In recent years, photoacoustic imaging has become a new non-destructive medical imaging technology. In this paper, a photoacoustic imaging technology for human bladder cancer was proposed, which combined transurethral endoscopic photoacoustic excitation in bladder cavity with a transrectal photoacoustic signal detection. By establishing a three-dimensional( 3D) optical model of bladder tissue, the distribution of light energy deposition in the bladder tissue was obtained through the 3D Monte Carlo method. The velocity potential was used to calculate the photoacoustic signal, and the scanning photoacoustic image of bladder tissue was reconstructed. The results showed that the proposed photoacoustic imaging technique with transurethral photoacoustic excitation in bladder cavity was expected to detect early bladder cancer nondestructively.
Ultrasound-modulated optical tomography (UOT) is a promising nondestructive technique for biological tissue imaging, and possesses both high sensitivity of optical imaging and good spatial resolution of ultrasonic imaging. In this paper, ultrasound-modulation of near infrared light is used to detect foreign bodies buried in turbid media. Experimental resultsshow that there is a linear increasing relationship between the modulation depth of acousto-optic signals andtheabsorption and scattering coefficients of turbid media. The position and shape of the foreign body (scatterer and absorber)buried in the tissue simulation sample can be reconstructed by the acousto-optic signals in UOT, and the strengthofscattering objects and absorption objects can be detected. But the scattering objects and absorption objects aren’t distinguishable in the imaging.
Biological tissue is a multiple random scattering medium. The study of the propagation of acousto-optic signals in biological tissues is an important and complex issue in acousto-optical tomography(AOT). In this paper, the finite element simulation software COMSOL Multiphysics is used to simulate the propagation of acousto-optic signal modulated by ultrasound in double-layer tissue. The effects of different types of ultrasounds on acousto-optic signals in tissues are studied. The influence of the optical properties of the target tissue and non-target tissue on the acousto-optic signal in the double-layered tissue is also discussed. The simulation results show that the waveform of the acousto-optic signal is very similar to that of the ultrasonic wave. The acousto-optic signal presents a periodic variation as the ultrasonic frequency changes. The peak-to-peak value and average value of the acousto-optic signal are affected by the optical properties of double-layer tissue. However, the modulation depth of the acousto-optic signal only depends on the optical characteristics of the tissue in the ultrasound focal zone (target tissue), and has nothing to do with the optical characteristics of the tissue outside the ultrasound zone (non-target tissue). The modulation depth has a good antiinterference performance, which is conducive to image processing and reconstruction in AOT.
Ultrasound-modulated optical tomography (UOT) combines optical and acoustic techniques, and has high spatial resolution of ultrasonic location and high sensitivity of optical detection. In this technique, a focused ultrasound is used to locate and label the scattered light. It determines the spatial resolution of UOT and the modulation efficiency of the scattering light. Four kinds of acousto-optic signals modulated by 1, 2.25, 5, and 10 MHz center frequencies of impulse ultrasound are obtained in this letter. The frequency spectrum of these four kinds of acousto-optic signals are achieved by Fast Fourier Transform (FFT). By analyzing the spectrum information of acousto-optic signals modulated by ultrasound at different frequencies, we can find useful feature information and choose an appropriate parameter of ultrasonic probe to improve the signal-to-noise ratio and sensitivity of UOT.
In recent years, bladder cancer has been a serious health concern around the world. As a rapidly growing imaging technique, photoacoustic imaging (PAI) was now being explored as an alternative for bladder imaging due to its non-invasive and non-ionizing nature. It was essential to know absorbed light distribution in bladder tissue which would influence the imaging depth and range of PAI. In the paper, optical model of human bladder was established, in which diffused light source was delivered through the urethra into the bladder cavity for endoscopic illumination. And Monte Carlo simulation method was adopted to calculate the light absorption distribution (LAD) in the bladder tissue. The shape and wavelength of light source were investigated in the simulation. The relevant conclusions would be significant for optimizing the light illumination in a PAI system for bladder cancer detection.
KEYWORDS: Photoacoustic spectroscopy, Prostate, Monte Carlo methods, Signal generators, Absorption, Imaging systems, Photoacoustic imaging, Tissue optics, Light sources, Signal detection
Photoacoustic image has recently emerged as a promising imaging modality for imaging prostate cancer.This paper made a qualitative analysis of photoacoustic signal generation according to the relationship between photoacoustic signal and the changes of light absorption energy. A 3D prostate optical model embedded tumors was established based on human prostate morphology through programming. The light energy distribution in the prostate with pulsed light was obtained by use of Monte Carlo method. The time-dependent spatial distribution of light absorption energy was obtained for photoacoustic signal generation at different positions. Comparison has been made between each other. Meanwhile, photoacoustic imaging experiment has been carried out. Our work might also be helpful for future simulation of photoacoustic imaging and investigation of detection sensitivity and imaging depth of photoacoustic imaging system.
