Biomedical subjects

G Michalski

Publications and source records attributed to G Michalski.

5 recordsLinked to original sources

PubMed2005

Comparison of rovibronic density of asymmetric versus symmetric NO2 isotopologues at dissociation threshold: broken symmetry effects.

We have measured the rovibronic densities of four symmetric (C2v) and two asymmetric (Cs) isotopologues of nitrogen dioxide just below their photodissociation threshold. At dissociation threshold and under jet conditions the laser-induced fluorescence abruptly disappears because the dissociation into NO(2pi(1/2)) + O(3P2) is much faster than the radiative decay. As a consequence, in a narrow energy range below D0, the highest bound rovibronic energy levels of J=1/2 and J=3/2 can be observed and sorted. A statistical analysis of the corresponding rovibronic density, energy spacing, and rovibronic transition intensities has been made. The observed intensity distributions are in agreement with the Porter-Thomas distribution. This distribution allows one to estimate the number of missing levels, and therefore to determine and compare the rovibronic and the vibronic densities. The four symmetric NO2 isotopologues, 16O14N16O, 18O14N18O, 16O15N16O, and 18O15N18O, have, respectively, a sum of J=1/2 and J=3/2 rovibronic densities of 18+/-0.8, 18.3+/-1.4, 18.4+/-2.7, and 19.8+/-3.5 cm(-1), while for the two asymmetric isotopologues, 18O14N16O and 18O15N16O, the corresponding densities are 20.9+/-4.5 and 23.6+/-5.6 cm(-1). The corresponding vibronic densities are in agreement only if we include both the merging of symmetry species (from those of C2v to those of Cs) and the contribution of the long-range tail(s) of the potential-energy surface along the dissociation coordinate. The effects of isotopic substitution on dissociation rates and the possible relation to mass-independent isotopic fractionation are discussed.

Journal Article↗

PubMed2004

Dissociation energies of six NO2 isotopologues by laser induced fluorescence spectroscopy and zero point energy of some triatomic molecules.

We have measured the rotationless photodissociation threshold of six isotopologues of NO2 containing 14N, 15N, 16O, and 18O isotopes using laser induced fluorescence detection and jet cooled NO2 (to avoid rotational congestion). For each isotopologue, the spectrum is very dense below the dissociation energy while fluorescence disappears abruptly above it. The six dissociation energies ranged from 25 128.56 cm(-1) for 14N16O2 to 25 171.80 cm(-1) for 15N18O2. The zero point energy for the NO2 isotopologues was determined from experimental vibrational energies, application of the Dunham expansion, and from canonical perturbation theory using several potential energy surfaces. Using the experimentally determined dissociation energies and the calculated zero point energies of the parent NO2 isotopologue and of the NO product(s) we determined that there is a common De = 26 051.17+/-0.70 cm(-1) using the Born-Oppenheimer approximation. The canonical perturbation theory was then used to calculate the zero point energy of all stable isotopologues of SO2, CO2, and O3, which are compared with previous determinations.

Journal Article↗

PubMed2002

[Therapy of acute mastoiditis].

BACKGROUND: Acute otitis media is a common disease, mostly contracted at childhood. The development of acute mastoiditis has been decreased since the introduction of antibiotics. Currently it is only developed in 0.004 % cases of acute otitis media. But despite of this fact, even today one should not neglect this condition as the complications such as intracranial spread and lateral sinus thrombosis are still life threatening. METHODS AND PATIENTS: In a retrospective study from 01/96 - 09/00 we reviewed the cases of acute mastoiditis as a result of acute otitis media at our department. Additionally we compared study results out of 1972 until 1989 with our current results. RESULTS: Altogether mastoidectomy has been carried out at 157 patients. The cases have steadily increased since 1996. This is confirmed by comparison with study results of previous years. The majority of the patients were between 8 months and 3 years old (60 %). When the patients first presented at our department, the first signs of otitis media were 19.5 days ago in average. 38 % of the patients received no antibiotic treatment before admission. A thickened mucous membrane was seen by the mastoidectomy mostly (58 %). A subperiostal abscess we noted in 8.5 %. The most common isolated bacteria were Streptococcus pneumoniae (33 %) and Streptococcus pyogenes (11 %). The patients stayed at the department about 10 days. In comparison to recent study results the "typical" mastoiditis has decreased. The causative pathogens have not changed. CONCLUSIONS: In the last years we realised an increasing number of mastoiditis at our department. The isolated bacteria are the same as presented in the literature. Early surgery combined with an effective antibiotic treatment can avoid the known complications of mastoiditis.

Acute Disease↗

PubMed1999

[Assessment of the effective dose for routine protocols in conventional CT, electron beam CT and coronary angiography].

PURPOSE: To compare the effective dose applied by sequential CT (SEQ), spiral CT (SCT), electron beam CT (EBT) and coronary angiography for investigations of the chest, abdomen and the heart. METHODS: The Alderson Phantom was used to compare the effective dose for all modalities. In addition, the effective dose for conventional CT (SEQ and SCT) was estimated with a mathematical phantom. RESULTS: For CT investigation of the chest and abdomen the dose was highest for the EBT (11 mSv and 25 mSv, respectively) and slightly lower for the SEQ (7.8 mSv and 21.5 mSv, respectively), whereas spiral CT required the least dose (5.3 mSv and 8.8 mSv, respectively). For coronary calcium screening (0.8 mSv) and EBT coronary angiography (1.7 mSv) the dose was lower than for coronary catheter angiography (3.3 mSv). For conventional CT the difference between the effective dose derived by the mathematical phantom and by the Alderson phantom was 2% to 20%. CONCLUSIONS: For investigations of the chest and abdomen the effective dose applied by SCT is significantly lower than that with EBT and SEQ. For investigation of the coronary arteries the effective dose applied by EBT is lower than that for coronary catheter angiography.

Body Burden↗

PubMed1998

[Virtual colonoscopy using CT and MRI].

PURPOSE: To evaluate experimentally and in patients the sensitivity and effective dose of virtual electron-beam tomography (EBT) colonoscopy for detecting small colon tumors and to compare the methods and results with virtual colonoscopy using spiral CT and MR imaging in a review of the literature. MATERIALS AND METHODS: Six polyps with diameters between 3 and 12 mm were created and randomly placed in resected pig colon. After distension with air, the pig colon was scanned with continuous volume scanning (CVS, 3 mm collimation) and a pitch of 0.4, 0.8 and 1.5. Twenty patients positive for the fecal blood test were examined after rectal CO2 insufflation and i.v. administration of 1 mg glucagon. A 13 s CVS scan was used to cover the entire colon within one breath-hold. 3D volume-rendered fly-throughs were evaluated by two independent radiologists. Effective dose equivalent was estimated using an Alderson phantom equipped with thermoluminescence dosimeters. RESULTS: In the tumor model, all polyps were detectable at a pitch of 1.5. A further reduction of the pitch ratio did not improve the conspicuity of the polyps. In patient studies, all tumors (n = 4) and polyps (n = 3) were correctly identified on 3D fly-throughs. Two false positive results were obtained. Effective dose equivalent was calculated at 3.2 mSv per scan. CONCLUSIONS: Our preliminary results indicate that virtual EBT colonoscopy holds promise for fast screening for colon polyps. The best technique for virtual colonoscopy (Spiral CT, EBT, MRI) has not yet been determined and the future role of virtual colonoscopy must still be defined.

Colonic Polyps↗