Spatial Frequency Components Research Articles

High-speed flame chemiluminescence imaging using time-multiplexed structured detection

In this work, high-speed flame chemiluminescence has been obtained by using the time-multiplexed structured detection (TMSD) imaging method from a single snapshot. TMSD sheers the time lapse into the spatial frequency shifts, which allows multiple high-speed images to be frequency upshifted into distinct spatial frequency regions from the original image. A cumulative exposure captured in a single snapshot image contains distinct time evolution. Each distinct image is demultiplexed and recovered by hyperdyne mixing with the modulation frequency. TMSD is an optical frequency domain analog to carrier frequency modulation in radio and microwave detections. Specifically, a digital micromirror device (DMD) spatially modulates flame chemiluminescence just prior to the camera. Spatial frequency of each distinct image is mixed between the original spatial frequency components and DMD modulation pattern frequency, resulting in a coded snapshot. The high-speed flame chemiluminescence image is recovered by demodulation. TMSD is similar to structured illumination used in super-resolution microscopy, but offers more advantages, for it does not alternate incident illumination light. Since DMDs are available with speeds up to 40kHz, this technique shows promise as a cost-effective means of high-speed imaging and diagnostics of combustion phenomena.

THE FOURIER RADIAL ERROR SPECTRUM PLOT: A MORE NUANCED QUANTITATIVE EVALUATION OF IMAGE RECONSTRUCTION QUALITY.

In the modern biomedical image reconstruction literature, the quality of a reconstructed image is often numerically quantified using scalar error measures such as mean-squared error or the structural similarity index. While such measures provide a rough summary of image quality, they also suffer from well-known limitations. For example, a substantial amount of information is necessarily lost whenever the characteristics of a high-dimensional image are summarized by a single number. In this work, we introduce the Fourier radial Error Spectrum Plot (ESP), which provides a novel and more nuanced assessment of error by decomposing the error into its different spatial frequency components. The usefulness of ESP is illustrated in the context of MRI reconstruction from under-sampled data. In addition, we demonstrate that the extra dimension of insight provided by ESP can be used to improve the performance of existing image reconstruction techniques.

On the matching medium for microwave-based medical diagnosis**This work was supported in part by the University of Queensland under the University of Queensland Postdoctoral Research Fellowship Scheme, Chalmers University of Technology under the Karl G Eliasson Supplementary Fund, and Swedish Research Council under Grant number 2010-7262-78830-59.

In microwave-based medical diagnosis, reflections of electromagnetic waves from the air–skin interface can be reduced with a proper choice of matching medium such that electromagnetic radiation can be effectively penetrated into and through human bodies. Due to the heterogeneous and lossy nature of tissue and the fact that the electromagnetic problem varies as a function of matching medium, frequency, incident angles and polarization, it is not trivial to analyze the entire propagation phenomena. In this study, transmission of electromagnetic wave through a multi-layer planar human tissue model with different matching medium is considered. The reflected, absorbed and transmitted power components are computed to quantify the transmission performance of the matching medium. Our results show that although reflection can be minimized through a proper choice of matching medium, it does not necessary result in an optimal transmission as the transmitted signal is severely attenuated inside the tissue. Our results also show that the oblique incidence plane wave components, which in general correspond to the non-zero spatial frequency components of a near field distribution, can better penetrate through the tissue when a low-permittivity matching medium is used. These findings suggest that a better signal integrity can be obtained when a low-permittivity matching medium ( between 5 and 30) is used.

An improved non-uniformity correction algorithm and its GPU parallel implementation

The performance of SLP-THP based non-uniformity correction algorithm is seriously affected by the result of SLP filter, which always leads to image blurring and ghosting artifacts. To address this problem, an improved SLP-THP based non-uniformity correction method with curvature constraint was proposed. Here we put forward a new way to estimate spatial low frequency component. First, the details and contours of input image were obtained respectively by minimizing local Gaussian curvature and mean curvature of image surface. Then, the guided filter was utilized to combine these two parts together to get the estimate of spatial low frequency component. Finally, we brought this SLP component into SLP-THP method to achieve non-uniformity correction. The performance of proposed algorithm was verified by several real and simulated infrared image sequences. The experimental results indicated that the proposed algorithm can reduce the non-uniformity without detail losing. After that, a GPU based parallel implementation that runs 150 times faster than CPU was presented, which showed the proposed algorithm has great potential for real time application.

