Improved Contrast Ratio Research Articles

Spatial domain reconstruction for imaging speed-of-sound with pulse-echo ultrasound: simulation and in vivo study

Despite many uses of ultrasound, some pathologies such as breast cancer still cannot reliably be diagnosed in either conventional B-mode ultrasound imaging nor with more recent ultrasound elastography methods. Speed-of-sound (SoS) is a quantitative imaging biomarker, which is sensitive to structural changes due to pathology, and hence could facilitate diagnosis. Full-angle ultrasound computed tomography (USCT) was proposed to obtain spatially-resolved SoS images, however, its water-bath setup involves practical limitations. To increase clinical utility and for widespread use, recently, a limited-angle Fourier-domain SoS reconstruction was proposed, however, it suffers from significant image reconstruction artifacts. In this work, we present a SoS reconstruction strategy, where the forward problem is formulated using differential time-of-flight measurements based on apparent displacements along different ultrasound wave propagation paths, and the inverse problem is solved in spatial-domain using a proposed total-variation scheme with spatially-varying anisotropic weighting to compensate for geometric bias from limited angle imaging setup. This is shown to be robust to missing displacement data and easily allow for incorporating any prior geometric information. In numerical simulations, SoS values in inclusions are accurately reconstructed with 90% accuracy up to a noise level of 50%. With respect to Fourier-domain reconstruction, our proposed method improved contrast ratio from 0.37 to 0.67 for even high noise levels such as 50%. Numerical full-wave simulation and our preliminary in vivo results illustrate the clinical applicability of our method in a breast cancer imaging setting. Our proposed method requires single-sided access to the tissue and can be implemented as an add-on to conventional ultrasound equipment, applicable to a range of transducers and applications.

25‐4: Visibility Evaluation of Direct‐Bonded Signage Display for Outdoor Use

Technology of the direct bonded signage display that we developed can easily convert a glass space to digital signage by spot construction. For evaluating its outdoor visibility, we built an artificial ambient illumination environment of 10000 lux, and evaluation methods for bright conditions considering contrast sensitivity function. We found improved contrast ratio of 1.2 times and visibility of gradation difference.

Deep Neural Networks for Ultrasound Beamforming.

We investigate the use of deep neural networks (DNNs) for suppressing off-axis scattering in ultrasound channel data. Our implementation operates in the frequency domain via the short-time Fourier transform. The inputs to the DNN consisted of the separated real and imaginary components (i.e. in-phase and quadrature components) observed across the aperture of the array, at a single frequency and for a single depth. Different networks were trained for different frequencies. The output had the same structure as the input and the real and imaginary components were combined as complex data before an inverse short-time Fourier transform was used to reconstruct channel data. Using simulation, physical phantom experiment, and in vivo scans from a human liver, we compared this DNN approach to standard delay-and-sum (DAS) beamforming and an adaptive imaging technique that uses the coherence factor. For a simulated point target, the side lobes when using the DNN approach were about 60 dB below those of standard DAS. For a simulated anechoic cyst, the DNN approach improved contrast ratio (CR) and contrast-to-noise (CNR) ratio by 8.8 dB and 0.3 dB, respectively, compared with DAS. For an anechoic cyst in a physical phantom, the DNN approach improved CR and CNR by 17.1 dB and 0.7 dB, respectively. For two in vivo scans, the DNN approach improved CR and CNR by 13.8 dB and 9.7 dB, respectively. We also explored methods for examining how the networks in this paper function.

Microbubble Axial Localization Errors in Ultrasound Super-Resolution Imaging.

