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.     

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.     

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.     

Mammographic microcalcifications: detection with xerography, screen- film, and digitized film display

Pulverized bone specks and aluminum oxide specks were measured by hand into sizes ranging from 0.2 mm to 1.0 mm and then arranged in clusters. These clusters were superimposed on a human breast tissue phantom, and xeromammograms and screen-film mammograms of the clusters were made. The screen-film mammograms were digitized using a high-resolution laser scanner and then displayed on cathode ray tube (CRT) monitors. Six radiologists independently counted the microcalcifications on the xeromammograms, the screen-film mammograms, and the digitized-film mammograms. The xeromammograms were examined with a magnifying glass; the screen-film images were examined with a magnifying glass and by hot light; and the digitized-film images were examined by electronic magnification and image processing. The bone speck size that corresponded to a mean 50% detectability level for each technique was as follows: xeromammography, 0.550 mm; digitized film, 0.573 mm; and screen-film, 0.661 mm. We postulate that electronic magnification and image processing with edge enhancement can improve the capability of screen-film mammography to enhance the detection of microcalcifications.     

Clinical evaluation of twin screen-film chest radiography: cost effective lung and mediastinal imaging

Objective: A new twin screen-film cassette system optimised for conventional chest radiography was evaluated by four thoracic radiologists. Materials and Methods: The twin screen-film cassette system produces two film images, the front film optimised for the mediastinal region of the chest, the rear for the lung region. Image degradation on either screen-film system due to internal photon scatter has been virtually eliminated due to the use of a dividing filter. Fifty patients were included in a trial that resulted in a set of chest images for each patient, taken on the same inspiration, by both the twin screen-film cassette and the conventional system. The resultant fifty sets of images were evaluated by four chest radiologists who scored 12 radiographic features of the chest and patient pathologies present, using a paired difference technique. Results: The image quality of the twin screen-film cassette system was judged to be significantly superior to the conventional screen-film system in nine of the 12 radiographic features scored (P<0.003). In the three other regions and for the patient pathologies, no significant conclusions were drawn. Conclusion: The new twin screen-film system showed improved visualisation of radiographic features, particularly in the mediastinal and retrocardiac lung regions. This new system shows promise in both standard and portable clinical applications.     

Digital radiography of subtle pulmonary abnormalities: an ROC study of the effect of pixel size on observer performance

Forty conventional radiographs with examples of mild interstitial infiltrates and subtle pneumothoraces and 40 normal studies of the chest were selected and digitized, with pixel sizes of 1.0, 0.5, 0.2, and 0.1 mm. Observer performance tests were carried out using receiver operating characteristic analysis. Conventional radiographs and digitized images were compared. The results indicate that, in such cases, diagnostic accuracy increases significantly as the pixel size is reduced, at least to the 0.1-mm level. We conclude that, for digital systems using screen-film or similar image receptors, use of a pixel size substantially larger than 0.1 mm may result in some loss of diagnostic accuracy.     

Digital mammography. ROC studies of the effects of pixel size and unsharp-mask filtering on the detection of subtle microcalcifications

We investigated the spatial resolution requirement and the effect of unsharp-mask filtering on the detectability of subtle microcalcifications in digital mammography. Digital images were obtained by digitizing conventional screen-film mammograms with a 0.1 X 0.1 mm2 pixel size, processed with unsharp masking, and then reconstituted on film with a Fuji image processing/simulation system (Fuji Photo Film Co., Tokyo, Japan). Twenty normal cases and 12 cases with subtle microcalcifications were included. Observer performance experiments were conducted to assess the detectability of subtle microcalcifications in the conventional, the unprocessed digital, and the unsharp-masked mammograms. The observer response data were evaluated using receiver operating characteristic (ROC) and LROC (ROC with localization) analyses. Our results indicate that digital mammograms obtained with 0.1 X 0.1 mm2 pixels provide lower detectability than the conventional screen-film mammograms. The detectability of microcalcifications in the digital mammograms is improved by unsharp-mask filtering; the processed mammograms still provide lower accuracy than the conventional mammograms, however, chiefly because of increased false-positive detection rates for the processed images at each subjective confidence level. Viewing unprocessed digital and unsharp-masked images in pairs resulted in approximately the same detectability as that obtained with the unsharp-masked images alone. However, this result may be influenced by the fact that the same limited viewing time was necessarily divided between the two images.     

