Imaging findings in MR imaging-guided focused ultrasound treatment for patients with essential tremor

Neuronavigation-Guided Transcranial Histotripsy (NaviTH) System

OBJECTIVE

The goal of the work described here was to develop the first neuronavigation-guided transcranial histotripsy (NaviTH) system and associated workflow for transcranial ablation.

METHODS

The NaviTH system consists of a 360-element, 700 kHz transmitter-receiver-capable transcranial histotripsy array, a clinical neuronavigation system and associated equipment for patient-to-array co-registration and therapy planning and targeting software systems. A workflow for NaviTH treatments, including pre-treatment aberration correction, was developed. Targeting errors stemming from target registration errors (TREs) during the patient-to-array co-registration process, as well as focal shifts caused by skull-induced aberrations, were investigated and characterized. The NaviTH system was used in treatments of two <96 h post-mortem human cadavers and in experiments in two excised human skullcaps.

RESULTS

The NaviTH was successfully used to create ablations in the cadaver brains as confirmed in post-treatment magnetic resonance imaging A total of three ablations were created in the cadaver brains, and targeting errors of 9, 3.4 and 4.4 mm were observed in corpus callosum, septum and thalamus targets, respectively. Errors were found to be caused primarily by TREs resulting from transducer tracking instrument design flaws and imperfections in the treatment workflow. Transducer tracking instrument design and workflow improvements reduced TREs to <2 mm, and skull-induced focal shifts, following pre-treatment aberration correction, were 0.3 mm. Total targeting errors of the NaviTH system following the noted improvements were 2.5 mm.

CONCLUSIONS

The feasibility of using the first NaviTH system in a human cadaver model has been determined. Although accuracy still needs to be improved, the proposed system has the potential to allow for transcranial histotripsy therapies without requiring active magnetic resonance treatment guidance.

Magnetic resonance-guided focused ultrasound unilateral thalamotomy for medically refractory essential tremor: 3-year follow-up data

Introduction

Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy of the ventralis intermediate (Vim) nucleus is an "incisionless" treatment for medically refractory essential tremor (ET). We present data on 49 consecutive cases of MRgFUS Vim thalamotomy followed-up for 3 years and review the literature on studies with longer follow-up data.

Methods

A retrospective chart review of patients who underwent MRgFUS thalamotomy (January 2018-December 2020) at our institution was performed. Clinical Rating Scale for Tremor (CRST) and Quality of Life in Essential Tremor (QUEST) scores were obtained pre-operatively and at each follow-up with an assessment of side effects. Patients had post-operative magnetic resonance imaging within 24 h and at 1 month to figure out lesion location, size, and extent. The results of studies with follow-up ≥3 years were summarized through a literature review.

Results

The CRST total (baseline: 58.6 ± 17.1, 3-year: 40.8 ± 18.0) and subscale scores (A + B, baseline: 23.5 ± 6.3, 3-year: 12.8 ± 7.9; C, baseline: 12.7 ± 4.3, 3-year: 5.8 ± 3.9) and the QUEST score (baseline: 38.0 ± 14.8, 3-year: 18.7 ± 13.3) showed significant improvement that was stable during the 3-year follow-up. Three patients reported tremor recurrence and two were satisfactorily retreated. Side effects were reported by 44% of patients (severe: 4%, mild and transient: 40%). The improvement in tremor and quality of life in our cohort was consistent with the literature.

Conclusion

We confirmed the effectiveness and safety of MRgFUS Vim thalamotomy in medically refractory ET up to 3 years.

Magnetic resonance-guided focused ultrasound thalamotomy for essential tremor patients with low skull density ratio: a case-matched analysis

Introduction

Skull density ratio (SDR) is the ratio between the mean Hounsfield units of marrow and cortical bone, impacting energy transmission through the skull. Low SDR has been used as an exclusion criterion in major trials of magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy for medication-refractory essential tremor (ET). However, some studies have suggested that patients with low SDR can safely undergo MRgFUS with favorable outcomes. In this case-matched study, we aim to compare the characteristics, sonication parameters, lesion sizes, and clinical outcomes of patients with low SDR vs. patients with high SDR who underwent unilateral MRgFUS thalamotomy for medication-refractory ET.

Methods

Between March 2016 and April 2023, all patients (n = 270) who underwent unilateral MRgFUS thalamotomy for medication-refractory ET at a single institution were classified as low SDR (<0.40) and high SDR (≥0.40). All clinical and radiological data was prospectively collected and retrospectively analyzed using non-case-matched and 1:1 case-matched methodology.

Results

Thirty-one patients had low SDR, and 239 patients had high SDR. Fifty-six patients (28 in each cohort) were included in 1:1 case-matched analysis. There were no significant differences in baseline characteristics between the two groups in both non-case-matched and 1:1 case-matched analyses. In both analyses, compared to patients with high SDR, patients with low SDR required a significantly higher maximum sonication power, energy, and duration, and reached a lower maximum temperature with smaller lesion volumes. In the non-case-matched and case-matched analyses, low SDR patients did not have significantly less tremor control at any postoperative timepoints. However, there was a higher chance of procedure failure in the low SDR group with three patients not obtaining an appropriately sized lesion. In both analyses, imbalance was observed more often in high SDR patients on postoperative day 1 and month 3.

Discussion

ET patients with SDR <0.40 can be safely and effectively treated with MRgFUS, though there may be higher rates of treatment failure and intraoperative discomfort.

Outcomes and Prognostic Factors of Magnetic Resonance-guided Focused Ultrasound Thalamotomy for Essential Tremor at 2-year Follow-up

Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is an effective treatment for essential tremor (ET). However, its long-term outcomes and prognostic factors remain unclear. This study aimed to retrospectively investigate 38 patients with ET who underwent MRgFUS thalamotomy and were followed up for >2 years. The improvement in tremor was evaluated using the Clinical Rating Scale for Tremor (CRST). Adverse events were documented, and correlations with factors, such as skull density ratio (SDR), maximum mean temperature (T-max), and lesion size, were examined. Furthermore, the outcomes were compared between two groups, one that met the cutoff values, which was previously reported (preoperative CRST-B ≤ 25, T-max ≥ 52.5°C, anterior-posterior size of lesion ≥ 3.9 mm, superior-inferior [SI] size of lesion > 5.5 mm), and the other that did not. The improvement rate was 59.4% on average at the 2-year follow-up. Adverse events, such as numbness (15.8%), dysarthria (10.5%), and lower extremity weakness (2.6%), were observed even after 2 years, although these were mild. The factors correlated with tremor improvement were the T-max and SI size of the lesion (p < 0.05), whereas the SDR showed no significance. Patients who met the aforementioned cutoff values demonstrated a 69.8% improvement at the 2-year follow-up, whereas others showed a 43.6% improvement (p < 0.05). In conclusion, MRgFUS is effective even after 2 years. The higher the T-max and the larger the lesion size, the better the tremor control. Previously reported cutoff values clearly predict the 2-year prognosis, indicating the usefulness of MRgFUS.

Focused Ultrasound Central Lateral Thalamotomy for the Treatment of Refractory Neuropathic Pain: Phase I Trial

BACKGROUND AND OBJECTIVES

Magnetic resonance-guided focused ultrasound (MRgFUS) central lateral thalamotomy (CLT) has not yet been validated for treating refractory neuropathic pain (NP). Our aim was to assess the safety and potential efficacy of MRgFUS CLT for refractory NP.

METHODS

In this prospective, nonrandomized, single-arm, investigator-initiated phase I trial, patients with NP for more than 6 months related to phantom limb pain, spinal cord injury, or radiculopathy/radicular injury and who had undergone at least one previous failed intervention were eligible. The main outcomes were safety profile and pain as assessed using the brief pain inventory, the pain disability index, and the numeric rating scale. Medication use and the functional connectivity of the default mode network (DMN) were also assessed.

RESULTS

Ten patients were enrolled, with nine achieving successful ablation. There were no serious adverse events and 12 mild/moderate severity events. The mean age was 50.9 years (SD: 12.7), and the mean symptom duration was 12.3 years (SD: 9.7). Among eight patients with a 1-year follow-up, the brief pain inventory decreased from 7.6 (SD: 1.1) to 3.8 (SD: 2.8), with a mean percent decrease of 46.3 (SD: 40.6) (paired t -test, P = .017). The mean pain disability index decreased from 43.0 (SD: 7.5) to 25.8 (SD: 16.8), with a mean percent decrease of 39.3 (SD: 41.6) ( P = .034). Numeric rating scale scores decreased from a mean of 7.2 (SD: 1.8) to 4.0 (SD: 2.8), with a mean percent decrease of 42.8 (SD: 37.8) ( P = .024). Patients with predominantly intermittent pain or with allodynia responded better than patients with continuous pain or without allodynia, respectively. Some patients decreased medication use. Resting-state functional connectivity changes were noted, from disruption of the DMN at baseline to reactivation of connectivity between DMN nodes at 3 months.

CONCLUSION

MRgFUS CLT is feasible and safe for refractory NP and has potential utility in reducing symptoms as measured by validated pain scales.

Changes in cerebral cortex activity during a simple motor task after MRgFUS treatment in patients affected by essential tremor and Parkinson's disease: a pilot study using functional NIRS

Objective.Magnetic resonance imaging-guided focused ultrasound surgery (MRgFUS) is a non-invasive thermal ablation method that involves high-intensity focused ultrasound surgery (FUS) and Magnetic Resonance Imaging for anatomical imaging and real-time thermal mapping. This technique is widely employed for the treatment of patients affected by essential tremor (ET) and Parkinson's disease (PD). In the current study, functional near-infrared spectroscopy (fNIRS) was used to highlight hemodynamics changes in cerebral cortex activity, during a simple hand motor task, i.e. unimanual left and right finger-tapping, in ET and PD patients.Approach.All patients were evaluated before, one week and one month after MRgFUS treatment.Main results.fNIRS revealed cerebral hemodynamic changes one week and one month after MRgFUS treatment, especially in the ET group, that showed a significant clinical improvement in tremor clinical scores.Significance.To our knowledge, our study is the first that showed the use of fNIRS system to measure the cortical activity changes following unilateral ventral intermediate nucleus thalamotomy after MRgFUS treatment. Our findings showed that therapeutic MRgFUS promoted the remodeling of neuronal networks and changes in cortical activity in association with symptomatic improvements.

