Dissertation > Medicine, health > Clinical > Diagnostics > Diagnostic Imaging > Magnetic resonance imaging

MRI Guoded Experimental Cryoablation of Rabbit’s Sciatic Nerve for MRI and Pathology Contrast Study

Author ZuoZhenLi
Tutor LiChengLi
School Taishan Medical College
Course Medical Imaging and Nuclear Medicine
Keywords rabbit sciatic nerve cryoablation magnetic resonance imaging
CLC R445.2
Type Master's thesis
Year 2011
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ObjectiveTo observe the apprearance of MRI, pathology and ultra microstructure of the rabbit’s sciatic nerve after argon-helium cryoablation, evaluate the influence of the argon-helium cryoablation to rabbit’s sciatic nerve and the sciatic nerve repair and regeneration after cryoablation , provide the experimental evidence for the safety and feasibility of the treatment of tumors, which are adjacent to peripheral nerve, by argon-helium cryoabation under imaging guided in clinical.Materials and methods20 Normal New Zealand white rabbits were randomly divided into two groups (A group and B group), each group has 10 rabbits. Each left leg was experimental side, right as control side. Under general anesthesia, All 20 rabbits’bilateral sciatic nerves were scanned with 3.0T MRI in order to choose the experimental sciatic nerve and definite the frozen region. Argon-helium cryoablation were performed under an open 0.23T MRI guidance with 1.47mm diameter cryoablational probe by a twice repeated freeze-thaw cycle, which 100% flow rate of argon gas was maintained to achieve freezing for 12 minutes and correspondingly helium gas was used to thaw for 3minutes. In A group, experimental sciatic nerve with 3mm diameter area was in the center of the ice ball. In B group, experimental sciatic nerve with 3mm diameter area was near the ice ball. The follow-up imaging were scanned with 3.0T MRI after cryoablation immediately, 7d, 14d, 30d and 60d to observe the rabbit’s sciatic nerves and their surrounding imaging changes and adjacent areas imaging changes, measure the signal intensity of sciatic nerves and muscle, and then calculate the signal intensity ratio of nerve and muscle and then examined the nerves pathology and the ultra microstructure. 2 rabbits were sacrificed in the same time. Take left and right sciatic nerve to observe the changes of tissue by light microscope and transmission electron microscope.Results1. Intraoperative imaging appearance of MRI: The ice ball appears as a dark signal void in both FE T1WI and CBASS sequences. During the cryoablation, the size of ice ball is gradually increased. The ice ball reach biggest size for 10min. In A group,the experimental position is in the center of the ice ball. In B group, the experimental position is near the ice ball.2. General observation after cryoablation: The activity of the rabbit’s left leg changes after cryoablation; the ankle down, toe show loss of function. Motor function are not recovered at 60d in the A group (both 2 rabbits) and obviously recovered in the B group than A group(both 2 rabbits). Ulcers were appeared in the rabbit’s foot at 30 days after cryoablation in both two groups. In A group, the ulcers do not heal at 60 days (both 2 rabbits); in B group ulcers partly heal at 60 days (both 2 rabbits).3. Imaging appearance of rabbit sciatic nerve before cryoablation and in immediately, 7days, 14days, 30days and 60 days after cryoablation: There were no obvious changes in T1WI sequence in experimental sides in all 20 rabbits. However, in T2WI sequence, the cryoablational segment of the sciatic nerve become thick and twist, the signal of the injured nerve become higher than normal. The sciatic nerve/ muscle signal intensity ratio (SIR) of the injured sides was significantly higher than the control. The difference of SIR between two group experimental sides is significant. The SIR of experimental side increase immediately after cryoablation and reach the peak at 7d, whereafter ,the SIR decreased in 30d and 60d after cryoablation, but still higher than control. There is no abnormality in the control side in MRI.4. Pathology appearance of the rabbits’sciatic nerve tissue after Argon-helium cryoablation: In the A group, the sciatic nerve appearance severe injury immediately after argon-helium cryoablation, nerve fiber degeneration, axonal swelling and myelin sheath loose. The damage reached a peak at 14d, nerve fibers sheath performed, arranged disorder. Whereafter, the nerve began to repair. At 60d, the regeneration of axons and Schwann cells appear, but necrotic nerve fibers still can be seen. In B group, the nerve also appear injury immediately after cryoablation, but not as serious as A group. There is only a part of the nerve fiber degeneration, at 7d the damage reach a peak also. Then the nerves begin to repair and regeneration, at 60d bulk fibers have repaired.Conclusions1. The formation of ice ball and the extent of the injury region could be demonstrated accurately by intraoperative MRI2. The pathology and function of sciatic nerve with 3mm diameter could be influenced by Argon-helium cryoablation under image-guided.3. The peripheral nerve with 3mm could be damaged by cryoablation when the ice ball wrapped the nerve, including appeared nerve degeneration and necrosis. The nerve damage reach the peak at 14d after freezing, and then, the nerve begin to repair. In 60d, the damage can not be repaired completely. In clinical, when treating tumors which wraps peripheral nerve, we should be careful. When treating the tumors adjacent to peripheral nerve, we should be consider that the function of the nerve would loss at a long time.4. MRI can make the diagnosis of the freezing injury and repair of peripheral nerve with normal sequence.

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