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Improved signal to noise in high-resolution magic angle spinning total correlation spectroscopy studies of prostate tissues using rotor-synchronized adiabatic pulses.

Zektzer AS, Swanson MG, Jarso S, Nelson SJ, Vigneron DB, Kurhanewicz J

Center for Molecular and Functional Imaging, Department of Radiology, University of California, 185 Berry Street, San Francisco, CA 94017, USA.

A rotor-synchronized WURST-8 adiabatic pulse scheme was compared to the conventional MLEV-17 hard pulse scheme for isotropic mixing in total correlation spectroscopy (TOCSY) studies of intact human prostate tissues under high-resolution magic angle spinning (HR-MAS) conditions. Both mixing schemes were extremely sensitive to the rotational resonance condition and dramatic reductions in signal to noise were observed when pulse durations deviated from 1/(spin rate). A significant increase in cross-peak intensities was observed using rotor-synchronized WURST-8 adiabatic pulses versus those observed using the rotor-synchronized MLEV-17 hard pulse scheme in both solution and tissue. In tissue, absolute signal intensities ranged from 1.5x to 10.5x greater (average: 4.75x) when WURST-8 was used in place of MLEV-17. Moreover, the difference was so dramatic that several metabolite cross peaks observed using WURST-8 pulses were not observed using MLEV-17 pulses, including cross peaks corresponding to many of the choline- and ethanolamine-containing metabolites. Due to the complex modulation of TOCSY cross peaks for multiply coupled spins and the shorter T(2) relaxation times of tissue metabolites, maximum cross-peak intensities occurred at shorter mixing times than predicted by theory. In summary, a WURST-8 adiabatic mixing scheme produced significantly greater absolute cross-peak signal intensities than MLEV-17 hard pulse mixing, and maximum cross-peak intensity versus mixing time must be established for specific spin systems and T(2) relaxation times.

Published 3 February 2005 in Magn Reson Med, 53(1): 41-8.
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