MR-Guided Focused Ultrasound Versus Radiofrequency Capsulotomy for Treatment-Refractory Obsessive-Compulsive Disorder: A Cost-Effectiveness Threshold Analysis

The persistent value of lesions in psychiatric neurosurgery

Neurosurgery for intractable psychiatric conditions has seen a resurgence with the increasing use of deep brain stimulation (DBS). Although DBS promises reversible neuromodulation and has become more popular than older lesioning methods, lesioning might still be preferred in specific cases. Here, we review the evidence for DBS and lesions in the treatment of intractable neuropsychiatric conditions and consider the factors that favour the continued use of lesioning procedures in appropriately selected cases. Broadly, systemic factors including comparative effectiveness, cost, and ethical arguments support an ongoing role for lesioning. Such a role is also supported by practical considerations including patient experiences of this type of therapy, the relative intensity of follow-up care, access to sparse or specialised follow-up care, and relative infection risk. Overall, we argue that neurosurgical lesion procedures remain an important alternative to DBS and their continued availability is necessary to fulfil the imperatives of mental health parity and enhance access to effective mental health treatments. Nonetheless, the efficacy of DBS and recent advances in closed-loop stimulation and remote programming might provide solutions to some of the challenges associated with wider use of electrical neuromodulation. Concerns about the scarcity of high-level evidence for the efficacy of lesioning procedures as well as the potential irreversible adverse effects of lesioning remain to be addressed.

Neuroablative Intervention for Refractory Obsessive-Compulsive Disorder

OBJECTIVE

This review aims to investigate the progression of neuroablation, along with documented clinical efficacy and safety, in the management of treatment-resistant obsessive-compulsive disorder (OCD).

METHODS

We searched and compiled clinical research results of neuroablation therapy reported to date. We extracted outcomes related to clinical efficacy, side effects, and surgical complications. Additionally, we summarized key claims and findings.

RESULTS

Neuroablative intervention is a potential treatment approach for refractory OCD. Recent advancements, such as real-time magnetic resonance monitoring and minimally invasive techniques employing ultrasound and laser, offer distinct advantages in terms of safety and comparative efficacy when compared to conventional methods. However, the absence of randomized controlled trials and long-term outcome data underscores the need for cautious consideration when selecting neuroablation.

CONCLUSION

Neuroablative intervention shows promise for refractory OCD, but vigilant consideration is essential in both patient selection and surgical method choices due to the potential for rare yet serious complications.

Mechanisms underlying capsulotomy for refractory obsessive-compulsive disorder: neural correlates of negative affect processing overlap with deep brain stimulation targets

Ablative procedures such as anterior capsulotomy are potentially effective in refractory obsessive-compulsive disorder (OCD). Converging evidence suggests the ventral internal capsule white matter tracts traversing the rostral cingulate and ventrolateral prefrontal cortex and thalamus is the optimal target for clinical efficacy across multiple deep brain stimulation targets for OCD. Here we ask which prefrontal regions and underlying cognitive processes might be implicated in the effects of capsulotomy by using both task fMRI and neuropsychological tests assessing OCD-relevant cognitive mechanisms known to map across prefrontal regions connected to the tracts targeted in capsulotomy. We tested OCD patients at least 6 months post-capsulotomy (n = 27), OCD controls (n = 33) and healthy controls (n = 34). We used a modified aversive monetary incentive delay paradigm with negative imagery and a within session extinction trial. Post-capsulotomy OCD subjects showed improved OCD symptoms, disability and quality of life with no differences in mood or anxiety or cognitive task performance on executive, inhibition, memory and learning tasks. Task fMRI revealed post-capsulotomy decreases in the nucleus accumbens during negative anticipation, and in the left rostral cingulate and left inferior frontal cortex during negative feedback. Post-capsulotomy patients showed attenuated accumbens-rostral cingulate functional connectivity. Rostral cingulate activity mediated capsulotomy improvement on obsessions. These regions overlap with optimal white matter tracts observed across multiple stimulation targets for OCD and might provide insights into further optimizing neuromodulation approaches. Our findings also suggest that aversive processing theoretical mechanisms may link ablative, stimulation and psychological interventions.

