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

Açıkel, Volkan; Atalar, Ergin

doi:10.1118/1.3662865

Cited by 43 publications

(61 citation statements)

References 21 publications

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“…If the field variation is small compared to electrode and IPG case size, we predict that the overall performance of the proposed analysis method will be similar to that of MoTLiM alone. As it was discussed in the original MoTLiM study, 11 the current distribution on the lead can be predicted reasonably well when the electric field variation along the lead is small. Also, during these analyses, bare cylindrical leads were used with a rectangular IPG case, a cylindrical electrode, and a spherical electrode.…”

Section: Discussionmentioning

confidence: 95%

“…This circuit model is easy to use with previously published model, which is based on the modified transmission line circuit model 11 as shown in Fig. 2(b).…”

mentioning

confidence: 99%

“…In our earlier study, the leads of the AIMDs were modeled using the modified transmission line method (MoTLiM). 11 This model is not complete since it does not include the effects of the implantable pulse generator (IPG) cases and the electrodes. These, however, significantly change the induced currents on the leads and alter the implant heating problem.…”

Section: Introductionmentioning

confidence: 99%

“…Z is the series impedance, and Y is the shunt admittances of the lead. From the circuit model of the lead, wavenumber along the lead was defined as In the MoTLiM, 11 the behavior of the induced currents was modeled using the following second order differential equation:…”

mentioning

confidence: 99%

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Modeling of electrodes and implantable pulse generator cases for the analysis of implant tip heating under MR imaging

Açıkel

Uslubas²,

Atalar

2015

Medical Physics

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Purpose: The authors purpose is to model the case of an implantable pulse generator (IPG) and the electrode of an active implantable medical device using lumped circuit elements in order to analyze their effect on radio frequency induced tissue heating problem during a magnetic resonance imaging (MRI) examination. Methods: In this study, IPG case and electrode are modeled with a voltage source and impedance. Values of these parameters are found using the modified transmission line method (MoTLiM) and the method of moments (MoM) simulations. Once the parameter values of an electrode/IPG case model are determined, they can be connected to any lead, and tip heating can be analyzed. To validate these models, both MoM simulations and MR experiments were used. The induced currents on the leads with the IPG case or electrode connections were solved using the proposed models and the MoTLiM. These results were compared with the MoM simulations. In addition, an electrode was connected to a lead via an inductor. The dissipated power on the electrode was calculated using the MoTLiM by changing the inductance and the results were compared with the specific absorption rate results that were obtained using MoM. Then, MRI experiments were conducted to test the IPG case and the electrode models. To test the IPG case, a bare lead was connected to the case and placed inside a uniform phantom. During a MRI scan, the temperature rise at the lead was measured by changing the lead length. The power at the lead tip for the same scenario was also calculated using the IPG case model and MoTLiM. Then, an electrode was connected to a lead via an inductor and placed inside a uniform phantom. During a MRI scan, the temperature rise at the electrode was measured by changing the inductance and compared with the dissipated power on the electrode resistance. Results: The induced currents on leads with the IPG case or electrode connection were solved for using the combination of the MoTLiM and the proposed lumped circuit models. These results were compared with those from the MoM simulations. The mean square error was less than 9%. During the MRI experiments, when the IPG case was introduced, the resonance lengths were calculated to have an error less than 13%. Also the change in tip temperature rise at resonance lengths was predicted with less than 4% error. For the electrode experiments, the value of the matching impedance was predicted with an error less than 1%. Conclusions: Electrical models for the IPG case and electrode are suggested, and the method is proposed to determine the parameter values. The concept of matching of the electrode to the lead is clarified using the defined electrode impedance and the lead Thevenin impedance. The effect of the IPG case and electrode on tip heating can be predicted using the proposed theory. With these models, understanding the tissue heating due to the implants becomes easier. Also, these models are beneficial for implant safety testers and designers. Using these models, worst case conditions can be det...

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Section: Discussionmentioning

confidence: 95%

“…This circuit model is easy to use with previously published model, which is based on the modified transmission line circuit model 11 as shown in Fig. 2(b).…”

mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Modeling of electrodes and implantable pulse generator cases for the analysis of implant tip heating under MR imaging

Açıkel

Uslubas²,

Atalar

2015

Medical Physics

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“…This rigorous approach has been used in recent models of RF-induced heating of lead wires during MRI [26]. Unfortunately, the geometry of our receiver makes a rigorous electromagnetic calculation extremely difficult.…”

Section: Body Loading In a 2d Systemmentioning

confidence: 99%