We recently reported on a new swept source polarization sensitive optical coherence tomography system and its application to skin imaging [Biomed. Opt. Express 3, 2987 (2012)]. In some of the tomographic images, two skin layers were labeled wrongly (interchanged). We present figures with corrected labeling.
(170.4500) Optical coherence tomography; (230.5440) Polarization-selective devices; (170.4580) Optical diagnostics for medicine
We correct an error in the methods reported in our previous paper [Biomed. Opt. Express 3, 2752
(2012)]; the liquid used for the final step of specimen preparation was 100% mineral oil, not a
mixture of oil and glycerol.
(170.6900) Three-dimensional microscopy; (170.6930) Tissue; (110.0113) Imaging through turbid media
We present a novel application of optical microangiography (OMAG) imaging technique for
visualization of depth-resolved vascular network within retina and choroid as well as measurement of
total retinal blood flow in mice. A fast speed spectral domain OCT imaging system at 820nm with a
line scan rate of 140 kHz was developed to image the posterior segment of eyes in mice. By applying
an OMAG algorithm to extract the moving blood flow signals out of the background tissue, we are able
to provide true capillary level imaging of the retinal and choroidal vasculature. The microvascular
patterns within different retinal layers are presented. An en face Doppler OCT
approach [Srinivasan et al., Opt Express 18, 2477 (2010)] was adopted for retinal blood
flow measurement. The flow is calculated by integrating the axial blood flow velocity over the
vessel area measured in an en face plane without knowing the blood vessel angle.
Total retinal blood flow can be measured from both retinal arteries and veins. The results indicate
that OMAG has the potential for qualitative and quantitative evaluation of the microcirculation in
posterior eye compartments in mouse models of retinopathy and neovascularization.
(170.4500) Optical coherence tomography; (170.3880) Medical and biological imaging
An interesting method to measure and correct chromatic magnification offsets in a
multi-wavelength retinal imaging microscope was recently reported [Harmening et al., Biomed. Opt.
Express 3, 2066 (2012)]. These values were in part related to the ocular transverse
chromatic aberration (TCA). This method could be potentially used in the future to overcome the
fundamental limitation to estimate the eye’s TCA with ophthalmoscopic (double-pass)
(170.4460) Ophthalmic optics and devices; (330.5370) Physiological optics
Abstract: The authors provide corrections to tabular data and a figure, which do not alter the conclusions of the original paper [Biomed. Opt. Express 2, 2068 (2011)].
(170.1470) Blood or tissue constituent monitoring; (170.3660) Light propagation in tissues; (170.3890) Medical optics instrumentation
Correction of the eye’s monochromatic aberrations using adaptive optics (AO) can improve the resolution of in vivo mouse retinal images [Biss et al., Opt. Lett. 32(6), 659 (2007) and Alt et al., Proc. SPIE 7550, 755019 (2010)], but previous attempts have been limited by poor spot quality in the Shack-Hartmann wavefront sensor (SHWS). Recent advances in mouse eye wavefront sensing using an adjustable focus beacon with an annular beam profile have improved the wavefront sensor spot quality [Geng et al., Biomed. Opt. Express 2(4), 717 (2011)], and we have incorporated them into a fluorescence adaptive optics scanning laser ophthalmoscope (AOSLO). The performance of the instrument was tested on the living mouse eye, and images of multiple retinal structures, including the photoreceptor mosaic, nerve fiber bundles, fine capillaries and fluorescently labeled ganglion cells were obtained. The in vivo transverse and axial resolutions of the fluorescence channel of the AOSLO were estimated from the full width half maximum (FWHM) of the line and point spread functions (LSF and PSF), and were found to be better than 0.79 μm ± 0.03 μm (STD)(45% wider than the diffraction limit) and 10.8 μm ± 0.7 μm (STD)(two times the diffraction limit), respectively. The axial positional accuracy was estimated to be 0.36 μm. This resolution and positional accuracy has allowed us to classify many ganglion cell types, such as bistratified ganglion cells, in vivo.
