Biosynthesis of elsinochrome A, the perylenequinone from Elsinoë spp. I.
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Acetates↗
Biomedical subjects
C T Chen
Publications and source records attributed to C T Chen.
Automated surface interpolation technique for 3-D object reconstruction from serial cross sections.
A method for automatically reconstructing a three-dimensional object from serial cross-sections is presented in this paper. The method combines the techniques of dynamic elastic contour interpolation, spline theory, and quadratic-variation-based surface interpolation. In the proposed method, the initial description of the object is formed by applying the elastic interpolation algorithm to generate a series of intermediate contours between each pair of consecutive cross-sections. After this, a preliminary processing for surface computation is carried out by mapping the contours into the domain of surface function and then using spline functions to calculate the initial surface values. Based on the output from the preliminary processing, we apply the quadratic-variation-based surface interpolation algorithm to calculate the final surface representation. Since our method takes the continuity of high order derivatives into consideration, the smooth and complete surface of a 3-D object can thus be reconstructed.
Arteries↗
A fiber matrix model for interstitial fluid flow and permeability in ligaments and tendons.
Collagen fibrils in ligaments and tendons are highly organized into parallel arrays which influence interstitial fluid transport. Finite element (FE) models were developed analogous to the fibrillar arrays in ligaments and tendons to investigate interstitial fluid flow and tissue permeability as a function of interfibrillar spacing and fluid properties. Collagen fibrils were assumed to be a periodic square array of impermeable cylinders. A two-dimensional FE model was used to study transverse fluid flow and a three-dimensional model was used to study flow parallel to the collagen fibrils. Parametric FE analysis provided data to formulate empirical expressions for permeability (kappa) as a function of porosity (phi). Results show that longitudinal permeability (kappa = 1.1.10(-15)phi 2.5[1 - phi]-0.333) can be up to 50 times higher than transverse permeability (kappa = 1.2.10(-15)phi 0.5[phi - phi min]2.5) in a compact array. Maximum fluid shear stresses occur at the narrowest zones of adjacent fibrils (1.21 Pa or 12.1 dyn/cm2 at 10 microns/s of average transverse influx). If interstitial fluid is highly non-Newtonian, the permeability should be considered as flow (shear)-dependent. The computational results suggest that tissue permeability in ligaments and tendons is highly anisotropic, porosity-dependent, and can be estimated by analytic expressions.
Extracellular Space↗
Donor-specific transfusion in the nude rat prolongs survival of subsequently transplanted hamster cardiac xenografts.
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Animals↗
Polymer-supported benzotriazoles as catalysts in the synthesis of tetrahydroquinolines by condensation of aldehydes with aromatic amines.
Four polymer-supported benzotriazoles were prepared by linkage of 5-(hydroxymethyl)benzotriazole and benzotrizaole-5-carboxylic acid with Wang resin, Merrifield resin, and (monomethoxy)poly(ethylene glycol). The solid-phase and liquid-phase syntheses of tetrahydroquinolines were achieved by two-pair coupling reactions of aldehydes and aromatic amines using these polymer-supported benzotriazoles as the promoters. The ether-type benzotriazole prepared by loading 5-(hydroxymethyl)benzotriazole onto Merrifield resin turned out to be the catalyst of choice. Thus, a series of tetrahydroquinoline products were obtained in high purity by simple filtration, and the resin was recovered for reuse without loss of activity.
Journal Article↗
Reduction of chromium(VI) and its relationship to carcinogenesis.
Although Cr(VI)-containing compounds are well-documented carcinogens, their mechanism of action is still not well understood. Recent studies have suggested that reduction of Cr(VI) to its lower oxidation states and related free-radical reactions play an important role in carcinogenesis. This article summarizes recent studies on (1) the reduction of Cr(VI) by ascorbate, diol- and thiol-containing molecules, certain flavoenzymes, cell organelles, intact cells, and whole animals; (2) free-radical production with emphasis on hydroxy radical generation via Fenton or Haber-Weiss type reactions; and (3) free-radical-induced cellular damage, such as DNA strand breaks, hydroxylation of 2'-deoxyguanosine, and activation of nuclear transcription factor kappa B.