Cognitive outcomes following functional neurosurgery in refractory OCD patients: a systematic review

Neurosurgery is a therapeutic option for patients with refractory obsessive-compulsive disorder who do not respond to previous treatments. Although its efficacy in reducing clinical symptomatology has been proven, few studies have analyzed its effects at the cognitive level. The aim of this systematic review was to describe the cognitive outcomes of functional neurosurgery in patients that went through capsulotomies or cingulotomies. PubMed, Medline, Scopus, PsycInfo, PsyArticles, and Web of Knowledge were searched for studies reporting cognitive outcomes in refractory obsessive-compulsive patients after capsulotomies and cingulotomies. The risk of bias was assessed with the Assessment Tool for Before-After (Pre-Post) Studies With No Control Group tool; 13 studies met inclusion criteria, including 205 refractory obsessive-compulsive disorder patients for both surgical procedures. Results showed a substantial number of studies that did report significant cognitive improvement after surgery, being this improvement specially related to memory and executive functions. The second-most frequent finding is the maintenance of cognitive performance (nor improvement or worsening). From a neuropsychological point of view, this outcome might be considered a success, given that it is accompanied by amelioration of obsessive-compulsive symptoms. Subtle cognitive adverse effects have also been reported. Neurosurgery procedures appear to be safe from a cognitive point of view. Methodological issues must be improved to draw clearer conclusions, but capsulotomies and cingulotomies constitute an effective alternative treatment for refractory obsessive-compulsive disorder patients.

Economic Analyses of Obsessive-Compulsive Disorder Interventions: A Systematic Review

BACKGROUND

Obsessive-compulsive disorder (OCD) is a neuropsychiatric condition featuring patterns of obsessions, compulsions, and avoidant behaviors that are often time consuming and distressing to affected individuals. Cognitive-behavioral therapy (CBT) with exposure and response prevention and/or serotonin reuptake inhibitors are first-line treatments for OCD, though other therapeutic interventions may serve as economically practical modalities under various circumstances. Exploring and understanding the cost effectiveness of all indicated OCD interventions are important to inform therapeutic decisions and provide quality patient-centered care at a cost that is not burdensome to the patient and/or healthcare system.

METHODS

A systematic literature review was performed and studies were extracted from PubMed, Embase, Ovid MEDLINE, and Cochrane. All cost-effectiveness studies that included economic analyses with respect to OCD treatment modalities and were written in English and published between January 2010 and July 2022 were eligible for inclusion in the present study. We report a narrative synthesis of the findings and quality appraisal of the selected references.

RESULTS

Of the 707 references returned in the literature search, a total of 18 cost-effectiveness studies were included for review. Compared with treatment as usual, several studies reported clinical superiority and cost effectiveness of Internet-based CBT programs for adults and children with OCD at various willingness-to-pay thresholds and economic reference indicators, though cost effectiveness relative to in-person CBT with exposure and response prevention is unclear and estimates of efficacy are likely lower for Internet-based CBT. One study favored the cost utility of serotonin reuptake inhibitor monotherapy over CBT with exposure and response prevention although efficacy estimates of the former tend to be lower, and relative cost differences were low. Five studies evaluated the cost effectiveness of high-intensity neuroaugmentation, including deep brain stimulation and stereotactic radiosurgical capsulotomy, in the context of treatment-refractory OCD.

CONCLUSIONS

Despite the relatively high prevalence of OCD worldwide, cost-effectiveness data for therapeutic modalities remain sparse. Because of the chronic nature of OCD, the cost of treatment accumulates and may lead to a significant financial burden over time, particularly when non-evidence-based interventions are used. However, several alternative therapeutic modalities hold promise for economic practicality without significant sacrifice in clinical efficacy. Future studies are necessary to directly compare the cost effectiveness of such therapeutic alternatives with the current standard of care, CBT with exposure and response prevention.

Neuroethical implications of focused ultrasound for neuropsychiatric illness

BACKGROUND

MR-guided focused ultrasound is a promising intervention for treatment-resistant mental illness, and merits contextualized ethical exploration in relation to more extensive ethical literature regarding other psychosurgical and neuromodulation treatment options for this patient population. To our knowledge, this topic has not yet been explored in the published literature.

OBJECTIVE

The purpose of this paper is to review and discuss in detail the neuroethical implications of MR-guided focused ultrasound for neuropsychiatric illness as an emerging treatment modality.

METHODS

Due to the lack of published literature on the topic, the approach involved a detailed survey and review of technical and medical literature relevant to focused ultrasound and established ethical issues related to alternative treatment options for patients with treatment-resistant, severe and persistent mental illness. The manuscript is structured according to thematic and topical findings.

