Detectability of lung nodules using flat panel detector with dual energy subtraction by two shot method: evaluation by ROC method

The aim of this study was to evaluate the effectiveness of dual-exposure dual energy subtraction technique in flat-panel chest radiography for lung nodules detection. Chest radiographs were acquired in 100 patients (57 men and 43 women; mean age, 60.2 years; range, 18-89 years) using a flat-panel digital chest system. These images were evaluated by seven radiologists. A continuous rating scale of 0-100 was used to represent each observer's confidence level regarding the presence or absence of lung nodules. Observer performance for detection of lung nodules with subtraction images was tested by using receiver operating characteristic (ROC) analysis of individual and averaged reader data. The average area under the ROC curve (Az value) significantly increased with subtraction images (Az=0.79 in standard radiographs versus Az=0.84 with subtraction images, p<0.05). In conclusion, the two-exposure dual-energy subtraction chest radiography significantly would improve detection of lung nodules.     

Accuracy of caries detection with four storage phosphor systems and E-speed radiographs

OBJECTIVE: To evaluate the accuracy of caries detection using four intra-oral storage phosphor plate systems exposed with two different exposure times and one film system. METHODS: Under in vitro and standardised conditions 365 approximal and 159 occlusal surfaces were radiographed using four storage phosphor plate systems: DenOptix, Cd-dent, Digora (blue and white plates) and one film system: Ektaspeed Plus. The plates were exposed twice with 10% and 25% of the time needed for the film. Four observers recorded approximal enamel/dentine and occlusal dentine caries using a five-point confidence scale. Caries presence was validated histologically and diagnostic accuracy of the systems by using ROC curve areas (Az). RESULTS: The shorter exposure time for approximal caries, Digora(white)(Az=0.68) and Ekta Plus (Az=0.69) were significantly more accurate than the other systems (Az=0.64-0.65). For occlusal caries using the same exposure time, no significant difference was found between the digital systems (Az=0.76-0.77), which all showed to be significantly less accurate than Ekta Plus (Az=0.81). Using the longer exposure time for approximal caries, no significant difference was found between DenOptix (Az=0.68), Digora(blue) (Az=0.69), Digora(white) (Az=0.69) and Ekta Plus (Az=0.69) which were all significantly more accurate than Cd-dent (Az=0.65). For occlusal caries using the same exposure time, Digora(blue) (Az=0.81) was the most significantly accurate of the digital systems. When approximal caries was the diagnostic task, the longer exposure time resulted in significantly higher accuracy with the DenOptix and Digora(blue) systems but not with the Cd-dent and Digora(white) systems. For occlusal caries, the longer exposure time resulted in a significant improvement only with the Digora(blue) system. CONCLUSION: For approximal caries using the longer exposure time, no significant difference in diagnostic accuracy was found between DenOptix, Digora(blue), Digora(white) and Ekta Plus which were all significantly more accurate than the Cd-dent. For occlusal caries using the longer exposure time, Digora(blue) was found to be the most accurate of the digital systems. The exposure time had an influence on the diagnostic accuracy with the DenOptix and Digora(blue) systems for approximal and with the Digora(blue) system for occlusal caries detection.     

Detection of approximal caries in digital radiographs before and after correction for attenuation and visual response. An in vitro study

OBJECTIVE: To evaluate if digital compensation for exponential attenuation and the characteristics of the human visual system improves the diagnosis of approximal caries from digital radiographs. MATERIAL AND METHODS: Forty premolar teeth were mounted in plaster blocks. Radiographs of the teeth were exposed with the Dixi digital intraoral system employing a Prostyle Intra dental X-ray unit (Planmeca Oy, Helsinki, Finland). Thirteen radiographs were then processed to compensate for the exponential attenuation and for the characteristic of the human visual system using equations presented in the paper. Ten observers were asked to diagnose approximal caries in all radiographs. ROC analyses were performed. The teeth were subsequently sectioned for histological validation of the lesions. The areas under ROC curves of original and processed radiographs were compared and analysed using Wilcoxon's signed-ranks test. RESULTS: There were significant diagnostic differences between the two types of radiographs (all lesions P=0.005. enamel P=0.028, and dentine P=0.050). CONCLUSION: Digital radiographs processed to compensate for exponential attenuation and the characteristics of the human visual system significantly improves the diagnosis of approximal caries in vitro.     

