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Biomedical subjects

M Seemann

Publications and source records attributed to M Seemann.

At least 19 recordsLinked to original sources
PubMed2003

Clinical aspects and strategy for biomaterial engineering of an auricle based on three-dimensional stereolithography.

At the present time, the partial and/or complete reconstruction of an auricle from autologous rib cartilage is one of most widely published techniques. In the field of tissue engineering, different techniques have been described to generate cartilage tissue using isolated chondrocytes. The basis of these tissue-engineering techniques is bioresorbable or non-bioresorbable biomaterials, which serve as a three-dimensional cell carrier. Tissue engineering of an auricle requires preformed bioresorbable biomaterials designed to fit the form of a patient's auricular defect. Three-dimensional imaging acquired from computed tomography scans or laser surface scanning has become an important tool in modern medicine. This study represents the preoperative procedures for the reconstruction of an auricle through tissue engineering in accordance with the clinical aspects. Hyaff 11, a hyaluronic acid derivative, was used as a three-dimensional cell carrier for isolated human nasoseptal chondrocytes. The chondrocytes were amplified in a conventional monolayer culture before the cells were seeded on a hyaluronic non-woven mesh and cultured in vitro for 4 weeks. The chondrogenic potential of human nasal chondrocytes in Hyaff 11 was investigated by confocal laser scanning microscopy, histology (toluidine blue) and immunohistochemistry (collagen type II). Computer-aided design (CAD) and manufacture of an auricle model with stereolithographical methods were used for the prefabrication of a bioresorbable three-dimensional cell carrier designed in the form of a patient's auricular defect. The cell carrier used was Hyaff 11, a fully benzyl-esterified hyaluronic acid derivative. Confocal laser scanning microscopy has shown good cell attachment, a homogenous distribution of amplified chondrocytes and a viability of more than 90%. After 4 weeks in vitro culture the human nasoseptal chondrocytes synthesized new cartilage with the expression of cartilage-specific collagen type II. In order to shape a patient's designed scaffold the auricle model was fitted exactly and symetrically to the contralateral side. Subsequently, the mirror image patient-specific model was used to prepare an identical scaffold model made of a fully benzyl-esterified hyaluronic acid derivative. The bioresorbable scaffold that was produced gave a satisfactory representation of auricle structure. Bioresorbable preformed biomaterials in the form of a patient's auricle defect represent an important prerequisite for the tissue engineering of autologous auricle grafts. Hyaff 11 seems to be a promising material for tissue engineering of cartilage transplants, and the application of this approach will improve conventional reconstructive surgery in the future.

Absorbable Implants↗
PubMed2002

[MRI of intraosseous fistulous systems and sequesters in chronic osteomyelitis with standard spin echo sequences, highly selective chemical-shift imaging, diffusion weighted imaging, and magnetization-transfer].

PURPOSE: To study and test the impact of modern MRI techniques in diagnostic imaging in the evaluation of intra-osseous fistulous systems and sequesters. MATERIALS AND METHODS: In a prospective study, nine patients with chronic osteomyelitis of the legs were examined by MRI. Patients with clinical signs of osteomyelitis requiring surgery were included in the study. T1-weighted spin echo (SE) sequences, proton density (PD) and T2-weighted fast spin echo (FSE) sequences, water- and fat-selective FSE sequences, and diffusion weighted (DW) PSIF sequences were used preoperatively. Furthermore, magnetizing transfer (MT) with gradient echo (GRE) sequences was evaluated. RESULTS: Water selective sequences revealed the highest sensitivity for the detection of fistulas (100%), providing the best delineation of the extent of the entire fistulous systems. Fat-selective sequences (sensitivity 55.6%) and T1-weighted sequences (sensitivity 77.8%) displayed fistulas as hypointense bands, which, however, cannot be well differentiated from cortical bone in the transcortical areas. PD and T2-weighted images were found to have a poor sensitivity (55.6% and 66.7%) for fistulas in any location. The sensitivity of water-selective sequences to demonstrate intraosseous sequesters was 100%. The sensitivity was low for the other sequences. In 4 of 5 patients with surgically proven infection, DW and MT revealed an abnormal spatial distribution, with high diffusion in the central parts of the fistulas and high MT effect peripherally surrounding a weak MT effect centrally. CONCLUSION: Water-selective sequences are superior when demonstrating fistulous systems and intraosseous sequesters. The combined use of MT and DW sequences seems to allow a differentiation between solid granulation tissue and liquid pus.

Adult↗
PubMed2001

Identification of gcpE as a novel gene of the 2-C-methyl-D-erythritol 4-phosphate pathway for isoprenoid biosynthesis in Escherichia coli.

