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Pre-operative axial MR imaging of deep brain nuclei after cochlear implant magnet removal. (A) Axial T2-weighted MRI Turbo Spin-Echo sequence depicting subthalamic nuclei (arrow) (B) Axial MRI Fast Gray Matter Acquisition T1 Inversion Recovery sequence depicting globus pallidus internus (arrow), but the image is significantly degraded with artifact from the cochlear implants despite magnet removal.
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Inversion Recovery sequences) for surgical planning. The magnets were replaced the same day following MRI. In spite of magnet removal, there was significant artifact that made targeting STN more favorable than Globus Pallidus internus (GPi) (Figure 1).
Microelectrode recording. This image demonstrates microelectrode recordings along the right DBS trajectory. (A) Microelectrode recordings from thalamus, STN, and STN + active cochlear implant (CI). (B) Microelectrode recordings with time up-scaled (2 ms) showing an action potential from individual neurons in thalamus, STN, and STN + active CI. Activation of the cochlear implant distorts STN microelectrode recordings at a frequency equal to the cochlear implant's total stimulation rate (7.2 KHz). The total stimulation rate is the frequency of the biphasic current pulse that the cochlear implant delivers. It is calculated by multiplying the per channel rate (900 Hz) by the number of maxima (8).
(C) Microelectrode recording from deep nuclei showing a transition between true nuclei recording (off) and the distorted cochlear implant recording (on).
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After turning off the left cochlear device, microelectrode-guided technique proceeded (Figure 2), and characteristic subthalamic signals were recorded.
Post-operative images. Post-operative CT Head (A) bone window and (B) scout view depict preexisting bilateral cochlear implants after successful microelectrode-guided STN DBS implantation. Using Medtronic StealthStation, we fused the post-operative CT Head to the pre-operative MRI Brain. Reconstructed coronal images reveal satisfactory placement of DBS electrodes into the (C) right STN and (D) left STN.
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DBS electrodes positions were verified by fusing the post-operative CT images with the pre-operative MRI (Figure 3).
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