinical EI is obtained by exposure under the national radiography conditions of Korea for 7 extremity examinations. The EI value when the ESD is the DRL is set as the clinical EIT, and the change of DI is then checked.
Results:
The clinical EI has proportional relationship with ESD and is affected by the beam quality. When the clinical EIT is not adjusted according to the revision of DRLs, there is a difference of up to 2.03 in the DI value and may cause an evaluation error of up to 1.6 time for patient dose.
Conclusions:
If the clinical EIT is periodically managed according to the environment of medical institution, the appropriate patient dose and image exposure can be managed based on the clinical EI, EIT, and DI.
... Therefore, the clinical EI values for each examination protocol may differ for each manufacturer [15,16]. However, the clinical EI also shows a proportional relationship with the incident dose on the detector [15,17]. Therefore, several studies have demonstrated the utility of the EI as a real-time dose-monitoring tool [14][15][16][17][18]. ...
... However, the clinical EI also shows a proportional relationship with the incident dose on the detector [15,17]. Therefore, several studies have demonstrated the utility of the EI as a real-time dose-monitoring tool [14][15][16][17][18]. ...
... A previous study reported that the EI could be used as a quality control tool for the detector through the relationship between EI and air kerma incident on the detector under radiation beam quality (RQA) 5, a calibration condition according to the IEC standard [14]. In addition, the possibility of using clinical EI as a dose-monitoring tool was suggested by setting an appropriate target exposure index (EI T ) based on national diagnostic reference levels (DRLs) [15,17]. A study was conducted on the considerations when using EI as a dose monitoring tool in clinical practice through the change in EI according to the patient's thickness in an environment where an automatic exposure control (AEC) system is applied [18]. ...
The clinical anteroposterior (AP) chest images taken with a mobile radiography system were analyzed in this study to utilize the clinical exposure index (EI) as a patient dose-monitoring tool. The digital imaging and communications in medicine header of 6048 data points exposed under the 90 kVp and 2.5 mAs were extracted using Python for identifying the distribution of clinical EI. Even under the same exposure conditions, the clinical EI distribution was 137.82–4924.38. To determine the cause, the effect of a patient's body shape on EI was confirmed using actual clinical chest AP image data binarized into 0 and 255-pixel values using Python. As a result, the relationship between the direct X-ray area of the chest AP image, the higher the clinical EI, the larger the rate of the direct X-ray area. A conversion equation was also derived to infer entrance surface dose through clinical EI based on the patient thickness. This confirmed the possibility of directly monitoring patient dose through EI without a dosimeter in real-time. Therefore, to use the clinical EI of the mobile radiography system as a patient dose-monitoring tool, the derivation method of clinical EI considers several factors, such as the relationship between patient factors.
... The radiation dose received by patients in radiographic examinations can vary depending on the modality, techniques, and exposure factors. Exposure parameters can be optimized through the exposure index (EI) information from computed radiography (CR) or digital radiography (DR) systems to maintain the lowest possible dose while achieving good image quality [4][5][6][7][8]. ...
This study aimed to develop an electrometer for dose area product (DAP) measurement to monitor patient doses on X-ray radiography examinations. The electrometer was developed based on the Atmega8535 microcontroller as the processing unit. This electrometer was operated at 12 volts of direct current (DC) and controlled by buttons for navigation. The system (i.e. in-house electrometer and DAP meter) was carefully designed so that it can easily perform calibration and dose measurements. The system was evaluated at variations of tube voltage, tube current, and exposure time. The developed system results in high accuracy and precision as indicated by low percent error (PE) and relative standard deviation (RSD) compared to standard system. The highest PE and RSD are 1.69% and 1.42% for tube voltage variation, 3.85% and 3.58% for tube current variations, and 12.10% and 0.92% for exposure time variations. In conclusion, the developed system is feasible to be used as a patient dose measurement tool to meet the needs of radiation protection to achieve the principle of "as low as reasonably achievable (ALARA)".
Objective:
To present an optimized examination model by analyzing the risk of disease and image quality according to the combination of the ion chamber of automatic exposure control (AEC) with digital radiography (DR).
