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.     

Determination of leaching rates of precious metals by electrochemical techniques

The leaching rates of gold, silver, palladium and platinum in cyanide solutions have been determined from the corrosion potential and voltammograms of the anodic oxidation reaction. The order of reactivity was Au>Ag>Pd>Pt and the leaching rate was a maximum at about pH 10 for each metal. An assessment was made of the applicability of PAR M342C Softcorr Corrosion Software, devised for computing corrosion currents, to the measurement of leaching rates of precious metals. The software does not yield accurate rates due to the nature of the individual oxygen reduction and metal dissolution processes, but could be applied to rapidly estimate the influence of variation in solution composition on the leaching of an individual metal.     

Development of a rotating ring-disc electrode for high temperature studies in cryolite-based melts

A compact rotating ring-disc electrode incorporating a molybdenum disc, gold ring and boron nitride insulator has been designed, constructed and evaluated in molten cryolite-based electrolytes at temperatures up to 1000°C and rotation rates between 0 and 2000 rpm. The electrode design is extremely versatile and relatively maintenance free, with no visible evidence of melt leakage at the ring-insulator and disc-insulator interfaces. The operating performance of the gold-molybdenum rotating ring-disc electrode was evaluated from collection efficiency measurements based on the dissolution of the disc surface and subsequent detection of soluble species transported to the ring. The observed collection efficiency was less than the theoretical value determined from the geometry of the electrode, primarily because of noncoplanarity of the electrode surface at the working temperature. The results confirm that the electrode should be useful for mechanistic studies in high temperature molten fluoride electrolytes.     

Almansi's problem in micropolar elasticity

The present paper is concerned with Almansi's problem in the linear theory of micropolar elasticity. The problem is solved using the results from [8], [10–13].     

Stevens's brightness law, contrast gain control, and edge integration in achromatic color perception: a unified model

The brightness of an isolated test patch is related to its luminance by a power law having an exponent of about 1/3, a result known as Stevens's brightness law. The brightness law exponent characterizes the rate at which brightness grows with luminance and can thus be thought of as an "exponential" gain factor. We studied changes in this gain factor for incremental and decremental test squares as a function of the size of a surrounding frame of homogeneous luminance. For incremental targets, the gain decreased as an approximately linear function of the frame width. For decremental targets, the gain increased as an approximately linear function of the frame width. We modeled the brightness of the frame-embedded target with a quantitative theory based on the assumption that the target brightness is determined by the sum of achromatic color induction signals originating from the inner and outer edges of the surround, a theory that has previously been used to account for the results of several other brightness matching experiments. To account for the frame-width-dependent gain changes observed in the present study, we elaborate this edge integration theory by proposing the existence of a cortical contrast gain control mechanism by which the gains applied to neural edge detectors are influenced by the responses of other edge detectors responding to the nearby edges.     

Synthesis of platinum nanowire networks using a soft template

Platinum nanowire networks have been synthesized by chemical reduction of a platinum complex using sodium borohydride in the presence of a soft template formed by cetyltrimethylammonium bromide in a two-phase water-chloroform system. The interconnected polycrystalline nanowires possess the highest surface area (53 +/- 1 m2/g) and electroactive surface area (32.4 +/- 3.6 m2/g) reported for unsupported platinum nanomaterials; the high surface area results from the small average diameter of the nanowires (2.2 nm) and the 2-10 nm pores determined by nitrogen adsorption measurements. Synthetic control over the network was achieved simply by varying the stirring rate and reagent concentrations, in some cases leading to other types of nanostructures including wormlike platinum nanoparticles. Similarly, substitution of a palladium complex for platinum gives palladium nanowire networks. A mechanism of formation of the metal nanowire networks is proposed based on confined metal growth within a soft template consisting of a network of swollen inverse wormlike micelles.     