The 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway for isoprenoid biosynthesis is essential in most eubacteria and plants and has remarkable biotechnological interest. However, only the first steps of this pathway have been determined. Using bioinformatic and genetic approaches, we have identified gcpE as a novel gene of the MEP pathway. The distribution of this gene in bacteria and plants strictly parallels that of the gene encoding 1-deoxy-D-xylulose 5-phosphate reductoisomerase, which catalyses the first committed step of the MEP pathway. Our data demonstrate that the gcpE gene is essential for the MEP pathway in Escherichia coli and indicate that this gene is required for the trunk line of the isoprenoid biosynthetic route.

Bacterial Proteins↗
PubMed2001

[Use of VR (virtual reality) software for preoperative implantation fitting with an implantable hearing aid as an example].

PURPOSE: To prove the feasibility of a preoperative fitting test for an implantable hearing aid using a VR environment. METHODS: A high-resolution spiral CT was performed after mastoidectomy in 10 temporal bone specimens. The bony structures were segmented and merged with the Computer-Aided Design (CAD) data of the hearing aid in a VR environment. For each specimen a three-dimensional fitting test was carried out by three examiners determining the implantability of the hearing aid. The implantation simulation was compared with the real implantation procedure performed by an experienced ENT surgeon. RESULTS: The used VR system enabled real-time 3D-visualisation and manipulation of CT- and CAD-data. All objects could be independently moved in all three dimensions. The VR fitting test corresponded closely with the real implantation. The implantability of the hearing aid was properly predicted by all three examiners. CONCLUSION: Merging CT and CAD data in a virtual reality environment bears high potential for the pre-surgical determination of the fit and mountability of medical implants in complex anatomical regions.

Cochlear Implantation↗
PubMed2000

Synergistic effect between iron and gadolinium in MRI.

Different combinations of iron glycerophosphate (Fe) and gadolinium-diethylene triamine pentaacetic acid (DTPA) (Gd) were imaged with a three-dimensional (3D) gradient-recalled echo (GRE), a 2D GRE, and a HASTE sequence on a 1.5-T MR scanner. A combination of Fe and Gd results in a synergistic effect, which improves the signal gain for selective 3D imaging of the colon and simultaneously decreases the endoluminal signal on the HASTE and 2D GRE images for better visualization of water and Gd-enhanced structures in the gut wall.

Colonic Diseases↗
PubMed2000

Human SPRY2 inhibits FGF2 signalling by a secreted factor.

Growth factor signalling pathways and their inhibitors coordinate the formation of three-dimensional patterns of vertebrates and invertebrates. Temporal and spatial restriction of the response to a few well-defined cells is crucial and needs the integration of positive and negative signals. Recently, Spry has been identified as an inhibitor of fibroblast growth factor (FGF) signalling during Drosophila trachea development. Spry has been described as an intracellular protein that can exert its function in a cell autonomous or a paracrine manner. Here we describe the role of SPRY2, a human homologue of Spry, in human FGF2 signalling. We show that in primary human dermal endothelial cells (MVEC) SPRY2 mRNA is transiently upregulated in response to FGF2. Overexpression of SPRY2 in A375 cells leads to the secretion of a soluble factor that inhibits FGF2- but not VEGF-stimulated proliferation of MVEC. Direct administration of recombinant SPRY2 protein has no effect on MVEC proliferation. However, SPRY2 protein binds the intracellular adaptor protein GRB2, indicating an intracellular localization. A SPRY2/GFP fusion protein remains in the cell, further supporting the intracellular localization of SPRY2. So the intracellular protein SPRY2 is involved in the non-cell autonomous inhibitory effect indirectly, via regulating the secretion of an inhibitor of FGF2 signalling in vertebrates, the evidence of which is presented here for the first time.

Adaptor Proteins, Signal Transducing↗
PubMed1999

[Evaluation of right heart load with spiral CT in patients with acute lung embolism].

PURPOSE: Purpose of this study was to evaluate whether spiral-CT allows judgment of right ventricular failure in patients with acute pulmonary embolism. MATERIALS AND METHODS: 61 patients underwent spiral-CT due to suspicion of acute pulmonary embolism. Patients with pulmonary embolism were divided into subpopulations according to the severity of pulmonary embolism in the CT scan. Cardiac measurements were performed on axial spiral-CT images and compared to those of patients without suspicion of pulmonary embolism or cardiac diseases. RESULTS: In 30 patients spiral-CT revealed acute pulmonary embolism. Significant differences in cardiac measurements in patients with severe and less severe pulmonary embolism were found on comparing the following dimensions: left ventricular width (p = 0.0003), left (p = 0.008) and right (p = 0.009) ventricular cross-sectional area, proportion of right to left ventricular width (p = 0.0003) and proportion of right to left ventricular cross-sectional area (p = 0.0001). The proportion of the cross-sectional areas (r = 0.65) and the proportion of the width (r = 0.60) of both ventricles correlated well with the severity of central pulmonary embolism. CONCLUSION: Besides reliable assessment of pulmonary embolism spiral-CT allows the evaluation of cardiac dimensions for judgment of right ventricular failure.

