Once I had to model human skull and I acquired very accurate geometrical info from MRI files. Although MRI files needs to be changed in format and adjusted to your desired level of accuracy (distance between sections) in some software, one of which is "MIMICS" by MATERIALISE company. Probably there are other softwares out there to do the same mediation between MRI equipment and a PC.
Dear friends, thanks a lot for your valuable answers. I do not have any experience in this field. Could you give me a source for more information about this technique and the usual distance of segments for a 3D model which will be used for finite element analysing?