Biomedical subjects

Z Liang

Publications and source records attributed to Z Liang.

174 records · Page 10Linked to original sources

PubMed1988

Study and performance evaluation of statistical methods in image processing.

Two statistical image processing formalisms involving the entropy concept and Bayesian analysis are studied. Iterative imaging algorithms of the formalisms are formulated by employing, for the purpose of performance evaluation and easy implementation, the steepest descent method for the solution of entropy concept and the expectation maximization technique for the solution of Bayesian analysis. Quantitative evaluation and comparison of the convergence performance of the iterative algorithms on computer generated ideal and experimental radioisotope phantom imaging noisy data are given. The study concludes that the entropy algorithm can converge relatively fast, but it is very sensitive to noise in measured data due to the ill-posed nature of inverse problems and its lack of ability to consider the statistics of data fluctuation; while the Bayesian algorithm converges monotonically even with noisy data and has the advantage of considering both the a priori source distribution information and the statistical fluctuation of measured data.

Algorithms↗

PubMed1984

Conversion of glycerate to serine in intact spinach leaf peroxisomes.

Intact spinach (Spinacia oleracea L.) leaf peroxisomes converted glycerate to serine in the presence of NAD and alanine. The reaction proceeded optimally at pH9. Addition of oxaloacetate or alpha-ketoglutarate plus aspartate enhanced the conversion about three-fold. Alteration of the concentration of one of the reaction components, consisting of 2 mM glycerate, 0.2 mM NAD, 0.5 mM oxaloacetate, and 2 mM alanine, revealed half-saturation constants of 0.45 mM for glycerate, 0.06 mM for NAD, 0.02 mM for oxaloacetate, and 0.33 mM for alanine. The conversion proceeded with the formation of hydroxypyruvate followed by serine; hydroxypyruvate did not accumulate to a high amount in the presence or absence of alanine. The amino group donor could be alanine (half-saturation constant, 0.33 mM), glycine (0.45 mM), or asparagine (0.67 mM); the three amino acids produced roughly similar Vmax values. The results indicate that, in the conversion of glycerate to serine, the transamination is catalyzed by a hydroxypyruvate aminotransferase with characteristics unknown among all other studied leaf peroxisomal aminotransferases. The peroxisomal membrane is sparsely permeable to NAD/NADH, and the participation of the peroxisomal malate dehydrogenase in an electron shuttle system across the membrane in the regeneration of NAD/NADH is suggested.

Alanine↗

PubMed1984

Glyoxylate transamination in intact leaf peroxisomes.

Intact spinach (Spinacia oleracea L.) leaf peroxisomes were supplied with glycolate and one to three of the amino acids serine, glutamate, and alanine, and the amount of the respective alpha-keto acids formed in glyoxylate transamination was assayed. At 1 millimolar glycolate and 1 millimolar each of the three amino acids in combination, the transamination reaction reached saturation; reduction of either glycolate or amino acid concentration decreased the activity. The relative serine, glutamate, and alanine transamination at equal amino acid concentrations was roughly 40, 30, and 30%, respectively. The three amino acids exhibited mutual inhibition to one another in transamination due to the competition for the supply of glyoxylate. In addition to this competition for glyoxylate, competitive inhibition at the active site of enzymes occurred between glutamate and alanine, but not between serine and glutamate or alanine. Alteration of the relative concentrations of the three amino acids changed their relative transamination. Similar work was performed with intact oat (Avena sativa L.) leaf peroxisomes. At 1 millimolar of each of the three amino acids in combination, the relative serine, glutamate, and alanine transamination was roughly 60, 23, and 17%, respectively. Similarly, alteration of the relative concentration of the three amino acids changed their relative transamination. The contents of the three amino acids in leaf extracts were analyzed, and the relative contribution of the three amino acids in glycine production in photorespiration was assessed and discussed.

Journal Article↗

PubMed1983

Metabolism of glycolate and glyoxylate in intact spinach leaf peroxisomes.

