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Biomedical subjects

R Seemann

Publications and source records attributed to R Seemann.

At least 19 recordsLinked to original sources

Fast DRR generation for 2D/3D registration.

We present a simple and rapid method for generation of perspective digitally rendered radiographs (DRR) for 2D/3D registration based on splat rendering. Suppression of discretization artefacts by means of computation of Gaussian footprints--which is a considerable computational burden in classical splat rendering--is replaced by stochastic motion of either the voxels in the volume to be rendered, or by simulation of a X-ray tube focal spot of finite size. The result is a simple and fast perspective rendering algorithm using only a small subset of voxels. Our method generates slightly blurred DRRs suitable for registration purposes at framerates of approximately 10 Hz when rendering volume images with a size of 30 MB on a standard PC.

Algorithms↗

Basic research and 12 years of clinical experience in computer-assisted navigation technology: a review.

Computer-aided surgical navigation technology is commonly used in craniomaxillofacial surgery. It offers substantial improvement regarding esthetic and functional aspects in a range of surgical procedures. Based on augmented reality principles, where the real operative site is merged with computer generated graphic information, computer-aided navigation systems were employed, among other procedures, in dental implantology, arthroscopy of the temporomandibular joint, osteotomies, distraction osteogenesis, image guided biopsies and removals of foreign bodies. The decision to perform a procedure with or without computer-aided intraoperative navigation depends on the expected benefit to the procedure as well as on the technical expenditure necessary to achieve that goal. This paper comprises the experience gained in 12 years of research, development and routine clinical application. One hundred and fifty-eight operations with successful application of surgical navigation technology--divided into five groups--are evaluated regarding the criteria "medical benefit" and "technical expenditure" necessary to perform these procedures. Our results indicate that the medical benefit is likely to outweight the expenditure of technology with few exceptions (calvaria transplant, resection of the temporal bone, reconstruction of the orbital floor). Especially in dental implantology, specialized software reduces time and additional costs necessary to plan and perform procedures with computer-aided surgical navigation.

Computer Graphics↗

Levels of parotid and submandibular/sublingual salivary immunoglobulin A in response to experimental gingivitis in humans.

Salivary secretory IgA (s-IgA) is considered to act as an important first line of defense mechanism in the oral cavity. It has therefore been suggested that an increased antigenic load would induce an increase in salivary IgA production. This study investigated the pure glandular levels of salivary IgA in parotid and submandibular/sublingual (SM/SL) saliva during plaque accumulation leading to experimental gingivitis. Starting from regular oral hygiene, 14 healthy, nonsmoking men refrained from all oral hygiene measures for 12 days. On days -2, 0, 3, 6, and 12 a plaque index, a bleeding index, and unstimulated and stimulated saliva from the parotid and the SM/SL glands were measured. Salivary IgA was quantified using a sandwich ELISA. All subjects developed gingivitis as measured by a bleeding index. Compared to baseline the salivary flow rate was increased on day 12. Regarding the secretion rate of IgA there was a statistically significant increase in stimulated parotid saliva but not SM/SL saliva compared to baseline after 6 and 12 days without oral hygiene. No significant changes were observed for the concentration of IgA during the trial. Thus, in healthy subjects with regular oral hygiene the development of plaque induced gingivitis is associated with increased salivary gland output and increased total IgA output levels in stimulated parotid saliva but not in SM/SL saliva.

Adult↗

Viscoelastic dynamics of polymer thin films and surfaces.

The strain relaxation behavior in a viscoelastic material, such as a polymer melt, may be strongly affected by the proximity of a free surface or mobile interface. In this paper, the viscoelastic surface modes of the material are discussed with respect to their possible influence on the freezing temperature and dewetting morphology of thin polymer films. In particular, the mode spectrum is connected with mode coupling theory assuming memory effects in the melt. Based on the idea that the polymer freezes due to these memory effects, surface melting is predicted. As a consequence, the substantial shift of the glass transition temperature of thin polymer films with respect to the bulk is naturally explanied. The experimental findings of several independent groups can be accounted for quantitatively, with the elastic modulus at the glass transition temperature as the only fitting parameter. Finally, a simple model is put forward which accounts for the occurrence of certain generic dewetting morphologies in thin liquid polymer films. It demonstrates that by taking into account the viscoelastic properties of the film, a morphological phase diagram may be derived which describes the observed structures of dewetting fronts. It is demonstrated that dewetting morphologies may also serve to determine nanoscale rheological properties of liquids.

