Comparison of Velocity- and Acceleration-Selective Arterial Spin Labeling with [¹⁵O]H₂O Positron Emission Tomography

Abstract

In the last decade spatially nonselective arterial spin labeling (SNS-ASL) methods such as velocity-selective ASL (VS-ASL) and acceleration-selective ASL have been introduced, which label spins based on their flow velocity or acceleration rather than spatial localization. Since labeling also occurs within the imaging plane, these methods suffer less from transit delay effects than traditional ASL methods. However, there is a need for validation of these techniques. In this study, a comparison was made between these SNS-ASL techniques with [15 O]H 2 O positron emission tomography (PET), which is regarded as gold standard to measure quantitatively cerebral blood flow (CBF) in humans. In addition, the question of whether these techniques suffered from sensitivity to arterial cerebral blood volume (aCBV), as opposed to producing pure CBF contrast, was investigated. The results show high voxelwise intracranial correlation (0.72 to 0.89) between the spatial distribution of the perfusion signal from the SNS-ASL methods and the PET CBF maps. A similar gray matter (GM) CBF was measured by dual VS-ASL compared with PET (46.7 ± 4.1 versus 47.1 ± 6.5 mL/100 g/min, respectively). Finally, only minor contribution of aCBV patterns in GM to all SNS-ASL methods was found compared with pseudo-continuous ASL. In conclusion, VS-ASL provides a similar quantitative CBF, and all SNS-ASL methods provide qualitatively similar CBF maps as [15 O]H 2 O PET.

Quantitative measurement of cerebral blood volume using velocity‐selective pulse trains

“…This is similar to the ASL effect size for CBF mapping, thus providing similar spatial and temporal resolution, for both clinical and fMRI applications. Indeed, the mean temporal SNR values (1.2 in GM and 0.6 in WM) are close to the recently recorded values for velocity- and acceleration-selective ASL methods (44,69,70). Ideally, if a Vc slower than capillary blood can be used, labeling efficiency will be much higher and uniform across different microvessel compartments, as indicated in Table 1.…”

“…It was later realized that the velocity-compensated pulse train for the control was actually acceleration-sensitive with a cutoff acceleration (Ac) of 0.57 m/s 2 . Acceleration-selective ASL with similar Ac values has recently been demonstrated for CBF measurement (70,73). Thus pulsatile flow in large vessels would also cause blood suppression in the velocity-compensated control and lead to signal reduction in the final CBV images, whereas the velocity-insensitive control remains insensitive to acceleration and maintains the large vessel signal.…”

Improved sensitivity and temporal resolution in perfusion FMRI using velocity selective inversion ASL

“…Velocity and acceleration selective pulses have been recently shown to be an attractive option for ASL perfusion imaging because of potential gains in SNR and decreased sensitivity to bolus arrival time variations. [9][10][11][12][13][14] While typical ASL labeling schemes target inflowing arterial blood spins based on their spatial position relative to the tissue of interest (e.g., pseudocontinuous ASL, or PCASL, pulses label spins as they cross a plane upstream of the tissue of interest), velocity selective labeling, on the other hand, targets moving spins regardless of their location. As a result, the time elapsed between the spins getting labeled and arriving at the capillary bed is virtually removed.…”

Diagnostic and prognostic benefit of arterial spin labeling in subacute stroke

“…The combination of a delay in the ASL‐BAT map and an ipsilateral reduction of CBF signal associated with hyperintense spots can be interpreted as strong hypoperfusion (Kohno et al, ) or, alternatively, as effective leptomeningeal collateralization (Havenon, ; Lou et al, ). We interpreted ATDA as strong hypoperfusion but new imaging approaches may resolve this artifact in the future (Norris & Schwarzbauer, ; Schmid, ).…”