Coil Placement Research Articles

Audiovisual augmentation for coil positioning in transcranial magnetic stimulation

ABSTRACT Transcranial Magnetic Stimulation (TMS) is an effective non-invasive treatment method for major depressive disorder. Accurate placement of an electromagnetic coil on the patient’s head during repetitive TMS is the key for stimulation of the desired brain regions and positive treatment outcome. Neuronavigation systems constitute the state-of-the-art method to accurately stimulate the appropriate brain region. Local separation of navigation information and the patient anatomy in combination with intricate visualisations and cumbersome setup limits the benefits and usability of this method. The present study addresses these problems by proposing an audiovisual Augmented reality (AR) system for coil positioning during TMS. The system sonifies and visualises translational and rotational differences between a target and the current instrument position using a minimalistic graphical user interface and auditory display. Effects of cross-modal integration on usability and targeting precision were shown in an experiment comparing audiovisual AR, audio AR and visual neuronavigation. Our approach revealed significant improvements in task time of all proposed AR conditions over neuronavigation (p < 0.001). Conversely, the neuronavigation system achieved significantly better targeting accuracy (p < 0.001). A purely auditory guidance achieved comparable performance as the audiovisual interface designs.

Saliency-Based Rotor Spatial Position Displacement Self-Sensing for Self-Bearing Machines.

Self-bearing machines do not contain physical bearings but magnetic bearings. Both rotor rotary and spatial positions displacement are required in these types of machines to control the rotor position while it is levitating. Self-bearing machines often use external sensors for x (horizontal) and y (vertical) spatial position measurement, which will result in additional cost, volume, complexity, and number of parts susceptible to failure. To overcome these issues, this paper proposes a xy-position estimation self-sensing technique based on both main- and cross-inductance variation. The proposed method estimates x and y position based on inductive saliency between two sets of three-phase coils. The proposed idea is applied on a combined winding self-bearing machine which does not require additional suspension force winding. No additional search coil placement for xy-position estimation is required. Therefore, the proposed algorithm can result in a compact size self-bearing machine that does not require external sensors for xy-position measurement and suspension force winding.

Stellarator coil optimization supporting multiple magnetic configurations

We present a technique that can be used to design stellarators with a high degree of experimental flexibility. For our purposes, flexibility is defined by the range of values the rotational transform can take on the magnetic axis of the vacuum field while maintaining satisfactory quasisymmetry. We show that accounting for configuration flexibility during the modular coil design improves flexibility beyond that attained by previous methods. Careful placement of planar control coils and the incorporation of an integrability objective enhance the quasisymmetry and nested flux surface volume of each configuration. We show that it is possible to achieve flexibility, quasisymmetry, and nested flux surface volume to reasonable degrees with a relatively simple coil set through an NCSX-like example. This example coil design is optimized to achieve three rotational transform targets and nested flux surface volumes in each magnetic configuration larger than the NCSX design plasma volume. Our work suggests that there is a tradeoff between flexibility, quasisymmetry, and volume of nested flux surfaces.

S374 Endoscopic Coiling of Mesenteric Varices Causing Stomal Bleeding Caused by Extensive Portal Vein and Superior Mesenteric Thrombus

