The ongoing success of three-dimensional (3D) cinema fuels increasing efforts to spread the commercial success of 3D to new markets. The possibilities of a convincing 3D experience at home, such as three-dimensional television (3DTV), has generated a great deal of interest within the research and standardization community. A central issue for 3DTV is the creation and representation of 3D content. Acquiring scene depth information is a fundamental task in computer vision, yet complex and error-prone. Dedicated range sensors, such as the Time of-Flight camera (ToF), can simplify the scene depth capture process and overcome shortcomings of traditional solutions, such as active or passive stereo analysis. Admittedly, currently available ToF sensors deliver only a limited spatial resolution. However, sophisticated depth upscaling approaches use texture information to match depth and video resolution. At Electronic Imaging 2012 we proposed an upscaling routine based on error energy minimization, weighted with edge information from an accompanying video source. In this article we develop our algorithm further. By adding temporal consistency constraints to the upscaling process, we reduce disturbing depth jumps and flickering artifacts in the final 3DTV content. Temporal consistency in depth maps enhances the 3D experience, leading to a wider acceptance of 3D media content. More content in better quality can boost the commercial success of 3DTV.
Lens-free inline Holographic Microscopy (LHM) holds great promise for biomedical and industrial applications thanks to its conceptual simplicity. However, the challenge lies in achieving an image quality comparable to conventional microscopes. We demonstrate a high-throughput LHM system that is able to resolve 1.23μm-thin lines on a standard USAF 1951 test target with 1.67μm pixels at the full field-of-view (>29mm2). The system is based on a unique multiwavelength iterative-phase-retrieval method, using customized hardware and real-time post-processing software. We have evaluated our system in experiments ranging from single-cell inspection to in-vitro imaging of stem-cell colonies.
In this paper, we present a hardware design of stereo matching for depth extraction. It is capable of matching
high-definition images at real-time speed, producing high-quality disparity maps. The stereo algorithm comprises
three major components, i.e. census transform, dynamic programming and local-adaptive voting. The census
transform makes our method robust to radiometric differences. The dynamic programming method propagates
information along scanlines by imposing a smoothness criterion. The local-adaptive voting further improves the
matching quality, utilizing the correlation between intensity images and disparity maps. The whole algorithm
is prototyped on a FPGA platform, effectively harnessing the power of parallel computing. With a working
frequency of 65MHz, our design can produce high-quality 1024×768 disparity maps at 60fps.
In this study, photoacoustic imaging is utilized to probe information from oncogene surface molecules of cancer cell with
the aid of specific targeting. The ultimate goal is to provide prediction of clinical outcome and treatment response of
anti-cancer drugs. Different from single targeting in most research, we accomplished multiple targeting to obtain a
molecular profile potentially representing tumor characteristics or to locate the heterogeneous population in one lesion.
By conjugating different antibodies to gold nanorods corresponding to different peak absorption bands, multiple
targeting and simultaneous detection with photoacoustic imaging can be achieved with laser irradiation at the respective
peak optical absorption wavelength. Her2 and EGFR were chosen as our primary target molecules. The targeting
complex was evaluated in two types of oral cancer cells, OECM1 and Cal27. The OECM1 cell line overexpresses Her2
but has low expression of EGFR, while Cal27 cell line expresses both antibodies. Also, the targeting efficacy to OECM1
can be further improved by using mixed nanoprobes. The cancer cells were induced on the back of the mice by
subcutaneous injection. The captured images show that both cancer cells exhibit a higher photoacoustic response
(maximum 3 dB) than control groups with specific targeting, thus demonstrating the feasibility of multiple selective
targeting with bioconjugated gold nanorods. Images of multiple targeting with mixed nanoprobes of OECM1 cells also
reveal further enhancement of targeting (4 dB). The results showed potential of in vivo photoacoustic molecular imaging,
providing a better guidance for diagnosis and treatment of cancer.
