Lvming Zeng

Fast multielement phase-controlled photoacoustic imaging based on limited-field-filtered back-projection algorithm

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 5s. The later can greatly improve the lateral resolution of the multielement linear transducer array imaging system from 1.5mmto0.24mm. This method and system can provide a fast and reliable approach to photoacoustic imaging that could be applied to noninvasive imaging and clinic diagnosis.

Real-time optoacoustic monitoring of vascular damage during photodynamic therapy treatment of tumor

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.

Noninvasive monitoring of traumatic brain injury and post-traumatic rehabilitation with laser-induced photoacoustic imaging

A photoacoustic imaging system was used for noninvasive monitoring of traumatic mouse brain in vivo with high-quality reconstructed images. Traumatic lesions accompanying with hemorrhage in the mouse cortical surface were accurately mapped, and foreign bodies of two small copper wires inserted in the mouse brain were also detected. Furthermore, the time course of morphological changes of cerebral blood during rehabilitation process of a mouse brain with traumatic brain injury was obtained using a series of photoacoustic images. Experimental results demonstrate that photoacoustic technique holds the potential for clinical applications in brain trauma and cerebrovascular disease detection.

Detection of foreign body using fast thermoacoustic tomography with a multielement linear transducer array

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.

High antinoise photoacoustic tomography based on a modified filtered backprojection algorithm with combination wavelet

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.

Portable optical-resolution photoacoustic microscopy with a pulsed laser diode excitation

Optical-resolution photoacoustic microscopy (OR-PAM) has been significantly improved in terms of spatial resolution, detection sensitivity, imaging speed, and penetration depth. However, the popular producibility of OR-PAM system is still limited by the size and cost of solid-state laser excitation. Here, we developed a portable laser-diode-based OR-PAM (LD-OR-PAM) system using a pulsed semiconductor laser source, which was operated at 905u2009±u200915u2009nm with a pulse energy as low as 4.9u2009μJ. The measured lateral resolution has been improved to ∼1.5u2009μm from hundreds of microns. The compact and inexpensive natures of LD-OR-PAM would promote the potential clinical applications such as in dermatology.

Gold nanoshell-based photoacoustic imaging application in biomedicine

Gold nanoshell was used as a new contrast-enhancing agent for photoacoustic tomography. Gold nanoshells are concentric sphere nanoparticles consisting of a dielectric silica core and a gold shell. By varying the relative thickness of the core and shell layers, the plasmon-derived optical resonance of gold can be dramatically shifted in wavelength from the visible region into the infrared over a wavelength range that spans the region of highest physiological transmissivity. In this experimentation, nanoshells with 100 nm silica core diameter and 20 nm gold shells thickness has an optical absorption peak at 800 nm and deep penetrating pulse laser of 800 nm were employed to image the the vasculature architecture of a rat brain in vivo. Here we accurately imaged rat brain structures with gold nanoshell contrast agents. We also mapped the distribution of gold nanoshell in the in vivo rat brain. This experiment results demonstrated that nanoshell accumulation is greatly enhanced NIR optical contrast in the vasculature. Nanoshell-based photoacoustic imaging technique would be applied in biomedicine extensively. The further development of photoacoustic tomography to characterize and monitor the accumulation of nanoshells in vivo will be applied to the detection of tumors in situ as well as to guiding nanoshell-based thermal tumor therapy. Gold nanoshell can potentially provide an accurate noninvasive method, use as imaging contrast agents, to employ in functional photoacoustic at molecular and cellular level.

Cost-efficient laser-diode-induced optical-resolution photoacoustic microscopy for two-dimensional/three-dimensional biomedical imaging

Abstract. Solid-state laser systems, such as traditional Nd:YAG-based lasers, are commonly used for noninvasive biomedical photoacoustics with nanosecond pulse duration and millijoule pulse energy. However, such lasers are both bulky and expensive for use as a handy tool for clinical applications. As an alternative, a semiconductor light source has the advantages of being compact, inexpensive, and robust. In addition, the main drawback of low peak output power may make it exactly suitable for the imaging modalities, which require relatively low pulse energies, such as acoustic- and optical-resolution photoacoustic microscopy (AR/OR-PAM). We propose a cost-efficient OR-PAM for two-dimensional/three-dimensional (2-D/3-D) biological imaging based on a pulsed near-infrared laser diode. By raster scanning, typical 2-D photoacoustic images were obtained at different scales, and 3-D surface renderings were clearly reconstructed with a marching cubes algorithm. This initial study would promote the production of portable OR-PAM technology for clinical and biomedical applications.

Microwave-induced thermoacoustic imaging enhanced with a microwave contrast agent

Nanoparticles have drawn great attention as targeted imaging and therapeutic agents recently. However, so far, no research on radio-frequency absorption contrast agents in soft tissues has been reported. A microstructure agent, carbonyl iron, which has strong microwave absorption, is applied to microwave-induced thermoacoustic imaging. The size of this microsphere is approximately 2mum that is safe for biological and medical application. The carbonyl iron emulsion is prepared by the Sol-Gel process which makes carbonyl iron particles more hydrophilic and with good electromagnetic properties. A 320-element linear transducer array with a centre frequency of 3.5 MHz was adopted to capture thermoacoustic signals within limited field around the sample. Using 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 data acquisition time of less than 5 s at each step. The collected data was utilized to reconstruct the geometrical details based on limited-field-filtered back-projection algorithm. The effect of solid particles for enhancing thermoacoustic grey scale images was successfully investigated in tissue phantoms, the image brightness, i.e., mean grey scale level, increased with particle concentration. This particle may have potential to improve sensitivity and specificity for structural and functional thermoacoustic imaging and broadly expand the thermoacoustic imaging capability as a powerful medical diagnostic tool. This paper provides the first demonstration of a microwave contrast enhancing agent for thermoacoustic imaging.

Limited-view scanning microwave-induced thermoacoustic CT using a multi-element linear transducer array

In this paper, we have developed a limited-view scanning microwave-induced thermoacoustic computed tomography (CT) system based on the multi-element phase-controlled focus technique. A 320-element linear transducer array was relatively rotated to capture thermoacoustic signals within limited detection views, which effectively eliminated the problem that the focused ultrasonic transducer can but receive finite signal from boundaries of tissues which are nearly perpendicular to the axis of the transducer. Using 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 data acquisition time of less than 5 s in each view. The collected limited-view data was utilized to reconstruct the geometrical details based on limited-field-filtered back-projection algorithm. The system may provide a reliable approach to thermoacoustic imaging, which can potentially be developed as a powerful diagnostic tool for early-stage breast caners.