Friday, August 03, 2007

RNS Discussion with Dr. King-Stephens (Part 2)

Part 2 of my RNS discussion with Dr. King-Stephens:

I have generalized tonic-clonic seizures. My EEG shows that the electrical activity does not start at one point in the brain and spread, but occurs on both sides of the brain at once. Would I be a good candidate for an RNS?

At this time, only patients who have focal onset seizures, 1 or 2 foci, are candidates for the study. It might be that in the future, people with generalized seizure onsets might be candidates for this therapy.

The VNS has been around since the nineties and has been implanted in over 30,000 patients. It is well studied and effective for many people. Why would I want to consider an RNS as opposed to the VNS?

VNS is indicated for patient in whom we do not know where the seizures are coming from, have more than 2 foci or have generalized onset seizures. Thus, the indications for using VNS or RNS are very different at this time.

How do you find the specific point on the brain at which to place RNS leads? Is an EEG or regular MRI sufficient?

In order to determine where the seizures are originating in the brain, we do EEG, MRI and occasionally PET studies. If the non-invasive studies can not give us the answer, we sometimes introduce (implant) the EEG electrodes into or placed on the surface of the brain, to capture the seizures and investigate whether we can find the focus or foci. This requires a surgical procedure and observation in the hospital for 7 to 10 days.

Once you have received a VNS, Cyberonics recommends that you not have any further MRIs as the strong magnetic field could heat up the leads wrapping around the Vagus nerve. As an MRI is required to determine the locations to place RNS leads, could a person with a VNS have an RNS implanted?

A person with a RNS generally should not have a MRI scan of the brain because the device creates so much artifact that the information given by the scan is often useless. Also, the MRI may cause heating of the leads. If an imaging procedure is necessary, x-ray based technologies such as a CT scan should be used whenever possible. Hopefully, future RNS devices will be MRI compatible.

The study website indicates that the leads & electrodes are implanted in the brain and that the neurotransmitter is placed in the skull. When you say “in the skull”, does that mean in the cavity with the brain or under the scalp?

The device is embedded in the skull and does not go into the brain. It is then covered by the muscle, fat and scalp and is therefore not visible. The EEG electrodes do go into and/or sit on the surface of the brain and therefore are under the skull.

Previous Posts (Part 1)
More tommorow...

If you have epilepsy and are interested in finding out if you are a good match for the RNS clinical study, Call: 1-866-904-6630 or go to: www.seizurestudy.com

2 comments:

Herb said...

Dear Scott,

I want to wish you continued seizure free days and to thank you for your detailed and informative sharing of your experiences.

There is one point in your narrative which I came upon that I’d like to address and share with you.


“Once you have received a VNS, Cyberonics recommends that you not have any further MRIs as the strong magnetic field could heat up the leads wrapping around the Vagus nerve.” --- Scott


Technically and based upon real life experiences Cyberonics does not recommend full body imaging although I am aware of patients that have leg and back MRI successfully and uneventfully performed. I can also report that my spouse has had several MRI of the brain successfully and uneventfully with the understanding there are certain specifics to be followed by the radiological technician and equipment to be used as noted in the information below. I would certainly recommend that any VNS patient prescribed an MRI make certain that the physician and technicians collaborate with Cyberonics beforehand to insure patient safety.

Once again, thanks for your efforts and I wish you continued wellness.

Warmly,
Herb
VNSdepression.com




MRI with the
VNS Therapy™ System
July 2006
Worldwide Version
Cyberonics 26-0006-4200/1 (Worldwide) — 1 of 3


MAGNETIC RESONANCE IMAGING (MRI) ______
Caution: Magnetic resonance imaging (MRI) should not be
performed with a magnetic resonance body coil in the transmit
mode. The heat induced in the Lead by an MRI body scan can cause
injury.
If an MRI should be done, use only a transmit and receive type of
head coil. Magnetic and RF fields produced by MRI may change the
Pulse Generator settings (change to reset parameters) or activate the
device. Stimulation has been shown to cause the adverse events
reported in the “Adverse Events” section in the indication-specific
parts of the multi-part physician manuals. MRI compatibility was
demonstrated using a 1.5T General Electric Signa Imager with a
Model 100 only. The Model 102 and Model 102R are functionally
equivalent to the Model 100. Testing on this imager as performed on
a phantom1 indicated that the following Pulse Generator and MRI
procedures can be used safely without adverse events:
􀂄Pulse Generator output programmed to 0 mA for the MRI
procedure, and afterward, retested by performing the System
Diagnostics (Lead Test) and reprogrammed to the original
settings
􀂄Head coil type: transmit and receive only
􀂄Static magnetic field strength: ≤2.0 tesla
􀂄Specific absorption rate (SAR): 1.3 W/kg for a 154.5-lb (70-
kg) patient
􀂄Time-varying intensity: 10 tesla/sec
Use caution when other MRI systems are used, since adverse events may
occur because of different magnetic field distributions. Consider other
imaging modalities when appropriate.
Caution: Procedures in which the RF is transmitted by a body coil
should not be done on a patient who has the VNS Therapy™
System. Thus, protocols must not be used that utilize local coils that
are RF-receive only, with RF-transmit performed by the body coil.
Note that some RF head coils are receive-only, and that most other
local coils, such as knee and spinal coils, are also RF receive-only.
These coils must not be used in patients with the VNS Therapy
System.
1 A phantom is a material resembling a body in mass, composition, and dimensions that is used to
measure absorption of radiation.

Cyberonics 26-0006-4200/1 (Worldwide) — 3 of 3

Emeriol said...

Thanks for your comments Herb. I'm sure that the most important thing to consider when getting any test done after a VNS is to make sure that the physicians know about it before the attempt to run a test. Thanks again.