Methods:
The X-ray quality was analyzed by first calculating the percentage average error (PAE) of DR. After that, when using AEC, the combination of the ion chambers was the same as the left and centre and right, right and centre, left and centre, centre, right, and left, for a total of six. Accordingly, the entrance surface dose (ESD), risk of disease, and image quality were evaluated. ESD was obtained by attaching a semiconductor dosimeter to the L4 level of the lumbar spine, and then irradiating X-rays to dosimeter centre through average and standard deviation of radiation dose. The calculated ESD was input into the PCXMC 2.0 programme to evaluate disease risk caused by radiation. Meanwhile, image quality according to chamber combination was quantified as the signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) through Image J.
Results:
X-ray quality of DR used in the experiment was within the normal range of±10. ESD of six ion chamber combinations was 1.363mGy, 0.964mGy, 0.946mGy, 0.866mGy, 0.748mGy, 0.726mGy for lumbar anteroposterior (AP), and the lumbar lateral values were 1.126mGy, 0.209mGy, 0.830mGy, 0.662mGy, 0.111mGy, and 0.250mGy, respectively. Meanwhile, disease risk analyzed through PCXMC 2.0 was bone marrow, colon, liver, lung, stomach, urinary and other tissue cancer, and disease risk showed a tendency to increase in proportion to ESD. SNR and CNR recorded the lowest values when three chambers were combined and did not show proportionality with dose, while showed the highest values when two chambers were combined.
Conclusion:
In this study, combination of three ion chambers showed the highest disease risk and lowest image quality. Using one ion chamber showed the lowest disease risk, but lower image quality than two ion chambers. Therefore, if considering all above factors, combination of two ion chambers can optimally maintain the disease risk and image quality. Thus, it is considered an optimal X-ray examination parameter.
Objectives:
To evaluate skin dose differences between TPS (treatment planning system) calculations and TLD (thermo-luminescent dosimeters) measurements along with the dosimetric effect of applicator misplacement for patients diagnosed with gynecological (GYN) cancers undergoing brachytherapy.
Methods:
The skin doses were measured using TLDs attached in different locations on patients' skin in pelvic regions (anterior, left, and right) for 20 patients, as well as on a phantom. In addition, the applicator surface dose was calculated with TLDs attached to the applicator. The measured doses were compared with TPS calculations to find TPS accuracy. For the phantom, different applicator shifts were applied to find the effect of applicator misplacement on the surface dose.
Results:
The mean absolute dose differences between the TPS and TLDs results for anterior, left, and right points were 3.14±1.03, 6.25±1.88, and 6.20±1.97 %, respectively. The mean difference on the applicator surface was obtained 1.92±0.46 %. Applicator misplacements of 0.5, 2, and 4 cm (average of three locations) resulted in 9, 36, and 61%, dose errors respectively.
Conclusions:
The surface/skin differences between the calculations and measurements are higher in the left and right regions, which relate to the higher uncertainty of TPS dose calculation in these regions. Furthermore, applicator misplacements can result in high skin dose variations, therefore it can be an appropriate quality assurance method for future research.
In radiography, the exposure index (EI), as per the International Electrotechnical Commission standard, depends on the incident beam quality and exposure dose to the digital radiography system. Today automatic exposure control (AEC) systems are commonly employed to obtain the optimal image quality. An AEC system can maintain a constant incident exposure dose on the image receptor regardless of the patient thickness. In this study, we investigated the relationship between body thickness, entrance surface dose (ESD), EI, and the exposure indicator (S value) with the aim of using EI as the dose optimization tool in digital chest radiography (posterior-anterior and lateral projection). The exposure condition from the Korean national survey for determining diagnostic reference levels and two digital radiography systems (photostimulable phosphor plate and indirect flat panel detector) were used. As a result, ESD increased as the phantom became thicker with constant exposure indicator, which indicates similar settings to an AEC system, but the EI indicated comparatively constant values without following the tendency of ESD. Therefore, body thickness should be considered under the AEC system for introducing EI as the dose optimization tool in digital chest radiography.
Digital radiography is often performed at a higher dose rate than analogue radiography for image acquisition. The authors
measured the Entrance Surface Dose (ESD) of analogue and digital radiography techniques for 14 radiographic examinations from
randomly selected medical centres in the central district of Korea.
It was that the mean ESD of the digital examinations was 2.84 mGy (range, 0.37–6.38 mGy) and that of the analogue examinations
was 1.83 mGy (range, 0.38–4.74 mGy), resulting in a 55.25 % higher ESD for digital technique. Although this survey is not
completely representative of Korea, findings of this study indicate a need for closer exposure management in digital radiography
to minimise patient dose.
