Fast online‐customized (FOCUS) parallel transmission pulses: A combination of universal pulses and individual optimization

Purpose To mitigate spatial flip angle (FA) variations under strict specific absorption rate (SAR) constraints for ultra‐high field MRI using a combination of universal parallel transmit (pTx) pulses and fast subject‐specific optimization. Methods Data sets consisting of B0, B1+ maps, and virtual ob...

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Vydáno v:Magnetic resonance in medicine Ročník 85; číslo 6; s. 3140 - 3153
Hlavní autoři: Herrler, Jürgen, Liebig, Patrick, Gumbrecht, Rene, Ritter, Dieter, Schmitter, Sebastian, Maier, Andreas, Schmidt, Manuel, Uder, Michael, Doerfler, Arnd, Nagel, Armin M.
Médium: Journal Article
Jazyk:angličtina
Vydáno: United States Wiley Subscription Services, Inc 01.06.2021
Témata:
7 T
Adiabatic
Adolescent
Adult
Algorithms
Brain - diagnostic imaging
Brain Injuries - diagnostic imaging
Case-Control Studies
Circular polarization
Customization
Data acquisition
Datasets
Female
Homogeneity
Humans
Image Processing, Computer-Assisted - methods
kT points
Magnetic resonance imaging
Magnetic Resonance Imaging - methods
Male
Mathematical analysis
Optimization
parallel transmission (pTx)
Regularization
SPINS
ultra‐high‐field MRI
universal pulses
Young Adult
kT points
7 T
parallel transmission (pTx)
SPINS
ultra-high-field MRI
universal pulses
ISSN:0740-3194, 1522-2594, 1522-2594
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Shrnutí:Purpose To mitigate spatial flip angle (FA) variations under strict specific absorption rate (SAR) constraints for ultra‐high field MRI using a combination of universal parallel transmit (pTx) pulses and fast subject‐specific optimization. Methods Data sets consisting of B0, B1+ maps, and virtual observation point (VOP) data were acquired from 72 subjects (study groups of 48/12 healthy Europeans/Asians and 12 Europeans with pathological or incidental findings) using an 8Tx/32Rx head coil on a 7T whole‐body MR system. Combined optimization values (COV) were defined as combination of spiral‐nonselective (SPINS) trajectory parameters and an energy regularization weight. A set of COV was optimized universally by simulating the individual RF pulse optimizations of 12 training data sets (healthy Europeans). Subsequently, corresponding universal pulses (UPs) were calculated. Using COV and UPs, individually optimized pulses (IOPs) were calculated during the sequence preparation phase (maximum 15 s). Two different UPs and IOPs were evaluated by calculating their normalized root‐mean‐square error (NRMSE) of the FA and SAR in simulations of all data sets. Seven additional subjects were examined using an MPRAGE sequence that uses the designed pTx excitation pulses and a conventional adiabatic inversion. Results All pTx pulses resulted in decreased mean NRMSE compared to a circularly polarized (CP) pulse (CP = ~28%, UPs = ~17%, and IOPs = ~12%). UPs and IOPs improved homogeneity for all subjects. Differences in NRMSE between study groups were much lower than differences between different pulse types. Conclusion UPs can be used to generate fast online‐customized (FOCUS) pulses gaining lower NRMSE and/or lower SAR values.
Bibliografie:Funding information
Siemens Healthcare GmbH
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SourceType-Scholarly Journals-1
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ISSN:0740-3194
1522-2594
1522-2594
DOI:10.1002/mrm.28643