Pseudo-Continuous Arterial Spin Labeling (pCASL) MRI is a new ASL technique that has the potential of combining advantages of Continuous-ASL and Pulsed-ASL. However, unlike CASL, the labeling process of pCASL is not strictly an adiabatic inversion and the efficiency of labeling may be subject-specific.
We performed three experiments to study the labeling efficiency in pCASL MRI:
- The optimal labeling position was determined empirically to be 84 mm below Anterior-Commissure Posterior-Commissure line in order to achieve the highest sensitivity.
- An experimental method was developed to utilize phase-contrast MRI as a normalization factor and to estimate the labeling efficiency in vivo, which was founded to be 0.86±0.06 (n=10, mean±SD).
- We compared the labeling efficiency of pCASL MRI under normocapnic and hypercapnic (inhalation of 5 percent CO2) conditions, and showed that a higher flow velocity in the feeding arteries resulted in a reduction in the labeling efficiency.
In summary, our results suggest that labeling efficiency is a critical parameter in pCASL MRI not only in terms of achieving highest sensitivity but also in quantification of absolute CBF in ml/min/100g. We propose that the labeling efficiency should be estimated using phase-contrast MRI on a subject-specific and physiologic-condition-specific basis.