Transcript Brain MRI in patients with VNS Optimizing safety and

Control #: 1692
eEdE#: eEdE-20
Brain MRI in patients with VNS
Optimizing safety and image
quality
Eliana Bonfante MD
Rajan Patel MD
Elliott Friedman MD
Roy Riascos MD
NO DISCLOSURE
Epilepsy is a common
neurologic disease
• Epilepsy is the fourth most common neurologic
disorder in the United States and Europe.
• According to the WHO, the estimated worldwide
prevalence of epilepsy is 50 million people.
• One in 26 people will develop epilepsy during
their lifetime.
Epilepsy treatment--medical
• Goal of epilepsy therapy is for patients to be free
of seizures and medication side effects.
• 60-70% of patients with newly diagnosed epilepsy
will enter remission with antiepileptic drugs.
• Pharmacoresistant epilepsy is defined as failure of
seizures to respond to at least two appropriately
chosen medications for a sufficient period of time.
Pharmacoresistant epilepsy
• Patients with pharmacoresistant epilepsy are more
likely to have an underlying structural lesion.
• Seizure freedom requires complete resection of the
entire epileptogenic zone.
• Vagal nerve stimulator implantation is an
alternative therapy in patients with
pharmacoresistant epilepsy who are not
candidates for epilepsy surgery or who continue to
seize after surgery.
Vagus nerve stimulation (VNS)
• VNS was approved by the US FDA in 1997
as an adjunctive treatment for medically
refractory epilepsy.
• Considered for use in:
– Poor candidates for resection
– Resection has failed
– VNS was approved only for adults and
adolescents with partial epilepsy
– Its efficacy in children and in patients with
generalized epilepsy remains unclear.
Vagus nerve stimulation (VNS)
• Meta-analysis of VNS efficacy in epilepsy
– 74 clinical studies with 3321 patients suffering from intractable
epilepsy.
– 3 blinded, randomized controlled trials (Class I evidence)
– 2 nonblinded, randomized controlled trials (Class II evidence)
– 10 prospective studies (Class III evidence)
– numerous retrospective studies.
• After VNS:
– Seizure frequency was reduced by an average of 45%
– Patients with generalized epilepsy and children benefited
significantly from VNS
– Posttraumatic epilepsy and tuberous sclerosis were positive
predictors of a favorable outcome.
Englot et al. Vagus nerve stimulation for epilepsy: a meta-analysis of
efficacy and predictors of response. J Neurosurg 2011
Dec;115(6):1248-55
Vagus nerve stimulation (VNS)
• Review of 20 selected publications between 1980 and
2010 in pediatric and adult population.
– 2 articles provided Class I evidence
– 7 articles met criteria for Class II evidence
– 11 articles provided Class III evidence
• The majority of evidence supports VNS usage in
partial epilepsy with a seizure reduction of 50% or
more in the majority of cases and freedom from
seizure in 6%-27% of patients who responded to
stimulation.
• Predictors of positive response included absence of
bilateral interictal epileptiform activity and cortical
malformations.
Connor et al. Vagal nerve stimulation for the treatment of medically
refractory epilepsy: a review of the current literature. Neurosurg Focus
2012 Mar;32(3):E12.
Epilepsy imaging
• Epilepsy imaging is preferred on a 3T
system over 1.5T when medically feasible,
due to improved resolution of subtle
abnormalities and higher signal to noise
ratio (SNR)
• MRI at 3T results in higher specific
absorption rate (SAR), which is a measure
of the rate at which energy is absorbed by
the human body when exposed to a radio
frequency (RF) electromagnetic field,
resulting in increased the risk of heating.
VNS system components
A. VNS Therapy lead:
electrodes and
anchor tethered to
the left vagus
nerve.
B. VNS Therapy
pulse generator
(single receptacle
or dual receptacle)
implanted in a
pocket in the
chest wall.
VNS system components
VNS system operation
•
The pulse generator is programmed using
Cyberonics provided software on a laptop or
handheld computer dedicated only to
programming the VNS Therapy System.
•
A programming wand connected to a
compatible computer running the
programming software is needed to
communicate with the pulse generator.
•
A magnet can be used for one-way
communication to the pulse generator by
activating a reed switch in the electronic
circuitry. The magnet can be used to initiate
stimulation, temporarily inhibit stimulation,
perform Magnet Mode diagnostics, and reset
the pulse generator.
•
Both the Wand and the
Magnet are MR unsafe
devices that can not enter
the MRI environment.
VNS modes of operation
• Normal mode
• Magnet Mode
– Patients with epilepsy or their caregivers
pass the magnet over the implanted
pulse generator to activate on-demand
delivery of a single train of vagus nerve
stimulation and help abort or diminish a
seizure.
– Magnet Mode is not used for patients
with depression.
MRI with the VNS
VNS Therapy System is an MR Conditional device
Potential risks:
• Heating effects around the VNS Therapy System, especially
electrodes, from RF energy
• Non-significant levels of current induced through the VNS lead
wire by the time-varying gradient level
• Inadvertent device reset, which erases historical information
stored on the device (possibly including device serial number)
• Inadvertent Magnet Mode activation (i.e., brief magnet application
and removal, which initiates a stimulation) from magnetic fields
• Image distortion and artifacts
• Magnetic field interactions
• Device malfunction or damage
• Hazards from Cyberonics magnets (not implanted) in the vicinity
of the MRI scan room
VNS Therapy® System Physician’s Manual Cyberonics, Oct 2014
Imaging patients with VNS
INTACT VNS
EXPLANTED VNS
• Do not use the transmit
RF body coil for 3T or
1.5T imaging.
