Digital skeletal radiography: spatial resolution requirements for detection of subperiosteal resorption

Forty direct-magnification (2:1 enlargement) radiographs showing various severities of subperiosteal resorption and 40 normal studies were selected and digitized. Images were processed to produce varying resolution, from 1.42 to 11.4 Ip/mm, corresponding to pixel sizes ranging from 0.04 to 0.32 mm. The conventional and digitized images were evaluated by six radiologists giving their decision confidence on a graded scale. Receiver operating characteristic analyses were performed from these data to compare the digital images with the conventional films. The results show significant improvement in diagnostic accuracy as pixel size decreases to the level of 0.08 mm. Digital images with pixel sizes of 0.04 mm (11.4 Ip/mm) were not significantly different from the magnification radiographs in terms of observer performance. In conclusion, for high-resolution skeletal imaging as needed for detection of subperiosteal resorption, spatial resolution of 5.7 Ip/mm or less resulted in a significant loss of diagnostic accuracy, as compared with conventional films.     

Clinical evaluation of life size image of Fuji computed radiography for detection of diffuse interstitial lung diseases]

To evaluate the diagnostic accuracy of Fuji Computed Radiography (FCR) in the detection of interstitial pulmonary infiltrates, FCR life-size images at a pixel size of 0.1 mm were compared with conventional radiographs taken on the same day. Seventeen radiologists assessed the radiographs and FCR images of 56 cases, including 39 cases of various interstitial lung diseases such as interstitial pneumonia, pulmonary abnormalities associated with collagen disease, sarcoidosis, multiple pulmonary metastases, diffuse panbronchiolitis and pulmonary emphysema, and 17 normal controls. All of the pulmonary abnormalities were confirmed by high resolution CT. Observer performance tests were carried out using receiver operating characteristic analysis. In 21 cases of increased pulmonary density revealed by high resolution CT, FCR was significantly superior to conventional radiographs in the detection of reticular or linear shadows. In 11 cases of subtle interstitial abnormalities, there was no difference between FCR and conventional radiographs in the detection of any pulmonary abnormality, ground-glass opacities and reticular or linear shadows. There was also no difference between the two images in the detection of diffuse nodular shadow and pulmonary emphysema. These results indicate that FCR life-size images at a pixel size of 0.1 mm are useful for the detection of diffuse interstitial lung diseases.     

Comparative studies on physical characteristics and clinical efficacy of conventional and digitized chest radiographs

Comparative studies were performed between digitized and conventional radiographs of the chest in terms of their physical characteristics and diagnostic efficacy. The purpose of these studies is to confirm the diagnostic capability of digitized image whether it can use for primary diagnosis in routine works. The results of two studies show good correlation each other. It is strongly suggested that the conventional chest radiographs should be digitized with 100 microns pixel in 12 bit density resolution.     

Detection of lung nodules on digital chest radiographs: potential usefulness of a new contralateral subtraction technique

PURPOSE: To evaluate the potential usefulness of a contralateral subtraction technique developed for radiologists' performance in the detection of subtle lung nodules on chest radiographs. MATERIALS AND METHODS: Fifty chest radiographs (25 normal and 25 abnormal with a subtle lung nodule) that were digitized with a 0.175-mm pixel size and 4,096 gray levels were used. Twelve radiologists (10 attending and two residents) participated in observer tests and read both original and contralateral subtraction images with a sequential testing method. Radiologists' performance was evaluated by means of receiver operating characteristic analysis with use of a continuous rating scale. The beneficial and detrimental effects of the contralateral subtraction technique on the radiologists' performance were also evaluated. RESULTS: The area under the receiver operating characteristic curve values obtained without and with contralateral subtraction images were 0.926 and 0.962, respectively. Results indicated that the contralateral subtraction images significantly (P <.05) improved diagnostic accuracy, particularly for radiologists with limited experience. CONCLUSION: The contralateral subtraction technique can assist radiologists in the correct identification of subtle lung nodules on chest radiographs.     

Computerized analysis of the likelihood of malignancy in solitary pulmonary nodules with use of artificial neural networks

PURPOSE: To develop a computer-aided diagnostic scheme by using an artificial neural network (ANN) to assist radiologists in the distinction of benign and malignant pulmonary nodules. MATERIALS AND METHODS: Fifty-six chest radiographs of 34 primary lung cancers and 22 benign nodules were digitized with a 0.175-mm pixel size and a 10-bit gray scale. Eight subjective image features were evaluated and recorded by radiologists in each case. A computerized method was developed to extract objective features that could be correlated with the subjective features. An ANN was used to distinguish benign from malignant nodules on the basis of subjective or objective features. The performance of the ANN was compared with that of the radiologists by means of receiver operating characteristic (ROC) analysis. RESULTS: Performance of the ANN was considerably greater with objective features (area under the ROC curve, Az = 0.854) than with subjective features (Az = 0.761). Performance of the ANN was also greater than that of the radiologists (Az = 0.752). CONCLUSION: The computerized scheme has the potential to improve the diagnostic accuracy of radiologists in the distinction of benign and malignant solitary pulmonary nodules.     

