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Biomedical subjects

S Hafner

Publications and source records attributed to S Hafner.

At least 19 recordsLinked to original sources
PubMed2001

Gastrointestinal stromal tumors of the equine cecum.

Ten cecal tumors were identified during the postmortem examination of seven horse carcasses at slaughter (one horse had three tumors). The multinodular and hemorrhagic tumors ranged from 1 to 10 cm in diameter and consisted of spindle cells arranged in thin, interconnected trabeculae that were often separated by sinuses filled with mucinous fluid, erythrocytes, and siderophages. Spindle cells of all tumors were immunopositive for vimentin, neuron-specific enolase, and c-kit protein but lacked reactivity with antibodies to glial fibrillary acidic protein, S100 protein, and desmin. In one tumor, spindle cells diffusely bound antibodies to synaptophysin. Most tumors contained focal reactivity to smooth muscle actin antibodies; one tumor reacted diffusely. Ultrastructurally, tumor cells were connected by desmosome-like structures and exhibited extended cell processes; some contained dense core neurosecretory granules. These equine stromal tumors appeared to share some characteristics with human gastrointestinal stromal tumors.

Animals↗
PubMed2000

Analysis of multiple-pulse techniques under fast MAS conditions.

The combination of magic-angle spinning and multiple-pulse sequences for line-narrowing in solids with homogeneous spin interactions is analyzed using Floquet theory. It is found that, for quasi-static conditions and for special synchronization conditions, line-narrowing is possible while for other conditions destructive interference of the two techniques takes place. However, even for optimum line-narrowing conditions, fundamental limitations with respect to the achievable linewidth are found, whereas the conditions of recoupling spin interactions are more easily realized. The implications of these results with respect to improving existing line-narrowing techniques or techniques for the design of specific Hamiltonians are discussed.

Alanine↗
PubMed2000

An evaluation of methods for the detection of spinal cord in product derived from advanced meat recovery systems.

This study investigated the usefulness of immunohistochemistry, histochemistry, and polarization microscopy in documenting the presence of spinal cord in ground product produced by advanced meat recovery systems (AMRS). A battery of diagnostic stains proved most helpful for definitive documentation of spinal cord in the AMRS product. Antibodies to neurofilament and glial fibrillary acidic proteins were useful for highlighting the presence of neural tissue in comminuted product but when used alone did not definitively differentiate central nervous system tissue from peripheral nerve. Polariscopy, trichrome staining, and immunostaining for synaptophysin were very useful for differentiating spinal cord from peripheral nerve. Spinal cord was found in 2 of 196 AMRS samples when only hematoxylin and eosin staining was used. In a later immunohistochemical subset of the survey study, spinal cord was found in 7 of 17 AMRS samples. More recently, spinal cord tissue has been found in 3 of 26 regulatory samples using hematoxylin and eosin stains combined with immunohistochemical techniques.

Animals↗
PubMed1998

Resolution enhancement in multiple-quantum MAS NMR spectroscopy.

Two techniques for resolution and sensitivity enhancement are introduced in multiple-quantum (MQ) MAS spectroscopy of rigid solids. The first makes use of ultrafast MAS with spinning frequencies of up to 35 kHz, while the second combines MAS at moderately fast spinning frequencies of about 13 kHz with multiple-pulse (MP) dipolar decoupling. For the latter approach, a semiwindowless WHH-4 sequence is applied during the MQ evolution period (MQ dimension) and/or detection period (single-quantum dimension). In the MQ dimension, the MP sequence has to be supplemented by two bracketing pulses in order to preserve the order and the intensities of the evolving MQ coherences. Double-quantum 1H NMR spectra of l-alanine recorded using both decoupling techniques are shown and compared to each other. Triple-quantum 1H NMR spectra under ultrafast MAS conditions are also presented.

Alanine↗
PubMed1998

Pulsed field gradient selection in two-dimensional magic angle spinning NMR spectroscopy of dipolar solids

The utility of gradient selection in MAS spectroscopy of dipolar solids is explored in two examples. In the first, rotor-synchronized gradients of appropriate strength and duration are applied to select 1H double-quantum coherences. The resulting DQ MAS spectrum of adamantane is compared with that acquired by the corresponding phase-cycling technique. As a second example, a 1H 2D exchange MAS experiment is performed on an elastomer sample. In this experiment, a gradient is applied to remove undesired coherences that would otherwise distort the spectrum for short mixing times. The diagonal-peak intensities in the resulting spectrum show a linear decrease with increasing mixing time indicating cross-relaxation by slow chain motions as the relevant process. Both types of experiments demonstrate the potential of gradient-selection techniques for MAS spectroscopy of dipolar solids. Copyright 1998 Academic Press.

