BACKGROUND: The accurate localization of depth electrodes in epilepsy surgery is important for correct interpretation of stereoelectroencephalography recordings and neurosurgical resection. Unfortunately, image quality in postimplantation magnetic resonance imaging (MRI) is degraded by metal artifacts. The registration of postimplantation computed tomography (CT) or MRI to preimplantation (artifact-free) MRI facilitates electrode imaging and optimal visualization of brain anatomy. However, registration errors negatively affect electrode localization accuracy.
OBJECTIVE: To compare the relative registration deviation between postimplantation CT and MRI with preimplantation MRI.
METHODS: Retrospectively, 14 pharmacoresistant epilepsy patients were included who underwent stereotactic insertion of multiple depth electrodes and preimplantation and postimplantation MRI and postimplantation CT. Postimplantation MRI and CT image sets were registered to preimplantation MRI. The registration error between the registered postimplantation MRI and CT was quantified by measuring the geometrical distance between the electrodes of the registered postimplantation CT and the postimplantation MRI.
RESULTS: The registration error of postimplantation imaging to preimplantation MRI was dependent on the algorithm used. After optimization, the smallest registration error was 1.22 ± 0.29 mm (mean ± SD) at the tip and 2.25 ± 1.18 mm at the base of the electrode.
CONCLUSION: The good correspondence between the CT/MRI and the MRI/MRI registration suggests that either postimplantation MRI or CT is sufficient for accurate electrode localization. In case of postoperative morphological brain deformations, postimplantation MRI is still recommended.
ABBREVIATIONS: MI, mutual information
NMI, normalized mutual information