Effective Point Spread Function Research Articles

Recent research on stimulated emission depletion microscopy for reducing photobleaching.

Stimulated emission depletion (STED) microscopy is a useful tool in investigation for super-resolution realm. By silencing the peripheral fluorophores of the excited spot, leaving only the very centre zone vigorous for fluorescence, the effective point spread function (PSF) could be immensely squeezed and subcellular structures, such as organelles, become discernable. Nevertheless, because of the low cross-section of stimulated emission and the short fluorescence lifetime, the depletion power density has to be extremely higher than the excitation power density and molecules are exposed in high risk of photobleaching. The existence of photobleaching greatly limits the research of STED in achieving higher resolution and more delicate imaging quality, as well as long-term and dynamic observation. Since the first experimental implementation of STED microscopy, researchers have lift out variety of methods and techniques to alleviate the problem. This paper would present some researches via conventional methods which have been explored and utilised relatively thoroughly, such as fast scanning, time-gating, two-photon excitation (TPE), triplet relaxation (T-Rex) and background suppression. Alternatively, several up-to-date techniques, especially adaptive illumination, would also be unveiled for discussion in this paper. The contrast and discussion of these modalities would play an important role in ameliorating the research of STED microscopy.

Enhancing spectral unmixing by considering the point spread function effect

The point spread function (PSF) effect exists ubiquitously in real remotely sensed data and such that the observed pixel signal is not only determined by the land cover within its own spatial coverage but also by that within neighboring pixels. The PSF, thus, imposes a fundamental limit on the amount of information captured in remotely sensed images and it introduces great uncertainty in the widely applied, inverse goal of spectral unmixing. Until now, spectral unmixing has erroneously been performed by assuming that the pixel signal is affected only by the land cover within the pixel, that is, ignoring the PSF. In this paper, a new method is proposed to account for the PSF effect within spectral unmixingto produce more accurate predictions of land cover proportions. Based on the mechanism of the PSF effect, the mathematical relation between the coarse proportion and sub-pixel proportions in a local window was deduced. Area-to-point kriging (ATPK) was then proposed to find a solution for the inverse prediction problem of estimating the sub-pixel proportions from the original coarse proportions. The sub-pixel proportions were finally upscaled using an ideal square wave response to produce the enhanced proportions. The effectiveness of the proposed method was demonstrated using two datasets. The proposed method has great potential for wide application since spectral unmixing is an extremely common approach in remote sensing.

Simple fabrication of high focal number micro-lenses based on a microfluid pulse jetting method

In this paper, we demonstrate a simple and rapid high focal number (F # ) micro-lens (ML) fabrication method using a simple microfluid pulse jetting technology. The simulation of the microfluid pulse jetting is firstly studied to prove that the new jetting method have the potential for jetting the UV polymer with a low surface tension coefficient stably. As the high F # of the ML is ascribed to the low contact angle of the ML on the substrate, a simple surface treatment of the substrate is adopted to obtain a small contact angle of the UV polymer on the substrate. Based on this method, the spherical ML and cylindrical ML with a F # as high as 11.5 have been successfully fabricated. The fabricated high F # ML is characterized through simulating the modulation transfer function curve, wavefront aberration, and point spread function (PSF) and measuring the PSF and imaging effect, and the simulation and measurement results indicate that the diffraction limit optical performance of the high F # ML can be achieved and the clear images can be observed.

Improved lateral resolution with an annular vortex depletion beam in STED microscopy.

We report on the experimental demonstration of improved lateral resolution in stimulated emission depletion (STED) microscopy using an annular depletion beam configuration. A tight and finely tuned doughnut focal spot can be created by annular vortex illumination. Its application in STED microscopy for enhanced lateral resolution is systematically investigated by imaging 40nm fluorescent beads. An improved resolution with more than 20% reduced effective point spread function of the imaging system determined by the full width at half-maximum compared to that of the conventional STED is achieved. The proposed scheme also demonstrates its resolving capability for biological samples. The principle holds great potential in the research fields of biological superresolution imaging as well as STED-based nanolithography and high-density optical data storage.

Two-photon microscopy with enhanced contrast and resolution.

A method combining the saturation effect with the ratio concerned quadratic intensity weighted subtraction (RQIWS) algorithm for resolution and contrast enhancement in a two-photon microscopy system is presented in this paper. In the proposed method, the saturation effect is utilized to get a profile-extended solid spot and a center-shrunken doughnut-shaped spot for a smaller effective point spread function, which enhances the resolution of the system. The RQIWS algorithm uses the intensity ratio of the two original images acquired respectively with the solid spot and the doughnut-shaped spot as one of the subtraction parameters and takes the fluorescence quadratic dependence of excitation intensity into account for better subtraction results compared with the intensity weighted subtraction algorithm in a two-photon excitation system. The capability in the enhancement of resolution and contrast of the method proposed is demonstrated successfully both by theoretical simulations and experimental results.

