Comparison of pulsed arterial spin labeling encoding schemes and absolute perfusion quantification

Area of Science:

• Neuroimaging
• Physiology
• Medical Physics

Background:

• Arterial spin labeling (ASL) with magnetic resonance imaging (MRI) is a noninvasive method for assessing brain tissue physiology via cerebral blood flow (CBF).
• Numerous ASL sequences and quantification methods exist, varying in implementation, artifact sensitivity, and accuracy.
• Comparing studies using different ASL techniques can lead to erroneous conclusions due to inherent variability.

Purpose of the Study:

• To evaluate and compare the performance of three pulsed ASL sequences.
• To assess the impact of three different absolute quantification schemes on CBF measurements.
• To identify the most reliable ASL approach for accurate CBF quantification.

Main Methods:

• Comparison of three pulsed ASL sequences: FAIR-QUIPSSII, PICORE-Q2TIPS (FOCI), and PICORE-QUIPSSII (BASSI).
• Evaluation of three distinct absolute quantification methods for determining CBF from ASL data.
• Assessment of signal-to-noise ratio (SNR) and measured CBF values across different sequence and quantification combinations.

Main Results:

• The FAIR-QUIPSSII ASL sequence demonstrated a 10-20% higher SNR and 18% higher CBF compared to PICORE variants.
• Different quantification schemes resulted in up to a 35% variation in calculated CBF values.
• Substantial differences in both CBF values and SNR were observed across the evaluated ASL sequences and quantification methods.

Conclusions:

• Despite theoretical expectations of consistency, significant variations in CBF and SNR exist among ASL techniques.
• Consistent application of quantification schemes is essential to avoid erroneous intra- and intergroup comparisons.
• Quantification using local tissue proton density is proposed as the most accurate method for CBF determination, pending further validation.