Comparison of doses for bedside examinations of the chest with conventional screen-film and computed radiography: results of a randomized controlled trial

PURPOSE: To compare the radiation doses received by patients during bedside chest radiography when a computed radiography system was used and when a 400-speed screen-film system was used. MATERIALS AND METHODS: A randomized controlled trial was performed whereby all patients who were admitted to an intensive care unit were randomly assigned at admission to have all radiographic chest images obtained with either computed or conventional screen-film radiography. Doses were measured for 1 year, during which 269 patients underwent imaging. For these patients, surface entry doses were measured by means of individual thermoluminescent dosimeters placed on the skin at the center of the radiation beam. In addition, data were collected relating to the patient and examination characteristics, as well as to repeat examinations. Effective doses were calculated. RESULTS: The patients in the two arms of the study were well matched. The surface entry doses were higher in the computed radiography group (median, 0.21 mGy for computed radiography and 0.16 mGy for conventional radiography), and the effective doses were also higher (median, 0.036 mSv for computed radiography and 0.027 mSv for conventional radiography). Fewer examinations were repeated when computed radiography was used. CONCLUSION: When computed radiography was used, patient doses increased. The speed of this computed radiography system, which uses phosphor plate imaging, equates approximately to a 300-speed screen-film system.     

Digital chest radiography with a solid-state flat-panel x-ray detector: contrast-detail evaluation with processed images printed on film hard copy

PURPOSE: To evaluate and compare human observer performance in a contrast-detail test by using postprocessed hard-copy images from a digital chest radiography system and conventional screen-film radiographs. MATERIALS AND METHODS: The digital radiography system is based on a large-area flat-panel x-ray detector with a structured cesium iodide scintillator layer and an amorphous silicon thin-film transistor array for image readout. Images of a contrast-detail phantom were acquired at two exposure levels by using two standard thoracic screen-film systems and the digital system at matched dose. By using images of the phantom processed with standard chest image postprocessing techniques, a four-alternative forced-choice observer perception study was performed, and the number of detectable test signals (disk-shaped objects 0.3-4.0 mm in diameter) was determined for each image type. RESULTS: On average, observers detected more test signals on digital images than on screen-film radiographs at all diameters up to 2.0 mm and an equivalent number at larger diameters. Test signals with lower inherent subject contrast were detected more readily on digital images than on screen-film images, even when x-ray exposure levels for the digital system were reduced by 20%. CONCLUSION: Observer performance in a contrast-detail detection task can be improved by using images acquired with the flat-panel digital chest radiography system as compared with those acquired with state-of-the-art screen-film combinations.     

Clinical evaluation of digital radiography based on a large-area cesium iodide-amorphous silicon flat-panel detector compared with screen-film radiography for skeletal system and abdomen

The aim of this clinical study was to compare the image quality of digital radiography using the new digital Bucky system based on a flat-panel detector with that of a conventional screen-film system for the skeletal structure and the abdomen. Fifty patients were examined using digital radiography with a flat-panel detector and screen-film systems, 25 for the skeletal structures and 25 for the abdomen. Six radiologists judged each paired image acquired under the same exposure parameters concerning three observation items for the bone and six items for the abdomen. Digital radiographic images for the bone were evaluated to be similar to screen-film images at the mean of 42.2%, to be superior at 50.2%, and to be inferior at 7.6%. Digital radiographic images for the abdomen were judged to be similar to screen-film images at the mean of 43.4%, superior at 52.4%, and inferior at 4.2%; thus, digital radiographic images were estimated to be either similar as or superior to screen-film images at over 92% for the bone and abdomen. On the statistical analysis, digital radiographic images were also judged to be preferred significantly in the most items for the bone and abdomen. In conclusion, the image quality of digital radiography with a flat-panel detector was superior to that of a screen-film system under the same exposure parameters, suggesting that dose reduction is possible with digital radiography.     

