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Biomedical subjects

A Melzer

Publications and source records attributed to A Melzer.

At least 19 recordsLinked to original sources
PubMed2006

Obliquely propagating dust-density plasma waves in the presence of an ion beam.

Self-excited dust-density waves are experimentally studied in a dusty plasma under microgravity. Two types of waves are observed: a mode inside the dust volume propagating in the direction of the ion flow and a new mode propagating obliquely at the boundary between the dusty plasma and the space-charge sheath. A model for dust-density waves propagating at an arbitrary angle with respect to the ion-flow direction is presented, which explains the preference for oblique or parallel modes as a function of ion velocity.

Journal Article↗
PubMed2006

Targeted-HASTE imaging with automated device tracking for MR-guided needle interventions in closed-bore MR systems.

Percutaneous MR-guided interventions with needles require fast pulse sequences to image the needle trajectory with minimal susceptibility artifacts. Spin-echo pulse sequences are well suited for reducing artifact size; however, even with single-shot turbo spin-echo techniques, such as rapid acquisition with relaxation enhancement (RARE) or half-Fourier acquisition single-shot turbo spin-echo (HASTE), fast imaging remains challenging. In this work we present a HASTE pulse sequence that is combined with inner-volume excitation to reduce the scan time and limit the imaging field of view (FOV) to a small strip close to the needle trajectory (targeted-HASTE). To compensate for signal saturation from fast repeated acquisitions, a magnetization restore pulse (driven equilibrium Fourier transform (DEFT)) is used. The sequence is combined with dedicated active marker coils to measure the position and orientation of the needle so that the targeted-HASTE image slice is automatically repositioned. In an animal experiment the coils were attached to an MR-compatible robotic assistance system for MR-guided interventions. Needle insertion and infusion via the needle could be visualized with a temporal resolution of 1 s, and the needle tip could be localized even in the presence of a stainless steel mandrel.

Animals↗
PubMed2005

[Necessity for blood transfusion in head and neck surgery].

INTRODUCTION: Sometimes, use of blood products is necessary in head and neck surgery, but blood transfusion also entails risks for the patients and causes high costs for the department. Therefore, we examined the surgical procedures in our department and analysed how often transfusion of blood was necessary and which expenses were incurred. METHODS: Of 3989 operations performed in 1989, 187 patients were found to be at an increased risk for blood loss. The costs for blood group analysis (euro 23.16), cross-testing (euro 13.91) and the transfusion itself (euro 70.35) were estimated in each patient. RESULTS: In 1998 more than 60% of the 187 patients had undergone extensive head and neck surgery for advanced squamous cell carcinoma. Only 17 patients (<15%) received nearly 45% of all units of stored blood transfused that year. In patients who had undergone skull base surgery, the probability of receiving blood was 30%. The transfusion-related costs were estimated to be euro 20,000 during the observation period. Potential savings could have been achieved in cross-testing. CONCLUSION: Preparations should be done on an individual basis. Such preparations are sometimes unnecessary even in patients undergoing surgical procedures with a high risk for blood loss.

Blood Grouping and Crossmatching↗
PubMed2004

Melting and heating of two-dimensional Coulomb clusters in dusty plasmas.

The heating and melting of two-dimensional dust clusters with one additional particle in the lower layer has been investigated experimentally in a gas discharge. The full dynamical properties of the system during the entire phase transition were determined in terms of the spectral power densities of the crystal modes. A two-step melting transition is identified when the gas pressure in the discharge is reduced: first, a sudden increase of the dust temperature takes place due to an instability of the lower-layer particle resulting in a hot crystalline state of the cluster, and second, the actual transition into a fluid state is observed at a decisively lower gas pressure.

Journal Article↗
PubMed2004

Dust-free regions around Langmuir probes in complex plasmas under microgravity.

Dust-free regions around a Langmuir probe are studied in a complex plasma under microgravity. The dust particles settle in the presheath of the probe, where an equilibrium of the electric field force and the ion-drag force is established. The size and shape of the dust cloud are discussed with simple models. A more sophisticated presheath model is solved numerically to analyze the acting forces and the equilibrium position of the dust. The formation of distinct particle layers in the dust shell can be explained by the force gradients of the effective potential well.

