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Biomedical subjects

Rainer Schmidt

Publications and source records attributed to Rainer Schmidt.

At least 19 recordsLinked to original sources
PubMed2006

Beta dosimetry with microMOSFETs for endovascular brachytherapy.

The aim of this study was to investigate if microMOSFETs are suitable for the dosimetry and quality assurance of beta sources. The microMOSFET dosimeters have been tested for their angular dependence in a 6 MeV electron beam. The dose rate dependence was measured with an iridium-192 afterloading source. By varying the source-to-surface distance (SSD) in a 12 MeV electron beam the dose rate dependence in an electron beam was also investigated. To measure a depth dose curve the dose rate at 2, 5, 8 and 12 mm distance from the beta source train axis was determined with the OPTIDOS and the microMOSFET detector. A comparison between the two detector types shows that the microMOSFET is suitable for quality assurance of beta sources for endovascular brachytherapy (EVBT). The homogeneity of the source is checked by measurements at five points (for the 60 mm source at 10, 20, 30, 40 and 50 mm) along the source train. The microMOSFET was then used to evaluate the influence of a common stent type (single layer stainless steel) on the dose distribution in water. The stent led to a dose inhomogeneity of +/-8.5%. Additionally the percentage depth dose curves with and without a stent were compared. The depth dose curves show good agreement which means that the stent does not change the beta spectrum significantly.

Biophysical Phenomena↗
PubMed2006

Prognostic factors in head-and-neck cancer patients treated with surgery followed by intensity-modulated radiotherapy (IMRT), 3D-conformal radiotherapy, or conventional radiotherapy.

In 148 head-and-neck cancer patients treated with surgery plus radiotherapy (RT), IMRT, 3D-conformal RT, and conventional RT and 10 potential prognostic factors were evaluated for overall survival (OS), metastasis-free survival (MFS), and loco-regional control (LC). On univariate analysis, ECOG performance status, T-stage, AJCC-stage, extent of resection, and pre-RT hemoglobin level (>or=12 g/dl better than <12 g/dl) were significantly associated with treatment outcome, whereas RT technique had no significant impact. On multivariate analysis, performance status maintained significance for OS (P=0.019), AJCC-stage for LC (P=0.034), extent of resection for OS (P=0.045) and MFS (P=0.021), pre-RT hemoglobin for MFS (P<0.001). IMRT was associated with less xerostomia than conformal RT and conventional RT (17% versus 63% and 73%, P=0.037). Otherwise, acute and late toxicity was similar. Outcome was significantly associated with performance status, tumor stage, extent of resection, and pre-RT hemoglobin. The three radiation techniques provided similar disease control. IMRT was effective in significantly reducing xerostomia.

Carcinoma, Squamous Cell↗
PubMed2006

Ultrasound-guided spinal fracture repositioning, ligamentotaxis, and remodeling after thoracolumbar burst fractures.

STUDY DESIGN: Computed tomography aided evaluation of spinal decompression by ultrasound-guided spinal fracture repositioning, ligamentotaxis, and remodeling after thoracolumbar burst fractures. OBJECTIVES: To determine the necessity of spinal canal widening by ultrasound-guided fracture repositioning for fractures with and without neurologic deficit. SUMMARY OF BACKGROUND DATA: Ultrasound-guided spinal fracture repositioning is an alternative new approach. Reports have varied concerning ligamentotaxis and remodeling. METHODS: Computed tomography aided planimetry of the spinal canal (64 consecutive burst fractures) and neurologic evaluation by Frankel grades. RESULTS: Ultrasound-guided spinal fracture repositioning (n = 37) reduced the stenosis of the spinal canal area from 45% before surgery to 20% after surgery of the estimated original area. Fifteen patients had a primary neurologic deficit, which improved markedly in 11 cases after treatment. Patients with neurologic symptoms had a greater preoperative spinal stenosis than those without. No correlation was seen between the degree of pretreatment spinal stenosis, fracture type, and severity of the neurologic deficit. Ligamentotaxis (n = 27) reduced the stenosis from 30% before surgery to 18% after surgery and remodeling (n = 11) from 25% after surgery to 13% after metal removal. CONCLUSION: Ultrasound-guided fracture repositioning is an efficient method for spinal canal decompression of burst fractures with neurologic symptoms. The marked degree of widening of the spinal canal due to the effects of ligamentotaxis and remodeling may render the reposition of retropulsed fragments unnecessary in cases of fractures without a neurologic deficit.

