Quantification in Emission Tomography

Authored by: Brian F. Hutton , Kjell Erlandsson , Kris Thielemans

Handbook of Nuclear Medicine and Molecular Imaging for Physicists

Print publication date:  January  2022
Online publication date:  January  2022

Print ISBN: 9781138593268
eBook ISBN: 9780429489556
Adobe ISBN:


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Quantification is an important consideration for both positron emission tomography (PET) and single photon emission computed tomography (SPECT). Although these two modalities operate on different principles with significantly different instrumentation, they have in common the ability to demonstrate the spatial activity distribution following administration of a radioactive tracer and, to some extent, its variation in time. Several factors affect quantification, including detector calibration, image reconstruction parameters, physical effects (attenuation and scatter), system performance parameters (resolution, sensitivity, dead-time, randoms), and subject motion. Central to achieving quantification are techniques for correction of these factors, particularly attenuation and scatter, partial volume effects and motion, which are applicable to both SPECT and PET. Often in clinical practice, semi-quantitative parameters are derived that do not require calibration (e.g. tumour to background ratio) but only need to assume that the reconstructed data are directly proportional to the activity distribution. However, for internal dose estimation, there is a need for absolute calibration to allow direct conversion of measurements to absolute activity or, in the case of tracer kinetic analysis, relative calibration (or cross-calibration) is usually sufficient. Validation studies have demonstrated that accurate and precise quantification is feasible for both PET and SPECT.

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