A localized proton 2D double-quantum (DQ) spin-echo spectroscopy technique was implemented on 1.5 T clinical MRI scanners for the detection of ␥-aminobutyrate (GABA) in the brain. The 2D approach facilitates separation of peaks overlapping with GABA in 1D DQ-filtered (DQF) spectra. This technique was applied to four normal adult volunteers and four children with intractable epilepsy. The coefficient of variation of the level of GABA and overlapping macromolecules at F2 ‫؍‬ 3.0 ppm and F1 ‫؍‬ 4.8 ppm was 0.08 in normal subjects. Three patients received 2D MRS scans before and after initiation of the ketogenic diet (KD): one patient showed a trend of decreasing GABA throughout the study, and two patients showed low initial GABA levels that increased over time. In addition to major metabolites and GABA, low-level metabolites (valine, leucine, and glutathione) were also identified in the 2D spectra. Key words: magnetic resonance; 2D double-quantum spectroscopy; brain; GABA; ketogenic diet; epilepsy.Magnetic resonance spectroscopy (MRS) is the only tool capable of noninvasively measuring metabolite concentrations in the brain, and it has proven to be a valuable technique for evaluating neurologic diseases. Proton MRS is particularly informative concerning the nuclei available for signal detection (1). However, there are currently many limitations in clinical proton MRS examinations for both 1.5T and 3T MRI scanners. Signals from most metabolites are found in a narrow aliphatic spectral window between a chemical shift of about 1 and 4 parts per million (ppm), and numerous metabolites present in low concentrations are overshadowed by the resonance of a few metabolites present in high concentrations. Consequently, much potential information remains unrecovered.Because most metabolites have coupled spins, two-dimensional (2D) correlation spectroscopy (2) can be used to provide a means of spreading the spectral peaks in a second frequency dimension, greatly increasing the information content of the data and facilitating peak quantification and assignment. The 2D approach is widely used for in vitro studies, and can be adapted for in vivo human studies (3). There are many technical benefits to be derived from the use of 2D MRS. These methods will allow us to detect metabolites that are difficult to detect even with editing techniques. For example, some metabolites may have peaks with small chemical shift separations, and, consequently, selectively exciting one spin group without disturbing the others for editing purposes is difficult. However, 2D MRS can be employed to detect these metabolites without using selective pulses in the frequency domain. Furthermore, the use of a 2D correlation spectroscopic technique will enhance our ability to interpret and assign unexpected peaks found in patient examinations that are difficult to assign in 1D spectra.This report describes the application of 2D double-quantum (DQ) measurements of GABA levels in the brain of normal subjects and of patients undergoing ketogenic diet (KD) treatm...

Two perylene conductometric sensors with excellent selectivity and low detection limit towards ethylenediamine vapor have been developed by ionic self-assembly.

Three high-performance hydrazine sensing devices have been developed based on donor-acceptor perylenediimides (PDIs) with strongly electron-donating piperidinyl (PDI-PY), pyrrolidinyl (PDI-PI) and n-hexylamino (PDI-HE) as substituents at the perylene core. These PDI devices, compared with reported PDI molecules, displayed 1-2 orders of magnitude higher sensitivity, short response/recovery time and a lower detection limit towards hydrazine vapour. Experimental results demonstrated that PDI-HE possessed the most excellent sensing performance due to its larger electron density and well-defined crystalline structure with a smaller π-π distance of 3.55 Å, yet, poor crystalline structure, weak π-π orbital overlap as well as a larger interplanar spacing of 3.62 Å led to the poorest sensing performance of PDI-PY devices. This study clearly reveals that electron-donating substituents can remarkably improve the sensing performance of PDI devices by increasing the density of electrons, meanwhile, the steric hindrance of electron-donating groups can modulate the sensing performance by influencing the crystalline structure, π-π overlap and π-π distance. The excellent sensing performance makes donor-acceptor perylenes one of the candidates with the most potential for fabrication of highly efficient PDI sensing devices.