Adolescent↗
PubMed2006

Periacetabular bone changes after uncemented total hip arthroplasty evaluated by quantitative computed tomography.

BACKGROUND: There are few dual X-ray absorptiometry (DXA) studies on periacetabular bone density changes after cup implantation. This study was designed to analyze the load-transfer mechanism and stress pattern of periacetabular cortical and cancellous bone after implantation of a ihemispherical titanium alloy press-fit cup with alumina-alumina pairing in vivo. We introduced a novel method of computed tomography (CT)-assisted osteodensitometry. METHOD: We investigated 26 hips (26 patients) with osteoarthritis using conventional sequential CT examinations performed within the first 10 days after implantation, and after a mean period of 1.1 years postoperatively. Bone density of full, cancellous and cortical bone (mgCaHA/mL) was measured. RESULTS: At the time of follow-up, the mean bone density values of the cortical bone cranial to the cup increased by 3.6% (p = 0.03) while the cancellous bone density decreased by 18%. Cancellous bone loss was greater in the region ventral to the cup (-35%) than in the dorsal region (-30%). Cortical bone density decreased ventral to the cup (-6.4%). All these changes were statistically significant. The bone density changes in the dorsal cortical region were not significant. INTERPRETATION: The method presented is an excellent tool for detailed measurement of bone density changes around the cup after total hip arthroplasty, and allows a thorough assessment of stress shielding phenomena in vivo. The hemispherical titanium alloy press-fit cup is a rigid implant which stress shields cancellous bone and enhances load transfer to the cranial cortical bone. Further investigations will demonstrate the impact these factors have on the long-term results of the implant, and may allow a type-related predictable prognosis of the longevity of the prosthesis.

Absorptiometry, Photon↗
PubMed2006

Influence of calcium on the proteolytic degradation of the calmodulin-like skin protein (calmodulin-like protein 5) in psoriatic epidermis.

The calmodulin-like skin protein (CLSP) or so-called calmodulin-like protein 5, a recently discovered skin-specific calcium-binding protein, is closely related to keratinocyte differentiation. The 16-kDa protein is proteolytically degraded in the upper layers of the stratum corneum (SC) of healthy skin. With the use of specific new monoclonal antibodies to CLSP, we were able to demonstrate that the abnormal elevated levels of CLSP, characteristic of psoriatic epidermis, were probably not due to an overexpression of the protein, but most likely the result of its non-degradation. Further in vitro experiments using recombinant CLSP and in situ data clearly showed that calcium protected and chelator accelerated CLSP degradation. These data indicate that CLSP degradation in the SC of psoriatic skin might be hindered by the abnormally elevated calcium concentration. No degradation of CLSP in psoriatic epidermis keeping its ability to bind protein as transglutaminase 3 may have a physiological role in skin diseases such as psoriasis.

Adult↗
PubMed2006

[Analysis of the periprosthetic femoral bone reaction after uncemented total hip arthroplasty with computertomography assisted osteodensitometry in vivo: 6-year follow-up].

AIMS: We prospectively analyzed the cancellous and cortical periprosthetic femoral bone reaction after implantation of a cementless total hip arthroplasty with computertomography assisted osteodensitometry after a mean of 1 and 6 years. MATERIALS AND METHODS: Twenty-one patients (Ø age at implantation: 52 years) with osteoarthrits of the hip joint received 21 cementless hip prostheses with a three-dimensionally tapered design. All patients were analyzed clinically, with CT-osteodensitometry and plain radiography after a mean of 10 days, at 1 and 6 years postoperatively. Cancellous and cortical bone density was evaluated automatically using a special software tool. RESULTS: The proximal region of the stem showed progessive cortical (Ø -15% 1 year, -25% 6 years post-OP) and cancellous (Ø -26% 1 year, -49% 6 years post-OP) bone density loss. Cortical bone density loss was lower and non-progressive at the diaphysis (Ø -7% 1 year, -9% 6 years post-OP) and the distal region (Ø -6% 1 year, -4% 6 years post-OP) of the stem. All stems showed no signs of loosening on plain radiography and good clinical results according to the Harris hip score. CONCLUSION: Computertomography assisted osteodensitometry is the only method which allows discrimination between periprosthetic cortical and cancellous bone density changes in vivo. The analyzed uncemented stem fixates at the diaphysis and distal region. Due to the changed biomechanical loading after stem implantation, progressive proximal cancellous bone density loss was measured for the first time in vivo. Its role in the pathogenesis of implant loosening is still unknown and needs to be further elucidated.

