Efficacy of digital radiography for the detection of pneumothorax: comparison with conventional chest radiography.

As part of our continuing evaluation of the clinical applicability of digital radiography, we compared the abilities of radiologists to detect pneumothoraces on conventional chest radiographs with their performances when using three formats of digitally obtained images. Twenty-three frontal-view chest radiographs with pneumothoraces and 22 other chest radiographs, either normal or showing miscellaneous abnormalities, were interpreted by five experienced radiologists in each of four formats: conventional film-screen chest radiographs, small-format (17.8 x 21.6 cm) computed radiographs, large-format (35.6 x 43.1 cm) computed radiographs, and digital images viewed on an interactive electronic workstation. The receiver-operating-characteristic curve areas for each observer for the four types of images were compared by a z test on a critical ratio, and the mean sensitivity and specificity values were compared by the sign rank test. The mean areas under the receiver-operating-characteristic curves ranged from 0.869 for the digital workstation to 0.915 for film-screen images. The differences observed among formats were not statistically significant. Mean specificities also were not significantly different, ranging from 0.90 for large-format computed radiographs to 0.96 for the digital workstation. Mean sensitivity ranged from 0.65 for the digital workstation to 0.82 for film-screen images. Radiologists interpreting digital workstation images were significantly less sensitive in detecting pneumothoraces than with film-screen and small-format computed images (p = .06). In this study, radiologists detected pneumothoraces equally well on conventional film-screen radiographs and digital images printed on film; however, they detected pneumothoraces less well on electronic viewing consoles. This latter finding reflects an important practical difference in the working behavior of radiologists interacting with a digital workstation.     

Data compression: effect on diagnostic accuracy in digital chest radiography

High-resolution digital images make up very large data sets that are relatively slow to transmit and expensive to store. Data compression techniques are being developed to address this problem, but significant image deterioration can occur at high compression ratios. In this study, the authors evaluated a form of adaptive block cosine transform coding, a new compression technique that allows considerable compression of digital radiographs with minimal degradation of image quality. To determine the effect of data compression on diagnostic accuracy, observer tests were performed with 60 digitized chest radiographs (2,048 x 2,048 matrix, 1,024 shades of gray) containing subtle examples of pneumothorax, interstitial infiltrate, nodules, and bone lesions. Radiographs with no compression, with 25:1 compression, and with 50:1 compression ratios were presented in randomized order to 12 radiologists. The results suggest that, with this compression scheme, compression ratios as high as 25:1 may be acceptable for primary diagnosis in chest radiology.     

Computed radiography in musculoskeletal imaging: state of the art.

Computed radiography is a 2K x 2K x 10 bit digital radiographic system that replaces the film-screen combination with a photo-stimulable phosphor plate. The advantages of this relatively new technology include linear detector response, improved detector efficiency, and digital processing capabilities. Musculoskeletal applications benefit significantly from these attributes, which result clinically in the ability to reduce both radiation dose and number of exposures. Studies of observers' performance have shown no statistically significant difference in diagnostic accuracy between film-screen and computed radiographic musculoskeletal images. Computed radiography is particularly useful in the evaluation of the musculoskeletal system in traumatized patients with portable radiographs, spine radiographs, scoliosis studies, and depiction of soft-tissue abnormalities. Limitations include change in image format and size, high cost, decreased spatial resolution, restricted throughput, increased perception of noise, and new artifacts that must be recognized. Spatial resolution limitations of computed radiography in identification of fine detail information can be improved by using magnification techniques. Radiation dose reduction with an exposure decrease of 25-50% can be achieved without loss of diagnostic accuracy, although this depends on the examination and the abnormality. An interactive workstation is important in the use of a computed radiographic system with capabilities to adjust display parameters to best depict images and disease. We conclude that computed radiography is an alternative to film-screen radiography without significant differences in diagnostic quality in the evaluation of musculoskeletal images.     

Evaluation of a quadtree-based compression algorithm with digitized urograms

The effect of a quadtree-based data-compression algorithm on the diagnostic yield in digitized radiographs was studied for 100 urograms. Each image was digitized and reviewed at nine decreasing compression ratios ranging from 90:1 to 4.2:1, followed by a review of the uncompressed digital images. Four radiologists independently reviewed the digitized images and the original radiographs and agreed on a reference standard of 201 findings. Sensitivity, measured by the number of findings noted on the compressed digital images, decreased with increasing compression ratios at and above the 11:1 level. No loss of sensitivity was noted with a compression ratio of 4.2:1. Sensitivity decreased more precipitously for calcifications than for soft-tissue masses. Only a minimal loss of sensitivity for bilateral renal function was noted, even with high compression ratios. False-positive rates were unaffected by compression. The authors conclude that quadtree compression ratios of 11:1 and higher may result in loss of sensitivity in clinically relevant findings.     

