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Technical challenges and safety of magnetic resonance imaging with in situ neuromodulation from spine to brain
e u r o p e a n j o u r n a l o f p a e d i a t r i c n e u r o l o g y x x x ( 2 0 1 6 ) 1 e2
Official Journal of the European Paediatric Neurology Society
Editorial
Technical challenges and safety of magnetic resonance imaging with in situ neuromodulation from spine to brain
In this special issue of EJPN, John Thornton of UCLH reviews an important issue in neuromodulation, namely, how to obtain MRI safely after the implantation of the neuromodulation system.1 In particular, how should pediatric patients, who will reasonably expect to live several decades with the implanted system, be seen as likely candidates for MR imaging at some point in their life. Thornton's article covers all implantable neuromodulation systems currently in use: deep brain stimulation (DBS), vagus nerve stimulation (VNS), occipital nerve stimulation (ONS), spinal cord stimulation (SCS), sacral neuromodulation (SNM) and cochlear implants (CI). The author explores the subject comprehensively and addresses a number of concerns. Even the complex physical and technical challenges are suitably simplified. As Thornton states at the outset, it is important to realize that “neuromodulation and MRI both rely at the fundamental level on interactions between electromagnetic fields and tissue”. The MRI itself utilizes both the static magnetic field and the alternating high energy electromagnetic fields. Those usually harmless alternating electromagnetic fields may inductively connect to the implanted system generating abnormally high electrical current through the leads in the system. Following the laws of physics, electrical current moves toward the lowest impedance. Electrical current thus intensifies at the region of the electrical contacts or, in the case of the broken system, vicinity of the broken lead when in contact with tissue. Current density may become unbearably high causing severe and irreversible tissue injury. Serious neurological deficits2 or, in rare cases, death may result. In addition, the quality of MR images can be reduced when a component of the neuromodulation system is within the scanned area. Poor image quality can result in significant problems when diagnostic information is limited or even obstructed. The author goes on to consider the need for MRI after implantation surgery, proposing three different reasons for MRI. DOI of original article: http://dx.doi.org/10.1016/j.ejpn.2016.06. 001.
At that point it is important to stress the higher risk of cancer for radiation exposure at a younger age.3,4 Also, even one head-CT-scan at a young age may result in decreased IQ later in life.5 MRI is, therefore, strongly preferred to imaging modalities which use ionizing radiation such as CT. Technical requirements for MRI-conditional products must also be met. There should be continual pressure on manufacturers even though they do recognize the need for MRI-conditional systems. The possibility of MRI scanning should be a key criteria when selecting a neuromodulation system supplier. This will hopefully put pressure on commercial players to introduce new products, or in the very least make information available regarding the safety of their products in the MRI environment. However, despite ongoing developments multiple restrictions still exist. Various neuromodulation systems exist and this is further complicated by manufacturers adopting different approaches to achieve MRI compatibility. Also, MRI guidelines are strictly limited. Many academic papers, however, show that patients with neuromodulation are scanned without strict parameters as the author does indeed mention. Who, we might ask, is responsible when something goes wrong? Is it the doctor who requires the MR images, or one of several other agents: the neurologist, the radiologist, the manufacturer, the physicist or even the surgeon who implanted the system? When a problem occurs everyone may think the blame lies elsewhere. The entire process should be free of any weak link. Everyone involved should fully understand the implanted product and each possible combination of components. The pulse generator itself may be marked as MRI-conditional when using standard length of cables. Longer extension cables, however, can be problematic.2 Furthermore, all changes must be recorded. When, for example, the neuromodulation system is explanted, some parts must remain inside the patient. This is possible in the case of the VNS. Without a full and precise knowledge of implanted parts, all other experts in the process will be unable to properly evaluate MRI possibilities and address safety issues.
Please cite this article in press as: Katisko J, Technical challenges and safety of magnetic resonance imaging with in situ neuromodulation from spine to brain, European Journal of Paediatric Neurology (2016), http://dx.doi.org/10.1016/ j.ejpn.2016.11.006
2
e u r o p e a n j o u r n a l o f p a e d i a t r i c n e u r o l o g y x x x ( 2 0 1 6 ) 1 e2
references
1. Thornton J. Technical challenges and safety of magnetic resonance imaging with in situ neuromodulation from spine to brain. Eur J Pediatr Neurol 2016 [in this issue]. 2. Henderson JM, Tkach J, Phillips M, et al. Permanent neurological deficit related to magnetic resonance imaging in a patient with implanted deep brain stimulation electrodes for Parkinson's disease: case report. Neurosurgery 2005;57:E1063. 3. Miglioretti D, Johnson E, Williams A, et al. Pediatric computed tomography and associated radiation exposure and estimated cancer risk. JAMA Pediatr 2013;167:700e7. 4. Pearce M, Salotti J, Little M, et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet 2012;380:499e505.
5. Hall P, Adami HO, Trichopolous D, et al. Effect of low doses of ionising radiation in infancy on cognitive function in adulthood: Swedish population based cohort study. BMJ 2004;328:19.
