| Since its inception, fMRI has become a powerful imaging modality that determines functional activation of the brain. Unfortunately, the mechanism of the BOLD response, the physiological phenomenon that allows direct measurement of brain oxygenation levels, is not well understood. It has been shown that the BOLD response changes with inter-stimulus interval, brain region, and age. Current models of the BOLD response do not take these factors into account, so a deeper understanding of the physiological mechanism of the BOLD response will lead to better BOLD models in the future.;Three physiological parameters are known to contribute to the BOLD response: blood flow, blood volume, and oxygenation level. MR techniques to measure these parameters separately have been available for many years, but recently a technique was developed that allows simultaneous measurement of all three parameters. Using this triple-acquisition pulse sequence to study the BOLD mechanism is an attractive prospect because it will eliminate any trial-to-trial variability in the subject's response that could affect analysis of data collected by three different methods.;We have implemented and optimized the triple-acquisition sequence onto the available MR system and completed a visual fMRI study of three distinct age groups to determine how age affects the BOLD mechanism. Results show that there are significant differences in the timing of the brain's BOLD response between groups. We also show that the young age group may in fact have a different physiological mechanism of the BOLD response. |
