SignificanceThe classification of melasma is critical for correct clinical diagnosis, treatment selection, and postoperative measures. However, preoperative quantitative determination of melasma type remains challenging using conventional Wood’s lamp and optical dermoscopy techniques.AimUsing photoacoustic microscopy (PAM) to simultaneously obtain the two diagnostic indicators of melanin and blood vessels for melasma classification and perform quantitative analysis to finally achieve accurate classification, rather than relying solely on physicians’ experience.ApproachFirst, the patients were classified by experienced dermatologists with Wood’s lamp and optical dermoscopy. Next, the patients were examined in vivo using the PAM imaging system. Further, the horizontal section images (X-Y plane) of epidermal melanin and dermal vascular involvement were extracted from the 3D photoacoustic imaging results, which are important basis for PAM to quantitatively classify melasma.ResultsPAM can quantitatively reveal epidermal thickness and dermal vascular morphology in each case and obtain the quantitative diagnostic indicators of melanin and blood vessels. The mean vascular diameter in lesional skin (223.2 μm) of epidermal M+V-type was much larger than that in non-lesional skin (131.6 μm), and the mean vascular density in lesional skin was more than three times that in non-lesional skin. Importantly, vascular diameter and density are important parameters for distinguishing M type from M+V type.ConclusionsPAM can obtain the data of epidermal thickness, pigment depth, subcutaneous vascular diameter, and vascular density, and realize the dual standard quantitative melasma classification by combining the parameters of melanin and blood vessels. In addition, PAM can provide new diagnostic information for uncertain melasma types and further refine the typing.
Accurate localization of blood vessels with image navigation is a key element in vascular-related medical research and vascular surgery. However, current vascular navigation techniques cannot provide naked-eye visualization of deep vascular information noninvasively and with high resolution, resulting in inaccurate vascular anatomy and diminished surgical success rates. Here, we introduce a photoacoustic-enabled automatic vascular navigation method combining photoacoustic computed tomography with augmented and mixed reality, for the first time, to our knowledge, enabling accurate and noninvasive visualization of the deep microvascular network within the tissues in real time on a real surgical surface. This approach achieves precise vascular localization accuracy (<0.89 mm) and tiny vascular relocation latency (<1 s) through a zero-mean normalization idea-based visual tracking algorithm and a curved surface-fitting algorithm. Further, the subcutaneous vessels of minimum diameter (∼0.15 mm) in rabbit thigh and the maximum depth (∼7 mm) in human arm can be vividly projected on the skin surface with a computer vision-based projection tracking system to simulate preoperative and intraoperative vascular localization. Thereby, this strategy provides a way to visualize deep vessels without damage on the surgical surface and with precise image navigation, opening an avenue for the application of photoacoustic imaging in surgical operations.
The small-animal photoacoustic microscope can obtain microscopic imaging of small-animal tissues, and then quantitatively analyzes the blood vessel density, tumor distribution and treatment effect during photodynamic therapy. Through the different imaging modes of the depth-coded photoacoustic microscope, the three-dimensional structural information of the tumor tissue can be reconstructed. In this study, the small-animal photoacoustic microscope was used to quantitatively visualize the density, depth, and distribution of different specific absorbers during photodynamic therapy. This method successfully monitored the tumor's response during treatment, which indicates its good prospect in monitoring of photodynamic therapy. Overall, the small-animal photoacoustic microscope can dynamically monitor and evaluate the impact of photodynamic therapy on tumors, blood vessels, skin irritation and inflammation, etc. This is of great significance for the efficacy and safety evaluation of the development of therapeutic drugs. Therefore, the small-animal photoacoustic microscope has great potential in the biomedical research of basic biology.
Dual-modality photoacoustic/ultrasonic endoscopy has shown to be effective in the identification and staging of colorectal intramural tumors. In this study, we proposed a dual-modality endoscope with a spherical hollow PVDF-based transducer, which achieves center frequency of 34 MHz and -6 dB bandwidth of 15-60 MHz. The PVDF-based transducer will enable the system to achieve a large radial imaging range of more than 1 cm. In vivo imaging of the rabbit rectum proved that the dual-modality endoscope has the ability to perform the tissue stratification of the intestinal wall and the high-resolution visualization of the intestinal wall vascular network.
