Image quality and radiation dose on digital chest imaging: comparison of amorphous silicon and amorphous selenium flat-panel systems

Seven general radiography x-ray detectors with pixel sizes ranging from 175 to 76μm: technical evaluation with the focus on orthopaedic imaging

Aim. Flat panel detectors with small pixel sizes general can potentially improve imaging performance in radiography applications requiring fine detail resolution. This study evaluated the imaging performance of seven detectors, covering a wide range of pixel sizes, in the frame of orthopaedic applications.Material and methods. Pixel sizes ranged from 175 (detector A175) to 76μm (detector G76). Modulation transfer function (MTF) and detective quantum efficiency (DQE) were measured using International Electrotechnical Commission (IEC) RQA3 beam quality. Threshold contrast (CT) and a detectability index (d') were measured at three air kerma/image levels. Rabbit shoulder images acquired at 60 kV, over five air kerma levels, were evaluated in a visual grading study for anatomical sharpness, image noise and overall diagnostic image quality by four radiologists. The detectors were compared to detector E124.Results. The 10% point of the MTF ranged from 3.21 to 4.80 mm-1, in going from detector A175to detector G76. DQE(0.5 mm-1) measured at 2.38μGy/image was 0.50 ± 0.05 for six detectors, but was higher for F100at 0.62. High frequency DQE was superior for the smaller pixel detectors, howeverCTfor 0.25 mm discs correlated best with DQE(0.5 mm-1). Correlation betweenCTand the detectability model was good (R2= 0.964).CTfor 0.25 mm diameter discs was significantly higher for D150and F100compared to E124. The visual grading data revealed higher image quality ratings for detectors D125and F100compared to E124. An increase in air kerma was associated with improved perceived sharpness and overall quality score, independent of detector. Detectors B150, D125, F100and G76, performed well in specific tests, however only F100consistently outperformed the reference detector.Conclusion. Pixel size alone was not a reliable predictor of small detail detectability or even perceived sharpness in a visual grading analysis study.

The principles and effectiveness of X-ray scatter correction software for diagnostic X-ray imaging: A scoping review

PURPOSE

An anti-scatter grid is often used in X-ray radiography to reduce the scattered X-rays generated from the patient. However, the presence of a grid means the patient dose subsequently increases. Recently,severalmanufacturers have developedsoftwarethat is capable of correctingfor scattered X-rays withouttheuse ofa conventional grid. This scoping review aims to systematically map the research assessing scattering correction software and to identify any existing knowledge gaps.

METHODS

This scoping review involved conducting a systematic search in PubMed, Scopus, and Web of science to reveal studies that were relevant to the research question. Articles published between 01.01.2000 and 31.12.2021 examining X-ray scatter correction software for X-ray imaging were included. A part of the PRISMA model and PICO framework were utilised to establish eligibility criteria. A structured summary table was utilised to extract data from the selected articles.

RESULTS

In this scoping review, 20 years of literature in X-ray conventional radiography. 11 articles were included in the data synthesis. The study populations of the included studies were varied: patients, image quality phantoms and anatomical phantoms. The clinical applications of X-ray scatter correction software were found to be limited to specific body parts (cervical spine, chest, shoulder, lumbar spine, hip and pelvis). The scatter correction software appears to be effective in terms of image quality and in reducing the radiation dose. However, the conventional grid still provides a higher image quality.

CONCLUSIONS

X-ray scatter correction software can be effective and provides potentialbenefits for some circumstances or clinical scenarios.

Introduction of a New Parameter for Evaluation of Digital Radiography System Performance

Background

The aim of this study was to compare the image quality and radiation doses in various digital radiography systems using contrast-detail radiography (CDRAD) phantom.

Methods

The image quality and radiation dose for seven different digital radiography systems were compared using the CDRAD phantom. Incident air kerma (IAK) values were measured for certain exposure settings in all digital radiography systems. The images from the CDRAD phantom were evaluated by three observers. The results were displayed in the form of a contrast-detail (CD) curve. In addition, the inverse image quality figure (IQFinv)-to-IAK ratios were used for quantitative comparison of different digital radiography system performance.

