SNR-efficient whole-brain pseudo-continuous arterial spin labeling perfusion imaging at 7 T

Area of Science:

• Magnetic Resonance Imaging
• Neuroimaging
• Biophysics

Background:

• Pseudo-continuous arterial spin labeling (PCASL) is crucial for non-invasive brain perfusion quantification.
• High field (7 Tesla) MRI offers enhanced sensitivity but faces challenges with radiofrequency (RF) power deposition.
• Optimizing PCASL parameters is essential for maximizing SNR efficiency under RF power constraints.

Purpose of the Study:

• To optimize PCASL parameters for maximal SNR efficiency in whole brain perfusion imaging at 7T.
• To balance labeling efficiency and total RF power deposition.
• To reduce the specific absorption rate (SAR) burden during perfusion imaging.

Main Methods:

• Bloch simulations of pulsatile laminar flow were employed to optimize PCASL parameters.
• Key parameters adjusted included inter-RF pulse spacing (TR_PCASL), mean B₁ ⁺ (B₁ ⁺ _ave), and gradient amplitudes (G_max, G_ave).
• In vivo validation was performed on six volunteers at 7T, utilizing dynamic B₀-shimming and flip angle adjustments.

Main Results:

• Optimized PCASL parameters achieved a 3.3× reduction in RF power while maintaining high labeling efficiency.
• A 118% improvement in in vivo SNR efficiency was observed compared to previous protocols.
• Enhanced static tissue response reduced the necessary distance between the labeling plane and imaging volume.

Conclusions:

• The optimized PCASL parameters offer a robust and efficient method for 7T whole brain perfusion imaging.
• Significant improvements in SNR efficiency and reduced SAR burden were demonstrated.
• This approach facilitates advanced perfusion quantification at ultra-high fields.