Contrast-enhanced photoacoustic imaging

Photoacoustic (PA) imaging is rapidly evolving as a functional and molecular imaging tool. Contrast agents with high optical absorption, such as gold nanoparticles, have been used to target diseased cells and increase the specific contrast of PA imaging. However, background tissue absorption greatly limits the detection of PA signals and the specificity of these contrast agents. To sensitively identify PA signals from targeted regions, background PA signals must be suppressed or total PA signal sources must be increased and concentrated. In a previous study, we have demonstrated that contrast can be increased by magnetic manipulation of Au-shell encapsulated magnetic nanoparticles (MNPs) to create local motion and suppress unwanted stationary PA signals in the background using a motion filter. In some clinical applications, the initial concentration of a diseased cell type circulating in the vasculature is too low to be detected. Here, we further investigate the feasibility of locally accumulating/concentrating an object of interest (PA signal source) by the interaction of magnetic particles in the targeted objects with an external magnetic field. The accumulated PA sources were then dynamically manipulated to further enhance their specific contrast in PA imaging.