Improving Safety of MRI in Patients with Deep Brain Stimulation Devices

Depth-electrode stimulation and concurrent functional MRI in humans: Factors influencing heating with body coil transmission

Electrical-stimulation fMRI (es-fMRI) combines direct stimulation of the brain via implanted electrodes with simultaneous rapid functional magnetic resonance imaging of the evoked response. Widely used to map effective functional connectivity in animal studies, its application to the human brain has been limited due to safety concerns. In particular, the method requires reliable prediction and minimization of local tissue heating close to the electrodes, which will vary with imaging parameters and hardware configurations. Electrode leads for such experiments typically remain connected to stimulators outside the magnet room and cannot therefore be treated as electrically short at the radio frequencies employed for 1.5 T and 3 T fMRI. The potential for significant absorption and scattering of radiofrequency energy from excitation pulses during imaging is therefore a major concern. We report a series of temperature measurements conducted in human brain phantoms at two independent imaging centers to characterize factors effecting RF heating of electrically long leads with body coil transmission at 3 Tesla for temporal RMS RF transmit fields ( [Formula: see text] ) up to 3.5 µT including multiband echo planar imaging and 3D T2w turbo spin echo imaging. Under all conditions tested, with one exception, the temperature rise measured immediately adjacent to electrode contacts in a head-torso phantom with body coil RF transmission was less than 0.75 °C. We provide detailed quantification across a range of configurations and conclude with specific recommendations for cable routing that will help ensure the safety of es-fMRI in humans and provide essential data to institutional review boards.

Phantom Safety Assessment of 3 Tesla Magnetic Resonance Imaging in Directional and Sensing Deep Brain Stimulation Devices

INTRODUCTION

Magnetic resonance imaging (MRI) is both a crucial clinical and research tool for patients with deep brain stimulation (DBS) devices. However, safety concerns predominantly related to device heating have limited such imaging. Rigorous safety testing has demonstrated that scanning outside of vendor guidelines may be both safe and feasible, unlocking unique opportunities for advanced imaging in this patient population. Currently, however, 3T MRI safety data including advanced MRI sequences in novel directional and sensing DBS devices is lacking.

METHODS

An anthropomorphic phantom replicating bilateral DBS system was used to assess the temperature rise at the electrode tips, implantable pulse generator, and cranial loop during acquisition of routine clinical sequences (three dimensional [3D] T1, GRE T2*, T2 FSE) and advanced imaging sequences including functional MRI (fMRI), arterial spin labelling (ASL), and diffusion weighted imaging (DWI). Measures of radiofrequency exposure (specific absorption rate [SAR] and root-mean square value of the MRI effective component of the radiofrequency transmission field [B1+rms]) were also recorded as an indirect measure of heating. Testing involved both a new directional and sensing DBS device (Medtronic: B30015 leads and Percept PC neurostimulator) and a previous-generation DBS device (Medtronic: 3,387 leads and Percept PC neurostimulator) in combination with a state-of-the-art (Siemens MAGNETOM Prisma) and a previous-generation (GE Signa HDxt) 3T MRI scanner.

RESULTS

On the state-of-the-art 3T MRI scanner, the new DBS device produced safe temperature rises with clinically used sequences and fMRI but not with other advanced sequences such as DWI and ASL, which also exceeded B1+rms vendor guidelines (i.e., ≤2 μT). When scanned on the previous MRI scanner, the recent DBS device produced overall lower and slower temperature rises compared to the previous DBS model. Among the sequences performed on this scanner, several (3D T1, DWI, T2 FSE, and ASL) exceeded the approved SAR vendor limit (<1 W/kg), but only ASL resulted in an unacceptable temperature rise during scanning of the previous DBS model.

CONCLUSION

These phantom safety data show that both clinically used MRI sequences and research sequences such as fMRI can be successfully acquired on 3T MRI scanners with a novel directional and sensing DBS model. As several of these sequences were obtained outside regulatory-approved vendor guidelines, preemptive safety testing should be done. As directional leads become increasingly common, improving MRI safety knowledge is crucial to expand clinical and research possibilities.

INTRODUCTION

Magnetic resonance imaging (MRI) is both a crucial clinical and research tool for patients with deep brain stimulation (DBS) devices. However, safety concerns predominantly related to device heating have limited such imaging. Rigorous safety testing has demonstrated that scanning outside of vendor guidelines may be both safe and feasible, unlocking unique opportunities for advanced imaging in this patient population. Currently, however, 3T MRI safety data including advanced MRI sequences in novel directional and sensing DBS devices is lacking.

METHODS

An anthropomorphic phantom replicating bilateral DBS system was used to assess the temperature rise at the electrode tips, implantable pulse generator, and cranial loop during acquisition of routine clinical sequences (three dimensional [3D] T1, GRE T2*, T2 FSE) and advanced imaging sequences including functional MRI (fMRI), arterial spin labelling (ASL), and diffusion weighted imaging (DWI). Measures of radiofrequency exposure (specific absorption rate [SAR] and root-mean square value of the MRI effective component of the radiofrequency transmission field [B1+rms]) were also recorded as an indirect measure of heating. Testing involved both a new directional and sensing DBS device (Medtronic: B30015 leads and Percept PC neurostimulator) and a previous-generation DBS device (Medtronic: 3,387 leads and Percept PC neurostimulator) in combination with a state-of-the-art (Siemens MAGNETOM Prisma) and a previous-generation (GE Signa HDxt) 3T MRI scanner.

