Soft-copy reading of digital chest radiographs: effect of ambient light and automatic optimization of monitor luminance

OBJECTIVE: We sought to evaluate whether soft-copy reading of simulated pulmonary chest lesions is influenced by ambient light and automatic optimization of cathode ray tube (CRT) monitor luminance. MATERIALS AND METHODS: Four types of simulated lesions (nodules, lines, micronodules, and patchy opacities) were superimposed over an anthropomorphic chest phantom. Lesion detection with soft-copy reading was assessed using a high-contrast grayscale 2K CRT monitor under the following conditions: (1) subdued lighting (<50 lux); (2) normal lighting conditions (450 lux) without, and (3) with a sensitivity modulation to automatically adjust the CRT luminance to the increased amount of ambient light. Reading data were analyzed according to receiver operating curve. Significance of differences was tested using an analysis of variance for repeated measures. RESULTS: Ambient room light of 450 lux did not significantly influence the detection of nodules and patchy opacities. However, bright ambient light significantly decreased detection of micronodules (0.60 vs. 0.74) and lines (0.52 vs. 0.66) relative to subdued lighting conditions. Automatic luminance adjustment could compensate the effect of ambient light for the micronodules (0.77) but not for the lines (0.53). CONCLUSION: Bright ambient light significantly decreases detection of small low-contrast structures. This may be partially but not completely compensated by an automatic luminance adaptation.     

Comparison of observer performance on soft-copy reading of digital chest radiographs: high resolution liquid-crystal display monitors versus cathode-ray tube monitors

The purpose of this study is to compare observer performance for detection of abnormalities on chest radiographs with 5-megapixel resolution liquid-crystal displays (LCD) and 5-megapixel resolution cathode-ray tube (CRT) monitors under bright and subdued ambient light conditions. Six radiologists reviewed a total of 254 digital chest radiographs under four different conditions with a combination of two types of monitors (a 5-megapixel resolution LCD and a 5-megapixel resolution CRT monitor) and with two types of ambient light (460 and 50 lux). The abnormalities analyzed were nodules, pneumothorax and interstitial lung disease. For each reader, the detection performance using 5-megapixel LCD and 5-megapixel CRT monitors under bright and subdued ambient light conditions were compared using multi-case and multi-modality ROC analysis. For each type of ambient light, the average detection performance with the two types of monitors was also compared. For each reader, the observer performance of 5-megapixel LCD and 5-megapixel CRT monitors, under both bright and subdued ambient light conditions, showed no significant statistical differences for detecting nodules, pneumothorax and interstitial lung disease. In addition, there was no significant statistical difference in the average performance when the two monitor displays, under both bright and subdued ambient light conditions, were compared.     

Influence of monitor luminance change on observer performance for detection of abnormalities depicted on chest radiographs

RATIONALE AND OBJECTIVES: To investigate how changes in luminance affect the detection accuracy of radiologists viewing chest radiograph images on high-resolution CRT monitors. MATERIALS AND METHODS: Thirteen radiologists performed a detection task for 11 chest radiograph images with simulated nodules on a monitor with 11 luminance conditions (the maximum luminance ranges from 157.4-369.0 candela/m2) simulating CRT degraded by long-term usage, under the ambient illumination of 200 lux; the observation order was always from the darkest to the brightest. RESULTS: There was a statistically reliable effect of the 11 monitor display conditions on the detection of nodules (P < 0.001). In the conditions in which the maximum luminance of the CRT was 60.7% or below that of the standard display luminance, the correctly detected nodule number reliably deteriorated. CONCLUSIONS: The luminance change in CRT monitor display under long-term usage will have a detrimental effect on nodule detection performance in chest radiograph images.     