Microwave-induced thermoacoustic (TA) imaging combines the advantages of high imaging contrast due to electromagnetic absorption and high resolution of the ultrasound technology, and it is a potential alternative imaging technique for biomedical applications, particularly for breast tumor detection. The traditional TA system uses circular-scanning (CS) to obtain complete information to reconstruct a two-dimensional image, however, it needs a large operating space for rotation of the transducers and bulk of coupling medium limiting its medical applications. The linear-scanning (LS) system can overcome these problems partially but usually lose some information and cause image distortion. In this paper, in order to overcome above limitations, a TA imaging system with Sample-Cling-Scanning (SCS) model based on a flexible multi-element transducer is presented. It combines the advantages of both CS and LS modes, and overcome their limitations. Meanwhile, an adaptive back projection algorithm is presented to implement this scanning model. The experimental results show that the proposed system combines advantages including shape adaptation, information integrity, and efficient transmission. These advantages make it a preferred system for TA applications, especially in breast tumor detection.
We have developed a multimodality imaging system by optically integrating all-optical photoacoustic microscopy (AOPAM), optical coherence tomography (OCT) and fluorescence microscopy (FLM) to provide complementary information including optical absorption, optical back-scattering and fluorescence contrast of biological tissue. By sharing the same low-coherence Michelson interferometer, AOPAM and OCT could be organically optically combined to obtain the absorption and scattering information of the biological tissues. Also, owing to using the same laser source and objective lens, intrinsically registered photoacoustic and fluorescence signals are obtained to present the radiative and nonradiative transition process of absorption. Simultaneously photoacoustic angiography, tissue structure and fluorescence molecular in vivo images of mouse ear were acquired to demonstrate the capabilities of the optically integrated trimodality imaging system, which can present more information to study tumor angiogenesis, vasculature, anatomical structure and microenvironments in vivo.
A label-free high resolution photoacoustic microscopy (PAM) system for imaging cellular malformation is presented. The carbon fibers were used to testify the lateral resolution of the PAM. Currently, the lateral resolution is better than 2.7 μm. The human normal red blood cells (RBCs) were used to prove the imaging capability of the system, and a single red blood cell was mapped with high contrast. Moreover, the iron deficiency anemia RBCs were clearly distinguished from the cell morphology by using the PAM. The experimental results demonstrate that the photoacoustic microscopy system can accomplish label-free photoacoustic imaging and that it has clinical potential for use in the detection of erythrocytes and blood vessels malformation.
Photoacoustic imaging is a fast growing imaging technology depending on its high optical resolution of optics while taking the advantage of the high penetration depth of ultrasound. In this paper, we demonstrate the new progress in the photoacoustic imaging. Atherosclerosis is characterized by a progressive build-up of lipid in the arterial wall, which is known as plaque. Histological studies demonstrate that the primary cause of acute cardiovascular events is the rupture of atherosclerotic plaques. Lipid and inflammation within the plaque are related to influence the propensity of plaques to disrupt. Photoacoustic intravascular tomography (IVPAT) holds a great advantage in providing comprehensive morphological and functional information of plaques. Lipid relative concentration maps of atherosclerotic aorta were obtained and compared with histology. Furthermore, by selectively targeting the intravascular inflammatory cytokines, IVPAT is also capable of mapping the inflamed area and determining the degree of inflammation.
A method for noninvasive simultaneously detecting hemoglobin oxygen saturation (SO2) and carboxyhemoglobin saturation (SCO) in subcutaneous microvasculature with multi-wavelength photoacoustic microscopy (PAM) is presented. In vitro blood samples mixed with different concentration of carboxyhemoglobin were used to testify the feasibility and accuracy of the PAM. Moreover, fixed-point detection of SO2 and SCO of the vessel in mouse ear were obtained. And the changes of SO2 and SCO from normoxia to carbon monoxia hypoxia were dynamically recorded in vivo. Experimental results demonstrate that the PAM has the capability to detect SO2 and SCO, which has potential application in clinic.
