Biomedical subjects
Publications and source records attributed to M Wendt.
Our mobile monitoring and treatment station, for use in anaesthesia and intensive care, allows transport of patients around the medical unit without disconnection from medical equipment, with a maximum level of safety, and low workload and costs.
A new optical method of detuning parallel resonant circuits is described. This method involves the integration of a photoresistor in parallel with the inductor and capacitor of a parallel resonant circuit, in this case a magnetic resonance imaging (MRI) receiver coil. A fiberoptic cable extending the length of the interventional device is used in conjunction with an external light source to deliver light to the photoresistor. Exposing the photoresistor to light changes its bulk resistance and greatly lowers the Q of the parallel resonant circuit, effectively detuning it. By combining this optical detuning scheme with inductive coupling of the interventional device-mounted microcoils to a standard MRI coil, a completely wireless device for active device tracking has been created. This new device improves on current technology by simplifying device complexity and reducing patient risk by eliminating the need for electrical connections between the device-mounted microcoils to the MR receiver channel.
This project incorporated a novel inductive coupling structure of three micro coils into an invasive device tip to determine both its tip position and orientation. Moreover, with the introduction of a new target-navigation technique the MR scan plane was defined automatically by the invasive device orientation and target tissue location. A time domain multiplexing technique was applied for simultaneous MR imaging and device tracking. Using these techniques, the acquired MR images always showed both the invasive device and its target tissue. Thus, roadmap images and their potential misregistration errors were avoided. A graphical user interface (GUI) was also designed to assist interventional physicians in monitoring and guiding the insertion of the interventional device. Ex vivo phantom and in vivo animal experiments were performed to test this new technique. The methods developed in this project provide a new active technique for interventional device guidance using MRI. Magn Reson Med 44:56-65, 2000.
Various kinds of nonrectilinear Cartesian k-space trajectories have been studied, such as spiral, circular, and rosette trajectories. Although the nonrectilinear Cartesian sampling techniques generally have the advantage of fast data acquisition, the gridding process prior to 2D-FFT image reconstruction usually requires a number of additional calculations, thus necessitating an increase in the computation time. Further, the reconstructed image often exhibits artifacts resulting from both the k-space sampling pattern and the gridding procedure. To date, it has been demonstrated in only a few studies that the special geometric sampling patterns of certain specific trajectories facilitate fast image reconstruction. In other words, the inherent link among the trajectory, the sampling scheme, and the associated complexity of the regridding/reconstruction process has been investigated to only a limited extent. In this study, it is demonstrated that a Lissajous trajectory has the special geometric characteristics necessary for rapid reconstruction of nonrectilinear Cartesian k-space trajectories with constant sampling time intervals. Because of the applicability of a uniform resampling (URS) algorithm, a high-quality reconstructed image is obtained in a short reconstruction time when compared to other gridding algorithms.
PURPOSE: To test the feasibility of MR imaging (MRI)-guided percutaneous biliary drainages in patients using an open MR-system. METHODS: 6 patients with mechanical cholestasis underwent MRI-guided puncture and catheterization of the biliary system following intervention planning with magnetic resonance cholangiography (MRC) in an open low-field MR system. Data on the number of punctures required, success in establishing external and internal drainage, and total procedure time were compared to those of 6 patients who underwent biliary drainage with fluoroscopic guidance. RESULTS: MRC facilitated intervention planning in all patients. Near-real-time MR imaging enabled interactive positioning of the devices. The bile ducts were punctured under MRI control in three patients in the first, in two in the second, and in one in the third attempt. MRI-guided puncture was faster than the fluoroscopic procedure. Catheterization for external drainage was successful in all patients. Passing the obstructions was not possible under MRI guidance. The procedure time for MRI-guided catheterization was longer than in the conventional technique. CONCLUSION: MRI-guidance allows reliable placement of an external biliary drainage in an open low-field MR system.
