I am trying to modify the demri_3.c program to build a new program for 3dNLfim that would use nonlinear least squares to fit the Extended Toft’s model into my inputs [Ct.nii (a 3D+time dataset with the measured concentration of gadolinium in the brain) and Cp.1D (a 1D file with one value per timepoint, which is my vascular input function) ] to calculate Ktrans, Vp, and Ve (or Kep instead of Ve).
I am having issues in understanding what 3dNLfim needs for this purpose. As alternative approach, I also tried to simplify the Extended Toft’s equation as much as possible to use it in 3dNLfim with ‘Expr2’, but I failed (I guess because the parameter Kep is inside the integral, so I cannot calculate the integral, unless I provide an initial estimate for Kep, which does not seem to be useful since I still want Kep to be estimated by the nonlinear least squares fitting procedure).
Do you have any suggestion?
Thank you very much,