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Biomedical subjects

H Liu

Publications and source records attributed to H Liu.

At least 109 records · Page 6Linked to original sources
PubMed2003

Measurement and analysis of brain deformation during neurosurgery.

Recent studies have shown that the surface of the brain is deformed by up to 20 mm after the skull is opened during neurosurgery, which could lead to substantial error in commercial image-guided surgery systems. We quantitatively analyze the intraoperative brain deformation of 24 subjects to investigate whether simple rules can describe or predict the deformation. Interventional magnetic resonance images acquired at the start and end of the procedure are registered nonrigidly to obtain deformation values throughout the brain. Deformation patterns are investigated quantitatively with respect to the location and magnitude of deformation, and to the distribution and principal direction of the displacements. We also measure the volume change of the lateral ventricles by manual segmentation. Our study indicates that brain shift occurs predominantly in the hemisphere ipsi-lateral to the craniotomy, and that there is more brain deformation during resection procedures than during biopsy or functional procedures. However, the brain deformation patterns are extremely complex in this group of subjects. This paper quantitatively demonstrates that brain deformation occurs not only at the surface, but also in deeper brain structure, and that the principal direction of displacement does not always correspond with the direction of gravity. Therefore, simple computational algorithms that utilize limited intraoperative information (e.g., brain surface shift) will not always accurately predict brain deformation at the lesion.

Adult↗
PubMed2003

Increasing relative prevalence of HSV-2 infection among men with genital ulcers from a mining community in South Africa.

OBJECTIVES: To determine the aetiology of genital ulcer disease (GUD) and its association with HIV infection in the mining community of Carletonville, South Africa, from two cross sectional surveys of consecutive men presenting with genital lesions during October 1993 to January 1994 and July to November 1998. METHODS: A multiplex polymerase chain reaction (M-PCR) assay combined with amplicon detection was used to identify DNA specific sequences of Treponema pallidum, herpes simplex virus (HSV), and Haemophilus ducreyi. A real time PCR assay was used to differentiate between HSV-1 and HSV-2. RESULTS: M-PCR detected T pallidum, HSV, and H ducreyi in 10.3%, 17.2%, and 69.4% of 232 GUD patients during 1993-4 and in 12.4%, 36.0%, and 50.5% of 186 GUD patients in 1998. The proportion of patients with more than one agent increased significantly from 7.3% (17/232) in 1993-4 to 16.7% (31/186) in 1998 (p <0.01). HSV-2 was detected in a higher proportion of ulcer specimens from HIV infected patients than in specimens from HIV uninfected patients during both time periods (1993-4: 26.2% v 6.7%, p <0.001; 1998: 42.1% v 29.6%, p >0.09). CONCLUSIONS: Based on two cross sectional surveys, 4 years apart, chancroid remained the leading cause of GUD in men who presented at the STD clinic with genital ulcers in the mining community of Carletonville, South Africa. The relative prevalence of primary syphilis has remained low. However, HSV-2 has emerged as a more significant cause of GUD and the proportion of GUD patients infected with more than one agent also increased significantly. HSV-2 DNA was detected in a significantly higher proportion of ulcer specimens from HIV positive patients than from HIV negative patients. No association was found between HIV infection status and the relative prevalence of chancroid or syphilis.

Adult↗
PubMed2003

Do STD clinics correctly diagnose STDs? An assessment of STD management in Hefei, China.

The main purposes of the study were to assess the accuracy of laboratory testing and the diagnosis by physicians in sexually transmitted disease (STD) clinics in Hefei, China. Among 347 men complaining of urethral discharge or dysuria, 240 tested positive at the National Centre for either Neisseria gonorrhoeae or Chlamydia trachomatis, 310 tested positive according to the clinic laboratories, and 347 were diagnosed by the physicians. For chlamydia, the sensitivity and positive predictive value (PPV) of the clinic laboratories were 55% and 26%, and for the diagnosis by the physicians were 61% and 24%. Laboratory testing and the diagnosis by the physicians had low power to detect mixed infection. The PPVs for the diagnosis by the physicians were 50% for syphilis and 43% for herpes simplex virus (HSV), indicating that both syphilis and HSV were over-diagnosed. Over half of those previously infected had not received education to prevent reinfection. Thus, the quality of clinic laboratory testing was not high and physicians often misdiagnosed STDs.

