MRgFUS treatment of dystonia

General Information

Dystonia is a clinical syndrome characterized by involuntary, arrhythmic twisting movements in various parts of the body, as well as dynamic changes in muscle tone, leading to the formation of pathological postures or posture-dependent changes (Levin et al., 2022). Dystonia is characterized by: stereotypical contractions in a specific muscle group (rotational, flexion, or extension pattern, etc.); increased hyperkinesis during voluntary movements and its change with posture changes; improved control over involuntary dystonic hyperkinesias with certain tactile or proprioceptive stimuli (corrective gestures); involuntary contraction of additional muscle groups that do not anatomically coincide with the primary dystonic movement (the phenomenon of “overflow dystonia”), usually observed at the peak of a dystonic spasm Geyer, Bressman, 2006; Sitburana et al., 2009; Albanese et al., 2019).

Dystonic syndrome develops gradually: initially, hyperkinesias occur only for a short time and/or only during certain actions (positions), but over time their duration increases, the severity of dystonia escalates, pathological postures appear, and sometimes contractures Albanese et al., 2019). There is also a gradual spread of dystonic manifestations to various regions of the body (in generalized forms). Some patients with dystonia may experience one or more periods of complete or partial remission lasting from several hours to several years in the early years of the disease.

A special manifestation is dystonic tremor (Illarioshkin, Ivanova-Smolenskaya, 2011). It typically has a frequency of 3–7 oscillations per second and is equally common in generalized, segmental, or focal/multifocal dystonia. Its clinical features are similar to the dystonic hyperkinesis characteristics discussed above, which significantly facilitates diagnosis. In particular, dystonic tremor is characterized by significant variability, asymmetry, and dependence on maintaining a specific posture, intensification during voluntary movements or attempts to resist dystonic spasm, weakening at rest, and the presence of corrective gestures.

According to etiology, the following are distinguished: 1) primary dystonia – all forms (usually genetic), where dystonia is the only symptom of the disease (may only be combined with tremor), with no laboratory changes or clear signs of pathology in neuroimaging studies (CT, MRI); 2) dystonia plus – forms characterized by a combination of dystonic syndrome with myoclonus, parkinsonism, or chorea, where clinical and laboratory results suggest certain neurochemical disturbances without signs of neurodegeneration (dopa-responsive dystonia, myoclonus-dystonia, etc.); 3) secondary dystonias – drug-induced forms and syndromes caused by acquired reasons and external factors (neurotrauma, stroke, neuroinfections, demyelinating processes, etc.). Dystonia can also be one of the manifestations of a large number of multisystem neurodegenerative diseases ( Albanese et al., 2019).

The classification of dystonia by the prevalence of hyperkinesis is also generally accepted:

• focal dystonia (involving one part of the body – oromandibular dystonia, CD, etc.);
• segmental dystonia (involving ≥2 adjacent body areas, for example, Meige’s syndrome – a combination of blepharospasm, oromandibular dystonia, and CD)
• multifocal dystonia (involving ≥2 distant body areas, such as blepharospasm and foot dystonia)
• hemidystonia (involving muscles on one side of the body, which usually clearly indicates the secondary nature of dystonia and the location of the pathological process in the contralateral hemisphere of the brain)
• generalized dystonia (involving muscles of one or both legs, the torso, and at least one other part of the body)

Hereditary forms of dystonia are distinguished (they usually debut in childhood and tend to generalize) and sporadic forms (more often manifest in adulthood as focal phenotypes). To date, more than 30 genes associated with the development of hereditary dystonias are known (Levin et al., 2022; Domingo et al., 2021).

The overall prevalence of dystonia may be 3–11 cases per 100,000 population for generalized forms and 30–60 cases for focal forms ( Steeves et al., 2012). Thus, within the framework of movement disorders, dystonia is second in prevalence only to ET and PD. Among the various types of dystonia, CD (focal form) is the most common – 4.98 per 100,000 population ( Steeves et al., 2012).