RESULTS

This technology has potential benefits for patients suffering with severe mental illness, compared with established alternatives. The balance of technical, neuroscientific and clinical considerations should inform ethical deliberations. The nascent literature base, nuances in legal classification and permissibility depending upon jurisdiction, influences of past ethical issues associated with alternative treatments, tone and framing in media articles, and complexity of clinical trials all influence ethical assessment and evaluations of multiple stakeholders. Recommendations for future research are provided based on these factors.

CONCLUSION

Salient ethical inquiry should be further explored by researchers, clinicians, and ethicists in a nuanced manner methodologically, one which is informed by past and present ethical issues related to alternative treatment options, broader psychiatric treatment frameworks, pragmatic implementation challenges, intercultural considerations, and patients' ethical concerns.

Cost-effectiveness analysis of radiosurgical capsulotomy versus treatment as usual for treatment-resistant obsessive-compulsive disorder

OBJECTIVE

Stereotactic radiosurgical capsulotomy (SRS-C) is an effective neurosurgical option for patients with treatment-resistant obsessive-compulsive disorder (TROCD). Unlike other procedures such as deep brain stimulation and radiofrequency ablation, the cost-effectiveness of SRS-C for TROCD has not been investigated. The authors herein report the first cost-effectiveness analysis of SRS-C for TROCD.

METHODS

Using a decision analytic model, the authors compared the cost-effectiveness of SRS-C to treatment as usual (TAU) for TROCD. Treatment response and complication rates were derived from a review of relevant clinical trials. Published algorithms were used to convert Yale-Brown Obsessive Compulsive Scale scores into utility scores reflecting improvements in quality of life. Costs were approached from the healthcare sector perspective and were drawn from Medicare reimbursement rates and available healthcare economics data. A Monte Carlo simulation and probabilistic sensitivity analysis were performed to estimate the incremental cost-effectiveness ratio.

RESULTS

One hundred fifty-eight TROCD patients across 9 studies who had undergone SRS-C and had at least 36 months of follow-up were included in the model. Compared to TAU, SRS-C was more cost-effective, with an estimated incremental cost-effectiveness ratio of $28,960 per quality-adjusted life year (QALY) gained. Within the 3-year time horizon, net QALYs gained were greater in the SRS-C group than the TAU group by 0.27 (95% CI 0.2698-0.2702, p < 0.0001). At willingness-to-pay thresholds of $50,000 and $100,000 per QALY, the Monte Carlo simulation revealed that SRS-C was more cost-effective than TAU in 83% and 100% of iterations, respectively.

CONCLUSIONS

Compared to TAU, SRS-C for TROCD is more cost-effective under a range of possible cost and effectiveness values.

Concerns About Psychiatric Neurosurgery and How They Can Be Overcome: Recommendations for Responsible Research

Background

Psychiatric neurosurgery is experiencing a revival. Beside deep brain stimulation (DBS), several ablative neurosurgical procedures are currently in use. Each approach has a different profile of advantages and disadvantages. However, many psychiatrists, ethicists, and laypeople are sceptical about psychiatric neurosurgery.

Methods

We identify the main concerns against psychiatric neurosurgery, and discuss the extent to which they are justified and how they might be overcome. We review the evidence for the effectiveness, efficacy and safety of each approach, and discuss how this could be improved. We analyse whether and, if so, how randomised controlled trials (RCTs) can be used in the different approaches, and what alternatives are available if conducting RCTs is impossible for practical or ethical reasons. Specifically, we analyse the problem of failed RCTs after promising open-label studies.

Results

The main concerns are: (i) reservations based on historical psychosurgery, (ii) concerns about personality changes, (iii) concerns regarding localised interventions, and (iv) scepticism due to the lack of scientific evidence. Given the need for effective therapies for treatment-refractory psychiatric disorders and preliminary evidence for the effectiveness of psychiatric neurosurgery, further research is warranted and necessary. Since psychiatric neurosurgery has the potential to modify personality traits, it should be held to the highest ethical and scientific standards.

Conclusions

Psychiatric neurosurgery procedures with preliminary evidence for efficacy and an acceptable risk–benefit profile include DBS and micro- or radiosurgical anterior capsulotomy for intractable obsessive–compulsive disorder. These methods may be considered for individual treatment attempts, but multi-centre RCTs are necessary to provide reliable evidence.

