[Basic study on relationship between estimated rate constants and noise in FDG kinetic analysis].
For accurate estimation of the rate constants in 18F-FDG dynamic study, the shape of the estimation function (phi) is crucial. In this investigation, the relationship between the noise level in tissue time activity curve and the shape of the least squared estimation function which is the sum of squarred error between a function of model parameters and a measured data is calculated in 3 parameter model of 18F-FDG. In the first simulation, by using actual plasma time activity curve, the true tissue curve was generated from known sets of rate constants ranging 0.05 < or = k1 < or = 0.15, 0.1 < or = k2 < or = 0.2 and 0.01 < or = k3 < or = 0.1 in 0.01 step. This procedure was repeated under various noise levels in the tissue time activity curve from 1 to 8% of the maximum value in the tissue activity. In the second simulation, plasma and tissue time activity curves from clinical 18F-FDG dynamic study were used to calculate the phi. Results are: (1) In the noise-free case, because the global minima is separated from neighboring local minimums, it was easy to find out the optimum point. However, with increasing noise level, the optimum point was buried in many neighboring local minima. Making it difficult to find out the optimum point. (2) The optimum point was found within 20% of the convergence point by standard non-linear optimization method. (3) The shape of phi for the clinical data was similar to that with the noise level of 3 or 5% in the first simulation. Therefore direct search within the area extending 20% from the result of usual non-linear curve fitting procedure is recommended for accurate estimation of the constants.
Kimura
Y
Y
Institute for Medical & Dental Engineering, Tokyo Medical & Dental University, Japan.
Toyama
H
H
Senda
M
M
D003847:Deoxyglucose / Q000031:analogs & derivatives* / Q000493:pharmacokinetics; D005462:Fluorine Radioisotopes / Q000493:pharmacokinetics*; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008954:Models, Biological; D016012:Poisson Distribution; D013997:Time Factors; D014055:Tomography, Emission-Computed
D005462:Fluorine Radioisotopes; D019788:Fluorodeoxyglucose F18; D003847:Deoxyglucose