Adolescent↗
PubMed2003

Hydrogen production from wastewater by acidogenic granular sludge.

Sludge was granulated in a hydrogen-producing acidogenic reactor when operated at 26 degrees C, pH 5.5 treating a sucrose-rich wastewater. The influence of hydraulic retention time (HRT) and sucrose concentration on hydrogen production by the acidogenic granular sludge was investigated at a constant loading rate of 25 g-sucrose/(l x day). Results show that the gas composition was not greatly influenced by HRT or sucrose concentration. The hydrogen accounted for 57% to 68% of the biogas at HRT ranging 4.6-28.6 h and sucrose concentration ranging 4,800-29,800 mg/l. However, the hydrogen yield was more dependent on HRT and sucrose concentration. It ranged from 0.19 to 0.27 l/g-sucrose with the maximum yield occurring at HRT 13.7 h and sucrose concentration 14,300 mg/l in the wastewater. The acidified effluent was composed of volatile fatty acids and alcohols. The predominant products were butyrate (59-68%) and acetate (10-25%), plus smaller amounts of i-butyrate, valerate, i-valerate, caproate, methanol, ethanol, propanol, and butanol. The sludge yield averaged 0.2 g-VSS/g-sucrose. The carbon balance was 98-107% throughout the study.

Bacteria, Anaerobic↗
PubMed2002

Longitudinal flow of protons from (2-8)A GeV central Au+Au collisions.

Rapidity distributions of protons from central 197Au+197Au collisions measured by the E895 Collaboration in the energy range from (2-8)A GeV at the Brookhaven AGS are presented. Longitudinal flow parameters derived using a thermal model including collective longitudinal expansion are extracted from these distributions. The results show an approximately linear increase in the longitudinal flow velocity, (L), as a function of the logarithm of beam energy.

Journal Article↗
PubMed2002

Different excitation and reception distributions with a single-loop transmit-receive surface coil near a head-sized spherical phantom at 300 MHz.

Calculations and experiments were used to examine the B(1) field behavior and signal intensity distribution in a 16-cm diameter spherical phantom excited by a 10-cm diameter surface coil at 300 MHz. In this simple system at this high frequency very complex RF field behavior exists, resulting in different excitation and reception distributions. Included in this work is a straightforward demonstration that coil receptivity is proportional to the magnitude of the circularly polarized component of the B(1) field that rotates in the direction opposite to that of nuclear precession. It is clearly apparent that even in very simple systems in head-sized samples at this frequency it is important to consider the separate excitation and reception distributions in order to understand the signal intensity distribution.

Head↗
PubMed2002

Diffusion-weighted MR imaging findings in carbon monoxide poisoning.

Diffusion-weighted MR imaging (DWI) of two patients with carbon monoxide (CO) poisoning demonstrated white matter and cortical hyperintensities. In one patient, the changes on the FLAIR sequence were more subtle than those on DWI. The DWI abnormality in this patient represented true restriction. In the second patient, repeated exposure to CO caused restricted diffusion. DWI may be helpful for earlier identification of the changes of acute CO poisoning.

Acute Disease↗
PubMed2002

Microbial diversity of a mesophilic hydrogen-producing sludge.

