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Purpose:
Digital radiography technology has replaced conventional screen-film systems in many hospitals. Despite the different characteristics of new detector materials, frequently, the same radiological protocols previously optimised for screen film are still used with digital equipment without any critical review. This study addressed optimisati...
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Citations
... Although this has historically raised concerns of "dose creep," 2 digital detectors have led to dose reduction while maintaining acceptable image quality. 3 Following the principle of minimizing dose (As Low As Reasonably Achievablethe ALARA principle) 4 for radiography, it is important to define an image quality metric so that the minimum dose meeting the metric can be used. ...
... F I G . 2. The configuration for testing the image quality at high and low exposure index. Element[1] is the x-ray imaging device (either Siemens Multix room unit or portable Canon unit), element[2] is the Lucite thickness (varying from 5 cm to 20 cm), element[3] is the aluminum contrast-detail test object, and element[4] is the detector and grid (either a Carestream DRX-1c / DRX-Plus with a Siemens grid or a Canon CXDI 710C and portable grid).T A B L E 3 Grid information for the two experimental designs. The Carestream DRX detectors were mounted in a table bucky, while the Canon CXDI detector was sheathed in a portable grid. ...
The performance of three digital detectors was measured at two exposure index (EI) levels in terms of the effect on features at the borderline of detectability. The null hypothesis was that there would be no statistically significant difference in the CNR of marginally visible features of a baseline- (2.2 µGy) and reduced dose (1.4 µGy) images. The experiment used three digital detectors and a phantom composed of an aluminum contrast-recovery plate, with features of varying diameters and hole depths, which was placed between the detector/grid and 5-20 cm Lucite. Exposures were made using a kVp between 55 and 110 corresponding to the Lucite thickness and a mAs producing an EI of approximately 220 or 140. Images were acquired for all detectors, EI values, and all Lucite thicknesses, then scored by a team of physicists and technologists in terms of feature visibility for each feature size. Contrast-to-noise ratio (CNR) was calculated for each feature using an ROI over the feature and a local background annulus. The uncertainty in the CNR was determined by sampling the background at each feature size, finding residuals from an overall background fit, and then calculating a standard deviation in the noise for each size. The marginal feature pair for each feature size bracketed the reader score. The difference between the CNR values of corresponding marginal features in EI-paired images was significant (P < 0.05) for one detector and not significant (P > 0.05) for marginal features of the other two. Based on both reader scoring and CNR measurements of phantoms, patient doses can be lowered by 30% for those two detectors without a statistically significant difference in lesion perceptibility of the marginally visible feature, while for the other detector there was a statistically significant change in marginal feature detectability and dose reduction was not recommended.
... Doyle et al 33 and Dobbins et al 34 used physical phantoms to optimise a DR system and results were mixed; the former showed that lower tube voltages were superior for a matched effective dose in contrary to the latter. Low tube voltage was also shown to be optimum in a more recent study by Compagnone et al 35 . However, the phantoms used in these studies lacked anatomical detail and only measured physical metrics such as signal-to-noise ratio. ...
Objectives
The aim of this study was to investigate via computer simulation a proposed improvement to clinical practice by deriving an optimised tube voltage (kVp) range for digital radiography (DR) chest imaging.
Methods
A digitally reconstructed radiograph algorithm was used which was capable of simulating DR chest radiographs containing clinically relevant anatomy. Five experienced image evaluators graded clinical image criteria, i.e., overall quality, rib, lung, hilar, spine, diaphragm and lung nodule in images of 20 patients at tube voltages across the diagnostic energy range. These criteria were scored against corresponding images of the same patient reconstructed at a specific reference kVp. Evaluators were blinded to kVp. Evaluator score for each criterion was modelled with a linear mixed effects (LME) algorithm and compared with the score for the reference image.
Results
Score was dependent on tube voltage and image criteria in a statistically significant manner for both. Overall quality, hilar, diaphragm and spine criteria performed poorly at low and high tube voltages, peaking at 80–100 kVp. Lung and lung nodule demonstrated little variation. Rib demonstrated superiority at low kVp.
