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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 = 68 ms) and Lac editing (TE = 140 ms). Additionally, HERMES for GABA and GSH was performed using the universal sequence at TE = 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 GABA+/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.

Chemical exchange saturation transfer (CEST) enables detection of molecules such as glycogen, whose concentrations are too low to impact the signal intensity of standard MR imaging. Detection of these molecules is achieved by selectively saturating a molecule of interest and by measuring the reduction in water signal due to saturation transfer. CEST effects are dependent on parameters such as CEST agent concentration, pH, temperature, relaxation rate, magnetic field strength as well as on experimental parameters such as repetition time, RF irradiation amplitude, and the imaging readout scheme. Measurement of molecules with exchangeable protons that resonate very close to water, e.g., hydroxyl groups in glycogen, is challenging especially at lower magnetic field strengths, mainly due to the effect of direct water saturation. Therefore, optimal RF irradiation parameters that maximize the CEST signal and reduce the competing factors are important for better quantification of glycogen-weighted CEST effects. In this study, analytical solution of the Bloch-McConnell equations was used to find optimal continuous wave RF irradiation parameters for detection of glycogen. In vivo tests were performed on a human calf muscle at different saturation powers to validate the optimal saturation parameters determined via simulation. The selected parameters were applied in vitro to CEST measurements in a phantom with varying glycogen concentrations and also in vivo in a human calf muscle. Our results show the possibility of detecting glycogen using CEST MRI at 3 T. It is further shown that the glycoCEST signal can be maximized by optimizing the RF pulse irradiation parameters (duration and power) and that different glycogen concentrations can be identified when applying the optimized saturation pulse.

The pathogenesis of type 2 diabetes (T2D) in black African women is complex and differs from that in their white counterparts. However, earlier studies have been cross-sectional and provide little insight into the causal pathways. Exercise training is consistently used as a model to examine the mechanisms underlying insulin resistance and risk for T2D. The objective of the study was to examine the mechanisms underlying the changes in insulin sensitivity and secretion in response to a 12-week exercise intervention in obese black South African (SA) women. A total of 45 obese (body mass index, BMI: 30-40 kg/m ) black SA women were randomized into a control (n=22) or experimental (exercise; n=23) group. The exercise group completed 12 weeks of supervised combined aerobic and resistance training (40-60 min, 4 days/week), while the control group maintained their typical physical activity patterns, and both groups were requested not to change their dietary patterns. Before and following the 12-week intervention period, insulin sensitivity and secretion (frequently sampled intravenous glucose tolerance test) and its primary and secondary determinants were measured. Dietary intake, sleep quality and quantity, physical activity, and sedentary behaviors were measured every 4 weeks. The final sample included 20 exercise and 15 control participants. Baseline sociodemographics, cardiorespiratory fitness, anthropometry, cardiometabolic risk factors, physical activity, and diet did not differ between the groups (P>.05). The study describes a research protocol for an exercise intervention to understand the mechanisms underlying insulin sensitivity and secretion in obese black SA women and aims to identify causal pathways underlying the high prevalence of insulin resistance and risk for T2D in black SA women, targeting specific areas for therapeutic intervention. Pan African Clinical Trial Registry PACTR201711002789113; http://www.pactr.org/ATMWeb/ appmanager/atm/atmregistry?_nfpb=true&_pageLabel=portals_app_atmregistry_portal_page_13 (Archived by WebCite at http://www.webcitation.org/6xLEFqKr0).