Ann Otol Rhinol LaryngollOO: 1991
COCHLEAR IMPLANTS AS A CONTRAINDICATION TO MAGNETIC RESONANCE IMAGING WILLIAM
M.
KENNETH MATTUCCI, MD
PORTNOY, MD NEW YORK, NEW YORK
Magnetic resonance imaging poses little risk to the majority of patients undergoing scanning. However, cochlear implantation should pose a contraindication to this imaging process. This conclusion is based on several findings of in vitro testing of three cochlear implants: the 3M/House and 3M/Vienna designs and the Nucleus device. Specifically, tremendous torques are generated by each of these devices when they are introduced into the coil of a magnetic resonance imager; in addition, the 3M products not only were noted to induce an electrical current, but also were significantly magnetized and rendered afunctional. The clinical implications are discussed. KEY WORDS -
cochlear implant, magnetic resonance imaging.
its design, with seven turns of copper wire and 9010 platinum-iridium electrodes, also encapsulated with epoxy and insulated with silicone. The third cochlear implant is the Nucleus device (Cochlear Corp, Englewood, Colo), again a multichannel implant, which consists of 22 platinum-iridium circumferential bands around a single tapered Silastic carrier. The Nucleus device has several ferromagnetic components used in its construction: a minimagnet used to align the transcutaneous external transmitter coil, a ferrite transformer, and an iron alloy lid used on the stimulator chip.
INTRODUCTION
Magnetic resonance imaging (MRI) has revolutionized noninvasive diagnostic techniques by utilizing superconducting magnets and radio signals as opposed to ionizing radiation in order to generate images. Not only are the images produced of higher resolution and clarity than those produced by computed tomography, but the patient is spared exposure to potentially harmful doses of radiation. As such, MRI has become a widely used testing modality, posing little risk to the majority of patients undergoing scans. Of course, certain contraindications to its use do exist, and they are largely due to the tremendous magnetic fields inherent to this imaging process; these restrictions apply primarily to some pacemaker wearers and patients with particular cerebral aneurysm clips. Preliminary findings concerning MRI and cochlear implants were first reported by Mattucci et al t in an investigation of the effects of MRI on middle ear prostheses. The present investigation was undertaken to determine what the effects of MRI are on cochlear implants in vitro and assess whether or not this testing modality poses any hazards to patients who are cochlear implant recipients.
Each of the cochlear implants was then introduced into the coil of a 0.6-T superconducting magnetic resonance imager manufactured by Technicare (Solon, Ohio). The cochlear implants were suspended by a silk thread during Tl- and T2-weighted imaging to determine deviation off the vertical, ie, deflection forces. Next, the leads of the 3M cochlear implants were connected with several microfuses ranging from 2 to 100 rnA in a series fashion, and again placed into the magnetic field of the imager. The Nucleus device, in contrast, had two terminals fashioned to its electrode by the manufacturer, which in turn were connected to a voltmeter well outside the imaging area. A Micronta voltmeter (Tandy Corp) was used; it has the capability of measuring a minimum of 0 to 300 rnA (direct current). All the cochlear implants were returned to the manufacturers, along with the microfuses, and were examined to assess their function.
MATERIALS AND METHODS
Three different cochlear implants were included in the study. The first two were manufactured by 3M (3M Corp, Los Angeles, Calif), ie, the 3M/ House and 3M/Vienna designs. The 3M/House design is a single-channel cochlear implant constructed with a rare earth (samarium cobalt) magnet at its center and 670 turns of 40-gauge copper wire surrounding it, with platinum-iridium (90-10) electrodes, insulated with silicone, and encapsulated in epoxy. The second, in contrast, is the 3M/Vienna design, a multichannel cochlear implant that has no ferromagnetic materials listed in
RESULTS
While in the magnetic field of the imager, all three cochlear implants showed a significant deviation off the vertical; specifically, the 3M/House device demonstrated a 60° deflection, the 3M/Vienna, a 10° deflection, and the Nucleus device a 53° de-
From the Department of Otolaryngology, The New York Eye and Ear Infirmary, New York Medical College, New York, New York. Presented at the meeting of the American Otological Society, Inc, Palm Beach, Florida, April 28-29, 1990. REPRINTS - Kenneth Mattucci, MD, 333 East Shore Rd, Manhasset, NY 11030.