RESULTS

On the state-of-the-art 3T MRI scanner, the new DBS device produced safe temperature rises with clinically used sequences and fMRI but not with other advanced sequences such as DWI and ASL, which also exceeded B1+rms vendor guidelines (i.e., ≤2 μT). When scanned on the previous MRI scanner, the recent DBS device produced overall lower and slower temperature rises compared to the previous DBS model. Among the sequences performed on this scanner, several (3D T1, DWI, T2 FSE, and ASL) exceeded the approved SAR vendor limit (<1 W/kg), but only ASL resulted in an unacceptable temperature rise during scanning of the previous DBS model.

CONCLUSION

These phantom safety data show that both clinically used MRI sequences and research sequences such as fMRI can be successfully acquired on 3T MRI scanners with a novel directional and sensing DBS model. As several of these sequences were obtained outside regulatory-approved vendor guidelines, preemptive safety testing should be done. As directional leads become increasingly common, improving MRI safety knowledge is crucial to expand clinical and research possibilities.

Feasibility of using toroidal transceivers for acquiring intraoperative MR images around deep brain stimulation electrodes

INTRODUCTION

Magnetic resonance imaging (MRI) provides excellent soft tissue contrast for visualizing of deep brain stimulation (DBS) targets, allowing validation of the electrode placement, and assessing complications such as microhemorrhage and edema. However, the presence of the electrodes can introduce challenges such as radiofrequency (RF) induced current artifacts and excessive heating of the electrode contacts. Additionally, extended procedure times are also considered a disadvantage when using MRI as an intraoperative imaging modality following DBS electrode placement.

METHOD

We propose a novel approach of using toroidal resonators to inductively couple the shaft of the electrode to the scanner's transmit-receive chain thereby utilizing it as a localized imaging antenna. The small extent of the field generated by the electrode antenna allows fast imaging with smaller field-of-views (FOVs) spanning only a few centimeters. Furthermore, we present a fast and accurate safety monitoring strategy that can be used to predict the temperature increase at the electrical contacts of the electrode.

RESULTS AND DISCUSSION

Imaging with the toroidal transceiver yields a higher signal-to-noise ratio (SNR) efficiency in proximity to the electrodes. This approach reduced the RF induced current artifacts around the electrode which enhanced the visibility of the shaft and improved electrode localization. Moreover, the limited sensitivity around the electrode can be exploited to perform fast scans with small FOVs. The predicted heating around DBS contacts was in quantitative agreement with the experimental heating in swine studies with a normalized root-mean-square error (NRMSE) ≤ 0.09.

Nanomedicine in Neuroprotection, Neuroregeneration, and Blood-Brain Barrier Modulation: A Narrative Review

Nanomedicine is a newer, promising approach to promote neuroprotection, neuroregeneration, and modulation of the blood-brain barrier. This review includes the integration of various nanomaterials in neurological disorders. In addition, gelatin-based hydrogels, which have huge potential due to biocompatibility, maintenance of porosity, and enhanced neural process outgrowth, are reviewed. Chemical modification of these hydrogels, especially with guanidine moieties, has shown improved neuron viability and underscores tailored biomaterial design in neural applications. This review further discusses strategies to modulate the blood-brain barrier-a factor critically associated with the effective delivery of drugs to the central nervous system. These advances bring supportive solutions to the solving of neurological conditions and innovative therapies for their treatment. Nanomedicine, as applied to neuroscience, presents a significant leap forward in new therapeutic strategies that might help raise the treatment and management of neurological disorders to much better levels. Our aim was to summarize the current state-of-knowledge in this field.

Multimodal neuroimaging to characterize symptom-specific networks in movement disorders

Movement disorders, such as Parkinson's disease, essential tremor, and dystonia, are characterized by their predominant motor symptoms, yet diseases causing abnormal movement also encompass several other symptoms, including non-motor symptoms. Here we review recent advances from studies of brain lesions, neuroimaging, and neuromodulation that provide converging evidence on symptom-specific brain networks in movement disorders. Although movement disorders have traditionally been conceptualized as disorders of the basal ganglia, cumulative data from brain lesions causing parkinsonism, tremor and dystonia have now demonstrated that this view is incomplete. Several recent studies have shown that lesions causing a given movement disorder occur in heterogeneous brain locations, but disrupt common brain networks, which appear to be specific to each motor phenotype. In addition, findings from structural and functional neuroimaging in movement disorders have demonstrated that brain abnormalities extend far beyond the brain networks associated with the motor symptoms. In fact, neuroimaging findings in each movement disorder are strongly influenced by the constellation of patients' symptoms that also seem to map to specific networks rather than individual anatomical structures or single neurotransmitters. Finally, observations from deep brain stimulation have demonstrated that clinical changes, including both symptom improvement and side effects, are dependent on the modulation of large-scale networks instead of purely local effects of the neuromodulation. Combined, this multimodal evidence suggests that symptoms in movement disorders arise from distinct brain networks, encouraging multimodal imaging studies to better characterize the underlying symptom-specific mechanisms and individually tailor treatment approaches.