Improved detection of lung nodules by using a temporal subtraction technique

PURPOSE: To evaluate the effect of a temporal subtraction technique for digital chest radiography with regard to the accuracy of detection of lung nodules. MATERIALS AND METHODS: Twenty solitary lung nodules smaller than 30 mm in diameter, including 10 lung cancers and 10 benign nodules, were used. The nodules were grouped subjectively according to their subtlety. For non-nodular cases, 20 nodules without perceptible interval changes were selected. All chest radiographs were obtained by using a computed radiographic system, and temporal subtraction images were produced by using a program developed at the University of Chicago. The effect of the temporal subtraction image was evaluated by using an observer performance study, with use of receiver operating characteristic analysis. RESULTS: Observer performance with temporal subtraction images was substantially improved (A(z) = 0.980 and 0.958), as compared with that without temporal subtraction images (A(z) = 0.920 and 0.825) for the certified radiologists and radiology residents, respectively. The temporal subtraction technique clearly improved diagnostic accuracy for detecting lung nodules, especially subtle cases. CONCLUSION: The temporal subtraction technique is useful for improving detection accuracy for peripheral lung nodules on digital chest radiographs.     

Compression of radiological images with 512, 1,024, and 2,048 matrices

A comprehensive study was performed using the full-frame bit-allocation compression technique on 78 radiological images, including digitized radiographs, computed radiographs, and computed tomography images. Each radiograph was digitized to 2,048 X 2,048 X 10, 1,024 X 1,024 X 10, and 512 X 512 X 10 matrices, respectively, with a laser scanner. Five compression ratios were used to compress each image, and reconstructed images from each compressed data set were obtained. Altogether, the authors studied 842 images, including the original and compressed-reconstructed images and the images obtained from the difference between the original and the reconstructed images. The results indicate that acceptable compression ratios for 2,048, 1,024, and 512 matrices are 25:1, 20:1, and 10:1, respectively, based on a mean-square error of 0.02%.     

A comparison of conventional intra-oral radiography and computer imaging techniques for the detection of proximal surface dental caries.

The detection of proximal surface caries by the visual interpretation of bitewing radiographs is known to be relatively inaccurate. The present study was designed to examine whether computer image processing could improve the diagnostic accuracy. A computer-aided, software-driven, TV-based system was used to digitize conventional radiographs and digitally process the images using histogram equalization and grey-scale inversion to enhance the images. The computer-enhanced images were compared with conventional intra-oral radiographs for the detection of proximal surface caries using receiver operating characteristic analysis. The results indicate that the digital image processing techniques used did not improve the diagnostic accuracy of dental radiographs. No significant difference in diagnostic accuracy could be detected between the non-enhanced digital images and conventional film-based images for the detection of proximal surface caries.     

Digital imaging with a photostimulable phosphor in the chest of newborns

To evaluate use of a digital photostimulable phosphor imaging system in the neonatal nursery, 150 newborns were divided into three groups of 50. In the first two groups, screen-film and computed radiographs of the chest were obtained at the same radiation exposure; in the third group, computed radiographs were obtained with a 50% dose reduction (half-exposure computed radiographs). All images were blindly evaluated by three readers who scored the quality of visualization of the mediastinum, lung, bone, soft tissues, and endotracheal and nasogastric tubes, and also image density. No statistical differences in visualization of tubes existed among the three groups. Visualization of the mediastinum, lung, bones, and soft tissues was statistically significantly better on computed radiographs than on half-exposure computed radiographs; visualization of the lungs, bones, and soft tissues was statistically significantly better on screen-film radiographs than half-exposure computed radiographs. Image density was statistically better on computed and half-exposure computed radiographs than on screen-film radiographs.     

Traditional and digital urography compared. The authors' own experience

A computed radiographic system for generating and archiving digital radiographic images was employed in ivp. The system produces 2 digital images per exposure: the first one simulates a conventional radiograph, while the second enhances some spatial frequencies and emphasizes the structure borders. The conventional radiographs and the digital images of 50 patients submitted to ivp were reviewed by four experienced radiologists to evaluate their comparative quality, and the results were statistically analyzed. Digital images proved to be better than conventional radiographs for some of the selected parameters, especially in the evaluation of renal edges and sometimes for calyceal opacification. As for the other parameters, no statistically significant difference was observed between conventional radiographs and digital images.     