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.     

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).     

Pulmonary nodule detection of chest phantom with CRT images--comparison with conventional radiography (film-screen system) and FCR (Fuji Computed Radiography) hardcopy

Conventional Radiography, Fuji Computed Radiography (FCR) hardcopy and CRT images were evaluated about the detectability of pulmonary nodule using the chest phantom. Conventional and digitized chest radiographs (FCR) were used, including 45 normal cases and 45 abnormal cases with a variety pulmonary nodule. Observer performance tests were conducted to compare the effects on diagnostic accuracy of Conventional Radiography, FCR hardcopy and CRT images, and diagnostic accuracy was determined with receiver operating characteristic (ROC) analysis. ROC study was performed in which six radiologists were asked to locate nodule on three modalities. Two CRT monitors were used to observed CRT images. The left side CRT monitor was divided into two parts and displayed two images which were done as same image processing as FCR hardcopy. The right side CRT monitor was divided into four parts and displayed four images as a subsidiary diagnosis. The upper two images were displayed to diagnose the nodule of cardiac and diaphragmatic area, and lower two images were displayed to diagnose the nodule of the lung field. The results were summarized as follows: 1) CRT images were superior in sensitivity (78.5%) to the others, and FCR hardcopys were superior in specificity (95.9%). 2) About the accuracy of 5 and 8 mm in diameter nodule detection, there was no significant difference among three modalities. 3) Diagnostic accuracy of 3 mm in diameter nodule detection was significantly greater with digitized radiographs (FCR 44.4%, CRT images 54.4%) than with conventional radiograph (17.7%).(ABSTRACT TRUNCATED AT 250 WORDS)     

Digital gastrointestinal imaging: the effect of pixel size on detection of subtle mucosal abnormalities

Five radiographs of double-contrast colon examinations demonstrating subtle mucosal changes of inflammatory bowel disease and five radiographs of healthy colonic mucosa were selected and digitized to four levels of resolution. Pixel sizes of 0.1 mm, 0.2 mm, 0.4 mm, and 0.8 mm were used. Ten radiologists interpreted the images, which were displayed on laser-printed film. Analysis of variance with repeated measures was performed and receiver operator characteristic curves were determined. The results demonstrate that the sensitivity in detecting subtle mucosal abnormalities improved as the resolution improved, with the best sensitivity at the highest resolution; more experienced readers detected details well even at the poorer levels of resolution; the resolution necessary for successfully evaluating the colonic mucosa was lower than expected; and given low noise levels, the matrix size used in conventional television fluoroscopy would be adequate for mucosal evaluation.     

Pneumothorax and other lung diseases: effect of altered resolution and edge enhancement on diagnosis with digitized radiographs

Prior studies have shown that pneumothorax is one of the more difficult entities to diagnose with digitized radiography. This study was designed to test whether increasing resolution from 1.25 to 2.5 line pairs per millimeter (lp/mm) and image processing (edge enhancement from unsharp masking) would increase accuracy and confidence in the diagnosis of pneumothorax, as well as normal cases and other forms of lung disease. Conventional radiographs were digitized with use of a laser reader and then reformatted as film hard copy. Eleven observers read 35 cases reformatted in three different ways (1.25 lp/mm, 2.5 lp/mm, 1.25 lp/mm unsharp mask). The images with finer resolution (2.5 lp/mm) and unsharp mask images were superior to those with coarser resolution (1.25 lp/mm) for the diagnosis of pneumothorax. There was no difference in diagnostic accuracy for normal patients. For abnormalities other than pneumothorax, the unsharp mask images were significantly worse. Confidence in the diagnosis of pneumothorax and other abnormalities was highest with the finest resolution (2.5 lp/mm).     

ROC assessment of compressed wrist radiographs

The aim of this paper is to validate a compression scheme applied on a medical image database of digitized wrist radiographs. The compression scheme adapts itself to local statistical properties of the images. The diagnostic quality of the reconstructed images is evaluated using a ROC protocol involving five medical experts. The results of this evaluation enable us to validate the compression scheme on this database with a compression ratio of 40 (0.2 bits per pixel).     

