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Letters from Optical Engineering

Select this Article OPEN ACCESS		All-fiber vibration sensor based on nano-wire grid polarizer Yun Zhao, Feng Zhou, Hao Wu, Fei Xu, and Yan-qing Lu Opt. Eng. 51, 050504 (14 May 2012); http://dx.doi.org/10.1117/1.OE.51.5.050504 Online Publication Date: May 14, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We propose a novel all-fiber vibration sensor without any bulk optical element by employing an in-line nano-wire grid (NWG) fiber polarizer. The NWG is directly fabricated on tip of a single mode fiber (SMF) by focused ion beam technology. According to effective medium theory, the sub-wavelength NWG has strong polarization properties. In our experiment, the reflection contrast between transverse electric and transverse magnetic modes reaches 14 dB, which is sensitive enough to monitor polarization change induced by photoelastic effect. We apply a sinusoidal vibration signal generated by a piezoelectric transducer onto the fiber. The output light signal from the SMF coincides well with the vibration source. The frequency response of the sensor is measured from 20 Hz to 4 kHz showing great consistency.

Select this Article OPEN ACCESS		Single-heterostructure laser diode producing a 6 W/40 ps optical pulse from a 20 μm stripe width Brigitte Lanz, Juha T. Kostamovaara, Sergey N. Vainshtein, Vladimir M. Lantratov, and Nikolay A. Kalyuzhnyy Opt. Eng. 51, 050503 (10 May 2012); http://dx.doi.org/10.1117/1.OE.51.5.050503 Online Publication Date: May 10, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A compact, low-cost semiconductor laser diode producing 40 ps full width at half maximum (FWHM) single-spike lasing pulses with 6 Watts peak power from a 20 μm stripe width is realized in the form of a simple single-heterostructure, grown by metal-organic chemical vapor deposition. The structure possesses a linearly graded doping profile extending from the p⁺ and n⁺ sides towards the p-n junction. This laser diode is operated under room temperature conditions and applies pumping current pulses (roughly 10 to 20 A/2 to 3 ns FWHM) achievable with a commercially available silicon avalanche transistor as an electrical switch.

Select this Article OPEN ACCESS		Rapid three-dimensional surface mesh segmentation based on region dilation Jun-Bao Li and Meng Li Opt. Eng. 51, 050502 (7 May 2012); http://dx.doi.org/10.1117/1.OE.51.5.050502 Online Publication Date: May 07, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Three-dimensional laser scanned surface segmentation is an important step for computer-aided broken objection patching. Current methods still have high time consuming problem in practical applications. In order to solve this problem, we propose the rapid three-dimensional (3-D) surface segmentation based on region dilation. The procedure includes three steps of point cloud meshing, candidate region generating, and insignificant region eliminating. Some experiments are implemented on the 3-D surface with a Roland LPX-250 3-D laser scanner to testify the feasibility and performance of the proposed algorithm compared with other methods.

Select this Article OPEN ACCESS		Technique for passive scene imaging of gas and vapor plumes using transmission-waveband modulation David M. Benton Opt. Eng. 51, 050501 (4 May 2012); http://dx.doi.org/10.1117/1.OE.51.5.050501 Online Publication Date: May 04, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A new approach to locating gas and vapor plumes is proposed that is entirely passive. By modulating the transmission waveband of a narrow-band filter, an intensity modulation is established that allows regions of an image to be identified as containing a specific gas with absorption characteristics aligned with the filter. A system built from readily available components was constructed to identify regions of NO₂. Initial results show that this technique was able to distinguish an absorption cell containing NO₂ gas in a test scene.

Select this Article OPEN ACCESS		Ultrashort optical pulse phase stabilization using cross-polarization modulation method Hongwei Chen, Xingyao Gu, Minghua Chen, and Shizhong Xie Opt. Eng. 51, 040508 (23 April 2012); http://dx.doi.org/10.1117/1.OE.51.4.040508 Online Publication Date: Apr 23, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A simple method for phase stabilization of ultrashort optical pulse train is presented. By using cross-polarization effect in high nonlinear photonic crystal fiber, optical pulses from a mode-locked fiber laser are wavelength converted with stable phase character. A differential phase shift keying modulation system is successfully built to test the performance of this method.

Select this Article OPEN ACCESS		The demonstration of 10 Gbit/s time division multiplexing and 2.5 Gchip/s quasi-synchronous electrical code division multiplexing access passive optical network prototype system Siyuan Liang, Liqian Wang, Yingying Cao, Zhen Wang, Yamei Han, Dao Wang, and Xue Chen Opt. Eng. 51, 040507 (20 April 2012); http://dx.doi.org/10.1117/1.OE.51.4.040507 Online Publication Date: Apr 20, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The authors propose a novel architecture of passive optical network (PON), which consists of time division multiplexing (TDM) based downstream (10 Gbit/s) and quasi-synchronization (Q-S) electrical code division multiplexing access (ECDMA) based upstream (2.5 Gchip/s), and realize the prototype of this TDM-ECDMA PON. The high speed (2.5 Gchip/s) all digital en/decoding of upstream have been achieved by field-programmable gate array in this prototype. The frames error rate (FER) free transmission of Q-S ECDMA based upstream is demonstrated after 20 km fiber link. Then receiver sensitivity of optical line terminal in upstream transmission can be improved ∼ 6 dB by coding gain compared with traditional 2.5 Gbit/s TDM PON.

