Complex B1+ mapping with Carr‐Purcell spin echoes and its application to electrical properties tomography. Issue 3 (9th November 2021)

• Record Type: Journal Article
• Authors: Iyyakkunnel, Santhosh; Weigel, Matthias; Ganter, Carl; Bieri, Oliver
• Is Part Of: Magnetic resonance in medicine. Volume 87:Issue 3(2022)
• Page Start: 1250
• Page End: 1260
• Publication Date: 2021-11-09
• Subjects: B1 mapping -- CP -- CPMG -- electrical properties tomography -- spin echoes; Nuclear magnetic resonance -- Periodicals; Electron paramagnetic resonance -- Periodicals; 616.07548
• DOI: 10.1002/mrm.29020
• Languages: English
• ISSNs: 0740-3194

Abstract

Abstract : Purpose: To present a new complex‐valued B1 + 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 B1 + . To this end, a dictionary is used that takes into account the slice profile as well as T2 relaxation along the echo train. For validation, the retrieved B1 + map is compared with the actual flip angle imaging (AFI) method in a phantom (79 ε0, 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 B1 +, 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 B1 + maps retrieved from the CP echo train and the AFI method show excellent agreement, and both the reconstructed estimated permittivity (79 ± 3) ε0 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 B1 + information, the decay of the CP echo trains also yields an estimate for T2 . Conclusion: The CP sequence can be used to simultaneously provide both B1 + magnitude and phase estimations, and therefore allows for full reconstruction of the electrical properties.