Phase Contrast Method Research Articles

Imaging atomic-scale magnetism with energy-filtered differential phase contrast method

We propose differential phase contrast (DPC) imaging using energy-filtered electrons to image the magnetic properties of materials at the atomic scale. Compared to DPC measurements with elastic electrons, our simulations predict about two orders of magnitude higher relative magnetic signal intensities and sensitivity to all three vector components of magnetization. Published by the American Physical Society 2024

Imaging of micro-steps on as-grown surface of sapphire with X-ray phase contrast technique

Basal-faceted sapphire ribbons grown using the Stepanov–LaBelle technology have a low density of surface steps. We present our results on a study of steps on the surface of a ribbon, misoriented relative to the singular face (0001) by several arc minutes. The ribbon has been characterized by means of in-line phase contrast imaging technique at Pohang Light Source, South Korea. It was shown for the first time that a step height of about 1 μm can be determined directly from an image. The step height obtained using the phase contrast method was confirmed by atomic force microscopy measurements. We have found that the experimental contrast matches the theoretical simulations only if the calculated intensity profile has been convolved with a Gaussian function. The full width at half maximum of the Gaussian was independently got from previous measurements. We have obtained an analytical solution in the case of theoretical fully coherent phase contrast image. The inverse problem is easy to solve, since there is a direct proportionality between the contrast and the step height.

Research on adaptive optics technology based on phase contrast Gerchberg Saxton algorithm

Abstract In wireless optical communication, the optical signal passes through the atmospheric turbulence, resulting in the simultaneous distortion of the amplitude and phase of the optical signal at the receiving end. This article applies the idea of phase contrast method to simultaneously compensate the amplitude and phase of the optical signal at the receiving end, derives the mapping relationship between the compensated phase and light intensity, and obtains the required compensated phase for full-field compensation. Numerical calculations show that when the difference between zero-frequency phase compensation and nonzero-frequency phase compensation is ±π, the maximum light intensity compensation is obtained. Based on the Gerchberg Saxton algorithm, a new method is proposed to invert the compensated phase with the maximum light intensity after full-field compensation and perform full-field correction through the adaptive optical system. The numerical calculation and experiment show that the phase contrast Gerchberg Saxton algorithm can effectively compensate the distorted optical signals under different turbulence, and thus the received signals of optical wireless communication can be corrected in full field.

Clinical application of single-shot fast spin-echo sequence for cerebrospinal fluid flow MR imaging.

In normal-pressure hydrocephalus, disturbances in cerebrospinal fluid (CSF) circulation occur; therefore, understanding CSF dynamics is crucial. The two-dimensional phase-contrast (2D-PC) method, a common approach for visualizing CSF flow on MRI, often presents challenges owing to prominent vein signals and excessively high contrast, hindering the interpretation of morphological information. Therefore, we devised a new imaging method that utilizes T2-weighted high-signal intensification of the CSF and saturation pulses, without requiring specialized imaging sequences. This sequence utilized a T2-weighted single-shot fast spin-echo combined with multi-phase imaging synchronized with a pulse wave. Optimal imaging conditions (repetition time, presence/absence of fast recovery, and echo time) were determined using self-made contrast and single-plate phantoms to evaluate signal-to-noise ratio, contrast ratio, and spatial resolution. In certain clinical cases of hydrocephalus, confirming CSF flow using 2D-PC was challenging. However, our method enabled the visualization of CSF flow, proving to be useful in understanding the pathophysiology of hydrocephalus.

Phase-contrast visualization of human tissues using superimposed wavefront imaging of diffraction-enhanced x-rays.

