American Society of Radiologic Technologist (ASRT) Practice Exam

An increase in patient exposure will result from:

1. decreasing mAs

2. decreasing object-to-image distance (OID)

3. increasing grid ratio

4. increasing focal spot size

The correct answer is: increasing grid ratio

Increasing the grid ratio can lead to an increase in patient exposure. Grids are used in radiography to improve image quality by reducing the amount of scattered radiation that reaches the film or detector. However, with a higher grid ratio, a greater height of the lead strips is employed in relation to the distance between them, which enhances the grid's ability to absorb scatter. This also necessitates an increase in the amount of primary radiation required to penetrate the grid effectively, thereby increasing the overall radiation exposure to the patient. In contrast, decreasing mAs leads to a reduction in patient exposure, as this parameter directly influences the quantity of radiation produced. Decreasing object-to-image distance (OID) typically reduces patient exposure because it decreases the distance the primary beam must travel, which reduces scatter. Increasing focal spot size does not significantly affect the patient’s exposure; it mainly impacts the resolution and sharpness of the image rather than the amount of radiation received.