Adult↗
PubMed1999

Influence of helical CT parameters on spatial resolution in CT angiography performed with a subsecond scanner.

RATIONALE AND OBJECTIVES: In helical CT, the beam collimation, table feed (TF) per tube rotation, voltage, current, reconstruction increment, kernel, linear interpolation algorithm (LIA), and contrast are variable parameters. The purpose of this study was to determine which of these parameters are most important to minimize partial volume effects for improving spatial resolution in CT angiography. METHODS: Phantom vessel stenoses of different lengths (2, 8 mm) and diameters (0.5, 1, 2, 3, 4 mm) were scanned with helical CT using a constant tube rotation time of 0.75 sec and 42 selected combinations of the above-mentioned parameters. Orthogonal targeted maximum intensity projections of the stenoses were ordered according to the increase in blurring and noise in a consensus reading by two radiologists blinded to the parameters used. RESULTS: Three millimeters of collimation and TF in conjunction with a 180 degrees LIA and > 250 Hounsfield unit contrast density was considered the optimal parameter combination and enabled a continuous visualization of the stenoses down to 0.5 mm in diameter. A collimation of 1 or 2 mm and 5 mm was considered inferior to a collimation of 3 mm because of, respectively, noise and blurring. With 3 mm collimation, significant blurring occurred when a pitch larger than 1.5 was used. A 3 mm collimation with a pitch of 2 (6 mm TF) was found to be superior to a collimation of 5 mm in conjunction with a pitch of 1 (5 mm TF). With 5 mm collimation, the short stenoses could be visualized only when using a 180 degrees LIA and a TF per tube rotation smaller than 7 mm. Eight and 10 mm collimations failed to depict the short stenoses. CONCLUSIONS: Collimation had the most influence on image quality in CT angiography, followed by LIA, pitch, and contrast density. Decreasing the reconstruction increment to less than one third of the TF or increasing the voltage or current beyond standard values did not improve the delineation of the stenoses. For screening examinations, the authors recommend the use of 3 mm collimation, 180 degrees LIA, and a pitch of 2.

Angiography↗
PubMed1999

Effective contrast use in CT angiography and dual-phase hepatic CT performed with a subsecond scanner.

OBJECTIVE: To deduce an optimal injection protocol for CT angiography and fast dual-phase hepatic CT. METHODS: Fifty-two patients underwent fast dual-phase hepatic CT using one of three different injection protocols: A (0.9 g/sec iodine injection rate, 36 g dose); B (1.35 g/sec, 30 g); C (1.6 g/sec, 40 g). Aortic attenuation time curves as well as aorta-to-liver contrast and hepatic enhancement time curves obtained by region of interest measurements along the helical axis were analyzed. RESULTS: Protocol C revealed a significantly higher peak in aortic attenuation and hepatic enhancement than the other protocols. Approximately 50 seconds after the bolus injection, hepatic enhancement declined to a plateau similar to that seen with the other protocols. In terms of the areas under the curves of the aorta-to-liver contrast and hepatic enhancement dynamics, protocol C was significantly superior to the other protocols. CONCLUSIONS: A high iodine injection rate realized by a high iodine concentration in conjunction with fast dual-phase scanning (total scan time < 50 seconds) promises to enhance CT angiography and contrast of liver lesions.

Angiography↗
PubMed1998

Relations between cardiopulmonary exercise testing and quantitative high-resolution computed tomography associated in patients with alpha-1-antitrypsin deficiency.

