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.
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.
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.
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