• Not all head RF coils are
transmit and receive
type.
• Open MRI scanners or
systems other than 1.5T
and 3T should not be
used for scanning VNS
patients.
Surgical removal of the
VNS Therapy System will
be required if
– MRI using a transmit RF
body coil is needed.
– An MRI of the exclusion
zone is needed.
– An MRI of the brain with
multichannel coil is
needed.
MRI with intact VNS
• The VNS Therapy System can be scanned safely immediately
after placement under the following conditions:
• Static magnetic field of 1.5T or 3T only
• Spatial gradient field of 720 Gauss/cm or less
• Normal operating mode only
• Use only head or local transmit/receive coils.
• In non-clinical testing using a head transmit coil, the VNS
Therapy System produced a maximum temperature rise of
less than 2°C at a maximum head-averaged specific
absorption rate (SAR) of 3.2 W/kg, which was determined by
a validated calculation for 15 minutes of MRI scanning in a
1.5T or 3T scanner.
• Safety has not been demonstrated in patients with implanted
devices in addition to VNS Therapy.
VNS Therapy® System Physician’s Manual Cyberonics, Oct 2014
MRI with intact VNS
Exclusion zone
Clinical implications:
• MRI of the cervical
spine, neck,
thoracic spine and
chest are
contraindicated.
• Protocols for MRI
of included areas
are limited to the
use of a
Transmit/Receive
coil.
Protocol optimization for MRI
with intact VNS
• In order to maintain a safe SAR, Gorni et al
propose to divide the series into two or
three acquisitions (each with a reduced
number of slices), depending on patient
weight and desired spatial coverage.
• The multiple image acquisitions (e.g., the
three parts of the T1-FLAIR) were
retrospectively bound into a single series for
presentation in PACS.
• PROPELLER T2 imaging can replace the
axial FSE on patients who were prone to
movement during the exam.
Gorni et al. 3 Tesla MRI of Patients With a Vagus Nerve Stimulator:
Initial Experience Using a T/R Head Coil Under Controlled Conditions. J.
Magn. Reson. Imaging 2010;31:475–481.
MRI with intact VNS
High resolution T1 and T2WI acquired at
3T with single channel head coil in a
patient with intact VNS
Removal of the VNS system
If removal is medically necessary,
Cyberonics recommends removing as
much of the VNS Therapy System as can
be safely accomplished:
• Assess the degree of fibrotic ingrowth in and around the helices.
• Remove the entire system, if
possible.
• If fibrotic encapsulation hinders safe
removal of the entire system,
transect as much of the lead wire as
possible.
• Removal of the pulse generator alone
does not alter the hazards associated
with certain MRI procedures.
MRI with PARTIALLY explanted VNS
MRI can be performed
safely under the
following conditions:
1.5T or 3T with T/R
Head Coil or T/R
Extremity Coil
• If there is a
suspected lead break
(IPG is still
connected)
• If any length (43 cm
or less) remains (no
IPG)
Partially explanted VNS
Although the generator has been removed,
the wires are still in place. Therefore only TR
coils can be used.
MRI with explanted VNS
MRI can be
performed safely
under the following
conditions:
1.5T or 3T with
transmission of RF
with the Body Coil
(any landmark)
If there is ≤2 cm of
lead (i.e., electrodes
remain implanted)
CONCLUSION
• Brain MRI with an intact VNS can be safely
performed at 1.5 and 3T using only T/R head
single channel coil, with protocols that maintain a
low SAR.
• Patients with partially explanted VNS with long
remaining wires and patients with fractured wires
are scanned with the same protocol of an intact
VNS.
• Patients with explanted VNS with less than 2 cm
remaining wires can be scanned with 1.5T or 3T
with transmission of RF with the Body Coil.
References
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5.
Benbadis, S. R. et al. MRI of the brain is safe in patients
implanted with the vagus nerve stimulator. Seizure
2001;10:512–515
de Jonge, J. C., Melis, G. I., Gebbink, T. A., de Kort, G. A. P. &
Leijten, F. S. S. Safety of a dedicated brain MRI protocol in
patients with a vagus nerve stimulator. Epilepsia 2014;55:e112–
115
Gorny, K. R., Bernstein, M. A. & Watson, R. E. 3 Tesla MRI of
patients with a vagus nerve stimulator: initial experience using a
T/R head coil under controlled conditions. J. Magn. Reson.
Imaging JMRI 2010;31:475–481
Rezai, A. R. et al. Neurostimulation system used for deep brain
stimulation (DBS): MR safety issues and implications of failing to
follow safety recommendations. Invest. Radiol. 2004;39:300–
303
Englot, D. J., Chang, E. F. & Auguste, K. I. Vagus nerve
stimulation for epilepsy: a metaanalysis of efficacy and
predictors of response. J. Neurosurg. 2011;115:1248–1255