Who can help me to convert 3d artery stl or (.x_t) file to solid body?

Hi,
it appears that there are three bodies plus some 'stuff' (not connected/floating triangles).
The first thing to do is to make sure you have "good" data, otherwise conversions don't result in good data (the usual garbage-in, garbage-out applies).
I took a quick stab at this and worked with the first (outer most) body. I ran some re-meshing on it to get a better quality mesh while preserving the topology and then ran a Reverse Engineering (Surfacing, to NURBS) process to get 3900 patches (you may want more/less detail). Note that this results in a single, solid body without an 'interior' volume (i.e. ignoring thickness).
For this I used our (new) InStep Studio application: https://www.solveering.com/instep/instep.aspx
Attached the result (.STP) as well as the separate bodies which were used.
I would recommend you take a look and if this need more work post a follow-on here with specifics on what you are after. Also, if you want to take our InStep application for a spin to get more specific results, let me know and I can provide you with a full, 30 day license.

Regards
Ben

P.S. Yes, I know that some of the Nurbs Surface patches are self intersecting, this is a fairly (<5min) quick and dirty conversion. You should be able to clean that up in whatever Simulation package (?) you are using.