Distinguishing Myo-Inositol From Glycine in Brain MRS at 3T: A Pitfall Using Intermediate Echo Times

Area of Science:

• Neuroimaging
• Biochemistry
• Medical Physics

Background:

• Distinguishing glycine (Gly) from myo-inositol (mI) in brain magnetic resonance spectroscopy (MRS) is challenging due to overlapping signals.
• Traditional MRS methods utilize intermediate or long echo times (TE) to separate Gly and mI signals.
• Quantitative comparisons of clinically available MRS sequences for Gly/mI differentiation across various TEs are lacking.

Purpose of the Study:

• To quantitatively compare the performance of clinically available MRS sequences in differentiating myo-inositol (mI) and glycine (Gly) as a function of echo time (TE).
• To evaluate the utility of different echo times for metabolite signal separation in in vivo brain MRS.

Main Methods:

• In vivo brain spectra were acquired using single voxel PRESS and semi-LASER 2D-MRSI sequences.
• Spectra were recorded at short (35 ms), intermediate (135 ms), and long (280 ms) echo times.
• Comparisons were made between patient data, phantom studies, and spectral simulations.

Main Results:

• Short and intermediate echo times (TE) showed signals at 3.5 ppm potentially attributable to either myo-inositol (mI) or glycine (Gly).
• Long echo times (280 ms) resulted in the absence of signal at 3.5 ppm, consistent with the clinical diagnosis.
• Phantom data and simulations revealed that at intermediate TE, mI exhibits a 'pseudo-singlet' appearance closely resembling Gly.

Conclusions:

• Long echo times (TE) are crucial for reliably discriminating glycine (Gly) from myo-inositol (mI) in the absence of specialized MRS sequences and analysis techniques.
• Quantitative spectral analysis methods can enhance the accuracy of Gly and mI assignment in brain MRS.