Note that "Retention index" has several meanings in PET:
This page deals with the 3rd meaning.
- a term used in chromatography (not considered here, see IUPAC recommendations),
- it was previously used in the same meaning as Fractional Uptake Rate (FUR),
- and recently Retention index (RI) has been used a lot in clinical dual-time-point imaging (DTPI) studies (mainly [18F]FDG), representing fractional or percentage change in SUV between late and early PET scan.
RI can be calculated from two SUV measurements:
Dual-time point imaging, for example with an "early" [18F]FDG PET scan 1 h post injection, and a "late" scan 2 h p.i., have been suggested in some studies to differentiate benign and malignant lesions better than single PET scans at early or late times or to be useful in predicting response to cancer treatment (Nakamoto et al., 2000; Koike et al., 2003; Chen et al., 2008; Parghane & Basu, 2017). SUV from the early [18F]FDG scan may be related to glucose transporter expression and RI may be more related to hexokinase expression (Higashi et al., 2002).RI images can be helpful in finding lesions in diagnostic imaging and in defining regions of interest for quantitative analysis.
Note that if tracer concentration in either plasma or reference tissue is measured during the two PET scans, then surrogate parameters for Ki can be calculated from the dual time point data.
Retention index method is related to the method where parametric slope images are calculated from dynamic PET data, by just fitting a straight line to the SUV curve of every pixel (Herzog et al., 2008; Apostopoulos et al., 2011).
Since straight line does not often fit the data satisfactorily, more complex functions can be used: Lerche et al (2021) suggested function
, which can be transformed to
which can be solved with linear methods if β can be fixed to a value that holds for uptake kinetics in tissues of interest. Function parameters can be used to calculate peak value and peak time images.
Slope and peak time images can be helpful in finding lesions in diagnostic imaging and in defining regions of interest for quantitative analysis.
- Standardized uptake value (SUV)
- Fractional uptake rate (FUR)
- Late-time tissue-to-plasma ratio
- Asymmetry index (AI)
- Static late scan
- Tissue TAC fitting
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Koike I, Ohmura M, Hata M, Takahashi N, Oka T, Ogino I, Lee J, Umezawa T, Kinbara K, Watai K, Ozawa Y, Inoue T. FDG-PET scanning after radiation can predict tumor regrowth three months later. Int J Radiation Oncology Biol Phys. 2003; 57(5): 1231-1238. doi: 10.1016/S0360-3016(03)00757-0.
Nakamoto Y, Higashi T, Sakahara H, Tamaki N, Kogire M, Doi R, Hosatani R, Imamura M, Konishi J. Delayed 18F-fluoro-2-deoxy-D-glucose positron emission tomography scan for differentiation between malignant and benign lesions in the pancreas. Cancer 2000; 89: 2547-2554. PMID: 11135214.
Parghane RV, Basu S. Dual-time point 18F-FDG-PET and PET/CT for differentiating benign from malignant musculoskeletal lesions: opportunities and limitations. Semin Nucl Med. 2017; 47: 373-391. doi: 10.1053/j.semnuclmed.2017.02.009.
Updated at: 2021-12-10
Created at: 2011-08-23
Written by: Vesa Oikonen