Temperature measurement on neurological pulse generators during MR scans

Kainz, Wolfgang; Neubauer, Georg; Überbacher, Richard; Alesch, François; Chan, Dulciana

doi:10.1186/1475-925x-1-2

Cited by 37 publications

(19 citation statements)

References 7 publications

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“…Currently, it is considered safe to scan patients with implanted DBS systems only if specific guidelines are observed. 14,33 Recommended exposures for RF energy include SAR < 4.0 W/kg whole body for 15 minutes, 3.0 W/ kg averaged over the head for 10 minutes, 8.0 W/kg in any gram of tissue in the head or torso for 15 minutes, or 12.0 W/kg in any gram of tissue in the extremities for 15 minutes. In December 2015, the Activa portfolio (Medtronic, Inc.) of DBS neurostimulators received Food and Drug Administration approval for full-body MRI under specific conditions of use.…”

Section: Discussionmentioning

confidence: 99%

3-Tesla MRI in patients with fully implanted deep brain stimulation devices: a preliminary study in 10 patients

Sammartino¹,

Krishna²,

Sankar

et al. 2017

Journal of Neurosurgery

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OBJECTIVE The aim of this study was to evaluate the safety of 3-T MRI in patients with implanted deep brain stimulation (DBS) systems. METHODS This study was performed in 2 phases. In an initial phantom study, a Lucite phantom filled with tissue-mimicking gel was assembled. The system was equipped with a single DBS electrode connected to an internal pulse generator. The tip of the electrode was coupled to a fiber optic thermometer with a temperature resolution of 0.1°C. Both anatomical (T1- and T2-weighted) and functional MRI sequences were tested. A temperature change within 2°C from baseline was considered safe. After findings from the phantom study suggested safety, 10 patients with implanted DBS systems targeting various brain areas provided informed consent and underwent 3-T MRI using the same imaging sequences. Detailed neurological evaluations and internal pulse generator interrogations were performed before and after imaging. RESULTS During phantom testing, the maximum temperature increase was registered using the T2-weighted sequence. The maximal temperature changes at the tip of the DBS electrode were < 1°C for all sequences tested. In all patients, adequate images were obtained with structural imaging, although a significant artifact from lead connectors interfered with functional imaging quality. No heating, warmth, or adverse neurological effects were observed. CONCLUSIONS To the authors' knowledge, this was the first study to assess the clinical safety of 3-T MRI in patients with a fully implanted DBS system (electrodes, extensions, and pulse generator). It provided preliminary data that will allow further examination and assessment of the safety of 3-T imaging studies in patients with implanted DBS systems. The authors cannot advocate widespread use of this type of imaging in patients with DBS implants until more safety data are obtained.

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Section: Discussionmentioning

confidence: 99%

3-Tesla MRI in patients with fully implanted deep brain stimulation devices: a preliminary study in 10 patients

Sammartino¹,

Krishna²,

Sankar

et al. 2017

Journal of Neurosurgery

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“…Active medical devices such as pacemakers and implantable neurological pulse generators (IPGs) have been studied extensively since these devices are implanted inside vital parts of the human body, such as heart muscle or brain. Kainz et al [7] reported a maximum of 2.1°C temperature increases at the lead tip for neurological pulse generators. However, some other studies found much higher temperature rise which could be harmful to humans.…”

Section: Introductionmentioning

confidence: 99%

Numerical investigations of MRI RF field induced heating for external fixation devices

