December 2012

MRI – KOMPABILITET

Medels implantat C40/C40+, Pulsar CI100/SonataCI100 samt Concerto är CE-godkända för fältstyrkorna 0,2 Tesla, 1,0 Tesla och 1,5 Tesla.

(utan att implantatets interna magnet behöver avlägsnas kirurgiskt) om nedanstående säkerhets föreskrifter och riktlinjer följs.

Erfarenheterna grundar sig på:

Det inte längre krav på, att som tidigare, att i förväg fylla i och sända in en en särskild blankett

Med den nya märkningen kan alla MED-EL CI användare genomgå MRI undersökning med fälstyrkorna 0.2 T, 1.0 T or 1.5 T utan föregående godkännande av MED-EL.

Nedanstående säkerhets information och rekommenderade riktlinjer finns i användarinstruktionerna för implantatet respektive audioprocessorn.

 

MRI CAUTION

MRI is possible in patients with cochlear or auditory brainstem implants only with specified models of MRI machines.

Evidence has been provided for these implants to pose no known hazard in magnetic field strengths of 0.2 T, 1.0 T

and 1.5 T (without surgical removal of the internal magnet) when the following safety recommendations and

guidelines are adhered to. The physician/MRI operator should always be informed that a patient is a cochlear

implant or an auditory brainstem implant user and that special safety recommendations and guidelines have to be

followed:

 

Safety recommendations and guidelines for MRI scanning:

MRI scanner with static magnetic field strength of 0.2 T, 1.0 T or 1.5 T only. No other field strengths are allowed.

(When using other field strengths, injury to the patient and/or damage to the implant are possible.)

MRI scan not earlier than 6 months post implantation. (Performing an MRI at an earlier stage may result in implant

displacement and/or damage to the implant).

A minimum thickness of the bone underneath the implant magnet of 0.4 mm is required in order to withstand forces

of 5 N (equals a gravitational force of about 0.5 kg) or up to 9 N for the C40 cochlear implant. (In an MRI scanner

torque forces act on the implant magnet, exerting rotational pressure: the device will try to turn to line up with force

lines. The resulting forces on the edges of the implant are counterbalanced by the cranial bone and the skin flap.

Bone underneath the implant magnet should be thick enough to withstand these exerting forces.)

Patients with mechanically damaged implants must not undergo MRI. (Ignoring this guideline could result in injury to

the patient.)

 

Safety Guidelines:

Before patients enter any MRI room all external components of the implant system (audio processor and

accessories) must be removed. For field strengths of 1.0 T or 1.5 T a supportive head bandage must be placed over

the implant. A supportive head bandage may be an elastic bandage wrapped tightly around the head at least three

times (refer to Figure 1). The bandage shall fit tightly but should not cause pain.

 

Head orientation: The longitudinal axis of the head must be parallel to the main magnetic field of the scanner. For

example this is the case when the patient is in a supine position with the head kept straight. (The patient should not

turn or bend his/her head to the side; otherwise partial demagnetization of the implant magnet is possible.)

"Sequences in Normal Operating Mode shall be used only! During the scan patients might perceive auditory

sensations such as clicking or beeping. Adequate counseling of the patient is advised prior to performing the MRI.

The likelihood and intensity of auditory sensations can be reduced by selecting sequences with lower specific

absorption rate (SAR) and slower gradient slew rates"

Image artifacts are to be expected (refer to Figure 2).

 

 

The above instructions should also be followed if areas of the body other than the head are to be examined (e.g.

knee, etc.). When lower extremities are to be examined, it is recommended that the patient’s legs are positioned in

the scanner first to minimize any risk of weakening the implant magnet.

The above instructions also apply for patients with bilateral cochlear implants or bilateral auditory brainstem

implants.

If the conditions for MR safety and the Safety Guidelines are not followed, injury to the patient and/or damage to the

implant may result!