FAIR ASST

FAIR ASST and OPTIMAL FAIR perfusion imaging methods were two variants of the widely used pulsed arterial spin labeling (PASL) method, FAIR (Flow-sensitive Alternating Inversion Recovery), to better facilitate non-contrast enhanced brain perfusion imaging applications. These methods were first developed at UT Southwestern Medical Center and further improved/upgraded at CMRR.

Background

The intrinsic low signal-to-noise ratio (SNR) characteristics of arterial spin labeling (ASL) and reduced SNR in slices acquired later in the sequence due to signal losses from T1 relaxation and label washout make whole-brain high-resolution perfusion imaging challenging. High-resolution perfusion imaging can be better achieved by using only limited number of slices sufficiently covering brain regions of interest, such as the hippocampus or the cerebellum. However, when applying the widely used pulsed arterial spin labeling (PASL) method FAIR (Flow-sensitive Alternating Inversion Recovery) for such studies of regions in the mid-brain or lower brain, the superior labeling of FAIR can introduce confounding effects for cerebral blood flow (CBF) quantification and adverse artifacts (1-2). FAIR with Active Suppression of Superior Tagging (FAIR ASST) is a variant of FAIR that resolves those issues. In FAIR ASST, the superior tagging of FAIR is suppressed by applying saturations at the labeling stage on the superior side of the imaging slab. The implementation of FAIR ASST provided in this package uses the mode 12 for superior tagging suppression (2).

Features

The FAIR ASST sequence contains several important and flexible features, allowing further customizations to satisfy users’ specific needs.

1. Imaging slab pre-saturation is supported with two execution modes: a single saturation before ASL inversion RF pulses or three saturations using mode 12 as for ASST (1-2). The latter can provide improved imaging slab pre-saturation and minimize the subtraction errors caused by the imperfect inversion profile (3).
2. When both pre-saturation and superior saturation are requested, a single saturation RF pulse will be applied covering both the superior tagging region and imaging slab (Figure 1).
3. HSN RF pulse (N>= 4) can be selected for FAIR inversions to reduce RF peak power that is usually limited at ultra high fields, e.g. 7T.
4. Both QUIPSS II and Q2TIPS are supported with great flexibility via multiple user interface (UI) parameters: the number, duration, slab size and temporal gaps of saturation RF pulses to define temporal bolus width (please refer Figure 1 in the reference 2).
5. Up to two M0 images can be acquired at the end of ASL series acquisition.
6. Bi-polar flow-encoding/crushing gradients are available to suppress hyperintense intravascular signals.