Nontraumatic rupture of the thoracic aorta: chest radiographic features of an often unrecognized condition.

OBJECTIVE: The purpose of our study was to evaluate chest radiographic features of nontraumatic mediastinal hemorrhage occurring after extrapericardial thoracic aorta rupture. MATERIALS AND METHODS: Twenty-seven consecutive chest radiographs obtained at admission of patients with hemorrhage from ruptured thoracic aorta aneurysms, aortic dissections, or penetrating aortic ulcers were randomized with radiographs of 23 subjects with nonruptured thoracic aorta aneurysms, 20 subjects with nonruptured dissections, and 20 control subjects. Diagnoses were established by interpreting CT scans, MR images, and findings at surgery or autopsy or both. A retrospective review was performed by three independent radiologists who were unaware of patients' diagnoses. Observers assessed 20 parameters on each of these 90 radiographs and summarized their findings with final diagnoses. The 20 parameters were analyzed with logistic regression and rank correlation to determine the best predictors of hemorrhage. RESULTS: Logistic regression analysis showed a combination of obscuration or convexity of the aorticopulmonary window and a displaced left paraspinal interface to be the most useful predictor of hemorrhage (p < .05). Rank correlation analysis indicated obscuration or convexity of the aorticopulmonary window; a displaced left paraspinal interface; enlarged aortic knob width; enlarged thoracic aorta size; an enlarged, obscured, or irregular aortic margin; and left pleural or extrapleural space fluid were potential individual predictors of hemorrhage (p < .05). Observer sensitivities for recognizing hemorrhage were 30-59% and specificities were 83-91%. Sensitivities for distinguishing an abnormal (n = 70) from a normal (n = 20) mediastinum were 79-90% and specificities were 65-90%. CONCLUSION: Obscuration or convexity of the aorticopulmonary window and a displaced left paraspinal interface on radiographs may indicate mediastinal hemorrhage. Further imaging is required to establish a definitive diagnosis.

Bedside chest radiography.

Bedside chest radiography is one of the most frequently performed radiologic examinations, yet it is the examination with the most variation in image quality. The need to improve the quality of this examination has long been recognized, but it is a difficult problem to solve. Critically ill patients must undergo bedside chest radiography almost daily. These examinations are useful 76%-94% of the time. A national survey revealed that there is a wide variation in the methods used to perform bedside chest radiography, indicating that there is no excellent preferred technique. The reduced image quality is due to scatter radiation. The scatter fraction is about 0.95 in the mediastinum and is about 0.66 in the lung. When grids are used, the image quality is improved; acceptance has been slow, however, because the grid is frequently misaligned. Storage phosphor imaging/computed radiography with grids is a technology improvement that almost completely solves this problem. Radiologists should be sure to optimize the current techniques, as well as provide prompt examination reporting.

Improved imaging of bone with scan equalization radiography.

Use of scan equalization radiography (SER) for imaging bone in the head, face, neck, and shoulder was evaluated in a clinical comparison study with conventional radiographs of randomly selected patients. Two hundred nine pairs of normal and abnormal SER images and conventional radiographs were compared by four radiologists in a side-by-side viewing situation. The radiologists compared the visibility of specific anatomic features and rated the SER images as better than, equal to, or worse than the conventional radiographs. In the evaluation of the images of the cervical spine, the radiologists much preferred the SER images 63% of the time because of slight improvement in bone detail and marked improvement in detail of the soft tissues. In the evaluation of the images of the shoulder, the radiologists preferred the SER image 58% of the time and preferred the conventional radiograph only 5% of the time (p less than .05). In the evaluation of the images of the skull, face, and mandible, the radiologists preferred the SER images 62% of the time and the conventional images 4% of the time (p less than .05). The superior image quality with the SER technique was recognized by all radiologists in the study and was the overwhelmingly preferred way of imaging the shoulder, neck, head, and face.

Newer imaging methods in chest radiography.