Acoustic super-resolution imaging has allowed the visualization of microvascular structure and flow beyond the diffraction limit using standard clinical ultrasound systems through the localization of many spatially isolated microbubble signals. The determination of each microbubble position is typically performed by calculating the centroid, finding a local maximum, or finding the peak of a 2-D Gaussian function fit to the signal. However, the backscattered signal from a microbubble depends not only on diffraction characteristics of the waveform, but also on the microbubble behavior in the acoustic field. Here, we propose a new axial localization method by identifying the onset of the backscattered signal. We compare the accuracy of localization methods using in vitro experiments performed at 7-cm depth and 2.3-MHz center frequency. We corroborate these findings with simulation results based on the Marmottant model. We show experimentally and in simulations that detecting the onset of the returning signal provides considerably increased accuracy for super-resolution. Resulting experimental cross-sectional profiles in super-resolution images demonstrate at least 5.8 times improvement in contrast ratio and more than 1.8 times reduction in spatial spread (provided by 90% of the localizations) for the onset method over centroiding, peak detection, and 2-D Gaussian fitting methods. Simulations estimate that these latter methods could create errors in relative bubble positions as high as at these experimental settings, while the onset method reduced the interquartile range of these errors by a factor of over 2.2. Detecting the signal onset is, therefore, expected to considerably improve the accuracy of super-resolution.

Multi-mode interference-based photonic crystal logic gates with simple structure and improved contrast ratio

We present a MMI-based photonic crystal all-optical logic gate structure for logic functions such as XNOR, XOR, OR and NAND with square-type lattice of Si rods in air host. Phase-based logic inputs produce intensity-based logic outputs with high contrast ratio. The calculated ON to OFF contrast ratio for the logic functions XNOR/XOR and OR/NAND is 40.41 and 37.40 dB, respectively. Further, it is improved by 11.53 and 12.46% for XNOR/XOR and OR/NAND logic functions, respectively, by reducing the back reflection with the introduction of absorbing waveguides. The structure in both the forms has a fast response period that is less than or equal to 0.131 ps. The size of the structure is quite compact with dimension \(6.4\,\upmu \hbox {m} \times 8.8\,\upmu \hbox {m}\).

Improvement of contrast ratio in quadriphase-shift-keying optical label recognition with passive optical waveguide circuit

In photonic label routing networks, recognition of optical labels is one of the key functions. We have proposed waveguide-type optical circuits for recognition of optical labels encoded in quadriphase-shift-keying (QPSK) form. A basic device for the circuits consists of a 3-dB directional coupler, two Y-branches, and an asymmetric X-junction coupler. We employed a scheme of complete interference of optical waves between each coded pulse and a reference pulse in our previously reported paper. The contrast ratio of the output at the destination output port to the outputs at the other ports was reported to decrease to 1.6, 1.28, and 1.13 for two-, three-, and four-stage circuits for recognition of 16, 64, and 256 QPSK labels, respectively. We find optimum circuits with improved contrast ratio of 1.8, 1.6, and 1.47 for 16, 64, and 256 labels, respectively. The recognition operation with the improved circuits is numerically confirmed using the beam propagation method. Noise tolerance of the proposed circuits is also clarified by numerical simulation. The improved circuits are optimum from the viewpoint of efficient use of optical power and noise tolerance.

Changing liquid crystalline phase with field

ABSTRACTSince 1888, the liquid crystal display (LCD) industry is facing a fierce competition due to serious limitations such as poor contrast ratio and response time. Although some new materials have offered new applications and opened new markets for LCDs, materials with improved contrast ratio are highly desirable in LCD industry to sustain in the current market. This work reports a new behaviour in nano-material-doped liquid-crystal composite which is suitable for eradicating limitations of contrast ratio. Here, a high concentration of carbon nanotubes (CNTs) is doped in liquid crystal (LC) materials wherein the CNTs form aggregates in the LC composition. In these heavily doped samples, the phase change takes place with application of bias. This reversible process improves the contrast ratio as the material oscillates between crystalline and LC phases with field.

