Imaging Electric Conductivity with MRI

Voigt, Tobias; Katscher, Ulrich; Findeklee, Christian; Doessel, Olaf

doi:10.1007/978-3-642-03879-2_13

Cited by 4 publications

(4 citation statements)

References 7 publications

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“…As an alternative to model‐based SAR estimation, it was suggested to estimate SAR by postprocessing (complex) B 1 ‐maps. This was demonstrated in the framework of phantom simulations and experiments (10) as well as using realistic patient models (11–13). Recently, a first in vivo demonstration was reported (14).…”

Section: Introductionmentioning

confidence: 96%

“…In particular, it is challenging to estimate the B 1 ‐phase φ + . A sufficient estimation of φ + has been found for quadrature excitation (10–14), however, for nonquadrature excitation, the φ + estimation fails, and so does the B 1 ‐based SAR determination. One of the major features of parallel RF transmission is the ability to shape B 1 according to the user's demands.…”

Section: Introductionmentioning

confidence: 99%

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Impact of delirium and recall on the level of distress in patients with advanced cancer and their family caregivers

Bruera

Bush

Willey

et al. 2009

Cancer

244

211

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The current gold standard to estimate local and global specific energy absorption rate for MRI involves numerically modeling the patient and the transmit radiofrequency coil. Recently, a patient‐individual method was presented, which estimated specific energy absorption rate from individually measured B1 maps. This method, however, was restricted to quadrature volume coils due to difficulties distinguishing phase contributions from radiofrequency transmission and reception. In this study, a method separating these two phase contributions by comparing the electric conductivity reconstructed from different transmit channels of a parallel radiofrequency transmission system is presented. This enables specific energy absorption rate estimation not only for quadrature excitation but also for the nonquadrature excitation of the single elements of the transmit array. Though the contributions of the different phases are known, unknown magnetic field components and tissue boundary artifacts limit the technique. Nevertheless, the high agreement between simulated and experimental results found in this study is promising. B1‐based specific energy absorption rate determination might become possible for arbitrary radiofrequency excitation on a patient‐individual basis. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.

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Section: Introductionmentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Impact of delirium and recall on the level of distress in patients with advanced cancer and their family caregivers

Bruera

Bush

Willey

et al. 2009

Cancer

244

211

View full text Add to dashboard Cite

show abstract

“…EPT and similar approaches have been applied for simulation studies (21–24), for phantom studies using quadrature excitation (2, 25), phantom studies using parallel transmission (26), and for in vivo cases (27, 28). In this study, EPT is developed further and quantitative conductivity and permittivity values of the human brain are reconstructed using only a single component of the transmit field.…”

mentioning

confidence: 99%

Quantitative conductivity and permittivity imaging of the human brain using electric properties tomography

Voigt

Katscher

Dössel

2011

Magnetic Resonance in Med

194

360

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The electric properties of human tissue can potentially be used as an additional diagnostic parameter, e.g., in tumor diagnosis. In the framework of radiofrequency safety, the electric conductivity of tissue is needed to correctly estimate the local specific absorption rate distribution during MR measurements. In this study, a recently developed approach, called electric properties tomography (EPT) is adapted for and applied to in vivo imaging. It derives the patient's electric conductivity and permittivity from the spatial sensitivity distributions of the applied radiofrequency coils. In contrast to other methods to measure the patient's electric properties, EPT does not apply externally mounted electrodes, currents, or radiofrequency probes, which enhances the practicability of the approach. This work shows that conductivity distributions can be reconstructed from phase images and permittivity distributions can be reconstructed from magnitude images of the radiofrequency transmit field. Corresponding numerical simulations using finite-difference time-domain methods support the feasibility of this phase-based conductivity imaging and magnitude-based permittivity imaging. Using this approximation, three-dimensional in vivo conductivity and permittivity maps of the human brain are obtained in 5 and 13 min, respectively, which can be considered a step toward clinical feasibility for EPT. Magn Reson Med 66:456-466, 2011. V C 2011 Wiley-Liss, Inc.Key words: permittivity; conductivity; electric properties tomography; quantitative MRI; patient-specific SAR MR provides a vast variety of possible image contrasts. Because of reasons of reproducibility and comparability, contrasts comprising quantitative parameters are of particular clinical interest. Current examples of quantitative MRI techniques are diffusion, perfusion, and permeability imaging; however, electric conductivity and permittivity are also possible candidates for quantitative parameters. The idea of extracting these electric properties from MR images was already proposed in 1991 (1). However, only recently, the electric properties of the human body have been introduced as a quantitative image contrast in standard MRI via electric properties tomography (EPT) (2). EPT allows the determination of the conductivity and permittivity using the radiofrequency (RF) transmit field map of a standard MR scan (3).The task of imaging electric properties has been addressed by a variety of imaging modalities. Among these modalities, electric impedance tomography is probably the most prominent one. It is performed by applying low frequency currents through multiple electrodes and reconstructing electric properties by solving the resulting inverse problem (4-7). Magnetic induction tomography is a similar approach, however, using RF coils for current induction and reception of the resulting fields (8,9). MR electric impedance tomography is a method initially based on electric impedance tomography, including electrode mounting, however, taking advantage of the spatial encodin...

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“…Mapping of electrical properties using MRI has been demonstrated in vivo in both normal subjects and patients . The electrical properties of a material can be defined as the complex permittivity

κ : = ɛ - i true(\frac{σ}{ω} true)

where ɛ is permittivity, σ is conductivity, and ω is the resonant angular frequency.…”

Section: Introductionmentioning

confidence: 99%

A regularized, model‐based approach to phase‐based conductivity mapping using MRI

Ropella

Noll

2016

Magnetic Resonance in Med

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Imaging Electric Conductivity with MRI

Cited by 4 publications

References 7 publications

Impact of delirium and recall on the level of distress in patients with advanced cancer and their family caregivers

Impact of delirium and recall on the level of distress in patients with advanced cancer and their family caregivers

Quantitative conductivity and permittivity imaging of the human brain using electric properties tomography

A regularized, model‐based approach to phase‐based conductivity mapping using MRI

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