Introduction: Magnetic resonance-guided focused ultrasound (MRgFUS) represents an incisionless treatment option for essential or parkinsonian tremor. The incisionless nature of this procedure has garnered interest from both patients and providers. As such, an increasing number of centers are initiating new MRgFUS programs, necessitating development of unique workflows to optimize patient care and safety. Herein, we describe establishment of a multi-disciplinary team, workflow processes, and outcomes for a new MRgFUS program. Methods: This is a single-academic center retrospective review of 116 consecutive patients treated for hand tremor between 2020 and 2022. MRgFUS team members, treatment workflow, and treatment logistics were reviewed and categorized. Tremor severity and adverse events were evaluated at baseline, 3, 6, and 12 months post-MRgFUS with the Clinical Rating Scale for Tremor Part B (CRST-B). Trends in outcome and treatment parameters over time were assessed. Workflow and technical modifications were noted. Results: The procedure, workflow, and team members remained consistent throughout all treatments. Technique modifications were attempted to reduce adverse events. A significant reduction in CRST-B score was achieved at 3 months (84.5%), 6 months (79.8%), and 12 months (72.2%) post-procedure (p < 0.0001). The most common post-procedure adverse events in the acute period (<1 day) were gait imbalance (61.1%), fatigue and/or lethargy (25.0%), dysarthria (23.2%), headache (20.4%), and lip/hand paresthesia (13.9%). By 12 months, the majority of adverse events had resolved with a residual 17.8% reporting gait imbalance, 2.2% dysarthria, and 8.9% lip/hand paresthesia. No significant trends in treatment parameters were found. Conclusions: We demonstrate the feasibility of establishing an MRgFUS program with a relatively rapid increase in evaluation and treatment of patients while maintaining high standards of safety and quality. While efficacious and durable, adverse events occur and can be permanent in MRgFUS.

Magnetic resonance-guided focused ultrasound (MRgFUS) was approved by the European Union in 2013 and the Food and Drug Administration (FDA) in 2016 for unilateral treatment of refractory essential tremor (ET) [1‒3]. The perceived noninvasive nature of MRgFUS has attracted patients who were previously reluctant to undergo intervention. That along with accumulating data on efficacy and safety of MRgFUS has resulted in a rapid increase in the number of treatment centers worldwide. This, in turn, has resulted in large variability in treatment approaches. While there is evidence that tremor efficacy and prevalence of adverse events tend to improve as centers gain experience with MRgFUS technique [4, 5], there remains variability in tremor outcomes [6‒8].

MRgFUS is performed in the MRI suite and requires different support staff and clinical workflow compared to the traditional operating room. There are little data on programmatic considerations, multi-disciplinary team assembly, support staff, and clinical workflow of a newly established MRgFUS program. Here, we present our experience with establishing a new MRgFUS program at a tertiary academic center and treating an initial 116 patients. A multi-disciplinary team workflow is described along with practices that have been particularly impactful. Programmatic changes implemented as we gained experience with the technique are also described. Lastly, 1-year outcomes and adverse event data are provided to validate the described workflow.

Clinical Workflow

The MRgFUS multi-disciplinary treatment team consists of a clinical care coordinator, a neurosurgeon, four interventional movement disorders neurologists, a nurse practitioner or physician assistant (APP), a clinical nurse (RN), and a radiology technician. Responsibilities of team members at each stage of treatment are outlined in Figure 1. There is no anesthesiologist present during the procedure. A computed tomography scan of the skull is performed on the same day when possible to evaluate skull homogeneity, calculated as skull density ratio (SDR) which is the mean ratio between cortical and trabecular bone, with a higher value designated to a more homogenous skull [9].

Fig. 1.

Clinical workflow and team responsibilities.

Fig. 1.

Clinical workflow and team responsibilities.

