Biomedical Engineering Reference
In-Depth Information
Chapter6
CorrectionsforScanner-Related
Factors
Marc Huismann
Department of Nuclear Medicine & PET Research, VU University Medical
Center, Amsterdam, the Netherlands
6.1 Positron emission tomography ::::::::::::::::::::::::::::::::::: 105
6.1.1 Introduction ::::::::::::::::::::::::::::::::::::::::::::: 105
6.1.2 Data normalization :::::::::::::::::::::::::::::::::::::: 107
6.1.3 Noise equivalent count rates ::::::::::::::::::::::::::::: 108
6.1.4 System dead time :::::::::::::::::::::::::::::::::::::::: 108
6.1.5 Partial volume ::::::::::::::::::::::::::::::::::::::::::: 110
6.2 Single photon emission computed tomography :::::::::::::::::: 112
6.2.1 Linearity, center of rotation, and whole body imaging :: 112
6.2.2 Motion correction :::::::::::::::::::::::::::::::::::::::: 114
References ::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::: 115
6.1 Positron emission tomography
6.1.1 Introduction
In PET a positron annihilation event results in two 511 keV photons. Due
to conservation of momentum these photons are emitted in approximately
180-degree opposing directions. When detected as a prompt coincidence, the
detectors in which the photons were detected define a so-called line of response
(LOR; actually it is a tube of response, the volume of which is determined by
the distance between the detectors and the area of the detector surface).
The term detector is used to refer to a scintillation crystal that can be
individually identified. Usually, Anger-logic readout of block detectors leads
to the capability to address small individual crystals (e.g., 4 x 4 x 22 mm 3
LYSO crystals in the Philips Gemini TF PET-CT scanner [18], 4 x 4 x 20 mm 3
LSO crystals in the Siemens Biograph 16 HI-REZ PET-CT scanner [3] and
4.7 x 6.3 x 30 mm 3 BGO crystals in the GE Discovery STE PET-CT scanner
[12]). However, even a continuous distribution of scintillation crystals over a
ring of detectors leads to an inhomogeneous density distribution of LOR in
105
 
 
 
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