A method for noninvasive viscoelasticity detection of biological tissues using phase-resolved photoacoustic measurement
is presented. We deduced the process of photoacoustic effect on the basis of thermal viscoelasticity theory, and
established the relationship between the photoacoustic phase delay and the viscosity-elasticity ratio for soft solids. Agar
phantoms with different densities and different absorption coefficients were used to verify the dependence of
photoacoustic phase-resolved viscoelasticity measurement. Moreover, viscoelasticity detection of tissues was obtained
with a photoacoustic point scanning system. The photoacoustic phase-resolved method provides a basis for
viscoelasticity detection, which can potentially be used for detection of viscoelastic properties and lesions of biological
tissues.
It is well known that apoptotic cells (AC) participate in immune response. The immune response
induced by AC, either immunostimulatory or immunosuppressive, have been extensively studied.
However, the molecular mechanisms of the immunostimulatory effects induced by PDT-treated AC
remain unclear. Nitric oxide (NO) is an important signal transduction molecule and has been implicated
in a variety of functions. It has also been found to play an important role not only as a cytotoxic
effector but an immune regulatory mediator. In this study, we demonstrate that the PDT-induced
apoptotic tumor cells stimulate the production of NO in macrophages by up-regulating expression of
inducible nitric oxide synthase (iNOS). In addition, we show that AC, through toll-like receptors
(TLRs), can activate myeloid differentiation factor-88 (MyD88), indicating that AC serves as an
intercellular signal to induce iNOS expression in immune cells after PDT treatment. This study
provided more details for understanding the molecular mechanism of the immune response induced by
PDT-treated AC.
Cardiolipin is a unique and ubiquitous diphosphatidylglycerol phospholipid, located exclusively in inner
membrane of mitochondria and particularly intermembrane contact sites. Cardiolipin is essential for
mitochondrial to maintain its functions. Numerous mitochondrial proteins and processes require the presence of
cardiolipin. Recent researches gradually confirm that cardiolipin participates in several mitochondria-dependent
apoptotic steps: interactions between cardiolipin and cytochrome c, Bid and caspase-8 have now been
established. These functions are associated with the redistribution of cardiolipin in mitochondria. However, the
exact mechanism of the redistribution, which happens at the early stage of apoptosis, is still controversial. In this
study, we used 10-N-nonyl-3, 6-bis (dimethylamino) acridine (10-N-nonyl acridine orange), a specific probe for
cardiolipin to monitor changes of cardiolipin redistribution during apoptosis. We demonstrated that during
apoptosis cardiolipin moves to the outer leaflet of mitochondrial inner membrane from the inner leaflet, where it
used to be riched in. We also found that ROS (reactive oxygen species) may have association with the
redistribution of cardiolipin.
Based on the measurement of ultrasonic waves induced by electromagnetic pulses, photoacoustic imaging and
thermoacoustic imaging can reveal optical or dielectric properties of tissues that are closely related to the physiological
and pathological status of tissues and they have became the promising clinical imaging modalities. In this paper, a high
frame rate tomography instrument with 64-channel parallel data-acquisition system was designed and developed for
photoacoustic biomedical imaging. In the system, the pulse-laser-induced ultrasonic signals are converted to voltage
signals by a 128-element linear ultrasound transducer array. The 128-channel signals are acquired by the 64-channel
parallel data-acquisition system twice through the 2:1 multiplexer, and the OPO (optical parametric oscillator) laser
provides laser with a pulse repetition rate of 15 Hz. Therefore, the acquisition rate can reach about 7 frames per second
and photoacoustic images can be displayed dynamically. Based on the above signal acquisition system, biomedical
application of photoacoustic imaging was explored and successfully performed. Fast photoacoustic tomography for
flow-field visualization was demonstrated by flowing object. Thermoacoustic tomography was developed to detection of
low-density foreign targets in small animals which was indistinguishable with X-ray. All the experimental results show
that photoacoustic and thermoacoustic imaging with fast parallel data-acquisition system is a highly-efficient approach
for functional imaging of biomedical tissues.