Detection and measurement of fetal anatomies from ultrasound images using a constrained probabilistic boosting tree

We propose a novel method for the automatic detection and measurement of fetal anatomical structures in ultrasound images. This problem offers a myriad of challenges, including: difficulty of modeling the appearance variations of the visual object of interest, robustness to speckle noise and signal dropout, and large search space of the detection procedure. Previous solutions typically rely on the explicit encoding of prior knowledge and formulation of the problem as a perceptual grouping task solved through clustering or variational approaches. These methods are constrained by the validity of the underlying assumptions and usually are not enough to capture the complex appearances of fetal anatomies. We propose a novel system for fast automatic detection and measurement of fetal anatomies that directly exploits a large database of expert annotated fetal anatomical structures in ultrasound images. Our method learns automatically to distinguish between the appearance of the object of interest and background by training a constrained probabilistic boosting tree classifier. This system is able to produce the automatic segmentation of several fetal anatomies using the same basic detection algorithm. We show results on fully automatic measurement of biparietal diameter (BPD), head circumference (HC), abdominal circumference (AC), femur length (FL), humerus length (HL), and crown rump length (CRL). Notice that our approach is the first in the literature to deal with the HL and CRL measurements. Extensive experiments (with clinical validation) show that our system is, on average, close to the accuracy of experts in terms of segmentation and obstetric measurements. Finally, this system runs under half second on a standard dual-core PC computer.     

Scalable Trehalose‐Functionalized Hydrogel Synthesis for High‐Temperature Protection of Enzymes

Herein, a scalable, two‐step synthesis of a trehalose hydrogel for the thermostabilization of enzymes is reported. A reaction between vinylbenzyl chloride and trehalose in base, followed by a redox‐initiated radical polymerization of the resulting mixture, produces the gel in 88% yield. The reaction scale can be increased 100‐fold while maintaining a 76% yield. Additionally, various solvents are investigated for purification, and more sustainable manufacturing solvents are selected. When the three major enzymes utilized in animal feed, phytase, β‐glucanase, and xylanase, are heated to 90 °C in the hydrogel, greater than 98% activity is retained. Lastly, quantitative release of enzyme from the gel within 4 h is demonstrated. The scalable synthesis of the trehalose hydrogel, combined with its ability to stabilize and release a variety of animal feed enzymes, makes this technology promising for use with enzymes important in animal food production.     

Mapping the built-in electric field in polymer light-emitting electrochemical cells

A millimeter planar polymer light-emitting electrochemical cell was turned on in a cryogenic probe station and subsequently cooled to freeze the doping profile. A 442 nm laser beam guided by an optical fiber was scanned across the interelectrode gap of several millimeters and the photovoltaic response was measured as a function of position. Both photocurrent and photovoltage profiles display a prominent peak at the geometric boundary of the p- and n-doped regions. A non-zero photovoltaic response throughout the p- and n-doped regions can be explained by various broadening mechanisms including non-uniform doping and secondary excitation by waveguided light. The photovoltaic response is weakest at the electrode/polymer interfaces.     

Three-dimensional finite element analysis of current density andtemperature distributions during radio-frequency ablation

This study analyzed the influence of electrode geometry, tissue-electrode angle, and blood flow on current density and temperature distribution, lesion size, and power requirements during radio-frequency ablation. The authors used validated three-dimensional finite element models to perform these analyses. They found that the use of an electrically insulating layer over the junction between electrode and catheter body reduced the chances of charring and coagulation. The use of a thermistor at the tip of the ablation electrodes did not affect the current density distribution. For longer electrodes, the lateral current density decreased more slowly with distance from the electrode surface. The authors analyzed the effects of three tissue-electrode angles: 0, 45, and 90°. More power was needed to reach a maximal tissue temperature of 95°C after 120 s when the electrode-tissue angle was 45°. Consequently, the lesions were larger and deeper for a tissue-electrode angle of 45° than for 0 and 90°. The lesion depth, volume, and required power increased with blood flow rate regardless of the tissue-electrode angle. The significant changes in power with the tissue-electrode angle suggest that it is safer and more efficient to ablate using temperature-controlled RF generators. The maximal temperature was reached at locations within the tissue, a fraction of a millimeter away from the electrode surface. These locations did not always coincide with the local current density maxima. The locations of these hottest spots and the difference between their temperature and the temperature read by a sensor placed at the electrode tip changed with blood flow rate and tissue-electrode angle