Uniform Contrast Research Articles

Deep line-temporal focusing with high axial resolution and a large field-of-view using intracavity control and incoherent pulse shaping.

Line-temporal focusing has been recognized as an elegant strategy that provides two-photon microscopy with an effective means for fast imaging through parallelization, together with an improved resilience to scattering for deep imaging. However, the axial resolution remains sub-optimal, except when using high NA objectives and a small field-of-view. With the introduction of an intracavity control of the spectral width of the femtosecond laser to adaptively fill the back aperture of the objective lens, line-temporal focusing two-photon microscopy is demonstrated to reach near-diffraction-limited axial resolution with a large back-aperture objective lens, and improved immunity to sample scattering. In addition, a new incoherent flattop beam shaping method is proposed which provides a uniform contrast with little degradation of the axial resolution along the focus line, even deep in the sample. This is demonstrated in large volumetric imaging of mouse lung samples.

Fast Homogeneous En Bloc Staining of Large Tissue Samples for Volume Electron Microscopy.

Fixation and staining of large tissue samples are critical for the acquisition of volumetric electron microscopic image datasets and the subsequent reconstruction of neuronal circuits. Efficient protocols exist for the staining of small samples, but uniform contrast is often difficult to achieve when the sample diameter exceeds a few hundred micrometers. Recently, a protocol (BROPA, brain-wide reduced-osmium staining with pyrogallol-mediated amplification) was developed that achieves homogeneous staining of the entire mouse brain but requires very long sample preparation times. By exploring modifications of this protocol we developed a substantially faster procedure, fBROPA, that allows for reliable high-quality staining of tissue blocks on the millimeter scale. Modifications of the original BROPA protocol include drastically reduced incubation times and a lead aspartate incubation to increase sample conductivity. Using this procedure, whole brains from adult zebrafish were stained within 4 days. Homogenous high-contrast staining was achieved throughout the brain. High-quality image stacks with voxel sizes of 10 × 10 × 25 nm3 were obtained by serial block-face imaging using an electron dose of ~15 e−/nm2. No obvious reduction in staining quality was observed in comparison to smaller samples stained by other state-of-the-art procedures. Furthermore, high-quality images with minimal charging artifacts were obtained from non-neural tissues with low membrane density. fBROPA is therefore likely to be a versatile and efficient sample preparation protocol for a wide range of applications in volume electron microscopy.

Chemical vapor deposition of monolayer MoS2 on sapphire, Si and GaN substrates

Monolayer MoS2 grown on sapphire, Si, and GaN substrates by chemical vapor deposition (CVD) method under the same growth conditions have been demonstrated, and the effects of diverse substrates on the morphological and optical properties of monolayer MoS2 are systematically compared. The variations of the PL and Raman spectra of monolayer MoS2 on the three substrates are mainly attributed to the different lattice mismatch and thermal conductivity between MoS2 and the substrates. Moreover, uniform contrast of the PL and Raman intensity mappings suggest that the as-grown monolayer MoS2 on diverse substrates achieve high quality and uniformity. Accordingly, the ability to grow monolayer MoS2 with high quality to surface corrugation on diverse substrates would open a route toward the synthesis of heteroand composite structures.

Selective photo-oxidation induced bi-periodic plasmonic structures for high-density data storage.

Stable and controllable optical memory is necessary for the development of current information technology. In this context, Ag/TiO2 films have received much attention for their photosensitivity in wavelength and polarization, which can be applied to high-density optical storage. Here, we carried out dual-wavelength holographic recording using 403.4nm and 532nm lasers, and obtained mixed microfringes based on selective photodissolution of Ag nanoparticles of various sizes in TiO2 nanoporous films. Two recording methods of simultaneous and sequential multiplexing were investigated. It was found that using simultaneous irradiation it is easier to obtain equivalent efficiency in both spectral hole burning and multiplexed grating diffraction, compared with the sequential one. The results can be explained by the Time-accumulation effect during Ag+ ion diffusion and migration in holographic recordings. Based on such properties, multiplexed-holographic fringes with uniform contrast were reserved by simultaneous recording in Ag/TiO2 films. This work provides a new strategy for fabrication of photonic devices with complex microstructures.