Evaluation of Lossy data compression of chest X-rays: a receiver operating characteristic study

RATIONALE AND OBJECTIVES: To evaluate the quality of chest radiographs after 32:1 compression/decompression with different image compression algorithms. METHODS: Ten digital (Thoravison) radiographs of an anthropomorphic chest phantom with superimposed simulated nodular lesions (NL) and linear reticular lesions (LL) were obtained. Each radiograph was subdivided into 15 fields; they contained the lesions with a probability of 0.5. The radiographs were compressed and decompressed by using JPEG, fractal and wavelet algorithms at a compression rate of 32:1. Five radiologists evaluated the images. Data were analyzed with the receiver operating characteristic (ROC) method (comparison of area under curve). RESULTS: At 32:1 JPEG or wavelet compression, no statistically significant difference was observed for both NL and LL when compared with the original images. The fractal algorithm performed significantly lower for both NL and LL when compared with the original radiographs. CONCLUSION: The JPEG and wavelet image compression does not result in loss of relevant information for chest x-rays at a compression rate of 32:1.     

Reducing the radiation dose during excretory urography: flat-panel silicon x-ray detector versus computed radiography

OBJECTIVE: The purpose of the study was to examine the possibilities for reducing radiation exposure in uroradiology using digital flat-panel silicon X-ray detector radiography. We compared the subjectively determined image quality of abdominal radiographs and urograms obtained on a digital flat-panel detector radiography system with those obtained on a computed radiography system. SUBJECTS AND METHODS. Fifty patients who had a clinical indication for urography underwent unenhanced abdominal imaging that was alternately performed using flat-panel silicon X-ray detector radiography or computed radiography. For patients who required a second radiograph with contrast medium, the examination modality was changed to avoid exposing the patients to excess radiation. The images obtained on flat-panel X-ray detector radiography were obtained at half the radiation dose of the images obtained on computed radiography (800 speed vs 400 speed). The resulting 50 pairs of images were interpreted by four independent observers who rated the detectability of structures of bone and the efferent urinary tract relevant to diagnosis and compared the image quality. RESULTS: At half the radiation dose, digital flat-panel X-ray detector radiography provided equivalent image quality of the liver and spleen, lumbar vertebrae 2 and 5, pelvis, and psoas margin on abdominal radiographs. The image quality obtained with digital flat-panel X-ray detector radiography of the kidneys, the hollow cavities of the upper efferent urinary tract, and the urinary bladder was judged to be statistically better than those obtained with computed radiography. CONCLUSION: With half the exposure dose of computed radiography, the flat-panel X-ray detector produced urograms with an image quality equivalent to or better than computed radiography.     

Screening for tracheobronchial diseases with digital storage phosphor radiography]

Digital storage phosphor radiography (FCR: Fuji computed radiography) has a wide dynamic range and unique postprocessing capabilities. This study was designed to test whether chest imaging with FCR and its image processing would increase the accuracy of and confidence in the diagnosis of tracheobronchial abnormalities. In a phantom study, the performance of digital images having the appearance of a conventional chest radiograph was compared with that of a conventional system in detecting simulated tracheobronchial nodules. The digital images of lower kilovoltage (ROC area = 0.647 +/- 0.035) were equivalent to the conventional radiographs (ROC area = 0.620 +/- 0.028). On the other hand, nodule detectability was significantly improved in the digital images of higher kilovoltage (ROC area = 0.826 +/- 0.020). The author also compared the impact of five postprocessing algorithms (standard image, wide latitude image, enhanced image, reversed image, and subtraction image). ROC analysis indicated that the default standard image (ROC area = 0.826 +/- 0.020) was as good as an image with a linear rather than a sigmoid gradation curve (ROC area = 0.843 +/- 0.020), an image with strong enhancement of high frequencies (ROC area = 0.804 +/- 0.020), and an image with reversed gray scale polarity (ROC area = 0.775 +/- 0.015). Therefore these specific algorithms had no effect on the detection of tracheobronchial nodules. However, digital subtraction soft tissue images (ROC area = 0.961 +/- 0.030) were significantly better than the control images. Clinical study also indicated that subtraction images improve diagnostic accuracy in tracheobronchial diseases.     

Quadtree-based data compression of abdominal CT images

An ROC study was performed to evaluate the effect of quadtree-based data compression on the diagnostic yield of CT images. Seventy images were selected from a series of consecutive abdominal/pelvic CT scans. Following the application of quadtree-based compression, all images were reviewed independently by three radiologists. The images were analyzed at six decreasing irreversible compression ratios (30.6:1 to 7.4:1), as well as after reversible compression (2.9:1). ROC curves reveal a gradual decrease in clinical accuracy with increasing compression ratios. At a compression ratio of 7.4:1, sensitivity for all major abnormalities was 99% with a specificity of 93%. As the compression ratio was increased to 30.6:1, sensitivity and specificity dropped to 75% and 83% respectively. Execution times for compression and decompression of the CT images with a PC-AT based digital radiography system varied from 24.7 to 18.5 seconds and from 16.2 to 5.1 seconds respectively, decreasing with higher levels of compression. We conclude that quadtree-based compression of abdominal CT images may have practical applications for a PC based digital radiography system.     