Fusion of infrared intensity and polarization images using embedded multi-scale transform

Multi-scale transforms are considered to be the effective methods in image fusion. However, infrared intensity and polarization images fusion based on these methods frequently arise the issues such as limited contrast ratio improvement and marginal area distortion. The embedded multi-scale decomposition has been proposed to integrate the advantages of different methods in this paper, where the low-frequency image continues to be decomposed by another multi-scale transform. The detailed procedure is shown as the following. Firstly, the low-frequency components and support value image sequences of infrared intensity and polarization images are obtained respectively with support value transform (SVT). Secondly, multi-scale bright and dim information are extracted from the last layer of the low-frequency images using the multi-scale top-hat decomposition, respectively. Thirdly, the resulted images are respectively fused and enhanced, and then fused with the two low-frequency images to get the fused low-frequency image. After that, the image is reversely transformed with the support value image sequences fused by extracting maximum gray to get the final image. Compared with the simple SVT and the multi-scale top-hat decomposition, the method suggested successfully improves the contrast ratio, the distortion of marginal area and the local coarseness. The validity of the method proposed is proven.

Power generating reflective-type liquid crystal displays using a reflective polariser and a polymer solar cell.

We herein report the results of a study of a power generating reflective-type liquid crystal display (LCD), composed of a 90° twisted nematic (TN) LC cell attached to the top of a light-absorbing polymer solar cell (PSC), i.e., a Solar-LCD. The PSC consisted of a polymer bulk-heterojunction photovoltaic (PV) layer of poly[[9-(1-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophenediyl] and [6,6]-phenyl C71 butyric acid methyl ester (PCDTBT:PCBM70), and showed a high power conversion efficiency of about 5%. In order to improve the visibility of the Solar-LCD, between the TN-LC and the PV cells we inserted a reflective polariser of a giant birefringent optical (GBO) film. The reflectivity from the Solar-LCD was observed to be considerably increased by more than 13–15% under illumination by visible light. The Solar-LCD also exhibited a significantly improved contrast ratio of more than 17–19. We believe there is a clear case for using such Solar-LCDs in new power-generating reflective-type displays; taken as a whole these results also demonstrate the possibility of their application in a number of energy-harvesting opto-electrical display devices.

Adaptive diagonal loaded minimum variance beamforming applied to medical ultrasound imaging

In order to enhance the robustness and contrast in the minimum variance (MV) beamformer, adaptive diagonal loading method was proposed. The conventional diagonal loading technique has already been used in the MV beamformer, but has the drawback that its level is specified by predefined parameter and without consideration of input-data. To alleviate this problem, the level of diagonal loading was computed appropriately and automatically from the given data by shrinkage method in the proposed adaptive diagonal loaded beamformer. The performance of the proposed beamformer was tested on the simulated point target and cyst phantom was obtained using Field II. In the point target simulation, it is shown that the proposed method has higher lateral resolution than the conventional delay-and-sum beamformer and could be more robust in estimating the amplitude peak than the MV beamformer when acoustic velocity error exists. In the cyst phantom simulation, the proposed beamformer has shown that it achieves an improvement in contrast ratio and without distorting the edges of cyst.

Synthesis and Thermal Stability of Solvent Soluble Dyes Based on Dimerized Diketo-pyrrolo-pyrrole Pigment

These considerations are importantbecause industry is targeting both improved contrast ratio(over 18,000) and higher transmittance for the next to 8-generation of LCD filters. C.I. Pigment Red 254, which is based on DPP (Diketo-pyrrolo-pyrrole) and was first synthesized by Ciba-Geigy,has mainly found use in paints and inks as well as LCD colorfilters owing to its excellent thermal stability and bright redshade.

Synthesis of tricyanopyrrolidone derivatives as synergists for improving contrast ratio of liquid crystal displays

The contrast ratio is an important color property of liquid crystal displays. Color properties are classified as colors' purity, contrast ratio, and brightness; these mainly depend on pigment properties. The contrast ratio in particular can be improved by minimizing the light scattering of pigment particles, which is directly related to their degree of dispersion. Therefore, synergists are usually employed to increase the contrast ratio by augmenting the dispersion efficiency. In this study, tricyanopyrrolidone derivatives as blue color synergists were synthesized and examined for their performance to improve the contrast ratio of liquid crystal displays. The results of this study prove that tricyanopyrrolidone derivatives as synergists for blue pigment effectively improve the contrast ratio.

