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Biomedical subjects

F Wong

Publications and source records attributed to F Wong.

At least 199 records · Page 11Linked to original sources
PubMed1986

Bladder base dosage in patients undergoing intracavitary therapy.

The maximum dose rate being delivered to the base of the bladder during intracavitary therapy was assessed in 20 patients by CAT scanning during treatment. This value was compared with the I.C.R.U. bladder reference point dose rate calculated from lateral radiographs taken after insertion. The ratio of the maximum bladder base dose rate to the I.C.R.U. reference dose rate varied from 1.01 to 3.59. In ten patients the maximum bladder dose rate was not in the midline. Re-examination of five patients revealed significant changes in bladder base dose rate in two due to changes in applicator positioning and packing. The bladder base dose rate on the vertical plane through the middle of the vaginal ovoids was within +/- 25% of the maximum bladder base dose rate in 22/25 examinations.

Adult↗
PubMed1986

Use of a pocket personal computer in obstetric ultrasound.

Obstetric ultrasound is of increasing importance in obstetric practice. The conventional ultrasound prediction of fetal weight and gestational age using various fetal parameters, like biparietal diameter, abdominal circumference, femur length etc have to rely on various different charts or tables, which are both laborious and time consuming. Three programmes in Basic language using a pocket personal computer have been developed and their application is presented in this paper.

Anthropometry↗
PubMed1985

An evaluation of three ultrasound equations for fetal weight prediction.

Ultrasound fetal weight estimation based on the equations of Shepard et al (1), Warsof et al (2) using biparietal diameter and abdominal circumference, and Campbell et al (3) using abdominal circumference, were evaluated in 92 Chinese patients in labour. Our result shows that Campbell's equation (3), based on the abdominal circumference alone provides a higher accuracy and precision in predicting fetal weight than using a combination of biparietal diameter and abdominal circumference.

Birth Weight↗
PubMed1985

Molecular basis of an inherited retinal defect in Drosophila.

Fruitflies carrying the autosomal recessive mutation transient receptor potential (trp) are blind in bright light because the receptor potential of such a mutant decays almost completely during an intense stimulus. The trp gene has been localized and a set of partially overlapping genomic clones that include the trp gene has been isolated. The stretch of DNA represented by these genomic clones is found to contain genes that encode for four RNA species. Two of these RNA species are missing in the mutant. This observation is consistent with the notion that the mutation alters the DNA sequence in a region containing signals necessary for the expression of the gene. Accordingly, the molecular basis of the mutant phenotype may be due to the lack of a protein(s) that is/are important for normal visual transduction.

Animals↗
PubMed1984

Electron beam dosimetry study of the digits in total body surface irradiation.

Total body surface electron beam therapy has been used for treatment of patients with mycosis fungoides. Using a 3 MeV electron beam, four fields and a moving couch technique, it was noted that patients developed marked erythema of the hands with bullous reaction along the lateral aspects of their fingers. Cylindrical phantoms were devised to study thermoluminescent dosimetry of the digits in electron beam therapy. At the lateral surface, dosage as high as 154% of the nominal dose was noted. However, dosage at 3 mm from the periphery was more homogeneous. To exploit the more even dosage at depth, the dosimetry study was repeated with a layer of 2 mm Uvex covering the phantom digits. The variation in surface dose was much reduced without jeopardizing the dose at depth. Uvex hand moulds of 2 mm thickness were constructed for patients on total body surface electron treatment with similar reduction of the much enhanced dose at the lateral borders of the digits.

Dose-Response Relationship, Radiation↗
PubMed1984

Radiation oncology--the misunderstood specialty.

A shortage of radiation oncologists has been a problem in both Canada and the United States of America. The fundamental step to rectify this situation is the recruitment of interested medical students. A mail-in survey was sent to 214 third- and fourth-year medical students at the University of British Columbia to evaluate attitudes to and the level of understanding of radiation oncology. The response rate was 59%. Seventy-five percent of the students were planning postgraduate training in clinically orientated specialties with good lifestyle and availability of job opportunities. However, only 18% of the respondents considered radiation oncology as a possible specialty. This survey suggests that this lack of interest is the result of misconceptions about training in the practice of radiotherapy. To better inform the medical students, teaching clinics providing them with direct contact with radiation oncologists and their patients, are invaluable. In order to generate the correct image of the specialty and the types of patients encountered, teaching in an ambulatory care setting is not to be neglected. Distribution of information pamphlets describing the radiation oncology program and the nature of radiation oncology practice is also suggested as an efficient means of informing medical students.

Attitude of Health Personnel↗
PubMed1982

Adapting bump model for ventral photoreceptors of Limulus.

Light-evoked current fluctuations have been recorded from ventral photoreceptors of Limulus for light intensity from threshold up to 10(5) times threshold. These data are analyzed in terms of the adapting bump noise model, which postulates that (a) the response to light is a summation of bumps; and (b) the average size of bump decreases with light intensity, and this is the major mechanism of light adaptation. It is shown here that this model can account for the data well. Furthermore, the model provides a convenient framework to characterize, in terms of bump parameters, the effects of calcium ions, which are known to affect photoreceptor functions. From responses to very dim light, it is found that the average impulse response (average of a large number of responses to dim flashes) can be predicted from knowledge of both the noise characteristics under steady light and the dispersion of latencies of individual bumps. Over the range of light intensities studied, it is shown that (a) the bump rate increases in strict proportionality to light intensity, up to approximately 10(5) bumps per second; and (b) the bump height decreases approximately as the -0.7 power of light intensity; at rates greater than 10(5) bumps per second, the conductance change associated with the single bump seems to reach a minimum value of approximately 10(-11) reciprocal ohms; (c) from the lowest to the highest light intensity, the bump duration decreases approximately by a factor of 2, and the time scale of the dispersion of latencies of individual bumps decreases approximately by a factor of 3; (d) removal of calcium ions from the bath lengthens the latency process and causes an increase in bump height but appears to have no effect on either the bump rate or the bump duration.

