We present photoacoustic images of tumor neovascularization obtained over a 10-day period after subcutaneous inoculation of pancreatic tumor cells in a rat. The images were obtained from ultrasound generated by absorption in hemoglobin of short laser pulses at a wavelength of 1064 nm. The ultrasound signals were measured in reflection mode using a single scanning piezodetector, and images were reconstructed with a weighted delay-and-sum algorithm. Three-dimensional data visualize the development and quantify the extent of individual blood vessels around the growing tumor, blood concentration changes inside the tumor and growth in depth of the neovascularized region.

Materials for solid photoacoustic breast phantoms, based on poly(vinyl alcohol) hydrogels, are presented. Phantoms intended for use in photoacoustics must possess both optical and acoustic properties of tissue. To realize the optical properties of tissue, one approach was to optimize the number of freezing and thawing cycles of aqueous poly(vinyl alcohol) solutions, a procedure which increases the turbidity of the gel while rigidifying it. The second approach concentrated on forming a clear matrix of the rigid poly(vinyl alcohol) gel without any scattering, so that appropriate amounts of optical scatterers could be added at the time of formation, to tune the optical properties as per requirement. The relevant optical and acoustic properties of such samples were measured to be close to the average properties of human breast tissue. Tumour simulating gel samples of suitable absorption coefficient were created by adding appropriate quantities of dye at the time of formation; the samples were then cut into spheres. A breast phantom embedded with such 'tumours' was developed for studying the applicability of photoacoustics in mammography.

Photoacoustic imaging is a hybrid imaging modality that is based on the detection of acoustic waves generated by absorption of pulsed light by tissue chromophores such as hemoglobin in blood. For this technique, usually large and costly Q-switched Nd:YAG lasers are used. These lasers provide a pulse energy of at least several milliJoules. In search of alternative light sources, we investigated the use of a small and compact pulsed laser diode to image blood vessels. We proved that a pulsed laser diode can be applied for imaging blood vessels in vivo.

Abstract-We applied photoacoustics for noninvasive two-dimensional imaging of blood vessels in vivo, using near infrared light. This study was undertaken to develop photoacoustic tomography of tissue for the detection of embedded blood vessels using a newly developed piezoelectric double ring detector, featuring an extremely narrow aperture.

Abstract.A real-time photoacoustic imaging system is designed and built. This system is based on a commercially available ultrasound imaging system. It can achieve a frame rate of 8 frames/ sec. Vasculature in the hand of a human volunteer is imaged, and the resulting photoacoustic image is combined with the ultrasound image. The real-time photo acoustic imaging system with a hybrid ultrasound probe is demonstrated by imaging the branching of subcutaneous blood vessels in the hand. Blood vessels play a key role in homeostasis, growth, and repair of tissue. Knowledge on the presence of blood vessels, and the content of hemoglobin and its degree of oxygenation, yield crucial information regarding various applications in medicine, ranging from oncology to dermatology.A promising new technique to obtain both anatomical and functional information about the vascular bed is photoacoustic imaging. In photoacoustic imaging, a pressure transient is generated on absorption of a short pulse of light by a tissue chromophore ͑e.g., hemoglobin͒. Measurement of the pressure waves at the tissue surface enables reconstruction of the absorbed energy distribution, which yields information on the hemoglobin concentrations.Recently, photoacoustic imaging has successfully been applied to in vivo imaging of blood vessels in small animals [1][2][3] and humans. [4][5][6][7][8] Clinical application of photoacoustic imaging is hampered by its long imaging time, which leads to patient discomfort, movement artifacts, and consequently a low temporal resolution. Photoacoustic imaging systems based on a commercial ultrasound system are a logical next step toward clinical introduction. Systems reported in the literature that could be used for in vivo imaging in reflection mode ͑i.e., illumination and detection at the same side of the tissue͒ required a multichannel data-acquisition system and a computer to reconstruct the images. 5,9We present an approach in which we do not need this additional data-acquisition system and computer, as we utilize the data acquisition as well as hardware-implemented image reconstruction of a conventional ultrasound imaging system. The developed system is able to reconstruct the photoacoustic images of in vivo vasculature in real time with a frame rate of 8 frames/ sec. As this photoacoustic imaging system is based on a commercial ultrasound system, it provides hybrid photoacoustic and ultrasound imaging without the need for additional algorithms and hardware to capture the signals and reconstruct the images.An ultrasound imaging system ͑Picus, ESAOTE Europe BV, Maastricht, the Netherlands͒ was modified to synchronize the data acquisition with the firing of the laser. In addition, the emission of the ultrasound could be switched off during photoacoustic imaging. To detect the ͑laser-generated͒ ultrasound, a linear array ͑L10-5, 40 mm, 128 elements, 7.5-MHz central frequency, 75% −6-dB bandwidth͒ was connected to this ultrasound imaging system. An optical system was developed that could be connected to this linear a...