Digital radiography with photostimulable storage phosphors. Control of detector latitude in chest imaging.

RATIONALE AND OBJECTIVES. A widely used digital radiography system based on a photostimulable storage phosphor (PSP) detector was analyzed with regard to radiographic contrast changes that result from the adjustment of detector latitude (x-ray sensitivity range) in the normal processing of chest images. METHODS. Images of an acrylic step wedge were acquired using the digital system in a mode that permitted direct control of effective detector latitude. The images were post-processed in conditions duplicating those used for portable chest examinations, and contrast was measured. RESULTS. Increases in effective detector latitude provided only marginal radiographic contrast gains in the subdiaphragm-equivalent areas of the laser-printed digital film image, while causing large reductions in radiographic contrast in the lung-equivalent region. CONCLUSION. Detector latitude is an important variable that should be monitored or controlled in investigations that compare reader performance using conventional and digital systems.     

Investigation of beam quality for digital chest radiography with RbBr:Tl(+) photostimulable storage phosphors

Beam quality for digital chest radiography in digital radiography systems (DR systems) with RbBr:Tl(+) photostimulable storage phosphors was investigated. Measurements of overall Wiener spectrum (overall WS) and observer performance experiments by means of Scheffé's method of paired comparisons were performed under the same exposure (5.16x10(-7)C/kg) at the X-ray detector of DR systems (sampling distance: 175 micro m, 2,048x2,048 pixels, 12 bits, look-up table: THX2) with a phantom lung and metacryl plates. Overall WS values were indicated to be inferior at higher tube voltages. All of the overall WS values were greater than those of screen film systems (HGM/UR1:S/F) at radiographic density 0.50, which was considered the density of the mediastinum and the area below the diaphragm (low density area), and at radiographic densities 1.00 and 1.50, considered as lung, WS values of S/F were located between the overall WS values of 80 kV and 100 kV, and 120 kV and 140 kV, respectively. Evaluation of visibility including mediastinum, lung, and total were indicated to be superior at the lower tube voltages. In evaluation of the mediastinum, the base image, which was obtained by 100 kV tube voltage (effective energy: 46.0 kV) in this study, was not significant from 90 kV to 110 kV tube voltages (range, +/-10 kV), and in-lung and total evaluations were not significant from 90 kV to 120 kV (range, -10 kV to +20 kV), and from 80 kV to 120 kV (range, +/-20 kV) tube voltages by 99% confidence interval. In conclusion, optimal beam quality for digital chest radiography with RbBr:Tl(+) photostimulable storage phosphors was considered to be less than 110 kV tube voltage (effective energy, 47.9 keV) in 0.1 mm copper and 3.8 mm aluminum total filtration. In this case, the granularity in low-density areas were inferior to those of S/F systems but nearly equal to the middle and high-density areas of chest images, and exposure dose was 14.3% lower than that of the base image obtained by 100 kV (effective energy, 46.0 keV) tube voltage in this study.     

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.     

Digital chest radiography with a selenium-based flat-panel detector versus a storage phosphor system: comparison of soft-copy images

OBJECTIVE. We compared the soft-copy images produced by a digital chest radiography system that uses a flat-panel X-ray detector based on amorphous selenium with images produced by a storage phosphor radiography system for the visualization of anatomic regions of the chest. MATERIALS AND METHODS. Two chest radiologists and two residents analyzed 46 pairs of posteroanterior chest radiographs on high-resolution video monitors (2560 x 2048 x 8 bits). In each pair, one radiograph was obtained with a storage phosphor radiography system, and the other radiograph was obtained with a selenium-based flat-panel detector radiography system. Each pair of radiographs was obtained at the same exposure settings. The interpreter rated the visibility and radiographic quality of 11 different anatomic regions. Each pair of images was ranked on a five-point scale (1 = prefer image A, 3 = no preference, 5 = prefer image B) for preference of technique. Statistical significance of preference was determined using the Wilcoxon's signed rank test. RESULTS. The interpreters had a statistically significant preference for the selenium-based radiography system in six (unobscured lung, hilum, rib, minor fissure, heart border, and overall appearance) of 11 anatomic regions (p<0.001) and for the storage phosphor system in two regions (proximal airway and thoracic spine) (p<0.05). Chest radiologists strongly preferred selenium-based images in eight regions, and they did not prefer storage phosphor images in any region. CONCLUSION. The soft-copy images produced by the selenium-based radiography system were perceived as equal or superior to those produced by the storage phosphor system in most but not all anatomic regions.     

