Image Quality In Digital Radiography Research Articles

Developing a novel phantom for image quality evaluation in digital radiography

Evaluation of image quality in digital radiography is important to ensure accurate diagnosis. However, to perform image quality tests accurately and effectively, complex techniques and numerous phantoms are required. The aim of the study was to develop a novel phantom to allow a comprehensive evaluation of image quality in digital radiography. High-Density Polyethylene (HDPE) was used as the main material for the phantom. Physical image quality parameters such as effective Modulation Transfer Function (eMTF), effective Normalized Noise Power Spectra (eNNPS), effective Detective Quantum Efficiency (eDQE), as well as contrast and signal-to-noise ratio (SNR) evaluations can be conducted using the phantom. Preliminary preparation work was carried out through Monte Carlo simulations. The validation of the phantom was performed by comparing with standard phantom results. Physical image quality measurements were performed using an indirect digital radiography system. It was observed that there was a good agreement between the image quality measurement results performed with the standard phantom and the developed phantom. A strong correlation was determined between integrated effective DQE (IeDQE) results (R ≥ 0.97) obtained with HDPE and PMMA phantom. Simulation results regarding the transmission factor showed that HDPE could be an alternative to Polymethyl Methacrylate (PMMA) as a phantom material.

The effect of added filtration on radiation dose and image quality in digital radiography of newborns.

Repeated chest and/or abdomen radiographs are needed on mobile digital radiography (DR) units to assess infants' health status. Optimization of DR tube peak kilovoltage (kVp) and tube current time product (mAs) to derive images of diagnostic quality at as low as reasonably achievable radiation dose has been a challenging task. To investigate the effect of exposure parameters and additional filtration on entrance skin dose and image quality in newborn DR imaging. A physical anthropomorphic phantom that simulates the average full-term neonate was used. Chest and chest/abdomen DR images were acquired at the manufacturer's recommended kVp/mAs exposure parameters followed by a series of image acquisitions at different kVp/mAs and beam filtration combinations. Entrance skin dose (ESD) and signal difference to noise ratio (SdNR) for soft tissue, bone and feeding gastric tube were estimated in raw unprocessed images. A figure of merit (FOM) analysis provided the kVp/mAs and filtration that generated images of adequate quality at the lowest ESD. Signal difference increased with kVp and progressively decreased with increasing filtration. Compared to the manufacturer's recommended 53 kVp/1.6 mAs exposure parameters, ESD was reduced by 76% (47.61μGy versus 11.3μGy) in the chest and 66% (47.61μGy versus 16.14μGy) in the chest/abdomen when the exposure parameters and additional beam filtration provided by the FOM analysis were used. The results derived from this phantom study suggest that additional beam filtration along with the appropriate leverage of exposure parameters can lower ESD while maintaining image quality in full-term newborns.

Radiation Dose Reduction in Different Digital Radiography Systems: Impact on Assessment of Defined Bony Structures in Bearded Dragons (Pogona vitticeps).

Three different digital detector systems were used to study the effect of a defined radiation dose reduction on the image quality of digital radiographs in bearded dragons (Pogona vitticeps). A series of radiographs of seven bearded-dragon cadavers with a body mass ranging from 132 g to 499 g were taken in dorsoventral projection. The digital systems employed included two computed radiography systems (CR) (one system with a needle-based and one with a powdered-based scintillator) and one direct radiography system (DR). Three levels of the detector dose were selected: A standard dose (defined based on the recommended exposure value of the CRP, D/100%), a half dose (D/50%), and a quarter dose (D/25%). Four image criteria and one overall assessment were defined for each of four anatomic skeletal regions (femur, rib, vertebra, and phalanx) and evaluated blinded by four veterinarians using a predefined scoring system. The results were assessed for differences between reviewers (interobserver variability), radiography systems, and dosage settings (intersystem variability). The comparison of the ratings was based on visual grading characteristic (VGC) analysis. Dose reduction led to significantly lower scores in all criteria by every reviewer, indicating a linear impairment of image quality in different skeletal structures in bearded dragons. Scores did not differ significantly between the different systems used, indicating no advantage in using a computed or direct radiography system to evaluate skeletal structures in bearded dragons. The correlation was significant (p ≤ 0.05) for interobserver variability in 100% of the cases, with correlation coefficients between 0.50 and 0.59. While demonstrating the efficacy of the use of digital radiography in bearded dragons and the similar quality in using different computed or direct radiography systems, this study also highlights the importance of the appropriate level of detector dose and demonstrates the limits of post-processing algorithm to compensate for insufficient radiation doses in bearded dragons.

