Contrast-enhanced and targeted ultrasound
Résumé
Ultrasonic imaging is becoming the most popular medi- cal imaging modality, owing to the low price per ex- amination and its safety. However, blood is a poor scat- terer of ultrasound waves at clinical diagnostic transmit frequencies. For perfusion imaging, markers have been designed to enhance the contrast in B-mode imaging. These so-called ultrasound contrast agents consist of microscopically small gas bubbles encapsulated in bio- degradable shells. In this review, the physical principles of ultrasound contrast agent microbubble behavior and their adjustment for drug delivery including sonopora- tion are described. Furthermore, an outline of clinical imaging applications of contrast-enhanced ultrasound is given. It is a challenging task to quantify and predict which bubble phenomenon occurs under which acoustic condition, and how these phenomena may be utilized in ultrasonic imaging. Aided by high-speed photography, our improved understanding of encapsulated microbub- ble behavior will lead to more sophisticated detection and delivery techniques. More sophisticated methods use quantitative approaches to measure the amount and the time course of bolus or reperfusion curves, and have shown great promise in revealing effective tumor responses to anti-angiogenic drugs in humans before tumor shrinkage occurs. These are beginning to be ac- cepted into clinical practice. In the long term, targeted microbubbles for molecular imaging and eventually for directed anti-tumor therapy are expected to be tested.
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