Letter to the Editor: A paradigm shift toward MRI-guided and MRI-verified DBS surgery

Personalizing Deep Brain Stimulation Using Advanced Imaging Sequences

OBJECTIVE

With a growing appreciation for interindividual anatomical variability and patient-specific brain connectivity, advanced imaging sequences offer the opportunity to directly visualize anatomical targets for deep brain stimulation (DBS). The lack of quantitative evidence demonstrating their clinical utility, however, has hindered their broad implementation in clinical practice.

METHODS

Using fast gray matter acquisition T1 inversion recovery (FGATIR) sequences, the present study identified a thalamic hypointensity that holds promise as a visual marker in DBS. To validate the clinical utility of the identified hypointensity, we retrospectively analyzed 65 patients (26 female, mean age = 69.1 ± 12.7 years) who underwent DBS in the treatment of essential tremor. We characterized its neuroanatomical substrates and evaluated the hypointensity's ability to predict clinical outcome using stimulation volume modeling and voxelwise mapping. Finally, we determined whether the hypointensity marker could predict symptom improvement on a patient-specific level.

RESULTS

Anatomical characterization suggested that the identified hypointensity constituted the terminal part of the dentatorubrothalamic tract. Overlap between DBS stimulation volumes and the hypointensity in standard space significantly correlated with tremor improvement (R²  = 0.16, p = 0.017) and distance to hotspots previously reported in the literature (R²  = 0.49, p = 7.9e-4). In contrast, the amount of variance explained by other anatomical atlas structures was reduced. When accounting for interindividual neuroanatomical variability, the predictive power of the hypointensity increased further (R²  = 0.37, p = 0.002).

INTERPRETATION

Our findings introduce and validate a novel imaging-based marker attainable from FGATIR sequences that has the potential to personalize and inform targeting and programming in DBS for essential tremor. ANN NEUROL 2022;91:613-628.

Increased variance in second electrode accuracy during deep brain stimulation and its relationship to pneumocephalus, brain shift, and clinical outcomes: A retrospective cohort study

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Overall electrode accuracy was 0.22+/-0.4 ​mm with only 3 (4%) electrodes out with 2 ​mm from the intended target.

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Accuracy was significantly worse in the GPi versus the STN and on the second side implanted.

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Inaccuracy occurred in the X (lateral) plane but was not related to pneumocephalus or brain shift.

A literature review of magnetic resonance imaging sequence advancements in visualizing functional neurosurgery targets

OBJECTIVE

Historically, preoperative planning for functional neurosurgery has depended on the indirect localization of target brain structures using visible anatomical landmarks. However, recent technological advances in neuroimaging have permitted marked improvements in MRI-based direct target visualization, allowing for refinement of "first-pass" targeting. The authors reviewed studies relating to direct MRI visualization of the most common functional neurosurgery targets (subthalamic nucleus, globus pallidus, and thalamus) and summarize sequence specifications for the various approaches described in this literature.

METHODS

The peer-reviewed literature on MRI visualization of the subthalamic nucleus, globus pallidus, and thalamus was obtained by searching MEDLINE. Publications examining direct MRI visualization of these deep brain stimulation targets were included for review.

RESULTS

A variety of specialized sequences and postprocessing methods for enhanced MRI visualization are in current use. These include susceptibility-based techniques such as quantitative susceptibility mapping, which exploit the amount of tissue iron in target structures, and white matter attenuated inversion recovery, which suppresses the signal from white matter to improve the distinction between gray matter nuclei. However, evidence confirming the superiority of these sequences over indirect targeting with respect to clinical outcome is sparse. Future targeting may utilize information about functional and structural networks, necessitating the use of resting-state functional MRI and diffusion-weighted imaging.

CONCLUSIONS

Specialized MRI sequences have enabled considerable improvement in the visualization of common deep brain stimulation targets. With further validation of their ability to improve clinical outcomes and advances in imaging techniques, direct visualization of targets may play an increasingly important role in preoperative planning.

Imaging alone versus microelectrode recording-guided targeting of the STN in patients with Parkinson's disease

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.

