Proposed Imaging Methods Research Articles

Speckle autocorrelation separation method based on frequency intensity for tracking moving object beyond optical memory effect

Abstract Imaging objects behind a scattering medium beyond the optical memory effect (OME) range is vital in various imaging scenarios. Despite numerous proposed imaging methods aimed at separating objects, effectively tracking moving objects remains challenging. In this paper, we present a non-invasive scattering imaging method to reconstruct target beyond the OME range and track moving objects using a speckle separation and position estimation technique. A speckle autocorrelation separation method based on frequency intensity is proposed to eliminate the noise from the cross-correlation and to separate the objects from the mixed speckles. A position estimation technique is proposed to determine the positional relationships of the objects using speckle deconvolution using the point spread function of imaging regions. A non-invasive imaging system is designed to track the moving object without prior knowledge of the shape and distribution of objects. Experimental validation shows the efficiency of the method for separation and localization, allowing for the reconstruction of the target behind the scattering medium and tracking of the moving object behind the scattering medium. Moreover, the method is capable of separating and tracking a moving object when multiple objects are in the background.

Decorrelated compounding of synthetic aperture ultrasound imaging to detect low contrast thermal lesions induced by focused ultrasound

PurposeDecorrelated Compounding (DC) for synthetic aperture ultrasound can reduce speckle variation in images, suggesting enhanced detectability of low-contrast targets in tissue including thermal lesions produced by focused ultrasound (FUS). The DC imaging method has primarily been investigated in simulation and in phantom studies. This work investigates the feasibility of the DC method in monitoring thermal therapy via image guidance and non-invasive thermometry based on the change in backscattered energy (CBE). MethodsEx vivo porcine tissue was exposed to FUS exposures at acoustic powers of 5 W and 1 W, with peak pressure amplitudes of 0.64 MPa and 0.27 MPa respectively. During FUS exposure, RF echo data frames was acquired using a 7.8 MHz linear array probe and a Verasonics VantageTM ultrasound scanner (Verasonics Inc., Redmond, WA). RF echo data was taken to produce B-mode images, as reference images. Synthetic aperture RF echo data was also acquired and processed using delay-and-sum (DAS), a combination of spatial and frequency compounding referred to as Traditional Compounding (TC), and the proposed DC imaging methods. Image quality was assessed using the contrast-to-noise ratio (CNR) at the FUS beam focus, and the speckle SNR (sSNR) of the background region as preliminary metrics. A calibrated thermocouple was placed near the FUS beam focus for temperature measurements and calibrations using the CBE method. ResultsThe DC imaging method significantly improved image quality to detect low contrast thermal lesions in treated ex vivo porcine tissue in comparison to other imaging methods. In comparison to B-mode imaging, the lesion CNR measured using the DC imaging was shown to improve up to a factor of approximately 5.5. The corresponding sSNR improved by a factor of approximately 4.2 in comparison to B-mode imaging. CBE calculation using the DC imaging method yielded more precise measurements of the backscattered energy compared to other imaging methods studied. ConclusionsThe despeckling performance of the DC imaging method significantly improves the lesion CNR in comparison to B-mode imaging. This suggests that the proposed method can detect low-contrast thermal lesions induced by FUS therapy that are not detectable using standard B-mode imaging. Furthermore, the signal change at the focal point were more precisely measured by DC imaging, and the signal change in response to FUS exposure follows the temperature profile more closely than changes measured using B-mode, as well as synthetic aperture DAS and TC images. These suggest that DC imaging can potentially be used with the CBE method to improve non-invasive thermometry.

Multiparametric in vivo ultrasound shear wave viscoelastography on farm-raised fatty duck livers: human radiology imaging applied to food sciences

Nine mulard ducks that were being raised for foie gras (steatosis) production went through in vivo shear wave (SW) elastography imaging of their liver during the force-feeding period to investigate changes in liver tissue characteristics. A total of 4 imaging sessions at an interval of 3 to 4 d were conducted at the farm on each animal. Three ducks were sacrificed at the second, third, and fourth imaging sessions for histopathology analysis of all animals at these time points. Six SW elastography parameters were evaluated: SW speed, SW attenuation, SW dispersion, Young's modulus, viscosity, and shear modulus. Shear waves of different frequencies propagate with different phase velocities. Thus, SW speed and other dependent parameters such as Young's modulus, viscosity, and shear modulus were computed at 2 frequencies: 75 and 202 Hz. Each parameter depicted a statistically significant trend along the force-feeding process (P-values between 0.001 and 0.0001). The fat fraction of the liver increased over the 12-day period of feeding. All parameters increased monotonically over time at 75 Hz, whereas modal relations were seen at 202 Hz. Shear wave dispersion measured between 75 and 202 Hz depicted a plateau from day 5. Based on this validation, proposed imaging methods are aimed to be used in the future on naturally fed ducks and geese.

