Brief description not available

Prof. Jia Guo and colleagues from the University of California, Riverside have developed a method for improving perfusion Magnetic Resonance Imaging (MRI) using Velocity Selective Arterial Spin Labeling (VSASL). This method uses VS labeling pulses that are capable to only label the blood that is moving within a narrow band of velocities and keep the blood moving at higher velocities unperturbed. This creates a small bolus of label that can be detected readily and quickly. This method provides MRI imaging that is far superior than conventional ASL MRI techniques with a doubled temporal resolution, improved signal-to-noise ratio (SNR) efficiency and quantification accuracy. Fig 1: Schematics showing how UCR’s narrow-band velocity selectivity enables ultra-fast perfusion imaging  

In conventional vessel encoded pseudo-continuous arterial spin labeling (PASL), the temporal signal to noise (tSNR) is improved by repeatedly applying pulsed labeling pulses in between Look-Locker readouts.  This works optimally when the temporal width of the tagged boluses matches the inter-pulse spacing. However, because the feeding arteries generally have different velocities and geometries, the conventional labeling slab fails to achieve desirable tSNR.  

In conventional vessel encoded ASL (VEASL), pseudo-continuous ASL tagging is used with additional gradient pulses applied across the tagging plane to encode the data with information about the location of the feeding arteries. In most implementations, prior information on the locations of feeding arteries in the tagging plane has been used to optimize the encoding process. However, in some cases, the relevant supplying arteries are not known ahead of time, as there may be variant or collateral circulation. In addition, the resonance offset in the tagging plane is known to affect the tagging efficiency.

The ideal velocity selective arterial (ASL) method for MRI is one in which the tagging is: (1) continuous, (2) inverts blood, and (3) occurs right at the arterioles before the blood enters the capillary bed and tissue. An inherent advantage of velocity selective arterial spin labeling (VSASL) technique over other ASL methods is property #3—the tagging occurs all the way down the arterial tree to small arterioles, therefore intrinsically insensitive to transit delays and is useful in applications where transit delay can be long, such as perfusion imaging in white matter, and in stroke.