ZFIRE: The Evolution of the Stellar Mass Tully–Fisher Relation to Redshift ∼2.2

Abstract Using observations made with MOSFIRE on Keck I as part of the ZFIRE survey, we present the stellar mass Tully–Fisher relation at . The sample was drawn from a stellar-mass-limited, -band-selected catalog from ZFOURGE over the CANDELS area in the COSMOS field. We model the shear of the Hα emission line to derive rotational velocities at the scale radius of an exponential disk ( ). We correct for the blurring effect of a 2D point-spread function (PSF) and the fact that the MOSFIRE PSF is better approximated by a Moffat than a Gaussian, which is more typically assumed for natural seeing. We find for the Tully–Fisher relation at that +(0.193 ± 0.108) and infer an evolution of the zero-point of or compared to z = 0 when adopting a fixed slope of 0.29 or 1/4.5, respectively. We also derive the alternative kinematic estimator , with a best-fit relation , and infer an evolution of compared to if we adopt a fixed slope. We investigate and review various systematics, such as PSF effects, projection effects, systematics related to stellar mass derivation, selection biases, and slope. We find that discrepancies between the various literature values are reduced when taking these into account. Our observations correspond well with the gradual evolution predicted by semianalytic models.

Quasi-needle-like focus synthesized by optical coherence tomography.

It is known that lateral resolution and depth of focus (DOF) in an optical imaging system are coupled, and a compromise between them has to be made. In this Letter, we propose to resolve the trade-off between lateral resolution and the DOF by a synthetic effective point spread function in optical path length (OPL) domain. A quasi-needle-like focus is synthesized by optical coherence tomography. We demonstrate that the synthesized quasi-needle-like focus provides a four-fold extension of a conventional DOF, while maintaining a high lateral resolution of 2.5μm over a depth range of approximately 240μm. The focal range can be further extended with more optical path length coded beams for synthesis involved.

The effect of the point spread function on sub-pixel mapping

Sub-pixel mapping (SPM) is a process for predicting spatially the land cover classes within mixed pixels. In existing SPM methods, the effect of point spread function (PSF) has seldom been considered. In this paper, a generic SPM method is developed to consider the PSF effect in SPM and, thereby, to increase prediction accuracy. We first demonstrate that the spectral unmixing predictions (i.e., coarse land cover proportions used as input for SPM) are a convolution of not only sub-pixels within the coarse pixel, but also sub-pixels from neighboring coarse pixels. Based on this finding, a new SPM method based on optimization is developed which recognizes the optimal solution as the one that when convolved with the PSF, is the same as the input coarse land cover proportion. Experimental results on three separate datasets show that the SPM accuracy can be increased by considering the PSF effect.

Image scanning microscopy with radially polarized light

In order to improve the resolution of image scanning microscopy, we present a method based on image scanning microscopy and radially polarized light. According to the theory of image scanning microscopy, we get the effective point spread function of image scanning microscopy with the longitudinal component of radially polarized light and a 1AU detection area, and obtain imaging results of the analyzed samples using this method. Results show that the resolution can be enhanced by 7% compared with that in image scanning microscopy with circularly polarized light, and is 1.54-fold higher than that in confocal microscopy with a pinhole of 1AU. Additionally, the peak intensity of ISM is 1.54-fold higher than that of a confocal microscopy with a pinhole of 1AU. In conclusion, the combination of the image scanning microscopy and the radially polarized light could improve the resolution, and it could realize high-resolution and high SNR imaging at the same time.

Assessing the quality of restored images in optical long-baseline interferometry

Assessing the quality of aperture synthesis maps is relevant for benchmarking image reconstruction algorithms, for the scientific exploitation of data from optical long-baseline interferometers, and for the design/upgrade of new/existing interferometric imaging facilities. Although metrics have been proposed in these contexts, no systematic study has been conducted on the selection of a robust metric for quality assessment. This article addresses the question: what is the best metric to assess the quality of a reconstructed image? It starts by considering several metrics, and selecting a few based on general properties. Then, a variety of image reconstruction cases is considered. The observational scenarios are phase closure and phase referencing at the Very Large Telescope Interferometer (VLTI), for a combination of two, three, four and six telescopes. End-to-end image reconstruction is accomplished with the MiRA software, and several merit functions are put to test. It is found that convolution by an effective point spread function is required for proper image quality assessment. The effective angular resolution of the images is superior to naive expectation based on the maximum frequency sampled by the array. This is due to the prior information used in the aperture synthesis algorithm and to the nature of the objects considered. The l1 norm is the most robust of all considered metrics, because being linear it is less sensitive to image smoothing by high regularisation levels. For the cases considered, this metric allows the implementation of automatic quality assessment of reconstructed images, with a performance similar to human selection.