Close modal

Medications and Clinical Monitoring

All patients received a single pre-procedural dose of dexamethasone (4 mg intravenous or oral). Periprocedural dexamethasone is prescribed prophylactically based on empirical understanding of perilesional edema to be vasogenic in nature. Intra-procedural dizziness and nausea are managed by verbal support as well as ondansetron (4–8 mg intravenous or sublingual). If persistently elevated blood pressure is noted, labetalol is given (10 mg every 15 min as needed). All medications are administered by the RN present during the procedure. Continuous blood oxygenation saturation and heart rate are monitored. Blood pressure is measured every 10 min.

Patient Population

All patients’ demographic, treatment, referral, and outcome data were retrospectively analyzed from the MRgFUS database. 116 patients were consecutively treated between May 2020 and January 2022 at the authors’ institution. In 8 cases, ablative temperatures were not reached despite maximum energy and power delivery. Thus, a total of 108 treatments were evaluated in this study (Fig. 2). Patients with uncorrected coagulopathy, severe claustrophobia, and SDR less than 0.30 were not treated. Patients with SDR values between 0.31 and 0.40 and patients with hyperostosis frontalis were cautioned about possible unsuccessful treatment.

Fig. 2.

Flowchart summarizing patient outcome data included in study. LTFU, lost to follow-up.

Fig. 2.

Flowchart summarizing patient outcome data included in study. LTFU, lost to follow-up.

Close modal

MRgFUS Procedure and Treatment Parameters

MRgFUS was performed according to the previously described methods outlined in the literature [10, 11]. MRgFUS procedure was performed in an outpatient setting, with patients discharged home on the day of procedure. Baseline image acquisition includes a T2 (TR: >5000 ms, TE: >100 ms) sagittal volumetric sequence. Initial targeting is performed using subablative temperatures (50–53°C) at anatomical ventral intermediate nucleus (VIM) coordinates (Fig. 3a). Anatomical VIM targeting coordinates are 10 mm from the wall of third ventricle, 6.5 mm anterior to posterior commissure (PC), and 1 mm above the anterior commissure-posterior commissure (AC-PC) plane (1.5 mm after case 72 and 2.0 mm after case 113). Targeting is adjusted based on presence of side effects or lack of tremor control. For example, subablative sonications resulting in hypesthesia at the tip of the tongue or mouth due to inadvertent capturing of ventralis caudalis nucleus have target adjusted anteriorly.

Fig. 3.

Representative case of MRgFUS thalamotomy. a Pre-sonication planning. No pass zones are marked in red. Bony elements are shaded green. b Tissue heat map. c Tissue temperature during sonication. d T2-weighted MRI sequence immediately post-MRgFUS procedure. A characteristic owl-eye lesion is seen in the right thalamus. e T2-weighted MRI sequence of same patient 3 months post-sonication demonstrating lesion persistence.

Fig. 3.

Representative case of MRgFUS thalamotomy. a Pre-sonication planning. No pass zones are marked in red. Bony elements are shaded green. b Tissue heat map. c Tissue temperature during sonication. d T2-weighted MRI sequence immediately post-MRgFUS procedure. A characteristic owl-eye lesion is seen in the right thalamus. e T2-weighted MRI sequence of same patient 3 months post-sonication demonstrating lesion persistence.

Close modal

Generally, two lesions are created, one centered at coordinates described above and another 1.5 mm rostral and 1 mm anterior to the first lesion. Treatment is stopped when adequate tremor control is observed with temperature rise greater than 56°C on thermometry or adequate lesion visualization on T2 sequence (Fig. 3b–e).

MRgFUS Follow-Up and Outcome Assessments

Baseline, 3-, 6-, and 12-month post-treatment tremor was evaluated using part B of the Clinical Rating Scale for Tremor (CRST-B) which evaluates specific motor tasks for the right and left hand [12]. CRST-B was used specifically because it evaluates treatment-specific tremor reduction in the treated hand. Treatments that did not reach sufficient ablative temperatures were excluded from outcomes analysis (n = 8). During follow-up appointments, patients were asked about possible adverse effects.

