Butler matrix transmit channel compression in pTx: a SAR-aware study.
Mihir Rajendra Pendse1, Riccardo Stara1,2,3, Gianluigi Tiberi4, Alessandra Retico2, Michela Tosetti5, and Brian Rutt1
1Stanford University, Stanford, CA, United States, 2Istituto Nazionale di Fisica Nucleare (Pisa), Pisa, Italy, 3Universita' di Pisa, Pisa, Italy, 4IMAGO7, Pisa, Italy, 5ISRCC Stella maris, Calambrone (Pisa), Italy
The use of
a Butler matrix in pTx is thought to allow transmit channel compression by a
factor of 2 or more compared to direct drive, while maintaining similar flip
angle control. However, the SAR-related consequences of this compression strategy
are relatively unexplored. Using a SAR-aware pTx design method (IMPULSE), we
demonstrate that excellent flip angle uniformity is indeed possible using only
2 or 4 Butler modes compared to 8 direct drive channels; however, this comes at
the expense of increased SAR.
We also present a
generalized strategy for selecting the optimal subset of Butler modes, i.e. the
subset that provides adequate flip angle control at minimum SAR.
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