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Photoacoustic tomography (PAT) is presented to in vivo monitor neovascularization in tumour angiogenesis with high resolution and high contrast images in a rat. With a circular scan system, the photoacoustic signal, generated by laser pulses at a wavelength of 532 nm from a Q-switched Nd:YAG laser, is captured by a hydrophone with a diameter of 1 mm and a sensitivity of 850 nV/Pa. The vascular structure around the rat tumour is imaged clearly, with optimal contrast, because blood has strong absorption near this wavelength. Serial noninvasive photoacoustic images of neovascularization in tumour angiogenesis are also obtained consecutively from a growing tumour implanted under the skin of a rat over a period of two weeks. This work demonstrates that PAT can potentially provide a powerful tool for tumour angiogenesis detection in cancer research. It will bring us closer to clinical applications for tumour diagnosis and treatment monitoring.

We develop a fast microwave-induced thermoacoustic tomography system based on a 320-element phase-controlled focus linear transducer array. A 1.2-GHz microwave generator transmits microwave with a pulse width of 0.5 μs and an incident energy density of 0.45 mJ/cm2, and the microwave energy is delivered by a rectangular waveguide with a cross section of (80.01±0.02)×10−4 m2. Compared to single transducer collection, the system with the multi-element linear transducer array can eliminate the mechanical rotation of the transducer, hence can effectively reduce the image blurring and improve the image resolution. Using a phase-controlled focus technique to collect thermoacoustic signals, the data need not be averaged because of a high signal-to-noise ratio, resulting in a total data acquisition time of less than 5 s. The system thus provides a rapid and reliable approach to thermoacoustic imaging, which can potentially be developed as a powerful diagnostic tool for early-stage breast caners.

We report tumor detection using a photoacoustic technique for the imaging of angiogenesis and monitoring of agent pharmacokinetics on an animal model. We take 532-nm laser pulses to excite photoacoustic signals of blood vessels with acquisition by a broadband hydrophone, and the morphological characteristics of tumor angiogenesis are successfully image depicted. Furthermore, tumor pharmacokinetics is preformed and analyzed with fast multielement photoacoustic imaging of the intravenous-injected indocyanine green (ICG). Photoacoustic signals of ICG are excited with 805 nm laser pulses and recorded by transducer array as a function of time. The difference between the photoacoustic signal from the tumor side and that from the normal side is observed, and the ICG clearance velocity in the tumor area is found to lag behind that in the normal area. Experimental results demonstrate that photoacoustic imaging of morphological parameter and pharmacokinetics with specific agent may provide high sensitive approach for tumor detection and localization.

Photoacoustic imaging is a novel noninvasive imaging technique of biological tissue that overcomes the overwhelming scattering of light in biological tissue by utilizing ultrasonic wave to translate the image signal. In this study, near-infrared light and indocyanine green as an optical contrast agent were used to achieve the cerebrovascular distribution by photoacoustic imaging. Near-infrared light penetrates deep into the brain tissues through the skin and skull, and the indocyanine green enhances the photoacoustic signals of the blood vessels. A photoacoustic angiography of vascular distribution in the mouse brain in vivo was acquired that matches the anatomical photograph well. The experimental result demonstrates the photoacoustic imaging with near-infrared light and optical contrast agent has the potential for functional and molecular biomedical imaging.

Photoacoustics as a potential and noninvasive medical imaging technology，it combines the advantages of ultrasound imaging and optical imaging to provide high ultrasonic resolution and high optical contrast tissue images. A reconstruction algorithm named the modified simultaneous iterative reconstruction technique (MSIRT) using in limited-view data in photoacoustic imaging was studied. The simulation and experiments result demonstrated that MSIRT has good performance in photoacoustic imaging for limited-view data at angles 90°，135° and 180°. It works much better than traditional algebraic reconstruction algorithm in rectification of the measurement and the speed of convergence. A circular scan with a single-element transducer system was used to obtain photoacoustic signals through 180° in the experiment. This technique provides a high contrast and high resolution (about 60μm) photoacoustic imaging of blood vessels of a chicken embryo based on MSIRT. It greatly reduced the data acquisition time. This method could be potentially used to realtime monitoring of cerebral blood flow and the vascular damage during photodynamic therapy.

Photoacoustic imaging combines advantages of both ultrasound imaging and optical imaging to provide high ultrasonic resolution and high optical contrast in noninvasive medical images. A photoacoustic computer tomography （PCT） system with a focused digital phased array transducer is proposed. In particular each element of the transducer array has a thin cylindrical ultrasonic lens to select 2D image plane and suppress the out-of-plane signals to realize photoacoustic computed tomography. A fast full-view photoacoustic imaging system for visualizing tissue structures using a linear transducer array with combined scan, whies; detects photoacoustic signals by combined electronic and mechanical scanning. An improved limited-field filtered back projection algorithm with directivity factors was applied to reconstruct the optical absorption distribution and further improve the lateral resolution. In the experiment, the spatial resolution of this imaging system is determined as 0.2mm, and the slice resolution of Z axis is 1.5mm. Mechanical step scanning was performed, leading to a measurement time of 6.4 seconds per position, and a total scan duration of 150 seconds to obtain the two-dimensional photoacoustic image. High spatial resolution of 2D photoacoustic vascular image and quasi-3D photoacoustic CT for breast cancer imaging are achicned. The experimental results demonstrate that this method and imaging system can realize the high resolution photoacoustic tomography wtich can be applied to noninvasive detection of early breast cancer.