Animals↗
Stress analysis of different wall thicknesses of implant fixture with various boundary levels.
The aim of the present work is to develop 3D finite element models of implant fixture with different wall thicknesses to predict maximum stress concentration sites and distribution contours after loading. A maximum lateral force of 150 N was applied to simulate horizontal occlusal forces. When the fixtures were constrained to simulate different boundary levels, the maximum equivalent stress (max EQV) was always located at the implant-bone interface. Max EQV increased when the wall thickness or boundary level was reduced to a certain extent. The fixture with a wall thickness of 0.97 mm demonstrated the smallest stress increase ratio when the boundary level was lowered. Our results indicated that both wall thickness and the boundary level played important roles in maintaining a well-distributed stress level within the fixture. The stress concentration decreased when the fixture wall became thicker, however, this effect was less significant when the surrounding bone level was reduced.
Biomedical Engineering↗
Accurate three-dimensional registration of CT, PET, and/or MR images of the brain.
A surface matching technique has been developed to register multiple imaging scans of the brain in three dimensions, with accuracy on the order of the image pixel sizes. Anatomic information visualized in X-ray CT and magnetic resonance images may be integrated with each other and with functional information from positron emission tomography. Anatomical structures and other volumes of interest may be mapped from one scan to another, and corresponding sections through multiple scans may be directly compared. This capability provides a novel quantitative method to address the fundamental problem of relating structure to function in the brain. Applications include basic and clinical problems in the neurosciences and delivery and assessment of brain tumor therapy.
Brain↗
Retrospective fusion of radiographic and MR data for localization of subdural electrodes.
Prior to epilepsy surgery, subdural electrodes are often implanted and monitored for a few days to identify the focus of abnormal electrical activity. During the implantation and subsequent brain resection, there may be uncertainty about the exact location of the electrodes with respect to features of brain anatomy such as specific gyral convolutions or lesions. In experiments with a phantom and patients, implanted electrodes were imaged with multiplanar skull radiographs (or CT scans). After retrospective registration with preimplantation MR data, the electrodes were mapped from these studies onto an MR-derived three-dimensional brain model. The resulting multimodality displays showed the relationship of the electrodes to brain anatomy. In one patient the position of each electrode with respect to a metabolic lesion was also displayed by mapping preimplantation PET data onto the same brain model. This new display of electrode positions may strengthen the interpretation of subdural electrical recordings and thereby reduce uncertainty in planning the resection of epileptic tissue.
Adult↗
A 4-MV CT scanner for radiation therapy: the prototype system.
A Varian 4-MV isocentric therapy accelerator has been modified to perform also as a CT scanner. The goal is to provide a computed tomography capability for use in radiotherapy at low cost. We envision three principal uses for the system. These are (i) to provide two and three-dimensional maps of electron density distribution for CT assisted therapy planning; (ii) to aid in patient set up by providing sectional views of the treatment volume and high contrast scout-mode verification images; and (iii) to provide a means for periodically checking the patients anatomical conformation against that which was used to generate the original therapy plan. The machine was modified by mounting an array of detectors on a frame that is bolted to the counterweight end of the gantry in such a manner as to define a "third generation" CT scanner geometry. Details of the detectors and data acquisition electronics are provided. We present results of phantom studies which demonstrate that this prototype system has a spatial resolution of 4 mm and the ability to discriminate electron density differences of less than 1%. We also show that the system is exactly linear over a wide range of electron densities corresponding to those found in body tissues.
Particle Accelerators↗
Computed tomography with a linear accelerator with radiotherapy applications.
An earlier paper [Simpson et al., Med. Phys. 9, 574 (1982)] described a computed tomography (CT) scanner that was constructed by adding a detector array to a 4-MV isocentric linear accelerator. Since the previous article, the detector array has been improved and we now demonstrate better than 3-mm spatial resolution and better than 1% relative electron density discrimination. A series of pictures from volunteer patients is included. Normal anatomy is visualized with bone, muscle, fat, and air being clearly delineated.