Select this Article OPEN ACCESS		112 Gbit/s long-reach real-time coherent passive optical network downlink transmission experiment based on polarization multiplexing quadrature phase shift keying format Xiaobo Meng, Yan Liu, Yue Shi, Xue Chen, Chao Ge, and Weiqin Zhou Opt. Eng. 51, 040505 (20 April 2012); http://dx.doi.org/10.1117/1.OE.51.4.040505 Online Publication Date: Apr 20, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract An 112 Gbit/s real-time coherent passive optical network downlink transmission experiment over 100 km standard single mode fiber with 1∶128 splitting ratio is demonstrated. Adaptive dispersion compensation digital signal processing in the real-time receiver has compensated 100 km dispersion and 50 km dispersion difference with almost no power penalty and 43.5 dB power budget has been achieved.

Select this Article OPEN ACCESS		Optical security device providing fingerprint and designed pattern indicator using fingerprint texture in liquid crystal Keizo Nakayama and Junji Ohtsubo Opt. Eng. 51, 040506 (20 April 2012); http://dx.doi.org/10.1117/1.OE.51.4.040506 Online Publication Date: Apr 20, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract An optical security device providing the function of a fingerprint for authentication along with a designed pattern storage function has been proposed. The proposed device uses the random fingerprint texture in the chiral nematic phase of an ultraviolet-curable liquid crystal. Using photopolymerization along with a mask of the designed pattern, a unique pattern can be fixed in the shape of the designed pattern. The random patterns can be used as a fingerprint for such devices. This proposed device has the potential to be an optical security device and an authenticity or information indicator for the user.

Select this Article OPEN ACCESS		Fabrication of porous silicon-based silicon-on-insulator photonic crystal by electrochemical etching method Furu Zhong, Xiao-yi Lv, Zhen-hong Jia, and Jiaqing Mo Opt. Eng. 51, 040502 (18 April 2012); http://dx.doi.org/10.1117/1.OE.51.4.040502 Online Publication Date: Apr 18, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We present a fast, novel method for building porous silicon-based silicon-on-insulator photonic crystals in which a periodic modulation of the refractive index is built by alternating different electrochemical etching currents. The morphology and reflectance spectra of the photonic crystals, prepared by the proposed method, are investigated. The scanning electron micrograph and atomic force microscopy images show a very uniform structure and the porous silicon demonstrates an 829 nm wide photonic band gap.

Select this Article OPEN ACCESS		Filter design and its application for scanning format conversion Gwanggil Jeon and Jong-Kyu Lee Opt. Eng. 51, 040504 (11 April 2012); http://dx.doi.org/10.1117/1.OE.51.4.040504 Online Publication Date: Apr 11, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract This letter presents the issue of interpolating missing line components at the interlaced signals, a procedure called deinterlacing. A filter design method is introduced in detail, utilizing a least-squares algorithm with training set for the requested deinterlacing filter. A thorough research of deinterlacing performance and system complexity is executed. The proposed filter design and its application on deinterlacing is compared with other conventional filter-based deinterlacing methods in terms of quality measures. It was concluded to show outstanding performance and speed trade-off among the methods compared.

Select this Article OPEN ACCESS		Multidirectional edge-directed interpolation with region division for natural images Yujin Yun, Jonghyun Bae, and Jaeseok Kim Opt. Eng. 51, 040503 (11 April 2012); http://dx.doi.org/10.1117/1.OE.51.4.040503 Online Publication Date: Apr 11, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A multidirectional edge-directed interpolation algorithm that features a region division method is proposed. In the proposed method, an interpolation pixel is newly modeled as a weighted sum of 12 neighboring pixels representing 12 different directions. Each weight is estimated by Wiener filter theory using geometric duality. The proposed method for dividing the interpolation region reduces the heavy computational complexity of the proposed model. Analyzing edge continuities, the model divides an image into three regions, and only strong edge regions are interpolated. Simulation results show that several directional edges are restored clearly in a subjective test, with fair performance in an objective test.

Select this Article OPEN ACCESS		Kernel bandwidth estimation for moving object detection in non-stabilized cameras Carlos Cuevas, Raúl Mohedano, and Narciso García Opt. Eng. 51, 040501 (6 April 2012); http://dx.doi.org/10.1117/1.OE.51.4.040501 Online Publication Date: Apr 06, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Sophisticated strategies have been recently proposed for the detection of moving objects in non-stabilized camera setups. These strategies model both, background and foreground, using spatio-temporal non-parametric estimation. However, as no appropriate methods for dynamical kernel bandwidth are available, high-quality results cannot be obtained in all situations. Here, an automatic and efficient kernel bandwidth estimation strategy for spatio-temporal modeling is proposed. Background kernel bandwidth is estimated via a novel statistical analysis of spatially weighted data distributions, whereas foreground kernel bandwidth is estimated using a mean shift based analysis of previously detected foreground regions.

