Intraoperative in vivo confocal laser endomicroscopy imaging at glioma margins: can we detect tumor infiltration?

J Neurosurg 140:357–366, 2024

Confocal laser endomicroscopy (CLE) is a US Food and Drug Administration–cleared intraoperative real-time fluorescence-based cellular resolution imaging technology that has been shown to image brain tumor histoarchitecture rapidly in vivo during neuro-oncological surgical procedures. An important goal for successful intraoperative implementation is in vivo use at the margins of infiltrating gliomas. However, CLE use at glioma margins has not been well studied.

METHODS Matching in vivo CLE images and tissue biopsies acquired at glioma margin regions of interest (ROIs) were collected from 2 institutions. All images were reviewed by 4 neuropathologists experienced in CLE. A scoring system based on the pathological features was implemented to score CLE and H&E images from each ROI on a scale from 0 to 5. Based on the H&E scores, all ROIs were divided into a low tumor probability (LTP) group (scores 0–2) and a high tumor probability (HTP) group (scores 3–5). The concordance between CLE and H&E scores regarding tumor probability was determined. The intraclass correlation coefficient (ICC) and diagnostic performance were calculated.

RESULTS Fifty-six glioma margin ROIs were included for analysis. Interrater reliability of the scoring system was excellent when used for H&E images (ICC [95% CI] 0.91 [0.86–0.94]) and moderate when used for CLE images (ICC [95% CI] 0.69 [0.40–0.83]). The ICCs (95% CIs) of the LTP group (0.68 [0.40–0.83]) and HTP group (0.68 [0.39–0.83]) did not differ significantly. The concordance between CLE and H&E scores was 61.6%. The sensitivity and specificity values of the scoring system were 79% and 37%. The positive predictive value (PPV) and negative predictive value were 65% and 53%, respectively. Concordance, sensitivity, and PPV were greater in the HTP group than in the LTP group. Specificity was higher in the newly diagnosed group than in the recurrent group.

CONCLUSIONS CLE may detect tumor infiltration at glioma margins. However, it is not currently dependable, especially in scenarios where low probability of tumor infiltration is expected. The proposed scoring system has excellent intrinsic interrater reliability, but its interrater reliability is only moderate when used with CLE images. These results suggest that this technology requires further exploration as a method for consistent actionable intraoperative guidance with high dependability across the range of tumor margin scenarios. Specific-binding and/or tumor-specific fluorophores, a CLE image atlas, and a consensus guideline for image interpretation may help with the translational utility of CLE.

Intraoperative computed tomography as reliable navigation registration device in 200 cranial procedures

Acta Neurochirurgica (2018) 160:1681–1689

Registration accuracy is a main factor influencing overall navigation accuracy. Standard fiducial- or landmark-based patient registration is user dependent and error-prone. Intraoperative imaging offers the possibility for user-independent patient registration. The aim of this paper is to evaluate our initial experience applying intraoperative computed tomography (CT) for navigation registration in cranial neurosurgery, with a special focus on registration accuracy and effective radiation dose.

Methods A total of 200 patients (141 craniotomy, 19 transsphenoidal, and 40 stereotactic burr hole procedures) were investigated by intraoperative Craneotomía applying a 32-slice movable CTscanner, which was used for automatic navigation registration. Registration accuracy was measured by at least three skin fiducials that were not part of the registration process.

Results Automatic registration resulted in high registration accuracy (mean registration error: 0.93 ± 0.41 mm). Implementation of low-dose scanning protocols did not impede registration accuracy (registration error applying the full dose head protocol: 0.87 ± 0.36mmvs. the low dose sinus protocol 0.72 ± 0.43mm) while a reduction of the effective radiation dose by a factor of 8 could be achieved (mean effective radiation dose head protocol: 2.73 mSv vs. sinus protocol: 0.34 mSv).

Conclusion Intraoperative CT allows highly reliable navigation registration with low radiation exposure.

Complications in awake versus asleep DBS

J Neurosurg 127:360–369, 2017

As the number of deep brain stimulation (DBS) procedures performed under general anesthesia (“asleep” DBS) increases, it is more important to assess the rates of adverse events, inpatient lengths of stay (LOS), and 30-day readmission rates in patients undergoing these procedures compared with those in patients undergoing traditional “awake” DBS without general anesthesia.