Journal Article↗
PubMed2003

Mode spectra of thermally excited two-dimensional dust Coulomb clusters.

The mode spectra of finite Coulomb clusters, confined systems of charged microspheres in a complex plasma, have been determined experimentally. The spectral power density of all possible modes has been measured for particle numbers between N=3 and N=145 under different plasma conditions. The agreement between measured and calculated mode frequencies is found to be very good. From this, the parameters of the particle interaction, like particle charge and screening strength, have been extracted quantitatively. In addition, the particle and mode temperatures have been obtained. The modes and the particles show the same temperature and the principle of equipartitition holds for these systems. Moreover, certain modes of interest have been compared among the different clusters, as there are the breathing mode and intershell rotation as well as the lowest- and highest-frequency modes. Moreover, the mode-integrated spectrum shows two broad maxima which are explained from "shearlike" or "compressionlike" modes. From this analysis, the transition from finite number to crystal-like properties is observed to occur around N=12 particles. Finally, a model to visualize the transition from normal mode oscillations to wave dispersions in a 2D lattice has been proposed.

Journal Article↗
PubMed2001

Normal modes of 2D finite clusters in complex plasmas.

Finite clusters with a small number of charged particles immersed in a complex-plasma environment have been investigated experimentally. Finite clusters in complex plasmas are shown to be a unique system for the excitation and observation of normal modes in bounded charged-particle systems. In systems of 3, 4, and 7 particles, normal-mode oscillations have been excited and from the frequencies of the different modes the key parameters, particle charge, and the screening strength have been derived. This method is proposed to be applied in future microgravity experiments.

Journal Article↗
PubMed2001

Nonlinear resonances of particles in a dusty plasma sheath.

Vertical oscillations of microparticles trapped in the sheath of a capacitive rf discharge have been excited showing a strongly nonlinear resonance. The nonlinear oscillations are analyzed in terms of an anharmonic fourth-order potential energy curve. It is demonstrated that the observed nonlinearities can be related to a position dependent charge of the microspheres, whereas the electric field is found to be as nearly linearly increasing. The experimental results on the position dependent charging and electric field structure are compared to a numerical model.

Journal Article↗
PubMed2001

The active magnetic resonance imaging stent (AMRIS): initial experimental in vivo results with locally amplified MR angiography and flow measurements.

RATIONALE AND OBJECTIVES: Magnetic resonance (MR) is limited by artifacts in vessels after stenting. An active MR imaging stent (AMRIS) allows for artifact-free imaging with local improvement in signal-to-noise ratio (SNR). In a rabbit model, we evaluated the imaging properties by MR angiography (MRA) and flow measurements. METHODS: The AMRIS was placed in the abdominal aorta of five rabbits. At 1.5 T, MRA (three-dimensional fast low-angle shot) was performed before and after intravenous injection of an iron oxide-based, blood-pool contrast medium (dose, 50 micromol Fe/kg), and flow measurements were performed (electrocardiographically triggered phase-contrast cine gradient-echo sequence). Mean SNRs were calculated and flow volume curves were generated. RESULTS: The SNR was 6.0 +/- 0.6 (outside the stent) versus 12.3 +/- 1.1 (inside the stent, P < 0.05) for plain MRA, 21.2 +/- 0.6 versus 40.6 +/- 5.2 (P < 0.05) for contrast-enhanced MRA, and 5.4 +/- 0.4 versus 13.7 +/- 2.1 (P < 0.05) for the magnitude images of flow measurements. Flow volume curves within and distal to the stent were comparable. CONCLUSIONS: By using the AMRIS as a vascular stent, the stented vessel segment can be examined with enhanced signal intensity on MRI.

Animals↗
PubMed2001

Presentation of a kindred with familial medullary thyroid carcinoma and Cys611Phe mutation of the RET proto-oncogene demonstrating low grade malignancy.

