Patients with medical implants are often unable to receive Magnetic Resonance Imaging (MRI) diagnostic treatment because the conductive leads can concentrate the RF excitation field and generate dangerous heating of nervous tissue. We propose a simple low-cost solution that minimizes RF heating through the addition of one or more mutually-coupled filars to the lead without significant increase in lead diameter. Simulations and measurements at 128 MHz are presented to verify the effect in 3-Tesla MRI machines.

Magnetic Resonance Imaging (MRI) scans are contraindicated for many patients with medical implants. We establish the circumstances that cause, and the resistances required to ameliorate and to eliminate dangerous levels of MRI-induced heating that occur at the exposed, distal end of an electrical lead implanted in tissue. Simulated predictions are compared with measurements made at 128 MHz in a 3-Tesla MRI machine. A low resistance at kilohertz frequencies is sought by implant makers, in contrast with the high resistance demanded for safety. The practicality of presently-developed strategies to prevent tissue damage is brought into question. We examine the extent to which skin-depth and transmission-line properties can be manipulated to improve safety.Index Terms-Biomedical electrodes, medical diagnostic imaging, dipole antennas, electromagnetic modeling.

The standard technique for determining the compatibility of medical implants to the magnetic and RF fields present in Magnetic Resonance Imaging (MRI), requires access to an MRI machine. For implants comprising metals of mostly the non-ferrous kind, it is only the RF field of an MRI machine that is of concern. Implant electrodes can concentrate the RF field in the surrounding tissue and give rise to joule heating. The inherent design of Spinal Cord Stimulators (SCS) and Deep Brain Stimulators (DBS) makes these implants particularly susceptible to hazardous levels of RF heating. We propose a technique that offers a quick and indicative assessment of the compatibility of implant leads to the RF field in 3-Tesla MRI, without needing access to an MRI machine. A dipole antenna, driven by a power amplifier and Continuous Wave (CW), injects RF energy into a gelled saline phantom. The heating in the gel near a test implant electrode is monitored with a fiber optic thermometer. The results are calibrated against measurements made in a 3-Tesla MRI machine.

Medical implants often prevent patients having Magnetic Resonance Imaging (MRI) scans because the leads behave as antennas with respect to the RF excitation and cause hazardous heating in neural tissue. This manuscript describes an approach that virtually eliminates the risk of RF heating by means of easily-incorporated, mutually-coupled filars. The resulting leads need be neither physically larger nor significantly more costly than existing designs. Combined with thin insulation and surface roughening techniques, this manuscript represents the first complete release of recently-patented technologies. Both simulations and measurements at 128MHz are presented to confirm performance in 3-Tesla MRI machines.

Abstract-Band-pass microwave systems such as ultrawideband (UWB) antennas are traditionally characterized in the frequency-domain through a vector network analyzer (VNA) in an anechoic chamber. A recent study proved antennas could be accurately measured in the time-domain using a step-function time-domain reflectometer (TDR), without the need for an anechoic chamber. We propose a new advance in the TDR characterization method. An impulse generator is employed in place of the step generator in a TDR set-up. The advantage conferred by this change is that more energy is available beyond a given frequency than with a step, and so a higher signal-tonoise ratio (SNR) is achieved. The theoretical result is compared with measurement.