Multi-vendor standardized sequence for edited magnetic resonance spectroscopy

Abstract

Spectral editing allows direct measurement of low-concentration metabolites, such as GABA, glutathione (GSH) and lactate (Lac), relevant for understanding brain (patho)physiology. The most widely used spectral editing technique is MEGA-PRESS, which has been diversely implemented across research sites and vendors, resulting in variations in the final resolved edited signal. In this paper, we describe an effort to develop a new universal MEGA-PRESS sequence with HERMES functionality for the major MR vendor platforms with standardized RF pulse shapes, durations, amplitudes and timings. New RF pulses were generated for the universal sequence. Phantom experiments were conducted on Philips, Siemens, GE and Canon 3 T MRI scanners using 32-channel head coils. In vivo experiments were performed on the same six subjects on Philips and Siemens scanners, and on two additional subjects, one on GE and one on Canon scanners. On each platform, edited MRS experiments were conducted with the vendor-native and universal MEGA-PRESS sequences for GABA (TE ¼ 68 ms) and Lac editing (TE ¼ 140 ms). Additionally, HERMES for GABA and GSH was performed using the universal sequence at TE ¼ 80 ms. The universal sequence improves inter-vendor similarity of GABA-edited and Lac-edited MEGA-PRESS spectra. The universal HERMES sequence yields both GABA-and GSH-edited spectra with negligible levels of crosstalk on all four platforms, and with strong agreement among vendors for both edited spectra. In vivo GABAþ/Cr, Lac/Cr and GSH/Cr ratios showed relatively low variation between scanners using the universal sequence. In conclusion, phantom and in vivo experiments demonstrate successful implementation of the universal sequence across all four major vendors, allowing editing of several metabolites across a range of TEs.

Osprey: Open-Source Processing, Reconstruction & Estimation of Magnetic Resonance Spectroscopy Data

“…Quantitative MRS measurement outcomes are known to vary considerably depending on field strength, scanner vendor, localization technique, acquisition parameters, and choice of data processing and quantification practices. Recently, the MRS community has led efforts to converge towards standardized data acquisition Öz et al, 2020;Saleh et al, 2019;Wilson et al, 2019). In contrast, consensus on the processing and analysis of data has been slower to emerge.…”

Simultaneous edited MRS of GABA, glutathione, and ethanol

“…Briefly, the durations of the slice‐selective excitation and refocusing pulses were 7.2 ms and 7.0 ms, respectively, at a peak B 1 of 13.5 μT. Dual‐lobe editing pulses were generated based on a cosine modulation of the universal single‐lobe editing pulse . When inverting GSH and EtOH, the two editing lobes overlapped substantially, and the cosine splitting of the editing pulse was optimized for inversion using Bloch simulations.…”

“…Dual-lobe editing pulses were generated based on a cosine modulation of the universal single-lobe editing pulse. 16 When inverting GSH and EtOH, the two editing lobes overlapped substantially, and the cosine splitting of the editing pulse was optimized for inversion using Bloch simulations. The peak B 1 values of the single-lobe and dual-lobe editing pulses were 1.07 μT and 2.13 μT, respectively.…”

“…HERMES effectively allows multiple MEGA‐PRESS experiments to be conducted at the same time, offering substantial scan time reductions compared with sequentially acquired MEGA‐PRESS experiments. HERMES editing of GABA and GSH has recently been implemented on all major MR vendor platforms with standardized RF pulse shapes, durations, amplitudes, and timings . In this paper, we extend HERMES of GABA and GSH to also edit EtOH.…”

“…HERMES editing of GABA and GSH 11 has recently been implemented on all major MR vendor platforms with standardized RF pulse shapes, durations, amplitudes, and timings. 16 In this paper, we extend HERMES of GABA and GSH to also edit EtOH. We perform simulation, phantom, and in vivo experiments to establish the feasibility of simultaneous detection of GABA, GSH, and EtOH after alcohol consumption.…”