The benefits of rapid 3D fMRI

Functional magnetic resonance imaging (fMRI) provides the ability to image blood dynamics through the entire brain with a high spatial resolution. However, the temporal resolution is much slower than the underlying neuronal activity one seeks to infer. Recent developments in rapid imaging allow 3D fMRI studies to be performed at a temporal resolution of 100 ms; a 10-fold increase compared to standard approaches. This increase in temporal resolution offers a number of potential benefits. First, it allows the focus of analysis to be shifted from changes in blood flow taking place 5-8 s after neuronal activity to more transient changes taking place immediately following activation. We argue that studying these changes provides valuable information about the relative timing of activation across different regions of the brain, which is crucial for inferring brain pathways. Second, rapid imaging allows for the efficient modeling of physiological artifacts without problems with aliasing; something that is difficult at standard resolutions. We illustrate how removal of these artifacts provides the increase in signal-to-noise ratio required for studying the subtle changes in oxygenation we are interested in. Finally, we show how high temporal resolution data provides the opportunity to focus the analysis on the rate of change in oxygenation rather than the level of oxygenation as is the current practice. The price of performing rapid imaging studies is a decrease in spatial resolution. However, we argue that the resolution is still comparable to the effective resolution used in most fMRI studies. We illustrate our approach using two fMRI data sets.