Tri-modal In vivo Imaging of Pancreatic Islets Transplanted Subcutaneously in Mice.

Transplantation of pancreatic islets (PIs) is a promising therapeutic approach for type 1 diabetes. The main obstacle for this strategy is that the outcome of islet engraftment depends on the engraftment site. It was our aim to develop a strategy for using non-invasive imaging techniques to assess the location and fate of transplanted PIs longitudinally in vivo. In order to overcome the limitations of individual imaging techniques and cross-validate findings by different modalities, we have combined fluorine magnetic resonance imaging (F-19 MRI), fluorescence imaging (FLI), and bioluminescent imaging (BLI) for studying subcutaneously transplanted PIs and beta cell-like cells (INS-1E cell line) in vivo. We optimized the transduction (using lentiviral vectors) and labeling procedures (using perfluoro crown ether nanoparticles with a fluorescence dye) for PIs and INS-1E cell imaging. The feasibility of using the proposed imaging methods for PI assessment was demonstrated both in vitro and in vivo. Our data suggested that F-19 MRI is suitable for high-resolution localization of transplanted cells and PIs; FLI is essential for confirmation of contrast localization by histology; and BLI is a reliable method to assess cell viability and survival after transplantation. No significant side effects on cell viability and function have been observed. The proposed tri-modal imaging platform is a valuable approach for the assessment of engrafted PIs in vivo. It is potentially suitable for comparing different transplantation sites and evaluating novel strategies for improving PI transplantation technique in the future.

Multi-Channel Deconvolution for Forward-Looking Phase Array Radar Imaging

The cross-range resolution of forward-looking phase array radar (PAR) is limited by the effective antenna beamwidth since the azimuth echo is the convolution of antenna pattern and targets’ backscattering coefficients. Therefore, deconvolution algorithms are proposed to improve the imaging resolution under the limited antenna beamwidth. However, as a typical inverse problem, deconvolution is essentially a highly ill-posed problem which is sensitive to noise and cannot ensure a reliable and robust estimation. In this paper, multi-channel deconvolution is proposed for improving the performance of deconvolution, which intends to considerably alleviate the ill-posed problem of single-channel deconvolution. To depict the performance improvement obtained by multi-channel more effectively, evaluation parameters are generalized to characterize the angular spectrum of antenna pattern or singular value distribution of observation matrix, which are conducted to compare different deconvolution systems. Here we present two multi-channel deconvolution algorithms which improve upon the traditional deconvolution algorithms via combining with multi-channel technique. Extensive simulations and experimental results based on real data are presented to verify the effectiveness of the proposed imaging methods.

Signal Construction-Based Dispersion Compensation of Lamb Waves Considering Signal Waveform and Amplitude Spectrum Preservation.

The results of Lamb wave identification for the aerospace structures could be easily affected by the nonlinear-dispersion characteristics. In this paper, dispersion compensation of Lamb waves is of particular concern. Compared with the similar research works on the traditional signal domain transform methods, this study is based on signal construction from the viewpoint of nonlinear wavenumber linearization. Two compensation methods of linearly-dispersive signal construction (LDSC) and non-dispersive signal construction (NDSC) are proposed. Furthermore, to improve the compensation effect, the influence of the signal construction process on the other crucial signal properties, including the signal waveform and amplitude spectrum, is considered during the investigation. The linear-dispersion and non-dispersion effects are firstly analyzed. Then, after the basic signal construction principle is explored, the numerical realization of LDSC and NDSC is discussed, in which the signal waveform and amplitude spectrum preservation is especially regarded. Subsequently, associated with the delay-and-sum algorithm, LDSC or NDSC is employed for high spatial resolution damage imaging, so that the adjacent multi-damage or quantitative imaging capacity of Lamb waves can be strengthened. To verify the proposed signal construction and damage imaging methods, the experimental and numerical validation is finally arranged on the aluminum plates.

Beamspace Time-Reversal Microwave Imaging for Breast Cancer Detection

We propose novel beamspace-DORT and beamspace- TR-MUSIC for microwave imaging to detect breast cancer. The proposed imaging methods employ beamspace transformation in the receiving mode of time reversal process prior to back propagation of recorded received signals. We investigate the effectiveness of the proposed imaging methods using anatomically realistic MRI-derived dense numerical breast phantoms. It is found that the proposed methods, especially the beamspace-TR-MUSIC, achieve improved focusing ability even in the presence of dense fibroglandular tissue clutter.