Effects of luminance and resolution on observer performance with chest radiographs

PURPOSE: To examine the combined effects of image resolution and display luminance on observer performance for detection of abnormalities depicted on posteroanterior chest radiographs. MATERIALS AND METHODS: A total of 529 radiographs were displayed on a specially constructed view box at three luminance levels (770, 260, and 85 cd/m(2)) and three resolutions (100-microm, 200-microm, and 400-microm pixels). Each image was reviewed nine times by six radiologists who participated in this study. The abnormalities included nodule, pneumothorax, interstitial disease, alveolar infiltrates, and rib fracture. Negative (normal) radiographs were also included. RESULTS: Receiver operating characteristic curves indicated that the effect of image luminance was greater than that of resolution. The detection of pneumothorax, interstitial disease, and rib fracture showed statistically significant differences (P <. 05) due to luminance. The detection of pneumothorax was the only abnormality with a statistically significant difference due to resolution. There was no evidence that luminance was related to image resolution for any of the abnormalities. CONCLUSION: At a resolution of 400-microm pixels or higher across the field of view and a luminance of 260 cd/m(2) or more, primary diagnosis with posteroanterior chest radiographs is not likely to be affected by the quality of display.     

Impact of ambient light and window settings on the detectability of catheters on soft-copy display of chest radiographs at bedside

OBJECTIVE: The aim of this study was to evaluate how ambient light and interactive adjustment of density and contrast affect the detection of catheter fragments when interpreting bedside chest radiographs on soft-copy displays. MATERIALS AND METHODS: A total of 131 catheter fragments were superimposed over 10 bedside chest radiographs obtained with storage phosphor technology. Images were displayed on a clinical intensive care unit viewing station (color cathode-ray tube monitor, 21 inch [53 cm], 1280 x 1024 matrix) and were independently evaluated by five radiologists. The number of catheter fragments per image varied between 12 and 14, with an approximately equal distribution in high- and low-absorption areas. Detectability of catheter fragments was assessed under subdued and bright ambient light conditions with and without interactive adjustment of window width and level. RESULTS: Under subdued light, the detection rate of catheter fragments was significantly higher than under bright light (51.8% vs 56.6%, p < 0.05). Interactive window setting adjustment significantly increased the detection rate from 52.5% to 60.8% (p < 0.05) under subdued light and from 47.9% to 55.6% (p < 0.05) under bright light. With adjustment of window settings, the difference between the detection rates under subdued light (60.8%) and under bright light (55.6%) did not reach statistical significance. CONCLUSION: Detection of catheters on soft-copy display is significantly decreased by bright ambient light, an effect that can be largely compensated for by means of interactive adjustment of window settings.     

Effects of monitor luminance change on observer detection performance.

To confirm that the dimming luminance change in the CRT monitor will have a detrimental effect on diagnostic performance, we performed the four-alternative forced choice experiments on the CRT monitor with the 11 luminance conditions simulating CRT degraded by long-term usage. Six radiologists and one pulmonary physician performed a detection task for 11,000 test areas on 110 test images. The 11 monitor conditions significantly affected the correct detection rates of simulated nodules in the four-alternative forced choice experiments. The gradual deterioration in CRT monitor luminance will have certainly a detrimental effect on detection performance.     

Influence of film and monitor display luminance on observer performance and visual search

RATIONALE AND OBJECTIVES: The purpose of this study was to measure the influence of display luminance on detection performance and visual search behavior. The results of the study should be helpful in establishing minimally acceptable display conditions for viewing radiographs on cathode-ray tube (CRT) monitors. MATERIALS AND METHODS: Two groups of six radiologists each viewed 50 pairs of mammograms. One group viewed film images on a standard mammographic view box; the other viewed images on a high-resolution CRT monitor. Two luminance levels were studied for each display type. Observers reported on the presence or absence of masses or microcalcification clusters and on their confidence in that decision. Confidence data were analyzed by using alternative free-response receiver operating characteristic (AFROC) techniques. Eye position also was recorded as observers viewed the images. RESULTS: For both the film and monitor studies, detection performance (AFROC area under the curve) was not affected significantly by display luminance, but search behavior was. Total viewing and decision dwell times were shorter with the higher-luminance displays, especially for true-negative decisions. Significantly more fixation clusters were generated during the search of lesion-free than of lesion-containing images with the lower-luminance displays. CONCLUSION: Display luminance affects visual search performance with both film and monitor displays without affecting detection performance significantly. Higher-luminance displays yield more efficient search performance. The true-negative dwell times and number of clusters are suggestive that lower-luminance levels prolong the search and recognition of normal, lesion-free areas compared with lesion-containing areas.     