195
Downloaded from aor.sagepub.com at The University of Iowa Libraries on June 23, 2015
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Portnoy & Mattucci, Cochlear Implants & Magnetic Resonance Imaging
flection. The actual rotational forces or "torques" generated by the enormous magnetic field varied considerably depending on the orthogonal orientation of the devices relative to the constant static magnetic field of the imager. On the basis of this observation, it was believed the value of the torque could not be quantitatively evaluated. Nonetheless, the torque was subjectively determined to be of significant magnitude that could easily dislodge the implant from its supporting foundation in vitro, and most certainly in vivo. After careful examination by the manufacturer, both 3M devices were found to be significantly magnetized and "afunctional" as a result of their exposure to the magnetic resonance imager. In addition, all of the microfuses used were found to be overloaded or "burned out"; this finding indicates the induction of a minimum instantaneous current of at least 100 rnA (direct current). The Nucleus device, in contrast, showed no current generated or change in magnetization or function. DISCUSSION
Since the advent of MRI, few limitations or contraindications to its use have been established; hence, it is a diagnostic tool of enormous capacity. Naturally, much concern has been raised as to whether this imaging process poses any adverse biologic effects, since three powerful electromagnetic fields are generated during imaging. 1. A strong, static magnetic field, which remains virtually constant, is used to align the protons. 2. A small, rapidly varying magnetic field gradient is used for spatial localization. 3. Radio frequency pulses are used to produce changes in the energy states of the protons. At present it is generally accepted that these magnetic fields pose no reproducible adverse effects upon living tissue if used within specified guidelines." However, some contraindications to MRI exist in patients with ferromagnetic metallic implants or other ferromagnetic materials, largely because of the potential hazards associated with movement of these objects, as in the case of some aneurysm clips, which have been shown to become dislodged from clipped vessels in an animal model. 2 Other potential problems associated with MRI include heating of the material, the induction of electrical current, and the misinterpretation of artifact as an abnormality.? However, to date there have been no reports of induced electrical currents produced by MRI of metallic bioimplants, Furthermore, the temperature changes associated with small metallic bioimplants and larger orthopedic prostheses were shown to be negligible.P:" In the case of cardiac pacemakers, the hazards seem to lie in the alteration of normal pulsing parameters that may be induced by the magnetic resonance imager. 5
As outlined by Shellock and Crues" and Shellock;' several important factors influence the relative risk of using MRI in patients who have metallic biomedical implants. These include 1) the strength of the gradient and static magnetic fields, 2) the degree of ferromagnetism of the implant or material, 3) the geometry of the implant or material, 4) the location and orientation of the implant in situ, and 5) the amount of time the implant has been in place. In accordance with the laws of physics, magnetic materials align themselves in the direction of a static magnetic field, as evidenced by the aforementioned deflection forces. Clearly, when a magnetic material has changed its orientation within this static magnetic field, rotation forces will act to realign the material, generating significant torques, ie, rotational movements. Since the cochlear implants have not previously been studied in conjunction with MRI, several findings from this investigation bear emphasis. They suggest that subjects with cochlear implants should not be exposed to the magnetic field of a magnetic resonance imager. First, significant electrical currents were generated by the 3M cochlear implants, which certainly could result in severe injury to the cochlea and its related structures. Next, significant forces were generated by all three of the cochlear implants that potentially could cause movement of the implant within the patient's head and, in doing so, injure surrounding structures, damage the electrode, or even withdraw the electrode from within the cochlea. Of course, the effect depends on the degree of fixation and the integrity of the surrounding tissues. Since the sensitivity of the cochlear implant relies on its ability to electrically stimulate specific regions of the cochlea, even the slightest change in position of the intracochlear electrodes could alter the specific signals generated, requiring, at least, reprogramming of the device. The last consideration is the damage caused to the instrument itself, and not to the patient. After being exposed to what is now considered a relatively weak (0.6 T) magnetic resonance imager, both of the 3M cochlear implants were found to be significantly magnetized and afunctional; the Nucleus device, however, showed no loss of function and no change in magnetization. Other factors not brought out by our investigation but of consideration are the artifacts or "white-out" caused by the implant during imaging, which have been shown to be very significant, especially when magnetic materials are imaged," and finally the potential for heat generation, which has not proved to be significant in other Investigations." CONCLUSION
Previous studies have shown that most patients with metallic bioimplants (approximately 75 0/0) can be examined relatively safely by MRI. 7 These bio-
Downloaded from aor.sagepub.com at The University of Iowa Libraries on June 23, 2015
Portnoy & Mattucci, Cochlear Implants & Magnetic Resonance Imaging
implants included aneurysm and hemostatic clips; dental implants and materials; intravascular coils, filters, and stents; middle ear prostheses-P-": prosthetic heart valves; orthopedic implants; penile implants; and other miscellaneous metallic implants and materials. The hazards of performing MRI on patients with metallic bioimplants usually related to movement or dislodgment, but potentially can relate to temperature change, induction of electrical current, and the misinterpretation of artifacts as an abnormality.
