In vivo localized 1H MR spectroscopy of rat testes: Stimulated echo acquisition mode (STEAM) combined with short TI inversion recovery (STIR) improves the detection of metabolite signals

Abstract

A noninvasive NMR technique for evaluating testicular function was explored in this study. Localized in vivo 1H NMR spectroscopy was performed on rat testes using a stimulated echo acquisition mode (STEAM) sequence with a short echo time (TE). In the 1H spectra, large lipid signals dominated the chemical shift range of 0.89-2.78 ppm, which prevented the observation of metabolite signals in this region. To suppress these lipid signals, short inversion time (TI) inversion recovery (STIR) was combined with STEAM (STIR-STEAM). The optimal TI was typically 320 ms. STIR-STEAM with a TE of 15 ms allowed successful suppression of the lipid signals and the sensitive detection of several new metabolite signals. In normal testes, choline, creatine, glutamate, and glycine signals were identified. In addition to these metabolites, a lactate signal was observed in ischemic testes. To our knowledge, the signals of glutamate, glycine, and lactate have not been previously assigned in 1H MR spectra of testes in vivo. Lipid suppression by STIR aided in the detection of these metabolites, which would otherwise have been masked by the lipid signals.