The Optimal Targeting for Focused Ultrasound Thalamotomy Differs between Dystonic and Essential Tremor: A 12-Month Prospective Pilot Study

BACKGROUND

Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is increasingly used to treat drug-resistant essential tremor (ET). Data on MRgFUS thalamotomy in dystonic tremor (DT) are anecdotal.

OBJECTIVES

To investigate efficacy, safety, and differences in target coordinates of MRgFUS thalamotomy in DT versus ET.

METHODS

Ten patients with DT and 35 with ET who consecutively underwent MRgFUS thalamotomy were followed for 12 months. Although in both groups the initial surgical planning coordinates corresponded to the ventralis intermediate (Vim), the final target could be modified intraoperatively based on clinical response.

RESULTS

Tremor significantly improved in both groups. The thalamic lesion was significantly more anterior in DT than ET. Considering both ET and DT groups, the more anterior the lesion, the lower the odds ratio for adverse events.

CONCLUSIONS

MRgFUS thalamotomy is safe and effective in DT and ET. Compared to classical Vim coordinates used for ET, more anterior targeting should be considered for DT.

Outcomes of Focused Ultrasound Thalamotomy in Tremor Syndromes

BACKGROUND

The current literature comparing outcomes after a unilateral magnetic resonance image-guided focused ultrasound (MRgFUS) thalamotomy between tremor syndromes is limited and remains a possible preoperative factor that could help predict the long-term outcomes.

OBJECTIVE

The aim was to report on the outcomes between different tremor syndromes after a unilateral MRgFUS thalamotomy.

METHODS

A total of 66 patients underwent a unilateral MRgFUS thalamotomy for tremor between November 2018 and May 2020 at St Vincent's Hospital Sydney. Each patient's tremor syndrome was classified prior to treatment. Clinical assessments, including the hand tremor score (HTS) and Quality of Life in Essential Tremor Questionnaire (QUEST), were performed at baseline and predefined intervals to 36 months.

RESULTS

A total of 63 patients, comprising 30 essential tremor (ET), 24 dystonic tremor (DT), and 9 Parkinson's disease tremor (PDT) patients, returned for at least one follow-up. In the ET patients, at 24 months there was a 61% improvement in HTS and 50% improvement in QUEST compared to baseline. This is in comparison to PDT patients, where an initial benefit in HTS and QUEST was observed, which waned at each follow-up, remaining significant only up until 12 months. In the DT patients, similar results were observed to the ET patients: at 24 months there was a 61% improvement in HTS and 43% improvement in QUEST compared to baseline.

CONCLUSION

These results support the use of unilateral MRgFUS thalamotomy for the treatment of DT, which appears to have a similar expected outcome to patients diagnosed with ET. Patients with PDT should be warned that there is a risk of treatment failure. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Radiofrequency thalamotomy for tremor produces focused and predictable lesions shown on magnetic resonance images

Radiofrequency thalamotomy is a neurosurgical management option for medically-refractory tremor. In this observational study, we evaluate the MRI features of the resultant lesion, their temporal dynamics, and how they vary depending on surgical factors. We report on lesion characteristics including size and location, as well as how these vary over time and across different MRI sequences. Data from 12 patients (2 essential tremor, 10 Parkinson's disease) who underwent unilateral radiofrequency thalamotomy for tremor were analysed. Lesion characteristics were compared across five structural sequences. Volumetric analysis of lesion features was performed at early (<5 weeks) and late (>5 months) timepoints by manual segmentation. Lesion location was determined after registration of lesions to standard space. All patients showed tremor improvement (clinical global impressions scale) postoperatively. Chronic side-effects included balance disturbances (n = 4) and worsening mobility due to parkinsonism progression (n = 1). Early lesion features including a necrotic core, cytotoxic oedema and perilesional oedema were best demarcated on T2-weighted sequences. Multiple lesions were associated with greater cytotoxic oedema compared with single lesions (T2-weighted mean volume: 537 ± 112 mm³ versus 302 ± 146 mm³, P = 0.028). Total lesion volume reduced on average by 90% between the early and late scans (T2-weighted mean volume: 918 ± 517 versus 75 ± 50 mm³, t = 3.592, P = 0.023, n = 5), with comparable volumes demonstrated at ∼6 months after surgery. Lesion volumes on susceptibility-weighted images were larger than those of T2-weighted images at later timepoints. Radiofrequency thalamotomy produces focused and predictable lesion imaging characteristics over time. T2-weighted scans distinguish between the early lesion core and oedema characteristics, while lesions may remain more visible on susceptibility-weighted images in the months following surgery. Scanning patients in the immediate postoperative period and then at 6 months is clinically meaningful for understanding the anatomical basis of the transient and permanent effects of thalamotomy.

Longitudinal MR imaging after unilateral MR-guided focused ultrasound thalamotomy: clinical and radiological correlation

Introduction

Magnetic-resonance-guided focused ultrasound (MRgFUS) thalamotomy uses multiple converging high-energy ultrasonic beams to produce thermal lesions in the thalamus. Early postoperative MR imaging demonstrates the location and extent of the lesion, but there is no consensus on the utility or frequency of postoperative imaging. We aimed to evaluate the evolution of MRgFUS lesions and describe the incidence, predictors, and clinical effects of lesion persistence in a large patient cohort.

Methods

A total of 215 unilateral MRgFUS thalamotomy procedures for essential tremor (ET) by a single surgeon were retrospectively analyzed. All patients had MR imaging 1 day postoperatively; 106 had imaging at 3 months and 32 had imaging at 1 year. Thin cut (2 mm) axial and coronal T2-weighted MRIs at these timepoints were analyzed visually on a binary scale for lesion presence and when visible, lesion volumes were measured. SWI and DWI sequences were also analyzed when available. Clinical outcomes including tremor scores and side effects were recorded at these same time points. We analyzed if patient characteristics (age, skull density ratio), preoperative tremor score, and sonication parameters influenced lesion evolution and if imaging characteristics correlated with clinical outcomes.

Results

Visible lesions were present in all patients 1 day post- MRgFUS and measured 307.4 ± 128.7 mm3. At 3 months, residual lesions (excluding patients where lesions were not visible) were 83.6% smaller and detectable in only 54.7% of patients (n = 58). At 1 year, residual lesions were detected in 50.0% of patients (n = 16) and were 90.7% smaller than 24 h and 46.5% smaller than 3 months. Lesions were more frequently visible on SWI (100%, n = 17), DWI (n = 38, 97.4%) and ADC (n = 36, 92.3%). At 3 months, fewer treatment sonications, higher maximum power, and greater distance between individual sonications led to larger lesion volumes. Volume at 24 h did not predict if a lesion was visible later. Lesion visibility at 3 months predicted sensory side effects but was not correlated with tremor outcomes.

Discussion

Overall, lesions are visible on T2-weighted MRI in about half of patients at both 3 months and 1 year post-MRgFUS thalamotomy. Certain sonication parameters significantly predicted persistent volume, but residual lesions did not correlate with tremor outcomes.

Focused Ultrasound Thalamotomy for Tremor in Parkinson's Disease: Outcomes in a Large, Prospective Cohort

BACKGROUND

Magnetic resonance guided focused ultrasound (MRgFUS) is United States Food and Drug Administration approved for the treatment of tremor-dominant Parkinson's disease (TdPD), but only limited studies have been described in practice.

OBJECTIVES

To report the largest prospective experience of unilateral MRgFUS thalamotomy for the treatment of medically refractory TdPD.

METHODS

Clinical outcomes of 48 patients with medically refractory TdPD who underwent MRgFUS thalamotomy were evaluated. Tremor outcomes were assessed using the Fahn-Tolosa-Marin scale and adverse effects were categorized using a structured questionnaire and clinical exam at 1 month (n = 44), 3 months (n = 34), 1 year (n = 22), 2 years (n = 5), and 3 years (n = 2). Patients underwent magnetic resonance imaging <24 hours post-procedure.

RESULTS

Significant tremor control persisted at all follow-ups (P < 0.001). All side effects were mild. At 3 months, these included gait imbalance (38.24%), sensory deficits (26.47%), motor weakness (17.65%), dysgeusia (5.88%), and dysarthria (5.88%), with some persisting at 1 year.

CONCLUSIONS

MRgFUS thalamotomy is an effective treatment for sustained tremor control in patients with TdPD. © 2023 International Parkinson and Movement Disorder Society.

MRgFUS of the nucleus ventralis intermedius in essential tremor modulates functional connectivity within the classical tremor network and beyond

BACKGROUND

Magnetic resonance-guided focused ultrasound (MRgFUS) of the thalamic ventral intermediate nucleus is an incisionless lesional treatment for essential tremor.

OBJECTIVE

To examine relationships between tremor severity and functional connectivity in patients with essential tremor and to assess long-term changes in the tremor network after sonication of the ventral intermediate nucleus.

METHODS

Twenty-one patients with essential tremor (70.33 ± 11.32 years) were included in the final analysis and underwent resting state functional magnetic resonance imaging at 3 T before and 6 months after treatment. Tremor severity (Fahn-Tolosa-Marin Clinical Rating Scale) was evaluated and functional connectivity was investigated using independent component analysis.

RESULTS

MRgFUS of the thalamic ventral intermediate nucleus reduced contralateral tremor effectively. Multiple regression analysis revealed exclusively negative correlations between FC and tremor severity, notably in the right cerebellar lobe VI and the left cerebellar lobe VIIIa (cerebellar network), in the left occipital fusiform gyrus (lateral visual network), the anterior division of the left superior temporal gyrus (fronto-parieto-temporal network), and in the posterior division of the left parahippocampal gyrus and the bilateral lingual gyri (default mode network). Six months after treatment, increased functional connectivity was observed in almost all tremor-associated clusters, except the cluster localized in the left cerebellum.

CONCLUSIONS

Our findings suggest that tremor-related activity in essential tremor extends beyond the classical cerebellar network, additionally involving areas related to visual processing. Functional restoration of network activity after sonication of the ventral intermediate nucleus is observed within the classical tremor network (cerebellum) and notably also in visual processing areas.