Introduction: Ectopic varices are collateral vessels located outside the gastro-esophageal area. Small bowel varices, while an uncommon result of portal hypertension can be a life-threatening cause of gastrointestinal bleeding. We present a case of refractory stomal bleeding secondary to mesenteric varices, treated with endoscopic ultrasound (EUS) guided coiling. Case Description/Methods: A 54-year-old male presented with history of ulcerative colitis status post proctocolectomy and ileostomy, primary sclerosing cholangitis (PSC), and auto-immune hepatitis (AIH) overlap syndrome treated with a deceased donor liver transplant in 2019. This was further complicated by portal hypertension secondary to portal vein and superior mesenteric vein thrombus. The patient presented with refractory stomal bleeding at this ileostomy site requiring multiple blood transfusions. On CT imaging, prominent mesenteric varices extending to the area of the stoma were noted. An interventional radiology (IR) approach from the portal system was not feasible given thrombosis in the portal vein and superior mesenteric vein. Percutaneous IR approach was also felt to be suboptimal given the depth of the peri-stomal varices. After a multidisciplinary discussion, the patient underwent ileoscopy with EUS guided coiling of the terminal/culprit branches of the mesenteric varices. The linear echoendoscope was introduced through the ileostomy and advanced approximately 5-10cm. Multiple tubal anechoic structures consistent with varices were noted with flow seen on doppler examination. This was confirmed on pulse wave doppler. A large feeding variceal vein towards the patient’s left side was punctured with a 22G needle. Saline was injected and it was visualized on EUS to confirm location. Next, embolization coils (8mm x 2, 10mm x1) were inserted for varix eradication. Reduced flow downstream of the coiling site was confirmed on doppler exam after embolization. Brief fluoroscopic images showed appropriate placement of coils in the patients right lower quadrant, without any migration. There was no significant flow toward the lumen on EUS after coiling. Since this procedure, the patient’s stomal bleeding resolved. (Figure) Discussion: Small bowel varices in the setting of significant portal hypertension are a rare but clinically significant cause of gastrointestinal bleeding. EUS-guided interventions such as coil embolization can be an effective treatment modality, especially in patients who are poor interventional radiology candidates. Watch the video at https://tinyurl.com/ACGAbstractS374Figure 1.: (1a) Prominent mesenteric varices extending into the ostomy (1b) EUS-guided coil embolization (1c) Status post successful endoscopic coil embolization

S3041 Hepatic Artery Dissection – A Case Report

Introduction: Visceral artery aneurysms are rare pathologies with reported incidence rates between 0.01% to 0.2%; even rarer are hepatic artery dissections (HAD). Most aneurysms rupture or are incidentally found on autopsy, but imaging advancements has enabled earlier identification of aneurysms; in this case, a HAD. Case Description/Methods: A 77-year-old female with medical history pertinent for sickle cell trait, acquired factor VIII inhibitor coagulopathy, history of type 2 thoracic aortic dissection, and hypertension presented to the emergency room with a week of mild fatigue, postprandial epigastric burning pain, and intermittent stabbing right upper quadrant pain. Right upper quadrant ultrasound demonstrated a hypervascularized right hepatic lobe mass with large tortuous internal vessels. CT abdomen & pelvis without contrast showed a large hypodensity in the right liver with curvilinear density. MRI demonstrated large arteriovenous malformation (AVM) within the right hepatic lobe and focal hepatic parenchymal hemorrhage centered within AVM nidus. Gastroenterology was consulted and CT angiogram findings were suspicious for common HAD, proper hepatic & intrahepatic pseudoaneurysms, and intrahepatic rupture. Interventional radiology was consulted. Hepatic angiogram showed a large defect in the proximal hepatic artery with brisk opacification, thought to represent a pseudoaneurysm. This prompted framing coil placement across the large defect and coils extending from the proper hepatic artery to the common hepatic artery with significant reduction in forward flow & pseudoaneurysm opacification. Per hepatobiliary & vascular surgery, no need for additional surgical intervention. Postoperative course was complicated by fever & leukocytosis, worsening kidney injury, and anemia; attributed to the procedure and resolved with supportive care. Patient discharged on postoperative day 8 with outpatient follow-up. (Figure) Discussion: This case highlights the importance of imaging for earlier detection of hepatic artery aneurysms (HAA) in minimizing risk of catastrophic hemorrhage. HAA are rare but clinically important given they are associated with high incidence of rupture and mortality up to 20%. Although surgery is preferred for extrahepatic findings, endovascular interventions are favored for intrahepatic findings depending on size and presence of pseudoaneurysms, such as this case. They have led to more favorable short & longer-term outcomes and lower mortality & morbidity rates, particularly in poor surgical candidates.Figure 1.: Hepatic angiography and embolization was performed. A large defect with brisk opacification of the proper and common hepatic arteries were seen (A), prompting deploy of a framing coil. (B) Embolization was then performed on the hepatic artery with three coils (5mm, 6mm, & 8mm). Coils were examined from proper hepatic artery to the common hepatic artery. (C) Following placement of the coils, significant reduction in flow and opacification of the pseudoaneurysm was seen.