197
dislodge the cochlear implant and electrodes. 2. Significant electrical currents are generated in the 3M/House and 3M/Vienna cochlear implants when they are exposed to the magnetic field of a O.6-T imager. 3. Exposure to the magnetic field renders the 3M devices magnetized and afunctional. 4. The Nucleus device maintains both function and magnetization after exposure to the magnetic field. On the basis of these findings, MRI is contraindicated in patients with the cochlear implants reviewed. Further investigation is needed to determine if these findings can be applied to other models on the market today.
In the case of two 3M cochlear implants and the Nucleus device, we have shown the following primary effects: 1. Large torques are created that potentially can
REFERENCES 1. Mattucci KF, Setzen M, Hyman R, Chaturvedi G. The effect of magnetic resonance imaging on metallic middle ear prostheses. Otolaryngol Head Neck Surg 1986;94:441-3.
5. Pavlicek W, Geisinger M, Castle L, et al. The effects of nuclear magnetic resonance on patients with cardiac pacemakers. Radiology 1983;147:149-53.
2. New PFG, Rosen BR, Brady TJ, et a1. Potential hazards and artifacts of ferromagnetic and nonferromagnetic surgical and dental materials and devices in nuclear magnetic imaging. Radiology 1983;147:139-48.
6. Shellock F, Crues JV. High field strength MR imaging and metallic biomedical implants: an ex vivo evaluation of deflection forces. Am J Radiol 1988;151:389-92. 7. Shellock F. MR imaging of metallic implants and materials: a compilation of the literature. Am J RadioI1988;151:811-4.
3. Davis PL, Crooks L, Arakawa M, McRee R, Kaufman L, Margulis A. Potential hazards in NMR imaging: heating effects of changing magnetic fields and RF fields on small metallic implants. Am J Radiol 1981;137:857-60.
8. Applebaum EL, Valvassori CE. Effects of magnetic resonance imaging fields on stapedectomy prosthesis. Arch Otolaryngol 1985;111:820-1.
4. Mesgarzadeh M, Revesz G, Bonakdarpour A, Betz R. The effect on medical metal implants by magnetic fields of magnetic resonance imaging. Skeletal Radiol 1985;14:205-6.
9. Leon JA, Gabriele 0 F. Middle ear prosthesis: significance in magnetic resonance imaging. Magn Reson Imaging 1987;5: 405-6.
......... .........
FIRST INTERNATIONAL CONFERENCE ON ELECTROCOCHLEOGRAPHY AND MONITORING The First International Conference on Electrocochleography and Monitoring will be held Sept 20-24, 1992, in Wurzburg, Germany. For further information, contact Program Chairman, Dr Dirk Hoehmann, Dept of Otolaryngology, University of Wurzburg Medical School, [osef-Schneider-Str 11, D-8700, Wurzburg, Germany; telephone 49-931-201-2323, or FAX 49-931-201-2248.