How Does Ambient Light Affect the Image Quality of Phosphor Plate Digital Radiography? A Quantitative Analysis Using Contemporary Digital Radiographic Systems.

The aim of this study is to quantitatively evaluate the influence of the duration of ambient light exposure on the image quality of digital radiographs obtained with contemporary phosphor plate (PSP)-based systems. Radiographs of an aluminum step-wedge were obtained using VistaScan and Express systems at five X-ray exposure times: 0.10, 0.20, 0.32, 0.40, and 0.50 s; the resulting dose-area products were, respectively, 21.93, 43.87, 70.19, 87.75, and 109.6 mGycm2. Before PSP read-out, half of the sensitive surface of the PSP plates was exposed to ambient light for 5, 10, 30, 60, and 90 s. The effect of light exposure on brightness, contrast, contrast-to-noise ratio (CNR), signal-to-noise ratio (SNR), and image saturation was compared using ANOVA with the Tukey test (α = 0.05). Ambient light exposure increased brightness and contrast and reduced CNR and SNR in PSP-based radiographs of contemporary digital systems. At the longest X-ray exposure times, ambient light exposure reduced the dark saturation (mean gray values ≤ 1) observed in Express. In conclusion, the negative effects of ambient light observed on the image quality of PSP-based radiographs are directly proportional to the duration of exposure. Clinicians should be aware of such harmful effects when handling and scanning PSP plates in bright environments.

Digital radiography image quality evaluation using various phantoms and software.

To investigate the effect of the exposure parameters on image quality (IQ) metrics of phantom images, obtained automatically using software or from visual evaluation. Three commercial phantoms and a homemade phantom constructed according to the instructions given in the IAEA Human Health Series No. 39 publication were used, along with the respective software that estimate automatically various IQ metrics. Images with various exposure parameters were acquired in a digital radiography (DR) unit. For the commercial phantoms, visual evaluations were also performed. The IQ scores obtained were analyzed to investigate the effects of increasing incident air kerma (IAK), tube potential (kVp), additional filtration, and acquisition protocol on IQ. The effects of the exposure parameters on the IQ metrics, determined with the commercial and the IAEA phantoms, were not the same. For example, clear trends of improvement of IQ scores with increased IAK and reduction of most IQ scores with increased kVp were observed mostly with the IAEA phantom, but not with the commercial phantoms (for both automatic and visual scoring methods). For all phantoms, the maximum variations in IQ scores observed for repeated identical exposures were almost always below 10% with automatic evaluation whereas, for visual evaluation, reached 17%. Failure to detect some expected trends with the complex commercial phantoms may be attributed to the fact that IQ in DR is more strongly affected by the post-processing procedures, which may mask the effect of other parameters on IQ, something that was not observed with the simple IAEA phantom.