High-resolution computed tomography (HRCT) can be used to diagnose and quantify emphysema noninvasively, as significant correlations have been found between the histological grade on resected lung specimens and quantified (q) computed tomography (CT). In this study, we performed thin section qHRCT in patients with severe hereditary alpha-1-antitrypsin (AAT) deficiency. AAT deficiency is the most common genetic cause of emphysema in adults, and exercise intolerance is the most disabling, distressing consequence of emphysema for the majority of patients. qHRCT was used to quantify precisely the alterations in the lung parenchyma due to pulmonary emphysema. Up until now, the important relationship between the severity of emphysema and the reduced exercise capacity has received little attention. Therefore the purpose of the study was to investigate the relationship between emphysema as displayed by qHRCT and cardiopulmonary exercise testing (CPX) in patients with severe cardiopulmonary impairment. - qHRCT was performed in 21 patients with homozygous AAT deficiency. CT scans were obtained at three spirometrically standardized levels at the carina and (5 cm above and below the carina). The mean lung density at 50% of vital capacity and a quantitative histogram analysis of the frequencies of CT values were determined. All patients underwent symptom-limited CPX to analyse simultaneously cardiovascular and ventilatory systems responses. - In all patients, qualitative CT assessment demonstrated panlobular emphysema with large and extensive areas of uniform low attenuation, characteristically with a lower-lobe distribution. Mean CT density values of the patients (-845 +/- 6.9 (mean +/- SEM)) were significantly correlated with work capacity (r = 0.55, p <0.01), oxygen-pulse (r = 0.54, p <0.01) and functional dead space ventilation (r = -0.54, p <0.01). Moreover, severe emphysema index (CT values below a threshold value of 950 HU) correlated positively with functional dead space ventilation (r = 0.60, p <0.01) and alveolar-arterial oxygen difference (r = 0.70, p <0.001). - These results clearly demonstrate that CPX parameters, indicating a disturbed pulmonary gas exchange and a ventilation-perfusion-mismatch during exercise, are significantly related to the extent of lung emphysema.

Adult↗
PubMed1998

Hybrid rendering of the cervico-cranial arteries using spiral computed tomography.

PURPOSE: The purpose of this study was to develop a shaded-surface and volume display (hybrid rendering method) of the whole vascular system of the cervico-cranial arteries using spiral computed tomography (SCT). MATERIALS AND METHODS: We examined 12 patients with anatomic abnormalities and pathological conditions of the arterial vascular system. The cervico-cranial arteries were segmented using an interactive threshold interval density volume-growing method and visualized with a color-coded shaded-surface display (SSD) rendering method. The adjacent bone structures were visualized using a transparent volume rendering method. RESULTS: In all cases, the entire volume of the vascular system of the cervico-cranial arteries and the anatomic abnormalities and pathological conditions could be visualized. CONCLUSION: Hybrid rendering of the circulation of the cervico-cranial arteries using image data sets from a subsecond spiral CT scanner is useful for the visualization of anatomical and pathological abnormalities and offer a promising minimally invasive alternative compared with other diagnostic procedures.

Adult↗
PubMed1998

[Computer-assisted diagnosis based on computer-based image interpretation and 3D-visualization].

PURPOSE: To survey methods for 3D data visualization and image analysis which can be used for computer based diagnostics. MATERIAL AND METHODS: The methods available are explained in short terms and links to the literature are presented. Methods which allow basic manipulation of 3D data are windowing, rotation and clipping. More complex methods for visualization of 3D data are multiplanar reformation, volume projections (MIP, semi-transparent projections) and surface projections. Methods for image analysis comprise local data transformation (e.g. filtering) and definition and application of complex models (e.g. deformable models). RESULTS: Volume projections produce an impression of the 3D data set without reducing the data amount. This supports the interpretation of the 3D data set and saves time in comparison to any investigation which requires examination of all slice images. More advanced techniques for visualization, e.g. surface projections and hybrid rendering visualize anatomical information to a very detailed extent, but both techniques require the segmentation of the structures of interest. Image analysis methods can be used to extract these structures (e.g. an organ) from the image data. DISCUSSION: At the present time volume projections are robust and fast enough to be used routinely. Surface projections can be used to visualize complex and presegmented anatomical features.

Diagnosis, Computer-Assisted↗
PubMed1998

[Virtual and three-dimensional bronchoscopy with spiral and electron beam computed tomography].

PURPOSE: To compare spiral computed tomography (CT) and electron-beam CT (EBT) for 3D and virtual CT-bronchoscopy. MATERIALS AND METHODS: 17 patients with various disorders of the tracheobronchial system were examined using fiberoptic bronchoscopy, spiral CT and EBT. 3D images were reconstructed from CT data sets using automated segmentation based on volume-growing methods. Surface-rendered, volume-rendered, and hybrid reconstructions were visualized in real time using a data helmet. RESULTS: All data sets could be processed to high-quality three-dimensional (3D) and virtual reconstructions. The reduction of motion artifacts due to shorter scan times made EBT data sets better suited for automated segmentation and less susceptible to motion artifacts. 3D and virtual reconstructions did not increase the diagnostic sensitivity of CT compared to axial reconstructions alone. CONCLUSIONS: Shorter scan times of CT imaging yield higher-quality 3D and virtual reconstructions. Modern reconstruction techniques are valuable visualization tools for select indications and are the prerequisite for future developments in computer-aided medicine.