Dystonic syndromes significantly affect the quality of life: 25 to 50% of patients suffer from depression, and pain is one of the key complaints in 67–75% of patients. The deterioration in quality of life and impaired motor activity impact the professional activities of patients with dystonia, making the problem socially and economically significant ( Butler et al., 1998).

Treatment of dystonias is a challenging task. Medication therapy is highly effective only for a few forms: for instance, in dopa-responsive dystonia, small doses of levodopa have a dramatic effect, and in patients with ADCY5-with associated dystonia (dyskinesia), significant relief can be achieved with caffeine intake. Unfortunately, in the vast majority of cases of dystonia, such a favorable outcome from medication treatment is not expected. Usually, the first step involves attempts to prescribe anticonvulsants, benzodiazepines, anticholinergics, muscle relaxants, tetrabenazine, clozapine, etc., including in various combinations. Their intake may be accompanied by a certain (sometimes even persistent) symptomatic effect; however, most often, the results of such therapy are quite modest, and increasing the dosages of the drugs used leads to pronounced side effects (drowsiness, impaired coordination, general weakness, decreased mental performance, dry mouth, accommodation disorders, etc.). Particularly unfavorable for conservative therapy are generalized (dopa-unresponsive) forms of idiopathic dystonia.

In focal forms, the method of choice is the use of intramuscular injections of botulinum toxin ( Albanese et al., 2019), which in most cases allows for the complete or partial alleviation of dystonic spasms for an average period of 3 to 6 months. After this, re-administration of the drug is required. In addition to its peripheral action, botulinum toxin has a favorable effect on the central pathophysiology of dystonia by reducing afferentation from muscles involved in hyperkinesis (Levin et al., 2022). Cases of prolonged “therapeutic remission” have been described with regular administration of botulinum toxin, attributed to its beneficial effects on peripheral and central mechanisms of neuroplasticity. Repeat courses of botulinum therapy for patients with focal dystonias have been successfully used worldwide for over 40 years. However, in 6–14% of cases, botulinum toxin proves to be less effective. Treating patients with retrocollis and anterocollis, as well as with combined forms of CD, presents a particular challenge. Surgical treatment is indicated when medication is ineffective, and there is progression of segmental or generalized dystonia, or insufficient control of symptoms of focal dystonias.

Surgical Treatment of Dystonias

The first operation for spasmodic torticollis dates back to the mid XVII century, when the German surgeon Isaak Minnius performed a transection of the sternocleidomastoid muscle. In XIX in the century, I.V. Buyalsky first performed the transection of the accessory nerve in the neck for spasmodic torticollis, later W.W. Keen carried out the crossing of the first 3 anterior cervical roots, and at the beginning of the 20th century O. Foerster developed a technique of posterior rhizotomy for such patients. The effectiveness of peripheral operations, which continued to improve, was undeniable; however, extensive denervation of the neck muscles leads to serious complications (flaccid paralysis of the muscles, sensory disturbances, vertebral artery injuries), up to fatal outcomes. Therefore, surgeries at the level of muscles, nerves, and roots, as well as on the conduction pathways of the spinal cord (such attempts were also made), are currently not used for dystonias of any localization and are of only historical interest (Tyurnikov et al., 2007)

The basis of modern surgical treatment for patients with dystonic syndromes is various types of functional stereotactic operations on the brain. The two most adequate interventions are considered to be destruction VIM and some other subcortical nuclei and, mainly, DBS with an impact primarily on the globus pallidus ( GPi). Destructive surgeries, widely used in clinical practice since the mid-20th century and having played a significant role in treating patients with severe, disabling forms of dystonia, have become c 1990-years largely giving way to the method DBS, primarily due to the safety of bilateral stimulation and the ability to perform (if necessary) fine, dynamic adjustment of the stimulation mode

First Results of Bilateral Stimulation GPi were published P. Coubes et al. (1999). In the authors’ clinic, an 8-year-old girl with severe primary generalized dystonia, bedridden and requiring constant sedation and mechanical ventilation, underwent surgery. Six months after the operation, the patient was able to attend a regular school. Currently, worldwide, the number of patients with generalized, segmental, and focal forms of dystonia successfully receiving treatment through DBS GPi, runs into thousands. Bilateral surgery c conducting DBS GPi until recently, remains the most radical and effective method of providing real help to patients with severe movement disorders, impaired walking, and self-care (Levin et al., 2022; Alterman, Snyder, 2007).

