CAMRT Radiography Practice Exam

How will an image appear if only the center cell is selected using AEC for a PA chest?

1. Underexposed (light)

2. Overexposed (dark)

3. Correctly exposed

4. Blurry

The correct answer is: Overexposed (dark)

When only the center cell is selected using Automatic Exposure Control (AEC) for a posteroanterior (PA) chest radiograph, the resulting image is likely to be overexposed. In a PA chest X-ray, the heart and great vessels are located centrally, and the center cell is designed to measure the radiation transmitted through these structures. However, in practice, this method may lead to overexposure for a few reasons. The center cell receives a significant amount of radiation as it is positioned over denser areas, such as the heart and mediastinum. If the exposure timer does not account for additional attenuation created by the surrounding lungs, which are less dense, the resulting image may record more exposure than what is clinically appropriate, leading to a darker appearance. When using AEC, it is crucial to ensure that the selected cell accurately represents the anatomy of interest. For a PA chest radiograph, utilizing only the center cell may not provide an adequate representation of the overall thoracic structure, thus affecting the exposure settings and resulting image quality. To achieve the best imaging results, radiographers typically use multiple cells or an overall average to balance the varying densities encountered in the thoracic region.