Parallel transmit PUlse design for Saturation Homogeneity (PUSH) for Magnetization Transfer imaging at 7T
| Autor: | Leitão, David, Tomi-Tricot, Raphael, Bridgen, Pip, Wilkinson, Tom, Liebig, Patrick, Gumbrecht, Rene, Ritter, Dieter, Giles, Sharon L., Baburamani, Ana, Sedlacik, Jan, Hajnal, Joseph V., Malik, Shaihan J. |
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| Rok vydání: | 2022 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| Popis: | Purpose: This work proposes a novel RF pulse design for parallel transmit (pTx) systems to obtain uniform saturation of semisolid magnetization for Magnetization Transfer (MT) contrast in the presence of transmit field ($B_1^+$) inhomogeneities. The semisolid magnetization is usually modeled as being purely longitudinal, with the applied $B_1^+$ field saturating but not rotating its magnetization, thus standard pTx pulse design methods do not apply. Theory and Methods: Pulse design for Saturation Homogeneity (PUSH) optimizes pTx RF pulses by considering uniformity of root-mean squared $B_1^+$, $B_1^{rms}$, which relates to the rate of semisolid saturation. Here we considered designs consisting of a small number of spatially non-selective sub-pulses optimized over either a single 2D plane or 3D. Simulations and in vivo experiments on a 7T Terra system with an 8-TX Nova head coil in 5 subjects were carried out to study the homogenization of $B_1^{rms}$ and of the MT contrast by acquiring MT ratio maps. Results: Simulations and in vivo experiments showed up to 6 and 2 times more uniform $B_1^{rms}$ compared to circular polarized (CP) mode for 2D and 3D optimizations, respectively. This translated into 4 and 1.25 times more uniform MT contrast, consistently for all subjects, where 2 sub-pulses were enough for the implementation and coil used. Conclusion: The proposed PUSH method obtains more uniform and higher MT contrast than CP mode within the same SAR budget. Comment: 18 pages, 9 figures. Code available at: https://github.com/mriphysics/PUSH |
| Databáze: | arXiv |
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