Determination of crustal thickness under Tibet from gravity-gradient data

We develop a novel regional inversion algorithm to determinate the Moho geometry from the gravity-gradient data. The procedure involves two steps. Firstly, the refined gravity-gradient data, which comprise mainly the gravitational signal of the Moho geometry, are obtained from applying the gravimetric forward modeling by using a tesseroid method. Secondly, the refined gravity-gradient data are used to find the Moho depth. The functional relationship between the (known) refined gravity-gradient data and the (unknown and sought) Moho depth is defined by means of the (nonlinear) Fredholm integral equation of the first kind, which is further linearized by means of applying a Taylor series. To stabilize the inverse solution of the system of observation equations, the Tikhonov regularization is applied. The developed algorithm is tested at the study area of Tibet characterized by the largest crustal thickness. Results of the gravimetric inversion (for the uniform and variable Moho density contrast models) have a relatively good agreement with the seismic model (CRUST1.0) at the level of expected uncertainties of about 5km without the presence of a significant systematic bias.

Moho modeling in spatial domain: A case study under Tibet

We develop and apply the algorithm for a regional gravimetric Moho recovery in spatial domain. The functional relation between the (known) refined gravity field and the (unknown and sought) Moho depth is defined by means of solving the Fredholm integral equation of the first kind. Linearization is applied to define the Moho depth corrections with respect to the mean Moho depth. The system of linearized observation equations is solved to find the Moho depth corrections, and Tikhonov’s regularization is applied to stabilize this ill-posed inverse problem. Developed algorithm is applied to model the Moho depth regionally under the Tibetan Plateau and Himalayas, while adopting the uniform and variable Moho density contrast models, and gravimetric results are validated using the CRUST1.0 seismic model. Our results show a relatively good agreement between gravimetric and seismic models, without presence of a significant systematic bias. Our result, however, indicates that for a regional study the variable Moho density contrast might not improve the results especially when density structure of the lower crust and uppermost mantle is not know accurately. In that case, the use of the uniform Moho density contrast for a regional Moho recovery is more appropriate.

Synthesis of continuous hexagonal boron nitride films on alloy substrate

Large-scale hexagonal boron nitride (h-BN) film has been recognized to be extremely attractive for various applications since it is found as the best dielectric substrate for graphene devices. Here we report the successful synthesis of few-layer continuous h-BN film on Cu-Ni alloy containing 30at.% Ni. The h-BN films show uniform contrast both in scanning electron microscopy and optical images. The thickness of h-BN films can be controlled by modifying the weight of the source precursor. Results obtained from various characterizations show that the h-BN film is in a high quality of lattice structure. The method will facilitate both fundamental research and future applications based on large-area high-quality h-BN films.

Three-Dimensional Reconstruction of the Craniofacial Skeleton With Gradient Echo Magnetic Resonance Imaging ("Black Bone"): What Is Currently Possible?

Three-dimensional (3D) reconstructed computed tomography (CT) imaging has become an integral component of craniomaxillofacial patient care. However, with increasing concern regarding the use of ionizing radiation, particularly in children with benign conditions who require repeated examinations, dose reduction and nonionizing alternatives are actively being sought. The "Black Bone" magnetic resonance imaging (MRI) technique provides uniform contrast of the soft tissues to enhance the definition of cortical bone. The aim of this study was to develop methods of 3D rendering of the craniofacial skeleton and to ascertain their accuracy. "Black Bone" MRI datasets acquired from phantoms, adult volunteers and patients were segmented and surface and/or volume rendered using 4 commercially available or open source software packages. Accuracy was explored using a custom phantom (permitting direct measurement), CT and MRI. "Black Bone" MRI datasets were successfully used to create 3D rendered images of the craniofacial skeleton in all 4 software packages. Comparable accuracy was achieved between CT and MRI 3D rendered images of the phantom. The "Black Bone" MRI technique provides a viable 3D alternative to CT examination when imaging the craniofacial skeleton.

“Colossal” interstitial supersaturation in delta ferrite in stainless steels: (II) low-temperature nitridation of the 17-7 PH alloy

Low-temperature gas-phase nitridation has been studied in interstitially-hardened 17-7 precipitation-hardening stainless steel. After nitridation, conventional transmission electron microscopy reveals that delta ferrite grains in such alloys show a uniform weak diffraction contrast. Chemical analysis reveals that the weak-contrast ferrite grains contain an enormous interstitial nitrogen supersaturation (>20 at.%). Surprisingly, there is no significant tetragonality in these weak-contrast ferrite grains. Such weak diffraction contrast is attributed to a nanometer-scale nitridation-induced spinodal decomposition of delta ferrite grains. In addition, nitride nanoparticles are observed in the steel, and were identified as rocksalt-structured MN nitride (M: Fe, Cr, Ni, and Al). Further, platelets of hexagonal M2N1-x are observed at low nitriding temperatures (623 and 653 K), but were absent during nitridation at a higher temperature (713 K).

