Search

A short-lag filtered-delay multiply and sum (FDMAS) beamforming algorithm, which can be considered as a variant of F-DMAS, has recently been proposed. In this method, the signals in the regions of low lags (short-lag) are used, and the computation complexity is reduced accordingly. In fact, the short-lag regions can efficiently reflect the spatial coherence. Thus, we proposed a method to combine this algorithm with the Sign Coherence Factor (SCF). In the simulation test, our proposed method demonstrate better contrast and resolution in comparison with the F-DMAS.

This is the first article in a series of two dealing with a matrix approach \alex{for} aberration quantification and correction in ultrasound imaging. Advanced synthetic beamforming relies on a double focusing operation at transmission and reception on each point of the medium. Ultrasound matrix imaging (UMI) consists in decoupling the location of these transmitted and received focal spots. The response between those virtual transducers form the so-called focused reflection matrix that actually contains much more information than a raw ultrasound image. In this paper, a time-frequency analysis of this matrix is performed, which highlights the single and multiple scattering contributions as well as the impact of aberrations in the monochromatic and broadband regimes. Interestingly, this analysis enables the measurement of the incoherent input-output point spread function at any pixel of this image. A focusing criterion can then be built, and its evolution used to quantify the amount of aberration throughout the ultrasound image. In contrast to the standard coherence factor used in the literature, this new indicator is robust to multiple scattering and electronic noise, thereby providing a highly contrasted map of the focusing quality. As a proof-of-concept, UMI is applied here to the in-vivo study of a human calf, but it can be extended to any kind of ultrasound diagnosis or non-destructive evaluation.

Synthetic aperture focusing (SAF) and coherence factor weighting (CFW) have been used to improve the lateral resolution of ultrasound images. Although the two methods are effective for array-based ultrasound imaging, many researchers have also employed the methods for single-element-based imaging including intravascular ultrasound (IVUS) imaging. For single-element-based imaging, CFW is generally calculated from the scanlines obtained by SAF and applied to the scanline obtained after coherent summation of the SAF delayed scanlines, which is called a SAF-CFW method. In the paper, a theoretical model was derived to explore the effectiveness of SAF and CFW for single-element-based imaging, and the model was used to explain that SAF is not effective for IVUS imaging in terms of enhancing the spatial resolution, although it has the advantage of improving a contrast-to-noise ratio (CNR). This means that the SAF-CFW method is not optimal for improving the spatial resolution of IVUS imaging. In contrast, it was found in simulations and experiments that applying CFW to the target scanline itself is beneficial for the spatial resolution rather than a coherent summed scanline for IVUS SAF imaging, but CNR was not as good as SAF and SAF-CFW. As a result of both simulation and experimentation, it could be concluded that focused IVUS transducers without the application of those methods may be more advantageous to improve the spatial and contrast resolution simultaneously, considering the system complexity in the implementation of such imaging methods.

Coherent plane-wave compounding (CPWC) is widely used in medical ultrasound imaging, in which plane-waves tilted at multiple angles are used to reconstruct ultrasound images. CPWC helps to achieve a balance between frame rate and image quality. However, the image quality of CPWC is limited due to sidelobes and noise interferences. Filtering techniques and adaptive beamforming methods are commonly used to suppress noise and sidelobes. Here, we propose a neighborhood singular value decomposition (NSVD) filter to obtain high-quality images in CPWC. The NSVD filter is applied to adaptive beamforming by combining with adaptive weighting factors. The NSVD filter is advantageous because of its singular value decomposition (SVD) and smoothing filters, performing the SVD processing in neighboring regions while using a sliding rectangular window to filter the entire imaging region. We also tested the application of NSVD in adaptive beamforming. The NSVD filter was combined with short-lag spatial coherence (SLSC), coherence factor (CF), and generalized coherence factor (GCF) to enhance performances of adaptive beamforming methods. The proposed methods were evaluated using simulated and experimental datasets. We found that NSVD can suppress noise and achieve improved contrast (contrast ratio (CR), contrast-to-noise ratio (CNR) and generalized CNR (gCNR)) compared to CPWC. When the NSVD filter is used, adaptive weighting methods provide higher CR, CNR, gCNR and speckle signal-to-noise ratio (sSNR), indicating that NSVD is able to improve the imaging performance of adaptive beamforming in noise suppression and speckle pattern preservation.

We report a single-shot surface three-dimensional (3-D) imaging method that uses optical coherence as a contrast mechanism to acquire the vertical (z-direction) information of an object. The illumination of the imaging system comes from a light source with the optical coherence length similar to the depth of field (DoF) of the optical system. Holographic recording is used to retrieve the coherence visibility factor, which is then converted to z-direction information. In the experiment, we compare the imaging results of our method to conventional incoherent imaging results, showing that this contrast mechanism is able to provide additional information. We also validate our 3D imaging results by using axial scanning full-field optical coherence tomography.

