Brain stereotaxis protocol (MRI)

The brain MRI stereotactic study, also known as frame-based stereotactic MRI study or conventional brain MRI stereotaxis, is a localization MRI protocol that delineates an intracranial structure or lesion in relation to a three-dimension coordinate system allowing precise surgical access to them. This protocol is mainly used to perform a biopsy of the brain and in some functional neurosurgeries.

The traditional frame-based study demands a compatible head-containing stereotactic system (frame and skull screws) that should be well visualized on images and must be artifact-free. Nowadays, most studies are performed as a frameless stereotactic MRI with the images further processed by specific neuronavigation software.

Note: This article is intended to outline some general principles of protocol design. The specifics will vary depending on MRI hardware and software, radiologist's and referrer's preference, institutional protocols, patient factors (e.g. allergy) and time constraints.

Sequences

The sequence has to be obtained in accordance with the stereotaxis package employed by the surgeons which may or may not need special parameters. In some instances, for example, the entire face needs to be included in the field of view to allow for registration. In other situations, registration is achieved with the placement of temporary stick-on fiducials on the patient's scalp. 

The sequence is also dependent on the pathology being imaged. Most frequently a post-contrast T1 volumetric study is obtained, however, if the pathology is non-enhancing (e.g. low-grade diffuse glioma) then FLAIR or T2 weighted sequences may be preferable. More than one sequence can also be coregistered.