Gain In Resolution Research Articles

Results of hermetic transform signal processing to enhance the resolution and array gain of underwater acoustic arrays.

Results of applying the discrete hermetic transform (DHT) to the beamforming of underwater acoustic arrays are presented in terms of measured reductions in beam mainlobe width as well as the associated improvement in directivity index/array gain for practical cases of interest. Application of the DHT to array beamforming is shown to produce substantially enhanced resolution relative to the conventional beamforming diffraction limit as well as significant enhancement in array gain against ambient noise, without the use of data adaptive or nonlinear processing. As a result, enhanced sonar signal detection and/or the ability to use substantially smaller than normal arrays can be accomplished through the judicious use of DHT based beamforming algorithms. Results are favorably compared to theoretical predictions of algorithm performance.

Cooperative Multimonostatic SAR: A New SAR Configuration for Improved Resolution

This letter presents a new synthetic aperture radar (SAR) configuration that has been named cooperative multimonostatic SAR (CMM SAR). CMM SAR consists of a battery of monostatic SARs whose flight paths and frequency bands are coordinated in such a way that the final system produces high-resolution images. The point spread function (PSF) of CMM SAR has been used to quantify the gain in resolution as compared to a monostatic SAR system operating under the same k-space area. Three different configurations of CMM SAR have been proposed. Evaluations of these CMM SARs are done, and the results show substantial improvement in performance compared to the conventional monostatic SAR. One of these three CMM SARs is especially the most successful in terms of both gain in performance and simplicity in implementation.

Compound-Specific δ34S Analysis of Volatile Organics by Coupled GC/Multicollector-ICPMS

We have developed a highly sensitive and robust method for the analysis of delta(34)S in individual organic compounds by coupled gas chromatography (GC) and multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). The system requires minimal alteration of commercial hardware and is amenable to virtually all sample introduction methods. Isobaric interference from O(2)(+) is minimized by employing dry plasma conditions and is cleanly resolved at all masses using medium resolution on the Thermo Neptune MC-ICPMS. Correction for mass bias is accomplished using standard-sample bracketing with peaks of SF(6) reference gas. The precision of measured delta(34)S values approaches 0.1 per thousand for analytes containing >40 pmol S and is better than 0.5 per thousand for those containing as little as 6 pmol S. This is within a factor of 2 of theoretical shot-noise limits. External accuracy is better than 0.3 per thousand. Integrating only the center of chromatographic peaks, rather than the entire peak, offers significant gain in precision and chromatographic resolution with minimal effect on accuracy but requires further study for verification as a routine method. Coelution of organic compounds that do not contain S can cause degraded analytical precision. Analyses of crude oil samples show wide variability in delta(34)S and demonstrate the robustness and precision of the method in complex environmental samples.

Superresolved phase-shifting Gabor holography by CCD shift

Holography in the Gabor regime is restricted to weak diffraction assumptions. Otherwise, diffraction prevents an accurate recovery of the object's complex wavefront. We have recently proposed a modified Gabor-like setup to extend Gabor's concept to any sample provided that it be non-diffusive. However, the resolution of the final image becomes limited as a consequence of the additional elements considered in the proposed setup. In this paper we present an experimental approach to overcome such a limitation in which the former configuration is used while the CCD camera is shifted to different off-axis positions in order to generate a synthetic aperture. Thus, once the whole image set is recorded and digitally processed for each camera position, we merge the resulting band-pass images into one image by assembling a synthetic aperture. Finally, a superresolved image is recovered by Fourier transformation of the information contained in the generated synthetic aperture. Experimental results validate our concepts for a gain in resolution of close to 2.

Gain in spatial resolution of X-ray laboratory microtomographs with enlarging X-ray optical elements

Two types of x-ray optical elements are discussed – capillary air bubble lens and asymmetric cut single crystal. These elements are applied to laboratory microtomography. Several reconstructions using laboratory x-ray source (2 kW, 1×1 mm2 size) and the optical elements are obtained. Best voxel size of 1 μm is achieved using two crossed asymmetric cut single crystal (Bragg magnifier) and 14×14 μm pixel CCD camera. Two times magnifying x-ray microtomograph with 7.5 μm resolution was built using capillary air bubble lens.