Select this Article OPEN ACCESS		Two-wavelength holographic recording in thick phenanthrenequinone-doped poly(methyl methacrylate) photopolymer Po-Lin Chen, Sheng-Lung Cho, June-Hua Lin, Shiuan-Huei Lin, Ken Y. Hsu, and Sien Chi Opt. Eng. 51, 030503 (26 March 2012); http://dx.doi.org/10.1117/1.OE.51.3.030503 Online Publication Date: Mar 26, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Two-wavelength holographic recording in thick phenanthrenequinone-doped poly(methyl methacrylate) photopolymer is demonstrated. By using 325 nm laser as a gating illumination during the holographic recording with 647 nm laser, a volume hologram with diffraction efficiency of ∼ 4% can be recorded in a 2 mm thick sample. In addition, the Bragg selectivity curve with clear sinc nulls is demonstrated. These results support further applications as recording media for volume holographic device with extended spectral response and selective recording property.

Select this Article OPEN ACCESS		Fast coding unit decision method based on coding tree pruning for high efficiency video coding Kiho Choi and Euee S. Jang Opt. Eng. 51, 030502 (20 March 2012); http://dx.doi.org/10.1117/1.OE.51.3.030502 Online Publication Date: Mar 20, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A fast coding unit (CU) decision method is proposed for high efficiency video coding (HEVC) by determining early the CU sizes based on coding tree pruning. One of the most effective, a newly introduced concept in HEVC, is variable CU size. In determining the best CU size, the reference encoder of the HEVC tests every possible CU size in order to estimate the coding performance of each CU defined by the CU size. This causes major computational complexity within the encoding process, which should be overcome for the implementation of a fast encoder. A simple tree-pruning algorithm is proposed that exploits the observation where the subtree computations can be skipped if the coding mode of the current node is sufficient (e.g., SKIP mode). The experimental results show that the proposed method was able to achieve a 40% reduction in encoding time compared to the HEVC test model 3.0 encoder with only a negligible loss in coding performance. The proposed method was adopted in HEVC test model 4.0 encoder at JCT-VC 6th meeting.

Select this Article OPEN ACCESS		Holographic measurement of thermal distortion during laser spot welding Ingemar Eriksson, Peter Haglund, John Powell, Mikael Sjödahl, and Alexander Friedrich Hermann Kaplan Opt. Eng. 51, 030501 (8 March 2012); http://dx.doi.org/10.1117/1.OE.51.3.030501 Online Publication Date: Mar 08, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Welding distortion is an important engineering topic for simulation and modeling, and there is a need for experimental verification of such models by experimental studies. High-speed pulsed digital holography is proposed as a measurement technique for out-of-plane welding distortion. To demonstrate the capability of this technique, measurements from a laser spot weld are presented. A complete two-dimensional deformation map with submicrometer accuracy was acquired at a rate of 1000 measurements per second. From this map, particular points of interest can be extracted for analysis of the temporal development of the final distortion geometry.

Select this Article OPEN ACCESS		Automatic human body modeling for vision-based motion capture system using B-spline parameterization of the silhouette Antoni Jaume-i-Capó, Javier Varona, Manuel González-Hidalgo, Ramon Mas, and Francisco J. Perales Opt. Eng. 51, 020501 (7 March 2012); http://dx.doi.org/10.1117/1.OE.51.2.020501 Online Publication Date: Mar 07, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Human motion capture has a wide variety of applications, and in vision-based motion capture systems a major issue is the human body model and its initialization. We present a computer vision algorithm for building a human body model skeleton in an automatic way. The algorithm is based on the analysis of the human shape. We decompose the body into its main parts by computing the curvature of a B-spline parameterization of the human contour. This algorithm has been applied in a context where the user is standing in front of a camera stereo pair. The process is completed after the user assumes a predefined initial posture so as to identify the main joints and construct the human model. Using this model, the initialization problem of a vision-based markerless motion capture system of the human body is solved.

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Letters from Journal of Biomedical Optics

Select this Article OPEN ACCESS		Functional photoacoustic microscopy of diabetic vasculature Arie Krumholz, Lidai Wang, Junjie Yao, and Lihong V. Wang J. Biomed. Opt. 17, 060502 (21 May 2012); http://dx.doi.org/10.1117/1.JBO.17.6.060502 Online Publication Date: May 21, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We used functional photoacoustic microscopy to image diabetes-induced damage to the microvasculature. To produce an animal model for Type 1 diabetes, we used streptozotocin (STZ), which is particularly toxic to the insulin-producing beta cells of the pancreas in mammals. A set number of ND4 Swiss Webster mice received intraperitoneal injections of STZ for five consecutive days at 50 mg/kg. Most mice developed a significant rise in blood glucose level ( ∼ 400 mg/dL) within three weeks of the first injection. Changes in vasculature and hemodynamics were monitored for six weeks. The mouse ear was imaged with an optical-resolution photoacoustic microscope at a main blood vessel branch from the root of the ear. There are noticeable and measurable changes associated with the disease, including decreased vessel diameter and possible occlusion due to vessel damage and polyurea. We also observed an increase in the blood flow speed in the vein and a decrease in the artery, which could be due to compensation for the dehydration and vessel diameter changes. Functional and metabolic parameters such as hemoglobin oxygen saturation, oxygen extraction fraction, and oxygen consumption rate were also measured, but showed no significant change.

