Time-efficient fast spin echo imaging at 4.7 T with low refocusing angles.

Area of Science:

• Magnetic Resonance Imaging
• Neuroimaging
• Biophysics

Background:

• Fast spin echo (FSE) is crucial for T2-weighted brain imaging.
• Specific absorption rate (SAR) limits can restrict imaging speed and quality.
• Reduced refocusing angles offer a potential solution to SAR constraints.

Purpose of the Study:

• To implement and evaluate a fast spin echo sequence at 4.7 Tesla for efficient human brain imaging.
• To assess the impact of reduced refocusing angles on image quality, SAR, and contrast.
• To investigate signal variations and magnetization transfer effects at varying refocusing angles.

Main Methods:

• Implementation of a fast spin echo sequence at 4.7 T with reduced refocusing angles (α < 180°).
• Assessment of image intensity, tissue contrast, and SAR effects.
• Investigation of incidental magnetization transfer (MT) effects during multislice acquisitions.
• Acquisition of subsecond Half Fourier Acquisition Single-shot Turbo Spin Echo (HASTE) and high-resolution FSE images.

Main Results:

• Intraslice signal variations were minimized near 180° refocusing angles.
• Apparent gray/white matter contrast remained independent of the refocusing angle.
• Incidental MT effects caused significant attenuation (25% WM, 15% GM) at 180°, reduced to <5% below 60°.
• Efficient multislice imaging was achieved without SAR-related delays.
• Subsecond HASTE and high-resolution (0.18 mm³ voxel) scans were acquired.

Conclusions:

• Reduced refocusing angles in FSE MRI at 4.7 T effectively mitigate SAR constraints.
• This approach allows for versatile and time-efficient T2-weighted brain imaging.
• Minimizing MT effects at lower flip angles preserves tissue contrast and signal intensity.