(MEGA)-sLASER Single-Voxel MRS Sequence (C2P)

This sequence is provided to support collaborative research projects between the MR SCIENCE Laboratory at Columbia University and users of Siemens MRI equipment

Overview

This semi-LASER single-voxel spectroscopy sequence originated from work by Slotboom et al. (1) that was modified by Scheenen et al. (2).

This version for the VE11 platform improves the original semi-LASER sequence in several ways:

The employed excitation pulse is a minimum-phase Shinnar-Le Roux (SLR) pulse (3), which has the benefits of reducing the echo time by approximately 1 ms compared to a linear-phase SLR pulse.
Refocusing GOIA pulses can be selected. These pulses developed by Andronesi et al. (4) can achieve much larger bandwidth, ~20 kHz vs 5 kHz in the case of conventional adiabatic pulses (e.g., hyperbolic secant pulses). Additionally, GOIA pulses require less RF power than conventional refocusing pulses.
Optimized crusher schemes were calculated by DOTCOPS by Landheer et al. (5).
The echo time can be reduced to 20 ms (6).
Optimized phase cycling schemes were calculated by Landheer et al. (7).
Water suppression is achieved by optimized VAPOR, originally developed by Tkáč et al. (8).

In addition, it includes several other functionalities for practical use:

Single- and double-inversion pulse techniques for signal nulling (9) and measurements of T1 relaxation times with the inversion recovery technique.
J-difference editing (JDE) capabilities using selective echo dephasing method (MEGA)(10) for measurements of coupled metabolites.

The following parameters can by adjusted by the user:

RF pulse selection and duration.
Spoiler gradient duration, ramp times and strength.
Water suppression flip angle and duration of the last timing in the VAPOR scheme.

How to Obtain the Sequence

Please contact your Siemens Regional Collaboration Manager and Christoph Juchem. After completion of the authorization form, the sequence binaries and manual will be sent to you directly from the MR Science Laboratory.

How to Cite the Sequence

If you publish or present results obtained using this pulse sequence, please acknowledge the researchers who developed it using the following language:

The MRS package was developed by Martin Gajdosik, Karl Landheer, Wolfgang Bogner and Christoph Juchem and provided by the Columbia University under a C2P agreement.

In addition, please cite this reference:

Landheer K, Gajdošík M, Juchem C. A semi-LASER, single-voxel spectroscopic sequence with a minimal echo time of 20.1 ms in the human brain at 3 T. NMR Biomed. 2020:e4324 doi: 10.1002/nbm.4324.

Updates, Bug Reports, and Security

For update requests or bug reports, please contact:

All our software is developed in a protected integrated development environment.

References

1. Slotboom J, Bovée WMMJ. Adiabatic slice-selective rf pulses and a single-shot adiabatic localization pulse sequence. Concepts Magn. Reson. 1995;7:193–217 doi: 10.1002/cmr.1820070303.

2. Scheenen TWJ, Heerschap A, Klomp DWJ. Towards 1H-MRSI of the human brain at 7T with slice-selective adiabatic refocusing pulses. Magn. Reson. Mater. Physics, Biol. Med.2008;21:95–101 doi: 10.1007/s10334-007-0094-y.

3. Pauly J, Le Roux P, Nishimura D, Macovski A. Parameter Relations for the Shinnar-Le Roux Selective Excitation Pulse Design Algorithm. IEEE Trans Med Imag 1991;10:53–65.

4. Andronesi OC, Ramadan S, Ratai EM, Jennings D, Mountford CE, Sorensen AG. Spectroscopic imaging with improved gradient modulated constant adiabaticity pulses on high-field clinical scanners. J. Magn. Reson. 2010;203:283–293 doi: 10.1016/j.jmr.2010.01.010.

5. Landheer K, Juchem C. Dephasing optimization through coherence order pathway selection (DOTCOPS) for improved crusher schemes in MR spectroscopy. Magn. Reson. Med. 2018:1–14 doi: 10.1002/mrm.27587.

6. Landheer K, Gajdošík M, Juchem C. A semi-LASER, single-voxel spectroscopic sequence with a minimal echo time of 20.1 ms in the human brain at 3 T. NMR Biomed. 2020:e4324 doi: 10.1002/nbm.4324.

7. Landheer K, Juchem C. Simultaneous optimization of crusher and phase cycling schemes for magnetic resonance spectroscopy: an extension of dephasing optimization through coherence order pathway selection. Magn Reson Med 2020;83:391–402.

8. Tkác I, Starcuk Z, Choi IY, Gruetter R. In vivo 1H NMR spectroscopy of rat brain at 1 ms echo time. Magn. Reson. Med. 1999;41:649–56.

9. Penner J, Bartha R. Semi-LASER 1H MR spectroscopy at 7 Tesla in human brain: Metabolite quantification incorporating subject-specific macromolecule removal. Magn. Reson. Med. 2014;12:1–9 doi: 10.1002/mrm.25380.