Results

Results of this study showed that the CD curves cannot be suitable criterion for determining the performance of digital radiography systems. For this reason, IQFinv-to-radiation dose (IAK) ratios in a fixed radiation condition were used. The highest performance in terms of producing high-quality images and low radiation dose was related to X-ray unit 1 and the lowest performance was for X-ray unit 5.

Conclusion

The ratio of IQFinv to IAK for performance evaluation of digital radiography systems is an innovation of this study. A digital radiography system with a higher IQFinv-to-IAK ratio is associated with lower patient dose and better image quality. Therefore, it is recommended to equip the new imaging centers with the systems that have higher IQFinv-to-IAK ratios.

Quantitative Analysis Methods Using Histogram and Entropy for Detector Performance Evaluation According to the Sensitivity Change of the Automatic Exposure Control in Digital Radiography

The purpose of this study is to evaluate detector performance using histogram and entropy analysis according to the sensitivity change of the automatic exposure control (AEC). The experiment was performed as follows: The sensitivity of the detector was analyzed through a normalized histogram with sensitivities of S200, S400, S800, and S1000 of the AEC; the entropy of the image was then analyzed, and the signal volume of the detector was evaluated according to the sensitivity change. As the sensitivity of the AEC was increased from S200 to S1000, the histogram showed underflow, quantization separation, and dynamic range discrepancy. In addition, entropy showed a decrease as sensitivity was set higher; in particular, entropy degradation was more prominent at sensitivities above S800. Through the histogram and entropy analysis, it was concluded that the detector does not reproduce the sensitivity and signal volume accurately when the sensitivity of the AEC is set high in performance evaluation.

Impact of Software Parameter Settings on Image Quality of Virtual Grid Processed Radiography Images: A Contrast-Detail Phantom Study

Mobile radiography systems are commonly used in the intensive care unit. The use of a physical antiscatter grid with these systems is uncommon because of drawbacks. In 2015, Virtual Grid (Fujifilm, Tokyo, Japan) became available for chest and abdomen examinations. In this study, we compared image quality (IQ) with a contrast-detail phantom (CDRAD 2.0; Artinis Medical Systems, Zetten, the Netherlands) of digital radiographs acquired without any grid (gridless) with those corrected for scatter by either software (SW)-based scatter correction (Virtual Grid) or a physical grid (grid). Furthermore, we determined the optimal Virtual Grid settings that lead to the best contrast-detail IQ score (inverse IQ figure).

MATERIALS AND METHODS

Images were obtained with a cassette spot film device with an inserted portable flat-panel detector (Fujifilm, Tokyo, Japan). The CDRAD phantom was sandwiched between polymethylmethacrylate (PMMA) with total thicknesses of 12, 16, 21, and 26 cm to simulate patient attenuation and scatter. Tube voltages of 81, 90, 109, and 125 kVp were used to make the radiographs. In total, 12 different Virtual Grid settings (grid ratio, line pairs (lp)/cm, and type of interstitial material) were applied for every phantom thickness and tube voltage.

RESULTS

An average increase of 32% in IQ was obtained when Virtual Grid images with a SW grid ratio 10:1 were compared with gridless images (P < 0.001). Increasing the SW grid ratio to 20:1 resulted in a further increased IQ. With a phantom thickness of 12 cm PMMA, Virtual Grid outperformed the removable physical grid presented in the cassette spot film device. The linear mixed-effects model showed that IQ is mainly affected by PMMA, tube voltage, and the SW grid ratio.

CONCLUSIONS

Virtual Grid improves images obtained without physical grid for a wide range of experimental conditions. Despite the different possible settings of the Virtual Grid SW, the most important parameter affecting IQ is the SW grid ratio.

An investigation into the validity of utilising the CDRAD 2.0 phantom for optimisation studies in digital radiography

OBJECTIVES

To determine if a relationship exists between low contrast detail (LCD) detectability using the CDRAD 2.0 phantom, visual measures of image quality (IQ) and simulated lesion visibility (LV) when performing digital chest radiography (CXR).