Thalamic DBS may be quite successful for dystonic tremor, especially for DYT1-form of the disease. In primary writing tremor, stimulation VIM accompanied by almost complete disappearance of tremor ( Racette et al., 2001). In some cases, such patients leave the generator turned off for most of the day and turn it on only when they need to write something.

There are also several recent reports in the literature about the successful application of DBS on the subthalamic nucleus area in the treatment of patients with primary (generalized, segmental, cervical) dystonia, tardive dystonia, dystonia-parkinsonism, isolated tongue dystonia ( Tisch, 2018; Liu et al., 2019; Wu et al., 2019; Li H. et al., 2021; Mercado-Pimentel et al., 2021). More detailed results of traditional functional stereotactic interventions for dystonia are presented in Chapter 1.

Treatment of Dystonia with MRgFUS

The global experience of surgical treatment of dystonias using the new MRgFUS method remains limited. There are about 15 publications on this topic in the literature, presenting a preliminary assessment of the dynamics of the clinical condition of patients after stereotactic ablation of subcortical nuclei using the MRgFUS method, conducted in several clinics worldwide, based on relatively small groups of patients with various forms of dystonias. Japanese researchers can be considered pioneers in this field S. Horisawa и T. Taira.

The initial results of using MRgFUS for dystonias indicate that this method, in terms of effectiveness, apparently does not fall short DBS. The ventrooral nucleus of the thalamus was used as a target for ultrasound ablation ( VO) и PTT (campotomy), only in a few reports is there mention of targeting GPi. The main work is currently limited to focal dystonias, dystonia-parkinsonism, and dystonic tremor. According to several authors Golfrè Andreasi et al., 2024; Peters et al., 2024), Thalamotomy using the MRgFUS method appears to be a very promising and less invasive alternative DBS to eliminate dystonic tremor, however, opinions regarding the most appropriate target VIM, GPi, PTT and others) differ, requiring further accumulation of experience

In Table 8.1, comparative data from some recent publications are presented, focusing on the analysis of the effectiveness of surgical treatment of various forms of dystonia using MRgFUS and DBS.

Thus, the treatment of dystonias using the MRgFUS method is at an early stage of development, and practically every newly described series of cases and even individual cases of different forms of this clinically heterogeneous movement disorder subjected to MRgFUS are of significant interest.

Table 8.1. Global Experience in Surgical Stereotactic Treatment of Dystonia: Comparison of Recent Studies in MRgFUS and DBS.

Personal Experience in Treating Patients with Dystonia Using MRgFUS

In Russia, the first stereotactic surgeries for patients with dystonia using the MRgFUS method were performed at the V.S. Buzaev International Medical Centre (Ufa) (Galimova et al., 2023; Galimova et al., 2022).

Treatment using the MRgFUS method was performed on 19 patients with various forms of dystonia. Among them were 13 patients with CD, 3 patients with myoclonus-dystonia, and 1 patient each with multifocal, tardive, and segmental dystonia. The following scales were used to assess the severity of the clinical picture: CRST, TWSTRS, UDRS, Burke-Fahn-Marsden Dystonia Rating Scale Burke–Fahn–Marsden Dystonia Rating Scale, BFMDRS) (Appendix 4)

We used various targets or combinations of targets ( PTT, VO, VIM, ZI, GPi), selecting them individually for each patient based on:

