NMTCB Instrument Operations & Quality Control 2 — Questions and Answers
Question 1: Which QC test is performed daily on a gamma camera to verify the uniformity of detector response across the field of view?
- Intrinsic uniformity flood (Correct answer)
- Energy resolution test
- Spatial linearity check
- Sensitivity calibration
Correct answer: Intrinsic uniformity flood
A daily flood uniformity acquisition (intrinsic or extrinsic) confirms that detector response is uniform across the entire field of view.
Question 2: On a PET scanner, what is the purpose of performing a normalization scan?
- To correct for detector efficiency variations between crystal pairs (Correct answer)
- To calibrate the energy window to 511 keV
- To verify time-of-flight resolution
- To measure the scanner's axial sensitivity profile
Correct answer: To correct for detector efficiency variations between crystal pairs
Normalization corrects for non-uniform detector efficiencies among the many crystal pairs in a PET ring so that reconstructed images have uniform sensitivity.
Question 3: A technologist notices that the center of rotation (COR) for a SPECT system is off by more than 2 pixels. What is the most likely consequence if imaging proceeds without correction?
- Ring artifacts in reconstructed SPECT images (Correct answer)
- Increased scatter in projection data
- Overestimation of administered activity
- Poor energy resolution on the peakogram
Correct answer: Ring artifacts in reconstructed SPECT images
An uncorrected COR offset causes ring or 'bull's-eye' artifacts in SPECT reconstructed images, degrading image quality significantly.
Question 4: What does the energy resolution of a scintillation detector describe?
- The ability to distinguish photons of slightly different energies (Correct answer)
- The maximum count rate the system can process
- The time required to process each detected event
- The spatial separation of two point sources
Correct answer: The ability to distinguish photons of slightly different energies
Energy resolution, expressed as % FWHM of the photopeak, reflects how well the detector discriminates between photons of closely spaced energies.
Question 5: Which quality control test for a well counter verifies that the system gives consistent counts for the same source activity on different days?
- Reproducibility (precision) test (Correct answer)
- Minimum detectable activity test
- Chi-square test
- Linearity test
Correct answer: Reproducibility (precision) test
A reproducibility or precision test involves repeated counting of a long-lived standard source to confirm day-to-day consistency of the well counter.
Question 6: What is the primary purpose of the chi-square (χ²) test in nuclear medicine instrumentation QC?
- To verify that a counting system exhibits Poisson (random) statistics (Correct answer)
- To measure detector dead time at high count rates
- To assess spatial resolution with a bar phantom
- To confirm energy window centering on the photopeak
Correct answer: To verify that a counting system exhibits Poisson (random) statistics
The chi-square test confirms that repeated counts of a stable source follow the expected Poisson distribution, indicating proper random counting behavior.
Question 7: When performing an extrinsic flood for gamma camera uniformity QC, the collimator is left ON. Why might an intrinsic flood (collimator removed) be preferred for routine uniformity testing?
- It detects subtle non-uniformities in the crystal and PMT array without collimator effects (Correct answer)
- It requires a higher-energy radionuclide source
- It takes far fewer counts to achieve statistical adequacy
- It eliminates the need for energy window adjustment
Correct answer: It detects subtle non-uniformities in the crystal and PMT array without collimator effects
Intrinsic floods bypass collimator-related artifacts and directly reveal non-uniformities in the NaI crystal and photomultiplier tube array.
NMTCB Instrument Operations & Quality Control 2
Which QC test is performed daily on a gamma camera to verify the uniformity of detector response across the field of view?