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Biomedical subjects

H H Liu

Publications and source records attributed to H H Liu.

At least 55 records · Page 3Linked to original sources
PubMed1997

A dual source photon beam model used in convolution/superposition dose calculations for clinical megavoltage x-ray beams.

A realistic model of photon beams generated by clinical linear accelerators has been incorporated in a convolution/superposition method to compute dose distributions in photon treatment fields. In this beam model, a primary photon source represents photons directly from the target, and an extra-focal photon source represents scattered photons from the primary collimator and the flattening filter. Monte Carlo simulation was used to study clinical linear accelerators producing photon beams. From the output of the Monte Carlo simulation, the fluence and spectral distributions of each photon component, as well as the geometrical characteristics of each photon source with respect to its distance to the isocenter and its source distribution, were analyzed. These quantities were used to reproduce realistic photon distributions in treatment fields, and thus to compute dose distributions using the convolution method. Our results showed that compared to the primary photon fluence, the extra-focal photon fluence from the primary collimator and the flattening filter was 11%-16% at the isocenter, among which 70% was contributed by the flattening filter. The variation of extra-focal photons in different treatment fields was predicted accurately by accounting for the finite size of the extra-focal source. Compared to measurements, dose distributions in photon treatment fields, including those of asymmetric jaw settings and at different SSDs were calculated accurately, particularly in the penumbral region, by using the convolution method with the new dual source photon beam model.

Computer Simulation↗
PubMed1997

Calculating output factors for photon beam radiotherapy using a convolution/superposition method based on a dual source photon beam model.

A realistic photon beam model based on Monte Carlo simulation of clinical linear accelerators was implemented in a convolution/superposition dose calculation algorithm. A primary and an extra-focal sources were used in this beam model to represent the direct photons from the target and the scattered photons from other head structures, respectively. The effect of the finite size of the extra-focal source was modeled by a convolution of the source fluence distribution with the collimator aperture function. Relative photon output in air (Sc) and in phantom (Scp) were computed using the convolution method with this new photon beam model. Our results showed that in a 10 MV photon beam, the Sc, Sp (phantom scatter factor), and Scp factors increased by 11%, 10%, and 22%, respectively, as the field size changed from 3 x 3 cm2 to 40 x 40 cm2. The variation of the Sc factor was contributed mostly by an increase of the extra-focal radiation with field size. The radiation backscattered into the monitor chamber inside the accelerator head affected the Sc by about 2% in the same field range. The output factors in elongated fields, asymmetric fields, and blocked fields were also investigated in this study. Our results showed that if the effect of the backscattered radiation was taken into account, output factors in these treatment fields can be predicted accurately by our convolution algorithm using the dual source photon beam model.

Computer Simulation↗
PubMed1997

Involvement of interleukin-1 receptor mechanisms in development of arterial hypotension in rat heatstroke.

Rats, under urethan anesthesia, were exposed to a high ambient temperature (42 degrees C) to induce heatstroke and to assess the hemodynamic changes associated with heatstroke. Compared with normothermic controls, rats with heatstroke showed higher values of colonic temperature, heart rate, and plasma levels of interleukin (IL)-1 but lower values of R wave amplitude, P-R and Q-T intervals, systolic wave amplitude, diastolic and dicrotic wave duration, mean arterial pressure, stroke volume, and cardiac output. Animals injected intravenously with an IL-1-receptor antagonist at the time of heatstroke induction were protected from some of the cardiovascular effects of heatstroke, such as depressed ventricular depolarization, decreased stroke volume, decreased cardiac output, and arterial hypotension. The hemodynamic changes associated with heatstroke could be mimicked by IL-1beta administration. Other cardiovascular parameters such as total peripheral vascular resistance were unaffected by heatstroke induction or IL-1beta treatment. The results indicate that a selective decline in stroke volume or ventricular depolarization resulting from increased plasma levels of IL-1 may be an important mechanism signaling arterial hypotension or circulatory failure in rat heatstroke.

