High-resolution thermoacustic computed tomography

Thermoacoustic computed tomography (TACT), sometimes also called optoacoustic or photoacoustic tomography, is an emerging technology for imaging of semitransparent objects, like soft biological tissue. When a semitransparent sample is illuminated by a short pulse of electromagnetic radiation, such as light or radio waves, a sound wave is generated in the sample by thermoelastic expansion. In TACT the goal is to recover the local distribution of the absorbed energy inside the illuminated sample from the acoustic pressure measured outside the sample. It is particularly suited for imaging of soft, biological tissue because certain tissue structures differ strongly in their optical absorption properties from the surrounding tissue. Therefore they can be imaged with high contrast, leading for example to a good distinction between cancerous and healthy tissue. Existing TACT techniques have used small detectors as approximations of point detectors to collect acoustic signals. To overcome the resolution limit due to the finite detector size we propose a novel measurement setup with detectors that are larger than the imaged object. Extended in one or two directions, e.g. as linear or planar detectors, they integrate the incoming pressure waves over their surface. This enables the use of numerically efficient and stable algorithms for TACT. The general objective of this project is the high-resolution, three dimensional imaging of semitransparent structures using such integrating detectors. A complete simulation of the imaging procedure with detectors of various shapes scanned around a sample verifies the theoretical background and helps to find new algorithms for TACT and to optimize them. Further new detectors (piezoelectrical or optical sensors) with the required shape are developed and optimised for high bandwidth detection. Based on these detectors together with the developed TACT algorithms a set-up for three dimensional imaging of small objects is designed, built and characterized. Finally the TACT set-up is tested by taking images of phantoms and of various biological samples.

Thermoacoustic computed tomography (TACT), sometimes also called optoacoustic or photoacoustic tomography, is an emerging technology for imaging of semitransparent objects, like soft biological tissue. When a semitransparent sample is illuminated by a short pulse of electromagnetic radiation, such as light or radio waves, a sound wave is generated in the sample by thermoelastic expansion. In TACT the goal is to recover the local distribution of the absorbed energy inside the illuminated sample from the acoustic pressure measured outside the sample. It is particularly suited for imaging of soft, biological tissue because certain tissue structures differ strongly in their optical absorption properties from the surrounding tissue. Therefore they can be imaged with high contrast, leading for example to a good distinction between cancerous and healthy tissue. Existing TACT techniques have used small detectors as approximations of point detectors to collect acoustic signals. To overcome the resolution limit due to the finite detector size we propose a novel measurement setup with detectors that are larger than the imaged object. Extended in one or two directions, e.g. as linear or planar detectors, they integrate the incoming pressure waves over their surface. This enables the use of numerically efficient and stable algorithms for TACT. The general objective of this project is the high-resolution, three dimensional imaging of semitransparent structures using such integrating detectors. A complete simulation of the imaging procedure with detectors of various shapes scanned around a sample verifies the theoretical background and helps to find new algorithms for TACT and to optimize them. Further new detectors (piezoelectrical or optical sensors) with the required shape are developed and optimised for high bandwidth detection. Based on these detectors together with the developed TACT algorithms a set-up for three dimensional imaging of small objects is designed, built and characterized. Finally the TACT set-up is tested by taking images of phantoms and of various biological samples.