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Biomedical subjects

N Leitgeb

Publications and source records attributed to N Leitgeb.

At least 19 recordsLinked to original sources
PubMed2001

[Risk from electric current greater than assumed].

Despite its importance for the assessment of the effects of electric current and for technical safety considerations, not only does the electric perception threshold remain uncertain, but essential questions are still unanswered and contradictions unresolved. Via measurements at 908 persons randomly selected from the general population, including 708 adults (349 men, 359 women aged between 16 and 60 years), the problems of extrapolation to the general population and adequate statistical representation have now been overcome for the first time. The results show that existing assumptions about electric current perception need to be drastically corrected. It has been shown that the assumed electric perception threshold has been too high by a factor of 10, and that women are substantially more sensitive than men. This means that present gender-specific differences in electrosensitivity need revising. On the basis of the evidence of significant underestimation of the reaction variability in the general population, present assumptions on safety limits and safety factors urgently need to be reviewed. By no means can a relaxation of safety regulations be justified.

Adolescent↗
PubMed1994

Quantitative assessment of fracture healing. The value of computerised sonometry in a correlative animal experiment in sheep.

Usually follow-up of the healing process of bone fractures is by subjective assessment of standard X-rays, based on the clinician's personal experience. It is therefore impossible to completely avoid misjudgements in the evaluation of the mechanical stability. Other authors have reported that the mechanical response of bony structures to a knock impulse allows a definitive statement about the stiffness of a fracture. The practicability of computerised sonometry in computer-aided evaluation of the mechanical vibration reaction and the acoustic transmission of sound through osseous structures for assessing stability has been proved in experimental and clinical studies. We designed an animal study that would allow a systematic correlation between the diagnostic investigations in general use. As a main goal, this study tries to correlate sonography with other quantitative techniques, even if they are not used under everyday clinical conditions. Our results show that methods based on direct assessment of the mechanical stability between fracture fragments allow a more exact evaluation of fracture healing. This study helps to classify the results of computerised sonometry together with other diagnostic procedures used for the evaluation of fracture healing, and furthermore provides a basis for clinical interpretation of the findings of a new, non-invasive technique for precise quantitative assessment of fracture healing.

Animals↗
PubMed1994

Early detection of delayed union in lower leg fractures using a computerised analysis of mechanical vibration reactions of bone for assessing the state of fracture healing.

Standard X-ray techniques are used to follow up the healing process of bone fractures. However, these methods allow only indirect conclusions about the stability of the healing bone, depending on the experience of the clinician. In addition, by radiologic means, delayed union or non-union can only be diagnosed on the basis of the absence of specific changes such as callus formation. Therefore, efforts have been made to develop alternative methods for monitoring the healing process. The measuring principle of a non-invasive method is based on evaluation of changes in mechanical vibration reactions. The measuring system is composed of two sound transducers, an amplifier module and an AD converter attached to a PC. The assessment of 150 healthy individuals as well as an initial measuring series after treatment of tibial fractures with an external fixator system revealed highly significant differences between intact and fractured tibias. Thus, computerised sonometry is capable of supplying quantitatively recordable information about the stability of a fractured bone at any time in the healing process. Furthermore, this non-invasive technique allows early diagnosis of disorders in the repair process by the absence of change in the parameters.

Biomechanical Phenomena↗
PubMed1993

[Computerized sonometry--use of a noninvasive procedure for evaluating stability after fractures].

Common techniques to assess the healing process of fractures are usually related to the experience of the clinician. However, standard x-rays allow only indirect conclusions on the stability of the healing bone. In addition to the radiological examination delayed union or non-union can only be diagnosed in the absence of specific changes such as callus formation. Computerised sonometry comprises the analysis of mechanical vibration as well as sound transmission during or after bone healing. This non-invasive method allows for assessing the stiffness of the bone quantitatively and gives objective data on bone stability.

Auscultation↗
PubMed1993

[Analysis of epidemiologic studies of magnetic field-induced cancer risk].

Since 1979 in numerous epidemiological studies with different design and conflicting results the possibility of a relationship between cancer and exposure to magnetic fields was investigated. By combined evaluation of 39 studies it can be stated that the time dependence of the results seems to support the hypothesis that no risk should be expected or that it is at least lower than presently assumed.

Brain Neoplasms↗
PubMed1990

[Ultrasonic diagnosis of fractures].

For the first time, sonographic callus diagnosis concentrates not on the fracture gap but on the conversion process within the surrounding callus region to determine healing and reloadability of fractures. On evaluation of callus texture in relation to the adjacent muscle tissue a sensitive diagnostic parameter can be determined from B-scan images even in a clinical routine situation which is suitable for the monitoring of healing as well as determination of the fracture status. The results of a clinical study are presented and a parameter range is determined which can be used as a criterium for tibia fracture stability and reloadability. Principal agreement of parameter dependence on healing time is shown by fibula fracture diagnosis, too.

Bone and Bones↗
PubMed1990

[Cyclotron resonance as a cause of biological effects of weak electric and magnetic fields?].

Even weak electric and magnetic fields have been found to cause interaction effects in vitro only within small frequency ranges. The existence of such "frequency windows" may be explained by a cyclotron resonance model which also takes the influence of the earth's magnetic field into consideration. In this paper analytical relations are developed which permit the determination of energy uptake and motion curve diameter. On the basis of this calculations it can be concluded that, giving consideration to interparticle interactions and the limitations of motion curve dimensions due to the limited dimensions of cells and cellular interspaces, energy uptake in vivo is many orders of magnitude below thermal energy, and can therefore be neglected.

Biophysical Phenomena↗
PubMed1988

[Technical aspects of ultrasound equipment today and tomorrow].

From the very beginning any progress in the technique of instruments used in sonography has been strongly dependent upon the general technical progress, and any such progress must take place within the physically postulated marginal conditions. Now that the image quality has been considerably improved, the present situation is characterised by the fact that sonographic diagnosis is developing from a qualitative method into a quantitative one. This will be made possible by means of computerised tissue differentiation which is already being utilised in practice by means of trend analyses, by new sonography parameters (multiparameter imaging) and by the use of digital reconstruction methods. Another substantial improvement in the technique of instruments will be brought about mainly by the extremely rapid strides made by digital technique, by further development of the weak point represented by the transducers, and by improved possibilities of display.

Equipment Design↗
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↗