Digital camera resolution and proximal caries detection

OBJECTIVES: To evaluate the diagnostic accuracy of proximal caries detection from digitized film images captured by a digital camera at different resolution settings. METHODS: Twenty-five periapical radiographs of 50 premolar and 25 molar teeth were photographed using a digital camera, Sony Cyber-shot, DSC-S75 at three different resolution settings: 640 x 480, 1280 x 960 and 1600 x 1200. Seventy-five digital images were transferred to a computer, saved and opened using ACDSee software. In addition, a PowerPoint slide was made from each digital image. Five observers scored three groups of images (the films, the displayed 1:1 digital images on the ACDSee software, and the PowerPoint slides) for the existence of proximal caries using a 5-point confidence scale, and the depth of caries on a 4-point scale. Ground sections of the teeth were used as the gold standard. Az values under the receiver operating characteristic (ROC) curve of each group of images and at different resolutions were compared using the Friedman and Wilcoxon signed rank tests. Mean different values between the lesions' depth interpreted by the observers and that of the gold standard were analysed. RESULTS: Films showed the highest Az values. Only the 1280 x 960 images on the ACDSee software showed no significant difference of the Az value from the films (P=0.28). The digital images from three resolution settings on the PowerPoint slides showed no significant differences, either among each other or between them and the films. For caries depth, the 1280 x 960 images showed lower values of mean difference in enamel lesions compared with the other two resolution groups. CONCLUSIONS: This study showed that in order to digitize conventional films, it was not necessary to use the highest camera resolution setting to achieve high diagnostic accuracy for proximal caries detection. The 1280 x 960 resolution setting of the digital camera demonstrated comparable diagnostic accuracy with film and was adequate for digitizing radiographs for caries detection.     

Effect of temporal subtraction technique on the diagnosis of primary lung cancer with chest radiography

PURPOSE: The purpose of this study was to assess the diagnostic accuracy of the temporal subtraction technique in the detection of primary lung cancers by readers with different levels of experience. METHODS: Previous and current chest radiographs from 40 patients with histologically proven lung cancer and 40 controls were studied. Temporal subtraction images were produced using an automated digital subtraction technique. We evaluated the effect of temporal subtraction images in the diagnosis of lung cancer with chest radiographs via an observer performance study with the use of receiver operating characteristic analysis. Six experienced radiologists and six residents participated as observers. RESULTS: Observer performance for all observers was superior when temporal subtraction images were used (mean Az value increased from 0.764 to 0.836, p=0.0006). Although the average Az value for residents increased significantly, from 0.707 to 0.795 (p=0.0038), the average Az value for experienced radiologists increased only from 0.821 to 0.878 (n.s.). CONCLUSION: In conclusion, the temporal subtraction technique clearly improves diagnostic accuracy for the detection of primary lung cancer. The results indicated that the use of temporal subtraction images was more beneficial for the residents than for the experienced radiologists. This method would compensate to some extent for experience-dependent diagnostic accuracy in the detection of lung cancer.     

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.     

