Digital Chest Images Research Articles

Perceptual and objective physical quality of chest images: a comparison between digital radiographic chest images processed for cancer screening and pneumoconiosis screening in Japan.

This study (1) evaluated the perceptual and objective physical quality of digital radiographic chest images processed for different purposes (routine hospital use, lung cancer screening, and pneumoconiosis screening), and (2) quantified objectively the quality of chest images visually graded by the Japan National Federation of Industrial Health Organization (ZENEIREN). Four observers rated the images using a visual grading score (VGS) according to ZENEIREN's quality criteria. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were measured. Between groups, differences were assessed using ANOVA (followed by Bonferroni multiple comparisons) or unpaired t-test. The Pearson's correlation coefficients were calculated for the correlation between perceptual quality and objective physical image quality. The image quality perceived by the observers and the SNR measurements were highest for the images generated using parameters recommended for lung cancer screening. The images processed for pneumoconiosis screening were rated poorest by the observers and showed the lowest objective physical quality measurements. The chest images rated high quality by ZENEIREN generally showed a higher objective physical image quality. The SNR correlated well with VGS, but CNR did not. Highly significant differences between the processing parameters indicate that image processing strongly influences the perceptual quality of digital radiographic chest images.

Neonatal digital chest radiography- should we be using additional copper filtration?

Copper filtration removes lower energy X-ray photons, which do not enhance image quality but would otherwise contribute to patient radiation dose. This study explores the use of additional copper filtration for neonatal mobile chest imaging. A controlled factorial-designed experiment was used to determine the effect of independent variables on image quality and radiation dose. These variables included: copper filtration (0 Cu, 0.1 Cu and 0.2 Cu), exposure factors, source-to-image distance and image receptor position (direct / tray). Image quality was evaluated using absolute visual grading analysis (VGA) and contrast-to-noise ratio (CNR) and entrance surface dose (ESD) was derived using an ionising chamber within the central X-ray beam. VGA, CNR and ESD significantly reduced (p < 0.01) when using added copper filtration. For 0.1 Cu, the percentage reduction was much greater for ESD (60%) than for VGA (14%) and CNR (20%), respectively. When compared to the optimal combinations of parameters for incubator imaging using no copper filtration, an increase in kV and mAs when using 0.1-mm Cu resulted in better image quality at the same radiation dose (direct) or, equal image quality at reduced dose (in-tray). The use of 0.1-mm Cu for neonatal chest imaging with a corresponding increase in kV and mAs is therefore recommended. Using additional copper filtration significantly reduces radiation dose (at increased mAs) without a detrimental effect on image quality. This is the first study, using an anthropomorphic phantom, to explore the use of additional Cu for digital radiography neonatal chest imaging and therefore helps inform practice to standardise and optimise this imaging examination.

P157 - Patient dose and image quality assessment during digital chest imaging at different KV

P157 - Patient dose and image quality assessment during digital chest imaging at different KV

Risk assessment of farmers handling pelleted seeds containing crystalline silica and attapulgite.

ObjectivesThis study aimed to assess the risk to farmers from handling pelleted seeds that include crystalline silica and attapulgite.MethodsWe measured personal exposure levels to respirable crystalline silica and attapulgite in the experimenter representing a farmer in a simulated workplace. From these values, the annual occupational exposure levels were estimated and compared with the established occupational exposure limits. To assess the toxicity of respirable crystalline silica and attapulgite, digital chest images of workers in a factory producing pelleted seeds were examined.ResultsThe personal exposure measurement results showed that the concentrations of total dust, respirable dust, and respirable crystalline silica generated during work handling of pelleted seeds were 0.27, 0.06, and 0.00043 mg/m3, respectively. The estimated annual occupational exposure level to total dust, respirable dust, and respirable crystalline silica in farmers was 103 to 104 times lower than established occupational exposure limits. Attapulgite was not detected by analysis of the pelleted seeds themselves or dust collected during the personal exposure measurements. No pulmonary parenchymal or pleural lesions were detected in the digital chest images of the factory workers.ConclusionWe found that farmers handling pelleted seeds would not be exposed to levels of total dust, respirable dust, respirable crystalline silica, and attapulgite derived from pelleted seeds exceeding occupational exposure limits. These results suggest that the risk to farmers of handling pelleted seeds is negligible.

