Proton echo‐planar spectroscopic imaging of J‐coupled resonances in human brain at 3 and 4 Tesla

Abstract

In this multicenter study, 2D spatial mapping of J-coupled resonances at 3T and 4T was performed using short-TE (15 ms) proton echo-planar spectroscopic imaging (PEPSI). Water-suppressed (WS) data were acquired in 8.5 min with 1-cm 3 spatial resolution from a supraventricular axial slice. Optimized outer volume suppression (OVS) enabled mapping in close proximity to peripheral scalp regions. Constrained spectral fitting in reference to a non-WS (NWS) scan was performed with LCModel using correction for relaxation attenuation and partial-volume effects. The concentrations of total choline (tCho), creatine ؉ phosphocreatine (Cr؉PCr), glutamate (Glu), glutamate ؉ glutamine (Glu؉Gln), myo-inositol (Ins), NAA, NAA؉NAAG, and two macromolecular resonances at 0.9 and 2.0 ppm were mapped with mean Cramer-Rao lower bounds (CRLBs) between 6% and 18% and ϳ150-cm 3 sensitive volumes. Aspartate, GABA, glutamine (Gln), glutathione (GSH), phosphoethanolamine (PE), and macromolecules (MMs) at 1.2 ppm were also mapped, although with larger mean CRLBs between 30% and 44%. The CRLBs at 4T were 19% lower on average as compared to 3T, consistent with a higher signal-to-noise ratio (SNR) and increased spectral resolution. Metabolite concentrations were in the ranges reported in previous studies. Glu concentration was significantly higher in gray matter (GM) compared to white matter ( Key words: magnetic resonance spectroscopic imaging; proton echo planar spectroscopic imaging; glutamate; spectral quantification; human brain Proton magnetic resonance spectroscopic mapping ( 1 H-MRSI) of brain metabolites can identify biomarkers relevant to psychiatric and neurological disease. There is currently increasing interest in extending 1 H-MRSI techniques and processing capabilities to map J-coupled brain metabolite resonances. Glutamate (Glu) and glutamine (Gln) mapping is of particular interest because these metabolites are key components of energy metabolism and nitrogen homeostasis pathways, and are also involved in excitatory synaptic neurotransmission (1). In vivo mapping of Glu in clinically feasible acquisition times may have important diagnostic applications in psychiatric disorders (2,3) and studies of aging (4).Thus far, Glu and Gln have been studied mostly by single-voxel MR spectroscopy (MRS) using a variety of techniques, including model-based fitting of short-TE spectra (4 -7), use of optimized intermediate TE (8) and Carr-Purcell refocusing pulses (9), spectral editing (10), and 2D J-resolved spectroscopy (11,12). MRSI studies of Glu and Gln have used spectral fitting at short TE (13,14), J-refocused coherence transfer (15), and, more recently, 2D J-resolved spectroscopic imaging (16,17). Spectral editing and 2D J-resolved MRSI techniques enable highly selective mapping of Glu and Gln, but they require multistep encoding, which prolongs the acquisition times and limits the sensitivity gains at high field, as metabolite T 2 values have been shown to decrease with field strength (18,19). Short-TE acquisition of single-voxel spect...

Slice‐selective FID acquisition, localized by outer volume suppression (FIDLOVS) for 1H‐MRSI of the human brain at 7 T with minimal signal loss

“…To that end, FIDLOVS can be easily combined with MRSI acceleration methods such as sensitivity encoding (38), PEPSI (18) or spiral acquisition (25,39) in the future. In contrast, SSFP-based MRSI acceleration is less appropriate for 1 H-MRSI at 7 T due to its limited spectral resolution and thus information content (20,22,40).…”

Proton MRS in twin pairs discordant for schizophrenia

“…Further, although a CRLB cutoff of 25% is greater than LCModel's recommended 20%, several studies have used 25, 60,61 30, 62,63 40 64 and 50%. 65,66 The mean ± s.d. CRLBs in the mesPFC were 6.6 ± 1.7 for Cr, 10.7 ± 2.6 for mI, 5.7±1.4 for NAA, 14.9±4.0 for Glu and 7.7±1.9 for Cho.…”

Myoinositol and glutamate complex neurometabolite abnormality after mild traumatic brain injury

“…25,27 The corresponding values in the phantom were T 2 vitro 5 483, 288, 200, and 233 milliseconds and T 1 vitro 5 605, 336, 235, and 280 milliseconds. Because our phantom did not contain Glx, we used the in vivo NAA signal as "the reference" in Eqs.…”

“…using structure-and age-specific 3T T 2 vivo values for NAA, Cr, and Cho, 24 mI T 2 vivo of 200 milliseconds, 25,26 and T 1 vivo 5 1,360, 1,300, 1,145, and 1,170 milliseconds for NAA, Cr, Cho, and mI, respectively. 25,27 The corresponding values in the phantom were T 2 vitro 5 483, 288, 200, and 233 milliseconds and T 1 vitro 5 605, 336, 235, and 280 milliseconds.…”