Hemorrhagic Safety of Magnetic Resonance-Guided Focused Ultrasound Thalamotomy for Tremor without Interruption of Antiplatelet or Anticoagulant Therapy

INTRODUCTION

Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is an incision-less ablative technique used to treat medically refractory tremor. Although intracerebral hemorrhage has not been reported with MRgFUS thalamotomy for the treatment of movement disorders, clinicians commonly interrupt active blood thinning medications prior to the procedure or offer gamma knife radiosurgery instead. However, MRgFUS uses focal thermoablation, and bleeding risk is likely minimal. This study aimed to evaluate the safety of MRgFUS thalamotomy in patients with essential tremor (ET) and tremor-dominant Parkinson's disease (PD) without interrupting anticoagulant or antiplatelet therapies.

METHODS

This was a single-center retrospective case series of all patients with ET or PD undergoing MRgFUS from February 2019 through December 2022 (n = 96). Demographic variables and medications taken at the time of surgery were obtained. Our primary outcome was the type and frequency of hemorrhagic complications noted on the operative report or postoperative imaging.

RESULTS

The mean age of patients was 74.2 years, and 26% were female. Forty patients were taking ≥1 antiplatelet or anticoagulant medications. No patient actively taking anticoagulant or antiplatelet therapies had a hemorrhagic complication during or <48 h after the procedure.

CONCLUSION

The frequency of intra- or postoperative complications from MRgFUS was not higher in patients actively taking anticoagulant or antiplatelet therapies relative to those who were not. Our findings suggest that MRgFUS thalamotomy does not necessitate interrupting anticoagulant or antiplatelet therapies. However, given the limited number of patients actively taking these therapies in our cohort (n = 40), additional testing in large, prospective studies should be conducted to further establish safety.

A Systematic Review Comparing Focused Ultrasound Surgery With Radiosurgery for Essential Tremor

BACKGROUND

Focused ultrasound (FUS-T) and stereotactic radiosurgery thalamotomy (SRS-T) targeting the ventral intermediate nucleus are effective incisionless surgeries for essential tremor (ET). However, their efficacy for tremor reduction and, importantly, adverse event incidence have not been directly compared.

OBJECTIVE

To present a comprehensive systematic review with network meta-analysis examining both efficacy and adverse events (AEs) of FUS-T vs SRS-T for treating medically refractory ET.

METHODS

We conducted a systematic review and network meta-analysis according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, using the PubMed and Embase databases. We included all primary FUS-T/SRS-T studies with approximately 1-year follow-up, with unilateral Fahn-Tolosa-Marin Tremor Rating Scale or Clinical Rating Scale for Tremor scores prethalamotomy/post-thalamotomy and/or AEs. The primary efficacy outcome was Fahn-Tolosa-Marin Tremor Rating Scale A+B score reduction. AEs were reported as an estimated incidence.

RESULTS

Fifteen studies of 464 patients and 3 studies of 62 patients met inclusion criteria for FUS-T/SRS-T efficacy comparison, respectively. Network meta-analysis demonstrated similar tremor reduction between modalities (absolute tremor reduction: FUS-T: -11.6 (95% CI: -13.3, -9.9); SRS-T: -10.3 (95% CI: -14.2, -6.0). FUS-T had a greater 1-year adverse event rate, particularly imbalance and gait disturbances (10.5%) and sensory disturbances (8.3%). Contralateral hemiparesis (2.7%) often accompanied by speech impairment (2.4%) were most common after SRS-T. There was no correlation between efficacy and lesion volume.

CONCLUSION

Our systematic review found similar efficacy between FUS-T and SRS-T for ET, with trend toward higher efficacy yet greater adverse event incidence with FUS-T. Smaller lesion volumes could mitigate FUS-T off-target effects for greater safety.

Essential Tremor - Deep Brain Stimulation vs. Focused Ultrasound

INTRODUCTION

Essential Tremor (ET) is one of the most common tremor syndromes typically presented as action tremor, affecting mainly the upper limbs. In at least 30-50% of patients, tremor interferes with quality of life, does not respond to first-line therapies and/or intolerable adverse effects may occur. Therefore, surgery may be considered.

AREAS COVERED

In this review, the authors discuss and compare unilateral ventral intermedius nucleus deep brain stimulation (VIM DBS) and bilateral DBS with Magnetic Resonance-guided Focused Ultrasound (MRgFUS) thalamotomy, which comprises focused acoustic energy generating ablation under real-time MRI guidance. Discussion includes their impact on tremor reduction and their potential complications. Finally, the authors provide their expert opinion.

EXPERT OPINION

DBS is adjustable, potentially reversible and allows bilateral treatments; however, it is invasive requires hardware implantation, and has higher surgical risks. Instead, MRgFUS is less invasive, less expensive, and requires no hardware maintenance. Beyond these technical differences, the decision should also involve the patient, family, and caregivers.

Longitudinal brain functional connectivity changes induced by neurosurgical thalamotomy for tremor in Parkinson's disease: a preliminary study

The hypothesis that the effectiveness of neurosurgical procedures in Parkinson's disease (PD) would be related to connectivity dysfunctions between the site of the stimulation and other brain regions is growing. This study aimed to assess resting-state functional connectivity between thalamic ventral intermediate nucleus (Vim) and the rest of the brain before and after thalamotomy in PD. A 76-year-old right-handed woman with refractory tremor-dominant PD was selected as a candidate for left Vim radiosurgery thalamotomy. Clinical and motion sensor evaluation and brain resting-state functional MRI (rs-fMRI) were carried out before treatment and 3, 6, and 12 months later. Targeted Vim was selected as region of interest and a seed-based rs-fMRI analysis was performed in the patient and ten age- and sex-matched controls at baseline and over time. Furthermore, a correlation analysis between functional connectivity and tremor data was carried out. Both clinical and motion sensor measurements showed a progressive tremor improvement over time on right side after radiosurgery. In the patient, seed-based analysis showed a significantly increased functional connectivity between targeted Vim and ipsilateral visual areas relative to controls before treatment. Over 1 year, a normalization of aberrant pre-therapeutic functional connectivity between Vim and visual areas was obtained. At correlation analysis, the reduction of tremor metrics over time, assessed by clinical evaluation and wearable motion sensors, was related to the reduction of the left Vim-left visual cortex functional connectivity. Our findings support the evidence that fMRI was able to detect targeted Vim connectivity and its changes over time after thalamotomy.

Magnetic Resonance-guided Focused Ultrasound thalamotomy for refractory neuropathic pain: a systematic review and critical appraisal of current knowledge

Background

Magnetic Resonance-guided Focused Ultrasound (MRgFUS) is an innovative therapeutical approach for medically refractory tremor. It is currently under investigation for other neurological diseases including refractory neuropathic pain (NP).

Objective

The objective of this systematic review is to analyze available evidence about the effectiveness and safety profile of MRgFUS in the treatment of refractory NP.

Methods

Eligible studies were identified by searching published studies in PubMed and Scopus databases from inception to December 2022 and by identifying ongoing studies registered on the clinicaltrials.gov website. The study was registered in PROSPERO (ID: CRD42021277154).

Results

We found three published observational studies and nine ongoing studies. In published studies, the involved population ranged from 8 to 46 patients with overall 66 patients being included with NP or trigeminal neuralgia. The target lesion was in the posterior part of the central lateral nucleus of the thalamus, bilaterally. Outcomes were assessed at different times through the Visual Analog Scale, showing a variable degree of improvement. Adverse events were rare, mild, and transient (vertigo, paresthesias, and dysesthesias) with intracerebral bleeding being reported as major adverse event in one case only. Among ongoing studies, we found three prospective, randomized, sham-controlled, crossover trials (RCTs) and six observational studies. Inclusion criteria are previous failure of more than three pharmacological treatments and NP duration longer than 6 months. The thalamus is the main proposed target and measured outcomes are accuracy of the procedure and pain relief, with a follow-up period ranging from 1 week to 1 year.

Conclusion

This systematic review suggests that, although high-quality studies are lacking, available evidence endorses the effectiveness and safety of MRgFUS in the management of NP. Ongoing RCTs will provide more robust data to understand benefits and risks of the procedure.

Registration

PROSPERO (ID: CRD42021277154).

Advances in Focused Ultrasound for the Treatment of Brain Tumors

Employing the full arsenal of therapeutics to treat brain tumors is limited by the relative impermeability of the blood-brain and blood-tumor barriers. In physiologic states, the blood-brain barrier serves a protective role by passively and actively excluding neurotoxic compounds; however, this functionality limits the penetrance of therapeutics into the tumor microenvironment. Focused ultrasound technology provides a method for overcoming the blood-brain and blood-tumor barriers through ultrasound frequency to transiently permeabilize or disrupt these barriers. Concomitant delivery of therapeutics has allowed for previously impermeable agents to reach the tumor microenvironment. This review details the advances in focused ultrasound in both preclinical models and clinical studies, with a focus on its safety profile. We then turn towards future directions in focused ultrasound-mediated therapies for brain tumors.

Tremor suppression following treatment with MRgFUS: skull density ratio consistency and degree of posterior dentatorubrothalamic tract lesioning predicts long-term clinical outcomes in essential tremor

Objectives

Magnetic resonance-guided focussed ultrasound (MRgFUS) is an incisionless ablative procedure, widely used for treatment of Parkinsonian and Essential Tremor (ET). Enhanced understanding of the patient- and treatment-specific factors that influence sustained long-term tremor suppression could help clinicians achieve superior outcomes via improved patient screening and treatment strategy.

Methods

We retrospectively analysed data from 31 subjects with ET, treated with MRgFUS at a single centre. Tremor severity was assessed with parts A, B and C of the Clinical Rating Scale for Tremor (CRST) as well as the combined CRST. Tremor in the dominant and non-dominant hand was assessed with Hand Tremor Scores (HTS), derived from the CRST. Pre- and post-treatment imaging data were analysed to determine ablation volume overlap with automated thalamic segmentations, and the dentatorubrothalamic tract (DRTT) and compared with percentage change in CRST and HTS following treatment.