Journal Article↗

Chronic lithium downregulates cyclooxygenase-2 activity and prostaglandin E(2) concentration in rat brain.

Rats treated with lithium chloride for 6 weeks have been reported to demonstrate reduced turnover of arachidonic acid (AA) in brain phospholipids, and decreases in mRNA and protein levels, and enzyme activity, of AA-selective cytosolic phospholipase A(2)(cPLA(2)). We now report that chronic lithium administration to rats significantly reduced the brain protein level and enzyme activity of cyclooxygenase-2 (COX-2), without affecting COX-2 mRNA. Lithium also reduced the brain concentration of prostaglandin E(2) (PGE(2)), a bioactive product of AA formed via the COX reaction. COX-1 and the Ca(2+)-independent iPLA(2) (type VI) were unaffected by lithium. These and prior results indicate that lithium targets a part of the AA cascade that involves cPLA(2) and COX-2. This effect may contribute to lithium's therapeutic action in bipolar disorder.

Animals↗

Quantitative analysis of factors affecting intraoperative precision and stability of optoelectronic and electromagnetic tracking systems.

This study aims to provide a quantitative analysis of the factors affecting the actual precision and stability of optoelectronic and electromagnetic tracking systems in computer-aided surgery under real clinical/intraoperative conditions. A "phantom-skull" with five precisely determined reference distances between marker spheres is used for all measurements. Three optoelectronic and one electromagnetic tracking systems are included in this study. The experimental design is divided into three parts: (1) evaluation of serial- and multislice-CT (computed tomography) images of the phantom-skull for the precision of distance measurements by means of navigation software without a digitizer, (2) digitizer measurements under realistic intraoperative conditions with the factors OR-lamp (radiating into the field of view of the digitizer) or/and "handling with ferromagnetic surgical instruments" (in the field of view of the digitizer) and (3) "point-measurements" to analyze the influence of changes in the angle of inclination of the stylus axis. Deviations between reference distances and measured values are statistically investigated by means of analysis of variance. Computerized measurements of distances based on serial-CT data were more precise than based on multislice-CT data. All tracking systems included in this study proved to be considerably less precise under realistic OR conditions when compared to the technical specifications in the manuals of the systems. Changes in the angle of inclination of the stylus axis resulted in deviations of up to 3.40 mm (mean deviations for all systems ranging from 0.49 to 1.42 mm, variances ranging from 0.09 to 1.44 mm), indicating a strong need for improvements of stylus design. The electromagnetic tracking system investigated in this study was not significantly affected by small ferromagnetic surgical instruments.

Biophysical Phenomena↗

Sharper images by focusing soft X-rays with photon sieves.

Fresnel zone plates consisting of alternating transmissive and opaque circular rings can be used to focus X-rays. The spatial resolution that can be achieved with these devices is of the order of the width of the outermost zone and is therefore limited by the smallest structure (20-40 nm) that can be fabricated by lithography today. Here we show that a large number of pinholes distributed appropriately over the Fresnel zones make it possible to focus soft X-rays to spot sizes smaller than the diameter of the smallest pinhole. In addition, higher orders of diffraction and secondary maxima can be suppressed by several orders of magnitude. In combination with the next generation of synchrotron light sources (free-electron lasers) these 'photon sieves' offer new opportunities for high-resolution X-ray microscopy and spectroscopy in physical and life sciences.

Journal Article↗

Shape of a liquid front upon dewetting.

The profile of a liquid front of a polymer film dewetting a solid substrate is examined by atomic force microscopy. The material removed from the substrate is accumulated in a rim next to the three-phase contact line. Theory predicts the leading edge of the rim profile to be a damped harmonic oscillation for a large class of systems. This is investigated experimentally for the first time, and we show that a non-Newtonian liquid behaves qualitatively different due to viscoelastic effects. It is pointed out that analysis of the rim shapes allows one to study quantitatively the rheological properties of complex fluids on a nanometer scale.

Journal Article↗

Dewetting patterns and molecular forces: a reconciliation.

