Yu-Chen Shu

Using ultrasound Nakagami imaging to assess liver fibrosis in rats

This study explored the feasibility of using the ultrasound Nakagami image to assess the degree of liver fibrosis in rats. The rat has been widely used as a model in investigations of liver fibrosis. Ultrasound grayscale imaging makes it possible to observe fibrotic rat livers in real time. Statistical analysis of the envelopes of signals backscattered from rat livers may provide useful clues about the degree of liver fibrosis. The Nakagami-model-based image has been shown to be useful for characterizing scatterers in tissues by reflecting the echo statistics, and hence the Nakagami image may serve as a functional imaging tool for quantifying rat liver fibrosis. To validate this idea, fibrosis was induced in each rat liver (n=21) by an intraperitoneal injection of 0.5% dimethylnitrosamine. Livers were excised from rats for in vitro ultrasound scanning using a single-element transducer. The backscattered-signal envelopes of the acquired raw ultrasound signals were used for Nakagami imaging. The Metavir score determined by a pathologist was used to histologically quantify the degree of liver fibrosis. It was found that the Nakagami image could be used to distinguish different degrees of liver fibrosis in rats, since the average Nakagami parameter increased from 0.55 to 0.83 as the fibrosis score increased from 0 (i.e., normal) to 4. This correlation may be due to liver fibrosis in rats involving an increase in the concentration of local scatterers and the appearance of the periodic structures or clustering of scatterers that would change the backscattering statistics. The current findings indicate that the ultrasound Nakagami image has great potential as a functional imaging tool to complement the use of the conventional B-scan in animal studies of liver fibrosis.

Ultrasound temperature estimation based on probability variation of backscatter data

PURPOSE In recent years, ultrasound imaging has become an attractive modality for noninvasive temperature monitoring. Temperature variations that occur during tissue heating could induce changes in various acoustic parameters that may affect the echo interference so as to make ultrasound backscattering a random process. In this study, we assumed that the degree of variation in the probability distribution of the backscattered signals is temperature dependent. The feasibility of using the variation in the backscatter statistics for ultrasound temperature estimation was investigated in this study. METHODS We tested this hypothesis by carrying out experiments on agar phantoms and tissue samples using a temperature-regulated water tank and a microwave ablation system. During heating, raw images of the backscattered-signal envelope of each phantom and tissue at temperatures ranging between 37 °C and 45 °C were acquired to construct the parametric matrix based on the ratio of the change in the Nakagami parameter (RCN), which was used as a quantitative measure of the backscatter statistics. The absolute value of the RCN (ARCN) matrix was obtained, to which a polynomial approximation was applied to obtain the ARCN(pa) image. RESULTS The results showed that the RCN matrix locally increased or decreased with increasing temperature, indicating bidirectional changes in the backscatter statistics. We also found that the ARCN significantly increased with the temperature, demonstrating that the magnitude of the variation in the probability distribution of the backscattered-signal envelope is a monotonic function of temperature. Unlike the phantom, tissues tended to exhibit a nonlinear dependency of the ARCN on the temperature that may be attributable to tissue denaturation. Especially, the ARCN(pa) image is highly suitable for visualizing the contour of the temperature distribution during microwave ablation of tissue samples. CONCLUSIONS This study has demonstrated that temperature changes are reflected in variations in the envelope statistics. This novel approach makes it possible to develop an ultrasound temperature imaging method for simultaneously estimating the thermal dose and the tissue properties.

Using ultrasound CBE imaging without echo shift compensation for temperature estimation

Clinical trials have demonstrated that hyperthermia improves cancer treatments. Previous studies developed ultrasound temperature imaging methods, based on the changes in backscattered energy (CBE), to monitor temperature variations during hyperthermia. Echo shift, induced by increasing temperature, contaminates the CBE image, and its tracking and compensation should normally ensure that estimations of CBE at each pixel are correct. To obtain a simplified algorithm that would allow real-time computation of CBE images, this study evaluated the usefulness of CBE imaging without echo shift compensation in detecting distributions in temperature. Experiments on phantoms, using different scatterer concentrations, and porcine livers were conducted to acquire raw backscattered data at temperatures ranging from 37°C to 45°C. Tissue samples of pork tenderloin were ablated in vitro by microwave irradiation to evaluate the feasibility of using the CBE image without compensation to monitor tissue ablation. CBE image construction was based on a ratio map obtained from the envelope image divided by the reference envelope image at 37°C. The experimental results demonstrated that the CBE image obtained without echo shift compensation has the ability to estimate temperature variations induced during uniform heating or tissue ablation. The magnitude of the CBE as a function of temperature obtained without compensation is stronger than that with compensation, implying that the CBE image without compensation has a better sensitivity to detect temperature. These findings suggest that echo shift tracking and compensation may be unnecessary in practice, thus simplifying the algorithm required to implement real-time CBE imaging.

Electro-osmotic flow in a wavy microchannel: Coherence between the electric potential and the wall shape function

The electro-osmotic flow through a wavy microchannel is studied under the Debye–Huckel approximation. An analytic solution by perturbation with appropriate averaging is carried out up to the second-order in terms of the small amplitude of corrugation. It is shown that the wavelength and phase difference of the corrugations can be utilized to control the flow relative to the case of flat walls. In particular, for thick electric double layers the electro-osmotic flow can be enhanced at long-wavelength corrugations because of the coherence between the electric potential and the wall shape function. Notably, these findings are not restricted to small amplitudes of corrugation. By applying the Ritz method to solve for the electro-osmotic flow, it is found that the enhancement becomes even greater (up to 30%) with increases in corrugation. Moreover, the nonlinear Poisson–Boltzmann equation is solved by finite difference to study the electro-osmotic flow in terms of the relative strength of the zeta potential. The issue of overlapped electric double layers when they are very thick is also discussed. The relative flow rate is shown to increase under the following conditions: (i) completely out-of-phase corrugations with long wavelength and large amplitude, (ii) small zeta potential, and (iii) slight overlapping of electric double layers.

