Variable flip angle T1 mapping in the human brain with reduced T2 sensitivity using fast radiofrequency-spoiled...

Area of Science:

• Magnetic Resonance Imaging
• Quantitative MRI
• Biomedical Engineering

Background:

• Variable flip angle (VFA) T1 quantification using 3D radiofrequency (RF) spoiled gradient echo imaging enables rapid whole-brain T1 mapping.
• Conventional VFA T1 relaxometry is susceptible to bias from incomplete radiofrequency spoiling, leading to T2 dependency.
• Accurate T1 quantification is crucial for various neurological applications and research.

Purpose of the Study:

• To develop and validate a novel postprocessing approach to mitigate T2-related bias in VFA T1 relaxometry.
• To enhance the accuracy and reliability of whole-brain T1 mapping in the human brain.
• To overcome the limitations of conventional VFA methods that assume ideal spoiling.

Main Methods:

• T1 quantification was performed using the signal ratio of two spoiled gradient echo (SPGR) images acquired at different flip angles.
• An analytical solution for the RF-spoiled steady-state signal was employed, incorporating a global T2 guess.
• In vivo 3D SPGR imaging of the human brain at 3 Tesla and simulations were used for accuracy evaluation.

Main Results:

• Simulations confirmed that a global T2 guess significantly reduces the sensitivity of VFA T1 mapping to T2 variations.
• The proposed method yielded accurate and reliable in vivo T1 values for both white and gray matter.
• Results showed good agreement with established inversion recovery reference measurements.

Conclusions:

• A global T2 estimate substantially improves the accuracy of VFA T1 relaxometry in the human brain.
• The developed method offers a more robust alternative to conventional approaches that incorrectly assume ideal spoiling.
• This technique enhances the utility of VFA for precise T1 quantification in clinical and research settings.