A processing method is described whch allows to present images with equalized detail contrast, i.e. contrast that is the same in all parts of the image, independent of the chosen look-up table (LUT) or the local signal level. Basically, a multiresolution algorithm is used which splits the image in a number of bandpass images. Only the lowest band (lowpass image) is transmitted through the intensity LUT, while all higher frequency subimages are nonlinearly enhanced and added to the LUT-transformed low-pass image. Nonlinear enhancement is used in order to improve the visibility of weakly contrasting details whde minimizing artifacts at high contrast edges. Unfavorable noise enhancement can be avoided by limiting the enhancement in the low-dose areas of the highest frequency subimages. The resulting images
show good detail visibility in all parts. Detail rendition in images with equalized contrast is independent of image latitude and of slight variations in overall image brightness or density. Preliminary experience with clinical images show that the display does not need individual parameter tuning for different images, yet allows producing artifact-free, naturally looking lung images with improved detail visibility for a wide variety of input images. Improvements compared to standard (intensity) equalization processing are evident especially for the mediastinum and subdiaphragmal regions of chest images and in lateral spine examinations that have an inherently large dynamic range.
The exposure index is currently a method by which digital radiography manufacturers provide feedback to the technologist regarding the estimated exposure on the detector, as a surrogate for image signal-to-noise ratio and an indirect indication of digital image quality. Unfortunately, there are as many exposure index values and methods as there are manufacturers, and in an environment with multiple vendors and a need to share data across institutions and dose registry databases, the situation is complicated. Fortunately, a new exposure index of digital X-ray imaging systems has been implemented. Developed concurrently by the International Electrotechnical Commission and the American Association of Physicists in Medicine in cooperation with digital radiography system manufacturers, the index has been implemented as an international standard. As explained, the exposure index does not indicate patient dose but rather a linearly proportional estimate of the incident radiation exposure to the detector. However, the use of the standardized exposure index and its associated target exposure index and deviation index values will likely lead to improved technologist performance in terms of uniformity and use of optimized radiographic techniques, leading to safer care of children needing radiographic examinations. Radiologists will benefit from standardized terminology, and institutions and clinics will be able to compare exposure index values with others through a national dose index registry database now under development. The Alliance for Radiation Safety in Pediatric Imaging, in its role as a benefactor of and advocate for the pediatric patient, is using the Image Gently campaign to disseminate information regarding the exposure index standard for digital radiography so that these benefits can be achieved in a rapid and effective manner.
Many methods are used to track patient exposure during acquisition of plain film radiographs. A uniform international standard would aid this process.
To evaluate and describe a new, simple quality-assurance method for monitoring patient exposure. This method uses the "exposure index" and the "deviation index," recently developed by the International Electrotechnical Commission (IEC) and American Association of Physicists in Medicine (AAPM). The deviation index measures variation from an ideal target exposure index value. Our objective was to determine whether the exposure index and the deviation index can be used to monitor and control exposure drift over time.
Our Agfa workstation automatically keeps a record of the exposure index for every patient. The exposure index and deviation index were calculated on 1,884 consecutive neonatal chest images. Exposure of a neonatal chest phantom was performed as a control.
Acquisition of the exposure index and calculation of the deviation index was easily achieved. The weekly mean exposure index of the phantom and the patients was stable and showed <10% change during the study, indicating no exposure drift during the study period.
The exposure index is an excellent tool to monitor the consistency of patient exposures. It does not indicate the exposure value used, but is an index to track compliance with a pre-determined target exposure.
Digital radiographic imaging systems, such as those using photostimulable storage phosphor, amorphous selenium, amorphous silicon, CCD, and MOSFET technology, can produce adequate image quality over a much broader range of exposure levels than that of screen/film imaging systems. In screen/film imaging, the final image brightness and contrast are indicative of over- and underexposure. In digital imaging, brightness and contrast are often determined entirely by digital postprocessing of the acquired image data. Overexposure and underexposures are not readily recognizable. As a result, patient dose has a tendency to gradually increase over time after a department converts from screen/film-based imaging to digital radiographic imaging. The purpose of this report is to recommend a standard indicator which reflects the radiation exposure that is incident on a detector after every exposure event and that reflects the noise levels present in the image data. The intent is to facilitate the production of consistent, high quality digital radiographic images at acceptable patient doses. This should be based not on image optical density or brightness but on feedback regarding the detector exposure provided and actively monitored by the imaging system. A standard beam calibration condition is recommended that is based on RQA5 but uses filtration materials that are commonly available and simple to use. Recommendations on clinical implementation of the indices to control image quality and patient dose are derived from historical tolerance limits and presented as guidelines.