Diffusion and functional MRI in surgical neuromodulation

Surgical neuromodulation has witnessed significant progress in recent decades. Notably, deep brain stimulation (DBS), delivered precisely within therapeutic targets, has revolutionized the treatment of medication-refractory movement disorders and is now expanding for refractory psychiatric disorders, refractory epilepsy, and post-stroke motor recovery. In parallel, the advent of incisionless treatment with focused ultrasound ablation (FUSA) can offer patients life-changing symptomatic relief. Recent research has underscored the potential to further optimize DBS and FUSA outcomes by conceptualizing the therapeutic targets as critical nodes embedded within specific brain networks instead of strictly anatomical structures. This paradigm shift was facilitated by integrating two imaging modalities used regularly in brain connectomics research: diffusion MRI (dMRI) and functional MRI (fMRI). These advanced imaging techniques have helped optimize the targeting and programming techniques of surgical neuromodulation, all while holding immense promise for investigations into treating other neurological and psychiatric conditions. This review aims to provide a fundamental background of advanced imaging for clinicians and scientists, exploring the synergy between current and future approaches to neuromodulation as they relate to dMRI and fMRI capabilities. Focused research in this area is required to optimize existing, functional neurosurgical treatments while serving to build an investigative infrastructure to unlock novel targets to alleviate the burden of other neurological and psychiatric disorders.

Brain-implanted conductors amplify radiofrequency fields in rodents: Advantages and risks

Over the past few decades, daily exposure to radiofrequency (RF) fields has been increasing due to the rapid development of wireless and medical imaging technologies. Under extreme circumstances, exposure to very strong RF energy can lead to heating of body tissue, even resulting in tissue injury. The presence of implanted devices, moreover, can amplify RF effects on surrounding tissue. Therefore, it is important to understand the interactions of RF fields with tissue in the presence of implants, in order to establish appropriate wireless safety protocols, and also to extend the benefits of medical imaging to increasing numbers of people with implanted medical devices. This study explored the neurological effects of RF exposure in rodents implanted with neuronal recording electrodes. We exposed freely moving and anesthetized rats and mice to 950 MHz RF energy while monitoring their brain activity, temperature, and behavior. We found that RF exposure could induce fast onset firing of single neurons without heat injury. In addition, brain implants enhanced the effect of RF stimulation resulting in reversible behavioral changes. Using an optical temperature measurement system, we found greater than tenfold increase in brain temperature in the vicinity of the implant. On the one hand, our results underline the importance of careful safety assessment for brain-implanted devices, but on the other hand, we also show that metal implants may be used for neurostimulation if brain temperature can be kept within safe limits.

A workflow for predicting radiofrequency-induced heating around bilateral deep brain stimulation electrodes in MRI

BACKGROUND

Heating around deep brain stimulation (DBS) in magnetic resonance imaging (MRI) occurs when the time-varying electromagnetic (EM) fields induce currents in the electrodes which can generate heat and potentially cause tissue damage. Predicting the heating around the electrode contacts is important to ensure the safety of patients with DBS implants undergoing an MRI scan. We previously proposed a workflow to predict heating around DBS contacts and introduced a parameter, equivalent transimpedance, that is independent of electrode trajectories, termination, and radiofrequency (RF) excitations. The workflow performance was validated in a unilateral DBS system.

PURPOSE

To predict RF heating around the contacts of bilateral (DBS) electrodes during an MRI scan in an anthropomorphic head phantom.

METHODS

Bilateral electrodes were fixed in a skull phantom filled with hydroxyethyl cellulose (HEC) gel. The electrode shafts were suspended extracranially, in a head and torso phantom filled with the same gel material. The current induced on the electrode shaft was experimentally measured using an MR-based technique 3 cm above the tip. A transimpedance value determined in a previous offline calibration was used to scale the shaft current and calculate the contact voltage. The voltage was assigned as a boundary condition on the electrical contacts of the electrode in a quasi-static (EM) simulation. The resulting specific absorption rate (SAR) distribution became the input for a transient thermal simulation and was used to predict the heating around the contacts. RF heating experiments were performed for eight different lead trajectories using circularly polarized (CP) excitation and two linear excitations for one trajectory. The measured temperatures for all experiments were compared with the simulated temperatures and the root-mean-squared errors (RMSE) were calculated.

RESULTS

The RF heating around the contacts of both bilateral electrodes was predicted with ≤ 0.29°C of RMSE for 20 heating scenarios.

CONCLUSION

The workflow successfully predicted the heating for different bilateral DBS trajectories and excitation patterns in an anthropomorphic head phantom.

Movement disorder Deep brain stimulation Hybridization: Patient and caregiver outcomes

Background and Objectives

Deep brain stimulation (DBS) is a well-established surgical treatment for certain movement disorders and involves the implantation of brain electrodes connected to implantable pulse generators (IPGs). As more device manufacturers have entered the market, some IPG technology has been designed to be compatible with brain electrodes from other manufacturers, which has facilitated the hybridization of implant technology. The aim of this study was to assess the benefits of hybridization of non-rechargeable, constant voltage IPGs to rechargeable, constant current IPGs.

Methods

A list of DBS movement disorder patients who had their non-rechargeable, constant voltage IPGs replaced with rechargeable, constant current IPGs from a different manufacturer was compiled. Structured surveys of these patients, and their caregivers when applicable, were undertaken to determine both patient and caregiver satisfaction in this DBS hybridization strategy.

Results

Eighteen patients met inclusion criteria and twelve patients or their caregivers completed the structured survey (67% response rate). Nine patients had Parkinson's disease (75%), three had essential tremor (25%). Nine (75%) were converted from bilateral single-channel IPGs, and three (25%) were converted from a unilateral dual-channel IPGs. Overall, 92% of patients and caregivers surveyed reported improvement or no change in their symptoms, 92% reported a decrease or no change in their medication requirements, and 92% report they are satisfied or very satisfied with their IPG hybridization and would recommend the surgery to similar patients. There were no immediate surgical complications.

