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Biomedical subjects

T W Chan

Publications and source records attributed to T W Chan.

At least 37 records · Page 2Linked to original sources
PubMed1995

The knowledge and attitude of Hong Kong secondary school teachers and students towards HIV infection and dentistry.

Although human immunodeficiency virus (HIV) infection and acquired immune deficiency syndrome (AIDS) are firmly entrenched in Hong Kong no data are available on the knowledge and attitudes of Hong Kong secondary school teachers and teenage children towards this infection, and their perception of infection control measures currently undertaken by the dental profession to prevent such infectious diseases. Hence a postal questionnaire survey of a total of 2,886 teenagers and 372 school teachers of 21 secondary schools in Hong Kong was conducted. The questionnaire comprised a total of 13 questions divided into two categories; the first, aimed at assessing the respondents' general knowledge and attitudes towards AIDS, and the second related to AIDS, dentistry and infection control. More than half of the students and one quarter of the teachers surmised that HIV infection is equivalent to developing AIDS. Although the great majority of the respondents (85-97 per cent) were aware that HIV can not be transmitted through sharing combs and meals, one in two teachers and one in three students thought that the virus could be transmitted through saliva. A large majority of respondents believed television to be the most, and dentists the least, informative source on AIDS out of a list of eight options. Approximately one half of both groups were concerned about contracting HIV infection during dental treatment and 65 per cent of students and 57 per cent of teachers thought that dentists did not have sufficient knowledge to identify AIDS patients. Finally, more than three quarters of the respondents thought that it would be ill-advised to visit a dentist treating HIV-infected patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Acquired Immunodeficiency Syndrome↗
PubMed1993

The relationship between parenting stress and social support in mothers of children with learning disabilities: a Chinese experience.

This study examined the relationship between parenting stress and social support in a random sample of 100 mothers with children at a school for children with learning disabilities, and a control group of 75 mothers with similarly aged non-handicapped children. Mothers of children at Zhi Ling school were found to have significantly more stress and significantly less support than those in the control group. Parenting stress in the control group was also found to be relatively high when compared with what are considered to be normal levels in the West. No significant correlation was found between total parenting stress and social support. It is suggested that further studies need to differentiate between satisfaction with support that is actually received and the perceived quality of available support.

Adult↗
PubMed1993

Selective MR imaging of silicone with the three-point Dixon technique.

Selective magnetic resonance (MR) imaging of silicone with the three-point Dixon technique was evaluated. This technique, which conventionally allows separation of lipid and water signals, was modified to allow calculation of a silicone-only image and a lipid-water image. Imaging of fat and silicone implant phantoms was performed with a 1.5-T imager and was optimized in vivo in two volunteers who had breast reconstruction or augmentation. Six additional volunteers were then imaged to evaluate selective MR imaging of silicone. With an optimum frequency shift of 105 Hz, a repetition time of 1,000 msec, and an echo time of 28 msec, the modified three-point Dixon technique produced a silicone-only image containing 97.0% +/- 1.0 (standard deviation) of the total silicone signal, 2.6% +/- 0.5 of the fat signal, and 16.6% +/- 6.4 of the water signal. The silicone-fat contrast-to-noise ratio was 47.9 +/- 12.1. This method may be potentially useful in the evaluation of implant-related complications such as rupture.

Breast↗
PubMed1992

Magnetic resonance imaging of abscesses using lipid-coated iron oxide particles.

