Deep learning in ultrasound elastography imaging: A review.

It is known that changes in the mechanical properties of tissues are associated with the onset and progression of certain diseases. Ultrasound elastography is a technique to characterize tissue stiffness using ultrasound imaging either by measuring tissue strain using quasi-static elastography or natural organ pulsation elastography, or by tracing a propagated shear wave induced by a source or a natural vibration using dynamic elastography. In recent years, deep learning has begun to emerge in ultrasound elastography research. In this review, several common deep learning frameworks in the computer vision community, such as multilayered perceptron, convolutional neural network, and recurrent neural network, are described. Then, recent advances in ultrasound elastography using such deep learning techniques are revisited in terms of algorithm development and clinical diagnosis. Finally, the current challenges and future developments of deep learning in ultrasound elastography are prospected.

The Revisited Frequency-Shift Method for Shear Wave Attenuation Computation and Imaging.

Ultrasound (US) shear wave (SW) elastography has been widely studied and implemented on clinical systems to assess the elasticity of living organs. Imaging of SW attenuation reflecting viscous properties of tissues has received less attention. A revisited frequency shift (R-FS) method is proposed to improve the robustness of SW attenuation imaging. Performances are compared with the FS method that we originally proposed and with the two-point frequency shift (2P-FS) and attenuation measuring US SW elastography (AMUSE) methods. In the proposed R-FS method, the shape parameter of the gamma distribution fitting SW spectra is assumed to vary with distance, in contrast to FS. Second, an adaptive random sample consensus (A-RANSAC) line fitting method is used to prevent outlier attenuation values in the presence of noise. Validation was made on ten simulated phantoms with two viscosities (0.5 and 2 Pa [Formula: see text]) and different noise levels (15 to -5 dB), two experimental homogeneous gel phantoms, and six in vivo liver acquisitions on awake ducks (including three normal and three fatty duck livers). According to the conducted experiments, R-FS revealed mean reductions in coefficients of variation (CV) of 62.6% on simulations, 62.5% with phantoms, and 62.3% in vivo compared with FS. Corresponding reductions compared with 2P-FS were 45.4%, 77.1%, and 62.0%, respectively. Reductions in normalized root-mean-square errors for simulations were 63.9% and 48.7% with respect to FS and 2P-FS, respectively.

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.

In vivo Ultrafast Quantitative Ultrasound and Shear Wave Elastography Imaging on Farm-Raised Duck Livers during Force Feeding.

Shear wave elastography (speed and dispersion), local attenuation coefficient slope and homodyned-K parametric imaging were used for liver steatosis grading. These ultrasound biomarkers rely on physical interactions between shear and compression waves with tissues at both macroscopic and microscopic scales. These techniques were applied in a context not yet studied with ultrasound imaging, that is, monitoring steatosis of force-fed duck livers from pre-force-fed to foie gras stages. Each estimated feature presented a statistically significant trend along the feeding process (p values <10-3). However, whereas a monotonic increase in the shear wave speed was observed along the process, most quantitative ultrasound features exhibited an absolute maximum value halfway through the process. As the liver fat fraction in foie gras is much higher than that seen clinically, we hypothesized that a change in the ultrasound scattering regime is encountered for high-fat fractions, and consequently, care has to be taken when applying ultrasound biomarkers to grading of severe states of steatosis.

Reconstruction of Viscosity Maps in Ultrasound Shear Wave Elastography.

Change in viscoelastic properties of biological tissues may often be symptomatic of a dysfunction that can be correlated to tissue pathology. Shear wave elastography is an imaging method mainly used to assess stiffness but with the potential to measure viscoelasticity of biological tissues. This can enable tissue characterization; and thus, can be used as a marker to improve diagnosis of pathological lesions. In this study, a frequency-shift method based framework is presented for the reconstruction of viscosity by analyzing the spectral properties of acoustic radiation force-induced shear waves. The aim of the study was to investigate the feasibility of viscosity reconstruction maps in homogeneous as well as heterogeneous samples. Experiments were performed in four in vitro phantoms, two ex vivo porcine liver samples, two ex vivo fatty duck liver samples, and one in vivo fatty goose liver. Successful viscosity maps were reconstructed in homogeneous and heterogeneous phantoms with embedded mechanical inclusions having different geometries. Quantitative values of viscosity obtained for two porcine liver tissues, two fatty duck liver samples, and one goose fatty liver were (mean ± SD) 0.61 ± 0.21, 0.52 ± 0.35; 1.28 ± 0.54, 1.36 ± 0.73, and 1.67 ± 0.70 Pa.s, respectively.

