MRI guided Focused Ultrasound
(MRgFUS)
for essential tremor
Michael L. Schwartz, MD, MSc, FRCSC,
Neurosurgeon,
Professor of Surgery, University of Toronto,
m.schwartz@utoronto.ca
The development of MRgFUS has been
motivated by the desire to develop
less invasive functional neurosurgery
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
Prof. Lars Leksell
Karolinska Institute
1960s
Leksell Stereotactic Arc and Frame
1949
Prof. Ronald Tasker,
University of Toronto
1960s
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.”
Surgical Treatment with DBS
Ann neurol 1997;42:292-299
MRI guided Focused Ultrasound (MRgFUS)
http://www.insightec.com/contentManagment/uploadedFiles/fileGallery/transcranial_mrgfus_white_paper.pdf
MRI guided Focused Ultrasound (MRgFUS)
hemispheric array of 1024 transducers
rubber diaphragm
cold water circulation
transducer array
MRI guided Focused Ultrasound (MRgFUS)
Heating at the focal point: temporal progression
oC
Heat maps measured by MRI
60
55
Parallel to the
50
axis of the beam
45
40
60
55
Perpendicular to
50
the axis of the
45
beam
40
6s
13 s
sonication
20 s
27 s
cooling
MRgFUS Inclusion criteria
Age between 18-80 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)
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
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.
Nucleus ventralis intermedius (Vim)
Patient 4
October 2012
Patient 4
October 2012
Magnetic Resonance Imaging Guidance
Thermal imaging
Thermal feedback every 3 to 5 seconds
Showing temperature at the focus of sonication
Patient 2
July 2012
Post-treatment Imaging
Day 30
Day 1
Day 90
Patient 2
Day 7
CRST (B) pre
post
Mean Total CRST (N=5)
100
90
80
CRST - Total
70
60
50
40
30
20
10
0
Baseline
1-month
3-month
Clinical Rating Scale for Tremor (CRST)
Vertical lines are standard deviation around the mean
Mean Dominant Arm Score (N=5)
10
9
8
7
6
5
4
3
2
1
0
Baseline
1-month
3-month
Mean tremor scores for the dominant (treated arm) only
Vertical lines are standard deviation around the mean
Percentage Change - Baseline vs. 3-months (N=5)
50
30
10
-10
-30
-50
Total CRST
CRST A - Dom
-52.4
CRST B
CRST C
-57.2
-56.7
-85
-70
-90
-110
-130
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
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
Pre-treatment: all patients unable to write,
feed themselves, or dress themselves
At 1-month post-op: average 91.5% reduction in tremor score of dominant
(treated) arm
At 3-months post-op: average 85% reduction
Significant improvements in subjective and objective
disability.
All patients able to write, drink from a cup and eat unassisted
at 3-months follow-up
Adverse events: numbness in thumb/finger of treated arm (resolved in one
and persistent in another patient), gait unsteadiness (resolved)
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.
A patient’s story