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 CRT images of digitized film angiographs

X-ray sheet film images of the test chart, the vascular phantom and angiography were digitized at sampling pitch of 0.2 mm and 0.15 mm using film digitizer TFR-01 (Toshiba) and transferred to a device for image storage and display system with 1635-line display monitor (TDF-500AS, Toshiba). Comparison of image qualities between film- and CRT-images was performed in fundamental and clinical studies. Resolution of the test chart image of conventional radiography was worse on CRT than on the original film, although it was improved when film image was digitized at resolution of 0.15 mm/pixel in comparison with that at resolution of 0.2 mm/pixel. Moiré stripes which occurred due to interference were found on CRT images taken using a grid technique. On CRT images of X-ray sheet film using direct magnification technique moiré stripes were not produced because of non grid technique, and the resolution approached that of the original film. In the study using vascular phantom, the optimal image on CRT could be obtained by various image processing procedures, and image quality on CRT with resolution of 0.15 mm approached that of original film. In case of direct magnification CRT images were superior to film images. Subtraction image of the vascular phantom at resolution of 0.2 mm/pixel was obtained on CRT and compared with film subtraction image. On conventional subtraction CRT image moiré stripes impaired the image quality in comparison with the film subtraction. However, magnification subtraction image of the vascular phantom on CRT was superior to the film subtraction. The results obtained in the test chart studies and phantom studies were also confirmed in clinical studies using various kind of angiograms. In addition, ROC study using clinical angiograms showed no significant statistical differences between the original film and CRT image even with 0.2 mm matrix size. Angiographic image on CRT at resolution of 0.15 mm/pixel or less is available for clinical use in place of conventional film image.     

Subperiosteal resorption: effect of full-frame image compression of hand radiographs on diagnostic accuracy.

Image compression is essential to handle a large volume of digital images, including computed tomographic, magnetic resonance, computed radiographic, and digitized images in a digital radiology operation. Developed during the past few years, full-frame bit allocation performed with the cosine transform technique has been proved to be an excellent irreversible image compression method. This article describes the effect, on the accuracy of diagnosis of subperiosteal resorption, of using the hardware compression module to produce hand radiographs. Receiver operating characteristic analysis of the interpretation of 71 radiographs by five observers demonstrated that there is no statistically significant difference in diagnostic accuracy between the original radiographs and compressed and reconstructed images obtained with a compression ratio as high as 20:1.     

Evaluation of an automated adaptive unsharp masking technique in digital chest radiographs]

We are developing a fully automated adaptive unsharp masking technique with parameters that depend on the regional image features of digital chest radiographs. Regions such as the lung fields, retrocardiac area, and spine have extremely different texture patterns and optical densities on chest radiographs. Therefore, it is necessary to enhance the image contrast of each region by an optimum parameter for the regional image. In this study, a chest radiograph was automatically divided into three segments (lung field, retrocardiac area, and spine) by histogram analysis of pixel values. Then, the lung field and retrocardiac area were selectively enhanced with a small mask size and mild weighting factors that had been previously determined as optimum parameters. The spine was enhanced with a large mask size and adequate weighting factors. An observer performance test indicated that this technique provides excellent diagnostic accuracy for simulated nodules over the mediastinum and diaphragm without sacrificing diagnostic accuracy for nodules over the lung field. We believe that this adaptive processing technique may have the potential to be a useful aid for the diagnosis of chest radiographs.     

Linear and logarithmic subtraction for detecting enamel subsurface demineralization

OBJECTIVE: To compare the diagnostic performance of linear and logarithmically contrast-enhanced subtraction images, acquired with digital and digitized radiographs, in detecting approximal enamel subsurface demineralization. METHODS: Fifty caries-free human third molars were immersed in a demineralizing solution for 60, 75, 90, and 120 days, in order to induce artificial enamel subsurface demineralization. The teeth were coated with nail varnish, leaving only a circular window of approximately 7 mm2 in one of the approximal surfaces, allowing contact with the solution. Standardized radiographs of the teeth were taken prior to and after the demineralization period with three digital systems, CygnusRay MPS, DenOptix and DIGORA, and InSight film. Conventional, digital and digitized radiographs were assessed by three experienced radiologists. Linear and logarithmically contrast-enhanced subtraction images were acquired and then examined by a fourth independent radiologist. For the validation of the radiographic diagnosis, the enamel test areas were submitted to Knoop microhardness profiling. Radiographic interpretation data was evaluated using ROC analysis. The areas under the ROC curves (Az) were compared by the chi-squared test. The level of significance was set at P=0.05. RESULTS: No significant differences were found between linear and logarithmically contrast- enhanced subtraction images, acquired with the four studied modalities: CygnusRay MPSlinear (Az=0.95), CygnusRay MPSlog (Az=0.98), DenOptixlinear (Az=0.97), DenOptixlog (Az=0.99), DIGORAlinear (Az=0.98), DIGORAlog (Az=0.98), digitized radiographylinear (Az=0.99), digitized radiographylog (Az=0.99). CONCLUSION: Linear and logarithmically contrast-enhanced subtraction images, acquired with digital and digitized radiographs, were diagnostically comparable for assessing enamel subsurface demineralization.     