Three-dimensional velocity map imaging: Setup and resolution improvement compared to three-dimensional ion imaging

For many years the three-dimensional (3D) ion imaging technique has not benefited from the introduction of ion optics into the field of imaging in molecular dynamics. Thus, a lower resolution of kinetic energy as in comparable techniques making use of inhomogeneous electric fields was inevitable. This was basically due to the fact that a homogeneous electric field was needed in order to obtain the velocity component in the direction of the time of flight spectrometer axis. In our approach we superimpose an Einzel lens field with the homogeneous field. We use a simulation based technique to account for the distortion of the ion cloud caused by the inhomogeneous field. In order to demonstrate the gain in kinetic energy resolution compared to conventional 3D Ion Imaging, we use the spatial distribution of H(+) ions emerging from the photodissociation of HCl following the two photon excitation to the V (1)Sigma(+) state. So far a figure of merit of approximately four has been achieved, which means in absolute numbers Delta v/v = 0.022 compared to 0.086 at v approximately = 17,000 m/s. However, this is not a theoretical limit of the technique, but due to our rather short TOF spectrometer (15 cm). The photodissociation of HBr near 243 nm has been used to recognize and eliminate systematic deviations between the simulation and the experimentally observed distribution. The technique has also proven to be essential for the precise measurement of translationally cold distributions.

Yttrium-90 TOF PET scan demonstrates high-resolution biodistribution after liver SIRT

The decay of Y has a minor branch to the 0 excited state [1], followed by an internal ee creation which happens in 32 out of one million decays [2]. Consequently, Y PET scan was proposed in order to assess the biodistribution [3] of Y-labelled therapeutic agents. A 61-year-old woman was referred for treatment of chemorefractory colorectal liver metastasis. Based on the pretreatment evaluation (including a diagnostic FDG PET/CT scan on day 1, and a prophylactic embolization of the right gastric and gastroduodenal arteries followed by a Tc-MAA SPECT/CT scan on day 8), 1.3 GBq of Y-labelled SIR-Spheres were administered by sequential catheterization of both liver lobes (day 15). Subsequently, a 30-min Y TOF PET/CT scan was performed using a Philips GEMINI TF camera. In order to prevent saturation of the detectors, a copper ring of 2.5 mm thickness was inserted into the gantry to absorb the bremsstrahlung x-rays. The TOF data were reconstructed with attenuation and scatter correction using Philips RAMLA software (eight iterations, three subsets). An additional 20 min bremsstrahlung Y-SPECT was acquired using a Trionix XLT20 triple head camera (medium energy collimator, 30% window centred on 90 keV). Data were reconstructed using OSEM (four iterations, six subsets). As illustrated, despite the differences in their respective uptake mechanism, Y-PET better reflects the tumour heterogeneity assessed by FDG PET/CT (a necrotic core surrounded by active tumour margins) than traditional bremsstrahlung Y-SPECT. This gain in resolution should therefore contribute to increasing the accuracy of the dose distribution into the tumours and their surrounding healthy tissues.

Transverse-Dephasing Optimized Homonuclear J-Decoupling in Solid-State NMR Spectroscopy of Uniformly 13C-Labeled Proteins

A transverse-dephasing optimized S(3)E (spin-state selective excitation) method is implemented in solid-state NMR experiments of uniformly labeled protein samples, and it is shown to provide a simultaneous significant gain in both resolution (up to a factor of 2.2) and sensitivity (up to a factor of 1.4). This is illustrated with high-resolution NCO and NCA correlations of a microcrystalline sample of the oxidized form of the 153 residue human Cu(II)Zn(II) superoxide dismutase (SOD), a dimeric paramagnetic enzyme of 32 kDa. This method allows the resolution of 145 signals in the highly crowded carbonyl region in the NCO correlation spectrum.

Intravitreal Bevacizumab vs Sub-Tenon Triamcinolone Acetonide for Choroidal Neovascularization Attributable to Pathologic Myopia

To compare the visual outcomes of intravitreal bevacizumab (Avastin; Genentech Inc, South San Franciso, California, USA) and sub-Tenon triamcinolone acetonide (TA) for choroidal neovascularization attributable to pathologic myopia (mCNV). Retrospective, comparative, interventional case series. Fifty-four consecutive eyes of 53 patients with mCNV treated with either sub-Tenon TA or intravitreal bevacizumab in an institutional setting were included. Twenty eyes were treated with sub-Tenon TA and 34 eyes were treated with intravitreal bevacizumab. The main outcome measures included best-corrected visual acuity (BCVA) 12 months after the initial injection and logarithm of the minimum angle of resolution gain from baseline compared with analysis of covariance (ANCOVA). At 12 months, the BCVA improved by 1.9 lines in the intravitreal bevacizumab group and worsened by 0.3 lines in the sub-Tenon TA group. Thus, the intravitreal bevacizumab group had significantly greater visual improvement than the sub-Tenon TA group (P < .01). Statistical analysis (ANCOVA) revealed that age (P = .01), pretreatment BCVA (P < .01), and the treatment choice (intravitreal bevacizumab or sub-Tenon TA; P < .01) correlated significantly with the BCVA and the BCVA gain at 12 months. The refractive error was of borderline significance (P = .06). Although this study is limited because of its retrospective nature, intravitreal bevacizumab seems to result in a more favorable visual outcome than sub-Tenon TA in the treatment of mCNV. Patient age, the BCVA before treatment, and the refractive error must be considered to initiate the treatment.