Low contrast detectability of a new CR system with two-sided reading

A new imaging plate (IP) with a transparent support and reading system that can detect emissions from both sides of the IP has been developed and has already been introduced in some facilities. In this study, low contrast threshold detectability was investigated experimentally for a CR system with a two-sided reading system (new CR) and for a conventional CR system. Images of a Contrast-Detail phantom were obtained with the new and conventional CR systems at dose levels corresponding to 26%, 49%, 82%, 103%, and 164% of the dose used for the screen-film system. Using an observer performance study of Contrast-Detail phantom images, the threshold contrast of disk-shaped objects ranging from 0.3 mm to 4.0 mm in diameter was determined. We also calculated image quality figure (IQF) from the results of observation. The new CR system showed significantly better contrast detectability than the conventional CR system. The use of a new CR system provided a reduction of approximately 25% in radiographic dose while providing comparable IQF.     

Traumatic pneumothorax detection with thoracic US: correlation with chest radiography and CT--initial experience

PURPOSE: To prospectively compare the accuracy of ultrasonography (US) with that of supine chest radiography in the detection of traumatic pneumothoraces, with computed tomography (CT) as the reference standard. MATERIALS AND METHODS: Thoracic US, supine chest radiography, and CT were performed to assess for pneumothorax in 27 patients who sustained blunt thoracic trauma. US and radiographic findings were compared with CT findings, the reference standard, for pneumothorax detection. For the purpose of this study, the sonographers were blinded to the radiographic and CT findings. RESULTS: Eleven of 27 patients had pneumothorax at CT. All 11 of these pneumothoraces were detected at US, and four were seen at supine chest radiography. In the one false-positive US case, the patient was shown to have substantial bullous emphysema at CT. Sensitivity and negative predictive value of US were 100% (11 of 11 and 15 of 15 patients, respectively), specificity was 94% (15 of 16 patients), and positive predictive value was 92% (11 of 12 patients). Chest radiography had 36% (four of 11 patients) sensitivity, 100% (16 of 16 patients) specificity, a 100% (four of four patients) positive predictive value, and a 70% (16 of 23 patients) negative predictive value. CONCLUSION: In this study, US was more sensitive than supine chest radiography and as sensitive as CT in the detection of traumatic pneumothoraces.     

Digital image processing: effect on detectability of simulated low-contrast radiographic patterns

Detection studies of simulated low-contrast radiographic patterns were performed with a high-quality digital image processing system. The original images, prepared with conventional screen-film systems, were processed digitally to enhance contrast by a "windowing" technique. The detectability of simulated patterns was quantified in terms of the results of observer performance experiments by using the multiple-alternative forced-choice method. The processed images demonstrated a significant increase in observer detection performance over that for the original images. These results are related to the displayed and perceived signal-to-noise ratios derived from signal detection theory. The improvement in detectability is ascribed to a reduction in the relative magnitude of the human observer's "internal" noise after image processing. The measured dependence of threshold signal contrast on object size and noise level is accounted for by a statistical decision theory model that includes internal noise.     

Pneumothorax post CT-guided lung biopsy: a comparison between detection on chest radiographs and CT

Pneumothorax is reported to be a more common complication of lung biopsy performed under computed tomography (CT) than under fluoroscopic guidance. This may simply reflect the greater sensitivity of CT over chest radiographs (CXRs) in the detection of small pneumothoraces. This study aimed to determine the incidence of pneumothorax detected by CXR and by CT after CT-guided biopsy of non-pleurally based pulmonary masses, and to compare these incidences with previous reports in the literature of pneumothorax incidence post fluoroscopic biopsy. 88 consecutive CT-guided lung biopsies of masses not abutting the pleural surface were included. Immediate post-biopsy CT images, and 1 and 4 h CXRs were assessed independently by two observers for the presence and size of pneumothorax. 72 biopsies were fine needle aspirations (FNAs) performed with 22 G spinal needles only, seven were cutting needle biopsies (CNBs) performed with 18 G cutting needles only, and nine were both. 37 patients (42%) developed a pneumothorax. 35 were detected on CT (40%) and 22 on CXR (25%). None required tube drainage. Of the patients in whom CT demonstrated a pneumothorax, the average depth of this was significantly greater for those in whom CXR also detected a pneumothorax compared with those in whom CXR was negative (7.3 mm versus 3.4 mm, p < 0.05). The incidence of pneumothorax detected on CXR post CT-guided biopsy is similar to the reported incidence post fluoroscopic biopsy.     