Dose Optimization and Image Quality in Digital Radiography: A Review Article

Imaging techniques have been upgraded due to the invention of digital radiography. This advancement has made a massive change in the development of diagnostic procedures. This technique has displaced conventional radiography with digital methods of radiography. This radiography technique was accepted in all kinds of radiography, excluding mammography. There are many assets of using a digital process for imaging, like good quality of image with less dose. It gave accurate diagnosis for assured quality of image with high resolution and to avoid overdose proper guidelines are needed. The technician should be well trained and have adequate knowledge of the appropriate use of digital radiography. The flat detector system depicts a more efficient way to form an image of high quality with a low dose; the quality of the image increases due to the storage phosphor. Many institutions have accepted this digital radiography as it has proven beneficial for diagnostic procedures. Digital radiography has a flat panel detector that results in a high-resolution image. It has been noticed that screen-film radiography has been superseded by Digital radiography. Nowadays, manufacturers have made many improvements derived from the detector and different technology to Digital radiography equipment. Due to digital imaging techniques, x-rays are allowed to store digitally that can use anytime by adjusting contrast according to the interest of vision. This technology has given assurity of not losing any radiograph and allows dispensing throughout hospitals digital by online technology derived from the web. There are so many assets of using digital radiography as it increases patient count. The vigorous high scale of the digital detector with as low as possible radiation dose for the proper usage of this technology, radiologists and radiographers should have adequate knowledge of various technical postulates & image calibre. They should know how to tackle the problem of overexposure or radiation dose.

Long cone versus short cone for digital intraoral radiographic imaging

<h3>Background</h3> Intraoral radiographs are acquired by one of two methods: the long cone paralleling technique that uses a 30 cm distance from the focal spot to the end of the beam indicating device (BID) versus the short cone technique of 20 cm. The long cone paralleling technique (LCPT) reduces x-ray beam divergence, scatter radiation, penumbra, and magnification as well as entrance skin exposure. LCPT has been recommended for use with digital intraoral radiographic imaging. However, most intraoral generators are supplied with only a short cone BID. <h3>Objective</h3> This research project evaluated image quality of digital radiographs acquired with both long cone and short cone techniques. <h3>Study Design</h3> A series of incrementally increasing exposures of a digital intraoral quality assurance phantom was acquired with both long and short cone methods over a range of exposures from 10 ms to 800 ms to encompass all exposures in the clinical range. Image quality was evaluated using a scientifically validated method that has been published in other research studies on digital intraoral image quality. The image quality parameters assessed were dynamic range, contrast perceptibility, and spatial resolution as specified in ANSI /ADA Standard No. 1094 Quality Assurance for Digital Intra-oral Radiographic Systems. Images were visually evaluated and then objectively evaluated using the NIH ImageJ software for validation. <h3>Results</h3> The results support the use of the LCPT for the acquisition of digital intraoral radiographic images. <h3>Conclusion</h3> The additional purchase of the BID extension is substantiated by the results. <b>Statement of Ethical Review</b> Ethical Review or exemption was not warranted for this study

Evaluation of Non-Uniform Image Quality Caused by Anode Heel Effect in Digital Radiography Using Mutual Information.

Anode heel effects are known to cause non-uniform image quality, but no method has been proposed to evaluate the non-uniform image quality caused by the heel effect. Therefore, the purpose of this study was to evaluate non-uniform image quality in digital radiographs using a novel circular step-wedge (CSW) phantom and normalized mutual information (nMI). All X-ray images were acquired from a digital radiography system equipped with a CsI flat panel detector. A new acrylic CSW phantom was imaged ten times at various kVp and mAs to evaluate overall and non-uniform image quality with nMI metrics. For comparisons, a conventional contrast-detail resolution phantom was imaged ten times at identical exposure parameters to evaluate overall image quality with visible ratio (VR) metrics, and the phantom was placed in different orientations to assess non-uniform image quality. In addition, heel effect correction (HEC) was executed to elucidate the impact of its effect on image quality. The results showed that both nMI and VR metrics significantly changed with kVp and mAs, and had a significant positive correlation. The positive correlation is suggestive that the nMI metrics have a similar performance to the VR metrics in assessing the overall image quality of digital radiographs. The nMI metrics significantly changed with orientations and also significantly increased after HEC in the anode direction. However, the VR metrics did not change significantly with orientations or with HEC. The results indicate that the nMI metrics were more sensitive than the VR metrics with regards to non-uniform image quality caused by the anode heel effect. In conclusion, the proposed nMI metrics with a CSW phantom outperformed the conventional VR metrics in detecting non-uniform image quality caused by the heel effect, and thus are suitable for quantitatively evaluating non-uniform image quality in digital radiographs with and without HEC.

