MRI safety: RF-induced heating near straight wires

Park, S.M.; Kamondetdacha, R.; Amjad, A.; Nyenhuis, J.A.

doi:10.1109/tmag.2005.854803

Cited by 64 publications

(47 citation statements)

References 7 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…6, which shows that the resonant length for the bare wire is about 20 cm, which is approximately /2 for the medium. Park et al (14) measured RF-induced heating vs. the length of the wires, and the resonant length of the bare wire was measured to be in the range 20 -24 cm, which is consistent with the resonant length calculated here using the transfer function. However, the length for maximal heating of the wires with insulation thickness of 0.45 mm is nearly a factor of 2 than for the bare wire.…”

Section: Discussionsupporting

confidence: 83%

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

Park

Kamondetdacha

Nyenhuis

2007

Magnetic Resonance Imaging

200

210

View full text Add to dashboard Cite

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...

show abstract

Section: Discussionsupporting

confidence: 83%

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

Park

Kamondetdacha

Nyenhuis

2007

Magnetic Resonance Imaging

200

210

View full text Add to dashboard Cite

show abstract

“…The temperature rises that result can be found by in-vitro measurements made in phantoms. Alternatively, electromagnetic fields can be computed using a numerical method such as the method of moments (MoM) [1,2], or the finite difference time domain (FDTD) method [3,4], or the finite element method (FEM) [5,6]. Leads are often implanted below the skin and the implantation depth can vary.…”

Section: Introductionmentioning

confidence: 99%

Interaction of Medical Implants With the Mri Electromagnetic Fields

Mohsin¹,

Nyenhuis²,

Masood³

2010

PIER C

View full text Add to dashboard Cite

Abstract-Medical implants in the form of linear conductive structures partially insulated along their length are especially prone to induced heating when subjected to the radiofrequency field used during magnetic resonance imaging (MRI). Leads or similar structures are often implanted near the skin and we have analyzed such implants when the implantation depth is varied in steps from 3 mm to 9 mm or more. Current, electric field, and induced temperature rise distributions in tissue have been obtained. The results have been validated by laboratory measurements.

show abstract

“…Secondly, surface waves [12] may be excited on extended lengths of conductor by electric fields, particularly near tuning capacitors in the transmitter coil. If these waves are resonant, the result may be rapid heating [13][14][15][16]. Unfortunately, the conductors are often closely surrounded by tissue, whose dielectric constant is high at standard clinical frequencies (63.85 MHz for 1 H MRI at 1.5 T) [17], so the resonant length is short.…”

Section: Introductionmentioning

confidence: 99%

Design of Magneto-Inductive Magnetic Resonance Imaging Catheters

2014

View full text Add to dashboard Cite

Abstract-A catheter-based RF receiver for internal magnetic resonance imaging is described. The device consists of a doublesided thin-film circuit, mounted on a hollow catheter. The system was originally designed for biliary ductal imaging, but is also potentially useful for vascular imaging. Signals are detected using a resonant L-C circuit at the catheter tip, transmitted along the catheter using an array of coupled L-C resonators, and coupled into a conventional RF system using a demountable inductive transducer. Protection against external B 1 and E fields is obtained by using figure-of-eight-shaped elements with an electrical length shorter than that of an immersed half-wave dipole. Electromagnetic modeling software (AWR Microwave Office) is used to analyze a system designed for 1 H imaging at 1.5 T, determine the effect of the tissue surround, demonstrate signal detection and transmission and verify intrinsic safety.

show abstract

MRI safety: RF-induced heating near straight wires

Cited by 64 publications

References 7 publications

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

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

Interaction of Medical Implants With the Mri Electromagnetic Fields

Design of Magneto-Inductive Magnetic Resonance Imaging Catheters

Contact Info

Product

Resources

About