Functional imaging with Turbo-CASL: transit time and multislice imaging considerations

Area of Science:

• Neuroimaging
• Magnetic Resonance Imaging (MRI)

Background:

• Continuous Arterial Spin Labeling (CASL) is a magnetic resonance imaging technique used for non-invasive measurement of cerebral blood flow.
• Activation-induced changes in transit time (TT) can affect the accuracy of functional imaging with CASL.
• Turbo-CASL is a modified CASL technique designed to improve temporal resolution and potentially mitigate TT-related artifacts.

Purpose of the Study:

• To investigate the optimal parameters for Turbo-CASL in functional imaging, specifically addressing the impact of activation-induced transit time (TT) changes.
• To compare the functional sensitivity of Turbo-CASL with traditional CASL techniques.

Main Methods:

• Functional imaging was performed using a bilateral finger-tapping task.
• Turbo-CASL and traditional CASL techniques were compared across multiple subjects.
• Experimental and simulation studies were conducted to determine the optimal repetition time (TR) relative to resting-state TT.
• Simulations analyzed TT sensitivity variations across different slices and the effect of increasing slice numbers.

Main Results:

• Turbo-CASL demonstrated improved functional sensitivity compared to traditional CASL in four out of six subjects when using an appropriate TR.
• Optimal functional sensitivity with Turbo-CASL was observed when the pulse TR was set 100-200 ms below the resting-state TT.
• Despite a lower baseline ASL signal, Turbo-CASL achieved comparable or superior functional sensitivity due to signal enhancement from TT decrease during activation.
• Simulations highlighted slice-dependent TT sensitivity and signal loss with increased slice acquisition.

Conclusions:

• Turbo-CASL is a promising technique for functional ASL, offering improved sensitivity and higher temporal resolution.
• Careful selection of the repetition time (TR) relative to resting-state transit time (TT) is crucial for maximizing Turbo-CASL's functional imaging performance.
• Turbo-CASL effectively leverages activation-induced TT changes to enhance functional signal detection.