Photoacoustic imaging beyond our wildest dreams

By Chris Lee 

Lihong Wang from Washington University presented some fantastic results on photoacoustic imaging in a plenary talk at the Physics of Quantum Electronics conference …

One of the major difficulties in diagnosing diseases like cancer is our inability to see inside the body accurately and inexpensively. MRI is great, but it’s expensive and has relatively low resolution; while X-ray imaging had higher resolution, but it comes with dangers. Good old ultrasound is the happy medium, providing pretty good value for money in terms of resolution, safety, and cost.

Missing from that list of clinical techniques, you might notice, is light. This is because light and tissue don’t play nice together. Tissues scatter, absorb, and generally play havoc with light, limiting direct imaging to just a few millimeters in depth. Which is a shame, because light imaging has great resolution, uses relatively cheap equipment, and is pretty safe. Let’s just say that it is worth a bit of investment to see whether we can do more with light.

Photoacoustic imaging represents a sort of "best of both" approach to imaging. The basic process is that a relatively powerful pulse of light is sent into some part of the body. Wherever it is absorbed—and only small amounts of light are absorbed in any particular place, so it is safe—it generates heat, as its target expands and generates a small acoustic pressure wave. By picking up these sound waves with microphones, an image of the absorbing structures can be built up.

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