Phase-contrast computed tomography (CT) using high-brilliance, synchrotron-generated x-rays enable three-dimensional (3D) visualization of microanatomical structures within biological specimens, offering exceptionally high-contrast images of soft tissues. Traditional methods for phase-contrast CT; however, necessitate a gap between the subject and the x-ray camera, compromising spatial resolution due to penumbral blurring. Our newly developed technique, Superimposed Wavefront Imaging of Diffraction-enhanced x-rays (SWIDeX), leverages a Laue-case Si angle analyzer affixed to a scintillator to convert x-rays to visible light, capturing second-order differential phase contrast images and effectively eliminating the distance to the x-ray camera. This innovation achieves superior spatial resolution over conventional methods. In this paper, the imaging principle and CT reconstruction algorithm based on SWIDeX are presented in detail and compared with conventional analyzer-based imaging (ABI). It also shows the physical setup of SWIDeX that provides the resolution preserving second-order differential images for reconstruction. We compare the spatial resolution and the sensitivity of SWIDeX to conventional ABI. To demonstrate high-spatial resolution achievable by SWIDeX, the internal structures of four human tissues-ductal carcinoma in situ, normal stomach, normal pancreas, and intraductal papillary mucinous neoplasm of the pancreas-were visualized using an imaging system configured at the Photon Factory's BL14B beamline under the High Energy Accelerator Research Organization (KEK). Each tissue was thinly sliced after imaging, stained with hematoxylin and eosin (H&E) for conventional microscope-based pathology. A comparison of SWIDeX-CT and pathological images visually demonstrates the effectiveness of SWIDeX-CT for biological tissue imaging. SWIDeX could generate clearer 3D images than existing analyzer-based phase-contrast methods and accurately delineate tissue structures, as validated against histopathological images. SWIDeX can visualize important 3D structures in biological soft tissue with high spatial resolution and can be an important tool for providing information between the disparate scales of clinical and pathological imaging.

Machine Learning-Enhanced Estimation of Cellular Protein Levels from Bright-Field Images.

In this study, we aimed to develop a novel method for non-invasively determining intracellular protein levels, which is essential for understanding cellular phenomena. This understanding hinges on insights into gene expression, cell morphology, dynamics, and intercellular interactions. Traditional cell analysis techniques, such as immunostaining, live imaging, next-generation sequencing, and single-cell analysis, despite rapid advancements, face challenges in comprehensively integrating gene and protein expression data with spatiotemporal information. Leveraging advances in machine learning for image analysis, we designed a new model to estimate cellular biomarker protein levels using a blend of phase-contrast and fluorescent immunostaining images of epidermal keratinocytes. By iterating this process across various proteins, our model can estimate multiple protein levels from a single phase-contrast image. Additionally, we developed a system for analyzing multiple protein expression levels alongside spatiotemporal data through live imaging and phase-contrast methods. Our study offers valuable tools for cell-based research and presents a new avenue for addressing molecular biological challenges.

Speckle tracking phase-contrast computed tomography at an inverse Compton X-ray source

Speckle-based X-ray imaging (SBI) is a phase-contrast method developed at and for highly coherent X-ray sources, such as synchrotrons, to increase the contrast of weakly absorbing objects. Consequently, it complements the conventional attenuation-based X-ray imaging. Meanwhile, attempts to establish SBI at less coherent laboratory sources have been performed, ranging from liquid metal-jet X-ray sources to microfocus X-ray tubes. However, their lack of coherence results in interference fringes not being resolved. Therefore, algorithms were developed which neglect the interference effects. Here, we demonstrate phase-contrast computed tomography employing SBI in a laboratory-setting with an inverse Compton X-ray source. In this context, we investigate and compare also the performance of the at synchrotron conventionally used phase-retrieval algorithms for SBI, unified modulated pattern analysis (UMPA) with a phase-retrieval method developed for low coherence systems (LCS). We successfully retrieve a full computed tomography in a phantom as well as in biological specimens, such as larvae of the greater wax moth (Galleria mellonella), a model system for studies of pathogens and infections. In this context, we additionally demonstrate quantitative phase-contrast computed tomography using SBI at a low coherent set-up.