Detection of simulated pulmonary nodules by single-exposure dual-energy computed radiography of the chest: effect of a computer-aided diagnosis system (Part 2)

OBJECTIVE: To evaluate the performance of the computer-aided diagnosis (CAD) scheme on the detection of pulmonary nodules (PNs) in single-exposure dual-energy subtraction computed radiography (CR) images of the chest, and to evaluate the effect of this CAD scheme on radiologists' detectibilaties. METHODS AND MATERIAL: We compared the detectability by the CAD scheme with the detectability by 12 observers by using conventional CR (C-CR) and bone-subtracted CR (BS-CR) images of 25 chest phantoms with a low-contrast nylon nodule. RESULTS: Both in the CAD scheme and for the observers, the detectability of BS-CR images was superior to that of C-CR images (P<0.005). The detection performance of the CAD scheme was equal to that of the observers. The nodules detected by the CAD did not necessarily coincide with those by the observers. Thus, if observers can use the results of the CAD system as a 'second opinion', their detectabilities increase. CONCLUSION: The CAD system for detection of PNs in the single-exposure dual-energy subtraction method is promising for improving radiologists' detectabilities of PNs.     

Digital radiography versus conventional radiography during excretory urography: our experience

The authors describe a computed radiographic system employed to generate and archive digital images in intravenous urography. For each exposure the system produces two digital images: the first (left image) simulates a conventional screen-film radiograph, the second (right image); enhances some spatial frequencies and emphasizes the margins of the structures. These images can be modified in their chief parameters and then printed by a laser-printer and archived on optical disks. Four experienced radiologists evaluated digital images with regard to some chief diagnostic parameters and, in 50 patients, they compared digital images with conventional screen-film radiographs and submitted the results to statistical analysis. For some of the chosen parameters, particularly for the evaluation of renal margins before and after contrast medium injection, digital images gave statistically better results than conventional films, while, no statistically significant different was observed for the other parameters. From the results of this preliminary study digital radiography was found to be useful in intravenous urography by reducing the patient's exposition dose, by always obtaining images of good quality, and by enhancing some particular features of the standard image; on the other hand there were many unsolved problems regarding the communicating and archiving system (PACS), because of the slowness of the image transfer procedure, difficulties in data transmission and complexity of referential procedures.     

The floating cardiac fat pad—sign of occult pneumothorax

Pneumothoraces are a possible sequela of chest trauma with potential morbidity and mortality if not recognized and treated promptly. A portable supine chest radiograph is frequently the first radiologic study performed in the setting of trauma. While large pneumothoraces can be readily recognized on these radiographs, smaller pneumothoraces are missed in up to 15 % of trauma patients. There are many radiographic signs of occult pneumothoraces, and we are presenting a new radiographic sign of occult pneumothorax. The floating cardiac fat pad sign occurs when pleural air collects anteriorly and superiorly in the most non-dependent portion of the chest lifting the pericardial fat pad off the diaphragm. Lung markings are still seen surrounding the pericardial fat pad due to the inflated lower lobe of the lung resting dependently. Rapid and accurate identification of pneumothoraces is critical but often difficult on chest radiographs. Although there are many existing radiographic signs for identification of pneumothorax, prospective identification of small pneumothoraces is still relatively poor. Here, we describe an additional sign which aides in the detection of pneumothoraces, the floating cardiac fat pad. When present, this should prompt further evaluation with chest CT or upright chest radiograph.     

