In this paper, the multielement phase-controlled technique and the limited-field-filtered back-projection algorithm are used to investigate the two-dimensional fast noninvasive photoacoustic imaging. By the use of the former to collect photoacoustic signals, which are of high signal-to-noise ratio, one needs not to average the data and can acquire them in less than 5 s. The later can greatly improve the lateral resolution of the multielement linear transducer array imaging system from 1.5 mm to 0.24 mm. This method and system can provide a fast and reliable approach to photoacoustic imaging that could be applied to noninvasive imaging and clinic diagnosis.

The optoacoustic technique is a noninvasive imaging method with high spatial resolution. It potentially can be used to monitor anatomical and physiological changes. Photodynamic therapy (PDT)-induced vascular damage is one of the important mechanisms of tumor destruction, and real-time monitoring of vascular changes can have therapeutic significance. A unique optoacoustic system is developed for neovascular imaging during tumor phototherapy. In this system, a single-pulse laser beam is used as the light source for both PDT and for concurrently generating ultrasound signals for optoacoustic imaging. To demonstrate its feasibility, this system is used to observe vascular changes during PDT treatment of chicken chorioallantoic membrane (CAM) tumors. The photosensitizer used in this study is protoporphyrin IX (PpIX) and the laser wavelength is 532 nm. Neovascularization in tumor angiogenesis is visualized by a series of optoacoustic images at different stages of tumor growth. Damage of the vascular structures by PDT is imaged before, during, and after treatment. Rapid, real-time determination of the size of targeted tumor blood vessels is achieved, using the time difference of positive and negative ultrasound peaks during the PDT treatment. The vascular effects of different PDT doses are also studied. The experimental results show that a pulsed laser can be conveniently used to hybridize PDT treatment and optoacoustic imaging and that this integrated system is capable of quantitatively monitoring the structural change of blood vessels during PDT. This method could be potentially used to guide PDT and other phototherapies using vascular changes during treatment to optimize treatment protocols, by choosing appropriate types and doses of photosensitizers and doses of light.

Current imaging modalities face challenges in clinical applications due to limitations in resolution or contrast. Microwave-induced thermoacoustic imaging may provide a complementary modality for medical imaging, particularly for detecting foreign objects due to their different absorption of electromagnetic radiation at specific frequencies. A thermoacoustic tomography system with a multielement linear transducer array was developed and used to detect foreign objects in tissue. Radiography and thermoacoustic images of objects with different electromagnetic properties, including glass, sand, and iron, were compared. The authors' results demonstrate that thermoacoustic imaging has the potential to become a fast method for surgical localization of occult foreign objects.Significant progress has been made in the past several years in photoacoustic imaging. Microwave-induced thermoacoustic imaging which shares similar principles with photoacoustic imaging could potentially combine the advantages of microwave imaging and ultrasound imaging, to achieve high resolution and high absorption contrast. 1-5 Moreover, microwave-induced thermoacoustic imaging may provide wider medical applications because microwave radiation has higher tissue penetration depth than light and also has different contrast mechanisms. This feature of thermoacoustic imaging can be employed to detect occult foreign bodies in tissue.Thermoacoustic signal generation is a result of microwave-induced thermal effect. A small temperature surge can be produced when a biological tissue is irradiated by a microwave pulse of adequate energy. Subsequently, the heated structure thermally expands and contracts, becoming a source of acoustic wave. By detecting the sound wave and via signal reconstruction, thermoacoustic tomography (TAT) can be realized based on the differences in microwave absorption inside the target.Accidental invasion of foreign body into human tissue is rather frequent, especially in the case of a traumatic or iatrogenic injury. The common methods for locating foreign bodies present several drawbacks: Radiography is invasive and not ideal for detecting nonradiopaque substances such as glass and wood while magnetic resonance imaging (MRI) cannot function when metals are involved. And computed tomography and MRI are both cumbersome and expensive. TAT, which relies on microwave absorption, can help visualize electromagnetic differences in biological tissue. It has the potential to become an effective and low-cost biomedical imaging modality for disease diagnose. Furthermore, it could be used to recognize and locate foreign bodies rapidly and accurately. We have developed a fast photoacoustic imaging system using multielement linear transducer array. 6-9 A microwave-induced thermoacoustic tomography prototype was also designed and developed. 10 In this study, this system was applied to detect and localize occult foreign bodies in biological tissues. A phase-controlled focus technique is used to reduce data acquisition time and a limited-f...

Windowless ultrasound photoacoustic cell for in vivo mid-IR spectroscopy of human epidermis: Low interference by changes of air pressure, temperature, and humidity caused by skin contact opens the possibility for a noninvasive monitoring of glucose in the interstitial fluid Rev. Sci. Instrum. 84, 084901 (2013);

How to extract the weak photoacoustic signals from the collected signals with high noise is the key to photoacoustic signal processing. We have developed a modified filtered backprojection algorithm based on combination wavelet for high antinoise photoacoustic tomography. A Q-switched-Nd: yttrium-aluminum-garnet laser operating at 532 nm is used as light source. The laser has a pulse width of 7 ns and a repetition frequency of 20 Hz. A needle polyvinylidene fluoride hydrophone with diameter of 1 mm is used to capture photoacoustic signals. The modified algorithm is successfully applied to imaging vascular network of a chick embryo chorioallantoic membrane in situ and brain structure of a rat brain in vivo, respectively. In the reconstructed images, almost all of the capillary vessels and the vascular ramifications of the chick embryo chorioallantoic membrane are accurately resolved, and the detailed brain structures of the rat brain organization are clearly identified with the skull and scalp intact. The experimental results demonstrate that the modified algorithm has much higher antinoise capacity, and can greatly improve the reconstruction image quality. The spatial resolution of the reconstructed images can reach 204 microm. The modified filtered back-projection algorithm based on the combination wavelet has the potential in the practical high-noise signal processing for deeply penetrating photoacoustic tomography.