FIGURE 1.  (A) Time course of ¹¹C concentration associated with total plasma, unmetabolized L-[1-¹¹C]-leucine, and L-[1-¹¹C]-leucine in plasma protein. (B) Fraction of unmetabolized free L-[1-¹¹C]-leucine relative to total ¹¹C concentration in plasma fitted with a 3-parameter (offset, , ß) sigmoidal function. Parameter values that best fit data are reported. Fitted curve explains more than 90% of variance in data.