Corrections for Physical Factors - Correction Techniques in Emission Tomography - page 67

Chapter5

CorrectionsforPhysicalFactors

Florian Buther
Department of Nuclear Medicine and European Institute of Molecular Imaging,
University of Munster, Munster, Germany

5.1 Introduction :::::::::::::::::::::::::::::::::::::::::::::::::::::: 67

5.2 Decay correction ::::::::::::::::::::::::::::::::::::::::::::::::: 69

5.3 Randoms correction :::::::::::::::::::::::::::::::::::::::::::::: 71

5.3.1 Singles-based correction ::::::::::::::::::::::::::::::::: 71

5.3.2 Delayed window correction :::::::::::::::::::::::::::::: 72

5.4 Attenuation correction ::::::::::::::::::::::::::::::::::::::::::: 73

5.4.1 Stand-alone emission tomography systems :::::::::::::: 77

5.4.2 PET/CT and SPECT/CT systems ::::::::::::::::::::: 80

5.4.3 Attenuation correction artifacts ::::::::::::::::::::::::: 82

5.5 Scatter correction :::::::::::::::::::::::::::::::::::::::::::::::: 90

5.5.1 Energy windowing methods ::::::::::::::::::::::::::::: 91

5.5.2 Analytical methods :::::::::::::::::::::::::::::::::::::: 92

5.5.3 Direct calculation methods :::::::::::::::::::::::::::::: 94

5.5.4 Iterative reconstruction methods :::::::::::::::::::::::: 95

5.6 Concluding remarks :::::::::::::::::::::::::::::::::::::::::::::: 95

References ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 95

5.1 Introduction
The physical basis of both emission tomography technologies, PET
(positron emission tomography) and SPECT (single photon emission com-
puted tomography), is the fact that many atomic nuclei are not stable; they
decay into other nuclei under the emission of specific radiation (radioactivity ),
a property that was first discovered by Henri Becquerel in 1896 while investi-
gating the fluorescence of uranium compounds. In emission tomography, two
fundamental decay modes are of particular interest: the beta +

decay for PET

and the gamma decay for SPECT.
An atomic nucleus undergoing a beta + decay emits an electron neutrino
e and a positron e + , thereby decreasing its atomic number Z by 1 while

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