We present an enhanced imaging procedure for suppression of the rough surface clutter arising in forward-looking ground-penetrating radar (FL-GPR) applications. The procedure is based on a matched filtering formulation of microwave tomographic imaging, and employs coherence factor (CF) for clutter suppression. After tomographic reconstruction, the CF is first applied to generate a “coherence map” of the region in front of the FL-GPR system illuminated by the transmitting antennas. A pixel-by-pixel multiplication of the tomographic image with the coherence map is then performed to generate the clutter-suppressed image. The effectiveness of the CF approach is demonstrated both qualitatively and quantitatively using electromagnetic modeled data of metallic and plastic shallow-buried targets.

Terahertz (THz) arrays can be used to improve the data acquisition speed considerably in real-time imaging applications. However, the THz array imaging usually suffers from the side-lobe artifacts, which leads to a severe decline in the image quality. In this paper, a side-lobe suppression method based on coherence factor is proposed to improve the image quality. The influences of signal-to-noise ratio on the imaging results are analyzed by simulation. Furthermore, the results based on the real-world data validate the effectiveness of the proposed method, which indicates that the side-lobe is suppressed by 29 dB. This paper can benefit the development of THz imaging technique and its applications in real-time imaging realms.

Synthetic transmit aperture (STA) ultrasound imaging that obtain bi-directional focusing can create a high-resolution image. Delay-and-sum (DAS) approach is performed in both transmit and receive modes, which leads to low contrast and high sidelobe. Adaptive weighting technology is effective in improving image quality. This paper proposes a new adaptive weighting factor namely signal eigenvalue factor (SEF) for STA imaging. SEF performs eigenvalue decomposition on transmitting aperture, and then it uses the larger eigenvalues as the weighting factor to carry out the adaptive imaging. For comparison, conventional coherence factor (CF) method is also presented. Simulation and experimental results show that SEF method can get higher resolution than CF and DAS. In addition, the contrast radio and contrast-to-noise radio can be enhanced, especially for massive cyst.

The coherence factor (CF) and Wiener postfilter methods have been proposed as effective approaches for reducing the output noise of the delay-and-sum (DAS) beamformer in ultrasound imaging. The theoretical framework between them was also established. However, past researches about the CF and Wiener postfilter methods mainly focused on the summation of an array signal. This paper analyzes the CF and Wiener postfilter in the synthetic aperture (SA) imaging mode, where two-dimensional echo data are recorded. Different CF definitions in the SA imaging are first given and the corresponding Wiener postfilter methods are then proposed, including a Wiener postfilter especially for the SA imaging, named as WienerSA. The performances of different CF and Wiener postfilter methods were evaluated on both simulated and experimental SA data. Results showed that the proposed WienerSA outperformed the other Wiener postfilters in reducing the sidelobe noise level. It obtained the highest contrast ratio among the Wiener postfilter methods, which was even higher than some of the CF methods. Meanwhile it could benefit a much higher contrast-to-noise ratio than those CF methods with further suppression of incoherent noises. Consequently, the WienerSA is believed to be a promising approach in enhancing the SA image quality.

Image reconstruction in optoacoustic imaging is often based on a delay-and-sum (DAS) or a frequency domain (FD) algorithm. In this study, we performed a comprehensive comparison of these two algorithms together with coherence factor (CF) weighting using phantom and in-vivo mouse data obtained with optoacoustic microscopy. For this purpose we developed an FD based definition of the CF. Our results reveal the equivalence of DAS and FD, with and without CF weighting, in terms of spatial resolution and contrast-to-noise ratio (CNR) but highlight the clear advantage of FD in terms of computational cost, making it preferable for 3D reconstruction or real-time applications. An important additional result of this research is that, contradictory to previous studies, CF weighting does not lead to any improvement in lateral resolution. Keywords: Photoacoustic, Synthetic aperture focusing technique, Lateral resolution, In-vivo, Optoacoustic microscopy

The coherence factor (CF) is defined as the ratio of coherent to incoherent powers received by the radar aperture. Since the incoherent part is only obtained along the aperture direction, then the image sidelobes in down-range cannot be effectively suppressed. We propose a two-dimensional (2-D) CF by introducing another incoherent sum in the frequency dimension. In essence, we employ not only the antenna diversity but also the frequency diversity of the spatial spectrum of the targets to suppress sidelobes and ghosts in the radar image. Simulations and experimental results are provided to demonstrate the merits of the proposed approach.

