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Christopher S. Lozano, Manish Ranjan, Alexandre Boutet, David S. Xu, Walter Kucharczyk, Alfonso Fasano and Andres M. Lozano

OBJECTIVE

The clinical results of deep brain stimulation (DBS) of the subthalamic nucleus (STN) are highly dependent on accurate targeting and target implantation. Several targeting tactics are in current use, including image-only and/or electrophysiologically guided approaches using microelectrode recordings (MERs). The purpose of the present study was to make an appraisal of imaging only–based versus imaging with the addition of intraoperative MER-guided STN electrode targeting.

METHODS

The authors evaluated 100 consecutive patients undergoing STN DBS. The position of the STN target was estimated from preoperative MR images (direct target) or in relation to the position of the anterior and posterior commissures (indirect target). MERs were obtained for each trajectory. The authors tracked which targets were adjusted intraoperatively as a consequence of MER data. The final placement of 182 total STN electrodes was validated by intraoperative macrostimulation through the implanted DBS electrodes. The authors compared the image-based direct, indirect, MER-guided target adjustments and the final coordinates of the electrodes as seen on postoperative MRI.

RESULTS

In approximately 80% of the trajectories, there was a good correspondence between the imaging-based and the MER-guided localization of the STN target. In approximately 20% of image-based targeting trajectories, however, the electrophysiological data revealed that the trajectory was suboptimal, missing the important anatomical structures to a significant extent. The greatest mismatch was in the superior-inferior axis, but this had little impact because it could be corrected without changing trajectories. Of more concern were mismatches of 2 mm or more in the mediolateral (x) or anteroposterior (y) planes, discrepancies that necessitated a new targeting trajectory to correct for the mis-targeting. The incidence of mis-targetting requiring a second MER trajectory on the first and second sides was similar (18% and 22%).

CONCLUSIONS

According to the present analysis, approximately 80% of electrodes were appropriately targeted using imaging alone. In the other 20%, imaging alone led to suboptimal targeting that could be corrected by a trajectory course correction guided by the acquired MER data. The authors’ results suggest that preoperative imaging is insufficient to obtain optimal results in all patients undergoing STN DBS.

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Francesco Sammartino, Vibhor Krishna, Tejas Sankar, Jason Fisico, Suneil K. Kalia, Mojgan Hodaie, Walter Kucharczyk, David J. Mikulis, Adrian Crawley and Andres M. Lozano

OBJECTIVE

The aim of this study was to evaluate the safety of 3-T MRI in patients with implanted deep brain stimulation (DBS) systems.

METHODS

This study was performed in 2 phases. In an initial phantom study, a Lucite phantom filled with tissue-mimicking gel was assembled. The system was equipped with a single DBS electrode connected to an internal pulse generator. The tip of the electrode was coupled to a fiber optic thermometer with a temperature resolution of 0.1°C. Both anatomical (T1- and T2-weighted) and functional MRI sequences were tested. A temperature change within 2°C from baseline was considered safe. After findings from the phantom study suggested safety, 10 patients with implanted DBS systems targeting various brain areas provided informed consent and underwent 3-T MRI using the same imaging sequences. Detailed neurological evaluations and internal pulse generator interrogations were performed before and after imaging.

RESULTS

During phantom testing, the maximum temperature increase was registered using the T2-weighted sequence. The maximal temperature changes at the tip of the DBS electrode were < 1°C for all sequences tested. In all patients, adequate images were obtained with structural imaging, although a significant artifact from lead connectors interfered with functional imaging quality. No heating, warmth, or adverse neurological effects were observed.

CONCLUSIONS

To the authors' knowledge, this was the first study to assess the clinical safety of 3-T MRI in patients with a fully implanted DBS system (electrodes, extensions, and pulse generator). It provided preliminary data that will allow further examination and assessment of the safety of 3-T imaging studies in patients with implanted DBS systems. The authors cannot advocate widespread use of this type of imaging in patients with DBS implants until more safety data are obtained.

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Alexandre Boutet, Gavin J. B. Elias, Robert Gramer, Clemens Neudorfer, Jürgen Germann, Asma Naheed, Nicole Bennett, Bryan Li, Dave Gwun, Clement T. Chow, Ricardo Maciel, Alejandro Valencia, Alfonso Fasano, Renato P. Munhoz, Warren Foltz, David Mikulis, Ileana Hancu, Suneil K. Kalia, Mojgan Hodaie, Walter Kucharczyk and Andres M. Lozano

OBJECTIVE

Many centers are hesitant to perform clinically indicated MRI in patients who have undergone deep brain stimulation (DBS). Highly restrictive guidelines prohibit the use of most routine clinical MRI protocols in these patients. The authors’ goals were to assess the safety of spine MRI in patients with implanted DBS devices, first through phantom model testing and subsequently through validation in a DBS patient cohort.

METHODS

A phantom was used to assess DBS device heating during 1.5-T spine MRI. To establish a safe spine protocol, routinely used clinical sequences deemed unsafe (a rise in temperature > 2°C) were modified to decrease the rise in temperature. This safe phantom-based protocol was then used to prospectively run 67 spine MRI sequences in 9 DBS participants requiring clinical imaging. The primary outcome was acute adverse effects; secondary outcomes included long-term adverse clinical effects, acute findings on brain MRI, and device impedance stability.

RESULTS

The increases in temperature were highest when scanning the cervical spine and lowest when scanning the lumbar spine. A temperature rise < 2°C was achieved when 3D sequences were modified to 2D and when the number of slices was decreased by the minimum amount compared to routine spine MRI protocols (but there were still more slices than allowed by vendor guidelines). Following spine MRI, no acute or long-term adverse effects or acute findings on brain MR images were detected. Device impedances remained stable.

CONCLUSIONS

Patients with DBS devices may safely undergo spine MRI with a fewer number of slices compared to those used in routine clinical protocols. Safety data acquisition may allow protocols outside vendor guidelines with a maximized number of slices, reducing the need for radiologist supervision.

Clinical trial registration no.: NCT03753945 (ClinicalTrials.gov).