Tracking through the basal ganglia

Hi Experts,

Please see the image, I am wondering why is there such a difference in the FODs within the white matter compared with the ones in the basal ganglia? I am trying to generate tracks through the basal ganglia and I got chaotic streamlines, not even close like the ones in the thalamus for example. Both thalamus and basal ganglia are subcortical structures but I don’t understand the differences between them in terms of diffusion signal and CSD.

Please advice

Thank you