Interaction between noise and file compression and its effect on the recognition of caries in digital imaging

OBJECTIVES: To determine the interaction between image noise and file compression, with special emphasis on the accuracy of caries diagnosis. METHODS: Fifty-nine bitewing radiographs of patients were taken simultaneously with Ektaspeed Plus (Eastman-Kodak, Rochester, NY, USA) film without lead foil and the Digora storage phosphor system (Soredex, Helsinki, Finland). Three different levels of Gaussian noise were added to the original digital images which were then compressed with JPEG 53. Seven observers evaluated the presence and depth of caries lesions on selected approximal surfaces on a 5-point scale. The results of JPEG 27 compression from a previous study were also included. ROC analysis was used together with multivariate analysis of variance (MANOVA). RESULTS: JPEG 27 and 53 reduced the file size down to 7% and 4.6% of the original respectively. ROC curve analysis showed no significant difference between image conditions (original, JPEG 27, and JPEG 53) at the same noise level. JPEG 27 and 53 had larger Az scores than their original counterparts at the same noise level. However, MANOVA showed that for depth estimation of enamel lesions JPEG 53 resulted in a higher observer error. CONCLUSIONS: Both JPEG 53 and 27 could reduce some of the adverse effect of noise from the image by removing high spatial frequencies. JPEG 53, resulting in a compression ratio of 1:21, does not compromise the diagnostic performance in general. JPEG 53 compression may however affect the ability to detect enamel lesions.     

Development of a digital image database for chest radiographs with and without a lung nodule: receiver operating characteristic analysis of radiologists' detection of pulmonary nodules

OBJECTIVE: We developed a digital image database (www.macnet.or.jp/jsrt2/cdrom_nodules.html ) of 247 chest radiographs with and without a lung nodule. The aim of this study was to investigate the characteristics of image databases for potential use in various digital image research projects. Radiologists' detection of solitary pulmonary nodules included in the database was evaluated using a receiver operating characteristic (ROC) analysis. MATERIALS AND METHODS: One hundred and fifty-four conventional chest radiographs with a lung nodule and 93 radiographs without a nodule were selected from 14 medical centers and were digitized by a laser digitizer with a 2048 x 2048 matrix size (0.175-mm pixels) and a 12-bit gray scale. Lung nodule images were classified into five groups according to the degrees of subtlety shown. The observations of 20 participating radiologists were subjected to ROC analysis for detecting solitary pulmonary nodules. Experimental results (areas under the curve, Az) obtained from observer studies were used for characterization of five groups of lung nodules with different degrees of subtlety. RESULTS: ROC analysis showed that the database included a wide range of various nodules yielding Az values from 0.574 to 0.991 for the five categories of cases for different degrees of subtlety. CONCLUSION: This database can be useful for many purposes, including research, education, quality assurance, and other demonstrations.     

Temporal subtraction for detection of solitary pulmonary nodules on chest radiographs: evaluation of a commercially available computer-aided diagnosis system

PURPOSE: To evaluate the usefulness of a commercially available computer-aided diagnosis (CAD) system that incorporates temporal subtraction for the detection of solitary pulmonary nodules on chest radiographs by readers with different levels of experience. MATERIALS AND METHODS: Sixty pairs of chest radiographs in 30 patients with newly detected solitary pulmonary nodules and 30 normal cases, all confirmed with serial chest computed tomography (CT), were obtained from screen-film or digital radiographic systems and were digitized (spatial resolution, 0.171 mm/pixel). Temporal subtraction images were produced with an iterative image-warping technique. Five chest radiologists and five residents evaluated both image sets for solitary nodules: set A, current and prior radiographs with temporal subtraction images, and set B, current and prior radiographs only. Assessment was performed with receiver operating characteristic (ROC) analysis of the images on a monitor (pixel size, 1,280 x 1,024) equipped with the system. The reading time needed by each reader was recorded in each case. RESULTS: For the chest radiologists, no statistically significant difference was found between set A (area under the ROC curve [A(z)] = 0.934) and set B (A(z) = 0.964). For the residents, however, observer performance in set A (A(z) = 0.907) was superior to that in set B (A(z) = 0.855) (P <.05). For both groups, the mean reading time per case for set A (chest radiologists, 16.7 seconds; residents, 15.7 seconds) was significantly (P <.05) shorter than that for set B (chest radiologists, 20.4 seconds; residents, 26.2 seconds). CONCLUSION: For the detection of solitary pulmonary nodules, the CAD system with temporal subtraction can promote efficiency for established chest radiologists and improvement in accuracy for less experienced readers.     

