Parametric mapping of [18F]fluoromisonidazole positron emission tomography using basis functions

In this study, we show a basis function method (BAFPIC) for voxelwise calculation of kinetic parameters (K₁, k₂, k₃, K_i) and blood volume using an irreversible two-tissue compartment model. BAFPIC was applied to rat ischaemic stroke micro-positron emission tomography data acquired with the hypoxia tracer [¹⁸F]fluoromisonidazole because irreversible two-tissue compartmental modelling provided good fits to data from both hypoxic and normoxic tissues. Simulated data show that BAFPIC produces kinetic parameters with significantly lower variability and bias than nonlinear least squares (NLLS) modelling in hypoxic tissue. The advantage of BAFPIC over NLLS is less pronounced in normoxic tissue. K_i determined from BAFPIC has lower variability than that from the Patlak–Gjedde graphical analysis (PGA) by up to 40% and lower bias, except for normoxic tissue at mid-high noise levels. Consistent with the simulation results, BAFPIC parametric maps of real data suffer less noise-induced variability than do NLLS and PGA. Delineation of hypoxia on BAFPIC k₃ maps is aided by low variability in normoxic tissue, which matches that in K_i maps. BAFPIC produces K_i values that correlate well with those from PGA (r²=0.93 to 0.97; slope 0.99 to 1.05, absolute intercept <0.00002 mL/g per min). BAFPIC is a computationally efficient method of determining parametric maps with low bias and variance.