Quality assessment of digital X-ray chest images using an anthropomorphic chest phantom

The current study is focused on determining the optimal tube voltage for the conventional X-ray digital chest screening examinations, using a visual grading analysis method. Chest images of an anthropomorphic phantom were acquired in posterior-anterior projection on four digital X-ray units with different detector types. X-ray images obtained with an anthropomorphic phantom were accepted by the radiologists as corresponding to a normal human anatomy, hence allowing using phantoms in image quality trials without limitations.

Lung Segmentation Based on Customized Active Shape Model from Digital Radiography Chest Images

Lung Segmentation Based on Customized Active Shape Model from Digital Radiography Chest Images

Validation of the International Labour Office Digitized Standard Images for Recognition and Classification of Radiographs of Pneumoconiosis

Chest radiographs are recommended for prevention and detection of pneumoconiosis. In 2011, the International Labour Office (ILO) released a revision of the International Classification of Radiographs of Pneumoconioses that included a digitized standard images set. The present study compared results of classifications of digital chest images performed using the new ILO 2011 digitized standard images to classification approaches used in the past. Underground coal miners (N = 172) were examined using both digital and film-screen radiography (FSR) on the same day. Seven National Institute for Occupational Safety and Health-certified B Readers independently classified all 172 digital radiographs, once using the ILO 2011 digitized standard images (DRILO2011-D) and once using digitized standard images used in the previous research (DRRES). The same seven B Readers classified all the miners' chest films using the ILO film-based standards. Agreement between classifications of FSR and digital radiography was identical, using a standard image set (either DRILO2011-D or DRRES). The overall weighted κ value was 0.58. Some specific differences in the results were seen and noted. However, intrareader variability in this study was similar to the published values and did not appear to be affected by the use of the new ILO 2011 digitized standard images. These findings validate the use of the ILO digitized standard images for classification of small pneumoconiotic opacities. When digital chest radiographs are obtained and displayed appropriately, results of pneumoconiosis classifications using the 2011 ILO digitized standards are comparable to film-based ILO classifications and to classifications using earlier research standards.

A Comparison of Computer-Aided Detection (CAD) Effectiveness in Pulmonary Nodule Identification Using Different Methods of Bone Suppression in Chest Radiographs

This study aimed to compare the diagnostic effectiveness of computer-aided detection (CAD) software (OnGuard™ 5.2) in combination with hardware-based bone suppression (dual-energy subtraction radiography (DESR)), software-based bone suppression (SoftView™, version 2.4), and standard posteroanterior images with no bone suppression. A retrospective pilot study compared the diagnostic performance of two commercially available methods of bone suppression when used with commercially available CAD software. Chest images from 27 patients with computed tomography (CT) and pathology-proven malignant pulmonary nodules (8-34mm) and 25 CT-negative patient controls were used for analysis. The Friedman, McNemar, and chi-square tests were used to compare diagnostic performance and the kappa statistic was used to evaluate method agreement. The average number of regions of interest and false-positives per image identified by CAD were not found to be significantly different regardless of the bone suppression methods evaluated. Similarly, the sensitivity, specificity, and test efficiency were not found to be significantly different. Agreement between the methods was between poor and excellent. The accuracy of CAD (OnGuard™, version 5.2) is not statistically different with either DESR or SoftView™ (version 2.4) bone suppression technology in digital chest images for pulmonary nodule identification. Low values for sensitivity (<80%) and specificity (<50%) may limit their utility for clinical radiology.

SU‐FF‐I‐164: Automated Suppression of Ribs in Digital PA Chest Images by Means of Image Processing

