Abdominal T₁ relaxation times at 7T

Area of Science:

• Magnetic Resonance Imaging
• Biomedical Engineering
• Radiology

Background:

• Accurate T1 relaxation time quantification is essential for MRI-based tissue characterization.
• High magnetic field strengths (7T) offer potential for improved signal-to-noise ratio but present challenges like B1+ inhomogeneity.
• Abdominal organ T1 values at 7T are not well-established, limiting advanced quantitative applications.

Purpose of the Study:

• To precisely measure T1 relaxation times of key abdominal organs and tissues at 7T.
• To establish reference T1 values for the liver, kidney (cortex and medulla), spleen, and paraspinal muscles.
• To evaluate the efficacy of parallel transmission (pTx) in mitigating B1+ field imperfections at 7T for abdominal imaging.

Main Methods:

• Utilized a 7T whole-body MRI scanner equipped with a parallel transmission (pTx) system.
• Employed static pTx (B1+ shimming) to homogenize the radiofrequency field in target abdominal regions.
• Acquired data using eight snapshot gradient-echo inversion recovery sequences during breath-holds.
• Calculated voxel-wise T1 values via exponential model fitting from DICOM data.

Main Results:

• Mean T1 values (± coefficient of variation) were: kidney cortex (1829±3.3% ms), kidney medulla (2619±3.2% ms), liver (1378±3.5% ms), paraspinal muscle (1954±1.4% ms), and spleen (1770±2.0% ms).
• Demonstrated successful mitigation of B1+ dropouts using pTx, enabling accurate T1 mapping.
• Achieved high reproducibility with low coefficients of variation across all measured tissues.

Conclusions:

• Successfully quantified T1 relaxation times for major abdominal organs and skeletal muscle at 7T.
• Confirmed the utility of parallel transmission (pTx) in overcoming B1+ inhomogeneities at ultra-high fields for abdominal MRI.
• The B1+-insensitive snapshot gradient-echo inversion recovery method provides accurate and reproducible T1 maps essential for future quantitative MRI research and clinical applications.