Functional MRI Using Pseudo-continuous Arterial Spin Labeling.

Abstract

The widespread use of arterial spin labeling (ASL) for functional neuroimaging, has been hampered by its low signal to noise ratio (SNR) and poor temporal resolution. In this dissertation, we propose a novel method to optimize the SNR of pseudo-continuous arterial spin labeling (pCASL) technique. pCASL has been the most popular ASL method, however, in this study it is demonstrated through experiment and computer simulation that the SNR of this technique can be degraded due to off-resonance effects. The proposed method can effectively recover the lost SNR of pCASL using the B0 field map information. In our preliminary study the proposed method improved the inversion efficiency of the original pCASL by up to 56%. This method allows the use of pCASL in a wider range of conditions and applications, including real-time fMRI and ultra-high field MRI, where it may have otherwise been impractical.

ASL is traditionally used for measurement of cerebral blood flow (CBF). In this dissertation we also develop a new framework for dynamic imaging of arterial blood volume (aCBV) utilized for functional brain imaging. This method employs the developed optimized pCASL technique, takes advantage of the kinetics of ASL signal and provides a signal, which is primarily determined by arterial blood volume with little or no contributions from the parenchyma. The proposed aCBV ASL approach has several important advantages over existing fMRI techniques. The temporal resolution of the developed aCBV ASL technique is approximately half of the temporal resolution of the conventional CBF ASL. We also found that the activation detection sensitivity of the aCBV ASL was by average 30% higher than that of the CBF ASL. Consequently, aCBV produced wider activated areas compared to CBF. The active areas in the aCBV map were also more focal compared to BOLD.