In the Works: Photoacoustic Tomography Device

The New Scientist is reporting about the efforts of Dr. Paul Beard and colleagues from the Dept. of Medical Physics and Bioengineering at University College London to develop a portable surgical probe based on photoacoustic tomography. In essence, the device’s technology works on a near infrared laser that is fired into tissue. The laser’s energy, once absorbed by the tissues, generates heat, which in turn generates the photoacoustic signals that are picked up by an ultrasound transducer.
Here’s how Dr. Beard’s Photoacoustic Imaging Group website explains the technology:

The sensor is placed in acoustic contact with the surface of the target tissue, the excitation laser pulses transmitted through it and the resulting photoacoustic signals recorded at different points over the surface of the sensor. From the time-of-arrival of the signals, and with knowledge of the speed of sound, a 3D image of the tissue structure, based upon the absorbed optical energy distribution, can then be reconstructed. This type of imaging instrument has several important advantages over conventional piezoelectric based photoacoustic detection systems. Firstly, the system operates in “backward mode”. That is to say, the photoacoustic signals can be detected on the same side and over the same region of the tissue surface that is irradiated with the excitation light, a consequence of the transparent nature of the sensor. This is particularly important for imaging superficial anatomical features, such as blood vessels in the skin, where it would be problematic to deliver the excitation laser beam around an array of opaque piezoelectric receivers. Secondly, the concept provides excellent acoustic performance, with uniform broadband frequency response characteristics (to at least 30MHz) and wideband detection sensitivities (<0.1kPa noise-equivalent-pressure) comparable to piezoelectric PVDF receivers but with much smaller "element" sizes (<50μm) and "interelement" spacings -- the latter being a consequence of the optically addressable nature of the sensor which, in principle, affords near-optical diffraction limited spatial sampling of the incident acoustic field. These attributes make the instrument well suited to high resolution (10μm-100μm) tissue imaging applications - click here to see examples of some of the images that have been obtained with the system.

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