Biomedical subjects

K N Yu

Publications and source records attributed to K N Yu.

At least 37 records · Page 2Linked to original sources

PubMed2003

Determination of multi-element profiles of street dust using energy dispersive X-ray fluorescence (EDXRF).

Street dust samples have been collected in different areas in Hong Kong associated with various levels of traffic and pedestrian flow, and the concentrations of 23 chemical elements have been determined using energy dispersive X-ray fluorescence (EDXRF). The 23 studied elements were Na, Al, Si, Cl, Ti, Ba, V, Cr, Mn, Fe, Co, K, Ca, Ni, Cu, Zn, As, Pb, Rb, Sr, Y, Zr and Sn. A profile for average street dust for Hong Kong has been determined by taking average values for different areas. The values for the Hong Kong street dust are commensurate with the values derived in previous investigations or for other countries, except that Hong Kong street dust has much higher Cl, Ca and As concentrations. A factor analysis gives four sources for the street dust in Hong Kong: namely, mixture of metallic dust and crustal material, vehicles, road pavement materials, and mixture of marine aerosols and crustal material.

Air Pollutants↗

PubMed2003

Study of air pollutants in Hong Kong using energy dispersive X-ray fluorescence.

Airborne particulate samples were collected from various reference sites in Hong Kong and the energy dispersive X-ray fluorescence (EDXRF) intensities for 19 chemical elements were recorded. Principal component analysis (PCA) was employed so that the variances of these 19 original variables were captured by a few new indices called principal components or PCs. Data points for similar sources were automatically grouped together in a plot of the first three PCs (PC plot). Data for the monitoring site Mong Kok were located within the area defined by vehicular emissions. As such, the main air pollutant at this site was concluded to originate from vehicular emissions. A fraction of data for the Causeway Bay monitoring site also fell into this same identified area, so the main air pollutant could also be vehicular emissions. Some of the data located either on or outside the border can be explained in terms of meteorology.

Air Pollutants↗

PubMed2003

Deposition fractions of 218Po in diffusion chambers.

After radon gas diffuses into a diffusion chamber, 218Po will be formed. Due to its short half-life, a fraction f of 218Po decays before deposition onto available inner surfaces of the chamber, and the deposition fraction (1-f) represents the part which decays after deposition. In the present work, f has been experimentally determined for six diffusion chambers with different materials and dimensions using the radial distribution of track density on the LR115 detectors inside the diffusion chambers. For all the six studied diffusion chambers, f was found to be approximately 0.4. Therefore, the deposition fraction does not depend on the shape and dimensions of the diffusion chambers, the surface to volume ratios or the internal surface materials of the diffusion chambers.

Journal Article↗

PubMed2003

Absorbed fraction of radon progeny in human bronchial airways with bifurcation geometry.

PURPOSE: The absorbed fraction, defined as the portion of the initial particle energy which is absorbed in the tissue of interest, was calculated, under bifurcation geometry of the airway tubes, for alpha-particles emitted from radon progeny in the human respiratory tract. The results are given for all branching generations and compared with the data obtained for the commonly used infinite straight cylinders adopted by the International Commission on Radiological Protection (ICRP) Report 66. MATERIALS AND METHODS: A model was created to calculate the absorbed fraction of alpha-particle energy in the human lung using bifurcation geometry. Monte Carlo simulations of alpha-particle propagation in tissue and air were performed. The stopping powers of alpha-particles were adopted from the International Commission of Radiation Units and Measurements (ICRU) Report 49. RESULTS: The absorbed fractions for the bifurcation geometry are given for the 15 generations in the tracheobronchial tree for alpha-particle energies of 6 and 7.69 MeV. The sources were assumed to be the fast and slow moving mucus. CONCLUSIONS: Comparisons with ICRP66 data reveal that the assumption of long, straight cylinders was appropriate in some cases, but not in all. Adoption of the absorbed fractions obtained from the bifurcation model instead of the ICRP66 data caused 'redistribution' of doses in the bronchial (BB) and bronchiolar (bb) regions.

Bronchi↗

PubMed2003

Metakaolin as a radon retardant from concrete.

Granite aggregates are known to be the radon source in concrete. Recently, metakaolin has been introduced as a partial substitution of Portland cement to produce high strength concrete. It can effectively reduce the porosity of both the matrix and the aggregate/paste transition zone, which suggests its ability to retard radon emission from concrete aggregates. In the present work, radon exhalation rates from concrete cubes substituted with metakaolin were measured using charcoal canisters and gamma spectroscopy, and were considerably lower than those from normal concrete, by about 30%. The indoor radon concentration reduction is estimated as approximately 9 Bq m(-3) calculated using a room model, causing a 30% reduction in the indoor radon concentration and the corresponding radon dose. Therefore, metakaolin is a simple material to reduce the indoor radon concentration and the radon dose.