Theoretical characterization of annular array as a volumetric optoacoustic ultrasound handheld probe.

Optoacoustic ultrasound (OPUS) is a promising hybridized technique for simultaneous acquisition of functional and morphological data. The optical specificity of optoacoustic leverages the diagnostic aptitude of ultrasonography beyond anatomy. However, this integration has been rarely practiced for volumetric imaging. The challenge lies in the effective imaging probes that preserve the functionality of both modalities. The potentials of a sparse annular array for volumetric OPUS imaging are theoretically investigated. In order to evaluate and optimize the performance characteristics of the probe, series of analysis in the framework of system model matrix was carried out. The two criteria of voxel crosstalk and eigenanalysis have been employed to unveil information about the spatial sensitivity, aliasing, and number of definable spatial frequency components. Based on these benchmarks, the optimal parameters for volumetric handheld probe are determined. In particular, the number, size, and the arrangement of the elements and overall aperture dimension were investigated. The result of the numerical simulation suggests that the segmented-annular array of 128 negatively focused elements with 1λ × 20λ size, operating at 5-MHz central frequency showcases a good agreement with the physical requirement of both imaging systems. We hypothesize that these features enable a high-throughput volumetric passive/active ultrasonic imaging system with great potential for clinical applications.

The Bandwidth of Diagnostic Horizontal Structure for Face Identification.

Horizontally oriented spatial frequency components are a diagnostic source of face identity information, and sensitivity to this information predicts upright identification accuracy and the magnitude of the face-inversion effect. However, the bandwidth at which this information is conveyed, and the extent to which human tuning matches this distribution of information, has yet to be characterized. We designed a 10-alternative forced choice face identification task in which upright or inverted faces were filtered to retain horizontal or vertical structure. We systematically varied the bandwidth of these filters in 10° steps and replaced the orientation components that were removed from the target face with components from the average of all possible faces. This manipulation created patterns that looked like faces but contained diagnostic information in orientation bands unknown to the observer on any given trial. Further, we quantified human performance relative to the actual information content of our face stimuli using an ideal observer with perfect knowledge of the diagnostic band. We found that the most diagnostic information for face identification is conveyed by a narrow band of orientations along the horizontal meridian, whereas human observers use information from a wide range of orientations.

Large area deep subwavelength interference lithography with a 35 nm half-period based on bulk plasmon polaritons

Interference lithography is an important method for fabricating periodical nano-structures. Its resolution, however, is limited with the minimum period being half the wavelength of light due to the diffraction limit. In this study, we presented bulk plasmon polariton (BPP) interference lithography with the resolution far beyond the diffraction limit. As a demonstrative result, a periodical line pattern of a 35 nm half-period (about 1/10 the wavelength of laser) over a large area (20 × 20 mm) was achieved in an experiment. The break of diffraction limit arises from exciting BPP modes with the high kx spatial frequency components inside hyperbolic metamaterial (HMM) composed by metal-dielectric multifilms. To enhance the contrast and intensity of the interference fringe field of two BPP modes, a metal cladding resist layer and optimized materials are employed. In addition, the period of interference patterns could be tuned by exciting BPP modes with variant kx spatial frequency. It is believed that the method with low cost, large area, and high resolution advantages has potential applications for manufacturing functional structures like gratings, polarizers and photonic crystals, etc.

Examining the Spatial Frequency Components of a Digital Dental Detector

Digital X-ray detectors are widely used in dental radiography. The scope of this work is the examination of the spatial frequency component of a dedicated dental CMOS detector. A commercially available SCHICK CDR CMOS detector was irradiated at a Del Medical Eureka X-ray system at 60kVp and 70kVp. The irradiation setup included images of an edge, for Modulation Transfer Function (MTF) calculation. The air-KERMA was measured with an RTI PIRANHA X-ray multimeter. The images were evaluated in ‘for presentation’ format with the use of ImageJ software. The linear range of the detector was found in the range 13μGy-183μGy at 60 kVp and 18μGy-180μGy at 70 kVp. By inspecting the MTF curves it was found that MTF(6lp/mm)60kVp=0.29 and MTF(6lp/mm)70kVp=0.25. The inspection of the Normalized Noise Power Spetrum (NNPS) showed similar low noise components. Our results indicate that this detector presents comparable performance at both kVp, although its X-ray response (pixel value vs air KERMA) was not equal to previously published results, for the same detector type.