Downloaded from aor.sagepub.com at The University of Iowa Libraries on June 23, 2015
COCHLEAR IMPLANTS AS A CONTRAINDICATION TO MAGNETIC RESONANCE IMAGING WILLIAM
M.
KENNETH MATTUCCI, MD
PORTNOY, MD NEW YORK, NEW YORK
Magnetic resonance imaging poses little risk to the majority of patients undergoing scanning. However, cochlear implantation should pose a contraindication to this imaging process. This conclusion is based on several findings of in vitro testing of three cochlear implants: the 3M/House and 3M/Vienna designs and the Nucleus device. Specifically, tremendous torques are generated by each of these devices when they are introduced into the coil of a magnetic resonance imager; in addition, the 3M products not only were noted to induce an electrical current, but also were significantly magnetized and rendered afunctional. The clinical implications are discussed. KEY WORDS -
cochlear implant, magnetic resonance imaging.
its design, with seven turns of copper wire and 9010 platinum-iridium electrodes, also encapsulated with epoxy and insulated with silicone. The third cochlear implant is the Nucleus device (Cochlear Corp, Englewood, Colo), again a multichannel implant, which consists of 22 platinum-iridium circumferential bands around a single tapered Silastic carrier. The Nucleus device has several ferromagnetic components used in its construction: a minimagnet used to align the transcutaneous external transmitter coil, a ferrite transformer, and an iron alloy lid used on the stimulator chip.
INTRODUCTION
Magnetic resonance imaging (MRI) has revolutionized noninvasive diagnostic techniques by utilizing superconducting magnets and radio signals as opposed to ionizing radiation in order to generate images. Not only are the images produced of higher resolution and clarity than those produced by computed tomography, but the patient is spared exposure to potentially harmful doses of radiation. As such, MRI has become a widely used testing modality, posing little risk to the majority of patients undergoing scans. Of course, certain contraindications to its use do exist, and they are largely due to the tremendous magnetic fields inherent to this imaging process; these restrictions apply primarily to some pacemaker wearers and patients with particular cerebral aneurysm clips. Preliminary findings concerning MRI and cochlear implants were first reported by Mattucci et al t in an investigation of the effects of MRI on middle ear prostheses. The present investigation was undertaken to determine what the effects of MRI are on cochlear implants in vitro and assess whether or not this testing modality poses any hazards to patients who are cochlear implant recipients.
Each of the cochlear implants was then introduced into the coil of a 0.6-T superconducting magnetic resonance imager manufactured by Technicare (Solon, Ohio). The cochlear implants were suspended by a silk thread during Tl- and T2-weighted imaging to determine deviation off the vertical, ie, deflection forces. Next, the leads of the 3M cochlear implants were connected with several microfuses ranging from 2 to 100 rnA in a series fashion, and again placed into the magnetic field of the imager. The Nucleus device, in contrast, had two terminals fashioned to its electrode by the manufacturer, which in turn were connected to a voltmeter well outside the imaging area. A Micronta voltmeter (Tandy Corp) was used; it has the capability of measuring a minimum of 0 to 300 rnA (direct current). All the cochlear implants were returned to the manufacturers, along with the microfuses, and were examined to assess their function.
MATERIALS AND METHODS
Three different cochlear implants were included in the study. The first two were manufactured by 3M (3M Corp, Los Angeles, Calif), ie, the 3M/ House and 3M/Vienna designs. The 3M/House design is a single-channel cochlear implant constructed with a rare earth (samarium cobalt) magnet at its center and 670 turns of 40-gauge copper wire surrounding it, with platinum-iridium (90-10) electrodes, insulated with silicone, and encapsulated in epoxy. The second, in contrast, is the 3M/Vienna design, a multichannel cochlear implant that has no ferromagnetic materials listed in
RESULTS
While in the magnetic field of the imager, all three cochlear implants showed a significant deviation off the vertical; specifically, the 3M/House device demonstrated a 60° deflection, the 3M/Vienna, a 10° deflection, and the Nucleus device a 53° de-
From the Department of Otolaryngology, The New York Eye and Ear Infirmary, New York Medical College, New York, New York. Presented at the meeting of the American Otological Society, Inc, Palm Beach, Florida, April 28-29, 1990. REPRINTS - Kenneth Mattucci, MD, 333 East Shore Rd, Manhasset, NY 11030.