Study of the influence of the extract of pipsissewa on cell cultures

The development of new diuretics of plant origin is an actual direction. Chimaphila umbellata (L.) is a perennial herb with diuretic, astringent, analgesic and other effects; and it can treat various conditions such as edema, dropsy, etc. Pipsissewa herb helps the removal of nitrogenous and chloride salts from the body due to the content of arbutin glycoside, tannins (up to 5 %). The aim. Evaluation of the effect of pipsissewa extract on L929 cell culture. Materials and methods. Cell line L929 (fibroblasts of mouse adipose tissue) was obtained in the low-temperature bank of the Institute of Problems of Cryobiology and Cryomedicine of the National Academy of Sciences of Ukraine. Cells were cultured in DMEM medium (Bio West, France) enriched with 10 % FBS (Lonza, Germany) with 1 % antibiotic-antimycotic (Bio West, France), in a CO2 incubator (Thermo Fisher Scientific, USA) at 37 ºС in an atmosphere with 5 % CO2. Determination of the minimum toxic concentration at which the cells remained alive was evaluated by morphological features (shape, monolayer integrity, adhesion to plastic). The study of the effect of pipsissewa extract on various cell functions was determined by the following methods: the ability to preserve morphological integrity - by the phase-contrast microscopy method, energy exchange - by the MTT test method, pinocytotic function - by the neutral red absorption method, migratory function - by the scratch test method, proliferative activity - by the doubling calculation method population Results. It is proposed to use concentrations of 0.05, 0.02, 0.01, 0.005 % of pipsissewa extract for further research. After carrying out the MTT reaction, the transition of MTT to formazan was confirmed microscopically in the negative control (native cells), at PE concentrations of 0.01 % and below, and the absence of a reaction in the positive control (cells killed by ethanol) at PE concentrations above 0.02 %. When recording the parameters of the NP absorption reaction, it was determined that PE at a concentration of 0.02 % and higher sharply suppresses pinocytotic activity, despite the partial preservation of cell adhesion, reducing the concentration by two times no longer affects mitochondria. A concentration of 0.01 % reduces proliferative activity, and at a concentration of 0.005 %, no difference with the control values ​​was found. Conclusions. When studying the assessment of the effect of pipsisewa extract on L929 cell culture, a toxic effect on these cells was established when added to the culture medium at a concentration above 0.01 %. The toxic effect had a threshold effect. Migratory and proliferative functions were the most sensitive, energy, pinocytosis and preservation of morphological integrity of cells were less sensitive

Accuracy of Shunt Volume Measured by Three-Dimensional Echocardiography and Cardiac Magnetic Resonance in Patients With an Atrial Septal Defect and a Dilated Right Ventricle

The accuracy of right ventricular (RV) quantification by three-dimensional echocardiography (3DE) has been reported mainly in patients with a normal right ventricle (RV). However, there are no data regarding the accuracy of 3DE in patients with a dilated RV, as in shunt diseases. In this study, we evaluated the accuracy of 3DE and that of volumetric (Vol) cardiac magnetic resonance (CMR) for assessment of RV and left ventricular (LV) stroke volume (SV) and the pulmonary (Qp)/systemic (Qs) blood flow ratio in patients with an atrial septal defect (ASD) using the two-dimensional phase contrast (2DPC) method as the gold standard. We retrospectively investigated 83 patients with ASD who underwent transcatheter closure and clinically indicated CMR and 3DE examinations. The ratio Qp/Qs was calculated using RV and LV SV measured by full-volume volumetric 3DE (Vol-3DE) and CMR (Vol-CMR) and by two-dimensional pulsed Doppler quantification (2D-Dop); the parameters were compared using 2DPC-CMR as the gold standard. There was no significant difference in the Qp/Qs value between 2DPC-CMR and Vol-3DE (2.29±0.70 vs 2.21±0.63, P=.79) and 2D-Dop (vs 2.21±0.65, P=1.00); however, a significant difference was found between 2DPC-CMR and Vol-CMR (P<.001). The Qp/Qs value obtained using Vol-3DE showed the best correlation with 2DPC-CMR (r=0.93, P<.001). The RV and LV SV values obtained by Vol-3DE showed the best correlation with 2DPC-CMR (RV SV, r=0.82, P<.001; LV SV, r=0.73, P<.001), although the absolute values were underestimated. Qp/Qs was more accurately evaluated by Vol-3DE than by Vol-CMR or 2D-Dop. Three-dimensional echocardiography assessment was feasible and reproducible even in a dilated RV.

Comparison of differential phase Contrast, Lorentz and non-Lorentz transmission electron microscopy for microstructural and magnetic imaging of alnico magnet

In this work, non-Lorentz, Lorentz transmission electron microscopy (LTEM) and differential phase contrast (DPC) methods were used to observe the phase and magnetic structure of the alnico magnet. All observations were performed on alnico-5 in transverse orientation. The results showed the magnetic contrast of the domain walls in the conventional TEM images despite the effects of the lens magnetic field, which was verified and explained using DPC. Experimental methodology and sample results are summarized with advice for further research.

