Power deposition inside a phantom for testing of MRI heating

Amjad, A.; Kamondetdacha, R.; Kildishev, Alexander V.; Park, S.M.; Nyenhuis, A.

doi:10.1109/intmag.2005.1464006

Cited by 21 publications

(22 citation statements)

References 6 publications

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“…Different applications may require different levels of field accuracy in specific locations. An accurate assessment of the electromagnetic field inside the phantom is important when evaluating SAR levels as overall safety of the patient [9][10][11][12][13][14][15][16] or the RFinduced heating in patients with conductive medical devices that are fully implanted in the body [22] like deep brain stimulators [8,17,18] or pacemakers [1,20,21]. Conversely, an accurate representation of ||E ⃗ || in the space between the coil and the load is important when evaluating safety in patients with conductive medical devices that are partially implanted or in contact with the skin [7,23].…”

Section: Discussionmentioning

confidence: 99%

Assessing the Electromagnetic Fields Generated By a Radiofrequency MRI Body Coil at 64 MHz: Defeaturing Versus Accuracy

Lucano

Liberti

Mendoza

et al. 2016

IEEE Trans. Biomed. Eng.

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Goal-This study aims at a systematic assessment of five computational models of a birdcage coil for magnetic resonance imaging (MRI) with respect to accuracy and computational cost.Methods-The models were implemented using the same geometrical model and numerical algorithm, but different driving methods (i.e., coil "defeaturing"). The defeatured models were labeled as: specific (S2), generic (G32, G16), and hybrid (H16, H16 fr-forced ). The accuracy of the models was evaluated using the "Symmetric Mean Absolute Percentage Error" ("SMAPE"), by comparison with measurements in terms of frequency response, as well as electric (||E ⃗ ||) and magnetic (||B ⃗ ||) field magnitude. HHS Public Access Author Manuscript Author ManuscriptAuthor Manuscript Author ManuscriptResults-All the models computed the ||B ⃗ || within 35 % of the measurements, only the S2, G32, and H16 were able to accurately model the ||E ⃗ || inside the phantom with a maximum SMAPE of 16 %. Outside the phantom, only the S2 showed a SMAPE lower than 11 %. Conclusions-Resultsshowed that assessing the accuracy of ||B ⃗ || based only on comparison along the central longitudinal line of the coil can be misleading. Generic or hybrid coils -when properly modeling the currents along the rings/rungs -were sufficient to accurately reproduce the fields inside a phantom while a specific model was needed to accurately model ||E ⃗ || in the space between coil and phantom.Significance-Computational modeling of birdcage body coils is extensively used in the evaluation of RF-induced heating during MRI. Experimental validation of numerical models is needed to determine if a model is an accurate representation of a physical coil.

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Section: Discussionmentioning

confidence: 99%

Assessing the Electromagnetic Fields Generated By a Radiofrequency MRI Body Coil at 64 MHz: Defeaturing Versus Accuracy

Lucano

Liberti

Mendoza

et al. 2016

IEEE Trans. Biomed. Eng.

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“…The RF induced electric field in the phantom was calculated with the FDTD method (11). The component of the RF field useful for imaging, B 1cw , was determined to have amplitude of about 3.8 T, based on calorimetry measurements without an implant in the phantom.…”

Section: Experimental Validationmentioning

confidence: 99%

“…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.…”

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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

200

210

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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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“…Here, for computational simplicity and for keeping the size of the computational problem small, we solve the problem in two stages [22]. In the first stage, the RF field that exists in the interior of the MRI birdcage coil in the presence of body tissue with no implants present was computed using the FDTD method [23,24]. The computed field was available as matrix data.…”

Section: Computation Of the Resultant Rf Fieldmentioning

confidence: 99%

Concentration of the Specific Absorption Rate Around Deep Brain Stimulation Electrodes During Mri

Mohsin

2011

PIER

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Abstract-During Magnetic Resonance Imaging (MRI), the presence of an implant such as a Deep Brain Stimulation (DBS) lead in a patient's body can pose a significant risk. This is due to the fact that the MR radiofrequency (RF) field can achieve a very high strength around the DBS electrodes. Thus the specific absorption rate (SAR), which is proportional to the square of the magnitude of the RF electric field, can have a very high concentration in the near-field region of the electrodes. The resulting tissue heating can reach dangerous levels. The degree of heating depends on the level of SAR concentration. The effects can be severe, leading to tissue ablation and brain damage, and significant safety concerns arise whenever a patient with an implanted DBS lead is exposed to MR scanning. In this paper, SAR, electric field, and temperature rise distributions have been found around actual DBS electrodes. The magnitude and spatial distribution of the induced temperature rises are found to be a function of the length and structure of the lead device, tissue properties and the MR stimulation parameters.

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Power deposition inside a phantom for testing of MRI heating

Cited by 21 publications

References 6 publications

Assessing the Electromagnetic Fields Generated By a Radiofrequency MRI Body Coil at 64 MHz: Defeaturing Versus Accuracy

Assessing the Electromagnetic Fields Generated By a Radiofrequency MRI Body Coil at 64 MHz: Defeaturing Versus Accuracy

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

Concentration of the Specific Absorption Rate Around Deep Brain Stimulation Electrodes During Mri

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