Automated optimization of TMS coil placement for personalized functional network engagement

Transcranial magnetic stimulation (TMS) is used to treat multiple psychiatric and neurological conditions by manipulating activity in particular brain networks and circuits, but individual responses are highly variable. In clinical settings, TMS coil placement is typically based on either group average functional maps or scalp heuristics. Here, we found that this approach can inadvertently target different functional networks in depressed patients due to variability in their functional brain organization. More precise TMS targeting should be feasible by accounting for each patient's unique functional neuroanatomy. To this end, we developed a targeting approach, termed targeted functional network stimulation (TANS). The TANS approach improved stimulation specificity in silico in 8 highly sampled patients with depression and 6 healthy individuals and invivo when targeting somatomotor functional networks representing the upper and lower limbs. Code for implementing TANS and an example dataset are provided as a resource.

Devices and Technology in Transcranial Magnetic Stimulation: A Systematic Review.

The technology for transcranial magnetic stimulation (TMS) has significantly changed over the years, with important improvements in the signal generators, the coils, the positioning systems, and the software for modeling, optimization, and therapy planning. In this systematic literature review (SLR), the evolution of each component of TMS technology is presented and analyzed to assess the limitations to overcome. This SLR was carried out following the PRISMA 2020 statement. Published articles of TMS were searched for in four databases (Web of Science, PubMed, Scopus, IEEE). Conference papers and other reviews were excluded. Records were filtered using terms about TMS technology with a semi-automatic software; articles that did not present new technology developments were excluded manually. After this screening, 101 records were included, with 19 articles proposing new stimulator designs (18.8%), 46 presenting or adapting coils (45.5%), 18 proposing systems for coil placement (17.8%), and 43 implementing algorithms for coil optimization (42.6%). The articles were blindly classified by the authors to reduce the risk of bias. However, our results could have been influenced by our research interests, which would affect conclusions for applications in psychiatric and neurological diseases. Our analysis indicates that more emphasis should be placed on optimizing the current technology with a special focus on the experimental validation of models. With this review, we expect to establish the base for future TMS technological developments.

Gelatin sponge to close a tract after large-bore transhepatic access: tips for success.

Percutaneous transhepatic venous access has been utilised for numerous transcatheter cardiac procedures. Traditionally, a large transhepatic tract requires the placement of permanent occlusion devices or coils. We describe a successful closure using a simple technique (Surgifoam) without the need for metal hardware placement. Immediate hemostasis was achieved. No complications were encountered.

Neuronavigation maximizes accuracy and precision in TMS positioning: Evidence from 11,230 distance, angle, and electric field modeling measurements

BackgroundResearchers and clinicians have traditionally relied on elastic caps with markings to reposition the transcranial magnetic stimulation (TMS) coil between trains and sessions. Newer neuronavigation technology co-registers the patient's head and structural magnetic resonance imaging (MRI) scan, providing the researcher with real-time feedback about how to adjust the coil to be on-target. However, there has been no head to head comparison of accuracy and precision across treatment sessions. Objective/Hypothesis: In this two-part study, we compared elastic cap and neuronavigation targeting methodologies on distance, angle, and electric field (E-field) magnitude values. MethodsIn 42 participants receiving up to 50 total accelerated rTMS sessions in 5 days, we compared cap and neuronavigation targeting approaches in 3408 distance and 6816 angle measurements. In Experiment 1, TMS administrators saved an on-target neuronavigation location at Beam F3, which served as the landmark for all other measurements. Next, the operators placed the TMS coil based on cap markings or neuronavigation software to measure the distance and angle differences from the on-target sample. In Experiment 2, we saved each XYZ coordinate of the TMS coil from cap and neuronavigation targeting in 12 participants to compare the E-field magnitude differences at the cortical prefrontal target in 1106 cap and neuronavigation models. ResultsCap targeting was significantly off-target for distance, placing the coil an average of 10.66 mm off-target (Standard error of the mean; SEM = 0.19 mm) compared to 0.3 mm (SEM = 0.03 mm) for neuronavigation (p < 0.0001). Cap targeting also significantly deviated for angles off-target, averaging 7.79 roll/pitch degrees (SEM = 1.07°) off-target and 5.99 yaw degrees (SEM = 0.12°) off-target; in comparison, neuronavigation targeting positioned the coil 0.34 roll/pitch degrees (SEM = 0.01°) and 0.22 yaw (SEM = 0.004°) off-target (both p < 0.0001). Further analyses revealed that there were significant inter-operator differences on distance and angle positioning for F3 (all p < 0.05), but not neuronavigation. Lastly, cap targeting resulted in significantly lower E-fields at the intended prefrontal cortical target, with equivalent E-fields as 110.7% motor threshold (MT; range = 58.3–127.4%) stimulation vs. 119.9% MT (range = 115–123.3%) from neuronavigated targeting with 120% MT stimulation applied (p < 0.001). ConclusionsCap-based targeting is an inherent source of target variability compared to neuronavigation. Additionally, cap-based coil placement is more prone to differences across operators. Off-target coil placement secondary to cap-based measurements results in significantly lower amounts of stimulation reaching the cortical target, with some individuals receiving only 48.6% of the intended on-target E-field. Neuronavigation technology enables more precise and accurate TMS positioning, resulting in the intended stimulation intensities at the targeted cortical level.