(170.4460) Ophthalmic optics and devices; (110.1080) Active or adaptive optics; (330.7324) Visual optics, comparative animal models
We correct an error in our previous paper [Biomed. Opt. Express 2, 1218 (2011)] which led to an erroneous conclusion that a dispersive optical delay line (DODL) used in a swept source optical coherence tomography (SSOCT) system generated a pure phase modulation allowing for complex conjugate artifact removal in Fourier domain OCT via optical heterodyning. We now understand that an alternate phenomenon known as coherence revival was responsible for the observed phase modulation, while the DODL provided a compact means of generating a large group delay with readily adjustable group velocity dispersion compensation.
(170.4500) Optical coherence tomography; (230.4110) Modulators
In July 2011 a new concept of a closed microfluidic system equipped with a fixed micropipette, optical tweezers and a UV-Vis spectrometer was presented [Biomed. Opt. Express 2, 2299 (2011)]. Figure 1 showed falsely oriented mirrors. To clarify the design of the setup, this erratum presents a correct schematic.
(350.4855) Optical tweezers or optical manipulation; (170.3880) Medical and biological imaging; (300.1030) Absorption; (280.2490) Flow diagnostics; (220.4000) Microstructure fabrication; (110.0180) Microscopy
The Monte Carlo (MC) method is a popular approach to modeling photon propagation inside general turbid media, such as human tissue. Progress had been made in the past year with the independent proposals of two mesh-based Monte Carlo methods employing ray-tracing techniques. Both methods have shown improvements in accuracy and efficiency in modeling complex domains. A recent paper by Shen and Wang [Biomed. Opt. Express 2, 44 (2011)] reported preliminary results towards the cross-validation of the two mesh-based MC algorithms and software implementations, showing a 3–6 fold speed difference between the two software packages. In this comment, we share our views on unbiased software comparisons and discuss additional issues such as the use of pre-computed data, interpolation strategies, impact of compiler settings, use of Russian roulette, memory cost and potential pitfalls in measuring algorithm performance. Despite key differences between the two algorithms in handling of non-tetrahedral meshes, we found that they share similar structure and performance for tetrahedral meshes. A significant fraction of the observed speed differences in the mentioned article was the result of inconsistent use of compilers and libraries.
(170.3660) Light propagation through tissue; (170.5280) Photon migration; (170.7050) Turbid media
We compare the accuracy of TIM-OS and MMCM in response to the recent analysis made by Fang [Biomed. Opt. Express 2, 1258 (2011)]. Our results show that the tetrahedron-based energy deposition algorithm used in TIM-OS is more accurate than the node-based energy deposition algorithm used in MMCM.
(170.3660) Light propagation in tissues
We study the control of coherent light propagation through multiple-scattering media in the presence of measurement noise. In our experiments, we use a two-step optimization procedure to find the optimal incident wavefront that generates a bright focal spot behind the medium. We conclude that the control of coherent light propagation through a multiple-scattering medium is only determined by the number of photoelectrons detected per optimized segment. The prediction of our model agrees well with the experimental results. Our results offer opportunities for imaging applications through scattering media such as biological tissue in the shot noise limit.
(030.6600) Statistical optics; (110.7050) Turbid media; (290.4210) Multiple scattering
Optical coherence tomography (OCT) allows for non-invasive 3D visualization of biological tissue at cellular level resolution. Often hindered by speckle noise, the visualization of important biological tissue details in OCT that can aid disease diagnosis can be improved by speckle noise compensation. A challenge with handling speckle noise is its inherent non-stationary nature, where the underlying noise characteristics vary with the spatial location. In this study, an innovative speckle noise compensation method is presented for handling the non-stationary traits of speckle noise in OCT imagery. The proposed approach centers on a non-stationary spline-based speckle noise modeling strategy to characterize the speckle noise. The novel method was applied to ultra high-resolution OCT (UHROCT) images of the human retina and corneo-scleral limbus acquired in-vivo that vary in tissue structure and optical properties. Test results showed improved performance of the proposed novel algorithm compared to a number of previously published speckle noise compensation approaches in terms of higher signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and better overall visual assessment.