Purpose: Ribs in chest images have a negative effect on observer performance for detecting lung lesions. The purpose of this study was to develop a fully automated image processing technique for reducing the contrast of ribs by means of image processing and thereby to increase the sensitivity of lesion detection. Method and Materials: Digital chest radiography (ThoraScan, Delft Imaging Systems) provides sufficient large dynamic range and high bit depth to register accurately the entire range of radiation intensities in the latent PA chest image. This implies that visibility of lesions in the lungs should improve after suppression of ribs. The rib suppression technique incorporates four basic steps: lung field segmentation, global rib segmentation, rib contour detection and signal subtraction in rib regions. Ribs are suppressed using estimates of the pixel intensity in the rib structure and its adjacent background. The difference between these estimates is weighted and subtracted from the rib structure, the degree of suppression of the ribs can be adjusted by changing the weight. The result is optimized using model information of the rib. To provide a proof of concept, PA chest images of ten patients were included in a pilot study. Results: Ribs in PA digital chest radiographs of ten patients were automatically suppressed by means of image processing. The general appearance of lung tissue, vessels and lesions in the lung fields improved. Conclusion: An automated image‐processing technique for rib suppression has been developed. The impact of this technique on the sensitivity of detection of lung nodules in digital chest radiographs will be investigated in a future observer performance study.

Comparison of Digital Radiographs with Film Radiographs for the Classification of Pneumoconiosis 1

Digital chest imaging has replaced film chest radiographs in many centers, but the International Labour Organization classification system, which is the most widely used system for recognition and classification of dust-related abnormalities, is predicated on film chest radiographs. The purpose of this study was to evaluate the equivalency of digital chest radiographs (including both hard copy and soft copy) with film radiographs for the recognition and quantification of abnormalities consistent with pneumoconiosis using the International Labour Organization classification system. Digital chest images and film images, obtained from 107 subjects with a range of parenchymal and pleural abnormalities, were classified in random order by six B readers. Readings of film and soft copy images were equivalent for small opacity profusion; readings of hard copy images had significantly greater prevalence of small opacities compared to film and soft copy. The prevalence of large opacities differed significantly among all three image formats: hard copy greater than film greater than soft copy. However, film and soft copy readings for large opacities did not differ significantly when images demonstrating the coalescence of small opacities that had not yet become a large opacity were grouped with large opacities. The prevalence of pleural abnormalities differed significantly among all three image formats: film greater than hard copy greater than soft copy. Film and soft copy images can be recommended for the recognition and classification of dust-related parenchymal abnormalities using International Labour Organization classifications. The role of digital radiography in reading for pleural abnormalities requires additional investigation.

Ｆｌａｔｐａｎｅｌｄｅｔｅｃｔｏｒ（ＦＰＤ）装置を使用した小児ディジタル胸部撮影における最適ヒストグラム解析の検討

Optical density of the lung area in pediatric digital chest radiography using an indirect flat panel detector (FPD) system were changed enormously by the influence of such factors as the size of lung area, gas of retroperitoneum, and so on. Our purpose in this study was to improve the stability of lung density on output images by means of optimizing histogram analysis. Chest images of a lung phantom were taken at various X-ray tube voltages and processed using a half-type region of interest (ROI) for the lung area. The shape of the histogram obtained by two different calculation methods including frequency distribution and cumulative relative frequency were compared, and digital chest images of 110 clinical cases in our hospital were classified into three age-groups (under 6 years old, over 6 years old and under 13 years old, and over 13 years old) and their histograms were analyzed. In conclusion, it was important that to analyze the histograms of age-groups, a cumulative relative frequency histogram should be used because the influence of X-ray tube voltage was lower than the frequency distribution histogram, and stabilized lung density under 6 years old could be obtained if the value of the imaging parameter for lung density from default was 90% to 85% or 80% because the distribution of lung area and its center value were significantly lower than in those over 13 years old.

Medical Grade vs Off-the-Shelf Color Displays: Influence on Observer Performance and Visual Search

The goal of this study was to compare diagnostic accuracy of radiologists viewing clinical images on a top-of-the-line medical-grade vs a top-of-the-line commercial off-the-shelf (COTS) color display with the luminance values set to simulate a display that had been in use for 1 year. A set of 50 digital radiography chest images was selected for use in the study, half containing a solitary pulmonary nodule and half nodule-free. The images were displayed twice to each of six observers, once on each display. Eye position was recorded on a subset of the images. Overall, there was a statistically significant difference (F = 4.1496, p = 0.0471) between the medical-grade color display and the COTS color display in terms of receiver operating characteristic area under the curve values, with the medical-grade display yielding higher diagnostic accuracy. Total viewing time did not differ significantly, but eye position data revealed differences, suggesting better search and decision-making efficiency with the medical-grade display. Medical-grade color displays at 1 year old yield better diagnostic and search efficiency than COTS color displays and thus are recommended for primary reading if color displays are to be used.