Conclusion

In this series of movement disorder DBS patients, surgery was safe and patient and caregiver satisfaction were high with a hybridization of non-rechargeable, constant voltage IPGs to rechargeable, constant current IPGs.

Computational Neurosurgery in Deep Brain Stimulation

Computational methods and technologies are critical for neurosurgery in general and in deep brain stimulation (DBS) in particular. They increasingly inform every aspect of clinical DBS therapy, from presurgical planning and hardware implantation to postoperative adjustment of stimulation parameters. Computational methods also occupy a prominent position within the DBS research sphere, where they facilitate efforts to better understand DBS' underlying mechanisms and optimize and individualize its delivery. This chapter provides a high-level overview of the various computational tools and methods that have been applied to DBS. First, we discuss the invaluable contribution of computational neuroimaging (primarily magnetic resonance imaging) to DBS, targeting and the role of postoperative methods of image analysis-specifically, electrode localization, volume of activated tissue modeling, and sweet-spot mapping-in precisely localizing DBS' targets in the brain and discerning optimal treatment loci. We then address the growing field of connectomics, which leverages specific magnetic resonance imaging (MRI) sequences and post-acquisition processing algorithms to explore how DBS operates at the level of brain-wide networks. Next, the search for electrophysiological and imaging-based biomarkers of optimal DBS therapy is explored. We lastly touch on the incipient field of spatial characterization analysis and discuss the ongoing development of adaptive, closed-loop DBS systems.

Wirelessly interfacing sensor-equipped implants and MR scanners for improved safety and imaging

PURPOSE

To investigate a novel reduced RF heating method for imaging in the presence of active implanted medical devices (AIMDs) which employs a sensor-equipped implant that provides wireless feedback.

METHODS

The implant, consisting of a generator case and a lead, measures RF-inducedE $$ E $$ -fields at the implant tip using a simple sensor in the generator case and transmits these values wirelessly to the MR scanner. Based on the sensor signal alone, parallel transmission (pTx) excitation vectors were calculated to suppress tip heating and maintain image quality. A sensor-based imaging metric was introduced to assess the image quality. The methodology was studied at 7T in testbed experiments, and at a 3T scanner in an ASTM phantom containing AIMDs instrumented with six realistic deep brain stimulation (DBS) lead configurations adapted from patients.

RESULTS

The implant successfully measured RF-inducedE $$ E $$ -fields (Pearson correlation coefficient squared [R2 ] = 0.93) and temperature rises (R2  = 0.95) at the implant tip. The implant acquired the relevant data needed to calculate the pTx excitation vectors and transmitted them wirelessly to the MR scanner within a single shot RF sequence (<60 ms). Temperature rises for six realistic DBS lead configurations were reduced to 0.03-0.14 K for heating suppression modes compared to 0.52-3.33 K for the worst-case heating, while imaging quality remained comparable (five of six lead imaging scores were ≥0.80/1.00) to conventional circular polarization (CP) images.

CONCLUSION

Implants with sensors that can communicate with an MR scanner can substantially improve safety for patients in a fast and automated manner, easing the current burden for MR personnel.

Advances in Deep Brain Stimulation: From Mechanisms to Applications

Deep brain stimulation (DBS) is an effective therapy for various neurologic and neuropsychiatric disorders, involving chronic implantation of electrodes into target brain regions for electrical stimulation delivery. Despite its safety and efficacy, DBS remains an underutilized therapy. Advances in the field of DBS, including in technology, mechanistic understanding, and applications have the potential to expand access and use of DBS, while also improving clinical outcomes. Developments in DBS technology, such as MRI compatibility and bidirectional DBS systems capable of sensing neural activity while providing therapeutic stimulation, have enabled advances in our understanding of DBS mechanisms and its application. In this review, we summarize recent work exploring DBS modulation of target networks. We also cover current work focusing on improved programming and the development of novel stimulation paradigms that go beyond current standards of DBS, many of which are enabled by sensing-enabled DBS systems and have the potential to expand access to DBS.

Anesthetic Management of a Patient With Parkinson's Disease and a Deep Brain Stimulator Device for Hemiarthroplasty Surgery: A Case Report

Parkinson's disease (PD) is a common neurodegenerative disease. The multisystem effects of the disease and its pharmacological treatment have several anesthetic implications. With increasing duration of therapy, pharmacoresistance develops. Deep brain stimulation is a safe and effective treatment for symptom control in advanced PD. Its titratability and reversibility make it an attractive treatment option, and it has replaced surgical ablative procedures for advanced disease management. These devices have several implications in the perioperative period. A case is presented of a 75-year-old patient for urgent hemiarthroplasty surgery with advanced PD and a deep brain stimulator device in situ.

MRI safety screening of children with implants: updates and challenges

MRI is the imaging modality of choice for assessing many pediatric medical conditions. Although there are several inherent potential safety risks associated with the electromagnetic fields exploited for MRI, they are effectively mitigated through strict adherence to established MRI safety practices, enabling the safe and effective use of MRI in clinical practice. The potential hazards of the MRI environment may be exacerbated by/in the presence of implanted medical devices. Awareness of the unique MRI safety and screening challenges associated with these implanted devices is critical to ensuring MRI safety for the affected patients. In this review article, we will discuss the basics of MRI physics as they relate to MRI safety in the presence of implanted medical devices, strategies for assessing children with known or suspected implanted medical devices, and the particular management of several well-established common, as well as recently developed, implanted devices encountered at our institution.