Ultra-wideband (UWB) radar imaging has been applied in various applications such as synthetic aperture radar (SAR) imaging, through-wall-radar imaging and terahertz imaging. High level sidelobes raised by imaging approaches have serious impact on the image quality. In this paper a sidelobe reduction method for UWB radar imaging is proposed. The spatial spectrum coherence factor (CF) based sidelobe reduction method reduces the sidelobes and keeps the mainlobes simultaneously. The simulated and real data results have validated the effective, stable and convenient method.

A sparse and uniform multiple-input–multiple-output array is generally utilized in through-wall radar to implement real-time imaging of moving targets. However, the array sparsity with the interelement spacing much bigger than half a wavelength gives rise to grating lobe interference smearing the images. In order to enhance the signal-to-interference ratio, this letter introduces the sign coherence factor (SCF) to weigh through-wall images to suppress the grating lobes. The SCF is first proposed in medical ultrasound imaging and directly reflects the coherence of sign bits of all the transmit–receive channels in each pixel. Since the SCF calculated only by the sign bits, it has the smallest amount of computations compared with two other weighing factors, namely, the coherence factor (CF) and the phase coherence factor (PCF), which have been applied to through-wall imaging already. Moreover, the SCF has comparable performance in suppressing grating lobes with the PCF, much better than the CF. These two advantages make the SCF the most suitable for real-time imaging of moving targets. The experimental results with a two-transmitting eight-receiving stepped-frequency continuous-wave through-wall radar verifies the excellent performance of the SCF.

Measurements of the coherence factor R K 3 π , the average strong-phase difference δ D K 3 π and mean amplitude ratio r D K 3 π for the decay D → K − π + π + π − are presented. These parameters are important inputs to the determination of the unitarity triangle angle γ in B − → D K − decays, where D designates a superposition of D 0 and D ¯ 0 mesons decaying to a common final state. The results are based on a combined fit to observables obtained from a re-analysis of the CLEO-c ψ ( 3770 ) data set and those measured in a D 0 D ¯ 0 mixing study performed by the LHCb Collaboration.

The coherence factor (CF) is defined as the ratio of coherent power to incoherent power received by the radar aperture. The incoherent power is computed by the multi-antenna receiver based on only the spatial variable. In this respect, it is a one-dimensional (1-D) CF, and thereby the image sidelobes in down-range cannot be effectively suppressed. We propose a two-dimensional (2-D) CF by supplementing the 1-D CF by an incoherent sum dealing with the frequency dimension. In essence, we employ both spatial diversity and frequency diversity which, respectively, enhance imaging quality in cross range and range. Simulations and experimental results are provided to demonstrate the performance advantages of the proposed approach., Comment: 7 pages, 21 figures

In quasi-static elastography, the operator compresses the tissue under exam with the probe, while the scanner processes the beamformed frames, by means of correlation or signal phase analysis techniques, to estimate both the displacement and the strain. However, the quality of estimates may be influenced by the speckle quality and hence by the implemented beamforming algorithm. Therefore, in this work we investigate the effects of coherence-based beamforming techniques, providing better images than conventional Delay and Sum (DAS), on the estimation of axial/lateral displacement and strain in quasi-static elastography of the breast. Simulations were used to evaluate the error on axial and lateral displacement estimations obtained by 2D normalized cross-correlation (2D- NCC) with polynomial fitting, as compared to the ground truth given by finite-element modeling. Experimental breast phantom acquisitions where instead evaluated in terms of elastographic contrast-to-noise-ratio (CNRe) and non-uniformity (NU) level. Results show that similar performance in axial displacement estimation is achieved by 2D-NCC with all beamformers, while using coherence beamforming provides more accurate estimates of lateral displacement. However, the analysis of CNRe and NU in experimental axial/lateral strain images does not show any significant improvement as compared to DAS when any of these beamformers is employed.

We report a single-shot three-dimensional (3D) topographical imaging method, optical coherence factor (OCF) imaging, which uses optical coherence as the contrast mechanism to acquire the surface height ( z -direction) information of an object. A 4-f imaging system records the light field reflected from the surface of the object. The illumination of the imaging system comes from a laser source with the optical coherence length comparable to the depth of field (DoF) of the optical system. Off-axis holographic recording is used to retrieve the coherence factor from the interference fringes, which is then converted to z -direction information. In this experiment, we validate our 3D imaging results comparing them to axial scanning full-field optical coherence tomography images. We also analyze the contrast mechanism of OCF and show that it is able to provide additional information over conventional coherent and incoherent imaging using the same imaging setup. This single-shot computationally efficient method may have potential applications in industrial quality control inspection.