Statistical Analysis

Statistical analyses were performed using commercially available Prism GraphPad software (San Diego, CA). Dunnett’s multiple comparison’s test was used to compare differences between CRST-B scores at follow-up timepoints versus baseline. Repeated-measures one-way ANOVA was used to compare differences in CRST-B scores over multiple timepoints. D’Agostino and Pearson test was used to determine normality of distribution of CRST-B scores at different timepoints. Pearson’s correlation test was used to analyze correlation of patient treatment order and number of sonication cycles or maximal peak temperature used for treatment. A p value of <0.05 was considered to indicate statistical significance.

Patients

A total of 108 patients were included in the study. Summary of patient characteristics are listed in Table 1. The mean ± SD age was 72.5 ± 8.7 years (range 49–90). The study patients were primarily male (67.0%), right handed (82.6%), and had ET (83.3%) or Parkinson’s disease (PD) (16.7%) as a formal diagnosis. The average baseline CRST-B in the treated hand was 11.5 ± 4.4 (range 3–20). The average SDR for these patients was 0.54 ± 0.10 (range 0.30–0.76).

Table 1.

Summary of patient characteristics

 Summary of patient characteristics
 Summary of patient characteristics

Treatment Parameters

The treatment parameters are summarized in Table 2. The mean number of sonications was 6.8 ± 1.6 (range 4–12). The average maximal energy delivered was 15.5 ± 8.6 kJ (range 5–36). The maximal average temperature achieved in lesion area was 57.5 ± 2.5°C (range 50–67) and the maximal peak temperature was 62.0 ± 3.1°C (range 52–68). The mean available skull area was 352.6 ± 36.3 cm2 (range 250–432) with mean elements used 942.5 ± 43.0 (range 703–1,008). The left VIM was the target in 80 of our patients (74.0%) and the mean coordinates were 13.9 ± 0.7 mm lateral to midline, 7.1 ± 1.1 mm anterior from mid-commissural plane (AP), and 1.4 ± 0.3 mm superior to AC-PC plane (SI).

Table 2.

Summary of treatment parameters

 Summary of treatment parameters
 Summary of treatment parameters

Clinical Outcomes

Clinical outcome was evaluated by comparing 3-, 6-, and 12-month CRST-B score to baseline (Fig. 4a). 3-, 6-, and 12-month CRST-B scores were found to be normally distributed with K2values of 5.8, 5.7, and 5.1, respectively (p = 0.054, 0.057, and 0.078, D’Agostino and Pearson test). There was a significant reduction of 84.5% in mean CRST-B scores of the treated hand when comparing 3-month and baseline scores (1.8 vs. 11.6, n = 101, p < 0.0001, Dunnett’s multiple comparison’s test), 79.8% when comparing 6-month CRST-B score to baseline (2.3 vs. 11.4, n = 92, p < 0.0001, Dunnett’s multiple comparison’s test), and 72.2% when comparing 12-month CRST score to baseline (3.2 vs. 11.5, n = 41, p < 0.0001, Dunnett’s multiple comparison’s test). In patients with a full set of completed scales (3, 6, and 12 months, n = 41), durable tremor control can be seen up to 12 months (p < 0.0001, repeated-measures one-way ANOVA) (Fig. 4b).

Fig. 4.

MRgFUS treatment produces robust, durable tremor control. a Patient CRST scores at 3, 6 and 12 months are presented. Each dot represents a single patient with lines connecting paired baseline and follow-up scores (from left to right; ****, p< 0.0001; ****, p< 0.0001; ****, p< 0.001; Dunnett’s multiple comparison test). b CRST-B scores normalized to baseline in patients with complete set of scales at 3-, 6-, and 12-month follow-up (n= 41, ****, p< 0.0001, repeated-measures one-way ANOVA). Thick line connects mean normalized CRST scores.

Fig. 4.

MRgFUS treatment produces robust, durable tremor control. a Patient CRST scores at 3, 6 and 12 months are presented. Each dot represents a single patient with lines connecting paired baseline and follow-up scores (from left to right; ****, p< 0.0001; ****, p< 0.0001; ****, p< 0.001; Dunnett’s multiple comparison test). b CRST-B scores normalized to baseline in patients with complete set of scales at 3-, 6-, and 12-month follow-up (n= 41, ****, p< 0.0001, repeated-measures one-way ANOVA). Thick line connects mean normalized CRST scores.

