Neurostimulation systems for deep brain stimulation: In vitro evaluation of magnetic resonance imaging–related heating at 1.5 tesla

Rezai, Ali R.; Finelli, Daniel A.; Nyenhuis, J.A.; Hrdlicka, Greg; Tkach, Jean A.; Sharan, Ashwini; Rugieri, Paul; Stypulkowski, Paul H.; Shellock, Frank G.

doi:10.1002/jmri.10069

Cited by 259 publications

(304 citation statements)

References 33 publications

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“…11 On the other hand, MR imaging may not be possible in patients with metallic implants; many researchers have reported study of RF heating of such implants. [12][13][14] Even under identical RF irradiation power, in a patient with such an implant, the uniformity of the electricˆeld is disturbed near the implant, and the electric current density and energy absorption may greatly increase locally. Such local heating is termed a``hotspot.''…”

Section: Introductionmentioning

confidence: 99%

Dependence of RF Heating on SAR and Implant Position in a 1.5T MR System

Muranaka

Horiguchi

Usui

et al. 2007

MRMS

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Purpose: We evaluated radiofrequency (RF) heating of a humerus implant embedded in a gel phantom during magnetic resonance (MR) imaging for the speciˆc absorption rate (SAR), angle between the implant and static magneticˆeld (B 0 ), and position of the implant in the irradiation coil.Methods: We embedded a stainless steel humerus implant 2 cm deep in tissue-equivalent loop and mass phantoms, placed it parallel to the static magneticˆeld of a 1.5T MR scanner, and recorded the temperatures of the implant surface with RF-transparentˆberoptic sensors. We measured rises in temperature at the tips of the implant by varying the SAR from 0.2 to 4.0 W/kg and evaluated RF heating of the implant for its angle to B 0 and its displacement along B 0 from the center of the RF irradiation coil.Results: RF heating was similar for the loop and mass phantoms because the eddy current ‰ows through the periphery of both. As the SAR increased, the temperature at the implant tip increased, and there was a linear relationship between the SAR and temperature rise. The values were 6.49 C at 2.0 W/kg and 12.79 C at 4.0 W/kg. Rise in temperature decreased steeply as the angle between the implant and B 0 surpassed 459 . In addition, as the implant was displaced from the center of the RF coil to both ends, the rise in temperature decreased.Conclusion: The rise in temperature in deep tissue was estimated to be higher than 1.09 C for SAR above 0.4 W/kg. RF heating was greatest when the implant was set parallel to B 0 . In MR imaging of patients with implants, there is a risk of RF heating when the loop of the eddy current is formed inside the body.

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Section: Introductionmentioning

confidence: 99%

Dependence of RF Heating on SAR and Implant Position in a 1.5T MR System

Muranaka

Horiguchi

Usui

et al. 2007

MRMS

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“…Combinations of these have been previously studied in the context of scalp EEGfMRI [18] and active deep brain stimulation (DBS) during MRI [19][20][21][22][23][24]. Depending on their frequency and amplitude, excessive currents in tissue may cause electro-motive forces, electrolysis, depolarisation and stimulation, burning, coagulation, and vaporisation which can all lead to cell damage and ultimately cell death [25][26][27].…”

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confidence: 99%

Feasibility of simultaneous intracranial EEG-fMRI in humans: A safety study

Carmichael¹,

Thornton

Rodionov³

et al. 2010

NeuroImage

111

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In epilepsy patients who have electrodes implanted in their brains as part of their presurgical assessment, simultaneous intracranial EEG and fMRI (icEEG-fMRI) may provide important localising information and improve understanding of the underlying neuropathology. However, patient safety during icEEG-fMRI has not been addressed.Here the potential health hazards associated with icEEG-fMRI were evaluated theoretically and the main risks identified as: mechanical forces on electrodes from transient magnetic effects, tissue heating due to interaction with the pulsed RF fields and tissue stimulation due to interactions with the switched magnetic gradient fields.These potential hazards were examined experimentally in-vitro on a Siemens 3 T Trio, 1.5 T Avanto and a GE 3 T Signa Excite scanner using a Brain Products MR compatible EEG system. No electrode flexion was observed. Temperature measurements demonstrated thatheating well above guideline limits can occur. However heating could be kept within safe limits (<1.0°C) by using a head transmit RF coil, ensuring EEG cable placement to exit the RF coil along its central z-axis, using specific EEG cable lengths and limiting MRI sequence specific absorption rates (SARs). We found that the risk of tissue damage due to RF-induced heating is low provided implant and scanner specific SAR limits are observed with a safety margin used to account for uncertainties (e.g. in scanner-reported SAR). The observed scanner gradientswitching induced current (0.08mA) and charge density (0.2μC/cm 2 ) were well within safety limits (0.5mA and 30μC/cm 2 , respectively).3

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“…IMPLANTED MEDICAL DEVICES such as deep brain stimulators and cardiac pacemakers interact with the magnetic fields in magnetic resonance imaging (MRI) (1)(2)(3)(4)(5). One of the interactions is tissue heating.…”

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confidence: 99%

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

Park

Kamondetdacha

Nyenhuis

2007

Magnetic Resonance Imaging

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200

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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. Transfer functions were calculated at 64 MHz for different lengths of model implants in the form of bare wires and insulated wires with 1 cm of wire exposed at one or both ends.Results: Heating at the electrode depends on the magnitude and the phase distribution of the transfer function and the incident electric field along the length of the lead. For a uniform electric field, the electrode heating is maximized for a lead length of approximately one-half a wavelength when the lead is terminated open. The heating can be greater for a worst-case phase distribution of the incident field. Conclusion:The transfer function is proposed as an efficient method to calculate MRI-induced heating at an electrode of a medical lead. Measured temperature rises of a model implant in a phantom were in good agreement with the rises predicted by the transfer function. The transfer function could be numerically or experimentally determined. IMPLANTED MEDICAL DEVICES such as deep brain stimulators and cardiac pacemakers interact with the magnetic fields in magnetic resonance imaging (MRI) (1-5). One of the interactions is tissue heating. The heating arises from the scattered electric field due to interaction of the MRI radio frequency (RF) magnetic field (B 1 ) and a medical implant. The greatest, and potentially dangerous, temperature rises occur at the ends of elongated implants, such as at the electrode of an implanted lead (6,7).In vitro testing in phantoms has been undertaken to characterize the RF-induced temperature rise (8). Recently, there has been an increased interest in mathematical modeling to assess the in vivo temperature rise. Numerical modeling based on the finite difference time domain (FDTD) method has been used to calculate the RF-induced electric field in human (9,10) and phantom models (11). It is difficult to numerically solve human and lead models simultaneously due to the complex structure of medical lead systems. It may be advantageous to model the lead and the human separately and then combine the results to determine the heating. The focus in this work is on modeling the lead. We describe the transfer function of a lead that relates the incident electric field to the scattered electric field in the vicinity of the electrode. From knowledge of the transfer function, the heating at the electrode and the resonant behavior of leads in phantom and human models can be predicted. Figure 1 shows the concept of the transfer function of a lead wire. An incident electric field with a tangential component E tan couples with the lead. The overall length of the lead is L, is the dis...

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Neurostimulation systems for deep brain stimulation: In vitro evaluation of magnetic resonance imaging–related heating at 1.5 tesla

Cited by 259 publications

References 33 publications

Dependence of RF Heating on SAR and Implant Position in a 1.5T MR System

Dependence of RF Heating on SAR and Implant Position in a 1.5T MR System

Feasibility of simultaneous intracranial EEG-fMRI in humans: A safety study

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

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