Plewes D B, Wandtke J C
Radiology. 1982 Mar;142(3):765-8. doi: 10.1148/radiology.142.3.7063700.
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.
胸部后前位投照中吸收体厚度存在很大差异，这通常会导致胶片曝光不足，进而使纵隔、心后和膈区的对比度欠佳。我们提出一种特殊的扫描系统，通过调制垂直方向的窄扇形（43×2厘米）辐射的强度，并在患者胸部横向扫描，从而在图像上实现更均匀的胶片曝光。用置于暗盒后的探测器测量患者的衰减情况，以此来调整X射线管输出，以便在扫描过程中保持胶片曝光恒定。扫描在5秒内完成，与传统胸部X光片相比，所得图像的纵隔穿透力和对比度显著提高。
