Biomedical subjects

K H Ng

Publications and source records attributed to K H Ng.

At least 37 records · Page 2Linked to original sources

PubMed2000

Molybdenum nanowires by electrodeposition.

Metallic molybdenum (Mo(o)) wires with diameters ranging from 15 nanometers to 1.0 micrometers and lengths of up to 500 micrometers (0.5 millimeters) were prepared in a two-step procedure. Molybdenum oxide wires were electrodeposited selectively at step edges and then reduced in hydrogen gas at 500 degrees C to yield Mo(o). The hemicylindrical wires prepared by this technique were self-uniform, and the wires prepared in a particular electrodeposition (in batches of 10(5) to 10(7)) were narrowly distributed in diameter. Wires were obtained size selectively because the mean wire diameter was directly proportional to the square root of the electrolysis time. The metal nanowires could be embedded in a polystyrene film and lifted off the graphite electrode surface. The conductivity and mechanical resiliency of individual embedded wires were similar to those of bulk molybdenum.

Journal Article↗

PubMed2000

Clinicopathological study of peripheral odontogenic fibromas (WHO-type) in Malaysians (1967-95).

Analysis of case records of 46 patients with peripheral odontogenic fibroma (1967-95) diagnosed in the Division of Stomatology, Institute for Medical Research, Kuala Lumpur, disclosed a relatively young age of onset (mean, 32.2 years; range 5 months-64 years; peak incidence second decade of life), a slight female preponderance (M:F ratio 1:1.3), no racial predilection, a slight bias towards location in the mandible (52%) and a wide histomorphological range. All cases were treated by simple excision. Follow-up records were generally not available, so we do not know what the recurrence rate is.

Adolescent↗

PubMed2000

Reversible induction of rat hepatoma cell polarity with bile acids.

A dynamic model for inducing and isolating polarized cell colonies from differentiated rat hepatoma was established with chenodeoxycholic acid (CDCA). Cells were treated with 75 microM CDCA in a 1% solvent mix (DMSO/ethanol: 0.5%/0.5%) for 11 days and positive Fao-BA1 and C2rev7-BA1 clones were isolated, respectively, from Fao and C2rev7. Cell polarization in these two clones was demonstrated by (i) the detection of (gamma)-glutamyl transpeptidase activity (gamma)-GT) and the presence of specific proteins, namely aminopeptidase N (APN), bile acid export pump (Bsep), multidrug resistance-associated protein 2 (Mrp2) at the canalicular pole, (ii) the expression of tight junction (ZO-1) and basolateral (1-18) marker proteins, (iii) the presence of regular microvilli in the cavities sealed by tight junctions, and (iv) functional bile canaliculi-like structures with the capacity to metabolise and secrete carboxyfluorescein diacetate dye. The polarized phenotype was maintained for more than 200 cell generations in the presence of CDCA and could be modulated by cell density or omitting the inducing agent. Hence this cellular model is well suited for studies on hepatic differentiation, polarization and bile salt trafficking with therapeutic implications.

Animals↗

PubMed2000

Mammographic image quality and exposure in South East Asia.

Generally there is a significant delay before optimized performance of mammography is fully realized in the developing countries. To evaluate the status of mammographic performance, a survey of mammographic image quality and exposure was performed in nine hospitals from four selected South East Asian countries. The entrance exposure on the surface of the American College of Radiology (ACR) mammographic phantom (ACR-RMI model 156) was made using both thermoluminescent dosimeters (TLDs) and an ionization chamber. The TLDs were mailed from the University of Wisconsin Radiation Calibration Laboratory (UWRCL) to the cooperating hospitals. The surveyed hospitals processed the images and returned them to the UWRCL for subsequent evaluation of the image quality of the mammographic phantom. Machine-specific data, technique factors and sensitometric data were also obtained. At 28 kVp, the mean entrance exposure is 0.91 R (0.46 to 2.6 R), mean glandular dose is 1.61 mGy (0.90 to 4.15 mGy), mean optical density is 1.37 (0.66 to 2.30), mean total phantom image score is 9.1(4-12). Only three of the nine hospitals tested achieved an acceptable score above the minimum 10. Results for 25 and 30 kVp showed similar trend. The variation between the ion chamber measurements and TLD measurements ranged from 4 to 24%. There is a wide variation in the image quality and entrance exposure among hospitals in South East Asia. There is a need for a quality assurance program. The factors that cause low score in the phantom images must be corrected. Calibration and the use of appropriate ionization chambers for mammography is important.

