How to build a CT scan into a printable 3D model?
Using the terms "convert CT scan to 3D model," I found a number of links of tutorials. One of them is described as free, with registration and appears to be web based. The link, Embodi3D, appears to have a relatively comprehensive set of instructions to accomplish your goal.

Instructables also has a similar tutorial. Should neither of these prove suitable, the search terms above may be of value.

Image below via Instructables: