SEQUENCE PARAMETERS OF DOUBLE SPIN-ECHO SEQUENCES AFFECT QUANTIFICATION OF CITRATE

Quantification of citrate by localized H-1 spectroscopy is usually per formed using the water signal as reference, but the signal behavior of the J-coupled AB spin system of citrate after multipulse excitation i s not as trivial as for uncoupled substances, The influence of the tim ing scheme of double spin-echo sequences and of the spatial flip angle distribution of(nonideal) refocusing pulses was analyzed systematical ly for the citrate resonances, Both single echo times of the double sp in-echo sequence were varied between 20 ms and 250 ms in theoretical a nd experimental approaches, Relatively long total echo times (TE >120 ms) provide high selectivity to citrate signals, since signals from tr iglycerides at 2.6 ppm are markedly reduced, Asymmetrical timing schem es of the double spin-echo sequence with one short single echo time of 20 ms and one longer single echo time of about 120 ms result in high integral signal from the central lines of citrate, whereas symmetrical timing leads to high sensitivity for total echo times TE near 100 ms. The integral citrate signals in spectra with relatively long echo tim es (TE >120 ms) were found to depend markedly on the type of the refoc using pulses, affecting quantitative citrate measurements in vitro and in vivo.