Speckle Suppression in Ultrasonic Images Based on Undecimated Wavelets

An original method to denoise ultrasonic images affected by speckle is presented. Speckle is modeled as a signal-dependent noise corrupting the image. Noise reduction is approached as a Wiener-like filtering performed in a shift-invariant wavelet domain by means of an adaptive rescaling of the coefficients of an undecimated octave decomposition. The scaling factor of each coefficient is calculated from local statistics of the degraded image, the parameters of the noise model, and the wavelet filters. Experimental results demonstrate that excellent background smoothing as well as preservation of edge sharpness and fine details can be obtained

Modelling and assessment of signal-dependent noise for image de-noising

Publication in the conference proceedings of EUSIPCO, Toulouse, France, 200

Efficient Gating of Organic Electrochemical Transistors with In-Plane Gate Electrodes

AbstractOrganic electrochemical transistors (OECTs) are electrolyte‐gated transistors, employing an electrolyte between their gate and channel instead of an insulating layer. For efficient gating, non‐polarizable electrodes, for example, Ag/AgCl, are typically used but unfortunately, this simple approach limits the options for multiple gate integration. Patterned polarizable Au gates on the other hand, show strongly reduced gating due to a large voltage drop at the gate/electrolyte interface. Here, an alternative, simple yet effective method for efficient OECT gating by scalable in‐plane gate electrodes, is demonstrated. The fact that poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) exhibits a volumetric capacitance in an electrolyte is made use of. As a result, the capacitance of PEDOT:PSS‐based gates can be strongly enhanced by increasing their thickness, thereby reducing the voltage loss at the gate/electrolyte interface. By combining spin coating and electrodeposition, planar electrodes of various thicknesses are created on a multi‐gated OECT chip and their effect on the gating efficiency, examined. It is shown that the gating performed by an in‐plane PEDOT:PSS electrode can be tuned to be comparable to the one obtained by a Ag/AgCl electrode. Overall, the realization of efficient gating with in‐plane electrodes paves the way toward integration of OECT‐based biosensors and "organ‐on‐a‐chip" platforms

Ultra-high gain diffusion-driven organic transistor

Emerging large-area technologies based on organic transistors are enabling the fabrication of low-cost flexible circuits, smart sensors and biomedical devices. High-gain transistors are essential for the development of large-scale circuit integration, high-sensitivity sensors and signal amplification in sensing systems. Unfortunately, organic field-effect transistors show limited gain, usually of the order of tens, because of the large contact resistance and channel-length modulation. Here we show a new organic field-effect transistor architecture with a gain larger than 700. This is the highest gain ever reported for organic field-effect transistors. In the proposed organic field-effect transistor, the charge injection and extraction at the metal–semiconductor contacts are driven by the charge diffusion. The ideal conditions of ohmic contacts with negligible contact resistance and flat current saturation are demonstrated. The approach is general and can be extended to any thin-film technology opening unprecedented opportunities for the development of high-performance flexible electronics

There's plenty of light at the bottom: Statistics of photon penetration depth in random media

We propose a comprehensive statistical approach describing the penetration depth of light in random media. The presented theory exploits the concept of probability density function f(z|ρ, t) for the maximum depth reached by the photons that are eventually re-emitted from the surface of the medium at distance ρ and time t. Analytical formulas for f, for the mean maximum depth 〈zmax〉 and for the mean average depth 〈z〉 reached by the detected photons at the surface of a diffusive slab are derived within the framework of the diffusion approximation to the radiative transfer equation, both in the time domain and the continuous wave domain. Validation of the theory by means of comparisons with Monte Carlo simulations is also presented. The results are of interest for many research fields such as biomedical optics, advanced microscopy and disordered photonics

Case report of a patient who survived after cardiac arrest and cardiogenic shock by anaphylactic reaction to gadolinium during magnetic resonance imaging

We report the case of a young adult which survived to anaphylactic shock caused by gadolinium-based contrast agent (GBCA) contrast agent infusion. The patient had no comorbidities and previous history of allergic reactions to contrast agents and underwent elective magnetic resonance imaging (MRI) for parotid swelling. Seven years before he received intravenous GBCA administration during an MRI, which exact chemical composition is unknown, without any allergic reaction. After intravenous injection of GBCA for MRI the patient developed anaphylactic shock, causing respiratory failure, cardiac arrest, and cardiogenic shock after return of spontaneous circulation. Because of the rarity of the described event, this report has the aim to raise awareness in the healthcare personnel of the possibility of these life-threatening adverse reactions from GBCAs also in a patient without history of allergy to contrast agents and suggest a possible clinical management of these patients

About the amplification factors in organic bioelectronic sensors

A systematic comparison between electrochemical and organic bioelectronic sensors reveals a unified rational description for a transistor amplified detection

Why PEDOT:PSS Should Not Be Used for Raman Sensing of Redox States (and How It Could Be)

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) has been recently proposed for Raman sensing of redox-active species in solution. Here, we investigated the rationale of this approach through systematic experiments, in which the Raman spectrum of PEDOT:PSS was analyzed in the presence of either nonoxidizing or oxidizing electrolytes. The results demonstrated that Raman spectra precisely reflect the conformation of PEDOT units and their interactions with PSS. Two different responses were observed. In the case of oxidizing electrolytes, the effect of charge transfer is accurately transduced in Raman spectrum changes. On the other hand, reduction induces a progressive separation between the PEDOT and PSS chains, which decreases their mutual interaction. This stimulus determines characteristic variations in the intensity, shape, and position of the Raman spectra. However, we demonstrated that the same effects can be obtained either by increasing the concentration of nonoxidizing electrolytes or by deprotonating PSS chains. This poses severe limitations to the use of PEDOT:PSS for this type of Raman sensing. This study allows us to revise most of the Raman results reported in the literature with a clear model, setting a new basis for investigating the dynamics of mixed electronic/ionic charge transfer in conductive polymers

Depth sensitivity of frequency domain optical measurements in diffusive media

The depth sensitivity functions for AC amplitude, phase (PH) and DC intensity signals have been obtained in the frequency domain (where the source amplitude is modulated at radio-frequencies) by making use of analytical solutions of the photon diffusion equation in an infinite slab geometry. Furthermore, solutions for the relative contrast of AC, PH and DC signals when a totally absorbing plane is placed at a fixed depth of the slab have also been obtained. The solutions have been validated by comparisons with gold standard Monte Carlo simulations. The obtained results show that the AC signal, for modulation frequencies < 200 MHz, has a depth sensitivity with similar characteristics to that of the continuous-wave (CW) domain (source modulation frequency of zero). Thus, the depth probed by such a signal can be estimated by using the formula of penetration depth for the CW domain (Sci. Rep. 6, 27057 (2016)). However, the PH signal has a different behavior compared to the CW domain, showing a larger depth sensitivity at shallow depths and a less steep relative contrast as a function of depth. These results mark a clear difference in term of depth sensitivity between AC and PH signals, and highlight the complexity of the estimation of the actual depth probed in tissue spectroscopy.Postprint (published version