Assessment of Image Quality in Digital Radiographs Submitted for Hip Dysplasia Screening.

Digital radiography is widely seen to be forgiving of poor exposure technique and to provide consistent high quality diagnostic images. Optimal quality images are however not universal; sub-optimal images are encountered. Evaluators on hip dysplasia schemes encounter images from multiple practices produced on equipment from multiple manufacturers. For images submitted to the Danish Kennel Club for hip dysplasia screening, a range of quality is seen and the evaluators are of the impression that variations in image quality area associated with particular equipment. This study was undertaken to test the hypothesis that there is an association between image quality in digital radiography and the manufacturer of the detector equipment, and to demonstrate the applicability of visual grading analysis (VGA) for image quality evaluation in veterinary practice. Data from 16,360 digital images submitted to the Danish Kennel Club were used to generate the hypothesis that there is an association between detector manufacturer and image quality and to create groups for VGA. Image quality in a subset of 90 images randomly chosen from 6 manufacturers to represent high and low quality images, was characterized using VGA and the results used to test for an association between image quality and system manufacturer. The range of possible scores in the VGA was −2 to +2 (higher scores are better). The range of the VGA scores for the images in the low image quality group (n = 45) was −1.73 to +0.67, (median −1.2). Images in the high image quality group (n = 44) ranged from −1.52 to +0.53, (median −0.53). This difference was statistically significant (p < 0.001). The study shows an association between VGA scores of image quality and detector manufacturer. Possible causes may be that imaging hardware and/or software are not equal in terms of quality, that the level of support sought and given differs between systems, or a combination of the two. Clinicians purchasing equipment should be mindful that image quality can differ across systems. VGA is practical for veterinarians to compare image quality between systems or within a system over time.

The impact of image processing algorithms on digital radiography of patients with metalic hip implants

ObjectiveTo investigate the impact of image processing algorithms on image quality of digital radiographs. This study was motivated from a case of a patient with metallic hip implant, where the anatomy around the implant was misrepresented, due to failure of the processing algorithm. Materials & methodsA quality control phantom was imaged using a digital radiographic unit and the standard examination protocol for Pelvis anteroposterior (AP) projection. The original image was reprocessed with all available selections of Diamond View, which is a processing algorithm for optimizing image quality of different anatomic regions. The same procedure was repeated for two other examination protocols, Femur AP and Hip AP, which differ in terms of harmonization kernel and gain, and look up table settings. The whole procedure was repeated with a Pb strip, 2 cm wide and 3 mm thick, positioned close to the right phantom edge, in order to simulate a metallic hip implant.Using ImageJ a number of regions of interest (ROIs) were positioned on the phantom images and the impact of processing parameters on certain image characteristics and image quality indices was evaluated. ResultsProcessing parameters have a strong impact on image characteristics, but in terms of image quality, differences between images with and without the implant are small. Exception is the regions in the vicinity of the implant, where larger differences, that could affect diagnosis, were observed. ConclusionIn case of doubt, additional processing with settings which minimize the risk of anatomic misrepresentation should be used.

Needle-based storage-phosphor detector radiography is superior to a conventional powder-based storage phosphor detector and a high-resolution screen-film system in small patients (budgerigars and mice)