Acoustic radiation force induced resonance elastography of coagulating blood: theoretical viscoelasticity modeling and ex-vivo experimentation.

Deep vein thrombosis is a common vascular disease that can lead to pulmonary embolism and death. The early diagnosis and clot age staging are important parameters for reliable therapy planning. This article presents an acoustic radiation force induced resonance elastography method for the viscoelastic characterization of clotting blood. The physical concept of this method relies on the mechanical resonance of the blood clot occurring at specific frequencies. Resonances are induced by focusing ultrasound beams inside the sample under investigation. Coupled to an analytical model of wave scattering, the ability of the proposed method to characterize the viscoelasticity of a mimicked venous thrombosis in the acute phase is demonstrated. Experiments with a gelatin-agar inclusion sample of known viscoelasticity are performed for validation and establishment of the proof of concept. In addition, an inversion method is applied in-vitro for the kinetic monitoring of the blood coagulation process of six human blood samples obtained from two volunteers. The computed elasticity and viscosity values of blood samples at the end of the 90 min kinetics were estimated at 411 ± 71 Pa and 0.25 ± 0.03 Pa.s for volunteer #1, and 387 ± 35 Pa and 0.23 ± 0.02 Pa.s for volunteer #2, respectively. The proposed method allowed reproducible time-varying thrombus viscoelastic measurements from samples having physiological dimensions.

Computationally efficient error estimate for evaluation of regularization in photoacoustic tomography.

The model-based image reconstruction techniques for photoacoustic (PA) tomography require an explicit regularization. An error estimate (?2) minimization-based approach was proposed and developed for the determination of a regularization parameter for PA imaging. The regularization was used within Lanczos bidiagonalization framework, which provides the advantage of dimensionality reduction for a large system of equations. It was shown that the proposed method is computationally faster than the state-of-the-art techniques and provides similar performance in terms of quantitative accuracy in reconstructed images. It was also shown that the error estimate (?2) can also be utilized in determining a suitable regularization parameter for other popular techniques such as Tikhonov, exponential, and nonsmooth (?1 and total variation norm based) regularization methods.

Exponential filtering of singular values improves photoacoustic image reconstruction.

Model-based image reconstruction techniques yield better quantitative accuracy in photoacoustic image reconstruction. In this work, an exponential filtering of singular values was proposed for carrying out the image reconstruction in photoacoustic tomography. The results were compared with widely popular Tikhonov regularization, time reversal, and the state of the art least-squares QR-based reconstruction algorithms for three digital phantom cases with varying signal-to-noise ratios of data. It was shown that exponential filtering provides superior photoacoustic images of better quantitative accuracy. Moreover, the proposed filtering approach was observed to be less biased toward the regularization parameter and did not come with any additional computational burden as it was implemented within the Tikhonov filtering framework. It was also shown that the standard Tikhonov filtering becomes an approximation to the proposed exponential filtering.

Generalized Beer-Lambert model for near-infrared light propagation in thick biological tissues.

The attenuation of near-infrared (NIR) light intensity as it propagates in a turbid medium like biological tissue is described by modified the Beer­Lambert law (MBLL). The MBLL is generally used to quantify the changes in tissue chromophore concentrations for NIR spectroscopic data analysis. Even though MBLL is effective in terms of providing qualitative comparison, it suffers from its applicability across tissue types and tissue dimensions. In this work, we introduce Lambert-W function-based modeling for light propagation in biological tissues, which is a generalized version of the Beer­Lambert model. The proposed modeling provides parametrization of tissue properties, which includes two attenuation coefficients µ0 and η. We validated our model against the Monte Carlo simulation, which is the gold standard for modeling NIR light propagation in biological tissue. We included numerous human and animal tissues to validate the proposed empirical model, including an inhomogeneous adult human head model. The proposed model, which has a closed form (analytical), is first of its kind in providing accurate modeling of NIR light propagation in biological tissues.