Asia, Southeastern↗

PubMed1999

Medical radiation exposures for diagnostic radiology in Malaysia.

The medical radiation usage for diagnostic radiology in Malaysia (a Level II country) for 1990-1994 is reported, enabling a comparison to be made for the first time with the United Nations Scientific Committee on the Effects of Atomic Radiation Report. In 1994, the number of physicians, radiologists, x-ray units, and x-ray examinations per 1,000 population was 0.45, 0.005, 0.065, and 183, respectively. (Level I countries had averages of 2.6, 0.072, 0.35, and 860, respectively). In 1994, a total of 3.6 million x-ray examinations were performed; the annual effective dose per capita to the population was 0.05 mSv, and the collective effective dose was 1,000 person-Sv. Chest examinations contributed 63% of the total. Almost all examinations experienced increasing frequency from 1990 to 1994 except for barium studies, cholecystography, and intravenous urography (-23%, -36%, -51%). These decreases are related to the increasing use of ultrasound and greater availability of fiberoptic endoscopy. Notable increases during the same period were observed in computed tomography (161%), cardiac procedures (190%), and mammography (240%). In order to progress from Level II to Level I status Malaysia needs to expand and upgrade radiological service in tandem with the health care development of the country.

Humans↗

PubMed1999

Dependence of scatter on atomic number for x rays from tungsten and molybdenum anodes in the mammographic energy range.

A study was done to determine the relative amounts of scatter for the following materials with atomic numbers ranging from Z=6 to Z=82: C, Al, Ti, Fe, Cu, Zn, Zr, Y, Mo, Ta, and Pb. Measurements were performed for each material on two constant potential x-ray units--one fitted with a molybdenum (Mo) anode-Mo filter and the other with a tungsten (W) anode-aluminum (Al) filter (medium filtration) at 30 kVp. Theoretical calculations were also performed for each anode to explain the scatter behavior and to aid in predicting the behavior for materials where measurements were not made. There was good agreement between the theoretical calculations and the experimental data.

Biophysics↗

PubMed1999

The impact of teleradiology in clinical practice--a Malaysian perspective.

Teleradiology is the most mature and rapidly evolving specialty in telemedicine. The use of teleradiology has grown tremendously during the past few years. This article describes the role of teleradiology in health care along with a brief history of its development in tandem with advances in telecommunications and computer technologies. Teleradiology standards, image acquisition, data compression, transmission and image interpretation are summarised. The impact of teleradiology in the practice of radiology, traces the evolution of the modality especially in the Malaysian perspective and its current and future role are discussed.

Delivery of Health Care↗

PubMed1999

X-ray based radiological procedures in Malaysia--1990-1994.

X-ray based radiological procedure statistics and trend in Malaysia for 1990-1994 is reported; this information allows comparisons to be made with the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) Report. Additionally it is essential information for health care planners and providers. Malaysia is categorised as a health care level II country based on the UNSCEAR definition. In 1994, the number of physicians, radiologists, x-ray units and x-ray examinations per 1000 population was 0.45, 0.005, 0.065 and 183 respectively. 3.6 million x-ray examinations were performed in 1994, with chest radiography being the commonest study (63%). Information on x-ray examinations, number of hospitals and x-ray units is reported for the Ministry of Health, private practice and teaching hospitals. Examination frequency increased in computed tomography (161%), cardiac procedures (190%), and mammography (240%); while a decrease in barium studies (-23%), cholecystography (-36%), and intravenous urography (-51%) was noted. There is a potential and need to expand and upgrade radiological services.

Humans↗

PubMed1998

A prospective randomized control study to compare the effect of serum and a commercial serum substitute (Plasmanate) on the outcome of assisted reproduction program.

OBJECTIVES: To compare the effect of supplementation of serum and Plasmanate, a commercial serum substitute, to culture medium on the IVF outcome. METHODS: One hundred eighty-nine subfertile couples were prospective randomized into the serum and the Plasmanate group during their IVF treatment. In vitro experiment was also performed to determine the fraction of Plasmanate that might affect embryo development. RESULTS: The pregnancy rate were similar in both groups. The fertilization rate, the number of gestational sacs and good quality spare embryos suitable for cryopreservation were higher in the serum group than the Plasmanate group. However, these differences did not reach statistical significance. Significantly more embryos in the former cleaved to more than 4 cells at the time of transfer than the latter (p < 0.05). Ultrafiltration study showed that this inhibitory effect resided in the low molecular weight fraction (< 30-KD) of Plasmanate. CONCLUSION: Serum is slightly better than Plasmanate as a protein supplement. However, Plasmanate may still be used for short term embryo culture in assisted reproduction.

