Development of Microbubble Contrast Agents for High Frequency Ultrasound Microscopy

Purpose: To develop optimal microbubble contrast agents (MBCAs) for performing ultrasound microscopy when examining small animals. Materials and Methods: We prepared three types of MBCAs. First, a mixture of three parts of 40% dextran and one part of 5% human serum albumin were sonicated with perfluorocarbon (PFC) (MB1-D40A5P). Second, three parts of 40% dextran and one part of 1% human serum albumin were sonicated with PFC (MB2-D40A1P). Third, all parts of 1% bovine serum albumin were sonicated with PFC (MB3-A1P). We measured the microbubbles' sizes and concentrations with using image analysis software. The acoustic properties of the microbubbles were assessed both in vitro and in vivo. Results: The majority of the MB1-D40A5Ps had a diameter of 2-5 μm, the mean diameter of the MB2-D40A1Ps was 2.5 μm, and the mean diameter of the MB3-A1Ps was less than 2.0 μm. Among the microbubbles, the MB1-D40A5Ps and MB2-D40A1Ps showed increased echogenicity in the abdominal vessels, but the duration of their contrast effect was less than 30 sec. On the contrary, the MB3-A1Ps exhibited strong enhancement in the vessels and their duration was greater than 120 sec. Conclusion: A microbubble contrast agent consisting of all parts of 1% serum albumin sonicated with PFC is an effective contrast agent for ultrasound microscopy.