METHODS All patients in an institutional database who had undergone awake or asleep DBS procedures performed by a single surgeon between August 2011 and August 2014 were reviewed. Adverse events, inpatient LOS, and 30-day readmissions were analyzed.

RESULTS A total of 490 electrodes were placed in 284 patients, of whom 126 (44.4%) underwent awake surgery and 158 (55.6%) underwent asleep surgery. The most frequent overall complication for the cohort was postoperative mental status change (13 patients [4.6%]), followed by hemorrhage (4 patients [1.4%]), seizure (4 patients [1.4%]), and hardwarerelated infection (3 patients [1.1%]). Mean LOS for all 284 patients was 1.19 ± 1.29 days (awake: 1.06 ± 0.46 days; asleep: 1.30 ± 1.67 days; p = 0.08). Overall, the 30-day readmission rate was 1.4% (1 awake patient, 3 asleep patients). There were no significant differences in complications, LOS, and 30-day readmissions between awake and asleep groups.

CONCLUSIONS Both awake and asleep DBS can be performed safely with low complication rates. The authors found no significant differences between the 2 procedure groups in adverse events, inpatient LOS, and 30-day readmission rates.

Parkinson’s disease outcomes after intraoperative CT-guided “asleep” deep brain stimulation in the globus pallidus internus

Parkinson’s disease outcomes after intraoperative CT-guided “asleep” deep brain stimulation in the globus pallidus internus

J Neurosurg 124:902–907, 2016

Recent studies show that deep brain stimulation can be performed safely and accurately without microelectrode recording or test stimulation but with the patient under general anesthesia. The procedure couples techniques for direct anatomical targeting on MRI with intraoperative imaging to verify stereotactic accuracy. However, few authors have examined the clinical outcomes of Parkinson’s disease (PD) patients after this procedure. The purpose of this study was to evaluate PD outcomes following “asleep” deep brain stimulation in the globus pallidus internus (GPi).

Methods The authors prospectively examined all consecutive patients with advanced PD who underwent bilateral GPi electrode placement while under general anesthesia. Intraoperative CT was used to assess lead placement accuracy. The primary outcome measure was the change in the off-medication Unified Parkinson’s Disease Rating Scale motor score 6 months after surgery. Secondary outcomes included effects on the 39-Item Parkinson’s Disease Questionnaire (PDQ-39) scores, on-medication motor scores, and levodopa equivalent daily dose. Lead locations, active contact sites, stimulation parameters, and adverse events were documented.

Results Thirty-five patients (24 males, 11 females) had a mean age of 61 years at lead implantation. The mean radial error off plan was 0.8 mm. Mean coordinates for the active contact were 21.4 mm lateral, 4.7 mm anterior, and 0.4 mm superior to the midcommissural point. The mean off-medication motor score improved from 48.4 at baseline to 28.9 (40.3% improvement) at 6 months (p < 0.001). The PDQ-39 scores improved (50.3 vs 42.0; p = 0.03), and the levodopa equivalent daily dose was reduced (1207 vs 1035 mg; p = 0.004). There were no significant adverse events.

Conclusions Globus pallidus internus leads placed with the patient under general anesthesia by using direct anatomical targeting resulted in significantly improved outcomes as measured by the improvement in the off-medication motor score at 6 months after surgery.

Integration of Indocyanine Green Videoangiography With Operative Microscope: Augmented Reality for Interactive Assessment of Vascular Structures and Blood Flow

Integration of Indocyanine Green Videoangiography With Operative Microscope

Operative Neurosurgery 11:252–258, 2015

Preservation of adequate blood flow and exclusion of flow from lesions are key concepts of vascular neurosurgery. Indocyanine green (ICG) fluorescence videoangiography is now widely used for the intraoperative assessment of vessel patency.

OBJECTIVE: Here, we present a proof-of-concept investigation of fluorescence angiography with augmented microscopy enhancement: real-time overlay of fluorescence videoangiography within the white light field of view of conventional operative microscopy.

METHODS: The femoral artery was exposed in 7 anesthetized rats. The dissection microscope was augmented to integrate real-time electronically processed near-infrared filtered images with conventional white light images seen through the standard oculars. This was accomplished by using an integrated organic light-emitting diode display to yield superimposition of white light and processed near-infrared images. ICG solution was injected into the jugular vein, and fluorescent femoral artery flow was observed.