• described in the literature results of radiofrequency ablations and individual clinical cases of MRgFUS application in patients with dystonia, since for this condition there is currently no scientific basis for the advantages of any particular target
• clinical intraoperative assessment during trial reversible ultrasound interventions, which allow modeling the effect on a specific brain area and finding the most effective target for the patient

Targets were subjected to at least 2 exposures to ultrasound at temperatures above 55°C. The duration of operations ranged from 150 to 240 minutes, with energy variations from 20,096 to 35,731 J and temperature fluctuations in the range of 54–62°C C. During the trial sonications and final target selection, clinical focus was on the severity of dystonic symptoms (including dystonic hand tremor), assessment of muscle tone by palpation, and the patient’s sensations. Side effects were also monitored after each ultrasound exposure.

Given the diversity of phenotypes and the small number of operated patients with specific variants of dystonia, we present the obtained results not so much in a statistically generalized form, but as a series of clinical descriptions, some of which have global precedence

Cervical dystonia

Cervical dystonia is the most common form of focal dystonia, with a prevalence of 4.98 per 100,000 population ( Steeves et al., 2012). Cervical dystonia is particularly difficult to treat with botulinum toxin due to the complex anatomy of the neck muscles and the polymorphism of clinical manifestations of the developing motor syndrome. Therefore, improving surgical approaches to the treatment of cervical dystonia is considered a very important task.

In our clinic (V.S. Buzaev International Medical Centre, Ufa), treatment using the MRgFUS method was conducted on 13 patients with movement disorders. The average age of the patients was 42 [39; 53] years. In all cases, the family history for dystonia or other movement disorders was negative. All patients with CD received several courses of botulinum toxin injections (more than 5) and were refractory to this type of therapy. The possibility DBS was rejected due to subjective aversion to the implantation of a mechanical device in the brain (patient refusal) or due to difficulty accessing medical centers that can provide continuous monitoring with selection and adjustment of stimulation parameters

As targets for MRgFUS in this category of patients, we used PTT, VO, ZI ((rese) or a combination of targets (Table 8.2). Since there are currently no clearly scientifically based standards and algorithms for the destruction of any single target in patients with movement disorders, the choice was made individually, taking into account the experience described in the literature with specific features of the clinical syndrome. The median time for treatment using the MRgFUS method was 117 [79; 139] min, median number of sonications – 12.0 [11,0; 14,5].

The average clinical follow-up period for patients was 13.3 ± 3.4 months, from July 2021 to April 2023. Before treatment with MRgFUS, the average total score for TWSTRS (severity assessment of diabetes mellitus) was 19.0 [15,2; 22,2], after treatment (in the last available observation period) – 5.5 [4,0; 9,2]. Thus, as a result of the surgery, patients achieved an improvement of 71.7 [56,3; 77,8]% (r = 0.0025 by the paired Wilcoxon test) (Fig. 8.1)

All patients underwent MRI of the brain immediately and 2 hours after completing treatment with MRgFUS to assess the resulting lesions and edema around the target points (Fig. 8.2)

After the procedure, 6 patients experienced mild side effects such as gait disturbances and postural instability, which persisted for 3 weeks. Two patients had pronounced logorrhea, which completely regressed within 1 month while taking quetiapine (25 mg/day). Two patients experienced memory decline 1 month after treatment with MRgFUS, followed by gradual recovery by the end of the first year of observation. Two patients showed changes in handwriting with the development of slight micrographia and gradual recovery during postoperative monitoring.

In one patient with severe head tremor, hyperkinesis returned 6 months after the operation. He underwent repeat treatment 9 months after the first procedure, and in the following 4 months, there was no recurrence of head tremor symptoms. It should be noted that none of the operated patients experienced a return of laterocollis or torticollis symptoms.

As examples, we provide a brief description of several clinical observations of patients with diabetes mellitus operated on using the MRgFUS method.