Results

Tremor symptoms were significantly reduced following treatment. Combined pre-treatment CRST (mean: 60.7 ± 17.3) and HTS (mean: 19.2 ± 5.7) improved by an average of 45.5 and 62.6%, respectively. Percentage change in CRST was found to be significantly negatively associated with age (β = -0.375, p = 0.015), and SDR standard deviation (SDRSD; β = -0.324, p = 0.006), and positively associated with ablation overlap with the posterior DRTT (β = 0.535, p < 0.001). Percentage HTS improvement in the dominant hand decreased significantly with older age (β = -0.576, p < 0.01).

Conclusion

Our results suggest that increased lesioning of the posterior region of the DRTT could result in greater improvements in combined CRST and non-dominant hand HTS, and that subjects with lower SDR standard deviation tended to experience greater improvement in combined CRST.

Differences in intrinsic functional networks in patients with essential tremor who had good and poor long-term responses after thalamotomy performed using MR-guided ultrasound

OBJECTIVE

Thalamotomy at the nucleus ventralis intermedius using MR-guided focused ultrasound has been an effective treatment method for essential tremor (ET). However, this is not true for all cases, even for successful ablation. How the brain differs in patients with ET between those with long-term good and poor outcomes is not clear. To analyze the functional connectivity difference between patients in whom thalamotomy was effective and those in whom thalamotomy was ineffective and its prognostic role in ET treatment, the authors evaluated preoperative resting-state functional MRI in thalamotomy-treated patients.

METHODS

Preoperative resting-state functional MRI data in 85 patients with ET, who were experiencing tremor relief at the time of treatment and were followed up for a minimum of 6 months after the procedure, were collected for the study. The authors conducted a graph independent component analysis of the functional connectivity matrices of tremor-related networks. The patients were divided into thalamotomy-effective and thalamotomy-ineffective groups (thalamotomy-effective group, ≥ 50% motor symptom reduction; thalamotomy-ineffective group, < 50% motor symptom reduction at 6 months after treatment) and the authors compared network components between groups.

RESULTS

Seventy-two (84.7%) of the 85 patients showed ≥ 50% tremor reduction from baseline at 6 months after thalamotomy. The network analysis shows significant suppression of functional network components with connections between the areas of the cerebellum and the basal ganglia and thalamus, but enhancement of those between the premotor cortex and supplementary motor area in the noneffective group compared to the effective group.

CONCLUSIONS

The present study demonstrates that patients in the noneffective group have suppressed functional subnetworks in the cerebellum and subcortex regions and have enhanced functional subnetworks among motor-sensory cortical networks compared to the thalamotomy-effective group. Therefore, the authors suggest that the functional connectivity pattern might be a possible predictive factor for outcomes of MR-guided focused ultrasound thalamotomy.

Focused Ultrasound Thalamotomy: Correlation of Postoperative Imaging with Neuropathological Findings

Magnetic resonance-guided high-intensity focused ultrasound (MRgFUS) is a rapidly developing technique used for tremor relief in tremor-predominant Parkinson's disease (PD) and essential tremor that has demonstrated successful results. Here, we describe the neuropathological findings in a woman who died from a fall 10 days after successful MRgFUS for tremor-predominant PD. Histological analysis demonstrates the characteristic early postoperative MRI findings including 3 distinct zones on T2-weighted imaging: (1) a hypointense core, (2) a hyperintense region with hypointense rim, and (3) a slightly hyperintense, poorly marginated surrounding area. Histopathological analyses also demonstrate the suspected cellular processes composing each of these regions including central hemorrhagic necrosis with surrounding cytotoxic edema and a rim of mostly unaffected vasogenic edema with some reactive and reparative processes. Overall, this case demonstrates the correlation of postoperative imaging findings with the subacute neuropathological findings after MRgFUS for PD.

Pretherapeutic functional connectivity of tractography-based targeting of the ventral intermediate nucleus for predicting tremor response in patients with Parkinson's disease after thalamotomy with MRI-guided focused ultrasound

OBJECTIVE

Tractography-based direct targeting of the ventral intermediate nucleus (T-VIM) is a novel method that provides patient-specific VIM coordinates. This study aimed to explore the accuracy and predictive value of using T-VIM in combination with tractography and resting-state functional connectivity techniques to perform magnetic resonance imaging-guided focused ultrasound (MRgFUS) thalamotomy as a treatment of Parkinson's disease (PD).

METHODS

PD patients underwent MRgFUS thalamotomy and were recruited for functional MRI scanning. A subscore of the Clinical Rating Scale for Tremor was used to evaluate tremor improvement. T-VIM and surgical VIM (S-VIM) were defined on preoperative diffusion tensor MRI and 24-hour postoperative T1-weighted imaging, respectively. The overlapping volume and center distance between S-VIM and T-VIM were measured to determine their correlations with 12-month postoperative tremor improvement. Moreover, pretherapeutic functional connectivity of T-VIM or S-VIM, based on region-of-interest connectivity and whole-brain seed-to-voxel connectivity, was measured with the resting-state functional connectivity technique to investigate their correlations with tremor improvement.

RESULTS

All patients had excellent tremor improvement (mean [range] tremor improvement 74.82% [50.00%-94.44%]). The authors found that both overlapping volume and center distance between T-VIM and S-VIM were significantly correlated with tremor improvement (r = 0.788 and p = 0.012 for overlapping volume; r = -0.696 and p = 0.037 for center distance). Pretherapeutic functional connectivity of T-VIM with the ipsilateral sensorimotor cortex (r = 0.876 and p = 0.002), subthalamic nucleus (r = 0.700 and p = 0.036), and visual area (r = 0.911 and p = 0.001) was significantly and positively correlated with tremor improvement.

CONCLUSIONS

T-VIM may improve the clinical application of MRgFUS thalamotomy as a treatment of PD. Pretherapeutic functional connectivity of T-VIM with the ipsilateral sensorimotor cortex, subthalamic nucleus, and visual area may predict PD tremor responses after MRgFUS thalamotomy.

Ipsilateral and axial tremor response to focused ultrasound thalamotomy for essential tremor: clinical outcomes and probabilistic mapping

BACKGROUND

MR-guided focused ultrasound (MRgFUS) thalamotomy has been shown to be a safe and effective treatment for essential tremor (ET).

OBJECTIVE

To investigate the effects of MRgFUS in patients with ET with an emphasis on ipsilateral-hand and axial tremor subscores.

METHODS

Tremor scores and adverse effects of 100 patients treated between 2012 and 2018 were assessed at 1 week, 3, 12, and 24 months. A subgroup analysis of ipsilateral-hand tremor responders (defined as patients with ≥30% improvement at any time point) and non-responders was performed. Correlations and predictive factors for improvement were analysed. Weighted probabilistic maps of improvement were generated.

RESULTS

Significant improvement in axial, contralateral-hand and total tremor scores was observed at all study visits from baseline (p<0.0001). There was no significant improvement in ipsilateral subscores. A subset of patients (n=20) exhibited group-level ipsilateral-hand improvement that remained significant through all follow-ups (p<0.001). Multivariate regression analysis revealed that higher baseline scores predict better improvement in ipsilateral-hand and axial tremor. Probabilistic maps demonstrated that the lesion hotspot for axial improvement was situated more medially than that for contralateral improvement.

CONCLUSION

MRgFUS significantly improved axial, contralateral-hand and total tremor scores. In a subset of patients, a consistent group-level treatment effect was observed for ipsilateral-hand tremor. While ipsilateral improvement seemed to be less directly related to lesion location, a spatial relationship between lesion location and axial and contralateral improvement was observed that proved consistent with the somatotopic organisation of the ventral intermediate nucleus.

TRIAL REGISTRATION NUMBERS

NCT01932463, NCT01827904, and NCT02252380.

Altered Thalamic Connectivity Due to Focused Ultrasound Thalamotomy in Patients with Essential Tremor

BACKGROUND

Although stereotactic ablation surgery is known to ameliorate involuntary movement dramatically, little is known regarding alterations in whole-brain networks due to disruption of the deep brain nucleus. To explore changes in the whole-brain network after thalamotomy, we analyzed structural and functional connectivity alterations using resting-state functional magnetic resonance imaging and diffusion tensor imaging in patients with essential tremor who had undergone focused ultrasound (FUS) thalamotomy.

METHODS

Seven patients with intractable essential tremors and 7 age-matched healthy controls were enrolled in the study. The tremor score in essential tremor patients was assessed, and resting-state functional magnetic resonance imaging and diffusion tensor imaging were performed before and 3 months after left ventral intermediate nucleus thalamotomy using FUS.

RESULTS

There was a significant improvement in the tremor of the right hand after FUS thalamotomy. Seed-based functional connectivity analysis revealed a significant increase in functional connectivity between the left thalamus and the caudal part of the dorsal premotor cortex after FUS thalamotomy. Structural connectivity analysis did not detect statistically significant changes between before and after FUS. There was no correlation between the changes in functional connectivity and tremor score.

CONCLUSIONS

Although the number of cases is small, our results show that functional connectivity between the thalamus and the premotor cortex increases after the amelioration of tremors by FUS thalamotomy. The lack of correlation between increased functional connectivity and clinical tremor scores suggests that the observed increase in functional connectivity may be a compensatory change in the secondary sensorimotor changes that occur after thalamotomy.

Neuropathology of Parkinson's disease after focused ultrasound thalamotomy

Focused ultrasound (FUS) thalamotomy is an emerging treatment for tremor-dominant Parkinson's disease (PD). We report the first postmortem neuropathologic study of FUS thalamotomy in a 68-year-old man with tremor-dominant PD, which was performed seven months before he died. Although the peak voxel temperature at the target was <54 °C, his tremor improved on intraoperative and postoperative assessments. Additionally, postoperative MRI demonstrated a thalamic lesion. Lewy body-related pathology consistent with PD was detected. There was also a 5-mm lesion in the ventral lateral thalamus characterized by demyelination and neuropil loss, with many lipid-laden macrophages, but no lymphocytic infiltrates and relatively preserved neurons and axons. Additional pathological assessments after FUS thalamotomy are needed to determine if the observed brain changes are typical of this procedure.

