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Biomedical subjects

C T Koch

Publications and source records attributed to C T Koch.

11 recordsLinked to original sources
PubMed2006

Aspects regarding measurement of thickness of intergranular glassy films.

Materials such as Si(3)N(4), SiC and SrTiO(3) can have grain boundaries characterized by the presence of a thin intergranular amorphous film of nearly constant thickness, in some cases (e.g. Si(3)N(4)) almost independent of the orientation of the bounding grains, but dependent on the composition of the ceramic. Microscopy techniques such as high-resolution lattice fringe imaging, Fresnel fringe imaging and diffuse dark field imaging have been applied to the study of intergranular glassy films. The theme of the current investigation is the use of Fresnel fringes and Fourier filtering for the measurement of the thickness of intergranular glassy films. Fresnel fringes hidden in high-resolution micrographs can be used to objectively demarcate the glass-crystal interface and to measure the thickness of intergranular glassy films. Image line profiles obtained from Fourier filtering the high-resolution micrographs can yield better estimates of the thickness. Using image simulation, various kinds of deviation from an ideal square-well potential profile and their effects on the Fresnel image contrast are considered. A method is also put forth to objectively retrieve Fresnel fringe spacing data by Fourier filtering Fresnel contrast images. Difficulties arising from the use of the standard Fresnel fringe extrapolation technique are outlined and an alternative method for the measurement of the thickness of intergranular glassy films, based on zero-defocus (in-focus) Fresnel contrast images is suggested. The experimental work is from two ceramic systems: Lu-Mg-doped Si(3)N(4) and SrTiO(3) (stoichiometric and nonstoichiometric). Further, a comparison is made between the standard high-resolution lattice fringe technique, the standard Fresnel fringe extrapolation technique and the methods of analyses introduced in the current work, to illustrate their utility and merits. Taking experimental difficulties into account, this work is intended to be a practical tool kit for the study of intergranular glassy films.

Journal Article↗
PubMed2005

Determining the radial pair-distribution function within intergranular amorphous films by numerical nanodiffraction.

We report on an alternative method to electron nanodiffraction and fluctuation microscopy for the determination of the reduced density function G(r) of amorphous areas with small cross-sections. This method is based on the numerical extraction of diffraction data from the complex-valued exit-face wave function as obtained by HRTEM focal series reconstruction or electron holography. Since it is thus possible to obtain "diffraction data" from rectangular areas of any aspect ratio, this method is particularly suited for intergranular glassy films of only 1-2 nm width, but lengths of several 100 nm. A critical comparison of this method with the already established nanodiffraction and fluctuation microscopy will be made.

Electronic Data Processing↗
PubMed2004

Iterative phase retrieval without support.

An iterative phase retrieval method for nonperiodic objects has been developed from the charge-flipping algorithm proposed in crystallography. A combination of the hybrid input-output (HIO) algorithm and the flipping algorithm has greatly improved performance. In this combined algorithm the flipping algorithm serves to find the support (object boundary) dynamically, and the HIO part improves convergence and moves the algorithm out of local minima. It starts with a single intensity measurement in the Fourier domain and does not require a priori knowledge of the support in the image domain. This method is suitable for general image recovery from oversampled diffuse elastic x-ray and electron-diffraction intensities. The relationship between this algorithm and the output-output algorithm is elucidated.

Journal Article↗
PubMed1983

Cholescintigraphy with 99mTc-diethyl-IDA for the detection of rejection of auxiliary liver transplants in pigs.

In 15 pigs an auxiliary liver was transplanted and cholescintigraphy with 99mTc-diethyl-IDA was performed to study the function of the livers separately. Serial scintigraphy of the recipient and donor liver was performed on days 3, 8 and 18 after transplantation and time-activity curves over 1 h after injection of the radio-tracer were generated for each liver. From these data the time at which the maximal activity was present in the liver (Tmax) and the time at which during the excretion phase half of this activity was still present in the organ (T1/2) were determined. Liver biopsy material from the recipient liver and the donor liver was obtained at (approximately) the day of one of the scintigraphic examinations and at autopsy. In all cases no histological abnormalities were found in the recipient liver. In 4 pigs there were no histological signs of rejection of the donor liver, in which cases the values for Tmax and T1/2 were normal. In 11 pigs histological signs of rejection were noticed and in all of these cases T1/2 was significantly prolonged, whereas no changes in Tmax were observed. Cholescintigraphy revealed an abnormal value for T1/2 a few days before the biopsy was taken in 10 of these 11 cases. Normal functioning or the prediction of rejection of the auxiliary liver transplant in pigs correlated significantly (P less than 0.01) with normal or prolonged T1/2 values. It is concluded that cholescintigraphy may be helpful in establishing the diagnosis of rejection of liver transplants.

Animals↗
PubMed1979

Influence of matching for HLA-DR antigens on skin graft survival.

HLA-DR typing results of 47 skin transplant donor-recipient pairs were analysed. HLA-A, B, and C typing and mixed lymphocyte culture (MLC) testing was also included in this study. Skin transplants exchanged between HLA-A-, B-, and DR-identical, MLC-negative donor-recipient pairs had the longest graft survival (mean survival time, 17 days), whereas skin grafts exchanged between completely nonidentical donor-recipient combinations had the shortest survival (mean survival time, 10 days). Because of the correlation between identity for the DR antigens and the low or nonreactivity in the MLC test, identity for DR will predict a better skin graft survival than nonidentity. It was concluded that the best match between donor and recipient of a graft, using only serological techniques, is one where there is identity for HLA-A, B, and DR.

B-Lymphocytes↗
PubMed1979

Human skin grafts from mixed lymphocyte culture-positive donors provide help for the rapid rejection of simultaneously transplanted skin grafts from mixed lymphocyte culture-negative donors.

The influence of grafting more than one skin transplant simultaneously on one recipient was investigated. When a mixed lymphocyte culture (MLC)-negative skin was transplanted along with an MLC-positive skin, the MLC-negative skin survived for a significantly shorter time than when transplanted alone. This indicated that the MLC-positive skin provided a stimulus that could provide help to reject the MLC-negative skin. This finding might be important clinically. When an MLC-negative transplant is given to a patient, one should not transfuse this patient with MLC-positive leukocyte-rich blood.

Graft Rejection↗
PubMed1976

The immunologic system, immunologic deficiency disorders and lymphoid hyperplasia of the small intestine.

The purpose of this paper is to review our current concept of the systems that subserve immunological functions. It concerns specifically the immunodeficiency diseases probably due to a B cell immunodeficiency. An attempt is made to classify those diseases clinically as well as roentgenologically. At last using the enteroclysis technique some examples of immunodeficiency syndromes are shown with special emphasis on developing a malignant disease.

Animals↗