Biomedical subjects

A van Meeteren

Publications and source records attributed to A van Meeteren.

14 recordsLinked to original sources

PubMed1990

Characterization of task performance with viewing instruments.

Recognition of one military vehicle of a group of six was investigated experimentally as a realistic observation task both for vision through image intensifiers and for thermal viewing devices. It is shown that recognition of real targets is visually equivalent to the detection of a circular disk of a certain size. The size of the equivalent disk is characteristic of the difficulty of the observation task. The image quality of viewing instruments can be related to the size of the disk that can just be detected. This measure of image quality includes resolution, low contrast, low luminance, and noise effects. The effective range of viewing instruments is directly scaled to equivalent-disk size and can be taken as a practical measure of image quality.

Contrast Sensitivity↗

PubMed1988

Effects of pictorial noise interfering with visual detection.

In order to evaluate the potential gain of noise-suppression techniques, visual detection of sine-wave gratings in images with additive fine- and coarse-grain pictorial noise was investigated. An important part of the threshold elevations caused by pictorial noise can be explained in terms of masking. The threshold elevation can be reduced by about a factor of 7 through intelligent image processing. In addition to masking by similar noise components, the detection of low-spatial-frequency target detail can also be hindered by high-spatial-frequency noise components. Correspondingly, the detection of lower spatial frequencies can be improved moderately by blurring.

Humans↗

PubMed1984

Analysis of X-ray-induced cell-cycle perturbations in mouse osteosarcoma cells: a two-signal cell-cycle model.

The effects of X-irradiation on mouse osteosarcoma cells have been studied by time-lapse cinematography and the resulting pedigrees have been analysed statistically. It is shown that the irradiation treatment causes three types of cell kinetic lesions: cell death (disintegration), cell sterilization (failure to divide) and proliferation delay. The first two lesions are the most important with regard to survival of the irradiated cell in a clonal assay. Of these two lesions, sterilization appears to be highly correlated for sister cells, while this is not true for cell disintegration. This indicates that cell survival in a clonal assay may be a function of the ratio of the incidences of these two types of lesions. The X-ray-induced proliferation delay was studied in terms of intermitotic time distributions, mother-daughter correlation and sibling correlation in relation to the current cell-cycle phase at the time of treatment. This analysis shows that the effects of irradiation on these cell-cycle characteristics is highly cell-cycle-dependent. A qualitative model to account for the observations is presented.

Animals↗

PubMed1983

Image quality of the human eye for eccentric entrance pupils.

The human eye has a considerable amount of chromatic aberration and a moderate amount of spherical aberration. If a small artificial pupil is placed in front of such optics and moved away from the centre towards the periphery the chromatic aberration will result in lateral colour shifting, and the spherical aberration will cause coma. Starting from available experimental data on the chromatic aberration and the spherical aberration, modulation transfer functions (MTF's) are calculated for central and eccentric positions of small pupils placed in front of the human eye. These calculations may help to separate optical and retinal contributions to the well-known reduction of visual acuity measured with eccentric pupils. It appears that measurements with pupils smaller than 1 mm in monochromatic light can be considered optically as diffraction limited. Changes of visual acuity found in this way must be assigned to the retina.

Humans↗

PubMed1983

Effects of exogenous cyclic AMP on growth characteristics and radiation response of Reuber H35 hepatoma cells.

Reuber H35 rat hepatoma cells, clone KRC, were used to study the effect of cyclic AMP on radiation-induced cell death. Treatment of logarithmically growing cultures with 0.5 mM cAMP for 17 hr prior to irradiation resulted in a decreased cell survival. Similar results were obtained with cultures irradiated after treatment with Bt2cAMP. Treatment of H35 cells with cAMP or Bt2cAMP caused inhibition of their proliferation and resulted in an accumulation of cells in early S phase and a depletion of G2-phase cells. In synchronized cultures cells were relatively radioresistant during their S phase. In addition to single-dose treatment with X rays, the effect of Bt2cAMP on radiation-induced cell death was studied during fractionated irradiation with 2.5 Gy per day. This fractionated irradiation resulted in a dose-reduction factor of 1.6 at the 10% survival level and a 10-fold decrease in the surviving cell population due to the cooperative effects of Bt2cAMP on growth rate and radiation survival. The effect of cAMP on radiation-induced mitotic delay was also studied. It appeared that whereas cAMP had no effect on the progression of G2 cells into mitosis, it prevented cells from recovery from the X-ray mitotic delay in G2.

Animals↗

PubMed1982