Technical developments for MR-based electrical property mapping

Abstract

Purpose: To demonstrate the feasibility of transceive phase mapping with the planet method and its application for conductivity reconstruction in the brain. Methods: Accuracy and precision of transceive phase (φ ±) estimation with planet, an ellipse fitting approach to phase-cycled balanced steady state free precession (bssfp) data, were assessed with simulations and measurements and compared to standard bssfp. Measurements were conducted on a homogeneous phantom and in the brain of healthy volunteers at 3T. Conductivity maps were reconstructed with Helmholtz-based electrical properties tomography (ept). In measurements, planet was also compared to a reference technique for transceive phase mapping, i.e. spin echo (se). Results: Accuracy and precision of φ ± estimated with planet depended on the chosen flip angle (FA) and TR. planet-based φ ± was less sensitive to perturbations induced by off-resonance effects and partial volume (e.g. white matter + myelin) than bssfp-based φ ±. For FA = 25 • and TR = 4.6 ms, planet showed an accuracy comparable to that of reference se but a higher precision than bssfp and se (factor of 2 and 3, respectively). The acquisition time for planet was 5 min; 2 min faster than se and 8 times slower than bssfp. However, planet simultaneously reconstructed T 1 , T 2 , B 0 maps besides mapping φ ±. In the phantom, planet-based conductivity matched the true value and had the smallest spread of the three methods. In vivo, planet-based conductivity was similar to se-based conductivity. Conclusion: Provided that appropriate sequence parameters are used, planet delivers accurate and precise φ ± maps, which can be used to reconstruct brain tissue conductivity while simultaneously recovering T 1 , T 2 and B 0 maps.