Air Pollutants, Radioactive↗

PubMed2003

Quality factors for alpha particles in the human respiratory tract.

Quality factors of alpha particles emitted by radon progeny in the human lung have been calculated by using the formula recommended by the International Commission on Radiological Protection. Calculations have been carried out for different combinations of sources, energies, and targets. The values obtained are between 20 and 26, with an average of about 24. These are comparable to previously published results for the human lung and for the general consideration of alpha particles emitted in tissue.

Alpha Particles↗

PubMed2003

Dose distribution close to metal implants in Gamma Knife Radiosurgery: a Monte Carlo study.

Materials with high atomic numbers favor the occurrence of the photoelectric effect when they are irradiated with gamma rays. Therefore, the photoelectric effects of metal implants within the target regions in Gamma Knife Radiosurgery are worth studying. In the present work, Monte Carlo simulations using EGS4 were employed to investigate the resulting dose enhancements. A dose enhancement as high as 10% was observed close to a platinum implant along the x and y axes, while no significant dose enhancements were observed for silver, stainless steel 301, and titanium ones. A dose enhancement as high as 20% was observed close to the platinum implant along the z axis at the superior position of the metal-phantom interface and was 10% higher for other metal implants.

Humans↗

PubMed2002

Mathematical modeling of PCB bioaccumulation in Perna viridis.

In the present work, we built a mathematical model of polychlorinated biphenyl (PCB) bioaccumulation in Perna viridis, namely, a one-compartment model with a time dependent incorporation rate R (microg g(-1) lipid per ppb water per day), with positive substrate cooperativity as the underlying physical mechanism. The temporal change of the PCB concentration Q (microg g(-1) lipid) in the soft tissues of the mussel depends on the competition of the input rate R Wand the output rate kQ, where W is the concentration of PCB in water (ppb water) and k is the elimination rate (per day). From our experimental data, k = 0.181 +/- 0.017 d(-1). The critical concentration in water Wc for positive substrate cooperativity was found to be approximately 2.4 ppb. Below Wc, R is a constant. For a water concentration of 0.5 ppb Aroclor 1254, R = 24.0 +/- 2.4 microg g(-1) lipid ppb(-1) d(-1). Above Wc, positive substrate cooperativity comes into effect and R becomes a function of time and dependent on the concentration Q in a form R = gammaQ/(Q + delta). This is the case for a water concentration of 5 ppb Aroclor 1254, where gamma = 15.1 microg g(-1) lipid ppb(-1) d(1) and delta approximately 200 microg g(-1) lipid. From this model, the uptake is exponentially increasing when the PCB concentration in the mussel is small compared to 200 microg g(-1) lipid, and hyperbolically increasing when the concentration is large compared to 200 microg g(-1) lipid, which are consistent with the experimental data. The model is useful for understanding the true processes taking place during the bioaccumulation and for risk assessment with higher confidence. Future experimental data which challenge the present model are anticipated and in fact desirable for improvement and perfection of

Animals↗

PubMed2002

Absorbed dose delivered by alpha particles calculated in cylindrical geometry.

The present work aims to develop a semi-analytical method to calculate the absorbed dose delivered by alpha particles in a cylindrical geometry. This method will be employed to reproduce the dose conversion coefficients or absorbed fraction of alpha particles in sensitive cells of the tracheobronchial tree obtained by NRC and ICRP, respectively. The difference caused by using water stopping power and tissue stopping power will also be investigated. Linear stopping powers for alpha particles in tissue and air were calculated, and the dependences of stopping powers on the traveled distance were established. A geometry model is set up for our calculations, and two different cases have been considered, namely the near-wall and far-wall cases. The total energy imparted to a unit-diameter sphere around a point is shown to be obtainable from a triple integral, which can be solved numerically. The absorbed dose is found to be independent of the diameter of the sphere being considered and additional assumptions about its diameter were not needed. The results obtained are in good agreement with those obtained previously by NRC and ICRP66. Using the semi-analytical method developed in the present work, the dose conversion coefficients or absorbed fraction previously obtained by NRC and ICRP, respectively, have been satisfactorily reproduced. Using the tissue stopping power instead of the water stopping power can slightly lower the values for dose conversion coefficients in the bronchial region.

Absorption↗

PubMed2002

Effects of different deposition models on the calculated dose conversion factors from 222Rn progeny.

