Functional MRI of brain during breath holding at 4 T.

Both theoretical considerations and animal experiments predict increased signal intensity in brain cortex on T2*-weighted images that develops over a breath hold period. This has not been observed in recent human studies performed at 1.0 and 1.5 T. To clarify this inconsistency, we undertook a study in normal volunteers at 4.0 T. Unlike the earlier studies, we observed a 3-10% signal intensity increase in the gray matter. Possible reasons for the discrepant results are discussed. We conclude that regional cerebral hemodynamics are observable by fMRI in man and this may have clinical applications.