Adult↗
Radiation absorbed dose to bladder walls from positron emitters in the bladder content.
A method to calculate absorbed doses at depths in the walls of a static spherical bladder from a positron emitter in the bladder content has been developed. The beta ray dose component is calculated for a spherical model by employing the solutions to the integration of Loevinger and Bochkarev point source functions over line segments and a line segment source array technique. The gamma ray dose is determined using the specific gamma ray constant. As an example, absorbed radiation doses to the bladder walls from F-18 in the bladder content are presented for static spherical bladder models having radii of 2.0 and 3.5 cm, respectively. Experiments with ultra-thin thermoluminescent dosimeters (TLD's) were performed to verify the results of the calculations. Good agreement between TLD measurements and calculations was obtained.
Beta Particles↗
Application of the EM algorithm to radiographic images.
The expectation maximization (EM) algorithm has received considerable attention in the area of positron emitted tomography (PET) as a restoration and reconstruction technique. In this paper, the restoration capabilities of the EM algorithm when applied to radiographic images is investigated. This application does not involve reconstruction. The performance of the EM algorithm is quantitatively evaluated using a "perceived" signal-to-noise ratio (SNR) as the image quality metric. This perceived SNR is based on statistical decision theory and includes both the observer's visual response function and a noise component internal to the eye-brain system. For a variety of processing parameters, the relative SNR (ratio of the processed SNR to the original SNR) is calculated and used as a metric to compare quantitatively the effects of the EM algorithm with two other image enhancement techniques: global contrast enhancement (windowing) and unsharp mask filtering. The results suggest that the EM algorithm's performance is superior when compared to unsharp mask filtering and global contrast enhancement for radiographic images which contain objects smaller than 4 mm.
Algorithms↗
Automatic segmentation of liver structure in CT images.
The segmentation and three-dimensional representation of the liver from a computed tomography (CT) scan is an important step in many medical applications, such as in the surgical planning for a living-donor liver transplant and in the automatic detection and documentation of pathological states. A method is being developed to automatically extract liver structure from abdominal CT scans using a priori information about liver morphology and digital image-processing techniques. Segmentation is performed sequentially image-by-image (slice-by-slice), starting with a reference image in which the liver occupies almost the entire right half of the abdomen cross section. Image processing techniques include gray-level thresholding, Gaussian smoothing, and eight-point connectivity tracking. For each case, the shape, size, and pixel density distribution of the liver are recorded for each CT image and used in the processing of other CT images. Extracted boundaries of the liver are smoothed using mathematical morphology techniques and B-splines. Computer-determined boundaries were compared with those drawn by a radiologist. The boundary descriptions from the two methods were in agreement, and the calculated areas were within 10%.
Biophysical Phenomena↗
Non-lethal Candida albicans cph1/cph1 efg1/efg1 transcription factor mutant establishing restricted zone of infection in a mouse model of systemic infection.
The cph1/cph1 efg1/efg1 Candida albicans mutant cells were non-lethal in a mouse model of systemic infection. We investigated in vivo proliferation and invasion of C. albicans cells in infected mice to elucidate the interaction between the host and the pathogen. Homogenates of kidneys from the mice infected with the wild-type and the mutant C. albicans cells yielded a mean of 2.1 x 10 7 CFU/g and 2.2 x 10 6 CFU/g, respectively. The kidneys from the mice infected with the wild-type cells showed extensive renal cortical necrosis associated with neutrophilic infiltration. There were also wild-type hyphal cells present in abundance. Hence, tubular necrosis leading to renal failure in the mice may be the cause of death. Although the cph1/cph1 efg1/efg1 mutant cells were not lethal, they were capable of establishing restricted zones of infection and colonization near the renal pelvis instead of simply being cleared by the immune system in mice.
