Multi-Segment Leads To Reduce RF Heating in MRI: A Computational Evaluation at 1.5T and 3T.

Implanted neurostimulators are currently in widespread use and allow patients to receive therapeutic nerve stimulation for a variety of conditions. Such devices often make use of long leads extending from the device to the relevant nerve to deliver their stimulation. These leads carry a significant radiofrequency (RF) safety concern for patients who also receive magnetic resonance imaging (MRI) scans.

Effect of direct voltage induction by low-frequency security systems on neurostimulator lead.

Low-frequency (LF) security systems, such as antitheft electronic article surveillance (EAS) gates emit strong magnetic fields that could potentially interfere with neurostimulator operation. Some patients reported pain and shocking sensations near EAS gates, even after they turned off their pulse generator. To investigate the direct voltage induction of EAS systems on neurostimulator leads, we evaluated voltages induced by two EAS systems (14 kHz continuous wave or 58 kHz pulsed) on a 40 cm sacral neurostimulator lead formed in a circular loop attached to a pulse generator that was turned off.

Parameters Affecting Worst-Case Gradient-Field Heating of Passive Conductive Implants.

Background: Testing MRI gradient-induced heating of implanted medical devices is required by regulatory organizations and others. A gradient heating test of the ISO 10974 Technical Specification (TS) for active implants was adopted for this study of passive hip implants. All but one previous study of hip implants used nonuniform gradient exposure fields in clinical scanners and reported heating of less than 5 °C.

Electric Field Comparison for TMS Using Different Neuroimaging Segmentation Methods.

Computational electromagnetic modeling is a powerful technique to evaluate the effects of electrical stimulation of the human brain. The results of these simulations can vary depending on the specific segmentation of the head and brain generated from the patient images. Using an existing boundary element fast multipole method (BEM-FMM) electromagnetic solver, this work evaluates the electric field differences modeled using two neuroimaging segmentation methods.

Comparison of SAR distribution of hip and knee implantable devices in 1.5T conventional cylindrical-bore and 1.2T open-bore vertical MRI systems.

Purpose: There is increasing use of open-bore vertical MR systems that consist of two planar RF coils. A recent study showed that the RF-induced heating of a neuromodulation device was much lower in the open-bore system at the brain and the chest imaging landmarks. This study focused on the hip and knee implants and compared the specific absorption rate (SAR) distribution in human models in a 1.

Survey of Acoustic Output in Neonatal Brain Protocols.

Background: Auditory and non-auditory safety concerns associated with the appreciable sound levels inherent to magnetic resonance imaging (MRI) procedures exist for neonates. However, current gaps in knowledge preclude making an adequate risk assessment.

Purpose: To measure acoustic exposure (duration, intensity, and frequency) during neonatal brain MRI and compare these values to existing hearing safety limits and data.