title: Diffusion fractional anisotropy-based transformation in skeletal muscle caused by pressure.
abstract: OBJECTIVE
  We used diffusion tensor imaging (DTI) to evaluate anisotropic changes in skeletal muscle cells under external pressure.
  
  
  METHODS
  In 6 healthy volunteers, we compared DTI of the tibialis anterior (TA) and soleus (SOL) muscles under pressure. We performed imaging using a 1.5-tesla magnetic resonance (MR) scanner and diffusion-weighted stimulated-echo echo-planar pulse sequences optimized for skeletal muscle. We calculated diffusion tensor eigenvalues (λ), apparent diffusion coefficients, and fractional anisotropy (FA) values in a series of axially acquired DTI and compared them between the pressurized and nonpressurized lower limbs. We also measured a cross-sectional area of skeletal muscle.
  
  
  RESULTS
  We observed clear differences in FA and λ₃ between pressurized muscles and the nonpressurized muscles we used as controls. The mean control FAs were 0.36±0.02 (TA) and 0.30±0.02 (SOL). The mean control λ₃s were 0.74±0.02 s/mm² (TA) and 0.85±0.03 s/mm² (SOL). FA values in the pressurized (200 mmHg) limbs increased to 0.39±0.02 (TA) and 0.35±0.04 (SOL) compared with those values in the nonpressurized controls. λ₃ values in the pressurized (200 mmHg) limbs decreased to 0.68±0.05 s/mm² (TA) and 0.77±0.06 s/mm² (SOL) compared with those in controls. Moreover, the mean value of cross-sectional area of skeletal muscle (control) was 907.3±140.1 mm² (TA) and 1522±201.0 mm² (SOL). The cross-sectional area in the pressurized (200 mmHg) limbs decreased to 590.3±68.1 mm² (TA) and 1131±112.6 mm² (SOL) compared with those in controls. One-way analysis of variance (ANOVA) and post hoc Tukey-Kramer tests showed significant differences.
  
  
  CONCLUSIONS
  Anisotropy changed markedly on pressurizing the lower limb based on the correlation of the cross-sectional area and λ₃ suggested marked changed in anisotropy following application of pressure to the lower limb. If compression of the cross-sectional area is assumed to represent compression of the cell, change in λ₃ reflected the change in the size of muscle cells.
authors.affiliation: Department of Radiology, University of Tokyo Hospital, Tokyo, Japan. hataj-rad@h.u-tokyo.ac.jp
authors.forename: Junichi
authors.initials: J
authors.lastname: Hata
authors.forename: Kazuo
authors.initials: K
authors.lastname: Yagi
authors.forename: Keigo
authors.initials: K
authors.lastname: Hikishima
authors.forename: Yuji
authors.initials: Y
authors.lastname: Komaki
authors.forename: Masami
authors.initials: M
authors.lastname: Goto
authors.forename: Keichi
authors.initials: K
authors.lastname: Yano
mesh_terms: D000465:Algorithms; D016880:Anisotropy; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008297:Male; D018482:Muscle, Skeletal / Q000033:anatomy & histology* / Q000502:physiology*; D010812:Physical Stimulation / Q000379:methods*; D011312:Pressure; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D055815:Young Adult