(110.4500) Optical coherence tomography; (030.6140) Speckle; (100.2980) Image enhancement; (100.3010) Image reconstruction techniques; (170.4460) Ophthalmic optics and devices
The rapid growth of microfluidic cell culturing in biological and biomedical research and industry calls for fast, non-invasive and reliable methods of evaluating conditions such as pH inside a microfluidic system. We show that by careful calibration it is possible to measure pH within microfluidic chambers with high accuracy and precision, using a direct single-pass measurement of light absorption in a commercially available phenol-red-containing cell culture medium. The measurement is carried out using a standard laboratory microscope and, contrary to previously reported methods, requires no modification of the microfluidic device design. We demonstrate the validity of this method by measuring absorption of light transmitted through 30-micrometer thick microfluidic chambers, using an inverted microscope fitted with a scientific-grade digital camera and two bandpass filters. In the pH range of 7–8, our measurements have a standard deviation and absolute error below 0.05 for a measurement volume smaller than 4 nL.
(120.0120) Instrumentation, measurement, and metrology; (120.3940) Metrology; (120.7000) Transmission; (300.1030) Absorption; (170.1420) Biology
This work reports a multimodal system for label-free tissue diagnosis combining fluorescence lifetime imaging (FLIm), ultrasound backscatter microscopy (UBM), and photoacoustic imaging (PAI). This system provides complementary biochemical, structural and functional features allowing for enhanced in vivo detection of oral carcinoma. Results from a hamster oral carcinoma model (normal, precancer and carcinoma) are presented demonstrating the ability of FLIm to delineate biochemical composition at the tissue surface, UBM and related radiofrequency parameters to identify disruptions in the tissue microarchitecture and PAI to map optical absorption associated with specific tissue morphology and physiology.
(300.6500) Spectroscopy, time-resolved; (170.7180) Ultrasound diagnostics; (170.5120) Photoacoustic imaging; (170.3880) Medical and biological imaging
Angle-resolved low coherence interferometry (a/LCI) is an approach for assessing tissue structure based on light scattering data. Recent advances in a/LCI have extended the analysis to study scattering distributions in two dimensions. In order to provide suitable scattering phantoms for 2D a/LCI, we have developed phantoms based on soft lithography which can provide a range of structures including long range order. Here we characterize these phantoms and demonstrate their utility for providing standardized multi-scale structural information for light scattering measurements.
(290.0290) Scattering; (290.3200) Inverse scattering; (290.5820) Scattering measurements; (120.3180) Interferometry
Non-invasive reflectance imaging of the human RPE cell mosaic is demonstrated using a modified
confocal adaptive optics scanning light ophthalmoscope (AOSLO). The confocal circular aperture in
front of the imaging detector was replaced with a combination of a circular aperture 4 to 16 Airy
disks in diameter and an opaque filament, 1 or 3 Airy disks thick. This arrangement reveals the RPE
cell mosaic by dramatically attenuating the light backscattered by the photoreceptors. The RPE cell
mosaic was visualized in all 7 recruited subjects at multiple retinal locations with varying degrees
of contrast and cross-talk from the photoreceptors. Various experimental settings were explored for
improving the visualization of the RPE cell boundaries including: pinhole diameter, filament
thickness, illumination and imaging pupil apodization, unmatched imaging and illumination focus,
wavelength and polarization. None of these offered an obvious path for enhancing image contrast. The
demonstrated implementation of dark-field AOSLO imaging using 790 nm light requires low light
exposures relative to light safety standards and it is more comfortable for the subject than the
traditional autofluorescence RPE imaging with visible light. Both these factors make RPE dark-field
imaging appealing for studying mechanisms of eye disease, as well as a clinical tool for screening
and monitoring disease progression.
