An Optimized Frequency Offset for Refocusing RF Pulses in Measurement of Lactate Using PRESS MR Spectroscopy

Yan Zhang¹, Jun Shen¹

This work demonstrates the use of an optimized RF frequency offset for the point resolved spectroscopy (PRESS) in measurement of Lactate. The partially refocused methine proton spins due to limited RF bandwidth give rise to anomalous J-modulation for methyl proton spins, resulting in signal cancellation. With the offset of 4.1ppm, all selected methine proton spins are on resonance, and therefore no methyl proton spins are anomalously modulated, except there is a portion of the methyl proton spins are outside the RF bandwidth due to the chemical shift. But this part of methyl proton spins are to be saturated by the out volume suppression. The phantom experiment shows the net signal (ratio to NAA at 2 ppm) is enhanced by ~50% compared with that using the offset at 1.3ppm.