Brain Tissue Conductivity Measurements with MR-Electrical Properties Tomography: An In Vivo Study
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ORIGINAL PAPER
Brain Tissue Conductivity Measurements with MR‑Electrical Properties Tomography: An In Vivo Study Stefano Mandija1,2 · Petar I. Petrov3 · Jord J. T. Vink3 · Sebastian F. W. Neggers3 · Cornelis A. T. van den Berg1,2 Received: 19 September 2020 / Accepted: 28 November 2020 © The Author(s) 2020
Abstract First in vivo brain conductivity reconstructions using Helmholtz MR-Electrical Properties Tomography (MR-EPT) have been published. However, a large variation in the reconstructed conductivity values is reported and these values differ from ex vivo conductivity measurements. Given this lack of agreement, we performed an in vivo study on eight healthy subjects to provide reference in vivo brain conductivity values. MR-EPT reconstructions were performed at 3 T for eight healthy subjects. Mean conductivity and standard deviation values in the white matter, gray matter and cerebrospinal fluid (σWM, σGM, and σCSF) were computed for each subject before and after erosion of regions at tissue boundaries, which are affected by typical MR-EPT reconstruction errors. The obtained values were compared to the reported ex vivo literature values. To benchmark the accuracy of in vivo conductivity reconstructions, the same pipeline was applied to simulated data, which allow knowledge of ground truth conductivity. Provided sufficient boundary erosion, the in vivo σWM and σGM values obtained in this study agree for the first time with literature values measured ex vivo. This could not be verified for the CSF due to its limited spatial extension. Conductivity reconstructions from simulated data verified conductivity reconstructions from in vivo data and demonstrated the importance of discarding voxels at tissue boundaries. The presented σWM and σGM values can therefore be used for comparison in future studies employing different MR-EPT techniques. Keywords Conductivity · Electrical properties · MR-EPT · Brain
Introduction
Handling Editor: Jens Haueisen. Supplementary information The online version of this article (https://doi.org/10.1007/s10548-020-00813-1) contains supplementary material, which is available to authorized users. * Stefano Mandija [email protected] 1
Computational Imaging Group for MR Diagnostic & Therapy, Center for Image Sciences, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, The Netherlands
2
Division of Imaging & Oncology, Department of Radiotherapy, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, The Netherlands
3
Rudolf Magnus Institute of Neuroscience, University Medical Center Utrecht, Heidelberglaan 100, Utrecht 3584 CX, The Netherlands
Tissue Electrical Properties (EPs: conductivity and permittivity) regulate how electromagnetic fields, such as the MR radiofrequency fields (RF: 64–300 MHz) (Katscher et al. 2009; Voigt et al. 2011), interact with the human body. Dielectric probe measurements have shown a significant change of these properties as a function of frequency (Gabriel et al. 1996a, b, c). For medical applicatio
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