Digital radiography of the chest: clinical experience with a prototype unit

A prototype digital unit dedicated to chest radiography was used to examine 50 selected patients for a comparison study of the capability of digital images and conventional chest radiographs to reveal normal anatomic structures and a variety of pathologic states. The images in both modes were submitted for interpretation to seven experienced radiologists and a standardized questionnaire completed for each. Visibility of seven anatomic structures in the mediastinum was consistently better on the digital images than on the conventional radiographs. With minor exceptions, pathologic states were equally well seen in the two systems. Despite the less familiar viewing format of the digital images, the mean confidence levels achieved were higher than for those on the conventional radiographs; this difference was statistically significant both for normal anatomic structures (p = 0.001) and pathologic states (p = 0.01). The advantages and disadvantages of the digital technique are discussed.     

Digital chest radiography: performance evaluation of a prototype unit

Measurements of the physical performance of a prototype digital chest unit (DCU) are presented. The parameters evaluated were entrance skin exposure, system exposure response and dynamic range, system modulation transfer function (MTF), image noise levels, detective quantum efficiency (DQE) of the detector, and scatter suppression efficiency. Compared with conventional chest imaging systems, the unit has markedly greater exposure latitude, limited spatial resolution, a lower detector DQE, and virtually scatter-free images. Routine clinical exposure levels are comparable with the 1982 national average.     

Comparing image quality of flat-panel chest radiography with storage phosphor radiography and film-screen radiography

OBJECTIVE: To evaluate image quality of a large-area direct-readout flat-panel detector system in chest radiography, we conducted an observer preference study. A clinical comparative study was conducted of the flat-panel system versus the storage phosphor and standard film-screen systems. MATERIALS AND METHODS: Routine chest radiographs (posteroanterior) of 30 patients that were obtained using flat-panel, storage phosphor, and film screen systems were compared. The visibility of 10 anatomic regions and the overall image quality criteria were rated independently by three radiologists using a 5-point scale. The significance of the differences in diagnostic performance was tested with a Wilcoxon's signed rank test. Dose measurements for the three modalities were performed. RESULTS: The flat-panel radiography system showed an improved visibility in most anatomic structures when compared with a state-of-the-art conventional film-screen system and an equal visibility when compared with a storage phosphor system. The flat-panel system showed the greatest enhancement in the depiction of small detailed structures (p < 0.05) and achieved this with a reduction in overall radiation dose of more than 50%. CONCLUSION: The visibility of anatomic structures provided by this flat-panel detector system is as good as if not better than that provided by conventional or storage phosphor systems while emitting a reduced radiation dose.     

Detection of small bone lesions with digital radiography using storage phosphors

To date, the skeletal imaging capabilities of digital radiography with storage phosphors have been poorly investigated, and the diagnostic accuracy of this technique has not been thoroughly assessed. To evaluate the performance of storage phosphor digital radiography we compared 66 conventional and 66 digital radiographs of small abnormalities of the extremities (fractures, erosions, calcifications). Conventional images were obtained with a low-speed screen-film system while digital ones were acquired with high-resolution (5 lp/mm max) phosphors and laser-printed on a 8" x 10" film. Two experienced radiologists defined the gold standard (389 abnormalities) and four radiologists scored the findings (1,556 observations) on a five-point discrete scale. ROC analysis indicated film and storage radiography to be equally effective in the overall detection of abnormalities. No difference was found in the individual performances of the four readers, in the site subclasses (wrist, hand), and in the specific detection of fractures and erosions. Digital radiography proved to be superior to conventional radiography in the detection of calcifications in all sites and particularly in the wrist (p less than 0.05). Storage phosphor radiography may replace conventional radiography of the extremities without causing any significant decrease in diagnostic accuracy.     

Postbiopsy pneumothorax: estimating the risk by chest radiography and pulmonary function tests

Pulmonary function tests and chest radiographs of 160 patients who had had percutaneous needle biopsy of lung lesions were reviewed to determine the value of these examinations in estimating the risk of postbiopsy pneumothorax. Chest radiographs were evaluated subjectively for changes of obstructive and restrictive airway disease and for size and depth of lesion. Pulmonary function tests, consisting of simple spirometry (forced vital capacity, percentage of predicted forced vital capacity, forced expiratory volume in 1 sec, percentage of predicted forced expiratory volume in 1 sec, and [forced expiratory in 1 sec/forced vital capacity] X 100), and the pulmonologist's interpretation were evaluated. Pneumothorax developed in 46% (31/67) of patients who had obstructive airway disease according to the results of pulmonary function tests and in 42% (34/81) of those who had obstructive airway disease according to changes on chest radiographs, compared with 19% (10/53) and 25% (17/67) of those who had normal pulmonary function tests and chest radiographs, respectively. Pneumothorax developed in 46% (23/50) of patients who had findings of obstructive airway disease on both pulmonary function tests and on chest radiographs, compared with 7% (2/28) of patients who were classified as normal by both criteria. None of the patients who had normal pulmonary function tests required placement of a chest tube, whereas 19% (13/67) of those who had obstructive airway disease required chest tubes. Decreasing size of lesion and increasing depth of lesion were associated with a significant increase in the risk of pneumothorax. We conclude that the results of chest radiographs and pulmonary function tests are useful parameters for estimating the risk of postbiopsy pneumothorax.     

