Georg Oeltzschner1,2, Karim Snoussi1,2, Nicolaas A Puts1,2, Mark Mikkelsen1,2, Ashley D Harris3,4,5, Subechhya Pradhan6,7, Kyrana Tsapkini8, Michael Schär1, Peter B Barker1,2, Richard A E Edden1,2. 1. Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA. 2. F. M. Kirby Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, Maryland, USA. 3. CAIR Program, Alberta Children's Hospital Research Institute, University of Calgary, AB, Canada. 4. Department of Radiology, University of Calgary, AB, Canada. 5. Hotchkiss Brain Institute and Alberta Children's Hospital Research Institute, Calgary, AB, Canada. 6. Diagnostic Imaging and Radiology, Children's National Health System, Washington, DC, USA. 7. Department of Radiology, George Washington University, Washington, DC, USA. 8. Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
Abstract
PURPOSE: To investigate frequency-offset effects in edited magnetic resonance spectroscopy (MRS) experiments arising from B0 eddy currents. MATERIALS AND METHODS: Macromolecule-suppressed (MM-suppressed) γ-aminobutyric acid (GABA)-edited experiments were performed at 3T. Saturation-offset series of MEGA-PRESS experiments were performed in phantoms, in order to investigate different aspects of the relationship between the effective editing frequencies and eddy currents associated with gradient pulses in the sequence. Difference integrals were quantified for each series, and the offset dependence of the integrals was analyzed to quantify the difference in frequency (Δf) between the actual vs. nominal expected saturation frequency. RESULTS: Saturation-offset N-acetyl-aspartate-phantom experiments show that Δf varied with voxel orientation, ranging from 10.4 Hz (unrotated) to 6.4 Hz (45° rotation about the caudal-cranial axis) and 0.4 Hz (45° rotation about left-right axis), indicating that gradient-related B0 eddy currents vary with crusher-gradient orientation. Fixing the crusher-gradient coordinate-frame substantially reduced the orientation dependence of Δf (to ∼2 Hz). Water-suppression crusher gradients also introduced a frequency offset, with Δf = 0.6 Hz ("excitation" water suppression), compared to 10.2 Hz (no water suppression). In vivo spectra showed a negative edited "GABA" signal, suggesting Δf on the order of 10 Hz; with fixed crusher-gradient coordinate-frame, the expected positive edited "GABA" signal was observed. CONCLUSION: Eddy currents associated with pulsed field gradients may have a considerable impact on highly frequency-selective spectral-editing experiments, such as MM-suppressed GABA editing at 3T. Careful selection of crusher gradient orientation may ameliorate these effects. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:673-681.
PURPOSE: To investigate frequency-offset effects in edited magnetic resonance spectroscopy (MRS) experiments arising from B0 eddy currents. MATERIALS AND METHODS: Macromolecule-suppressed (MM-suppressed) γ-aminobutyric acid (GABA)-edited experiments were performed at 3T. Saturation-offset series of MEGA-PRESS experiments were performed in phantoms, in order to investigate different aspects of the relationship between the effective editing frequencies and eddy currents associated with gradient pulses in the sequence. Difference integrals were quantified for each series, and the offset dependence of the integrals was analyzed to quantify the difference in frequency (Δf) between the actual vs. nominal expected saturation frequency. RESULTS: Saturation-offset N-acetyl-aspartate-phantom experiments show that Δf varied with voxel orientation, ranging from 10.4 Hz (unrotated) to 6.4 Hz (45° rotation about the caudal-cranial axis) and 0.4 Hz (45° rotation about left-right axis), indicating that gradient-related B0 eddy currents vary with crusher-gradient orientation. Fixing the crusher-gradient coordinate-frame substantially reduced the orientation dependence of Δf (to ∼2 Hz). Water-suppression crusher gradients also introduced a frequency offset, with Δf = 0.6 Hz ("excitation" water suppression), compared to 10.2 Hz (no water suppression). In vivo spectra showed a negative edited "GABA" signal, suggesting Δf on the order of 10 Hz; with fixed crusher-gradient coordinate-frame, the expected positive edited "GABA" signal was observed. CONCLUSION: Eddy currents associated with pulsed field gradients may have a considerable impact on highly frequency-selective spectral-editing experiments, such as MM-suppressed GABA editing at 3T. Careful selection of crusher gradient orientation may ameliorate these effects. LEVEL OF EVIDENCE: 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;47:673-681.
Authors: Kimberly L Chan; Nicolaas A J Puts; Michael Schär; Peter B Barker; Richard A E Edden Journal: Magn Reson Med Date: 2016-04-19 Impact factor: 4.668
Authors: Richard A E Edden; Georg Oeltzschner; Ashley D Harris; Nicolaas A J Puts; Kimberly L Chan; Vincent O Boer; Michael Schär; Peter B Barker Journal: J Magn Reson Imaging Date: 2016-05-30 Impact factor: 4.813
Authors: C John Evans; Nicolaas A J Puts; Siân E Robson; Frederic Boy; David J McGonigle; Petroc Sumner; Krish D Singh; Richard A E Edden Journal: J Magn Reson Imaging Date: 2012-11-27 Impact factor: 4.813
Authors: Kimberly L Chan; Georg Oeltzschner; Muhammad G Saleh; Richard A E Edden; Peter B Barker Journal: Magn Reson Med Date: 2019-02-22 Impact factor: 4.668
Authors: Muhammad G Saleh; Daniel Rimbault; Mark Mikkelsen; Georg Oeltzschner; Anna M Wang; Dengrong Jiang; Ali Alhamud; Jamie Near; Michael Schär; Ralph Noeske; James B Murdoch; Lars Ersland; Alexander R Craven; Gerard Eric Dwyer; Eli Renate Grüner; Li Pan; Sinyeob Ahn; Richard A E Edden Journal: Neuroimage Date: 2019-01-22 Impact factor: 6.556
Authors: Georg Oeltzschner; Muhammad G Saleh; Daniel Rimbault; Mark Mikkelsen; Kimberly L Chan; Nicolaas A J Puts; Richard A E Edden Journal: Neuroimage Date: 2018-10-06 Impact factor: 6.556