Real blood vessels from a person who donated their body for artistic/scientific display purposes

How did they do this?
They injected a plastinating agent into the blood, hardening the vessels, and then dissolved the body in a special acid solution, leaving behind only the blood vessel structures.

Plastination is a technique of body tissue preservation with a great variety in its processes and development which is originally introduced to the medical world by Dr. Gunther von Hagens in 1977. In these processes, water and lipids in biological tissues are replaced by curable polymers mostly silicone, epoxy, and polyester which then will harden and finally result in natural looking, dry, odorless and durable specimens.