NONINVASIVE ESTIMATION OF THE NET INFLUX CONSTANT USING THE STANDARDIZED UPTAKE VALUE FOR QUANTIFICATION OF FDG UPTAKE OF TUMORS

To reduce the variability of the standardized uptake value (SUV) which is widely used to evaluate 2 [F-18]fluoro-2-deoxy-D-glucose (FDG) upt ake by neo plasma, net influx constant (Ki) was derived from SUV. The relationship Ki=SUV.k(p).V-o. where k(p) is the plasma clearance rate and V-o is the initial distribution volume of FDG, was utilized. A tot al of 71 plasma input functions were measured up to 60 min after intra venous injection of FDG in 55 patients and were analysed to obtain k(p ) and V-o. SUV and V-o were calculated based on either body weight or body surface area. To validate the Ki estimation, another group of eig ht patients with squamous cell carcinoma of the head and neck was incl uded. Para metric images of the net influx constant were obtained by P atlak graphical analysis of dynamic positron emission tomography (PET) data and measured plasma input function, V-o based on body weight was 0.1627+/-0.0329 (ml/g) and showed a weak negative correlation with bo dy weight (y=0.23356-0.00138x, r=0.591). V-o based on body surface are a was 5540+/-871 (ml/m(2)) and had no significant correlation with bod y weight. k(p) at 50 min post injection was 0.03272+/-0.00243 (1/min), and had no correlation with the plasma glucose concentration. A highl y significant positive correlation was noted between true Ki and estim ated Ki based on both body weight (y=0.0033+1.0371x, r(2)=0.897), and body surface area (y=0.0033+1.0351x, r(2)=0.926). Ki, a better indicat or of FDG uptake by tumour than SUV, is derivable non-invasively. Quan tification of FDG uptake by Ki will aid standardization of diagnostic criteria of FDG PET oncology.