Computer-aided method for quantification of cartilage thickness and volume changes using MRI: validation study using a synthetic model

The primary objective of this study was to develop a computer-aided method for the quantification of three-dimensional (3-D) cartilage changes over time in knees with osteoarthritis (OA). We introduced a local coordinate system (LCS) for the femoral and tibial cartilage boundaries that provides a standardized representation of cartilage geometry, thickness, and volume. The LCS can be registered in different data sets from the same patient so that results can be directly compared. Cartilage boundaries are segmented from 3-D magnetic resonance (MR) slices with a semi-automated method and transformed into offset-maps, defined by the LCS. Volumes and thickness are computed from these offset-maps. Further anatomical labeling allows focal volumes to be evaluated in predefined subregions. The accuracy of the automated behavior of the method was assessed, without any human intervention, using realistic, synthetic 3-D MR images of a human knee. The error in thickness evaluation is lower than 0.12 mm for the tibia and femur. Cartilage volumes in anatomical subregions show a coefficient of variation ranging from 0.11% to 0.32%. This method improves noninvasive 3-D analysis of cartilage thickness and volume and is well suited for in vivo follow-up clinical studies of OA knees.     

Prediction based collaborative trackers (PCT): a robust and accurate approach toward 3D medical object tracking

Robust and fast 3D tracking of deformable objects, such as heart, is a challenging task because of the relatively low image contrast and speed requirement. Many existing 2D algorithms might not be directly applied on the 3D tracking problem. The 3D tracking performance is limited due to dramatically increased data size, landmarks ambiguity, signal drop-out or complex nonrigid deformation. In this paper, we present a robust, fast, and accurate 3D tracking algorithm: prediction based collaborative trackers (PCT). A novel one-step forward prediction is introduced to generate the motion prior using motion manifold learning. Collaborative trackers are introduced to achieve both temporal consistency and failure recovery. Compared with tracking by detection and 3D optical flow, PCT provides the best results. The new tracking algorithm is completely automatic and computationally efficient. It requires less than 1.5 s to process a 3D volume which contains millions of voxels. In order to demonstrate the generality of PCT, the tracker is fully tested on three large clinical datasets for three 3D heart tracking problems with two different imaging modalities: endocardium tracking of the left ventricle (67 sequences, 1134 3D volumetric echocardiography data), dense tracking in the myocardial regions between the epicardium and endocardium of the left ventricle (503 sequences, roughly 9000 3D volumetric echocardiography data), and whole heart four chambers tracking (20 sequences, 200 cardiac 3D volumetric CT data). Our datasets are much larger than most studies reported in the literature and we achieve very accurate tracking results compared with human experts' annotations and recent literature.     

The SQUOD: A versatile and accurate scheme for measuring signal strengths

The SQUOD (selected quantile output device) is a simple scheme using rank-order statistics for estimating received signal strength, even following detection in a nonlinear (e.g., logarithmic) receiver. Numerical results are presented that show that for any number of steady sinusoids having incommensurable frequencies or randomly distributed mutually independent phases plus additive Gaussian noise, the populationp-quantile of the envelope can be used for estimating the rms value of the envelope with a maximum error of 0.797 dB for p = 0.5650. Analysis and numerical examples show the effects of using a finite-samplep-quantile.     

Standing-wave and RF penetration artifacts caused by ellipticgeometry: an electrodynamic analysis of MRI

Motivated by the observation that the diagonal pattern of intensity nonuniformity usually associated with linearly polarized radio-frequency (RF) coils is often present in neurological scans using circularly polarized coils, a theoretical analysis has been conducted of the intensity nonuniformity inherent in imaging an elliptically shaped object using 1.5-T magnets and circularly polarized RF coils. This first principle analysis clarifies, for the general case of conducting objects, the relationship between the excitation field and the reception sensitivity of circularly and linearly polarized coils. The results, validated experimentally using a standard spin-echo imaging sequence and an in vivo B₁ field mapping technique, are shown to be accurate to within 1%-2% root mean square, suggesting that these electromagnetic interactions with the object account for most of the intensity nonuniformity observed     

The role of analysis in an age of computers: view from theanalytical side

The role of both past and current analysis in computer-based electromagnetics research is examined. Some observations on the current status of computer-based solutions are presented. It is concluded that analysis will remain an essential tool for making discoveries of electromagnetic phenomena, for providing physical insight into complex phenomena, and for the development of robust problem formulations and numerical methods, so that computed results with verifiable accuracy can be achieved. It is also concluded that more attention to verifying the accuracy of numerical results obtained from computer solutions is needed     

Mass Media and the Spiral of Silence: The Philippines from Marcos to Aquino

An analysis of the alternative media and their reporting up to the February 1986 revolution shows that they broadened the context in which key events could be interpreted and influenced those segments of the audience that provided the new leadership.     

The contact resistance at the interface between a disc electrode and an infinite slab: Mixed-boundary-value solutions

We consider the contact-resistance problem that arises when a circular-disc electrode is in imperfect contact with a semiconductor slab, the imperfect contact being modelled by an infinitely thin layer of resistive material at the interface between the disc electrode and the slab. The resulting mixed-boundary-value problem is solved through the use of basis functions that satisfy the boundary conditions outside the source region identically. Calculations of the source current-density and the total slab resistance (including the effect of the contact resistance) are performed for homogeneous slabs of different thicknesses and with different substrate resistivities, for a wide range of values of the contact resistivity of the interface layer. The results obtained show that the presence of a contact resistance tends to make the source current density distribution more uniform. They also confirm the existence of upper and lower bounds for the difference between the total slab resistance and the layer contact-resistance, as predicted by Foxhall and Lewis. Although applied only to slabs of uniform resistivity, the method can be readily extended to slabs of nonuniform resistivity.     

