Automatic Exposure Control Devices Research Articles

Study on Usefulness of Entrance Surface Dose (ESD), Entropy Analysis Method to Evaluate Ionization Chamber Performance and Implementation of Optimal Chamber Combination Model when using Automatic Exposure Control (AEC) Device in Digital Radiography (DR)

Study on Usefulness of Entrance Surface Dose (ESD), Entropy Analysis Method to Evaluate Ionization Chamber Performance and Implementation of Optimal Chamber Combination Model when using Automatic Exposure Control (AEC) Device in Digital Radiography (DR)

VERIFICATION AND OPTIMISATION OF PRESELECTED EXPOSURE PARAMETERS IN SCREENING MAMMOGRAPHY: A CENTRAL COMPOSITE DESIGN METHODOLOGY.

In screening mammography, the automatic exposure control (AEC) device selects the optimum exposure parameters for each patient exposure. In practice, this device is calibrated to deliver an optimum figure of merit (FOM) for each set of exposure parameters. This study utilises the central composite design methodology to verify the operating level of the AEC performance for polymethyl methacrylate (PMMA) thicknesses of 4 and 5cm. Quadratic surface plots reveal that the exposure parameters of the default AEC mode are optimised for the 4-cm thickness of the PMMA. However, the exposure parameters of the 5-cm thickness of PMMA need fine-tuning to obtain a maximum value for the FOM.

A practical method to calibrate and optimise automatic exposure control devices for computed radiography (CR) and digital radiography (DR) imaging systems using the signal-to-noise ratio (SNR) metric

We have established in recent virtual clinical trials that signal-to-noise ratio (SNR) is the most appropriate metric for calibrating AEC devices used with digital imaging systems for chest, abdomen, pelvis and spine radiography. However, the practical calibration of such devices is not straightforward. The purpose of this study was to expand on previous work by developing a practical method for AEC calibration using the validated SNR metric that may be used by medical physicists in the field for phosphor plate radiography (CR) and direct digital radiography (DR - wireless and integrated) imaging systems. This methodology used a uniform tissue equivalent phantom (Poly-methyl methacrylate (PMMA)) so comparison was made with an installation vendor’s method of using copper plates. System transfer properties (STP) of each system were derived to linearise all images required for analyses. All STP correction was done in real time. The relationship between detector air kerma (DAK) and STP corrected SNR was then derived at four tube voltages (60, 80, 100 and 120 kVp) and using this relationship, together with the target value of the calibration metric (SNRtarget), it was possible to calculate the DAK required at each tube voltage to derive a calibration curve for each system; CR systems exhibited a linear increase with kVp, DR systems exhibited a ‘U’ shape. The curve derived using the vendor’s method was not considered optimised because it did not hold SNR constant. This work has demonstrated that a relatively simple method to calibrate AEC devices, using an easily accessible tissue equivalent phantom, can be used in the field in real time by medical physicists working with installation engineers. AEC calibration curves that produce clinically adequate image quality with acceptable patient dose have been installed in our radiology department for CR and DR systems using the methodology described in this paper.

Evaluation of Radiation Exposure From Computed Tomography of the Head

In an effort to reduce radiation exposure from computed tomography (CT), practitioners and facilities need to monitor radiation exposure while delivering high-quality diagnostic examinations. One way to minimize a patient's exposure to radiation from CT is the use of an automatic exposure control device. Current research is focusing on these devices and their actual benefits to patients. To assess the effectiveness of such a device, analysis of radiation doses per CT examination must occur. Machine-specific dose-length product and/or CT dose index are the only indicators of specific dose levels. This project compares current levels of radiation exposure to patients undergoing CT scans of the head versus the national levels as evaluated by the Nationwide Evaluation of X-ray Trends program.

Excess of Radiation Burden for Young Testicular Cancer Patients using Automatic Exposure Control and Contrast Agent on Whole-body Computed Tomography Imaging.

