Quantitative rotating frame relaxometry methods in MRI

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysics
• Biochemistry

Background:

• Macromolecular degeneration and biochemical changes in tissues are quantifiable using MRI.
• Rotating frame relaxation rates, R1ρ and R2ρ, serve as sensitive biomarkers for cellular-level phenomena.

Purpose of the Study:

• To present existing MRI methods for investigating biophysical mechanisms influencing rotating frame relaxation rates (R1ρ and R2ρ).
• To review theoretical and experimental approaches for designing RF excitation schemes to improve R1ρ and R2ρ measurements.
• To summarize current clinical applications of rotating frame MRI sequences.

Main Methods:

• Review of existing MRI techniques for probing biophysical mechanisms affecting R1ρ and R2ρ.
• Description of theoretical and experimental approaches for designing hard RF pulse cluster- and adiabatic RF pulse-based excitation schemes.
• Review of MRI acquisition strategies for quantitative relaxation rate measurement in the rotating frame regime.

Main Results:

• Identified long acquisition times and high RF energy deposition as major barriers for R1ρ and R2ρ MRI at high magnetic fields.
• Presented strategies for accurate and precise measurements of R1ρ and R2ρ using optimized RF excitation schemes.
• Summarized current clinical uses of rotating frame MRI sequences.

Conclusions:

• Clinical applications of R1ρ and R2ρ MRI remain challenging due to technical limitations.
• Optimized RF pulse designs and acquisition strategies are crucial for accurate quantitative measurements.
• Rotating frame MRI holds potential for assessing tissue biophysics and biochemistry, pending further development.