Woman, 39 years old , has been ill since 2006, when isolated head tremor first appeared, gradually intensifying. In 2012, a diagnosis of ET was made, and clonazepam 2 mg/day was prescribed. The patient noted a positive effect with the cessation of tremor when taking the medication, but the effectiveness of clonazepam gradually decreased, and its dosage could not be increased due to the side effect of drowsiness. In 2020, head tilt to the right appeared, and the diagnosis was revised in favor of idiopathic CD. Courses of botulinum therapy were started, initially with a positive effect, but their effectiveness gradually decreased and almost disappeared after 4 courses. Since 2021, she has been taking propranolol up to 120 mg/day, with some reduction in head tremor, but with a short-term and insufficient effect. The patient underwent treatment using the MRgFUS method: the targets were selected PTT и VO on the left, after the operation, a good effect was noted in the form of a significant reduction in head tremor hyperkinesis and the disappearance of laterocollis. However, after 3 months, there was a 70% recurrence of head tremor, while the symptoms of laterocollis were still absent. After 10 months, a repeat operation was performed with different targets – VIM on the right, ZI on the left. After repeated exposure to MRgFUS, a 90% regression of head tremor was achieved; the indicator for TWSTRS decreased from 4 to 0 points. The treatment was deemed effective.

Man, 30 years old , complaints of head tilt to the left and its tremor. Parents noticed episodic head tremor at 3 years old, and by 15, the head tremor intensified, becoming noticeable to others and the patient himself. A diagnosis of ET was established. At 23, left-sided laterocollis suddenly developed subacutely, and the diagnosis was revised in favor of focal idiopathic CD. Botulinum therapy was prescribed with significant improvement, and subsequently, botulinum therapy courses were repeated 5 times. The latest botulinum therapy courses were ineffective, and clonazepam was taken up to 4 mg/day with a slight positive effect. The patient underwent treatment with MRgFUS: after ablation PTT on the right, there was a subjective improvement of 85%. However, the patient had difficulty enduring the treatment – during the MRgFUS procedure, headache, nausea, and a single instance of vomiting occurred. Of the planned target points, it was only possible to perform the impact on PTT, but with a good result and a reduction in the total score for TWSTRS from 9 to 4. The effect lasts for 1 year, the treatment conducted is considered effective

Woman, 32 years old, dystonic head tremor with a tilt to the right. She has been ill since 2007 when episodic head twitching first appeared, gradually increasing in duration. Positive family history: head tremor is present in the older sister, head tilt in the father. In 2009, the patient was diagnosed with ET and prescribed propranolol, which she took for 1 month with little effect. In 2015, a diagnosis of CD was established. Clonazepam 0.5 mg/day was prescribed, but even at this initial dose, poor tolerance of the drug was noted, and it was discontinued. A course of botulinum therapy was conducted with significant improvement, and such courses were subsequently conducted regularly, but since 2021, their effect gradually decreased and shortened. Currently, she occasionally takes propranolol at a dose of 20–40 mg/day. The patient underwent treatment with the MRgFUS method: impact on the PTT и ZI on the left, VO crights. Achieved subjective improvement of 80%, indicator by TWSTRS decreased from 17 to 5 points. The effect lasts for 10 months, and the treatment is considered effective.

Myoclonus-dystonia

Myoclonus-dystonia (myoclonic dystonia) is a rare form of dystonia that, according to the modern classification, belongs to the “dystonia plus” group. The prevalence of myoclonus-dystonia is approximately 0.2 per 100,000 population ( https://rarediseases. info.nih.gov/diseases/7139/myoclonus-dystonia). Idiopathic forms of myoclonus-dystonia (usually genetically determined) and secondary forms are distinguished

Among the secondary forms, post-hypoxic myoclonus-dystonia—Lance-Adams syndrome—should be mentioned. This is a chronic condition characterized by peculiar myoclonus-like hyperkinesias of the facial, limb, and trunk muscles, occurring in the weeks following brain hypoxia experienced by the patient (usually due to cardiac arrest) Freund et al., 2017). Lance–Adams syndrome – a very rare disease ( Zhu et al., 2018). In a study by the University of Ontario, it was noted that 12.5% of people who survived cardiac arrest had some moderate or severe neurological disorders, including Lance–Adams syndrome ( Stiell et al., 2009). Drug therapy for Lance–Adams syndrome is often ineffective. In the literature, there are isolated cases of application DBS, results of which are quite controversial in this category of patients (Ö ztürk et al., 2021).