OBJECTIVE: Both multiple endocrine neoplasia type 2A (MEN 2A) and familial medullary thyroid carcinoma (FMTC) are caused by germline mutations of the RET proto-oncogene. A broad spectrum of malignancy within and between families has been described with no clear genotype-phenotype correlation due to a scarcity of available data of large kindreds. DESIGN: Here we present the only known family with a germline mutation of codon 611 TGC to TTC (exon 10) in the RET proto-oncogene leading to a replacement of cysteine by phenylalanine (Cys611Phe or C611F). RESULTS: Twenty family members of this large kindred are gene carriers (GCs) and seven (5-13 years old) are potential carriers but have yet to be analysed. The clinical course of medullary thyroid carcinoma (MTC) in this family is characterized by a very slow evolution and progression of the tumour with no MTC-related death to date. Of 11 patients (30-69 years old) having undergone thyroidectomy six were classified as pT1, four as pT2 and one as C-cell hyperplasia according to the TNM system of the International Union Against Cancer. Due to cervical and mediastinal lymph node metastasis one patient (44 years old) had to be operated on a second time. The seven non-operated GCs of the fourth and fifth generation (17-26 years old) are yearly monitored with pentagastrin stimulation tests; one non-operated GC (43 years old) has refused any further investigations. Screening for primary hyperparathyroidism and phaeochromocytoma was negative in all cases. CONCLUSION: We suggest from these experiences that the general advice for thyroidectomy in early childhood should be modified in certain families, depending on genotype.

Adrenal Gland Neoplasms↗
PubMed2001

The influence of nurses' knowledge, attitudes, and health beliefs on their safe behavior with cytotoxic drugs in Israel.

The purpose of this study was to examine the influence of the nurses' knowledge, attitudes, and health beliefs on their behavior and their actual usage of safety measures while handling cytotoxic drugs in their daily work surroundings. The Health Belief Model (HBM) and its extensive form, the Protection Motivation Theory (PMT), were used as the theoretical frameworks. Sixty-one nurses participated in the study, 31 hospital-based nurses daily exposed to cytotoxic drugs for the last 5 years, and 30 non-exposed community nurses. An occupational questionnaire was used to test the nurses' actual safe behavior and compliance with the recommended guidelines. A randomly selected group of exposed nurses were observed to validate their compliant behavior. A gap was found between the nurses' knowledge and their actual behavior concerning the potential risks of cytotoxic drugs and their use of protective measures (p < .005). Significant correlations were found among the components of the extensive HBM (perceived susceptibility, barriers, benefits and self-efficacy). The observational findings supported the above results. The study's findings support the need to promote primary prevention by providing a safe environment for the employee by means of education, training with regard to safety measures, clear policy, written guidelines and their enforcement.

Adult↗
PubMed2000

Melting of dust plasma crystals with defects

The role of defects in the melting transition of a bilayer dust plasma crystal with vertical alignment is studied using Langevin molecular dynamics simulations. Two types of defects are considered: (i) point defects and dislocations and (ii) additional particles which are placed below and above the bilayer crystal (i.e., the so-called strong defects). It is shown that the presence of point defects and a few dislocations does not change the two-step melting scenario previously found for nondefect bilayer crystals. This contrast with the influence of the strong defects which leads to a substantial increase of the kinetic energy of particles and to local heating of the bilayer dust crystal.

Journal Article↗
PubMed2000

Laser-excited mach cones in a dusty plasma crystal

Experimental studies of the formation and structure of Mach cones in a plasma crystal are presented. Plasma crystals are ordered structures of charged microspheres trapped in the sheath of an rf discharge plasma. Using a monolayer crystal with a hexagonal lattice, Mach cones were excited by the radiation pressure of a focused laser beam. The beam was swept at a supersonic speed through the crystal, in a controlled and repeatable manner. A multiple Mach cone structure was observed, with at least three distinct Mach cones. The Mach angle relation was verified over a wide range of Mach numbers, for both the first and second cones. The sound speed, measured from the first Mach angle, was found to increase with the particle number density. Two methods of determining the particle charge and screening distance are developed, making use of the sound speed and an assumption of a Yukawa interparticle potential. Molecular-dynamics simulations of the experiment were carried out, using a monolayer of particles interacting through a Yukawa potential, and these show close agreement with the experiment.