Perioperative Management of Nonorthopaedic Devices in the Pediatric Neuromuscular Patient Population

Pediatric patients with neuromuscular conditions often have nonorthopaedic implants that can pose a challenge for MRI acquisition and surgical planning. Treating physicians often find themselves in the position of navigating between seemingly overly risk-averse manufacturer's guidelines and an individual patient's benefits of an MRI or surgery. Most nonorthopaedic implants are compatible with MRI under specific conditions, though often require reprogramming or interrogation before and/or after the scan. For surgical procedures, the use of electrosurgical instrumentation poses a risk of electromagnetic interference and implants are thus often programmed or turned off for the procedures. Special considerations are needed for these patients to prevent device damage or malfunction, which can pose additional risk to the patient. Additional planning before surgery is necessary to ensure appropriate equipment, and staff are available to ensure patient safety.

Deep Brain Stimulation Electrode Reconstruction: Comparison between Lead-DBS and Surgical Planning System

BACKGROUND

Electrode reconstruction for postoperative deep brain simulation (DBS) can be achieved manually using a surgical planning system such as Surgiplan, or in a semi-automated manner using software such as the Lead-DBS toolbox. However, the accuracy of Lead-DBS has not been thoroughly addressed.

METHODS

In our study, we compared the DBS reconstruction results of Lead-DBS and Surgiplan. We included 26 patients (21 with Parkinson's disease and 5 with dystonia) who underwent subthalamic nucleus (STN)-DBS, and reconstructed the DBS electrodes using the Lead-DBS toolbox and Surgiplan. The electrode contact coordinates were compared between Lead-DBS and Surgiplan with postoperative CT and MRI. The relative positions of the electrode and STN were also compared between the methods. Finally, the optimal contact during follow-up was mapped onto the Lead-DBS reconstruction results to check for overlap between the contacts and the STN.

RESULTS

We found significant differences in all axes between Lead-DBS and Surgiplan with postoperative CT, with the mean variance for the X, Y, and Z coordinates being -0.13, -1.16, and 0.59 mm, respectively. Y and Z coordinates showed significant differences between Lead-DBS and Surgiplan with either postoperative CT or MRI. However, no significant difference in the relative distance of the electrode and the STN was found between the methods. All optimal contacts were located in the STN, with 70% of them located within the dorsolateral region of the STN in the Lead-DBS results.

CONCLUSIONS

Although significant differences in electrode coordinates existed between Lead-DBS and Surgiplan, our results suggest that the coordinate difference was around 1 mm, and Lead-DBS can capture the relative distance between the electrode and the DBS target, suggesting it is reasonably accurate for postoperative DBS reconstruction.

Artifacts Can Be Deceiving: The Actual Location of Deep Brain Stimulation Electrodes Differs from the Artifact Seen on Magnetic Resonance Images

INTRODUCTION

Deep brain stimulation (DBS) is a common treatment for a variety of neurological and psychiatric disorders. Recent studies have highlighted the role of neuroimaging in localizing the position of electrode contacts relative to target brain areas in order to optimize DBS programming. Among different imaging methods, postoperative magnetic resonance imaging (MRI) has been widely used for DBS electrode localization; however, the geometrical distortion induced by the lead limits its accuracy. In this work, we investigated to what degree the difference between the actual location of the lead's tip and the location of the tip estimated from the MRI artifact varies depending on the MRI sequence parameters such as acquisition plane and phase encoding direction, as well as the lead's extracranial configuration. Accordingly, an imaging technique to increase the accuracy of lead localization was devised and discussed.

METHODS

We designed and constructed an anthropomorphic phantom with an implanted DBS system following 18 clinically relevant configurations. The phantom was scanned at a Siemens 1.5 Tesla Aera scanner using a T1MPRAGE sequence optimized for clinical use and a T1TSE sequence optimized for research purposes. We varied slice acquisition plane and phase encoding direction and calculated the distance between the caudal tip of the DBS lead MRI artifact and the actual tip of the lead, as estimated from MRI reference markers.

RESULTS

Imaging parameters and lead configuration substantially altered the difference in the depth of the lead within its MRI artifact on the scale of several millimeters - with a difference as large as 4.99 mm. The actual tip of the DBS lead was found to be consistently more rostral than the tip estimated from the MR image artifact. The smallest difference between the tip of the DBS lead and the tip of the MRI artifact using the clinically relevant sequence (i.e., T1MPRAGE) was found with the sagittal acquisition plane and anterior-posterior phase encoding direction.

DISCUSSION/CONCLUSION

The actual tip of an implanted DBS lead is located up to several millimeters rostral to the tip of the lead's artifact on postoperative MR images. This distance depends on the MRI sequence parameters and the DBS system's extracranial trajectory. MRI parameters may be altered to improve this localization.

Necessity of MRI-compatible deep brain stimulation systems - Hits and hints for decision making

OBJECTIVES

Deep brain stimulation (DBS) is a safe and effective treatment option for patients with movement disorders as Parkinson's disease, essential tremor and dystonia[1]. For many of these patients the need for imaging may arise in the following years after implantation. The study's aim was to get an overview of the amount of patients with a DBS system who needed an MRI after successful implantation, and if they did, whether the imaging led to a surgical consequence.

MATERIALS AND METHODS

In this retrospective descriptive work patients were included if they had their DBS implantation for at least 12 months at the time of analysis. Data were collected by retrospective analysis of the electronic patient files as well as a telephone interview. The reason of each imaging performed was assessed, if patients got MRI after the implantation, it was additionally recorded whether imaging led to a consequence (conservative treatment or surgery). An independent neurologist assessed if an MRI would have been better than a CT for the particular indication.

