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Biomedical subjects

N Leitgeb

Publications and source records attributed to N Leitgeb.

32 records · Page 2Linked to original sources
PubMed1986

A new noninvasive quantitative method for fracture diagnosis.

Due to insufficient diagnostic possibilities the removal of the fixation in many cases is still a gamble with the patient as a loser. The urgent need for a sensitive and harmless method that can assist radiology can be met by new ultrasonic approach. Results of animal investigations are presented that prove that ultrasonic callus analysis (UCA) can be a useful tool for diagnosis of the fracture-healing progress, which provides efficient quantitative parameters for diagnosis and a new objective stability criterion.

Animals↗
PubMed1984

[Measuring the image quality of ultrasound B scanners].

Experience shows that both in the evaluation and in the purchase of ultrasonic scanners the subjective impression of the images plays a dominant role. The image intelligibility is investigated via tissue equivalent test phantoms and quantitatively analysed using the ROC (Receiver Operating Characteristic) method. Comparison of devices of different price categories shows that this investigation is an important addition to the analysis of image fidelity, provides additional important data for a comprehensive comparison of devices, and allows an objective determination of the price-benefit relation.

Humans↗
PubMed1982

[Experimental studies of signal fields of ultrasound broad band transducers].

Quantitative analysis of ultrasonic signals, as increasingly practised, makes it necessary to increase the band width as well as the efficiency of ultrasonic transducers. An broad band ultrasonic transducer is presented which meets the requirements by double lambda/4 layer matching and was specially designed for medical ultrasonic spectroscopy. In an extended measurement programme transmitter characteristic, spatial dependence of the spectral content of the transmitter signals as well as beam geometry and its frequency dependence are investigated and compared with conventional transducers.

Fourier Analysis↗
PubMed1979

Ultrasonic vitrectomy - an alternative technique to presently used mechanical procedures. Experimental results.

The liquification of the corpus vitreum by ultrasound is a promising new alternative to presently used mechanical methods of vitrectomy. With regard to the duration time of insonation, as well as to the ultrasonic intensity, there exist thresholds, the exceeding of which causes a discontinuous breakdown of the vitreous frame in a spherical zone around the transducer tip which can be verified by ultrasonic pulse echo methods. Viscosity measurements showed that the vitreous isonified in this area has almost the same viscosity as water whereas its optical transparency remains unchanged. The dependence of the diameter of the liquified zone on insonation time was measured.

Animals↗
PubMedDate not supplied

Electric current perception study challenges electric safety limits.

Although a key parameter for safety regulations, the electric current perception threshold is not sufficiently established yet. Present knowledge suffers from a lack of women's data, small numbers of data on investigation of men and investigated samples non-representative for the general population. With measurement at 708 adults aged between 16 and 60 years (349 men and 359 women) these deficiencies could be overcome. The results are important. They show that the perception variability among the general population is 100-fold higher than estimated so far and that the currently used estimate of the threshold is more than 10-fold too high. Besides this, it could be shown that there are an over-proportion of more sensitive women compared with men indicating the need for revision of the present assumptions on gender-specific differences in electrosensibility. The results show that the existing assumptions on safety limits and remaining safety factors need serious review. In any case, relaxation of safety requirements is not justified.

Adolescent↗
PubMedDate not supplied

Electric current perception of the general population including children and the elderly.

Although the 50 Hz electric current perception threshold is a key parameter for limiting electric touch currents in electrical technology and for limiting indirect effects of external electromagnetic fields, the data available mainly reflect men's perception ability; with only sparse data for women and almost none for children or the elderly. Measurements with 240 children aged 9 - 16 years, and 123 elderly people, allow this gap of knowledge to be filled. Taking into account the demographic age distribution, it was possible to generate a probability distribution representing the perception ability of the overall general population, and thus to provide a more established basis for deriving safety limits. The results show that the existing limit values for electric touch currents are considerably too high if compared with results derived from the new data with the same criteria. On the other hand, it appeared that children do not exhibit such a high sensitivity to electricity as assumed to date. Therefore, former rule-of-thumb estimates to account for higher sensitivities of children lie on the safe side. The presented assessment of the general population's electric current perception ability should stimulate a critical review of the existing regulations.

Adolescent↗
PubMedDate not supplied

Electric current perception of children: the role of age and gender.

Although it is widely accepted that children merit increased protection, little is known about the quantitative consequences of electric currents when setting safety limits. Measurements were performed on 240 children (117 girls and 123 boys) older than 9 years. It was found that the electrosensitivity of children was higher than that of adults, but did not exceed the overall span of adult electrosensitivity. Girls' results depend only weakly on age. Therefore, no major change should be expected below the age of 9. The electrosensitivity of boys increases with decreasing age; however, it finally approaches and merges with that of girls. The results imply that the factor by which the allowed touch current should be reduced for children depends on the perception probability level considered. The reduction factor of 2, as chosen in the past, would need revision either in regard to its value or to the related perception probability level. If related to the still existing rationale for safety limits the factor would need to be far higher.

Adolescent↗
PubMedDate not supplied

[Ultrasound hemolysis].

An ultrasound unit for hemolysis for an analytic device is presented which permits hemolysis without the need of a specific insonification chamber which is an unwanted discontinuity along the probe path. This is possible by direct insonification of a flexible tube which contains the flowing blood. The influence of ultrasound power, insonification time and coupling conditions on the result of hemolysis is investigated.

Blood Chemical Analysis↗
PubMedDate not supplied

[Eye heating caused by microwave ovens].

To clarify the question as to whether microwave ovens represent a risk for the eyes, a worst-case situation was investigated in which it was assumed that a child observes the internal heating process with its eyes as close to the door of a microwave oven as it is possible to get. As expected, heating of the eyes was observed, which, however, was caused mainly by the conventional heating process rather than by microwave radiation. Significant microwave heating was observed only when increased scattered radiation was simulated by inactivating the safety contacts and opening the door of the microwave oven. When the door is opened to a clearly visible gap width (2.3 cm), the contribution of the microwave component to the overall temperature increase of 5 degrees C after one hour of continuous exposure did not exceed 16%. Even at the maximum possible door gap width which just did not cause the oven to switch off automatically (2.6 cm), 15 minutes of continuous exposure contributed only 50% to the 2 degrees C temperature increase. On the basis of these results, damage to the eye through the use of microwave ovens can be excluded.

Animals↗