Cone-beam X-ray microtomography attracts increasing attention due to its applications in biomedical sciences, material engineering, and industrial nondestructive evaluation. Rapid volumetric image reconstruction is highly desirable in all these areas for prompt visualization and analysis of complex structures of interest. In this article, we reformulate a generalized Feldkamp cone-beam image reconstruction algorithm, utilize curved voxels and mapping tables, improve the reconstruction efficiency by an order of magnitude relative to a direct implementation of the standard algorithm, and demonstrate the feasibility with numerical simulation and experiments using a prototype cone-beam X-ray microtomographic system. Our fast algorithm reconstructs a 256-voxel cube from 100 projections within 2 min on an Intel Pentium II® 233 MHz personal computer, produces satisfactory image quality, and can be further accelerated using special hardware and/or parallel processing techniques.

A sample preparation method has been developed whereby sharp needle-shaped specimens for atom probe analysis are fabricated from multilayer thin films deposited onto silicon substrates. The specimens are fabricated in an orientation such that atom probe composition profiles across the layer interfaces can be determined with atomic-layer spatial resolution, i.e., the layer normals are parallel to the needle axis. The method uses standard silicon etching techniques and focused ion-beam milling. The feasibility and utility of this technique are shown through its application to a NiFe/CoFe/Cu/CoFe-based thin film structure.

We have been researching the capability of atomic force microscopy to reveal nontopographic properties of tissue embedded in plastic and sectioned with standard electron microscopic techniques. We present topography and elasticity maps of plastic-embedded, thin sections of muscle tissue. The images show topography correlated with the normal repeating structure of the sarcomere. Elasticity mapping using force modulation revealed contrast between the actin- and myosin-rich areas. We attribute the observed contrast in elasticity to the difference in local concentrations of biological material in embedding plastic.

A method is described for the estimation of mean cell volume of phagocytosing cells. The cells are coembedded with yeast particles of known size. By combination of data obtained from morphometrical analysis of sections in both the light and transmission electron microscopes, an estimate of the ratio between cell volume and yeast particle volume is obtained. The method makes use of the dissector but does not require measurements on serial sections or knowledge of section thickness. Evaluation of the method was done by studying the effect of phagocytosis of latex beads on macrophage cell volume and surface area. It was found that the surface area of phagocytosing macrophages remained constant although the cell volume increased by 27%. Furthermore, in phagocytosing macrophages, the amount of membrane enclosing intracellular vacuoles decreased by 28%, but this loss of membrane was balanced by the appearance of membrane enclosing the phagocytosed latex beads. The method described here may prove useful for morphometrical studies on phagocytosing leukocytes, as well as on intracellular parasites located within these cells.

An increase in extracellular adenosine triphosphate (ATP) is arrhythmogenic in rat cardiac myocytes and extracellular ATP levels are elevated during cardiac ischemia. To gain insight into the mechanism by which the arrhythmic contractions are generated, we investigated changes in subcellular elemental content by electron probe microanalysis (EPMA) in isolated adult rat cardiac myocytes stimulated by the ATP analog, 2-methylthio- ATP (2-M-S-ATP). We also measured the effects of 2-M-S-ATP stimulation on myocyte cell shortening. In electrically stimulated myocytes, 2-M-S-ATP stimulation generated arrhythmic contractions and also increased the amplitude of cell shortening. However, only the arrhythmic contractions were reversed by 2-MS- ATP washout. EPMA of freeze-dried cryosections of rapidly frozen 2-M-S-ATP-stimulated myocytes showed increased cytosolic Na and Cl, decreased K, but no significant change in mitochondrial Ca upon 2-M-S-ATP stimulation. The arrhythmias were abolished upon 2-M-S-ATP washout, and the observed changes in cytosolic elemental content also reversed upon agonist washout, thus suggesting that the increased Na and Cl, and decreased K, are specifically associated with the ATP-dependent spontaneous contractile activity. The observed increase in intracellular Na upon 2-M-S-ATP stimulation may explain our observation of prolonged relaxation time of 2-M-S-ATP-stimulated contractions. This may be due to inhibition of Ca2+ efflux via the Na+ Ca2+ exchanger.

In this report, we describe the distribution of the platelet-derived growth factor receptor α (PDGFRα) by immunolocalization in the embryonic day 10.5 mouse heart and defects in heart development associated with the absence of this receptor in the Patch mouse. The Patch mouse is a naturally occurring mutant that has been accepted as a model for determining the role of the PDGFRα in early cardiac development. Even though other genetic defects exist in this naturally occurring mutant, most defects associated with cardiac development are believed to be a result of the absence of this receptor. Gross morphological defects including improper septation of the outflow tract, dysmorphic shape of the heart, and lack of trabecular development are similar to those that have been previously described. Many of these defects have been attributed to the failure of a subset of non-neuronal neural crest cells to properly migrate into the region of the developing outflow tract. In these studies, we have also used confocal scanning laser and transmission electron microscopy to describe and compare the organization and differentiation of the cytoskeletal proteins actin and myosin in littermate control and Patch mouse hearts. Cytoskeletal organization of the cardiac myocytes in Patch mouse hearts has not previously been described. In most cardiac myocytes of Patch mice, actin was found only on the periphery of the cells, and the organization of actin, myosin, and precursor Z-band material into distinct myofibrils was greatly reduced.