Cutoff values for the best management strategy for magnetic resonance-guided focused ultrasound ablation for essential tremor

OBJECTIVE

The efficacy of magnetic resonance-guided focused ultrasound (MRgFUS) ablation for essential tremor (ET) is well known; however, no prognostic factors have been established. The authors aimed to retrospectively investigate MRgFUS ablation outcomes and associated factors and to define the cutoff values for each prognostic factor.

METHODS

Sixty-four Japanese patients who underwent unilateral ventral intermediate nucleus thalamotomy with MRgFUS for ET were included. Follow-up evaluations were performed at 1 week and 1, 3, 6, 12, and 24 months postoperatively. Tremor suppression was evaluated using the Clinical Rating Scale for Tremor (CRST), and adverse effects were recorded postoperatively. Outcome-associated factors were examined preoperatively, intraoperatively, and postoperatively using multivariate analyses. The cutoff values for the prognostic factors were calculated using receiver operating characteristics.

RESULTS

Percentage improvements in the CRST scores of the affected upper limb were 82.4%, 72.2%, 68.6%, and 65.9% at 1, 3, 6, and 12 months, respectively. Preoperatively, a high skull density ratio (SDR) (p ≤ 0.047), low CRST part B score (used to assess tremors during several tasks) (cutoff value 25, p ≤ 0.041), and nonoccurrence of resting tremors (p = 0.027) were significantly associated with improved tremor control. An intraoperatively high maximum mean temperature (cutoff value 52.5°C, p ≤ 0.047), postoperatively large lesion (cutoff value 3.9 mm in the anterior-posterior direction, p ≤ 0.002; cutoff value 5.0-5.55 mm in the superior-inferior direction, p ≤ 0.026), and small transducer focus correction (p ≤ 0.015) were also associated with improved tremor control. No valid cutoff value was found for SDR. Adverse effects (limb weakness, sensory disturbance, ataxia/walking disturbance, dysgeusia, dysarthria, and facial swelling) occurred transiently and were associated with high SDR, high temperature, high number of sonication sessions, large lesion, and occurrence of resting tremor. Patients who developed leg weakness experienced greater percentage improvement in tremors at 3 months postoperatively than those who did not.

CONCLUSIONS

MRgFUS ablation could be used to achieve good tremor control with acceptable adverse effects in Japanese patients with ET. The relatively low SDR in Asian ethnic groups as compared with that of Western populations makes treatment difficult; however, the cutoff values obtained in this study may be useful for achieving good treatment outcomes even in such patients. Clinical trial registration no.: UMIN000026952 (University Hospital Medical Information Network).

ABBREVIATIONS

ACPC = anterior commissure-posterior commissure; AP = anterior to posterior; CRST = Clinical Rating Scale for Tremor; ET = essential tremor; MRgFUS = magnetic resonance-guided focused ultrasound; PC = posterior commissure; PSA = posterior subthalamic area; RL = right to left; ROC = receiver operating characteristic; SDR = skull density ratio; SI = superior to inferior; T2WI = T2-weighted imaging; VIM = ventral intermediate nucleus.

Magnetic Resonance Image Guided Focused Ultrasound Thalamotomy. A Single Center Experience With 160 Procedures

Introduction

MRgFUS thalamotomy has gained popularity as an FDA approved, non-invasive treatment for patients with Essential Tremor and tremor predominant Parkinson's Disease. We present our initial clinical experience with 160 consecutive cases of MRgFUS thalamotomy and describe the clinical outcomes with long term follow-up.

Methods

A retrospective chart review of all patients who underwent MRgFUS thalamotomy at our institution was performed. CRST Part A tremor scores were obtained pre-operatively and at each follow-up visit along with an assessment of side effects (SE). All patients had a post-operative MRI within 24 h to determine the location, size, and extent of the MRgFUS lesion.

Results

One hundred and sixty unilateral MRgFUS Thalamotomies (Left, n = 128; Right, n = 32) were performed for medically refractory essential Tremor (n = 150) or tremor predominant Parkinson's disease (n = 10). Mean age at surgery was 75 Years (range: 48-93) and the mean skull density ratio (SDR) was 0.48 (range: 0.32-0.75; median: 0.46). In ET patients, both rest and postural tremor was abolished acutely and remained so at follow-up whereas intention tremor was reduced acutely by 93% below baseline, 87% at 3 months, 83.0% at 1-year, and 78% at 2 years. On post-operative day 1, the most common SE's included imbalance (57%), sensory disturbances (25%), and dysmetria (11%). All adverse events were rated as mild on the Clavien-Dindo Scale and improved over time. At 2-years follow-up, imbalance was seen in 18%, sensory disturbance in 10% and dysmetria in 8% patients. Mean clinical follow-up for all patients was 14 months (range: 1-48 months).

Conclusion

MRgFUS thalamotomy is a safe and effective procedure for long term improvement of unilateral tremor symptoms, with the most common side-effects being imbalance and sensory disturbance.

Magnetic Resonance-Guided Focused Ultrasound Thalamotomy for Essential Tremor Under General Anesthesia: Technical Note

BACKGROUND

Magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy is an incisionless therapy for the treatment of medication-resistant essential tremor. Although its safety and efficacy has been demonstrated, MRgFUS is typically performed with the patient awake, with intraprocedural neurological assessments to guide lesioning.

OBJECTIVE

To report the first case of MRgFUS thalamotomy under general anesthesia in a patient whose medical comorbidities prohibit him from being in a supine position without a secured airway.

METHODS

The dentatorubrothalamic tract was directly targeted. Two sonications reaching lesional temperatures (≥54°C) were delivered without any complications.

RESULTS

Lesioning was confirmed on intraoperative magnetic resonance imaging, and the patient experienced 89% improvement in his tremor postoperatively.

CONCLUSION

This demonstrates the safety and feasibility of MRgFUS thalamotomy under general anesthesia without the benefit of intraprocedural neurological assessments.

Resting State Functional Connectivity Signatures of MRgFUS Vim Thalamotomy in Parkinson's Disease: A Preliminary Study

Magnetic Resonance-guided high-intensity Focused Ultrasound (MRgFUS) of the thalamic ventral intermediate nucleus (Vim) for tremor has increasingly gained interest as a new non-invasive alternative to standard neurosurgery. Resting state functional connectivity (rs-FC) correlates of MRgFUS have not been extensively investigated yet. A region of interest (ROI)-to-ROI rs-FC MRI “connectomic” analysis focusing on brain regions relevant for tremor was conducted on 15 tremor-dominant patients with Parkinson's disease who underwent MRgFUS. We tested whether rs-FC between tremor-related areas was modulated by MRgFUS at 1 and 3 months post-operatively, and whether such changes correlated with individual clinical outcomes assessed by the MDS-UPDRS-III sub items for tremor. Significant increase in FC was detected within bilateral primary motor (M1) cortices, as well as between bilateral M1 and crossed primary somatosensory cortices, and also between pallidum and the dentate nucleus of the untreated hemisphere. Correlation between disease duration and FC increase at 3 months was found between the putamen of both cerebral hemispheres and the Lobe VI of both cerebellar hemispheres, as well as between the Lobe VI of untreated cerebellar hemisphere with bilateral supplementary motor area (SMA). Drop-points value of MDS-UPDRS at 3 months correlated with post-treatment decrease in FC, between the anterior cingulate cortex and bilateral SMA, as well as between the Lobe VI of treated cerebellar hemisphere and the interpositus nucleus of untreated cerebellum. Tremor improvement at 3 months, expressed as percentage of intra-subject MDS-UPDRS changes, correlated with FC decrease between bilateral occipital fusiform gyrus and crossed Lobe VI and Vermis VI. Good responders (≥50% of baseline tremor improvement) showed reduced FC between bilateral SMA, between the interpositus nucleus of untreated cerebellum and the Lobe VI of treated cerebellum, as well as between the untreated SMA and the contralateral putamen. Good responders were characterized at baseline by crossed hypoconnectivity between bilateral putamen and M1, as well as between the putamen of the treated hemisphere and the contralateral SMA. We conclude that MRgFUS can effectively modulate brain FC within the tremor network. Such changes are associated with clinical outcome. The shifting mode of integration among the constituents of this network is, therefore, susceptible to external redirection despite the chronic nature of PD.

MR relaxation properties of tissue-mimicking phantoms

High quality tissue-mimicking phantoms (TMPs) have a critical role in the preclinical testing of emerging modalities for diagnosis and therapy. TMPs capable of accurately mimicking real tissue in Magnetic Resonance guided Focused Ultrasound (MRgFUS) applications should be fabricated with precise T1 and T2 relaxation times. Given the current popularity of the MRgFUS technology, we herein performed a systematic review on the MR relaxation properties of different phantoms types. Polyacrylamide (PAA) and agar based phantoms were proven capable of accurately replicating critical thermal, acoustical, and MR relaxation properties of various body tissues. Although gelatin phantoms were also proven factional in this regard, they lack the capacity to withstand ablation temperatures, and thus, are only recommended for hyperthermia applications. Other gelling agents identified in the literature are Poly-vinyl alcohol (PVA), Polyvinyl Chloride (PVC), silicone, and TX-150/ TX-151; however, their efficacy in thermal studies is yet to be established. PAA gels are favorable in that they offer optical transparency enabling direct visualization of coagulative lesions. On the other hand, agar phantoms have lower preparation costs and were proven very promising for use with the MRgFUS technology, without the toxicity issues related to the preparation and storage of PAA materials. Remarkably, agar turned out to be the prominent modifier of the T2 relaxation time even for phantoms containing other types of gelling agents instead of agar. This review could be useful in manufacturing realistic MRgFUS phantoms while simultaneously indicating an opportunity for further research in the field with a particular focus on the MR behavior of agar-based TMPs.

Feasibility of Magnetic Resonance-Guided Focused Ultrasound Thalamotomy for Essential Tremor in the Setting of Prior Craniotomy

BACKGROUND

Magnetic resonance imaging-guided focused ultrasound (MRgFUS) thalamotomy is a rapidly evolving therapy for the treatment of essential tremor. Although the skull is a major determinant of the delivery of acoustic energy to the target, how the presence of a prior craniotomy must be accounted for during lesioning is unclear.