195
Downloaded from aor.sagepub.com at The University of Iowa Libraries on June 23, 2015
196
Portnoy & Mattucci, Cochlear Implants & Magnetic Resonance Imaging
flection. The actual rotational forces or "torques" generated by the enormous magnetic field varied considerably depending on the orthogonal orientation of the devices relative to the constant static magnetic field of the imager. On the basis of this observation, it was believed the value of the torque could not be quantitatively evaluated. Nonetheless, the torque was subjectively determined to be of significant magnitude that could easily dislodge the implant from its supporting foundation in vitro, and most certainly in vivo. After careful examination by the manufacturer, both 3M devices were found to be significantly magnetized and "afunctional" as a result of their exposure to the magnetic resonance imager. In addition, all of the microfuses used were found to be overloaded or "burned out"; this finding indicates the induction of a minimum instantaneous current of at least 100 rnA (direct current). The Nucleus device, in contrast, showed no current generated or change in magnetization or function. DISCUSSION
Since the advent of MRI, few limitations or contraindications to its use have been established; hence, it is a diagnostic tool of enormous capacity. Naturally, much concern has been raised as to whether this imaging process poses any adverse biologic effects, since three powerful electromagnetic fields are generated during imaging. 1. A strong, static magnetic field, which remains virtually constant, is used to align the protons. 2. A small, rapidly varying magnetic field gradient is used for spatial localization. 3. Radio frequency pulses are used to produce changes in the energy states of the protons. At present it is generally accepted that these magnetic fields pose no reproducible adverse effects upon living tissue if used within specified guidelines." However, some contraindications to MRI exist in patients with ferromagnetic metallic implants or other ferromagnetic materials, largely because of the potential hazards associated with movement of these objects, as in the case of some aneurysm clips, which have been shown to become dislodged from clipped vessels in an animal model. 2 Other potential problems associated with MRI include heating of the material, the induction of electrical current, and the misinterpretation of artifact as an abnormality.? However, to date there have been no reports of induced electrical currents produced by MRI of metallic bioimplants, Furthermore, the temperature changes associated with small metallic bioimplants and larger orthopedic prostheses were shown to be negligible.P:" In the case of cardiac pacemakers, the hazards seem to lie in the alteration of normal pulsing parameters that may be induced by the magnetic resonance imager. 5
As outlined by Shellock and Crues" and Shellock;' several important factors influence the relative risk of using MRI in patients who have metallic biomedical implants. These include 1) the strength of the gradient and static magnetic fields, 2) the degree of ferromagnetism of the implant or material, 3) the geometry of the implant or material, 4) the location and orientation of the implant in situ, and 5) the amount of time the implant has been in place. In accordance with the laws of physics, magnetic materials align themselves in the direction of a static magnetic field, as evidenced by the aforementioned deflection forces. Clearly, when a magnetic material has changed its orientation within this static magnetic field, rotation forces will act to realign the material, generating significant torques, ie, rotational movements. Since the cochlear implants have not previously been studied in conjunction with MRI, several findings from this investigation bear emphasis. They suggest that subjects with cochlear implants should not be exposed to the magnetic field of a magnetic resonance imager. First, significant electrical currents were generated by the 3M cochlear implants, which certainly could result in severe injury to the cochlea and its related structures. Next, significant forces were generated by all three of the cochlear implants that potentially could cause movement of the implant within the patient's head and, in doing so, injure surrounding structures, damage the electrode, or even withdraw the electrode from within the cochlea. Of course, the effect depends on the degree of fixation and the integrity of the surrounding tissues. Since the sensitivity of the cochlear implant relies on its ability to electrically stimulate specific regions of the cochlea, even the slightest change in position of the intracochlear electrodes could alter the specific signals generated, requiring, at least, reprogramming of the device. The last consideration is the damage caused to the instrument itself, and not to the patient. After being exposed to what is now considered a relatively weak (0.6 T) magnetic resonance imager, both of the 3M cochlear implants were found to be significantly magnetized and afunctional; the Nucleus device, however, showed no loss of function and no change in magnetization. Other factors not brought out by our investigation but of consideration are the artifacts or "white-out" caused by the implant during imaging, which have been shown to be very significant, especially when magnetic materials are imaged," and finally the potential for heat generation, which has not proved to be significant in other Investigations." CONCLUSION
Previous studies have shown that most patients with metallic bioimplants (approximately 75 0/0) can be examined relatively safely by MRI. 7 These bio-
Downloaded from aor.sagepub.com at The University of Iowa Libraries on June 23, 2015
Portnoy & Mattucci, Cochlear Implants & Magnetic Resonance Imaging
implants included aneurysm and hemostatic clips; dental implants and materials; intravascular coils, filters, and stents; middle ear prostheses-P-": prosthetic heart valves; orthopedic implants; penile implants; and other miscellaneous metallic implants and materials. The hazards of performing MRI on patients with metallic bioimplants usually related to movement or dislodgment, but potentially can relate to temperature change, induction of electrical current, and the misinterpretation of artifacts as an abnormality.
