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.

1 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:421-430.

A number of studies investigating the biological effects of transcranial direct current stimulation (tDCS) using magnetic resonance spectroscopy (MRS) have found that it may affect local levels of γ-aminobutyric acid (GABA), glutamate and glutamine (commonly measured together as “Glx” in spectroscopy), and N-acetyl aspartate (NAA), however, these effects depend largely on the stimulation parameters used and the cortical area targeted. Given that different cortical areas may respond to stimulation in different ways, the purpose of this experiment was to assess the as yet unexplored biological effects of tDCS in the posterior superior temporal gyrus (pSTG), an area that has attracted some attention as a potential target for the treatment of auditory verbal hallucinations in schizophrenia patients. Biochemical changes were monitored using continuous, online MRS at a field strength of 3 Tesla. Performing intrascanner stimulation, with continuous spectroscopy before, during and after stimulation, permitted the assessment of acute effects of tDCS that would otherwise be lost when simply comparing pre- and post-stimulation differences. Twenty healthy participants underwent a repeated-measures experiment in which they received both active anodal and sham intrascanner stimulation in a stratified, randomized, double-blind experiment. No significant changes in GABA, Glx, or NAA levels were observed as a result of anodal stimulation, or between active and sham stimulation, suggesting that a single session of anodal tDCS to the pSTG may be less effective than in other cortical areas that have been similarly investigated.

Through the four years spent on this PhD project, I'm very grateful to have had so many wonderful people around me as supervisors, co-authors, co-workers, colleagues, friends and family. Two people I can never thank enough are my supervisor Renate Grüner, and cosupervisor Kenneth Hugdahl. During my Master's thesis project, where she was also my main supervisor, I remember apologising to Renate for spending an inordinate amount of time trying to find an answer to a rather trivial question, to which she simply said "Don't apologise for wanting to find answers to your questions, this is what makes you a good scientist" and I have not forgotten this. My thanks and my gratitude to Renate for her continued assistance and encouragement. Kenneth Hugdahl, in addition to making this PhD project possible, and sending us around the world to soak our sponge-like brains in knowledge, has also been a great inspiration. Clarke's first law states "When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong." Listening to Kenneth, one feels as if anything is possible, they need only figure out how it needs to be done. Clarke's third law states that "Any sufficiently advanced technology is indistinguishable from magic," by extension, Alex Craven is nothing short of a magician. Alex is the "sine qua non" of this project, and his invaluable work is greatly appreciated. Massive thanks and gratitude go to everyone that helped in the planning, organisation, data collection and analysis involved with the three articles presented here, namely