ANOMALOUS TRANSVERSE RELAXATION IN H-1 SPECTROSCOPY IN HUMAN BRAIN AT4-TESLA

Longitudinal (T-1) and apparent transverse relaxation times (T-2) of c holine-containing compounds (Cho), creatine/phosphocreatine (Cr/PCr), and N-acetyl aspartate (NAA) were measured in vivo in human brain at 4 Tesla. Measurements were performed using a water suppressed stimulate d echo pulse sequence with complete outside volume presaturation to im prove volume localization at short echo times. T-1-values of Cho (1.2 +/- 0.1 s), Cr (1.6 +/- 0.3 s), and NAA (1.6 +/- 0.2 s) at 4 Tesla in occipital brain were only slightly larger than those reported in the l iterature at 1.5 Tesla. Thus, TR will not adversely affect the expecte d enhancement of signal-to-noise at 4 Tesla. Surprisingly, apparent T- 2-values of Cho (142 +/- 34 ms), or (140 +/- 13 ms), and NAA (185 +/- 24 ms) at 4 Tesla were significantly smaller than those at 1.5 Tesla a nd further decreased when increasing the mixing interval TM. Potential contributing factors, such as diffusion in local susceptibility relat ed gradients, dipolar relaxation due to intracellular paramagnetic sub stances and motion effects are discussed. The results suggest that sho rt echo time spectroscopy is advantageous to maintain signal to noise at 4 Tesla.