In recent years the application of computers to chest radiography has resulted in a wide variety of innovative research. Major research efforts have resulted in the development of new types of x-ray detectors, such as storage phosphor technology, for use with computers. Storage phosphor imaging is one of the most promising new techniques, and almost 100 systems have been installed worldwide. Radiologists are quickly evaluating the image quality provided by this new detector system, which has the potential to improve image quality. It has wide latitude and is coupled with a computer to perform image processing. Another promising technology, originally studied in the form of scan equalization radiography, is now commercially available in the form of advanced multiple-beam equalization radiography. This film technique uses computers to modulate the x-ray exposure to take maximum advantage of the imaging capabilities of radiographic film. Digital solid-state detectors have been studied in conjunction with computerized image enhancement systems. These currently show improvement in nodule detection and quantification of the calcium content of a lesion. Application of large image intensifiers to a digital image system is being studied, but there are currently limitations on spatial resolution.

Comparison of scanning equalization and conventional chest radiography.

A clinical comparison study of scanning equalization radiography (SER) and conventional chest radiography was performed with the latest prototype SER system. Conventional chest radiography was performed at 120 kVp with Lanex regular screens (Eastman Kodak, Rochester, NY) and Kodak Ortho-G or Ortho-C film (Eastman Kodak). The 253 volunteer patients were examined with both techniques. The chest radiographs were interpreted by four radiologists. The study group was composed of 58 normal and 195 abnormal posteroanterior and lateral chest radiographs. In 31 cases there were two major radiologic diagnoses. The number of correct interpretations increased when the SER images were examined, compared with the conventional Ortho-G (chi 2 = 4.17, P less than .05) and conventional Ortho-C (chi 2 = 16.9, P less than .001) radiographs. The overall accuracy of disease detection improved for all radiologists with the SER system. There was no disease category in which the accuracy of interpretation decreased when the SER system was used. The SER system is a clinically reliable method of improving image quality and increasing diagnostic accuracy.

Lung weight in vivo measured with computed tomography and rebreathing of soluble gases.

In nine anesthetized dogs, accuracy of noninvasive measurements of lung weight (W) and gas volume in vivo was determined from volume and density determined by computed tomography (CT) and by rebreathing helium and the soluble gases dimethyl ether (WDME) and acetylene (WC2H2). Reference standards were obtained from the postmortem scale weight of the frozen lungs (Wscale) and compared with the CT lung weights measured in the living dog (WCT-38) and the frozen carcass (WCT-cold). WCT-cold did not significantly differ from Wscale [-2 +/- 9% (SD), P = 0.7]. WCT-cold was 10% greater than WCT-38 (0.10 greater than P greater than 0.05), suggesting an increase in lung weight despite immediately commencing freezing after death. WDME measured 64 +/- 6% and WC2H2 56 +/- 12% of WCT-38. Serial multiple measurements in three dogs over 14 wk showed a coefficient of variation (CV) of 10 +/- 2% for WDME, 18 +/- 2% for WC2H2, 4.1 +/- 0.9% for WCT, 2.6 +/- 0.8% for CT density, and 3.5 +/- 1.6% for functional residual capacity (FRC) by CT. FRC calculated from CT consistently underestimated FRC measured by rebreathing helium by 18 +/- 8% (P less than 0.005). This error, despite good agreement between WCT and Wscale, was explained by underestimation of CT total lung volume and overestimation of lung density by factors known to affect CT readings, such as partial volume effects, beam hardening, and limited number of input signals. These data show that CT scanning can provide serial measurement of the mass, density, and volume of the lungs with a CV in the order of 5%, but the rebreathing of soluble gases gives more than double this variability. Measurements of WDME performed on the same day had a CV of 3 +/- 1%, so that WDME provides a precise noninvasive means to measure lung weight in acute studies.

Improved pulmonary nodule detection with scanning equalization radiography.

