ASL specifically refers to magnetic labeling of arterial blood below or in the imaging slab, without the need of gadolinium contrast.
[1] A number of ASL schemes are possible, the simplest being flow alternating inversion recovery (FAIR) which requires two acquisitions of identical parameters with the exception of the out-of-slice saturation; the difference in the two images is theoretically only from inflowing spins, and may be considered a 'perfusion map'.
Alternatively, the average control image can be used to generate CBF, which is the case for Phillips pCASL readouts.
Due to the different variations of each implementations, it is recommended that a large multi-scanner study should design a protocol minimizing the variety of readout methods used by each scanner.
In continuous arterial spin labeling (CASL), the blood water is inverted as it flows through the brain in one plane.
This may be disadvantageous for certain scanners that are not designed to maintain a radiofrequency pulse that long, and therefore would require adjustments to a RF amplifier.
Many ASL-specific toolboxes have been developed to assist in ASL analysis, such as BASIL (Bayesian inference for arterial spin labelling MRI), part of the FSL neuroimaging package and also Ze Wang's ASL toolbox (using MATLAB) to assist in the subtraction and averaging of the tagged/control pairs.
[17] Functional MRI (fMRI) has been the modality of choice to visualize brain activity, and takes advantages of a range of techniques that can be used to interpret it.
[20] Additionally, DP-pCASL has promising potential for assessing blood-brain barrier integrity in patients with ischemic stroke.
Additionally, there is a lot less development on the segmentation of theses specific organs, so the studies are relatively small scale.
[26] ASL, like other MRI modalities generate a fair amount of acoustic noise during the scan, so earplugs are advised.