Multiple Choice
Passage
Positron emission tomography (PET) is a medical imaging technique used for the detection of tumors and the evaluation of neurological functions. A radiopharmaceutical (radioactive tracer) injected into a patient undergoes positive beta decay and emits a positron. The positron undergoes an annihilation event with a nearby electron (<1 mm away) , which emits a pair of 511 keV gamma ray photons traveling in opposite directions. The gamma rays are detected by a ring of scintillation detectors surrounding the patient, as shown in Figure 1. The difference in detection time between the two gamma rays from the same annihilation event is used to determine its location. An image is constructed from data collected from multiple emission events.
Figure 1 Basic setup and process of positron emission tomographyScintillation, the emission of detectable light when excited electrons return to their ground state, occurs in crystals within the detectors due to the transfer of energy from the high energy gamma rays. The wavelength of the emitted light depends exclusively on the type of scintillation material used (Table 1) .Table 1 Common PET Scintillating Crystal Materials
The electrons in the scintillating crystals are excited through Compton scattering, a process in which a gamma ray photon acts as a particle, and transfers energy to an electron via collision. Subsequently, the photon scatters (travels in a new direction) and its wavelength changes. The percent change in the wavelength of the photon due to the energy loss is
Equation 1where θ is the angle between the scattered photon and electron. Equation 1 is represented in Figure 2.
Figure 2 Percent change in photon wavelength due to Compton scattering
-The radiopharmaceutical administered to a patient is carefully chosen to provide a specific number of positron emissions per second. If the rate of positron emissions is increased, which of the following can be expected?
A) Higher individual gamma ray energy
B) Higher gamma ray intensity
C) Higher scintillation photon frequency
D) Higher scintillation photon velocity
Correct Answer:

Verified
Correct Answer:
Verified
Q33: Circularly polarized light results from the vector
Q34: Uniform magnetic fields created by advanced medical
Q35: Two transverse waveforms (A and B) travel
Q36: Passage<br>During deep underwater dives, scuba divers must
Q37: Passage<br>Laparoscopy is a minimally invasive surgical procedure
Q39: An 8-F parallel plate capacitor generates a
Q40: A gram-negative bacterium moves along a flat
Q41: Passage<br>The effects of gravity are effectively negated
Q42: In the presence of an external magnetic
Q43: What expression gives the wavelength of the