Select this Article OPEN ACCESS		Simultaneous imaging of multiple focal planes for three-dimensional microscopy using ultra-high-speed adaptive optics Martí Duocastella, Bo Sun, and Craig B. Arnold J. Biomed. Opt. 17, 050505 (7 May 2012); http://dx.doi.org/10.1117/1.JBO.17.5.050505 Online Publication Date: May 07, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Traditional white-light and fluorescent imaging techniques provide powerful methods to extract high-resolution information from two-dimensional (2-D) sections, but to retrieve information from a three-dimensional (3-D) volume they require relatively slow scanning methods that result in increased acquisition time. Using an ultra-high speed liquid lens, we circumvent this problem by simultaneously acquiring images from multiple focal planes. We demonstrate this method by imaging microparticles and cells flowing in 3-D microfluidic channels.

Select this Article OPEN ACCESS		Whole-body ring-shaped confocal photoacoustic computed tomography of small animals in vivo Jun Xia, Muhammad R. Chatni, Konstantin Maslov, Zijian Guo, Kun Wang, Mark Anastasio, and Lihong V. Wang J. Biomed. Opt. 17, 050506 (4 May 2012); http://dx.doi.org/10.1117/1.JBO.17.5.050506 Online Publication Date: May 04, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We report a novel small-animal whole-body imaging system called ring-shaped confocal photoacoustic computed tomography (RC-PACT). RC-PACT is based on a confocal design of free-space ring-shaped light illumination and 512-element full-ring ultrasonic array signal detection. The free-space light illumination maximizes the light delivery efficiency, and the full-ring signal detection ensures a full two-dimensional view aperture for accurate image reconstruction. Using cylindrically focused array elements, RC-PACT can image a thin cross section with 0.10 to 0.25 mm in-plane resolutions and 1.6 s/frame acquisition time. By translating the mouse along the elevational direction, RC-PACT provides a series of cross-sectional images of the brain, liver, kidneys, and bladder.

Select this Article OPEN ACCESS		Potential clinical impact of three-dimensional visualization for fluorescent in situ hybridization image analysis Zheng Li, Shibo Li, Zheng Bin, Roy Zhang, Yuhua Li, Huimin Tian, Wei Chen, and Hong Liu J. Biomed. Opt. 17, 050501 (4 May 2012); http://dx.doi.org/10.1117/1.JBO.17.5.050501 Online Publication Date: May 04, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Chromosomal translocation is strong indication of cancers. Fluorescent in situ hybridization (FISH) can effectively detect this translocation and achieve high accuracy in disease diagnosis and prognosis assessment. For this purpose, whole chromosome paint probes are utilized to image the configuration of DNA fragments. Although two-dimensional (2-D) microscopic images are typically used in FISH signal analysis, we present a case where the translocation occurs in the depth direction where two probed FISH signals are overlapped in the projected image plane. Thus, the translocation cannot be identified. However, when imaging the whole specimen with a confocal microscope at 27 focal planes with 0.5-μm step interval, the translocation can be clearly identified due to the free rotation capability by the three-dimensional (3-D) visualization. Such a translocation detection error of using 2-D images might be critical in detecting and diagnosing early or subtle disease cases where detecting a small number of abnormal cells can make diagnostic difference. Hence, the underlying implication of this report suggests that utilizing 3-D visualization may improve the overall accuracy of FISH analysis for some clinical cases. However, the clinical efficiency and cost of using 3-D versus 2-D imaging methods are also to be assessed carefully.

Select this Article OPEN ACCESS		Optical vortex behavior in dynamic speckle fields Sean J. Kirkpatrick, Kosar Khaksari, Dennis Thomas, and Donald D. Duncan J. Biomed. Opt. 17, 050504 (4 May 2012); http://dx.doi.org/10.1117/1.JBO.17.5.050504 Online Publication Date: May 04, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The dynamic behavior of phase singularities, or optical vortices, in the pseudo-phase representation of dynamic speckle patterns is investigated. Sequences of band-limited, dynamic speckle patterns with predetermined Gaussian decorrelation behavior were generated, and the pseudo-phase realizations of the individual speckle patterns were calculated via a two-dimensional Hilbert transform algorithm. Singular points in the pseudo-phase representation are identified by calculating the local topological charge as determined by convolution of the pseudo-phase representations with a series of 2×2 nabla filters. The spatial locations of the phase singularities are tracked over all frames of the speckle sequences, and recorded in three-dimensional space (x,y,f), where f is frame number in the sequence. The behavior of the phase singularities traces ‘vortex trails’ which are representative of the speckle dynamics. Slowly decorrelating speckle patterns results in long, relatively straight vortex trails, while rapidly decorrelating speckle patterns results in tortuous, relatively short vortex trails. Optical vortex analysis such as described herein can be used as a descriptor of biological activity, flow, and motion.