RATIONALE AND OBJECTIVES: The authors investigated whether iron oxide particles can be used as a magnetic resonance imaging (MRI) contrast agent to image abscesses in a two-stage experimental design. METHODS: Human buffy coat was incubated with iron oxide particles of different sizes and coatings. Smears of the incubation mixture were made on a glass slide and stained for iron. The percentage of iron oxide uptake was determined by counting 100 neutrophils and monocytes and scoring the number of cells that contain iron. Subcutaneous abscesses were created in the flanks of 18 Sprague-Dawley rats by injecting them with 0.1 mL of turpentine. Iron oxide was given intravenously, and the animals were imaged by MRI (1.5 T) 12 to 24 hours later. Different iron oxide coatings and doses were compared. RESULTS: The four different types of coating (constant fragment [Fc] of IgG, bovine serum albumin [BSA], lipid [Ferrosome], and dextran) had an uptake of 72% +/- 5.3%, 61% +/- 6.2%, 30.5% +/- 6.8%, and 5% +/- 2.5%, respectively. Comparison of two particle sizes (mean, 90 versus 35 nm) showed the large particles to have higher uptake (61% +/- 6.2%) compared with the small particles (6% +/- 1.8%) (P less than .001). Post-contrast imaging of the rats showed a hypointense ring around the abscess only in the animals injected with the lipid-coated agent. The effect was discernible within 12 hours after contrast injection and at a dose of 25 mumols iron/kg. Histologic sections showed phagocytic cells with iron granules in the periphery of the abscess. No hypointense ring on MRI or iron granules on histologic sections was seen around the abscess of the control animals or those injected with BSA-iron oxide or Fc-iron oxide. CONCLUSIONS: Lipid-coated iron oxide particles can be used to image abscesses by virtue of their phagocytosis into surrounding inflammatory cells. Positive uptake of these particles by human phagocytes in vitro suggests that similar results may be applicable in humans.

Abscess↗
PubMed1991

MRI appearance of femoral head osteonecrosis following core decompression and bone grafting.

We used magnetic resonance imaging (MRI) to evaluate retrospectively 32 hips with avascular necrosis of the femoral head before and after core decompression and bone grafting. At a median follow-up time of 15 months, 4 of 9 large lesions had undergone femoral head collapse; 2 small lesions had decreased in size; and 14 small, 6 moderate, and 5 large lesions were unchanged. One hip with biopsy-proven avascular necrosis had diffuse marrow edema which resolved after surgery. The signal pattern within the lesions was analyzed in 17 hips. Fifteen lesions were unchanged, while one fat-like lesion became fibrous-like and one edema-like lesion resolved. Analysis of the femoral neck marrow signal in one patient revealed that premature fatty marrow conversion had reverted to hemopoietic marrow 2 years after surgery. Most lesions that appeared stable on MRI were clinically stable or improved. MRI can demonstrated changes in size and signal characteristics as well as femoral head collapse after core decompression and bone grafting. Changes in the surrounding marrow signal, including resolution of marrow edema and reconversion from fatty to hemopoietic marrow, can also be detected.

Adult↗
PubMed1991

Biceps tendon dislocation: evaluation with MR imaging.

The magnetic resonance (MR) images from six patients with biceps tendon dislocation--two in whom it was surgically proved and four in whom it was suspected--were retrospectively evaluated. The dislocated tendon can be identified medial to the bicipital groove, best seen on the axial and oblique coronal and sagittal images. Associated abnormalities of the biceps tendon include thickening (n = 3), high signal intensity (n = 3), and surrounding fluid (n = 4). The factors thought to contribute to dislocation can also be well seen on MR images. These include abnormal shape of the bicipital groove (n = 2), disruption of the coracohumeral ligament (n = 6), disruption (n = 4) and thinning (n = 1) of the subscapularis tendon, and supraspinatus tendon tear (n = 4). Since MR imaging is becoming the modality of choice for the evaluation of shoulder derangements, familiarity with the appearance of biceps tendon dislocation on MR images is important.

Adult↗
PubMed1991

Combined chemical-shift and phase-selective imaging for fat suppression: theory and initial clinical experience.

Incomplete fat suppression with a chemical-shift-selective (CHESS) or phase-selective (Dixon) technique is partially due to the olefinic fat component, which precesses at the same frequency as water. The authors developed a new method of fat suppression--the opposed-fat saturation (OP-ES) sequence--that combines both techniques to obtain superior fat saturation. Fat suppression was verified in phantom studies, which showed that the CHESS portion can eliminate most of the aliphatic fat signal except for a small residual component because of steady state effects and magnetic field imperfections. This residual component is cancelled by the olefinic fat with the phase-selective opposed portion of the sequence. Furthermore, this sequence was superior to another hybrid technique, chopper Dixon in combination with CHESS. When used in 10 healthy volunteers, the OP-FS sequence showed consistently better suppression of the subcutaneous and retroperitoneal fat compared with CHESS alone. Additional advantages for clinical abdominal imaging include its compatibility with respiratory compensation, use of a single excitation, and ease of implementation with gradient-echo imaging. Preliminary application in 10 patients illustrated other potential advantages, including clarification of fat-containing diseases and increasing conspicuity of some lesions.

Adipose Tissue↗
PubMed1991

Rectal carcinoma: staging at MR imaging with endorectal surface coil. Work in progress.