Evaluation of carotid artery stenosis: contrast-enhanced magnetic resonance angiography compared with conventional digital subtraction angiography.

OBJECTIVE: To compare retrospectively high-resolution contrast-enhanced magnetic resonance angiography with centric k-space filling and digital subtraction angiography in the assessment of degree of carotid artery stenosis. METHODS: Two neuroradiologists independently evaluated 14 carotid arteries (in 7 patients), and the degree of carotid stenosis determined was compared to calculate interobserver reliability. Thirty-six carotid arteries (in 18 patients) were then assessed with both contrast-enhanced magnetic resonance angiography and digital subtraction angiography. The degree of stenosis was determined by consensus, and the findings of the 2 modalities were compared. RESULTS: Close interobserver agreement was found with an intraclass correlation coefficient of 0.98 (95% confidence interval 0.95-0.99). Sensitivity of 86% and specificity of 91% were found for contrast-enhanced magnetic resonance angiography detection of surgically significant carotid stenosis compared with digital subtraction angiography. The Spearman rank correlation test also found a significant correlation (R(s) = 0.90, p < 0.001) in the comparison of the classifications of degree of carotid artery stenosis. CONCLUSION: Contrast-enhanced magnetic resonance angiography shows excellent correlation with digital subtraction angiography for the evaluation of carotid artery disease and has the potential to replace it in the assessment of degree of carotid artery stenosis.     

Temporal subtraction for the detection of hazy pulmonary opacities on chest radiography

OBJECTIVE: The purpose of this study was to evaluate the accuracy of temporal subtraction with a commercially available computer-assisted diagnosis system for the detection of multifocal hazy pulmonary opacities on chest radiographs, which are sometimes difficult to detect directly on chest radiographs. MATERIALS AND METHODS: Thirty healthy patients and 30 patients with new multifocal hazy pulmonary opacities that were confirmed by serial chest CT examinations were evaluated with and without temporal subtraction images. Chest radiographs were taken from either film-screen or digital radiography images and were digitized with a spatial resolution of 0.171 mm per pixel. Temporal subtraction images were produced by an iterative image-warping technique. We designed an observer performance study in which observers (six chest radiologists and four residents) indicated their confidence level for the presence or absence of hazy pulmonary opacities on two sets of images, current and previous radiographs only (set A), and current and previous radiographs with temporal subtraction images (set B). Receiver operating characteristic curves were generated. RESULTS: For chest radiologists, observer performance with set B (with temporal subtraction images; A(z) = 0.947) was superior to that with set A (without temporal subtraction images; A(z) = 0.916) (p < 0.05). For residents, no statistically significant difference was found between sets A and B. CONCLUSION: The temporal subtraction technique clearly improves diagnostic accuracy for the detection of multifocal hazy pulmonary opacities on chest radiographs, especially when the observers are experienced chest radiologists who have sufficient skill to evaluate the patient's condition as revealed on the images.     

Optimizing parameters for computer-aided diagnosis of microcalcifications at mammography

