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Biomedical subjects

S Schalla

Publications and source records attributed to S Schalla.

9 recordsLinked to original sources
PubMed2007

Influence of different dose rates on cell recovery and RBE at different spatial positions during protracted conformal radiotherapy.

The effect of simultaneous induction and repair of sub-lethal lesions during protracted irradiation is potentially important for conformal irradiation techniques and may influence the relative biological effectiveness (RBE) of different radiation qualities. The importance of repair for 50 kV X rays from a miniaturised X-ray source producing an essentially isotropic dose distribution for intra-operative radiotherapy (IORT) was verified for inactivation of V79 cells in different distances from the source. The experimental data were evaluated in terms of the linear-quadratic model and the generalised Lea-Catcheside time factor. Furthermore, the shape of survival curves for 14 MeV [d(0.25) + T] neutrons at different dose rates implicated a role of repair for fast neutrons. Microdosimetric measurements have previously demonstrated variations in radiation quality between different positions in a therapy phantom for conformal moving-beam therapy with this radiation. Experimental data on the effectiveness for inactivation of V79 cells irradiated at such positions are presented and the influence of repair is analysed.

Animals↗
PubMed2001

Comparison of magnetic resonance real-time imaging of left ventricular function with conventional magnetic resonance imaging and echocardiography.

This study analyzes the accuracy of a new real-time magnetic resonance imaging (MRI) technique (acquisition duration, 62 ms/image) and echocardiography for the determination of left ventricular (LV) end-diastolic volume, end-systolic volume, ejection fraction, and muscle mass when compared with turbo gradient echo imaging as the reference standard. Thirty-four patients were examined with digital echocardiography, standard, and real-time MRI. A close correlation was found between the results of real-time imaging and the reference standard for end-diastolic volume, end-systolic volume, and ejection fraction (r >0.95), with a lower correlation for LV muscle mass (r = 0.81). Correlations between echocardiography and the reference standard were lower for all parameters. Real-time MRI enables the acquisition of high-quality cine loops of the entire heart in minimal time without electrocardiographic triggering or breath holding. Thus, patient setup and scan time can be reduced considerably. Results are similar to the reference standard and superior to echocardiography for determining LV volumes and ejection fraction. This technique is a valid alternative to current approaches and can form the basis of every cardiac MRI examination.

Adult↗
PubMed2001

Multi-slice dynamic imaging: complete functional cardiac MR examination within 15 seconds.

A new magnetic resonance (MR) sequence was developed to acquire real-time images in a multi-slice dynamic imaging mode to cover the complete heart in 15 seconds without the need for electrocardiogram (ECG) triggering and multiple breath holds. In 34 patients, left ventricular function was assessed with the new technique and a standard technique. The new technique proved to be feasible and accurate for functional cardiac examinations.

Adult↗
PubMed2001

Magnetic resonance flow measurements in real time: comparison with a standard gradient-echo technique.

Ultrafast gradient systems and hybrid imaging sequences offer the opportunity to acquire phase contrast flow data in real time. In a 1.5-Tesla magnetic resonance (MR)-tomograph, peak velocity and volume flow were assessed in 36 large vessels (aorta) and 33 medium-sized vessels (carotid and iliac artery) using a real-time (segmented k-space turbo gradient-echo planar imaging sequence) in comparison with a gradient-echo technique. With the real-time technique, the matrix was reduced from 116 to 64, and temporal resolution changed from 30 msec to 124 msec. Measurements of peak velocity correlated in large (r = 0.88) and medium-sized vessels (r = 0.81). Volume flow measurements correlated in large vessels (r = 0.87), however, a poor correlation (r = 0.64) was found in medium-sized vessels. Thus, scan time can be significantly reduced and images acquired without electrocardiogram (ECG)-triggering. Flow volume can only be determined in large vessels with sufficient accuracy, mainly due to reduced spatial resolution in smaller vessels.

Blood Flow Velocity↗
PubMed2000

Magnetic resonance real-time imaging for the evaluation of left ventricular function.

