Diffusion Tensor Imaging of Extraocular Muscle Using Two-dimensional Single-shot Interleaved Multiple Inner Volume Imaging Diffusion-weighted EPI at 3 Tesla

Purpose: To evaluate the feasibility of diffusion tensor imaging (DTI) for the medial and lateral rectus extraocular muscle (EOM) evaluation, to investigate the normal DTI parameters of the medial and lateral rectus EOM, and to compare with other skeletal muscle.

Materials And Methods: Seven multiple sclerosis patients and five normal subjects (M:F = 5:7, mean age = 31.6 ± 9.2) without EOM disorder were included. The orbital DTIs using 2D-ss-IMVI-DWEPI were scanned with b = 500 s/mm(2) and 12 directions. The mean diffusivity (MD) and fractional anisotrophy (FA) of medial and lateral rectus EOMs in both orbits, and temporalis muscles were measured in regions of interest on two consecutive axial slices. Student t-test was performed to compare the mean apparent diffusion coefficient and FA values between medial and lateral rectus EOMs, and between EOMs and temporalis muscles.

Results: The MDs in medial (0.58 ± 0.18 × 10(-3) mm(2) /s) and lateral rectus EOMs (0.71 ± 0.18 × 10(-3) mm(2) /s) were significantly lower than temporalis muscle (0.84 ± 0.14 × 10(-3) mm(2) /s) (P < 0.001, respectively). The MD in medial rectus EOM was significantly lower than lateral rectus EOM (P = 0.001). The FAs in medial (0.40 ± 0.05) and lateral rectus EOMs (0.40 ± 0.05) were significantly higher than temporalis muscle (0.25 ± 0.05) (P < 0.001, respectively). There was no significant difference between the FAs in medial and lateral rectus EOMs (P > 0.05).

Conclusion: The MDs of EOMs were lower and the FAs were higher than those of skeletal muscle. These are well correlated to the unique characteristics of EOMs.