Development of breathing chest radiography: study of exposure timing

The flat-panel detector (FPD) has been introduced into clinical practice. A modified FPD, which has the ability to obtain dynamic chest radiographs, was introduced into our hospital, and clinical testing is ongoing. Both the inspiratory and expiratory phases have to be included in dynamic chest radiographs. The purpose of this study was to investigate the most appropriate chest radiography signal for observation of the respiratory process. We prepared ten protocol patterns that differed in terms of respiratory phase at X-ray exposure, exposure duration, and signal multiplicity. We also performed preliminary experiments and administered several questionnaires to ten volunteers. The volunteers breathed according to vocal and visual signals, and their respiratory waves were recorded by spirometer. The most appropriate protocol was similar to the method used for conventional chest radiography.     

Digital radiography of the chest: design features and considerations for a prototype unit

The general features of a prototype digital chest unit are described along with the rationale for the choice of design factors employed. It is shown that the scanning-slit, linear-detector-array approach employed can, with available x-ray tube technology, achieve a spatial resolution of 1 cy/mm and detector radiation levels comparable with those obtained with conventional screen-film systems. Also discussed are the unit's exposure latitude and its ability virtually to eliminate scatter.     

Preoperative chest radiography: value as a baseline examination for comparison

An important use of the preoperative chest radiograph is as a baseline for comparison when complications occur after surgery. Many authors have commented on the value of preoperative chest radiography as a screening examination, but no statistics have been presented regarding its impact on postoperative management. In 369 consecutive general surgical patients, the need for a baseline chest radiograph was evaluated. In 65 patients undergoing chest radiography postoperatively, a preoperative baseline was essential in making an accurate interpretation in 33 (51%). The value of preoperative chest radiography proved to be twofold. Some minimal abnormalities on postoperative radiographs were demonstrated to be clearly new, necessitating treatment or further evaluation. Second, significant abnormalities detected on postoperative radiographs that may have otherwise been subjected to expensive evaluation were often shown to have been present preoperatively. In approximately 9% of patients the preoperative chest radiograph had a significant impact on postoperative management.     

Subtle gastric abnormalities in a canine model: detection with low-dose imaging with storage phosphors and its equivalence to conventional radiography

The authors compared low-dose (32% of standard exposure) storage phosphor digital imaging (system resolution: 0.2-mm pixels, 10 bits) with isovoltage 75-kVp conventional radiography (standard exposure) in the detection of subtle simulated gastric abnormalities by using air contrast barium studies. Subtle simulated abnormalities (3-7-mm polyps, 4-15-mm ulcer craters, 4-11-mm-diameter edema, and 11-12-mm linear ulcers) were produced in resected canine stomachs. Receiver operating characteristic analysis of 1,800 observations by six readers indicated that the digital images with and without high-frequency edge enhancement were equivalent to conventional radiographs (mean receiver operating characteristic areas [+/- standard deviation]: 0.76 +/- 0.06, 0.78 +/- 0.04, and 0.77 +/- 0.04, respectively). The accuracy of the diagnosis was equivalent for all three modalities. The following mean accuracies of negative and positive responses, respectively, for unenhanced digital, edge-enhanced digital, and conventional images were determined: 0.71 +/- 0.05 and 0.41 +/- 0.07, 0.71 +/- 0.04 and 0.51 +/- 0.09, and 0.68 +/- 0.04 and 0.43 +/- 0.05. It was concluded that low-dose storage phosphor air-contrast barium studies were equivalent to conventional radiography in the detection of subtle gastric abnormalities.     