Close modal

Adverse Events

Table 3 provides a summary of adverse events. The most common immediate adverse events (<1 day) observed after MRgFUS procedure were gait imbalance (61.1%), fatigue or lethargy (25.0%), dysarthria (23.2%), headaches (20.4%), and lip/hand paresthesia (13.9%). Other adverse events included nausea, dizziness, and swelling from frame placement. Of the 82 patients evaluated at 6 months, 20 patients (24.4%) had persistent gait imbalance, 6 patients (7.3%) had persistent lip or tongue paresthesia with 1 (1.2%) also reporting loss of taste, 2 (2.4%) patients with loss of taste without associated paresthesia, 1 patient (1.2%) with persistent generalized weakness, and one (1.2%) had persistent headaches. At 12 months, 8 out of 45 patients (17.8%) had persistent gait imbalance. The severity of gait imbalances at 1, 3, 6 months, and 1 year was grade 1 in all patients based on the Clavien-Dindo criteria [13]. Three patients required use of assistive walking devices for about 1 week after the procedure. At 1 year, none of the 8 patients with long-term gait imbalance required physical therapy, medication, or assistive devices, nor did they report a decrease in quality of life related to gait imbalance. However, they did note a perceptible change in gait and balance when compared to before MRgFUS. Gait imbalance resolution did not impact tremor control (Fig. 5).

Table 3.

Summary of adverse events

 Summary of adverse events
 Summary of adverse events
Fig. 5.

Average CRST-B scores overlaying percent of patients experiencing gait imbalance. Error bars denote standard error of mean.

Fig. 5.

Average CRST-B scores overlaying percent of patients experiencing gait imbalance. Error bars denote standard error of mean.

Close modal

MRgFUS Evolution of Techniques and Adverse Events

While maximal peak temperature (Fig. 6a) and sonications delivered (Fig. 6b) trended downward with patient treatment order, these trends did not reach significance (r = −0.17, p = 0.10 and r = −0.15 and p = 0.13, Pearson’s coefficient). Adverse event occurrence was compared to patient order to determine if adverse event occurrence was associated with a learning curve. Occurrence of adverse events, specifically gait imbalance and paresthesias, did not cluster near a particular treatment time in the cohort (Fig. 6c).

Fig. 6.

MRgFUS side-effect trends. Line graph demonstrating decreasing maximal peak temperature (a) and number of sonications (b) per treatment with increasing treatment order (n= 108). c Adverse events present at 6 months in relation to patient treatment order (n= 82).

Fig. 6.

MRgFUS side-effect trends. Line graph demonstrating decreasing maximal peak temperature (a) and number of sonications (b) per treatment with increasing treatment order (n= 108). c Adverse events present at 6 months in relation to patient treatment order (n= 82).

Close modal

Program Growth and Patient Referral Outcomes

Referral data for the first 79 patients treated were available for analysis. During this time (January 2020 to August 2021), a total of 543 referrals for MRgFUS were made directly to our program. Of these, 252 patients passed initial screening and were evaluated (46.41%). From these 252 evaluated patients, 73 declined treatment, 100 did not quality for MRgFUS treatment (low SDR, poor cognition, severe baseline balance difficulties), and 79 ultimately completed treatment (Fig. 7a). Referral numbers grew from an average of 12.2 ± 7.2 per month in 2020 to 49.6 ± 9.0 per month in 2021 (Fig. 7b).

Fig. 7.

Patient referral outcomes and program growth. a Pie chart demonstrating outcomes of 543 total referrals received between January 2020 and August 2021. b Stacked bar chart demonstrating referral number and outcome by month. LTFU, lost to follow-up.

Fig. 7.