As técnicas NASVD e MNF e sua aplicação na redução de ruídos em dados gamaespectrométricos

A desintegração radioativa é um processo aleatório e a estimativa de todas as medidas associadas é governada por leis estatísticas. Os perfis de taxas de contagem são sempre "ruidosos" quando utilizados períodos curtos como um segundo para cada medida. Os filtros utilizados e posteriormente as correções feitas no processamento atual de dados gamaespectrométricos não são suficientes para remover ou diminuir, consideravelmente, o ruído oriundo do espectro. Dois métodos estatísticos que atuam diretamente nos dados coletados, isto é, nos espectros, vêm sendo sugeridos na literatura para remover e minimizar estes ruídos remanescentes o Noise-Adjusted Singular Value Decomposition - NASVD e Maximum Noise Fraction - MNF. Estes métodos produzem uma redução no ruído de forma significativa. Neste trabalho eles foram implementados dentro do ambiente de processamento do software Oasis Montaj e aplicados na área compreendida pelos blocos I e II do levantamento aerogeofísico que recobre a porção oeste da Província Mineral do Tapajós, entre os Estados do Pará e Amazonas. Os dados filtrados e não-filtrados com as técnicas de NASVD e MNF foram processados com os parâmetros e constantes fornecidos pela empresa Lasa Engenharia e Prospecções S.A., sendo estes comparados. Os resultados da comparação entre perfis e mapas apresentaram-se de forma promissora, pois houve um ganho na resolução dos produtos.

Sinogram bow‐tie filtering in FBP PET reconstruction

Low-pass filtering of sinograms in the radial direction is the most common practice to limit noise amplification in filtered back projection (FBP) reconstruction of positron emission tomography studies. Other filtering strategies have been proposed to prevent the loss in resolution due to low-pass radial filters, although results have been diverse. Using the well-known properties of the Fourier transform of a sinogram, the authors defined a binary mask that matches the expected shape of the support region in the Fourier domain of the sinogram ("bow tie"). This mask was smoothed by a convolution with a ten-point Gaussian kernel which not only avoids ringing but also introduces a pre-emphasis at low frequencies. A new filtering scheme for FBP is proposed, comprising this smoothed bow-tie filter combined with a standard radial filter and an axial filter. The authors compared the performance of the bow-tie filtering scheme with that of other previously reported methods: Standard radial filtering, angular filtering, and stackgram-domain filtering. All the quantitative data in the comparisons refer to a baseline reconstruction using a ramp filter only. When using the smallest size of the Gaussian kernel in the stackgram domain, the authors achieved a noise reduction of 33% at the cost of degrading radial and tangential resolutions (14.5% and 16%, respectively, for cubic interpolation). To reduce the noise by 30%, the angular filter produced a larger degradation of contrast (3%) and tangential resolution (46% at 10 mm from the center of the field of view) and showed noticeable artifacts in the form of circular blurring dependent on the distance to the center of the field of view. For a similar noise reduction (33%), the proposed bow-tie filtering scheme yielded optimum results in resolution (gain in radial resolution of 10%) and contrast (1% increase) when compared with any of the other filters alone. Experiments with rodent images showed noticeable image quality enhancement when using the proposed bow-tie filtering scheme.

High peak capacity separation of peptides through the serial connection of LC shell‐packed columns

High peak capacity was obtained for the separation of a HSA tryptic digest through the serial connection of three LC columns packed with shell material (C18, 15 cmx4.6 mm, 2.7 mum particle size). A major benefit of these particles, consisting of a 1.7 mum solid core and a 0.5 mum porous shell, is the small diffusion path, which reduces axial dispersion of solutes and minimizes peak broadening allowing for higher resolving power to be obtained. Increase in the temperature decreases the viscosity and the backpressure on the columns and in this way allowed to couple multiple columns. Single and multicolumn systems were first evaluated for the separation of a standard sample mixture in the isocratic mode; afterwards three columns could be coupled at 60 degrees C, generating more than 90,000 effective plates (200,000 plates/meter) for the separation of HSA in gradient mode on a conventional HPLC instrument. Peak capacity ratios were found in good accordance with the theoretical gain in resolution, i.e. values of 1.37 and 1.67 were measured, when doubling and tripling the length of stationary phases, respectively (the highest measured peak capacity on three coupled columns was 367).

