Roberto Sonnino has an implementation of MultiScaleImage (Deep Zoom) for WPF, compatible with Deep Zoom Composer and Zoom.it.
Source: The Code Project
One of the most "magical" features of Silverlight is Deep Zoom. Through the use of clever partitioning of images, Deep Zoom allows users to pan and zoom smoothly through immense (and potentially infinite) images with excellent performance.
Since the release of Deep Zoom with Silverlight 2, it has been one of the most requested missing features from WPF - at the time this article was written, it was ranked within the top 10 requests on the UserVoice site for WPF.