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.
Photoacoustic imaging technique, which provided high ultrasonic resolution and high optical contrast tissue images, can
overcome the disadvantages of pure optical imaging by measurement of laser-induced sound waves. The waves
produced by tissue are high-frequency ultrasounds, meaning that they cannot be heard by human ear. However, it can be
picked up with ultrasonic transducer and analyze them with a computer. The laser-induced ultrasonic signals from a
biological sample can be used to reveal the tissues structure based on optical contrast. In current experiment system, an
integrity multi-element synthetic aperture focusing (M-SAF) photoacoustic imaging system using real-time digital
beamformer is developed. This system relies on pumping laser source to irradiate the biological tissue to produce
photoacoustic signal, a linear ultrasonic transducer array is connected to a multichannel signal acquisition and real-time
digital beam-formation system providing techniques of real-time dynamic receiving focus and dynamic receiving
apodization to process the photoacoustic signal. Each element of the transducer array has a thin cylinder ultrasonic lens
to select 2D image plane and suppress the out-of-plane signals to realize photoacoustic computed tomography. This
method and system can provide a fast and reliable photoacoustic tomography approach that could be applied to
noninvasive imaging and clinic diagnosis.
Noninvasive monitoring of the microvascular network and detection the angiogenesis around tumors is one of the most
active areas in biomedical research. In this paper, we present a multi-element photoacoustic imaging system for fast
imaging the blood vessels. In this system, a Q-switched Nd: YAG pulse laser operated at 532nm with a 6 ns pulse width
is used to generate a photoacoustic signals; a 64-element linear transducer array with the central frequency of 7.5MHz is
used to measure the photoacoustic waves. The limited-field filtered back projection algorithm is used to reconstruct the
optical absorption distribution in tissue. The experiments of a phantom model and in vitro blood vessels were performed
with this system. A clear photoacoustic image of microvascular network was obtained with high resolution. The
experimental results demonstrate that our multi-element photoacoustic imaging system has the ability of imaging
microvascular network and may potentially be used to monitor the angiogenesis around tumors.
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.
The customary methods for localizing the foreign body in human body present several disadvantages, radioscopy has
significant radiation exposure, MRI can not work with the metal, and also they are expensive and neither is portable.
Microwave-induced thermoacoustic imaging which shares similar mechanism with photoacoustic imaging can achieve
high ultrasound resolution and good microwave absorption contrast. Besides, microwave can reach deeply hidden sample
in biological tissue because of its long wavelength, hence, this new imaging modality can be potentially applied to detect
the foreign body hidden in human body. Our detecting methods were validated by imaging simulated foreign body
embedded in biological tissue at different depths, the unknown samples embedded deeply were discernible and the signal
to noise ratio was good. By employing the multi-element linear transducer array and phase-controlled focus algorithm, a
circular scan of thermoacoustic signals at 20 angles needs no more than 2 minutes. Our established thermoacoustic
imaging system has potential to supply a novel and fast method for surgical localization of an unknown foreign body.
The high contrast and high resolution photoacoustic tomography was used to image the gold nanoshell clearance in rat
brain in vivo. With our current imaging system, the acquisition of photoacoustic signals is realized through a circular
scan of a single-element transducer. Therefore, the data acquisition is slow. In this case, an improved simultaneous
iterative reconstruction algorithm was developed to reduce the acquisition time by using limited data in the experiments.
This algorithm is based on the least square principle; it can be used to reconstruct high quality images from the limited
data containing much noise. Furthermore, it is always convergent. So it can improve the imaging quality comparison
with conventional filter back-projection algorithm (FBP) and algebraic reconstruction algorithm (ART). Here we
accurately mapped rat brain structures with gold nanoshell contrast agents. We also imaged the clearance of gold
nanoshell in the rat brain. It provides an accurate non-invasive monitoring method for fluid pathways in biological
tissues, which makes photoacoustic tomography as a powerful method for imaging pathologic tumor vessels, delineating
neovascularization, and studying global and regional hemodynamic activities in the brain.
A unique photoacoustic system was developed for neovascular imaging during tumor photodynamic therapy (PDT). In
this system, a single pulse laser beam is used as the light source for both PDT treatment and for concurrently generating
ultrasound signals for photoacoustic imaging. To demonstrate its feasibility, this system was used to observe vascular
changes during PDT treatment of chicken chorioallantoic membrane (CAM) tumors. The photosensitizer used in this
study was protoporphyrin IX (PpIX) and the laser wavelength was 532 nm. Damage of the vascular structures by PDT
was imaged before, during and after treatment. Rapid, real-time determination of the size of targeted tumor blood vessels
was achieved, using time difference of positive and negative ultrasound peaks during PDT treatment. The experimental
results show that a pulse laser can be conveniently used to hybridize PDT treatment and photoacoustic 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.
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 signicance. 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.
