Single Photon Emission Tomography (SPECT) is a technique for producing 3D images from 2D images of injected radionuclide in the body. The 2D image is obtained by using a device such as a gamma camera. This comprises of a large (0.5 diameter) crystal of NAI, which emits flashes of light when γ-rays impinge on it. A metal plate with parallel holes drilled through it select only those γ-rays traveling in lines normal to the surface of the crystal, ensuring a 2D representation in the crystal of where the radionuclide is positioned. These flashes of light are then detected by an array of photomultiplier tubes which give location and photon energy information. By rotating the Gamma camera around the subject, a series of projections are obtained, which can then be combined into a 3D image in the same way as CT and MRI.
Double and triple camera systems are often employed to speed up data acquisition. SPECT is used frequently in cardiology, to gauge the severity of myocardial disease. Image acquisition is aided by the use of ECG gating referred to as MUGA or Multiple Gated Acquisition, which entails data from corresponding epochs from several cardiac cycles being aggregated to enhance image quality.
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