We propose and demonstrate a new photoacoustic method to calculate the absolute optical absorption coefficient of a
sample. An exact solution of the wave equation is employed to iteratively fit the detected photoacoustic signals. We fit
the ratio of the amplitudes of the characteristic peaks of photoacoustic signals in order to increase fitting speed and
reduce the influences of background signals. This method is tested by both numerical simulations and experimental
results.
We demonstrate an improved image-forming optics for transmission optical projection tomography (TOPT), with which
the parallel integral throughout an object can be obtained. This is performed by introducing a shutter with an appropriate
diameter at the back focus of the objective lens. We evaluate and compare the performances of the improved and the
conventional TOPT systems with different parameters to obtain the optimal configuration. The optimal reconstruction is
achieved by the improved configuration with α =0.8° ~1.6°, and the spatial resolution reaches 25 μm. The Optimal configuration is validated by TOPT of a phantom sample and a five days chick embryo.
Previous studies on measurements of hemoglobin concentrations and oxygen saturations of human blood by
photoacoustic spectroscopy assume that the exponential attenuation of the optical radiation in blood results in
photoacoustic signals with exponential temporal profiles and absorption coefficients could be extracted by fitting
exponential functions. In this paper, we demonstrate that the detected photoacoustic signals are the convolutions of the
optical absorption distributions in samples, and the first derivative of the temporal profile of the excitation laser, and the
impulse response of the ultrasound detector. The detected photoacoustic signals from absorbers with exponential optical
absorption distributions do not keep exponential profiles. In addition, we present an improved approach to calculate the
absorption coefficient by fitting the detected photoacoustic signal with a function that is the convolution of an
exponential function, and the first derivative of the temporal profile of the laser, and the impulse response of the
detector. This approach is validated by both numerical simulations and experimental results.
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.
A real-time photoacoustic (PA) imaging system based on multi-element linear transducer array was developed and test on phantoms. A Q switched Nd:YAG laser operating at 532 nm and 20Hz repeat rate was used in our experiment as thermal source. The multi-element linear transducer array consists of 320 elements. By phase-controlled method, 64 signals, one of which gathered by 11-group element, make up of an image. It was acquired in only about 3 seconds. Phantom experiment results can map the distribution of the optical absorption correctly. 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.
Ultrasound-modulated optical tomography affords a very promising noninvasive imaging method for biomedical diagnosis. In this technology ultrasonic beams are focused into a scattering medium to provided accurate localization and simultaneously modulate light inside the medium. The detected ultrasound-tagging photons will bring the information of the characteristics of the medium. Based on the high-sensitivity detection technique, we develop a unique reflective configuration that the ultrasound and light are kept coaxial, which is more convenient and practical than other configurations. A completely absorbing object imbedded in a tissue is imaged using the corresponding experimental setup designed by us which is based on the configuration.
Optical projection tomography (OPT) is a potential novel technique for the studies of developmental biology and gene function. It can be used to produce high-resolution 3D images of both fluorescent and nonfluorescent biological specimens. In this technique, the raw data must be mathematically transformed to reconstruct the original specimens using the principle of projection tomography. But in fact, OPT doesn't satisfy the condition of the principle, which requires that the raw data must be parallel linear integral through the specimen. In this paper, based on the fundamental of OPT, we have founded a simulation system by means of simulating a non-correlative diffraction-limited optical system, it is useful for designing or evaluating an OPT system. Using this simulation system, we have explored the influences of different parameters of OPT on reconstructed images. In addition, some suggestions are presented to improve future designs.
In this paper, a novel method for photoacoustic (PA) waves to imaging is proposed. A focused probe ultrasonic beam passes through a specimen and tags the position of the interested PA signal. Reconstruction of the original PA signal in situ is accomplished by demodulating the probe-beam. The method provides new measurement system with to improve signal-to-noise ratio and to take out more original messages. Applied the proper impulse of the detector and filter-back-project algorithm, a 2D PA tomograph was obtained.
Optical projection tomography (OPT) microscopy is a new technique to produce high-resolution 3D images of both fluorescent and nonfluorescent biological specimens. It can be used to rapidly map the tissue distribution of RNA and protein expression in intact embryos or organ systems. In optical projection tomography, the specimen is rotated through 360 degrees around a single axis while held in position for imaging. Light passing through specimens is focused onto a digital camera by lenses. After the images of all angles are taken. Sections of specimen are independently reconstructed using the filtered back projection algorithm. This paper presents general guidelines for designing and constructing an OPT microscopy. These guidelines are based on the difficulties encountered during the process of building the system and cover theoretical concepts, optical imaging system and reconstruction algorithm required to build the system. In addition, some suggestions are presented to improve future designs.
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