Abstract:
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Purpose: To visualize micro-vessels in the liver by overlaying interspersed echo signals from microbubble-based contrast agents.
Methods and Materials: The subjects were white house rabbits weighing 3.0-3.3 kg. Tracheal intubation was performed under general anesthesia for breath-holding. Contrast agents used were SonoVueTM (Bracco, Italy) and SonazoidTM (Amersham Health, UK). The infusion rate was 0.04 ml/kg/min for SonoVue and 0.15 ml/kg/min for Sonazoid. Ultrasound images were obtained after contrast agents reached stable concentration. US system (AplioTM, Toshiba Co., Japan) was used with the programmable "Flash-replenishment" sequence: i.e., high MI(mechanical index) burst(=1.3) to break the microbubbles is done for 0.3 sec and low MI scan (<0.1) to observe the replenishment is done for 5 sec. Scanning frame rate was 31 Hz, and all images between the initial frame after the high MI scan and the current frame were overlaid using a built-in maximum intensity-holding processing. Probes used were 3.75 MHz convex and 7.5 MHz linear transducers. Imaging mode was "Wide-band harmonic imaging" with a very low MI (=0.08).
Results: The overlaid replenishment image for two seconds after the high MI burst revealed micro-vessels in the liver, while the original images did not show structures of the small vessels, since the echo signals in the small vessels were spatially interspersed. Overlaid imaging showed that portal vessels branch gradually, 4 to 6 small vessels were visualized in an area of 5 mm square. Lobule like staining was also imaged after these fine vessels were opacified.
Conclusion: The imaging method in this study can visualize microcirculation of the liver. It was suggested that the fine vessels visualized in the present study were terminal branches of hepatic artery and portal vein, since the actual size of the lobule is 1 mm. It is expected that the technique can be used not only for characterization of liver tumors but also differential diagnosis of arterio-portal shunting as seen in liver cirrhosis from heptocellular carcinoma.
Questions about this event email: moriyasu@tokyo-med.ac.jp
Moriyasu MD, F,
Ultrasound Contrast Imaging of Hepatic Microcirculation Using a Flash-replenishment Sequence. Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL.
http://archive.rsna.org/2003/3101403.html
