In vivo demonstration of microscopic anisotropy in the human kidney using multidimensional diffusion MRI

Area of Science:

• Medical Imaging
• Biophysics
• Renal Physiology

Background:

• Conventional diffusion MRI provides limited microstructural information in the kidney.
• Microscopic fractional anisotropy (µFA) offers a more detailed probe of tissue microstructure.
• Developing advanced MRI techniques is crucial for non-invasive renal assessment.

Purpose of the Study:

• To demonstrate the feasibility of multidimensional diffusion MRI for in vivo quantification of µFA in human kidneys.
• To compare µFA with conventional fractional anisotropy (FA) in renal tissues.
• To explore the potential of µFA for probing novel microstructural details.

Main Methods:

• Utilized linear tensor encoding (LTE) and spherical tensor encoding (STE) diffusion MRI in 10 healthy volunteers.
• Employed respiratory triggering and image registration to minimize motion artifacts.
• Performed semi-automated segmentation of renal cortex and medulla, followed by model-free analysis and µFA estimation.

Main Results:

• Observed the characteristic µFA effect (LTE vs. STE signal divergence) in all subjects.
• Found statistically significant differences between LTE and STE signals in cortex and medulla at specific b-values.
• Demonstrated higher µFA values (cortex: 0.53 ± 0.09, medulla: 0.65 ± 0.05) compared to conventional FA.

Conclusions:

• Successfully demonstrated the feasibility of multidimensional diffusion MRI for µFA quantification in human kidneys.
• Highlighted that µFA provides microstructural information inaccessible by conventional diffusion encoding.
• Identified technical limitations requiring further development for broader application in body MRI.