et al. 2013

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BackgroundThe magnetic resonance imaging (MRI) radio frequency (RF) field induced heating on external fixation devices can be very high in the vicinity of device screws. Such induced RF heating is related to device constructs, device placements, as well as the device insertion depth into human subjects. In this study, computational modeling is performed to determine factors associated with such induced heating.MethodsNumerical modeling, based on the finite-difference time-domain (FDTD) method, is used to evaluate the temperature rises near external device screw tips inside the ASTM phantom for both 1.5-T and 3-T MRI systems. The modeling approach consists of 1) the development of RF coils for 1.5-T and 3-T, 2) the electromagnetic simulations of energy deposition near the screw tips of external fixation devices, and 3) the thermal simulations of temperature rises near the tips of these devices.ResultsIt is found that changing insertion depth and screw spacing could largely affect the heating of these devices. In 1.5-T MRI system, smaller insertion depth and larger pin spacing will lead to higher temperature rise. However, for 3-T MRI system, the relation is not very clear when insertion depth is larger than 5 cm or when pin spacing became larger than 20 cm. The effect of connection bar material on device heating is also studied and the heating mechanism of the device is analysed.ConclusionsNumerical simulation is used to study RF heating for external fixation devices in both 1.5-T and 3-T MRI coils. Typically, shallower insertion depth and larger pin spacing with conductive bar lead to higher RF heating. The heating mechanism is explained using induced current along the device and power decay inside ASTM phantom.

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“…The MoTLiM may have applications beyond the heating of implants during MRI, such as in cell phone implant interactions. There are studies that have analyzed SAR gain in the presence of a deep brain stimulator 22 during the use of cell phones. The MoTLiM may also be used to calculate induced currents on these implants when they interact with cell phones.…”

Section: Discussionmentioning

confidence: 99%

Modeling of radio‐frequency induced currents on lead wires during MR imaging using a modified transmission line method

Açıkel

Atalar

2011

Medical Physics

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Purpose: Metallic implants may cause serious tissue heating during magnetic resonance (MR) imaging. This heating occurs due to the induced currents caused by the radio-frequency (RF) field. Much work has been done to date to understand the relationship between the RF field and the induced currents. Most of these studies, however, were based purely on experimental or numerical methods. This study has three main purposes: (1) to define the RF heating properties of an implant lead using two parameters; (2) to develop an analytical formulation that directly explains the relationship between RF fields and induced currents; and (3) to form a basis for analysis of complex cases. Methods: In this study, a lumped element model of the transmission line was modified to model leads of implants inside the body. Using this model, leads are defined using two parameters: impedance per unit length, Z, and effective wavenumber along the lead, k t . These two parameters were obtained by using methods that are similar to the transmission line theory. As long as these parameters are known for a lead, currents induced in the lead can be obtained no matter how complex the lead geometry is. The currents induced in bare wire, lossy wire, and insulated wire were calculated using this new method which is called the modified transmission line method or MoTLiM. First, the calculated induced currents under uniform electric field distribution were solved and compared with method-of-moments (MoM) calculations. In addition, MoTLiM results were compared with those of phantom experiments. For experimental verification, the flip angle distortion due to the induced currents was used. The flip angle distribution around a wire was both measured by using flip angle imaging methods and calculated using current distribution obtained from the MoTLiM. Finally, these results were compared and an error analysis was carried out. Results: Bare perfect electric, bare lossy, and insulated perfect electric conductor wires under uniform and linearly varying electric field exposure were solved, both for 1.5 T and 3 T scanners, using both the MoTLiM and MoM. The results are in agreement within 10% mean-square error. The flip angle distribution that was obtained from experiments was compared along the azimuthal paths with different distances from the wire. The highest mean-square error was 20% among compared cases. Conclusions: A novel method was developed to define the RF heating properties of implant leads with two parameters and analyze the induced currents on implant leads that are exposed to electromagnetic fields in a lossy medium during a magnetic resonance imaging (MRI) scan. Some simple cases are examined to explain the MoTLiM and a basis is formed for the analysis of complex cases. The method presented shows the direct relationship between the incident RF field and the induced currents. In addition, the MoTLiM reveals the RF heating properties of the implant leads in terms of the physical features of the lead and electrical properties of the medium.

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Temperature measurement on neurological pulse generators during MR scans

Cited by 37 publications

References 7 publications

3-Tesla MRI in patients with fully implanted deep brain stimulation devices: a preliminary study in 10 patients

3-Tesla MRI in patients with fully implanted deep brain stimulation devices: a preliminary study in 10 patients

Numerical investigations of MRI RF field induced heating for external fixation devices

Modeling of radio‐frequency induced currents on lead wires during MR imaging using a modified transmission line method

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