Focused ultrasound: Innovation in use for neurologic conditions

Focused ultrasound has emerged as a key tool for neurologic disorders. In this focused review, we discuss the utility in disrupting the blood brain barrier to maximize treatment. This can facilitate creating direct coagulative lesions and aid in the administration of chemotherapy. Furthermore, it can facilitate neuromodulation when used in pulse sequencing. The current literature regarding brain tumors, essential tremor, and obsessive-compulsive disorder is reviewed. Additionally, concepts and experimental outcomes for neurodegenerative disease such as Alzheimer's is presented. Focused ultrasound as a tool is still in its infancy but the potential for adjuvant and direct therapy is promising. More clinical uses will become apparent in coming decades.

Magnetic Resonance-Guided Focused Ultrasound Capsulotomy for Treatment-Resistant Psychiatric Disorders

BACKGROUND

Psychiatric surgery is an important domain of functional neurosurgery and involves deep brain stimulation (DBS) or lesional procedures performed for treatment-resistant psychiatric illness. It has recently become possible to use magnetic-guided focused ultrasound (MRgFUS) to perform bilateral capsulotomy, a lesional technique commonly carried out with surgical radiofrequency ablation or stereotactic radiosurgery. MRgFUS offers several advantages, including improved safety and real-time imaging of the lesions.

OBJECTIVE

To describe the clinical and technical aspects of performing bilateral MRgFUS capsulotomy in patients with severe refractory depression and obsessive-compulsive disorder.

METHODS

We describe the clinical and technical considerations of performing MRgFUS capsulotomy. Topics discussed include patient selection, headframe application, targeting, sonication strategies, and follow-up procedures.

RESULTS

MRgFUS capsulotomy was performed in 16 patients without serious clinical or radiographic adverse events.

CONCLUSION

MRgFUS allows for a safe, less invasive technique for performing a well-studied psychiatric surgery procedure-the anterior capsulotomy.

Focused ultrasound: growth potential and future directions in neurosurgery

Over the past two decades, vast improvements in focused ultrasound (FUS) technology have made the therapy an exciting addition to the neurosurgical armamentarium. In this time period, FUS has gained US Food and Drug Administration (FDA) approval for the treatment of two neurological disorders, and ongoing efforts seek to expand the lesion profile that is amenable to ultrasonic intervention. In the following review, we highlight future applications for FUS therapy and compare its potential role against established technologies, including deep brain stimulation and stereotactic radiosurgery. Particular attention is paid to tissue ablation, blood-brain-barrier opening, and gene therapy. We also address technical and infrastructural challenges involved with FUS use and summarize the hurdles that must be overcome before FUS becomes widely accepted in the neurosurgical community.

Magnetic Resonance-Guided Focused Ultrasound Surgery for Obsessive-Compulsive Disorders: Potential for use as a Novel Ablative Surgical Technique

Surgical treatment for psychiatric disorders, such as obsessive-compulsive disorder (OCD) and depression, using ablative techniques, such as cingulotomy and capsulotomy, have historically been controversial for a number of scientific, social, and ethical reasons. Recently, with the elucidation of anatomical and neurochemical substrates of brain function in healthy controls and patients with such disorders using various functional neuroimaging techniques, these criticisms are becoming less valid. Furthermore, by using new techniques, such as deep brain stimulation (DBS), and identifying more precise targets, beneficial effects and the lack of serious complications have been demonstrated in patients with psychiatric disorders. However, DBS also has many disadvantages. Currently, magnetic resonance-guided focused ultrasound surgery (MRgFUS) is used as a minimal-invasive surgical method for generating precisely placed focal thermal lesions in the brain. Here, we review surgical techniques and their potential complications, along with anterior limb of the internal capsule (ALIC) capsulotomy by radiofrequency lesioning and gamma knife radiosurgery, for the treatment of OCD and depression. We also discuss the limitations and technical issues related to ALIC capsulotomy with MRgFUS for medically refractory OCD and depression. Through this review we hope MRgFUS could be considered as a new treatment choice for refractory OCD.

Cost-effectiveness analysis of magnetic resonance-guided focused ultrasound ablation for palliation of refractory painful bone metastases

OBJECTIVE

The aim of this study was to determine if magnetic resonance-guided focused ultrasound (MRgFUS) is cost-effective compared with medication, for refractory pain from bone metastases in the United States.

METHODS

We constructed a Markov state transition model using TreeAge Pro software (TreeAge Software, Inc., Williamstown, MA, USA) to model costs, outcomes, and the cost-effectiveness of a treatment strategy using MRgFUS for palliative treatment of painful bone metastases compared with a Medication Only strategy (Figure 1). Model transition state probabilities, costs (in 2018 US$), and effectiveness data (quality-adjusted life-years [QALYs]) were derived from available literature, local expert opinion, and reimbursement patterns at two U.S. tertiary academic medical centers actively performing MRgFUS. Costs and QALYs, discounted at three percent per year, were accumulated each month over a 24-month time horizon. One-way and probabilistic sensitivity analyses were performed.