Affective blindsight relies on low spatial frequencies

The human brain can process facial expressions of emotions rapidly and without awareness. Several studies in patients with damage to their primary visual cortices have shown that they may be able to guess the emotional expression on a face despite their cortical blindness. This non-conscious processing, called affective blindsight, may arise through an intact subcortical visual route that leads from the superior colliculus to the pulvinar, and thence to the amygdala. This pathway is thought to process the crude visual information conveyed by the low spatial frequencies of the stimuli.In order to investigate whether this is the case, we studied a patient (TN) with bilateral cortical blindness and affective blindsight. An fMRI paradigm was performed in which fearful and neutral expressions were presented using faces that were either unfiltered, or filtered to remove high or low spatial frequencies. Unfiltered fearful faces produced right amygdala activation although the patient was unaware of the presence of the stimuli. More importantly, the low spatial frequency components of fearful faces continued to produce right amygdala activity while the high spatial frequency components did not. Our findings thus confirm that the visual information present in the low spatial frequencies is sufficient to produce affective blindsight, further suggesting that its existence could rely on the subcortical colliculo-pulvino-amygdalar pathway.

Trypophobic Discomfort is Spatial-Frequency Dependent.

Clusters of holes, such as those in a lotus seedpod, induce trypophobic discomfort. Previous research has demonstrated that high-contrast energy at midrange spatial frequencies in images causes trypophobic discomfort. The present study examined the effects on discomfort of eliminating various spatial frequency components from the images to reveal how each spatial frequency contributes to the discomfort. Experiment 1 showed that eliminating midrange spatial frequencies did not affect trypophobic discomfort, while Experiment 2 revealed that images of holes that consisted of only high-spatial frequencies evoked less discomfort than other images and that images containing only low or midrange spatial frequencies induced as much trypophobic discomfort as did the original images. Finally, Experiment 3 found that participants with a high level of the trypophobic trait experienced stronger discomfort from the original images and the images containing only low or midrange spatial frequencies than participants with a low level of the trypophobic trait. Our findings thus suggest that trypophobic discomfort can be induced by middle and low spatial frequencies.

Improvement in spatial frequency characteristics of magneto-optical Kerr microscopy

The spatial resolution of a conventional magneto-optical Kerr microscope, compared with those of conventional optical microscopes, inevitably deteriorates owing to oblique illumination. An approach to obtaining the maximum spatial resolution using multiple images with different illumination directions is demonstrated here. The method was implemented by rotating the illumination path around the optical axis using a motorized stage. The Fourier transform image of the observed magnetic domain indicates that the spatial frequency component that is lost in the conventional method is restored.

Bottom profile degradation mechanism in high aspect ratio feature etching based on pattern transfer observation

The hypothetical mechanism of bottom profile degradation, such as distortion and twisting in high aspect ratio feature etching, was verified based on the pattern transfer observation of etched pattern. The authors mainly focused on trench pattern sample to make the investigation easier, that is, direct observation of the sidewall roughness, using an atomic force microscope, as well as analysis of the depth dependence of pattern deformation in high aspect ratio trench etching. Using Fourier transformation analysis for the trench sidewall roughness, it was found that lower spatial frequency component of the mask's sidewall roughness is amplified at the bottom region of the trench and that higher spatial frequency component of over 10 μm−1 disappears. However, the higher spatial frequency component is transferred directly to the upper sidewall of the trench. The observation of the pattern deformation profile, as a function of etch depth, revealed that the ratio of line width roughness to line edge roughness decreases linearly with increasing etch depth. This indicates that the deformation mode changes from “roughness” to “wiggling” as a function of etch depth. Also, the twisting depth, as determined by the cross section images, was found to be shallower when using lower wafer bias etching condition. Based upon these results, and previously proposed mechanisms, the authors conclude that the mask deformation should be considered as one of the root causes when bottom deformation occurs. This is due to the imbalance between ion flux and deposition amount created by mask asymmetric profile. In addition, the etching profile and etching direction should be affected by this phenomenon under polymer-rich process condition. In order to verify our assumed mechanism, the relationship between mask deformation degree, and bottom distortion and twisting amount was also evaluated by using different pitch hole patterns. As a result, the authors determined that the distortion is improved by 22% and the twisting is improved by 20% when the mask deformation is reduced by 50% with using a wider pitch pattern.