OBJECTIVE: To test the feasibility and safety of the laser-induced thermotherapy (LITT) for liver metastases in open MR imaging system operating at 0.2 Tesla. METHOD: Laser therapy using the Nd:YAG laser was performed on 25 patients with a total of 41 liver metastases. An open low-field MRI scanner was used for puncture, positioning of the laser applicator, and monitoring the therapy. A true FISP sequence was used to track the puncture in close to real-time. Localization diagnostics and temperature monitoring were aided by T1-weighted gradient echo sequences in the breath-holding technique. In the first follow up after 24-48 hours, a contrast-enhanced T1-weighted gradient-echo sequence was performed in an MRI scanner at 1.5T. The pre-, intra- and postinterventional volumes of the liver metastases as well as the thermolesions and the thermonecroses were determined. RESULTS: LITT in an open MRI system was technically feasible in all patients with no clinically relevant complications. The mean volumes of the thermolesions measured during intervention in low-field MRI were lower than the volumes of the thermonecroses measured after intervention in high-field MRI. CONCLUSION: The technique presented here of laser-induced thermotherapy for liver metastases in an open MRI system is technically feasible and safe.
The semisynthetic streptogramin combination quinupristin/dalfopristin (Synercid) is a promising alternative for treatment of infections due to multiply resistant gram-positive bacteria including vancomycin-resistant Enterococcus faecium. Resistance is mediated by acetyltransferases SatA (VatD) or SatG (VatE). Recent papers have indicated a possible link between the use of the streptogramin virginiamycin S/M as a feed additive in commercial animal husbandry and a selection of quinupristin/dalfopristin-resistant E. faecium (QDRE). We screened manure samples from two different turkey farms and from six different pig farms (using virginiamycin), samples from a sewage water treatment plant, 24 broiler carcasses, 10 pork samples, and 200 stool samples of nonhospitalized humans for QDRE. Our strain culture collection of hospital E. faecium isolates from the last 2 years was also reviewed for QDRE. All manure and sewage samples were positive for QDRE, as well as 11 from broiler carcasses (46%), 1 from pork (10%), and 28 from human stool specimens (14%). Thirty-six hospital isolates of E. faecium exhibited resistance to quinupristin/dalfopristin. In 141 QDRE of different origin satA (vatD) and satG (vatE) genes were detected (seven isolates from humans with an unknown resistance mechanism). Streptogramin resistance determinants were tansferable in filtermating experiments for 5 of 10 satA (vatD) and 9 of 22 satG (vatE) isolates. Different EcoRI patterns of satG (vatE) plasmids and corresponding hybridizations of the satG (vatE) gene indicated nonhomologous resistance plasmids in isolates of different origin. The results of this study indicate a common gene pool for streptogramin resistance in E. faecium of different ecological origin. A selection of QDRE using the streptogramin virginiamycin S/M as a feed additive and a spread of the resistance via the food chain to humans is probable.
Interventional procedures using magnetic resonance imaging (MRI) guidance have increased in interest during the last few years. Central to the success and safety of MRI-guided procedures is the accurate visualization of the interventional instruments relative to the surrounding anatomy. A variety of methodologies for visualizing and automatically tracking instruments, including needles, radiofrequency and laser ablation devices, endoscopes, catheters, and guidewires have been developed and introduced to help the interventionalist to safely guide the device toward the target region. This article describes and compares characteristics of the four most commonly used localization and tracking systems used for MRI-guided interventional procedures: those based on the susceptibility artifact of the device, those that intentionally create field inhomogeneity along the device, those that rely on an optical tracking system, and active tracking systems using micro receive coils.
BACKGROUND: There is evidence to suggest that inflammation plays a role in the development of atherosclerosis. Chronic infections may activate an inflammatory response in the walls of blood vessels. OBJECTIVE: To investigate the possibility of there being an association between infection with Helicobacter pylori (H. pylori) and coronary heart disease. METHODS: We examined 100 consecutive patients documented to have recently suffered acute myocardial infarction and 100 control subjects from the same geographical area for whom there was no evidence of coronary heart disease, carefully matched both for age and sex. Blood samples were tested for the presence of immunoglobulin G antibodies against H. pylori with a serological test. RESULTS: In comparison with controls, patients were more commonly smokers (26 versus 12%/0, P < 0.05) and had more commonly been treated for hypertension (37 versus 20%, P< 0.01). There was a significant association between seropositivity for H. pylori and having previously suffered acute myocardial infarction (68 versus 53%, odds ratio 1.36 with 95% confidence interval 1.02-1.82, P=0.034). These findings remained valid in a multivariate analysis including possible confounding factors (age, sex, smoking and hypertension; odds ratio 1.35 with 95% confidence interval 1.01-1.83, P=0.046). CONCLUSIONS: The positive association between seropositivity for H. pylori and having previously suffered acute myocardial infarction found in this study provides further support for the hypothesis that there is a causal association between chronic infection with H. pylori and the development of coronary heart disease.
