Bidirectional crusher gradient method to estimate the labeling efficiency of pseudo-continuous arterial spin labeling MRI in mice.

Purpose: To develop an experimental method for measuring the labeling efficiency of pseudo-continuous arterial spin labeling (pCASL) MRI in mice.

Methods: We propose a method using bidirectional crusher gradients to modulate vascular signals in the azygos pericallosal artery (azPA) of the mouse brain, applied with and without pCASL labeling. The combination of corresponding signals allows the estimation of labeling efficiency. A series of studies were conducted to optimize post-labeling delay, labeling duration, TR, and slice thickness. The sensitivity of labeling efficiency measurements to changes in the labeling scheme was examined. Finally, a physiological challenge with 5% CO₂ was used to assess the potential effect of hypercapnia on labeling efficiency.

Results: Upon systematic testing, optimal acquisition parameters included a labeling duration ≥1170 ms, a TR of 3 s, and an imaging slice thickness of 0.75 mm. To quantitatively estimate labeling efficiency, the bolus arrival time to azPA was required and found to be 209.2 ± 19.1 ms. Typical labeling efficiencies in mouse pCASL scans were 0.780 ± 0.048 (mean ± SD). Furthermore, hypercapnia was found to increase pCASL labeling efficiency.

Conclusion: Our proposed method facilitates perfusion measurement using pCASL MRI by accounting for intersubject variations in labeling efficiency, offering great potential for applications in pathophysiological studies.