Animals↗
PubMed1996

[McNamara cephalometric analysis for Shanghai adolescents and adults]

This paper collects 101 Shanghai adolescents and adults with normal occlusion and balance facial profile.Using McNamara cephalometric analysis,it develops linear cephalometric standards for Shanghai adolescents and adults.By mean of SAS statistic software package,the characteristics of craniofacial linear parameters were observed.

Journal Article↗
PubMed1996

[Expression of cDNA of human chorionic gonadotropin beta-subunit (beta-hCG) cDNA in insect cells and effect of expressed product on mouse lymphocytes in vitro].

Expression vector pVL 1393-hCG beta containing beta-hCG cDNA has been constructed using an unfused protein nuclear polyhedrosis virus (AcNPV) expression vector. The insect cells (Sf 9) were cotransfected by the expression vector and nuclear polyhedrosis virus genomic DNA, and recombinant virus AcNPV-hCG beta was screened out, beta-hCG cDNA was expressed in insect cells infected by recombinant virus and recombinant beta-hCG (r beta-hCG) was secreted into medium. The purity of r beta-hCG, purified by immuno-affinity chromatography, was about 90% and the molecular weight of r beta-hCG was 22,500 Da. Like hCG, r beta-hCG suppressed significantly proliferation of induced lymphocytes, as well as production of IL-2 to some extent, on a parallel with suppression of lymphoproliferation.

Animals↗
PubMed1995

Improved gene expression by a modified bicistronic retroviral vector.

We have previously described the construction of a bicistronic retroviral vector using the picornavirus internal ribosome entry site (IRES), which allows two genes expression simultaneously from a single transcript. This vector transcribes RNA efficiently; however, in some cases the levels of protein production are low. In this report, we further modified the bicistronic vector by abolishing the functional viral gag initiation codon that is retained in the vector at 5' to the first initiation codon of transduced gene. Five different genes, human interleukin 2 (hIL-2), human interleukin 4 (hIL-4), human granulocyte macrophage stimulating factor (hGM-CSF), herpes simplex virus thymidine kinase (HSV-tk) gene, and hepatitis C virus (HCV) core gene (C190), were tested on this modified vector for gene transfer and expression. Our results demonstrated that the new bicistronic vector greatly increased the protein levels when compared with the original one. As the RNA levels and splicing patterns from these two vectors remained similar, the improvement was most likely resulted from the increased translational efficiency.

Animals↗
PubMed1995

Breast dose during electron-beam CT: measurement with film dosimetry.

PURPOSE: To measure the breast dose and dose distribution from examinations performed with electron-beam computed tomography (CT). MATERIALS AND METHODS: Radiographic film was placed bilaterally at three depths in the breasts of an anthropomorphic phantom and exposed with clinically relevant protocols. The average breast dose and the dose distribution were obtained from the digitized and calibrated film and compared with those obtained with conventional CT. RESULTS: Breast doses from electron-beam CT chest, coronary artery calcium, and cardiac function examinations were 21.9, 2.87, and 1.55 mGy, respectively. Within the breast, the dose decreased linearly by a factor of three from the axilla to the sternum. The breast dose from a conventional CT chest examination ranged from 18 to 33 mGy and did not vary substantially across the breast. CONCLUSION: For chest examinations, the average breast dose from an electron-beam CT scanner was comparable to that from conventional CT scanners, despite the differences in dose distribution.

Breast↗
PubMed1995

[The application of Edgewise technique auxillary with extra oral anchorage and class III elastic in the treatment of bimaxillary protrusion.].

In the treatment of growing bimaxillary protrusion patients,Edgewise technique auxillary with extra oral anchorage and class III elastic help to improve the patient's chin shape,recover his beauty of lower facial part and get a good occlusion along with the growing of mandible.The purpose of this study is:analysis the force system in the treatment and evaluate the result of the treatment with some typical cases.

English Abstract↗
PubMed1995

[Cell-specific expression of AFP gene is dependent on some nuclear proteins].

