If you display such highly transparent surface then the perspective does not even matter. You can place the camera in the X-ray source position, set up the camera parameters to match the X-ray projection parameters and you are done. Everything appears in the rendering, there is nothing in front or behind. Of course you need to put the fluoro image farther from the camera if you rely on the renderer’s alpha blending to fuse the images (but most likely you want to have a bit more sophisticated image fusion algorithm than just alpha blending).
Reverse perspective is only needed if you want occlusion within the rendered 3D model. For example, instead of showing the entire left ventricle, you may want to show only one side to make it easier to understand the 3D shape.