1. MRI guided Focused Ultrasound
(MRgFUS)
for essential tremor
Michael L. Schwartz, MD, MSc, FRCSC, Neurosurgeon,
Professor of Surgery, University of Toronto,

2. The development of MRgFUS has been motivated by the desire to develop
less invasive functional neurosurgery

3. Essential Tremor Background
The most common movement disorder
Prevalence 0.4 – 5%
Essential tremor features
Postural (with maintenance of a position) or
Kinetic (during voluntary movement)
Often familial
Often disabling: 15 – 25% retire early, 60% do not apply for promotion
May respond to ethanol, primidone, propranolol
but often progressive with medication failing and
~1/3 abandoning medication
Surgery may be offered to patients with disabling, medication-resistant tremor

4. Leksell Stereotactic Arc and Frame
Movement disorder surgery started to become very common around the world…thanks to the standardization of the procedure
The huge advantage is the uniformity of it, and how it standardized the procedure, so surgeons around the world can do the same procedure in the same way. Leksell in action, and it was transported around the world, including to Toronto. Indeed, even today, surgeons in Toronto, ad surgeons in New York, and surgeons in Shanghai perform DBS in more or less a similar fashion.
Prof. Lars Leksell
Karolinska Institute
1960s
Prof. Ronald Tasker,
University of Toronto
1960s
Leksell Stereotactic Arc and Frame
1949

5. RF thalamotomy circa 1974
No cross-sectional imaging! Air and iodinated contrast in the ventricles to measure the AC-PC line and see the top of the thalamus.
Computer generated “operative template” customizing the S&B atlas.
Stimulation mapping to correct for distortions. “…somatosensory data
plotted exactly where obtained, fall over the expected location of Vim,
5mm rostral to where they would have been expected from radiological
localization of the anterior and posterior commissures.”

6. Surgical Treatment with DBS
Ann neurol 1997;42:

7. MRI guided Focused Ultrasound (MRgFUS)

8. MRI guided Focused Ultrasound (MRgFUS)
hemispheric array of 1024 transducers
rubber diaphragm
cold water circulation
transducer array

9. MRI guided Focused Ultrasound (MRgFUS) Heat maps measured by MRI
Heating at the focal point: temporal progression oC
Heat maps measured by MRI
Parallel to the
axis of the beam
Perpendicular to
the axis of the
beam
6 s
13 s
20 s
27 s
sonication
cooling

10. MRgFUS Inclusion criteria
Age between years and able to consent
Diagnosis of essential tremor by movement disorder neurologist
Tremor refractory to medication: adequate dose or side effects
(propranolol, primidone)
Stable doses of medication for 30 days prior to treatment
Able to communicate during the procedure
Clinical Rating Sale for Tremor (CRST)
postural or intention tremor = or > 2 (tremor amplitude in cm)
disability subsection score = or > 2
(unable to bring food to mouth with one hand = 3)

11. MRgFUS Exclusion criteria
Standard MRI contraindications (pacemaker, size limitations)
Allergy to MRI contrast material
Inability to lie still or communicate during the procedure
Cardiovascular instability (angina, recent infarct, heart failure, hypertension)
Cerebrovascular disease (recent stroke)
Presence of other neurodegenerative diseases (Parkinson’s +, PSP etc.)
Brain tumors
Recent seizures (<1yr)
Unstable psychiatric disease or cognitive impairment (MMS < 25)
Pregnancy or lactation
Bleeding disorders
Previous DBS or thalamotomy

12. MRgFUS Study Methods
All patients were awake during the procedure and were examined after each sonication.
Average of 22.5 sonications across the 4 patients. Nucleus ventralis intermedius was the target
One patient reported tingling and numbness at the corner of the mouth and in the index finger at temperatures below 50oC.

13. Nucleus ventralis intermedius (Vim)
Patient 4
October 2012

14. Patient 4
October 2012

16. Magnetic Resonance Imaging Guidance
Thermal imaging
Thermal feedback every 3 to 5 seconds
Showing temperature at the focus of sonication

17. Patient 2
July 2012

18. Post-treatment Imaging
Day 30
Day 1
Day 90
Patient 2
Day 7

19. CRST (B) pre post

20. Clinical Rating Scale for Tremor (CRST)
Vertical lines are standard deviation around the mean

21. Mean tremor scores for the dominant (treated arm) only
Vertical lines are standard deviation around the mean

22. Total CRST = Total score on Clinical Rating Scale for Tremor
CRST A Dom = Tremor score for dominant (treated) hand only
CRST B Dom = Objective disability score on gross and fine motor tasks using the dominant (treated) hand
CRST C = Subjective disability secondary to tremor
Vertical lines are standard deviation around the mean

23. Significant improvements in subjective and objective disability.
Summary of Results
Five patients followed to 3 months
All Male, average age 70 (4 Right hand dominant, 1 Left hand dominant)
Average duration of illness 17 years
All patients trying and failing multiple medications and followed
by movement disorder neurologist
At 1-month post-op: average 91.5% reduction in tremor score of dominant (treated) arm
At 3-months post-op: average 85% reduction
Adverse events: numbness in thumb/finger of treated arm (resolved in one and persistent in another patient), gait unsteadiness (resolved)
Pre-treatment: all patients unable to write, feed themselves, or dress themselves
Significant improvements in subjective and objective disability.
All patients able to write, drink from a cup and eat unassisted at 3-months follow-up

24. Conclusion
MRgFUS may offer a non-invasive alternative to standard neurosurgical techniques.
The sample is very small but we have treated six patients safely and effectively.
From a radiographic perspective,
the lesions are indistinguishable from those made by the standard RF method.
The treatment has produced a lasting reduction in the tremor of six patients.

25. A patient’s story