Calculating RF-Induced Voltages for Implanted Medical Devices in MRI Using Computational Human Models.

Despite its import as a diagnostic tool, patients with active implantable medical devices (AIMDs) are generally denied access to magnetic resonance imaging (MRI). The complexity of MRI environments stems from a multiplicity of fields and numerous scan parameters. In order to perform a risk assessment for RF-induced malfunction, manufacturers perform electromagnetic simulations using computational human models (CHMs) to calculate RF induced energy at the AIMD ports. This work explores the impact of the CHMs on the calculation of RF-induced voltages at the RF antenna port for cardiovascular implantable electronic devices (CIEDs).

Virtual Humans for Implantable Device Safety Assessment in MRI: Mitigating Magnetic Resonance Imaging Hazards for Implanted Medical Devices.

Magnetic resonance imaging (MRI) is the preferred modality for soft tissue imaging because of its nonionizing radiation and lack of contrast agent. Due to interactions between the MR system and active implantable medical devices (AIMDs), patients with implants such as pacemakers are generally denied access to MRI, which presents a detriment to that population. It has been estimated that 50-75% of patients with a cardiac device were denied access to MRI scanning and, moreover, that 17% of pacemaker patients need an MRI within 12 months of implantation [1]. In recent years, AIMD manufacturers, such as Biotronik, have assessed the conditional safety of devices in MRI.

SAW-LC coupled resonator wideband VCO for medical telemetry.

Wireless links with implantable devices can help in real-time monitoring of symptoms, irregularities, implanted device efficacy and their reconfiguration. We present the design of a low-power wideband voltage controlled oscillator (VCO) to facilitate implantable wireless telemetry. A coupled SAW-LC resonator design combines high Q and spectral purity of a SAW element and tunability of an LC-tank. The designed 2.7 MHz bandwidth VCO is suitable for full duplex communication protocols in the MedRadio band with frequency agility and higher duty cycles, in conformance with FCC regulations. Output power at the fundamental frequency is above -7.5 dBm for a wide range of load impedances. Output power load insensitivity provides a wide margin for selection of communication system parameters, variability in device placement, temporal variation in tissue properties and flexibility for implants at different locations (e.g. heart, gastrointestinal tract, brain). The maximum output power variation in the entire 2.7 MHz band is limited to 1.3 dBm. Sensitivity of oscillation frequency to loading can be addressed by individual device calibration. The small size, component count and low DC power consumption (1.9 V, ~1.95 mW) is favorable for including in a miniaturized and integrated design assembly with a battery-powered implanted device.

MR conditional safety assessment of implanted medical devices: advantages of computational human phantoms.

Until recently, patients with active implantable medical devices (AIMDs) have been contraindicated for magnetic resonance imaging (MRI). Current efforts to demonstrate safety of these devices separate the interaction of the device and MRI into several hazards. For several of these hazards, computational human phantoms (CHPs) are used to provide conservative conditions for a risk-based analysis. This use of CHPs for the identification of conservative conditions provides a substantial benefit to the assessment of MR conditional safety over experimental techniques, as the evaluation of millions of test cases is possible in simulation, but impractical (due to economic constraints) and, in some cases, unethical for an experimental effort.