Functional magnetic resonance imaging of the human brain and spinal cord by means of signal enhancement by extravascular protons

Abstract

AbstractA review of functional magnetic resonance imaging (fMRI) signal changes in spin–echo image data is presented. Spin–echo fMRI data from the human brain and spinal cord show a consistent departure from that expected with blood oxygen level dependent (BOLD) contrast. Studies to investigate this finding demonstrate fMRI signal changes of 2.5% in the spinal cord and 0.7% in the brain at 1.5 T, which is extrapolated to an echo time of zero. Consistent evidence of a non‐BOLD contrast mechanism arising from a proton‐density change at sites of neuronal activation is demonstrated. A mathematical model and physiological explanation for signal enhancement by extravascular protons is also presented. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 16A: 28–34, 2003