Development and preclinical evaluation of a hybrid stereoelectroencephalographic-laser depth electrode for magnetic resonance imaging-guided interstitial thermal therapy in drug-resistant epilepsy.

OBJECTIVE

This study was undertaken to design and validate a hybrid depth electrode combining stereoelectroencephalographic (sEEG) recording and magnetic resonance-guided laser interstitial thermal therapy (MRgLITT) under real-time magnetic resonance thermometry, to streamline the transition from invasive localization to focal ablation in patients with drug-resistant focal epilepsy.

METHODS

We engineered a magnetic resonance imaging (MRI)-compatible depth probe that integrated intracerebral EEG contacts and a central optical fiber for laser delivery. The contact materials and geometry were optimized to reduce susceptibility artifacts and preserve the proton resonance frequency (PRF) thermometry. Preclinical testing included MRI artifact screening in phantoms, thermal performance testing, PRF thermometry validation against temperature sensors in phantoms and ovine brain, artifact quantification versus clinical depth electrodes, electrophysiologic signal quality assessment before/after thermal stress, and in vivo canine feasibility with serial MRI and histology. MRI compatibility was confirmed for a next generation contact variant.

RESULTS

The optimized contact design produced small MRI artifacts and preserved PRF thermometry outside an approximately 2-mm pericontact exclusion zone. Thermal testing showed localized heating with rapid postlaser decay, modulation by coolant flow, and performance comparable to that of clinical LITT applicators. In dipole-phantom testing, baseline electrophysiological recordings from the new hybrid electrode were comparable to clinical depth-electrode controls, whereas a previously heated hybrid electrode showed increased noise under low-amplitude conditions. In vivo, MRgLITT produced sharply demarcated lesions that scaled with the delivered energy without hemorrhage, edema, midline shift, or device damage. Histological examination revealed coagulative necrosis with a narrow perilesional zone and no carbonization at the contacts.

SIGNIFICANCE: This patented hybrid sEEG-laser electrode supports a "diagnose-model-treat-verify" strategy along a single stereotactic trajectory, enabling sEEG confirmation followed by MRgLITT without a second stereotactic implantation in selected patients. These data support progression to first-in-human evaluation and integration into epilepsy surgery workflows, particularly for MRI-negative focal epilepsies, where minimally invasive strategies are favored.