Evaluation of radiofrequency safety by high temperature resolution MR thermometry using a paramagnetic lanthanide complex.

Purpose: The current practice of calculating the specific absorption rate (SAR) relies on local temperature measurements made using temperature probes. For an accurate SAR measurement, a temperature imaging method that provides high temperature sensitivity is desirable, because acceptable levels of SAR produce small temperature changes. MR thermometry using paramagnetic lanthanide complexes can be used to obtain absolute temperature measurements with sub-degree temperature and sub-millimeter spatial resolution.

ACR guidance document on MR safe practices: 2013.

Because there are many potential risks in the MR environment and reports of adverse incidents involving patients, equipment and personnel, the need for a guidance document on MR safe practices emerged. Initially published in 2002, the ACR MR Safe Practices Guidelines established de facto industry standards for safe and responsible practices in clinical and research MR environments. As the MR industry changes the document is reviewed, modified and updated.

An evaluation of MRI safety and compatibility of a silver-impregnated antimicrobial wound dressing.

Purpose: Wound infections can slow healing, increase pain, and have negative effects on a patient's quality of life. The recent emergence of antibiotic-resistant bacterial strains has led wound care specialists to revisit alternative topical agents such as silver to control wound bioburden. Aquacel Ag is an ionic silver-containing barrier dressing that is able to absorb large amounts of wound exudate.

Calculation of MRI-induced heating of an implanted medical lead wire with an electric field transfer function.

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 of the lead. The transfer function is numerically calculated with the method of moments.

Reduction of magnetic resonance imaging-related heating in deep brain stimulation leads using a lead management device.

Objective: To evaluate the ability of a lead management device to reduce magnetic resonance imaging (MRI)-related heating of deep brain stimulation (DBS) leads and thereby to decrease the risks of exposing patients with these implants to MRI procedures.

Methods: Experiments were performed using the Activa series (Medtronic, Inc., Minneapolis, MN) DBS systems in an in vitro, gelled-saline head and torso phantom.

Thresholds for 60 Hz magnetic field stimulation of peripheral nerves in human subjects.

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 anatomical models of the body by that same exposure system. PNS thresholds at power frequencies (50/60 Hz) can be predicted from these data due to the wide range of pulse durations (70 mus to 1 ms), the length of the pulse trains (several tens of ms), and the exposure of a large part of the body to the magnetic field.

Neurostimulation systems: assessment of magnetic field interactions associated with 1.5- and 3-Tesla MR systems.

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 neurostimulation systems.

Peripheral nerve stimulation by gradient switching fields in magnetic resonance imaging.

A heterogeneous model of the human body and the scalar potential finite difference method are used to compute electric fields induced in tissue by magnetic field exposures. Two types of coils are considered that simulate exposure to gradient switching fields during magnetic resonance imaging (MRI). These coils producing coronal (y axis) and axial (z axis) magnetic fields have previously been used in experiments with humans.

Implantable microstimulator: magnetic resonance safety at 1.5 Tesla.

Rationale And Objective: Ex vivo testing is necessary to characterize implants to determine if it is safe for the patient to undergo a magnetic resonance imaging (MRI) examination. Therefore, the objective of this study was to evaluate MR safety for an implantable microstimulator in association with a 1.5 Tesla MR system.

Evaluation of specific absorption rate as a dosimeter of MRI-related implant heating.

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.

Neurostimulation system used for deep brain stimulation (DBS): MR safety issues and implications of failing to follow safety recommendations.

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 associated with heating, magnetic field interactions, induced currents, and the functional disruption of these devices. The exact safety recommendations for the particular neurostimulation system with regard to the pulse generator, leads, electrodes, operational conditions for the device, the positioning of these components, and the MR system conditions must be carefully followed for MRI.

MR imaging-related heating of deep brain stimulation electrodes: in vitro study.

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.

Simulation of human respiration in fMRI with a mechanical model.

Obtaining functional magnetic resonance images of the brain is a challenging measurement process having a low characteristic signal-to-noise ratio. Images contain various forms of noise, including those induced by physiologic processes. One of the prevalent disturbances is hypothesized to result from susceptibility fluctuations caused by abdominal volume changes during respiration.

Comparison of the threshold for peripheral nerve stimulation during gradient switching in whole body MR systems.

Purpose: To compare thresholds for peripheral nerve stimulation from gradient switching in whole body magnetic resonance (MR) equipment of different design.

Materials And Methods: Threshold data obtained in three experiments were reformatted into a single joint data set describing thresholds for anterio-posterior (AP) gradient orientation and Echo Planar Imaging (EPI) waveforms with bipolar ramp times between 0.07 and 1.

Neurostimulation systems for deep brain stimulation: in vitro evaluation of magnetic resonance imaging-related heating at 1.5 tesla.

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 worst-case and clinically relevant positioning scenarios. In vitro testing was performed using a 1.