Polarization-Transfer Effects in Localized Double-Spin-Echo Spectroscopy of Weakly Coupled Homonuclear Spin Systems

Abstract

In point-resolved spectroscopy (PRESS), fast echo-time-dependent signal modulations of the multiplets of weakly coupled homonuclear spin systems occur. They are caused by polarization-transfer effects that are explained by calculations with the product-operator formalism. The impact of slice profiles and transmitter adjustment and the difference of the polarization-transfer effects between AX and AX 3 systems are explained. Experiments with echo-time variation were performed with slice-selective pulses of different quality of profile. Experiments were carried out with a solution of calcium lactate in a 1.5 T Siemens whole-body imager. The experimental results confirm the theoretical calculations. It is stated that in localized double-spin-echo spectroscopy, especially at echo times of TE = 2/ J, the polarization-transfer effects must be considered. This knowledge is important in lactate spectroscopy in vivo, where the assumptions for 2/ J range between 270 and 290 ms, leading to different signal intensities of lactate in PRESS spectra.