3D-mapping of TMS effects with automatic robotic placement improved reliability and the risk of spurious correlation

• An SPM approach can be used on TMS-induced magnetic fields to image its effects. • This method enables 3D statistical maps of conditions to be generated and compared. • It also enables 3D group results and group comparisons. • Robotic coil placement improved reliability thanks to its increased accuracy.

Brachial Plexus Magnetic Resonance Neurography: Technical Challenges and Solutions.

Magnetic resonance neurography of the brachial plexus (BP) is challenging owing to its complex anatomy and technical obstacles around this anatomic region. Magnetic resonance techniques to improve image quality center around increasing nerve-to-background contrast ratio and mitigating imaging artifacts. General considerations include unilateral imaging of the BP at 3.0 T, appropriate selection and placement of surface coils, and optimization of pulse sequences. Technical considerations to improve nerve conspicuity include fat, vascular, and respiratory artifact suppression techniques; metal artifact reduction techniques; and 3-dimensional sequences. Specific optimization of these techniques for BP magnetic resonance neurography greatly improves image quality and diagnostic confidence to help guide nonoperative and operative management.

Vertebrobasilar dissecting aneurysms: microsurgical management in 42 patients.

Vertebrobasilar dissecting (VBD) aneurysms are rare, and patients with these aneurysms often present with thromboembolic infarcts or subarachnoid hemorrhage (SAH). The morphological nature of VBD aneurysms often precludes conventional clip reconstruction or coil placement and encourages parent artery exclusion or endovascular stenting. Treatment considerations include aneurysm location along the vertebral artery (VA), the involvement of the posterior inferior cerebellar artery (PICA), and collateral blood flow. Outcomes after endovascular treatment have been well described in the neurosurgical literature, but microsurgical outcomes have not been detailed. Patient outcomes from a large, single-surgeon, consecutive series of microsurgically managed VBD aneurysms are presented, and 3 illustrative case examples are provided. The medical records of patients with dissecting aneurysms affecting the intracranial VA (V4), basilar artery, and PICA that were treated microsurgically over a 19-year period were reviewed. Patient demographics, aneurysm characteristics, surgical procedures, and clinical outcomes (according to modified Rankin Scale [mRS] scores at last follow-up) were analyzed. Forty-two patients with 42 VBD aneurysms were identified. Twenty-six aneurysms (62%) involved the PICA, 14 (33%) were distinct from the PICA origin on the V4 segment of the VA, and 2 (5%) were located at the vertebrobasilar junction. Thirty-four patients (81%) presented with SAH with a mean Hunt and Hess grade of 3.2 at presentation. Six (14%) of the 42 patients had been previously treated using endovascular techniques. Nineteen aneurysms (45%) underwent clip wrapping, 17 (40%) were treated with bypass trapping, and 6 (14%) underwent parent artery sacrifice. The complete aneurysm obliteration rate was 95% (n = 40), and the surgical complication rate was 7% (n = 3). The 8 patients with unruptured VBD aneurysms were significantly more likely to be discharged home (n = 6, 75%) compared with 34 patients with ruptured aneurysms (n = 9, 27%; p = 0.01). Good outcomes (mRS score ≤ 2) were observed in 20 patients (48%). Eight patients (19%) died. These data demonstrate that patients with VBD aneurysms often present after a rupture in poor neurological condition, but favorable results can be achieved with open microsurgical repair in almost half of such cases. Microsurgery remains a viable treatment option, with the choice between bypass trapping and clip wrapping largely dictated by the specific location of the aneurysm and its relationship to the PICA.

