| Photoacoustic (PA) imaging is an emerging hybrid modality that combines the benefits of optical contrast with the deep-tissue image resolution of ultrasound. PA images are created by illuminating the body with a short laser pulse, which excites pressure waves from light-absorbing structures, and detecting the pressure waves outside the body. These images provide the distribution of the light-absorbing structures, such as blood vessels, and can also provide functional information based on spectroscopic measurements.;In this work, the development and validation of SPAI is presented. Its design guidelines and principles of operation are described, as well as the technical advancements realized during the duration of the project. The ability of SPAI to image 3-D structures of increasing complexity and to accurately localize them to within the image resolution is demonstrated. Image resolution of 1.5-2.0 mm axially and 2.5-3.0 mm laterally is quantified and shown to be related to the detection geometry. The high-speed capability is validated on a range of moving targets that are imaged at a rate of 10 frames-per-second (fps). Performance related to sensitivity and tissue penetration is estimated via phantoms that mimic breast lesions in tissue, and imaging depths of 10-20 mm are demonstrated. Imaging limitations are discussed; especially those due to the sparse nature of the array, and future improvements are suggested to address them.;SPAI provides 3-D optical images to depths of few centimetres in tissue and at real-time speeds. These unique features show promise for applications in preclinical cancer research, for high throughput optical characterization of tumour models, as well as for detection and identification of lesions in clinical breast screening.;We have developed a unique technique that provides three-dimensional (3-D) PA images in high speed. The method, called Sparse-array PA Imaging (SPAI), employs a sparse array of ultrasound transducers to capture the PA waves from around the subject, and converts them to an image by an iterative image reconstruction algorithm. Since a full 3-D image can be produced using a single laser pulse, the frame-rate of SPAI is limited only by the pulse repetition rate of the laser. |