METHODS

Using a range of acquisition parameters, a CDRAD 2.0 phantom was used to acquire a set of images with different levels of image quality. LCD detectability using the CDRAD 2.0 phantom, represented by an image quality figure inverse (IQF_inv) metric, was determined using the phantom analyser software. A Lungman chest phantom was loaded with two simulated lesions, of different sizes/placed in different locations, and was imaged using the same acquisition factors as the CDRAD 2.0 phantom. A relative visual grading analysis (VGA) was used by seven observers for IQ and LV evaluation of the Lungman images. Correlations between IQF_inv, IQ and LV were investigated.

RESULTS

Pearson's correlation demonstrated a strong positive correlation (r = 0.91; p < 0.001) between the IQ and the IQF_inv. Spearman's correlation showed a good positive correlation (r = 0.79; p < 0.001) and (r = 0.68; p < 0.001) between the IQF_inv and the LV for the first lesion (left upper lobe) and the second lesion (right middle lobe), respectively.

CONCLUSIONS

From results presented in this study, the automated evaluation of LCD detectability using CDRAD 2.0 phantom is likely to be a suitable option for IQ and LV evaluation in digital CXR optimisation studies. Advances in knowledge: This research establishes the potential of the CDRAD 2.0 phantom in digital CXR optimisation studies.

The impact of greyscale inversion for nodule detection in an anthropomorphic chest phantom: a free-response observer study

Objective:

The aim of this work was to assess the impact of greyscale inversion on nodule detection on posteroanterior chest X-ray images. Previous work has attempted this, with no consensus opinion formed. We assessed the value of “fast-flicking” between standard and inverted display modes for nodule detection.

Methods:

Six consultant radiologists (with 5–32 years' reporting experience) completed an observer task under the free-response paradigm. An anthropomorphic chest phantom was loaded with 50 different configurations of simulated nodules (1–4 nodules per case) measuring 5, 8, 10 and 12 mm in spherical diameter; each configuration represented a single case. In addition, 25 cases contained no nodules. Images were displayed in three modes: (i) standard, (ii) inverted and (iii) fast-flicking between standard and inverted display modes. Each observer completed the study in a different order of display (i, ii, iii) using a calibrated 5-megapixel monitor. Nodules were localized with mouse clicks and ratings assigned using a 1–10 discrete slider-bar confidence scale. Rjafroc (Pittsburgh, PA) was used for data analysis; differences in nodule detection performance were considered significant at 0.05.

Results:

The observer-averaged weighted jackknife alternative free-response receiver-operating characteristic figures of merit were 0.715 (standard), 0.684 (inverted) and 0.717 (fast-flicking). Random-reader fixed-case analysis revealed no statistically significant difference between any treatment pair [F(2,8) = 1.22; p = 0.345].

Conclusion:

No statistically significant difference in nodule detection was found for the three display conditions.

Advances in knowledge:

We have investigated the impact of fast-flicking between standard and inverted display modes for the detection of nodules. We found no benefit.

Characterization of atherosclerotic plaque: a contrast-detail study using multidetector and cone-beam computed tomography

A Hindmarsh-Rose model perceptibility phantom containing inserts with various in vitro atherosclerotic plaque compositions was constructed and imaged on a clinical 64 slice multidetector (MDCT) system using 80 and 120 kVp settings and two other cone-beam (CBCT) systems at 80 kVp. Perceptibility of the simulated lipid-fibrotic plaque solutions in the images was evaluated by six observers. The effective doses of the protocols employed were estimated using phantom CTDI-vol measurements placed at identical settings. The CBCT system allowed reduction in effective dose in comparison with the conventional MDCT system for imaging of the carotid plaque phantoms without degrading image quality. The CBCT dose was less than MDCT, with a mean dose of 1.14 ± 0.01 mSv and 1.11 ± 0.02 mSv for MDCT using two measuring techniques vs. 0.35 ± 0.01 mSv for CBCT. The image quality analysis showed no significant differences in the contrast-detail (C-D) curves of the best performing CBCT vs. clinical MDCT (p &gt; 0.05) using a Mann-Whitney U test. Results indicate that low-tube-potential CBCT may produce comparable C-D resolution for phantom-based representations of soft plaque types with respect to MDCT systems. This study suggests that the utility of low kVp CT techniques for evaluating carotid vulnerable atherosclerotic plaque merits further study.