Jani Katisko, Ph.D., Specialist Medical Physicist Neurosurgery, Operative Care Unit, Oulu University Hospital, Finland E-mail address: [email protected] http://dx.doi.org/10.1016/j.ejpn.2016.11.006 1090-3798/© 2016 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Katisko J, Technical challenges and safety of magnetic resonance imaging with in situ neuromodulation from spine to brain, European Journal of Paediatric Neurology (2016), http://dx.doi.org/10.1016/ j.ejpn.2016.11.006
Official Journal of the European Paediatric Neurology Society
Editorial
Technical challenges and safety of magnetic resonance imaging with in situ neuromodulation from spine to brain
In this special issue of EJPN, John Thornton of UCLH reviews an important issue in neuromodulation, namely, how to obtain MRI safely after the implantation of the neuromodulation system.1 In particular, how should pediatric patients, who will reasonably expect to live several decades with the implanted system, be seen as likely candidates for MR imaging at some point in their life. Thornton's article covers all implantable neuromodulation systems currently in use: deep brain stimulation (DBS), vagus nerve stimulation (VNS), occipital nerve stimulation (ONS), spinal cord stimulation (SCS), sacral neuromodulation (SNM) and cochlear implants (CI). The author explores the subject comprehensively and addresses a number of concerns. Even the complex physical and technical challenges are suitably simplified. As Thornton states at the outset, it is important to realize that “neuromodulation and MRI both rely at the fundamental level on interactions between electromagnetic fields and tissue”. The MRI itself utilizes both the static magnetic field and the alternating high energy electromagnetic fields. Those usually harmless alternating electromagnetic fields may inductively connect to the implanted system generating abnormally high electrical current through the leads in the system. Following the laws of physics, electrical current moves toward the lowest impedance. Electrical current thus intensifies at the region of the electrical contacts or, in the case of the broken system, vicinity of the broken lead when in contact with tissue. Current density may become unbearably high causing severe and irreversible tissue injury. Serious neurological deficits2 or, in rare cases, death may result. In addition, the quality of MR images can be reduced when a component of the neuromodulation system is within the scanned area. Poor image quality can result in significant problems when diagnostic information is limited or even obstructed. The author goes on to consider the need for MRI after implantation surgery, proposing three different reasons for MRI. DOI of original article: http://dx.doi.org/10.1016/j.ejpn.2016.06. 001.
At that point it is important to stress the higher risk of cancer for radiation exposure at a younger age.3,4 Also, even one head-CT-scan at a young age may result in decreased IQ later in life.5 MRI is, therefore, strongly preferred to imaging modalities which use ionizing radiation such as CT. Technical requirements for MRI-conditional products must also be met. There should be continual pressure on manufacturers even though they do recognize the need for MRI-conditional systems. The possibility of MRI scanning should be a key criteria when selecting a neuromodulation system supplier. This will hopefully put pressure on commercial players to introduce new products, or in the very least make information available regarding the safety of their products in the MRI environment. However, despite ongoing developments multiple restrictions still exist. Various neuromodulation systems exist and this is further complicated by manufacturers adopting different approaches to achieve MRI compatibility. Also, MRI guidelines are strictly limited. Many academic papers, however, show that patients with neuromodulation are scanned without strict parameters as the author does indeed mention. Who, we might ask, is responsible when something goes wrong? Is it the doctor who requires the MR images, or one of several other agents: the neurologist, the radiologist, the manufacturer, the physicist or even the surgeon who implanted the system? When a problem occurs everyone may think the blame lies elsewhere. The entire process should be free of any weak link. Everyone involved should fully understand the implanted product and each possible combination of components. The pulse generator itself may be marked as MRI-conditional when using standard length of cables. Longer extension cables, however, can be problematic.2 Furthermore, all changes must be recorded. When, for example, the neuromodulation system is explanted, some parts must remain inside the patient. This is possible in the case of the VNS. Without a full and precise knowledge of implanted parts, all other experts in the process will be unable to properly evaluate MRI possibilities and address safety issues.
Please cite this article in press as: Katisko J, Technical challenges and safety of magnetic resonance imaging with in situ neuromodulation from spine to brain, European Journal of Paediatric Neurology (2016), http://dx.doi.org/10.1016/ j.ejpn.2016.11.006
2
e u r o p e a n j o u r n a l o f p a e d i a t r i c n e u r o l o g y x x x ( 2 0 1 6 ) 1 e2
references
1. Thornton J. Technical challenges and safety of magnetic resonance imaging with in situ neuromodulation from spine to brain. Eur J Pediatr Neurol 2016 [in this issue]. 2. Henderson JM, Tkach J, Phillips M, et al. Permanent neurological deficit related to magnetic resonance imaging in a patient with implanted deep brain stimulation electrodes for Parkinson's disease: case report. Neurosurgery 2005;57:E1063. 3. Miglioretti D, Johnson E, Williams A, et al. Pediatric computed tomography and associated radiation exposure and estimated cancer risk. JAMA Pediatr 2013;167:700e7. 4. Pearce M, Salotti J, Little M, et al. Radiation exposure from CT scans in childhood and subsequent risk of leukaemia and brain tumours: a retrospective cohort study. Lancet 2012;380:499e505.
5. Hall P, Adami HO, Trichopolous D, et al. Effect of low doses of ionising radiation in infancy on cognitive function in adulthood: Swedish population based cohort study. BMJ 2004;328:19.
Jani Katisko, Ph.D., Specialist Medical Physicist Neurosurgery, Operative Care Unit, Oulu University Hospital, Finland E-mail address: [email protected] http://dx.doi.org/10.1016/j.ejpn.2016.11.006 1090-3798/© 2016 European Paediatric Neurology Society. Published by Elsevier Ltd. All rights reserved.
Please cite this article in press as: Katisko J, Technical challenges and safety of magnetic resonance imaging with in situ neuromodulation from spine to brain, European Journal of Paediatric Neurology (2016), http://dx.doi.org/10.1016/ j.ejpn.2016.11.006