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Ultrasound contrast agents are encapsulated microbubbles with diameters of the order of 1 to 10 mm. Owing to the density and compressibility of their gas core, these stabilized microbubbles are substantially more echogenic than the interfaces between different types of tissue, and therefore improve the sensitivity and specificity of 2-D and 3-D ultrasound imaging by increasing the reflection of sound waves. The size of a microbubble contrast agent affects its ability to cross the pulmonary microcirculation as well as the degree of its reflectivity of ultrasound. They must be below 7 mm in diameter to safely pass through the microvessels of the lungs without causing obstruction, but the ultrasound scattering efficiency of a microbubble is a function of the sixth power of its radius, meaning that smaller microbubbles also have poor reflectivity. Thus the optimum microbubble size is between 2 and 5 mm in diameter. Microfluidic systems are ideal for biomedical (bio-MEMS) applications due to their small size and batch manufacturability, providing a versatile platform for rapidly performing complex syntheses, measurements, and analysis. The potential exists for the use of microfluidics for highly specialized applications in large markets. For example, the ability to form micron-sized bubbles or drops is important in many pharmaceutical and food processing applications, from processes to actual products. Microfluidic techniques have been shown to generate highly controlled droplet dispersionsand microbubbles. |
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Using Microbubbles for Improving Sensitivity in Molecular Imaging |
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Microbubbles |