Effect of ambient light and monitor brightness and contrast settings on the detection of approximal caries in digital radiographs: an in vitro study

OBJECTIVES: The aim of this study was to investigate how brightness and contrast settings of the display monitor and ambient light level (illuminance) in the viewing room affect the clinician's ability to diagnose carious lesions in digital radiographs. METHODS: Standardized radiographs were taken of 100 extracted teeth. Seven observers evaluated the images for approximal carious lesions twice, once under 50 lux and once under 1000 lux room illumination. Monitor brightness and contrast were varied +/-50% and +/-6%, respectively, to mimic the normal limits of monitor adjustment by an inexperienced user and one optimal setting. This was done by adjusting radiograph brightness and contrast by +/-25%. Thus, five radiographs of each tooth were evaluated. Receiver operating characteristic (ROC) analyses were performed. Histological examinations of the teeth served as the criterion standard. A paired t-test was used to evaluate whether differences in the areas under the ROC curves were significant and kappa was used to evaluate intraobserver agreement. RESULTS: When a monitor with optimal brightness and contrast settings was used to detect approximal carious lesions, ambient light levels less than 50 lux were significantly better than levels above 1000 lux (dentin and enamel lesions, P < 0.01; dentin lesions, P < 0.02). Increasing the contrast setting of the monitor by 6% did not change these results; 50 lux was still significantly better than 1000 lux (enamel lesions, P < 0.01; dentin and enamel lesions, P < 0.02) for evaluating radiographs. Intraobserver agreement differed from fair to good. CONCLUSIONS: Reducing ambient light to less than 50 lux significantly increased the accuracy of diagnosing approximal carious lesions on a monitor with an optimal brightness setting and an optimal or slightly higher than optimal contrast setting.     

Spatial resolution requirements for digital chest radiographs: an ROC study of observer performance in selected cases

Thirty-eight selected clinical radiographs were digitized and displayed on a 1,024-line monitor at pixel sizes of 1.6, 0.8, 0.4, and 0.2 mm. Eighteen experienced radiologists assessed the radiographs and digital images, which included 12 examples of abnormal solitary nodular density, ten examples of septal lines, and 16 controls, six of which showed diffuse lung abnormalities. For each level of spatial resolution and for film reading, observers gave their decision confidence on a sliding scale of probability. Receiver operating characteristic curves were generated from these data. It was found that while spatial resolution requirements for solitary nodules were not critical for pixel sizes at or below 0.8 mm, the requirement for septal lines was likely to be 0.4 mm (1.25 line pairs/mm).     

影响胸片软阅读诊断系统效能的因素

目的 探讨应用医用液晶显示器进行软阅读时,影响诊断系统效能的因素及主次关系.方法 从PACS中选取30幅胸部后前位的影像资料.由高、中、低年资放射科医师各3名独立阅片.将影响诊断效能的5个显示因素(观察距离、分辨率、室内照度值、观察视角、负效光角度)各设计4个显示水平(观察距离选取0.3、0.6、0.9、1.2m,显示器分辨率选择1、2、3、5百万像素,室内照度值选取50、100、200、400 lx,观察视角选取0°、15°、30°、45°,负效光角度选取0°、30°、60°、90°).分析误诊次数、诊断时间及无法诊断次数.使用SPSS13.0软件,采用正交实验设计,对统计结果进行极差值分析.结果 各分析指标随显示因素、显示水平的不同,有较大差别.就平均误诊次数而言,因素“观察视角”的极差值最小,为1.4次.因素“负效光角度”的极差值最大,为5.0次.观察距离、显示器分辨率、室内照度值等因素的极差值分别为2.9、2.8、2.5次.结论 对诊断系统效能影响因素的主次顺序为:负效光角度、观察距离、显示器分辨率、室内照度值、观察视角.     

