GAMMA CAMERA MACHINE (2)

COMPONENTS OF GAMA CAMERA:

2) SCINTILLATION DETECTOR [NaI(Tl)]:
 The radiation coming from the collimator is received by the crystals to be converted into light photons. NaI(Tl) crystal with 1.25cm thick x 30-50 cm in diameter.Thinner crystal is preferred for Anger camera in order to get better intrinsic resolution therefore better image.

 

3)  PHOTOMULTIPLIER TUBES (PMT's): 

  At the face of the PMT is a photocathode which converts the light photons into electrons. PM tubes (37,61,75 or 91, round, hexagonal or square shapes) arranged in hexagonal pattern, Then the electrons get amplified during the passage through many dynodes. This process is repeated for each electron. The final large cluster of electrons is collected at the anode in order to convert them into electrical signals. Part of the signal processing circuitry (preamplifier, pulse height analyzers, amplifier, pulse pile-up rejection etc.) is attached to each PM tube and sealed in a light-tight protective housing.

SCHEMATIC DIAGRAM OF PMT

 

GROUP OF PMT's IN HEAD OF GAMMA CAMERA

4) PRE-AMPLIFIER:
Preamps attach above the PMT.The amount of charge given by PMT is very small. Even though we have used a sophisticated photodetector like a PMT we still end up with quite a small electrical signal.A very sensitive amplifier is therefore needed to amplify this signal. This type of amplifier is generally called a pre-amplifier.

5)  Position logic circuit:
Using resistive-coupled network to provide positional information from outputs of photomultiplier tubes .

6) Computer:
This works to process the incoming data to be finally displayed as a readable image for diagnosis. Images can be stored also.