Intact and broken (osmotically disrupted) spinach (Spinacia oleracea) leaf peroxisomes were compared for their enzymic activities on various metabolites in 0.25 molar sucrose solution. Both intact and broken peroxisomes had similar glycolate-dependent o(2) uptake activity. In the conversion of glycolate to glycine in the presence of serine, intact peroxisomes had twice the activity of broken peroxisomes at low glycolate concentrations, and this difference was largely eliminated at saturating glycolate concentrations. However, when glutamate was used instead of serine as the amino group donor, broken peroxisomes had slightly higher activity than intact peroxisomes. In the conversion of glyoxylate to glycine in the presence of serine, intact peroxisomes had only about 50% of the activity of broken peroxisomes at low glyoxylate concentrations, and this difference was largely overcome at saturating glyoxylate concentrations. In the transamination between alanine and hydroxypyruvate, intact peroxisomes had an activity only slightly lower than that of broken peroxisomes. In the oxidation of NADH in the presence of hydroxypyruvate, intact peroxisomes were largely devoid of activity. These results suggest that the peroxisomal membrane does not impose an entry barrier to glycolate, serine, and O(2) for matrix enzyme activity; such a barrier does exist to glutamate, alanine, hydroxypyruvate, glyoxylate, and NADH. Furthermore, in intact peroxisomes, glyoxylate generated by glycolate oxidase is channeled directly to glyoxylate aminotransferase for a more efficient glycolate-glycine conversion. In related studies, application of in vitro osmotic stress to intact or broken peroxisomes had little effect on their ability to metabolize glycolate to glycine.

Journal Article↗

PubMed1982

Isolation of spinach leaf peroxisomes in 0.25 molar sucrose solution by percoll density gradient centrifugation.

A procedure for isolating spinach (Spinacia oleracea L.) leaf peroxisomes in 0.25 molar sucrose solution by Percoll density gradient centrifugation followed by removal of the Percoll by washing and centrifugation was established. The preparation contains more than 90% peroxisomes as intact organelles with no detectable chlorophyll or cytochrome oxidase contamination. The peroxisomes are stable at 0 to 4 degrees C or 25 degrees C for at least 2 hours.

Journal Article↗

PubMed1982

The structural analysis of hemoglobin Handsworth.

The present paper describes the structural analysis of an abnormal hemoglobin variant of alpha-chain found in a Chinese woman in the Hechi district of the Zhuang Autonomous Region of Guangxi, and finds it to be hemoglobin Handsworth (alpha 18(A16) Gly leads to Arg).

Amino Acid Sequence↗

PubMedDate not supplied

Laparoscopic radical trachelectomy or parametrectomy and pelvic and para-aortic lymphadenectomy for cervical or vaginal stump carcinoma: report of six cases.

The aim of this study was to investigate the feasibility and safety of laparoscopic radical parametrectomy and pelvic and para-aortic lymphadenectomy after previous supracervical or extrafascial hysterectomy. This is a prospective study of six patients with vaginal or cervical stump carcinoma after previous supracervical or extrafascial hysterectomy. The technique of radical parametrectomy with pelvic and para-aortic lymphadenectomy as used for open surgical cases for years was performed laparoscopically. The average operating time was 180 min, the estimated average blood loss was 220 mL, and the duration of hospitalization was 11.8 days. There was no intraoperative or postoperative complication. Laparoscopic radical parametrectomy with pelvic and para-aortic lymphadenectomy for cervical or vaginal stump carcinoma can be successfully and safely accomplished.

Adult↗

PubMedDate not supplied

Source continuity and boundary discontinuity considerations in Bayesian image processing.

This paper extends the Bayesian image processing (BIP) formalism by considering the effect of simple source continuity and boundary discontinuity and a priori information in estimating an optimal source distribution from observed data. The a priori source information is formulated in terms of probability density functions of source element strengths and spatial correlations. The estimation is carried out iteratively by a BIP algorithm derived by applying the expectation maximization technique to the a priori source probability density functions and assuming the data obey Poisson statistics. The suppression of boundary oscillations and enhancement of overall image are demonstrated for computer generated ideal and Poisson randomized data.

Algorithms↗

PubMedDate not supplied

Simultaneous reconstruction, segmentation, and edge enhancement of relatively piecewise continuous images with intensity-level information.