Dual-energy chest radiography with a flat-panel digital detector: revealing calcified chest abnormalities

OBJECTIVE: The aim of this study was to assess the value of dual-energy chest radiography obtained using a cesium iodide flat-panel detector in addition to standard posteroanterior chest radiography for the detection of calcified chest abnormalities. MATERIALS AND METHODS: The study included 20 patients with a total of 37 calcified chest lesions (16 pulmonary nodules, 17 mediastinal calcifications, and four pleural calcifications) as confirmed on CT. Twenty-eight locations in the chests of the same patients who were free of lesions were used as negative controls. Four radiologists reviewed posteroanterior chest radiographs in a blinded manner alone and in conjunction with dual-energy soft-tissue and bone images. We calculated sensitivity, specificity, the negative predictive value (NPV), and the positive predictive value (PPV) for lesion prediction. The Wilcoxon's and the Brunner and Langer's tests were performed for statistical analysis. RESULTS: For posteroanterior chest radiography, sensitivity was 36%, the PPV was 64%, and the NPV was 47%. When dual-energy images were added, sensitivity increased significantly to 66% (p < 0.05), the PPV to 76%, and the NPV to 62%. The specificity remained constant at 73%. Brunner and Langer's test revealed a highly significant difference between posteroanterior chest radiography and dual-energy imaging in the detection of calcified chest abnormalities (p < 0.01). CONCLUSION: Dual-energy images added to standard posteroanterior chest radiographs significantly improve the detection of calcified chest lesions.     

Cardiothoracic ratio in postmortem chest radiography with regard to the cause of death

It is difficult to examine the intact in situ status of thoracic organs, including the heart and lungs, after opening the chest at autopsy. The present study investigated the pathological diagnostic significance of the cardiothoracic ratio (CTR) with regard to heart and lung weight in postmortem plain chest radiography. The pathological diagnostic significance of the CTR in postmortem plain chest radiography using serial forensic autopsy cases of adults (>19 years of age, n = 367, within 72 h postmortem) was retrospectively investigated. In natural deaths, CTR was larger for heart diseases, and was smaller for pulmonary infection and gastrointestinal bleeding, showing correlations to the heart weight except in cases of hemopericardium. In traumatic deaths, CTR was larger in cases of fire fatality and acute methamphetamine intoxication, and varied in cases of blunt injury, showing correlations to the heart weight. However, CTR was smaller for sharp instrument injury and drowning, independently of the heart weight. These findings suggest that postmortem CTR (median, 55.6%, measured using a mobile X-ray apparatus) primarily depends on the heart weight, but is substantially modified during the process of death: the CTR may be enlarged by cardiac dilatation due to terminal congestive heart failure, but may be reduced by inflated lungs in drowning or hypovolemia due to fatal hemorrhage. CTR showed a mild correlation to the right diaphragm level, which was also related to the cause of death, but was independent of the left diaphragm level. Plain chest radiographic findings may also be helpful in investigating the pathophysiology of death, and are to some extent comparable with clinical findings. This also suggests the potential usefulness of postmortem CT and MRI for analysis of terminal cardiac function.     

The scatter-to-primary ratio as a function of varying X-ray absorption measured by computed radiography.

Some scatter studies have previously been conducted using film as a detector. The serious limitations caused by the narrow latitude, the non-linear density response, and the required optical densitometric measurements of film can be avoided by computed radiography (CR) which provides linear numeric data over a wide dynamic range. The imaging plate is used as a large-area detector and the data is analyzed from the computer memory. Variation in the scatter-to-primary ratio within an image caused by absorption differences was simulated in a water-aluminum phantom. The measurement technique showed repeatable results, being comparable to the values expected on the basis of previous studies. A multiple pencil-beam (MPB) imaging device was also compared to a standard 1:12 grid by this technique. The maximal scatter-to-primary ratio in our model was up to 7.9 with no scatter reduction, 1.5 with grid, and 0.4 with the MPB device. The variation caused by the absorption of primary radiation was much less in the MPB modality, and the MPB system was also less sensitive to an increase in the used tube voltage from 60 to 120 kVp. The benefits of multiple pencil-beam imaging in scatter reduction are briefly discussed.     

Digital chest radiography with a large image intensifier. An ROC study with an anthropomorphic phantom

The diagnostic performance of two systems for chest radiography was studied. One system was based on a large image intensifier, the other was a conventional film-screen system. The images from the image intensifier were studied either on a digital TV screen or on 100 mm photofluorograms. Receiver operating characteristic curve analysis was performed on images of an anthropomorphic chest phantom. Low-contrast MMAP (methyl methacrylate polymer) nodules and simulated vessels were positioned over the parenchymal and the mediastinal region of the phantom. Five observers assessed the digital monitor images, photofluorograms, and conventional full-size radiograms. The results showed a significantly superior detectability for the full-size radiograms over the digital monitor images both in the parenchyma and in the mediastinum. No significant difference was found between photofluorograms and digital images.