The International Electrotechnical Commission introduced the concepts of exposure index (EI), target exposure index (EI T) and deviation index (DI) to manage and optimize patient dose in real time. In this study, we have proposed an appropriate method for setting the EI T based on the Korean national diagnostic reference levels (DRLs). Furthermore, we evaluated the use of clinical EI, EI T and DI as tools for patient dose optimization in clinical environments by observing the changes in DI with those in EI T. According to the Korean national exposure conditions, we conducted experiments on three representative radiographic examinations (chest posterior-anterior, lateral and abdomen anterior-posterior) of clinical environments. As the exposure conditions and DRLs varied, the clinical EI, EI T and DI also varied. These results reveal that the clinical EI, EI T and DI can be used as tools for optimizing the patient dose if EI T is periodically and properly updated.
Background:
Computed Tomographic (CT) imaging procedures have been reported as the main source of radiation in diagnostic procedures compared to other modalities. To provide the optimal quality of CT images at the minimum radiation risk to the patient, periodic inspections and calibration tests for CT equipment are required. These tests involve a series of measurements that are time consuming and may require specific skills and highly-trained personnel.
Objective:
This study aims to develop a new computational tool to estimate the dose of CT radiation outputs and assist in the calibration of CT scanners. It may also provide an educational resource by which radiological practitioners can learn the influence of technique factors on both patient radiation dose and the produced image quality.
Methods:
The computational tool was developed using MATLAB in order to estimate the CT radiation dose parameters for different technique factors. The CT radiation dose parameters were estimated from the calibrated energy spectrum of the x-ray tube for a CT scanner.
Results:
The estimated dose parameters and the measured values utilising an Adult CT Head Dose Phantom showed linear correlations for different tube voltages (80 kVp, 100 kVp, 120 kVp, and 140 kVp), with R2 nearly equal to 1 (0.99). The maximum differences between the estimated and measured CTDIvol were under 5 %. For 80 kVp and low tube currents (50 mA, 100 mA), the maximum differences were under 10%.
Conclusions:
The prototyped computational model provides a tool for the simulation of a machine-specific spectrum and CT dose parameters using a single dose measurement.
International Electrotechnical Commission (IEC) established the framework for the use of exposure index (EI) for evaluating the exposure conditions with various digital systems. In this study, we investigated the feasibility of EI, as per the IEC, by comparing the EIs obtained through manual calculated and that displayed on the console of two computed radiography (CR) and digital radiography (DR) systems with radiation beam qualities of RQA3,5,7 and 9. As a result, both two systems indicated an uncertainty of less than 20% for both calculated and displayed EI with all beam qualities except displayed EI obtained by RQA3. However, the displayed EI values were different even under the same exposure conditions because of the characteristics of the imaging receptor materials, such as BaFI or CsI, of two systems. Therefore, when an operator attempts to introduce displayed EI for managing radiation dose, it is essential to understand the characteristics of the digital system.
Purpose
The objective of this study is to determine the quality of chest X-ray images using a deep convolutional neural network (DCNN) and a rule base without performing any visual assessment. A method is proposed for determining the minimum diagnosable exposure index (EI) and the target exposure index (EIt).
Methods
The proposed method involves transfer learning to assess the lung fields, mediastinum, and spine using GoogLeNet, which is a type of DCNN that has been trained using conventional images. Three detectors were created, and the image quality of local regions was rated. Subsequently, the results were used to determine the overall quality of chest X-ray images using a rule-based technique that was in turn based on expert assessment. The minimum EI required for diagnosis was calculated based on the distribution of the EI values, which were classified as either suitable or non-suitable and then used to ascertain the EIt.
Results
The accuracy rate using the DCNN and the rule base was 81%. The minimum EI required for diagnosis was 230, and the EIt was 288.