RESULTS: Fluorescence angiography with augmented microscopy enhancement was able to detect ICG fluorescence in a small artery of interest. Fluorescence appeared as a bright-green signal in the ocular overlaid with the anatomic image and limited to the anatomic borders of the femoral artery and its branches. Surrounding anatomic structures were clearly visualized. Observation of ICG within the vessel lumens permitted visualization of the blood flow. Recorded video loops could be reviewed in an offline mode for more detailed assessment of the vasculature.

CONCLUSION: The overlay of fluorescence videoangiography within the field of view of the white light operative microscope allows real-time assessment of the blood flow within vessels during simultaneous surgical manipulation. This technique could improve intraoperative decision making during complex neurovascular procedures.

Changes in cerebrospinal fluid flow assessed using intraoperative MRI during posterior fossa decompression for Chiari malformation

Changes in cerebrospinal fluid flow assessed using intraoperative MRI during posterior fossa decompression for Chiari malformation

J Neurosurg 122:1068–1075, 2015

The authors completed a prospective, institutional review board–approved study using intraoperative MRI (iMRI) in patients undergoing posterior fossa decompression (PFD) for Chiari I malformation. The purpose of the study was to examine the utility of iMRI in determining when an adequate decompression had been performed.

Methods Patients with symptomatic Chiari I malformations with imaging findings of obstruction of the CSF space at the foramen magnum, with or without syringomyelia, were considered candidates for surgery. All patients underwent complete T1, T2, and cine MRI studies in the supine position preoperatively as a baseline. After the patient was placed prone with the neck flexed in position for surgery, iMRI was performed. The patient then underwent a bone decompression of the foramen magnum and arch of C-1, and the MRI was repeated. If obstruction was still present, then in a stepwise fashion the patient underwent dural splitting, duraplasty, and coagulation of the tonsils, with an iMRI study performed after each step guiding the decision to proceed further.

Results Eighteen patients underwent PFD for Chiari I malformations between November 2011 and February 2013; 15 prone preincision iMRIs were performed. Fourteen of these patients (93%) demonstrated significant improvement of CSF flow through the foramen magnum dorsal to the tonsils with positioning only. This improvement was so notable that changes in CSF flow as a result of the bone decompression were difficult to discern.

Conclusions The authors observed significant CSF flow changes when simply positioning the patient for surgery. These results put into question intraoperative flow assessments that suggest adequate decompression by PFD, whether by iMRI or intraoperative ultrasound. The use of intraoperative imaging during PFD for Chiari I malformation, whether by ultrasound or iMRI, is limited by CSF flow dynamics across the foramen magnum that change significantly when the patient is positioned for surgery.

Fluorescent Cancer-Selective Alkylphosphocholine Analogs for Intraoperative Glioma Detection

Fluorescent_Cancer_Selective_Alkylphosphocholine

Neurosurgery 76:115–124, 2015

5-Aminolevulinic acid (5-ALA)-induced tumor fluorescence aids brain tumor resections but is not approved for routine use in the United States. We developed and describe testing of 2 novel fluorescent, cancer-selective alkylphosphocholine analogs, CLR1501 (green) and CLR1502 (near infrared), in a proof-of-principle study for fluorescence-guided glioma surgery.

OBJECTIVE: To demonstrate that CLR1501 and CLR1502 are cancer cell-selective fluorescence agents in glioblastoma models and to compare tumor-to-normal brain (T:N) fluorescence ratios with 5-ALA.

METHODS: CLR1501, CLR1502, and 5-ALA were administered to mice with magnetic resonance imaging-verified orthotopic U251 glioblastoma multiforme- and glioblastoma stem cell-derived xenografts. Harvested brains were imaged with confocal microscopy (CLR1501), the IVIS Spectrum imaging system (CLR1501, CLR1502, and 5-ALA), or the Fluobeam near-infrared fluorescence imaging system (CLR1502). Imaging and quantitative analysis of T:N fluorescence ratios were performed.

RESULTS: Excitation/emission peaks are 500/517 nm for CLR1501 and 760/778 nm for CLR1502. The observed T:N ratio for CLR1502 (9.28 6 1.08) was significantly higher (P , .01) than for CLR1501 (3.51 6 0.44 on confocal imaging; 7.23 6 1.63 on IVIS imaging) and 5-ALA (4.81 6 0.92). Near-infrared Fluobeam CLR1502 imaging in a mouse xenograft model demonstrated high- contrast tumor visualization compatible with surgical applications.