OBJECTIVE

To demonstrate novel application of this therapeutic option in a patient with a history of prior craniotomies for unrelated intracranial pathologies.

METHODS

A 55-yr-old man with a history of right frontal craniotomy for resection of a colloid cyst underwent a left ventrointermedius nucleus thalamotomy through MRgFUS. The prior craniotomy flap was not excluded in the treatment plan; however, all bony defects and hardware were marked as "no-pass" regions. Clinical outcomes were collected at the 6-mo follow-up.

RESULTS

Transducer elements whose acoustic paths would have been altered by the craniotomy defect were turned off. Sonications reaching lesional temperatures of up to 56°C were successfully delivered. The procedure was well-tolerated, without any persistent intra-ablation or postablation adverse effects. The presence of a lesion was confirmed on MRI, which was associated with a significant reduction in the patient's tremor that was sustained at the 6-mo follow-up.

CONCLUSION

This case demonstrates the safety and efficacy of MRgFUS thalamotomy in a patient with prior craniotomies and highlights our strategy for acoustic lesioning in this setting.

Technical Comparison of Treatment Efficiency of Magnetic Resonance-Guided Focused Ultrasound Thalamotomy and Pallidotomy in Skull Density Ratio-Matched Patient Cohorts

Objective

MR-guided focused ultrasound (MRgFUS) is increasingly being used to treat patients with essential tremor (ET) and Parkinson's disease (PD) with thalamotomy and pallidotomy, respectively. Pallidotomy is performed off-center within the cranium compared to thalamotomy and may present challenges to therapeutic lesioning due to this location. However, the impact of target location on treatment efficiency and ability to create therapeutic lesions has not been studied. This study aimed to compare the physical efficiency of MRgFUS thalamotomy and pallidotomy.

Methods

Treatment characteristics were compared between patients treated with thalamotomy (n = 20) or pallidotomy (n = 20), matched by skull density ratios (SDR). Aspects of treatment efficiency were compared between these groups. Demographic and comparative statistics were conducted to assess these differences. Acoustic field simulations were performed to compare and validate the simulated temperature profile for VIM and GPi ablation.

Results

Lower SDR values were associated with greater energy requirement for thalamotomy (R² = 0.197, p = 0.049) and pallidotomy (R² = 0.342, p = 0.007). The impact of low SDR on efficiency reduction was greater for pallidotomy, approaching significance (p = 0.061). A nearly two-fold increase in energy was needed to reach 50°C in pallidotomy (10.9kJ) than in thalamotomy (5.7kJ), (p = 0.002). Despite lower energy requirement, the maximum average temperature reached was higher in thalamotomy (56.7°C) than in pallidotomy (55.0°C), (p = 0.017). Mean incident angle of acoustic beams was lesser in thalamotomy (12.7°) than in pallidotomy (18.6°), (p < 0.001). For all patients, a lesser mean incident angle correlated with a higher maximum average temperature reached (R² = 0.124, p = 0.026), and less energy needed to reach 50°C (R²=0.134, p = 0.020). Greater skull thickness was associated with a higher maximum energy for a single sonication for thalamotomy (R² = 0.206, p = 0.045) and pallidotomy (R² = 0.403, p = 0.003). An acoustic and temperature field simulation validated similar findings for thalamotomy and pallidotomy in a single patient.

Conclusion

The centrally located VIM offers a more efficient location for therapeutic lesioning compared to GPi pallidotomy in SDR matched cohort of patients. The impact on therapeutic lesioning with lower SDR may be greater for pallidotomy patients. As newer off-center targets are investigated, these findings can inform patient selection and treatment requirements for lesion production.

Hyperostosis in Combination With Low Skull Density Ratio: A Potential Contraindication for Magnetic Resonance Imaging-Guided Focused Ultrasound Thalamotomy

Since its approval in treating a number of movement disorders, magnetic resonance imaging–guided focused ultrasound (MRgFUS) has been adopted rapidly as one of the standard treatment modalities internationally. However, the efficiency of the energy delivered by the ultrasonic waves is largely determined by the highly variable bone morphology and density characteristics of the skull. One of the widely accepted indices used to facilitate patient selection is the skull density ratio (SDR). Earlier literature suggested that an SDR of less than 0.4 would be unfavorable for MRgFUS treatment. Some prior studies have excluded patients with hyperostosis. However, there is little published data regarding the impact of other skull features such as hyperostosis on treatment success. We present the case of a 66-year-old man with medically refractory essential tremor who had an SDR of 0.38 and extensive hyperostosis frontalis interna and underwent attempted MRgFUS thalamotomy treatment. However, intraoperatively the treatment was unsuccessful in generating sufficiently elevated temperature to create a lesion of the usual desired volume, and as expected, there was minimal clinical improvement. For comparison, we also summarize a case series of 4 other patients with an SDR of less than 0.4 who had successful outcomes. We believe that SDR should not be used as the only means of selecting patients for MRgFUS. Instead, important factors such as hyperostosis should be taken into consideration for patient selection and pretreatment counseling.

Lesion location and lesion creation affect outcomes after focused ultrasound thalamotomy

MRI-guided focused ultrasound thalamotomy has been shown to be an effective treatment for medication refractory essential tremor. Here, we report a clinical-radiological analysis of 123 cases of MRI-guided focused ultrasound thalamotomy, and explore the relationships between treatment parameters, lesion characteristics and outcomes. All patients undergoing focused ultrasound thalamotomy by a single surgeon were included. The procedure was performed as previously described, and patients were followed for up to 1 year. MRI was performed 24 h post-treatment, and lesion locations and volumes were calculated. We retrospectively evaluated 118 essential tremor patients and five tremor-dominant Parkinson's disease patients who underwent thalamotomy. At 24 h post-procedure, tremor abated completely in the treated hand in 81 essential tremor patients. Imbalance, sensory disturbances and dysarthria were the most frequent acute adverse events. Patients with any adverse event had significantly larger lesions, while inferolateral lesion margins were associated with a higher incidence of motor-related adverse events. Twenty-three lesions were identified with irregular tails, often extending into the internal capsule; 22 of these patients experienced at least one adverse event. Treatment parameters and lesion characteristics changed with increasing surgeon experience. In later cases, treatments used higher maximum power (normalized to skull density ratio), accelerated more quickly to high power, and delivered energy over fewer sonications. Larger lesions were correlated with a rapid rise in both power delivery and temperature, while increased oedema was associated with rapid rise in temperature and the maximum power delivered. Total energy and total power did not significantly affect lesion size. A support vector regression was trained to predict lesion size and confirmed the most valuable predictors of increased lesion size as higher maximum power, rapid rise to high-power delivery, and rapid rise to high tissue temperatures. These findings may relate to a decrease in the energy efficiency of the treatment, potentially due to changes in acoustic properties of skull and tissue at higher powers and temperatures. We report the largest single surgeon series of focused ultrasound thalamotomy to date, demonstrating tremor relief and adverse events consistent with reported literature. Lesion location and volume impacted adverse events, and an irregular lesion tail was strongly associated with adverse events. High-power delivery early in the treatment course, rapid temperature rise, and maximum power were dominant predictors of lesion volume, while total power, total energy, maximum energy and maximum temperature did not improve prediction of lesion volume. These findings have critical implications for treatment planning in future patients.

Techniques, Indications, and Outcomes in Magnetic Resonance-guided Focused Ultrasound Thalamotomy for Tremor

Magnetic resonance (MR)-guided focused ultrasound surgery (MRgFUS) is the latest minimally invasive stereotactic procedure, and thalamotomy using this novel modality has demonstrated its effectiveness and safety, especially for patients with essential tremor (ET) and Parkinson's disease (PD). In Japan, the application of MRgFUS to treat ET and PD has recently been covered by health insurance. Technically, the transducer with 1024 elements emits ultrasound beams, which are then focused on the target with a phase control, resulting in optimal ablation by thermal coagulation. The technical advantages of MRgFUS are continuous intraoperative monitoring of clinical symptoms and MR images and fine adjustment of the target by the steering function. Postoperative tremor control is compatible with other modalities, although long-term follow-up is necessary. The adverse effects are usually transient and acceptable. Prognostic factors for good tremor control include high temperature and large lesion size. A high skull density ratio is a factor to achieve high temperature and large lesioning, but it may not be necessary and sufficient for clinical outcomes. For patients with advanced symptoms such as bilateral tremor or head/neck tremor, deep brain stimulation may be recommended because of the adjustability of stimulation and the possibility of bilateral treatment. Patients have high expectations of MRgFUS because of its non-invasiveness. To perform this treatment safely and effectively, physicians need to understand the technological aspects, the physiological principles. To choose the appropriate modality, physicians also should recognize the clinical advantages and disadvantages of MRgFUS compared to other modalities.

Patient-specific effects on sonication heating efficiency during magnetic resonance-guided focused ultrasound thalamotomy

PURPOSE

During magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy for refractory tremor, high temperatures must be achieved and sustained for tissue necrosis. We assessed the impact of both patient-specific as well as procedure-related factors on the efficiency of acoustic energy transfer, or heating efficiency (HE).

METHODS

Retrospective analysis of 92 consecutive patients (857 sonications) with essential tremor or tremor-dominant Parkinson's disease treated at a single institution. Temperature elevations at the target were measured for each sonication with MR thermometry. HE of each sonication was defined as the ratio of peak temperature elevation and the delivered energy. HE was analyzed with respect to patient skull features (area, thickness, skull density ratio [SDR]), computed from CT scans, as well as demographic and clinical variables (age, sex, diagnosis, and duration of symptoms).

RESULTS

Across the full range of sonication energies that can be delivered with current devices (up to 36 kJ), average sonication HE was diminished in patients with lower SDR. In individual subjects, there was a progressive loss in HE as sonication energy was titrated up throughout the course of treatment, with a more rapid decline in patients with higher SDR. This energy-dependent loss in HE was not related to procedural factors, namely, the number of previous sonications, or the cumulative energy deposited during previous sonications. In contrast to SDR, neither skull area nor thickness was an independent predictor of average HE or the rate of its decline with increasing energies. In 11% of patients, all of whom with SDR < 0.45, sonication HE fell below the threshold to reach 54°C even with delivery of maximum energy. In contrast, temperatures ≥ 50°C could be obtained in all but one patient.

