The present inventions provide assemblies, probes, and methods for creating circumferential lesions in tissue, e.g., the tissue within or around the ostium of a vessel. An ablation probe with an ablative structure can be placed in contact within or around the ostium of the vessel. A diagnostic probe can be introduced through a lumen within the ablation probe and inserted into the vessel. The energy can be provided to the ablative structure to create a circumferential lesion within or around the ostium of the vessel, and the diagnostic structure can be used to diagnose the tissue to determine whether the circumferential lesion can be properly created.