BackgroundThe aim of the study was to assess patient dose from whole-body computed tomography (CT) in association with patient size, automatic exposure control (AEC) and intravenous (IV) contrast agent.Patients and methodsSixty-five testicular cancer patients (mean age 28 years) underwent altogether 279 whole-body CT scans from April 2000 to April 2011. The mean number of repeated examinations was 4.3. The GE LightSpeed 16 equipped with AEC and the Siemens Plus 4 CT scanners were used for imaging. Whole-body scans were performed with (216) and without (63) IV contrast. The ImPACT software was used to determine the effective and organ doses.ResultsPatient doses were independent (p < 0.41) of patient size when the Plus 4 device (mean 7.4 mSv, SD 1.7 mSv) was used, but with the LightSpeed 16 AEC device, the dose (mean 14 mSv, SD 4.6 mSv) increased significantly (p < 0.001) with waist cirfumference. Imaging with the IV contrast agent caused significantly higher (13% Plus 4, 35% LightSpeed 16) exposure than non-contrast imaging (p < 0.001).ConclusionsGreat caution on the use of IV contrast agent and careful set-up of the AEC modulation parameters is recommended to avoid excessive radiation exposure on the whole-body CT imaging of young patients.

일반촬영 자동노출제어장치 사용 시 잔존 CT 조영제와 MRI 조영제에 따른 면적선량의 상관성 연구

The purpose of this study is to investigate the effect of CT contrast agent and MRI contrast agent on the area dose in the body when using automatic exposure control system in general radiography. After making rectangular holes in the center of the abdominal thickness paraffin phantom, CT contrast agent and MRI contrast agent were respectively diluted with physiological saline solution for contrast medium dilution ratio of 10:0, 9:1, 8:2, 7:3, 6:4, 5:5, 4:6, 3:7, 2:8, 1:9, 0:10%. Each experiment was set to 78 kVp, 320 mA, which is the proper condition for KUB photography, and thereafter a total of 30 inspections were made for each dilution ratio using an automatic exposure control device, and the area dose corresponding to the dilution ratio of each contrast agent, Average comparison and correlation analysis were performed on the exposure index. As a result, the CT contrast agent and the MRI contrast agent appeared different in area dose according to the dilution ratio(p<0.05), and as the dilution ratio increased, the area dose increased for CT contrast agent and MRI contrast agent(P<0.05). In each test, the exposure index showed the manufacturer's recommendation of 200-800 EI value, and the exposure index and area dose increased as the area dose increased(p<0.05). In conclusion, CT contrast agent and MRI contrast agent confirmed to increase the area dose by general imaging test using all automatic exposure control device. Therefore, it is considered that it is necessary to perform it after the contrast medium has been excreted sufficiently when using usual imaging test after using the contrast agent in CT and MRI examination.

Automatic exposure control calibration and optimisation for abdomen, pelvis and lumbar spine imaging with an Agfa computed radiography system

The use of three physical image quality metrics, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and mean effective noise equivalent quanta (eNEQm) have recently been examined by our group for their appropriateness in the calibration of an automatic exposure control (AEC) device for chest radiography with an Agfa computed radiography (CR) imaging system. This study uses the same methodology but investigates AEC calibration for abdomen, pelvis and spine CR imaging. AEC calibration curves were derived using a simple uniform phantom (equivalent to 20 cm water) to ensure each metric was held constant across the tube voltage range. Each curve was assessed for its clinical appropriateness by generating computer simulated abdomen, pelvis and spine images (created from real patient CT datasets) with appropriate detector air kermas for each tube voltage, and grading these against reference images which were reconstructed at detector air kermas correct for the constant detector dose indicator (DDI) curve currently programmed into the AEC device. All simulated images contained clinically realistic projected anatomy and were scored by experienced image evaluators. Constant DDI and CNR curves did not provide optimized performance but constant eNEQm and SNR did, with the latter being the preferred calibration metric given that it is easier to measure in practice. This result was consistent with the previous investigation for chest imaging with AEC devices. Medical physicists may therefore use a simple and easily accessible uniform water equivalent phantom to measure the SNR image quality metric described here when calibrating AEC devices for abdomen, pelvis and spine imaging with Agfa CR systems, in the confidence that clinical image quality will be sufficient for the required clinical task. However, to ensure appropriate levels of detector air kerma the advice of expert image evaluators must be sought.

