Eric K Gibbons1,2, Patrick Le Roux3, John M Pauly2, Adam B Kerr2. 1. Department of Bioengineering, Stanford University, Stanford, California, USA. 2. Magnetic Resonance Systems Research Laboratory, Department of Electrical Engineering, Stanford University, Stanford, California, USA. 3. Praecedentia Libra, Palaiseau, France.
Abstract
PURPOSE: To determine the effects of the RF refocusing pulse profile on the magnitude of the transverse signal smoothness throughout the echo train in non-Carr-Purcell-Meiboom-Gill (nCPMG) single-shot fast spin echo (SS-FSE) imaging and to design an RF refocusing pulse that provides improved signal stability. THEORY AND METHODS: nCPMG SS-FSE quadratic phase modulation requires sufficiently high and uniform refocusing flip angle to achieve a stable signal. Typically, refocusing pulses used in SS-FSE sequences are designed for minimum duration to minimize echo spacing and as a consequence have poor selectivity. However, delay-insensitive variable rate excitation Shinnar-Le Roux (DV-SLR) refocusing pulses can achieve both improved selectivity as well as a short duration. This class of RF pulse is compared against a traditional low time-bandwidth refocusing pulse in a nCPMG SS-FSE in simulation, phantom, and in vivo. RESULTS: DV-SLR pulses achieve a more stable signal in simulation, phantom, and in vivo cases while maintaining an appropriately short duration as well as not dramatically increasing specific absorption rate (SAR) accumulation. CONCLUSION: The nCPMG SS-FSE method demonstrates improved robustness when a more selective refocusing pulse is used. Refocusing pulses that use a time-varying excitation gradient can achieve this selectivity while maintaining short echo spacing. Magn Reson Med 79:430-438, 2018.
PURPOSE: To determine the effects of the RF refocusing pulse profile on the magnitude of the transverse signal smoothness throughout the echo train in non-Carr-Purcell-Meiboom-Gill (nCPMG) single-shot fast spin echo (SS-FSE) imaging and to design an RF refocusing pulse that provides improved signal stability. THEORY AND METHODS: nCPMG SS-FSE quadratic phase modulation requires sufficiently high and uniform refocusing flip angle to achieve a stable signal. Typically, refocusing pulses used in SS-FSE sequences are designed for minimum duration to minimize echo spacing and as a consequence have poor selectivity. However, delay-insensitive variable rate excitation Shinnar-Le Roux (DV-SLR) refocusing pulses can achieve both improved selectivity as well as a short duration. This class of RF pulse is compared against a traditional low time-bandwidth refocusing pulse in a nCPMG SS-FSE in simulation, phantom, and in vivo. RESULTS: DV-SLR pulses achieve a more stable signal in simulation, phantom, and in vivo cases while maintaining an appropriately short duration as well as not dramatically increasing specific absorption rate (SAR) accumulation. CONCLUSION: The nCPMG SS-FSE method demonstrates improved robustness when a more selective refocusing pulse is used. Refocusing pulses that use a time-varying excitation gradient can achieve this selectivity while maintaining short echo spacing. Magn Reson Med 79:430-438, 2018.
Authors: Andreas M Loening; Manojkumar Saranathan; Nichanan Ruangwattanapaisarn; Daniel V Litwiller; Ann Shimakawa; Shreyas S Vasanawala Journal: J Magn Reson Imaging Date: 2015-06-19 Impact factor: 4.813
Authors: Reed F Busse; Anja C S Brau; Anthony Vu; Charles R Michelich; Ersin Bayram; Richard Kijowski; Scott B Reeder; Howard A Rowley Journal: Magn Reson Med Date: 2008-09 Impact factor: 4.668
Authors: Eric K Gibbons; Patrick Le Roux; Shreyas S Vasanawala; John M Pauly; Adam B Kerr Journal: IEEE Trans Med Imaging Date: 2017-08-17 Impact factor: 10.048