Select this Article OPEN ACCESS		Label free in vivo laser speckle imaging of blood and lymph vessels Vyacheslav Kalchenko, Yuri Kuznetsov, Igor Meglinski, and Alon Harmelin J. Biomed. Opt. 17, 050502 (4 May 2012); http://dx.doi.org/10.1117/1.JBO.17.5.050502 Online Publication Date: May 04, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The peripheral lymphatic vascular system is a part of the immune body system comprising a complex network of lymph vessels and nodes that are flowing lymph toward the heart. Traditionally the imaging of lymphatic vessels is based on the conventional imaging modalities utilizing contrast fluorescence materials. Given the important role of the lymphatic system there is a critical need for the development of noninvasive imaging technologies for functional quantitative diagnosis of the lymph vessels and lymph flow without using foreign chemicals. We report a label free methodology for noninvasive in vivo imaging of blood and lymph vessels, using long-exposure laser speckle imaging approach. This approach entails great promise in the noninvasive studies of tissues blood and lymph vessels distribution in vivo.

Select this Article OPEN ACCESS		Real time processing of Fourier domain optical coherence tomography with fixed-pattern noise removal by partial median subtraction using a graphics processing unit Yuuki Watanabe J. Biomed. Opt. 17, 050503 (4 May 2012); http://dx.doi.org/10.1117/1.JBO.17.5.050503 Online Publication Date: May 04, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract The author presents a graphics processing unit (GPU) programming for real-time Fourier domain optical coherence tomography (FD-OCT) with fixed-pattern noise removal by subtracting mean and median. In general, the fixed-pattern noise can be removed by the averaged spectrum from the many spectra of an actual measurement. However, a mean-spectrum results in artifacts as residual lateral lines caused by a small number of high-reflective points on a sample surface. These artifacts can be eliminated from OCT images by using medians instead of means. However, median calculations that are based on a sorting algorithm can generate a large amount of computation time. With the developed GPU programming, highly reflective surface regions were obtained by calculating the standard deviation of the Fourier transformed data in the lateral direction. The medians and means were then subtracted at the observed regions and other regions, such as backgrounds. When the median calculation was less than 256 positions out of a total 512 depths in an OCT image with 1024 A-lines, the GPU processing rate was faster than that of the line scan camera (46.9 kHz). Therefore, processed OCT images can be displayed in real-time using partial medians.

Select this Article OPEN ACCESS		Optimizing in vivo small animal Cerenkov luminescence imaging Antonello E. Spinelli and Federico Boschi J. Biomed. Opt. 17, 040506 (23 April 2012); http://dx.doi.org/10.1117/1.JBO.17.4.040506 Online Publication Date: Apr 23, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract In vivo Cerenkov luminescence imaging is a rapidly growing molecular imaging research field based on the detection of Cerenkov radiation induced by beta particles when traveling though biological tissues. We investigated theoretically the possibility of enhancing the number of the detected Cerenkov photons in the near infrared (NIR) region of the spectrum. The analysis is based on applying a photon propagation diffusion model to Cerenkov photons in the tissue. Results show that despite the smaller number of Cerenkov photons in the NIR region, the fraction exiting the tissues is greater than in the visible range, and thus, a charge-coupled device detector optimized for the NIR range will allow to obtain a higher signal. The comparison was performed considering Cerenkov point sources located at different depths inside the animal. We concluded that the improvement can be up to 35% and is more significant when the Cerenkov source to be imaged is located deeper inside the animal.

Select this Article OPEN ACCESS		In vivo imaging of unstained tissues using a compact and flexible multiphoton microendoscope Christopher M. Brown, David R. Rivera, Ina Pavlova, Dimitre G. Ouzounov, Wendy O. Williams, Sunish Mohanan, Watt W. Webb, and Chris Xu J. Biomed. Opt. 17, 040505 (9 April 2012); http://dx.doi.org/10.1117/1.JBO.17.4.040505 Online Publication Date: Apr 09, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We use a compact and flexible multiphoton microendoscope (MPME) to acquire in vivo images of unstained liver, kidney, and colon from an anesthetized rat. The device delivers femtosecond pulsed 800 nm light from the core of a raster-scanned dual-clad fiber (DCF), which is focused by a miniaturized gradient-index lens assembly into tissue. Intrinsic fluorescence and second-harmonic generation signal from the tissue is epi-collected through the core and inner clad of the same DCF. The MPME has a rigid distal tip of 3 mm in outer diameter and 4 cm in length. The image field-of-view measures 115 μm by 115 μm and was acquired at 4.1 frames/s with 75 mW illumination power at the sample. Organs were imaged after anesthetizing Sprague-Dawley rats with isofluorane gas, accessing tissues via a ventral-midline abdominal incision, and isolating the organs with tongue depressors. In vivo multiphoton images acquired from liver, kidney, and colon using this device show features similar to that of conventional histology slides, without motion artifact, in ∼ 75% of imaged frames. To the best of our knowledge, this is the first demonstration of multiphoton imaging of unstained tissue from a live subject using a compact and flexible MPME device.