RATIONALE AND OBJECTIVES: The purpose of this study was to optimize selection of the mammographic features most useful in discriminating benign from malignant clustered microcalcifications. MATERIALS AND METHODS: The computer-aided diagnosis (CAD) system automatically extracted from digitized mammograms 13 quantitative features characterizing microcalcification clusters. Archival cases (n = 134; patient age range, 31-77 years; mean age, 56.8 years) with known histopathologic results (79 malignant, 55 benign) were selected. Three radiologists at three facilities independently analyzed the microcalcifications by using the CAD system. Stepwise discriminant analysis selected the features best discriminating benign from malignant microcalcifications. A classification scheme was constructed on the basis of these optimized features, and its performance was evaluated by using receiver operating characteristic (ROC) analysis. RESULTS: Six of the 13 variables extracted by the CAD system were selected by stepwise determinant analysis for generating the classification scheme, which yielded an ROC curve with an area (Az) of 0.98, specificity of 83.64%, positive predictive value of 89.53%, and accuracy of 91.79% for 98% sensitivity. When patient age was an additional variable, the scheme's performance improved, but this was not statistically significant (Az = 0.98). The ROC curve of the classifier (without age as an additional variable) yielded a high Az of 0.96 for patients younger than 50 years and an even higher (P < .02) Az of 0.99 for those 50 years or older. CONCLUSION: Stepwise discriminant analysis optimized performance of a classification scheme for microcalcifications by selecting six optimized features. Scheme performance was significantly (P < .02) higher for women 50 years or older, but the addition of patient age as a variable did not produce a statistically significant increase in performance.     

ROC analysis of detection of interval changes in interstitial lung diseases on digital chest radiographs using the temporal subtraction technique

PURPOSE: To demonstrate the clinical usefulness of a temporal subtraction technique for the detection of interval changes in various interstitial lung diseases on digital chest radiographs. MATERIALS AND METHODS: One hundred pairs of chest radiographs in 34 patients (63 with and 37 without interval changes) with various interstitial lung diseases were selected. All cases were confirmed by serial chest computed tomography (CT) and ascertained by radiologists. All chest radiographs were obtained with a computed radiography (CR) system, and temporal subtraction images were produced with an iterative image-warping technique. Four radiologists and two thoracic physicians provided confidence levels for interval changes in interstitial lung diseases with and without temporal subtraction. Their performances with and without temporal subtraction were evaluated by means of receiver operating characteristic (ROC) analysis using a sequential test. RESULTS: The area under the ROC curve (Az) values of six observers obtained with and without temporal subtraction were 0.90 and 0.78, respectively. Results showed that the detection of interval changes in interstitial lung diseases was significantly improved by the use of temporal subtraction images compared with CR images alone(P = 0.002). Furthermore, the high detection rate was achieved with temporal subtraction images regardless of the subtlety and location of interval changes. CONCLUSION: Temporal subtraction improved the diagnostic accuracy of radiologists in detecting interval changes in interstitial lung diseases on chest radiographs. It was also useful for cases of multiple interval changes.     

Detection of monitoring materials on bedside chest radiographs with the most recent generation of storage phosphor plates: dose increase does not improve detection performance

PURPOSE: To evaluate the performance of the most recent generation of storage phosphor plates for the detection of low-contrast catheter material on bedside chest radiographs. MATERIALS AND METHODS: In 10 patients in the intensive care unit, bedside chest radiographs were obtained with a 400-speed conventional screen-film system and with storage phosphor plates with exposure levels comparable to a 200-, 400-, or 800-speed conventional system. The chest radiograph was divided into 20 regions, 60% of which were superimposed with low-contrast catheter fragments. Six observers independently assessed the presence of catheter fragments by using a receiver operating characteristic (ROC) methodology. RESULTS: Detection performance (mean area under the ROC curve [Az]) with the storage phosphor plates was significantly superior to that with the screen-film system (Az = 0.76) at all three dose levels (Az = 0.88, 0.87, and 0.83 for 200-, 400-, and 800-speed doses, respectively; P <.05). Increasing the dose to a 200-speed system did not significantly increase detection performance compared with that with the 400-speed digital radiographs (Az = 0.88 vs 0.87). Dose reduction to 800 speed significantly deteriorated the detection performance (Az = 0.83) compared with that with the 400- and 200-speed digital radiographs, respectively. CONCLUSION: The most recent generation of storage phosphor plates is superior to a 400-speed screen-film system for the detection of catheter material, even at an exposure level of 800 speed.     