Classifying breast cancer and fibroadenoma tissue biopsies from paraffined stain-free slides by fractal biomarkers in Fourier Ptychographic Microscopy

Breast cancer is one of the most spread and monitored pathologies in high-income countries. After breast biopsy, histological tissue is stored in paraffin, sectioned and mounted. Conventional inspection of tissue slides under benchtop light microscopes involves paraffin removal and staining, typically with H&E. Then, expert pathologists are called to judge the stained slides. However, paraffin removal and staining are operator-dependent, time and resources consuming processes that can generate ambiguities due to non-uniform staining. Here we propose a novel method that can work directly on paraffined stain-free slides. We use Fourier Ptychography as a quantitative phase-contrast microscopy method, which allows accessing a very wide field of view (i.e., mm2) in one single image while guaranteeing high lateral resolution (i.e., 0.5 µm). This imaging method is multi-scale, since it enables looking at the big picture, i.e. the complex tissue structure and connections, with the possibility to zoom-in up to the single-cell level. To handle this informative image content, we introduce elements of fractal geometry as multi-scale analysis method. We show the effectiveness of fractal features in describing and classifying fibroadenoma and breast cancer tissue slides from ten patients with very high accuracy. We reach 94.0 ± 4.2% test accuracy in classifying single images. Above all, we show that combining the decisions of the single images, each patient’s slide can be classified with no error. Besides, fractal geometry returns a guide map to help pathologist to judge the different tissue portions based on the likelihood these can be associated to a breast cancer or fibroadenoma biomarker. The proposed automatic method could significantly simplify the steps of tissue analysis and make it independent from the sample preparation, the skills of the lab operator and the pathologist.

Validation of 2D flow MRI for helical and vortical flows

PurposeThe main objective of this study was to develop two-dimensional (2D) phase contrast (PC) methods to quantify the helicity and vorticity of blood flow in the aortic root.MethodsThis proof-of-concept study...

Plug-and-play DPC-based quantitative phase microscope.

Point-of-care testing (POCT) plays an increasingly important role in biomedical research and health care. Quantitative phase microscopes (QPMs) with good contrast, no invasion, no labeling, high speed and automation could be effectively applied for POCT. However, most QPMs are fixed on the optical platform with bulky size, lack of timeliness, which remained challenging in POCT solutions. In this paper, we proposed a plug-and-play QPM with multimode imaging based on the quantitative differential phase contrast (qDPC) method. The system employs a programmable LED array as the light source and uses the GPU to accelerate the calculation, which can realize multi-contrast imaging with six modes. Accurate phase measurement and real-time phase imaging are implemented by the proposed qDPC algorithms for quantitative phase targets and biomedical samples. A 3D electric control platform is designed for mechanical control of field of view and focusing without manual operations. The experimental results verify the robustness and high performance of the setup. Even a rookie could finish the POCT scheme for biomedical applications at the scene using the QPM with a compact size of 140 × 165 × 250 mm3.

Study of Optical Properties and Structural Features of Object using the X-ray Phase Contrast Method

Study of Optical Properties and Structural Features of Object using the X-ray Phase Contrast Method

Investigation of an Improved Angular Spectrum Method Based on Holography

Digital holography (DH) is a novel, real-time, non-destructive, and quantitative phase-contrast imaging method that is particularly suitable for label-free live biological cell imaging and real-time dynamic monitoring. It is currently a research hotspot in the interdisciplinary field of optics and biomedical sciences, both domestically and internationally. This article proposes an improved angle spectrum algorithm based on holographic technology, which reconstructs a cellular hologram based on phase information. Optical images and chromosome cell images, reconstructed using holographic technology at different diffraction distances under the improved angle spectrum algorithm, were analyzed and compared. The optimal diffraction distance for reconstructing chromosome cell images was selected, and chromosome cell images reproduced using traditional angle spectrum algorithms, angle spectrum algorithms combined with GS, and improved angle spectrum algorithms were compared. Comparative experiments with the different models show that the proposed algorithm is superior to traditional angle spectrum algorithms in reconstructing cell images based on phase information. Furthermore, experiments have shown that images reconstructed using the improved algorithm can resolve high signal-to-noise ratio information. This algorithmic improvement provides new applications for cellular detection in clinical diagnostics and is more suitable for cell phase reconstruction in practical applications.

Propagation-based phase-contrast imaging method for full-field X-ray microscopy using advanced Kirkpatrick-Baez mirrors.