New ultrafast gradient systems and hybrid imaging sequences make it possible to acquire a complete image in real time, without the need for breathholding or electrocardiogram (ECG) triggering. In 21 patients, left ventricular function was assessed by the use of a turbo-gradient echo technique, an echo-planar imaging (EPI) technique, and a new real-time imaging technique. End-diastolic and end-systolic volumes, left ventricular muscle mass, and ejection fraction of the ultrafast techniques were compared with the turbo-gradient echo technique. Inter- and intraobserver variability was determined for each technique. Image quality was sufficient for automated contour detection in all but two patients in whom foldover occurred in the real-time images. Results of the ultrafast imaging techniques were comparable with conventional turbo-gradient echo techniques. There was a tendency to overestimate the end-diastolic volume by 3.9 and 1.3 ml with EPI real-time imaging, the end-systolic volume by 0.9 and 5.0 ml, and the left ventricular mass by 2.6 and 23.8 g. Ejection fraction showed a tendency to be overestimated by 1.1% with EPI and underestimated by 4.5% with real-time imaging. Correlation between EPI real-time imaging and turbo-gradient echo were 0.94 and O.95, respectively, for end-diastolic volumes, 0.98 and 0.96, respectively, for end-systolic volumes, and 0.96 and 0.89, respectively, for left ventricular mass. Inter- and intraobserver variability was low with all three techniques. Real-time imaging allows an accurate determination of left ventricular function without ECG triggering. Scan times can be reduced significantly with this new technique. Further studies will have to assess the value of real-time imaging for the detection of wall motion abnornmalities and the imaging of patients with atrial fibrillation.

Analysis of Variance↗
PubMed1999

Morphological and compositional changes in a planktonic bacterial community in response to enhanced protozoan grazing.

We analyzed changes in bacterioplankton morphology and composition during enhanced protozoan grazing by image analysis and fluorescent in situ hybridization with group-specific rRNA-targeted oligonucleotide probes. Enclosure experiments were conducted in a small, fishless freshwater pond which was dominated by the cladoceran Daphnia magna. The removal of metazooplankton enhanced protozoan grazing pressure and triggered a microbial succession from fast-growing small bacteria to larger grazing-resistant morphotypes. These were mainly different types of filamentous bacteria which correlated in biomass with the population development of heterotrophic nanoflagellates (HNF). Small bacterial rods and cocci, which showed increased proportion after removal of Daphnia and doubling times of 6 to 11 h, belonged nearly exclusively to the beta subdivision of the class Proteobacteria and the Cytophaga-Flavobacterium cluster. The majority of this newly produced bacterial biomass was rapidly consumed by HNF. In contrast, the proportion of bacteria belonging to the gamma and alpha subdivisions of the Proteobacteria increased throughout the experiment. The alpha subdivision consisted mainly of rods that were 3 to 6 microm in length, which probably exceeded the size range of bacteria edible by protozoa. Initially, these organisms accounted for less than 1% of total bacteria, but after 72 h they became the predominant group of the bacterial assemblage. Other types of grazing-resistant, filamentous bacteria were also found within the beta subdivision of Proteobacteria and the Cytophaga-Flavobacterium cluster. We conclude that the predation regimen is a major structuring force for the bacterial community composition in this system. Protozoan grazing resulted in shifts of the morphological as well as the taxonomic composition of the bacterial assemblage. Grazing-resistant filamentous bacteria can develop within different phylogenetic groups of bacteria, and formerly underepresented taxa might become a dominant group when protozoan predation is the major selective pressure.

Animals↗
PubMed1998

Changes in RBE of 14-MeV (d + T) neutrons for V79 cells irradiated in air and in a phantom: is RBE enhanced near the surface?

PURPOSE: The relative biological effectiveness (RBE) for inactivation of V79 cells was determined as function of dose at the Heidelberg 14-MeV (d + T) neutron therapy facility after irradiation with single doses in air and at different depths in a therapy phantom. Furthermore, to assess the reproducibility of RBE determinations in different experiments we examined the relationship between the interexperimental variation in radiosensitivity towards neutrons with that towards low LET 60Co photons. METHODS: Clonogenic survival of V79 cells was determined using the colony formation assay. The cells were irradiated in suspension in small volumes (1.2 ml) free in air or at defined positions in the perspex phantom. Neutron doses were in the range, Dt = 0.5-4 Gy. 60Co photons were used as reference radiation. RESULTS: The radiosensitivity towards neutrons varied considerably less between individual experiments than that towards photons and also less than RBE. However, the mean sensitivity of different series was relatively constant. RBE increased with decreasing dose per fraction from RBE = 2.3 at 4 Gy to RBE = 3.1 at 0.5 Gy. No significant difference in RBE could be detected between irradiation at 1.6 cm and 9.4 cm depth in the phantom. However, an approximately 20% higher RBE was found for irradiation free in air compared with inside the phantom. Combining the two effects, irradiation with 0.5 Gy free in air yielded an approximately 40% higher RBE than a dose of 2 Gy inside the phantom. CONCLUSION: The measured values of RBE as function of dose per fraction within the phantom is consistent with the energy of the neutron beam. The increased RBE free in air, however, is greater than expected from microdosimetric parameters of the beam and may be due to slow recoil protons produced by interaction of multiply scattered neutrons or to an increased contribution of alpha particles from C(n, alpha) reactions near the surface. An enhanced RBE in subcutaneous layers of skin combined with an increase in RBE at low doses per fraction outside the target volume could potentially have significant consequences for normal tissue reactions in radiotherapy patients treated with fast neutrons.

Air↗