Adult↗

PubMed1998

Doses to patients in routine X-ray examinations in Malaysia.

A collaborative national survey initiated by the University of Malaya and the Ministry of Health was conducted from 1993 to 1995 to establish baseline patient dose data for seven common types (12 projections) of X-ray examinations in Malaysia. A total of 12 randomly selected public hospitals and 867 patients were included in this survey. The entrance surface doses (ESD) received by the patients were measured using thermoluminescent dosemeters (TLDs) attached to the patient's skin. Histograms are presented showing wide, positively skewed distributions of measured entrance surface doses for each examination. Mean, median, first and third quartile values of ESD and median effective dose are reported. Survey results are generally comparable with those reported in the UK, USA and by the International Atomic Energy Agency (IAEA). The results also provide information on dose level for a lower weight population (mean weight 60 kg) compared with the international reference dose values based on a 70 kg standard. The findings support the importance of the on-going national quality assurance programme to ensure doses are kept to a level consistent with optimum image quality. The data will also be useful for the formulation of national guidance levels as recommended by the IAEA. Furthermore, this study provides patient dosimetry information on healthcare level II countries.

Adult↗

PubMed1998

An in vitro study comparing two different film-screen combinations in the detection of impacted fish bones.

Dried fish bones from eight species of Malaysian fish were placed in an animal cadaver at four sites (tonsil, valleculae, larynx and oesophagus) and radiographed using a double and a single film-screen combination. The use of the single film-screen combination resulted in visibility of all fish bones placed in the larynx, two of which were not visible on the double film-screen combination. There was a 50% increase of the visibility of the fish bones in the oesophagus using the single film-screen combination. The difference in dose and cost between the two different film-screen combinations was not significant.

Animals↗

PubMed1997

Antigen-induced interferon-gamma and interleukin-2 responses of cattle inoculated with Mycobacterium bovis.

Bovine purified protein derivative (PPD)-induced interferon-gamma (IFN-gamma) and interleukin-2 (IL-2) mRNA expression was measured in peripheral blood lymphocyte cultures of cattle inoculated with Mycobacterium bovis and compared to cytokine protein levels as measured by IFN-gamma enzyme-linked immunosorbent assay and IL-2 bioassay. For individual animals, positive correlations were observed between mRNA and protein levels of bovine PPD-induced IFN-gamma and IL-2, although the correlations were stronger for IFN-gamma. Expression of these two cytokines also correlated with responses from a comparative intradermal test and a M. bovis antibody test. At 7 and 20 weeks after inoculation, bovine PPD-induced IFN-gamma and IL-2 mRNA expression was detected in all animals with tuberculous lesions and in a proportion of the M. bovis-inoculated animals with no lesions. Correlation of antigen-induced IFN-gamma and IL-2 with other immune parameters suggests that these two cytokines play an important role in the immune response to bovine tuberculosis.

Animals↗

PubMed1997

Discriminant analysis of normal and malignant breast tissue based upon INAA investigation of elemental concentration.

Discriminant analysis of six trace element concentrations measured by instrumental neutron activation analysis (INAA) in 26 paired-samples of malignant and histologically normal human breast tissues shows the technique to be a potentially valuable clinical tool for making malignant-normal classification. Nonparametric discriminant analysis is performed for the data obtained. Linear and quadratic discriminant analyses are also carried out for comparison. For this data set a formal analysis shows that the elements which may be useful in distinguishing between malignant and normal tissues are Ca, Rb and Br, providing correct classification for 24 out of 26 normal samples and 22 out of 26 malignant samples.

Breast↗

PubMed1997

Sarcoid-like foreign body reaction in body piercing: a report of two cases.

We report two cases of body piercing as a religious practice that subsequently led to the development of granulomatous nodules at previously punctured sites of the skin and oral mucosa. These lesions were diagnosed as sarcoid-like foreign body reaction after other possible causes including sarcoidosis, tuberculosis, tuberculoid leprosy, fungal infections, viral infections, and Crohn's disease were excluded.

Adult↗

PubMed1997

Entrance skin exposure and mean glandular dose: effect of scatter and field gradient at mammography.

