PhotoAcoustic imaging is an imaging modality that uses laser light and ultrasound detectors to image tissues. Photo = Light. Acoustic = Sound. The imaging uses the photoacoustic effect principle. The photoacoustic effect is not new in terms of discovery as it was reported by none other than Alexander Graham Bell (yes! Rings a bell doesn’t it?) as early as 1880. But, the unavailability of proper detectors and instruments at his time was an obstacle to expanding research in this field.
Light + Sound? How?
Laser light is used to deliver energy to tissues. The tissues absorb some energy from the laser light and get heated up. After heating, the tissues expand or vibrate to release the absorbed heat energy. This sudden and fast expansion of tissues causes sound waves to be generated and they are in the frequency range of Mega Hertz (Ultrasound). These ultrasound waves are detected using piezoelectric detectors. The time taken to receive ultrasound after the laser light was given is used to find the location of the tissue which vibrates.
Wondering how light penetrates through the skin? Near Infrared light (wavelength range of 700 – 2500 nanometers) can penetrate skin because skin does not absorb/absorbs very less light at longer wavelengths. However, as NIR (Near InfraRed) light skips past the skin to deeper tissues, water and other components in deeper tissues absorb NIR and they get heated.
Future Trends
Photoacoustic imaging is one of the rapidly growing fields in healthcare. Development of biocompatible nanoparticles for contrast, improvement in ultrasound transducer for higher resolution, increasing efficiency of laser and much more awaits those who wish to enter this field of photoacoustic imaging. Interested in a diagnostic tool for cancer detection that doesn’t involve radiation and biopsy? Imagining a small portable system that flashes light and detects your cancer? It may all be possible in the future.
Sources & References
Graham Bell’s abstract – http://ieeexplore.ieee.org/abstract/document/5300478/
Image sources – https://en.wikipedia.org/wiki/Photoacoustic_imaging || https://goo.gl/V9ugoy || https://goo.gl/V9fVSf || https://goo.gl/03ez4p
NIR organic nanoparticle article- http://onlinelibrary.wiley.com/doi/10.1002/smll.201700710/full
Advances in photoacoustic article – https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5118603/
Video link – https://www.youtube.com/watch?v=sJ9ZWnvZkRI
