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P Blümler

Publications and source records attributed to P Blümler.

10 recordsLinked to original sources
PubMed2006

Diffusion in binary gas mixtures studied by NMR of hyperpolarized gases and molecular dynamics simulations.

The dependence of the individual mean square displacement of rare gases in binary mixtures is studied by a combined experimental and theoretical approach. We show that the diffusion constant can be varied in a considerable range by changing the molar fractions of the mixtures. On the experimental side, NMR diffusion measurements are done on hyperpolarized 3He and 129Xe, mixed with several inert buffer gases, in the presence of a magnetic field gradient. The results are compared to diffusion coefficients obtained from atomistic molecular dynamics simulations based on Lennard-Jones type potentials of the corresponding gas mixtures, and to appropriate analytical expressions, yielding very good mutual agreement. This study is the first quantitative validation of the effects of the mutual interactions between gas particles on the individual diffusion properties. It is shown that the dependency of gas phase diffusion properties on the local chemical environment may not be neglected, e.g. in diffusion-controlled chemical reactions.

Complex Mixtures↗
PubMed2004

Surface normal imaging with a hand-held NMR device.

Recently the capabilities of single sided nuclear magnetic resonance (NMR) devices have been extended towards three-dimensional imaging. This paper details the use of a magnetic field sweep coil to obtain spatial resolution in the plane normal to the surface of a hand-held NMR device-the NMR-Mobile Universal Surface Explorer (MOUSE). One-dimensional depth profiles can be recorded by varying the current in the sweep coils. Preliminary results from multi-layer rubber and glass sample phantoms demonstrate a sample penetration depth of 7 mm. Two-dimensional images were acquired via the inclusion of phase encoding coils. Non-destructive cross-sectional images of small rubber phantoms were successfully recorded.

Journal Article↗
PubMed2004

Imaging of a mixture of hyperpolarized 3He and 129Xe.

With the use of hyperpolarized gases, a great number of experiments have been carried out in order to improve the diagnostics of the lung, both from a structural and a functional point of view. 3He is best suited for structural studies, whereas 129Xe gives more detailed information about the functionality of the lung because it enters the bloodstream. In this work, we propose the use of a gas mixture to perform consecutive analysis of lung structure and functionality upon the delivery of a single bolus of gas. We show images of a helium-xenon gas mixture in the presence of a small amount of liquid toluene in order to demonstrate how both nuclei can be detected independently, extracting the spectroscopic information provided by the 129Xe spectra and obtaining an image with high sensitivity for 3He. A second experiment performed on a dissected mouse lung was used to demonstrate how the mixture of gases can enhance sensitivity in the larger airways of the lung.

Animals↗
PubMed2004

[A software program for quantitative analysis of alveolar oxygen partial pressure (p(A)O(2)) with oxygen-sensitive (3)He-MRI].

PURPOSE: To develop a software tool for quantitative analysis of alveolar oxygen partial pressure (p(A)O(2)) as well as its time course during apnea. MATERIAL AND METHODS: T (1)-relaxation times of hyperpolarized (3)He are reduced by paramagnetic oxygen rendering (3)He-MRI sensitive to oxygen and thus allowing the assessment of the local oxygen partial pressure in the pulmonary airspaces. Oxygen-related relaxation and loss of polarization by RF-excitation can be discriminated by acquiring two image series with varying interscan delay and/or flip angles. Software was developed to calculate the p(A)O(2) and the decay rate in user-defined regions of interest (ROIs) automatically. Moreover, parameter maps can be calculated. In addition to the analysis of 2-dimensional data sets, the software allows the evaluation of 3-dimensional measurements for the first time. Artifacts due to lung motion were reduced by implementing a motion correction algorithm. RESULTS: The software was successfully applied to data sets from healthy volunteers and from patients with various lung diseases. The parameter maps demonstrated a more homogeneous distribution of p(A)O(2) for the volunteers than for the patients. A regional increase in p(A)O(2) was found in a few patients. CONCLUSION: The described software allows the absolute quantification of p(A)O(2) as well as its variation over time. In the future, therefore, the software may gain importance for detecting mismatches between ventilation and perfusion, e. g., in patients with pulmonary embolism or chronic obstructive lung diseases.