Computer-Generated Index for Evaluation of Idiopathic Scoliosis in Digital Chest Images: A Comparison with Digital Measurement

An intelligence system was used to generate index for scoliosis. Tests were designed to evaluate the consistency of the automatic computer-generated index and to quantify the correlation between Cobb angle and computer generated scoliosis classification index (SCI). A fully automatic computer-generated index can be used to assess the extent of spinal curvature rather than manual measurement on radiographs. This study aims to evaluate the relation of an automatic computer-generated index in assessing the spinal curvature of scoliosis quantitatively on digital chest images. Sixty chest radiographs were obtained in this study. Cobb angle measurement and the index generated were compared by parametric statistical tests. The SCI method was demonstrated to be reproducible. There was also statically significant positive correlation between Cobb angle and SCI (Pearson's correlation: r = 0.9229). The Computer-generated index method is valid and reliable in quantifying measurement of spinal curvature of scoliosis as the correlation between Cobb's angle and SCI in nearly perfect positive for Cobb angle more than 10 degree. It is noted that with widely use of this computer method, this quantitative method proposed is a promising method in improving the reliability of scoliosis assessment and reducing the workload of clinical staff.

SU‐FF‐I‐76: Slot Scan Imaging Versus Anti‐Scatter Grid Method in Digital Chest Imaging‐ a 4‐AFC Study

Purpose: To investigate and compare the anti‐scatter grid and slot scanning methods for their effects on the observers' performance in digital chest imaging. Materials and Methods: Anthropomorphic chest phantom was imaged with an a‐Si/a‐Se flat‐panel based digital radiography system. The system was operated in both the slot scanning and full‐field modes. An anti‐scatter grid was used. Imaging technique was 120 kVp and 0.15 to 16 mAs for both modes. After that, the grid was removed and same imaging technique was applied to acquire phantom images for both modes. 1‐cm diameter computer‐simulated nodule with a nominal peak contrast ratio of 5% was used to generate simulated nodules at hilum and sub‐diaphragm locations by applying SPR values for all images. 4‐AFC experiment was conducted to measure the ratio of correct observations as a function of the exposure level for various imaging conditions and locations. 24 sets of four‐512×512 images were generated for each exposure level, resulting in generating 192 sets for each imaging condition and location. These images were displayed randomly on a review workstation. The ratios of correct observations versus exposure levels were computed for various imaging conditions and locations. Result: With low exposure, the observers' performance improved with the exposure level but reached the maximum at ∼4 mAs for all techniques. At the hilum location, slot scan imaging without grid performed the best, followed by full‐field imaging without grid. The use of an anti‐scatter grid in both full‐field and slot scan modes seemed to degrade the performance significantly. Conclusion: Improvement with the exposure level has been observed for all imaging techniques. However, the observers' performance reached the maximum at different rates depending on the nodule location and techniques.(This work was supported in part by a research grant EB000117 from the NIH‐NIBIB and a research grant CA104759 from the NIH‐NCI).

Does the Age of Liquid Crystal Displays Influence Observer Performance?

As liquid crystal displays (LCDs) age, the whitepoint shifts toward a yellow hue, changing the appearance of the displayed images. This study examined whether this shift in whitepoint influences observer performance and visual search efficiency of radiologists interpreting clinical images. Six radiologists viewed 50 digital radiography chest images (half with a solitary pulmonary nodule, half without) on three LCDs that had their whitepoint adjusted to simulate monitor age: new, 1 year old, and 2.5 years old. Presence or absence of nodules was reported along with reader confidence. Results were analyzed using receiver operating characteristic techniques. Visual search was measured on a subset of 15 images using eye position recording techniques. There was no statistically significant difference in receiver operating characteristic performance as a function of monitor age (F = 0.4901, P = .6187). In terms of total viewing time, there were not statistically significant differences between the three monitors (F = 0.056, P = .9452). The dwell times associated with each decision type (true and false, positive and negative) did not differ significantly as a function of monitor age for any decision. At least up to 2.5 years of age, the shift in whitepoint toward the yellow range does not significantly impact diagnostic accuracy or visual search efficiency of radiologists.

