Physiological noise in oxygenation-sensitive magnetic resonance imaging

The physiological noise in the resting brain, which arises from fluctuation s in metabolic-linked brain physiology and subtle brain pulsations, was inv estigated in six healthy volunteers using oxygenation-sensitive dual-echo s piral MRI at 3.0 T. In contrast to the system and thermal noise, the physio logical noise demonstrates a signal strength dependency and, unique to the metabolic-linked noise, an echo-time dependency. Variations of the MR signa l strength by changing the flip angle and echo time allowed separation of t he different noise components and revealed that the physiological noise at 3.0 T (1) exceeds other noise sources and (2) is significantly greater in c ortical gray matter than in white matter regions. The SNR in oxygenation-se nsitive MRI is predicted to saturate at higher fields, suggesting that nois e measurements of the resting brain at 3.0 T and higher may provide a sensi tive probe of functional information. (C) 2001 Wiley-Liss, Inc.