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A B Fig. 1. Stent-type radio-frequency electrode and its loading catheter. A. Self-expandable nitinol stent with proximal and distal PTFE-insulations. The central portion is connected to the temperature sensing wire (arrow) and copper wire (arrowheads) from RF generator. B. Stent loading catheter is similar to that of other usual type of stent system. The wires connected to the stent are located in the lumen of the catheter. Half-deployed state. 448
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A B Fig. 2. Stent insertion into common bile duct. A. After ultrasound-guided gallbladder puncture, water-soluble contrast media was injected to visualize gallbladder and common bile duct. B. Selection of common bile duct with Cobra catheter and 0.035- inch guidewire. The guide wire was inserted into the lumen of common bile duct and duodenum. C. Stent catheter was inserted along the guidewire. Then, the stent (arrowheads) was deployed using the pusher of stent loading catheter. C 450
Table 1. Sizes of Ablated Lesions in Longitudinal Sections According to the Specific Target Temperatures and Correlations between Target Temperatures and Sizes of the Lesions, in Vitro Study Thickness (mm) Length (mm) Superior Inferior Distal covered Proximal Covered Overall Area (mm 2 ) 070 C group 04.5 08.5 05.8 06.5 55.5 0567.2 080 C group 07.0 11.8 07.8 06.0 55.8 0828.0 090 C group 10.0 21.3 10.0 08.8 59.3 1447.7 100 C group 13.0 22.3 14.5 12.0 70.5 2004.7 r* 0.741 0.798 0.781 0.589 0.680 0.795 p 0.001 0.001 0.000 0.016 0.004 0.000 Note. - Data are the mean values of each field. * Pearson correlation coefficient, significant when >0.4 Probability, significant when <0.05 A B Fig. 3. Esophageal ablation. A. Fully deployed stent-type electrode is seen at the level of diaphragmatic dome during the first ablation of the distal esophagus. B. After the distal ablation, the stent is pulled to the level of carina for the second ablation of the proximal esophagus. 451
A B C D Fig. 4. Longitudinal sections of the bovine livers after RF ablation, in-vitro study. A. Specimen of 70 C group shows dumbbell-shaped ablated area with central thinning (arrow). Other specimens show fusiform areas of ablation. The higher the target temperature is, the larger the area of ablated lesion is. B. 80 C group, C. 90 C group, D. 100 C group 452
A B C D Fig. 5. Microscopic findings of ablated tissue of bile duct (H-E stain, 40). A. Tissue just beyond the stent shows normal mucosa (a), inner stroma (b), and outer stroma (c). Note normal continuous wavy pattern of inner stroma. B. Covered portion shows mild disruption of inner stroma (b) with intact mucosa (a). This finding suggests coagulation necrosis of inner stroma. C. Bare portion shows severe destruction of mucosa (a), inner (b) and outer stroma (c) due to coagulation necrosis. D. Liver parenchyma adjacent to the stent shows patchy areas of enlarged sinusoids and disrupted architectures of hepatic cords (a), which suggest coagulation necrosis 453
A C B Fig. 6. Gross and microscopic findings of the ablated tissue of esophagus. A. Gross specimen shows irregular areas of hyperemia and bulla formation that has been caused by the thermal injury. Note the extent of the lesion is longer than the stent considering the shortening of stent, which can be explained by frequent migration of stent during ablation. B. Microscopic findings show shedding of mucosa (a), coagulation necrosis and edema of submucosal matrix (b & c), and destruction of submucosal gland (d). Muscle layers which can not be seen due to severe submucosal edema, show no change at all. This is obtained from the center of the ablated lesion. (H-E stain, 40) C. There is no definite abnormality in the mucosa (a), submucosal matrix (b & c) and glands (d), inner and outer muscle layer (e). This tissue is obtained from the periphery of the lesion which may be in contact with the covered portion of the stent. (H-E stain, 40) 454
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radio-frequency tissue ablation of liver metastases: treatment and follow-up in 16 patients. Radiology 1997;202:195-203 3. Rhim H, Goldberg SN, Dodd GD, et al. Essential techniques for successful radio-frequency thermal ablation of malignant hepatic tumors. RadioGraphics 2001;21:S17-S39 4. Lee BH. Biliary stent. In Han MC, Park JH. Interventional radiology. Seoul: Ilchokak, 1999:571-580 5. Song HY, Yoon HK, Sung KB. Esophageal stent placement. In Han MC, Park JH. Interventional radiology. Seoul: Ilchokak, 1999:687-693 6. Goldberg SN, Ryan TP, Hahn PF, et al. Transluminal radiofrequency tissue ablation with use of metallic stents. J Vasc Interv Radiol 1997;8:835-843 7.,,. :. 