진단영상 시스템에서 선량크리프 현상의 최소화를 위한 고감도 AEC 센서에 관한 연구

선량 크리프는 임상적 오류 중 하나로 검사자의 미숙 또는 부주의에 기인하여 발생하는 현상으로 AAPM Task Group #116에 의하면 디지털 방식의 시스템에서 지속적인 발생이 보고되고 있다. 이러한 현시점에서 선량 크리프 현상을 최소화할 뿐만 아니라 재현성 향상이 가능한 자동노출제어장치의 요구가 증가하고 있다. 이에 본 연구에서는 제작이 쉬울 뿐만 아니라 고효율 반도체 센서에 대한 연구를 수행함으로써 선량 크리프 현상을 저감할 수 있는 자동노출제어장치의 센서에 대하여 고찰하고자 하였다. 연구 수행 결과, 제작된 I형 센서 및 PIN형 센서의 경우 Ref 센서와 비교하면 광학적 특성이 우수하여 음영효과가 적게 나타날 것으로 사료되고, 대체로 낮은 민감도 특성이 나타나지만, 조사 조건 변화에 따른 일정한 추세를 가짐으로써 정확한 피드백 신호를 자동노출제어장치에 제공할 수 있을 것으로 사료된다. Dose creep is one of clinical errors that arises from the tester's inexperience or carelessness, and according to Task Group #116 of American Association of Physicists in Medicine, its continued occurrence is being reported in the digital method. At this point, the demand for an automatic exposure control device that minimizes the dose creep phenomenon and can improve reproducibility is increasing. In this study is to consider the automatic exposure control device sensor that can is not only easy to produce, but also reduce the dose creep phenomenon by conducting a research on high-efficient semiconductor sensor. As a result, the Intrinsic-type and PIN-type sensors have excellent optical property compared to Ref sensor, would have less shading effect, and have relatively low sensitivity, but would provide accurate feedback signals to automatic exposure control device with its consistent tendency according to exposure condition changes.

자동노출제어장치 센서적용을 위한 스크린 프린팅 제작방식의 고흡수율 광도전체 특성평가

Abstract In diagnostic radiology, the use of automatic exposure control device is internationally recommended for diagnosis and optimization. However, if exposed to prolonged radiation is a complicated manufacturing process, there is a problem that occurs decrease of various performance overall brightness sensor, which is commercially available conventional. Therefore, in this study, absorption of X-ray is high, and I want to evaluate the AEC applicability of the sensor of the photoconductor-based production has an easy advantage. Experimental results confirms the possibility of fabrication of the sensor through an increase in the SNR, with the detection efficiency superior, accurate turn-off. In addition, it is confirmed that the experimental results of the transmittance and the latent image, Ghost effect by the light conductor does not appear, in the case of a photoconductor with the exception of the PbO, 80% - and it was confirmed good transmittance of 90%. Therefore, excellent mechanical stability and poor performance due to a change of the doping concentration than the existing products that have been put to practical use, the sensor easy photoconductor based, fabrication and can be applied as AEC sensor is expected.

An investigation of automatic exposure control calibration for chest imaging with a computed radiography system

The purpose of this study was to examine the use of three physical image quality metrics in the calibration of an automatic exposure control (AEC) device for chest radiography with a computed radiography (CR) imaging system. The metrics assessed were signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and mean effective noise equivalent quanta (eNEQm), all measured using a uniform chest phantom. Subsequent calibration curves were derived to ensure each metric was held constant across the tube voltage range. Each curve was assessed for its clinical appropriateness by generating computer simulated chest images with correct detector air kermas for each tube voltage, and grading these against reference images which were reconstructed at detector air kermas correct for the constant detector dose indicator (DDI) curve currently programmed into the AEC device. All simulated chest images contained clinically realistic projected anatomy and anatomical noise and were scored by experienced image evaluators. Constant DDI and CNR curves do not appear to provide optimized performance across the diagnostic energy range. Conversely, constant eNEQm and SNR do appear to provide optimized performance, with the latter being the preferred calibration metric given as it is easier to measure in practice. Medical physicists may use the SNR image quality metric described here when setting up and optimizing AEC devices for chest radiography CR systems with a degree of confidence that resulting clinical image quality will be adequate for the required clinical task. However, this must be done with close cooperation of expert image evaluators, to ensure appropriate levels of detector air kerma.