Several photoacoustic (PA) techniques, such as photoacoustic imaging, spectroscopy, and parameter sensing,
measure quantities that are closely related to optical absorption, position detection, and laser irradiation parameters. The
photoacoustic waves in biomedical applications are usually generated by elastic thermal expansion, which has
advantages of nondestructiveness and relatively high conversion efficiency from optical to acoustic energy. Most
investigations describe this process using a heuristic approximation, which is invalid when the underlying assumptions
are not met. This study developed a numerical solution of the general photoacoustic generation equations involving the
heat conduction theorem and the state, continuity, and Navier-Stokes equations in 2.5D axis-symmetric cylindrical
coordinates using a finite-difference time-domain (FDTD) scheme. The numerical techniques included staggered grids
and Berenger's perfectly matched layers (PMLs), and
linear-perturbation analytical solutions were used to validate the
simulation results. The numerical results at different detection angles and durations of laser pulses agreed with the
theoretical estimates to within an error of 3% in the absolute differences. In addition to accuracy, the flexibility of the
FDTD method was demonstrated by simulating a photoacoustic wave in a homogeneous sphere. The performance of
Berenger's PMLs was also assessed by comparisons with the traditional first-order Mur's boundary condition. At the
edges of the simulation domain, a 10-layer PML medium with polynomial attenuation grading from zero to 5x106
m3/kg/s was designed to reduce the reflection to as low as -60 and
-32 dB in the axial and radial directions, respectively.
The reflections at the axial and radial boundaries were 32 and 7 dB lower, respectively, for the 10-layer PML absorbing
layer than for the first-order Mur's boundary condition.
A quantitative flow measurement method that utilizes a sequence of photoacoustic images is described. The method is based on the use of gold nanorods as a contrast agent for photoacoustic imaging. The peak optical absorption wavelength of a gold nanorod depends on its aspect ratio, which can be altered by laser irradiation (we establish a wash-in flow estimation method of this process). The concentration of nanorods with a particular aspect ratio inside a region of interest is affected by both laser-induced shape changes and replenishment of nanorods at a rate determined by the flow velocity. In this study, the concentration is monitored using a custom-designed, high-frame-rate photoacoustic imaging system. This imaging system consists of fiber bundles for wide area laser irradiation, a laser ultrasonic transducer array, and an ultrasound front-end subsystem that allows acoustic data to be acquired simultaneously from 64 transducer elements. Currently, the frame rate of this system is limited by the pulse-repetition frequency of the laser (i.e., 15 Hz). With this system, experimental results from a chicken breast tissue show that flow velocities from 0.125 to 2 mm/s can be measured with an average error of 31.3%.
In this paper, an efficient algorithm for quantitative reconstruction of optical absorption coefficient in backward mode
photoacoustic imaging is presented. Compared to forward mode and sideward mode (tomographic) imaging, the setup of
backward mode imaging generally has a wider range of clinical applications. However, due to the limited detection
angles, quantitative image reconstruction has also been difficult. Previously, we proposed a method for reconstruction of
optical energy deposition in backward mode imaging. This method is derived from the photoacoustic wave equations
with line focusing, with which the focusing is utilized to reduce the reconstruction problem from three dimensions to one
dimension. In this paper, we extend the previous reconstruction method for absorbed optical energy to a two-step
procedure for optical absorption coefficient. By adding the second step, backward mode photoacoustic imaging becomes
more quantitative as the image is directly related to the inherent properties of an image object. In the proposed method,
comparison between the reconstructed and the predicted absorbed energy is then iteratively performed to find the optical
absorption distribution. Numerical simulations are conducted to verify efficacy of this method. The errors in
reconstructed optical absorption coefficient are generally within 10%. Phantom experiments are also performed. The
results are presented with a discussion on effects of object position and geometry.
Cancer cells presented altered surface molecules to encourage their growth and metastasis. Expression of oncogeneic surface molecules also play important roles in the prediction of clinical outcome and treatment response of anti-cancer drugs. It is thus conceivable that imaging of cancer lesions while simultaneously obtaining their pathogenic information at molecular level of as many oncogenic proteins as possible is of great clinical significance. Gold nanoparticles have been used as a contrast agent for photoacoustic imaging. In addition, gold nanoparticles can be bioconjugated to probe certain molecular processes. An intriguing property of gold nanoparticles is its ability to tailor its optical properties. For
example, size effects on the surface plasmon absorption of spherical gold nanoparticles have shown that the peak optical absorption red-shifts with the increasing particle size. In addition, the optical absorption spectrum of cylindrical gold nanoparticles (i.e., gold nanorods) exhibits a strong absorption band that is directly related to the aspect ratio. With these unique characteristics, selective targeting can be achieved in photoacoustic molecular imaging. Specifically, gold nanorods with different aspect ratios can be bioconjugated to different antibodies. Multiple targeting and simultaneous detection can then be achieved by using laser irradiation at the respective peak optical absorption wavelength. In this study, photoacoustic multiple targeting using gold nanorods is experimentally demonstrated. We have chosen Her2 and CXCR4 as our primary target molecule as Her2 expression is associated with growth characteristics and sensitivity to Herceptin chemotherapy. On the other hand, CXCR4 expression predict the organ-specific metastatic potential of the cancer cells for clinical intervention in advance. Monoclonal antibody (mAb) against Her2/neu was conjugated to nanorods with several different aspect ratios. The agarose gel is suitable for photoacoustic signal acquisition. A wavelength tunable Ti-Sapphire laser was used for laser irradiation and a 1 MHz ultrasound transducer was used for acoustic detection. The optical wavelength of the laser was tuned between 800 nm and 940 nm, corresponding to gold nanorods of an aspect ratio ranging from 3.7 to 5.9. The results clearly show the potential of photoacoustic molecular imaging with multiple targeting in revealing different oncogene expression levels of the cancer cells.
