A photoacoustic tomography imaging system using a low-coherence interferometer with rapid detection of phase modulation was designed, fabricated, and tested for biologic imaging. A noncontact probing technique was applied to improve the practicability of the system. The technique is experimentally verified by the image of a simulated tissue sample and the blood vessels within a mouse ear flap (pinna) in vivo. The system’s axial and lateral resolutions are evaluated at 45 and ~15 μm, respectively. The system’s imaging depth is 1mm in a special phantom. The results show that the system has the feasibility to be used as a photoacoustic tomography imaging method, and it may provide a kind of possibility of noncontact real-time PAT.
A simultaneous photoacoustic (PA) tomography imaging technique in multilayer samples was developed. Instead of using the PA image reconstruction methods on the basis of complex algorithms, obtaining a two-dimensional PA image in real time is available by using an acoustic lens that has the ability of parallel imaging. The imaging system can acquire the complete PA signals of high signal-to-noise ratio from all the object planes by utilizing the advantages of the acoustic lens with long focal depth and a fast data acquisition system with a high sampling rate. With the time-resolved technique, the PA signals from different object planes can be distinguished and then the high optical contrast multilayer PA images can be reconstructed simultaneously without any algorithms. The experimental results show that the reconstructed sections agree well with the original samples.
This study aims to develop a simultaneous photoacoustic tomography imaging technique in multilayer media. With an
acoustic lens which has the ability of parallel imaging instead of other PA image reconstruction methods on the basis of
complex algorithms, obtaining a two-dimensional (2D) PA image in real-time is available. Combining the advantages of
the acoustic lens which has long focal depth and the fast data acquisition system, the new system is particularly excellent
that it can acquire the complete PA signals from all the object planes. With the time-resolved technique, the PA signals
from different object planes can be distinguished. As a result, the multilayer PAT images can be reconstructed
simultaneously without any complicated reconstruction algorithms. According to the experimental results, the
reconstructed multilayer images agree well with the original samples.
We describe a new method for evaluating the viscoelastical characterization of biological tissue by photoacoustic technique in this paper. The amplitude attenuation curse of the tissue photoacoustic signals (the stress waves) induced by Q-YAG laser provides necessary data for us to work out the decay time of the stress waves. According to the theory of viscoelasticity, the decay time is equal to the tissue viscosity-elasticity ratio. The result we get from measuring gelatin shows the viscosity-elasticity ratio of Kelvin-Voigt model tissue obtained by photoacoustic measurement almostly equals that by conventional rheometer. The agreement is almost 97%. Furthermore, we firstly apply the method to measure the tissue viscosity-elasiicity ratio of Maxwell model. From the theorical analysis and the experimental result, we can conclude that the method can be applied to any model tissue, because it is only related with its acoustic impedance, having nothing to do with tissue state. In short, photoacoustic measurement is real-time, noninvasive and highly sensitive and repetitive. Based on the virtues mentioned above, it can be widely applied to biology and medicine.
Optoacoustic tomography can be applied into medical imaging, which can detect the light absorption distribution of
target hidden inside scattering media. When a short laser pulse illuminates the optical turbid media, such as biological
tissue, the media will generate ultrasound pulses, which is linearly proportional to the optical absorption of the media.
The acoustic pressure distribution can be imaged with an acoustic lens. Similar to an optically imaging system, the
optoacoustic signals from a plane in tissue require the same delay time to reach a detecting plane. While the optoacoustic
signals from different planes in media require different delay time to reach an image plane. A BOXCAR was used to go
on with the same delay-time, and a 64-element linear transducer array was one-dimensional scanned on an imaging plane,
and thus the acoustic pressure distribution was acquired. The signals were recorded and reconstructed by a computer. By
scanning the sampling gate of BOXCAR, the optoacoustic images of different planes in media could be obtained. The
experimental result indicates that the system is able to obtain optoacoustic tomography images of targets hidden optical
turbid media, and the reconstructed images agree well with the original samples. The results show that the lateral
resolution is about 5mm and the axial resolution is about 1.5mm.
In general, the high resolution of a microscopy could be acquired by increasing the NA (numerical aperture) of lens, and simultaneously increasing the luminous flux. But many experiments shows: in turbid media, the NA of the lens we use is larger, the radius of focal spot is larger and the resolution decreases on the contrary. Because of highly scattering, there are different characters of focusing and propagation in turbid media .We simulate the process of photons motion in turbid media by means of Monte Carlo method according to a known model with representative parameter: changing the NA of lens in the program, the gray-scale images of the light spot in various layer are obtained. We also plot two figures; (1) distribution of the normalized light intensity versus the transverse axis; (2) the radius of light spots as a function of depth. In the figures: the trends of distribution of the normalized light intensity are coincident and centralized; when lens with larger NA is used, the normalized light intensity curve is further from the axis; it is also found the size of the focal spot is bigger and light beams focus in turbid media deeper. All above expound: the NA of the lens is larger; the radius of focal spot is larger in turbid media. In addition, it also suggests various factors including scattering, absorption and scalar diffraction etc must be taken into account when we choose the lens to focus in turbid media.
Total suspended particles (TSP) are one of the main atmospheric pollutants. The ingredients are very complex, mainly including black carbon (C),organic compound, inorganic compound and biologic component, which will do great harm to human's health. During environmental monitoring, the airborne suspended particle always is an index for evaluating the quality of atmosphere. In this article, possible mixture of TSP is proposed to determine its ingredients and content by photoacoustic spectroscopy. The normalized photoacoustic (PA) signal of the sulfur powder, mixtures of sulfur and black carbon in different proportions are obtained respectively. Simulation with linear equation says that the PA signal has a certain relationship with the content of sample. The normalized PA spectroscopy of various materials is acquired via examining the sample of the powder of cupric sulfate mixed with nitro compound (2, 5 -methoxybenzoic-4nitro-dehyde), Portland cement, residual particles of automobile exhaust pipe, ash of power plant's stocks. The experimental results have important reference value to the practical analysis of TSP, it also provides new possible methodology to the environmental monitoring.
The nonlinear imaging theory of second harmonic generation (SHG) and third harmonic generation (THG) in confocal microscopy is presented in this paper. The nonlinear effect of SHG and THG on the imaging properties of confocal microscopy has been analyzed in detail by these imaging theory. It is proved that the imaging process of SHG and THG in confocal microscopy, which is different from conventional coherent imaging or incoherent imaging, can be divided into two different processes of coherent imaging. The three-dimensional point spread functions (3D-PSF) of SHG and THG confocal microscopy are derived based on the nonlinear principles of SHG and THG. The imaging properties of SHG and THG confocal microscopy are discussed in detail according to its 3D-PSF. It is showed that the resolution of SHG and THG confocal microscopy are higher than that of single- and two-photon confocal microscopy.
Photoacoustic (PA) imaging is a new imaging modality, which converts pressure signals received by an array of transducers to a regional distribution of electromagnetic absorption density. In this paper we present an experiment result of a photoacoustic imaging to depths of approximately 3mm for a fabricated absorber within a real tissue, using a 1064-nm pulse YAG laser. The time-resolved stress detection technique was used for PA signal detection and an in-phase- sum-focus algorithm was used for image reconstruction. To obtain excellent temporal resolution, a wideband PVDF membrane hydrophone and a fast-digitizing oscilloscope was used for time-resolved detection of PA signals. A computer controlled translation stage on which the sample cell was fixed was used to a 2D scanning mode. Images of different depth profile was obtained with a lateral and depth resolution of approximately 0.5mm.