MRI Examination Guide For Nurotron Cochlear Implant
MRI Safety Information
Nurotron cochlear implant CS-10A is MR Conditional. Before MRI examination, the patient should clearly inform Nurotron of which MRI examination is to be performed. You can contact local Nurotron staff or Nurotron clinical personnel through customer service hotline 400-6333571. Visit www.nurotron.com/MRIWarning for current MRI conditional labelling. Before MRI, the patients should see their implantation surgeon to make sure they are safe to take MRI examination.
All external processors and accessories are MR Unsafe. Patient should remove them before entering MRI room.
CS-10A cochlear implant is MRI Conditional. During MRI, the implant magnet may move from normal position if not properly bonded; the magnet strength may change; Patients may feel discomfort or pain in the implant site. The magnet and the metallic shell of implant can cause artifact. 1.5T MRI can be done with implant magnet in position if Nurotron’s MRI examination guide is followed. For 3T MRI, implant magnet should be removed by a qualified surgeon.
Do not allow patients with a CS-10A cochlear implant to be in the area of an MRI scanner unless the following conditions have been met:
· The external sound processor and headpiece are removed before entering a room where an MRI scanner is located.
· Patient has no fever.
· For 3T MRI, implant magnet should be removed by a qualified surgeon.
· For 1.5T MRI with implant magnet in position, the bandaging procedure in Nurotron’s MRI examination guide should be followed, to avoid magnet movement, patient discomfort, or trauma and pain to the patient.
· Caution: The bandaging procedure in Nurotron’s MRI examination guide was developed to prevent magnet displacement and counteract magnet torque during a 1.5T MRI procedure, but some discomfort and pain at the implant site may still be experienced. Please consult with your physician if this is an issue.
· Caution: If discomfort persists following an MRI, please notify your physician.
· Caution: Please consult with your physician prior to MRI to determine if the benefits of MRI are worthwhile over other imaging techniques.
3.0T with the magnet removed
· Maximum spatial field gradient of 2,000 Gauss/cm (20 T/m)
· Maximum RMS gradient magnetic field dB/dt 42 T/s
· Maximum MR system reported, whole body averaged specific absorption rate (SAR) of ≤ 2 W/kg at 3T (Normal Operating Mode) for RF body coils
· Under the scan conditions defined above the CS-10A series implant is expected to produce a maximum temperature rise of <3°C after 15 minutes of continuous 3T scanning.
1.5T with the magnet in place
· Maximum spatial field gradient of 1,000 Gauss/cm (10 T/m)
· Maximum RMS gradient magnetic field dB/dt 42 T/s
· Maximum MR system reported, whole body averaged specific absorption rate (SAR) of ≤ 2 W/kg at 1.5T (Normal Operating Mode) for RF body coils
· Under the scan conditions defined above the CS-10A series implant is expected to produce a maximum temperature rise of <3°C after 15 minutes of continuous 1.5T scanning.
Guide For Radiologist
1. The preparation before MRI examination
The radiologist should be aware of the following information before performing MRI on the patient.
1) The implant magnet is required to be removed under MRI examinations over 1.5T. Under MRI examination equal to or less than 1.5T, the magnet is not required to be removed, but it is required to be elastically bandaged with an elastic bandage and an elastic plastic piece to prevent shifting (See the 1.5T MRI examination for details).
2) Before the examination, make sure patient has no fever; take caution to wait the swelling caused by the implantation surgery reduced, and for most patients it takes two to four weeks. Whether the patient takes out the magnet for MRI examination or not, the metal case may cause shadows around the implant. Please inform the patient beforehand.
2. Patients’ comfort
Please explain to the patient as follows.
1) Compression bandages (for MRI over 0.2T) may prevent the implant magnet from twisting and shifting, but the patient may still feel pressure. This sensation is similar to the feeling of pressing the thumb against the skin, which does not damage the implant or harm the patient.
2) If the patient feels uncomfortable or feels too tight, remove the patient from the magnetic resonance machine and consider 0.2T MRI examination (no bandage required). Or consult the patient's attending physician to determine if the magnet should be removed or using local anesthesia to reduce discomfort.
3. MRI examination kit
When performing 1.5T MRI examination, an MRI examination kit is required. The MRI examination kit includes the following:
Plastic piece: used to cover the magnet of the implant coil, size: 80*50*1.5mm (Fig. 1 is the plastic piece for MRI examination).
Figure 1. Front and back sides of plastic pieces (Translation of printed scripts as follows)
Front Side: Plastic piece for MRI Examination
◊ Before the examination, the patient should clearly inform Nurotron of which MRI examination is to be performed. You can contact Nurotron local staff or Nurotron clinical personnel through customer service hotline 400-6333571.
◊ The implant magnet is required to be removed under MRI examinations over 1.5T.
