Extraction of left-ventricular chamber from 3-D CT images of the heart

A semiautomatic method is described for extracting the volume and shape of the left ventricular (LV) chamber from a dynamic spatial reconstructor cardiac volume. For a given volume, the operator first performs some simple manual edits. Then, an automated stage, which incorporates concepts from 3-D mathematical morphology and technology, the maximum-homogeneity filter, and an adaptive 3-D thresholder, extracts the LV chamber. The method gives more consistent measurements and demands considerably less operator time than manual slice-editing.     

Tunable microwave resonators and oscillators using magnetostatic waves

The status of magnetostatic wave (MSW) straight-edge resonators (SERs) and their applications in tunable oscillator circuits are reviewed. The resonators are based on magnetostatic waves propagating in high-Q cavities fabricated in thin ferrimagnetic yttrium iron garnet (YIG) films. The resonance frequency of these resonators can be tuned using a bias magnetic field. The theory of operation and design criteria for the straight-edge resonators are described with emphasis on the effect of the resonator parameters on the tuning range, power handling, and phase noise performance. The use of the SER as the frequency-selective element in oscillator circuits is reported. Examples of tunable oscillators are included.     

Correlation-based aberration correction in the presence of inoperable elements

Estimation of phase aberrations using correlation processing between neighboring elements in a phased array is explored in the presence of inoperable elements. Using a CORDIC-based implementation of a complex baseband correlator, inactive elements can be identified simultaneous with correlation processing. Following detection of inoperable elements, a simple rerouting of the adaptive beam former is used to eliminate these elements from correlation analysis. Experimental results on a 3.33-MHz, 64-element array system with four contiguous, inactive elements demonstrate the robustness of the simple rerouting method for accurate phase aberration estimation.     

Impact of physical handicaps on operators of agricultural equipment

Physically handicapped farm operators and agricultural workers face barriers which make the completion of many essential farm-related tasks difficult or even impossible. These barriers are especially burdensome with respect to the operation and maintenance of agricultural equipment. This paper reports on work being done at Purdue University to assist handicapped farmers and agricultural workers who wish to continue working in spite of their disabilities. The nature of physical handicaps and proportion of farmers affected by these handicaps is discussed. Potential health and safety risks that these operators are exposed to when operating agricultural equipment are addressed. In addition, a brief overview of the Purdue project and recent activities is provided.     

Localizing overlapping parts by searching the interpretation tree

This paper discusses how local measurements of positions and surface normals may be used to identify and locate overlapping objects. The objects are modeled as polyhedra (or polygons) having up to six degrees of positional freedom relative to the sensors. The approach operates by examining all hypotheses about pairings between sensed data and object surfaces and efficiently discarding inconsistent ones by using local constraints on: distances between faces, angles between face normals, and angles (relative to the surface normals) of vectors between sensed points. The method described here is an extension of a method for recognition and localization of nonoverlapping parts previously described in [18] and [15].     

Electrostatic force microscopy of self-assembled peptide structures

In this report electrostatic force microscopy (EFM) is used to study different peptide self-assembled structures such as tubes and particles. It is shown that not only geometrical information can be obtained using EFM, but also information about the composition of different structures. In particular we use EFM to investigate the structures of diphenylalanine peptide tubes, particles, and CSGAITIG peptide particles placed on pre-fabricated SiO(2) surfaces with a backgate. We show that the cavity in the peptide tubes could be due to the presence of water residues. Additionally we show that self-assembled amyloid peptides form spherical solid structures containing the same self-assembled peptide in its interior. In both cases transmission electron microscopy is used to verify these structures. Further, the limitations of the EFM technique are discussed, especially when the observed structures become small compared with the radius of the AFM tip used. Finally, an agreement between the detected signal and the structure of the hollow peptide tubes is demonstrated.     

Nonlinear filtering approach to 3-D gray-scale image interpolation

Three-dimensional (3-D) images are now common in radiology. A 3-D image is formed by stacking a contiguous sequence of two-dimensional cross-sectional images, or slices. Typically, the spacing between known slices is greater than the spacing between known points on a slice. Many visualization and image-analysis tasks, however, require the 3-D image to have equal sample spacing in all directions. To meet this requirement, one applies an interpolation technique to the known 3-D image to generate a new uniformly sampled 3-D image. The authors propose a nonlinear-filter-based approach to gray-scale interpolation of 3-D images. The method, referred to as column-fitting interpolation, is reminiscent of the maximum-homogeneity filter used for image enhancement. The authors also draw upon the paradigm of relaxation labeling to devise an improved column-fitting interpolator. Both methods are typically more effective than traditional gray-scale interpolation techniques.     

Practical considerations for high spatial and temporal resolution dynamic transmission electron microscopy

Although recent years have seen significant advances in the spatial resolution possible in the transmission electron microscope (TEM), the temporal resolution of most microscopes is limited to video rate at best. This lack of temporal resolution means that our understanding of dynamic processes in materials is extremely limited. High temporal resolution in the TEM can be achieved, however, by replacing the normal thermionic or field emission source with a photoemission source. In this case the temporal resolution is limited only by the ability to create a short pulse of photoexcited electrons in the source, and this can be as short as a few femtoseconds. The operation of the photo-emission source and the control of the subsequent pulse of electrons (containing as many as 5 x 10(7) electrons) create significant challenges for a standard microscope column that is designed to operate with a single electron in the column at any one time. In this paper, the generation and control of electron pulses in the TEM to obtain a temporal resolution <10(-6)s will be described and the effect of the pulse duration and current density on the spatial resolution of the instrument will be examined. The potential of these levels of temporal and spatial resolution for the study of dynamic materials processes will also be discussed.