Photoacoustic imaging is a powerful technique that can be used to obtain images of tissues and small animals that have optical contrast and high resolution. Optical contrast can indicate haemoglobin concentration and oxygen saturation of tissues, which are important indicators of tissue health and useful for distinguishing malignant lesions from benign during cancer diagnostics. However, photoacoustic imaging is usually slow to capture images since the existing reconstruction techniques require many projections. This requires translation of a single transducer through many angles (slow) or extremely expensive high-density transducer arrays that are only now becoming available. In these contributions, we describe a method to image in 3D with photoacoustics using a limited number of transducers and iterative image reconstruction. This advancement increases the imaging speed to that of a high-density ultrasound transducer array, but at greatly reduced cost. Furthermore, the reduced transducer count relaxes the number of data acquisition channels to an affordable number so that all detectors can be sampled simultaneously, which enables a 3D image to be collected for each laser pulse. With the technology, it will be possible to image processes in the nanosecond regime in 3D and with good resolution. The systems described in the contributions have ~2 mm near isotropic resolution for image volumes of approximately 30 mm x 30 mm x 30 mm. The contributions from my group describe what is believed to be the world’s first single-shot 3D photoacoustic image of an extended object. What is believed to be the world's first demonstration of 4D photoacoustic imaging, i.e. the capture of a sequence of 3D photoacoustic images of objects under translation and rotation. These contributions represent the basis for developing 3D photoacoustic imaging applications such as breast imaging for identifying lesions as malignant or benign.

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