Conclusion
The results indicated that the proposed method using the DCNN and the rule base could discriminate different image qualities without any visual assessment; moreover, it could determine both the minimum EI required for diagnosis and the EIt.
To develop a second set of diagnostic reference levels (DRLs) and achievable doses (ADs) for 13 adult computed tomography (CT) protocols and a paediatric head CT protocol in Korea. A survey of 13,625 CT examinations was performed based on 13 adult CT protocols and a paediatric non-contrast brain CT protocol using 369 CT systems, with patients grouped according to age. Most CT protocols in this survey had DRLs similar to those reported in other countries. However, chest and abdomen-pelvic CT had lower DRLs than those reported in the first Korean national survey and those from other countries. Paediatric non-contrast brain CT in each age group, with the exception of the 11-15-year age group, had lower DRLs than those reported in other countries. The DRLs presented here are similar to (or lower than for some protocols) those reported in the first Korean national survey and those from other countries.
According to the International Electro-technical Commission, manufacturers of X-ray equipment should indicate the number of
radiation doses to which a patient can be exposed. Dose–area product (DAP) meters are readily available devices that provide
dose indices. Collimators are the most commonly employed radiation beam restrictors in X-ray equipment. DAP meters are attached
to the lower surface of a collimator. A DAP meter consists of a chamber and electronics. This separation makes it difficult
for operators to maintain the accuracy of a DAP meter. Developing a comprehensive system that has a DAP meter in place of
a mirror in the collimator would be effective for measuring, recording the dose and maintaining the quality of the DAP meter.
This study was conducted through experimental measurements and a simulation. A DAP meter built into a collimator was found
to be feasible when its reading was multiplied by a correction factor.
Background
Little information exists concerning appropriate exposure and measuring overall patient dose in pediatric digital radiography.
Objective
To establish a convenient method of appropriate exposure from target exposure index (EI) and thickness in pediatric digital radiography and estimate patient entrance-surface dose (ESD) and dose-area product (DAP) associated with chest, abdomen and pelvis radiography.
Materials and methods
A formula was deduced to calculate appropriate mAs changed with children’s weight and height. EI was used to control image quality. With this formula, dose-optimized procedures were carried out. Data were collected from 180 pediatric examinations, including chest, abdomen and pelvis anterior-posterior (AP) projections. The children were divided into the following age bands: newborns (0–28 days), infants (28 days-2 years) and older children (2–7 years). In each age band, ten children were exposed with the calculated appropriate mAs and EI values were kept steady in appropriate range (referred as target group) and ten children were exposed to the factors routinely used in practice (referred to as the routine group). DAP to children was measured with a DAP meter, and ESD was calculated using measured DAP and data from the National Radiological Protection Board. Data were compared between groups.
Results
ESD ranges in the target group were 32–202 μGy (chest AP), 57–333 μGy (abdomen AP) and 52–372 μGy (pelvis AP). For every radiographic procedure, chi-square Student’s t tests showed a significant difference in average ESD and DAP between the two groups (P < 0.005). Most ESD values from the routine group were two times higher than those from the target group.
Conclusions
The study established a convenient method to set appropriate exposure parameters (mAs) to reach a target EI using the child’s weight and height in pediatric radiography. By this method, ESD and DAP can be significantly reduced in children.
Abstract Ever since the discovery of X-rays in 1895, X-ray imaging has played a large role in the cognitive and practical organization of medicine. This article analyses the way X-ray images were introduced and made sense of in medical thinking and acting around the turn of the century. The implicit assumption in many histories of radiology is that the specific (diagnostic) message of the X-ray images resided inside them from the beginning, and that it is obscured either by technological or epistemological problems. These being solved, it would then be no problem to see directly what information the image contains.
In this article this assumption is contested. It is argued that the specific content of the images was shaped by the activities of X-ray workers within the context of medical developments of the time. This shaping, as it is historically reconstructed here, consisted of four methods. X-ray workers (be they physicians, technicians or scientists) experimented with the technology, the images, the photographic materials and the objects that were X-rayed. They used X-ray images of dead bodies to compare them with radiographs of living patients. Radiologists tried to‘translate’diagnostic information acquired with other methods into the shadows of the X-ray images. And finally they compared images with images.