Single-Molecule Imaging of Iron-Phthalocyanine-Catalyzed Oxygen Reduction Reaction by in Situ Scanning Tunneling Microscopy

We report herein an in situ electrochemical scanning tunneling microscopy (ECSTM) investigation of iron-phthalocyanine (FePc)-catalyzed oxygen reduction reaction (ORR). A highly ordered FePc adlayer is revealed on a Au(111) electrode. The center ions in the FePc adlayer show uniform high contrast in an oxygen-saturated electrolyte, which is attributed to the formation of an FePc-O2 complex. In situ STM results reveal the sharp contrast change upon shifting the electrode potential to trigger the ORR. Theoretical simulation has supplied further evidence for the contrast difference of the adsorbed FePc species.

Synthesis of BiFeO3 thin films on single-terminated Nb : SrTiO3 (111) substrates by intermittent microwave assisted hydrothermal method

We report on a simple and fast procedure to create arrays of atomically flat terraces on single crystal SrTiO3 (111) substrates and the deposition of ferroelectric BiFeO3 thin films on such single-terminated surfaces. A microwave-assisted hydrothermal method in deionized water and ammonia solution selectively removes either (SrO3)4− or Ti4+ layers to ensure the same chemical termination on all terraces. Measured step heights of 0.225 nm (d111) and uniform contrast in the phase image of the terraces confirm the single termination in pure and Nb doped SrTiO3 single crystal substrates. Multiferroic BiFeO3 thin films were then deposited by the same microwave assisted hydrothermal process on Nb : SrTiO3 (111) substrates. Bi(NO3)3 and Fe(NO3)3 along with KOH served as the precursors solution. Ferroelectric behavior of the BiFeO3 films on Nb : SrTiO3 (100) substrates was verified by piezoresponse force microscopy.

A Review of Damaged Manuscripts Using Binarization Techniques.

Image binarization is the procedure of separating pixel values into two parts, black as foreground and white as background. In binarization document image is converted into binary image using thresholding techniques. Many binarization algorithms have been proposed for different types of degraded document images. The main objective of image enhancement is to modify attributes of an image to make it more suitable for a given task . To remove the noise and improve the quality of the document binarization techniques are used. Thresholding is one of such binarzation technique which is used for this purpose. Thresholding is further divided into the global and local thresholding techniques. In the document with uniform contrast delivery of background and foreground, global thresholding has been found to be best technique. Local thresholding , is an approach for the situations in which single value thresholding does not yield proper result, to overcome this a hybrid approach is introduced which is a combination of local with Otsu’s thresholding.

Characterization of deformation and physical force in uniform low contrast anatomy and its impact on accuracy of deformable image registration.

Little is known about the effect of force on organ deformation and consequently its impact on precision dose delivery. The purpose of this study was to evaluate the fundamental relationship between anatomic deformation and its causative physical force to ascertain if a threshold limit exists for deformable image registration (DIR) accuracy in uniform low contrast anatomy, beyond which its applicability may be clinically inappropriate. To simulate a simplified model, a tissue equivalent deformable bladder phantom with 21 implanted fiducial markers was developed using a viscoelastic polymer. The bladder phantom was deformed by applying a force in increments from 10 to 70 N. DIR accuracy was studied using intensity based mim and Velocity B-spline algorithms by comparing the 3D vector of the 21 marker locations at the original target image with the synthetically derived marker positions from each target image obtained from DIR. The relationship between applied force in 1D deformation along the axis of applied force and 3D deformation of the phantom showed a linear response. The maximum and average displacements of markers exhibited a nonlinear response to the applied force. In the absence of implanted markers, DIR performance was suboptimal with a threshold limit of only 20 N (5 mm deformation) beyond which the average marker error was ≥3 mm. DIR performance improved significantly with the addition of only one marker for the intensity based mim algorithm. In contrast, the Velocity B-spline algorithm showed reduced sensitivity to the number of markers introduced in both the source and target images. The limits of applicability of DIR are strongly dependent on the magnitude of deformation. There is a threshold limit beyond which the accuracy of DIR fails in uniform low contrast anatomy. The sensitivity of the DIR performance to the number of fiducial markers present indicates that if DIR performance is solely assessed with the contrast rich features present in clinical anatomy, the results may not be reflective of the true DIR performance in uniform low contrast anatomy.

Simultaneous polarization Mirau interferometer based on pixelated polarization camera.

