Comparing Electric Properties Tomography at 1.5, 3 and 7 T
نویسندگان
چکیده
Introduction: Recently, the principle feasibility of Electrical Properties Tomography (EPT) has been shown at different field strengths, 1.5 T [1], 3 T [1b], and 7 T [2]. Using the Helmholtz equation to investigate the effect of the local electrical properties on the B1 field (Eq.1 see also [2]) one can obverse that the effect of the local dielectric properties on the B1 field scales with the (square of the) used angular frequency ω. Therefore, it is expected that at higher field strengths the precision of EPT increases. Furthermore, measurements at higher field benefit from the increased intrinsic SNR. On the other hand, the increased field strength leads to a larger difference between the phase φ of the quadrature transmit (B1) and the phase φ of the quadrature receive field (B1), which complicates the derivation of φ from the measurable transceiver phase φm = φ + φ resulting in systematic errors. Generally, φm = 2φ is assumed [1,2]. However, it can be shown that this is only true under low field conditions and that the validity will deteriorate with increasing field strength [1,2]. To determine the optimal field strength for EPT, a systematic study was performed comparing phantom measurements and simulations at 1.5, 3, and 7T.
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