Small molecular dyes are used extensively for in vivo fluroescence imaging as well as in microscopy for identifying cellular and molecular processes. Since photoacoustic imaging with the Vevo LAZR system relies on optical absorption in the near-infrared part of the spectrum, dyes with excitation peaks in this range can be used as contrast agents. While higher doses are typically required than for optical imaging, photoacoustic imaging can overcome limitations of optical modalities such as autofliorescence, resolution at depth and accurate quantification.

Coregistered ultrasound (greyscale) and photoacoustic (green) image of a 3D longitudinal section of the mouse hindlimb showing indocyanine green (ICG) in the popliteal lymph node and afferent lymphatics after foot pad injection of ICG.

Photoacoustic compatible dyes include:
• Methylene blue, Evan's blue, Trypan blue, Patent blue
• Indocyanine Green (ICG)
• IRDye800CW
• DiR
• Cy7, Cy7.5
• Porphyrins