The model for calculating the MBF parametric maps was derived from the parametric mapping method developed by Harms et al [48] for water scans. The operational equation for cardiac PET includes two geometric spillover fractions (Vlv, Vrv) from left ventricular and right ventricular blood (Clv, Crv):
The tracer concentration in myocardium Cmyo(t) is modeled by a one-tissue compartment model and can be obtained by the convolution of the metabolite-corrected input curve with a decaying exponential, multiplied by K1:
For the ammonia tracer K1 corresponds to mycocardial blood flow (MBF), and k2 to the tissue washout. The linear metabolite correction with slope -mCorr which is applied in this equation was derived by de Grado et al [30] and is only valid for scan durations up to 4 minutes.
The solution of the operational equation uses basis functions of the form
With the basis functions, the operational equation can be reformulated as a multi-linear equation
with
The data analysis methodology then consists of the following two steps:
1.As a preprocessing step the basis functions are calculated for a set of k2 values which span the physiologic relevant range.
2.In each pixel the TAC is fitted by solving the operational equation for all basis functions and selecting the solution which best fits the measurement. From the resulting parameters θ1, Vlv, and Vrv the MBF (=K1) can readily be calculated.
3.If the blood contribution in a pixel is too high (Vlv+Vrv>0.75), the MBF result is discarded.