Magnification mammography: a comparison of full-field digital mammography and screen-film mammography for the detection of simulated small masses and microcalcifications

The objective of this study was a comparison of a full-field digital mammography (FFDM) system and a conventional screen-film mammography (SFM) system with respect to the detectability of simulated small masses and microcalcifications in the magnification mode. All images were obtained using 1.8 times magnification. The FFDM images were obtained at radiation dose levels of 1.39, 1.0, 0.7, 0.49 and 0.24 times that of the SFM images. A contrast-detail phantom was used to compare the detection of simulated lesions using a four alternative forced-choice reader study with three readers. The correct observation ratio (COR) was calculated as the fraction of correctly identified lesions to the total number of simulated lesions. Soft-copy reading was performed for all digital images. Direct magnification images acquired with the digital system showed a lower object contrast threshold than those acquired with the conventional system. For equal radiation dose, the digital system provided a significantly increased COR (0.95) compared with the screen-film system (0.82). For simulated microcalcifications, the corresponding difference was 0.90 to 0.72. The digital system allowed equal detection to screen-film at 40% of the radiation dose used for screen film. Digital magnification images are superior to screen-film magnification images for the detection of simulated small masses and microcalcifications even at a lower radiation dose.     

Subtle lung nodules: influence of local anatomic variations on detection

PURPOSE: To assess the influence of local anatomic noise on the detection of subtle lung nodules depicted on chest radiographs. MATERIALS AND METHODS: Six 8 x 8-cm lung regions were extracted from digital chest radiographs obtained in healthy subjects. Simulated nodules emulating the radiographic characteristics of subtle tissue-equivalent lesions 3.2-6.4 mm in diameter (equivalent to 0.1-0.4 mm in contrast-diameter product [CD]) were added to the images. On multiple renditions of each image, nodules were inserted at slightly different locations within 6 mm of the center; this process allowed different local background patterns to overlie the nodules. An observer detection study involving 15 experienced radiologists was performed. The authors performed analysis of variance and pairwise t test analyses to determine variations in nodule detectability related to nodule location and size on each image. RESULTS: Results indicated a strong correlation between nodule size and observer detection score and significant variation in nodule detectability as a function of location. Changes in nodule position caused observer score variations that were equivalent to the variation caused by an up to 185% change in nodule CD (78% average over all six images), an up to 68% change in diameter (32% average), and an up to 28% change in area under the receiver operating characteristic curve (Az) (14% average). CONCLUSION: Local anatomic variations surrounding and overlying a subtle lung nodule on a chest radiograph that are created by the projection of anatomic features in the thorax, such as ribs and pulmonary vessels, can greatly influence the detection of nodules, altering the Az by as much as 28%.     

Improved detection of lung nodules on chest radiographs using a commercial computer-aided diagnosis system

OBJECTIVE: The aim of this study was to evaluate the usefulness of a new commercially available computer-aided diagnosis (CAD) system with an automated method of detecting nodules due to lung cancers on chest radiograph. MATERIALS AND METHODS: For patients with cancer, 45 cases with solitary lung nodules up to 25 mm in diameter (nodule size range, 8-25 mm in diameter; mean, 18 mm; median, 20 mm) were used. For healthy patients, 45 cases were selected on the basis of confirmation on chest CT. All chest radiographs were obtained with a computed radiography system. The CAD output images were produced with a newly developed CAD system, which consisted of an image server including CAD software called EpiSight/XR. Eight radiologists (four board-certified radiologists and four radiology residents) participated in observer performance studies and interpreted both the original radiographs and CAD output images using a sequential testing method. The observers' performance was evaluated with receiver operating characteristic analysis. RESULTS: The average area under the curve value increased significantly from 0.924 without to 0.986 with CAD output images. Individually, the use of CAD output images was more beneficial to radiology residents than to board-certified radiologists. CONCLUSION: This CAD system for digital chest radiographs can assist radiologists and has the potential to improve the detection of lung nodules due to lung cancer.