Configuration‐based electrical properties tomography

Abstract

To introduce phase-based conductivity mapping from a configuration space analysis. Methods: The frequency response function of balanced SSFP (bSSFP) is used to perform a configuration space analysis. It is shown that the transceive phase for conductivity mapping can be directly obtained by a simple fast Fourier transform of a series of phase-cycled bSSFP scans. For validation, transceive phase and offresonance mapping with fast Fourier transform is compared with phase estimation using a recently proposed method, termed PLANET. Experiments were performed in phantoms and for in vivo brain imaging at 3 T using a quadrature head coil. Results: For fast Fourier transform, aliasing can lead to systematic phase errors. This bias, however, decreases rapidly with increasing sampling points. Interestingly, Monte Carlo simulations revealed a lower uncertainty for the transceive phase and the off-resonance using fast Fourier transform as compared with PLANET. Both methods, however, essentially retrieve the same phase information from a set of phase-cycled bSSFP scans. As a result, configuration-based conductivity mapping was successfully performed using eight phase-cycled bSSFP scans in the phantoms and for brain tissues. Overall, the retrieved values were in good agreement with expectations. Conductivity estimation and mapping of the field inhomogeneities can therefore be performed in conjunction with the estimation of other quantitative parameters, such as relaxation, using configuration theory. Conclusions: Phase-based conductivity mapping can be estimated directly from a simple Fourier analysis, such as in conjunction with relaxometry, using a series of phase-cycled bSSFP scans.

Phantom evaluation of electrical conductivity mapping by MRI: Comparison to vector network analyzer measurements and spatial resolution assessment

“…For example, advanced methods 35 make use of T 2 and B 0 maps as well as two bSSFP scans. Additionally, faster techniques such as the fast Fourier transform 19 or PLANET 44,45 methods rely on phase‐cycled bSSFP scans. In the 2D SE sequence, “phase jumps,” that is, random phase offsets 46 between slices consequently lead to “conductivity jumps” when a 3D derivative kernel is applied.…”

“…However, these simulations generally use the same birdcage coil model for RF transmission (B 1 + field) and reception (B 1 − field) so they do not include the use of receive coil arrays and coil combination methods. 11,15,17,18 In terms of absolute quantification, some studies compared EPT 11,15,19 to EP values estimated from salt concentration 20 in phantoms, but few studies used an open-ended coaxial probe, connected to a vector network analyzer (VNA), to measure EPs at Larmor frequency. The latter method is considered as the gold standard for EP measurements.…”

Robust T2 estimation with balanced steady state free precession

“…( 14)) and directly using a discrete Fourier transform (DFT) of y, as described in related work. 23 In addition, the DFT also allows to yield an estimate of A either from the decay of the modes using a matrix pencil approach 24 or directly from m (1) /m (0) . As a result, the DFT-related estimate of θ0 and  was used as a meaningful starting value of ẑ = e i θ0  for the VARPRO minimization.…”

Feasibility of undersampled spiral trajectories in MREPT for fast conductivity imaging

“…In contrast, bSSFP‐based sequences offer a shorter acquisition time, but can suffer from “banding artifacts” for specific off‐resonance values, which substantially distorts the phase images 14 . Several methods have been proposed to address the issue of banding artifacts in bSSFP imaging, 17,18 including MREPT applications 19–22 . Nevertheless, these approaches can increase acquisition time and suffer from registration problems, highlighting the importance of selecting the appropriate pulse sequence for MREPT, to minimize artifacts and optimize measurement accuracy.…”

“…14 Several methods have been proposed to address the issue of banding artifacts in bSSFP imaging, 17,18 including MREPT applications. [19][20][21][22] Nevertheless, these approaches can increase acquisition time and suffer from registration problems, highlighting the importance of selecting the appropriate pulse sequence for MREPT, to minimize artifacts and optimize measurement accuracy.…”