The potential for improved pulmonary nodule detection with scanning equalization radiography (SER) was evaluated by means of observer performance testing during the interpretation of posteroanterior conventional radiographs and SER images of an anthropomorphic chest phantom with simulated nodules. A test set of 200 conventional and 200 SER radiographs of phantoms containing either one nodule or none was interpreted by four radiologists attempting to detect a nodule and indicate a confidence value. Their ability to detect nodules positioned over the lung was slightly improved with SER compared with conventional radiography (sensitivity, .56 vs .70); for nodules over the mediastinum or diaphragmatic areas, it was much improved (sensitivity, .29 vs .64). The results were also analyzed with receiver-operating characteristic methods, which revealed a significant improvement in lesion detect-ability over the thicker body parts with SER images. The capability of equalized chest radiographs to provide improved lesion detectability suggests that SER may set a new standard for film-based chest radiography and have a large clinical application.

Computerized search of chest radiographs for nodules.

A computer program that recognizes potential pulmonary nodules in PA chest radiographs has been developed. This program produces a display of candidate nodules that require interpretation by a radiologist. Some false positives are rejected by a program, the Nodule Expert. Detection performance with and without Nodule Expert has been evaluated. Using the untrained program (no Nodule Expert), and after inspecting 45 candidate nodules, a radiologist may be confident that a nodule was inspected, if one was located by the program. When pattern recognition techniques are incorporated, the number of false positives presented for inspection is reduced. The radiologist must inspect, at most, 10 candidate nodules to be confident of having inspected a nodule, if one was located by the program. Concomitant with this decrease in the candidate nodule false-positive rate is a decrease in sensitivity (film true-positive rate) from 92 to 86%. This program was trained on candidate nodules from 37 radiographs and also tested on these 37. Some of the features used by the pattern classifier to classify candidate nodules are comparable to those used by human observers.

Measurement of lung gas volume and regional density by computed tomography in dogs.

To determine if computed tomography (CT) can accurately measure lung volume, we compared lung gas volume measured by helium dilution with the equivalent volume calculated from CT total lung volume and density in 13 supine dogs. CT lung gas volume underestimated helium volume by 34% (range: -63 to 0%). Studies of wooden lung phantoms varying in density from 0.082g/cc to 0.776g/cc showed that only 15% of this error could be mimicked by the phantoms. The rest of the discrepancy is attributed to the lung's irregular borders, and the sharp density gradients surrounding and within the lung that result in x-ray beam hardening, sampling limitations, and partial volume measurement errors. Serial biweekly measurements in three dogs for 14 weeks showed CT gas volume to be highly reproducible with less scatter than seen in the helium measurements. Density in the lungs of all dogs showed a uniform gradual decrease from approximately 0.60g/cc at the dependent surface to 0.20g/cc at the superior surface with relatively constant density at any horizontal level. These studies show that whereas CT underestimates gas volume in the lungs, serial measurements are highly reproducible in experimental studies and are a promising technique to monitor diseases or response to therapy. Density gradients in the lungs were sufficiently uniform so that disruption of the normal gradient may be an indicator of early lung disease.

Chest equalization radiography.

The conventional chest radiograph has a number of limitations as a diagnostic method of evaluating chest disease. The wide variation in attenuation between the lung and mediastinum frequently results in images with low contrast over the thicker portions. This, coupled with the presence of intense body-scattered radiation that must be adequately removed, makes chest radiography one of the most challenging diagnostic procedures in conventional radiography. Scanning equalization radiography (SER) is an alternative method of chest imaging that overcomes these limitations without employing other highly complex or expensive solutions such as digital imaging. Recent clinical studies have shown that diagnostic efficacy is improved with SER, and that SER offers the potential of significantly reducing the frequency of diagnostic errors and repeated examinations while producing cost savings.

Scanning equalization radiography of the chest: assessment of image quality.

An evaluation of the image quality of scanning equalization radiography (SER) of the chest was conducted with 60 volunteer patients. Posteroanterior chest radiographs by SER and conventional methods were compared by six radiologists to determine the adequacy and uniformity of the film exposure and the visualization of normal anatomic structures. The radiographs by the SER technique were deemed to be superior for visualization of most anatomic features. With SER there were no film artifacts from the scanning technique and there was only occasional blurring of some structures with a 4.7-sec scan time.

