OPTIMAL FAIR

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

Arterial spin labeling (ASL) measurements of blood flow in human hippocampus are complicated by its relatively small size and unusual shape. The diameter of the human hippocampus tapers posteriorly along its 45–50-mm curved length from a relatively wide head (8–12 mm) to a thinner body (6–8 mm) and even thinner tail (2–6 mm). The coarse spatial resolution (isotropic 3.5-mm voxels) of standard ASL imaging limited the number of voxels that could be sampled without partial volume effects where the narrow aspects of the body and tail of the hippocampus curved through the slice planes, hindering the ability to conclusively characterize and distinguish middle and posterior regions. To overcome these limitations, a standard FAIR (Flow-sensitive Alternating Inversion Recovery) pulse sequence was modified by rotating the imaging slice plane orthogonal to the oblique axial plane of the tagging inversion. With this Orthogonally Positioned Figure 1 Spatial definitions of different slabs Tagging Imaging Method for Arterial Labeling with FAIR (OPTIMAL FAIR) technique, oblique coronal imaging slices with high in-plane resolution can be placed perpendicular to the longitudinal axis of the hippocampus along the A–P direction (Figure 1). This reduces partial volume effects and increases resolution, allowing the detection of finer details of the A–P differences in perfusion parameters, thus enabling reliable studies of these perfusion differences in both normal and compromised or diseased hippocampus (1-3).

Features

1. The OPTIMAL FAIR sequence contains a sequence module for temporal bolus width definition by using either QUIPSS II or Q2TIPS methods, and these two methods can also be turned off when the number of saturation pulses (via user interface (UI) parameter “QSAT.No.”) is set to zero.
2. Imaging slab pre-saturation is supported with two execution modes: a single saturation before ASL inversion RF pulses or one pre-inversion saturation combined with two post-inversion saturation and minimize the subtraction errors caused by the imperfect inversion profile (4).
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 UI parameters: the number, duration, slab size and temporal gaps of saturation RF (please refer Figure 1 in the reference 4).
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.