Novel imaging methods of stepped frequency radar based on compressed sensing

The theory of compressed sensing (CS) provides a new chance to reduce the data acquisition time and improve the data usage factor of the stepped frequency radar system. In light of the sparsity of radar target reflectivity, two imaging methods based on CS, termed the CS-based 2D joint imaging algorithm and the CS-based 2D decoupled imaging algorithm, are proposed. These methods incorporate the coherent mixing operation into the sparse dictionary, and take random measurements in both range and azimuth directions to get high resolution radar images, thus can remarkably reduce the data rate and simplify the hardware design of the radar system while maintaining imaging quality. Experiments from both simulated data and measured data in the anechoic chamber show that the proposed imaging methods can get more focused images than the traditional fast Fourier transform method. Wherein the joint algorithm has stronger robustness and can provide clearer inverse synthetic aperture radar images, while the decoupled algorithm is computationally more efficient but has slightly degraded imaging quality, which can be improved by increasing measurements or using a robuster recovery algorithm nevertheless.

超音波を用いた鉄筋形状および付着評価のための一解析法

The shape and location of reinforcing bars in the structural material are reconstructed from ultrasonic scattered waveforms in the low frequency. Two linearized inverse scattering methods are investigated for the imaging of reinforcing bars. The Born and Kirchhoff inversions reconstruct domains and boundaries of the bars, respectively. Although the dynamic interaction effect exists in the adjacent part of multiple bars, we can reconstruct the whole shape of bars with the Born inversion. On the other hand, the Kirchhoff inversion leads to the classification of the damaged area around a reinforcing bar. These performances of proposed imaging methods are demonstrated by numerical simulations using the boundary element method.

Myocardial Strain Imaging Based on Two-Dimensional Displacement Vector Measurement

The abnormalities of myocardial wall motion caused by changes in wall stiffness often appear in the early stage of ischemic heart disease. Since the myocardium exhibits complex and large motion, a two-dimensional (2D) or three-dimensional (3D) assessment of stiffness distribution is required for accurate diagnosis. Although a 3D assessment is ultimately required, as a stepped approach for practical use, we propose novel methods for tracking the 2D motion using a one-dimensional (1D) phased array and for assessing myocardial malfunction by visualizing the invariant of a strain tensor. The feasibilities of the proposed methods were evaluated by numerically simulating the short-axis imaging of a 3D myocardial model. This model includes a hard infarction located between 1 and 3 o'clock, which is difficult to detect by conventional tissue Doppler and strain rate imaging, and the motions of the model were assigned by referring to actual myocardial motion. These results revealed that the proposed imaging methods clearly depicted the hard infarction area which conventional imaging could not detect.

Measuring molecular wave functions using laser Coulomb explosion imaging with ultraviolet lasers

A high-frequency laser (λ<40 nm) can ionize the H2+ molecule via a one-photon transition to the electron–nuclei continua. From exact non-Born–Oppenheimer simulations of dynamics of H2+ in intense laser fields we show that it is possible to reconstruct the shape of the initial, stationary vibrational wave function |ψv(R)|2 by measuring kinetic energy spectra of either protons or electrons. The reconstruction procedure from proton spectra is based on a perturbative one-photon transition to the electron–proton continua and formally is similar to the previously discussed laser Coulomb explosion imaging technique. For sufficiently high explosion energy, proton spectra are directly proportional to |ψv(q2/EN)|2, where EN is the nuclear energy. Alternatively, one can measure kinetic energy of electrons, from which the proton energy can be deduced via the conservation of energy for a one-photon transition to the electron–proton continuum, and thus the shape of the first peak in the electron spectrum is also directly proportional to the initial vibrational probability distribution. We compare these two methods and also compare them with the previously proposed imaging methods based on Coulomb explosions induced by multiphoton transitions. We find that high-frequency lasers allow us to perform the imaging of a stationary wave function with longer and less intense pulses than pulses required in the previously discussed long-wavelength regime. Imaging based on electron spectra requires longer pulses, since the spread of photon energy in short pulses does not allow us to determine nuclear energy, in an accurate way, via conservation of energy. In general, the photo-electron spectra from H2+ are found to be very different from atomic spectra, the latter having much narrower peaks, while the former are greatly enlarged due to sharing the final energy with nuclei. The photo-electron and nuclear spectra show a very clear imprint of the nuclear wave function, e.g. if the molecule is prepared in the v-state that has v nodes, both spectra will also have v nodes.