MO‐D‐103‐01: Mammography QA

2D Digital Mammography ‐ An Update on Vendor‐Recommended QC TestsQuality Assurance (QA) and Quality Control (QC) are especially important in mammography, where achieving high image quality within reasonable dose limits is vitally important for a number of reasons including the following:1. Early and accurate detection profoundly improves the prognosis for the patient with breast cancer2. Population screening delivers radiation to a large number of asymptomatic women3. Optimization of image quality and minimization of radiation dose is essential to accomplish the goals of mammography screeningThe requirements for QC in mammography are also significant in that they are the first to be defined and regulated by a federal law, i.e. the Food and Drug Administration's Mammography Quality Standards Act (MQSA). Under current FDA MQSA regulations, manufacturers must define a QC program for each mammography imaging system offered, and this program must be followed in detail by both physicists testing the device and other clinical users performing routine QA functions on a daily basis.In this lecture the QC testing programs currently specified by all digital mammography vendors will be summarized. Recent advances in the automation of QC measurements by manufacturers will be highlighted and potential future developments will be presented.Learning Objectives:1. Attendees will gain an understanding of the general requirements for mammography QC2. Attendees will gain an understanding of the QC programs currently specified by mammography vendors3. Attendees will become aware of potential future universal QC requirements in mammographyStereotactic Breast Imaging System QCThe performance of the eleven specified physics tests on a Stereotactic Breast Biopsy (SBB) System required for accreditation by the American College of Radiology (ACR) will be covered in this presentation, for systems both with and without Automatic Exposure Control (AEC) devices, and for both prone biopsy tables and add‐on SBB units for digital FFDM units. Image Quality, expected values for Half‐Value‐Layer (HVL) measurements and typical patient doses for each matrix size available on SBB systems will be discussed. Clinical advantages/disadvantages of both types of systems will be covered relative to approach methods and areas available for sampling. The importance of testing the location of the biopsy needle or tissue sampling device for reproducibility and accuracy will be discussed relative to various phantoms that may be used to verify this location accuracy. Quality Control (QC) tests to be performed by the mammography technologist will be covered in addition to the required physics tests. Requirements for training and education of the staff (physician, physicist, and technologist) required to achieve ACR accreditation will be reviewed in light of the additional requirement for SBB units to be accredited for those breast imaging centers wishing to obtain the ACR designation of a Breast Imaging Center of Excellence.Learning Objectives:1. Attendees will be aware of the required physics tests to be performed annually and for acceptance of Stereotactic Breast Biopsy (SBB) System.2. Attendees will be aware of the expected values of Half‐Value Layer and patient doses for SBB systems for common matrix sizes available on these units.3. Attendees will be aware of the requirements for personnel performing SBB exams or physics evaluations in both Continuing Education and Continuing Experience for accreditation by the American College of Radiology.4. Attendees will be aware of the required Quality Control Tests to be performed by both the technologist and physicist on SBB units.

Doses measured using AEC on direct digital radiographic (DDR) X-rays systems: updated results withan RP 162 perspective

As digital technology in diagnostic radiology systems becomes more prevalent, there is a need to provide comparative dose information for these new systems. This is needed in particular for testing the automatic exposure control (AEC) devices on direct digital radiography (DDR) systems as there is no consensus on the receptor dose level in the current guidelines. The new European Commission RP 162 document sets the suspension level for the 'verification of kerma at receptor entrance in computed radiography and DDR systems under AEC' as ≥10 µGy. This document also notes that alternate methodologies are acceptable, and may require adjustment in the suspension level if used. This study provides a range of typical doses under AEC for DDR systems, for a variety measurement methodologies, including that described in RP 162.