RESULTS

In the base-case analysis, the MRgFUS treatment strategy costs an additional $11,863 over the 2-year time horizon to accumulate additional 0.22 QALYs, equal to a $54,160/QALY ICER, thus making MRgFUS the preferred strategy. One-way sensitivity analyses demonstrate that for the base-case analysis, the crossover point at which Medication Only would instead become the preferred strategy is $23,341 per treatment. Probabilistic sensitivity analyses demonstrate that 67 percent of model iterations supported the conclusion of the base case.

CONCLUSIONS

Our model demonstrates that MRgFUS is cost-effective compared with Medication Only for palliation of painful bone metastases for patients with medically refractory metastatic bone pain across a range of sensitivity analyses.

Effectiveness and safety of neuroablation for severe and treatment-resistant obsessive-compulsive disorder: a systematic review and meta-analysis

Background

Several neuroablative procedures are available for severe and treatment-resistant obsessive-compulsive disorder (OCD), but limited knowledge about their relative clinical advantages and disadvantages poses obstacles for treatment decision-making.

Methods

We searched PubMed, Embase, Scopus, Web of Knowledge and the Cochrane Library for reports up to February 2019. We reviewed the literature on the effectiveness (assessed using the Yale-Brown Obsessive Compulsive Scale [Y-BOCS]) and safety of various neuroablative interventions for severe and treatment-resistant OCD.

Results

We included 23 studies involving 487 patients in the systematic review; 21 studies with 459 patients entered meta-analysis. Overall, neuroablation achieved a response rate (proportion of patients with ≥ 35% reduction in Y-BOCS) of 55%. Most of the adverse events (88.4%) were mild and transient. The top 3 adverse events were headache (14.9%), cognitive deficits (9.1%) and behaviour problems (8.1%). Severe or permanent adverse events included personality changes (2.3%) and brain edema or brain cyst (1.5%). The response rates associated with capsulotomy, limbic leucotomy and cingulotomy were 59% (95% confidence interval [CI] 54-65), 47% (95% CI 23-72) and 36% (95% CI 23-50), respectively. Interventions with different coverages of the dorsal part of the internal capsule were associated with different adverse-event profiles but were unlikely to modify clinical effectiveness.

Limitations

The level of evidence of most included studies was relatively low.

Conclusion

Ablative surgeries are safe and effective for a large proportion of patients with severe and treatment-resistant OCD. Among the available procedures, capsulotomy seemed to be the most effective. Further research is needed to improve clinical effectiveness and minimize risks.

Magnetic resonance-guided focused ultrasound capsulotomy for refractory obsessive compulsive disorder and major depressive disorder: clinical and imaging results from two phase I trials

Obsessive compulsive disorder (OCD) and major depressive disorder (MDD) are common, often refractory, neuropsychiatric conditions for which new treatment approaches are urgently needed. Magnetic resonance-guided focused ultrasound (MRgFUS) is a novel surgical technique permitting incisionless ablative neurosurgery. We examined the safety profile, clinical response, and imaging correlates of MRgFUS bilateral anterior capsulotomy in patients with refractory obsessive compulsive disorder (OCD, N = 6) and major depressive disorder (MDD, n = 6). There were no serious adverse events. Nonserious adverse events included headaches and pin-site swelling in 7/12 patients. The response rate was 4/6 and 2/6 in the OCD and MDD cohorts respectively. To delineate the white-matter tracts impacted by capsulotomy, a normative diffusion MRI-based structural connectome was used, revealing tracts terminating primarily in the frontal pole, medial thalamus, striatum, and medial-temporal lobe. Positron emission tomography (PET) analysis (nine subjects) revealed widespread decreases in metabolism bilaterally in the cerebral hemispheres at 6 months post treatment, as well as in the right hippocampus, amygdala, and putamen. A pretreatment seed-to-voxel resting-state functional magnetic resonance imaging (rs-fMRI) analysis (12 subjects) revealed three voxel clusters significantly associated with eventual clinical response. MRgFUS capsulotomy appears to be safe, well tolerated, and according to these initial results, may be an important treatment option for patients with refractory OCD and MDD. MRgFUS capsulotomy results in both targeted and widespread changes in neural activity, and neuroimaging may hold potential for the prediction of outcome.