We studied the dewetting of thin liquid polymer films from solid surfaces. Our experimental results lead to a consistent picture demonstrating the interplay between short- and long-range interfacial forces. Observations comprise nucleation and spinodal dewetting, as well as thermal nucleation of holes. The effective interface potential of the system, as reconstructed from the morphology of the dewetting patterns, agrees quantitatively with what is computed from the optical properties of the system. This shows that the assumption of additivity of dispersion potentials in multilayer systems yields good results.

Journal Article↗

The effect of a preventive program, including the application of low-concentration fluoride varnish, on caries control in high-risk children.

The aim of this 2-year prospective randomized clinical study was to evaluate the efficacy of a prevention program for schoolchildren with high caries risk. A sample of 419 subjects was divided into a test (T, n = 259) and control group (C, n = 160). Four times a year, the test group received professional tooth-cleaning and application of a 0.1% fluoride varnish as well as motivation and instruction in oral hygiene. The control group received only oral hygiene instruction and took part in supervised toothbrushing once a year. At baseline and after 2 years, the D3,4MFS and the incipient lesions (D1,2) were recorded. After 2 years, 318 subjects (T = 187, C = 131) were included in the data analysis. The baseline D1,2 was 6.18 (T) and 5.50 (C), the D3,4MFS 2.13 (T) and 2.08 (C), respectively. No statistically significant difference was found for the baseline values. At the final examination, the D1,2 increment was 3.96 in the test and 6.53 in the control group, showing a statistically significant difference (P < 0.001). No such difference was found for the D3,4MFS increment (T: 2.22; C: 2.61). The results indicate that it might not be possible to prevent cavities in high caries risk children by means of the described program.

Cariostatic Agents↗

[Effective of preventive programs on oral hygiene of adults and school children].

The improvement of dental hygiene is considered to be one of the most important measures in dental health education. Hence, it was the aim of the present study to investigate the influence of two similar preventive programmes on oral hygiene performed in adults and schoolchildren. In the adult study, the oral hygiene indices PI (Quigley-Hein) and API (Lange) could be significantly improved after six months by an individualized preventive programme performed every three months. Besides repeated instructions and motivations in oral hygiene, the programme included professional toothcleaning. In contrast, nine-year old schoolchildren showed no improvement in the oral hygiene indices PI and PBI (Mühlemann and Son) after applying a similar programme over three years. For the PI, even a deterioration from 1.86 at the beginning of the study to 2.65 at the final examination was seen. Other authors were more successful by applying a programme without professional toothcleaning but with inclusion of the parents. It is therefore concluded that children should be educated to oral self-care by including their parents and by taking their status of psychological development into account.

Adult↗

Effectiveness of mechanical tongue cleaning on oral levels of volatile sulfur compounds.

BACKGROUND: Mechanical tongue cleaning may be an effective method for decreasing oral levels of volatile sulfur compounds, or VSC, and oral malodor. The authors conducted a study to compare the effectiveness of a specially designed tongue cleaner (One Drop Only Tongue Cleaner, One Drop Only, Berlin), a tongue scraper and a toothbrush in reducing oral VSC levels. METHODS: In this balanced, crossover study, 30 subjects had four morning appointments each with a waiting period of one week between appointments. At each appointment, a dental professional performed a single standardized tongue cleaning procedure using one of the cleaning tools. The authors monitored the subjects' oral VSC values using a portable sulfide monitor until their baseline VSC values were reached. RESULTS: The baseline values showed no significant difference between the three groups. The tongue cleaner and the tongue scraper (42 percent and 40 percent, respectively) reduced oral VSC levels more than the toothbrush (33 percent) did. Reduced VSC values could be detected significantly longer after using the tongue cleaner than after using the tongue scraper or the toothbrush. The authors, however, could not detect a significant VSC reduction for more than 30 minutes in any of the subjects. CONCLUSIONS AND CLINICAL IMPLICATIONS: The tongue cleaner, a combination brush and scraper, was slightly more effective in reducing oral VSC levels than were the tongue scraper and a regular toothbrush. Because of the limited duration of the effect, however, the clinical efficacy on the reduction of oral malodor remains questionable.

Analysis of Variance↗

The effect of an oral hygiene program on oral levels of volatile sulfur compounds (VSC).

