The Road to fMRI Using Endogenous MR Blood Contrast

Abstract

Looking back at my MRI result collected on May 9, 1991, recording visual cortex activation using deoxyhemoglobin contrast, it was clear that fortune smiled on the initial functional MRI (fMRI) experiment. The highly hypothetical link between endogenous MR blood contrast and brain activation turned out to be a clean MR signal response observable by the naked eye through a simple subtraction of the images of the baseline epoch from the images of stimulus ON epoch. I learned about the role of deoxyhemoglobin on the effect of the MR parameter T2 from the work of Dr. Keith Thulborn who was a radiology resident at the Massachusetts General Hospital (MGH) in early 1991. I was yet unaware of Dr. Seiji Ogawa’s published results on blood oxygenation level-dependent (BOLD) contrast, now a synonym for the MRI contrast of deoxyhemoglobin. Dr. Thulborn’s comments on deoxyhemoglobin suggested to me the possibility of applying the gradient-echo sequence, known to be highly sensitive to magnetic susceptibility, to look for MR brain signal change upon the challenges of sensory and cognitive stimuli. In the 3–4 years leading up to 1991, a constant research theme of the MGH Nuclear Magnetic Resonance (MGH-NMR) Center was MR susceptibility contrast. Major strides have been made in the use of spin echo, offset spin echo, and gradient-echo MR sequences to image the various manifestations of magnetic susceptibility. The innovative research on susceptibility at MGH provided the indispensable intellectual framework and inspiration for my pursuit of the deoxyhemoglobin signal contrast for functional studies.