| Partâ… . Muscle magnetic resonance imaging of denervation and reinnervation: correlation with histologic and functional recoveryObjective To prospectively evaluate magnetic resonance (MR) signal abnormalities and the time course of T2 values in denervated muscle of rabbit models and investigate the correlation between MRI, histologic and functional recovery. Materials and methods Acute denervated muscle models were set up by crushing the right sciatic nerves in each of 44 rabbits. Rabbits were randomly divided into two groups. In group A, there were 8 rabbits underwent sequential MR imaging and T2 measurements, as well as measurements of functional changes over a 70-day follow-up period. In parallel, there were 36 rabbits in group B. The rabbits were scanned once followed by histologic processing of the gastrocnemius muscle in postoperative 1 hour, days 1, 2, 3, week 1, 2, 3, 4, 5, 6, 8, 10. These findings were related to the corresponding images. The contralateral sham-operated sides served as controls. The change of signal intensity and morphological changes of the gastrocnemius muscle were observed. On the SE multiple echo sequence, T2 of the gastrocnemius muscle were measured and their evolution with time were analyzed. The circumferences of both legs were measured in the same section segment on T1-weighted images. On each time point before MR imaging, the function of injured hind limbs were evaluated. The depilation ulcer, toenail lost, phalange expose were observed and the ankle drop and the toe-extention reflex were evaluated. The Tarlov sciatic nerve function was scored. On each time point above, three rabbits were randomly scleceted to sacrifice histopathological examination. The gastrocnemius muscle were obtained for light microscopy examination.Results The normal gastrocnemius muscle manifested homogeneous intermediate signal intenstisy on T1WI,STIR,3DT2W. The denervated muscle displayed slightly hyperintense signals on STIR and 3DT2W as early as 5 days after surgery, further increased from week 1 to week 4,and signal intensity became high at week 5 in all rabbits. Signal intensity began to decrease to the intermediate level at 9～10 weeks after surgery. The denervated gastrocnemius muscle showed slightly hyperintense signals on T2 maps as early as 48 hours, T2 value at 48 hours was 32.49±0.98ms, further increased from week 1 to week 4, reached a maximum at week 5 (50.62±1.75ms). Subsequently, the T2 values began to decreased at week 6 (45.41±1.39ms), then normalized until week 10 (31.73±0.73ms) . The T2 values were significantly higher in denervated group than in the control group from day 2 to week 9 (F=13.00694.12, P<0.05). There was no statictically significant difference in the mean signal intensities on STIR,3DT2W images and T2 relaxation time changes of the sham-operated and the contralateral normal sides at any time point.At or less than 48 hours after denervation, no differences in the circumference of the lower leg were found. Seven days after surgery, the denervated leg had a smaller circumference than that of the control leg, the ratio of the circumference of the lower leg of the denervated sides with respect to the contralateral unaffected sides was 0.87±0.07, further decreased from week 1 to week 5, reached a minimum at week 6, the circumference ratio was 0.65±0.05. The dernervated leg revealed a increase in circumference at week 7. Moreover, the time course of the circumference ratio was opposite to dynamic T2 value measurement of denervated muscle. With the prolonging of T2, the circumference of the denervated hind limb gradually decreased, and vice versa. The changes of T2 values is an early sign of muscle denervation and regeneration, which markedly preceded muscle atrophy and regeneration.T2 of gastrocnemius muscles were negatively correlated with the parameters of the functional evalutation(r=-0.843～-0.482, P<0.05). That is, the pattern of a rapid rise followed by gradual recovery in T2 values were well correlated with the functional recovery pattern that showed initial maximal impairment followed by gradual improvement.On light microcopy, the gastrocnemius muscle showed normal tissue microstructure in 1 hour after operated. Extracellular water volume increased in 24 hours after surgery. Inflammatory reaction and an enlargement of the muscle capillaries developed after denervation which were clearly visible at 48 hours. Significant muscle fiber atrophy could be detected 7 days after the lesion with a decrease of the mean fiber area. Subsequently, the fiber area decreased. After week 6 or week 7, the capillary size and extracellular fluid decreased and muscle fiber atrophy resolved. The pathophysiological basis for the MR relaxation time changes is the enlargement of the capillary bed and extracellular fluid. The rise of T2 values is consistent with edema, enlargement of muscle caplliaries and degeneration of muscle fiber, indicating increased blood volume and extracellular fluid within the denervated muscles. T2 values began to normalize after beginning of regeneration which was associated with a histological regression of the capillary enlargement and extracellular fluid.Conclusion The changes of T2 values is an early sign of muscle denervation and regeneration, which markedly preceded the finding of MR conventional examiantion. The dynalmic change of T2 of denervated muscle was consistent with histologic and functional recovery. MR imaging could be used to help monitor the process of muscle recovery in acute peripheral nerve injury and predict the degree of nerve damage and functional recovery. Dynamic T2 value measurement of denervated muscles is a sensitive and reliable method to monitor the change of denevated muscles. Partâ…¡. Preliminary quantitatively analysis of DTI of the brachial plexusObjective To prospectively analyze normal diffusion tensor imaging (DTI) parameters of asymptomatic adult brachial plexus, and to assess the feasibility and value of diffusion tensor imaging (DTI) and tractography (DTT) in the normal brachial plexus at 1.5 T.Materials and methods DTI of the brachial plexus was performed in 34 healthy adult volunteers. Maps of the apparent diffusion coefficient (ADC) and fractional anisotropy (FA), as well as tractography of the brachial plexus were obtained. FA and ADC values of each root from C5 to C8 were measured. A single-shot spin-echo-based echo-planar imaging sequence was performed in each subject at three different b values including 700, 900, and 1100 mm2/s. Length of reconstructed fiber tracts, fiber density index were calculated for the right C6 root. Signal-to-noise ratio (SNR)was also calculated for each acquisition.Results Reconstructed DTI (32/34) were of good quality. Measurements performed for each root from C5 to C7 indicated no statistically significant difference in FA or ADC mean values between individual root levels (P>0.05): FA/ADC= 0.456±0.035/1.157±0.151 at C5; FA/ADC=0.453±0.042/1.132±0.192 at C6; 0.444±0.039/1.181±0.186 at C7, FA/ADC=0.394±0.050/1.256±0.183 at C8. No significant differences were found in the FA or ADC value of the bilateral brachial plexus (P>0.05). There were statistical differences in average fiber length and fiber density index among the three groups at different b values including 700, 900, and 1100 mm2/s (P <0.05). Longest fibers and maximum fiber density index were found at b values of 900 s/mm2.Conclusion DTI and DTT can show the FA and architecture of the brachial plexus ,the optimal b value for diffusion tensor imaging and fiber tractography of the brachial plexus at 1.5 T was 900 s/mm2. |
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