Regional lung deposition for radon progeny (size range, 1 nm to 1000 nm, monodispersed) has been determined employing Gormley-Kennedy, Ingham, Cohen-Asgharian and Yu-Cohen expressions (which describe diffusion deposition), together with Gurman and Cheng formulae for impaction and sedimentation, respectively. The deposition values have been compared with those obtained by using the algebraic expressions recommended by ICRP66. The behavior of the deposition curves for breathing rates of 0.45, 0.78 and 1.2 m3 h(-1) are similar, with a broad maximum in the range (1-100) nm. In the particle size range (1-100) nm, where the thermodynamic efficiency predominates, there are large differences among the five approaches, with ICRP values lying somewhat in the middle. Dose Conversion Factors nearly follow the regional deposition trends, Cohen-Asgharian and Ingham, close to the highest values, Yu-Cohen the lowest and ICRP, again, somewhat in the middle.

Humans↗

PubMed2002

Sensitivity of LR115 detector in diffusion chamber to 222Rn in the presence of 220Rn.

Determination has been made of the sensitivity of LR115 type 2-track detectors (in units of m) to 222Rn, measured in the presence of 220Rn. Measurements have been made by means of a widely used diffusion chamber while Monte Carlo simulations have also been conducted. The experimentally derived sensitivities for 222Rn and 220Rn were found to be 0.470+/-0.022 and 0.486+/-0.042 m, respectively. For Monte Carlo simulations, the sensitivities to 222Rn gas were found to range from 0.618 x 10(-2) m (assuming that all 218Po progeny decay before deposition onto the internal walls of the diffusion chamber) to 0.405 x 10(-2) m (assuming that all 215Po progeny are deposited on the internal walls of the same containment vessel before decaying). The sensitivity to 220Rn gas of 0.465 x 10(-2) m found from Monte Carlo simulations agrees to within uncertainty with experimental findings. The experimentally derived sensitivity value for 222Rn indicates that 30% of the 218Po progeny decay before deposition onto the internal walls of the diffusion chamber.

Computer Simulation↗

PubMed2002

Determination of multi-element profiles of soil using energy dispersive X-ray fluorescence (EDXRF).

The source profile for soil in Hong Kong is important both for determination of the main air pollutant source in Hong Kong and for assessment of the impact of Asian dust storms on Hong Kong. Soil associated with different rock types have been sampled, and the concentrations of 19 chemical elements, Na, Al, Si, Ti, V, Cr, Mn, Fe, Co, K, Ca, Ni, Cu, Zn, Pb, Rb, Sr, Y and Zr, have been determined using energy dispersive X-ray fluorescence. A profile for the average soil for Hong Kong has been determined by taking average values for the different soil categories. The values for the Hong Kong soil are commensurate with values for rural soil derived by other workers, except that Hong Kong soil has much lower Fe and Ca concentrations. The abundance of Al, Ca and Fe in the average Hong Kong soil are 9.23%, 0.11% and 0.85%. We conclude that Ca provides a good marker element for identifying dust episodes in Hong Kong while Al does not.

Journal Article↗

PubMed2002

Measurements of atmospheric 7Be properties using high-efficiency gamma spectroscopy.

Two 7Be-related properties have been measured using a high-efficiency germanium gamma spectrometer (relative efficiency of 90%), namely, the activity median aerodynamic diameter (AMAD) of 7Be-associated atmospheric aerosols and the airborne 7Be radioactivity. With time resolutions of about 1-3d correlations between these 7Be-related properties and different meteorological parameters were identified. We found that AMAD is anti-correlated to 7Be counts. It is correlated with the relative humidity (RH) and mean cloud cover with high confidence, but not with temperature. We also found that 7Be radioactivity was correlated with the RH with a moderate confidence, but not with the mean cloud cover or temperature. Furthermore, wet precipitation present in the middle of the sampling period decreased the 7Be activity and increased the AMAD, while wet precipitation before or at the beginning of the sampling period decreased both 7Be activity and AMAD. Finally, after a cold front passed by, the AMAD decreased and the 7Be activity increased. Possible explanations are also given.

Journal Article↗

PubMed2002

Alpha-particle lineal energy spectra for the human lung.