Journal Article↗
PubMed1998

Selective residual dipolar couplings in cross-linked elastomers by 1H double-quantum NMR spectroscopy.

1H double-quantum (DQ) solid-state NMR spectroscopy under fast magic-angle spinning (MAS) is introduced as a new spectroscopic tool for the investigation of the structure and local chain dynamics of elastomers. Dipolar connectivities between the protons of the various functional groups can be directly established from the highly resolved DQ solid-state NMR spectra as is shown for a series of cross-linked poly(styrene-co-butadiene). More quantitatively, residual dipolar couplings within and between the functional groups are evaluated selectively from the build-up curves of the double-quantum signals in the limit of the spin-pair approximation. In particular, the CH-CH and the CH2-CH couplings of butadiene, which both act predominantly along the chain-segment direction, have been measured relative to the CH2 coupling. The total build-up intensity is correlated with the cross-link density.

Cross-Linking Reagents↗
PubMed1997

Investigation of aging in polymer networks by T1 rho material property NMR imaging.

Material property (MAP) imaging was found to be a promising method for the investigation of aging processes in elastomer materials. Based on conventional parameter-selective imaging, MAP imaging directly reveals the properties of the material by use of a theoretical description to relate the measured nuclear magnetic resonance data--in this investigation, T1 rho values--with the properties of the material. Following this concept, T1 rho images with different strengths of lock amplitude have been acquired for a rubber sample consisting of four pieces of natural rubber that were oxidatively aged under different conditions. The data were analyzed using a defect-diffusion model and transformed into images of those material parameters, which were found to be suitable for the characterization of the aging process. Images correlating with the crosslink density and the power law of T1 rho dispersion were obtained indicating the degree of aging.

Algorithms↗
PubMed1997

Multiple-pulse assisted line-narrowing by fast magic-angle spinning.

Combined rotation and multiple-pulse experiments (CRAMPS) are reported that are performed under the conditions of fast magic-angle spinning. Quasi-static conditions, as are required for CRAMPS experiments, can be fulfilled approximately also for fast sample spinning conditions when windowless or semiwindowless sequences are applied. In order to allow direct detection for these cases also, appropriately timed detection windows are introduced without loss of resolution. In contrast to conventional CRAMPS experiments, high-speed MAS was found to play an important role also in the averaging of residual dipolar contributions. The resolution achieved in these first experiments is comparable to that of conventional CRAMPS experiments and the demands with respect to spectrometer hardware and tuning are much lower.

Magnetic Resonance Spectroscopy↗
PubMed1997

Malignant chromatophoroma in a canebrake rattlesnake (Crotalus horridus atricaudatus).

An adult female canebrake rattlesnake (Crotalus horridus atricaudatus) at Zoo Atlanta (Atlanta, Georgia, USA) had a subcutaneous mass on the left lateral abdomen. Microscopically, the tumor contained a pleomorphic population of cells with abundant intracytoplasmic brown to gold nonrefractile pigment (chromatophores), large stellate cells resembling neurons, and small stellate cells whose cytoplasmic processes formed a fibrillar matrix. The pigment stained black with the Fontana-Masson technique and was positive with the periodic acid-Schiff technique (prior to and after diastase treatment). Neuron-specific enolase was detected in the large stellate cells using an immunohistochemical staining technique. In addition, glial fibrillary acidic and S-100 proteins were detected in the chromatophores with immunohistochemical staining. The smaller stellate cells were strongly S-100 positive. Ultrastructurally, chromatophores contained intracytoplasmic structures composed of concentric lamellar membranes bordered by a triple-layer outer membrane. The morphology of these structures was compatible with pterinosomes. Three fluorescent pigments were isolated from the neoplasm by one-dimensional chromatography and characterized by spectrophotometry and spectrofluorometry.

