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In vivo diffusion tensor imaging of human calf muscle
1Department of Radiological Sciences, UCLA School of Medicine, Los Angeles, California, USA.
Purpose:
To investigate a tetrahedral diffusion gradient encoding scheme to measure the diffusion tensor in vivo for human calf muscle.
Materials And Methods:
The theoretical TE which maximizes the signal-to-noise ratio (SNR) of the diffusion images was derived for both the orthogonal and tetrahedral sampling strategies and the SNR advantage verified experimentally. A diffusion echo-planar imaging (EPI) sequence was used to image five volunteers. Gradient cycling and geometric averaging was performed to eliminate cross-terms between the imaging and diffusion gradients.
Results:
Trace diffusion coefficients in human muscle are spatially invariant and have low intersubject variability (<4%). Images of the off-diagonal terms confirm the anisotropy of muscle, and fiber orientation maps were derived from these off-diagonal images. A noninvariant index of anisotropy, A(ratio) (average value: 1.28), was found to be less susceptible to noise than the invariant index.
Conclusion:
This technique is robust and can be readily implemented on clinical scanners with EPI capabilities.