[Study of lower extremity muscle function in stroke patients by velocity-encoded phase-contrast magnetic resonance imaging].

OBJECTIVE

To compare the difference of muscle dynamic characteristics for the ankle dorsiflexors and plantarflexors between stroke patients at the chronic stage and healthy controls so as to provide a new method of assessing the in vivo muscle function in patients with hemiplegia.

METHODS

From May 2008 to May 2009, 26 stroke patients and 21 age-and gender-matched normal controls were recruited. All subjects were positioned on a scanner table and requested to perform the voluntary movement of ankle flexion-extension. The velocity encoded phase contrast magnetic resonance imaging (VE-PC MRI) provided the images of tibialis anterior muscle (TA), medial head of gastrocnemius muscle (MG) and soleus muscle (SOL) during a movement cycle. By measuring the calf muscle contraction velocity, the balance function was assessed by Berg balance scale (BBS). The correlation between scores of BBS and the mean maximum velocity were compared and analyzed.

RESULTS

The peak velocity of TA (1 - 8 phase, 8.900 - 21.120 mm/s vs 12.99 - 34.50 mm/s), MG (12-19phase, 13.60 - 13.28 mm/s vs 25.85 - 18.38 mm/s) and SOL (12 - 16 phase, 18.63 - 33.62 mm/s vs 27.68 - 47.22 mm/s) was lower in the affected side than that in the controls during ankle extension (P < 0.05); During ankle dorsiflexion, the co-contraction index of SOL/TA (2 - 9 phase, 0.81 - 0.82 vs 0.27 - 0.44) and the co-contraction index of GM/TA (2 - 9 phase, 0.73 - 0.58 vs 0.10 - 0.11) was markedly higher in the affected side than the controls. The patient score of BBS was negatively correlated with the mean velocity of TA (r = -0.69, P = 0.001) and GM (r = -0.47, P = 0.01) in the affected side. There was correlation between TA (r = -0.60, P = 0.001) and GM (r = -0.49, P = 0.01) in the unaffected side.

CONCLUSION

During the movement of active ankle flexion-extension, the velocities of TA, SOL and MG are lower in the affected side. The co-contraction index is markedly higher in the affected side during ankle dorsiflexion. This in turn leads to a decline of balance function in patients. VE-PC MRI can provide quantitative in vivo measurements of lower extremity muscle function in stroke patients.