Complex B1+ mapping with Carr-Purcell spin echoes and its application to electrical properties tomography

Purpose To present a new complex-valued B-1(+) mapping method for electrical properties tomography using Carr-Purcell spin echoes. Methods A Carr-Purcell (CP) echo train generates pronounced flip-angle dependent oscillations that can be used to estimate the magnitude of B-1(+). To this end, a dictionary is used that takes into account the slice profile as well as T-2 relaxation along the echo train. For validation, the retrieved B-1(+) map is compared with the actual flip angle imaging (AFI) method in a phantom (79 epsilon(0), 0.34 S/m). Moreover, the phase of the first echo reflects the transceive phase. Overall, the CP echo train yields an estimate of the complex-valued B-1(+), allowing electrical properties tomography with both permittivity and conductivity. The presented method is evaluated in phantom scans as well as for in vivo brain at 3 T. Results In the phantom, the obtained magnitude B-1(+) maps retrieved from the CP echo train and the AFI method show excellent agreement, and both the reconstructed estimated permittivity (79 +/- 3) epsilon(0) and conductivity (0.35 +/- 0.04) S/m values are in accordance with expectations. In the brain, the obtained electrical properties are also close to expectations. In addition to the retrieved complex B-1(+) information, the decay of the CP echo trains also yields an estimate for T-2. Conclusion The CP sequence can be used to simultaneously provide both B-1(+) magnitude and phase estimations, and therefore allows for full reconstruction of the electrical properties.