Page 425 - Libro 2

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Vascular Applications of Ultrasound Contrast Agents
Daniel A. Merton
OBJECTIVES
KEY TERMS
contrast-enhanced sonography | microbubbles | ultrasound contrast agent
GLOSSARY
contrast-enhanced sonography the use of medi- cal ultrasound imaging after administration of an ultrasound contrast agent
microbubbles encapsulated gas-containing struc- tures that are typically smaller than 8 􏰀m in size
The use of ultrasound (US) contrast agents in the United States is currently limited to echocardiograph- ic applications. However, in other parts of the world, the use of contrast-enhanced sonography (CES) has been established as a valuable imaging procedure for many applications. The use of ultrasound contrast agents (UCAs) that are administered intravenously has been shown to improve the evaluation of blood flow through both large and small vessels as well as through cardiac chambers. CES has been shown to reduce or eliminate some of the current limitations of US imaging. These limitations include contrast reso- lution on grayscale (B-mode) US, as well as the detec- tion of slow blood flow and flow in very small vessels using color flow imaging (CFI) or pulsed Doppler with spectral analysis. Advances in US equipment technol- ogyhaveresultedincontrast-specificimagingmodes that, when combined with UCAs, markedly improve the capabilities of diagnostic sonography and expand its already impressive range of clinical applications.
ultrasound contrast agent compositions that, after administration, alter the acoustic properties of body tissues (including blood), typically result- ing in higher ultrasound signal reflectivity; also known as ultrasound contrast medium
TYPES OF ULTRASOUND CONTRAST AGENTS
The concept of using contrast agents to enhance the diagnostic potential of US dates back to 1968 when Gramiak and Shah injected agitated saline directly into the ascending aorta and cardiac chambers dur- ing echocardiographic examinations.1 These and subsequent investigations revealed that microbub- bles formed by agitation of saline resulted in strong reflections of the ultrasound beam arising from within the normally echo-free lumen of the aorta and chambers of the heart. Currently, intravenously administered agitated saline is used for the so-called bubble study echocardiography examinations, in- cluding the assessment of patients with suspected pulmonary hypertension or intracardiac shunts (Fig. 27-1).2,3 However, microbubbles produced by simple agitation of saline are nonuniform in size, rel- atively large, and unstable. After peripheral venous
Describe the basic characteristics of ultrasound contrast agents
Describe how ultrasound contrast agents enhance ultrasound images
List the most important characteristics of ultrasound contrast agents
Describe the basic concepts of contrast-specific ultrasound imaging technology
List the most common vascular applications of contrast-enhanced sonography
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