The collimated boundaries of the exposure field should always be equal in size to the:

• A. Image receptor size
• B. Anatomy of interest
• C. Physical grid dimensions
• D. Patient weight

Answer: (B)

Target the exposure with collimation to the anatomy of interest. Bounding the beam to exactly the area you're examining keeps the entire structure within the field while excluding surrounding tissues. This focused field reduces patient dose and minimizes scatter, which improves image contrast and sharpness.

In practice, you want the exposure field to cover the anatomy of interest with a small margin for positioning—just enough to ensure the entire structure is captured but not so large that extra tissue is irradiated. For example, when imaging a hand, collimate to just the hand bones and adjacent soft tissue rather than the size of the image receptor or the forearm.

The other factors listed don’t determine the field size. The image receptor size may be larger than the anatomy and isn’t what fixes the field to the region of interest. Grid dimensions and patient weight influence dose and scatter management, not the fundamental boundary of the exposure field.