Patient referral outcomes and program growth. a Pie chart demonstrating outcomes of 543 total referrals received between January 2020 and August 2021. b Stacked bar chart demonstrating referral number and outcome by month. LTFU, lost to follow-up.

Close modal

This study presents the initial experience, treatment outcomes, and adverse events after establishment of a new MRgFUS program. Establishment of an MRgFUS program as an adjunct to an already established interventional movement disorders surgical program is feasible and effective with significant reduction in tremors at 3, 6, and 12 months while maintaining an adverse event profile similar to previously published results. Here, we also discuss nuances and evolution of the clinical workflow and the care team assembled to mitigate the initial learning curve and aid in successful MRgFUS treatments.

Clinical Care Team

Our program’s core clinical care team consists of a clinical care coordinator, movement disorders neurologists, APP, RN, radiology technician, and neurosurgeon. These members remain consistent throughout all treatments, which ensures familiarity and accrual of collective experience as treatments accumulate. Later in our program, when it became clear that gait imbalance was emerging as a potential side effect of MRgFUS treatment, a physical therapist with specialization in gait and balance therapy was added to the team. Experienced DBS centers will likely have many of these same team members, enabling ease of adoption of the workflow.

Previous studies have noted the use of an anesthesia team during the procedure [14, 15]. Patients tolerated the procedure well through a combination of local anesthetic for pain, ondansetron for dizziness, and verbal reassurance from the APP/RN team which obviated the need for an anesthesiologist. No cases were aborted due to patient tolerance, and we did not encounter any adverse events attributed to lack of anesthesia.

Outcomes

Patients were evaluated using the CRST-B scale at baseline, 3-, 6-, and 12-month intervals. In this study, tremor improved by 84.5%, 79.8%, and 72.2% at 3, 6, and 12 months, respectively, which appear to be concordant with the outcomes seen at other centers [1, 2, 6, 8, 11, 16]. CRST-B evaluates specific motor tasks including handwriting, spiral drawing, and water pouring. One limitation of our study is the use of CRST-B to monitor tremor outcomes in both ET and PD patients. PD tremors decrease in amplitude with actions such as handwriting; thus, using this scale might underrepresent tremor improvement in these patients.

Eight out of our 116 treatments were technically unsuccessful. Despite having reasonable SDR values (0.42 ± 0.1, mean ± SD), we were unable to achieve sufficient temperatures to create a lesion in these patients despite maximal energy and power delivery. While age, baseline CRST score, SDR, and skull volume have been shown to predict response to MRgFUS, the difficulty in predicting therapeutic ablation in some patients suggests the need for a more robust method to predict skull responses to phased array ultrasound energy [9, 17]. Some authors have suggested skull thickness, angle of incidence, and local variance of skull density as alternate factors that may influence treatment outcome, but these variables need to be evaluated in larger studies [18, 19]. Repeated sonications with temperatures in the 50–54°C range have been reported to produce long-term durability in tremor control as a treatment approach for low SDR skulls [20]. Anecdotally, we have also noted success in treating skull SDRs ranging between 0.3 and 0.4 by repeated sonications that achieve temperatures in the 50–54°C range. However, long-term efficacy evaluation beyond 6 months is being evaluated.

Tremor recurrence rate of 21.9% (9/41) was noted in our series of patients at 1-year follow-up. This is consistent with the current literature reporting recurrence ranges of 0–33% [1, 2, 7, 17]. The mechanism of tremor return is a matter of current investigation. It is likely that a combination of lesion retraction [21, 22], inadequate therapeutic temperature at the lesion site, and possible involvement of extra-VIM tremor generators all contribute to tremor recurrence in various patients. Utilization of tractography to delineate the relevant critical tracts and the relationship with the ablation volume may further our understanding of this issue.

Adverse Events

Common adverse events at 6 months in our series included gait instability, paresthesia, dysarthria, and headaches in 24.4%, 7.3%, 6.1%, and 1.2% of patients, respectively. These findings are consistent with prior reports [1, 2, 6, 8, 11, 16]. In our cohort, the majority of patients developing transient numbness did so in a delayed fashion, which is likely related to edema encroachment into the neighboring ventral caudal (Vc) nucleus [23]. Sensory disturbances often involved the peri-oral region, thumb-index finger, or tongue. Focal examination of the face, buccal region, tongue, and hand in comparison to the control side is essential for early identification of sensory deficits.