Coils for large standoff relaxometry with unilateral magnets

Maximizing standoff distance by direct placement of probe coils on magnet bodies, while maximizing signal-to-noise is critical to the successful application of unilateral NMR. Two types of radio frequency (rf) coils for linear array, unilateral magnets are described: “simple fringe” and “split fringe coils.” These coils are designed to fully exploit the standoff distance of the unilateral magnet by placement directly on the magnet surface. Such placement fails for normal surface coils used for magnetic resonance due to eddy current induced shielding by the conductive magnet surface. The coil design strategy includes a rectangular cross section solenoid coil, either continuous or split in the center, mounted with the center axis of the coil parallel to the magnet surface. These geometries, when placed on a conducting surface, enhance the rf field produced in the sample region, outside of the solenoid coil. The spatial homogeneity of both rf coils are characterized using the ANSYS™ finite element modelling software. ANSYS™ modeled coil geometries led to homogeneous, surface displaced rf fields. These coils were then constructed and characterized with magnetic resonance imaging. Finally, two experiments that use these coils to perform large standoff relaxation measurements are described.

In-silico optimisation of ICD defibrillation efficacy by modifying lead/can configurations using a cohort of high-resolution whole-torso heart models

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Medical Research Council, UK Background ICD is an effective direct therapy against VT/VF by applying a strong electrical shock across the heart between the shocking coil and can. Conventionally, patients will have a shocking coil inside the right ventricle (RV) and a can at the upper left chest. However, due to infections or other conditions, the can may need to place towards the right chest. The placement of the RV coil may also vary in different cases, for example avoiding scar. However, it is unclear how defibrillation efficacy may be altered by these unavoidable modifications to conventional lead/can configurations and whether optimisation may be possible. Purpose To compare defibrillation efficacy of modifications of ICD configurations in a cohort of whole-torso models. Methods A cohort of 15 whole torso models was generated from high resolution CT data and contrast CT cardiac scans, including 5 dilated cardiomyopathy (DCM), 5 hypertrophic cardiomyopathy (HCM) and 5 structurally normal patients (Fig A). Transvenous ICDs were represented by a shocking coil inside the RV (near apex) and a (ground) can at the upper left chest as default settings. Configurations were then varied by moving the can to the right chest, moving the RV coil up the mid-septum or adding extra grounds (Superior Vena Cava (SVC) coil, coronary sinus (CS) coil (Fig A)). Defibrillation-strength shocks were applied to all models (Fig B). DFTs and mean electrical field were evaluated across the whole heart as well as specific LV, RV, RV insertion regions, along with overall impedance. Results Shifting the can from left to right significantly increased DFT for the whole heart (23 J vs 15 J, P=0.03) and LV (25 J vs 17 J, P=0.03) (Fig C) and reduced the mean electrical field. Moving the RV coil further up the septum did not significantly alter DFT (Fig D), but did reduce mean electrical field for all regions and reduce impedance significantly. Additional separate coils significantly reduced DFT for all regions (Fig D) by increasing mean electrical field, whilst adding both coils significantly reduced DFT the most (whole heart: 15 J vs 6 J, P=0.03) (Fig E). Impedance was increased significantly by adding SVC coil, but reduced significantly by adding CS coil. Adding both coils increased impedance slightly. Conclusions Although a right-sided can increases DFT by over 50%, additional leads (grounds) may mitigate this increase by increasing mean electrical field. Moving the RV coil closer to the mid-septum reduces DFT slightly, but also reduces mean electrical field and impedance significantly.