We demonstrate a propagation-based phase-contrast imaging method for full-field X-ray microscopy based on advanced Kirkpatrick-Baez (AKB) mirrors to achieve high-contrast observations of weak phase objects and correct field curvature aberrations. Through a demonstration performed at SPring-8, the phase contrast of weak phase objects such as polystyrene spheres and chemically fixed cells was successfully observed with high sensitivity (∼0.03 rad). Furthermore, the field of view of the AKB mirrors was expanded to the full area of the obtained images (25 × 30 µm) by correcting the field curvature aberration using reconstructed complex wavefields.

Single-shot quantitative differential phase contrast imaging combined with programmable polarization multiplexing illumination.

We propose a single-shot quantitative differential phase contrast method with polarization multiplexing illumination. In the illumination module of our system, a programmable LED array is divided into four quadrants and covered with polarizing films of four different polarization angles. We use a polarization camera with polarizers before the pixels in the imaging module. By matching the polarization angle between the polarizing films over the custom LED array and the polarizers in the camera, two sets of asymmetric illumination acquisition images can be calculated from a single-shot acquisition image. Combined with the phase transfer function, we can calculate the quantitative phase of the sample. We present the design, implementation, and experimental image data demonstrating the ability of our method to obtain quantitative phase images of a phase resolution target, as well as Hela cells.

Optimal control flow encoding for time-efficient magnetic resonance velocimetry

Phase contrast velocimetry relies on bipolar gradients to establish a direct and linear relationship between the phase of the magnetic resonance signal, and the corresponding fluid motion. Despite its utility, several limitations and drawbacks have been reported, the most important being the extended echo time due to the encoding after the excitation. In this study, we elucidate a new approach based on optimal control theory that circumvents some of these disadvantages. An excitation pulse, termed FAUCET (flow analysis under controlled encoding transients), is designed to encode velocity into phase already during the radiofrequency excitation. As a result of concurrent excitation and flow encoding, and hence elimination of post-excitation flow encoding, FAUCET achieves a shorter echo time than the conventional method. This achievement is a matter of significance not only because it decreases the loss of signal due to spin–spin relaxation and B0 inhomogeneity, but also because a shorter echo time is always preferred in order to reduce the dimensionless dephasing parameter and the required residence time of the flowing sample in the detection coil. The method is able to establish a non-linear bijective relationship between phase and velocity, which can be employed to enhance the resolution over a specific range of velocities, for example along flow boundaries. A computational comparison between the phase contrast and optimal control methods reveals that the latter’s encoding is more robust against remnant higher-order-moment terms of the Taylor expansion for faster voxels, such as acceleration, jerk, and snap.

Superimposed wavefront imaging of diffraction-enhanced x-rays: A method to achieve higher resolution in crystal analyzer-based x-ray phase-contrast imaging

In conventional phase-contrast imaging methods, an optimum distance that is essential for x-ray interference and wavefront separation must be maintained between the object and the x-ray detector. This distance determines the apparent focal size of the x-ray source and affects spatial resolution of the system. To improve the spatial resolution, we proposed a phase-contrast imaging method that eliminates the distance required for x-ray interference and wavefront separation by placing a scintillator in close contact with a Laue angle analyzer (LAA). We mathematically described the image formed by superposition of diffracted beams in two directions of LAA and introduced a method to reconstruct tomographic sections from multiple projections captured by this setup. We experimentally demonstrated the validity and the usefulness of the proposed method. Using a physical phantom, we showed that the proposed method provides higher spatial resolution than conventional x-ray dark-field imaging. The proposed method may be useful for studying and elucidating the fine 3D microanatomy and histopathology of various biological specimens.

IN-LINE METHOD OF X-RAY PHASE-CONTRAST MICRO-CT USING A WIDE-FOCUS LABORATORY SOURCE

An experimental implementation of the “in-line” method of X-ray phase contrast using a standard wide-focus X-ray tube as a polychromatic source is described. Using the proposed experimental scheme, in vitro tomographic measurements of a sample of human brain pineal gland are carried out, and the morphological structure of the soft tissues of this organ is visualized based on the results obtained. The advantage of phase-contrast tomography in comparison with traditional absorption tomography for studying the structural features of soft tissues is experimentally demonstrated. The “in-line” phase-contrast scheme, implemented on a laboratory setup, allows tomographic study of samples with linear dimensions of several millimeters and a resolution of ∼20 μm.