PURPOSE: To investigate the effect of scatter and x-ray field gradient on entrance skin exposure and mean glandular dose by using the measurement protocol of the American College of Radiology. MATERIALS AND METHODS: The exposure difference between the off-axis geometry of the American College of Radiology protocol and the central-axis geometry was measured by using eight common ionization chambers and two mammographic units (Senographe DMR; GE Medical Systems, Milwaukee, Wis; and Mam-CP II; Transcontinental X-ray, Charlotte, NC) at 25, 28, and 30 kVp. The field gradient was also measured on film with a scanning densitometer. RESULTS: The central-axis exposure was 2.0%-3.6% higher than the off-axis exposure for the Senographe DMR unit and 3.1%-8.0% higher for the Mam-CP II unit. The maximum phantom scatter was 0.7% (Senographe DMR) and 1.3% (Mam-CP II). CONCLUSION: Entrance skin exposure varies, depending on the type of ionization chamber and the characteristics of the mammographic unit. Determination of mean glandular dose with the American College of Radiology protocol may lead to underestimates of the actual measured dose by 4%-8% for the x-ray machines used in this study.

Breast↗

PubMed1997

Elevated trace element concentrations in malignant breast tissues.

In vitro neutron activation analysis (NAA) was performed on malignant and adjacent normal tissue from 46 human female breast tumours. The objective was to investigate the chemical environment of the tissues within which microcalcifications develop and to develop a method for discrimination between malignant and normal breast tissue. The elements Al, Br, Ca, Cl, Co, Cs, Fe, K, Mn, Na, Rb and Zn were significantly higher in the cancer tissues (all p < 0.001; except for Co, p < 0.003, Wilcoxon signed-ranks test). In addition, a significant correlation (0.80, Spearman rank correlation) was found for Rb and Zn in tumour tissues. Present results are supported by the findings of others. The relevance of elevated concentrations of these elements in cancer breast tissue remains a matter of conjecture. Evidence suggests that there is a connection both with increased cellular activity and blood supply and the formation of microcalcifications in malignant breast tissues. This study suggests an association between the elemental composition of breast tissues and the formation of breast particles. That is, elevations of elemental concentration and clustered calcifications in breast are possibly related.

Adult↗

PubMed1997

A clinicopathologic study of odontomas: Malaysian findings.

This report reviews the clinicopathologic characteristics of 104 cases of odontomas diagnosed in the Division of Stomatology, Institute for Medical Research, Kuala Lumpur, over a 29-year period (1967-1995). The results showed no real predilection in terms of sex (M:F ratio, 1:1), race (45.2% Malays, 40.4% Chinese, 10.6% Indians and 3.8% other races) or site (maxilla:mandible ratio, 1: 1.04) distribution. The mean age at presentation was 24.8 years and the age range was 3-74 years. There were 102 intraosseous and 2 extraosseous odontomas. Swelling was the most common presenting complaint. The majority of cases (81.9%) were clinically diagnosed as odontomas. The treatment of choice was surgical enucleation. Compound (43.3%) and complex (35.5%) odontomas were the two most common histological types encountered. The present findings correlate favorably with reported studies from other geographic areas.

Adolescent↗

PubMed1996

Accurate three-dimensional reconstruction of intravascular ultrasound data. Spatially correct three-dimensional reconstructions.

BACKGROUND: The geometrical accuracy of conventional three-dimensional (3D) reconstruction methods for intravascular ultrasound (IVUS) data (coronary and peripheral) is hampered by the inability to register spatial image orientation and by respiratory and cardiac motion. The objective of this work was the development of improved IVUS reconstruction techniques. METHODS AND RESULTS: We developed a 3D position registration method that identifies the spatial coordinates of an in situ IVUS catheter by use of simultaneous ECG-gated biplane digital cinefluoroscopy. To minimize distortion, coordinates underwent pincushion correction and were referenced to a standardized calibration cube. Gated IVUS data were acquired digitally, and the spatial locations of the imaging planes were then transformed relative to their respective 3D coordinates, rendered in binary voxel format, resliced, and displayed on an image-processing workstation for off-line analysis. The method was tested by use of phantoms (straight tube, 360 degrees circle, 240 degrees spiral) and an in vitro coronary artery model. In vivo feasibility was assessed in patients who underwent routine interventional coronary procedures accompanied by IVUS evaluation. Actual versus calculated point locations were within 1.0 +/- 0.3 mm of each other (n = 39). Calculated phantom volumes were within 4% of actual volumes. Phantom 3D reconstruction appropriately demonstrated complex morphology. Initial patient evaluation demonstrated method feasibility as well as errors if respiratory and ECG gating were not used. CONCLUSIONS: These preliminary data support the use of this new method of 3D reconstruction of vascular structures with use of combined vascular ultrasound data and simultaneous ECG-gated biplane cinefluoroscopy.

Blood Vessels↗