A multinomial image model is proposed which uses intensity-level information for reconstruction of contiguous image regions. The intensity-level information assumes that image intensities are relatively constant within contiguous regions over the image-pixel array and that intensity levels of these regions are determined either empirically or theoretically by information criteria. These conditions may be valid, for example, for cardiac blood-pool imaging, where the intensity levels (or radionuclide activities) of myocardium, blood-pool, and background regions are distinct and the activities within each region of muscle, blood, or background are relatively uniform. To test the model, a mathematical phantom over a 64 x 64 array was constructed. The phantom had three contiguous regions. Each region had a different intensity level. Measurements from the phantom were simulated using an emission-tomography geometry. Fifty projections were generated over 180 degrees, with 64 equally spaced parallel rays per projection. Projection data were randomized to contain Poisson noise. Image reconstructions were performed using an iterative maximum a posteriori probability procedure. The contiguous regions corresponding to the three intensity levels were automatically segmented. Simultaneously, the edges of the regions were sharpened. Noise in the reconstructed images was significantly suppressed. Convergence of the iterative procedure to the phantom was observed. Compared with maximum likelihood and filtered-backprojection approaches, the results obtained using the maximum a posteriori probability with the intensity-level information demonstrated qualitative and quantitative improvement in localizing the regions of varying intensities.

Algorithms↗

PubMedDate not supplied

Compensation for attenuation, scatter, and detector response in SPECT reconstruction via iterative FBP methods.

Iterative filtered backprojection (FBP) reconstruction is a fast method for single photon emission computed tomography (SPECT) that can provide simultaneous compensation for nonuniform attenuation, scatter, and distance-dependent detector response. The iterative FBP method was applied to the reconstruction of SPECT images of a chest phantom consisting of nonuniform attenuating media. One hundred twenty projections containing 20 million counts were reconstructed on an image array of 128 x 128 x 64. The accuracy of reconstruction was significantly improved, in terms of concentration ratio, object shape, and noise reduction. Results of this experimental study indicate that interactive FBP can effectively reconstruct SPECT images, while other iterative methods, such as maximum a posteriori probability (MAP), will spend at least ten times more computing effort in the reconstruction on the same computer. The disadvantage of iterative FBP is its inability to model the noise properties of data collection accurately, as compared to the MAP methods.

Algorithms↗

PubMedDate not supplied

Identification of IgG and Fc-binding proteins in human seminal plasma and sperm.

Human seminal plasma contains two novel soluble proteins capable of binding IgG and Fc, but not Fab. The IgG- and Fc-binding proteins were identified by immunoblotting using IgG of various species, Fc and Fab fragments. Their estimated molecular sizes are 16-kD and 20-kD. The monoclonal antibody (MAb), Leu 11b, raised against Fc gamma RIII interacts with the 16-kD protein, whereas other mAbs (32.2, IV.3, and 3G8) raised against FcR did not. The 16-kD protein is capable of binding IgG of several species (human, mouse, rabbits, and goat), whereas the 20-kD protein interacted only with human IgG-Fc fragment. The 16-kD IgG and the 20-kD Fc-binding proteins were found in the PBS extract of human sperm. Human seminal plasma/sperm contain an IgG- and a Fc-binding protein with estimated Mr of 16 and 20 kD, respectively.

Antibodies, Monoclonal↗

PubMedDate not supplied

Transmission electron microscopic study of the hemorrhagic spots in patients with epidemic hemorrhagic fever in the early stage.

Epidemic hemorrhagic fever (EHF) virus particles were found in the squamous epithelial cells and the capillary endothelial cells of the petechial spots located on the mucous membrane of the soft palate in 3 patients with severe early-stage EHF with transmission electron microscopy. The virus particles were round or oval in shape, about 100 nm in diameter, with a two-layer lipid envelope from which spikes were protruding. The nucleocapsid of the virus appeared to be hollow microfilamentoid or dense granules. Meanwhile, budding virus particles with a diameter of 80 nm were found in the enlarged Golgi apparatus. The infected cells displayed an enlarged and proliferating Golgi apparatus. The morphological characteristics of the viron mentioned above coincided with those of the virus particles of the family Bunyaviridae. This study is the first to demonstrate that the squamous epithelial cells on the mucous membrane of the soft palate are the target cells of EHF infection and to provide subcellular morphological evidence of petechial hemorrhage at the soft palate.

Adult↗