RF-Induced Unintended Stimulation for Implantable Medical Devices in MRI

Abstract

Historically, patients with implantable medical devices have been denied access to magnetic resonance imaging (MRI) due to several potentially hazardous interactions. There has been significant interest in recent years to provide access to MRI to patients with implantable medical devices, as it is the preferred imaging modality for soft tissue imaging. Among the potential hazards of MRI for patients with an active implantable medical device is radio frequency (RF)-induced unintended stimulation. RF energy incident on the device may be rectified by internal active components. Any rectified waveform present at the lead electrodes may stimulate nearby tissue. In order to assess the risk to the patient, device manufacturers use computational human models (CHMs) to quantify the incident RF on the device and perform in vitro testing to determine the likelihood of unintended stimulation. The use of CHMs enables the investigation of millions of scenarios of scan parameters, patient sizes and anatomies, and MR system technologies.

Computational Tool Comprising Visible Human Project® Based Anatomical Female CAD Model and Ansys HFSS/Mechanical® FEM Software for Temperature Rise Prediction Near an Orthopedic Femoral Nail Implant During a 1.5 T MRI Scan

“…Some recent uses of the VHP Female v3.0-5.0 computational human model have been documented in the literature -cf. for example [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31] -and compared with experimental data on radio frequency propagation. A number of studies have focused on the characteristics and behaviors of antennas near the human body [15][16][17][18][19][20][21][22][23].…”

“…A number of studies have focused on the characteristics and behaviors of antennas near the human body [15][16][17][18][19][20][21][22][23]. Others have examined through simulation various biomedical applications including transmission channel modeling [24], transcranial direct current stimulation [25], estimation of bone density [26], gastroenterology [27,28], SAR simulations in MRI coils at 3 T [29], and safety of active implants under MRI procedures [30,31].…”

“…• The tool currently does not provide heating estimates for gradient-coil induced power deposition for orthopedic implants. • The computational human model margins are limited to women aged 50-70 and with a high obesity (BMI of [30][31][32][33][34][35][36].…”

RF-induced Heating Near Active Implanted Medical Devices in MRI: Impact of Tissue Simulating Medium

“…For thin insulation leads, the TSM at the lead tip is no longer dominant and the choice in TSM should align with the average along the lead body [40]. While the focus of this work has been RF-induced heating, most of these principles are extensible to other RF-induced hazards, such as RF-induced unintended stimulation [41].…”

Visible Human Project® female surface based computational phantom (Nelly) for radio-frequency safety evaluation in MRI coils

“…Some recent uses of the VHP Female v3.0-5.0 computational human model have been documented in the literature-cf. for example [25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42]-and compared with experimental data on radio frequency propagation. A number of studies have focused on the characteristics and behaviors of antennas near the human body [26][27][28][29][30][31][32][33][34].…”