UNLABELLED: Our current concept of stationary workplaces results in an interruption in patient monitoring and treatment. Because transfers are invariably associated with a reduction or interruption in the monitoring and treatment chain, an endangerment to critically-ill patients, as well as a significant increase in the mortality rates, can result. DESIGN: In the new construction of the Cardiac Clinic, the previous concept of immobile anesthesia and intensive care workstations has been completely abandoned. The complete treatment workstation, including monitoring and fluid management, is set up on a bedside cart which accompanies the patients uninterruptedly--from anesthesia administration, to the operating room, to the ICU or recovery room, as well as during elective or emergency interventions outside the ICU. Transport times and complications from 995 transports (ASA III and IV) were analysed and compared with 880 transports with the conventional system. RESULTS: During all intrahospital transfers with the mobile workplace, there were no complications resulting from faulty operation or accidental adjustment of the perfusors, or from disconnecting the monitoring,-, respiration-, or infusion lines. On the whole, there were fewer cases of circulatory instability during transport, since infusion treatment and medication could be administered without interruption. All hemodynamic parameters were recorded during transport, as were cardiac minute output and right- and left-atrial filling pressures. The mobile workplace system allows for the shortest possible transport and exchange times--13.5 min, as compared to 42.5 min with the conventional system. The reconnection of monitoring equipment with zeroing, adjustment of the alarm limits, as well as exchanging perfusors and infusomats before and after transport is eliminated entirely. CONCLUSION: This mobile workplace, in which all components of the anesthesiological and intensive care workstations are integrated, guarantees the highest possible level of patient safety, since nothing has to be disconnected until the patient is transferred to a normal-care ward. In addition to the improved ergonomic design of the nurse's and doctor's workplace, substantial savings can also be made.
To investigate the prevalence of chlamydial infection and their significance for reproductive disorders in sow breeding herds in Germany, blood samples of 1493 pigs were taken for a serological survey by enzyme-linked-immunosorbent-assay (ELISA). Antibodies to Chlamydiae were found in 33% of the samples, in all herds investigated responders could be detected. The rate of seropositive animals in different farms varied from 4.3% to 72.7%. The percentage of positive responders in the farms correlated positively with the occurrence of MMA-syndrome (mastitis, metritis, agalactia), return to oestrus and diseases of the piglets. Also these herds showed less weaned piglets per sow and litter. Comparison of seronegative and seropositive sows within single farms revealed also worse reproductive data for seropositive sows. A significant relationship could be found between farms with a high quota of sero-positive sows and poor hygiene status as well as poultry keeping. As a second step 124 cervical swabs and 9 aborted piglets were investigated for chlamydial antigen by capture-ELISA and polymerase chain reaction (PCR). Using the capture-ELISA for investigation only 3 probes with chlamydial antigen could be detected, however, examination by the more sensible PCR gave positive results in 50% of the probes. 20% of the PCR-positive animals were clinically healthy sows, 80% of the PCR-positive probes originated from sows with reproductive disorders. A significant relationship could be shown between PCR-positive probes and the incidence of abortion and litters with stillborn piglets and piglets with low viability. Swabs from 93 of the 124 sows were investigated as well for other bacterial pathogens of reproductive disorders. A high degree of micro-organisms of different species could be detected in 70% of the samples of sows with reproductive disorders and in 35% of the samples of clinically healthy sows. Species differentiation of the chlamydial antigen positive samples was done by southern blot hybridisation. Herewith C. psittaci could be diagnosed in all positive samples. Additionally 8 probes revealed a mixed infection with C. psittaci and C. trachomatis. The results of the present study show, that the prevalence of chlamydial infections in breeding herds is high and underline the importance of chlamydial infections for reproductive disorders. Single chlamydial infections as well as mixed infections with other pathogens must be considered.
