Ultrashort echo time and zero echo time MRI at 7T

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysics
• Medical Imaging Technology

Background:

• Zero echo time (ZTE) and ultrashort echo time (UTE) pulse sequences in MRI are crucial for detecting signals from rapidly decaying short-T2 tissue components.
• These advanced MRI techniques offer unique advantages over conventional methods for specific tissue characterization.

Purpose of the Study:

• To compare the performance and identify differences between 3D ZTE and UTE pulse sequences at 7 Tesla (7T) for MRI.
• To assess the ability of ZTE and UTE sequences to detect and characterize ultrashort, short, and long T2 tissues.

Main Methods:

• Matched ZTE and UTE pulse sequences for readout trajectories and image contrast at 7T.
• Utilized water- and fat-suppressed solid-state proton projection imaging for ZTE k-space center filling.
• Acquired images from healthy volunteers and performed qualitative comparisons alongside signal-to-noise (SNR) and contrast-to-noise (CNR) measurements.

Main Results:

• Achieved nearly identical CNR/SNR for ultrashort, short, and long-T2 components in the brain, knee, and ankle within similar scan times.
• Observed gradient fidelity artifacts in UTE and shading artifacts in ZTE, both correctable with advanced reconstruction or protocol adjustments.

Conclusions:

• 3D ZTE and UTE pulse sequences demonstrate comparable contrast and SNR efficiency for volumetric imaging of ultrashort-T2 components at 7T.
• ZTE is limited to volumetric imaging but significantly reduces acoustic noise; UTE offers greater flexibility but exhibits higher acoustic noise and gradient sensitivity.