Select this Article OPEN ACCESS		Monitoring of tumor response to cisplatin by subsurface fluorescence molecular tomography Fei Liu, Xu Cao, Wei He, Jinping Song, Zhongquan Dai, Bin Zhang, Jianwen Luo, Yinghui Li, and Jing Bai J. Biomed. Opt. 17, 040504 (6 April 2012); http://dx.doi.org/10.1117/1.JBO.17.4.040504 Online Publication Date: Apr 06, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Subsurface fluorescence molecular tomography (FMT) has promising potential for noninvasive characterization of molecular and cellular activities in small animals by tomographic means in reflectance geometry. In this work, subsurface FMT is employed to monitor the therapeutic response of cisplatin in tumor-bearing mice in vivo. The localization and quantification accuracy of subsurface FMT are demonstrated in phantom. In the in vivo study, the red fluorescent protein activities not only on the surface but in the interior tumor are tracked three-dimensionally during the antitumor treatment.

Select this Article OPEN ACCESS		In vivo terahertz imaging of rat skin burns Priyamvada Tewari, Colin P. Kealey, David B. Bennett, Neha Bajwa, Kelli S. Barnett, Rahul S. Singh, Martin O. Culjat, Alexander Stojadinovic, Warren S. Grundfest, and Zachary D. Taylor J. Biomed. Opt. 17, 040503 (6 April 2012); http://dx.doi.org/10.1117/1.JBO.17.4.040503 Online Publication Date: Apr 06, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A reflective, pulsed terahertz (THz) imaging system was used to acquire high-resolution (d_10–90/ λ ∼ 1.925) images of deep, partial thickness burns in a live rat. The rat’s abdomen was burned with a brass brand heated to ∼ 220°C and pressed against the skin with contact pressure for ∼ 10 sec. The burn injury was imaged beneath a Mylar window every 15 to 30 min for up to 7 h. Initial images display an increase in local water concentration of the burned skin as evidenced by a marked increase in THz reflectivity, and this likely correlates to the post-injury inflammatory response. After ∼ 1 h the area of increased reflectivity consolidated to the region of skin that had direct contact with the brand. Additionally, a low reflecting ring of tissue could be observed surrounding the highly reflective burned tissue. We hypothesize that these regions of increased and decreased reflectivity correlate to the zones of coagulation and stasis that are the classic foundation of burn wound histopathology. While further investigations are necessary to confirm this hypothesis, if true, it likely represents the first in vivo THz images of these pathologic zones and may represent a significant step forward in clinical application of THz technology.

Select this Article OPEN ACCESS		Using graphics processing units to accelerate perturbation Monte Carlo simulation in a turbid medium Fuhong Cai and Sailing He J. Biomed. Opt. 17, 040502 (6 April 2012); http://dx.doi.org/10.1117/1.JBO.17.4.040502 Online Publication Date: Apr 06, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We report a fast perturbation Monte Carlo (PMC) algorithm accelerated by graphics processing units (GPU). The two-step PMC simulation [Opt. Lett. 36, 2095 (2011)] is performed by storing the seeds instead of the photon’s trajectory, and thus the requirement in computer random-access memory (RAM) becomes minimal. The two-step PMC is extremely suitable for implementation onto GPU. In a standard simulation of spatially-resolved photon migration in the turbid media, the acceleration ratio between using GPU and using conventional CPU is about 1000. Furthermore, since in the two-step PMC algorithm one records the effective seeds, which is associated to the photon that reaches a region of interest in this letter, and then re-run the MC simulation based on the recorded effective seeds, radiative transfer equation (RTE) can be solved by two-step PMC not only with an arbitrary change in the absorption coefficient, but also with large change in the scattering coefficient.

Select this Article OPEN ACCESS		Anisotropic light scattering of individual sickle red blood cells Youngchan Kim, John M. Higgins, Ramachandra R. Dasari, Subra Suresh, and YongKeun Park J. Biomed. Opt. 17, 040501 (5 April 2012); http://dx.doi.org/10.1117/1.JBO.17.4.040501 Online Publication Date: Apr 05, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We present the anisotropic light scattering of individual red blood cells (RBCs) from a patient with sickle cell disease (SCD). To measure light scattering spectra along two independent axes of elongated-shaped sickle RBCs with arbitrary orientation, we introduce the anisotropic Fourier transform light scattering (aFTLS) technique and measured both the static and dynamic anisotropic light scattering. We observed strong anisotropy in light scattering patterns of elongated-shaped sickle RBCs along its major axes using static aFTLS. Dynamic aFTLS analysis reveals the significantly altered biophysical properties in individual sickle RBCs. These results provide evidence that effective viscosity and elasticity of sickle RBCs are significantly different from those of the healthy RBCs.

