One from David Rothman back in January 2007, updated with help from Steven Chan at radRounds, to say it’s now on a Ning-based med imaging search engine. Note, it’s currently by invitation only too:
“Yottalook is a free radiology-centric search engine based on Google’s indexing technology with proprietary relevance algorithm by iVirtuoso. Currently, Yottalook Images and Yottalook References search engines are available for use. Yottalook Image has specially been designed to search radiology images from various peer-reviewed online sources and currently has access to over 100,000 images. Yottalook References has been designed to search online radiology sources only. Try various refinement options to narrow your search requests even further.”