2002;46: 543-549 8. Song HY, Park SI, Jung HY, et al. Benign and malignant esophageal strictures: treatment with a polyurethane-covered retrievable expandable metallic stent. Radiology 1997;203:747-752 9. Hausegger KA, Thurnher S, Bodendorfer G, et al. Treatment of malignant biliary obstruction with polyurethane covered Wallstents. AJR Am J Roentgenol 1998;170:403-408 10. Kalinowski M, Alfke H, Kleb B, Durfeld F, Joachim Wagner H. Paclitaxel inhibits proliferation of cell lines responsible for metal stent obstruction: possible topical application in malignant bile duct obstructions. Invest Radiol 2002;37:399-404 11.,,,,.. 1994;31:1045-1049 12. Park KH, Cho SG, Kang SG, et al. Intraluminal brachytherapy after metallic stent placement in primary bile duct carcinoma. 2001;44:675-682 13. Dotter CT, Buschmann RW, McKinney MK, Rosch J. Transluminal expandable nitinol coil stent grafting: preliminary report. Radiology 1983;147:259-260 14. Black MR, Scoccianti M, White RA. Biomaterial consideration for endovascular devices. In White RA, Forgarty TJ (eds). Peripheral Endovascular Interventions. St. Louis : Mosby-Year Book, 1996:203-234 15. Lee BH, Kim KH, Chin SY. Mechanical characteristics of self-expandable metallic stents: in vitro study with three types of stress. 1998;39:497-502 16., Homepage (http://sma-inc.com/information.html) of Shape Memory Applications, Inc. San Jose, CA, USA 17., Homepage (http://www.webelements.com) of 1. Gazelle GS, Goldberg SN, Solbiati L, Livraghi T. Tumor ablation WebElementsTM, The University of Sheffield and with radio-frequency energy. Radiology 2000;217:633-646 WebElements Ltd, Western Bank, Sheffield, UK. 2. Solbiati L, Ierace T, Goldberg SN, et al. Percutanaeous US-guided 457
Transluminal Radio-Frequency Thermal Ablation Using a Stent-Type Electrode: an Experimental Study 1 Young-sun Kim, M.D., Hyunchul Rhim, M.D., Ho-Young Song, M.D. 2, Ji Hoon Shin, M.D. 2, Tae-Seok Seo, M.D. 3, Tae-Hyung Kim, B.S. 2, Seung Sam Paik, M.D. 4, Yongsoo Kim, M.D., Byung-Hee Koh, M.D., On Koo Cho, M.D., Heung-Seok Seo, M.D., Byung-Cheul Cho 5, Jeung-Hee Nam 5, Si-Hoon Kim 5, Eui Duck Jin, M.S. 6, Jong Kyu Kim 7, Jong-Heon Lee 8 1 Department of Diagnostic Radiology, Hanyang University College of Medicine 2 Department of Radiology, Asan Medical Center, University of Ulsan College of Medicine 3 Department of Radiology, Gil Medical Center, Gachon Medical School 4 Department of Pathology, Hanyang University College of Medicine 5 TAEWOONG MEDICAL Co. Ltd. 6 Medstar Co. Ltd. 7 S&G Biotech Co. Ltd. 8 Department of Orthopedic Surgery, Asan Medical Center, University of Ulsan College of Medicine Purpose: To assess the feasibility of transluminal radiofrequency thermal ablation using a stent-type electrode and to determine, by means of in-vitro and in-vivo animal studies, the appropriate parameters. Materials and Methods: In vitro: The radiofrequency electrode used was a self-expandable nitinol stent with 1- cm insulated ends. A stent was placed in the portal vein of bovine liver, and ablations at target temperatures of 70, 80, 90, and 100 C were performed. Ablated sizes were measured longitudinally. In vivo: Four mongrel dogs were anesthetized, and a stent was inserted in the common bile duct under fluoroscopic guidance through an ultrasound-guided gall bladder puncture site. The ablation temperature was set at 80 C, and each dog underwent proximal and distal esophageal ablations lasting 12 minutes. They were sacrificed immediately. Results: In-vitro: Ablated sizes showed significant correlation with target temperatures (r>0.04; p<0.05). Although most lesions were fusiform, dumbbell-shaped lesions with central thinning were found in two cases in the 70 C group. In all cases in the 70 C and 80 C group, the length of the insulated segment was less than 1 cm. In-vivo: At microscopy, tissues at the center of the biliary stent showed more prominent pathological change than those at the periphery while those remote from the stent showed minimal or no change. In esophageal ablations, the mean highest temperature was 48.6 C. Microscopy demonstrated the destruction and shedding of mucosa, edema, and coagulation necrosis of submucosa, but in muscle layers no abnormalities were apparent. Conclusion: Transluminal radio-frequency thermal ablation using a stent-type electrode may be useful for elongating patency. The appropriate target temperature for biliary ablation is 80 C. Index words : Interventional procedures, experimental studies Radiofrequency (RF) ablation Esophagus, interventional procedures Bile ducts, interventional procedures Address reprint requests to : Hyunchul Rhim, M.D., Department of Diagnostic Radiology, Hanyang University College of Medicine, 17 Haengdang-dong, Seongdong-gu, Seoul 133-791, Korea. Tel. 82-2-2290-9160 Fax. 82-2-2293-2111 E-mail: rhimhc@hanyang.ac.kr 458