Comparative diagnostic performance of TACT slices and its multiple source images: an in vitro study

OBJECTIVE: To compare the diagnostic performances provided by tuned aperture computed tomography (TACT) slices and the multiple images that they originate from in the detection of primary caries on the proximal surfaces of posterior teeth. STUDY DESIGN: Eight direct digital radiography images of each of 40 posterior teeth were acquired with a digital sensor. These source images were used to generate TACT slices of the teeth. Eight trained observers were calibrated in the use of both TACT slices and the eight source images of each tooth. They were asked to assess the presence/absence of proximal caries in the teeth using a 5-point rating scale. Observers' assessments were compared with the ground truth provided by histological examination of tooth sections. Areas under the receiver operating characteristic (ROC) curves (Az) were calculated for each combination of observer and image modality. Analysis of variance (ANOVA) was used to test the ROC values for potential statistical differences. RESULTS: Mean ROC Az values were 0.760 for TACT slices and 0.771 for its multiple source images for the detection of primary proximal caries. ANOVA showed no statistically significant differences either between modalities (P = 0.656) or between observers (P = 0.851). CONCLUSION: TACT slices and its multiple source images provide comparable diagnostic performance for proximal caries detection.     

Detection of subtle lung nodules: relative influence of quantum and anatomic noise on chest radiographs

PURPOSE: To assess the relative influence of quantum mottle and structured lung patterns (anatomic noise) on the detection of subtle lung nodules on chest radiographs. MATERIALS AND METHODS: Sixty 8 x 8-cm lung pattern images were extracted from digital chest radiographs in healthy individuals. Sixty quantum mottle images of the same size and quantum noise level were extracted from uniformly exposed digital radiographs. Simulated nodules with various peak contrast-diameter products (CD) that emulated subtle tissue-equivalent lung nodules were numerically superimposed at the center on three-fourths of the images. Printouts were independently viewed and scored by five experienced radiologists. The area under the receiver operating characteristic curve (Az) was estimated as a measure of the detectability of the nodules. RESULTS: At a fixed observer performance level (e.g., Az = 0.8), much smaller and lower-contrast nodules were detected on quantum mottle images (1-mm diameter, CD = 0.01 mm), compared with those on anatomic images (4.5-mm diameter, CD = 0.20 mm). The findings generally agreed with the signal-to-noise ratio calculations based on statistical observer models. CONCLUSION: The detection of subtle lung nodules on chest radiographs is limited by anatomic noise.     

双能量数字减影胸片对于不同肺野区域内结节性病变的检出差异(ROC分析)

目的　评价双能量数字减影胸片和常规DR胸片对于不同肺野区域内结节性病变的检出差异。方法　 2 0名正常成年志愿者前胸粘贴模拟结节 ,拍摄双能量数字减影正位胸片 ,应用ROC分析比较常规DR胸片与减影后软组织图像的诊断结果。结果　在双上、中肺野 ,软组织图像的曲线下面积大于常规DR胸片 ;在双上肺野、双中肺野外带 2种方法具有显著性差异。结论　双能量数字减影技术对双上肺野及双中肺野外带胸部结节性病变的检出具有优势 ,故应结合减影及常规胸片 ,以助诊断。     

Diagnostic accuracy of two software modalities for detection of caries lesions in digital radiographs from four dental systems