Volatile sulfur compounds (VSCs) produced by bacteria in niches of the oral cavity play a major role in the etiology of bad breath, and can be easily detected by a portable sulfide monitor (Halimeter). To investigate the effect of an oral hygiene program on VSC levels, Halimeter readings were taken from 55 healthy dental students during a course in oral hygiene training, including instruction on brushing, flossing and professional tooth cleaning. Ten students who received no oral hygiene training served as a negative control. The oral hygiene status was measured using the papillary bleeding index (PBI). PBI and VSC values did not show significant changes during the study period of 10 weeks in the control group. In the test group, PBI values significantly decreased compared to baseline and the control, indicating that the oral hygiene program had a benefit on the oral hygiene status. The VSC values also decreased significantly during the study period compared to baseline and the control. It was concluded that in a group of dental students, a thorough oral hygiene training program was capable of reducing the oral level of VSC Halimeter readings.

Adult↗

85 kDa cytosolic phospholipase A2 is a target for chronic lithium in rat brain.

The mechanism by which chronic lithium exerts its therapeutic effect in brains of bipolar patients is not known. One possibility, suggested by our demonstration in the rat brain, is that chronic lithium inhibits turnover of arachidonic acid (AA) by reducing the activity of an AA-specific phospholipase A2 (PLA2). To test this further, mRNA levels of two AA-specific PLA2s, cytosolic PLA2 (cPLA2) type IV and intracellular PLA2 (iPLA2) type VIII, and protein level of cPLA2 were quantified in the brain of rats given lithium for 6 weeks. Chronic lithium markedly reduced brain mRNA and protein level of cPLA2, but had no effect on mRNA level of iPLA2. These results suggest that the final common path effect of chronic lithium administration is to reduce turnover of AA in brain by down-regulating cPLA2.

Animals↗

c-kit ligand gene expression in normal and sublethally irradiated mice.

The c-kit ligand (KL; Steel factor, mast cell growth factor, stem cell factor) is a hematopoietic factor that has been shown to act as a potent cofactor for hematopoietic growth and differentiation in vitro. The in vivo effects of KL, however, have been variable. To study the hematopoietic role of KL in vivo, we evaluated KL gene expression in both normal mice and mice recovering from myelosuppressive radiation exposure using the reverse transcriptase-polymerase chain reaction (RT-PCR) technique. In a single RNA sample, we found that the RT-PCR technique has high precision (co-efficient of variation, 15.7%). Amplifications of serial 1:2 dilutions of template RNA precisely correlated with starting RNA concentrations at 20 cycles or at 25 cycles, depending on the level of expression. Amplification of individual normal bone marrow and spleen cell RNA showed basal expression in all normal bone marrows but irregular expression in normal spleens. On day 2 after a sublethal 7.75-Gy (0.4 Gy/min) 60Co irradiation, splenic KL gene expression increased approximately 2.5-fold (P = .011), and bone marrow expression increased 15-fold (P = .004). During a 28-day postirradiation recovery period, KL expression increased in bone marrow on days 2 through 7. Splenic expression during the same period was more variable. In conclusion, the KL gene is invariably expressed in normal murine spleens. Postirradiation, recovering bone marrow and spleen both express increased levels of KL mRNA at day 2 and continue to express increased levels for several days postexposure. These data support a role for KL in the endogenous recovery of hematopoiesis after hypoplastic injury.

Animals↗

Comparison of interleukin-1 alpha gene expression and protein levels in the murine spleen after lethal and sublethal total-body irradiation.

To understand the effects of ionizing radiation on the production of IL-1 alpha in vivo within a hematopoietic organ, we evaluated acute changes in splenic IL-1 alpha mRNA and IL-1 alpha protein after exposing B6D2F1 mice to lethal and sublethal 60Co radiation. Results suggest that in vivo, ionizing radiation induces a time- and dose-dependent accumulation of IL-1 alpha mRNA in the mouse spleen after exposure to gamma radiation. Time-dependent increases in the level of IL-1 alpha protein were also observed, although the magnitude of increased protein expression did not complement the magnitude of the accumulation of the message. Selective concentration of cells producing IL-1 alpha does not appear to account completely for the increase in splenic IL-1 alpha mRNA observed in this in vivo system.

Animals↗