Lambda Pi Eta: The Founding and Evolution of Communication's Undergraduate Honor Society from a Systems Perspective

From a systems standpoint, Lambda Pi Eta is an influential subsystem within the Communication discipline. The input–throughput–output teaching-learning dialectic arguably achieves maximum potential at the point where the student is positioned. The evolution of the Arkansas Alpha LPH chapter into an accredited national honor society, documented in the words of the founding student and professor, illustrate key concepts of systems thinking, sense-making, and “learning organizations.” Envisioning the student-scholar, the honor society, NCA and its institutional members, and their interconnected partners as a transformative “super-system” fosters appreciation of the active role students play in networked realms of 21st century communication and education.     

The Impact of X-Ray Radiation on Chemical and Optical Properties of Triple-Cation Lead Halide Perovskite: from the Surface to the Bulk

Understanding the effects of X-rays on halide perovskite thin films is critical for accurate and reliable characterization of this class of materials, as well as their use in detection systems. In this study, advanced optical imaging techniques are employed, both spectrally and temporally resolved, coupled with chemical characterizations to obtain a comprehensive picture of the degradation mechanism occurring in the material during photoemission spectroscopy measurements. Two main degradation pathways are identified through the use of local correlative physico-chemical analysis. The first one, at low X-Ray fluence, shows minor changes of the surface chemistry and composition associated with the formation of electronic defects. Moreover, a second degradation route occurring at higher fluence leads to the evaporation of the organic cations and the formation of an iodine-poor perovskite. Based on the local variation of the optoelectronic properties, a kinetic model describing the different mechanisms is proposed. These findings provide valuable insight on the impact of X-rays on the perovskite layers during investigations using X-ray based techniques. More generally, a deep understanding of the interaction mechanism of X-rays with perovskite thin films is essential for the development of perovskite-based X-ray detectors and solar for space applications.     

Stepwise co-sensitization as a useful tool for enhancement of power conversion efficiency of dye-sensitized solar cells: The case of an unsymmetrical porphyrin dyad and a metal-free organic dye

A tertiary arylamine compound (DC), which contains a terminal cyano-acetic group in one of its aryl groups, and an unsymmetrical porphyrin dyad of the type Zn[Porph]-L-H₂[Porph] (ZnP-H₂P), where Zn[Porph] and H₂[Porph] are metallated and free-base porphyrin units, respectively, and L is a bridging triazine group functionalized with a glycine moiety, and were synthesized and used for the fabrication of co-sensitized dye-sensitized solar cells (DSSCs). The photophysical and electronic properties of the two compounds revealed spectral absorption features and frontier orbital energy levels that are appropriate for use in DSSCs. Following a stepwise co-sensitization procedure, by immersing the TiO₂ electrode in separate solutions of the dyes in different sequence, two co-sensitized solar cells were obtained: devices C (ZnP-H₂P/DC) and D (DC/ZnP-H₂P).The two solar cells were found to exhibit power conversion efficiencies (PCEs) of 6.16% and 4.80%, respectively. The higher PCE value of device C, which is also higher than that of the individually sensitized devices based on the ZnP-H₂P and DC dyes, is attributed to enhanced photovoltaic parameters, i.e. short circuit current (J_sc = 11.72 mA/cm²), open circuit voltage (V_oc = 0.72 V), fill factor (FF = 0.73), as it is revealed by photovoltaic measurements (J–V curves) and by incident photon to current conversion efficiency (IPCE) spectra of the devices, and to a higher total dye loading. The overall performance of device C was further improved up to 7.68% (with J_sc = 13.45 mA/cm², V_oc = 0.76 V, and FF = 0.75), when a formic acid treated TiO₂ ZnP-H₂P co-sensitized photoanode was employed (device E). The increased PCE value of device E has been attributed to an enhanced J_sc value (=13.45 mA/cm²), which resulted from an increased dye loading, and an enhanced V_oc value (=0.76 V), attributed to an upward shift and increased of electron density in the TiO₂ CB. Furthermore, dark current and electrochemical impedance spectra (EIS) of device E revealed an enhanced electron transport rate in the formic acid treated TiO₂ photoanode, suppressed electron recombination at the photoanode/dye/electrolyte interface, as well as shorter electron transport time (τ_d), and longer electron lifetime (τ_e).     

The adsorption of basic dye (Alizarin red S) from aqueous solution onto activated carbon/γ-Fe2O3 nano-composite: Kinetic and equilibrium studies

The adsorption behavior of Alizarin red S (ARS) from aqueous solution onto magnetic activated carbon (MAC) nano-composite was investigated under various experimental conditions. Characterization of the obtained MAC nano-composite was achieved by FT-IR, BET, FE-SEM, EDX, XRD and VSM techniques. The influence of variables including pH, concentration of the dye, amount of adsorbents and contact time was investigated by the batch method. High maximum adsorption capacity was obtained at 108.69 mg g⁻¹ for ARS. The equilibrium data was evaluated using Langmuir and Freundlich isotherm. The Langmuir model best describes the uptake of ARS dye, which implies that the adsorption of ARS dye onto MAC nano-composite is homogeneous. The kinetic data were analyzed using Lagergren pseudo-first order and pseudo-second equation. The pseudo-second order exhibited the best fit for the kinetic studies (R²=0.9999), which indicates that adsorption of ARS is limited by chemisorption process. This study shows that the as-prepared MAC composite could be utilized as an efficient, magnetically separable adsorbent for the environmental cleanup.