Adult↗
PubMed1998

Analysis of polymer materials by surface NMR via the MOUSE.

Applications are discussed of a novel NMR device, the NMR MOUSE (mobile universal surface explorer), for characterization of polymers. Different properties of elastomers can be related to an effective transverse relaxation parameter T2eff. Effects of multi-echo sequences influence the decay curve and can be described in terms of B0 inhomogeneity and spin-lock effects. Furthermore, the signal-to-noise ratio (SIN) can be improved by use of steady-state free precession (SSFP) pulse sequences modified for use in inhomogeneous magnetic fields.

Magnetic Resonance Spectroscopy↗
PubMed1996

Hadamard NMR imaging with slice selection.

Stochastic NMR imaging is one of the less common NMR imaging techniques. Nevertheless, stochastic rf excitation is characterized by some remarkable features: the rf excitation power is at least two orders of magnitude lower in comparison to conventionally pulsed NMR imaging schemes. Thus, the technique is of interest for imaging of large objects. The systematic noise inherent in images obtained with random noise excitation has been eliminated by using pseudorandom noise together with Hadamard transformation for data evaluation. Data acquisition times are comparable to those of ultrafast imaging techniques. For slice selection, z magnetization is destroyed outside the slice region with specially designed low power pulses. Thus, gradient switching times are only limited by T1 and not T2*. Images are reconstructed by the backprojection algorithm. We have set up a stochastic imaging procedure on a conventional Bruker MSL 300 spectrometer, and have drawn a comparison between images obtained by the pseudorandom noise excitation and by conventional Fourier imaging.

Fourier Analysis↗
PubMed1994

Two-dimensional one-pulse rotational echo spectra.

Recently a two-dimensional representation of one-dimensional spinning sideband magic-angle spinning (MAS) spectra has been published with applications to deuteron MAS nuclear magnetic resonance (NMR). The introduction of a new time axis, based on the rotor period, allows the separation of isotropic and anisotropic chemical shifts. It is shown here that, in addition to untangling spinning sideband spectra, data-processing steps can be incorporated which enabled applications of the method to signals from nuclei with anisotropies smaller than those of the quadrupole coupling of deuterons. This is achieved by linear prediction of the rotary echo signals. Advantages and limitations of the algorithm are discussed and demonstrated with experimental results of 13C cross-polarization (CP) MAS spectra of glycine.

Algorithms↗
PubMed1992

Magnetization filters: applications to NMR imaging of elastomers.

The general Fourier scheme for parameter selective imaging is subdivided into three periods: A preparation period for application of magnetization filters, an evolution period for space encoding, and a detection period for acquisition of the spectroscopic dimension. Depending on sample requirements and available time, the first and the last period can be omitted. Preparation of the initial magnetization for space encoding by appropriate filters is a powerful and time-saving way to introduce parameter-selective image contrast. This is illustrated by filters of molecular dynamics, which are sensitive to segmental motion in different time windows for contrast enhancement in composite and aged elastomers. Further contrast amplification is achieved by computing the difference of images acquired with different filter settings.

Filtration↗
PubMedDate not supplied

The NMR-mouse: construction, excitation, and applications.

A mobile nuclear magnetic resonance (NMR) device similar to a bore-hole probe has been developed for applications in materials science and biomedicine. Inhomogeneous polarizing and radio-frequency (rf) magnetic fields are applied to arbitrarily large samples from one side. Different experimental techniques have been tested to measure transverse and longitudinal relaxation times and translational diffusion constants. Good contrast for discrimination of material properties is gained when the residual dipolar coupling is retained in soft matter by avoiding spinlock effects in multi-pulse techniques. Applications to characterization of products from technical elastomers, skin, and coatings on iron sheets are reported.

Animals↗