Optimisation of radiological protocols for chest imaging using computed radiography and flat-panel X-ray detectors

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 optimisation of exposure settings for chest examinations with digital systems, considering both image quality and patient dose.

MATERIALS AND METHODS

Images acquired with direct digital radiography equipment and a computed radiography system were analysed with specially developed commercial software with a four-alternative forced-choice method: the most promising protocols were then scored by two senior radiologists.

RESULTS

Digital technology offers a wide dynamic range and the ability to postprocess images, allowing use of lower tube potentials in chest examinations. The computed radiography system showed both better image quality and lower dose at lower energies (85 kVp and 95 kVp) than those currently used (125 kVp). Direct digital radiography equipment confirmed both its superior image quality and lower dose requirements compared with the storage phosphor plate system.

CONCLUSIONS

Generally, lowering tube potentials in chest examinations seems to allow better image quality/effective dose ratio when using digital equipment.

Correlation of contrast-detail analysis and clinical image quality assessment in chest radiography with a human cadaver study

PURPOSE

To determine the correlation between the clinical and physical image quality of chest images by using cadavers embalmed with the Thiel technique and a contrast-detail phantom.

MATERIALS AND METHODS

The use of human cadavers fulfilled the requirements of the institutional ethics committee. Clinical image quality was assessed by using three human cadavers embalmed with the Thiel technique, which results in excellent preservation of the flexibility and plasticity of organs and tissues. As a result, lungs can be inflated during image acquisition to simulate the pulmonary anatomy seen on a chest radiograph. Both contrast-detail phantom images and chest images of the Thiel-embalmed bodies were acquired with an amorphous silicon flat-panel detector. Tube voltage (70, 81, 90, 100, 113, 125 kVp), copper filtration (0.1, 0.2, 0.3 mm Cu), and exposure settings (200, 280, 400, 560, 800 speed class) were altered to simulate different quality levels. Four experienced radiologists assessed the image quality by using a visual grading analysis (VGA) technique based on European Quality Criteria for Chest Radiology. The phantom images were scored manually and automatically with use of dedicated software, both resulting in an inverse image quality figure (IQF). Spearman rank correlations between inverse IQFs and VGA scores were calculated.

RESULTS

A statistically significant correlation (r = 0.80, P < .01) was observed between the VGA scores and the manually obtained inverse IQFs. Comparison of the VGA scores and the automated evaluated phantom images showed an even better correlation (r = 0.92, P < .001).

CONCLUSION

The results support the value of contrast-detail phantom analysis for evaluating clinical image quality in chest radiography.

Needle image plates compared to conventional CR in chest radiography: is dose reduction possible?

PURPOSE

To compare image quality of standard-dose computed radiography and dose reduced needle-technology CR for supine CXR in a clinical setting.

MATERIALS AND METHODS

We prospectively evaluated 128 radiographs of 32 immunocompromised patients. For each patient four clinical CXR were performed within one week, two with powder image plates (PIP; Fuji ST-V) and two with needle image plates (NIP; Agfa DXS) at standard and half dose, respectively. One experienced radiologist and two residents blinded to dose level and kind of imaging system rated different anatomical structures, image noise, tubes/lines and abnormalities on a image quality scale from 1 to 10 (1=poor, 10=excellent). The rating scores were tested for statistical differences using analysis of variance with repeated measures.

RESULTS

A statistical difference (p<0.05) was found for the two systems as well as for the two dose levels. Overall rating scores were 6.5 for PIP with full dose, 6.2 for PIP with half dose, 7.6 for NIP with full dose and 7.4 for NIP with half dose. There was a significant difference in favour of the NIP system at the same dose level. Also the NIP images obtained at half dose were ranked significantly better compared to the PIP images at standard dose. The differences in ranking of anatomical structures and abnormalities were more pronounced in low absorption areas (pulmonary vessels, parenchyma) than in high absorption areas (mediastinum, spine).

CONCLUSION

For supine chest radiograms the NIP technology allows for a dose reduction of 50% while providing higher image quality.