Conclusions
A virtual clinical trial has been performed with simulated chest DR images. Results indicate mid-range tube voltages of 80–100 kVp are optimum for average adults.
Advances in knowledge
There are currently no specific recommendations for optimised tube voltage parameters for DR chest imaging. This study, validated with images containing realistic anatomical noise, has investigated and recommended an optimal tube voltage range.
... Standard mathematical tools can be used for the optimization analysis if the relationship function is properly defined. In X-ray imaging, various kinds of relationships were demonstrated between image quality and radiation dose previously, such as logistic [4,5], logarithmic [6], and linear functions [7]. This is because images were acquired at various radiation dose levels and various image quality indices have been employed for the purpose in general. ...
... This is because images were acquired at various radiation dose levels and various image quality indices have been employed for the purpose in general. For example, image quality indices of the area under the receiver operating characteristic curve [4] and of contrast details [6], as well as visual grading scales [5,7], were used in these studies. In general, clinical images which involve ionizing radiation need to be acquired at an image quality that is above the acceptable level in diagnosis. ...
... Conversely, phantoms may be used to study very low or very high dose images that are not intended for diagnosis [5,7]. It is not surprising that various relationships have been reported between radiation dose and image quality, depending on the objectives of these studies [4][5][6][7]. ...
The purpose of this work was to examine the effects of relationship functions between diagnostic image quality and radiation dose on the governing equations for image acquisition parameter variations in X-ray imaging. Various equations were derived for the optimal selection of peak kilovoltage (kVp) and exposure parameter (milliAmpere second, mAs) in computed tomography (CT), computed radiography (CR), and direct digital radiography. Logistic, logarithmic, and linear functions were employed to establish the relationship between radiation dose and diagnostic image quality. The radiation dose to the patient, as a function of image acquisition parameters (kVp, mAs) and patient size (d), was used in radiation dose and image quality optimization. Both logistic and logarithmic functions resulted in the same governing equation for optimal selection of image acquisition parameters using a dose efficiency index. For image quality as a linear function of radiation dose, the same governing equation was derived from the linear relationship. The general equations should be used in guiding clinical X-ray imaging through optimal selection of image acquisition parameters. The radiation dose to the patient could be reduced from current levels in medical X-ray imaging.
... With developing digital technology and computers, different digital x-ray imaging modalities such as storage phosphor-based computed radiography (CR) and Flat-Panel (FP) detectors and data collection methods have been developed to replace screen-film radiography (2)(3)(4). Due to greater dynamic and exposure range, feasibility of post-processing of images, cost savings, easier access to images and the ability to archaving and comunication using Picture Archive and Communication System (PACS), digital radiography have been considered. It has been shown that picture quality in FP digital systems have improved respect to CR and film-screens or analog systems (5,6). ...
... The results of this study; tables 1, 2 and diagrams 1, 2 shows, for all of the imaging conditions with growing the imaging parameters, IQFinv and IQFinv/E 2 are decreasing. This is consistent with the findings of Compagnone's study (2). Also, the results of this study shows with an increase in kV, the ED, which represents the ED of the patient, has also increased. ...
... Whilst, lower tube voltages can be used in digital systems. Although, technical appropriate imaging conditions to be revised (2). On the other hand the digital systems have wide dynamic range that makes a high range of patient dose changes without any damages on the images. ...
ABSTRACT
BACKGROUND AND OBJECTIVE: Digital systems have been replacing with screen-film analogue systems in
diagnostic radiology departments, rapidly. Despite the differences in the properties of new x-ray imaging detectors, the same radiographic protocols that had been used for radiographic film-screen are used for digital imaging systems, without any review yet. In this study, the image quality and the patient dose in digital imaging of the chest are evaluated and optimized.
METHODS: Two digital radiography machines, Shimadzu RDA Speed and Siemens G2107 have been used in this experimental research. Imaging and dose measurement are carried out at different source to phantom distances and kilo-voltages. For measurement of the image quality, a contrast-detail radiography (CDRAD) phantom is used. For evaluation of optimization, the Inverse Image Quality Figure per patient dose squared (IQF_inv/E^2) is used.
