Quantitative sodium imaging with a flexible twisted projection pulse sequence.

Area of Science:

• Biomedical Imaging
• Magnetic Resonance Imaging
• Biophysics

Background:

• Accurate quantification of tissue sodium concentration is crucial for understanding sodium ion homeostasis.
• Current sodium MRI methods face challenges in balancing readout time, signal-to-noise ratio (SNR), and susceptibility artifact sensitivity.

Purpose of the Study:

• To develop and validate a novel methodology for quantifying tissue sodium concentration using a flexible twisted projection imaging sequence.
• To optimize imaging parameters for improved SNR efficiency and reduced artifacts in sodium MRI.

Main Methods:

• A flexible twisted projection imaging sequence was employed, with gradient waveform design regularized by slew rate constraints.
• Frequency-segmented conjugate phase reconstruction was used for artifact correction, utilizing field maps from proton imaging.
• Phantom and volunteer studies were conducted on a 3-T clinical scanner.

Main Results:

• High-quality quantitative sodium MR images were obtained with an isotropic spatial resolution of 7.5 x 7.5 x 7.5 mm³.
• Imaging was achieved in approximately 8 minutes for the slow T(2) component.
• After corrections, gray matter sodium concentration was measured at 36.6 ± 0.6 µmol/g wet weight, and white matter at 27.6 ± 1.2 µmol/g wet weight.

Conclusions:

• The proposed methodology enables accurate and efficient quantification of tissue sodium concentration using MRI.
• This technique provides valuable insights into spatially resolved sodium ion homeostasis in vivo.
• The method demonstrates potential for clinical applications requiring precise sodium imaging.