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

PurposeTo 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. TheoryElectrical 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. MethodsElectromagnetic simulations and MRI measurements of phantoms and the human head. ResultsReconstructed 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. ConclusionThe 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 71:354-363, 2014. (c) 2013 Wiley Periodicals, Inc.