Quality Control & Equipment Assurance Flashcards

What is the primary purpose of performing a daily flood field uniformity test on a gamma camera?

Answer: To detect non-uniformities in detector sensitivity that could degrade image quality

Flood field uniformity tests reveal variations in detector sensitivity across the field of view, which can produce artifactual hot or cold regions in clinical images.

An intrinsic flood field uniformity test is performed by:

Answer: Removing the collimator and using a distant point source to irradiate the bare crystal uniformly

Without a collimator, a distant point source provides a uniform flux of photons across the NaI crystal, isolating intrinsic detector performance from collimator effects.

Which term describes the maximum count-rate difference between any pixel and the mean count rate across the entire detector field of view in a uniformity test?

Answer: Integral uniformity

Integral uniformity expresses the global maximum deviation from the mean count rate across the full useful field of view, while differential uniformity measures local pixel-to-pixel variation.

The 'peaking' procedure performed before gamma camera imaging refers to:

Answer: Adjusting the photomultiplier tube high voltage to center the energy window on the radionuclide photopeak

Peaking ensures the energy window is correctly positioned at the photopeak of the radionuclide in use, maximizing true coincidence detection and minimizing scatter acceptance.

A bar phantom placed in front of a gamma camera is used primarily to assess:

Answer: Spatial resolution and spatial linearity

Bar phantoms contain alternating lead strips of known widths; the ability to distinguish individual bars evaluates spatial resolution, and any curvature of bar images indicates spatial non-linearity.

The acceptable limit for integral uniformity on a modern digital gamma camera, as recommended by NEMA standards, is:

Answer: Less than 5%

NEMA standards specify that integral uniformity should be less than 5% for clinical cameras; values exceeding this threshold can introduce significant image artifacts.

Which of the following best describes the energy resolution of a gamma camera?

Answer: The full-width at half-maximum (FWHM) of the photopeak expressed as a percentage of the peak energy

Energy resolution is expressed as the FWHM of the photopeak divided by the peak energy, expressed as a percentage; better resolution means the camera more effectively rejects scattered photons.