Improved chest disease detection with scanning equalization radiography.

The efficacy of chest disease detection with scanning equalization radiography (SER) was evaluated in a clinical study of 95 patients: 51 normals and 44 with abnormal chest radiographs. A conventional and an SER image of each patient were interpreted independently by four radiologists. The increased numbers of true positives (3%) and true negatives (9%) when the SER images were interpreted were statistically significant. There was also a reduced number of false positives (7%) with SER. This improved disease detection was noted by each of the radiologists and led to more frequent agreement (11%) of the correct interpretation among the radiologists.

Amiodarone pulmonary toxicity. Chest radiography and CT in asymptomatic patients.

Two asymptomatic patients from a group of 30 being treated with the antiarrhythmic drug amiodarone developed roentgenographic pulmonary and pleural reactions. Computed tomography in one patient with an uncommon radiographic pattern of fuzzy nodules showed the spatial distribution of the parenchymal changes, as well as unrecognized pleural thickening. The disease in these asymptomatic patients was presumably detected on the periodic chest roentgenogram at an early stage because the changes disappeared after withdrawal of the drug. Periodic chest radiographs are recommended during amiodarone therapy and CT may be useful in evaluation of patients with unusual chest radiographic findings.

Exposure equalization radiography of the chest: clinical comparison of slit and raster scanning techniques.

Exposure equalization radiography systems with scanning slit and raster geometries were constructed and tested with 75 patients. The scanning equalization radiography (SER) technique uses a detector, placed behind the patient, connected in a feedback loop to a microprocessor-controlled x-ray source. The detector monitors the transmitted radiation, and in turn the x-ray output is varied to equalize the radiographic film density over the entire image. The clinical evaluation of these systems included 25 posteroanterior (PA) chest radiographs by an SER slit-geometry system (5.0-sec scan time), 25 PA chest radiographs by an SER raster-geometry system with an 8.8-sec scan time, and 25 PA chest radiographs by an SER raster-geometry system with a 4.7-sec scan time. These SER radiographs were compared to conventional radiographs of the same patients by two radiologists. The observers noted that the SER slit radiographs had seriously overexposed areas in 80% of instances, and that any potential gains from this system were offset by the overexposure problems. The radiographs obtained by the SER raster technique with a 4.7-sec scan time showed more uniform and adequate exposure in 80% of instances and better visualization of normal anatomic detail in the lung (52%) and mediastinum (84%) than conventional radiographs. The radiographs obtained by the SER raster technique with an 8.8-sec scan time showed fewer peripheral lung markings in 15 of 25 cases, presumably due to motion. In all other respects, the images were similar in quality to the SER raster 4.7-sec radiographs.

The development of a standard set of chest radiographs to test a radiologist's expertise.

Six test sets of normal and abnormal chest radiographs were presented to eight radiologists for their interpretation. Based upon their responses to these tests, it was determined that some radiologists consistently overread, some underread, and others do neither. From an analysis of the radiologist's responses, cases from the two best test sets could be combined to produce a standard test set of 50 to 60 chest radiographs representing a variety of pulmonary diseases. This test then could measure a radiologist's proficiency at interpretating the normal and abnormal chest, and those who consistently differ with their colleagues would be so informed.

A scanning equalization system for improved chest radiography.

The wide variation in absorber thickness characteristic of the posteroanterior projection of the chest routinely results in film underexposure and attendant suboptimal contrast in the mediastinal, retrocardiac, and diaphragmatic regions. We propose a special scanning system to deliver a more uniform film exposure over the image by modulating the intensity of a vertically oriented narrow fan (43 x 2 cm) of radiation, swept laterally across the patient's chest. Measurements of patient attenuation obtained with a detector placed behind the film cassette are used to adjust the x-ray tube output so as to maintain a constant film exposure during the course of the scan. The scan is completed in 5 seconds and results in images of significantly improved mediastinal penetration and contrast compared with those of conventional chest radiographs.