FINDINGS: Evaluation of measured data for optimization shows that for both of these two digital radiography
machines, despite of increasing in patent dose, with reducing of kilo-voltage, the IQF_inv/E^2 is increased. The maximum values of this parameter for Imam Khomeini and Bu Ali Hospitals are measured 0.0180 and 0.0083, respectively.
CONCLUSION: The results of this study indicate that despite the traditional notion of using higher kilo-voltages for chest radiography, with increasing kilo-voltage, the ratio of image quality per patient dose is reduced. So, for optimization of chest radiography, as much as possible the kilo-voltage should be reduced based on the size of patient and clinical purpose.
KEY WORDS: Digital Radiography, Chest radiography, Contrast-Detail Phantom, Optimization
... The relationship between image quality and radiation dose to patient has been studied by a number of published works (2,(9)(10)(11) . A logarithmic function has been demonstrated (10,11) although a linear relationship has also been shown (2) for this relationship. ...
... Figure 1 shows the plots of the image quality figure, IQF, as a function of the effective (absorbed) dose to patients, E(μSv), both for computed radiography (CR) and direct radiography (DR). The data were from the contrast-detail studies of Compagnone et al. (9) The best fit is a logarithmic function. ...
... The plots of image quality figure (IQF) vs the effective dose E(µSv): (a) the plot of Siemens computed radiography system and (b) the plot of Siemens direct digital radiography system. Data were from Compagnone et al.(9) ...
A patient size based guiding equation for the automatic selections of mAs and peak voltage kVp in general medical X-ray projection radiography was derived from the first principles of dose and image quality optimization. Under various specific conditions of constant patient size d, kVp or mAs, this equation leads to various longstanding ‘rules of thumbs’ currently being employed in clinical practice. For automatic mAs control, this work suggests that the current level of dose to patient in X-ray radiography should be halved without compromise image quality. Further studies on the dependence of the absorbed dose on the patient's thickness are required in general X-ray projection radiography.
... Figure 3 demonstrated a week linear relationship (r 2 =0.52) between the dose and image quality in chest X-ray imaging, consistent with a recent work of Tavares et al 18 . Other works appeared to have a logarithmic relationship 21,22 . A dose efficient index may be defined as the slope of the linear function between the image quality and the dose, which is the ratio of the image quality to radiation dose. ...
The purposes of this work were to determine the optimal peak voltage for chest computed radiography (CR) using visual grading scores and to compare visual grading characteristics (VGC) and ordinal regression in visual grading analysis. An Afga CR system was used to acquire images of an anthropomorphic chest phantom. Both entrance surface dose and detector surface dose were measured using the Piranha 657 dosimeter. The images were acquired under various voltages from 80 to 120 kVp and exposures from 0.5 to 12.5 mAs. The image qualities were evaluated by 5 experienced radiologists/radiographers based on modified European imaging criteria using 1-5 visual grading scale. The VGC, ordinal regression as well as the conventional visual grading analysis (VGA) were employed for the image quality analysis. Both VGC and ordinal regression yielded the same results with both 100 kVp and 120 kVp producing the best image quality. The image quality of the 120 kVp was slightly higher than that of the 100 kVp but its dose was also higher than that of the 100kVp. On balancing image quality with dose, the 100 kVp should be the optimal kVp for the chest imaging using the Afga CR system. The ordinal regression is a powerful tool in the analysis of image quality using visual grading scores and the VGC can be handled by the ordinal regression.
... The transition from film/screen to digital technology for image acquisition in radiography departments has been progressing for 30 years. 1 Digital radiography encompasses both computed radiography (CR) and direct digital radiography (DDR). There are many advantages of digital imaging that make it preferable to film/screen technology, including digital storage and transfer of images, non-chemical processing, reusability, wider exposure latitude and post-processing algorithms. 2 Wider exposure latitude and post-processing algorithms adjust the image to a standard displayed optical density (OD) regardless of X-ray exposure, thereby disguising exposure errors. ...
... This is important because the materials used to construct the digital X-ray system, particularly the receptor phosphors differs from film/ screen; thus there will be variations in their response to X-ray exposure. 1 Since all of Australia and most of the developed world is now using digital radiography systems, there is a necessity for research in this field. ...