A hydrogen-producing sludge degraded 99% of glucose at 36 degrees C and pH 5.5, producing a methane-free biogas (comprising 64% hydrogen) and an effluent comprising mostly butyrate, acetate, and ethanol. The yield was 0.26 l H2 g(-1) glucose and the production rate per gram of volatile suspended solids was 4.6 1 H2 day(-1). A 16S rDNA library was constructed from the sludge for microbial species determination. A total of 96 clones were selected for plasmids recovery, screened by denaturing gradient gel electrophoresis, and sequenced for rDNA. Based on the phylogenetic analysis of the rDNA sequences, 64.6% of all the clones were affiliated with three Clostridium species (Clostridiaceae), 18.8% with Enterobacteriaceae, and 3.1% with Streptococcus bovis (Streptococcaceae). The remaining 13.5% belonged to eight operational taxonomic units, the affiliations of which were not identified.

Bacteria↗
PubMed2002

Targeted beta-globin gene conversion in human hematopoietic CD34(+ )and Lin(-)CD38(-)cells.

Chimeric oligonucleotides have been used successfully to correct point and frameshift mutations in several cell types, as well as in animal and plant models. However, their application to primitive human blood cells has been limited. In this investigation, chimeric oligonucleotides designed to direct a site-specific nucleotide exchange in the human beta-globin gene (an A to T substitution within codon 6) were introduced into normal human CD34(+) and Lin(-)CD38(-) cells via microinjection. This A to T nucleotide exchange introduces the single site mutation responsible for sickle cell anemia. In 23% of experimental samples, gene conversion was detected in the progeny of microinjected CD34(+) and Lin(-)CD38(-) cells that were cultured for at least 4 weeks. In addition, gene conversion was detected in the erythroid progeny of Lin(-)CD38(-) cells at the mRNA level. Conversion rates as high as 10-15% in 11% (five of 44) of experimental samples were confirmed by allele-specific PCR and sequence analysis of genomic DNA from the progeny of microinjected Lin(-)CD38(-) cells. Given that as few as 10% normal hematopoietic cells are sufficient to keep patients free of sickle cell disease, the level of conversion we have achieved in some samples may well be of therapeutic benefit in patients with sickle cell disease.

ADP-ribosyl Cyclase↗
PubMed2002

Accelerating flap maturation by vascular endothelium growth factorin a rat tube flap model.

The effect of exogenous vascular endothelium growth factor (VEGF) on the survival of the distal skin paddle with early pedicle division was studied in a rat tubed pedicle flap model. In part I, tubed pedicle skin flaps were created on the backs of 14 rats. The pedicle was divided after an interval of 3, 4, 5 or 7 days, and the survival area of each distal skin paddle was measured 5 days after the pedicle was divided. The percentages of survival were 0, 24.9%, 89.9% and 100%, respectively. In part II, tube flaps were created in 20 rats. In the experimental group, 2 ml of VEGF (50 microg ml(-1)) was injected into the recipient bed during tube flap creation in each rat. In the control group, 2 ml of saline was given. The tubed pedicle was divided 4 days after creation. The mean survival area of the distal skin paddle in the group treated with VEGF was 7.32 +/- 1.36 cm(2) (80.91%) at 5 days after pedicle division, which was of statistical significance when compared with the survival in the control group of 2.70 +/- 1.89 cm(2) (27.9%). The histology showed angiogenesis at the skin paddle-recipient bed interface following VEGF injection. These results demonstrate that the subcutaneous administration of VEGF into the recipient bed of the tube flap transfer can induce angiogenes is at the junction between the donor and the recipient bed, and improve skin paddle survival with early pedicle division.

Analysis of Variance↗
PubMed2002

Molecular typing of Treponema pallidum in South Africa: cross-sectional studies.

We evaluated a molecular subtyping system for Treponema pallidum for its ability to differentiate between strains obtained from male patients with primary syphilis in South Africa. Of 201 T. pallidum-positive specimens, 161 were typeable, revealing 35 subtypes. The unique subtypes identified in Durban, Cape Town, and Carletonville and the total number of subtypes suggested that the strain population was very diverse and varied geographically.

Bacterial Typing Techniques↗
PubMed2002

A 3D unsteady flow analysis in a doubly constricted arterial vessel.