OBJECTIVE: To compare the caries diagnostic accuracy of two software modalities used in the assessment of digital radiographs obtained with four different dental systems, and to evaluate whether the software used for image assessment influenced the mutual comparison of those four dental systems relating to their caries diagnostic accuracy. METHODS: Under in vitro and standardized conditions 122 teeth (with 228 unrestored approximal and 99 occlusal surfaces) were radiographed in blocks of 3 test teeth and 2 non-test teeth using two storage phosphor plate systems: Digora (Soredex, Helsinki, Finland) and DenOptix (Gendex, Dentsply, Milan, Italy) and two charge coupled device (CCD)-based sensor systems: Dixi (Planmeca, Helsinki, Finland) and Sidexis (Sirona, Bensheim, Germany). The images were displayed and examined in two software modalities: their own dedicated software and a general software. Three observers examined all images for the presence of approximal enamel and dentine and occlusal dentine caries lesions using a 5-point confidence scale. The true presence of caries was validated by ground section histology. The diagnostic accuracy of the software modalities was expressed as ROC curve areas (A(z)) and differences between modalities were tested by paired t-test. Comparison of systems was analysed by post hoc t-test. RESULTS: Results of approximal and occlusal surfaces assessed together revealed nearly identical mean A(z) with the two software modalities on images obtained with the Digora (A(z)=0.71) and DenOptix (A(z)=0.72) systems. On Dixi images the mean A(z) was 0.75 using the system's own software and 0.73 using the general software. On Sidexis images the corresponding mean A(z)s were 0.79 and 0.75. None of those differences were significant. CONCLUSION: No significant difference in caries diagnostic accuracy was found between two software modalities used for examination of digital radiographs obtained with four different digital systems, and the software modality did not influence the mutual rank of the four systems relating to their diagnostic accuracy.     

Improved detection of lung cancer arising in diffuse lung diseases on chest radiographs using temporal subtraction

RATIONALE AND OBJECTIVES: The purpose of this study was to evaluate the usefulness of temporal subtraction for the detection of lung cancer arising in pneumoconiosis, idiopathic pulmonary fibrosis, and pulmonary emphysema. MATERIALS AND METHODS: Fifteen cases of lung cancer arising in diffuse lung diseases, including three cases of pneumoconiosis, six of idiopathic pulmonary fibrosis, and six of pulmonary emphysema, were evaluated. Pathologic proof was obtained by surgery or transbronchial lung biopsy. The average interval between previous and current radiographs was 356 days (range, 31-947 days). All chest radiographs were obtained with a computed radiography system, and temporal subtraction images were produced by subtracting of a previous image from a current one with a nonlinear image-warping technique. The effect of the temporal subtraction image was evaluated by observer performance study with receiver operating characteristic analysis. RESULTS: The average observer performance with temporal subtraction was significantly improved (Az = 0.935) compared with that without temporal subtraction (Az = 0.857, P < .0001). CONCLUSION: The temporal subtraction technique is useful for the detection of lung cancer arising in pneumoconiosis, idiopathic pulmonary fibrosis, and pulmonary emphysema.     

"Single-exposure" dual energy digital radiography in the detection of pulmonary nodules and calcifications

We studied the detectability of mineralized and non-mineralized simulated pulmonary nodules with dual energy digital radiography. "Soft tissue" and "bone" images (pixel size = 0.2 mm, 10 bits deep) were obtained with subtraction image processing after a single simultaneous exposure (100 kVp, 8 mAs, 17 mR skin exposure dose) of two storage phosphors with an interleaved 0.9 mm copper wafer. Three classes of paraffin-based nodules (0.5 to 3.0 cm) of varying mineral concentration (0, 120 and 190 mg/cm3 K2HPO4) were randomly positioned on the chest wall of two healthy volunteers to simulate calcified and non-calcified nodules. The average receiver operating characteristics (ROC) area of six readers (n = 2880 observations) showed that digital "bone" images (ROC area: 0.77 +/- 0.03) were significantly better (P less than 0.04) than conventional radiographs (OC Film, Lanex medium screens, 141 kVp, 19 mR skin exposure dose) (ROC area: 0.71 +/- 0.05) in detecting calcification in nodules. The unsubtracted digital images of lower kilovoltage were not superior to the 141 kVp conventional radiographs in a subgroup of two readers (ROC area: 0.73 +/- 0.02). Digital "soft tissue" images were equivalent to conventional chest radiographs in detecting soft tissue pulmonary nodules (ROC areas: 0.92 +/- 0.04 and 0.92 +/- 0.05, respectively.