Detection of Simulated Nodules on Clinical Radiographs: Dose Reduction at Digital Posteroanterior Chest Radiography

To determine to what extent dose reduction results in decreased detection of simulated nodules on patient digital posteroanterior (PA) chest radiographs. Raw data from 20 clinical digital PA chest images that were reported as having normal findings and that were obtained with a slot-scan charge-coupled device system were used. For research protocol that concerns data with patient identities concealed, institutional review board approval is not required. One hundred twenty nodules varying in size and signal intensity were digitally simulated and added to the chest images. Hard copies were printed to represent a 100% dose and, by adding noise, to represent simulated patient doses of 50%, 25%, and 12%. Four radiologists reviewed images. Each lesion was registered as "detected" or "not detected." A semiparametric logistic regression model was used for statistical analysis. The decrease in radiation dose from 100% to 50%, 25%, or 12% had no effect on lesion detection in the lungs. The decrease in radiation dose had an effect on lesion detection in the mediastinum, as probabilities deteriorated from the 100% dose to the 50%, 25%, and 12% dose with each step. Probabilities of smaller detection rates when compared with that of the reference category (100% dose) were 0.97 (95% confidence interval [CI]: -0.86, 0.012) for the 50% dose, 1 (CI: -0.59, -0.61) for the 25% dose, and 1 (CI: -2.41, -1.22) for the 12% dose. CIs for the effects were on the log(odds). Detection probability decreased with smaller and lower signal intensity lesions. At clinical digital radiography, dose reduction resulted in decreased observer detection of simulated nodules in the mediastinum but not in the lungs.

Image Quality and Radiation Dose on Digital Chest Imaging: Comparison of Amorphous Silicon and Amorphous Selenium Flat-Panel Systems

The aim of this study was to compare the image quality and radiation dose in chest imaging using an amorphous silicon flat-panel detector system and an amorphous selenium flat-panel detector system. In addition, the low-contrast performance of both systems with standard and low radiation doses was compared. In two groups of 100 patients each, digital chest radiographs were acquired with either an amorphous silicon or an amorphous selenium flat-panel system. The effective dose of the examination was measured using thermoluminescent dosimeters placed in an anthropomorphic Rando phantom. The image quality of the digital chest radiographs was assessed by five experienced radiologists using the European Guidelines on Quality Criteria for Diagnostic Radiographic Images. In addition, a contrast-detail phantom study was set up to assess the low-contrast performance of both systems at different radiation dose levels. Differences between the two groups were tested for significance using the two-tailed Mann-Whitney test. The amorphous silicon flat-panel system allowed an important and significant reduction in effective dose in comparison with the amorphous selenium flat-panel system (p < 0.0001) for both the posteroanterior and lateral views. In addition, clinical image quality analysis showed that the dose reduction was not detrimental to image quality. Compared with the amorphous selenium flat-panel detector system, the amorphous silicon flat-panel detector system performed significantly better in the low-contrast phantom study, with phantom entrance dose values of up to 135 muGy. Chest radiographs can be acquired with a significantly lower patient radiation dose using an amorphous silicon flat-panel system than using an amorphous selenium flat-panel system, thereby producing images that are equal or even superior in quality to those of the amorphous selenium flat-panel detector system.

Computer‐aided diagnostic scheme for the detection of lung nodules on chest radiographs: Localized search method based on anatomical classification