Incisionless MR-guided focused ultrasound: technical considerations and current therapeutic approaches in psychiatric disorders

INTRODUCTION

MR-guided focused ultrasound operating at higher intensities have been reported to effectively and precisely ablate deeper brain structures like the basal ganglia or the thalamic nuclei for the treatment of refractory movement disorders, neuropathic pain and most recently neuropsychiatric disorders, while low-intensity focused ultrasound represents an approach promoting mechanical blood-brain-barrier opening and neuromodulation. This narrative review summarizes the technical development and the therapeutic potential of incisionless MRgFUS in order to treat neuropsychiatric disorders.

AREAS COVERED

A narrative review of clinical trials assessing the safety and efficacy of MRgFUS. A literature review was performed using the following search terms: MR-guided focused ultrasound, psychiatric disorders, noninvasive and invasive brain modulation/stimulation techniques.

EXPERT OPINION

MRgFUS ablation is under clinical investigation (unblinded study design) for obsessive-compulsive disorders (OCDs) [capsulotomy; ALIC] and depression/anxiety disorders [capsulotomy] and has demonstrated an improvement in OCD and depression, although of preliminary character. Low-intensity ultrasound applications have been explored in Alzheimer´s disease (phase 1 study) and healthy subjects. Currently, limited evidence hinders comparison and selection between MRgFUS and noninvasive/invasive brain modulation therapies. However, comparative, sham-controlled trials are needed to reexamine the preliminary findings for the treatment of psychiatric disorders.

Acute MR-Guided High-Intensity Focused Ultrasound Lesion Assessment Using Diffusion-Weighted Imaging and Histological Analysis

Objectives: The application of magnetic resonance-guided focused ultrasound (MRgFUS) for the treatment of neurological conditions has been of increasing interest. Conventional MR imaging can provide structural information about the effect of MRgFUS, where differences in ablated tissue can be seen, but it lacks information about the status of the cellular environment or neural microstructure. We investigate in vivo acute changes in water diffusion and white matter tracts in the brain of a piglet model after MRgFUS treatment using diffusion-weighted imaging (DWI) with histological verification of treatment-related changes.

Methods: MRgFUS was used to treat the anterior body of the fornix in four piglets. T1 and diffusion-weighted images were collected before and after treatment. Mean diffusion-weighted imaging (MDWI) images were generated to measure lesion volumes via signal intensity thresholds. Histological data were collected for volume comparison and assessment of treatment effect. DWI metric maps of fractional anisotropy (FA), apparent diffusion coefficient (ADC), axial diffusivity (AD), radial diffusivity (RD), and mean diffusivity (MD) were generated for quantitative assessment. Fornix-related fiber tracts were generated before and after treatment for qualitative assessment.

Results: The volume of treated tissue measured via MDWI did not differ significantly from histological measurements, and both were significantly larger than the treatment cell volume. Diffusion metrics in the treatment region were significantly decreased following MRgFUS treatment, with the peak change seen at the lesion core and decreasing radially. Histological analysis confirmed an area of coagulative necrosis in the targeted region with sharp demarcation zone with surrounding brain. Tractography from the lesion core and the fornix revealed fiber disruptions following treatment.

Conclusions: Diffusion maps and fiber tractography are an effective method for assessing lesion volumes and microstructural changes in vivo following MRgFUS treatment. This study demonstrates that DWI has the potential to advance MRgFUS by providing convenient in vivo microstructural lesion and fiber tractography assessment after treatment.

Transcranial Focused Ultrasound (tFUS) and Transcranial Unfocused Ultrasound (tUS) Neuromodulation: From Theoretical Principles to Stimulation Practices

Transcranial focused ultrasound is an emerging technique for non-invasive neurostimulation. Compared to magnetic or electric non-invasive brain stimulation, this technique has a higher spatial resolution and can reach deep structures. In addition, both animal and human studies suggest that, potentially, different sites of the central and peripheral nervous system can be targeted by this technique. Depending on stimulation parameters, transcranial focused ultrasound is able to determine a wide spectrum of effects, ranging from suppression or facilitation of neural activity to tissue ablation. The aim is to review the state of the art of the human transcranial focused ultrasound neuromodulation literature, including the theoretical principles which underlie the explanation of the bioeffects on neural tissues, and showing the stimulation techniques and parameters used and their outcomes in terms of clinical, neurophysiological or neuroimaging results and safety.