Ultrasound Imaging

Ultrasound imaging has played an important role in oncological imaging for more than five decades now. It can be applied in all tissues that are not occluded by bone or gas-filled regions. The quality of ultrasound images benefitted strongly from improved electronics, advanced reconstruction algorithms, and increased computational power. To the morphological imaging, several functional imaging methods were added: Flow visualization became possible by Doppler techniques, and the elastic properties of tissues can be imaged by elastographic methods with transient shear wave imaging. In the beginning of molecular imaging, ultrasound with its contrast based on mechanical tissue properties was an unlikely candidate to play a role. However, with contrast agents consisting of micrometer-sized gas bubbles, which can be imaged with high sensitivity, ligands addressing targets in the vascular wall could be used. Because even single bubbles can be detected, this led to various ultrasound molecular imaging techniques and the ongoing development of clinical molecular contrast media. In this chapter, the basic properties of ultrasonic imaging, like its contrast mechanisms and spatiotemporal resolution, are discussed. The image formation and its change from line-oriented scanning to full-volume reconstructions are explained. Then, the ultrasound contrast media and imaging techniques are introduced. Finally, emerging new methods like super-resolution vascular imaging demonstrate the ongoing development in this field.