Admissible Shape Parameters for a Planar Quasi-Static Constraint Mode Tire Model

Abstract : The interaction between the tire and terrain has long been of interest for vehicle dynamic simulation. Detailed tire models produce accurate results, but are too computationally intensive for the iterative vehicle design process. The objective of this work is to develop a computationally efficient way to estimate the tire's deformed shape, from which the tire forces can be evaluated. A novel, planar, quasi-static, constraint mode tire model is developed to address this objective. The required model parameters are reduced to two non-dimensional shape parameters and an overall stiffness factor. An admissible domain of the shape parameters is developed based on the deformation limitations of a physical tire. Specifically, no single harmonic may dominates the tire shape and the low spatial frequency components must contribute more than higher frequency components to the overall tire shape. The ability of the model to accurately predict the spindle force is evaluated by comparing simulation and experimental responses for quasi-static flat plate and cleat tests. This work provides a simple, accurate tire model for circumferential displacement and vertical spindle force prediction to improve the vehicle design process.

Determination of a Sampling Criterion for 3D Reconstruction

A sampling criterion for a surface reconstruction using structured light patterns is derived in this article. The problem of signal recovery from its samples is addressed, and a salient spatial frequency component of an object is defined for a sampling rate determination. The authors introduce 3D object coordinate extraction from a 2D captured image by employing structured light systems (a set of concentric circular light patterns), without any prior information about an object of interest. To achieve an efficient 3D reconstruction (approximate reconstruction result), a minimal sampling rate, defined as the minimum number of circular patterns to be projected onto the 3D scene, is derived using specific geometric information (e.g., curvature) of an object. This article chiefly deals with theoretical algorithms for efficient 3D scene reconstruction, recognition and other applications of 3D imaging techniques, and the proposed algorithms can be applied to diverse applications in the field of computer vision, 3D graphics, etc.

Speed limits of structured illumination microscopy.

A theoretical framework for widefield structured illumination microscopy (SIM) reconstruction from fewer than the commonly used nine raw frame acquisitions is introduced and applied in silico and in vitro. The proposed scheme avoids the recording of redundant spatial frequency components, which was necessary in previous SIM algorithms. This allows for gentler superresolution imaging at faster speeds. A doubling of frame rates is possible solely via changes in the computational reconstruction procedure. Furthermore, we explore numerically the effect of the sample movement on the reconstruction quality and the number of raw frames recordable. Our results show that there exists a limit above which deconvolution microscopy becomes superior to SIM.

Development and testing of low spatial frequency holographic concentrator elements for collection of solar energy

Abstract The aim of this research is to use holographically recorded diffractive optical elements (DOEs) recorded in photopolymer in order to effectively collect and concentrate solar radiation. The potential for recording high diffraction efficiency DOEs with a large angular and wavelength range of operation in acrylamide based photopolymer and the optimum recording conditions have been presented in our previous work (Akbari et al., 2014b, 2014a). Theoretical modelling and experimental test are presented which demonstrate that low spatial frequency components, around 300 line pairs/mm, have an appropriate spectral bandwidth, high efficiency and very limited polarization dependence. Pairs of concentrating off-axis lenses are fabricated in photopolymer and arranged to concentrate light on a c-Si cell. The optical recording process is described and discussed. The results from electrical characterization confirm that with the (two) spherical DOEs (each of area 113 mm 2 ) in place, the output current of c-Si solar cells is approximately doubled for the solar cells with area of 12 mm 2 .

Personal familiarity enhances sensitivity to horizontal structure during processing of face identity.

What makes identification of familiar faces seemingly effortless? Recent studies using unfamiliar face stimuli suggest that selective processing of information conveyed by horizontally oriented spatial frequency components supports accurate performance in a variety of tasks involving matching of facial identity. Here, we studied upright and inverted face discrimination using stimuli with which observers were either unfamiliar or personally familiar (i.e., friends and colleagues). Our results reveal increased sensitivity to horizontal spatial frequency structure in personally familiar faces, further implicating the selective processing of this information in the face processing expertise exhibited by human observers throughout their daily lives.

