Compared with CT, planar radiography doses are generally:

• A. Higher
• B. Lower
• C. Similar
• D. Unknown

Answer: (B)

The key idea is how much energy is deposited in the body to create the image. Plain radiography uses a single, brief x-ray exposure in one projection, so the total energy delivered is relatively small. CT, on the other hand, rotates around the patient and collects hundreds of views to reconstruct cross-sectional images, often with higher tube current and longer cumulative exposure per slice. Even with modern dose-saving features, the overall amount of radiation from CT is much greater because you’re irradiating the patient through many angles and slices.

For context, a typical single-view chest radiograph is on the order of hundredths of a millisievert, whereas a chest CT is usually several millisieverts. So, in general, planar radiography doses are lower than CT.