Optimized magnetic resonance image-guided stereotaxis: a technique with validation based on the anterior commissure-posterior commissure line

Some of the earliest successful frame-based stereotactic interventions directed toward the thalamus and basal ganglia depended on identifying the anterior commissure (AC) and posterior commissure (PC) in a sagittal venticulogram and defining the intercommissural line that connects them in the midsagittal plane. The AC-PC line became the essential landmark for the localization of neuroanatomical targets in the basal ganglia and diencephalon and for relating them to stereotactic atlases. Stereotactic functional neurosurgery has come to rely increasingly on magnetic resonance (MR) imaging guidance, and methods for accurately determining the AC-PC line on MR imaging are being developed. Our technique uses MR sequences that minimize geometric distortion and registration error, thereby maximizing accuracy in AC-PC line determinations from axially displayed MR data. The techniques are based on our experience with the Leksell G-frame, but can be generalized to other MR imaging-based stereotactic systems. This methodology has been used in a series of 62 stereotactic procedures in 47 adults (55 pallidotomies and seven thalamotomies) with preliminary results equivalent or superior to results reported using microelectrode recordings. The measurements of the AC-PC line reported here compare favorably with those based on ventriculography and computerized tomography previously reported. The methodology reported here is critical in maintaining the accuracy and utility of MR imaging as its role in modern stereotaxy expands. Accurate parameters such as these aid in ensuring the safety, efficacy, and reproducibility of MR-guided stereotactic procedures.