To increase the accuracy of local staging of rectal carcinomas at magnetic resonance (MR) imaging, the authors placed on endorectal coil mounted on a balloon in a position adjacent to the lesion. Use of such a local coil resulted in increased signal-to-noise ratio compared with use of a body coil; higher-resolution images were obtained because the field of view was decreased. The depth of wall invasion by rectal carcinoma was correctly staged with endorectal MR imaging in 11 of 12 patients. In the detection of perirectal adenopathy, use of MR enabled correct identification of positive perirectal nodes in four of seven patients (57%). There were no false-positive diagnoses of perirectal adenopathy at MR. Endorectal MR imaging is an evolving and promising technique for the local staging of rectal carcinomas, but further studies are needed to demonstrate its efficacy.

Female↗
PubMed1991

Differential diagnosis of hepatic neoplasms: spin echo versus gadolinium-diethylenetriaminepentaacetate-enhanced gradient echo imaging.

Early results are reported of hepatic neoplasms studied with dynamic gadolinium-diethylenetriaminepentaacetate (Gd-DTPA)-enhanced magnetic resonance imaging (MRI). The purpose of this study was to evaluate the potential of the Gd enhancement pattern for characterizing these neoplasms and to compare the performance of spin-echo (SE) to SE plus dynamic Gd-enhanced gradient-echo (GRE) pulse sequences. Forty-two patients with hepatic neoplasms were examined at 1.5 T field strength. In each patient, short and long repetition time/echo time (TR/TE) SE images were obtained, followed by pre- and post-Gd-DTPA (0.1 mmol/kg body wt), single-slice, breath-hold (13 s/scan) GRE images, which were serially acquired less than or equal to 12 min postinjection. The patterns of contrast enhancement of the various hepatic lesions were documented and analyzed. The time to peak Gd signal enhancement-to-noise ratio (SE/N), contrast-to-noise ratio (C/N), contrast (defined as the signal intensity ratio [SIR]), as well as the peak values of these quantities, were determined. The C/N and SIR values on the short and long TR/TE SE and pre-Gd GRE images for all hepatic neoplasms were also obtained. The discriminating abilities (hemangiomas vs. malignant neoplasms) of these quantities were analyzed statistically. In addition, the impact of lesion characterization on the SE versus the SE plus the Gd-enhanced GRE scans was assessed by means of a blinded reader study. Malignant hepatic neoplasms could be differentiated from hemangiomas by visual inspection of their enhancement patterns (p = 0.0009), by the time to peak C/N on Gd-enhanced images (p = 0.0002), and by the magnitude of such peak (p = 0.02). Combined SE + Gd-enhanced GRE scans afforded minor, though statistically significant (p less than 0.01), improvement of the accuracy in differentiating benign from malignant hepatic neoplasms. Late scans (12 min post-Gd) may be particularly useful in identifying hemangiomas that, unlike other neoplasms, have a significant high signal of their enhancing portions on such images.

Adult↗
PubMed1988

Formulation of vaccine adjuvant muramyldipeptides (MDP). 1. Characterization of amorphous and crystalline forms of a muramyldipeptide analogue.

A relatively nonhygroscopic crystalline form of the glycopeptide, N-acetylmuramyl-L-alpha-aminobutyryl-D-isoglutamine (I), containing approximately one molecule of water was prepared from amorphous material. The crystalline material, consisting of a mixture of the alpha and beta anomers, exhibited better physical and chemical stability than the lyophilized amorphous material. The alpha/beta-anomer ratios of I in both the crystalline and the amorphous state were approximately equal but different from that in solution.

Acetylmuramyl-Alanyl-Isoglutamine↗
PubMed1986

Glucose regulates its own transport in Ehrlich ascites tumour cells.

The capacity of Ehrlich ascites tumour cells to take up 2-deoxy-D-glucose and to bind cytochalasin B varies adaptatively with the level of glucose in the plasma or culture medium. The effect of glucose is exerted directly on the cells and does not necessarily require the participation of hormones such as insulin, glucagon or corticosterone, although glucagon and the glucocorticoids, but not insulin, can also increase the number of glucose carrier molecules administered in vitro. Cycloheximide suppresses the acute inductive effect of glucose, suggesting that protein synthesis might be required for the increased transport activity.

