MRI Guidelines for the Axonics Sacral Neuromodulation System

Transcription

1 MRI Guidelines for the Axonics Sacral Neuromodulation System For Healthcare Professionals Rx only Note: This document is a supplement to the physician manuals provided with the Axonics SNM System. This document only contains information related to MRI use with the Axonics SNM System. For more information on the Axonics SNM System, consult the Tined Lead Implant Manual and the Neurostimulator Implant Manual. Axonics, Axonics Modulation, Axonics Modulation Technologies and Axonics Sacral Neuromodulation System are trademarks of Axonics Modulation Technologies, Inc., registered or pending registration in the U.S. and other countries. English June,

2 Table of Contents SAFE MRI CONDITIONS... 3 POTENTIAL RISKS OF MRI WITH THE AXONICS SNM SYSTEM... 3 Heating Effects... 3 Unintended Stimulation... 4 Image Distortion and Artifacts... 4 Magnetic Field Interactions... 4 Device Malfunction or Damage... 4 Other Precautions... 4 MRI Unsafe Devices... 5 MRI GUIDELINES... 5 Before Starting MRI Head Scan... 5 During MRI Head Scan... 6 Post MRI Head Scan... 7 GLOSSARY... 8 English June,

3 SAFE MRI CONDITIONS The Axonics Sacral Neuromodulation (SNM) System is an MRI Conditional device. MRI examinations of the head can be safely conducted in patients with the Axonics SNM System under the following conditions: Head transmit/receive coil only (No RF transmit body coil) Static magnetic field of 1.5T or 3T horizontal closed bore Normal operating mode Spatial gradient field of 2,500 Gauss/cm or less Gradient slew rate limited to 200 T/m/s Maximum head-averaged specific absorption rate (SAR) of 3.2 W/kg. Axonics Neurostimulator (Model 1101) and Tined lead (Model 1201) implanted Turn the Axonics Neurostimulator Stimulation off In vitro tests and simulations have shown that the patients with the Axonics SNM System may be safely exposed to MRI environments that follow the guidelines described in this document. When using a head transmit coil, the Axonics SNM System is expected to produce a maximum temperature rise of less than 1 C at a maximum head-averaged specific absorption rate (SAR) of 3.2 W/kg. Always obtain the latest MRI guidelines. Refer to the contact information on the last page of this manual, or go to POTENTIAL RISKS OF MRI WITH THE AXONICS SNM SYSTEM The potential risks of performing MRI on patients with an implanted SNM System include: Heating effects around the SNM System, especially electrodes, from radiofrequency (RF) energy Unintended stimulation due to current induced through the SNM lead wire by the timevarying magnetic gradient field or RF field Image distortion and artifacts Magnetic field interactions Device malfunction or damage Heating Effects Modeling and simulation show that with the RF transmit head coil, heating of the Axonics SNM System is minimal. If the specific MRI conditions are not met, e.g., RF body coil is used, heating at a lead electrode could damage the sacral nerve and/or surrounding structures. MRI-related heating is primarily influenced by location of the patient in the MR system and by lead configuration and length. English June,

4 Unintended Stimulation Non-clinical testing suggests that gradient induced or combined field induced current is small so that unintended stimulation to the surrounding tissue is unlikely. Risk of tissue damage due to current induced by the gradient or combined field is extremely low. If a patient suspects any unintended stimulation while in MRI, he/she should inform the MRI technician immediately and then contact their physician. Image Distortion and Artifacts No artifacts or distortion of the brain imaging should be seen when imaging with a RF Head Coil. Magnetic Field Interactions The Axonics SNM System may experience magnetic field interactions associated with the static magnetic field of the MRI system due to small amounts of material in the Neurostimulator being sensitive to magnetic fields. This may cause the Neurostimulator to shift or move slightly within the implant pocket and/or may place mechanical stress on tissues and/or the lead. Patients may feel a slight tugging sensation at the site of the Neurostimulator. Device Malfunction or Damage Tests in various MRI systems have not shown damage to, or malfunction of, the Axonics SNM System. If device malfunction or damage were to occur, it could cause discomfort, unintended stimulation, painful stimulation or direct current stimulation which may result in nerve damage and other associated problems. If a patient suspects a malfunction, he/she should be instructed to exit the MRI system room and use the patient Remote Control to stop stimulation. The patient should then contact their physician for further evaluation. Other Precautions MRI should not be performed in patients with multiple implanted devices. Safety has not been demonstrated in patients with implanted devices in addition to the Axonics SNM System. Do not use the transmit RF body coil for 1.5 T or 3 T imaging. Not all head RF coils are transmit and receive type. Many are receive only. The use of any local receive coil with the body coil in RF transmit mode presents the same RF heating hazards as the body coil alone with no local coils. Open MRI scanners have not been evaluated and should not be used for scanning SNM patients. Exposure of the Axonics SNM System to any RF transmit coil must be avoided. Surgical removal of the entire Axonics Therapy System may be required if an MRI of the lumbar or pelvic area is needed. External devices are MRI Unsafe in the MRI environment. Refer to MRI Unsafe Device section for details. No testing at field strengths other than 1.5 T and 3 T has been performed to evaluate migration or heating. English June,