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.     

Diagnostic accuracy of fracture detection in suspected non-accidental injury: the effect of edge enhancement and digital display on observer performance

AIM: To compare the effect of varying degrees of edge enhancement and method of digital image display on fracture detection in suspected non-accidental injury (NAI). MATERIALS AND METHODS: Fifty radiographs from post-mortem skeletal surveys in 13 children with suspected NAI were selected. Images were obtained using a Fuji 5000R computed radiography system. Hard copies were printed with edge enhancement factors 0, 0.5 and 1.2. Images (edge enhancement 0.5) were also displayed on a 1K(2) monitor. Six observers independently evaluated all 200 images for the presence of abnormality. Observers also scored each image for visualization of soft tissues, visualization of trabecular markings and overall image quality. The paired Student's t-test and location receiver operating curve (ROC) analysis were used to compare quality scores and diagnostic accuracy of each display method. Individual and pooled true-positive rates (sensitivity) were determined. For the purposes of ROC analysis, histology was taken as the gold standard. RESULTS: There was no difference in duration of hard and soft-copy reading sessions (p=0.76). After image manipulation soft-copy radiographs scored significantly better for image quality than hard copy (p<0.0001). Pooled observer sensitivity (at a specificity of 90%) was below 50% for all display methods. Diagnostic accuracy varied significantly between observers. Diagnostic accuracy of individual observers was not affected by display method. CONCLUSION: In suspected NAI, diagnostic accuracy of fracture detection is generally low. Diagnostic accuracy appears to be affected more by observer-related factors than by the method of digital image display.     

Accuracy of digital and film panoramic radiographs for assessment of position and morphology of mandibular third molars and prevalence of dental anomalies and pathologies

OBJECTIVES: To compare the accuracy of digital and film panoramic radiographs for determining (1) the position and morphology of mandibular third molars before surgical removal and (2) the prevalence of dental anomalies and pathologies. METHODS: Three hundred and eighty-eight third mandibular molars were available for examination. Position and morphology of third molars observed on film radiographs and on digital panoramic images from five systems (DenOptix, DigiDent, Digora, Dimax2 and Orthophos Plus) were recorded by two observers and were compared with surgeons' findings at the time of the operation (gold standard). One observer further recorded the prevalence of dental anomalies and pathologies on both imaging modalities. RESULTS: Few differences were found between the digital and film-based panoramic systems in the assessment of accuracy of position and morphology of mandibular third molars. The prevalence of dental anomalies and pathologies determined with the two modalities was roughly similar. CONCLUSION: The five digital panoramic systems evaluated in this study were equally as useful for third molar treatment planning and diagnosis of dental anomalies and pathologies as conventional film-based panoramic radiographs.     

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.     

Detection of pneumothorax: comparison of digital and conventional chest imaging

To investigate radiologists' performance at interpreting digital radiographic images, we compared the detectability of pneumothoraces on computed radiographic chest images with 0.2-mm pixel size (2.5 Ip/mm) with their detectability on matched conventional screen-film images (5 Ip/mm). Eight radiologists reviewed 50 computed and 50 screen-film chest radiographs from 25 patients with pneumothoraces and 25 patients with other (or no) abnormalities. Four of the readers who best detected pneumothoraces on screen-film examinations performed worse when interpreting computed radiographic studies; the other four readers detected pneumothoraces similarly with both techniques. No relationship was found between the size of a pneumothorax and its likelihood of detection by either technique. These results raise concerns about implementing computed radiography for comprehensive chest imaging.     

Low-dose digital computed radiography in pediatric chest imaging

A prototype digital computed radiographic imaging system that uses laser-stimulated luminescence was evaluated for its ability to achieve reproducible, high-detail, low-dose pediatric chest radiographs. Using this system, we performed a total of 401 examinations in infants and children, and achieved an 85% reduction in radiation dose, as compared with that delivered when film-screen techniques were used. We also achieved satisfactory image resolution, and the images obtained were of acceptable diagnostic quality. A direct comparison of analog and digital radiographs showed that comparable quality and clinical acceptability could be readily maintained between the two techniques. This study shows that high-quality images can be produced by this system at radiation doses reduced by 85% when compared with doses from standard radiographic techniques.     

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.