Animals↗
PubMed1985

Suppression of Ehrlich ascites tumor growth in mice by starvation and streptozotocin-induced diabetes.

Starvation-induced hypoglycaemia and streptozotocin-induced diabetes suppressed the growth of Ehrlich ascites tumor in mice. The suppression of tumor growth by diabetes was alleviated by administration of insulin. The number of glucose carriers on tumour cells was found to be reduced in diabetes and partial resumption of glucose carriers was observed in tumour cells of diabetes after insulin administration. Insulin had no direct effect on tumour growth in vivo and did not affect the number of glucose carriers on tumour cells in vitro. The physiological significance of these observations is discussed.

Animals↗
PubMed1983

Glucose transport in developing Ehrlich ascites tumor cells: parallel changes in the rate of glucose uptake and cytochalasin B binding activity during tumor development and methotrexate treatment.

The ability of Ehrlich ascites tumor cells to take up glucose increased progressively during the course of tumor development. Simultaneously as the rate of uptake rose, the density of a class of glucose-reversible binding sites for cytochalasin B on the cell surface also increased. In its stereospecificity requirement toward competing sugars and in its sensitivity to phloretin and diethylstilbestrol, this class of binding sites resembled the putative glucose carriers identified in various other cell systems and may represent the glucose transporter in Ehrlich ascites cells. Work with methotrexate (MTX) substantiated this view. Methotrexate arrested tumor growth, inhibited glucose uptake, and reduced the number of cytochalasin B binding sites. In both MTX-treated and untreated cells, the magnitude of changes in number of cytochalasin B binding sites closely paralleled and sufficiently accounted for the magnitude of changes in glucose uptake. Qualitative changes in the turnover and affinity for substrate of the putative glucose carrier need not be invoked.

Animals↗
PubMed1978

Importance of C4a- and N5-covalent adducts in the flavin oxidation of carbanions.

The reaction of nitroalkanes, furoin, and phenacyl alcohol with 7- and 8-cyano-3,10-dimethylisoalloxazine (7-CNFlox, 8-CNFlox), 5-ethyl-3-methyllumiflavinium ion (Flox+Et), and 2.6-dichloroindophenol (DCI) have been studied. Nitromethane anion forms an adduct on reaction with Flox +Et. The condensation reaction has been shown (nuclear magnetic resonance) to occur through addition of the methylene carbon of the nitromethane anion to the 4a position of Flox+Et. This adduct undergoes spontaneous dissociation to its components in acid. It does not undergo conversion in base to reduced flavin (1,5-F1EtH), NO2-, and CH2O. For this reason one may conclude that nitroalkane anion oxidation by flavin does not involve the intermediacy of a 4a-covalent intermediate. Oxidation of nitroalkane anion through formation of an N5-flavin adduct is discussed in terms of the peculiar requirements of the substrate when compared with carbanions derived from normal flavoenzyme substrates. It is concluded that the mechanism of nitroalkane oxidation by flavin must bear no relationship to the flavin oxidation of normal substrates. Furoin and phenacyl alcohol (compounds containing the-CH(OH)--CO-functionality) are oxidized by 8-CNFlOX, 7-CNFlOX, DCI and by the N5-blocked flavin Flox+Et. These reactions are found to be zero order in oxidant at the concentrations of oxidants (approximately 1.0 X 10(-5) M) and reductant (approximately 10(-3) to 10(-4) M) employed. This finding, and that of an 1H/2H kinetic isotope effect of 3.5, as well as certain equalities of the determined rate constants establish the rate-determining step in all these oxidations to be carbanion formation. That the N5-blocked flavin (Flox+Et) serves just as well as an oxidant as do substituted and unsubstituted isoalloxazines provides evidence that the flavin oxidation of carbanions of general structure (-C-(OH)--CO-) does not require the formation of an intermediate N5-flavin adduct. This conclusion when taken with the fact that the N5-flavin adduct formed on reaction of dihydroflavin with -C(=O)--CO-is not an intermediate in the reduction of -C(=O)--CO-to -CH(OH)--CO- by dihydroflavin shows that N5 adducts do not arise as intermediates in these oxidations. Remaining mechanisms (4a addition and radical pair formation) are discussed. 4a addition of carbanions to Flox+Et is shown to be subject to considerable steric strain by the instability of the nitroethane adduct and the inability to observe the formation of the 2-nitropropane adduct.

Anions↗