Developing the next-generation photoacoustic microscopy systems

Photoacoustic imaging (PAI) is a biomedical technique 100% sensitive to optical absorption produced by either absorbing sources such as tissue or contrast agents upon laser illumination. In the past decade, photoacoustic microscopy (PAM) has advanced as a PAI technique able to image high-resolution specimens and break the optical diffusion limit reaching several millimeters in tissue depth. However, in order to implement this promising technique in real clinical scenarios it is required to refine a new generation of PAI devices which are safe, user friendly, and affordable, and which operate in vivo and in real time with fast acquisition and high sensitivity and resolution. Solving these problems vis-a-vis PAM is the main motivation behind this work. Firstly, photoacoustic shadow-casting microscopy (PASM) has been developed in our laboratory, a technique with unprecedented sensitivity that makes use of an optical absorber in contact with a biological sample and enhances the low signal-to-noise ratio originating from weak absorbers or low laser fluence when dealing with sensitive samples. As opposed to previous techniques, it is an easy and cost-effective technique that does not rely on contrast agents, averaging or increasing the laser pulse energy in order to compensate for low signal-to-noise ratio. Secondly, our current work is also explained, namely, the miniaturization of all-optical PAI systems, which is a key step toward expanding its applications such as endoscopy. In contrast to conventional piezoelectric transducers, whose miniaturization is non-trivial, the design, fabrication and implementation of all-optical methods such as whispering gallery modes or Fabry-Perot sensors meet the aforementioned requirements of the next generation of PAI systems