Power Doppler Imaging of Acute Renal Vein Occlusion and Recanalization in Canine Model MATERIALS AND METHODS Animal Preparation All procedures were conducted with the approval of the animal research committee at our institution. We used nine adult mongrel dogs (mean body weight of 25 kg). Each dog was sedated with an intramuscular injection of 4 mg /kg xylazine hydrochloride (Rompun, Bayer Korea, Seoul, Korea) and 10 mg/kg ketamine hydrochloride (Ketara, Yuhan Yanghang, Seoul, Korea) for the procedure and examination. All the dogs were immobilized in the supine position on a fluoroscopy table and subsequently intubated, mechanically ventilated, and anesthetized with 2% enflurane gas. Next, after the cutdown of the left jugular vein, a 7 Fr introducing sheath (Cook, Blooming, IN) was placed. Moreover, the left renal vein was selected and an 11-mm occlusion balloon catheter (B5F-25 70-C2; Clinical Supply Co., Ltd, Hashima-gun, Japan) was placed within the left renal vein. According to a predetermined amount of contrast media for the graded occlusion of the left renal vein (which was obtained through a pilot study using seven dogs with similar body weights), the balloon occlusion of the renal vein was performed by injecting contrast media 0.0, 0.3 and 0.6 mL at each step resulting in no, partial, and complete occlusion respectively, followed by a venography to confirm the occlusion. The balloon position was intermittently monitored with fluoroscopy to minimize the change in position during US examination. After a complete occlusion, a graded recanalization was performed by a sequential balloon deflation, followed by a venography to confirm the recanalization. Image Acquisition A US examination was performed by the same radiolo- gist using a HDI 3000 (Advanced Technology Laboratories, Bothwell, WA) and a convex 7 4 MHz transducer. A conventional gray-scale US of each kidney was carried out along its long axis, followed by a PD with an identical setting (dynamic range 50 dB, persistence Med, Frame rate Med, 2D opt: general, color gain: 85%, wall filter Med, PRF 700 Hz, flow opt: low V) in each kidney. PD images were captured for 5 minutes in each step at 1-min intervals between the steps according to the timetable. The image with the maximum flow by visual inspection was captured and scanning was performed with a hand-held technique to maintain a constant imaging plane during the examination. In addition, care was taken to minimize motion artifact. Next, a SD was also obtained in the segmental artery of the upper pole at each corresponding step. Moreover, special precaution was taken to maintain the conditions of the examined artery constant at each step. Image Analysis The captured images were saved on a hard disc and were transferred onto a personal computer using a Magneto Optical Disk. The images were converted to 24-bit color BMP format files using ACDSee software (ACD Systems, Arlington, TX). In a PD image, the background gray-scale image is mapped with gray pixels and the PD signal is mapped with color pixels. A personal computer-based image-analysis software (quant PDI ), which was specially developed to quantify the PD signal, was used to analyze the PD signal. The algorithm for the analysis was based on the separation of color and grayscale information by digital processing from digitized PD images. Moreover, the higher Fig. 1. Analysis of the power Doppler signal using quant PDI . Upon manual delineation of region of interest along border of kidney, power values within region of interest as histogram (open arrow) and set of local statistical power Doppler features (curved arrow) are calculated and displayed. Note segmented image (arrow) in which gray scale component of power Doppler image was discarded. Korean J Radiol 9(2), April 2008 129