CONCLUSIONS

SDR is predictive of sonication HE, and determines patient-specific limits on the magnitude of temperature elevation that can be achieved with current devices. These data inform strategies for predictable lesioning in MRgFUS thalamotomy.

Focused Ultrasound Thalamotomy Sensory Side Effects Follow the Thalamic Structural Homunculus

Objective

Focused ultrasound thalamotomy is an effective treatment for tremor; however, side effects may occur. The purpose of the present study was to investigate the spatial relationship between thalamotomies and specific sensory side effects and their functional connectivity with somatosensory cortex and relationship to the medial lemniscus (ML).

Methods

Sensory adverse effects were categorized into 4 groups based on the location of the disturbance: face/mouth/tongue numbness/paresthesia, hand-only paresthesia, hemibody/limb paresthesia, and dysgeusia. Then, areas of significant risk (ASRs) for each category were defined using voxel-wise mass univariate analysis and overlaid on corresponding odds ratio maps. The ASR associated with the maximum risk was used as a region of interest in a normative functional connectome to determine side effect-specific functional connectivity. Finally, each ASR was overlaid on the ML derived from normative template.

Results

Of 103 patients, 17 developed sensory side effects after thalamotomy persisting 3 months after the procedures. Lesions producing sensory side effects extended posteriorly into the principle sensory nucleus of the thalamus or below the thalamus in the ML. The topography of sensory adverse effects followed the known somatotopy of the ML and the sensory nucleus. Functional connectivity patterns between each sensory-specific thalamic seed and the primary somatosensory areas supported the role of the middle insula in processing of gustatory information and in multisensory integration.

Conclusions

Distinct regions in the sensory thalamus and its afferent connections rise to specific sensory disturbances. These findings demonstrate the relationship between the sensory thalamus, ML, and bilateral sensory cortical areas.

Bilateral Magnetic Resonance Imaging-Guided Focused Ultrasound Thalamotomy for Essential Tremor

INTRODUCTION

Essential tremor is the most common movement disorder in adults. Bilateral symptoms are typical; however, bilateral thalamotomy for essential tremor is associated with a high probability of adverse events. We retrospectively investigated the efficacy and safety of staged bilateral ventral intermediate nucleus thalamotomy for refractory essential tremor using magnetic resonance imaging-guided focused ultrasound.

METHODS

We enrolled 5 consecutive patients with refractory essential tremor between September 2016 and March 2020. Patients underwent a second operation at least 1 year after the first operation. The second lesion was created asymmetrically to the first lesion.

RESULTS

Mean patient age was 57.6 years, and the mean interval between the 2 operations was 27.8 months. The second lesion center was superior to the first lesion in all patients. The mean baseline, second preoperative, and second postoperative Clinical Rating Scale for Tremor total scores were 63.6, 49.2, and 21.8, respectively. The mean baseline, second preoperative, and second postoperative Clinical Rating Scale for Tremor part C scores were 18.4, 8.2, and 2.6, respectively. One patient had permanent adverse events of slight dysarthria and discomfort in the tongue. No patient experienced dysphagia or cognitive dysfunction after the second operation. Four of the 5 patients were satisfied with the results of the bilateral treatment, including the patient who had permanent adverse events.

CONCLUSIONS

Magnetic resonance imaging-guided focused ultrasound is an effective method for bilateral thalamotomy when adhering to the following considerations: (1) asymmetrical lesions are created and (2) sufficient interval (>1 year) between operations.

Convergent structural network and gene signatures for MRgFUS thalamotomy in patients with Parkinson's disease

MRgFUS has just been made available for the 1.7 million Parkinson's disease patients in China. Despite its non-invasive and rapid therapeutic advantages for involuntary tremor, some concerns have emerged about outcomes variability, non-specificity, and side-effects, as little is known about its impact on the long-term plasticity of brain structure. We sought to dissect the characteristics of long-term changes in brain structure caused by MRgFUS lesion and explored potential biological mechanisms. One-year multimodal imaging follow-ups were conducted for nine tremor-dominant Parkinson's disease patients undergoing unilateral MRgFUS thalamotomy. A structural connectivity map was generated for each patient to analyze dynamic changes in brain structure. The human brain transcriptome was extracted and spatially registered for connectivity vulnerability. Genetic functional enrichment analysis was performed and further clarified using in vivo emission computed tomography data. MRgFUS not only abolished tremors but also significantly disrupted the brain network topology. Network-based statistics identified a U-shape MRgFUS-sensitive subnetwork reflective of hand tremor recovery and surgical process, accompanied by relevant cerebral blood flow and gray matter alteration. Using human brain gene expression data, we observed that dopaminergic signatures were responsible for the preferential vulnerability associated with these architectural alterations. Additional PET/SPECT data not only validated these gene signatures, but also suggested that structural alteration was significantly correlated with D1 and D2 receptors, DAT, and F-DOPA measures. There was a long-term dynamic loop between structural alteration and dopaminergic signature for MRgFUS thalamotomy, which may be closely related to the long-term improvements in clinical tremor.

Correlation of visual area with tremor improvement after MRgFUS thalamotomy in Parkinson's disease

OBJECTIVE

MRI-guided focused ultrasound (MRgFUS) thalamotomy is a novel and minimally invasive alternative for medication-refractory tremor in Parkinson's disease (PD). However, the impact of MRgFUS thalamotomy on spontaneous neuronal activity in PD remains unclear. The purpose of the current study was to evaluate the effects of MRgFUS thalamotomy on local fluctuations in neuronal activity as measured by the fractional amplitude of low-frequency fluctuations (fALFF) in patients with PD.

METHODS

Participants with PD undergoing MRgFUS thalamotomy were recruited. Tremor scores were assessed before and 3 and 12 months after treatment using the Clinical Rating Scale for Tremor. MRI data were collected before and 1 day, 1 week, 1 month, 3 months, and 12 months after thalamotomy. The fALFF was calculated. A whole-brain voxel-wise paired t-test was used to identify significant changes in fALFF at 12 months after treatment compared to baseline. Then fALFF in the regions with significant differences were extracted from fALFF maps of patients for further one-way repeated-measures ANOVA to investigate its dynamic alterations. The association between fALFF changes induced by thalamotomy and tremor improvement were evaluated using the nonparametric Spearman rank test.

RESULTS

Nine participants with PD (mean age ± SD 64.7 ± 6.1 years, 8 males) were evaluated. Voxel-based analysis showed that fALFF in the left occipital cortex (Brodmann area 17 [BA17]) significantly decreased at 12 months after thalamotomy compared to baseline (voxel p < 0.001, cluster p < 0.05 family-wise error [FWE] corrected). At baseline, fALFF in the left occipital BA17 in patients was elevated compared with that in 9 age- and gender-matched healthy subjects (p < 0.05). Longitudinal analysis displayed the dynamic changes of fALFF in this region (F (5,40) = 3.61, p = 0.009). There was a significant positive correlation between the falling trend in fALFF in the left occipital BA17 and hand tremor improvement after treatment over 3 time points (Spearman's rho = 0.44, p = 0.02).

CONCLUSIONS

The present study investigated the impact of MRgFUS ventral intermediate nucleus thalamotomy on spontaneous neural activity in medication-refractory tremor-dominant PD. The visual area is, for the first time, reported as relevant to tremor improvement in PD after MRgFUS thalamotomy, suggesting a distant effect of MRgFUS thalamotomy and the involvement of specific visuomotor networks in tremor control in PD.

Focused ultrasound for functional neurosurgery

INTRODUCTION

Brain lesioning is a fundamental technique in the functional neurosurgery world. It has been investigated for decades and presented promising results long before novel pharmacological agents were introduced to treat movement disorders, psychiatric disorders, pain, and epilepsy. Ablative procedures were replaced by effective drugs during the 1950s and by Deep Brain Stimulation (DBS) in the 1990s as a reversible neuromodulation technique. In the last decade, however, the popularity of brain lesioning has increased again with the introduction of magnetic resonance-guided focused ultrasound (MRgFUS).

OBJECTIVE

In this review, we will cover the current and emerging role of MRgFUS in functional neurosurgery.

METHODS

Literature review from PubMed and compilation.

RESULTS

Investigated since 1930, MRgFUS is a technology enabling targeted energy delivery at the convergence of mechanical sound waves. Based on technological advancements in phased array ultrasound transducers, algorithms accounting for skull penetration by sound waves, and MR imaging for targeting and thermometry, MRgFUS is capable of brain lesioning with sub-millimeter precision and can be used in a variety of clinical indications.

CONCLUSION

MRgFUS is a promising technology evolving as a dominant tool in different functional neurosurgery procedures in movement disorders, psychiatric disorders, epilepsy, among others.

Focused Ultrasound Thalamotomy for the Treatment of Essential Tremor: A 2-Year Outcome Study of Chinese People

Background: Essential tremor (ET) is a common movement disorder among elderly individuals worldwide and is occasionally associated with a high risk for mild cognitive impairment and dementia. This retrospective study aimed to determine the clinical outcome of unilateral magnetic resonance-guided focused ultrasound (MRgFUS) thalamotomy in Chinese patients with ET. Methods: In total, 31 male and 17 female patients with drug-refractory ET were enrolled in this research study from January 2017 to September 2019. The severity of tremor and disability were assessed using the Clinical Rating Scale for Tremor (CRST) within a 2-year follow-up period. Results: The mean age of the participants was 59.14 ± 13.5 years. The mean skull density ratio (SDR) was 0.5 ± 0.1. The mean highest temperature was 57.0 ± 2.4°C. The mean number of sonications was 10.0 ± 2.6. The average maximum energy was 19,710.5 ± 8,624.9 J. The total CRST scores and sub-scores after MRgFUS thalamotomy significantly reduced during each follow-up (p < 0.001). All but four (8.3%) of the patients had reversible adverse events (AEs) after the procedure. Conclusions: MRgFUS had sustained clinical efficacy 2 years after treatment for intractable ET. Only few patients presented with thalamotomy-related AEs including numbness, weakness, and ataxia for an extended period. Most Chinese patients were treated safely and effectively despite their low SDR.

