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Gamma Camera

Basic Principles


By Muhammad Afiq
Detector Head of Gamma Camera
Gamma rays which are not travelling in proper
direction will be absorbed by collimator before they
reach the detector.

COLLIMATOR
Collimator projects an image of the source
distribution onto the detector by allowing only those
gamma rays travelling along certain directions to
reach detector.

Inherently inefficient; over 99.9% of potentially useful
radiation travelling toward detector are stopped by
collimator resulting poor quality image

COLLIMATOR TYPES
• Allow acquisition of image that representing the
actual size of body part as close as possible.
• Eg: LEHR, LEHS, LEAP/LEGP, MEHR, HEAP/HEGP,
HEHR, slanted hole
Parallel hole
LEHR
COLLIMATOR TYPES
• Allow acquisition of image that representing the
actual size of body part as close as possible.
• Eg: LEHR, LEHS, LEAP/LEGP, MEHR, HEAP/HEGP,
HEHR, slanted hole
Parallel hole
HEGP
• Allow acquisition of image depending on
procedure (magnification or minification)
• Eg: fan beam, pinhole, diverging, converging
Non-parallel hole
COLLIMATOR TYPES
SCINTILLATION DETECTOR
SCINTILLATION DETECTOR
Incident photon
Atom
Atomic Electron
Scattered photon
Light photon
Secondary electron
Ejected Electron
Photomultiplier tube (PMT)
High Voltage supply
Electronic Circuitries
(Analog)
Digital Positioning Circuit
Phosphor
Crystal
PM Tube
X
-

signal
Y
-

signal
Y
+

signal
X
+

signal
Continue..
After the position of interaction is determined using positioning circuit, the analog signal is sent
to summing circuit to determine the amplitude of signal.
The analog signal is then sent to Pulse Height Analyzer (PHA), which analyzes
their amplitude and selects only those of desired energy by the use of appropriate
peak and window settings.
The signals is then sent to CRT for viewing or to be digitized using Analog to Digital Converter
(ADC) to adapt with the use of present digital computer and video monitor.