Question

(a) Name 4 major components of a Gamma camera. Briefly explain the function of each component.
Also, describe the advantages and disadvantages of using “thin” scintillating crystal.

(b) In an experiment with 51.80 MBq 99mTc, 5.88×105 counts are measured in 2 minutes. According to the manufacturer the sensitivity is 202 cnts/(min⋅μCi) (American manufacturers still use Ci instead of Bq, 1μCi = 37 kBq). What is the difference between the sensitivity of the measurement and the factory specification?

(c) in a NM scan, we use a specific contrast agent with half-life of 2h and emitted gamma radiation with wavelength of the 8.79x0-12 m. We image the patient immediately after the injection and the scan takes 20 minutes. Injecting 1 mCi, the acquired NM images have signal-to-noise ratio of 40. Calculate the SNR if we inject the patient with 3 mCi and scan him for 60 minutes.

Answer 1

(a) The major components and there functions in a gamma camera are:

1. Photomultiplier Tubes: These are responsible for amplifying the number of photons. This makes sure that the number of photons falling on the detector is above a threshold value and can be detected by using the detector.

2. Scintillation crystal: These crystals produce the photons in response to detecting gamma radiation. These photons then goes through the photomultiplier tubes before going to detector. As the name implies the crystal scintillates on detecting incoming gamma radiation.

The advantage of using thin scintillation crystal is that it is sensitive to low energy X-rays and are completely impervious to the high energy background radiation. The disadvantage is that, as the scinillators becomes more thin the amount of photons generated in response to detected gamma radiation also decreases, and for better detection we need to increase the number of photomultiplier tubes so that we can detect the gamma radiation signals.