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

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Abstract
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 1.5× to 10.5× greater (average: 4.75×) 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 T2 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 T2 relaxation times. Magn Reson Med 53:41–48, 2005.