RESULTS

From 54 included patients, 28 patients received imaging after implantation, either CT or MRI. 7 patients underwent MRIs, of whom 3 patients received cranial MRIs and 4 patients received lumbar spine MRIs. All cranial MRIs led to conservative therapy, in 2 lumbar MRIs the diagnosis led to surgery. Nearly 13 % of the imaging performed in our study population occurred because of fall events, 9 of the included patients developed or have had a tumor diagnosis.

CONCLUSIONS

Safety of MRI for patients with implanted DBS-systems is and remains an important consideration. Since it can be assumed that patients at a younger age are more likely to get an MRI in the course of their disease, we suggest paying particular attention to the MRI's suitability of the DBS device by patients age. In the end it remains always an individual decision for the surgeon or the consulting physician, which system to use.

A Systematic Review of Treatment Outcome Predictors in Deep Brain Stimulation for Refractory Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) is a chronic and debilitating mental disorder. Deep brain stimulation (DBS) is a promising approach for refractory OCD patients. Research aiming at treatment outcome prediction is vital to provide optimized treatments for different patients. The primary purpose of this systematic review was to collect and synthesize studies on outcome prediction of OCD patients with DBS implantations in recent years. This systematic review (PROSPERO registration number: CRD42022335585) followed the PRISMA (Preferred Reporting Items for Systematic Review and Meta-analysis) guidelines. The search was conducted using three different databases with the following search terms related to OCD and DBS. We identified a total of 3814 articles, and 17 studies were included in our review. A specific tract confirmed by magnetic resonance imaging (MRI) was predictable for DBS outcome regardless of implant targets, but inconsistencies still exist. Current studies showed various ways of successful treatment prediction. However, considering the heterogeneous results, we hope that future studies will use larger cohorts and more precise approaches for predictors and establish more personalized ways of DBS surgeries.

Neurobiological effects of deep brain stimulation: A systematic review of molecular brain imaging studies

Deep brain stimulation (DBS) is an established treatment for several brain disorders, including Parkinson's disease, essential tremor, dystonia and epilepsy, and an emerging therapeutic tool in many other neurological and psychiatric disorders. The therapeutic efficacy of DBS is dependent on the stimulation target, but its mechanisms of action are still relatively poorly understood. Investigating these mechanisms is challenging, partly because the stimulation devices and electrodes have limited the use of functional MRI in these patients. Molecular brain imaging techniques, such as positron emission tomography (PET) and single photon emission tomography (SPET), offer a unique opportunity to characterize the whole brain effects of DBS. Here, we investigated the direct effects of DBS by systematically reviewing studies performing an `on' vs `off' contrast during PET or SPET imaging. We identified 62 studies (56 PET and 6 SPET studies; 531 subjects). Approximately half of the studies focused on cerebral blood flow or glucose metabolism in patients Parkinson's disease undergoing subthalamic DBS (25 studies, n = 289), therefore Activation Likelihood Estimation analysis was performed on these studies. Across disorders and stimulation targets, DBS was associated with a robust local increase in ligand uptake at the stimulation site and target-specific remote network effects. Subthalamic nucleus stimulation in Parkinson's disease showed a specific pattern of changes in the motor circuit, including increased ligand uptake in the basal ganglia, and decreased ligand uptake in the primary motor cortex, supplementary motor area and cerebellum. However, there was only a handful of studies investigating other brain disorder and stimulation site combinations (1-3 studies each), or specific neurotransmitter systems, preventing definitive conclusions of the detailed molecular effects of the stimulation in these cases.

No Adverse Effects following Off-Label Magnetic Resonance Imaging in a Patient with Two Deep Brain Stimulation Systems: A Case Report

Magnetic resonance imaging (MRI) in patients with implanted deep brain stimulation (DBS) systems is subject to strict guidelines in order to ensure patient safety. Criteria include limits on the number of implanted leads. Here, we describe the case of a 29-year-old patient with generalized dystonia implanted with 4 DBS electrodes and 2 implantable pulse generators, who had an off-label spinal MRI without regard for manufacturer guidance yet suffered no adverse effects. This suggests that manufacturer guidelines might be overly restrictive with regards to limits on implanted DBS hardware. Further research in this area is needed to widen access to this fundamental imaging modality for patients with DBS.

Probing responses to deep brain stimulation with functional magnetic resonance imaging

BACKGROUND

Deep brain stimulation (DBS) is an established treatment for certain movement disorders and has additionally shown promise for various psychiatric, cognitive, and seizure disorders. However, the mechanisms through which stimulation exerts therapeutic effects are incompletely understood. A technique that may help to address this knowledge gap is functional magnetic resonance imaging (fMRI). This is a non-invasive imaging tool which permits the observation of DBS effects in vivo.

OBJECTIVE

The objective of this review was to provide a comprehensive overview of studies in which fMRI during active DBS was performed, including studied disorders, stimulated brain regions, experimental designs, and the insights gleaned from stimulation-evoked fMRI responses.

METHODS

We conducted a systematic review of published human studies in which fMRI was performed during active stimulation in DBS patients. The search was conducted using PubMED and MEDLINE.