◊ The magnet should be in the center of the bandage and the plastic piece. The medical bandage must be completely wrapped with plastic piece.
◊ Bandaging: Firmly tighten the bandage to its elastic limit, stretch it for at least four turns around the head, and make sure that the four turns stick together.
◊ Use medical tape around the center of the elastic bandage to ensure that the tape is tightly attached to the elastic bandage.
◊ See MRI examination of Nurotron Cochlear Implant guide for details.
Elastic bandage: used to fix the plastic piece. It is recommended to use elastic bandage with a width of more than 10cm (as shown in Figure 2).
Figure 2. Example of elastic bandage
1) Medical tape: used to fix elastic bandage and plastic piece.
1. 1.5T MRI Examination
Before entering the MRI room, first remove the speech processor and the coil; draw a contour at the scalp of the coil to mark the center of the magnet. If the patient's hair is too dense, shave the hair at the coil to better fix the elastic piece. If the position of the coil is not found, use magnetic material such as a paper clip or the like. However, this magnetic material must be removed before entering the MRI room.
Figure 3. The inner magnet position
2) Take out the plastic piece from the MRI examination kit and place it at the coil position of the implant to make sure the magnet is in the center of the plastic piece. See Figure 4, fix the plastic piece with medical tape, and then tightly bandage with medical bandage. Make sure that the centerline of the bandage is at the implant position and try to place the magnet in the exact center of the bandage. The medical bandage must completely cover the plastic piece.
Figure 4. The diagram of the fixing of plastic piece and elastic bandages
3) Bandaging: Firmly tighten the bandage to its elastic limit, stretch it for at least four turns around the head, and make sure that the four turns stick together.
4) Use medical tape around the center of the elastic bandage to ensure that the tape is tightly attached to the elastic bandage.
5) After 15 minutes of continuous MRI scanning , take break and make sure there is no overheating in the implant position.
5. After 1.5T MRI examination
After the MRI examination, remove the elastic bandage and the plastic piece, and wear the speech processor. After the speech processor turned on, confirm the sound is normal and there is no discomfort to the patient. If in doubt, contact your surgeon or Nurotron clinical personnel as soon as possible.
6. MRI examination over 1.5T up to 3.0T
The implant magnet is required to be removed under MRI examinations over 1.5T up to 3.0T, and bandage according to above method before examination. After 15 minutes of continuous MRI scanning , take break and make sure there is no overheating in the implant position.
Precautions for implant magnet removal
1) The implant magnet needs to be removed by a professional doctor.
2) If the patient needs multiple MRI examinations, a sterile non-magnetic metal plug is required to replace the magnet implant in order to prevent fibrous tissue from entering the crypt for the inner magnet.
3) After the inner magnet is removed, the patient could wear a device such as soft belt to fix the coil of the speech processor between multiple MRI examinations.
4) When MRI is no longer required, the sterile non-magnetic metal plug should be removed and a new sterile internal magnet implanted.
The removal of the implant magnet —surgeon guide
Perform systemic or local anesthesia and remove the magnet under aseptic conditions:
Figure 5 Incision on the side of implant Figure 6 Incision of the implant with magnet removed
1. Make a small incision to make sure the magnet can be reached. The incision must be on the side of the implant (do not exceed the coil), see Figure 5.
2.Cut along the fiber growth site around the implant to expose the magnet.
3. Using separator or similar device, carefully lift the top of the silicone elastic crypt around the magnet and remove the magnet from the implant. If there are residual sutures around the magnet, remove the suture. See Figure 6.
The procedure will vary depending on whether the patient needs single or multiple MRI examination.
1. Make a small incision to remove the magnet.
2. Leave the magnet crypt empty. Do not close the wound, cover it with a dry and sterile dressing. The crypt can hold up to 4 hours of sterile empty state.
3. Perform the MRI.
4. After the examination, insert a new sterile magnet with the mark “十” (polarity) facing up. Use separator to raise the hidden lip and place the magnet.
5. Suture the wound layered.
If the patient needs multiple MRI examinations, a sterile non-magnetic metal plug is required to replace the magnet implant in order to prevent fibrous tissue from growing into the crypt.
Insert a metal plug into the crypt as follows:
1. Make a small incision to remove the magnet. (Figure 6).
2. Use a separator to lift the lip of the crypt and press the non-magnetic metal plug into the place. Be careful not to put too much pressure on the implant.
3. Suture the wound layered.
When regular MRI examination is no longer needed:
1.Make a small incision to expose the magnet crypt.
2. Remove the non-magnetic metal plug according to the above procedure.
3. Insert a new sterile magnet with the mark “十” (polarity) facing up. Use a separator to lift the lip of the crypt and press the sterile magnet into the place.
4. Suture the wound layered.