Scatter Reflection

Chapter 1

1.1 INTRODUCTION

The aim of this research work is to investigate the scatter correction by dual and triple energy windows in SPECT system. SPECT that stands for (single Photon Emission Computed Tomography) is a technique for tracing radioactive tracers in the body and provide three dimensional maps of in vivo radiopharmaceutical distributions. The primary objective of SPECT is to provide accurate quantitative cross-sectional image. Its main benefit is to Increase the image contrast due to reduction in background activity super imposed on object activity, gives depth information about the deep laying lesions, and to increase the accuracy of quantification. In SPECT require correction for both attenuation and scatter. Scatter correction

[2]. Hence, SPECT imaging is performed by using a device “gamma camera” which is given below; INSTRUMENTATION

1.3.1 Gamma Camera

The gamma or scintillation camera is an imaging device that is mostly used in nuclear medicine imaging [3] and was developed by Hal Anger in 1958 to image Gamma radiations which are emitted by the body [4]. The schematic gamma camera is shown in figure 1.2 Figure 1.2: Shows the schematic diagram of Gamma camera.

The gamma camera system performs two functions: the detection of single photons events and the measurement of its energy and position. [5] The gamma camera consists of several components which are Collimator scintillation crystal an array of photomultiplier tubes (PMTs) a pulse height analyzer computer and picture archiving system.

The electrodes between the photocathode and the anode are called “dynodes,” [22]. When an electron hit a dynode, not only does it bounce to the next dynode, but it also several additional electrons are released and sent to next dynode. At the next dynode, the process repeats and so on resulting in a dramatic multiplication of the initially released electrons. [23]

1.3.5.3ANODE

Anode is the last component if photo multiplier tube. An anode basically collects the electron avalanche, providing output signal. [26]

1.3.6 Pulse height analyzer:

Those gamma rays emitted by the source and absorbed within the crystal by photoelectric effect, produce scintillation light emission just in site of interaction and some gamma rays can deviate from the original path way by Compton scattering inside the body of the patient. These gamma rays reach the crystal with lower energy than that of the emission. Compton scattering can also be produced within the crystal. The scattered gamma rays have less energy than that of the original emission, they can eliminate by using pulse height analyzer (PHA) is shown figure 1.8 within a certain window.

Figure 1.8 shows the operation of pulse height analyzer only those pulse within the window should be excepted for