This method comparison study used radiographs of 20 mice and 20 budgerigars to investigate comparability between computed radiography (CR) and high-resolution screen-film systems and study the effects of reduced radiation doses on image quality of digital radiographs of small patients. Exposure settings used with the mammography screen-film system (SF) were taken as baseline settings. A powder-based storage-phosphor system (CRP) and a needle-based storage-phosphor system (CRN) were used with the same settings (D/100%) and half the detector dose (D/50%). Using a scoring system four reviewers assessed five criteria per species covering soft tissue and bone structures. Results were evaluated for differences between reviewers (interobserver variability), systems and settings (intersystem variability, using visual grading characteristic analysis). Correlations were significant (p ≤ 0.05) for interobserver variability in 86.7% of the cases. Correlation coefficients ranged from 0.206 to 0.772. For mice and budgerigars, the CRN system was rated as superior to the SF and CRP system for most criteria, being significant in two cases each. Comparing the SF and CRP system, the conventional method scored higher for all criteria, in one case significantly. For both species and both digital systems, dose reduction to 50% resulted in significantly worse scores for most criteria. In summary, the needle-based storage-phosphor technique proved to be superior compared to the conventional storage-phosphor and mammography screen-film system. Needle-based detector systems are suitable substitutes for high-resolution screen–film systems when performing diagnostic imaging of small patients. Dose reduction to 50% of the corresponding dose needed in high-resolution film-screen systems cannot be recommended.

Digital radiography image denoising using a generative adversarial network.

Statistical noise may degrade the x-ray image quality of digital radiography (DR) system. This corruption can be alleviated by extending exposure time of detectors and increasing the intensity of radiation. However, in some instances, such as the security check and medical imaging examination, the system demands rapid and low-dose detection. In this study, we propose and test a generative adversarial network (GAN) based x-ray image denoising method. Images used in this study were acquired from a digital radiography (DR) imaging system. Promising results have been obtained in our experiments with x-ray images for the security check application. The Experiment results demonstrated that the proposed new image denoising method was able to effectively remove the statistical noise from x-ray images, while kept sharp edge and clear structure. Thus, comparing with the traditional convolutional neural network (CNN) based method, the proposed new method generates more plausible-looking images, which contains more details.

Method of measuring contrast‐to‐noise ratio (CNR) in nonuniform image area in digital radiography

SummaryOne of the physical indices for evaluating the image quality of digital radiography is the contrast‐to‐noise ratio (CNR). The CNR was reported to simulate human perception. Thus, the CNR is a variable index for evaluating detectability in digital radiography. However, it is difficult to evaluate the CNR in a nonuniform image area. In this study, we have devised a new method for measuring the CNR in a nonuniform image area on digital radiography using the top‐hat transform. Furthermore, we investigated the radiation dose dependence of CNR in the digital image of an anthropomorphic breast phantom containing a simulated calcification. We have shown that the CNR in a nonuniform image area can be analyzed with high accuracy by the devised method for measuring the CNR. As for the radiation dose dependence of the CNR, the CNR increased with the mAs values and fell depending on the increase in the density of mammary glands in the anthropomorphic breast phantom. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(7): 32–41, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11416

Dosisreduktion und adäquate Bildqualität in der digitalen Radiographie: ein Widerspruch?

Dose reduction and adequate image quality in digital radiography - a contradiction? Digital radiography has already replaced traditional screen-film systems. Substantial improvements in both dose efficiency and spatial resolution demonstrate the rapid developments in digital radiography. Needle-detector systems have shown up to a 50% dose reduction compared to traditional screen-film systems. There is also a dose reduction capability of up to 50% comparing direct radiography (DR) systems to computed radiography (CR) systems for chest X-rays. However, despite the most recent achievements of CR technology, the dose efficiency of DR systems (caesium iodide flat-panel detector) is unparalleled. The progress in detector technology has contributed to dose reduction and improved image quality, while saving time and providing a higher examination rate. The use of dose indicators and longitudinal dose control are important to avoid substantial accidental dose increase. The dose applied to patients should fall markedly below the defined diagnostic reference levels within the European Union. Regular quality control, as well as continuous education and training of medical and technical personnel, contribute to ensure that the ALARA (as low as reasonably achievable) principle is consistently followed.