In our clinic, treatment using the MRgFUS method was performed on 3 patients with myoclonus-dystonia, one of whom had post-hypoxic myoclonus-dystonia (Lance–Adams syndrome). Below are brief descriptions of the clinical observations.

Male, 73 years old , right-handed, has been ill for 10 years. At the first visit to the neurologist, symptoms of segmental dystonia were identified, involving hyperkinesis of the left arm, left-sided torticollis, and myoclonus in the face, neck, arms, and mouth. Treatment with clonazepam at a dose of 4 mg/day was ineffective, and higher doses were intolerable due to unacceptable sedative effects. Levodopa test was negative. Family history negative. Initial overall severity assessment of dystonia according to UDRS made up 38 points, according to TWSTRS – 22 points, on the Unified Myoclonus Rating Scale ( Unified Myoclonus Rating Scale, UMRS) – 84 points. Treatment was conducted using MRgFUS with targeting PTT и VIM on the right. On the first day after treatment, the subjective regression of symptoms was 65%, and upon examination after 3 months, it was already 85%. Indicators for UDRS decreased from 38 to 29 points, according to TWSTRS – c 22 up to 19 points, according to UMRS – from 84 to 22 points.

Woman, 47 years old , with generalized persistent idiopathic myoclonus-dystonia. Onset in early adulthood, with manifestations of right-sided laterocollis and torticollis, as well as involvement of the trunk and lower limbs in the form of postural tremor, resting tremor, and myoclonus of both legs. MRI-guided focused ultrasound was applied to areas GPi и PTT on the left, the subjective regression of symptoms was 50%. The total score for UDRS decreased from 45.5 to 27.5, according to TWSTRS – from 25 to 14, by CRST – from 34 to 21. The patient is satisfied with the result of the 1st stage of treatment; dynamic monitoring continues and the 2nd stage is planned.

Woman, 55 years old , a case of post-hypoxic myoclonus (Lance–Adams syndrome). Severe generalized myoclonus and aphonia developed 8 weeks after traumatic asphyxia in 2019. The patient could not stand and required assistance with care and feeding. Clonazepam, levetiracetam, pregabalin, normokinesin, and levodopa in maximum tolerated doses were ineffective. Consultations were held in several medical centers regarding the possibility of conducting DBS, but the operation was declined due to the lack of global experience in treating patients with Lance–Adams syndrome using this method. Upon examination, the patient exhibited mild spontaneous myoclonic jerks in the right hand. Action myoclonus occurred with every active movement in each limb. Stimulus-induced myoclonus was detected upon tactile stimulation of the right limbs. Due to pronounced negative myoclonus in the legs, the patient required assistance to stand up.

Pallidothalamotractotomy using MRgFUS was performed in January 2022. We selected as the target PTT, since, according to our previous experience in treating dystonia, the impact on this structure is characterized by a favorable safety and efficacy profile. After the surgery, the total score on the UDRS decreased from 49 to 29, by BFMDRS – from 58 to 40, according to UMRS – from 100 to 60. During treatment with MRgFUS, the patient began to communicate with simple words. After treatment, the severity of myoclonus in the right limbs decreased to a mild degree; the intensity of negative myoclonus in the legs decreased, allowing the patient to stand, leaning on a walker or stationary support with both hands, and walk several meters with the help of one person. She could hold objects with each hand. However, the patient retained a range of diverse post-hypoxic neurological symptoms, many of which cannot be eliminated with MRgFUS. Despite documented improvement, the patient’s subjective satisfaction with the achieved result was minimal, raising complex ethical questions about patient selection for such essentially palliative treatment in the future.