(170.4460) Ophthalmic optics and devices; (170.4470) Ophthalmology; (290.4210) Multiple scattering; (110.1080) Active or adaptive optics
Superoxide anion is the key radical that causes intracellular oxidative stress. The lack of a method to directly monitor superoxide concentration in vivo in real time has severely hindered our understanding on its pathophysiology. We made transgenic zebrafish to specifically express yellow fluorescent proteins, a reversible superoxide-specific indicator, in the liver and used a fiber-optic fluorescent probe to noninvasively monitor the superoxide concentration in real time. Several superoxide-inducing and scavenging reagents were administrated onto the fish to alter superoxide concentrations. The distinct biochemical pathways of the reagents can be discerned from the transient behaviors of fluorescence time courses. These results demonstrate the feasibility of this method for analyzing superoxide dynamics and its potential as an in vivo pharmaceutical screening platform.
(060.2370) Fiber optics sensors; (170.1470) Blood or tissue constituent monitoring; (170.2655) Functional monitoring and imaging; (170.6280) Spectroscopy, fluorescence and luminescence
We propose and demonstrate a dark-field imaging technique capable of automated identification of individual bacteria. An 87-channel multispectral system capable of angular and spectral resolution was used to measure the scattering spectrum of various bacteria in culture smears. Spectra were compared between various species and between various preparations of the same species. A 15-channel system was then used to prove the viability of bacterial identification with a relatively simple microscope system. A simple classifier was able to identify four of six bacterial species with greater than 90% accuracy in bacteria-by-bacteria testing.
(170.0180) Microscopy; (170.4580) Optical diagnostics for medicine; (290.5820) Scattering measurements
High resolution microscopy is essential for advanced study of biological structures and accurate diagnosis of medical diseases. The spatial resolution of conventional microscopes is light diffraction limited. Structured illumination has been extensively explored to break the diffraction limit in wide field light microscopy. However, deployable application of the structured illumination in scanning laser microscopy is challenging due to the complexity of the illumination system and possible phase errors in sequential illumination patterns required for super-resolution reconstruction. We report here a super-resolution scanning laser imaging system which employs virtually structured detection (VSD) to break the diffraction limit. Without the complexity of structured illumination, VSD provides an easy, low-cost and phase-artifact free strategy to achieve super-resolution in scanning laser microscopy.
(100.6640) Superresolution; (110.3080) Infrared imaging; (170.3880) Medical and biological imaging; (180.5810) Scanning microscopy
Optical coherence microscopy (OCM) is a widely used structural imaging modality. To extend its application in molecular imaging, gold nanorods are widely used as contrast agents for OCM. However, they very often offer limited sensitivity as a result of poor signal to background ratio. Here we experimentally demonstrate that a novel OCM implementation based on dark-field circular depolarization detection can efficiently detect circularly depolarized signal from gold nanorods and at the same time efficiently suppress the background signals. This results into a significant improvement in signal to background ratio.
(110.4500) Optical coherence tomography; (120.5820) Scattering measurements; (180.3170) Interference microscopy; (290.5850) Scattering, particles; (290.5855) Scattering, polarization
Fluorescence correlation spectroscopy (FCS) is one of the most sensitive methods for enumerating low concentration nanoparticles in a suspension. However, biological nanoparticles such as viruses often exist at a concentration much lower than the FCS detection limit. While optically generated trapping potentials are shown to effectively enhance the concentration of nanoparticles, feasibility of FCS for enumerating field-enriched nanoparticles requires understanding of the nanoparticle behavior in the external field. This paper reports an experimental study that combines optical trapping and FCS to examine existing theoretical predictions of particle concentration. Colloidal suspensions of polystyrene (PS) nanospheres and HIV-1 virus-like particles are used as model systems. Optical trapping energies and statistical analysis are used to discuss the applicability of FCS for enumerating nanoparticles in a potential well produced by a force field.