IntroductionDigital technology has wider exposure latitude and post-processing algorithms which can mask the evidence of underexposure and overexposure. Underexposure produces noisy, grainy images which can impede diagnosis and overexposure results in a greater radiation dose to the patient. These exposure errors can result from inaccurate adjustment of exposure factors in response to changes in patient thickness. This study aims to identify all published radiographic exposure adaptation systems which have been, or are being, used in general radiography and discuss their applicability to digital systems.Methods
Studies in EMBASE, MEDLINE, CINAHL and SCOPUS were systematically reviewed. Some of the search terms used were exposure adaptation, exposure selection, exposure technique, 25% rule, 15% rule, DuPont™ Bit System and radiography. A manual journal-specific search was also conducted in The Radiographer and Radiologic Technology. Studies were included if they demonstrated a system of altering exposure factors to compensate for variations in patients for general radiography. Studies were excluded if they focused on finding optimal exposures for an ‘average’ patient or focused on the relationship between exposure factors and dose.ResultsThe database search uncovered 11 articles and the journal-specific search uncovered 13 articles discussing systems of exposure adaptation. They can be categorised as simple one-step guidelines, comprehensive charts and computer programs.Conclusion
Only two papers assessed the efficacy of exposure adjustment systems. No literature compares the efficacy of exposure adaptations system for film/screen radiography with digital radiography technology nor is there literature on a digital specific exposure adaptation system.
This study aimed to determine the optimal radiographic conditions for detecting lesions on digital chest radiographs using an indirect conversion flat-panel detector with a copper (Cu) filter. First, we calculated the effective detective quantum efficiency (DQE) by considering clinical conditions to evaluate the image quality. We then measured the segmentation accuracy using a U-net convolutional network to verify the effectiveness of the Cu filter. We obtained images of simulated lung tumors using 10-mm acrylic spheres positioned at the right lung apex and left middle lung of an adult chest phantom. The Dice coefficient was calculated as the similarity between the output and learning images to evaluate the accuracy of tumor area segmentation using U-net. Our results showed that effective DQE was higher in the following order up to the spatial frequency of 2 cycles/mm: 120 kV + no Cu, 120 kV + Cu 0.1 mm, and 120 kV + Cu 0.2 mm. The segmented region was similar to the true region for mass-area extraction in the left middle lobe. The lesion segmentation in the upper right lobe with 120 kV + no Cu and 120 kV + Cu 0.1 mm was less successful. However, adding a Cu filter yielded reproducible images with high Dice coefficients, regardless of the tumor location. We confirmed that adding a Cu filter decreases the X-ray absorption efficiency while improving the signal-to-noise ratio (SNR). Furthermore, artificial intelligence accurately segments low-contrast lesions.
4th International Science Post Graduate Conference, University Teknologi Malaysia 2016
Purpose:
To evaluate image quality for chest radiography at different radiation qualities, using phantoms with scatter fractions similar to those of lungs.
Methods:
Two base phantoms with 10 and 4 cm thicknesses, respectively, made of a soft tissue-equivalent material, were used to mimic the X-ray attenuation of the human lung. Two plates with soft tissue- and bone-equivalent materials, respectively, were placed on the base phantom as contrast objects. The image data were obtained with the same entrance surface dose in each radiation quality. Six radiation qualities generated using 120 and 90 kV, and additional copper filters with thicknesses 0, 0.1, and 0.2 mm were selected. The signal-difference-to-noise ratio (SdNR) and a contrast ratio of the soft tissue to the bone were measured for the six radiation qualities.
Results:
The thicker the additional filter, the better the SdNR at both tube voltages. The SdNR values were not significantly different between 120 and 90 kV for the same filter thickness. The contrast ratio was higher at 120 than at 90 kV by approximately 8%.
Conclusions:
Because of the advantage of the contrast ratio and the highest SdNR, the radiation quality with 120 kV and 0.2-mm copper filtration was the best. It was indicated that the conventional tube voltage of 120 kV remains to be better than the lower tube voltage of 90 kV.
