For SID 80 cm, the light field should match the exposure field within +/- 2% of SID. What is this distance in centimeters?

For SID 80 cm, the light field should match the exposure field within +/- 2% of SID. What is this distance in centimeters?

• A. 1.6 cm
• B. 0.8 cm
• C. 4.0 cm
• D. 8.0 cm

Answer: (A)

The light field alignment tolerance is expressed as a percentage of the source-to-image distance (SID). Here, 2% of SID means 0.02 times SID. At an SID of 80 cm, that is 0.02 × 80 = 1.6 cm. So the light field must match the exposure field within about 1.6 cm. The other distances reflect different percentages (1% would be 0.8 cm, 5% would be 4 cm, 10% would be 8 cm), which are outside the specified 2% tolerance. This 1.6 cm margin ensures the irradiated area aligns with the intended exposure and helps minimize unnecessary radiation outside the field.

The light field alignment tolerance is expressed as a percentage of the source-to-image distance (SID). Here, 2% of SID means 0.02 times SID. At an SID of 80 cm, that is 0.02 × 80 = 1.6 cm. So the light field must match the exposure field within about 1.6 cm. The other distances reflect different percentages (1% would be 0.8 cm, 5% would be 4 cm, 10% would be 8 cm), which are outside the specified 2% tolerance. This 1.6 cm margin ensures the irradiated area aligns with the intended exposure and helps minimize unnecessary radiation outside the field.