Superresolution parallel magnetic resonance imaging: Application to functional and spectroscopic imaging

Standard parallel magnetic resonance imaging (MRI) techniques suffer from residual aliasing artifacts when the coil sensitivities vary within the image voxel. In this work, a parallel MRI approach known as Superresolution SENSE (SURE-SENSE) is presented in which acceleration is performed by acquiring only the central region of k-space instead of increasing the sampling distance over the complete k-space matrix and reconstruction is explicitly based on intra-voxel coil sensitivity variation. In SURE-SENSE, parallel MRI reconstruction is formulated as a superresolution imaging problem where a collection of low resolution images acquired with multiple receiver coils are combined into a single image with higher spatial resolution using coil sensitivities acquired with high spatial resolution. The effective acceleration of conventional gradient encoding is given by the gain in spatial resolution, which is dictated by the degree of variation of the different coil sensitivity profiles within the low resolution image voxel. Since SURE-SENSE is an ill-posed inverse problem, Tikhonov regularization is employed to control noise amplification. Unlike standard SENSE, for which acceleration is constrained to the phase-encoding dimension/s, SURE-SENSE allows acceleration along all encoding directions — for example, two-dimensional acceleration of a 2D echo-planar acquisition. SURE-SENSE is particularly suitable for low spatial resolution imaging modalities such as spectroscopic imaging and functional imaging with high temporal resolution. Application to echo-planar functional and spectroscopic imaging in human brain is presented using two-dimensional acceleration with a 32-channel receiver coil.

Sensory Neurons in the Drosophila Genital Tract Regulate Female Reproductive Behavior

Females of many animal species behave very differently before and after mating. In Drosophila melanogaster, changes in female behavior upon mating are triggered by the sex peptide (SP), a small peptide present in the male's seminal fluid. SP activates a specific receptor, the sex peptide receptor (SPR), which is broadly expressed in the female reproductive tract and nervous system. Here, we pinpoint the action of SPR to a small subset of internal sensory neurons that innervate the female uterus and oviduct. These neurons express both fruitless (fru), a marker for neurons likely to have sex-specific functions, and pickpocket (ppk), a marker for proprioceptive neurons. We show that SPR expression in these fru+ ppk+ neurons is both necessary and sufficient for behavioral changes induced by mating. These neurons project to regions of the central nervous system that have been implicated in the control of reproductive behaviors in Drosophila and other insects.

An efficient pre‐object collimator based on an x‐ray lens

A multiprism lens (MPL) is a refractive x-ray lens with one-dimensional focusing properties. If used as a pre-object collimator in a scanning system for medical x-ray imaging, it reduces the divergence of the radiation and improves on photon economy compared to a slit collimator. Potential advantages include shorter acquisition times, a reduced tube loading, or improved resolution. We present the first images acquired with a MPL in a prototype for a scanning mammography system. The lens showed a gain of flux of 1.32 compared to a slit collimator at equal resolution, or a gain in resolution of 1.31-1.44 at equal flux. We expect the gain of flux in a clinical setup with an optimized MPL and a custom-made absorption filter to reach 1.67, or 1.45-1.54 gain in resolution.

On the assignment of19F MAS NMR spectra of fluoroaluminates using through-space spectral edition of19F–27Al and19F–19F connectivities

Advantages and limitations of (19)F-(27)Al and (19)F-(19)F dipolar-based 2D NMR experiments for (19)F MAS spectra assignments of fluoroaluminates are presented. In beta-BaAlF(5), combination of 2D MAS (19)F-(27)Al CP-HETCOR and (19)F-(19)F DQ-SQ NMR correlation experiments allows complete unambiguous assignment of the ten poorly resolved resonances of same relative intensities of the (19)F MAS NMR spectrum. The gain in resolution of the (19)F MAS 2D spectrum compared to a 1D spectrum is evidenced, allowing distinction of the two shared-fluorine resonances of Ba(3)Al(2)F(12). Limitations of the (19)F MAS DQ-SQ NMR experiment are shown for Ba(3)Al(2)F(12) and for alpha-CaAlF(5). For beta-BaAlF(5) and Ba(3)Al(2)F(12), final line assignments question those previously established from (19)F isotropic chemical shift calculations, which demonstrate that such experiments are essential for correct line assignments and assessment of calculation results.