Absorptiometry, Photon↗
PubMed2005

Inter- and intraobserver assessment of periacetabular osteodensitometry after cemented and uncemented total hip arthroplasty using computed tomography.

INTRODUCTION: This study was initiated to evaluate the reproducibility of a novel method for measuring the periacetabular bone density after insertion of cemented and uncemented acetabular cups using CT in vivo. MATERIALS AND METHODS: CT scans were obtained from 20 patients after cemented polyethylene cup implantation (ZCA, Zimmer, USA) and 20 patients after uncemented titanium alloy cup fixation (Cerafit, Ceraver, France). A manual segmentation of cancellous and cortical pelvic bone ventral, dorsal and cranial to the cup was undertaken. Values are given in Hounsfield units. Inter- and intraobserver studies were conducted using a special analysis software tool. To define the reproducibility of the method, all measurements were evaluated according to Bland and Altman. RESULTS: For both cemented and uncemented acetabular cups, reproducibility of bone density measurement for cortical and cancellous bone cranial, ventral and dorsal to the cup was high. There was no significant difference between the intraobsever study (two repeated measurements) and the interobserver study (two investigators), indicating the reproducibility of the method independent of the investigator. CONCLUSION: In conclusion, the periacetabular bone density measurement as conducted in this CT study is a new reproducible method for in vivo evaluation of cortical and cancellous pelvic bone after cemented and uncemented acetabular cup implantation. In vivo CT measurements will allow a thorough assessment of periacetabular stress-shielding phenomena.

Acetabulum↗
PubMed2005

Geomedical warning system against epidemics.

We describe aims, usage and evaluation of the computer-based early warning system telecommunication on medical events (TeCoMed), which achieves tracking down of temporal and spatial spread of epidemics for seasonal communicable diseases. It uses experiences from former waves of communicable diseases down to fine-grained local areas. Data is delivered by the biggest German insurance scheme. The results are presented by means of a commercial, geomedical information system. The evaluation of the system's performance concerning influenza shows that timely risk assessment and warnings are possible.

Communicable Disease Control↗
PubMed2005

A prognostic model for temporal courses that combines temporal abstraction and case-based reasoning.

Since clinical management of patients and clinical research are essentially time-oriented endeavours, reasoning about time has become a hot topic in medical informatics. Here we present a method for prognosis of temporal courses, which combines temporal abstractions with case-based reasoning. It is useful for application domains where neither well-known standards, nor known periodicity, nor a complete domain theory exist. We have used our method in two prognostic applications. The first one deals with prognosis of the kidney function for intensive care patients. The idea is to elicit impairments on time, especially to warn against threatening kidney failures. Our second application deals with a completely different domain, namely geographical medicine. Its intention is to compute early warnings against approaching infectious diseases, which are characterised by irregular cyclic occurrences. So far, we have applied our program on influenza and bronchitis. In this paper, we focus on influenza forecast and show first experimental results.

Computer Simulation↗
PubMed2005

The cornified envelope: a model of cell death in the skin.

The epidermis functions as a barrier against the environment by means of several layers of terminally differentiated, dead keratinocytes - the cornified layer, which forms the endpoint of epidermal differentiation and death. The cornified envelope replaces the plasma membrane of differentiating keratinocytes and consists of keratins that are enclosed within an insoluble amalgam of proteins, which are crosslinked by transglutaminases and surrounded by a lipid envelope. New insights into the molecular mechanisms and the physiological endpoints of cornification are increasing our understanding of the pathological defects of this unique form of programmed cell death, which is associated with barrier malfunctions and ichthyosis.

Animals↗
PubMed2005

[Investigations of beta-dosimetry at two different sources for the cardiovascular brachytherapy].

