Controlled Experiment Study Of Imaging And Pathological Changes After MR-Guided Cryoablation In Porcine Models

ObjectiveTo observe the changes of imaging, pathological and ultra-structure of normal experimental pig renals in differtnt periods after MR-guided targeted argon-helium cryoablation, make clear of quantitative determination of red blood cells, and determine the effect of cryoablation on renal parenchyma, renal microcirculation and collecting system in the porcine kidney. This experiment shows theoretical basement for the safety and efficacy of renal tumor cryoablation clinically.Material and MethodsEight wuzhishan pigs inbreeding line(WZSP) were divided into two groups randomly. The experiment group include6swine which were treated with cryoablation procedures with general anesthesia under the guidance of0.23T open-configuration MR scanner mounted with optical tracking system (iPath200, Philips Medical System). A1.47mm MR-compatible superfine cryoprobe was advanced into the target renal parenchyma nearby the collecting system. Then a double freeze/thaw cycle, with100%gas output of argon, kept the freezing process for12minutes along with3times thawing (1minute per time) by helium,which was adopted by opening the MR-compatible low-temperature refrigeration system CRYO-HITTM(Israel,Galil Medical Ltd). The gas pressure were3600Kpa and2500Kpa respectively. The control group, two swines, were punctured with barely superfine cryoprobes under MR guidence, and harvested without cryoablation for optical and electron microscopic examination. Then compared with the experiment group. We selected the sequences of FSE and CBASS with transverse, sagittal images for demonstrating the ice ball and the target position dynamically. The general condition of the porcine after procedures were oberserved. MR images of1d,14d,30d were obtained after the procedure with a1.5T MR scanner. The target area and its surrounding tissue can be shown clearly with plain and enhanced (Gd-DTPA)MRI scan. At the same time, two kidneys were harvested for gross, pathological and ultra-structure analysis. Quantitative determination of red blood cells in urine was planning to get before procedures and1d,7d,14d and30d after the cryoablation.Statistical analysis:package SPSS17.0was applied for Statistical data-processing. All the data were described as means±standard. Singal factor analysis of variance was used to compare the differences between the groups before and after the procedure. The test standard was α=0.05.P<0.05for the differences were statistically significant.ResultsIn the animal experiments, cryoprobes were advanced into the target point correctly in all8cases, and the cryoablation was performed successfully in the experiment group.1. Intraoperative appearance of MR imagings:The size of the iceball increased gradually in the MR imagings during the targeted argon-helium cryoablation. The maximum cross-sectional2.9cm×3.8cm can be got about10minues after the freezing process, which was mostly located in the target tissue. The iceball appeared as an oval-shaped, dark signal void in both FSE and CBASS sequences.2. General condition after cryoablation:The experiment porcine endured quite well during the operation, all survived before sacrificed for pathological examination, immune to infection.2hours after the general anesthesia, the swine was fully awake and began to eat. Their food intake and activity were slightly worse than preoperation, and recovered two days later. No significant changes were found in animal weight before and after the operation. Quantitative determation of the number of red blood cells in urine showed increased1day after cryoablation, and it decreased after7days.3. MR appearences in different periods of time:1.5T MR T1WI and T2WI of the target tissue1day after the protocol showed low signal with discontinuous patchy high signal (ribbon bleeding area)surrounding with edema signal. After the injection of GD-DTPA, homogeneous enhancement ring can be seen around the iceball without center enhancement.14days later, mild strengthen can be seen around, without center enhancement.The patchy high signal and edema disappeared after1month, and the scope of the enhancement area around the ablation zone was gradually reduced.4. Pathological and ultra-structure changes of target kidney tissue after cryoablation:Acute cryolesions (1day) appeared well circumscribed,dark red early coagulative necrosis and extensive vascular congestion zone. Electron microscopy showed the cell death. At2-week follow-up harvest cryolesions were pale. The calyceal and pelvic urothelium was mucin-like degeneration. One month follow-up, the chronic cryolesion demonstrated complete necrosis within the central portion of the scar and surrounding chronic inflammatory cell infiltrated.Conclusion1. The formation of ice ball and the extent of the injury region could be demonstrated accurately by intraoperative MRI during the argon-helium cryoablation.2.1.5T high-field MR could assess the repairing process of kidneys effectively after cryoablations.3. After cryoablation, the necrosis tissue absorbed along with the hyperplasia of the surrounding tissue can be found and1month later cured with scar. There were no serious complications, such as injury to the collecting system, hematuria and fistula happened. In conclusion, MR-guided argon-helium cryoablation play an important role in treating small renal cell carcinoma and dieases in proximity to the collecting system.