A review is given about the clinical symptoms, pathogenesis and aetiology of the porcine stress syndrome, furthermore aspects of animal welfare are discussed. The current breeding programmes of pig industry in Germany in many cases include animals with a mutation of the ryanodine-receptor (RYR-1)-gene--homozygous or heterozygous. This situation is the result of an intensive breeding of pigs during the last decades with the intention of increased lean carcass content and corresponding proceeds. The homozygous pigs are more stress susceptible (porcine stress syndrome) and produce meat of poor quality (PSE), which is also the case to some extend in heterozygous animals. The clinical symptoms of this muscle disease are characterised by a deficit of oxygen and a rapid glycolysis accompanied by a production of lactic acid and acidosis primarily in II B white muscle fibres. There is no doubt that a very close causal relation exists between the mutation of the RYR-1 and the porcine stress syndrome as well as the poor meat quality. The present knowledge of this disease, the genetic background, the physiology and pathophysiology of the mutation of the RYR-1 leads to the imperative conclusion to eliminate this mutated RYR-1 by selection of healthy pigs, which has been done successfully in other countries with important pig production. This conclusion is also supported by simple economic reasons because fertility, reproduction and daily weight gain are significantly reduced in stress susceptible pigs. Furthermore, it should be emphasised that regular breeding with the mutated RYR-1 is also a matter of animal welfare. The evident correlation between the mutated RYR-1 and the porcine stress syndrome, which includes degeneration of the muscle, pain and even life threatening malignant hyperthermia, can easily lead to the accusation in the public that diseased animals are used for pig meat production. Consequently, the authors would like to urge the breeding companies and the responsible authorities to discuss the problem with the intention to finish the current breeding programmes using animals with the mutated RYR-1 within a reasonable period of time.
The infectious agent of swine dysentery, Brachyspira (Br.) hyodysenteriae, seems to be widespread in German pig herds. Due to different reasons the eradication is increasingly difficult. Not only the success of therapeutic procedures but also the possibilities of diagnostics are unsatisfactory. Although only the bacteriological investigation of faeces or intestinal probes by culture techniques allows the typing of Brachyspira strains and the testing of drug resistance, however, the rate of false negative results is relatively high. In comparison with the cultural method an easy, prompt and cheap immunofluorescent test (IFT) resulted in a good sensitivity (90%). The higher rate of negative results by culture techniques can not be attributed to a lower specificity of the IFT, but to an insufficient transport of samples to the laboratory. The IFT therefore has to be considered as a valuable supplement to the cultural diagnostic of Br. hyodysenteriae. It is absolutely necessary to establish strategies in eradication of swine dysentery which result in pig breeding herds free of Br. hyodysenteriae. Only weaner pigs which are reliable free of this germ guarantee a fattening period sufficiently free of swine dysentery. The principles of different measures in effective eradication are described.
The objective of this study was to demonstrate in an animal model the feasibility of a passive tracking technique for catheter visualization of magnetic resonance (MR)-guided endovascular procedures. All experiments were performed in a 0.2 Tesla open MR system. Susceptibility-based catheters and guide wires were introduced into the aorta and were advanced selectively into the splenic and renal arteries under MR guidance. Based on a previously acquired contrast-enhanced magnetic resonance angiography (MRA) data set, the catheter positioning was performed by using a single-slice true fast imaging with steady state precession (FISP) sequence with a frame rate of 1.3 seconds. Contrast-enhanced MRA was performed in all animals. All catheters were advanced without complications into the aorta and were introduced into the proximal parts of the right renal and splenic arteries under MR guidance. Catheter manipulations were more difficult in the distal parts of these vessels due to the more complex anatomy. Passive catheter tracking is a valuable and technically robust alternative to active tracking methods, because it does not require additional hardware and, thus, can be implemented and used easily with any open MR imaging system. J. Magn. Reson. Imaging 1999;10:841-844.
