Electrical Properties Tomography in the Human Brain at 1.5, 3, and 7T: A Comparison Study.

PURPOSE:
To investigate the effect of magnetic field strength on the validity of two assumptions (namely, the "transceive phase assumption" and the "phase-only reconstruction") for electrical properties tomography (EPT) at 1.5, 3, and 7T.
THEORY:
Electrical properties tomography is a method to map the conductivity and permittivity using MRI; the B(1) (+) amplitude and phase is required as input. The B(1) (+) phase, however, cannot be measured and is therefore deduced from the measurable transceive phase using the transceive phase assumption. Also, earlier studies showed that the B(1) (+) amplitude is not always required for a reliable conductivity reconstruction; this is the so-called "phase-only conductivity reconstruction." METHODS: Electromagnetic simulations and MRI measurements of phantoms and the human head.
RESULTS:
Reconstructed conductivity and permittivity maps based on B(1) (+) distributions at 1.5, 3, and 7T were compared to the expected dielectric properties. The noise level of measurements was also determined.
CONCLUSION:
The transceive phase assumption is most accurate for low-field strengths and low permittivity and in symmetric objects. The phase-only conductivity reconstruction is only applicable at 1.5 and 3T for the investigated geometries. The measurement precision was found to benefit from a higher field strength, which is related to increased signal-to-noise ratio (SNR) and increased curvature of the B(1) (+) field. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.
Copyright © 2013 Wiley Periodicals, Inc.
PMID: 23401276