When patients implanted with deep brain stimulation (DBS) or cardiac pacing (CP) lead systems are exposed to external Radio Frequency (RF) fields, local tissue damage around the electrodes of these leads can occur as has bees reported by various researchers. See, e.g., Baker et al., Neurostimulation systems: assessment of magnetic field interactions associated with 1.5- and 3-Tesla MR systems, J Magn Reson Imaging 2005;21(1):72-77; Bhidayasiri et al., Bilateral neurostimulation systems used for deep brain stimulation: in vitro study of MRI-related heating at 1.5 T and implications for clinical imaging of the brain; Magn Reson Imaging 2005;23(4):549-555; Rezai et al., Neurostimulators: potential for excessive heating of deep brain stimulation electrodes during magnetic resonance imaging, J Magn Reson Imaging 2001;14(4):488-489; Chou et al., RF heating of implanted spinal fusion stimulator during magnetic resonance imaging, IEEE Trans Biomed Eng 1997;44(5):367-373; and Luechinger et al., In vivo heating of pacemaker leads during magnetic resonance imaging, Eur Heart J 2005;26(4):376-383; discussion 325-377.
There are several external RF sources such as, for example, RF exposure during MRI or during RF diathermy. Local tissue damage during RF diathermy procedures in patients with implanted deep brain stimulator lead systems has also been reported. RF/microwave diathermy treatments can use leads that employ an alternating current to cauterize tissue. The diathermy alternating current delivered during the therapy can be in the range of between about 1 KHz-350 MHz (believed to be typically at about 27.5 MHz). In certain situations, the lead system may undesirably act as an antenna, receiving and depositing current in localised tissue where the leads are exposed, thereby potentially increasing the specific absorption rate (SAR) (a way of measuring the quantity of radiofrequency (RF) energy that is absorbed by the body).
RF heating of tissue in close proximity to long conductors (such as metallic wires) in an MRI environment has also been reported in literature. Local tissue damage can be caused by RF deposition in the tissue that is in close proximity to the linear conductors or electrodes of the lead system, when patients with implanted leads or interventional devices are placed in an external RF field. This RF heating mechanism may be explained as follows. During an MRI scan, the transmit RF field creates a voltage along the long linear conductors (individual or part of any interventional device) or the conductors/filers of the DBS and cardiac pacing lead systems. Currents are then created through the conductors and into the surrounding tissue. Where the current emerges from the distal tip of the device (or adjacent to the electrode in the case of an implantable lead), it can be concentrated and can cause heating and subsequent tissue damage.
In view of the foregoing, there remains a need for alternative medical lead configurations.