Piezo-phototronic Effect Enhanced UV/Visible Photodetector Based on Fully Wide Band Gap Type-II ZnO/ZnS Core/Shell Nanowire Array.

A high-performance broad band UV/visible photodetector has been successfully fabricated on a fully wide bandgap ZnO/ZnS type-II heterojunction core/shell nanowire array. The device can detect photons with energies significantly smaller (2.2 eV) than the band gap of ZnO (3.2 eV) and ZnS (3.7 eV), which is mainly attributed to spatially indirect type-II transition facilitated by the abrupt interface between the ZnO core and ZnS shell. The performance of the device was further enhanced through the piezo-phototronic effect induced lowering of the barrier height to allow charge carrier transport across the ZnO/ZnS interface, resulting in three orders of relative responsivity change measured at three different excitation wavelengths (385, 465, and 520 nm). This work demonstrates a prototype UV/visible photodetector based on the truly wide band gap semiconducting 3D core/shell nanowire array with enhanced performance through the piezo-phototronic effect.

Biodegradation of hexahydro-1,3,5-trinitro-1,3,5-triazine by novel fungi isolated from unexploded ordnance contaminated marine sediment.

Undersea deposition of unexploded ordnance (UXO) constitutes a potential source of contamination of marine environments by hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). Using sediment from a coastal UXO field, Oahu Island, Hawaii, we isolated four novel aerobic RDX-degrading fungi HAW-OCF1, HAW-OCF2, HAW-OCF3 and HAW-OCF5, tentatively identified as members of Rhodotorula, Bullera, Acremonium and Penicillium, respectively. The four isolates mineralized 15-34% of RDX in 58 days as determined by liberated 14CO2. Subsequently we selected Acremonium to determine biotransformation pathway(s) of RDX in more details. When RDX (100 microM) was incubated with resting cells of Acremonium we detected methylenedinitramine (MEDINA), N2O and HCHO. Also we detected hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) together with trace amounts of hexahydro-1,3-dinitroso-5-nitro-1,3,5-triazine (DNX) and hexahydro-1,3,5-trinitroso-1,3,5-triazine (TNX). Under the same conditions MNX produced N2O and HCHO together with trace amounts of DNX and TNX, but we were unable to detect MEDINA. TNX did not degrade with Acremonium. These experimental findings suggested that RDX degraded via at least two major initial routes; one route involved direct ring cleavage to MEDINA and another involved reduction to MNX prior to ring cleavage. Nitrite was only detected in trace amounts suggesting that degradation via initial denitration did take place but not significantly. Aerobic incubation of Acremonium in sediment contaminated with RDX led to enhanced removal of the nitramine.

Degradation of CL-20 by white-rot fungi.

In previous studies, we found that the emerging energetic chemical, CL-20 (C6H6N12O12, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane), can be degraded following its initial denitration using both aerobic and anaerobic bacteria. The C and N mass balances were not determined due to the absence of labeled starting compounds. The present study describes the degradation of the emerging contaminant by Phanerochaete chrysosporium using ring-labeled [15N]-CL-20 and [14C]-CL-20. Ligninolytic cultures degraded CL-20 with the release of nitrous oxide (N2O) in amounts corresponding to 45% of the nitrogen content of CL-20. When ring-labeled [15N]-CL-20 was used, both 14N14NO and 15N14NO were observed, likely produced from -NO2 and N-NO2, respectively. The incubation of uniformly labeled [14C]-CL-20 with fungi led to the production of 14CO2 (> 80%). Another ligninolytic fungus, Irpex lacteus, was also able to degrade CL-20, but as for P. chrysosporium, no early intermediates were observed. When CL-20 was incubated with manganese peroxidase (MnP), we detected an intermediate with a [M-H]- mass ion at 345 Da (or 351 and 349 Da when using ring-labeled and nitro-labeled [15N]-CL-20, respectively) matching a molecular formula of C6H6N10O8. The intermediate was thus tentatively identified as a doubly denitrated CL-20 product. The concomitant release of nitrite ions (NO2-) with CL-20 degradation by MnP also supported the occurrence of an initial denitration prior to cleavage and decomposition.

