Table of Contents
Introduction to OR-PAM and hybrid imaging
Scientists from Hong Kong have developed a new hybrid imaging technique that is called optical-resolution photoacoustic microscopy (OR-PAM). The system is based on a fiber laser with a highly concentrated laser beam. It consists of five wavelengths, which makes it highly effective in studies, and it can be employed in several fields.
Applications and functionality of OR-PAM
The OR-PAM can be applied mostly for multi-contrast functional imaging.
Development challenges
During the development, the research team faced certain restrictions, like the limited laser beam wavelength of most fiber lasers and the limitations of the scanning methods. To get better results, the scientists created a multimode laser based on a single-fiber wavelength nanosecond laser module source. It takes sub-microseconds to switch between different wavelengths that make multifunctional OR-PAM simultaneous.
Principle of operation
The whole fiber laser system is created based on the stimulated Raman scattering (SRS) effect. A fiber laser applies a laser beam with a longer wavelength than the usual one. The generated SRS wavelength remains at high rates when the energy of the laser beam source goes beyond the threshold. Photoacoustic imaging uses the fact that when a surface or tissue is illuminated by a laser beam, it absorbs the light and produces heat. The heat causes thermal expansion, which generates a photoacoustic (PA) wave or a mechanical ultrasonic wave. After that, the scientists can get an image that demonstrates the light absorption distribution.
Advantages of fiber laser-based OR-PAM
Medical applications
This invention, based on fiber laser technology, can be an enormous boon for medicine because it can make a multiparameter image for accounting for physiological parameters in vessels, like the diameter, depth, and more. That would help to make a disease model for research or treatment. With the help of this five-wavelength OR-PAM, the scientists could also get imaging of tumor development, lymphatic clearance, and brain imaging.
Subcellular measurements
This new system, based on the fiber laser, can also show the subcellular measures like hemoglobin concentration, blood flow speed, blood oxygen saturation, and lymphatic concentration. It allows the scientists to study disease models, for instance, cancer, and find new ways of treatments for it.
Challenges in developing multifunctional OR-PAM
The research team met two main problems while developing multifunctional OR-PAM. The first problem is that the microenvironment of blood vessels changes with time, so long-term scanning with a multimodal laser can cause some inaccuracy. The other problem is the asynchrony among the different laser sources, which may cause systematic errors in calculation. For this reason, they developed a multimode laser comprising five fiber lasers. This new system can produce multifunctional imaging with a single multimodal laser and in a single scan. It shortens the time for making an image and improves its accuracy.