Quality parameters and assessment methods of digital radiography images

AbstractThis article reviews the parameters that characterise the image quality of digital radiography and the available evaluation methods that are used to measure these parameters. The article also discusses the factors that affect each parameter of image quality. Digital imaging systems are the most commonly utilised technology in the field of radiology. Screen‐film radiography systems are almost replaced by digital radiography. The data acquisition and image processing principles of digital radiography differ from that of conventional radiography. The required exposure factors for each digital radiography system are not the same. Therefore, the image quality should be optimised while lower radiation dose is maintained according to the properties of the specific imaging system. Distinguishing image quality parameters and understanding the factors that control each image quality parameter are essential to optimise and maintain image quality and to reduce radiation dose to the patient. The degree of factors effects on the images of different digital radiography types and systems are not exactly same. There are different methods and approaches that are used to evaluate the quality of medical images and to assess the performance of imaging systems and each has its own rewards and limits. Therefore, these methods should be utilised and employed according to their aptitudes to improve imaging process.

A study on evaluating the image quality in DR a system with and without a grid

The purpose of this study was to determine the appropriateness of grid use by comparing and evaluating the signal-to-noise ratio (SNR), the peak signal-to-noise ratio (PSNR), the root-mean-squared error (RMSE), and the mean absolute error (MAE) in the image quality for a digital radiography (DR) system with and without a grid with the view that the study results could be used as basic data in the future. The study method for evaluating the dependence of the image quality on grid use was to mount a Bucky table on the DR system and to acquire images by scanning under phantom conditions by using acryl phantoms with thicknesses of 2.54 cm 1.0 mmAl, 5.08 cm 1.0 mmAl, and 7.62 cm 2.0 mmAl. Then, Image J (1.45f) was used to set a region of interest (ROI) on the images acquired with and without a grid before the SNR, PSNR, RMSE, and MAE were analyzed to evaluate the quality of the image. According to the results of the image-quality analysis via an image analysis program, the measured SNR was 23.07 dB, the PSNR 29.95 dB, the RMSE 163.92, and the MAE 149.11 when the dose for the image was constant. Second, there was no significant difference in image quality between using or not using a grid in the acryl phantom. When the grid was not used, the values of the PSNR were 30.10 dB, 30.07 dB, and 30.01 dB when the acryl phantom thickness was 2.54 cm 1.0 mmAl under the conditions of 48 kVp and 1.6 mAs, 2 mAs, and 2.5 mAs, respectively. The values of the PSNR were 30.06 dB and 30.12 dB when the acryl phantom thickness was 5.08 cm 1.0 mmAl under the conditions of 50 kVp and 3.2 mAs and 4 mAs, respectively, and the values of the PSNR was 30.04 dB and 30.06 dB when the acryl phantom thickness was 7.62 cm 2.0 mmAl under the conditions of 70 kVp and 2.5 mAs and 5 mAs, respectively. In conclusion, when an image is acquired in the DR system, factors that can increase the patient dose or decrease image quality must be precisely determined before scanning is conducted.

Relationship of Image Quality and Radiation Dose for Chest Radiography in the Medical Institutions for Pneumoconiosis: A Comparison to the Korean Diagnostic Reference Level

Copyrights © 2012 The Korean Society of Radiology Purpose: To evaluate the relationship of image quality to the measurement of radiation dose for chest radiography in the medical institutions for pneumoconiosis (MIPs). Materials and Methods: Film-screen radiography (FSR) (n = 24) and digital radiography (DR) (n = 5) were used as chest radiography modalities. The entrance surface dose (ESD) was measured from the exposure conditions routinely used for chest radiography using an ionization chamber dosimeter. All images were randomly selected for evaluating image quality from each of the MIPs, and independently rated by two experienced radiologists using a 3-point scale. Results: ESD of DR was higher than FSR, excluding flat panel. However, image quality of DR was significantly higher than that of FSR, especially in flat panel and the charge-coupled device. ESD and tube voltage were not significantly correlated with image quality. DR more frequently exceeded the Korean diagnostic reference level for ESD than FSR (41.7% vs. 20.0%), though the difference was not statistically significant. Conclusion: DR used a higher radiation dose than FSR; however, there was a possibility of a radiation dose reduction in relation to image quality. We suggest that the MIPs transfer to a flat panel with automatic exposure control for a more effective radiation dose management. Index terms Radiography Image Quality Radiation Dosage Thoracic Relationship of Image Quality and Radiation Dose for Chest Radiography in the Medical Institutions for Pneumoconiosis: A Comparison to the Korean Diagnostic Reference Level 진폐요양기관에서 흉부방사선촬영을 위해 사용되는 선량과 화질의 관계: 국내 진단참고준위와 비교