THE SYSTEMATIC ERROR TEST FOR PSF CORRECTION IN WEAK GRAVITATIONAL LENSING SHEAR MEASUREMENT BY THE ERA METHOD BY IDEALIZING PSF

ABSTRACT We improve the ellipticity of re-smeared artificial image (ERA) method of point-spread function (PSF) correction in a weak lensing shear analysis in order to treat the realistic shape of galaxies and the PSF. This is done by re-smearing the PSF and the observed galaxy image using a re-smearing function (RSF) and allows us to use a new PSF with a simple shape and to correct the PSF effect without any approximations or assumptions. We perform a numerical test to show that the method applied for galaxies and PSF with some complicated shapes can correct the PSF effect with a systematic error of less than 0.1%. We also apply the ERA method for real data of the Abell 1689 cluster to confirm that it is able to detect the systematic weak lensing shear pattern. The ERA method requires less than 0.1 or 1 s to correct the PSF for each object in a numerical test and a real data analysis, respectively.

Spatial Correlations in SMOS Antenna: The Role of Effective Point Spread Functions

Since its launch in 2009, the European Space Agency mission Soil Moisture and Ocean Salinity (SMOS) has provided valuable information on soil moisture, sea surface salinity data, and other geophysical variables. Due to its innovative instrument, an L-band 2-D synthetic aperture interferometric radiometer, SMOS is able to provide high-resolution L2 data (as compared with other L-band missions). However, SMOS processing is complex, giving rise to the emergence of some unexpected biases. In this paper, we have analyzed the spatial structure of two-point correlations owing to the SMOS synthetic antenna, finding that they are not negligible. Those correlations can be characterized by means of effective point spread functions (PSFs). This paper indicates that the SMOS PSF matrix can be computed in a fast way from measured data without the need for any model or auxiliary data. Furthermore, this matrix can be described in terms of a convolution kernel. The knowledge of that convolution kernel can be used to improve the quality of the SMOS image and to assess the effect of changes of processing procedures, including calibration methods.

Three-dimensional resolution and contrast-enhanced confocal microscopy with array detection.

What we believe is a novel method for improving confocal microscopy's resolution and contrast in 3D space is proposed. Based on a conventional confocal microscopy setup, we use an array detector composed of 32 photomultiplier tubes (PMTs) to replace one point-detector, where the location offset of each PMT caused a different effective point spread function (PSF). By applying array detection and the fluorescence emission difference method of an image with a solid PSF and another with a donut-shaped PSF, we can enhance lateral resolution about 27% in real time with only one scan, and improve the axial resolving ability by about 22% simultaneously. Experimental results of both fluorescent beads and living cells are presented to verify the applicability and effectiveness of our method.

Optimization of depletion focal spot in STED nanoscopy using amplitude manipulation

To optimize the performance of stimulated emission depletion (STED) nanoscopy, a high-quality ring-shaped depletion pattern with a “zero”-intensity point at the center is mandatory. Here, we propose a novel strategy to enhance the two-dimensional (2D) resolution of STED nanoscopy by amplitude manipulation. In particular, we employ an annular mask to the depletion beam to enable a compression to the size of effective point spread function (PSF) by at least 20%.

Quantitative comparison of PET performance-Siemens Biograph mCT and mMR.

