Methylene Blue Microbubbles (MB2) as a Dual Modal Contrast Agent for Photoacoustic and Ultrasound Imaging

We have demonstrated a novel microbubbles methylene blue solution, called to "MB2" solution for a dual modality contrast. We have photoacoustically and ultrasonically imaged and quantified aqueous solutions of MB2 by varying the concentration of either microbubbles or methylene blue to investigate the dual modal imaging capability. Interestingly, as the microbubbles concentration increased with the constant methylene blue concentration, photoacoustic (PA) signal was greatly attenuated in the MB2 solution. Conversely, when methylene blue concentration increased with the fixed microbubbles concentration, no interference was observed in ultrasound (US) signals. To further confirm our findings, we switched the PA and ultrasound (US) signals using conventional ultrasound. We compared the PA and US signals of the MB2 solution before and after sonication. The PA amplitude increased 2.5 times. Conversely, the US signals were initially strong, but decreased 2.5 times following sonication. Moreover, we used a clinically modified PA/US imaging system to disrupt the microbubbles in MB2 and recover the PA signals.