A three-dimensional photoacoustic imaging method is presented that uses a Mach–Zehnder interferometer for measurement of acoustic waves generated in an object by irradiation with short laser pulses. The signals acquired with the interferometer correspond to line integrals over the acoustic wave field. An algorithm for reconstruction of a three-dimensional image from such signals measured at multiple positions around the object is shown that is a combination of a frequency-domain technique and the inverse Radon transform. From images of a small source scanning across the interferometer beam it is estimated that the spatial resolution of the imaging system is in the range of 100 to about $300\mu \mathrm{m}$, depending on the interferometer beam width and the size of the aperture formed by the scan length divided by the source–detector distance. By taking an image of a phantom it could be shown that the imaging system in its present configuration is capable of producing three-dimensional images of objects with an overall size in the range of several millimeters to centimeters. Strategies are proposed how the technique can be scaled for imaging of smaller objects with higher resolution.

A photoacoustic tomograph based on optical ultrasound detection is demonstrated, which is capable of high resolution real-time projection imaging and fast three-dimensional (3D) imaging. Snapshots of the pressure field outside the imaged object are taken at defined delay times after photoacoustic excitation by use of a charge coupled device (CCD) camera in combination with an optical phase contrast method. From the obtained wave patterns photoacoustic projection images are reconstructed using a back propagation Fourier domain reconstruction algorithm. Applying the inverse Radon transform to a set of projections recorded over a half rotation of the sample provides 3D photoacoustic tomography images in less than one minute with a resolution below 100 µm. The sensitivity of the device was experimentally determined to be 5.1 kPa over a projection length of 1 mm. In vivo images of the vasculature of a mouse demonstrate the potential of the developed method for biomedical applications.

Photoacoustic tomography (PAT) is based on the generation of ultrasound waves by heating an object with short light pulses. A three-dimensional image of the distribution of absorbed energy within the object is reconstructed from signals measured around the object with either point-like or extended, linear sensors. Limited angle artefacts arise when the curve or surface connecting neighbouring detectors is not closed around the object. For this case, there exists a 'detection region' in which all boundaries of an object are visible in the reconstruction. All straight lines passing through each point in this region intersect the detection curve or surface at least once. Although for these points an accurate reconstruction is possible, direct back projection leads to artefacts when some of the straight lines intersect the detection surface twice and others just once. In this work, special weight functions for direct, non-iterative back projection are presented that reduce these kinds of artefacts. A clear improvement in image quality is shown in simulations for three-dimensional (3D) imaging with point detectors and for two-dimensional (2D) imaging using line detectors compared to reconstruction without weight factors. For the 2D case also an experiment is shown. The presented weight factors make commonly used back projection formulae suitable for a more accurate reconstruction of the initial pressure distribution in cases where the detection aperture only covers a limited angle, and the region of interest lies within the detection region.

For photoacoustic imaging, usually point-like detectors are used. As a special sensing technology for photoacoustic imaging, integrating detectors have been investigated that integrate the acoustic pressure over an area or line that is larger than the imaged object. Different kinds of optical fiber–based detectors are compared regarding their sensitivity and resolution in three-dimensional photoacoustic tomography. In the same type of interferometer, polymer optical fibers yielded much higher sensitivity than glass fibers. Fabry-Pérot glass-fiber interferometers in turn gave higher sensitivity than Mach-Zehnder-type interferometers. Regarding imaging resolution, the single-mode glass fiber showed the best performance. Last, three-dimensional images of phantoms and insects using a glass-fiber-based Fabry-Pérot interferometer as integrating line detector are presented.