Flow saturation pulses are spatially selective saturation bands applied to suppress unwanted flow artifacts from vessels entering a slice. The saturation band is applied parallel to the imaged slice a location a few centimeters upstream (optimal position depends on flow velocity). Although mostly used to suppress arterial flow for routine imaging, in time-of-flight (TOF) MR angiography vascular saturation slabs are used to suppress venous flow.
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A fourth important type of RF-pulse also exists called the Spatial-Spectal (SPSP) Pulse. This can be thought of as a hybrid between spatial and spectral saturation pulses that excites magnetization in a specific location and with a specific spectral content.
The SPSP pulse has shorter duration than the two pulses separately and offers better intolerance to B1 inhomogeneity. Many SPSP variants exist, but all consist of multiple RF subpulses played out under a broad RF-envelope with a concurrent oscillating bipolar slice-selection gradient. SPSP pulses are becoming more commonly used, especially for echo-planar and spiral acquisition techniques.
Felmlee JP, Ehman RL. Spatial presaturation: a method for suppressing flow artifacts and improving depiction of vascular anatomy in MR imaging. Radiology 1987;164:559 –564.
Rosen BR, Wedeen VJ, Brady TJ. Selective saturation NMR imaging. J Comput Assist Tomogr 1984;8:813-818.
How do Fat-Sat pulses work?