Suppression of background signal in magnetomotive photoacoustic imaging of magnetic microspheres mimicking targeted cells.

Contrast-enhanced photoacoustic (PA) imaging has been proposed to identify circulating metastatic cancer cells magnetically trapped in the vasculature. However, its sensitivity is limited by the presence of a strong blood-background signal. This technique can be further improved by the significant suppression of blood background. In the phantom study presented here, significant background suppression is demonstrated with magnetomotive photoacoustic imaging. Magnetic particles with a mean diameter of 10 μm were integrated (concentration of 0.05 mg/ml) into an ink-water solution with an optical absorption coefficient of 5 cm(-1) to mimic cells targeted with magnetic nanoparticles and magnetically trapped in the human vasculature. Two mechanically moveable permanent magnets were used to accumulate microparticles in the investigated solution and manipulate them within a thin, 1.6-mm-diameter Teflon tube mimicking a blood vessel. Our results clearly indicate that the undesirable background can be effectively suppressed using the difference of PA images corresponding to different locations of accumulated particles.