MR and X-Ray Angiography registration intensity based approach

As we know during interventional studies X-ray angiography provides us a high resolution and refresh rate, but as a trade off it doesn't have soft tissue contrast. MR imaging provides us 3-D anatomic imaging, and soft tissue contrast. Our aim is to fuse 2-D X-ray images with 3-D MR volume (XFM). We are using an intensity based algorithm to find mutual information between two modalities.