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Biomedical subjects

T Sandor

Publications and source records attributed to T Sandor.

At least 73 records · Page 4Linked to original sources
PubMed1981

Reproducibility of the densitometric analysis of fluorescein angiograms.

Computer-aided operator-interactive densitometry was applied to assess the reproducibility or retinal-fluorescein angiograms. To achieve this, the fundus camera images of glass tubings of various diameter filled with fluorescein of varying concentrations were subjected to densitometric analysis. These studies were carried out repeatedly at 9-micrometer and 29-micrometer scanning resolutions by three observers and thus the inter- and intra-operator errors could be estimated. The scanned data were analyzed as both optical densities and intensities for some of the measurements. In both analyzing modes good linearity was obtained when the densitometric response was plotted against tubing diameter for various concentrations. To determine the reproducibility of transit time and retinal circulation time analyses, a randomly selected patient's angiogram was repeatedly analyzed by three observers and compared. From these data the inter- and intra-operator errors were also determined for successive frames and the reproducibility of the area under the dye dilution curves for both arteries and veins was computed. The overall densitometric reproducibility was found to be good; however, practical usefulness of the retinal circulation time remains to be established.

Angiography↗
PubMed1980

On the feasibility of densitometric assessment of cerebral aneurysms.

Computer-aided operator-interactive densitometry was used to study the feasibility of quantitating the radiographic images of cerebral aneurysms. Contrast-filled tubings of varying diameter were used to investigate the linearity of the system and to assess the general accuracy and reproducibility of the densitometric method. To study the reproducibility of the technique on aneurysms, a vein pouch aneurysm model was developed in rabbits. Inter- and intra-operator errors were determined by four observers, who performed multiple measurements on various projections of aneurysm images taken both in vitro and in vivo. These errors ranged between 3 and 8% for the in vitro data, and 7 and 22% for the in vivo data. It was found that the current approach that utilizes the linear segment of the film-screen characteristic curve has to be extended to involve the non-linear segment at the 'toe' section of the characteristic curve for future clinical applications.

Absorptiometry, Photon↗
PubMed1980

Visibility and sharpness of lung structure at 90, 140, and 350 kV.

Human lung specimens containing a variety of lesions were radiographed at 90, 140, and 350 kV. Nodules less than 3 mm in diameter and linear shadows less than 0.3 mm in diameter were either not visible or poorly seen at 350 kV. Larger lesions were seen well with all three kilovoltages, although the interfaces were more distinct on the 90- and 140-kV views. The best images were obtained at 90, slightly worse at 140, and least satisfactory at 350 kV; in general, however, most features of the normal and diseased lung were readily seen at all three kilovoltages. The apparent degradation of the lung image at high kV levels may be explained by the large focal spot of the 350-kV system and the attenuation properties of high-energy photons.

Humans↗
PubMed1980

Effect of radiographic magnification on image contrast of blood vessels.

Blood vessel phantoms 0.5--4 mm in diameter were radiographed with a 0.1 mm x-ray tube with and without scattering medium. The contrast of the blood vessel images was determined by densitometry. Without scattering medium, magnification did not increase the image contrast for 1 mm or larger vessels. With scattering medium, contrast improved significantly due to the reduction of scattered radiation by the air gap between object and film.

Absorptiometry, Photon↗
PubMed1979

Cine-densitometric measurement of coronary arterial stenoses.

Computer-aided operator-interactive densitometry has been developed and applied to determine the percent stenosis for obstructive lesions in the coronary arterial tree. Phantom experiments performed to assess system linearity, accuracy of densitometric measurements, nonuniformity in image amplified response, and the interference of structure noise in measuring precision have been described. Three observers assessed the reproducibility of the method by repeating analyses on 20 stenoses in man recorded on 35-mm cine angiograms. Calculation of the intra- and interobserver errors found that their values significantly decrease with increasing percent stenosis. The reproducibility of the technique was also tested on stenoses that were exposed at multiple angles. The results agreed with those found for the intra- and interoperator errors. Limitations of the densitometric approach and desirability of further automation of the measurements are also discussed.

Cineangiography↗
PubMed1979

Remote densitometric analysis of stenotic lesions.

In conventional densitometric evaluation of stenoses the digitized angiogram is displayed on a multi-grey-level scope to facilitate operator interaction. With a remote terminal, linked to the computer with regular telephone lines, such display is unacceptably slow. To circumvent this difficulty, the projection of the original image is used for interactions through a sonic pen digitizer interfaced to the computer. A coordinate system can be defined on the projected image, in addition to the blood vessel segment to be analyzed by the operator. The computer can retrieve these features on the stored-pre-digitized image to carry out the quantitative evaluation of the stenosis. This method reduces the time of analysis and allows several institutions to share the same computing facility.

Absorptiometry, Photon↗
PubMed1979

Minimum blood vessel diameter measured by magnification angiography.

Visibility of small blood vessels was improved by magnification angiography of biologic specimens. Blood vessel diameter was determined for increasing magnifications by various screen-film combination. Significantly smaller vessels were recognized with the magnification technique in all screen combinations. Noisy screen-film combinations with better square wave transfer functions did not allow visualization of blood vessels as small as those screen-film combinations with poorer square wave transfer functions but less noise.

Angiography↗
PubMed1979

Resting host and tumor perfusion as determinants of tumor vascular responses to norepinephrine.

Blood flow determinations and arteriograms were obtained in rat (Walker carcinoma) and rabbit (V2 carcinoma) liver tumors at rest and after norepinephrine administration. Resting tumor blood flow exceeded resting hepatic flow in both models, and both tumors responded with vasoconstriction and reduced blood flow. In tumors and the surrounding normal host tissue, the greater the perfusion prior to drug administration, the greater is the response (decrease in perfusion) to the vasoconstrictor. Although tumor perfusion decreased after vasoconstrictor, post-norepinephrine angiograms revealed an improved diagnostic image because of the enlarged but unresponsive tumor feeder vessels, persistent tumor blush, and simultaneous vasoconstriction in the normal liver. In these models, improved tumor visualization resulted even though a decrease in tumor blood flow had occurred. The angiographic image is related therefore to the lack of vasoconstriction in the tumor feeder vessel, which has, however, a decreased blood flow and the correspondingly greater volume of normally constricting hepatic arteries which results in a marked decrease in the background of vessels upon which the tumor image is superimposed.

Animals↗