A full-view photoacoustic tomography system with dual-scanning using a linear transducer array for fast imaging of
complicated blood network was developed. In this system, a 128-element linear transducer array was used to detect
photoacoustic signals by combined scanning of electronic scan and mechanical scan. An improved limited-field filtered
back projection algorithm with directivity factors was applied to reconstruct the distribution of the absorbed optical
energy deposit. An in vivo experiment on a mouse brain was performed to evaluate the ability of this composite system.
A clear view of the cerebrovascular network on the brain cortex was acquired successfully. Furthermore, the reconstruct
images with different number of scanning positions were also investigated and analyzed to induce a compromised
proposal between scanning time and scanning number. The experimental results demonstrate the multi-element
photoacoustic imaging system has the potential to acquire the time-resolved functional information for fundamental
research of small animal brain imaging.
KEYWORDS: Single walled carbon nanotubes, Photoacoustic spectroscopy, Molecular imaging, Tumors, In vivo imaging, Absorption, Blood, Absorbance, Transducers, In vitro testing
Single-walled carbon nanotubes (SWNT) in a poly(ethylene)ghycol solution are a biocompatible transporters with strong optical absorption in the near-infrared region, in which the biological tissue is almost transparent with very low absorbance. Here, antibody-functionalized SWNTs for tumor early detection with photoacoustic molecular imaging in vivo are reported. To lay the groundwork for this goal and insure system stability, images were collected in tissue simulating phantoms to determine appropriate detectable concentrations of SWNTs. Preliminary in vitro and in vivo results showed that a high contrast and a high efficient targeting of integrin v3 positive U87 human glioblastoma tumours in mice could be achieved. The nontoxicity of functionalized SWNTs has also been demonstrated in our experiment; this feature ensures that SWNTs can be used for clinical applications. This study suggests that photoacoustic molecular imaging with antibody-functionalized SWNTs has the potential to be an effective early tumor diagnosis method.
As a novel hybrid imaging modality, photoacoustic (PA) imaging combines the merits of high optical contrast, good ultrasonic resolution and sufficient imaging depth, which may be of great benefit to noninvasively detect and monitor the pathological changes of subcutaneous vasculature, e.g., congenital vascular tumor and vascular malformation. In this paper, we apply a set of photoacoustic imaging system to image a sample of subcutaneous blood vessels, which is used to simulate the location of human's subcutaneous vasculature. Furthermore, an image of subcutaneous vasculature of the abdomen in a mouse is acquired in vivo. Laser pulses at a wavelength of 532 nm from a Q-switched Nd:YAG laser are employed as light source to generate PA signals in the experiments, because the optical absorption of whole blood is much stronger than that of other tissues at this wavelength. A needle polyvinylidene fluoride (PVDF) hydrophone with a diameter of 1mm is used to capture PA signals through a circular scan. The experimental results show that detailed structural information of subcutaneous vasculature, such as the shape and position of the blood vessels and the vessel branching, is clearly revealed by the PA imaging system. The spatial resolution of the PA imaging system reaches 80μm. Moreover, the reconstructed image of a mouse's abdomen in vivo demonstrates that this technique is suitable for noninvasive subcutaneous vasculature imaging. All of the results prove that the PA imaging can be used as a helpful tool for monitoring the pathological changes of subcutaneous vasculature.
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.
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.
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.
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.
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.
In this paper, Influences of the acoustic path difference on photoacoustic (PA) images caused by mismatch of ultrasonic
velocities were studied. We first proposed using the concentration-adjustable glycerite as an ultrasonic transmitting
medium. By switching a appropriate concentration of the glycerite, it can make the velocities of the PA signals keep
constant between transmitting medium and biological tissues, and avoid the acoustic path difference (APD) in image
reconstruction. The experiments demonstrate that the acoustic path difference influences the imaging qualities badly:
especially, the spatial resolution of PA image is extremely reduced. After matching ultrasonic velocity by glycerite the
contrast of the reconstructed image is improved greatly and the background artifacts are reduced obviously. The spatial
resolution of the reconstructed image is improved from 0.5mm to
0.15mm. It has great practical significance for applying
photoacoustic tomography to noninvasive clinic diagnosis of cancer.
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