Influence of ZnO nanoparticle concentration on electro-optic and dielectric properties of ferroelectric liquid crystal mixture

We present here the electro-optic and dielectric properties of ZnO nanoparticle doped ferroelectric liquid crystal (FLC) mixtures. A small quantity of ZnO nanoparticles (0.0, 0.1, 0.3, 0.5 and 1.0wt.%) was dispersed into FLC with a thickness of 5.0±0.2μm. The enhancement in physical parameters is found to be dependent on ZnO nanoparticle concentration. The lower concentration of ZnO nanoparticles (0.1–0.3wt.%) enhances the value of spontaneous polarization and decreases for higher concentration (0.5–1.0wt.%). The fastening of response time has also been noticed in the doped sample cells up to 0.3wt.% concentration. Dielectric measurements revealed a concentration dependence effect in all sample cells. A low threshold voltage and improved contrast ratio has been noticed for 0.3wt.% concentration over other doped samples.

P.95: Process Technology of Flexible and Transparent Display by Stacking OLED and PDLC Embedded with OPV

AbstractIn this paper, we have demonstrated a flexible and transparent display consisting of PDLC with in‐cell OLED and OPV. PDLC, OLED, and OPV were stacked vertically inside two flexible substrates, where PDLC and OLED served as the functions of reflective‐ and emissive‐modes, respectively, while OPV can be used for energy harvesting and light sensing. Besides, it was the black background for PDLC and OLED for improving contrast ratio.

Quantitative contrast ratio comparison between T1 (TSE at 1.5T, FLAIR at 3T), magnetization prepared rapid gradient echo and subtraction imaging at 1.5T and 3T.

Creating contrast between normal anatomy and pathology is the main goal of imaging. Here we compare contrast ratios of enhancing brain lesions at 1.5T between T1 TSE, magnetization prepared rapid gradient echo (MPRAGE) and subtraction and at 3T between T1 FLAIR, MPRAGE and subtraction. Contrast ratio between enhancing lesions and normal contralateral brain was measured for above mentioned sequences during the same imaging session. A total of 27 exams on 25 patients were evaluated. A total of 90 enhancing brain lesions were utilized. Of these 46 were <5 mm diameter. Taking all lesions into account there was a small but statistically significant improvement in contrast ratio at 1.5T with MPRAGE compared to T1 TSE and at 3T for T1 FLAIR compared to MPRAGE. However, there was no statistically significant difference between these sequences for lesions 5 mm or less in diameter. However, subtraction provided a marked and statistically significant improvement in contrast ratio for both all lesions and including only lesions 5 mm or less in diameter. Our data indicate that for small lesions at 1.5T there is no significant difference in contrast ratio (CR) between T1 TSE and MPRAGE or at 3T between T1 FLAIR and MPRAGE despite the MPRAGE having the advantage of much thinner slices and a higher matrix. However, subtraction provided a markedly improved CR for all lesions at 1.5T and 3T regardless of lesion size. Subtraction should be considered for clinical use to improve detection of small or subtle enhancing lesions.

High contrast blue organic light-emitting diodes using inorganic multilayers of Al and ZnSe

High contrast blue organic light-emitting diodes were fabricated using an inorganic multilayer of NPB (700 Å)/MADN (200 Å)/Alq3 (300 Å)/LiF (10 Å)/Al (70 Å)/ZnSe (300 Å)/Al (1000 Å). The optical and electrical characteristics were measured and compared to conventional organic light-emitting devices (OLEDs) and OLEDs with polarizers. OLEDs with the metal multilayer cathodes had an improved contrast ratio of 135∶1 compared to 104∶1 for OLEDs with polarizers. In addition, the multilayer OLEDs had a low turn-on voltage of 3.5 V due to energy band fitting of ZnSe with Al and the electron transport layer.

