B1-based SAR reconstruction using contrast source inversion\u2013electric properties tomography (CSI-EPT)

Edmond Balidemaj,Cornelis A T Van Den Berg,Rob F Remis,Lukas J A Stalpers,Aart J Nederveen,Hans Crezee,Astrid L H M W Van Lier

doi:10.1007/s11517-016-1497-6

Abstract

Specific absorption rate (SAR) assessment is essential for safety purposes during MR acquisition. Online SAR assessment is not trivial and requires, in addition, knowledge of the electric tissue properties and the electric fields in the human anatomy. In this study, the potential of the recently developed CSI-EPT method to reconstruct SAR distributions is investigated. This method is based on integral representations for the electromagnetic field and attempts to reconstruct the tissue parameters and the electric field strength based on B_{1}^{ + } field data only. Full three-dimensional FDTD simulations using a female pelvis model are used to validate two-dimensional CSI reconstruction results in the central transverse plane of a 3T body coil. Numerical experiments demonstrate that the reconstructed SAR distributions are in good agreement with the SAR distributions as determined via 3D FDTD simulations and show that these distributions can be computed very efficiently in the central transverse plane of a body coil with the two-dimensional approach of CSI-EPT.

Highlights

Assessment of the specific absorption rate (SAR) due to electromagnetic (EM) fields in human tissue is relevant in many applications such as hyperthermia [9, 10, 16], telecommunications [23], and high field MRI [5, 8, 21, 30, 35]
As an alternative to local electric properties tomography (EPT) methods, we have recently proposed an iterative contrast source inversion EPT method (CSI-EPT) [2], which is based on global integral representations for the electromagnetic field [2, 3]
Elsewhere we reported a more detailed description of the Contrast source inversion (CSI)-EPT algorithm [2] which includes the multiplicative total variation factor for noise suppression and the ability to include more than one B1 data set in the iterative process

Summary

Introduction

Assessment of the specific absorption rate (SAR) due to electromagnetic (EM) fields in human tissue is relevant in many applications such as hyperthermia [9, 10, 16], telecommunications [23], and high field MRI [5, 8, 21, 30, 35]. For reliable SAR assessment, knowledge of the electric properties (EPs) of biological tissues is required (in particular, the conductivity σ and permittivity ε) and the electric field strength must be known as well. This information is usually not directly available and has to be determined by other means. One of the drawbacks of the EPT methods mentioned above is that these methods typically suffer from reconstruction artifacts especially near tissue boundaries These artifacts occur mainly because currently used EPT methods are based on local field equations (either Maxwell’s equations or Helmholtz’s equation) and do not take the electromagnetic boundary conditions into account.

Methods

Results

Discussion

Conclusion