Analysis of in-flow effect and susceptibility effect in functional brain imaging

Abstract

In functional brain imaging, the signal change during photic activation is known to be affected by two terms; the flow effect and the susceptibility effect. In this thesis, these two effects will be separated by adjusting imaging parameters. By use of the conventional RF fast gradient echo(CGE) technique, a flow dependent time course data has been obtained with large flip angle $(90\,^\circ\!C)$ and short echo time (15msec). As decreasing the flip angle down to $30\,^\circ\!C$ with constant TE, the acquired time course data shows that the amount of signal change of the time course data lowered according to the flip angle. Similarly, the time course data also obtained by increasing the echo time TE up to 35msec with constant flip angle. The results with varying flip angle and echo time show that the bigger flip angle and the smaller echo time produce the larger signal change resulting in the stronger flow dependency. On the contrary, a small flip angle with large echo time makes the signal intensity decrease and thereby it is shown that signal change is affected by the susceptibility. However the results, susceptibility effect dominated signal change, have some fraction of flow effect contribution, since the CGE sequence has inherently flow dependent characteristics, especially signal enhancement characteristic for in-flowing spins. By adopting the suitable tailored-RF pulse with fast gradient echo (TRFGE) sequence, susceptibility effect changes only functional brain imaging with relatively short echo time (15msec) can be possible and thereby improving signal to noise ratio.