Changes in material parameters for dye-doped ferroelectric liquid crystal

Addition of the dichroic anthraquinone dye molecules in pure ferroelectric liquid crystal (FLC) matrix results in many improvement in the various vital parameters of the pure FLC. However, addition of anthraquinone dye molecules in pure FLC matrix is not advantageous every time. There are certain constraints which are crucial for the application of these systems into many devices. In this article, we have discussed the concentration and temperature dependence of vital properties of dye-doped FLC. In this study there is improvement in contrast ratio by dye doping due to enhancement in plane switching for dye-doped FLC.

Applications of multidirectional reflective light-control films on reflective polymer-dispersed liquid crystal displays for enhancement in image quality at lower viewing angles

In this paper, multidirectional light-control reflective (LCR) films are developed in order to create an active reflective structure that will enhance the image brightness and contrast ratio of reflective dye-doped polymer-dispersed liquid crystal (D-PDLC) displays at lower viewing angles. Advantages of LCR films are that their production is low cost and they require a simple photolithographic fabrication method. The optimum design prism-type light-control reflective film succeeded in minimising the surface scattering effect; thus, the contrast ratio is much enhanced. The symmetric and asymmetric LCR films produced multidirectional scattering that enhances the reflectance at lower viewing angles, which has importance in future display applications. In particular, the prism LCR film has been found to be more influential on the reflectance of D-PDLC films due to multidirectional scattering of light by non-symmetric arrays. The improvement in contrast ratio has been confirmed by the enhancement of optical properties for reflective D-PDLC displays at lower viewing angles below 30°.

Improvement of contrast ratio in saturated OPCPA system by using pump pulse shaping and time delay control

We theoretically investigated the temporal profile of a background pedestal in a single-stage optical parametric chirped pulse amplification (OPCPA) system, and showed that the amplified spontaneous emission (ASE) prepulse in the saturation regime degrades the contrast ratio. To improve the contrast ratio in a saturated OPCPA system, a method using pump pulse shaping and the time delay control between pump and seed pulses was utilized. Through numerical simulations, the effect of the rising time and the time delay of a pump pulse on the background pedestal was subsequently investigated in terms of the contrast ratio. From the simulation results, it was determined that an optimal rising time and the time delay of the pump pulse are critical for obtaining a high-contrast broadband laser pulse from a saturated OPCPA system.

Static and dynamic characterization of pull-in protected CMOS compatible poly-SiGe grating light valves

Grating light valve (GLV) display pixels are reflection type diffraction gratings consisting of electrostatically movable coplanar microbeams. Once actuated, the alternate movable beams deflect downwards which produces controlled diffraction of light creating bright and dark pixels in a display system. GLV displays provide a huge improvement in contrast ratio and resolution over other MOEMS devices. At the same time, compared to hybrid integration, post processing of MEMS monolithically on top of CMOS can lead to increased functionality, performance and reliability. Poly-SiGe structural layers can be deposited at low temperature (∼450°C), allowing to retain the performance of underlying CMOS electronics though possessing the desired material properties for MEMS. Hence the aim of this work is to fabricate CMOS compatible poly-SiGe GLVs and to study their static and dynamic behavior. A novel process flow was developed regarding the deposition of thin poly-SiGe structures which is well within the maximum thermal range to retain the full functionality of the underlying CMOS circuitry. A contrast of over 1500:1 was obtained showing excellent optical response of the devices. The effect of squeeze film damping in determining the dynamic response of the GLVs is thoroughly investigated. Influence of variation in dimensional parameters on the settling time of the structures is discussed in detail. A minimum settling time of 2μs was achieved for our devices. We also showed the analog gray scale nature of the GLVs. In addition, we also use the technique of mechanical stoppers to avoid accidental destruction of the devices because of the pull-in phenomenon.