Faithful reconstruction, which is a key phenomenon in optical data storage, is significant in polarization holography and has attracted much attention. It is defined as the reconstructed wave being identical to the signal wave. We design an experiment to observe the faithful reconstruction of elliptical polarization holography in which the two orthogonal elliptical polarization waves are applied in the recording stage. In the experiment, phenanthrenequinone-doped poly methyl methacrylate is used as the recording material, and the angle between the signal and reference waves is ∼56 deg. We control the exposure time of recording material to observe the faithful reconstruction of orthogonal elliptical polarization holography. How to obtain the faithful reconstruction is interesting work; therefore, we propose a prerequisite for faithful reconstruction. Although the prerequisite is derived from orthogonal elliptical polarization holography, it could also be applied in orthogonal linear and circular polarization holography. The result may be helpful for understanding the faithful reconstruction of orthogonal polarization holography.
Biological tissue is a kind of complex and highly scattering medium. The study of the ultrasound-modulated scattered light propagation in biological tissue is a fundamental problem that must be solved in acousto-optic tomography (AOT). Due to the action of the ultrasonic field, the optical properties of the scattering medium change with time-space, and the propagation of light in it becomes more complicated. In this paper, the finite element simulation software COMSOL Multiphysics is used to simulate the propagation of light in biological tissue under the action of different types of ultrasonic field. The effects of ultrasonic field distribution, ultrasonic intensity and frequency on the light diffusion in the scattered medium are studied. The relationship between the ultrasound-modulated scattering light and the optical properties of biological tissue is discussed. The numerical simulation results are in agreement with the experimental results.
With high spatial resolution of ultrasonic location and high sensitivity of optical detection, ultrasound-modulated optical tomography (UOT) is a promising noninvasive biological tissue imaging technology. In biological tissue, the ultrasound-modulated light signals are very weak and are overwhelmed by the strong unmodulated light signals. It is a difficulty and key to efficiently pick out the weak modulated light from strong unmodulated light in UOT. Under the effect of an ultrasonic field, the scattering light intensity presents a periodic variation as the ultrasonic frequency changes. So the modulated light signals would be escape from the high unmodulated light signals, when the modulated light signals and the ultrasonic signal are processed cross correlation operation by a lock-in amplifier and without a chopper. Experimental results indicated that the signal-to-noise ratio of UOT is significantly improved by a lock-in amplifier, and the higher the repetition frequency of pulsed ultrasonic wave, the better the signal-to-noise ratio of UOT.
Improving signal to noise ratio in ultrasound-modulated optical tomography (UOT) is a research topic. Laying apertures
in front of a photomultiplier tube (PMT) can reduce the ambient noise collected by the PMT, and efficiently improve the
signal to noise ratio of UOT. In addition, the effective area of detection and the off-axis position of the PMT would be
varied by changing the aperture size and position in front of the PMT. Experimental results indicated that
ultrasound-modulated signal is dependent on the area of detection. The greater the detector area, the smaller the
ultrasound-modulated signal and its modulation depth. The modulated signal also depended on the off-axis position of
the PMT from the optic axis. In particular, the modulated signal did not reach the biggest value when the PMT just
placed on the optics axis. Choosing appropriate size, position of aperture, can improve the signal to noise ratio and image
contrast.
A new optical technique for continuous, noninvasive monitoring of blood glucose levels based on ultrasonic modulation
of scattering light is proposed. The ultrasound-modulated scattered light has an accurate separation of scattering and
absorption changes in tissue. And the optical scattering and absorbing coefficient of tissue depend on the concentration
of glucose in the extracellular fluid. As the glucose induced to scattering and absorption changes, the ultrasoundmodulated
light also changes. In this paper, a correlation is observed between ultrasound-modulated light intensity as
well as its modulation depth and blood glucose concentration in phantom experiments. In addition, some researches
about ultrasound-modulated signal affected by the temperature of glucose aqueous solution are done. Preliminary
experiments find that this method is a promising noninvasive blood glucose measurement.