We conducted a database search PubMed и Google Scholar by the following keywords: « Lance Adams syndrome», «myoclonus dystonia», «MRgFUS», «focused ultrasound». At the time of writing this chapter, we did not find any cases in the literature of using MRgFUS for the treatment of myoclonus-dystonia, and our experience Gali­mova et al., 2022) turned out to be the only publication on this topic

Other Dystonias (Multifocal, Segmental, Tardive)

We provide brief descriptions of individual cases of other forms of dystonia successfully operated on by us using the MRgFUS method

Male, 57 years old , with multifocal progressive idiopathic dystonia (without family history), involving the distal parts of the arms, masticatory muscles, and right-sided lateroretrocollis. Onset at age 31, the disease is progressing. Has repeatedly received courses of botulinum therapy with limited effect. Treatment with MRgFUS was carried out in stages, with the points of impact selected PTT и VO on the left at the 1st stage of treatment VO on the right – at the 2nd stage. During the treatment, symptom regression was subjectively assessed by the patient at 60%. Indicator by BFMDRS before treatment was 40 points, after treatment – 26 points, the indicator for TWSTRS – 29 and 15 points respectively, the indicator for CRST – 46 and 25 points, respectively

Male, 51 years old , with craniocervical idiopathic dystonia (without family history) with adult-onset and dystonia manifestations more in the left limbs, as well as right-sided laterocollis. In the first stage of treatment, ablation was performed using MRgFUS PTT on the left with a regression of symptom severity subjectively by 50%; score indicators for BFMDRS decreased c 20 up to 5, per UDRS – from 34 to 13, according to TWSTRS – c 17 up to 6. The patient experienced a return of symptoms after 3-4 months, after which the second stage of treatment was conducted: the points of impact were selected GPi и PTT on the right, resulting in the total score for UDRS decreased from 49 to 15.

Male, 39 years old, with tardive orofacial dystonia combined with left-sided laterocollis and torticollis, retrocollis. MRgFUS was performed on PTT и VO on the right VO on the left. As a result, the total score for UDRS decreased from 20 to 6, according to BFMDRS – c 20 up to 6, by TWSTRS – from 27 to 9; subjectively, immediately after the operation, improvement was 55%, and after 5 months – already 90%. It should be noted that within 1 week after the operation, the patient experienced symptoms of logorrhea, which resolved after 1 month.

Thus, our experience indicates that MRgFUS is an effective and safe method for treating patients with various forms of dystonia. If necessary, a repeat non-invasive procedure can be successfully performed in patients who did not achieve optimal clinical effect after the first MRgFUS treatment.

Assessment of head tremor fixed in a stereotactic frame

When treating patients with dystonia (less commonly with other diseases), an important aspect is the objective assessment of head tremor. The challenge is that during treatment with MRgFUS, the patient’s head is fixed with a stereotactic frame, preventing movement during the procedure. While hand tremor control during the operation is easily performed visually using standard tests, assessing the effectiveness of head tremor treatment is complicated due to its rigid fixation.

Existing methods for assessing head tremor fixed in a stereotactic helmet do not meet modern requirements for MRI compatibility, as they affect image quality, interfere with precise surgical procedures due to interference from the electrical wiring system, or make the operation impossible or even dangerous ( Kreiner, 2003). H.J. Kreiner (2003) proposed a method for determining head movements based on recording responses from elements of the stereotactic helmet or the patient’s neck muscles caused by spontaneous head movements; it was suggested to use strain gauges attached to the support elements of the stereotactic helmet, transmitting signals via electrical wires to the interface and operator monitor area. However, this method of data transmission is accompanied by interference, degrading the output on modern MRI scanners, making its application impossible. Additionally, strain resistors require relatively high forces for measurement, indicating low sensitivity of the device. Thus, there is a need to improve the design for head fixation in the MRgFUS device to accurately and safely assess head tremor during surgery.