MO-0212 Dosimetric and geometric impact of on-patient placement of air coils in a clinical MRI-only workflow

MO-0212 Dosimetric and geometric impact of on-patient placement of air coils in a clinical MRI-only workflow

Advanced Technology or Manual Skills: Evidence That The Accuracy of Corticospinal Responsiveness Is Not Ameliorated by Neuronavigation

PurposeTranscranial magnetic stimulation (TMS) is a noninvasive technique to assess corticospinal excitability and inhibition. TMS over the motor cortex during a voluntary contraction elicits short‐latency excitatory (motor‐evoked potential, MEP) and inhibitory (silent period, SP) responses in the target muscle. However, the technique for searching and determining the optimal site to elicit MEPs (“hotspot”), an essential component in order to correctly place the TMS coil, is not unanimously standardized. This can be a problem since changes in coil position and/or orientation may influence the magnitude of MEP and SP responses. Usually, the “hotspot” is marked either on a swim cap or on the scalp and the investigator holds the coil manually during the entire testing session. However, the capacity to maintain the coil placement within and between sessions may be limited. To reduce variability in coil position and orientation in space and over time, neuronavigated TMS (nTMS) is used. However, no studies investigated the accuracy of the assessment of corticospinal excitability and inhibition using nTMS versus a traditional manual approach for the maintenance of coil positioning.Methods18 healthy participants (10W/8M) volunteered in two identical and randomized sessions ~30 days apart. Maximal and submaximal neuromuscular evaluations were performed with TMS six times before (PRE), and at the end (POST) of a 2‐min sustained maximal voluntary isometric contraction (MVIC) (100%, 75%, 50% MVIC and 25%isoEMG). The “hotspot” was maintained either with a grid demarcated on the participants’ scalp or with visual feedback provided by nTMS on a computer screen. In both sessions, “hotspot” was considered as the site where the largest MEPs in the rectus femoris were elicited.ResultsThere were not a “hotspot” technique × contraction intensities × time points interactions for both MEP (P = 0.217) and SP (P = 0.627). Bland‐Altman plots display adequate agreements between the difference in the two “hotspot” techniques and the means of the two “hotspot” techniques. The slopes of the resulting regression lines were not significantly different from zero (horizontal to x‐axis) for both MEP (all r ≤ 0.335, all P ≥ 0.162) and SP (all r ≤ 0.382, all P ≥ 0.131), indicating a uniformity of systematic error at all contraction intensities and time points.ConclusionsSpatial stability of the TMS coil position over the motor cortex did not influence corticospinal excitability and inhibition responses in unfatigued and fatigued knee extensors. This is because the variability in MEP and SP responses is due to spontaneous fluctuations in corticospinal and motoneuron excitability and inhibition; and this variability is not affected by spatial accuracy. Therefore, nTMS or a traditional manual approach could be interchangeably use in order to maintain the TMS coil position in the exact “hotspot”.

Radiation dose to nuclear medicine technologists when operating PET/MR compared with PET/CT

Since 2010, positron emission tomography/magnetic resonance (PET/MR) has been increasingly used as clinical routine in nuclear medicine departments. One advantage of PET/MR over PET/computed tomography (CT) is the lower dose of ionising radiation delivered to patients. However, data on the radiation dose delivered to staff operating PET/MR compared with the new generation of PET/CT equipment are still lacking. Our aim was to compare the radiation dose to nuclear medicine technologists performing routine PET/MR and PET/CT in the same department. We retrospectively measured the daily radiation dose received by PET technologists over 13 months by collecting individual dosimetry measurements (from electronic personal dosimeters). Data were analysed taking into account the total number of studies performed with each PET modality (PET/MR with Signa 3T, General Electric Healthcare versus PET/CT with Biograph mCT flow, Siemens), the type of exploration (brain versus whole-body PET), the 18F activity injected per day and per patient as well as the time spent in contact with patients after tracer injection. Our results show a significantly higher whole-body exposure to technologists for PET/MR compared with PET/CT (10.3 ± 3.5 nSv versus 4.7 ± 1.2 nSv per 18F injected MBq, respectively; p < 0.05). This difference was related to prolonged contact with injected patients during patient positioning with the PET/MR device and MR coil placement, especially in whole-body studies. For an equal injected activity, radiation exposure to PET technologists for PET/MR was twice that of PET/CT. To minimise the radiation dose to staff, efforts should be made to optimise patient positioning, even in departments with extensive PET/CT experience.

