Photoacoustic Imaging

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Photoacoustic Imaging is a non-invasive medical imaging technique used to detect vascular disease, skin abnormalities, and some types of cancer. It works by flashing a laser at low energy with a near infrared wavelength onto a target area. The near infrared wavelength helps the light scatter and penetrate deep into the body, this creates a large radiated area for a more detailed picture. As the light is absorbed into the body it expands the tissue through thermoelastic expansion, this expansion creates ultrasonic acoustic waves which can be picked up by very sensitive ultrasound detectors. From there they can be interpreted using different mathematical equations to create 2D or 3D images of the target area.

This technique works because of the different types of tissue in the body. Each one absorbs different amounts of the laser making each different tissue unique. These unique identifiers are combined together to create a very highly detailed image of the target area. This allows doctors to see abnormalities in the skin, vascular disease, and cancer, which can then be treated very directly. Haemoglobin for example, has a very high optical contrast when a near infrared wavelength is applied. This makes viewing blood vessels with this technology very accurate and doctors can identify many different problems that would be very hard to pick up using other techniques. This technology is also much safer than other imaging techologies because it is non-ionising this means that it does not affect the molecules in the body. The X-ray is an example of an ionising technology and if used imporperly it can cause severe damage to a person. Photoacoustic imaging is a cheaper, safer, and more effective way to identify many different problems that may have been overlooked in other tests.

The idea of photoacoustics being used to create acoustic waves by the absoption of light is a relatively old technology. Alexander Graham Bell discovered that you can transmit sound by flashing a focused beam of light onto selenium in the 1880's. The sound produced from the selenium could then be picked up by a hearing tube. There was very little use for this kind of technology in the 1880's and it would be 50 years before the technology advanced to the stages of a microphone which made any measurements much more accurate. In 1973 Allan Rosencwaig, working at Bell Laboratories, renewed interest in Graham Bell's discovery of photoacoustic effects by creating a model of the photoacoustic effects. Rosencwaig's research laid the foundation for more advanced sensors and imaging technology.

[edit] External links

• [1] Photoacoustic Imaging Group, Department of Medical Physics and Bioengineering, University College London