Select this Article OPEN ACCESS		Addressable multiregional and multifocal multiphoton microscopy based on a spatial light modulator Yonghong Shao, Wan Qin, Honghai Liu, Junle Qu, Xiang Peng, Hanben Niu, and Bruce Z. Gao J. Biomed. Opt. 17, 030505 (3 April 2012); http://dx.doi.org/10.1117/1.JBO.17.3.030505 Online Publication Date: Apr 03, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Through a combination of a deflective phase-only diffractive spatial light modulator (SLM) and galvo scanners, an addressable multiregional and multifocal multiphoton microscope (AM-MMM) is developed. The SLM shapes an incoming mode-locked, near-infrared Ti:sapphire laser beam into multiple beamlet arrays with addressable shapes and sizes that match the regions of interest on the sample. Compared with conventional multifocal multiphoton microscope (MMM), AM-MMM achieves the effective use of the laser power with an increase of imaging rate and a decrease of photodamage without sacrifice of resolution.

Select this Article OPEN ACCESS		Time-reversed ultrasonically encoded optical focusing in biological tissue Puxiang Lai, Xiao Xu, Honglin Liu, and Lihong V. Wang J. Biomed. Opt. 17, 030506 (8 March 2012); http://dx.doi.org/10.1117/1.JBO.17.3.030506 Online Publication Date: Mar 08, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We report an experimental investigation of time-reversed ultrasonically encoded optical focusing in biological tissue. This technology combines the concepts of optical phase conjugation and ultrasound modulation of diffused coherent light. The ultrasonically encoded (or tagged) diffused light from a tissue sample is collected in reflection mode and interferes with a reference light in a photorefractive crystal (used as a phase conjugation mirror) to form a hologram. Then a time-reversed copy of the tagged light is generated and traces back the original trajectories to the ultrasonic focus inside the tissue sample. With our current setup, we can achieve a maximum penetration depth of 5 mm in a chicken breast sample and image optical contrasts within a tissue sample with a spatial resolution approximately equaling 1/ of the ultrasound focal diameter.

Select this Article OPEN ACCESS		Noncontact diffuse correlation spectroscopy for noninvasive deep tissue blood flow measurement Yu Lin, Lian He, Yu Shang, and Guoqiang Yu J. Biomed. Opt. 17, 010502 (3 February 2012); http://dx.doi.org/10.1117/1.JBO.17.1.010502 Online Publication Date: Feb 03, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A noncontact diffuse correlation spectroscopy (DCS) probe has been developed using two separated optical paths for the source and detector. This unique design avoids the interference between the source and detector and allows large source-detector separations for deep tissue blood flow measurements. The noncontact probe has been calibrated against a contact probe in a tissue-like phantom solution and human muscle tissues; flow changes concurrently measured by the two probes are highly correlated in both phantom (R² = 0.89, p<10⁻⁵) and real-tissue (R² = 0.77, p<10⁻⁵, n = 9) tests. The noncontact DCS holds promise for measuring blood flow in vulnerable (e.g., pressure ulcer) and soft (e.g., breast) tissues without distorting tissue hemodynamic properties.

Select this Article OPEN ACCESS		Reflection-mode submicron-resolution in vivo photoacoustic microscopy Chi Zhang, Konstantin Maslov, Song Hu, Ruimin Chen, Qifa Zhou, K.Kirk Shung, and Lihong V. Wang J. Biomed. Opt. 17, 020501 (23 February 2012); http://dx.doi.org/10.1117/1.JBO.17.2.020501 Online Publication Date: Feb 23, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract Submicron-resolution photoacoustic microscopy (PAM) currently exists only in transmission mode, due to the technical difficulties of combining high numerical-aperture (NA) optical illumination with high NA acoustic detection. The lateral resolution of reflection-mode PAM has not reached <2 μm in the visible light range. Here we develop the first reflection-mode submicron-resolution PAM system with a new compact design. By using a parabolic mirror to focus and reflect the photoacoustic waves, sufficient signals were collected for good sensitivity without distorting the optical focusing. By imaging nanospheres and a resolution test chart, the lateral resolution was measured to be ∼ 0.5 μm with an optical wavelength of 532 nm, an optical NA of 0.63. The axial resolution was measured at 15 μm. Here the axial resolution was measured by a different experiment with the lateral resolution measurement. But we didn’t describe the details of axial resolution measurement due to space limit. The maximum penetration was measured at ∼ 0.42 mm in optical-scattering soft tissue. As a comparison, both the submicron-resolution PAM and a 2.4 μm-resolution PAM were used to image a mouse ear in vivo with the same optical wavelength and similar pulse energy. Capillaries were resolved better by the submicron-resolution PAM. Therefore, the submicron-resolution PAM is suitable for in vivo high-resolution imaging, or even subcellular imaging, of optical absorption.

Select this Article OPEN ACCESS		Optical coherence photoacoustic microscopy: accomplishing optical coherence tomography and photoacoustic microscopy with a single light source Xiangyang Zhang, Hao F. Zhang, and Shuliang Jiao J. Biomed. Opt. 17, 030502 (2 March 2012); http://dx.doi.org/10.1117/1.JBO.17.3.030502 Online Publication Date: Mar 02, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We developed optical coherence photoacoustic microscopy (OC-PAM) to demonstrate that the functions of optical coherence tomography (OCT) and photoacoustic microscopy (PAM) can be achieved simultaneously by using a single illuminating light source. We used a pulsed broadband laser centered at 580 nm and detected the absorbed photons through photoacoustic detection and the back-scattered photons with an interferometer. In OC-PAM, each laser pulse generates both one OCT A-line and one PAM A-line simultaneously; as a result, the two imaging modalities are intrinsically co-registered in the lateral directions. In vivo images of the mouse ear were acquired to demonstrate the capabilities of OC-PAM.