RESULTS

The rate of fMRI DBS studies is increasing over time, with 37 studies identified overall. The median number of DBS patients per study was 10 (range = 1-67, interquartile range = 11). Studies examined fMRI responses in various disease cohorts, including Parkinson's disease (24 studies), essential tremor (3 studies), epilepsy (3 studies), obsessive-compulsive disorder (2 studies), pain (2 studies), Tourette syndrome (1 study), major depressive disorder, anorexia, and bipolar disorder (1 study), and dementia with Lewy bodies (1 study). The most commonly stimulated brain region was the subthalamic nucleus (24 studies). Studies showed that DBS modulates large-scale brain networks, and that stimulation-evoked fMRI responses are related to the site of stimulation, stimulation parameters, patient characteristics, and therapeutic outcomes. Finally, a number of studies proposed fMRI-based biomarkers for DBS treatment, highlighting ways in which fMRI could be used to confirm circuit engagement and refine DBS therapy.

CONCLUSION

A review of the literature reflects an exciting and expanding field, showing that the combination of DBS and fMRI represents a uniquely powerful tool for simultaneously manipulating and observing neural circuitry. Future work should focus on relatively understudied disease cohorts and stimulated regions, while focusing on the prospective validation of putative fMRI-based biomarkers.

Mapping Motor Pathways in Parkinson’s Disease Patients with Subthalamic Deep Brain Stimulator: A Diffusion MRI Tractography Study

Introduction

This study assessed the safety of postoperative diffusion tensor imaging (DTI) with on-state deep brain stimulation (DBS) and the feasibility of reconstruction of the white matter tracts in the vicinity of the stimulation site of the subthalamic nucleus (STN). The association between the impact of DBS on the nigrostriatal pathway (NSP) and the treatment effect on motor symptoms in Parkinson’s disease (PD) was then evaluated.

Methods

Thirty-one PD patients implanted with STN-DBS (mean age: 66 years; 25 male) were scanned on a 1.5-T magnetic resonance imaging (MRI) scanner using the DTI sequence with DBS on. Twenty-three of them were scanned a second time with DBS off. The NSP, dentato-rubro-thalamic tract (DRTT), and hyperdirect pathway (HDP) were generated using both deterministic and probabilistic tractography methods. The DBS-on-state and off-state tractography results were validated and compared. Afterward, the relationships between the characteristics of the reconstructed white matter tracts and the clinical assessment of PD symptoms and the DBS effect were further examined.

Results

No adverse events related to DTI were identified in either the DBS-on-state or off-state. Overall, the NSP was best reconstructed, followed by the DRTT and HDP, using the probabilistic tractography method. The connection probability of the left NSP was significantly lower than that of the right side (p < 0.05), and a negative correlation (r = −0.39, p = 0.042) was identified between the preoperative symptom severity in the medication-on state and the connection probability of the left NSP in the DBS-on-state images. Furthermore, the distance from the estimated left-side volume of tissue activated (VTA) by STN-DBS to the ipsilateral NSP was significantly shorter in the DBS-responsive group compared to the DBS-non-responsive group (p = 0.046).

Conclusions

DTI scanning is safe and delineation of white matter pathway is feasible for PD patients implanted with the DBS device. Postoperative DTI is a useful technique to strengthen our current understanding of the therapeutic effect of DBS for PD and has the potential to refine target selection strategies for brain stimulation.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40120-022-00331-1.

For some more seriously affected Parkinson’s disease (PD) patients, drugs are no longer effective in treating their symptoms. An alternate treatment is to use deep brain stimulation (DBS), a commonly used neurosurgical therapy for PD patients. For those DBS treatments targeting the subthalamic nucleus (STN), the electrical stimulation used may impact nearby white matter tracts and alter the effectiveness of the DBS treatment. The nigrostriatal pathway (NSP), dentato-rubro-thalamic tract, and hyperdirect pathway are three white matter tracts near the STN. They are all relevant to motor symptoms in PD. This study examined whether imaging these tracts using magnetic resonance imaging (MRI) is safe and feasible in the presence of DBS leads. The relationships between the fiber-tracking characteristics and distance to the DBS leads were then evaluated. For this purpose, 31 PD patients with stimulation-on were scanned on a 1.5 T MRI scanner using a diffusion tensor imaging sequence. A total of 23 subjects underwent another scan using the same sequence with stimulation-off. No adverse events related to diffusion tensor imaging were found. Among the white matter tracts near the STN, the NSP was best delineated, followed by the dentato-rubro-thalamic tract and the hyperdirect pathway. The connection probability of the left NSP was significantly lower than that of the right side as were the subject’s motor symptoms. The closer the distance between the NSP and the stimulation location, the better the DBS outcome. These findings indicate that imaging white matter tracts with DBS on is safe and useful in mapping DBS outcomes.

Target Selection for Magnetic Resonance-Guided Focused Ultrasound in the Treatment of Parkinson's Disease

Parkinson's disease (PD) is a common, progressive, and incurable neurodegenerative disease. Pharmacological treatment is the first-line therapy for PD, including carbidopa-levodopa, dopamine agonists. However, some patients respond poorly to medication. For these patients, functional neurosurgical treatment is an important option. Magnetic resonance-guided focused ultrasound (MRgFUS) is a novel, minimally invasive surgical option for patients refractory to drugs. Currently, several important anatomical structures can be targeted by MRgFUS in the treatment of PD. However, there is no uniform standard for target selection. This review summarizes the clinical studies on MRgFUS for PD, focusing on the relationship between different treatment targets and the relieved symptoms, to help clinicians determine the ideal therapeutic target for individual patients. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 4.

