Chapter 22: Source-to-Image Receptor Distance (SID) Objectives

The effect of increasing SID on image penumbra and spatial resolution is:

• Penumbra increases, spatial resolution decreases

• Penumbra decreases, spatial resolution increases

• Both penumbra and spatial resolution increase

• Both penumbra and spatial resolution decrease

The effect of SID on image magnification is:

• Increased SID decreases magnification

• Increased SID increases magnification

• SID has no effect on magnification

• Magnification is only affected by OID

Describe the diagnostic advantage of the effect of lengthened SID on increased field-of-view.

• It reduces image distortion and improves spatial resolution.

• It increases patient dose significantly.

• It decreases the field-of-view.

• It causes more image blurring.

Calculate the ratio differences between SID and SSD to show how increasing SID can reduce patient entrance skin dose.

• Increasing SID increases the ratio, reducing entrance skin dose.

• Increasing SID decreases the ratio, increasing entrance skin dose.

• SID and SSD ratio has no effect on entrance skin dose.

• Increasing SID does not change the entrance skin dose.

The inverse square law applies to changes in the SID because:

• The intensity of radiation is directly proportional to the square of the distance from the source.

• The intensity of radiation is inversely proportional to the distance from the source.

• The intensity of radiation is inversely proportional to the square of the distance from the source.

• The intensity of radiation does not change with distance from the source.

Any change greater than 15% in the SID should be compensated for with technique, especially for digital images because:

• It affects image contrast significantly.

• It can result in improper image exposure.

• It increases patient discomfort.

• It improves image sharpness.

Calculate exposure changes using the inverse square law.

• Exposure is inversely proportional to the square of the distance.

• Exposure is directly proportional to the distance.

• Exposure is not affected by distance.

• Exposure is inversely proportional to the distance.

Calculate various technique adjustments using the square law.

• By doubling the distance, the intensity becomes one-fourth.

• By doubling the distance, the intensity becomes half.

• By doubling the distance, the intensity remains the same.

• By doubling the distance, the intensity becomes double.

State the rules of thumb for landmark SID changes, especially between 100 and 180 cm.

• The exposure should be doubled when increasing SID from 100 to 180 cm.

• The exposure should be halved when increasing SID from 100 to 180 cm.

• No change in exposure is needed when increasing SID from 100 to 180 cm.

• The exposure should be reduced to one-fourth when increasing SID from 100 to 180 cm.

List those image qualities not directly affected by SID.

• Contrast and spatial resolution are not directly affected by SID.

• Density and magnification are not directly affected by SID.

• Contrast and magnification are not directly affected by SID.

• Spatial resolution and density are not directly affected by SID.