Structural noise from automatic exposure control device and its relationship to X-ray tube voltage used for calibration of a flat-panel detector system

In flat-panel detector (FPD) systems, the ion-chamber dosimeters used for automatic exposure control (AEC), which are placed between the detector and the source, should not affect clinical images because of FPD gain correction, but can sometimes still introduce fixed-pattern noise. In this study, we investigated whether such artifacts were caused by structural noise from the AEC detector on the basis of the noise power spectrum (NPS) and the mean square error (MSE) of FPD images taken at various tube voltages either with or without the AEC detector. When the NPS was measured without the AEC detector, the NPS did not increase in the low special-frequency band at all radiation qualities tested, irrespective of X-ray calibration tube voltages. However, when the NPS was measured while the AEC detector was used, the NPS increased in the low special-frequency band at all radiation qualities when the X-ray calibration tube voltages were at low levels. Similarly, the MSE increased when the X-ray calibration tube voltages were at low levels. From these results, artifacts in the AEC detector appear to be suppressed when a radiation quality of approximately 90kV is used at four different standardized radiations quality (RQA3, RQA5, RQA7, and RQA9).

An evaluation of semiconductor and ionization chamber detectors for diagnostic x-ray dosimetry measurements

Dosemeters for performance testing of x-ray equipment may utilize semiconductor technology or ionization chambers (ICs). Semiconductor dosemeters incorporate several elements into the detectors from which compensation for variations in response with photon energy is derived. The design of the detectors influences their response with angle and this is different from that of ICs. The responses of semiconductor detectors (SDs) and ICs to x-ray beams with a variety of radiation qualities have been measured in order to assess differences in response. Measurements have been made with experimental arrangements simulating use of the detectors in performance testing of digital radiography and fluoroscopy equipment. Results show that differences in photon energy responses between the detectors are small, but because ICs are sensitive to radiation incident from all angles, they record more scattered radiation than SDs. Implications of differences in detector responses are discussed and recommendations made about their use. SDs are more appropriate for measurements of image receptor doses and are recommended for setting up automatic exposure control devices for digital radiography. ICs are suitable for assessment of patient entrance surface dose rate measurements. Correction factors that could be applied to allow comparisons between measurements with different dosemeters are proposed.

Calibrating automatic exposure control devices for digital radiography

The energy responses of digital radiography detectors differ from those of screen-film systems. To provide a consistent level of image quality at different tube potentials automatic exposure control (AEC) devices must be calibrated to suit the energy response of the image receptor with which they are intended for use. AEC calibration for digital radiography systems requires an alternative parameter to optical density, ideally one related to the quality of a digital image. Energy responses of computed radiography (CR) and indirect digital radiography (IDR) image receptors have been calculated, and compared with those for screen-film systems. Practical assessments of the relative sensitivities of a CR detector made using the detector dose indicator (DDI), pixel value and signal-to-noise ratio showed similar variations with tube potential. The DDI has been used to determine the correct kV compensation curve required to calibrate the AECs for the loss in detector sensitivity with tube potential. AECs are set up relative to a predetermined air kerma incident on the detector at 80 kV for CR and IDR systems using this curve and the method used is described. Factors influencing the calibration of AECs for digital radiography including techniques, types of phantom and contributions from scatter are reviewed, and practical methods recommended for use.

AEC set-up optimisation with computed radiography imaging

Phototimer set-up is a critical procedure for dose and image quality optimisation in computed radiography (CR) systems. While a conventional radiography automatic exposure control device (AEC) can be calibrated in order to gain a constant optical density on the film independent of beam quality and patient size, CR detectors present a high dynamic range which allows a much larger dose interval, but with different image quality levels. CR leads to a less frequent exam repetition, but may produce quite noisy images if the exposure level on the plate is not correct. The aim of this work is to evaluate the performance of a CR plate (Agfa MD40) in order to optimally calibrate an AEC device. The plate response has been characterised in terms of digital signal, exposure on the plate and signal-to-noise ratio for different beam qualities, in a patient of standard size.