To ensure MRI compatibility, it is necessary to use strain sensors or gauges that do not contain electronic components and ferromagnetic materials, as they are placed directly in the MRI machine’s operating area. We have proposed a new device for determining spontaneous head movements of the patient in real-time with a high sampling rate and the ability to graphically visualize head movements of the patient, rigidly fixed by a stereotactic helmet. We proposed using a piezo-optical transducer, which can be installed on the structural elements of a standard stereotactic helmet or its mounting elements during MRgFUS treatment. It is known that piezo-optical transducers used for measuring deformations (stresses) have the highest sensitivity compared to others.

The device we developed for detecting spontaneous head movements of a patient using a piezo-optical transducer allows for the recording of stresses on a highly sensitive element caused by elastic deformations of the rod, enabling the determination of movements of the patient’s fixed head. It consists of a sensor integrated into the body of a support screw, optical pathways in the form of optical fiber, and a signal processing interface. The sensor consists of a screw-shaped body with a photoelastic element installed. The body and elements of the device are made from non-ferromagnetic materials such as polymers (e.g., polyamide), non-ferrous metals and their alloys (e.g., duralumin or brass), as well as other types of carbon. This allows the device to be used in the MRI machine’s operational area. Three fiber optic cables are connected to the device, which are routed from the control room into the MRI machine’s magnetic field area. One optical cable strand delivers light from an LED to the sensor, and then the signal goes from the sensor through two optical strands to a dual-area photodetector, returning to the control room from the MRI exposure area. In the control room, outside the MRI machine’s magnetic field, the fiber optic cables are connected to an analog-to-digital converter, which is connected via an interface to a computer. The measured values are transmitted through the interface to a personal computer, where they are graphically visualized in real-time and saved using special software.

Our device differs from the proposed one H.J. Kreiner and taken as a prototype because it does not contain magnetic elements and electrical components, this allows it to be used in the MRI machine’s operating area. It enables real-time graphical visualization of the patient’s head movements, rigidly fixed by a stereotactic helmet, with a high sampling rate (≥5000 measurements per second)

Sensors and/or detectors can be attached to one or several structural elements of the stereotactic frame and/or its mounting elements (Fig. 8.3). In the frame used, four support posts have special screws for head fixation (Fig. 8.4). A transducer or sensor is installed on one of the posts (Fig. 8.5), which registers elastic deformations from the pressure of the head on one of the support screws. The presence of tremor is visualized by the output signal from the optical sensor, which registers stresses from elastic deformations on the structural element of the stereotactic helmet. The light beam from the light source, located in the operator’s area, travels through the optical fiber to the sensor’s sensitive element and returns to the photodetector with a magnitude proportional to the stress magnitude from elastic deformations on the structural element of the stereotactic helmet caused by head tremor. The amplitude of the output signal (transmitted by the sensor to the monitoring system for visual display) is used to assess the severity of head tremor hyperkinesis.

In some model variants, it is possible to use multiple sensors installed on both the structural elements of the stereotactic helmet or its mounting elements, as well as on the neck muscles involved in head tremor. Visual information is displayed from the sensors independently and in parallel, allowing for more precise monitoring of the patient’s condition and minimizing the possibility of error during the treatment procedure.

The application of this method does not require any structural or technological changes to the existing equipment for treatment using MRgFUS, and the sensor is installed reliably through a mechanical method without using glue. Establishing a connection with the operator does not require complex, costly work, eliminates possible magnetic and electrical interference, and does not require expenses for shielding the data transmission line to reduce the level of “noise”.

In Fig. 8.6, the sensor manufactured and assembled for the project is shown, in Fig. 8.7, the entire set for measuring head tremor with the sensor attached to the stand and corresponding devices is presented. In Fig. 8.8, a screenshot of the software with tremor visualization is provided.

The device we developed and tested for assessing head tremor, fixed in a stereotactic frame, proved to be very useful and informative during MRgFUS procedures. Considering the possibilities for its further modernization, the device can also be used in other areas of modern stereotactic neurosurgery