A high frame rate photoacoustic imaging system is described. Applications of this system to perfusion measurements are also presented as a demonstration of its potential usage. The system consists of an ultrasound front-end sub-system for acquisition of acoustic array data. The ultrasound front-end sub-system is also known as the DiPhAS (digital phased array system) which is capable of simultaneously acquiring radio frequency data from 64 transducer channels at a rate up to 40 MSamples/sec per channel. In this study, an ultrasonic linear array with a 5 MHz center frequency was employed as part of the integrated photoacoustic probe. The photoacoustic probe also had two linear light guides mounted on the sides of the ultrasonic array for broad laser irradiation from a Q-switched Nd:YAG pulsed laser. After the acquired ultrasound array data were transferred to a personal computer via a high speed digital I/Q card, dynamic focusing and image reconstruction were done off-line. The 64-channel array data can be acquired and transferred every 4 milliseconds, thus making the frame rate of the system up to 250 Hz. The actual frame rate of the current system is limited by the pulse repetition frequency of the laser at 15 Hz. To demonstrate capabilities of the system, photoacoustic perfusion measurements with gold nanorods were performed. A previously proposed time-intensity based flow estimation technique utilizing the shape transitions of gold nanorods under laser irradiation was employed. Good estimation results were achieved and potential of this high frame rate photoacoustic imaging system is clearly demonstrated.
Optoacoustic imaging takes advantage of high optical contrast and low acoustical scattering, and has found several biomedical applications. Optoacoustic signals are produced by irradiating laser pulse to a sample, which absorbs light energy and generates ultrasound waves. In the common backward mode optoacoustic imaging, a laser beam illuminates the image object and an acoustic transducer located on the same side as the laser beam. A cross-sectional image is formed by laterally scanning the transducer. Although the laser beam width is generally narrow, strong optical scattering in tissue broadens the optical illumination energy and thus degrades the lateral resolution in optoacoustic image. Therefore, a time-domain delayed and summed technique has been proposed to locate the optoacoustic sources in the tissue. In this study, a combination of synthetic aperture focusing technique and coherence weighting is proposed. Specifically, the focusing quality of the synthetic aperture technique is further improved by using the signal coherence as an image quality index. In this article, we demonstrate the efficacy of the proposed method using numerical simulations and phantom experiments with a phantom comprising hair threads in a 1% milk solution. The results show that the proposed technique improved lateral resolution by 4-8 times and the signal-to-noise ratio by 7-23 dB over the conventional techniques.
The indicator-dilution theory has been used for flow rate measurements in various imaging modalities, including magnetic resonance imaging, computed tomography and ultrasound. The experimental procedure generally involves the injection of a dose of indicator (i.e., the contrast agent), after which the concentration of the agent is monitored as a function of time; it is therefore also known as the time-intensity method. Although the time-intensity method has been widely applied to other imaging modalities, it has not been demonstrated with optoacoustic imaging. In this study, we experimentally test the hypothesis that quantitative blood flow measurements are feasible with the time-intensity based method in optoacoustic imaging. Gold nanospheres (broad band absorption spectrum peaks at 520 nm) were used as the optoacoustic contrast agent. The imaging system consisted of a frequency-doubled Nd:YAG laser operating at 532 nm for optical illumination, and an ultrasonic single crystal transducer with a center frequency of 3.5 MHz and a focal depth of 7 cm for detection. The volumetric flow rate ranged from 0.23 to 4.29 ml/sec, and the volume of the mixing chamber was from 30 to 80 ml. Results show good agreement between the measured mean transit times and the predicted time constants (correlation coefficient higher than 0.88), thus demonstrating the feasibility of the time-intensity based flow measurement technique. In addition to describing the method and experimental results, issues regarding the system sensitivity and estimation of the dilution transfer function are also discussed.
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