Nuclear Medicine
Instrumentation
242 NMT
Dr. Abdo Mansour
Assistant Professor of radiology
E-mail : a_mansour@inaya.edu.sa
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Lecture No. 3
Scintillation
Detectors
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1- SODIUM IODIDE WELL COUNTER
 Well counters are common in nuclear medicine
laboratories for performing in vitro studies as well
as quality control and assurance procedures.
 Many sodium iodide well counters are designed for
counting radioactive samples in standard test
tubes.
 Generally, there is a solid cylindrical sodium iodide
crystal with a cylindrical well, into which the test
tube is placed.
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Well counter. Well counters are heavily
shielded scintillation crystals used to measure
and identify small amounts of radioactivity
contained in small volumes such as a test tube.
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Photomultiplier tube (PMT)
 A photomultiplier tube (PMT) is optically coupled
to the crystal base.
 Radiation from the sample interacts with the
crystal and is detected by the PMT, which feeds into
a scalar.
 The scalar readout directly reflects the amount of
radioactivity in the sample and is usually recorded
in count for the time period during which the
sample is measured.
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Photomultiplier tube, cont.
Reflected light and scattering inside
the well and the thickness of the
crystal limits the energy resolution
of the well counter.
Because the sample is essentially
surrounded by the crystal, the
geometric efficiency for detection of
gamma rays is high.
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GAMMA SCINTILLATION CAMERA
The most widely used imaging
devices in nuclear medicine are
the simple gamma scintillation
(Anger) camera. The singlephoton emission computed
tomography
(SPECT)
and
Positron Emission tomography
(PET) capable gamma camera.
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Function of gamma camera

A gamma camera converts photons
emitted by the radionuclide in the
patient into a light pulse and
subsequently into a voltage signal.
This signal is used to form an image
of
the
distribution
radionuclide into organ.
of
the
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Components of gamma camera
 The basic components of gamma camera
system are:
1- The collimator,
2- The scintillation crystal,
3- An array of photomultiplier tubes (PMTs),
preamplifiers,
4- A pulse height analyzer (PHA),
5- digital correction circuit,
6- The control console.
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Crystal and Other Photon Detector Devices
 Radiation emitted from the patient and
passing through the collimator typically
interacts with a thallium activated
sodium iodide crystal.
 Crystals also can be made with thallium
activated cesium iodide or even
lanthanum bromide, but these are
uncommon.
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Function of Crystal
Interaction of the gamma ray or
gamma photons with the crystal
may result in ejection of an orbital
electron
(photoelectric
absorption), producing a pulse of
fluorescent light or light photons
(scintillation event) proportional
in intensity to the energy of the
gamma ray.
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Function of PMTs
 PMTs situated along the posterior face of
crystal to detect these light photons and
amplify it.
 PMTs convert light photons into electric
current.
 About 30% of the light from each event
reaches the PMTs.
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Finally,
the
electrical
current
forming
the
medical image for organ in
interest.
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Thank You
for your
Attention