Abstract
Functional brain imaging in humans is almost exclusively performed using blood oxygenation level dependent (BOLD) contrast. This typically requires a period of tens of milliseconds after excitation of the spin system to achieve maximum contrast, leading to inefficient use of acquisition time, reduced image quality, and inhomogeneous sensitivity throughout the cortex. We utilise magnetisation transfer to suppress the signal differentially from grey matter relative to blood so that the local increase in blood volume associated with brain activation (mainly occurring in the arterioles and capillaries) will increase the measured signal. Arterial blood contrast (ABC) is additive to the residual BOLD effect, but will have its maximum value at the time of excitation. We measured brain activation using combined ABC and residual BOLD contrast at different times post-excitation and compared this to BOLD data acquired under otherwise identical conditions. We conclude that using ABC and measuring shortly after excitation gives comparable sensitivity to standard BOLD but will provide greater efficiency, spatial specificity, improved image quality, and lower inter-subject variability. ABC offers new perspectives for performing functional MRI.
Competing Interest Statement
The authors have declared no competing interest.
Footnotes
We have rerun the analysis using higher thresholds as recommended in (Eklund A, Nichols TE, Knutsson H. Cluster failure: Why fMRI inferences for spatial extent have inflated false-positive rates. Proceedings of the National Academy of Sciences of the United States of America 2016;113(28):7900-7905). We also now include both a fixed and a mixed effects analysis. As a result some of the previous figures have become redundant. We have also added a simulation to show the contribution of different compartments to the total signal. We have made a range of other improvements in response to the comments we received from the Maastricht group, and which have occurred to us independently.