Dear AFNI experts,
I have a very basic question related to the gradient file. I’m going to use AFNI for probabilistic tractography and now I’m doing preprocessing of the datasets with TORTOISE V3.0.0. I have some very basic question related to the gradient file.
Two datasets with opposite phase encoding directions (blip_up and blip_down datasets) were collected. Each dataset in addition to b=1000 contains intermediate b-values (b=300 and b=500). In the tutorial page of TORTOISE toolbox it is noted that the gradients have to be scaled to the maximum b-value. I converted the DICOM images with dcm2nii, so that the gradients in the bvec files are of unit length for all b-values: g_x^2 +g_y^2 +g_z^2 =1.
Is it correct,that if the maximum b-value is 1000 then to represent images with b=300 one have to multiply g_x, g_y, g_z gradient components with
sqrt(b=300 / b=1000) ?
Best regrrds,
Maksym