Reconfigurable MRI technology for low-SAR imaging of deep brain stimulation at 3T: Application in bilateral leads, fully-implanted systems, and surgically modified lead trajectories

Patients with deep brain stimulation devices highly benefit from postoperative MRI exams, however MRI is not readily accessible to these patients due to safety risks associated with RF heating of the implants. Recently we introduced a patient-adjustable reconfigurable coil technology that substantially reduced local SAR at tips of single isolated DBS leads during MRI at 1.5 T in 9 realistic patient models. This contribution extends our work to higher fields by demonstrating the feasibility of scaling the technology to 3T and assessing its performance in patients with bilateral leads as well as fully implanted systems. We developed patient-derived models of bilateral DBS leads and fully implanted DBS systems from postoperative CT images of 13 patients and performed finite element simulations to calculate SAR amplification at electrode contacts during MRI with a reconfigurable rotating coil at 3T. Compared to a conventional quadrature body coil, the reconfigurable coil system reduced the SAR on average by 83% for unilateral leads and by 59% for bilateral leads. A simple surgical modification in trajectory of implanted leads was demonstrated to increase the SAR reduction efficiency of the rotating coil to >90% in a patient with a fully implanted bilateral DBS system. Thermal analysis of temperature-rise around electrode contacts during typical brain exams showed a 15-fold heating reduction using the rotating coil, generating <1°C temperature rise during ∼4-min imaging with high-SAR sequences where a conventional CP coil generated >10°C temperature rise in the tissue for the same flip angle.

Deep brain stimulation outcomes in patients implanted under general anesthesia with frame-based stereotaxy and intraoperative MRI

OBJECTIVEThe authors' aim in this study was to evaluate placement accuracy and clinical outcomes in patients who underwent implantation of deep brain stimulation devices with the aid of frame-based stereotaxy and intraoperative MRI after induction of general anesthesia.METHODSThirty-three patients with movement disorders (27 with Parkinson's disease) underwent implantation of unilateral or bilateral deep brain stimulation systems (64 leads total). All patients underwent the implantation procedure with standard frame-based techniques under general anesthesia and without microelectrode recording. MR images were acquired immediately after the procedure and fused to the preoperative plan to verify accuracy. To evaluate clinical outcome, different scales were used to assess quality of life (EQ-5D), activities of daily living (Unified Parkinson's Disease Rating Scale [UPDRS] part II), and motor function (UPDRS part III during off- and on-medication and off- and on-stimulation states). Accuracy was assessed by comparing the coordinates (x, y, and z) from the preoperative plan and coordinates from the tip of the lead on intraoperative MRI and postoperative CT scans.RESULTSThe EQ-5D score improved or remained stable in 71% of the patients. When in the off-medication/on-stimulation state, all patients reported significant improvement in UPDRS III score at the last follow-up (p < 0.001), with a reduction of 25.2 points (46.3%) (SD 14.7 points and 23.5%, respectively). There was improvement or stability in the UPDRS II scores for 68% of the Parkinson's patients. For 2 patients, the stereotactic error was deemed significant based on intraoperative MRI findings. In these patients, the lead was removed and replaced after correcting for the error during the same procedure. Postoperative lead revision was not necessary in any of the patients. Based on findings from the last intraoperative MRI study, the mean difference between the tip of the electrode and the planned target was 0.82 mm (SD 0.5 mm, p = 0.006) for the x-axis, 0.67 mm (SD 0.5 mm, p < 0.001) for the y-axis, and 0.78 mm (SD 0.7 mm, p = 0.008) for the z-axis. On average, the euclidian distance was 1.52 mm (SD 0.6 mm). In patients who underwent bilateral implantation, accuracy was further evaluated comparing the first implanted side and the second implanted side. There was a significant mediolateral (x-axis) difference (p = 0.02) in lead accuracy between the first (mean 1.02 mm, SD 0.57 mm) and the second (mean 0.66 mm, SD 0.50 mm) sides. However, no significant difference was found for the y- and z-axes (p = 0.10 and p = 0.89, respectively).CONCLUSIONSFrame-based DBS implantation under general anesthesia with intraoperative MRI verification of lead location is safe, accurate, precise, and effective compared with standard implantation performed using awake intraoperative physiology. More clinical trials are necessary to directly compare outcomes of each technique.