Functional magnetic resonance imaging of primary visual processing using a 1.0 Tesla scanner.

Recent advances in functional magnetic resonance imaging (fMRI) at > or = 1.5 T magnetic field strength and with high speed single-shot echo planar imaging techniques have made it possible to monitor local changes in cerebral blood volume, cerebral blood flow, and blood oxygenation level in response to sensory stimulation, simple motor activity, and possibly also to more complex cognitive processing. However, fMRI has also been accomplished on conventional MR scanners of medium field strength (approximately 1.0 T) using special pulse sequences and appropriate methods for image analysis. We present results from six subjects on photic stimulation using a standard 1.0 T MR scanner together with special software for off-line image analysis. Continuous serial T2-weighted imaging were performed for 6 minutes in the plane of the calcarine fissure. There were 3 repetitions of 1 minute resting state of darkness (OFF) and 1 minute activated state (ON) with 8 Hz flicker stimulation. To directly map these functional images to the underlying anatomy we also acquired a high resolution T1-weighted image from the same axial slice. The results demonstrated that stimulus-related signals can be obtained from primary visual cortex with a conventional 1.0 T MR scanner. Further methodological improvements are discussed and related to present and future possibilities for the use of fMRI within psychophysiology.