HLSL see through effect

Hi,

Can anybody tell me how to create  a see through effect using HLSL?

For instance, I use a camera to take a picture of the human chest.

Then I use volume rendering based on 3D CT/MRI to render the lung.

How to combine the real image (chest) and the virtual lung together to create a realistic see through effect such as we can see part of the lung through the skin of the chest?

Thank you so much!

YL