胸片中肺癌的计算机辅助检测(CAD):对阅片者绩效的影响

目的评价在胸片发现的早期肺癌中,计算机辅助检测(CAD)是如何影响阅片者的绩效。材料与方法经伦理委员会批准,本回顾性研究包括46例CT发现并经组织学证实     

Influence of the digital image display monitor on observer performance.

OBJECTIVE: To assess the influence of the display monitor on observer performance. MATERIAL AND METHODS: Artificial enamel lesions were created in 40 extracted teeth at random using 1/4 and 1/2 round burs. Teeth were mounted in dental stone blocks to simulate a hemidentition. Approximate exposures were recorded at 70 kVp using a Digota (Soredex, Orion Corp, Helsinki, Finland) digital imaging system, calibrated to achieve optimum density. Six dentists rated each image on a five-point scale for the presence or absence of a lesion. Radiographic images were viewed on the following monitors: (1) AlphaScan 711 (Sampo Corp.); (2) Multiscan 17 Se II (Sony Electronics Inc.); (3) DS 2000 (Clinton Electronics Corp.) and (4) Latitude CP Laptop (Dell Computer Corp.). Raters were allowed to magnify and to adjust density and contrast of each image at will. Receiver Operating Characteristic (ROC) analysis was performed and curves were plotted for each image. Data was subjected to repeated measures analysis of variance and ordinal logistic regression to test for significance between variables and to determine odds ratios. RESULTS: Mean ROC curve areas ranged from 0.8728 for the Sampo monitor to 0.8395 for the Sony. Repeated measures analysis of variance showed significant differences between observers (P < 0.0001), lesion size (P < 0.0001), examiner/monitor interaction (P < 0.033) and examiner/block interaction (P < 0.013). However, no significant difference was found between monitors. CONCLUSION: This study suggests that observer performance is independent of the visual characteristics of the display monitor.     

Using edge enhancement to identify subtle findings on soft-copy neonatal chest radiographs.

OBJECTIVE: The purpose of this study was to evaluate whether edge enhancement could improve the visibility of subtle findings on soft copies of neonatal chest radiographs. MATERIALS AND METHODS: Two radiologists reviewed 82 soft-copy neonatal chest radiographs before and after the application of edge enhancement on our picture archiving and communication system (PACS). The visibility of a pneumothorax (n = 22), central venous catheter (n = 32), umbilical arterial catheter (n = 36), endotracheal tube (n = 40), and normal anatomic structures (the minor fissure, anterior segmental bronchus of the right upper lobe, and aortic arch, n = 57) was evaluated. Six of 22 soft-copy images depicting a pneumothorax were excluded from the evaluation of image quality either because of the large size of the pneumothorax itself (n = 7) or because of the lack of confirmatory evidence that would have been provided by an additional lateral decubitus (n = 6) or cross-table lateral radiograph (n = 3). Image quality was evaluated by visual grading analysis. RESULTS: The visibility of a pneumothorax (p < 0.01), vascular catheters (p < 0.001), the minor fissure (p < 0.001), and the anterior segmental bronchus of the right upper lobe (p < 0.001) improved significantly after applying edge enhancement to soft copies of neonatal chest radiographs, whereas the visibility of the aortic arch did not improve. Evaluations of the improvements in the visibility of the endotracheal tube were inconsistent. CONCLUSION: Application of edge enhancement to soft copies of neonatal chest radiographs helps radiologists to identify small pneumothoraces, vascular catheters, and delicate normal structures, thereby improving the detection of subtle chest findings in the neonatal intensive care unit.     