(350.4855) Optical tweezers or optical manipulation; (140.7010) Laser trapping; (290.1990) Diffusion; (180.2520) Fluorescence microscopy; (170.1790) Confocal microscopy
Light sheet microscopy allows rapid imaging of three-dimensional fluorescent samples, using illumination and detection axes that are orthogonal. For imaging large samples, this often forces the objective to be tilted relative to the sample’s surface; for samples that are not precisely matched to the immersion medium index, this tilt introduces aberrations. Here we calculate the nature of these aberrations for a simple tissue model, and show that a low-dimensional parametrization of these aberrations facilitates online correction via a deformable mirror without introduction of beads or other fiducial markers. We use this approach to demonstrate improved image quality in living tissue.
(110.1080) Active or adaptive optics; (180.2520) Fluorescence microscopy
In a blood-lipid liquid phantom the prototype near-infrared spectroscopy oximeter OxyPrem was calibrated against the INVOS® 5100c adult sensor in respect to values of regional tissue oxygen haemoglobin saturation (rStO2) for possible inclusion in the randomised clinical trial - SafeBoosC. In addition different commercial NIRS oximeters were compared on changing haemoglobin oxygen saturation and compared against co-oximetry. The best calibration was achieved with a simple offset and a linear scaling of the OxyPrem rStO2 values. The INVOS adult and pediatric sensor gave systematically different values, while the difference between the NIRO® 300 and the two INVOS sensors were magnitude dependent. The co-oximetry proved unreliable on such low haemoglobin and high Intralipid levels.
(170.1470) Blood or tissue constituent monitoring; (300.6190) Spectrometers
Optical pacing has been demonstrated to be a viable alternative to electrical pacing in embryonic hearts. In this study, the feasibility of optically pacing an adult rabbit heart was explored. Hearts from adult New Zealand White rabbits (n = 9) were excised, cannulated and perfused on a modified Langendorff apparatus. Pulsed laser light (λ = 1851 nm) was directed to either the left or right atrium through a multimode optical fiber. An ECG signal from the left ventricle and a trigger pulse from the laser were recorded simultaneously to determine when capture was achieved. Successful optical pacing was demonstrated by obtaining pacing capture, stopping, then recapturing as well as by varying the pacing frequency. Stimulation thresholds measured at various pulse durations suggested that longer pulses (8 ms) had a lower energy capture threshold. To determine whether optical pacing caused damage, two hearts were perfused with 30 µM of propidium iodide and analyzed histologically. A small number of cells near the stimulation site had compromised cell membranes, which probably limited the time duration over which pacing was maintained. Here, short-term optical pacing (few minutes duration) is demonstrated in the adult rabbit heart for the first time. Future studies will be directed to optimize optical pacing parameters to decrease stimulation thresholds and may enable longer-term pacing.
(140.3460) Lasers; (170.3890) Medical optics instrumentation
Spectrally encoded confocal microscopy (SECM) is a reflectance confocal microscopy technology that uses a diffraction grating to illuminate different locations on the sample with distinct wavelengths. SECM can obtain line images without any beam scanning devices, which opens up the possibility of high-speed imaging with relatively simple probe optics. This feature makes SECM a promising technology for rapid endoscopic imaging of internal organs, such as the esophagus, at microscopic resolution. SECM imaging of the esophagus has been previously demonstrated at relatively low line rates (5 kHz). In this paper, we demonstrate SECM imaging of large regions of esophageal tissues at a high line imaging rate of 100 kHz. The SECM system comprises a wavelength-swept source with a fast sweep rate (100 kHz), high output power (80 mW), and a detector unit with a large bandwidth (100 MHz). The sensitivity of the 100-kHz SECM system was measured to be 60 dB and the transverse resolution was 1.6 µm. Excised swine and human esophageal tissues were imaged with the 100-kHz SECM system at a rate of 6.6 mm2/sec. Architectural and cellular features of esophageal tissues could be clearly visualized in the SECM images, including papillae, glands, and nuclei. These results demonstrate that large-area SECM imaging of esophageal tissues can be successfully conducted at a high line imaging rate of 100 kHz, which will enable whole-organ SECM imaging in vivo.
(170.1790) Confocal microscopy; (170.2680) Gastrointestinal; (170.4730) Optical pathology