Provided is a method and system for delivering a diagnostic agent to a site in the brain of a subject for imaging at least a portion of the brain site on a medical imaging system. The method and system includes a catheter device with associated lumens having diagnostic agent ports for delivering the diagnostic agent (e.g., infusate) through the lumens and advancing the diagnostic agent so as to exit out from the lumens to at least a portion of the brain site and while sealing a portion of the brain site thereby preventing the exited diagnostic agent from travelling proximally beyond the sealing location, and at the same time imaging at least a portion of the brain site during at least a portion of the sealing duration so that the brain site can be visualized on a medical imaging system. The diagnostic agent (infusate) is able to highlight borders and internal patterns of the deep structures of the brain thereby enabling direct targeting. Ultimately this leads to reduced complications, enhanced therapy, and the elimination of the need for awake surgery. The method and system provides the capability heretofore not possible to visualize the small, often indistinct regions, which will greatly improve clinical outcomes with therapeutic interventions.