Estimation of labeling efficiency in pseudocontinuous arterial spin labeling

Area of Science:

• Magnetic Resonance Imaging
• Cerebrovascular Physiology
• Medical Physics

Background:

• Pseudocontinuous arterial spin labeling (PCASL) MRI combines benefits of continuous and pulsed ASL techniques.
• Unlike continuous ASL, PCASL labeling is not strictly adiabatic, leading to subject-specific labeling efficiency.
• Accurate quantification of cerebral blood flow (CBF) necessitates understanding and accounting for labeling efficiency.

Purpose of the Study:

• To investigate and characterize labeling efficiency in PCASL MRI.
• To establish methods for optimizing PCASL sensitivity and quantifying labeling efficiency in vivo.
• To assess the impact of physiological conditions like hypercapnia on PCASL labeling efficiency.

Main Methods:

• Empirical determination of optimal labeling position (84 mm below AC-PC line) for maximal sensitivity.
• Development of a phase-contrast velocity MRI method for in vivo normalization and labeling efficiency estimation.
• Comparison of PCASL labeling efficiency under normocapnic and hypercapnic conditions (5% CO2 inhalation).

Main Results:

• Optimal labeling position identified for enhanced sensitivity in PCASL.
• In vivo labeling efficiency estimated at 0.86 ± 0.06 using phase-contrast velocity MRI normalization.
• Increased arterial flow velocity under hypercapnia reduced PCASL labeling efficiency.

Conclusions:

• Labeling efficiency is crucial for both PCASL sensitivity and absolute CBF quantification.
• Subject-specific estimation of labeling efficiency using phase-contrast velocity MRI is recommended.
• Understanding factors affecting labeling efficiency, such as flow velocity, is vital for accurate PCASL applications.