This paper reports on the analysis of the query logs of a visual medical information retrieval system that provides access to radiology resources. Our analysis shows that, despite sharing similarities with general Web search and also with biomedical text search, query formulation and query modification when searching for visual biomedical information have unique characteristics that need to be taken into account in order to enhance the effectiveness of the search support offered by such systems. Typical information needs of medical professionals searching radiology resources are also identified with the goal to create realistic search tasks for a medical image retrieval evaluation benchmark.