constructing a lattice that resembles anatomy of a partially blocked vein

Hi…

I want to construct a lattice that resembles a semi blocked vein ( irregular fat deposition) I tried to import an image, but i couldn’t simulate the flow through it.

My next option is to construct a lattice that resembles that irregular internal shape (something lile this where U and M are solid obstructions)

. U…

M…

Could you give an idea how to go about this.
or in the worst case flow pass multiple cylinder could be a choice.

Thanks
Nikhi!