Nuclear Cardiology Boards Practice Test

Decreasing collimator hole size results in which changes to resolution and sensitivity?

Resolution increases; sensitivity decreases Resolution decreases; sensitivity increases Both increase No change

Correct Answer:

Resolution increases; sensitivity decreases

Explanation:

Smaller collimator holes improve spatial resolution because only photons traveling very close to the hole axis can reach the detector, reducing geometric blur from photons entering at oblique angles. This tighter angular acceptance sharpens the image, giving better detail. However, the smaller hole also limits how many photons can pass through, so the overall photon flux reaching the detector drops—lower sensitivity. The net effect is a gain in resolution at the cost of reduced sensitivity, so the correct description is that resolution increases while sensitivity decreases.

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