Keyhole acquisition techniques have been used to reduce image acquisition times primarily in contrast agent studies and via simulation in interventional MRI procedures. More recent simulations have suggested that improved definition of an interventional device [e.g., biopsy needles, radio frequency (RF) electrodes] could be achieved by rotating the keyhole pattern in k-space so that the read out direction lies perpendicular to the device orientation in real space. This study seeks to validate the earlier predictions of improved efficacy of a rotated stripes keyhole acquisition in actual in vitro and in vivo interventional MR imaging procedures. A true-FISP sequence was modified to perform central stripes keyhole (as known as conventional keyhole) acquisitions after a full initial reference data set was acquired. The gradients of this sequence were then modified to rotate the k-space definition and the keyhole stripes by 10 degrees, 20 degrees, 30 degrees, 45 degrees, and 60 degrees from their conventional k-space orientation. Acquisitions were performed during insertion of interventional devices in phantom and in vivo RF ablation procedures, using the modified sequence selected which placed the phase encoding axis at parallel and perpendicular orientations to the devices. Resulting images were compared between the two orientations for needle width and tip accuracy. Apparent needle width was thinner and tip position more accurately determined for placement of phase encoding parallel to the needle in all cases. Rotated keyhole imaging provides the required temporal advantage of conventional keyhole imaging along with a near optimal definition of an interventional device when the phase encoding is oriented parallel to the direction of the needle motion. Magn Reson Med 42:554-560, 1999.
PURPOSE: The aim of this study is to introduce a fast, T2 weighted true FISP keyhole sequence implemented on an open C arm low field magnetic resonance (MR) scanner for interventional procedure guidance. METHOD: Following the acquisition of a reference data set using a true FISP (fast Imaging with Steady Precision) sequence, only the 32 central raw data lines (keyhole) are acquired in a fluoroscopic-like mode enabling continuous image reconstruction and update. The keyhole true-FISP sequence was tested in animal experiments and used in MR-guided interventions in 10 patients. RESULTS: The described true FISP keyhole sequence is characterized by an image frame rate of 2.5 images per second and a T2-like contrast. Due to system constraints with respect to the reconstruction, the actual displaying of images was delayed by up to 180 ms. CONCLUSIONS: The use of the described keyhole sequence enabled a fluoroscopy-like guidance of interventional devices in an open, low-field system.
PURPOSE: To determine whether contrast medium containing superparamagnetic iron oxide (SPIO) alters radio-frequency (RF)-related temperature distribution in acrylamide phantoms and in an in vivo model. MATERIALS AND METHODS: In nine acrylamide phantoms with increasing SPIO content, RF was applied with simultaneous measurement of temperature profile along the probe track. Additionally, magnetic resonance imaging-guided RF ablation was performed in the liver of six rabbits after the intravenous administration of SPIO (0.05 mL per kilogram of body weight) 40 minutes prior to ablation (SPIO group) and in another six rabbits without prior SPIO administration (control group). Coagulation diameter was evaluated on the basis of postprocedural imaging and subsequent gross pathologic findings. Statistical analysis was performed with the Student t test. RESULTS: In the phantoms, progressive increases in iron content resulted in higher temperatures along the RF electrode track (P < .05). In the in vivo model, however, SPIO at physiologic concentrations did not significantly increase the diameter of coagulation on the basis of either postprocedural imaging or subsequent gross pathologic findings. Additionally, no significant differences were seen in other RF-related parameters including impedance, voltage, current, and grounding pad temperature. CONCLUSION: Administration of SPIO in conjunction with RF ablation of focal liver lesions is feasible and safe, but no significant difference in the extent of induced coagulation can be expected.
OBJECTIVE: The purpose of this study was to assess the safety and feasibility of MR-guided percutaneous nephrostomy of the nondilated contrast-enhanced upper urinary tract in a porcine model. SUBJECTS AND METHODS: Six MR-guided percutaneous nephrostomies of the nondilated upper urinary tract were performed in four domestic farm pigs (body weight range, 20-25 kg) using a 0.2-T system. Ten minutes after IV administration of 0.2 mmol/kg of gadodiamide and 0.4 mg/kg of furosemide, a fast T1-weighted sequence was used to guide insertion of an 18-gauge MR-compatible needle into a predetermined calix. After confirmation of needle position using a turbo spin-echo T1-weighted sequence, a 0.035-inch catheter coated with superparamagnetic iron oxide was inserted during MR monitoring. Insertion was followed by tract dilatation and insertion of a 4-French sheath. The final position of the sheath was confirmed by injection of diluted superparamagnetic iron oxide into the collecting system. RESULTS: Needle insertion was successful for all six procedures, with no complications. Instrumentation time ranged from 4 to 13 min (mean, 6+/-4 min). Sheath placement was successful in five of six kidneys. Placement time ranged from 6 to 28 min (mean, 16+/-9 min). CONCLUSION: MR-guided percutaneous nephrostomy of the nondilated contrast-enhanced upper urinary tract in a porcine model is feasible and safe.