CONCLUSION: CLR1501 (green) and CLR1502 (near infrared) are novel tumor-selective fluorescent agents for discriminating tumor from normal brain. CLR1501 exhibits a tumor-to-brain fluorescence ratio similar to that of 5-ALA, whereas CLR1502 has a superior tumor-to-brain fluorescence ratio. This study demonstrates the potential use of CLR1501 and CLR1502 in fluorescence-guided tumor surgery.

Intraoperative Contrast-Enhanced Ultrasound for Brain Tumor Surgery

INTRAOPERATIVE CEUS FOR BRAIN SURGERY

Neurosurgery 74:542–552, 2014 

Contrast-enhanced ultrasound (CEUS) is a dynamic and continuous modality that offers a real-time, direct view of vascularization patterns and tissue resistance for many organs. Thanks to newer ultrasound contrast agents, CEUS has become a wellestablished, live-imaging technique in many contexts, but it has never been used extensively for brain imaging. The use of intraoperative CEUS (iCEUS) imaging in neurosurgery is limited.

OBJECTIVE: To provide the first dynamic and continuous iCEUS evaluation of a variety of brain lesions.

METHODS: We evaluated 71 patients undergoing iCEUS imaging in an off-label setting while being operated on for different brain lesions; iCEUS imaging was obtained before resecting each lesion, after intravenous injection of ultrasound contrast agent. A semiquantitative, offline interobserver analysis was performed to visualize each brain lesion and to characterize its perfusion features, correlated with histopathology.

RESULTS: In all cases, the brain lesion was visualized intraoperatively with iCEUS. The afferent and efferent blood vessels were identified, allowing evaluation of the time and features of the arterial and venous phases and facilitating the surgical strategy. iCEUS also proved to be useful in highlighting the lesion compared with standard B-mode imaging and showing its perfusion patterns. No adverse effects were observed.

CONCLUSION: Our study is the first large-scale implementation of iCEUS in neurosurgery as a dynamic and continuous real-time imaging tool for brain surgery and provides the first iCEUS characterization of different brain neoplasms. The ability of CEUS to highlight and characterize brain tumor will possibly provide the neurosurgeon with important information anytime during a surgical procedure.

Modern intraoperative imaging modalities for the vascular neurosurgeon treating intracerebral hemorrhage

modern OR

Neurosurg Focus 34 (5):E2, 2013

This paper reviews the current intraoperative imaging tools that are available to assist neurosurgeons in the treatment of intracerebral hemorrhage (ICH). This review shares the authors’ experience with each modality and discusses the advantages, potential limitations, and disadvantages of each.

Surgery for ICH is directed at blood clot removal, reduction of intracranial pressure, and minimization of secondary damage associated with hematoma breakdown products. For effective occlusion and safe obliteration of vascular anomalies associated with ICH, vascular neurosurgeons today require a thorough understanding of the various intraoperative imaging modalities available for obtaining real-time information. Use of one or more of these modalities may improve the surgeon’s confidence during the procedure, the patient’s safety during surgery, and surgical outcome.

The modern techniques discussed include 1) indocyanine green–based video angiography, which provides realtime information based on high-quality images showing the residual filling of vascular pathological entities and the patency of blood vessels of any size in the surgical field; and 2) intraoperative angiography, which remains the gold standard intraoperative diagnostic test in the surgical management of cerebral aneurysms and arteriovenous malformations. Hybrid procedures, providing multimodality image-guided surgeries and combining endovascular with microsurgical strategies within the same surgical session, have become feasible and safe. Microdoppler is a safe, noninvasive, and reliable technique for evaluation of hemodynamics of vessels in the surgical field, with the advantage of ease of use. Intraoperative MRI provides an effective navigation tool for cavernoma surgery, in addition to assessing the extent of resection during the procedure. Intraoperative CT scanning has the advantage of very high sensitivity to acute bleeding, thereby assisting in the confirmation of the extent of hematoma evacuation and the extent of vascular anomaly resection. Intraoperative ultrasound aids navigation and evacuation assessment during intracerebral hematoma evacuation surgeries. It supports the concept of minimally invasive surgery and has undergone extensive development in recent years, with the quality of ultrasound imaging having improved considerably.