Gait instability has been identified as a common long-term side effect of MRgFUS thalamotomy [6, 8, 22, 24, 25]. Despite the high prevalence of this adverse outcome, no specific pathogenic mechanism has been clearly described. As published studies mostly rely on patients’ subjective reporting of their gait and balance, lack of objective baseline measurements of gait and balance make this spectrum of clinical outcomes difficult to categorize. Several hypotheses have been put forth regarding the origin of gait and balance decline after MRgFUS [8, 26‒28]. The timeline of perilesional edema formation in VIM seems to correlate with the onset and cessation of balance changes postoperatively [9, 22]. The spread of edema infero-laterally has been shown to strongly correlate with post-procedure gait deficit development [23, 27, 29, 30]. Thus, involvement of the cerebellothalamic pathway has been suggested to mediate balance disturbances [27, 29]. The dentatorubothalamic tract is a major efferent cerebellar outflow useful for VIM targeting during MRgFUS and DBS procedures. Due to its close anatomical relationship with the VIM, the potential contribution of dentatorubothalamic tract to the development of gait instability is likely and warrants further investigation.

Based on these observations, we made two modifications. First, all patients with pre-existing gait or balance issues underwent formal physical therapy before and after MRgFUS to optimize balance and gait. Second, during each treatment, we meticulously evaluated the caudal extension of the heat map on alignment sonications in both coronal and sagittal planes. The initial targeting was modified to 1.5 millimeters above the AC-PC plane with a second lesion 1.5 and 1 millimeter superior and anterior to the first lesion, respectively, after case 72. We noticed a slight decrease in gait imbalance with no change in tremor control; thus, we continued to adjust the initial targeting superior (2.0 millimeters above the AC-PC plane) in an attempt to further decrease gait imbalance occurrence. These modifications occurred after case number 113 and thus are not reflected in the above results.

Dysarthria rates were higher than the published literature at 23.2% at 24 h follow-up [2, 29]. This side effect decreased with time and became consistent with the literature at 6 months and 1 year. Why these initially high rates of dysarthria occurred is unclear but may be related to the learning curve associated with the procedure. Also, to capture this side effect, patients were specifically asked about symptoms of “slurred speech,” which may have increased recognition of the symptom. On review of our imaging, there was no difference in laterality of our targeting coordinates from the literature and we did not visualize significant encroachment of the internal capsule as would be expected to lead to this adverse effect. However, a recent study noted dysarthria to be more frequent in patients with larger lesions and those with lesion margins in the infero-lateral direction [22]. While not included in the above results, our modification of initial targeting to 2.0 mm superior to AC-PC may lead to improvement in rates of dysarthria and will be a subject of further study.

The present study describes the relevant workflow for establishing a multi-disciplinary program to inform, manage, and treat patients with MRgFUS. Feasibility of establishing an MRgFUS program with a relatively rapid increase in evaluation and treatment of patients while maintaining high standards of safety and quality is demonstrated. While efficacious and durable, adverse events occur and can be permanent in MRgFUS. Future studies should aim at reducing complications while improving long-term efficacy of MRgFUS.

This study was approved by the Rush University Institutional Review Board, IRB identifier number 20051905. Patient consent was not required under this IRB study protocol as this research only involved information collection and analysis of deidentified patient data.

Sepehr Sani discloses paid proctorship from Insightec and fellowship training grants from Boston Scientific, Abbott, and Medtronic. Neepa Patel is a consultant for Revance Therapeutics, Abbott, and Boston Scientific and a speaker for Teva Pharmaceuticals.

There were no sources of funding for this study.

