Experimental study of dynamic diffusion tensor imaging in spinal cord of goats under persistent compression / 中华放射学杂志

ABSTRACT

Objective To explore the dynamic changes of diffusion tensor imaging(DTI) in spinal cord of goats with persistent compression injury. Methods Eighteen goats weighted 20--25 kg were divided into three groups with completely random design: A, B and C. A balloon catheter was inserted into the epidural space at C3-4 level via intervertabral foramen for each goat. The balloon was inflated by injection of variable volumes of saline in group A and B 10 days following operation. The volume of saline was 0. 3 ml in group A and 0. 2 ml in group B,respectively. The compression sustained for 40 days. Group C served as uncompressed control without injection of saline. The locomotor rating score was applied to each group. Conventional MRI and DTI were performed. The apparent diffusion coefficient (ADC)and fractional anisotropy (FA) values were measured. Histopathological assessments of the compressed spinal cord were performed 50 days following operation with light microscope and transmission electron microscopy. Results Before operation, the locomotor rating score was 5, the ADC value was ( 1.23 ± 0. 05 ) × 10-3 mm2/s and the FA value was (0. 72 ± 0. 05 ) each group. Of six goats in Group A, the locomotor rating score severely decreased and reached( 1.5±0. 4)on the 40 th day after compression. The ADC value at compression site decreased soon and reached the minimum (0. 75±0. 04) × 10-3mm2/s on the 5 th day after compression. Then the ADC value increased gradually, restored normal on the 10 th day or so, then became markedly higher than normal and reached( 1.61±0. 05) × 10-3mm2/s on the 40 th day. The FA value at compression site decreased soon, reached(0. 54±0. 04)on the 1st day, then decreased gradually and reached(0. 43 ± 0.05) on the 40 th day. It appeared high signal intensity on T2WI on the 10 th day. In Group B, the locomotor rating score was moderately decreased and reached(3.4±0. 5 )on the 40 th day. The ADC value at compression site decreased slightly firstly, reached( 1.08±0. 04) × 10-3mm2/s on the 1st day, restored normal on the 20 th day or so, then increased gradually, became higher than normal and reached ( 1.27 ± 0. 05) × 10-3mm2/s on the 40 th day. The FA value increased slightly firstly, reached (0. 78±0. 05 )on the 1st day, then decreased gradually, restored normal on the 15 th day or so, became lower than normal and reached(0. 67±0. 05) on the 40 th day. There was no abnormality on conventional MRI. In Group C, the locomotor rating score, ADC value and FA value remained unchanged. There was no abnormality on conventional MRI. There were dynamic changes over time of the ADC value and FA value in Group A and B, which was more marked in Group A than that in Group B ( repeated measurements analysis of variance, F=426. 7 for the ADC value and F =7895.2 for the FA value, P < 0. 01 ). Histopathologically, swelling and degeneration of axons and neurons as well as the disarrangement of myelin sheathes could be seen. The pathological changes were more marked in Group A than in Group B. In Group C, no abnormality could be seen. Conclusion There are dynamic changes of DTI in cervical spinal cord with compressive injury that correlated with the degree and duration of compression. The ADC value decreased firstly, restored normal and then increased. The FA value increased firstly, restored normal and then decreased in mild compression while solely decreased in serious compression.