PURPOSE: To determine the distribution of lineal energy in the target cells and the parameters of distribution for various combinations of sources, targets and energies in the human tracheobronchial tree. Frequency average and average of the square of the lineal energy were also calculated from the lineal energy distribution. METHOD: A model was created to simulate the geometric distribution of cell nuclei in the airway of the tracheobronchial tree. Propagation of alpha particles in such a model was simulated by the Monte Carlo method. Microdosimetric distributions of lineal energy were calculated. RESULTS: Distributions of lineal energy were substantially different for basal and secretory cells. The frequency average of specific energy was found to be between 0.3 Gy and 0.4 Gy. CONCLUSIONS: Interactions of alpha particles with basal and secretory cells show significant differences: events with small energy transfer are dominant for basal cells, while those with large transfer are dominant for secretory cells. This finding can influence dose weightings and yield lower values of the dose-to-exposure coefficient.

Alpha Particles↗

PubMed2002

Choice of phantom materials for dosimetry of Leksell Gamma Knife unit: a Monte Carlo study.

In calculations for the Leksell Gamma Knife, GammaPlan employs a tissue equivalent material without the presence of a skull bone, while dosimetry work is based on a polystyrene phantom. The compatibility of these dose distributions is uncertain. The Monte Carlo technique was employed to determine the radial dose distributions from a single 14 mm collimator helmet in 160 mm diam phantoms with different materials. The materials studied were polystyrene, perspex, water, and water with skull bone. Results showed no significant differences among the radial doses in different phantom materials for the 14 mm collimator helmet. The Monte Carlo simulation was repeated with the inclusion of all 201 sources. Again, no significant differences were observed.

Humans↗

PubMed2002

Distributions of specific energy in sensitive layers of the human respiratory tract.

The purpose of the present work was to calculate the specific energy distribution in sensitive cells of the human lung. Specific energy distributions were calculated by applying Monte Carlo methods and the ICRP 66 model of the human respiratory tract. Specific energies were calculated at various depths in the epithelium and combined according to the relative cell abundance. Distributions are given for various combinations of sources, alpha-particle energies, targets and regions of the lung. The chord length does not follow the triangular distribution when the particle range is comparable to the diameter of the target. The notion of "effective volume" is introduced and defined, which is needed for estimation of hit frequency in some particular targets. It has been shown that basal cells are subjected to a larger proportion of alpha-particle hits with small energy transfer than secretory cells. Small energy transfer events that lead to minor damage of the DNA are more efficient in cancer induction than are hits with large energy deposition that lead to cell killing.

Alpha Particles↗

PubMed2001

Indoor dose conversion coefficients for radon progeny for different ambient environments.

Inhaled progeny of 222Rn (radon progeny) are the most important source of irradiation of the human respiratory tract. Their attachment to atmospheric aerosols follows a well-established relationship between the activity size distribution (ASD) and the number size distribution. Recent studies have shown that indoor aerosols are derived primarily from outdoor sources, so it is pertinent to study the effects of different ambient environments on the indoor radon dose (in terms of the dose conversion coefficient or DCC, in units of mSv WLM-1). Commonly encountered ambient aerosols were studied here, which included the traffic-, urban-, and marine-influenced aerosols. The ASDs of attached radon progeny for all three studied ambient environments were well-represented by normal distributions. From these ASDs, the DCCs were calculated using the ICRP66 model and the scaled Yeh-Schum model. All other employed parameters were adopted from original references or authoritative reports. The DCCs for a nominal home calculated using the James model and the Yeh-Schum model were 12 and 8 mSv WLM-1, respectively. The DCCs were largest for urban-influenced ambient environments and smallest for marine-influenced ambient environments, and those for traffic-influenced ambient environments were close to that for a nominal home. If we adopt the stochastic model, the probability of contracting radon-induced lung cancer by a person living with a marine-influenced ambient environment will be half that of a person living with an urban-influenced ambient environment.

Aerosols↗

PubMed2001

Microdosimetric calculation of absorption fraction and the resulting dose conversion factor for radon progeny.

It is an established fact that radon progeny can induce lung cancers. However, there is a well-known discrepancy between the epidemiologically derived dose conversion factor for radon progeny (4 mSv/WLM) and the dosimetrically derived value (15 mSv/WLM) (mSv is a unit of the dose while WLM is a unit of exposure to radon progeny). Up to now there is no satisfactory explanation to this. In the present study we propose that microdosimetry will help reduce the discrepancy significantly. The ICRP Human Respiratory Tract Model (HRTM) has been applied to calculate the effective dose conversion factor. All parameters have been kept at their best estimates. Modifications were made in the calculation of the absorbed fractions of alpha particles. In contrast to the ICRP approach where the energy has been considered to be deposited in the layer containing the sensitive cells, we used a microdosimetric approach in which the alpha particles deposit their energy only in the nuclei of sensitive cells. This modification alone has lowered the dose conversion factor by about one-third (from 15 mSv/WLM down to approximately 10 mSv/WLM).

Cell Nucleus↗