Automated diagnosis of congenital dislocation of the hip.

A study of the automated diagnosis of luxatio coxae congenita (LCC) was performed to establish an automated screening system for hip radiographs. A specific parameter with high diagnostic accuracy was selected by the use of information theory. Pattern recognition programs were written to extract the parameter from digitized hip radiographs. Parameter measurement was performed on 10 radiographs and compared with manual measurements. Results showed good agreement with measurements obtained by specialists. This study confirms the possibilities of automated diagnosis of LCC.     

Digital subtraction radiography in artificial recurrent caries detection.

The diagnostic accuracy of digital subtraction radiography in detection of artificial recurrent caries lesions was assessed in this project. The use of digital subtraction radiography has been shown to markedly increase the accuracy of the detection of destruction in the periodontal bone, but the method has not been evaluated in secondary caries detection. Defects of three different sizes, simulating recurrent caries, were sequentially prepared in the interproximal cavity preparation margins of 28 teeth. Two composite restorative materials with different radiographic densities were used as posterior restorations, and a radiograph was obtained of each defect size and restorative material. The radiographs were digitized and subtracted from the reference images, and the conventional radiographs and the subtraction images were evaluated by seven observers. The data were analysed with ROC statistics. Subtraction radiography was found to be superior to conventional radiography in recurrent caries detection, mainly by reducing the false-positive diagnoses. The radiopacity of the restorative material had a significant effect on accuracy with conventional but not with subtraction radiography.     

Simulated bone erosions in a hand phantom: detection with conventional screen-film technology versus cesium iodide-amorphous silicon flat-panel detector

PURPOSE: To assess the diagnostic performance of an active-matrix flat-panel x-ray detector for reduced-dose imaging of simulated arthritic lesions. MATERIALS AND METHODS: A digital x-ray detector based on cesium iodide and amorphous silicon technology with a panel size of 43 x 43 cm, matrix of 3,000 x 3,000 pixels, pixel size of 143 micrometer, and digital output of 14 bits was used. State-of-the-art screen-film radiographs were compared with digital images obtained at doses equivalent to those obtained with system speeds of 400, 560, and 800. The phantom was composed of a human hand skeleton on an acrylic plate with drilled holes simulating bone erosions of different diameters and depths. Results of four independent observers were evaluated with receiver operating characteristic curve analysis. RESULTS: The cesium iodide and amorphous silicon detector resulted in better diagnostic performance than did the screen-film combination, with the dose being the same for both modalities (P <.05). For digital images obtained at reduced doses, no significant differences were found. CONCLUSION: The improved diagnostic performance with digital radiographs obtained with the cesium iodide and amorphous silicon detector suggests that this detector technology holds promise in terms of dose reduction for specific diagnostic tasks, without loss of diagnostic accuracy.     

Dependence of radiomic features on pixel size affects the diagnostic performance of radiomic signature for the invasiveness of pulmonary ground-glass nodule

Objective:To investigate the effect of reducing pixel size on the consistency of radiomic features and the diagnostic performance of the downstream radiomic signatures for the invasiveness for pulmonary ground-glass nodules (GGNs) on CTs.Methods:We retrospectively collected the clinical data of 182 patients with GGNs on high resolution CT (HRCT). The CT images of different pixel sizes (0.8mm, 0.4mm, 0.18 mm) were obtained by reconstructing the single HRCT scan using three combinations of field of view and matrix size. For each pixel size setting, radiomic features were extracted for all GGNs and radiomic signatures for the invasiveness of GGNs were built through two modeling pipelines for comparison.Results:The study finally extracted 788 radiomic features. 87% radiomic features demonstrated inter pixel size variation. By either modeling pipeline, the radiomic signature under small pixel size performed significantly better than those under middle or large pixel sizes in predicting the invasiveness of GGNs (p’s value <0.05 by Delong test). With the independent modeling pipeline, the three pixel size bounded radiomic signatures shared almost no common features.Conclusions:Reducing pixel size could cause inconsistency in most radiomic features and improve the diagnostic performance of the downstream radiomic signatures. Particularly, super HRCTs with small pixel size resulted in more accurate radiomic signatures for the invasiveness of GGNs.Advances in knowledge:The dependence of radiomic features on pixel size will affect the performance of the downstream radiomic signatures. The future radiomic studies should consider this effect of pixel size.