We propose a polarization Mirau interferometer using the pixelated polarization camera to acquire the four phase-shifted interferograms simultaneously by which motionless phase shift can be realized. A wire-grid polarizer is employed as the polarization beam splitter to realize the adjustable fringe contrast. Due to the limited contrast ratio of split orthogonally polarized beams with a wire grid polarizer, the corresponding calibration method by superposition of exchanged transmitted and reflected beams is proposed to obtain the uniform fringe contrast in four phase-shifted interferograms. The accuracy of the proposed system is demonstrated experimentally, and a precision better than 1/500 wavelength is achieved. The proposed system provides a feasible way to obtain the instantaneous measurement with minimizing environmental disturbance.

Bad Colour Maps Hide Big Features and Create False Anomalies

SUMMARY Many colour maps provided by vendors have highly uneven perceptual contrast over their range. It is not uncommon for colour maps to have perceptual flat spots that can hide a feature as large as one tenth of the total data range. The opposite can also occur whereby perceptual discontinuities in the colour map can induce the appearance of false anomalies. This paper presents a set of design techniques that allow colour maps to be constructed with uniform perceptual contrast across their full range. The most important factor in designing a colour map is to ensure that the magnitude of the incremental change in perceptual lightness of the colours across the map is uniform. The rate of incremental change in hue or saturation of the colours in the map prove to be relatively unimportant when one is seeking to discern features at fine spatial frequencies. Accordingly, the colour maps presented here are designed in CIELAB colour space. In contrast to RGB this colour space provides a perceptual organization of colours in terms of their lightness, hue and chroma/saturation which facilitates the design process. The utility of the colour maps presented here is demonstrated using a simple test image that allows the perceptual uniformity of colour maps to be readily evaluated.

Microwave dielectric properties of Ga3+ and Ta5+ co-doped CaTiO3

Compositions in the (1 − x)CaTiO3–xCa(Ta1/2Ga1/2)O3 (x = 0.4, 0.45, 0.50, 0.55) series were processed through a solid-state mixed-oxide route. X-ray diffraction (XRD) of x = 0.5 and 0.55 compositions revealed the formation of single-phase ceramics with orthorhombic (Pbnm) symmetry. At x ≤ 0.45, a couple of low intensity XRD peaks matching PDF# 04-002-5066 for Ca3TiTaGa3O12 were also observed which indicated second-phase formation. The microstructure of the sintered pellets for x = 0.5 and 0.55 compositions comprised densely packed irregular-shaped large grains with uniform contrast. The unit cell volume increased with increasing Ta5+ and Ga3+ contents at the B-site, which caused a decrease in both the relative permittivity (er) and temperature coefficient of resonance frequency (τf) but an increase in quality factor (Q × fo). The optimum microwave dielectric properties (i.e., er ~ 47, Q × fo ~ 26,630 GHz and τf ~ −2.64 ppm/ °C) were achieved for the x = 0.5 composition (i.e., CaTi0.5Ta0.25Ga0.25O3) which can be a potential candidate material for microwave dielectric applications. Thus, the substitution of Ta and Ga at the B-site of CaTiO3 was useful in tuning the larger positive τf through zero and increasing Q × fo without too much compromise on er.

Microstructural pore analysis of the catalyst layer in a polymer electrolyte membrane fuel cell: A combination of resin pore-filling and FIB/SEM

An analytical method was developed for focused ion beam (FIB)/scanning electron microscope (SEM) analysis of the microstructural pore properties of the catalyst layers in a polymer electrolyte membrane fuel cell (PEMFC). Generally, cross-sectional images of the catalyst layer obtained by FIB/SEM do not have uniform contrast in the pore area because carbons are often visible behind the cross-section, which makes conventional analysis inadequate. In the present study, by filling the pores of the catalyst layer with metalliferous epoxy polymer and using FIB/SEM, uniform contrast across the entire pore area was achieved without damage. The pore area was differentiated from the carbon network to produce a bi-segmented cross-sectional image. Subsequent digital image analysis revealed catalyst layer properties such as pore distribution and porosity at the microscopic level. The method was validated by comparing the porosity thus obtained from this method with that from mercury intrusion porosimetry measurements.