Predictors of thermal response and lesion size in patients undergoing magnetic resonance-guided focused ultrasound thalamotomy

Magnetic resonance-guided focused ultrasound (MRgFUS) is being increasingly utilized in the treatment of movement disorders such as essential tremor (ET) and Parkinson's disease (PD). Whilst skull density ratio (SDR) has previously been correlated with achieving lesional temperature rises, other patient factors such as brain and cerebrospinal fluid (CSF) volume have not previously been investigated. We aimed to investigate the effect of brain and CSF volumes on lesional temperature rises, as well as the effect of brain and CSF volumes and SDR on post-treatment lesion sizes. Fifty-four consecutive patients were studied with patient and treatment-related variables collected along with post-treatment lesion sizes. Linear regression analysis identified that SDR alone was associated with lesional temperatures. Both SDR and brain atrophy were associated with post-treatment lesion sizes on linear regression analysis. On multiple linear regression analysis SDR was significantly associated with post-treatment lesion size, and the association between brain atrophy and lesion sizes approached significance, a finding that warrants further investigation.

Is Transcranial Magnetic Resonance Imaging-Guided Focused Ultrasound a Repeatable Treatment Option? Case Report of a Retreated Patient With Tremor Combined With Parkinsonism

INTRODUCTION

In recent years, transcranial Magnetic Resonance Imaging-guided Focused Ultrasound (tcMRgFUS) treatments for functional neurological disorders are giving a new thrust to the field of therapeutic brain lesioning.

OBJECTIVE

To present the case of a patient affected by tremor combined with Parkinsonism who underwent a second tcMRgFUS thalamotomy because of relapsing tremor after a few months from the first tcMRgFUS treatment.

METHODS

A 72-yr-old, right-handed man, came to our observation because of a disabling tremor affecting his upper limbs, refusing any invasive surgical procedure and already treated by tcMRgFUS left Vim thalamotomy. However, clinical benefit had brief duration, as a progressive recurrence of tremor on the right upper limb was observed after a few months from the first treatment. Thus, the patient underwent a new left-sided tcMRgFUS procedure 6 mo after the former treatment.

RESULTS

After the second procedure, an immediate and complete relief from tremor on the right upper limb was achieved with clinical benefit that persisted up to a 6-mo follow-up.

CONCLUSION

Since tcMRgFUS doesn't use ionizing radiations and it is incision-less, repeated and staged treatment procedures have always been hypothesized. Our report suggests that tcMRgFUS retreatment might actually be a feasible, safe, and effective option in selected patients in whom an optimal clinical outcome is not achieved after the first treatment session. However, future well-designed studies in large samples are needed to assess the possible risks of retreatment and the optimal timing of reintervention as well as eligibility and exclusion criteria.

Technical and operative factors affecting magnetic resonance imaging-guided focused ultrasound thalamotomy for essential tremor: experience from 250 treatments

OBJECTIVE

Magnetic resonance imaging-guided focused ultrasound (MRgFUS) provides real-time monitoring of patients to assess tremor control and document any adverse effects. MRgFUS of the ventral intermediate nucleus (VIM) of the thalamus has become an effective treatment option for medically intractable essential tremor (ET). The aim of this study was to analyze the correlations of clinical and technical parameters with 12-month outcomes after unilateral MRgFUS thalamotomy for ET to help guide future clinical treatments.

METHODS

From October 2013 to January 2019, data on unilateral MRgFUS thalamotomy from the original pivotal study and continued-access studies from three different geographic regions were collected. Authors of the present study retrospectively reviewed those data and evaluated the efficacy of the procedure on the basis of improvement in the Clinical Rating Scale for Tremor (CRST) subscore at 1 year posttreatment. Safety was based on the rates of moderate and severe thalamotomy-related adverse events. Treatment outcomes in relation to various patient- and sonication-related parameters were analyzed in a large cohort of patients with ET.

RESULTS

In total, 250 patients were included in the present analysis. Improvement was sustained throughout the 12-month follow-up period, and 184 (73.6%) of 250 patients had minimal or no disability due to tremor (CRST subscore < 10) at the 12-month follow-up. Younger age and higher focal temperature (Tmax) correlated with tremor improvement in the multivariate analysis (OR 0.948, p = 0.013; OR 1.188, p = 0.025; respectively). However, no single statistically significant factor correlated with Tmax in the multivariate analysis. The cutoff value of Tmax in predicting a CRST subscore < 10 was 55.8°C. Skull density ratio (SDR) was positively correlated with heating efficiency (β = 0.005, p < 0.001), but no significant relationship with tremor improvement was observed. In the low-temperature group, 1-3 repetitions to the right target with 52°C ≤ Tmax ≤ 54°C was sufficient to generate sustained tremor suppression within the investigated follow-up period. The high-temperature group had a higher rate of balance disturbances than the low-temperature group (p = 0.04).

CONCLUSIONS

The authors analyzed the data of 250 patients with the aim of improving practices for patient screening and determining treatment endpoints. These results may improve the safety, efficacy, and efficiency of MRgFUS thalamotomy for ET.

Magnetic resonance-guided focused ultrasound treatment for essential tremor shows sustained efficacy: a meta-analysis

Although magnetic resonance-guided focused ultrasound (MRgFUS) is a viable treatment option for essential tremor, some studies note a diminished treatment benefit over time. A PubMed search was performed adhering to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Studies were included if hand tremor scores (HTS), total Clinical Rating Scale for Tremor (CRST) scores, or Quality of Life in Essential Tremor Questionnaire (QUEST) scores at regular intervals following MRgFUS treatment for essential tremor were documented. Data analyses included a random effects model of meta-analysis and mixed-effects model of meta-regression. Twenty-one articles reporting HTS for 395 patients were included. Mean pre-operative HTS was 19.2 ± 5.0. Mean HTS at 3 months post-treatment was 7.4 ± 5.0 (61.5% improvement, p < 0.001). Treatment effect was mildly decreased at 36 months at 9.1 ± 5.4 (8.8% reduction). Meta-regression of time since treatment as a modifier of HTS revealed a downward trend in effect size, though this was not statistically significant (p = 0.208). Only 4 studies included follow-up ≥ 24 months. Thirteen included articles reported total CRST scores with standardized follow-up for 250 patients. Mean pre-operative total CRST score decreased by 46.2% at 3 months post-treatment (p < 0.001). Additionally, mean QUEST scores at 3 months post-treatment significantly improved compared to baseline (p < 0.001). HTS is significantly improved from baseline ≥ 24 months post-treatment and possibly ≥ 48 months post-treatment. There is a current paucity of long-term CRST and QUEST score reporting in the literature.

Preoperative imaging findings in patients undergoing transcranial magnetic resonance imaging-guided focused ultrasound thalamotomy

The prevalence and impact of imaging findings detected during screening procedures in patients undergoing transcranial MR-guided Focused Ultrasound (tcMRgFUS) thalamotomy for functional neurological disorders has not been assessed yet. This study included 90 patients who fully completed clinical and neuroradiological screenings for tcMRgFUS in a single-center. The presence and location of preoperative imaging findings that could impact the treatment were recorded and classified in three different groups according to their relevance for the eligibility and treatment planning. Furthermore, tcMRgFUS treatments were reviewed to evaluate the number of transducer elements turned off after marking as no pass regions the depicted imaging finding. A total of 146 preoperative imaging findings in 79 (87.8%) patients were detected in the screening population, with a significant correlation with patients' age (rho = 483, p < 0.001). With regard of the group classification, 119 (81.5%), 26 (17.8%) were classified as group 1 or 2, respectively. One patient had group 3 finding and was considered ineligible. No complications related to the preoperative imaging findings occurred in treated patients. Preoperative neuroradiological findings are frequent in candidates to tcMRgFUS and their identification may require the placement of additional no-pass regions to prevent harmful non-targeted heating.

Transcranial Magnetic Resonance Imaging-Guided Focused Ultrasound with a 1.5 Tesla Scanner: A Prospective Intraindividual Comparison Study of Intraoperative Imaging

BACKGROUND

High-quality intraoperative imaging is needed for optimal monitoring of patients undergoing transcranial MR-guided Focused Ultrasound (tcMRgFUS) thalamotomy. In this paper, we compare the intraoperative imaging obtained with dedicated FUS-Head coil and standard body radiofrequency coil in tcMRgFUS thalamotomy using 1.5-T MR scanner.

METHODS

This prospective study included adult patients undergoing tcMRgFUS for treatment of essential tremor. Intraoperative T2-weighted FRFSE sequences were acquired after the last high-energy sonication using a dedicated two-channel FUS-Head (2ch-FUS) coil and body radiofrequency (body-RF) coil. Postoperative follow-ups were performed at 48 h using an eight-channel phased-array (8ch-HEAD) coil. Two readers independently assessed the signal-to-noise ratio (SNR) and evaluated the presence of concentric lesional zones (zone I, II and III). Intraindividual differences in SNR and lesional findings were compared using the Wilcoxon signed rank sum test and McNemar test.

RESULTS

Eight patients underwent tcMRgFUS thalamotomy. Intraoperative T2-weighted FRFSE images acquired using the 2ch-FUS coil demonstrated significantly higher SNR (R1 median SNR: 10.54; R2: 9.52) compared to the body-RF coil (R1: 2.96, p < 0.001; R2: 2.99, p < 0.001). The SNR was lower compared to the 48-h follow-up (p < 0.001 for both readers). Intraoperative zone I and zone II were more commonly visualized using the 2ch-FUS coil (R1, p = 0.031 and p = 0.008, R2, p = 0.016, p = 0.008), without significant differences with 48-h follow-up (p ≥ 0.063). The inter-reader agreement was almost perfect for both SNR (ICC: 0.85) and lesional findings (k: 0.82-0.91).

CONCLUSIONS

In the study population, the dedicated 2ch-FUS coil significantly improved the SNR and visualization of lesional zones on intraoperative imaging during tcMRgFUS performed with a 1.5-T MR scanner.