Amplitude models are constructed to describe the resonance structure of $${D^{0}\rightarrow K^{-}\pi ^{+}\pi ^{+}\pi ^{-}}$$ D0→K-π+π+π- and $${D^{0} \rightarrow K^{+}\pi ^{-}\pi ^{-}\pi ^{+}}$$ D0→K+π-π-π+ decays using pp collision data collected at centre-of-mass energies of 7 and 8 TeV with the LHCb experiment, corresponding to an integrated luminosity of 3.0 $$fb^{-1}$$ fb-1 . The largest contributions to both decay amplitudes are found to come from axial resonances, with decay modes $$D^{0} \rightarrow a_1(1260)^{+} K^{-}$$ D0→a1(1260)+K- and $$D^{0} \rightarrow K_1(1270/1400)^{+} \pi ^{-}$$ D0→K1(1270/1400)+π- being prominent in $${D^{0}\rightarrow K^{-}\pi ^{+}\pi ^{+}\pi ^{-}}$$ D0→K-π+π+π- and $$D^{0}\rightarrow K^{+}\pi ^{-}\pi ^{-}\pi ^{+}$$ D0→K+π-π-π+ , respectively. Precise measurements of the lineshape parameters and couplings of the $$a_1(1260)^{+}$$ a1(1260)+ , $$K_1(1270)^{-}$$ K1(1270)- and $$K(1460)^{-}$$ K(1460)- resonances are made, and a quasi model-independent study of the $$K(1460)^{-}$$ K(1460)- resonance is performed. The coherence factor of the decays is calculated from the amplitude models to be $$R_{K3\pi } = 0.459\pm 0.010\,(\mathrm {stat}) \pm 0.012\,(\mathrm {syst}) \pm 0.020\,(\mathrm {model})$$ RK3π=0.459±0.010(stat)±0.012(syst)±0.020(model) , which is consistent with direct measurements. These models will be useful in future measurements of the unitary-triangle angle $$\gamma $$ γ and studies of charm mixing and $$C\!P$$ CP violation.

Natural seepage of methane into the oceans is considerable, and plays a role in the global carbon cycle. Estimating the amount of this greenhouse gas entering the water column is important in order to understand their environmental impact. In addition, leakage from man-made structures such as gas pipelines may have environmental and economical consequences and should be promptly detected. Split beam echo sounders (SBES) detect hydroacoustic plumes due to the significant contrast in acoustic impedance between water and free gas. SBES are also powerful tools for plume characterization, with the ability to provide absolute acoustic measurements, estimate bubble trajectories, and capture the frequency dependent response of bubbles. However, under challenging conditions such as deep water and considerable background noise, it can be difficult to detect the presence of gas seepage from the acoustic imagery alone. The spatial coherence of the wavefield measured across the split beam sectors, quantified by the coherence factor (CF), is a computationally simple, easily available quantity which complements the acoustic imagery and may ease the ability to automatically or visually detect bubbles in the water column. We demonstrate the benefits of CF processing using SBES data from the Hudson Canyon, acquired using the Simrad EK80 SBES. We observe that hydroacoustic plumes appear more clearly defined and are easier to detect in the CF imagery than in the acoustic backscatter images.

Quantum sources and single photon detectors have improved, allowing quantum algorithms for communication, encryption, computing, and sensing to transition from theory and small-scale laboratory experiments to field experiments. One such quantum algorithm, Quantum Key Distribution, uses optical pulses to generate shared random bit strings between two locations. These shared bit strings can be turned into encryption keys to be used as a one-time-pad or integrated with symmetric encryption techniques such as the Advanced Encryption Standard. This method of key generation and encryption is resistant to future advances in quantum computing which significantly degrade the effectiveness of current asymmetric key sharing techniques. This research first reviews previous and current efforts in free-space Quantum Key Distribution. Next, a derivation of the propagation and atmospheric simulation techniques used to model the propagation of an optical pulse from a LEO satellite to ground through turbulence is provided. An Adaptive Optics system, including both lower order tracking as well as higher order corrections using a Self-Referencing Interferometer, is modeled to correct for the aberrations caused by the atmosphere. The propagation, atmospheric, and adaptive optics models are then organized into a general optical propagation toolkit. Satellite positions are calculated using the Simplified General Perturbations model and are used with the optical propagation models to show the effects of using an adaptive optics system during a realistic satellite pass. Finally, the results from the models are compared to experimental data taken from a recent Japanese satellite experiment.