Image-guided therapy, combined with modern intraoperative imaging modalities, has changed the fundamentals of conventional vascular neurosurgery by presenting real-time visualization of both normal tissue and pathological entities. These imaging techniques are important adjuncts to the surgeon’s standard surgical armamentarium. Familiarity with these imaging modalities may help the surgeon complete procedures with improved safety, efficiency, and clinical outcome

Stereoelectroencephalography: Surgical Methodology, Safety, and Stereotactic Application Accuracy in 500 Procedures

Stereoelectroencephalography___Surgical

Neurosurgery 72:353–366, 2013

Stereoelectroencephalography (SEEG) methodology, originally developed by Talairach and Bancaud, is progressively gaining popularity for the presurgical invasive evaluation of drug-resistant epilepsies.

OBJECTIVE: To describe recent SEEG methodological implementations carried out in our center, to evaluate safety, and to analyze in vivo application accuracy in a consecutive series of 500 procedures with a total of 6496 implanted electrodes.

METHODS: Four hundred nineteen procedures were performed with the traditional 2- step surgical workflow, which was modified for the subsequent 81 procedures. The new workflow entailed acquisition of brain 3-dimensional angiography and magnetic resonance imaging in frameless and markerless conditions, advanced multimodal planning, and robot-assisted implantation. Quantitative analysis for in vivo entry point and target point localization error was performed on a sub–data set of 118 procedures (1567 electrodes).

RESULTS: The methodology allowed successful implantation in all cases. Major complication rate was 12 of 500 (2.4%), including 1 death for indirect morbidity. Median entry point localization error was 1.43 mm (interquartile range, 0.91-2.21 mm) with the traditional workflow and 0.78 mm (interquartile range, 0.49-1.08 mm) with the new one (P , 2.2 · 10216). Median target point localization errors were 2.69 mm (interquartile range, 1.89-3.67 mm) and 1.77 mm (interquartile range, 1.25-2.51 mm; P, 2.2 · 10216), respectively.

CONCLUSION: SEEG is a safe and accurate procedure for the invasive assessment of the epileptogenic zone. Traditional Talairach methodology, implemented by multimodal planning and robot-assisted surgery, allows direct electrical recording from superficial and deep-seated brain structures, providing essential information in the most complex cases of drug-resistant epilepsy.

Stereoelectroencephalography: Surgical Methodology, Safety, and Stereotactic Application Accuracy in 500 Procedures

Stereoelectroencephalography- Surgical Methodology, Safety, and Stereotactic Application Accuracy in 500 Procedures

Neurosurgery 72:353–366, 2013

Stereoelectroencephalography (SEEG) methodology, originally developed by Talairach and Bancaud, is progressively gaining popularity for the presurgical invasive evaluation of drug-resistant epilepsies.

OBJECTIVE: To describe recent SEEG methodological implementations carried out in our center, to evaluate safety, and to analyze in vivo application accuracy in a consecutive series of 500 procedures with a total of 6496 implanted electrodes.

METHODS: Four hundred nineteen procedures were performed with the traditional 2- step surgical workflow, which was modified for the subsequent 81 procedures. The new workflow entailed acquisition of brain 3-dimensional angiography and magnetic resonance imaging in frameless and markerless conditions, advanced multimodal planning, and robot-assisted implantation. Quantitative analysis for in vivo entry point and target point localization error was performed on a sub–data set of 118 procedures (1567 electrodes).

RESULTS: The methodology allowed successful implantation in all cases. Major complication rate was 12 of 500 (2.4%), including 1 death for indirect morbidity. Median entry point localization error was 1.43 mm (interquartile range, 0.91-2.21 mm) with the traditional workflow and 0.78 mm (interquartile range, 0.49-1.08 mm) with the new one (P < 2.2 · 10*16). Median target point localization errors were 2.69 mm (interquartile range, 1.89-3.67 mm) and 1.77 mm (interquartile range, 1.25-2.51 mm; P< 2.2 · 10*16), respectively.

CONCLUSION: SEEG is a safe and accurate procedure for the invasive assessment of the epileptogenic zone. Traditional Talairach methodology, implemented by multimodal planning and robot-assisted surgery, allows direct electrical recording from superficial and deep-seated brain structures, providing essential information in the most complex cases of drug-resistant epilepsy.

