Dec 4, 2007
A focus on photo- and thermo-acoustics
Photo- and thermo-acoustic imaging are hybrid techniques that exploit the contrast in electromagnetic absorption between different tissue types to create high-resolution ultrasound images. The techniques show promise for a range of biomedical applications, including small-animal imaging, and early detection of breast and skin cancers. In this month's issue of IOP Publishing's applied mathematics journal Inverse Problems, a special section focuses on thermo- and photo-acoustics for cancer diagnostics.
Photo-acoustic imaging works by irradiating the region of interest with pulsed near-infrared light. When this light is absorbed by the tissue, it causes localized heating, which in turn yields a pressure wave. The wave is detected by ultrasound transducers at the tissue surface and can be used to generate an image of the absorbed energy density.
Within cancer diagnostics, the excessive angiogenesis (new blood vessel growth) that generally accompanies tumour development causes such masses to preferentially absorb electromagnetic energy and heat up more quickly than neighbouring healthy tissue. Mapping the resulting ultrasound signal can therefore create an image of any cancerous regions. Another emerging application involves using antibody-gold nanoparticle conjugates to selectively increase the absorption of tumour cells.
Thermo-acoustic imaging exploits exactly the same effects, except that the ultrasound wave is generated via microwave or radiofrequency heating. Inverse Problems' special section focuses mostly on tomographic photo- and thermo-acoustic applications, and the issue of image reconstruction. The articles in this section comprise:
• Guest Editors' introduction Sarah K Patch and Otmar Scherzer
• Application of inverse source concepts to photoacoustic tomography Mark A Anastasio et al
•The spherical mean value operator with centers on a sphere David Finch and Rakesh