197
dislodge the cochlear implant and electrodes. 2. Significant electrical currents are generated in the 3M/House and 3M/Vienna cochlear implants when they are exposed to the magnetic field of a O.6-T imager. 3. Exposure to the magnetic field renders the 3M devices magnetized and afunctional. 4. The Nucleus device maintains both function and magnetization after exposure to the magnetic field. On the basis of these findings, MRI is contraindicated in patients with the cochlear implants reviewed. Further investigation is needed to determine if these findings can be applied to other models on the market today.
In the case of two 3M cochlear implants and the Nucleus device, we have shown the following primary effects: 1. Large torques are created that potentially can
REFERENCES 1. Mattucci KF, Setzen M, Hyman R, Chaturvedi G. The effect of magnetic resonance imaging on metallic middle ear prostheses. Otolaryngol Head Neck Surg 1986;94:441-3.
5. Pavlicek W, Geisinger M, Castle L, et al. The effects of nuclear magnetic resonance on patients with cardiac pacemakers. Radiology 1983;147:149-53.
2. New PFG, Rosen BR, Brady TJ, et a1. Potential hazards and artifacts of ferromagnetic and nonferromagnetic surgical and dental materials and devices in nuclear magnetic imaging. Radiology 1983;147:139-48.
6. Shellock F, Crues JV. High field strength MR imaging and metallic biomedical implants: an ex vivo evaluation of deflection forces. Am J Radiol 1988;151:389-92. 7. Shellock F. MR imaging of metallic implants and materials: a compilation of the literature. Am J RadioI1988;151:811-4.
3. Davis PL, Crooks L, Arakawa M, McRee R, Kaufman L, Margulis A. Potential hazards in NMR imaging: heating effects of changing magnetic fields and RF fields on small metallic implants. Am J Radiol 1981;137:857-60.
8. Applebaum EL, Valvassori CE. Effects of magnetic resonance imaging fields on stapedectomy prosthesis. Arch Otolaryngol 1985;111:820-1.
4. Mesgarzadeh M, Revesz G, Bonakdarpour A, Betz R. The effect on medical metal implants by magnetic fields of magnetic resonance imaging. Skeletal Radiol 1985;14:205-6.
9. Leon JA, Gabriele 0 F. Middle ear prosthesis: significance in magnetic resonance imaging. Magn Reson Imaging 1987;5: 405-6.
......... .........
FIRST INTERNATIONAL CONFERENCE ON ELECTROCOCHLEOGRAPHY AND MONITORING The First International Conference on Electrocochleography and Monitoring will be held Sept 20-24, 1992, in Wurzburg, Germany. For further information, contact Program Chairman, Dr Dirk Hoehmann, Dept of Otolaryngology, University of Wurzburg Medical School, [osef-Schneider-Str 11, D-8700, Wurzburg, Germany; telephone 49-931-201-2323, or FAX 49-931-201-2248.
Downloaded from aor.sagepub.com at The University of Iowa Libraries on June 23, 2015