TAP: targeting and analysis pipeline for optimization and verification of coil placement in transcranial magnetic stimulation

Objective. Transcranial magnetic stimulation (TMS) can modulate brain function via an electric field (E-field) induced in a brain region of interest (ROI). The ROI E-field can be computationally maximized and set to match a specific reference using individualized head models to find the optimal coil placement and stimulus intensity. However, the available software lacks many practical features for prospective planning of TMS interventions and retrospective evaluation of the experimental targeting accuracy. Approach. The TMS targeting and analysis pipeline (TAP) software uses an MRI/fMRI-derived brain target to optimize coil placement considering experimental parameters such as the subject’s hair thickness and coil placement restrictions. The coil placement optimization is implemented in SimNIBS 3.2, for which an additional graphical user interface (TargetingNavigator) is provided to visualize/adjust procedural parameters. The coil optimization process also computes the E-field at the target, allowing the selection of the TMS device intensity setting to achieve specific E-field strengths. The optimized coil placement information is prepared for neuronavigation software, which supports targeting during the TMS procedure. The neuronavigation system can record the coil placement during the experiment, and these data can be processed in TAP to quantify the accuracy of the experimental TMS coil placement and induced E-field. Main results. TAP was demonstrated in a study consisting of three repetitive TMS sessions in five subjects. TMS was delivered by an experienced operator under neuronavigation with the computationally optimized coil placement. Analysis of the experimental accuracy from the recorded neuronavigation data indicated coil location and orientation deviations up to about 2 mm and 2°, respectively, resulting in an 8% median decrease in the target E-field magnitude compared to the optimal placement. Significance. TAP supports navigated TMS with a variety of features for rigorous and reproducible stimulation delivery, including planning and evaluation of coil placement and intensity selection for E-field-based dosing.

New concept in neurovascular navigation: technical description and preclinical experience with the Bendit 17 and Bendit 21 microcatheters in a rabbit aneurysm model

BackgroundEndovascular treatment of intracranial vascular diseases, such as aneurysms, is often challenged by unfavorable vascular anatomy. The Bendit Steerable Microcatheter (Bendit Technologies, Tel Aviv, Israel) has bending and torqueing capabilities...

Genetic Algorithm for TMS Coil Position Optimization in Stroke Treatment.

Transcranial magnetic stimulation (TMS), a non-invasive technique to stimulate human brain, has been widely used in stroke treatment for its capability of regulating synaptic plasticity and promoting cortical functional reconstruction. As shown in previous studies, the high electric field (E-field) intensity around the lesion helps in the recovery of brain function, thus the spatial location and angle of coil truly matter for the significant correlation with therapeutic effect of TMS. But, the error caused by coil placement in current clinical setting is still non-negligible and a more precise coil positioning method needs to be proposed. In this study, two kinds of real brain stroke models of ischemic stroke and hemorrhagic stroke were established by inserting relative lesions into three human head models. A coil position optimization algorithm, based on the genetic algorithm (GA), was developed to search the spatial location and rotation angle of the coil in four 4 × 4 cm search domains around the lesion. It maximized the average intensity of the E-field in the voxel of interest (VOI). In this way, maximum 17.48% higher E-field intensity than that of clinical TMS stimulation was obtained. Besides, our method also shows the potential to avoid unnecessary exposure to the non-target regions. The proposed algorithm was verified to provide an optimal position after nine iterations and displayed good robustness for coil location optimization between different stroke models. To conclude, the optimized spatial location and rotation angle of the coil for TMS stroke treatment could be obtained through our algorithm, reducing the intensity and duration of human electromagnetic exposure and presenting a significant therapeutic potential of TMS for stroke.