In this work, we have studied the propagation of ultrasound modulation scattering signal in multi-layer scattering media.
The relations to the modulation light intensity and its modulation depth contributed by the thickness, absorption
coefficient and scattering coefficient of two- and three- layered scattering media are figured out. The results of Monte
Carlo simulation and experiments show that the modulated depth of the modulated light is only dependent on optical and
ultrasonic properties of scattering media within the ultrasound zoom, and doesn't change in the propagation in
multi-layer scattering media. And the modulated depth is a key factor in ultrasound-modulated optical tomography.
In this presentation, several ultrasound-modulated optical phenomena in a tissue phantom were observed by a pulsed
ultrasound transducer. Some factors affected the modulated signal value were studied including the changing of the
experimental conditions such as the distance between the focused volume of ultrasound beam and the detector as well as
the frequency of ultrasound transducer. The experimental results and the analysis suggest that a compositive parameter
concerning the intensity of the modulated signal, namely the modulation depth which is a key parameter to measure the
scattering property even as a sensor to indicate the glucose concentration.
Because it has the advantages of optical contrast and ultrasonic resolution, the ultrasound-modulated optical tomography
becomes a new and promising method for biomedical imaging. The propagation of the light modulated by ultrasound in
the tissue plays an important role in this new technique. We already proved that the modulated depth of the modulated
light (Identical Modulated Depth, ignoring the background diffused light) was dependent on optical and ultrasonic
properties of tissue within the ultrasound zoom, and didn't change in the propagation in the recent research. However, the
modulation depth detected at the surface in experiment (Real Modulated Depth) differs from the Identical Modulated
Depth, which includes the background diffused light. In Diffuse theory and experiments it is shown that the Real
Modulated Depth is dependent on the propagation process of the diffused light. The relations to the Real Modulated
Depth contributed by the tissue thickness, optical properties, etc. are figured out in this paper. So the Real Modulated
Depth detected in the experiments should be transformed into the Identical Modulated Depth (a dominant parameter to imaging) by a set of iterated algorithm decoding. All these should contribute to the practical applications of ultrasound-modulated optical tomography.
Ultrasound-modulated optical tomography is a promising and noninvasive method for biomedical imaging. The
advantage of this technology is its combination of optical contrast and ultrasonic resolution. In order to reconstruct the
tissue imaging effectively and reliably, the propagation of the light modulated by ultrasound in the tissue should be
understood extensively. In our opinion, there are three light transport processes in tissue as follows: Firstly, the incident
light goes from the surface to the focused region. If the distance, tagged as Iis long enough (Z>>mfp, mean free path).
the light transport obeys diffuse theory. Secondly, the diffuse light can be modulated in the focused region at Z due to the
light-sound interaction. Finally, the modulation light from the Z can be regarded as a spot light source which emits the
ballistic or snake photons to reach the surface and so as to be collected by a detector outside of tissue in the third process.
the propagation of the diffused light modulated by ultrasound play an important role in particularly because it reflects
some information about the optical and ultrasonic properties of tissue. Based on the Monte Carlo simulation, the relations
to the modulation light intensity and its modulation depth contributed by the tissue thickness, optical properties, etc. are
figured out and supported by an equivalent experiment and at an extended condition also agree with the diffuse theory.
As a promising and noninvasive method for biomedical imaging, the advantage of ultrasound-modulated optical tomography is its combination of optical contrast and ultrasonic resolution. In order to reconstruct the tissue imaging effectively and reliably, the propagation of the diffused light modulated by ultrasound in the tissue should be understood extensively. In the process, the propagation of the diffused light modulated by ultrasound play an important role in particularly because it reflects some information about the optical and ultrasonic properties of tissue. Based on the diffuse theory, the relations to the modulation depth contributed by the tissue thickness, optical properties, irradiation configuration, etc. are figured out at an extended condition.
Ultrasound modulated optical tomography, a combination of optical and acoustic technology, has become a noninvasive biomedical tomography with promising future. However for long days its spatial resolution was always limited by ultrasound waist size. In this paper a new method using deconvolution algorithm was suggested to solve this problem. Ultrasound modulated optical signals were processed by deconvolution algorithm before they are used for image reconstruction. Both theory analysis and numerical calculation results have shown that the spatial resolution could be greatly improved and image quality became better. This method requires no modification of optical geometry and detection system, only appropriate mathematical processing was needed. It is believed to be a simple, practical and effective way in realizing super resolution in ultrasound modulated optical tomography.
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