Advanced single voxel 1H magnetic resonance spectroscopy techniques in humans: Experts' consensus recommendations

• Published in: NMR in biomedicine Vol. 34; no. 5; pp. e4236 - n/a
• Main Authors: Öz, Gülin, Deelchand, Dinesh K., Wijnen, Jannie P., Mlynárik, Vladimír, Xin, Lijing, Mekle, Ralf, Noeske, Ralph, Scheenen, Tom W.J., Tkáč, Ivan, Andronesi, Ovidiu, Barker, Peter B., Bartha, Robert, Berrington, Adam, Boer, Vincent, Cudalbu, Christina, Emir, Uzay E., Ernst, Thomas, Fillmer, Ariane, Heerschap, Arend, Henry, Pierre‐Gilles, Hurd, Ralph E., Joers, James M., Juchem, Christoph, Kan, Hermien E., Klomp, Dennis W. J., Kreis, Roland, Landheer, Karl, Mangia, Silvia, Marjańska, Małgorzata, Near, Jamie, Ratai, Eva M., Ronen, Itamar, Slotboom, Johannes, Soher, Brian J., Terpstra, Melissa, Valette, Julien, Van der Graaf, Marinette, Wilson, Martin
• Format: Journal Article
• Language: English
• Published: Oxford Wiley Subscription Services, Inc 01.05.2021
• Subjects: Biological products; body; brain; Chemical equilibrium; chemical shift displacement; Eddy currents; Homogeneity; Localization; Longitudinal studies; Magnetic fields; Magnetic resonance spectroscopy; Metabolites; Platforms; Quality assurance; Reproducibility; semiadiabatic LASER; shimming; SPECIAL; Spectrum analysis
• ISSN: 0952-3480; 1099-1492
• DOI: 10.1002/nbm.4236

Conventional proton MRS has been successfully utilized to noninvasively assess tissue biochemistry in conditions that result in large changes in metabolite levels. For more challenging applications, namely, in conditions which result in subtle metabolite changes, the limitations of vendor‐provided MRS protocols are increasingly recognized, especially when used at high fields (≥3 T) where chemical shift displacement errors, B0 and B1 inhomogeneities and limitations in the transmit B1 field become prominent. To overcome the limitations of conventional MRS protocols at 3 and 7 T, the use of advanced MRS methodology, including pulse sequences and adjustment procedures, is recommended. Specifically, the semiadiabatic LASER sequence is recommended when TE values of 25‐30 ms are acceptable, and the semiadiabatic SPECIAL sequence is suggested as an alternative when shorter TE values are critical. The magnetic field B0 homogeneity should be optimized and RF pulses should be calibrated for each voxel. Unsuppressed water signal should be acquired for eddy current correction and preferably also for metabolite quantification. Metabolite and water data should be saved in single shots to facilitate phase and frequency alignment and to exclude motion‐corrupted shots. Final averaged spectra should be evaluated for SNR, linewidth, water suppression efficiency and the presence of unwanted coherences. Spectra that do not fit predefined quality criteria should be excluded from further analysis. Commercially available tools to acquire all data in consistent anatomical locations are recommended for voxel prescriptions, in particular in longitudinal studies. To enable the larger MRS community to take advantage of these advanced methods, a list of resources for these advanced protocols on the major clinical platforms is provided. Finally, a set of recommendations are provided for vendors to enable development of advanced MRS on standard platforms, including implementation of advanced localization sequences, tools for quality assurance on the scanner, and tools for prospective volume tracking and dynamic linear shim corrections. Vendor‐provided MRS protocols suffer from multiple limitations at high and ultrahigh fields (≥3 T), including increased chemical shift displacement errors, increased B0 and B1 inhomogeneities and insufficient transmit B1 field. We provide an overview of two advanced MRS sequences, sLASER and SPECIAL, which largely overcome the limitations of conventional MRS protocols. We provide guidelines for their use, quality assurance and quality control, and a set of recommendations for vendors to enable advanced MRS on standard platforms.