AFP is an oncodevelopmental protein. Its level decreases abruptly after birth and reaches almost undetectable level during normal adult life. However, reexpression of the gene can be observed during hepatocarcinogenesis. To further understand mechanism of regulating AFP expression, we checked several restriction enzyme map of 5' terminal and flanking sequences of AFP gene. There are no differences among adult rat liver, fetal liver and hepatoma cells. Using +2(-)-255 bp sequence probe of AFP gene to do southwestern blotting assay, the result showed that the gene-active cells, such as hepatoma cells, contained binding-proteins which were apparently lacking in adult rat liver, lung, spleen, heart and kidney cells. While the fractions of nuclear proteins from adult rat liver cells were devoid of any stimulatory effect on transcription, those of binding-proteins from hepatoma stimulated the transcription of AFP gene in vitro. The hepatoma binding-proteins can rescue transcription activity of fraction of nuclear proteins from adult rat liver cells. These results indicate that cell-specific expression of AFP gene is regulated by protein-factors.

Animals↗
PubMed1995

[Cloning and overexpression of rat ovary LH/hCG receptor cDNA in insect cells].

Luteinizing hormone/human chorionic gonadotropin receptor (LH/hCG receptor) is a glycosylated protein coupled with G-protein. This paper reports screening of LH/hCG receptor cDNA from rat ovary cDNA library and the overexpression of the cDNA in insect cells. Full length of LH/hCG receptor cDNA is 2403 bp encoding signal peptide and matured protein of LH/hCG receptor. The cDNA is overexpressed in insect cells using baculovirus expression vector pVL 1393. The apparent molecular weight of purified receptor using immunoaffinity chromatography is 120 Kd and 92 Kd under non-reducing and reducing conditions, respectively. Ligand binding assay and Scatchard Plot analysis indicates that Kd is 8.4 x 10(-9) mol/L which is similar to that of the purified receptor from CHO cells.

Animals↗
PubMed1995

[Expression of the extracellular domain (1-341) of rat ovarian lutropin receptor in insect cells and preliminary characterization of the expressed product].

Extracellular domain residues 1-341 (designed R 341) of luteinizing hormone/human chorionic gonadotropin receptor (LH/hCG receptor) has high binding affinity for ligand. This paper describes expression of cDNA coding for R 341 in insect cells and preliminary identification of the expressed protein. SDS-PAGE silver staining and immunoblotting analysis show expressed product appears in two bands, major band has molecular weight 38.5 Kd, and weak band, 40.0 Kd. Ligand binding immunoblotting and 125I-hCG-binding blotting analysis indicate that expressed product R 341 has specific binding affinity for ligand. Ligand binding assay and Scatchard analysis indicate that recombinant receptor R 341 has high binding affinity for hCG and Kd is 5.68 x 10(-10) mol/L.

Animals↗
PubMed1995

Cracked teeth--treatment rationale and case management: case reports.

The treatment rationale for, and successful management of, six teeth with cracks in the form of incomplete vertical fractures are reported. Further crack propagation was prevented by placement of either stainless steel orthodontic bands or aluminum or acrylic resin provisional crowns, and endodontic treatment was subsequently carried out. The teeth were restored with intraradicular amalgam cores and complete veneer crowns. The teeth were reexamined periodically for up to 3.5 years after treatment. During the period of review, all teeth remained asymptomatic.

Adult↗
PubMed1993

Infections due to penicillin-resistant pneumococci. Clinical, epidemiologic, and microbiologic features.

Pneumococcal infection remains a common cause of serious morbidity and mortality throughout the world. Until recently, clinical isolates of pneumococci that were penicillin resistant were rare. However, 4% to 5% of the clinical isolates in the United States were recently found to be either intermediately resistant or highly resistant to penicillin. Clinicians in every field of medicine must therefore be better informed regarding penicillin-resistant pneumococcal infections to minimize their attendant morbidity and mortality and increase compliance with preventive measures. We reviewed the molecular, genetic, and epidemiologic aspects of penicillin-resistant pneumococcal infections, with emphasis on their microbiologic and clinical features.

Adult↗