Receiver-operating-characteristic study of chest radiographs in children: digital hard-copy film vs 2K x 2K soft-copy images.

Two methods are commonly used to visualize digital radiologic imaging data: (1) hard-copy viewing, in which the digital data are used to modulate the intensity of a laser beam that exposes an analog film and (2) soft-copy viewing, in which the digital data are converted to an analog video signal and presented on a CRT monitor. The film method allows new digital imaging systems to be easily integrated into conventional radiologic management and viewing methods. The second method, soft-copy viewing, allows digital imaging data to be managed and viewed electronically in a picture archiving and communication system (PACS). These PACS systems are hypothesized to have improved operational efficiency and enhanced image-analysis capabilities. The quality of soft-copy images is still not widely accepted. This article reports on the results of a large-scale receiver-operating-characteristic study comparing observers' performance in detecting various pediatric chest abnormalities on soft-copy 2048 x 2048K byte displays with their performance with digital laser-printed film from computed radiography. The disease categories studied were pneumothorax, linear atelectasis, air bronchogram, and interstitial disease. The selected data set included 239 images; 77 contained no proved abnormality and 162 contained one or more of the abnormalities mentioned. Seven pediatric radiologists participated in the study, two as judges and five as observers. Our results show no significant difference between viewing images on digital hard copy and soft copy for the detection of pneumothoraces and air bronchograms. A slight performance edge for soft copy was seen for interstitial disease and linear atelectasis. This result indicates that computed chest radiographs in children viewed in a soft-copy PACS environment should result in diagnoses similar to or slightly more accurate than those obtained in a laser-printed film-based environment.     

Personal computer versus workstation display: observer performance in detection of wrist fractures on digital radiographs

PURPOSE: To retrospectively compare the accuracy of observer performance with personal computer (PC) compared with that with dedicated picture archiving and communication system (PACS) workstation display in the detection of wrist fractures on computed radiographs. MATERIALS AND METHODS: This study was conducted according to the principles of the Declaration of Helsinki (2002 version) of the World Medical Association. The institutional clinical board approved the study; informed consent was not required. Seven observers independently assessed randomized anonymous digital radiographs of the wrist from 259 subjects; 146 had fractures, and 113 were healthy control subjects (151 male and 108 female subjects; average age, 33 years). Follow-up radiographs and/or computed tomographic scans were used as the reference standard for patients with fractures, and follow-up radiographs and/or clinical history data were used as the reference standard for controls. The PC was a standard hospital machine with a 17-inch (43-cm) color monitor with which Web browser display software was used. The PACS workstation had two portrait 21-inch (53-cm) monochrome monitors that displayed 2300 lines. The observers assigned scores to the radiographs on a scale of 1 (no fracture) to 5 (definite fracture). Receiver operating characteristic (ROC) curves, sensitivity, specificity, and accuracy were compared. RESULTS: The areas under the ROC curves were almost identical for the PC and workstation (0.910 vs 0.918, respectively; difference, 0.008; 95% confidence interval: -0.029, 0.013). The average sensitivity with the PC was almost identical to that with the workstation (85% vs 84%, respectively), as was the average specificity (82% vs 81%, respectively). The average accuracy (83%) was the same for both. CONCLUSION: The results of this study showed that there was no difference in accuracy of observer performance for detection of wrist fractures with a PC compared with that with a PACS workstation.     

Evaluation of cardiopulmonary devices on chest radiographs: digital vs analog radiographs

We compared digital and analog radiographs of the chest for use in detecting and evaluating a variety of cardiopulmonary devices in 40 patients. The devices included 23 endotracheal tubes, 21 Swan-Ganz catheters, 14 central venous pressure catheters, 11 prosthetic valves, 10 chest tubes, six pacemaker wires, and five intraaortic balloon pumps. Each patient had at least one device, with a maximum of five devices (average, 2.3). Forty digital/analog film pairs were compared by five radiologists, who assigned confidence levels for various judgments about each device. The results showed that there were no statistically significant differences in the identification of the devices except for prosthetic valves (all valves were detected on digital radiographs, compared with 62% on analog radiographs). The devices were detected on 96% of the digital radiographs and 90% of the analog radiographs. Although digital and analog radiographs were comparable for detection of most devices, the digital radiographs allowed greater confidence in the identification of the devices and in the identification of the tip and course of Swan-Ganz and central venous pressure catheters.     

