Nuclear Medicine Instrumentation 242 NMT 1 Dr. Abdo Mansour Assistant Professor of radiology

2 Lecture No. 3 Scintillation Detectors

1- SODIUM IODIDE WELL COUNTER 3 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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5 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.

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. 6 Photomultiplier tube (PMT)

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. 7 Photomultiplier tube, cont.

GAMMA SCINTILLATION CAMERA The most widely used imaging devices in nuclear medicine are the simple gamma scintillation (Anger) camera. The single- photon emission computed tomography (SPECT) and Positron Emission tomography (PET) capable gamma camera. 8

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 of the radionuclide into organ. 9 Function of gamma camera

The basic components of gamma camera system are: 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. 10 Components of gamma camera

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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. 16

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. 17 Function of Crystal

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. 18 Function of PMTs

19 Finally, the electrical current forming the medical image for organ in interest.

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