Select this Article OPEN ACCESS		Photoacoustic section imaging using an elliptical acoustic mirror and optical detection Robert Nuster, Sibylle Gratt, Klaus Passler, Dirk Meyer, and Guenther Paltauf J. Biomed. Opt. 17, 030503 (2 March 2012); http://dx.doi.org/10.1117/1.JBO.17.3.030503 Online Publication Date: Mar 02, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract A method is proposed that utilizes the advantages of optical ultrasound detection in two-dimensional photoacoustic section imaging, combining an optical interferometer with an acoustic mirror. The concave mirror has the shape of an elliptical cylinder and concentrates the acoustic wave generated around one focal line in the other one, where an optical beam probes the temporal evolution of acoustic pressure. This yields line projections of the acoustic sources at distances corresponding to the time of flight, which, after rotating the sample about an axis perpendicular to the optical detector, allows reconstruction of a section using the inverse Radon transform. A resolution of 120 µm within and 1.5 mm between the sections can be obtained with the setup. Compared to a bare optical probe beam, the signal-to-noise ratio (SNR) is seven times higher with the mirror. Furthermore, the imaging system is tested on a biological sample.

Select this Article OPEN ACCESS		Polarization-sensitive optical coherence tomography using continuous polarization modulation with arbitrary phase modulation amplitude Zenghai Lu, Deepa K. Kasaragod, and Stephen J. Matcher J. Biomed. Opt. 17, 030504 (8 March 2012); http://dx.doi.org/10.1117/1.JBO.17.3.030504 Online Publication Date: Mar 08, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We demonstrate theoretically and experimentally that the phase retardance and relative optic-axis orientation of a sample can be calculated without prior knowledge of the actual value of the phase modulation amplitude when using a polarization-sensitive optical coherence tomography system based on continuous polarization modulation (CPM-PS-OCT). We also demonstrate that the sample Jones matrix can be calculated at any values of the phase modulation amplitude in a reasonable range depending on the system effective signal-to-noise ratio. This has fundamental importance for the development of clinical systems by simplifying the polarization modulator drive instrumentation and eliminating its calibration procedure. This was validated on measurements of a three-quarter waveplate and an equine tendon sample by a fiber-based swept-source CPM-PS-OCT system.

Select this Article OPEN ACCESS		Modified Wiener estimation of diffuse reflectance spectra from RGB values by the synthesis of new colors for tissue measurements Shuo Chen and Quan Liu J. Biomed. Opt. 17, 030501 (2 March 2012); http://dx.doi.org/10.1117/1.JBO.17.3.030501 Online Publication Date: Mar 02, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We present a new method for the accurate estimation of diffuse reflectance spectra from RGB values based on Wiener estimation. In the proposed method, a system matrix obtained from the original RGB values is combined with a set of synthetic optical filters to generate another three values corresponding to new colors. A modified Wiener matrix can then be created with the original RGB values and the new color values, which will yield a more accurate estimation because of the new color information that has been incorporated. This method was tested on in vivo color measurements from 200 skin sites in 10 volunteers. The results show that the proposed method is able to improve the estimation accuracy significantly compared with the traditional Wiener estimation method. The fast speed of this method may enable the estimation of diffuse reflectance spectra at multiple tissue locations from color images in real time, which provides a cost-effective alternative to spectral imaging with the additional advantage of high spectral resolution.

Select this Article OPEN ACCESS		Hybrid method for fast Monte Carlo simulation of diffuse reflectance from a multilayered tissue model with tumor-like heterogeneities Caigang Zhu and Quan Liu J. Biomed. Opt. 17, 010501 (1 February 2012); http://dx.doi.org/10.1117/1.JBO.17.1.010501 Online Publication Date: Feb 01, 2012 Full Text: Read Online (HTML) \| Download PDF
	+ -	Show Abstract We present a hybrid method that combines a multilayered scaling method and a perturbation method to speed up the Monte Carlo simulation of diffuse reflectance from a multilayered tissue model with finite-size tumor-like heterogeneities. The proposed method consists of two steps. In the first step, a set of photon trajectory information generated from a baseline Monte Carlo simulation is utilized to scale the exit weight and exit distance of survival photons for the multilayered tissue model. In the second step, another set of photon trajectory information, including the locations of all collision events from the baseline simulation and the scaling result obtained from the first step, is employed by the perturbation Monte Carlo method to estimate diffuse reflectance from the multilayered tissue model with tumor-like heterogeneities. Our method is demonstrated to shorten simulation time by several orders of magnitude. Moreover, this hybrid method works for a larger range of probe configurations and tumor models than the scaling method or the perturbation method alone.

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