MB-EPI PCASL

Background

High-resolution arterial spin labeling (ASL) imaging is highly desirable in both neuroscience research and clinical applications to reduce partial volume effects on gray matter (GM) and white matter (WM) cerebral blood flow (CBF) quantification, to improve the ability to assess perfusion abnormality in sub-cortical brain structures, e.g. the hippocampus, and to identify small brain lesions. Decreased perfusion SNR for high-resolution imaging is a consequence of multiple factors including; 1) increased in-plane resolution, 2) increased through-plane resolution and 3) the need for more slices to cover the same volume resulting in prolonged delay times between labeling and signal acquisition during which labeled spins experience longitudinal relaxation. The necessity of increasing the number of label/control image pairs for sufficient perfusion SNR greatly increases the total imaging acquisition time, limiting the practice of acquiring high-resolution whole brain ASL perfusion data using traditional 2D echo planar imaging method (or called single-band (SB) EPI). To overcome such challenges, different strategies have been previously proposed to increase perfusion SNR of ASL methods: using pulsed- or pseudo-continuous arterial spin labeling (PCASL) coil and 3D imaging acquisition.

Multi-band imaging, or simultaneous multi-slice imaging, provides an attractive and alternative solution to reduce the total acquisition time of high-resolution whole brain imaging with 2D EPI, especially when increased spatial or temporal resolution is desired. Recently theoretical and experimental evaluation of MB-EPI for PCASL imaging [1] indicates that

• MB leakage contamination has minimal impact on CBF quantification in PCASL imaging
• MB improves SNR efficiency for high-resolution PCASL imaging using 2D EPI
• MB-EPI better supports the single-blood compartment model for CBF quantitation

In contrast to 3D imaging methods, MB-EPI does not suffer adverse within and across slice T2 blurring.

Features

1. Some EPI parameters have been specifically customized to avoid errors in MB-EPI PCASL imaging protocol preparation or modification.
2. The implemented MB-EPI PCASL sequence acquires two M0 images after label/control images series. The mean image of these two M0 images can be used for CBF quantification.