The aim of this study is to examine the interaction between two mild atherosclerotic proliferations spaced apart by a distance S by analyzing their influence on flow structure, pressure drop and stress field in an arterial vessel under pulsatile flow conditions. This has been achieved numerically by employing a time accurate, cell centered finite volume method in solving the Navier-Stokes equations governing the 3D unsteady flow dynamics in a conceptual model of an multiply constricted arterial vessel. In comparison to the pressure drop across a single stenosis, nearly a 50% increase in the late systolic and early diastolic pressure drops has been observed across the two mild constrictions when they are spaced within a distance of S<or=4. When S<or=4, more than a 25% reduction in the peak systolic wall shear stress (WSS) on the downstream constriction is noted.

Arteries↗
PubMed2001

The BCL11 gene family: involvement of BCL11A in lymphoid malignancies.

Many malignancies of mature B cells are characterized by chromosomal translocations involving the immunoglobulin heavy chain (IGH) locus on chromosome 14q32.3 and result in deregulated expression of the translocated oncogene. t(2;14)(p13;q32.3) is a rare event in B-cell malignancies. In contrast, gains and amplifications of the same region of chromosome 2p13 have been reported in 20% of extranodal B-cell non-Hodgkin lymphomas (B-NHL), in follicular and mediastinal B-NHL, and in Hodgkin disease (HD). It has been suggested that REL, an NF-kappaB gene family member, mapping within the amplified region, is the pathologic target. However, by molecular cloning of t(2;14)(p13;q32.3) from 3 cases of aggressive B-cell chronic lymphocytic leukemia (CLL)/immunocytoma, this study has shown clustered breakpoints on chromosome 2p13 immediately upstream of a CpG island located about 300 kb telomeric of REL. This CpG island was associated with a Krüppel zinc finger gene (BCL11A), which is normally expressed at high levels only in fetal brain and in germinal center B-cells. There were 3 major RNA isoforms of BCL11A, differing in the number of carboxy-terminal zinc fingers. All 3 RNA isoforms were deregulated as a consequence of t(2;14)(p13;q32.3). BCL11A was highly conserved, being 95% identical to mouse, chicken, and Xenopus homologues. BCL11A was also highly homologous to another gene (BCL11B) on chromosome 14q32.1. BCL11A coamplified with REL in B-NHL cases and HD lymphoma cell lines with gains and amplifications of 2p13, suggesting that BCL11A may be involved in lymphoid malignancies through either chromosomal translocation or amplification.

Amino Acid Sequence↗
PubMed2001

An intramolecular quadruplex of (GGA)(4) triplet repeat DNA with a G:G:G:G tetrad and a G(:A):G(:A):G(:A):G heptad, and its dimeric interaction.

The structure of d(GGAGGAGGAGGA) containing four tandem repeats of a GGA triplet sequence has been determined under physiological K(+) conditions. d(GGAGGAGGAGGA) folds into an intramolecular quadruplex composed of a G:G:G:G tetrad and a G(:A):G(:A):G(:A):G heptad. Four G-G segments of d(GGAGGAGGAGGA) are aligned parallel with each other due to six successive turns of the main chain at each of the GGA and GAGG segments. Two quadruplexes form a dimer stabilized through a stacking interaction between the heptads of the two quadruplexes. Comparison of the structure of d(GGAGGAGGAGGA) with the reported structure of d(GGAGGAN) (N=G or T) containing two tandem repeats of the GGA triplet revealed that although the two structures resemble each other to some extent, the extension of the repeats of the GGA triplet leads to distinct structural differences: intramolecular quadruplex for 12-mer versus intermolecular quadruplex for 7-mer; heptad versus hexad in the quadruplex; and three sheared G:A base-pairs versus two sheared G:A base-pairs plus one A:A base-pair per quadruplex. It was also suggested that d(GGAGGAGGAGGA) forms a similar quadruplex under low salt concentration conditions. This is in contrast to the case of d(GGAGGAN) (N=G or T), which forms a duplex under low salt concentration conditions. On the basis of these results, the structure of naturally occurring GGA triplet repeat DNA is discussed.

Base Pairing↗