Sandeep K Ganji1,2,3, Zhongxu An1, Vivek Tiwari1, Yongmin Chang4, Toral R Patel5,6,7, Elizabeth A Maher8,6,9,10, Changho Choi1,2,9. 1. Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA. 2. Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA. 3. Philips Healthcare, Andover, Massachusetts, USA. 4. Department of Molecular Medicine, School of Medicine, Kyungpook National University, Daegu, Republic of Korea. 5. Department of Neurological Surgery, University of Texas Southwestern Medical Center, Dallas, Texas, USA. 6. Department of Neurology and Neurotherapeutics, University of Texas Southwestern Medical Center, Dallas, Texas, USA. 7. Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, Texas, USA. 8. Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, Texas, USA. 9. Harold C. Simmons Cancer Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA. 10. Annette G. Strauss Center for Neuro-Oncology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
Abstract
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.
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.
Authors: Akshay Madan; Sandeep K Ganji; Zhongxu An; Kevin S Choe; Marco C Pinho; Robert M Bachoo; Elizabeth M Maher; Changho Choi Journal: Magn Reson Med Date: 2014-07-07 Impact factor: 4.668
Authors: Muhammad G Saleh; Georg Oeltzschner; Kimberly L Chan; Nicolaas A J Puts; Mark Mikkelsen; Michael Schär; Ashley D Harris; Richard A E Edden Journal: Neuroimage Date: 2016-08-14 Impact factor: 6.556
Authors: A A Maudsley; R K Gupta; R Stoyanova; N A Parra; B Roy; S Sheriff; N Hussain; S Behari Journal: AJNR Am J Neuroradiol Date: 2014-01-30 Impact factor: 3.825
Authors: Vivek Tiwari; Zhongxu An; Sandeep K Ganji; Jeannie Baxter; Toral R Patel; Edward Pan; Bruce E Mickey; Elizabeth A Maher; Marco C Pinho; Changho Choi Journal: NMR Biomed Date: 2017-05-26 Impact factor: 4.044
Authors: Changho Choi; Sandeep K Ganji; Ralph J DeBerardinis; Kimmo J Hatanpaa; Dinesh Rakheja; Zoltan Kovacs; Xiao-Li Yang; Tomoyuki Mashimo; Jack M Raisanen; Isaac Marin-Valencia; Juan M Pascual; Christopher J Madden; Bruce E Mickey; Craig R Malloy; Robert M Bachoo; Elizabeth A Maher Journal: Nat Med Date: 2012-01-26 Impact factor: 53.440
Authors: Adam Berrington; Natalie L Voets; Puneet Plaha; Sarah J Larkin; James Mccullagh; Richard Stacey; Muhammed Yildirim; Christopher J Schofield; Peter Jezzard; Tom Cadoux-Hudson; Olaf Ansorge; Uzay E Emir Journal: Tomography Date: 2016-06