National Conference on Dose Reduction in CT, with an Emphasis on Pediatric Patients

321 he clinical value of CT is unquestioned, and the uses of newer helical and multidetector units are growing. The dose received by some patients, particularly children, is higher than desired and must and can be reduced without any significant loss of diagnostic information. These were the conclusions of a 2-day symposium on the subject of CT dose conducted November 6–7, 2002, by the National Council on Radiation Protection and Measurements. CT dose reduction will require a combination of approaches, a series of speakers agreed. These include user education for physicians and radiologic technologists, development of technique charts by medical physicists, development of automatic exposure control devices by manufacturers, and possible retrofits of these devices for older machines. It also will require creation of a climate of opinion in which radiologists will demand attention to dose reduction in their purchase of new CT scanners, one industry participant commented. The National Council on Radiation Protection and Measurements conference was more a work in progress than a starting call to action, said the conference chairman, Fred A. Mettler, Jr., of the University of New Mexico at Albuquerque. He observed that articles about excessive CT dose have multiplied in the radiologic literature and presentations on the subject have appeared on national society programs during the past year. The American College of Radiology (ACR) has announced a new CT facility accreditation program. “Our task is to define where we are on CT dose and to make recommendations on where we go from here.”

Strahlenexposition bei der digitalen Vollfeldmammographie mit einem Flachdetektor aus amorphem Silizium im Vergleich zur konventionellen Film-Folien-Mammographie

Comparison of radiation exposure between a digital amorphous silicon and a screen-film based mammography system. Evaluation of a possible potential of full-field digital mammography in order to decrease the radiation dose. The average glandular dose for phantom thicknesses from 30 to 60 mm was calculated from experimentally determined entrance surface air kerma for a digital and a conventional mammography system. The effect of reducing the detector dose and of changing the radiation quality on radiation exposure and on image quality were investigated. By using the delivered settings of the automatic exposure control (AEC) devices, both mammographic systems needed nearly the same doses. Regulations and guidelines on radiation doses were complied. With the digital system, a reduction of radiation exposure of up to 40% by using a higher radiation quality and decreasing slightly the detector dose without loss of diagnostic image quality, might be possible. The potential of full-field digital mammography for radiation dose reduction, as shown in the present phantom study, needs however, a careful examination under clinical conditions.

Daily quality control programme in mammography.

The Medical Physics Department of S. Chiara Hospital (Trento, Italy) has developed, promoted and organized a quality control programme in mammography in the Department of Diagnostic Radiology. The aim of this paper is to describe the procedure for daily quality control carried out by the radiological technologist and analysed by the medical physicist, and also to discuss some interesting results obtained in the various departments during 1994. A sensitometric strip provides the film characteristic parameters to meet the requirements of DIN 6868 Part II (base plus fog level, average gradient, relative speed, maximum density, speed index and contrast index). A test phantom radiograph provides information on the detection of microcalcifications and simulated tumours (high and low contrast resolution) as well as on the central background density and the contrast. The exposure time-current product, mAs, needed to expose the phantom is always noted. Characteristic parameters of the two systems are compared with limiting values given by International Protocols or with the permissible ranges calculated in advance. It has been possible to discover variations in the performance of mammographic and automatic processing units due to the quality control programme. In one department, for example, the malfunctioning of the automatic exposure control device was observed. In another, replacement of mammography films and the automatic processing unit resulted in a better image quality.

An Initial Report on the Investigation of High Patient Doses for the Lateral Lumbosacral Projection in the Lumbar Spine Examination

Lumbar spine investigations in our diagnostic imaging department were included in a recent European study of patient dose and image quality. On average, for views other than the lateral projection of the lumbosacral junction, the study found a relatively good image quality at a reasonable average patient dose. For the lumbosacral view the average dose was high and the spread of doses involved was broader than expected. As this is a relatively high dose examination (approx. 40 mGy to skin) a formal investigation of the methodology involved in this projection was undertaken. A reject analysis for this projection revealed that it was discarded with a high frequency, given the extent to which it is performed and the fact that automatic exposure control (AEC) devices are commonly used for it. This paper presents results for (a) a survey of the pattern of use of AEC and pre-programmed exposure control facilities by radiographers for the lumbosacral view and (b) the aforementioned reject analysis of lumbosacral junction and related projections. From the survey of radiographers and related studies, the following are identified as possibly being of importance: (i) use of AEC and related devices for this view, (ii) the occasions on which such devices are or are not used, and (iii) the reasons why such systems are often not trusted. In the case of the reject analysis, the relatively high reject rate for the projection and the impact and significance of such a rate are highlighted.