Precision assessment of label-free psoriasis biomarkers with ultra-broadband optoacoustic mesoscopy

Imaging plays a critical role in the diagnosis and assessment of dermatological conditions. However, optical or optoacoustic microscopy techniques are limited to visualizing superficial skin features owing to strong photon scattering, whereas ultrasound methods, which can probe deeper-seated tissue, lack the contrast to image pathophysiological mechanisms in detail. Here, we demonstrate that raster-scan optoacoustic mesoscopy (RSOM) implemented in ultra-broadband (10–180 MHz) detection mode bridges the depth capabilities of ultrasound and the resolution range and high contrast of optical methods in clinical dermatology. Using tomographic reconstruction and frequency equalization to represent low and high spatial-frequency components, we visualize skin morphology and vascular patterns in the dermis and sub-dermis of psoriasis patients, enabling quantification of inflammation and other biomarkers of psoriasis without the need for contrast agents. Implemented in a handheld device, we showcase how label-free biomarkers detected by RSOM correlate with clinical score. The method can also be extended to assess a larger spectrum of dermatological conditions. Ultra-broadband optoacoustic mesoscopy implemented in a handheld device enables the visualization of vascular patterns in the dermis and sub-dermis of psoriasis patients, and the quantification of inflammatory biomarkers of psoriasis.

Early Recognition of Alzheimer’s Disease using Brain MRI

Abstract—Alzheimer’s disease (AD) is a brain disease that causes a slow decline in memory, thinking and reasoning skills. It represents a major public health problem. Magnetic Resonance Imaging (MRI) have shown that the brains of people with (AD) shrink significantly as the disease progresses. This shrinkage appears in specific brain regions such as the hippocampus which is a small, curved formation in the brain that plays an important role in the limbic system also involved in the formation of new memories and is also associated with learning and emotions. Medical information on brain MRI is used in detecting the abnormalities in physiological structures. Structural MRI measurements can detect and follow the evolution of brain atrophy which is a marker of the disease progression; therefore, it allows diagnosis and prediction of AD. The research’s main target is the early recognition of Alzheimer’s disease automatically, which will thereby avoid deterioration of the case resulting in complete brain damage stage. Alzheimer’s disease yields visible changes in the brain structures. The aim is to recognize if the patient belongs to Alzheimer’s disease category or a normal healthy person at an early stage.
 Initially, image pre-processing and features extraction techniques are applied including data reduction using Discrete Cosine Transform (DCT) and Cropping, then traditional classification techniques like Euclidean Distance, Chebyshev Distance, Cosine Distance, City Block Distance, and Black pixel counter, were applied on the resulting vectors for classification. Image pre-processing includes noise reduction, Gray-scale conversion and binary scale conversion were applied for the MRI images. Feature extraction techniques follow including cropping and low spatial frequency components (DCT). This paper aims to automatically recognize and detect Alzheimer’s infected brain using MRI, without the need of clinical expert. This early recognition would be helpful to postpone the disease progression and maintain it at an almost steady stage. It was concluded after collecting a dataset of 50 MRI , 25 for normal MRI and 25 for AD MRI that Chebyshev Distance classifier yielded the highest success rate in the recognition of Alzheimer’s disease with accuracy 94% compared to other classification techniques used where, Euclidean Distance is 91.6%, Cosine Distance is 86.8%, City block Distance is 89.6%, Correlation Distance is 86.4% and Black pixels counter is 90%.

Near-field spectroscopic properties of complementary gold nanostructures: applicability of Babinet's principle in the optical region.

We examine the far-field and near-field properties of complementary screens made of nanostructured gold thin films, a rectangular nanowire and a nanovoid, using an aperture-type scanning near-field optical microscope and electromagnetic field calculations, and discuss the applicability of Babinet's principle in the optical region. The far-field transmission spectra of the complementary screens are considerably different from each other. On the other hand, genuine near-field extinction spectra exhibit nearly complementary characteristics. The spatial features of the observed near-field images for the complementary screens show little correlation. We have found from the Fourier analysis of the simulated images that high spatial-frequency components of the electromagnetic fields show mutual spatial correlation. These results suggest that Babinet's principle is applicable to the high spatial-frequency components of electromagnetic fields for the complementary screens.