Extraction of temporal information in functional MRI

The temporal resolution of functional MRI is limited by the shape of the hemodynamic response function (HRF) and the vascular architecture underlying the activated region. Normally, the temporal resolution is typically around 1 s. We have developed a new data processing approach to extract temporal information on a per-pixel basis at the level of approximately 200 ms. Instead of correlating or fitting the time-course of each pixel to a single reference function, which is the common practice in MRI, we correlate each pixel´s time-course to a series of reference functions (~40) where each reference function represents a delay of about 200 ms in the hemodynamic response. The reference function yielding the highest correlation coefficient for a pixel is then used as a time marker for that pixel. This method has been applied to extract timing information from an event related motor movement study where the subject flexed a finger on cue. The event was repeated 18 times. Assuming a stationary HRF, the event´s presentation was staggered to yield an approximately 100 ms temporal sampling of the hemodynamic response over the entire presentation cycle. The timing differences among different regions of the brain activated by the motor task were clearly visualized by this method. The results suggest that it is possible to achieve a temporal resolution of ~200 ms with this approach