Effects of image processing on nodule detection rates in digitized chest radiographs: ROC study of observer performance

To evaluate the effects of image processing in digitized chest radiographs when high-resolution images are used, an examination was done in which the detection of pulmonary nodules in unprocessed digitized chest radiographs was compared with that in images that had undergone processing with two methods, adaptive filtration and histogram equalization. The processing techniques have been optimized in previous work to selectively enhance the retrocardiac and subdiaphragmatic areas without significant alteration of detail in the lung. Eight observers were shown 150 test radiographs (50 unprocessed, 50 processed with adaptive filtration, 50 processed with histogram equalization) containing 150 nodules. The results indicate a statistically significant (P less than .03) difference, with highest observer performance in the chest radiographs processed with adaptive filtration (median area under ROC curve = 0.78), compared with unprocessed images (median = 0.68) and chest radiographs processed with histogram equalization (median = 0.62). Performance in the lung was not significantly different. Adaptive filtration applied to selectively enhance underexposed areas of film images may improve nodule detection. Histogram equalization provided no improvement in performance.     

Influence of liquid crystal display monitors on observer performance for detection of diffuse pulmonary disease on chest radiographs

Purpose The purpose of this study was to assess the influence of liquid crystal display (LCD) monitors on the detectability of diffuse pulmonary diseases depicted on chest radiographs by comparing them with a high-resolution cathode ray tube (CRT) monitor. Materials and methods A group of 17 radiologists interpreted 87 soft-copy images on LCD monitors with pixel arrays of 1024 × 1280, 1200 × 1600, 1536 × 2048, and 2048 × 2560 and on a CRT monitor with a pixel array of 2048 × 2560. They were asked to indicate their individual confidence levels regarding the presence of diffuse pulmonary diseases. The luminance distributions of all monitors were adjusted to the same distributions, and the ambient illumination was 200 lux. Observer performance was analyzed in terms of the receiver operating characteristics (ROC). Results The average ROC curves for the five monitor types were similar, and there were no statistically reliable effects of the five monitor types on the readers’ diagnostic performances (P = 0.7587). Conclusion The detectability of diffuse pulmonary disease on the LCD monitors with a spatial resolution equal to or higher than a matrix size of 1024 × 1280 was found to be equivalent to that on the high-resolution CRT monitor.     

Observer variability in screen-film mammography versus full-field digital mammography with soft-copy reading

Full-field digital mammography (FFDM) with soft-copy reading is more complex than screen-film mammography (SFM) with hard-copy reading. The aim of this study was to compare inter- and intraobserver variability in SFM versus FFDM of paired mammograms from a breast cancer screening program. Six radiologists interpreted mammograms of 232 cases obtained with both techniques, including 46 cancers, 88 benign lesions, and 98 normals. Image interpretation included BI-RADS categories. A case consisted of standard two-view mammograms of one breast. Images were scored in two sessions separated by 5 weeks. Observer variability was substantial for SFM as well as for FFDM, but overall there was no significant difference between the observer variability at SFM and FFDM. Mean kappa values were lower, indicating less agreement, for microcalcifications compared with masses. The lower observer agreement for microcalcifications, and especially the low intraobserver concordance between the two imaging techniques for three readers, was noticeable. The level of observer agreement might be an indicator of radiologist performance and could confound studies designed to separate diagnostic differences between the two imaging techniques. The results of our study confirm the need for proper training for radiologists starting FFDM with soft-copy reading in breast cancer screening. Presented at ECR, Wien 2006.