Method for Measuring Contrast-to-Noise Ratio (CNR) in Non-uniform Image Area on Digital Radiography

One of physical indices for evaluating the image quality of digital radiography is contrast-to-noise ratio (CNR). The CNR was reported to simulate the human perception. Thus, the CNR is a variable index for evaluating detectability for digital radiography. However, it is difficult to evaluate the CNR in non-uniform image area. In this study, we have devised a new method for measuring CNR in non-uniform image area on digital radiography using top-hat transform. Furthermore, we investigated the radiation dose dependence of CNR in the digital image of an anthropomorphic breast phantom containing a simulated calcification. We have shown that the CNR in non-uniform image area can be analyzed with high accuracy by our devised method for measuring CNR. In the radiation dose dependence of CNR, CNR increased with mAs values and reduced depending on the increase in the concentration of glandular in the anthropomorphic breast phantom.

MULTISCALE IMAGE PROCESSING AND ANTISCATTER GRIDS IN DIGITAL RADIOGRAPHY

Scatter radiation is a source of noise and results in decreased signal-to-noise ratio and thus decreased image quality in digital radiography. We determined subjectively whether a digitally processed image made without a grid would be of similar quality to an image made with a grid but without image processing. Additionally the effects of exposure dose and of a using a grid with digital radiography on overall image quality were studied. Thoracic and abdominal radiographs of five dogs of various sizes were made. Four acquisition techniques were included (1) with a grid, standard exposure dose, digital image processing; (2) without a grid, standard exposure dose, digital image processing; (3) without a grid, half the exposure dose, digital image processing; and (4) with a grid, standard exposure dose, no digital image processing (to mimic a film-screen radiograph). Full-size radiographs as well as magnified images of specific anatomic regions were generated. Nine reviewers rated the overall image quality subjectively using a five-point scale. All digitally processed radiographs had higher overall scores than nondigitally processed radiographs regardless of patient size, exposure dose, or use of a grid. The images made at half the exposure dose had a slightly lower quality than those made at full dose, but this was only statistically significant in magnified images. Using a grid with digital image processing led to a slight but statistically significant increase in overall quality when compared with digitally processed images made without a grid but whether this increase in quality is clinically significant is unknown.

Laminate structure detectors for low dark current with photoconductors in digital X-ray imaging

The Particle-In-Binder method is one of the excellent processes for a direct conversion X-ray detector. Although detectors coated by the particle-in-binder method provide high sensitivity in X-ray exposure, the dark current is quite high in medical devices. To decrease the dark current and improve the efficiency of detectors, we investigated the potential for a flat-panel X-ray detector with a laminate structure including a plurality of metal halide films. The dark current decreased by laminating the hexagonal lattice, matching the metal halide photoconductive layers and adjusting the Fermi level so it had a different band gap. Film samples of PbO on PbI 2 and BiI 3 on HgI 2, 3 cm×3 cm in area, were deposited by the particle-in-binder process onto glass substrates with conductive coatings, and indium-tin oxide (ITO) was deposited onto laminate layers as a top electrode by using the sputtering process. They were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD) to observe structural and morphological properties. To also investigate electrical characteristics, dark current, and sensitivity to X-ray exposure in the energy range of chest radiography, diagnosis and signal lag were measured at the range of operating voltage. As a result, although the sensitivity of the film decreased, the efficiency of the film improved due to a decrease in dark current. It is proposed that a laminate structure of photoconductors to reduce dark current in flat-panel detector for image quality in digital radiography can be used.