Sparse recovery algorithms have shown great potential to accurately reconstruct images using limited-view optoacoustic (photoacoustic) tomography data sets, but these are computationally expensive. In this paper, we propose an improvement of the fast converging Split Augmented Lagrangian Shrinkage Algorithm method based on least square QR inversion for improving the reconstruction speed. We further show image fidelity improvement when using a coherence factor to weight the reconstruction result. Phantom and in vivo measurements show that the accelerated Split Augmented Lagrangian Shrinkage Algorithm method with coherence factor weighting offers images with reduced artifacts and provides faster convergence compared with existing sparse recovery algorithms.

Sparse recovery algorithms have shown great potential to reconstruct images with limited view datasets in optoacoustic tomography, with a disadvantage of being computational expensive. In this paper, we improve the fast convergent Split Augmented Lagrangian Shrinkage Algorithm (SALSA) method based on least square QR (LSQR) formulation for performing accelerated reconstructions. Further, coherence factor is calculated to weight the final reconstruction result, which can further reduce artifacts arising in limited-view scenarios and acoustically heterogeneous mediums. Several phantom and biological experiments indicate that the accelerated SALSA method with coherence factor (ASALSA-CF) can provide improved reconstructions and much faster convergence compared to existing sparse recovery methods.

Cavitation erosion in blood vessel plays an important role in ultrasound thrombolysis, drug delivery, and other clinical applications. The controllable superficial vessel erosion based on ultrasonic standing wave (USW) has been used to effectively prevent vessel ruptures and haemorrhages, and optical method is used to observe the experiments. But optical method can only work in transparent media. Compared with standard B-mode imaging, passive acoustic mapping (PAM) can monitor erosion in real time and has better sensitivity of cavitation detection. However, the conventionally used PAM has limitations in imaging resolution and artifacts. In this study, a unique PAM method that combined the robust Capon beamformer (RCB) with the sign coherence factor (SCF) was proposed to monitor the superficial vessel erosion in real time. The performance of the proposed method was validated by simulations. In vitro experiments showed that the lateral (axial) resolution of the proposed PAM was 2.31±0.51 (3.19±0.38) times higher than time exposure acoustics (TEA)-based PAM and 1.73±0.38 (1.76±0.48) times higher than RCB-based PAM, and the cavitation-to-artifact ratio (CAR) of the proposed PAM could be improved by 22.5±3.2dB and 7.1±1.2dB compared with TEA and RCB-based PAM. These results showed that the proposed PAM can precisely monitor the superficial vessel erosion and the erosion shift after USW modulation. This work may have the potential of developing a useful tool for precise spatial control and real-time monitoring of the superficial vessel erosion.

This paper presents the development and testing of a Perceived Restorativeness Soundscape Scale (PRSS). The scale is designed to assess perceptions of a soundscape’s potential to provide psychological restoration. In study one, 123 participants were presented with audio–visual recordings from a UK urban, urban park and rural environment, which they rated using the created PRSS. A series of factor analyses resulted in a two factor solution consisting of a General Factor and a Being-Away-To and Coherence Factor to represent PRSS results and its theoretical components. An urban soundscape was perceived as lower in restorative potential than an urban park soundscape, which was perceived as lower in restorative potential than the rural soundscape. In study two, 194 participants used the developed PRSS to rate the soundscape of a UK urban park they had just visited. Factor analyses resulted in a General one Factor solution. The PRSS was able to differentiate between soundscapes from different urban parks. The success of considering a positive benefit of soundscapes, psychological restoration, via the PRSS is discussed.

Various spatial compounding techniques have been proposed to improve contrast to noise ratio (CNR) of targets in ultrasound imaging by incoherently averaging sub-aperture images. However, spatial compounding (SC) sacrificed lateral resolution due to the decreased width of the selected sub-aperture. This paper presents the application of combining the SC and modified coherence factor (CF) techniques to single transmission plane wave imaging. The spatial resolution and contrast to noise ratio (CNR) of the tested phantoms were improved in the proposed method, compared to the conventional delay-and-sum technique.

All adaptive beamformers aim at increased resolution and better contrast. However, the same effect can be produced by dynamic range stretching. Adaptive beamformers are often tested on wire targets or uniform cysts, which do not allow to study dynamic range alterations. This work shows that dynamic range stretching may account for some of the benefits of some adaptive beamformers in the literature. We propose a phantom allowing us to do a dynamic range calibration. We demonstrate this calibration for the Mallart-Fink Coherence Factor (CF), the Camacho-Fritsch Phase Coherence Factor (PCF) and Capon'sMinimum Variance (MV) beamformer.We show that the increased resolution and contrast reported for the CF and PCF are to a great extent due to the alterations of the dynamic range.