Resolution improvement and noise reduction in human pinhole SPECT using a multi-ray approach and the SHINE method

This work aimed at quantifying the gains in spatial resolution and noise that could be achieved when using resolution modelling based on a multi-ray approach and additionally the Statistical and Heuristic Noise Extraction (SHINE) method in human pinhole single photon emission tomography (PH-SPECT). PH-SPECT of two line phantoms and one homogeneous cylinder were recorded using parameters suited for studies of the human neck area. They were reconstructed using pinhole dedicated ordered subsets expectation maximisation algorithm including a resolution recovery technique based on 7 or 21 rays. Optionally, the SPECT data were SHINE pre-processed. Transverse and axial full widths at half-maximum (FWHM) were obtained from the line phantoms. The noise was quantified using the coefficient of variation (COV) derived from the uniform phantom. Two human PH-SPECT studies of the thyroid (a hot nodule and a very low uptake) were processed with the same algorithms. Depending on the number of iterations, FWHM decreased by 30 to 50% when using the multi-ray approach in the reconstruction process. The SHINE method did not affect the resolution but decreased the COV by at least 20% and by 45% when combined with the multi-ray method. The two human studies illustrated the gain in spatial resolution and the decrease in noise afforded both by the multi-ray reconstruction and the SHINE method. Iterative reconstruction with resolution modelling allows to obtain high resolution human PH-SPECT studies with reduced noise content. The SHINE method affords an additional noise reduction without compromising the resolution.

Widefield fluorescence microscopy with extended resolution

Widefield fluorescence microscopy is seeing dramatic improvements in resolution, reaching today 100 nm in all three dimensions. This gain in resolution is achieved by dispensing with uniform Köhler illumination. Instead, non-uniform excitation light patterns with sinusoidal intensity variations in one, two, or three dimensions are applied combined with powerful image reconstruction techniques. Taking advantage of non-linear fluorophore response to the excitation field, the resolution can be further improved down to several 10 nm. In this review article, we describe the image formation in the microscope and computational reconstruction of the high-resolution dataset when exciting the specimen with a harmonic light pattern conveniently generated by interfering laser beams forming standing waves. We will also discuss extensions to total internal reflection microscopy, non-linear microscopy, and three-dimensional imaging.

Stimulated emission depletion (STED) nanoscopy of a fluorescent protein-labeled organelle inside a living cell

We demonstrate far-field optical imaging with subdiffraction resolution of the endoplasmic reticulum (ER) in the interior of a living mammalian cell. The diffraction barrier is overcome by applying stimulated emission depletion (STED) on a yellow fluorescent protein tag. Imaging individual structural elements of the ER revealed a focal plane (x, y) resolution of <50 nm inside the living cell, corresponding to a 4-fold improvement over that of a confocal microscope and a 16-fold reduction in the focal-spot cross-sectional area. A similar gain in resolution is realized with both pulsed- and continuous-wave laser illumination. Images of highly convoluted parts of the ER reveal a similar resolution improvement in 3D optical sectioning by a factor of 3 along the optic axis (z). Time-lapse STED recordings document morphological changes of the ER over time. Thus, nanoscale 3D imaging of organelles in the interior of living cells greatly expands the scope of light microscopy in cell biology.

From Nano to Subnano Resolution: Reconstitution of Hydrofobin Structure from a SPM Scan of HFBI Layer~!2008-03-24~!2008-05-07~!2008-06-12~!

Applying Scanning Probe Microscopy (SPM) methods to determine structural details of biomolecules (e.g. proteins) is one of the key trends in nanotechnology. Here we present the analysis of a Langmuir-Blodgett film of hydrofobin HFBI. The statistical analysis is based on an accurate procedure of data detrending to study the quasi-crystalline clusters of the HFBI layer. A statistical improvement method of signal to noise ratio was used. It relies on the variation of the crystallographic lattice superimposed on a quasi-periodical data set. The procedure produces optimal values of crystallographic periods and orientations of the symmetry axes. This information is used for selecting coherent data sets within a crystallographic cluster. Superposition of cells from the same cluster and calculation of an average periodical structure improves the signal to noise ratio, which leads from nano to subnano resolution of the protein structure. The number of superimposed cells N defines the resolution gain factor N 1/2 . In the case of hydrofobin, the value of N lies in the range of 25-100. This allows for the determination of fine structural details of HFBI. Average structures obtained from different domains of the protein layer also show a high degree of reproducibility.