The intracoronary brachytherapy is used at the Hamburg University Hospital as a method to treat in-stent restenosis. Two different radiochromic film types were applied to obtain dosimetric information of the beta-sources used (32P and 90Sr/90Y). First, these films were analyzed for their suitability for dosimetry. Within the investigated dose range (MD-55-2: 0 to 33 Gy, HD-810: 0 to 105 Gy), both films showed a linear behavior between the dose and the optical density (OD). Because radiochromic films are subject to time-based changes in OD, a method for colour stabilization was investigated (RCS-method). This method allowed to greatly shorten the time between irradiation and evaluation from 24 hours (time necessary for the film to reach a quasi-stable status) to 2.5 hours. Colour-stabilized films can also be stored for a long time and reanalyzed with almost the same results. Within the limits of the measurements error, both film types showed an energy independent response. Within the dose profiles, analyses of the two source types resulted in differences of 13.5% (32P) and 21% (90Sr/90Y). These inhomogenities are consistent with the fabrication tolerances given by the manufactures.

Beta Particles↗
PubMed2005

Prototypical cases and adaptation rules for diagnosis of dysmorphic syndromes.

Since diagnosis of dysmorphic syndromes is a domain with incomplete knowledge and where even experts have seen only few syndromes themselves during their lifetime, documentation of cases and the use of case-oriented techniques are popular. In dysmorphic systems, diagnosis usually is performed as a classification task, where a prototypicality measure is applied to determine the most probable syndrome. These measures differ from the usual Case-Based Reasoning similarity measures, because here cases and syndromes are not represented as attribute value pairs but as long lists of symptoms, and because query cases are not compared with cases but with prototypes. In contrast to most dysmorphic systems our approach additionally applies adaptation rules. These rules do not only consider single symptoms but combinations of them, which indicate high or low probabilities of specific syndromes.

Humans↗
PubMed2004

Emergency localization of radioactive seeds lost during intracoronary brachytherapy.

Recently, it has been reported that brachytherapy catheters ruptured in vivo. Localization of lost beta-radiation-emitting seeds is a problem because no appropriate technique is available that is rapid and precise. We developed a technique to localize beta-emitting seeds utilizing the effect that beta-radiation induces bremsstrahlung. The loss of a single radioactive source was simulated in an Alderson Phantom representing a human body. The beta-induced bremsstrahlung could be detected selectively by a gamma-camera. The position of the radioactive seed could be located within 5 min with an accuracy of +/- 0.5 cm. The result of this study suggests that in an emergency case of loss of a brachytherapy source, a commercially available gamma-camera can be a valuable tool to detect lost beta-radiation-emitting seeds rapidly and precisely. In addition, the technique minimizes the patient's as well as the surgeon's exposure to radiation and reduces the extent of surgical trauma.

Beta Particles↗
PubMed2004

Human gingival mucosal keratinocytes exhibiting anchorage-independent growth express increased inducible nitric oxide synthase: regulation by MAP kinases.

Inducible nitric oxide synthase (iNOS) has been implicated in cancer formation because of its vast presence cancer tissues. Studies to support such a role during transformation of human cells are very limited. We have developed a cell culture system, which renders a more transformed epithelial phenotype. The model cells generated from immortalized human gingival mucosal (GM) keratinocytes are consisted of less transformed epithelial-like (EPI) cells and more transformed fibroblast-like (FIB) cells. The latter exhibit anchorage independent growth (AIG). Our data showed that iNOS at mRNA and protein levels was up-regulated in more transformed FIB cells in comparison with less transformed EPI cells. FIB cells at low passages (p<22) were unstable being able to morphologically and functionally revert back to EPI phenotype, while no reversion was observed in FIB cells at high passages (p>43). The morphological reversion of FIB cells was associated with the reversal of vimentin expression as well as AIG. More importantly, these revertants showed reduced levels of iNOS mRNA as well as MAP kinase ERK and phospho-ERK protein expression, while FIB cells without reversion maintained the expression. Furthermore, the MEK1/2 inhibitor U0126 could reduce detectable iNOS mRNA levels suggesting that MAP kinases were upstream regulators of iNOS transcription. U0126 caused both morphological and functional reversion of FIB cells indicating involvement of MAP kinases in these functions. Taken together, we provide evidence for an up-regulation of iNOS in cultured human keratinocytes which exhibit AIG. This up-regulation may reflect progressive transformation which still requires further changes to reach tumorigenic conversion.

Butadienes↗