Principles of Organizing an MRgFUS Center
To achieve optimal treatment results using MRgFUS technology, the proper functioning of the relevant medical center is extremely important. This concerns both specialized equipment and the organization of the operating room, as well as the coordinated actions of the entire team of specialists, including training in this complex technique.
Equipment
Neurosurgical focused ultrasound device for the treatment of neurological disorders ( ExAblate, InSightec) is a specially designed helmet with a phased array transducer containing 1024 ultrasound elements. The helmet is mounted on a table and equipped with a manually operated positioning system integrated with MRI (see Fig. 2.1). The MRgFUS procedure itself is performed inside the MRI machine. To date, it has been demonstrated that the MRgFUS procedure can be safely and effectively performed using 1.5 and 3 T devices, allowing for high-resolution intraoperative imaging thanks to a special MRI coil ( Iacopino et al., 2018). Preoperative and intraoperative MRI scanning of the brain allows for precise calculation of target coordinates and assessment of the overall view of the area of interest. In our country, the focused ultrasound table ExAblate 4000 (InSightec, v. 7.0.404) compatible with MRI equipment from the company General Electric, in other countries, MRI machines are also used Siemens.
The focused ultrasound system consists of several components: a patient table with an integrated helmet; stereotactic frame; workstation; water system for cooling the patient’s head surface; equipment cabinet; electronic systems unit ( front-end). The workstation is a computer with a monitor installed in the MRI control room and used by the neurosurgeon to connect the ultrasound device with the MRI and conduct treatment. During treatment, the standard MRI table is replaced with a patient table equipped with an integrated ultrasound wave transducer, a system for securing the stereotactic frame and positioning, which connects to the water and front-end Blocks.
Block front-end and the equipment cabinet serves as the electronic control center for the entire system operation – from performing sonications and maintaining proper water circulation to monitoring the workstation.
The water system is installed in the technical room and provides degassing, circulation, and cooling of the water that fills the space between the patient’s head and the transducer; the cooled circulating water in the circuit is necessary to prevent excessive heating of the skin surface and to prevent burns.
During the procedure, the patient is conscious, and after each ultrasound exposure (sonication), the functional effect of the manipulation is assessed. This allows the interdisciplinary team of specialists (neurosurgeons, neurologists, neuroradiologists) to refine and confirm the correct target and determine the necessary number of sonications. Trial low-power sonications are used to assess the thermal map, confirming the absence of overheating areas outside the impact zone and ensuring beam focus on the target point. After this, the amount of energy delivered is gradually increased. At this stage, the patient, who remains conscious throughout the procedure, undergoes an assessment of neurological status and clinical condition after each sonication, real-time thermography, and anatomical verification based on MRI data. After neuroimaging and clinical confirmation of the target (neurological improvement without side effects), the power of the exposure and, accordingly, the temperature at the target point are increased (heating from 55 to 60°C), which causes actual tissue damage ( Fishman, 2017; Health Quality Ontario, 2018).
Unlike stereotactic ablative radiosurgery, MRgFUS does not involve irradiation of surrounding tissues, allowing for the avoidance of potential side effects (such as edema of brain structures not adjacent to the target point, aseptic meningitis, actinic keratosis, alopecia, etc.). The procedure is performed under conditions of short-term hospitalization or day hospital care ( Fasano et al., 2018; Weidman et al., 2019; Valentino et al., 2020).
Our experience treating over 200 patients over 3 years shows that, considering possible clinical situations (including emergencies), it is advisable to always have the following additional equipment on hand: electric suction, defibrillator, oxygen concentrator, electrocardiography machine with attachment straps; electric trimmer and razor; Ambu bag valve mask; sharp scissors (for membrane adjustment); glucometer; blood pressure monitor; video camera
The main necessary consumables for performing MRgFUS are as follows: a) for equipment preparation: phantom for daily quality control ( daily quality assurance, DQA), a tank of clean filtered water for filling the water system of the MRgFUS, a special detergent for cleaning the water system of the MRgFUS; b) for the patient: special membrane InSightec (see below), a set of peripheral venous catheters, compression stockings, diapers, skin marker, etc.; b) medications: resuscitation kit and kit for treating anaphylactic shock, antihypertensive, antiemetic, decongestant medications, non-steroidal anti-inflammatory drugs, 5% glucose solution, crystalloid fluids; c) materials for patient protocol and intraoperative testing: MRI-guideded focused ultrasound safety checklist, spiral test and letter sheets, pencil or pen, plastic bottle with water level, plastic spoon, toothpick or non-magnetic plastic skewer for sensitivity testing
Among the consumables for the patient, a special membrane deserves a separate description InSightec, mandatory when performing treatment using the MRgFUS method. It is an elastic silicone membrane placed on the patient’s head to isolate the space between the transducer and the scalp using cool degassed water. The membrane functions as a full-fledged MRI coil, achieved by special rings installed on the right and left, allowing high-quality visualization of brain structures during treatment planning and enabling the creation of a thermal map during the procedure. The membrane adapts to the patient’s head size by adjusting the circumference of the inner ring. After positioning the patient on the focused ultrasound table, the membrane forms multiple folds that should be smoothed out. If it is impossible to eliminate the folds, they must be marked during planning as areas through which ultrasound waves do not pass due to the large number of air bubbles in these formations.