Frameless deep brain stimulation using intraoperative O-arm technology

J Neurosurg 115:301–309, 2011. DOI: 10.3171/2011.3.JNS101642

Correct lead location in the desired target has been proven to be a strong influential factor for good clinical outcome in deep brain stimulation (DBS) surgery. Commonly, a surgeon’s first reliable assessment of such location is made on postoperative imaging. While intraoperative CT (iCT) and intraoperative MR imaging have been previously described, the authors present a series of frameless DBS procedures using O-arm iCT.

Methods. Twelve consecutive patients with 15 leads underwent frameless DBS placement using electrophysiological testing and O-arm iCT. Initial target coordinates were made using standard indirect and direct assessment. Microelectrode recording (MER) with kinesthetic responses was performed, followed by microstimulation to evaluate the side-effect profile. Intraoperative 3D CT acquisitions obtained between each MER pass and after final lead placement were fused with the preoperative MR image to verify intended MER movements around the target area and to identify the final lead location. Tip coordinates from the initial plan, final intended target, and actual lead location on iCT were later compared with the lead location on postoperative MR imaging, and euclidean distances were calculated. The amount of radiation exposure during each procedure was calculated and compared with the estimated radiation exposure if iCT was not performed.

Results. The mean euclidean distances between the coordinates for the initial plan, final intended target, and actual lead on iCT compared with the lead coordinates on postoperative MR imaging were 3.04 ± 1.45 mm (p = 0.0001), 2.62 ± 1.50 mm (p = 0.0001), and 1.52 ± 1.78 mm (p = 0.0052), respectively. The authors obtained good merging error during image fusion, and postoperative brain shift was minimal. The actual radiation exposure from iCT was invariably less than estimates of exposure using standard lateral fluoroscopy and anteroposterior radiographs (p < 0.0001).

Conclusions. O-arm iCT may be useful in frameless DBS surgery to approximate microelectrode or lead locations intraoperatively. Intraoperative CT, however, may not replace fundamental DBS surgical techniques such as electrophysiological testing in movement disorder surgery. Despite the lack of evidence for brain shift from the procedure, iCT-measured coordinates were statistically different from those obtained postoperatively, probably indicating image merging inaccuracy and the difficulties in accurately denoting lead location. Therefore, electrophysiological testing may truly be the only means of precisely knowing the location in 3D space intraoperatively. While iCT may provide clues to electrode or lead location during the procedure, its true utility may be in DBS procedures targeting areas where electrophysiology is less useful. The use of iCT appears to reduce radiation exposure compared with the authors’ traditional frameless technique.

Intraoperative Computed Tomography for Deep Brain Stimulation Surgery: Technique and Accuracy Assessment

Neurosurgery 68[ONS Suppl 1]:ons114–ons124, 2011. DOI: 10.1227/NEU.0b013e31820781bc

The efficacy of deep brain stimulation (DBS) is highly dependent on the accuracy of lead placement.

OBJECTIVE: To describe the use of intraoperative computed tomography (iCT) to confirm lead location before surgical closure and to study the accuracy of this technique.

METHODS: Fifteen patients underwent awake microelectrode-guided DBS surgery in a stereotactic frame. A portable iCT scanner (Medtronic O-arm) was positioned around the patient’s head throughout the procedure and was used to confirm lead location before fixation of the lead to the skull. Images were computationally fused with preoperative magnetic resonance imaging (MRI), and lead tip coordinates with respect to the midpoint of the anterior commissure-posterior commissure line were measured. Tip coordinates were compared with those obtained from postoperative MRI.

RESULTS: iCT was integrated into standard frame-based microelectrode-guided DBS surgery with a minimal increase in surgical time or complexity. Technically adequate 2-dimensional and 3-dimensional images were obtained in all cases. Head positioning and fixation techniques that allow unobstructed imaging are described. Lead tip measurements on iCT fused with preoperative MRI were statistically indistinguishable from those obtained with postoperative MRI.

CONCLUSION: iCT can be easily incorporated into standard DBS surgery, replaces the need for C-arm fluoroscopy, and provides accurate intraoperative 3-dimensional confirmation of electrode tip locations relative to preoperative images and surgical plans. iCT fused to preoperative MRI may obviate the need for routine postoperative MRI in DBS surgery. Technical nuances that must be mastered for the efficient use of iCT during DBS implantation are described.