Super-Low-Dose Functional and Molecular Photoacoustic Microscopy

Area of Science:

• Biomedical Optics
• Medical Imaging
• Nanotechnology

Background:

• Photoacoustic microscopy (PAM) images biological molecules and nano-agents using ultrasonic sensing.
• Insufficient sensitivity is a major limitation for imaging low-absorbing substances and requires high laser power, causing photobleaching and toxicity.
• Delicate tissues like the eye and brain are particularly susceptible to perturbation from current imaging techniques.

Purpose of the Study:

• To develop a highly sensitive photoacoustic microscopy technique with reduced laser power for improved in vivo imaging.
• To overcome the sensitivity limitations of conventional PAM for imaging low-absorbing chromophores.
• To enable safer and more versatile molecular and functional imaging in delicate biological tissues.

Main Methods:

• Optimized photoacoustic probe design and implemented a spectral-spatial filter.
• Developed multi-spectral super-low-dose photoacoustic microscopy (SLD-PAM).
• Evaluated imaging of microvessels, oxygen saturation, and deoxyhemoglobin concentration in vivo.

Main Results:

• Achieved a sensitivity improvement of approximately 33 times compared to conventional PAM.
• Enabled in vivo imaging of microvessels and oxygen saturation at ~1% of maximum permissible exposure.
• Demonstrated direct imaging of deoxyhemoglobin concentration without spectral unmixing, reducing errors and noise.
• Reduced photobleaching by ~85% and required 80% fewer contrast agents for similar molecular imaging quality.

Conclusions:

• SLD-PAM significantly enhances sensitivity and reduces laser power, minimizing phototoxicity and perturbation to delicate tissues.
• The technique allows for direct quantification of deoxyhemoglobin concentration and broadens the scope of usable low-absorbing nano-agents and biomarkers.
• SLD-PAM presents a powerful tool for advanced anatomical, functional, and molecular imaging in various biological applications.