ABSTRACT
Contrast agents are an essential part of ultrasound molecular imaging. The contrast agent serves to recognize the molecule of interest through ligand-receptor binding and then acts as an echo responder for detection with the ultrasound scanner. Unlike other imaging modalities, which primarily use electromagnetic waves to see inside the body, ultrasound uses only acoustic waves. High-frequency sound waves are generated by the ultrasound transducer, and the image is reconstructed based on the received acoustic echoes. The backscattered energy in this case is better described by classical continuum mechanics rather than quantum mechanics. Nanoparticles are defined as liquid or solid colloids in the 10- to 1000-nm diameter size range. In general, nanoparticles are difficult to detect by ultrasound without high accumulation at a target surface, necessitating copious and densely confined receptors. This is largely due to their relatively incompressible core and small size, which results in nanoparticles acting as simple Rayleigh scatterers without the resonance behavior of microbubble.