Conception and experimental design: Daniel Y. Zhang, Jacob Mazza, and Sepehr Sani; data acquisition: Daniel Y. Zhang, John J. Pearce, Jacob Mazza, Edgar Petrosyan, and Alireza Borghei; drafting of manuscript: Daniel Y. Zhang, John J. Pearce, and Sepehr Sani; revision of manuscript and final approval: Daniel Y. Zhang, John J. Pearce, Jacob Mazza, Edgar Petrosyan, Alireza Borghei, Neepa Patel, and Sepehr Sani; and project supervision: Sepehr Sani.

All data generated or analyzed during this study are included in this article. Further inquiries can be directed to the corresponding author.

1.
Lipsman N, Schwartz ML, Huang Y, Lee L, Sankar T, Chapman M, et al. MR-guided focused ultrasound thalamotomy for essential tremor: a proof-of-concept study. Lancet Neurol. 2013;12(5):462–8.
2.
Elias WJ, Lipsman N, Ondo WG, Ghanouni P, Kim YG, Lee W, et al. A randomized trial of focused ultrasound thalamotomy for essential tremor. N Engl J Med. 2016;375(8):730–9.
3.
Bond AE, Shah BB, Huss DS, Dallapiazza RF, Warren A, Harrison MB, et al. Safety and efficacy of focused ultrasound thalamotomy for patients with medication-refractory, tremor-dominant Parkinson disease: a randomized clinical trial. JAMA Neurol. 2017;74(12):1412–8.
4.
Okada A, Morita Y, Fukunishi H, Takeichi K, Murakami T. Non-invasive magnetic resonance-guided focused ultrasound treatment of uterine fibroids in a large Japanese population: impact of the learning curve on patient outcome. Ultrasound Obstet Gynecol. 2009;34(5):579–83.
5.
Krishna V, Sammartino F, Cosgrove R, Ghanouni P, Schwartz M, Gwinn R, et al. Predictors of outcomes after focused ultrasound thalamotomy. Neurosurgery. 2020;87(2):229–37.
6.
Mohammed N, Patra D, Nanda A. A meta-analysis of outcomes and complications of magnetic resonance-guided focused ultrasound in the treatment of essential tremor. Neurosurg Focus. 2018;44(2):E4.
7.
Harary M, Segar DJ, Hayes MT, Cosgrove GR. Unilateral thalamic deep brain stimulation versus focused ultrasound thalamotomy for essential tremor. World Neurosurg. 2019;126:e144–e152.
8.
Giordano M, Caccavella VM, Zaed I, Foglia Manzillo L, Montano N, Olivi A, et al. Comparison between deep brain stimulation and magnetic resonance-guided focused ultrasound in the treatment of essential tremor: a systematic review and pooled analysis of functional outcomes. J Neurol Neurosurg Psychiatry. 2020;91(12):1270–8.
9.
Chang KW, Park YS, Chang JW. Skull factors affecting outcomes of magnetic resonance-guided focused ultrasound for patients with essential tremor. Yonsei Med J. 2019;60(8):768–73.
10.
Meng Y, Jones RM, Davidson B, Huang Y, Pople CB, Surendrakumar S, et al. Technical principles and clinical workflow of transcranial MR-guided focused ultrasound. Stereotact Funct Neurosurg. 2021;99(4):329–42.
11.
Elias WJ, Huss D, Voss T, Loomba J, Khaled M, Zadicario E, et al. A pilot study of focused ultrasound thalamotomy for essential tremor. N Engl J Med. 2013;369(7):640–8.
12.
Fahn S TE, Marin C. Clinical rating scale for tremor. In: Jankovic J TE, editor. Parkinson’s disease and movement disorders. Baltimore: Williams &amp; WIlkins; 1993. p. 225–34.
13.
Dindo D, Demartines N, Clavien PA. Classification of surgical complications: a new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann Surg. 2004;240(2):205–13.
14.
Sinai A, Katz Y, Zaaroor M, Sandler O, Schlesinger I. The role of the anesthesiologist during magnetic resonance-guided focused ultrasound thalamotomy for tremor: a single-center experience. Parkinsons Dis. 2018 Jul 5;2018:9764807.
