Optimization of spectrally selective 180° radiofrequency pulse timings in J-difference editing (MEGA) of lactate.

Autor: Ganji SK; Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.; Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.; Philips Healthcare, Andover, Massachusetts, USA., An Z; Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA., Tiwari V; Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA., Chang Y; Department of Molecular Medicine, School of Medicine, Kyungpook National University, Daegu, Republic of Korea., Patel TR; Department of Neurological Surgery, University of Texas Southwestern Medical Center, Dallas, Texas, USA.; Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Dallas, Texas, USA.; Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, Texas, USA., Maher EA; Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA.; Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Dallas, Texas, USA.; Harold C. Simmons Cancer Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.; Annette G. Strauss Center for Neuro-Oncology, University of Texas Southwestern Medical Center, Dallas, Texas, USA., Choi C; Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.; Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.; Harold C. Simmons Cancer Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Jazyk: angličtina
Zdroj: Magnetic resonance in medicine [Magn Reson Med] 2022 Mar; Vol. 87 (3), pp. 1150-1164. Date of Electronic Publication: 2021 Oct 17.
DOI: 10.1002/mrm.29051
Abstrakt: Purpose: J-Difference editing (MEGA) provides an effective spectroscopic means of selectively measuring low-concentration metabolites having weakly coupled spins. The fractional inphase and antiphase coherences are determined by the radiofrequency (RF) pulses and inter-RF pulse intervals of the sequence. We examined the timings of the spectrally selective editing 180° pulses (E180) in MEGA-PRESS to maximize the edited signal amplitude in lactate at 3T.
Methods: The time evolution of the lactate spin coherences was analytically and numerically calculated for non-volume localized and single-voxel localized MEGA sequences. Single-voxel localized MEGA-PRESS simulations and phantom experiments were conducted for echo time (TE) 60-160 ms and for all possible integer-millisecond timings of the E180 pulses. Optimized E180 timings of 144, 103, and 109 ms TEs, tailored with simulation and phantom data, were tested in brain tumor patients in vivo. Lactate signals, broadened to singlet linewidths (~6 Hz), were compared between simulation, phantom, and in vivo data.
Results: Theoretical and experimental data indicated consistently that the MEGA-edited signal amplitude and width are sensitive to the E180 timings. In volume-localized MEGA, the lactate peak amplitudes in E180-on and difference spectra were maximized at specific E180 timings for individual TEs, largely due to the chemical-shift displacement effects. The E180 timings for maximum lactate peak amplitude were different from those of maximum inphase coherence in in vivo linewidth situations.
Conclusion: In in vivo MEGA editing, the E180 pulse timings can be effectively used for manipulating the inphase and antiphase coherences and increasing the edited signal amplitude, following TE optimization.
(© 2021 International Society for Magnetic Resonance in Medicine.)
Databáze: MEDLINE
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