An exploration of diffusion tensor eigenvector variability within human calf muscles.

Area of Science:

• Biomedical Engineering
• Medical Imaging
• Musculoskeletal Imaging

Background:

• Diffusion tensor imaging (DTI) is crucial for assessing skeletal muscle microstructure.
• Understanding DTI acquisition parameter effects is vital for reliable muscle imaging.
• Eigenvector stability is key for accurate DTI-based biomechanical analysis.

Purpose of the Study:

• To investigate how diffusion tensor imaging (DTI) acquisition parameters influence the stability of principal (ε1) and minor (ε2) eigenvectors in human lower leg muscles.
• To determine the impact of signal averaging and number of diffusion directions on eigenvector orientation consistency.

Main Methods:

• DTI scans were performed on seven healthy subjects at 3T.
• Acquisition parameters included varying numbers of signal averages (NSA) and diffusion directions (NDD).
• Calculated metrics included eigenvalues, eigenvectors, fractional anisotropy (FA), mean diffusivity (MD), signal-to-noise ratio (SNR), and zenith angle.

Main Results:

• The first eigenvector (ε1) variation was influenced by the number of diffusion directions (NDD), while the second eigenvector (ε2) variation was affected by the number of signal averages (NSA).
• Vector variability showed a stronger relationship with the λ3:λ2 ratio than with fractional anisotropy (FA) or SNR.
• Zenith angle was strongly associated with ε1 variability but only weakly with ε2 variability.

Conclusions:

• The second eigenvector (ε2) exhibits greater directional variability compared to the first eigenvector (ε1).
• Experimental conditions that significantly impacted ε1 variability had only a marginal effect on ε2 variability.
• These findings highlight the differential sensitivity of eigenvectors to DTI acquisition parameters in skeletal muscle.