Frameless stereotaxy was first developed for neurosurgery, having evolved from an older method of matching medical images to the patient using a stereotactic frame as the common coordinate system. This frame was fixed to the patient's head before imaging, and was designed to act as a tool holder to allow the surgeon to guide tools to the desired location in the brain.

Frameless stereotaxy uses a position sensor instead of a stereotactic frame to define the real world coordinate system. The sensor monitors the position of tools and the subject's head, and reports this information to a computer. A registration, or matching/mapping procedure, is performed to calculate the mathematical relationship between the position sensor coordinate frame and the coordinate frame of the images. Once this relationship is established, tools tracked by the position sensor may be introduced and their position and orientation may be mapped to the image coordinate frame. This allows the frameless stereotaxy software to display a representation of the tools over the images. This type of tool is also often referred to as a neuronavigator or Image-Guided procedure.

Brainsight™ TMS is the first mainstream frameless stereotaxy tool to provide neuronavigation to research applications outside the operating room.

Brainsight™ TMS and Brainsight™ Primate