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. Author manuscript; available in PMC: 2020 Mar 1.
Published in final edited form as: Magn Reson Med. 2018 Oct 25;81(3):1964–1978. doi: 10.1002/mrm.27548

FIG. 1.

FIG. 1.

Simplified MRI pulse sequence diagrams are shown for both the ASL FAIR acquisitions without (a, -OVS) and with (c, +OVS) outer volume saturation (OVS) RF pulses. Inverted or FAIR labeled spins are represented by the red color while saturated spins are represented by the gray color. The theoretical ASL signal is shown for the –OVS (b) and +OVS (d) cases as a function of the blood spins arrival time from labeling region to the placental tissue at two time points during the pulse sequence: immediately after inversion (0 sec) and at imaging readout (TI = 2.0 sec). The remaining ASL signal is governed by assuming a T1 decay of labeled blood and constant blood flow from the labeling region into the imaging slice. The OVS pulses serve to saturate macrovascular signal in the imaging region and this is depicted as removing the ASL signal with the +OVS schematic.