text: In continuous arterial spin labeling (CASL), the blood water is inverted as it flows through the brain in one plane. CASL is characterized by one single long pulse (around 1–3) seconds. 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. This is rectified in pseudo-continuous arterial spin labeling (pCASL), where a single long pulse is replaced with multiple (up to a thousand) millisecond pulses. This leads to a higher labelling efficiency. pCASL is the preferred implementation of ASL. There are different readout modules for pCASL, depending on the scanner used, with 2D pCASL usually being implemented for all scanners and 3D pCASL stack of spirals implemented in GE scanners.