BackgroundIntegrated clinical whole-body PET/MR systems were introduced in 2010. In order to bring this technology into clinical usage, it is of great importance to compare the performance with the well-established PET/CT. The aim of this study was to evaluate PET performance, with focus on image quality, on Siemens Biograph mMR (PET/MR) and Siemens Biograph mCT (PET/CT).MethodsA direct quantitative comparison of the performance characteristics between the mMR and mCT system was performed according to National Electrical Manufacturers Association (NEMA) NU 2-2007 protocol. Spatial resolution, sensitivity, count rate and image quality were evaluated. The evaluation was supplemented with additional standardized uptake value (SUV) measurements.ResultsThe spatial resolution was similar for the two systems. Average sensitivity was higher for the mMR (13.3 kcps/MBq) compared to the mCT system (10.0 kcps/MBq). Peak noise equivalent count rate (NECR) was slightly higher for the mMR (196 kcps @ 24.4 kBq/mL) compared to the mCT (186 kcps @ 30.1 kBq/mL). Scatter fractions in the clinical activity concentration range yielded lower values for the mCT (34.9 %) compared to those for the mMR (37.0 %). Best image quality of the systems resulted in approximately the same mean hot sphere contrast and a difference of 19 percentage points (pp) in mean cold contrast, in favour of the mCT. In general, point spread function (PSF) increased hot contrast and time of flight (TOF) increased both hot and cold contrast. Highest hot contrast for the smallest sphere (10 mm) was achieved with the combination of TOF and PSF on the mCT. Lung residual error was higher for the mMR (22 %) than that for the mCT (17 %), with no effect of PSF. With TOF, lung residual error was reduced to 8 % (mCT). SUV was accurate for both systems, but PSF caused overestimations for the 13-, 17- and 22-mm spheres.ConclusionsBoth systems proved good performance characteristics, and the PET image quality of the mMR was close to that of the mCT. Differences between the systems were mainly due to the TOF possibility on the mCT, which resulted in an overall better image quality, especially for the most challenging settings with higher background activity and small uptake volumes.

Nano-Confined Polymer Structures for Protein Binding

Stimulated emission depletion lithography (STED-lithography), a further development of multiphoton polymerization (MPP) lithography, belongs to the most promising methods for 2D and 3D structuring of polymer scaffolds with structure sizes in the nanometer range. Already in the early developmental stages of STED-microscopy, it was pointed out that a nano-confined effective point-spread function (PSF) can be applied to spatially confine photo-chemical reactions to sub-diffraction volumes. In optical STED-lithography, one laser pulse excites photo-initiators for radical polymerization and a second donut-shaped laser beam locally inhibits these starter molecules in the outer rim of the PSF. This confinement of the excitation volume leads to a restriction of the size of the polymerized structures. Such a STED-based approach facilitates the creation of structures with sizes below the limits of conventional MPP. Currently, feature sizes as small as 55 nm and a resolution of 120 nm of adjacent lines can be achieved.We use stimulated emission depletion (STED) lithography for the assembly of polymeric structures down to several nanometers in any desired geometry. Protein adhesive photoresists allow manufacturing of nano-confined, protein functionalized structures. The structures show good biocompatibility and allow an easy biofunctionalization with proteins down to a single protein level. Furthermore, we use STED-lithography to create 3D compound structures of different acrylate polymers with distinct properties. A µm-sized protein repellent scaffold consists of multi-photon lithography (MPP) fabricated features, carrying STED-lithography written sub-100 nm protein-binding sites.Combining STED lithography with fluorescence microscopy allows us to produce well characterized, biocompatible structures, applicable to biological assays.

Generation and comparison of donut-shaped depletion beams in STED microscopy

The profile of donut-shaped depletion beam focused by a high numerical aperture (NA) microscope objective determines the resolution and signal to noise ratio (SNR) of image in stimulation emission depletion (STED) microscopy. Thus, the effects of different donut-shaped depletion beams on the STED microscopy are needed to be researched. In this paper, theoretical and experimental researches have been conducted on the effect of donut-shaped depletion beams on the resolution and SNR of image in stimulation emission depletion (STED) microscopy. Four kinds of donut-shaped depletion beams had been researched, including linear polarization with vortex phase, left circular polarization with vortex phase, right circular polarization with vortex phase and azimuthal polarization. Simulations of effective fluorescence point spread function (PSF) had been conducted with the different donut-shaped depletion beams mentioned above. The peak to peak distance for azimuthal polarization minimizes about 10% than right circular polarization. The donut-shaped beams were experimental tested. The effective fluorescence PSF was measured by fluorescence beads, evidencing a spatial resolution of 36nm in the focal plane. The results show that depletion beams of the right circular polarization combined with vortex phase and the azimuthal polarization are preferable for STED microscopy. Furthermore, higher resolution could be achieved with the azimuthally polarized depletion beam, while the right circularly polarized depletion beam could be generated more easily in the experiments.

