Adiabatic localized correlation spectroscopy (AL-COSY): application in muscle and brain

Magnetic Resonance Spectroscopy for Detection of 2-Hydroxyglutarate as a Biomarker for IDH Mutation in Gliomas

Mutations in the isocitrate dehydrogenase (IDH)1/2 genes are highly prevalent in gliomas and have been suggested to play an important role in the development and progression of the disease. Tumours harbouring these mutations exhibit a significant alteration in their metabolism resulting in the aberrant accumulation of the oncometabolite 2-hydroxygluarate (2-HG). As well as being suggested to play an important role in tumour progression, 2-HG may serve as a surrogate indicator of IDH status through non-invasive detection using magnetic resonance spectroscopy (MRS). In this review, we describe the recent efforts in developing MRS methods for detection and quantification of 2-HG in vivo and provide an assessment of the role of the 2-HG in gliomagenesis and patient prognosis.

Two-dimensional J-resolved LASER and semi-LASER spectroscopy of human brain

PURPOSE

Two-dimensional J-resolved localized and semi-localized by adiabatic selective refocusing (LASER and semi-LASER) spectroscopy, named "J-resolved LASER" and "J-resolved semi-LASER", were introduced to suppress chemical shift artifacts, additional J-refocused artifactual peaks from spatially dependent J-coupling evolution, and sensitivity to radiofrequency (RF) field inhomogeneity.

METHODS

Three pairs of adiabatic pulses were employed for voxel localization in J-resolved LASER and two pairs in J-resolved semi-LASER. The first half of t1 period was inserted between the last pair of adiabatic pulses, which was proposed in this work to obtain two-dimensional adiabatic J-resolved spectra of human brain for the first time. Phantom and human experiments were performed to demonstrate their feasibility and advantages over conventional J-resolved spectroscopy (JPRESS).

RESULTS

Compared to JPRESS, J-resolved LASER or J-resolved semi-LASER exhibited significant suppression of chemical shift artifacts and additional J-refocused peaks from spatially dependent J-coupling evolution, and demonstrated insensitivity to the change of RF frequency offset over large bandwidth.

CONCLUSION

Experiments on phantoms and human brains verified the feasibility and strengths of two-dimensional adiabatic J-resolved spectroscopy at 3T. This technique is expected to advance the application of in vivo two-dimensional MR spectroscopy at 3T and higher field strengths for more reliable and accurate quantification of metabolites.

Glutamate and glutamine: a review of in vivo MRS in the human brain

Our understanding of the roles that the amino acids glutamate (Glu) and glutamine (Gln) play in the mammalian central nervous system has increased rapidly in recent times. Many conditions are known to exhibit a disturbance in Glu-Gln equilibrium, and the exact relationships between these changed conditions and these amino acids are not fully understood. This has led to increased interest in Glu/Gln quantitation in the human brain in an array of conditions (e.g. mental illness, tumor, neuro-degeneration) as well as in normal brain function. Accordingly, this review has been undertaken to describe the increasing number of in vivo techniques available to study Glu and Gln separately, or pooled as 'Glx'. The present MRS methods used to assess Glu and Gln vary in approach, complexity, and outcome, thus the focus of this review is on a description of MRS acquisition approaches, and an indication of relative utility of each technique rather than brain pathologies associated with Glu and/or Gln perturbation. Consequently, this review focuses particularly on (1) one-dimensional (1)H MRS, (2) two-dimensional (1)H MRS, and (3) one-dimensional (13)C MRS techniques.

Two-dimensional semi-LASER correlation spectroscopy with well-maintained cross peaks

PURPOSE

To demonstrate that the limited bandwidth of the second 90° radiofrequency (RF) pulse in two-dimensional (2D) localized correlation spectroscopy (L-COSY) induces spatially dependent magnetization transfer that results in attenuated cross-peaks, and to propose a new 2D semi-adiabatically localized COSY sequence to solve this problem.

METHODS AND THEORY

A semi-localization by adiabatic selective refocusing (semi-LASER or sLASER) method was incorporated into the COSY sequence with the slice-selective first 90° RF pulse and the non-slice-selective second 90° RF pulse to form a new 2D sLASER localized COSY sequence, named "sLASER-first-COSY," to solve the problem of spatially dependent magnetization transfer. Experiments were performed to verify the feasibility and advantages of sLASER-first-COSY sequence over a recently reported other sLASER COSY sequence with a slice-selective second 90° RF pulse, named "sLASER-last-COSY".

RESULTS

Phantom, ex vivo, and in vivo human brain experiments demonstrated that sLASER-first-COSY yielded stronger cross peaks and higher ratios of cross peak volumes to diagonal peak volumes than sLASER-last-COSY.

CONCLUSION

As COSY relies on the cross peaks to obtain larger dispersion of peaks for quantification, the new sLASER-first-COSY sequence yielding well-maintained cross peaks will facilitate more reliable and accurate quantification of metabolites with coupled spin systems.