Time-encoded pseudocontinuous arterial spin labeling: basic properties and timing strategies for human applications

Area of Science:

• Magnetic Resonance Imaging
• Neuroimaging Techniques
• Quantitative Perfusion Imaging

Background:

• Arterial spin labeling (ASL) is a non-invasive MRI technique for measuring cerebral blood flow (CBF).
• Pseudocontinuous ASL (pCASL) is a widely used ASL method, but time-encoded pCASL (te-pCASL) offers additional flexibility.
• Optimizing te-pCASL acquisition parameters is crucial for improving image quality and extracting more physiological information.

Purpose of the Study:

• To investigate the fundamental properties and requirements of time-encoded pseudocontinuous arterial spin labeling (te-pCASL).
• To explore the impact of variable block durations on te-pCASL performance.
• To introduce and evaluate novel strategies for timing encoding blocks in te-pCASL.

Main Methods:

• Evaluation of minimal encoding block durations and the influence of cardiac triggering.
• Assessment of dividing the labeling period into blocks.
• Introduction of variable block duration for T1-decay compensation and a 'free lunch' approach for simultaneous arterial transit time (ATT) acquisition.
• Utilizing simulations to assess potential signal losses.

Main Results:

• No signal loss observed when labeling blocks exceed 50 ms.
• Cardiac triggering is not necessary for time-encoded perfusion imaging.
• Summing individual blocks in postprocessing significantly reduces temporal signal-to-noise ratio (tSNR).
• Encoding line order does not impact the quality of cerebral blood flow (CBF) maps.

Conclusions:

• Adjusting encoding block timing in te-pCASL allows for application-specific tailoring of the acquisition.
• The 'free lunch' strategy enables simultaneous acquisition of high-resolution CBF and ATT maps with a minor reduction in tSNR.