Select the single best answer for each question.
1. During a gamma-camera acquisition, gamma photons emitted from different locations within the patient may reach the detector. Which component provides the spatial information required to determine the probable direction of origin of the detected photons?
A. Scintillation crystal
B. Collimator
C. Photomultiplier tube
D. Pulse-height analyser
E. Positioning circuit
2. During a planar bone scan using a parallel-hole collimator, the technologist positions the detector 20 cm above the patient. The detector is subsequently moved as close as possible to the patient without changing any other acquisition parameter. What is the most likely effect on the acquired image?
A. Improved spatial resolution
B. Reduced intrinsic spatial resolution
C. Increased septal penetration
D. Increased scattered-photon rejection
E. Reduced radionuclide count rate
3. A patient is scheduled for a99mTc bone scan. Before imaging, the gamma-camera count rate is found to be approximately half the expected value. Image quality must be maintained without changing the collimator, energy window, matrix size or patient positioning. Assuming negligible detector dead-time and patient movement, which action is most appropriate to obtain approximately the same total number of counts as originally planned?
A. Halve the acquisition time
B. Double the acquisition time
C. Double the matrix size
D. Widen the energy window by a factor of two
E. Increase the source-to-detector distance
4. A technetium-99m acquisition is performed using an energy window centred on its 140-keV photopeak. What is the principal reason for selecting this energy window?
A. To correct for patient movement during acquisition
B. To improve the intrinsic spatial resolution of the detector
C. To preferentially accept unscattered photons and reject many scattered photons
D. To prevent high-energy photons from penetrating the collimator septa
E. To compensate for non-uniform photon attenuation within the patient
5. Following a SPECT uniformity quality-control test, several areas of non-uniform detector response are identified. A patient SPECT acquisition is subsequently performed without applying the appropriate uniformity correction. Which artefact is most likely to appear in the reconstructed transaxial images?
A. Ring artefact
B. Truncation artefact
C. Respiratory-motion artefact
D. Partial-volume artefact
E. Misregistration artefact