We developed an advanced computer-aided diagnostic (CAD) scheme for the detection of various types of lung nodules on chest radiographs intended for implementation in clinical situations. We used 924 digitized chest images (992 noncalcified nodules) which had a 500 x 500 matrix size with a 1024 gray scale. The images were divided randomly into two sets which were used for training and testing of the computerized scheme. In this scheme, the lung field was first segmented by use of a ribcage detection technique, and then a large search area (448 x 448 matrix size) within the chest image was automatically determined by taking into account the locations of a midline and a top edge of the segmented ribcage. In order to detect lung nodule candidates based on a localized search method, we divided the entire search area into 7 x 7 regions of interest (ROIs: 64 x 64 matrix size). In the next step, each ROI was classified anatomically into apical, peripheral, hilar, and diaphragm/heart regions by use of its image features. Identification of lung nodule candidates and extraction of image features were applied for each localized region (128 x 128 matrix size), each having its central part (64 x 64 matrix size) located at a position corresponding to a ROI that was classified anatomically in the previous step. Initial candidates were identified by use of the nodule-enhanced image obtained with the average radial-gradient filtering technique, in which the filter size was varied adaptively depending on the location and the anatomical classification of the ROI. We extracted 57 image features from the original and nodule-enhanced images based on geometric, gray-level, background structure, and edge-gradient features. In addition, 14 image features were obtained from the corresponding locations in the contralateral subtraction image. A total of 71 image features were employed for three sequential artificial neural networks (ANNs) in order to reduce the number of false-positive candidates. All parameters for ANNs, i.e., the number of iterations, slope of sigmoid functions, learning rate, and threshold values for removing the false positives, were determined automatically by use of a bootstrap technique with training cases. We employed four different combinations of training and test image data sets which was selected randomly from the 924 cases. By use of our localized search method based on anatomical classification, the average sensitivity was increased to 92.5% with 59.3 false positives per image at the level of initial detection for four different sets of test cases, whereas our previous technique achieved an 82.8% of sensitivity with 56.8 false positives per image. The computer performance in the final step obtained from four different data sets indicated that the average sensitivity in detecting lung nodules was 70.1% with 5.0 false positives per image for testing cases and 70.4% sensitivity with 4.2 false positives per image for training cases. The advanced CAD scheme involving the localized search method with anatomical classification provided improved detection of pulmonary nodules on chest radiographs for 924 lung nodule cases.

Detection of Small Pulmonary Nodules Using Direct Digital Radiography and Picture Archiving and Communication Systems

To evaluate the detection of small pulmonary nodules, in the diameter range of 5.4 to 15 mm, using direct digital chest imaging and soft copy interpretation on picture archiving and communication systems. The results of clinical computed tomography (CT) scans of the thorax were retrospectively reviewed from our radiology information system and picture archiving and communication systems archives. Patients with CT studies containing between 1 and 6 nodules, who also had a digital chest examination within 1 month of the CT scan were selected. Thirty patients with suitable nodules and 30 without nodules were included and form the data base for this study. The nodules were between 5.4 and 15 mm in average diameter. Four separate observers independently viewed the frontal and lateral chest studies of the 60 patients. The presence or absence of nodules was determined. Data were analyzed with Kappa, McNemar and Fischer exact tests for agreement and differences between observers, nodule size, and nodule zone. A total of 42 nodules between 5.4 and 15 mm were present. The overall detection rate for the 4 observers was 41.7%. For nodules between 5.4 and 8 mm the detection rate was 26.2%. Agreement between observer's detection was poor to moderate. Differences between observers for both nodule size and zone were not significant. Only 1 observer had a relationship between nodule detection and nodule size. Observer detection of pulmonary nodules in the range of 5 to 15 mm using current digital radiography systems is not reliable in the confusing environment of the lung. Additional modification of these systems is required to increase nodule conspicuity.

胸部結節状陰影と間質性肺病変の検出に関するＬＣＤとＣＲＴモニタの比較

Soft copy reading of digital images has been practiced commonly in the PACS environment. In this study, we compared liquid-crystal display (LCD) and cathode-ray tube (CRT) monitors for detection of pulmonary nodules and interstitial lung diseases on digital chest radiographs by using receiver operating characteristic (ROC) analysis. Digital chest images with a 1000x1000 matrix size and a 8 bit grayscale were displayed on LCD/CRT monitor with 2M pixels in each observer test. Eight and ten radiologists participated in the observer tests for detection of nodules and interstitial diseases, respectively. In each observer test, radiologists marked their confidence levels for diagnosis of pulmonary nodules or interstitial diseases. The detection performance of radiologists was evaluated by ROC analyses. The average Az values (area under the ROC curve) in detecting pulmonary nodules with LCD and CRT monitors were 0.792 and 0.814, respectively. In addition, the average Az values in detecting interstitial diseases with LCD and CRT monitors were 0.951 and 0.953, respectively. There was no statistically significant difference between LCD and CRT for both detection of pulmonary nodules (P=0.522) and interstitial lung diseases (P=0.869). Therefore, we believe that the LCD monitor instead of the CRT monitor can be used for the diagnosis of pulmonary nodules and interstitial lung diseases in digital chest images.