Journal Article↗
PubMed1999

Ultrasonic dissection for endoscopic surgery. The E.A.E.S. Technology Group.

With the development of endoscopic surgery, new hazards of high-frequency (HF) electrosurgery have been recognized. The potential risks of monopolar electrosurgery, the limitations of bipolar technique, and the need to reduce instrument interchange have favored the use of ultrasonic technology, which becomes more and more popular. This work aims at presenting the main features of the currently available ultrasonically activated scalpels, as well as their advantages, limitations, and indications.

Dissection↗
PubMed1999

Phylogeographic differentiation in the mitochondrial control region in the koala, Phascolarctos cinereus (Goldfuss 1817).

The koala, Phascolarctos cinereus, is a geographically widespread species endemic to Australia, with three currently recognized subspecies: P.c. adustus, P.c. cinereus, and P.c. victor. Intraspecific variation in the mitochondrial DNA (mtDNA) control region was examined in over 200 animals from 16 representative populations throughout the species' range. Eighteen different haplotypes were defined in the approximately 860 bp mtDNA control region, as determined by heteroduplex analysis/temperature gradient gel electrophoresis (HDA/TGGE). Any single population typically possessed only one or two haplotypes yielding an average within-population haplotypic diversity of 0.180 +/- 0.003, and nucleotide diversity of 0.16%. Overall, mtDNA control region sequence diversity between populations averaged 0.67%, and ranged from 0% to 1.56%. Nucleotide divergence between populations averaged 0.51%, and ranged from 0% to 1.53%. Neighbour-joining methods revealed limited phylogenetic distinction between geographically distant populations of koalas, and tentative support for a single evolutionarily significant unit (ESU). This is consistent with previous suggestions that the morphological differences formalized by subspecific taxonomy may be interpreted as clinal variation. Significant differentiation in mtDNA-haplotype frequencies between localities suggested that little gene flow currently exists among populations. When combined with microsatellite analysis, which has revealed substantial differentiation among koala populations, we conclude that the appropriate short-term management unit (MU) for koalas is the local population.

Animals↗
PubMed1998

Tomographic microtherapy.

Minimally invasive techniques using endoscopes for image-guided therapy are now common in the field of surgery. Fast real-time radiologic imaging should be integrated into the procedure for increased safety in access and guidance techniques for endoscopes and instruments. The transparency of computed tomography (CT) guidance, magnetic resonance imaging, and electron beam tomography scan techniques allows precise guidance of instruments and endoscopes while permitting their diameter to be minimized. This guarantees safe and transparent access into the body, especially in high-risk areas such as the spine and brain. Combining both technologies has the potential to reduce complications and offers significant advantages in microinvasive operative procedures such as biopsies; local tumor therapy with lasers, radio frequency, or drugs; and percutaneous diskectomies or implants. CT is the golden standard for microtherapeutic procedures because of its precise tip discrimination.

Diagnostic Imaging↗
PubMed1997

Technology and principles of tomographic image-guided interventions and surgery.

Image guidance of instruments can be performed by fluoroscopy, ultrasound imaging, computed tomography (CT), magnetic resonance imaging (MRI), and by stereotactic navigation. During the last year, there has been significant progress in MRI instrument guidance in the field of interventional radiology. Our first 168 clinical cases of MRI-guided interventional procedures, e.g., aspiration biopsy of neoplasms and tomographic microtherapy with local interstitial chemo-ablation, confirm the feasibility of MRI guidance. An expansion of MRI guidance during surgical endoscopic procedures is currently under evaluation and the initial results of this development are presented. Tomographic-guided surgery and the implementation of MRI or CT scanning within the environment of an operating room (OR) entail specific technological requirements and OR design considerations. Fast sequences, interventional protocols, in-room monitor, as well as MR-compatible probes, cannulae, catheters, instruments, endoscopes, and auxiliary equipment that are necessary for this combined surgical image-guided approach are described.

Endoscopes↗