Optical imaging is used extensively within many biomedical applications, however, it poses a challenge when imaging tissues at the centimetre depth with optic only systems.
A new emerging medical imaging technique is photoacoustic imaging (also known as optoacoustic imaging), that combines light and ultrasound to give substantial, non-invasive imaging that can view internal organs in the body. This can provide improved spatial and temporal resolution data for greater understanding of organ structures and their function, reports .
Much like many other medical imaging technologies, photoacoustic imaging uses contrast agents to improve its capabilities. Contrast agents improve the visibility of specific organs, blood vessels, and tissues when they are in the body.
Photoacoustic imaging can be performed using the blood that is already present in the body, as the blood acts as an intrinsic contrasting agent as it absorbs light, and converts it into a detectable acoustic wave. Sound travels further than light within the biological tissues, which therefore allows photoacoustic imaging to see deep inside tissues.
Due to the available intrinsic contrast properties of haemoglobin and other molecules in the body, photoacoustic imaging techniques are widely used for visualising blood vessels, blood oxygenation mapping, and functional brain mapping. Unfortunately, intrinsic blood contrast is not sufficient for imaging deeply seated blood vessels, and nanoparticles are required to solve this problem.
To attain more accurate imaging and diagnosis, contrast agents with properties that have a high absorption of near-infrared light have been developed, in particular nanoparticles made from semiconducting polymers that have shown interesting optical properties.
There are still limitations to this strategy, as the biodegradable materials and metabolisable nanoparticles suitable for photoacoustic imaging are rare, but recent progress in the field show potential for clinical use soon.
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