Animals↗
PubMed1997

[Efficient ambulatory and post-discharge thromboprophylaxis with fully automated pens].

Efficient prophylaxis of deep vein thrombosis is very important during and after hospitalisation as well as for outpatients. In a prospective randomised trial, a new automatic pen for subcutaneous injections of low molecular heparin was studied with 489 injections in 51 patients. The automatic pen with a covered needle allows a safe and standardised subcutaneous administration of low-molecular heparin with good patient comfort and at no additional costs.

Adolescent↗
PubMed1996

Magic echoes and NMR imaging of solids.

Solid state NMR imaging techniques based on magic echoes are reviewed. The theoretical background of magic echoes in general and their spatial encoding in particular is treated. The magic-echo imaging pulse sequences presently in use are described and discussed. Particular emphasis is devoted to those techniques, which allow the incorporation of spectroscopic or parameter-selective information. The applicability of these methods for the investigation of materials is demonstrated and perspectives for materials science are outlined.

Image Enhancement↗
PubMed1995

Magic-echo phase-encoding solid imaging with improved time resolution.

The magic-echo phase-encoding solid imaging (MEPSI) sequence is based on the magic-echo pulse sequence for the refocusing of the dipolar interaction and on pure phase-encoding for spatial resolution in all dimensions. MEPSI has many advantages; however, as a consequence of pure phase-encoding, it is very time-consuming. In the following, two strategies are proposed to decrease the time necessary for the acquisition of an image by a factor of 2 per dimension.

Magnetic Resonance Spectroscopy↗
PubMed1995

Aging of polymer networks as studied by material property NMR imaging.

Relaxation-weighted NMR imaging is a powerful tool for the investigation of aging processes in rubber networks, in particular if it is combined with a theoretical description to relate the NMR data with suitable parameters of the material. Following this concept, spin-spin relaxation decays in rubber samples, consisting of differently aged pieces of natural rubber have been acquired in a spatially resolved experiment. The data were evaluated using a dynamical model and transformed into images of those material properties, which are affected by the aging process. Images representing the crosslink density and the correlation times, which characterize the polymer chain dynamics, have been calculated. The differently aged rubber pieces can be easily discriminated in such material property (MAP) images.

Magnetic Resonance Spectroscopy↗
PubMed1995

Spontaneous equine pulmonary granular cell tumors: morphologic, histochemical, and immunohistochemical characterization.

Spontaneous equine pulmonary granular cell tumors were diagnosed in six mature horses at slaughter. These tumors were grossly recognized as multiple (5/6) or single (1/6) creamy white, firm nodules. The tumors, located adjacent to bronchi and bronchioles, often invaded airways, resulting in partial to complete occlusion of the lumina. Neoplastic cells were rounded to polyhedral with numerous eosinophilic cytoplasmic granules that reacted uniformly positive with S-100 and neuron-specific enolase antibodies and multifocally with glial fibrillary acidic protein antibodies. These cells were negative for muscle-specific actin, lysozyme, cytokeratin, chromogranin A, and myelin basic protein antigens and did not stain with silver by the Grimelius technique. Uniformly blue-green and scattered pink intracytoplasmic granules were evident with luxol fast blue and periodic acid-Schiff counterstain for myelin and myelin breakdown products. Histochemical and immunohistochemical staining results of these tumors suggest that they are composed primarily of myelinating Schwann cells with lesser numbers of scattered nonmyelinating Schwann cells. The morphologic features of the equine pulmonary granular cell tumors are strikingly similar to those of endobronchial granular cell tumors of human beings.

Animals↗
PubMed1995

Malignant melanocytic neural crest tumor in a young chicken (Gallus domesticus).

A malignant melanocytic tumor was found in an 8-week-old chicken. The tumor, which was composed of melanocytes, ganglion cells, nerves, and primitive pressure receptors, was examined by light microscopy, transmission electron microscopy, and immunohistochemistry. Antibodies to neuron-specific enolase (NSE), glial fibrillary acidic protein (GFAP), and S-100 protein variably stained nerves, but melanocytes were only rarely immunolabelled by NSE antibodies and there was no specific staining of these cells for S-100 or GFAP. Ultrastructurally, neoplastic melanocytes contained melanin within melanosomes and premelanosomes and did not resemble Schwann cells.

Adrenal Gland Neoplasms↗