Input data for simulation
Error-free input curves are needed to create simulated tissue data with compartmental models. What exactly is needed depends on the radiopharmaceutical and model, but usually the input data consists of total radioactivity concentration in arterial blood and the parent radiopharmaceutical concentration in arterial plasma.
As a rule, the steps in making input data are:
- Collect a representative set of measured blood and plasma time-activity curves (TACs), and parent radiotracer fractions in plasma.
- Normalize TACs to have identical AUC or convert to SUV units, and correct for different delay time, for instance by time shifting TACs to have a common peak time (Graham et al., 2000)
- Calculate average blood and plasma TAC, and average curve of parent radiotracer fractions in plasma.
- Fit appropriate function to average blood and plasma curves and to average parent radiotracer fractions, to remove noise and enable interpolation and extrapolation.
- Compute curves from the function parameters with frequent sample times.
While tissue data should be simulated using error-free input function with frequent sampling times, the analysis of simulated tissue data should be performed with realistic blood sampling schemes or time frames, possibly with dispersion and delay, and with added noise (Graham, 1997; Huang et al., 2004).
Ready-made input TACs for simulations:
- [15O]H2O bolus studies
- [18F]FDG bolus studies: fasting (Långsjö et al., 2005) and euglycemic clamp (Lautamäki et al., 2005)
- [11C]carfentanil bolus studies
- [11C]flumazenil bolus studies
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Feng D, Wang X. A computer simulation study on the effects of input function measurement noise in tracer kinetic modeling with positron emission tomography (PET). Comput Biol Med. 1993; 23(1): 57-68. doi: 10.1016/0010-4825(93)90108-D.
Feng D, Wang X, Yan H. A computer simulation study on the input function sampling schedules in tracer kinetic modeling with positron emission tomography (PET). Comput Methods Programs Biomed. 1994; 45(3): 175-186. doi: 10.1016/0169-2607(94)90201-1.
Li X, Feng D. Optimal image sampling schedule for both image-derived input and output functions in PET cardiac studies. IEEE Trans Med Imaging 2000; 19(3): 233-242. doi: 10.1109/42.845181.
Raylman RR, Caraher JM, Hutchins GD. Sampling requirements for dynamic cardiac PET studies using image-derived input functions. J Nucl Med. 1993; 34(3): 440-447.
Updated at: 2019-01-06
Created at: 2010-09-20
Written by: Vesa Oikonen