John A. Nyenhuis

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E. Kanal is a consultant for, is a member of the speakers bureau of, and provides research support for Bracco Diagnostics and GE Healthcare; is a member of the speakers bureau of and provides research support for Siemens Medical Solutions; and provides research support for Berlex and Medtronic. T. Gilk is a consultant for Mednovus, Inc. J. R. Gimbel(More)
The use of magnetic resonance imaging (MRI) in patients with neurostimulation systems used for deep brain stimulation requires the utmost care, and no individual should undergo an MR examination in the absence of empirical evidence that the procedure can be performed safely. The risks of performing MRI in patients with neurostimulators include those(More)
PURPOSE To compare the magnetic resonance imaging (MRI)-related heating per unit of whole body averaged specific absorption rate (SAR) of a conductive implant exposed to two different 1.5-Tesla/64 MHz MR systems. MATERIALS AND METHODS Temperature changes at the electrode contacts of a deep brain stimulation lead were measured using fluoroptic thermometry.(More)
In magnetic resonance, time-varying gradient magnetic fields (dB/dt) may stimulate nerves or muscles by inducing electric fields in patients. Models predicted mean peripheral nerve and cardiac stimulation thresholds. For gradient ramp durations of less than a few milliseconds, mean peripheral nerve stimulation is a safe indicator of high dB/dt. At(More)
PURPOSE To evaluate magnetic field interactions at 1.5- and 3-Tesla for implantable pulse generators (IPGs) and radiofrequency (RF) receivers used for implantable neurostimulation systems. MATERIALS AND METHODS Measurements of magnetically induced displacement force and torque were determined for 10 devices (seven IPGs, three RF receivers) used for(More)
The strength duration relationship for peripheral nerve stimulation by MR imaging pulsed gradient magnetic fields was measured in 84 human subjects. The data were fitted to the hyperbolic strength-duration relationship: dB/dt=b(1 + c/d), where b is rheobase, c is chronaxie, and d is duration, and dB/dt is reported as the maximal value on the axis of the(More)
BACKGROUND AND PURPOSE Recent work has shown a potential for excessive heating of deep brain stimulation electrodes during MR imaging. This in vitro study investigates the relationship between electrode heating and the specific absorption rate (SAR) of several MR images. METHODS In vitro testing was performed by using a 1.5-T MR imaging system and a head(More)
PURPOSE To assess magnetic resonance imaging (MRI)-related heating for a neurostimulation system (Activa Tremor Control System, Medtronic, Minneapolis, MN) used for chronic deep brain stimulation (DBS). MATERIALS AND METHODS Different configurations were evaluated for bilateral neurostimulators (Soletra Model 7426), extensions, and leads to assess(More)
PURPOSE To develop and demonstrate a method to calculate the temperature rise that is induced by the radio frequency (RF) field in MRI at the electrode of an implanted medical lead. MATERIALS AND METHODS The electric field near the electrode is calculated by integrating the product of the tangential electric field and a transfer function along the length(More)
The goal of the research reported here is to narrow the range of uncertainty about peripheral nerve stimulation (PNS) thresholds associated with whole body magnetic field exposures at 50/60 Hz. This involved combining PNS thresholds measured in human subjects exposed to pulsed magnetic gradient fields with calculations of electric fields induced in detailed(More)