Animals↗
Preparation and release properties of biodegradable chitin microcapsules: II. Sustained release of 6-mercaptopurine from chitin microcapsules.
Chitin microcapsules are prepared using a simple desolvation or nonsolvent addition phase separation method with 6-mercaptopurine (6-MP) as a reference core. Chitin with a molecular weight about 400,000 is used to prepare different core loaded microcapsules. The drug release rates of chitin microcapsules prepared by simple desolvation or nonsolvent addition method have different release profiles which are related to the rate of phase separation. With respect to the solubility parameter difference (delta delta) value between solvent and nonsolvent, the release rate of 6-MP from microcapsules decreases with increasing delta delta of the preparative system. The chitin beads show poor swelling properties and their release rates are pH-dependent. Sustained release of 6-MP from chitin microcapsules in low pH and neutral medium can be accomplished. To determine if the drug release from the polymer matrix is via a diffusion controlled or by an erosion controlled process, 6-MP release profiles of various chitin microcapsules degraded by lysozyme are investigated. The drug-release patterns of the chitin microcapsules prepared by nonsolvent addition (acetone, n-propanol, n-butanol) and simple desolvation in acetone are not only diffusion but also lysozyme digestion influenced. Whereas, by using water or ethanol as nonsolvent or desolvating agent, release profiles of the microcapsules prepared by nonsolvent addition and the simple desolvation method seem to be little affected by enzyme degradation. These results indicate that chitin might prove useful as a polymer carrier for the sustained release of drugs.
Antimetabolites, Antineoplastic↗
Preparation and release properties of biodegradable chitin microcapsules: I. Preparation of 6-mercaptopurine microcapsules by phase separation methods.
Chitin [poly-(N-acetyl-1,4-beta-D-glucopyranosamine)] microcapsules were prepared by the simple desolvation and the non-solvent addition phase separation methods. In the simple desolvation method, chitin droplets were dropped into the desolvation agent (water, ethanol, or acetone) and microcapsules soon formed. Several solvent-nonsolvent pairs: N,N-dimethylacetamide (DMAc)-water, DMAc-ethanol, DMAc-propanol, DMAc-n-butanol, and DMAc-acetone with different solubility parameter difference, (delta delta) were chosen to prepare chitin microcapsules containing 6-mercaptopurine by using the non-solvent-addition phase separation method. The results showed that the surface morphology and release behaviour of the microcapsules were greatly affected by different solvent-nonsolvent pairs. The surface of microcapsules prepared from the system of high delta delta was more smooth than those from the systems of low delta delta. The drug content using the simple desolvation method increased with decreasing delta delta because of the higher film formation rate of the microcapsules. On the other hand, the drug content using the nonsolvent addition method was lower than that using the simple desolvation method because of the dispersion forces, applied by mechanical stirring. Microcapsules prepared by the simple desolvation method had a narrower size distribution and larger mean size than those prepared by the nonsolvent addition method.
Antimetabolites, Antineoplastic↗
The 1995 Lindberg Award. Nonthermally mediated muscle injury and necrosis in electrical trauma.
Joule heating has long been considered the principal component of tissue damage in electrical injury. Recent studies suggest electroporation, a nonthermally mediated mechanism of cell membrane damage, is also a factor. We investigated whether electroporation-mediated muscle necrosis can occur in vivo without significant Joule heating. Pulsed electric fields approximately 150 V/cm were produced in the hind limbs of anesthetized rats. In shocked limbs core muscle temperature rose less than 1.8 degrees C, yet significant damage occurred as determined by technetium-99m pyrophosphate uptake, elevated serum creatine phosphokinase, and prominent hypercontraction band degeneration of myofibers on histopathologic examination. This study is significant because it directly addresses whether nonthermal mechanisms of cell damage can cause tissue necrosis. These results indicate that electroporation effects can mediate skeletal muscle necrosis without visible thermal changes. Thus the phenomenon of "progressive recognition" may be characteristically largely explained by the occurrence of nonthermally mediated tissue damage.
Animals↗