| Objective: To observe the diffusion-weighted imaging(DWI) and diffusion tensor imaging features of surgical margin of the experimental rat model by resecting partial brain tissue, and study the correlation between the MRI features and its pathologic basis.Materials and Methods: Thirty-six rats were randomly divided into five experimental groups(postoperative 1 d, 7 d, 14 d, 21 d, 28 d groups) and one contrast group. A partial resection of the parietooccipital region was performed under aseptic conditions after the animals were anesthetized by intraperitoneal injection with 10% Chloral Hydrate(4ml/kg). MR imaging procedures consisted of plain scan, DWI and DTI scanning were carried out on postoperative 1 d, 7 d, 14 d, 21 d, contrast-enhanced MRI were carried out on postoperative 1 d, 7 d, 14 d, 21 d, 28 d. Brain tissue samples were obtained to prepare for examinations immediately after MR examination. Histopathological study was made under microscope. To observe vascular proliferation by immunofluorescence staining and the findings of MRI were compared with pathology findings.Results: 1. Imaging result(1) The ADC value of the brain tissue of the surgical margin reached summit at postoperative 7 d(P<0.05). There are no significance between 7 d and 14 d.(2) The FA value of the brain tissue of the surgical margin reached minimum value at postoperative 7 d(P<0.05), and the differences of FA value among 1 d, 14 d and 21 d were no significance.(3) The earliest enhancement was observed around surgical margin on the first day after surgery, and this type of enhancement was present on images observed lasted until 28 day. The enhancement of the surgical margin was significantly increased after 7d. The degree of enhancement was not significantly changed in 14 d, and reduced at 21 d and 28 d. The shape of surgical margin on contrast enhancement images were patchy、circular、halfcircular、nodular corresponding to the cavity. 2. Pathology results(1) HE: The surgical margin of the 1-day-old lesion displayed large area seepage of red blood cells; The major changes of the surgical margin in the following two weeks are coagulation necrosis and vascularization. The infiltration is largely composed of macrophages and neutrophils; In the 21-day-old lesion, the margin of the cavity was better demarcated and edema was significant decreased. Edema and inflammatory cells was basically disappear after 28 d.(2) Immunofluorescence: a The number of neovessels reached the peak at 7d, which was higher than other experimental groups and contrast group(P<0.05); The amount of neovessels in 14 d, 21 d and 28 d had no obvious disparation(P>0.05). b The number of mature vessels reached the peak at 28 d, which was higher than other experimental groups(P<0.05); The amount of mature vessels in 21 d is higher than 14d(P<0.05), but between 7d and 14 d had no obvious disparation(P>0.05), the amount of mature vessels in 7d is higher than 1d(P<0.05). c Mature vessel index: group in 28 d was higher than other experimental groups(P<0.05); group in 21 d is higher than 14d(P<0.05), there is no obvious disparation in 1d, 7d and 14d(P>0.05).d Cell density of surgical margin: difference between contrast and experimental groups is significant, while there are no differences among experimental groups. 3. The ADC value of the brain tissue of the surgical margin was not correlated with the cell density.Conclusion: 1. The ADC value of surgical margin was related to different stage of postoperation, and the pathology basis was cerebral edema, neovascularization and the astrocytic hyperplasia. 2. The FA value of the brain tissue of the surgical margin was related to different stage of postoperation, and the pathology basis was nerve fibers damage, vasogenic brain edema and blood perfusion. 3. The ADC value of the brain tissue of the surgical margin is not correlational with cell density. 4. Thenumber of neovessels and mature vessel index of surgical margin regularly changes with time. |
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