5 MRI Unsafe Devices The Axonics SNM System Clinician Programmer, Remote Control and Charger and Dock (Figure 1) are MRI Unsafe. These devices must NOT be brought into the MRI system room. Clinician Programmer Remote Control Charger and Dock Figure 1. MRI Unsafe Devices MRI GUIDELINES Recommendations for Head Coil MRI with the Axonics SNM System are based on phantom tests and numerical simulations of worst-case and with the recommended implant configurations of the standard Axonics SNM Neurostimulator (Model 1101) and 30-cm Tined Lead (Model 1201). Before Starting MRI Head Scan 1. Turn the Axonics SNM Neurostimulator (Model 1101) stimulation off with the patient Remote Control or Clinician Programmer. English June,

6 2. Make sure the MRI System and settings used meet the following conditions: Static magnetic field of 1.5T or 3T horizontal closed bore only Spatial gradient field of 2,500 Gauss/cm or less Gradient slew rate limited to 200 T/m/s Normal operating mode only Head transmit/receive coils used only (No RF transmit body coil) Maximum head-averaged specific absorption rate (SAR) of 3.2 W/kg. 3. The patient should be placed in the MRI system in a supine position as shown in Figure 2. Figure 2. Head MR Imaging During MRI Head Scan 1. Monitor the patient both visually and audibly. Discontinue the MRI examination immediately if the patient reports any problems. 2. During the MRI head scan, the patient may feel slight tugging and/or vibration of the neurostimulator. If the tugging or vibration causes the patient considerable discomfort, stop the MRI head scan. English June,

7 After MRI Head Scan After the MRI procedure, turn the Axonics SNM Neurostimulator stimulation back on with the patient Remote Control or Clinician Programmer. If a patient suspects any unexpected change in stimulation after an MRI, he/she should contact their physician. English June,

8 GLOSSARY Hertz (Hz) a unit of frequency defined as cycles per second. One Megahertz (MHz) is one million cycles per second. MR Conditional an item with demonstrated safety in the MR environment within defined conditions. At a minimum, these address the conditions of the static magnetic field, the switched gradient magnetic field and the radio frequency fields. Additional conditions, including specific configurations of the item, may be required. MRI Magnetic Resonance Imaging. Radio Frequency (RF) high frequency electrical fields whose frequencies are in the range of 10,000 Hz and above. The RF used in the 1.5T MRI Scanner is ~64MHz. The RF used in the 3T MRI Scanner is ~128MHz. Specific Absorption Rate (SAR) radio frequency power absorbed per unit of mass (W/kg). Tesla (T) the unit of measure of magnetic field strength. One T is equal to 10,000 Gauss. MRI Transmit/Receive RF Body coil a coil used to transmit and to receive RF energy that encompasses the entire body region within the MR system bore. MRI Transmit/Receive RF Quadrature Head coil a coil used to transmit and to receive RF energy that is constrained to the head region, and configured to use circular polarization (CP). W/kg Watts per kilogram, a measure of the power that is absorbed per kilogram of tissue. English June,

9 Axonics Modulation Technologies, Inc Irvine Center Dr., Ste. 200 Irvine, CA (USA) Tel Fax HealthLink Europe Services BV De Tweeling MC 's-hertogenbosch The Netherlands All Rights Reserved. Copyright Axonics Modulation Technologies, Inc rD English June,