Animals↗
PubMed1980

Dispersion of latencies in photoreceptors of Limulus and the adapting-bump model.

To light stimuli of very low intensity, Limulus photoreceptors give a voltage response with a fluctuating delay. This phenomenon has been called "latency dispersion." If the generator potential is the superposition of discrete voltage events ("bumps"), and if the effect of light upon bump size is negligible, then the latency dispersion and the bump shape completely characterize the frequency response to sinusoidal flicker. For very low light intensities, the latency dispersion of the bumps, the bump shape, and the frequency response are measured. It is found that for data obtained at 20 degrees C, the frequency response can be accounted for completely by the latency dispersion and by the bump shape derived from steady-state noise characteristics. At 10 degrees C, the time scale of the response of the photoreceptor is lengthened. The dispersion of latencies and the bump shape are found not to have the same temperature dependence. However, just as those measured at 20 degrees C, the bump shape and the dispersion of latencies measured at 10 degrees C can predict the frequency response measured under the same conditions. These results strongly suggest that the major mechanisms involved in the generator potential are the latency process and the bump process. At high light intensities, the time scale of the generator potential shortens. The decrease in time scale of the generator potential can be attributed to the decreases in time scales of the bumps and of the latency dispersion process.

Animals↗
PubMed1980

Adapting-bump model for eccentric cells of Limulus.

Light-evoked intracellular voltage noise records have been obtained from Limulus eccentric cells, from threshold light intensity to an intensity .10(5) times threshold. These data are analyzed in terms of a simple "adapting-bump" noise model. It is shown how the model yields a data reduction procedure that slightly generalizes the familiar use of Campbell's theorem for Poisson shot noise: the correlative effect of adaptation amends Campbell's theorem by a single multiplicative factor, which may be estimated directly from the power spectrum of the noise data. The model also permits direct estimation of the bump shape from the power spectrum. The bump shape estimated from noise at dim light is in excellent agreement with the average shape of bumps observed directly in the dark. The data yield a bump rate that is linear with light up through about 50 times threshold intensity but that falls short of linearity by a factor of 35 at the brightest light. The bump height decreases as the -0.4 power of light intensity across the entire range. Bump duration decreases by a factor of 2 across the entire range, and the adaptation correlation factor descends from unity to about one-third. The modest change of the adaptation correlation shows that naive application of Campbell's theorem to such data is adequate for rough estimation of the model's physiological parameters. This simple accounting for all the data gives support to the adapting-bump model.

Animals↗
PubMed1977

Frequency characteristics in the visual system of Drosophila: genetic dissection of electroretinogram components.

Various drosophila mutants were used to dissect the electroretinogram (ERG) frequency response into components of different origins. The ommochrome granules in the receptor cell body are known to migrate in response to light, limiting the amount of light entering the rhabdomere. Comparison between the ERG frequency responses of the wild type and the mutant lacking the ommochrome granules indicates that the pigment migration reduces the amplitude gain at frequencies below 0.5 Hz. The ERG of drosophila compound eyes consists of contributions from receptor cells and the second-order cells in the lamina. Mutants with defective laminae showed a high-frequency cutoff with a corner frequency of about 20 Hz, while in wild type the response peaked in that frequency region. These results suggest that the lamina contributes mainly to the high-frequency components of the ERG transfer function. The shot noise model (Dodge et al., 1968) has been tested in drosophila by comparing the frequency response of the superimposed on the intracellular receptor potential. The results are consistent with the hypothesis that the receptor potential consists of a summation of small discrete potentials (bumps). In a mutant in which the bumps exhibit latency dispersion in response to a dim flash, the receptor showed a poor high-frequency response, the corner frequency being lowered to about 1-2 Hz. The slope of the cutoff was approximately 20 dB/dec indicating that the latency dispersion in this mutant is the major limiting factor in temporal resolution. Light-evoked high frequency oscillations have been observed in the ERG of another mutant. The oscillation was found sharply turned to light flickering at about 55 Hz.

Animals↗
PubMed1977

Lability of the prolonged depolarizing afterpotential in Balanus photoreceptors.

A large cell to cell variability of the prolonged depolarizing afterpotential (PDA) decay time constant (tau) has been measured in Balanus eberneus lateral ocelli. While 25% of the cells had PDA's of long duration, tau greater than 10 min. 45% of the cells tested showed either weak (tau less than 60 s) PDA or none at all. The variability was not reflected in the late receptor potential. All the cells showed normal light-coincident responses. The variability was not due to some alteration of the thermal stability of the pigment states, since after monochromatic adaptation the amplitude of the early receptor potential remained unchanged for at least 30 min. In addition, in some cells that initially showed PDAs of long duration, the decay time was either shortened or abolished after exposure to anoxia. Again, the late receptor potential and the stability of the pigments remained unaffected. These results indicate that the mechanisms which give rise to the PDA are not always tightly coupled to the direct chain of events that lead to the light-coincident response.

Action Potentials↗