Bronchial Neoplasms↗
PubMed1997

Molecular heterogeneity of neurotransporters: implications for neurodegeneration.

Neurotransporters are high-affinity transport proteins located in the plasma membrane of both presynaptic nerve and glial cells that mediate the removal of neurotransmitters from the synaptic cleft or represent intracellular transport systems that concentrate neurotransmitters in synaptic vesicles. They comprise three subgroups, Na+/Cl(-)- or Na+/K(+)-dependent cell surface transporters and H(+)-dependent transporters associated with synaptic vesicles. The new insights into neurotransporter diversity provide the means for novel approaches of studying neurotransmitter uptake processes at the molecular level, such as substrate translocation and antagonist binding as well as regulation of gene expression, of intracellular trafficking, and of posttranslational modification. Moreover, modeling neurotransporter-related disorders and therapeutic strategies in genetically engineered animals are now feasible research strategies. Through an improved understanding of the modulation of neurotransporter function in the brain, it may be possible to identify the molecular factors underlying the etiopathogenesis and pathophysiology of neurodegenerative disorders. Due to their specificity for distinct neuronal systems, neurotransporters and their genes are potential targets for novel therapeutic strategies.

Animals↗
PubMed1997

[CT subtraction angiography (CTSA). Results with an automated "elastic" subtraction algorithm].

PURPOSE: To develop and implement a method to obtain digital subtraction (DS) spiral computed tomography angiograms (SCTA) in order to avoid superimposition of bony structures and vascular calcifications on SCTA maximum intensity projections (MIPs) and shaded surface display (SSD). METHOD: Two SCTA data sets, one before and one during the injection of a contrast agent bolus, were obtained with identical scan parameters. Since ordinary subtraction of the two data sets fails to reliably separate bones and calcifications from the vascular lumen because of motion, a so-called elastic subtraction procedure was designed to correct 3D misregistration between the two data sets. It automatically accommodates for local position changes between baseline and contrast images, including regionally inconsistent non-linear displacements and arbitrary rotations. This method was tested in seven patients and evaluated against ordinary DS in terms of image quality and artifacts. RESULTS: In all patients "elastic" CTSA proved superior to ordinary DS. It provides automated and reliable separation of vessels from bones and calcifications. This improves the delineation of vessels in the neck and the skull base and of intracranial vessels. DS-SCTA facilitates MIPs and SSD without artifacts introduced by thresholding. CONCLUSION: Elastic DS-SCTA is a robust method for automated unmasking of vessels from bones and warrants clinical trials and comparison with MR- and conventional angiography.

Algorithms↗
PubMed1997

[MRI of fingers in systemic scleroderma. Initial results with contrast-enhanced studies using a dedicated MRI system].

PURPOSE: To estimate disease activity in patients with systemic sclerosis using contrast-enhanced MRI of the skin. MATERIAL AND METHODS: In a pre-study, sequences of a low-field (0.2 T) scanner (Artoscan, Esaote, Genova, Italy) were optimized for detection of intravenous contrast (0.1 mmol/l Gd-DTPA) in six patients with the autoimmune disease systemic scleroderma. Based on the results of the pre-study, 17 patients with scleroderma (7 sclerotic/10 active inflammatory disease) were scanned using gradient-spoiled 3D GRE sequences (FA 90 degrees, TR 100 ms, TE 18 ms), which had been established as most sensitive for intravenous contrast. Contrast enhancement of the skin was determined quantitatively by contrast-to-noise ratios (CNR), comparing post- to pre-contrast and dynamic scans (for 6 min, 1 acquisition/min). Patients in the chronic state with sclerodactylia and active inflammation of the hands were considered separately and compared to a control group (n = 10) matched according to age. RESULTS: CNR increase after intravenous contrast was significantly higher in patients with active disease (86 +/- 16% increase) than sclerosing disease (29 +/- 3%, p < 0.05) and the control group (4 +/- 2%, p < 0.05). The dynamic examination showed a significantly slower decrease after the peak rise in the first minute in patients with active disease (CNR 15.4 +/- 0.7 to 14.2 +/- 1.4) than in those with chronic disease (14.1 +/- 0.5 to 11.3 +/- 0.9, p < 0.05). DISCUSSION: Capillary leakage is the most likely explanation for the increased enhancement in patients with active scleroderma. Using sequences optimized for contrast detection, disease activity in the course of scleroderma and response to therapy can be determined by MRI in the future.

Adult↗