ASL has several intrinsic limitations, and is not currently as widely used as many other MRA techniques. First, because ASL-MRA relies on the replacement of saturated blood by tagged blood, reasonably high arterial velocities are required for success. ASL methods may thus not be suitable for MRA of vessels with significant stenoses. ASL-MRA also presumes the flow direction is known, which may not always be the case, again with diseased vessels where retrograde collateral flow may be present.
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The readout for ASL-MRA is typically either a 3D balanced-SSFE or 3D-FSE sequence. SSFP methods are generally better for fast flow, while FSE sequences are more frequently used for slower flows. FSE sequences are also preferred over SSFP methods for pulmonary MRA because of their reduced sensitivity to susceptibility distortions at air-lung interfaces.
Albert T, Kelly E. Time-Spatial labeling inversion pulse. Safe, simple and effective non-contrast MR angiography. From www.medical.toshiba.com, 2010.
Miyazaki M, Lee VS. Nonenhanced MR angiography. Radiology 2008;248:20-43.
Shimada T, Amanuma M, Takahasi A, Tsushima Y. Non-contrast renal MR angiography: value of subtraction of tagging and non-tagging technique. Ann Vasc Dis 2012; 5:161-165.
How do inflow-enhanced SSFP MRA sequences work? Where do you place the saturation bands?
What is arterial spin labeling (ASL) and how does it work?