Image Binarization for Degraded Document Images

Image binarization is the separation of each pixel values into two collections, black as a foreground and white as a background. Thresholding technique is used for document image binarization. Image binarization plays vital role in segmentation of text from the document images that are badly degraded due to the high inter\intra variations between the foreground text of document images and document background. This paper, proposes technique to address the issues of degraded images using adaptive image contrast. The adaptive image contrast technique is a combination of the local image contrast and the local image gradient. And they are tolerant to variation of text and background. Such variations are caused by number of document degradations. The proposed technique, constructs adaptive contrast map for degraded image .the contrast map is combined with Canny’s edge map, for the identification of text stroke edge pixels. Thresholding technique can be applied as global technique and local technique. Global thresholding is suitable for a document where there is uniform contrast delivery of background and foreground. However global thresholding fails to the applications where difference in contrast, Extensive background noise and difference in brightness exists. in such circumstances categorization of many pixels as a foreground or as a background is not so easy. Local thresholding plays significant role in such cases. Local thresholding technique uses local threshold t; w.r.t .local window to segment the document image .this local threshold t is estimated based on the intensities of detected text stroke edge pixels. The proposed method is simple, robust, and involves minimum parameter tuning. It has been tested on three public datasets that are used in the recent document image binarization contest (DIBCO) 2009 & 2011 and handwritten-DIBCO 2010.

Echocardiographic Algorithm for Post–Myocardial Infarction LV Thrombus: A Gatekeeper for Thrombus Evaluation by Delayed Enhancement CMR

ObjectivesThe goal of this study was to determine the prevalence of post–myocardial infarction (MI) left ventricular (LV) thrombus in the current era and to develop an effective algorithm (predicated on echocardiography [echo]) to discern patients warranting further testing for thrombus via delayed enhancement (DE) cardiac magnetic resonance (CMR). BackgroundLV thrombus affects post-MI management. DE-CMR provides thrombus tissue characterization and is a well-validated but an impractical screening modality for all patients after an MI. MethodsA same-day echo and CMR were performed according to a tailored protocol, which entailed uniform echo contrast (irrespective of image quality) and dedicated DE-CMR for thrombus tissue characterization. ResultsA total of 201 patients were studied; 8% had thrombus according to DE-CMR. All thrombi were apically located; 94% of thrombi occurred in the context of a left anterior descending (LAD) infarct-related artery. Although patients with thrombus had more prolonged chest pain and larger MI (p ≤ 0.01), only 18% had aneurysm on echo (cine-CMR 24%). Noncontrast (35%) and contrast (64%) echo yielded limited sensitivity for thrombus on DE-CMR. Thrombus was associated with stepwise increments in basal → apical contractile dysfunction on echo and quantitative cine-CMR; the echo-measured apical wall motion score was higher among patients with thrombus (p < 0.001) and paralleled cine-CMR decrements in apical ejection fraction and peak ejection rates (both p < 0.005). Thrombus-associated decrements in apical contractile dysfunction were significant even among patients with LAD infarction (p < 0.05). The echo-based apical wall motion score improved overall performance (area under the curve 0.89 ± 0.44) for thrombus compared with ejection fraction (area under the curve 0.80 ± 0.61; p = 0.01). Apical wall motion partitions would have enabled all patients with LV thrombus to be appropriately referred for DE-CMR testing (100% sensitivity and negative predictive value), while avoiding further testing in more than one-half (56% to 63%) of patients. ConclusionsLV thrombus remains common, especially after LAD MI, and can occur even in the absence of aneurysm. Although DE-CMR yielded improved overall thrombus detection, apical wall motion on a noncontrast echocardiogram can be an effective stratification tool to identify patients in whom DE-CMR thrombus assessment is most warranted. (Diagnostic Utility of Contrast Echocardiography for Detection of LV Thrombi Post ST Elevation Myocardial Infarction; NCT00539045)

Imaging Hepatocellular Carcinoma with Dynamic CT Before and After Transarterial Chemoembolization: Optimal Scan Timing of Arterial Phase

The aim of this study was to determine the optimal arterial phase delay for computed tomography imaging of hepatocellular carcinoma (HCC) before and after transarterial chemoembolization (TACE) using a low iodine dose protocol. A total of 39 patients with known HCC were imaged with dynamic computed tomography of the liver (40-second scan duration, 60 mL of contrast medium), both on the same day before TACE and 1 day after TACE. Time attenuation curves of vessels, nonmalignant liver parenchyma, and 62 HCCs were normalized to a uniform aortic contrast arrival and analyzed. Maximal arterial phase HCC to liver contrast was reached between 13 and 17 seconds after aortic contrast arrival, both before and after TACE. Using our low iodine dose protocol, arterial phase imaging of HCC should be performed between 13 and 17 seconds after aortic contrast arrival, both before and after TACE.