[Correlation between basic imaging properties and subjective evaluations of two digital radiographic X-ray systems based on direct-conversion flat panel detector]

The purpose of this study was to examine the correlation between the basic imaging properties of two digital radiographic X-ray systems with a direct conversion flat-panel detector and their image qualities, which were evaluated by the observer in hard copy and soft copy studies. The subjective image quality was evaluated and compared in terms of the low-contrast detectability and image sharpness in the two digital radiographic X-ray systems. We applied the radiographs of a contrast detail phantom to the evaluation of low-contrast detectability and analyzed the contrast detail diagrams. Finally, low-contrast detectability was evaluated by the image quality figure (IQF) calculated from the contrast detail diagrams. Also, the subjective image sharpness of human dry bones of two systems was examined and evaluated by the normalized-rank method. The results indicated that System A tended to provide superior subjective image quality compared to System B in both observer studies. We also found high correlations between IQFs and basic imaging properties, such as the noise power spectrum (NPS) and the noise equivalent quantum (NEQ). In conclusion, the low-contrast detectability of the two digital radiographic X-ray systems with a direct conversion flat-panel detector corresponded to the NPS and the NEQ in both outputs (soft copy and hard copy). On the other hand, the subjective image sharpness of human dry bones was affected by their noise properties.

Conebeam CT of the head and neck, part 1: physical principles

Conebeam x-ray CT (CBCT) is a developing imaging technique designed to provide relatively low-dose high-spatial-resolution visualization of high-contrast structures in the head and neck and other anatomic areas. This first installment in a 2-part review will address the physical principles underlying CBCT imaging as it is used in dedicated head and neck scanners. Concepts related to CBCT acquisition geometry, flat panel detection, and image quality will be explored in detail. Particular emphasis will be placed on technical limitations to low-contrast detectability and radiation dose. Proposed methods of x-ray scatter reduction will also be discussed.

Digital chest radiography: an update on modern technology, dose containment and control of image quality

The introduction of digital radiography not only has revolutionized communication between radiologists and clinicians, but also has improved image quality and allowed for further reduction of patient exposure. However, digital radiography also poses risks, such as unnoticed increases in patient dose and suboptimum image processing that may lead to suppression of diagnostic information. Advanced processing techniques, such as temporal subtraction, dual-energy subtraction and computer-aided detection (CAD) will play an increasing role in the future and are all targeted to decrease the influence of distracting anatomic background structures and to ease the detection of focal and subtle lesions. This review summarizes the most recent technical developments with regard to new detector techniques, options for dose reduction and optimized image processing. It explains the meaning of the exposure indicator or the dose reference level as tools for the radiologist to control the dose. It also provides an overview over the multitude of studies conducted in recent years to evaluate the options of these new developments to realize the principle of ALARA. The focus of the review is hereby on adult applications, the relationship between dose and image quality and the differences between the various detector systems.

Solid-state, flat-panel, digital radiography detectors and their physical imaging characteristics

Solid-state, digital radiography (DR) detectors, designed specifically for standard projection radiography, emerged just before the turn of the millennium. This new generation of digital image detector comprises a thin layer of x-ray absorptive material combined with an electronic active matrix array fabricated in a thin film of hydrogenated amorphous silicon (a-Si:H). DR detectors can offer both efficient (low-dose) x-ray image acquisition plus on-line readout of the latent image as electronic data. To date, solid-state, flat-panel, DR detectors have come in two principal designs, the indirect-conversion (x-ray scintillator-based) and the direct-conversion (x-ray photoconductor-based) types. This review describes the underlying principles and enabling technologies exploited by these designs of detector, and evaluates their physical imaging characteristics, comparing performance both against each other and computed radiography (CR). In standard projection radiography indirect conversion DR detectors currently offer superior physical image quality and dose efficiency compared with direct conversion DR and modern point-scan CR. These conclusions have been confirmed in the findings of clinical evaluations of DR detectors. Future trends in solid-state DR detector technologies are also briefly considered. Salient innovations include WiFi-enabled, portable DR detectors, improvements in x-ray absorber layers and developments in alternative electronic media to a-Si:H.