We have proposed additional methods for objectively assessing the effectiveness and safety of the MRgFUS procedure. Many patients note the greatest severity of tremor when performing certain actions, often related to professional activities. For example, for a patient serving in a law enforcement agency who had difficulties shooting a pistol, we created a special pistol mock-up with a laser pointer to assess the effect of the procedure (Fig. 3.1). For a patient whose work involved training locksmiths to use tools, we used plastic children’s toys such as adjustable wrenches, screwdrivers, and nuts for testing. For a patient who worked as a seamstress before the illness, we used thin toothpicks to simulate needles. This kind of experience is important in managing patients with kinesia-specific forms of movement disorders.
A particular challenge is the assessment of head tremor: this task cannot be solved in the usual way during the MRgFUS procedure due to the fixation of the patient’s head in a stereotactic frame. To assess head tremor oscillations in such situations, we developed a special device described in Chapter 8.
Team of specialists providing treatment using MRgFUS
The main team providing treatment using MRgFUS includes a neurosurgeon, neurologist, neuroradiologist, MRI-technician, and nurse.
The neurosurgeon bears full responsibility for the safe and correct execution of the entire treatment using MRgFUS, the coordinated work of the formed team, and the proper operation of the equipment. In many centers, a mandatory requirement for admission to perform MRgFUS is specialization in functional neurosurgery.
An important member of the team is a qualified neurologist specialized in movement disorders. The neurologist conducts the initial selection of patients, adjusts (if necessary) medication therapy, determines pharmacoresistance, and assesses the patient’s clinical condition using scales. During each stage of MRgFUS, the neurologist evaluates the neurological status and, together with the neurosurgeon, determines the course of further treatment. Additionally, the neurologist continues to monitor the patient in the postoperative period, overseeing the medication regimen, prescribing rehabilitation activities, and assessing the patient’s condition dynamics, including using special scales.
The neuroradiologist also participates in organizing treatment throughout its duration: initially determines the skull bone density coefficient using CT scanning, conducts brain MRI before the MRgFUS stage for surgery planning, collaborates with the neurosurgeon to develop a treatment plan in terms of safety and effectiveness, provides necessary intraoperative imaging during repeated sonications, and performs follow-up MRIs at various times after the procedure.
A universal nurse with procedural and dressing skills prepares the patient for treatment (insertion of a venous catheter, shaving hair, setting up a neurosurgical frame and placing the membrane together with the neurosurgeon, positioning the patient on the focused ultrasound table). During the MRgFUS procedure, the nurse administers medications as prescribed by the neurologist, measures blood pressure, and, if necessary, measures blood glucose levels, etc.
The MRI-technician assists the neuro-radiologist at every stage – in determining the patient’s skull density ratio, performing MRI for surgery planning, conducting quality control before the start of the MRgFUS procedure (using a phantom DQA) and so on
Additional team members who may be involved at various stages if necessary: therapist, cardiologist, endocrinologist, anesthesiologist, clinical psychologist, psychiatrist, etc.
Patient, Relatives, and the Concept of the “Open Operating Room”
Optimal results of MRgFUS can be achieved through coordinated work and a full understanding of the technical aspects of the procedure not only by all team members but also by those close to the patient. The presence and involvement of loved ones at all stages of treatment help form the right expectations from the intervention, objectively assess its outcomes, and maintain the necessary mindset of the patient.
During the procedure, constant contact with the patient is necessary. According to the equipment instructions, for the safety of the procedure, the patient must be given an emergency stop button. However, this is not enough; additional adequate instruction is very important. The patient should know in which cases to press the button and which sensations are normal and should not cause concern.
Common sensations experienced by patients during MRgFUS that should not hinder the continuation of treatment: dizziness, nausea, mild pain, taste sensations (bitterness)
Sensations and symptoms requiring cessation of sonication:
• severe headache
• new neurological symptoms arising during intraoperative monitoring (coordination disorders in limbs, sensory deficit, etc.);
• vomiting
The patient should feel safe and be able to communicate with the team while conscious throughout the procedure. This will help avoid interruptions in sonications and achieve both better results in terms of effectiveness and a smaller edema size in the impact area in terms of safety.
To create favorable conditions for the effective conduct of the procedure, we proposed the concept of an “open operating room.” The control room is separated by a glass partition with blinds. With the patient’s consent, the room can be made well-visible by placing chairs for the patient’s relatives behind the glass. Relatives are allowed to enter the control room, express their concerns, and offer help. If the patient has poor tolerance for being alone in the MRI room for an extended period, we allow relatives to be nearby and hold the patient’s hand during the procedure. Since there are no incisions, this treatment does not require sterile conditions, and loved ones can freely be near the patient. Feeling supported, the patient in the operating room is less focused on internal sensations and tolerates the treatment more easily, avoiding unnecessary pressing of the stop button. At the same time, relatives, participating in the course of treatment, feel additional responsibility for the patient’s postoperative care.
An advantage of having relatives nearby is the ability to discuss further treatment strategies if necessary. This is very helpful in complex situations where standard MRI-guided focused ultrasound achieves an incomplete clinical effect (e.g., partial regression of tremor), but further treatment in an attempt to improve the result carries a certain risk of developing neurological deficits. The patient and relatives receive the most complete information, see and evaluate the achieved effect, and can consciously, in close contact with the medical team, participate in making a balanced decision about the advisability and possibility of continuing the treatment. According to our data, discussion in the format of such an “expanded open consultation” may be required in 1/3 of cases of functional operations using MRI-guided focused ultrasound. Based on our experience, this approach increases patient and family satisfaction with the course and results of treatment even with a suboptimal clinical effect.
The presented concept of an “open operating room” implies high requirements for the preparation of a qualified team of specialists performing treatment using MRgFUS.