What is the actual width of a kidney imaged with an OID of 18 cm, where the projected width is 9 cm at a SID of 105 cm?

To determine the actual width of the kidney using the given information, we can use the principles of geometry related to object size, image size, source-to-image distance (SID), and object-to-image distance (OID).

The formula we can use relates these distances and measurements as follows:

Actual Width = (Projected Width × SID) / (SID - OID)

In this case:

• The projected width of the kidney is 9 cm.

• The SID is 105 cm.

• The OID is 18 cm.

Plugging in these values into the formula:

Actual Width = (9 cm × 105 cm) / (105 cm - 18 cm)

Actual Width = (945 cm²) / (87 cm)

Actual Width ≈ 10.86 cm

Given the available choices, rounding this value off to match the options suggests the closest is 11 cm.

The answer of 7.5 cm does not accurately reflect the calculation and is lower than the correctly calculated actual width based on the relationship defined in the formula. The same applies to the other options, which don't align with the calculation based on SID and OID considerations. Therefore, a more accurate understanding yields an actual width of approximately 11 cm,