The effect of pallet distance on torso kinematics and low back disorder risk.

Intervention research for prevention of occupational low back injuries has focused on the effects of reducing extreme torso flexion and the external moment. Little is known about prevention strategies for torso twisting and lateral bending. The objective of this study was to assess the effect of pallet distance with regard to a constant lift origin on the torso kinematics and a measure of low back disorder risk. Fifteen male participants transferred 11.3 kg boxes from a constant origin to six different regions on a pallet. Two pallet distances with regard to the lift origin were investigated. ANOVA indicated that increasing the pallet distance resulted in increases in torso kinematics (velocities and accelerations) as well as a measure of risk of low back disorder. The increases in torso kinematics (e.g. twisting and lateral awkward postures and bending velocities) occurred mostly at the lower height regions on the pallet. It is concluded that increasing the pallet distance with regard to the lifting origin, with the intention to influence the participant to take a step during a palletizing task does not appear to be an effective intervention strategy to reduce the risk of low back disorder associated with torso kinematics.

Biodegradation of cyclic nitramines by tropical marine sediment bacteria.

Undersea deposition of unexploded ordnance (UXO) constitutes a potential source of contamination of marine environments by hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) and octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX). The goal of the present study was to determine microbial degradation of RDX and HMX in a tropical marine sediment sampled from a coastal UXO field in the region of Oahu Island in Hawaii. Sediment mixed cultures growing in marine broth 2216 (21 degrees C) anaerobically mineralized 69% or 57% (CO2, 25 days) of the total carbon of [UL-14 C]-RDX (100 microM) or [UL-14 C]-HMX (10 microM), respectively. As detected by PCR-DGGE, members of gamma-proteobacteria (Halomonas), sulfate-reducing delta-proteobacteria (Desulfovibrio), firmicutes (Clostridium), and fusobacterium appeared to be dominant in RDX-enrichment and/or HMX-enrichment cultures. Among 22 sediment bacterial isolates screened for RDX and HMX biodegradation activity under anaerobic conditions, 5 were positive for RDX and identified as Halomonas (HAW-OC4), Marinobacter (HAW-OC1), Pseudoalteromonas (HAW-OC2 and OC5) and Bacillus (HAW-OC6) by their 16S rRNA genes. Sediment bacteria degraded RDX to N2O and HCHO via the intermediary formation of hexahydro-1-nitroso-3,5-dinitro-1,3,5-triazine (MNX) and methylenedinitramine. The present findings demonstrate that cyclic nitramine contaminants are likely to be degraded upon release from UXO into tropical marine sediment.

Enhancement of the biodegradability of aromatic groundwater contaminants.

Groundwater (GW) from the Bitterfeld industrial region, Central Germany, is contaminated mainly with monochlorobenzene (MCB). Accordingly, current research addresses the development of feasible in situ groundwater remediation technologies. Although easily degradable under aerobic conditions, MCB persists in the essentially anaerobic Bitterfeld aquifer. Therefore, we focused on primary oxidation of MCB and the subsequent anaerobic biodegradability of MCB oxidation products by the indigenous microbial community. In groundwater microcosms, most efficient MCB removal was observed upon treatment with Fenton's reagent (H2O2 + Fe2+), which produces the highly reactive hydroxyl radical and Fe3+ simultaneously. Phospholipid fatty acid analysis following different treatments suggested respective shifts of the microbial community compositions, and indicated that Fenton's reagent had a rather beneficial than an adverse effect on biomass development. Potential metabolites of hydroxyl radical attack on MCB such as chlorohydroquinone, hydroquinone, catechol, resorcinol, and phenol were anaerobically degraded by the groundwater microbial community under Fe3+ -reducing conditions.