Arterial spin labeling-based perfusion MRI with balanced steady-state free precession

Abstract

Arterial spin labeling (ASL) is a promising MRI technique that utilizes blood water spins as an endogenous tracer to noninvasively measure tissue perfusion. Since only a small fraction of blood can be labeled compared to the whole tissue volume and since the lifetime of magnetically labeled blood spins follows T1 decay after labeling, ASL inherently suffers from low signal-to-noise ratio (SNR) and is sensitive to tissues with heterogeneous arterial transit times (ATT). Recently, balanced steady-state free precession (bSSFP) imaging has been proposed as a readout sequence for ASL to provide high signal-to-noise ratio (SNR) and spatial resolution while reducing susceptibility artifacts, however, the spatial coverage of ASL with bSSFP readout is limited since perfusion signals decay as bSSFP reaches the steady-state. This dissertation focuses on the development of ASL with bSSFP readout to overcome the limitations of current ASL perfusion imaging method and to develop ASL for routine clinical usage in the future. First, methods to improve the spatial coverage of pseudo-continuous ASL (pCASL) with bSSFP readout are introduced for distortion-free, high resolution whole-brain perfusion imaging. Second, a new strategy that utilizes inter-slice blood flow and magnetization transfer (MT) effects in 2D multi-slice bSSFP imaging termed alternate ascending/descending directional navigation (ALADDIN) is investigated to simultaneously acquire perfusion, MT asymmetry (MTA), and MT ratio (MTR) maps in the whole-brain while overcoming the limitations of conventional pCASL imaging. Lastly, the control scans of pCASL are investigated at various labeling conditions and new strategies are introduced to improve the sensitivity and reliability of ASL imaging. The proposed methods allow to acquire perfusion maps with wide spatial coverage, reduced sensitivity to heterogeneous ATT, and improved signal sensitivity and SNR using ASL with bSSFP readout.