Photoacoustic tomography is a potential and noninvasive medical imaging technology. It combines the advantages of
pure optic imaging and pure ultrasound imaging. We have explored photoacoustic imaging with different filters, such as
RL, SL, Modi-SL arid Kwoh-Reed, which take important roles on reconstructed images. The results of simulations and
experiments show that the filter of Kwoh-Reed can restrain noise effectively and improve the contrast of images
compares with the filters of RL, SL, ModiSL in the presence of strong noise. A Q-switched Nd:YAG laser operating at
532nm was used as light source. The laser had a pulse width of 7ns and a repetition frequency of 30Hz. A needle PVDF
hydrophone with diameter of I mm was used to detect photoacoustic signals.
We developed a fast microwave-induced thermoacoustic tomography system based on a 320-element phase-controlled
linear transducer array. A 1.2GHz microwave generator transmits microwave with pulse duration of 0.5 us and an
incident energy density of 0.45 mJ/cm2. Compared to single transducer collection, the system with multi-element linear
transducer array can eliminate the mechanical rotation of the transducer, so can effectively reduce the image blurring and
improve the image resolution. Using phase-controlled technique to collect thermoacoustic signals, the data need not be
averaged because of the high signal-to-noise ratio, resulting in the total data acquisition time of less than 5 s. The system
thus provide a rapid and reliable approach to thermoacoustic imaging. which can potentially be developed as a powerful
diagnostic tool for early-stage breast caners.
In this paper, we have constructed an integrative fast photoacoustic (PA) imaging system for fast photoacoustic
imaging, which includes a fiber, ultrasonic coupling medium, and a multi-element linear transducer array (MLTA).
The PA signals were received by the MLTA in a reflection mode arid collected by a computer, reconstructed by
limited-field filtered back projection algorithm. The PA images of different depth of phantom and animal blood
vessels of different diameters were obtained. The lateral resolution of the system was 0.2mm. It would provide a new
approach to tissue functional images in vivo and may have potentials in developing into an appliance for clinic
diagnosis of disease.
The major approach to photoacoustic imaging is the filtered back projection (FBP) algorithm, which is based on direct
Fourier inversion. But the reconstruction with the FBP needs sufficient views to all points in the "detection region", it
requires a quite long time to get enough data, which restricts the application in the medical field. In this paper, the
limited-view photoacoustic imaging based on algebraic reconstruction techniques (ART) has been studied. A Q-switched
Nd: YAG laser operating at 1064 nm was used as light source. The laser had a pulse width of 6ns and a repetition
frequency of 20Hz. A needle PVDF hydrophone with diameter of 1mm was used to detect photoacoustic signals. Under
the same condition, the simulations and experiments demonstrated that ART works well for limited-view data in
photoacoustic imaging, and ART can improve the resolution and contrast of reconstruction images compared with the
FBP algorithm.
Photoacoustic imaging combines the contrast advantage of pure optical imaging and the resolution advantage of pure ultrasonic imaging. It has become a popular research subject at present. A fast photoacoustic imaging system based on multi-element linear transducer array and phase-controlled focus method was developed and tested on phantoms and tissues. A Q switched Nd:YAG laser operating at 532nm was used in our experiment as thermal source. The multi-element linear transducer array consists of 320 elements. By phase-controlled focus method, 64 signals, one of which gathered by 11-group element, make up of an image. Experiment results can map the distribution of the optical absorption correctly. The same transducer array also can operate as a conventional phase array and produced ultrasound imaging. Compared to other existing technology and algorithm, the PA imaging based on transducer array was characterize by speediness and convenience. It can provide a new approach for tissue functional imaging in vivo, and may have potentials in developing into an appliance for clinic diagnosis.
Photoacoustic tomography is a potential and noninvasive medical imaging technology. It combines the advantages of pure optic imaging and pure ultrasound imaging. Photoacoustic signals induced by a short pulse laser cover a wide spectral range. We have explored the frequency spectrum of absorbers with different sizes and the influence of photoacoustic signals with different spectral components on photoacoustic imaging. The simulations and experiments demonstrated that the major frequency ranges of photoacoustic pressures of absorbers with diameters of ~cm, ~mm and hundreds of mm are about 20kHz~300kHz, 70kHz~2.5MHz and 400kHz~20MHz, respectively. The low spectral components of photoacoustic signals contribute to the non-boundary region of absorbers, and the high spectral components contribute to small structures, especially, to boundaries. It suggests that the ultrasonic transducers used to detect photoacoustic pressures should be designed and selected according to the frequency ranges of absorbers.
Photoacoustic tomography is a potential and noninvasive medical imaging technology. It combines the advantages of pure optic imaging and pure ultrasound imaging. Photoacoustic signals induced by a short pulse laser cover a wide spectral range. We have explored the influences of attenuation of photoacoustic signals, which vary according to frequencies, to the quality of reconstructed photoacoustic images. It reveals that the attenuation of low frequent components are less than that of high frequencies, and the latter is more important for photoacoustic imaging with high resolution. Based on the ultrasonic attenuation theory, the photoacoustic imaging with rectification of the attenuation of different frequent component was performed. The experiments results show that this method improves the resolution of reconstructed images, which improves from 0.3mm to 0.2mm. A Q-switched Nd:YAG laser operating at 1064nm was used as light source. The laser had a pulse width of 6ns and a repetition frequency of 20Hz. A needle PVDF hydrophone with diameter of 1mm was used to detect photoacoustic signals.
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