Photoacoustic tomography using integrating line detectors

Abstract

Photoacoustic Imaging (also known as thermoacoustic or optoacoustic imaging) is a novel imaging method which combines the advantages of Diffuse Optical Imaging (high contrast) and Ultrasonic Imaging (high spatial resolution). In photoacoustic imaging, a short laser pulse excites the sample. The absorbed energy causes a thermoelastic expansion and thereby launches a broadband ultrasonic wave (photoacoustic signal). This way one can measure the optical contrast of a sample with ultrasonic resolution. For collecting photoacoustic signals our group introduced so called integrating detectors a few years ago. Such integrating detectors integrate the pressure in one or two dimensions (line or plane detectors). Thereby the three dimensional imaging problem is reduced to a two or a one dimensional problem for the pressure projections for line or plane detectors, respectively. Several reconstruction methods like Fourier or F-SAFT reconstruction or back projection are used for the two dimensional first step, but the model-based time reversal method shows a significant advantage: acoustical heterogeneity and attenuation, which both cause blurring of reconstructions, can be directly implemented in the reconstruction method. The integrating detectors are mainly optical detectors and thus can provide a high bandwidth up to several 100 MHz. Using these detectors the resolution is often limited by the acoustic attenuation in the sample itself, because attenuation increases with higher frequencies. For thin layers, small cylinders, and small spherical inclusions the effect of attenuation in human fat is simulated and the influence of dispersion on image reconstruction is shown.