Neuromodulation for Intractable Childhood Epilepsy

In the past few years significant advances made in the field of neuromodulation have led to practical therapeutic strategies for children with medically refractory epilepsy. Here, we briefly discuss the various options that are currently available including vagus nerve stimulation, responsive neurostimulation, deep brain stimulation, chronic subthreshold cortical stimulation, as well as repetitive transcranial magnetic and transcranial direct current stimulation. The current indications, proposed mechanisms, method of administration, efficacy, adverse effects, and mention of clinical trials currently in enrollment or development are discussed.

Anesthesia for deep brain stimulation: an update

PURPOSE OF REVIEW

Deep brain stimulation (DBS) is a rapidly expanding surgical modality for the treatment of patients with movement disorders. Its ability to be adjusted, titrated, and optimized over time has given it a significant advantage over traditional more invasive surgical procedures. Therefore, the success and popularity of this procedure have led to the discovery of new indications and therapeutic targets as well as advances in surgical techniques. The aim of this review is to highlight the important updates in DBS surgery and to exam the anesthesiologist's role in providing optimal clinical management.

RECENT FINDINGS

New therapeutic indications have a significant implication on perioperative anesthesia management. In addition, new technologies like frameless stereotaxy and intraoperative magnetic resonance imaging to guide electrode placement have altered the need for intraoperative neurophysiological monitoring and hence increased the use of general anesthesia. With an expanding number of patients undergoing DBS implantation, patients with preexisting DBS increasingly require anesthesia for unrelated surgery and the anesthesiologist must be aware of the considerations for perioperative management of these devices and potential complications.

SUMMARY

DBS will continue to grow and evolve requiring adaptation and modification to the anesthetic management of these patients.

Implantable Pulse Generators for Deep Brain Stimulation: Challenges, Complications, and Strategies for Practicality and Longevity

Deep brain stimulation (DBS) represents an important treatment modality for movement disorders and other circuitopathies. Despite their miniaturization and increasing sophistication, DBS systems share a common set of components of which the implantable pulse generator (IPG) is the core power supply and programmable element. Here we provide an overview of key hardware and software specifications of commercially available IPG systems such as rechargeability, MRI compatibility, electrode configuration, pulse delivery, IPG case architecture, and local field potential sensing. We present evidence-based approaches to mitigate hardware complications, of which infection represents the most important factor. Strategies correlating positively with decreased complications include antibiotic impregnation and co-administration and other surgical considerations during IPG implantation such as the use of tack-up sutures and smaller profile devices.Strategies aimed at maximizing battery longevity include patient-related elements such as reliability of IPG recharging or consistency of nightly device shutoff, and device-specific such as parameter delivery, choice of lead configuration, implantation location, and careful selection of electrode materials to minimize impedance mismatch. Finally, experimental DBS systems such as ultrasound, magnetoelectric nanoparticles, and near-infrared that use extracorporeal powered neuromodulation strategies are described as potential future directions for minimally invasive treatment.

Blood oxygen level-dependent (BOLD) response patterns with thalamic deep brain stimulation in patients with medically refractory epilepsy

OBJECTIVE

Anterior nucleus of thalamus (ANT) deep brain stimulation (DBS) has shown promise as a treatment for medically refractory epilepsy. To better understand the mechanism of this intervention, we used functional magnetic resonance imaging (fMRI) to map the acute blood oxygen level-dependent (BOLD) response pattern to thalamic DBS in fully implanted patients with epilepsy.

METHODS

Two patients with epilepsy implanted with bilateral ANT-DBS devices underwent four fMRI acquisitions each, during which active left-sided monopolar stimulation was delivered in a 30-s DBS-ON/OFF cycling paradigm. Each fMRI acquisition featured left-sided stimulation of a different electrode contact to vary the locus of stimulation within the thalamus and to map the brain regions modulated as a function of different contact selection. To determine the extent of peri-electrode stimulation and the engagement of local structures during each fMRI acquisition, volume of tissue activated (VTA) modeling was also performed.

RESULTS

Marked changes in the pattern of BOLD response were produced with thalamic stimulation, which varied with the locus of the active contact in each patient. BOLD response patterns to stimulation that directly engaged at least 5% of the anterior nuclear group by volume were characterized by changes in the bilateral putamen, thalamus, and posterior cingulate cortex, ipsilateral middle cingulate cortex and precuneus, and contralateral medial prefrontal and anterior cingulate.

SIGNIFICANCE

The differential BOLD response patterns associated with varying thalamic DBS parameters provide mechanistic insights and highlight the possibilities of fMRI biomarkers of optimizing stimulation in patients with epilepsy.

The Future of Neuroscience: Flexible and Wireless Implantable Neural Electronics

Neurological diseases are a prevalent cause of global mortality and are of growing concern when considering an ageing global population. Traditional treatments are accompanied by serious side effects including repeated treatment sessions, invasive surgeries, or infections. For example, in the case of deep brain stimulation, large, stiff, and battery powered neural probes recruit thousands of neurons with each pulse, and can invoke a vigorous immune response. This paper presents challenges in engineering and neuroscience in developing miniaturized and biointegrated alternatives, in the form of microelectrode probes. Progress in design and topology of neural implants has shifted the goal post toward highly specific recording and stimulation, targeting small groups of neurons and reducing the foreign body response with biomimetic design principles. Implantable device design recommendations, fabrication techniques, and clinical evaluation of the impact flexible, integrated probes will have on the treatment of neurological disorders are provided in this report. The choice of biocompatible material dictates fabrication techniques as novel methods reduce the complexity of manufacture. Wireless power, the final hurdle to truly implantable neural interfaces, is discussed. These aspects are the driving force behind continued research: significant breakthroughs in any one of these areas will revolutionize the treatment of neurological disorders.