15.
Chapman M, Park A, Schwartz M, Tarshis J. Anesthesia considerations of magnetic resonance imaging-guided focused ultrasound thalamotomy for essential tremor: a case series. Can J Anaesth. 2020;67(7):877–84.
16.
Miller WK, Becker KN, Caras AJ, Mansour TR, Mays MT, Rashid M, et al. Magnetic resonance-guided focused ultrasound treatment for essential tremor shows sustained efficacy: a meta-analysis. Neurosurg Rev. 2022;45(1):533–44.
17.
Fukutome K, Kuga Y, Ohnishi H, Hirabayashi H, Nakase H. What factors impact the clinical outcome of magnetic resonance imaging-guided focused ultrasound thalamotomy for essential tremor? J Neurosurg. 2020;134(5):1618–23.
18.
Chazen JL, Sarva H, Stieg PE, Min RJ, Ballon DJ, Pryor KO, et al. Clinical improvement associated with targeted interruption of the cerebellothalamic tract following MR-guided focused ultrasound for essential tremor. J Neurosurg. 2018;129(2):315–23.
19.
Abe K, Taira T. Focused ultrasound treatment, present and future. Neurol Med Chir. 2017;57(8):386–91.
20.
Jones RM, Kamps S, Huang Y, Scantlebury N, Lipsman N, Schwartz ML, et al. Accumulated thermal dose in MRI-guided focused ultrasound for essential tremor: repeated sonications with low focal temperatures. J Neurosurg. 2019;132(6):1802–9.
21.
Weidman EK, Kaplitt MG, Strybing K, Chazen JL. Repeat magnetic resonance imaging-guided focused ultrasound thalamotomy for recurrent essential tremor: case report and review of MRI findings. J Neurosurg. 2020;132:211–6.
22.
Harary M, Essayed WI, Valdes PA, McDannold N, Cosgrove GR. Volumetric analysis of magnetic resonance-guided focused ultrasound thalamotomy lesions. Neurosurg Focus. 2018;44(2):E6.
23.
Segar DJ, Lak AM, Lee S, Harary M, Chavakula V, Lauro P, et al. Lesion location and lesion creation affect outcomes after focused ultrasound thalamotomy. Brain. 2021;144(10):3089–100.
24.
Boutet A, Ranjan M, Zhong J, Germann J, Xu D, Schwartz ML, et al. Focused ultrasound thalamotomy location determines clinical benefits in patients with essential tremor. Brain. 2018;141(12):3405–14.
25.
Chang JW, Park CK, Lipsman N, Schwartz ML, Ghanouni P, Henderson JM, et al. A prospective trial of magnetic resonance-guided focused ultrasound thalamotomy for essential tremor: results at the 2-year follow-up. Ann Neurol. 2018;83(1):107–14.
26.
Gallay MN, Moser D, Jeanmonod D. MR-guided focused ultrasound cerebellothalamic tractotomy for chronic therapy-resistant essential tremor: anatomical target reappraisal and clinical results. J Neurosurg. 2021;134(2):376–85.
27.
Kim MJ, Park SH, Chang KW, Kim Y, Gao J, Kovalevsky M, et al. Technical and operative factors affecting magnetic resonance imaging-guided focused ultrasound thalamotomy for essential tremor: experience from 250 treatments. J Neurosurg. 2021;135(6):1780–8.
28.
Agrawal M, Garg K, Samala R, Rajan R, Naik V, Singh M. Outcome and complications of MR guided focused ultrasound for essential tremor: a systematic review and meta-analysis. Front Neurol. 2021;12:654711.
29.
Park YS, Jung NY, Na YC, Chang JW. Four-year follow-up results of magnetic resonance-guided focused ultrasound thalamotomy for essential tremor. Mov Disord. 2019;34(5):727–34.
30.
Sammartino F, Yeh FC, Krishna V. Intraoperative lesion characterization after focused ultrasound thalamotomy. J Neurosurg. 2022;137(2):459–67.