Accuracy of Resolution Recovery in PSF-based Fully-3D PET Image Reconstruction: Simulation and Phantom Study in Multicenter Trial

Recently, the quality of positron emission tomography (PET) images has rapidly improved using resolution recovery algorithm with point spread function (PSF). The aim of this study was to investigate the accuracy of the resolution recovery algorithm using three different PET systems. Three PET scanner models, the GE Discovery 600 M (D600M), SIEMENS Biograph mCT (mCT), and SHIMADZU SET-3000GCT/X (3000GCT) were used in this study. The radial dependences of spatial resolution (full width at half maximum: FWHM) were obtained by point source measurements (0.9 mmφ). All PET data were acquired in three-dimensional (3D) mode and reconstructed using the filtered back projection (FBP) , 3D-ordered subsets expectation maximization (3D-OSEM or dynamic row-action maximum likelihood algorithm) , and 3D-OSEM+PSF (PSF) algorithms. Two indicators, aspect ratio (ASR) and resolution recovery ratio (RRR), were calculated from measured FWHMs and compared among the three PET scanners. In D600 and 3000GCT, distortions of the radial direction were slightly increased at circumference of field of view (FOV). On the other hand, random distortions were occurred in both radial and tangential direction in mCT. ASRs calculated from 3D-OSEM images at circumference of FOV were 2.06, 1.22, and 2.04 on D600M, mCT, and 3000GCT, respectively. ASR improved with PSF in all PET scanners. On the other hand, RRR with PSF were calculated 57.6%, 61.4%, and 31.6%, respectively. Our results suggest that the spatial resolutions of PET images could be improved with PSF algorithm in all PET systems; however, effect of PSF was different depending on PET systems. Furthermore, PSF algorithm could not completely improve spatial resolutions in circumference of FOV.

Optimized Optomechanical Anti-Aliasing Filter for Digital Camera Photography

We investigated an anti-aliasing (AA) filter for digital camera photography by which the excessively high-frequency components of the image signal are suppressed to avoid the aliasing effect. Our optomechanical AA filter was implemented by applying rapid relative motions to the imaging sensor. By the engineered motion blur of the mechanical dithers, the effective point-spread function (PSF) of the imaging system could be tailored to reject the unwanted high-frequency components of the image. For optimal operations, we developed a spiral filter motion protocol that could produce a Gaussian-like PSF. We experimentally demonstrated that our AA filter provides an improved filtering characteristic with a better compromise of the rejection performance and the signal loss. We also found that the pass band characteristic can be enhanced further by a color-differential acquisition mode. Our filter scheme provides a useful method of digital photography for low-error image measurements as well as for ordinary photographic applications where annoying $moir{\acute{e}}$ patterns must be suppressed efficiently.

The MODIS (collection V006) BRDF/albedo product MCD43D: Temporal course evaluated over agricultural landscape

The assessment of uncertainties in satellite-derived global surface albedo products is a critical aspect for studying the climate, ecosystem change, hydrology or the Earth's radiant energy budget. However, it is challenged by the spatial scaling errors between satellite and field measurements. This study aims at evaluating the forthcoming MODerate Resolution Imaging Spectroradiometer (MODIS) (Collection V006) Bidirectional Reflectance Distribution Function (BRDF)/albedo product MCD43D over a Mediterranean agricultural area. Here, we present the results from the accuracy assessment of the MODIS blue-sky albedo. The analysis is based on collocated comparisons with higher spatial resolution estimates from Formosat-2 that were first evaluated against local in situ measurements. The inter-sensor comparison is achieved by taking into account the effective point spread function (PSF) for MODIS albedo, modeled as Gaussian functions in the North–South and East–West directions. The equivalent PSF is estimated by correlation analysis between MODIS albedo and Formosat-2 convolved albedo. Results show that it is 1.2 to 2.0 times larger in the East–West direction as compared to the North–South direction. We characterized the equivalent PSF by a full width at half maximum size of 1920 m in East–West, 1200 m in North–South. This provided a very good correlation between the products, showing absolute (relative) Root Mean Square Errors from 0.004 to 0.013 (2% to 7%), and almost no bias. By inspecting 1-km plots homogeneous in land cover type, we found poorer performances over rice and marshes (i.e., relative Root Mean Square Error of about 11% and 7%, and accuracy of 0.011 and − 0.008, respectively), and higher accuracy over dry and irrigated pastures, as well as orchards (i.e., relative uncertainty < 3.8% and accuracy < 0.003). The study demonstrates that neglecting the MODIS PSF when comparing the Formosat-2 albedo against the MODIS one induces an additional uncertainty up to 0.02 (10%) in albedo. The consistency between fine and coarse spatial resolution albedo estimates indicates the ability of the daily MCD43D product to reproduce reasonably well the dynamics of albedo.