The process of shaping the content and use of X-ray images, of making them represent reality, took place within specific institutions, and it took a different form in different countries, but also for different parts of the body. Developments of institutionalisation and professionalisation of radiology in England and the Netherlands are presented to provide a small part of the background of this shaping of knowledge of shadows.
Little is known about exposure differences among hospitals. Large differences might identify outliers using excessive exposure.
We used the newly described exposure index and deviation index to compare the difference in existing radiographic exposures for neonatal portable chest radiographs among four academic children's hospitals.
For each hospital we determined the mean exposure index. We also set target exposure indices and then measured the deviation from this target.
There was not a large difference in exposure index among sites. No site had an exposure index mean that was more than twice or less than half that of any other site. For all four sites combined, 92% of exposures had a deviation index within the range from -3 to +3. Thus exposures at each hospital were consistently within a reasonable narrow spectrum.
Mean exposure index differences are caused by operational differences with mean values that varied by less than 50% among four hospitals. Ninety-two percent of all exposures were between half and double the target exposure. Although only one vendor's equipment was used, these data establish a practical reference range of exposures for neonatal portable radiographs that can be recommended to other hospitals for neonatal chest radiographs.
We investigate the sensitivity of the conversions from entrance surface dose (ESD) or kerma-area product (KAP) to effective dose (E) or to energy imparted to the patient (epsilon) to the likely variations in tube potential, field size, patient size and sex which occur in clinical work. As part of a factorial design study for chest and lumbar spine examinations, the tube potentials were varied to be +/-10% of the typical values for the examinations while field sizes and the positions of the field centres were varied to be representative of values drawn from measurements on patient images. Variation over sex and patient size was based on anthropomorphic phantoms representing males and females of ages 15 years (small adult) and 21 years (reference adult). All the conversion coefficients were estimated using a mathematical phantom programmed with the Monte Carlo code EGS4 for all factor combinations and analysed statistically to derive factor effects. In general, the factors studied behaved independently in the sense that interaction of the physical factors generally gave no more than a 5% variation in a conversion coefficient. Taken together, variation of patient size, sex, field size and field position can lead to significant variation of E/KAP by up to a factor of 2, of E/ESD by up to a factor of 3, of epsilon/KAP by a factor of 1.3 and of epsilon/ESD by up to a factor of 2. While KAP is preferred to determine epsilon, the results show no strong preference of KAP over ESD in determining E. The mean absorbed dose D in the patient obtained by dividing epsilon (determined using KAP) by the patient's mass was found to be the most robust measure of E.
The International Commission on Radiological Protection (ICRP) approved the publication of a document on 'Managing patient dose in digital radiology' in 2003. The paper describes the content of the report and some of its key points, together with the formal recommendations of the Commission on this topic. With digital techniques exists not only the potential to improve the practice of radiology but also the risk to overuse radiation. The main advantages of digital imaging: wide dynamic range, post-processing, multiple viewing options, electronic transfer and archiving possibilities are clear but overexposures can occur without an adverse impact on image quality. It is expected that the ICRP report helps to profit from the benefits of this important technological advance in medical imaging with the best management of radiation doses to the patients. It is also expected to promote training actions before the digital techniques are introduced in the radiology departments and to foster the industry to offer enough technical and dosimetric information to radiologists, radiographers and medical physicists to help in the optimisation of the imaging.
Over the last 50 years, diagnostic imaging has grown from a state of infancy to a high level of maturity. Many new imaging modalities have been developed. However, modern medical imaging includes not only image production but also image processing, computer-aided diagnosis (CAD), image recording and storage, and image transmission, most of which are included in a picture archiving and communication system (PACS). The content of this paper includes a short review of research and development in medical imaging science and technology, which covers (a) diagnostic imaging in the 1950s, (b) the importance of image quality and diagnostic performance, (c) MTF, Wiener spectrum, NEQ and DQE, (d) ROC analysis, (e) analogue imaging systems, (f) digital imaging systems, (g) image processing, (h) computer-aided diagnosis, (i) PACS, (j) 3D imaging and (k) future directions. Although some of the modalities are already very sophisticated, further improvements will be made in image quality for MRI, ultrasound and molecular imaging. The infrastructure of PACS is likely to be improved further in terms of its reliability, speed and capacity. However, CAD is currently still in its infancy, and is likely to be a subject of research for a long time.
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