Augmented coupling interface method for solving eigenvalue problems with sign-changed coefficients

In this paper, we propose an augmented coupling interface method on a Cartesian grid for solving eigenvalue problems with sign-changed coefficients. The underlying idea of the method is the correct local construction near the interface which incorporates the jump conditions. The method, which is very easy to implement, is based on finite difference discretization. The main ingredients of the proposed method comprise (i) an adaptive-order strategy of using interpolating polynomials of different orders on different sides of interfaces, which avoids the singularity of the local linear system and enables us to handle complex interfaces; (ii) when the interface condition involves the eigenvalue, the original problem is reduced to a quadratic eigenvalue problem by introducing an auxiliary variable and an interfacial operator on the interface; (iii) the auxiliary variable is discretized uniformly on the interface, the rest of variables are discretized on an underlying rectangular grid, and a proper interpolation between these two grids are designed to reduce the number of stencil points. Several examples are tested to show the robustness and accuracy of the schemes.

High estimated prevalence of asymptomatic dengue viremia in blood donors during a dengue epidemic in southern Taiwan, 2015

Southern Taiwan experienced a severe dengue epidemic in 2015. Adult asymptomatic cases would raise concerns on transfusion‐transmitted dengue virus (DENV) infection. The aim of this study was to evaluate the magnitude of such a risk in Tainan City during this epidemic.

Monetary Discount Strategies for Real-Time Promotion Campaign

The effectiveness of monetary promotions has been well reported in the literature to affect shopping decisions for products in real life experience. Nowadays, e-commerce retailers are facing more fierce competition on price promotion in that consumers can easily use a search engine to find another merchant selling an identical product for comparing price. To achieve more effectiveness on real-time promotion in pursuit of better profits, we propose two discount-giving strategies: an algorithm based on Kernel density estimation, and the other algorithm based on Thompson sampling strategy. We show that, given a pre-determined discount budget, our algorithms can significantly acquire better revenue in return than classical strategies with simply fixed discount on label price. We then demonstrate its feasibility to be a promising deployment in e-commerce services for real-time promotion.

Symptoms associated with adverse dengue fever prognoses at the time of reporting in the 2015 dengue outbreak in Taiwan

Background Tainan experienced the most severe dengue epidemic in Taiwan in 2015. This study investigates the association between the signs and symptoms at the time of reporting with the adverse dengue prognoses. Methods A descriptive study was conducted using secondary data from the Dengue Disease Reporting System in Tainan, Taiwan, between January 1 and December 31, 2015. A multivariate stepwise logistic regression was used to identify the risk factors for the adverse prognoses: ICU admissions and mortality. Results There were 22,777 laboratory-confirmed reported cases (mean age 45.6 ± 21.2 years), of which 3.7% were admitted to intensive care units (ICU), and 0.8% were fatal. The most common symptoms were fever (92.8%), myalgia (26.6%), and headache (22.4%). The prevalence of respiratory distress, altered consciousness, shock, bleeding, and thrombocytopenia increased with age. The multivariate analysis indicated that being in 65–89 years old age group [Adjusted Odds Ratio (aOR):4.95], or the 90 years old and above age group (aOR: 9.06), and presenting with shock (aOR: 8.90) and respiratory distress (aOR: 5.31) were significantly associated with the risk of ICU admission. While old age (aOR: 1.11), respiratory distress (aOR: 9.66), altered consciousness (aOR: 7.06), and thrombocytopenia (aOR: 2.55) were significantly associated with the risk of mortality. Conclusions Dengue patients older than 65 and those with severe and non-specific signs and symptoms at the time of reporting were at a higher risk of ICU admission and mortality. First-line healthcare providers need to be aware of the varied presentations between the different age groups to allow early diagnosis and in-time management, which would prevent ICU admissions and fatalities in dengue patients.

Message Passing Using the Cover Text as Secret Key

Conventional secret message passing methods embed a message in the cover-text, so the receiver must use stego-text to extract the message content. In contrast, this paper proposes a new paradigm in which the receiver does not necessarily require stego-text to retrieve the message content. Under the proposed approach, the sender can produce keys without modifying the cover-image, and the intended recipient can use the keys and an image that resembles like the cover-image to recover the message. The feature has the potential to generate many new secret message passing applications that would probably be impossible under the current widely used paradigm. The performance criteria of the new paradigm are presented. We propose a subspace approach to implement the paradigm, demonstrate that the criteria can be satisfied, and consider some interesting application scenarios.

Solving guided wave modes in plasmonic crystals by interfacial operator and coupling interface approach

It has been di-cult to solve eigenmodes of plasmonic crystals in two or three dimensions either analytically or numerically. In this study, we present an interfacial opera- tor approach for solving guided wave modes of plasmonic crystals. They are formulated as an eigenvalue problem of the wavenumber along the axis of the crystal. In this formulation, the permittivity and permeability of the metallic component can be arbitrary functions of frequency. Moreover, a coupling interface method is introduced to facilitate accurate treatment of the in- terface conditions with an arbitrary shape between the metal and host materials. Numerical results are illustrated for difierent shapes of plasmonic crystals, layered, cylindrical and split-ring structures. The physical signiflcance is discussed. Finally, it is demonstrated that the present method can resolve flne eigenmodes of the split-ring structure.