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

Abstract

A 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.