ORIGINAL ARTICLE Feasibility of Interstitial CT Lymphography Using Optimized Iodized Oil Emulsion in Rats Yong Eun Chung, MD,* Woo Jin Hyung, MD,† Soonjae Kweon, MS,‡ Soo-Jeong Lim, PhD,‡ Junjeong Choi, MD,§ Myun Hee Lee, BS,¶ Hoguen Kim, MD,§ Sungmin Myoung, PhD, and Joon Seok Lim, MD** Objectives: To formulate an iodine-based contrast agent with an oil-in-water emulsion and to evaluate the feasibility of the agent for use as an interstitial computed tomographic (CT) lymphographic agent in a normal rat model. Materials and Methods: The effect of iodized oil (lipiodol) content and the type of surfactant/cosurfactant on the resultant emulsion size and polydis- persity was investigated to obtain an optimized lipiodol emulsion for CT lymphography. Optimized emulsions (144 mg/mL) were injected in the hind paws of 6 rats, using 0.5 mL per paw. As control groups, iopamidol solution and lipiodol diluted with squalene to adjust the injection volume with iodine concentration equivalent to the emulsions were used. Precontrast and post- contrast CT images up to 1 week after contrast agent injection were obtained. Time-enhancement curves of the popliteal lymph nodes were obtained. Analysis of variance and post hoc analysis with the Dunn procedure were used for comparing mean peak enhancement, time to peak enhancement, and sustained duration of contrast enhancement. Results: Optimized emulsion formulations composed of 30% lipiodol and 282 mg/mL of 9:1 surfactant mixture (Tween 80:TPGS alpha-tocopheryl polyethylene glycol succinate, Tween 80:Kollidon 12 PF, or Tween 80:Span 85) exhibited mean particle size less than 120 nm, and they were stable without significant particle size change up to 1 month. Targeted lymph nodes in all emulsion groups showed continuously increasing enhancement until 4 or 8 hours after injection, followed by continuous washout. Peak enhance- ment (time to peak enhancement) was 172.4  54.5 HU (Hounsfield unit) (384.0  131.5 minutes) for Tween 80:TPGS; 172.8  28.0 HU (432.0  107.3 minutes) for Tween 80:Kollidon 12 PF, and 177.2  68.9 HU (294.0  190.2 minutes) for Tween 80:Span 85. For iopamidol, peak enhancement of 153.0  46.1 HU (0.5  0.5 minutes) occurred early with rapid washout. For lipiodol as a reference agent, contrast enhancement continuously increased even 1 week after injection without washout (peak enhancement, 486.0  97.4 HU). Peak enhancement among the emulsion groups and the iopamidol group was not statistically different (P  0.95). All emulsion groups showed more prolonged enhancement than the iopamidol group; enhancement duration for the emulsion groups was 534.0  481.1 minutes for Tween 80:TPGS; 957.0  524.8 minutes for Tween 80:Kollidon 12 PF; and 750.0  566.0 minutes for Tween 80:Span 85, and enhancement duration for iopamidol was 8.2  12.3 minutes (all P  0.05 in multiple comparisons). However, there was no significant difference in enhancement duration among the 3 emulsion groups (P  0.05). Conclusions: Iodized oil emulsion made with a surfactant mixture (Tween 80 as the main surfactant and TPGS, Kollidon 12 PF, or Span 85 as the cosurfactant) provided sufficient and sustained contrast enhancement on CT of targeted lymph nodes with washout on delayed phase. Key Words: computed tomography, lymphography, emulsion, sentinel lymph node (Invest Radiol 2010;45: 142–148) I nterstitial computed tomographic (CT) lymphography has poten- tial to be used for sentinel lymph node localization for various oncologic surgeries. 1–3 Several investigators reported that interstitial CT lymphography using water-soluble, nonparticulate, iodine con- trast was feasible for sentinel lymph node navigation. 1,3– 4 However, lymphatic capillaries preferentially absorb lipophilic substances and particulate materials. 5 In addition, the water-soluble contrast agent tends to enter the venous capillaries rapidly, shunting lymphatic pathways. 6 Therefore, it may be useful to perform CT imaging of the lymphatic system, using a lipophilic contrast material containing delivery vehicle administered interstitially, because it has similar properties in common with lymphatic fluid components. Lipiodol, iodinated poppy seed oil which is currently used as an intravascular embolizing agent, has been traditionally used for lymphography on x-ray radiography. 7–8 Because of its lipophilic properties, use of lipiodol may provide a means to perform CT imaging of the lymphatic system. However, its possible long-term accumulation in the lymphatic system should be resolved before its application in lymphatic imaging. One possible solution may be dispersing lipiodol in an aqueous phase by formulating an oil-in- water emulsion, a structure in which oil is dispersed in an aqueous phase, 9 to alter the in vivo tissue distribution profile of lipiodol. The purpose of this study was to formulate a contrast agent with a form of oil-in-water emulsion, and to evaluate the feasibility of the agent for use as an interstitial CT lymphographic agent in a normal rat model. MATERIALS AND METHODS Polyoxyethylene sorbitan monooleate (Tween 80) and sor- bitan trioleate (Span 85) were purchased from Sigma-Aldrich (Mil- waukee, WI). Poloxamer 188 (2-methyloxirane), Pluronic L10, and Kollidon 12 PF (soluble polyvinylpyrrolidone) were purchased from BASF (Ludwigshafen, Germany). Alpha-tocopheryl polyethylene glycol succinate (TPGS) was kindly provided by Eastman Chemi- cals (Kingsport, TN). Lipiodol was purchased from Guerbet (Aulnay-Sous-Bois, France), and iopamidol was provided by Ac- cuzen (Seoul, Korea). Squalene was purchased from Sigma (St. Louis, MO). All other chemicals were of reagent grade and used without further purification. Received August 27, 2009, and accepted for publication, after revision, October 24, 2009. From the Departments of *Radiology and †Surgery, Yonsei University Health System, Seoul, Republic of Korea; ‡Department of Bioscience and Bioengi- neering, Sejong University, Seoul, Republic of Korea; §Department of Pa- thology, Yonsei University Health System, Seoul, Republic of Korea; ¶Brain Korea 21 Project for Medical Science, Yonsei University College of Medicine Seoul, Republic of Korea; Department of Medical Information, Jungwon University, Republic of Korea; and **Institute of Gastroenterology, Yonsei University Health System, Seoul, Republic of Korea. Supported by the Korea Research Foundation Grant funded by the Korean Government (MOEHRD) (KRF-2007–331-E00165) and by the Korea Science and Engineering Foundation (KOSEF) grant funded by the Korean govern- ment (MOST) (No. R01–2007– 000 –20501– 0). Reprints: Joon Seok Lim, MD, Department of Radiology, Yonsei University Health System, Seodaemun-ku, Shinchon-dong 134, Seoul 120 –752, Repub- lic of Korea. E-mail: jslim1@yuhs.ac. Copyright © 2010 by Lippincott Williams & Wilkins ISSN: 0020-9996/10/4503-0142 Investigative Radiology • Volume 45, Number 3, March 2010 142 | www.investigativeradiology.com