Implementation of Two-pulse Phase-modulated (TPPM) 1H Decoupling in a Clinical MR Scanner for the Detection of the C1-glycogen Peak in 13C MRS.

Abstract

Two-pulse phase-modulated (TPPM) ¹H-decoupling pulse sequence repeats a pair of 180^o RF pulses while changing the signs of the RF phase modulation angle and has been widely used for the ¹³C NMR of organic solids. TPPM was introduced into the ¹³C MRS pulse sequence on a clinical 3T MR scanner, and the ¹H-decoupling performance was compared with conventional ¹H-decoupling schemes using aqueous solutions containing glucose and oyster glycogen. The ¹³C C1-glucose peaks were ¹H-decoupled using TPPM with B₂ = 500 Hz, and the optimal RF phase modulation angle was up to 30^o. Cycling sidebands were not observed when TPPM was used but were observed when WALTZ-16 was used. The ¹³C C1-glycogen peak was ¹H-decoupled even with reducing TPPM duration to 8 ms, which reduced simulated specific absorption rate (SAR) to 39%. In conclusion, the TPPM ¹H decoupling is applicable to clinical MR scanners, and the low-SAR sequence may be more valuable at 7T.