Magnetic Resonance Imaging Features Of Rat Brain Glioma After Injection Of USPIO And The Initial Exploration Of Establishing Rat Brain Radiation Necrosis Model

PartⅠ:Establishment of the rat C6 glioma model and analysis of the related factorsObjective:C6 glioma cells were stereotactically implanted into the right caudate nucleus of young male Wistar rats. Neurological presentation, time of tumor growth and survival time were observed. The purpose was to explore the laboratory procedure, method and key point in establishing the rat glioma model for the further research.Methods:10μl of C6 cells (the concentration was 1×105/μl in free serum) cultured for exponential phase of growth in vitro were stereotaxically implanted into the right caudate nucleus for 5mm deep in the cranium in each of 50 Wistar rats.Results:24 Wistar rats were stereotaxically implanted into the right caudate nucleus in the first 5 times. Except 2 rats with accidental death 1 or 2 days after operation, the tumors were found the tumor in the brain in all other rats by MRI examination. In the first week, most of the rats were normal. In the second week, the rats were found depressed gradually, activity decreased, food and drink reduced, the fur tarnished, dry and withered hair, and body weight lightened obviously. In the third week, the above symptoms aggravated. Some of rats had epileptic seizure, and died in succession.2 rats survived for the tumors spontaneously regressed. The same condition was applied for the 6 and 7 times, but none of the rats were found to have glioma by MRI. After renewing the C6 tumor cells,6 rats were found to have glioma in brain after operation in the 8 times.Conclusion:We found that there were 2 key points for successful tumor growth. The first point was the cell selection. The recent derived C6 rat glioma cells was important for maintaining the antigenicity, for the cells would decreased in antigenicity after some times. The other was the method of operation. Enteringing 6 mm and withdrawing 1mm for detaining 1 mm3 space was important. Slow-moving injection and detaining 10 minutes after injection was also important for the cells can be preciptitated thoroughly. Withdrawal of needles should be slow for preventing the siphon effect which can induce extraaxial metastasis.PartⅡ:Magnetic resonance imaging features of rat brain glioma after injection of USPIOObjective:To explore the enhancement characters of rat glioma model with USPIO (ultrasmall superparamagnetic iron oxide).Methods:After 5,8, and 11 days of C6 glioma cell injection, the rats received MR examination. The time for data acquisition was that the tumor size was 4-7mm (the 11 day after tumor cell injection was considered the optimal time). MRI was performed using a 7.0T (Varian) with head coil including FSET2WI, T1WI, T2map sequence. Animals were placed on head coil with head first and a respiration trigger equipment was used to monitor vital signs. During the imaging procedure, anesthesia was maintained with 2% isoflurane and 98% oxygen or with 10% chloral hydrate in abdominal cavity. The maximum plane of tumor in T2 sequence was selected for T2map sequence scanning. ROI was chosen with software Vnmr 2.3A (Linux) in the machine, and T2 value was determined. Brain tissue was acquired and the same slice with T2map sequence was selected for HE staining and Prussian blue staining.Results:The T2 values in normal cortex and solid portion of tumor did not changed significantly (P>0.05), while the T2 values in peri-tumor region decreased significantly (P<0.05). Central necrosis, vascular hyperplasia, and endothelial proliferation were found in tumor on HE straining, all of which were consistent with high grade glioma. There was no ferri particle in tumor and normal cortex, while a lot of ferri particle was found in the conjunction of tumor and surrounding normal tissue.Conclusion:The T2 values can reflect the condition of ferri particle englobement. The areas enhanced by USPIO were the borderline of tumor and surrounding normal tissues, and the areas not enhanced by USPIO were tumor or normal brain tissue.Part III The initial exploration of establishing rat brain radiation necrosis model and the application of MRI morphology and ADC value measurement in the detection of radiation injuryObjective:To establishing the rat radiation necrosis model which could be detected by MRI with the methods of electron ray radiation and spinning top knife, and to identifying the occurrence of radiation necrosis by conventional sequence of MRI and diffusion weighted imaging (DWI) sequence compared with histology.Methods:After anesthesia, the rats were irradiated with collimated electron beam of 5-mm diameter at the medical linear accelerator. The radiation dose was 80 Gy for each hemisphere (160Gy total) (n=5) or 80 Gy for unilateral parietal cortex(n=5). The rats were scanned with CT, and the data were transfered to the spinning top knife stereotaxis systems. The rats were irradiated with collimated gamma beam of 5-mm diameter at spinning top knife. The radiation dose was delivered as a single dose of 80 Gy (n=3) or 60 Gy (n=7) of left local parietal lobe. The rats were scanned with conventional MRI and DWI after 1 and 5 weeks of spinning top knife irradiation.Results:The survival time of rats underwent medical linear accelerator was 7 to 14 days, and MR scanning showed that the whole brain depauperate obviously. All the rats irradiated with 80 Gy dose with spinning top knife died, but the rats with 60Gy survived. Conventional MR scanning and DWI showed normal 1 week after irradiation. The thickness of cortex became thinner 5 week after irradiation (1.50±0.01 mm), which was significantly thinner than that of the same moon's age rats (1.71±0.02 mm) (P<0.05). The mean ADC values of the irradiation focus areas was (0.643±0.042)×10-3 mm2/sec and the mean ADC values of the opposite areas was (0.701±0.037)×10-3 mm2/sec, both of which were significantly lower than that before irradiation (0.875±0.012)×10-3 mm2/sec (P<0.01). Cortex frame disorder, cellular swelling, enlargement of perivascular space and chronic inflammation cell infiltration (leukomonocyte mainly) in the irradiation areas were found by histology. Conclusion:Rat can not survive after radiation by a single doze of 80 Gy or more, neither by electron ray nor by gamma ray. Rats can survive after 60 Gy of gamma ray irradiation, with the atrophy of cortex on conventional MR sequence and the obviously decreased ADC values in DWI. Both of these features can be the diagnostic evidence of cerebral radiation injury.