Search PubMed⌕ Search

Biomedical subjects

B Waibel

Publications and source records attributed to B Waibel.

4 recordsLinked to original sources
PubMed2000

Storage of X-ray photons in a crystal resonator

The temporal structure and high brilliance of the X-ray beams produced by third-generation synchrotrons open up new possibilities in time-dependent diffraction and spectroscopy, where timescales down to the sub-nanosecond regime can now be accessed. These beam properties are such that one can envisage the development of the X-ray equivalent of optical components, such as photon delay lines and resonators, that have proved indispensable in a wide range of experiments--for example, pump-probe and multiple-interaction experiments--and (through shaping the temporal structure and repetition rate of the beams) time-dependent measurements in crystallography, physics, biology and chemistry. Optical resonators, such as those used in lasers, are available at wavelengths from the visible to soft X-rays. Equivalent components for hard X-rays have been discussed for more than thirty years, but have yet to be realized. Here we report the storage of hard X-ray photons (energy 15.817 keV) in a crystal resonator formed by two plates of crystalline silicon. The photons are stored for as many as 14 back-and-forth cycles within the resonator, each cycle separated by one nanosecond.

Journal Article↗
PubMed2000

Careful clinical monitoring in comparison to sequential Doppler sonography for the detection of acute rejection in the early phase after renal transplantation.

Acute rejection is the most frequent cause of early graft failure. There is unanimity that Doppler sonography is a helpful method for the detection of complications after kidney transplantation. In the past, the indication for renal biopsy relied mainly on clinical assessment, although this assessment has not been standardised. Therefore, we conducted this prospective study to compare the value of sequential Doppler measurements with a standardised clinical rejection score, based on renal function, weight gain, graft swelling and tenderness. Fifty-eight patients (37 males, 21 females, mean age 46 +/- 12 years) after kidney transplantation were consecutively enrolled into the study. Doppler investigations were obtained within the first 24 h after transplantation, followed by an interval of 48-72 h. At the same time, a clinical examination was scored by a transplant physician blinded to the Doppler results. Clinical score and Doppler results, both were referred to the histological results of renal biopsy. In 24 out of 58 patients 25 acute rejections occurred. In seven patients, acute rejection was superimposed on primary graft failure. The cut-off levels for rejection were set at RI > or = 0.80 and PI > or = 1.70 based on receiver-operator curves using data from 663 Doppler examinations. Sensitivity and specificity was 72% for RI, and 72% and 74% for PI, respectively. The calculation of the intraindividual increase (deltaRI > or = 3%, deltaPI > or = 10%) did not improve these values. The clinical score revealed a sensitivity and specificity of 82% and 87%, respectively. The combined analysis of Doppler indices and clinical score showed a sensitivity of 96% with a specificity of 66%. Careful clinical monitoring alone using a clinical score is an appropriate procedure with which to decide about renal biopsy. Our data show that Doppler sonography should be performed within the first 24 h after transplantation to evaluate graft perfusion and baseline values. Afterwards, it should be used when clinical signs of rejection occur to underline the decision for renal biopsy even in borderline cases.

Acute Disease↗