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Thermoacoustic tomography using optical line detection

Thermoacoustic computed tomography (TACT) is a method to visualize structures with optical contrast hidden in a light-scattering medium. Pulses of electromagnetic radiation that are absorbed in an optically heterogeneous object cause a distribution of energy density and thermoelastic pressure that is determined by the distribution of optical absorption. In conventional TACT, pressure waves emitted by the object are measured with small acoustic detectors and the temporal signals are used for reconstruction of the energy density distribution. To avoid the limitation of the spatial resolution of the image by the finite detector size we propose to use large, integrating detectors, where the object is always in the detector near field. This has the advantage that not only the finite size effect can be avoided but also that for image reconstruction the conventional, inverse Radon transform can be applied. In the present work the integrating detectors have the shape of a line, formed by a laser beam that is part of a Mach-Zehnder interferometer. By scanning the line detector and rotating the sample a data set can be acquired from which a full three-dimensional image of the energy density distribution in the object can be reconstructed. The data acquisition and image reconstruction procedures are described in detail. In a first imaging experiment a three-dimensional image of a phantom is presented. Finally, ways to improve the imaging speed as well as the spatial resolution are discussed.