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K G Strid

Publications and source records attributed to K G Strid.

28 records · Page 2Linked to original sources
PubMed1975

Intensifying screens in soft tissue radiography.

Certain screen-film combinations were tested in the low voltage range (26 to 40 kV, tungsten target) and compared with an optimal non-screen industrial film. The dose reduction was of no consequence as compared with the loss in image quality. Some physical properties of the screens giving rise to the failure are discussed.

Evaluation Studies as Topic↗
PubMed1975

Contrast formation in fluoroscopic videodensitometry. III. Relation between roentgen tube potential and exposure rate to produce constant video level.

The exposure rate required to produce a prescribed value of the video level in a vidicon television chain during fluoroscopy was measured for water layers and copper filters of varying thickness. The reduction of the patient exposure rate was found to be so large that, in spite of a reduction of the iodine extinction to 20 to 50 per cent of the value at 40 to 50 kV, examinations of the circulatory system are recommended to be performed at 100 kV with slight copper filtering.

Absorptiometry, Photon↗
PubMed1975

Spectral variation of the conversion factor of an image intensifier.

The conversion factor of the image intensifier Sirecon duplex 25/15 was investigated by means of a videodensitometer for varying values of the tube potential and varying filtering of the radiation. It was found that the conversion factor can be increased by Cu filtering. By analysis of the measurement data, the spectral variation of the conversion factor was determined. The conversion factor has a maximum for 60 keV photons and falls rapidly for photons of energy below 45 keV. By the method described, the spectral response function of an image intensifier can be determined experimentally without the use of a spectrometer.

Absorptiometry, Photon↗
PubMedDate not supplied

Migration of human granulocytes in filters: effects of gravity and movable gradients of f-MLP.

The Boyden chamber technique for chemotaxis uses a mesh filter that constitutes a matrix for cell locomotion and, at the same time, creates a local restriction for convective fluid movements that allows the establishment of a diffusive concentration gradient of chemotactic substance in the filter. In the present study, the Boyden chamber was modified by the introduction of a filter sandwich that allowed cell migration both upwards and downwards and by the use of a fluid density gradient controlling cell buoyancy and mechanically supporting a movable chemotactic gradient. This method was used to study chemotaxis and random migration of human granulocytes under the influence of gravitational forces and movable gradients of f-MLP. The results show that gravity affected cell motion significantly during random migration but not during chemotaxis. The rate of chemotactic migration was dependent on the steepness of the spatio-temporal f-MLP gradients. A stationary spatial gradient produced less migration than a gradient that was slowly moved through the filter sandwich in a direction opposite to that of the cell migration. The presence of f-MLP at constant concentration caused a minor, statistically insignificant, increase of the rate of random migration.

Cell Movement↗
PubMedDate not supplied

Bone mass determination from microradiographs by computer-assisted videodensitometry. II. Aluminium as a reference substance.

Aluminium was evaluated as a reference substance in the assessment of rabbit cortical bone by microradiography followed by videodensitometry. Ten dense, cortical-bone specimens from the same tibia diaphysis were microradiographed using prefiltered 27 kV roentgen radiation together with aluminium step wedges and bone simulating phantoms for calibration. Optimally exposed and processed plates were analysed by previously described computer-assisted videodensitometry. For comparison, the specimens were analysed by physico-chemical methods. A strict proportionality was found between the 'aluminium equivalent mass' and the ash weight of the specimens. The total random error was low with a coefficient of variation within 1.5 per cent. It was concluded that aluminium is an appropriate reference material in the determination of cortical bone, which it resembles in effective atomic number and thus x-ray attenuation characteristics. The 'aluminium equivalent mass' is suitably established as the standard of expressing the results of bone assessment by microradiography.

Aluminum↗
PubMedDate not supplied

Bone mass determination from microradiographs by computer-assisted videodensitometry. I. Methodology.

The mass of hard-tissue specimens is assessed by optimised microradiography followed by computer-assisted videodensitometry. Radiographs are produced with 27 kV roentgen radiation, filtered through 0.5 to 1 mm of aluminium, on high-resolution glass plates. Aluminium step wedges are used for density calibration, the result being expressed as 'aluminium equivalent mass'. The plates are subjected to digital image analysis by an operator in interaction with a computer-based image processor, a television camera being used for image input. The program stored in the computer provides calibration of geometry and--via the step wedge images--of densitometry, background adjustment, etc. Measurement takes place by integration over the specimen-image area. No assumptions being needed concerning a specific attenuation model, the errors stemming from the common presumption of exponential attenuation are eliminated. Density profiles or maps of mass distribution are readily obtained from the computer. From measurements of aluminium phantom samples, the total random error (coefficient of variation) was determined at 1.8 per cent, the microradiographic and videodensitometric procedures contributing 1.6 per cent and 0.9 per cent, respectively, whereas the systematic error was negligible. Since specimens need not be sectioned, this method does not interfere with subsequent histologic preparation.

Bone and Bones↗