Considering the fundamental difficulties to define the term 'depth of anaesthesia', a more feasible concept for assessment of 'adequacy of anaesthesia' will be explained. The basic requirements for a monitoring index are definite response, gradual scaling and independence from the anaesthetic technique used. Additionally the index should be predictive for appearance of clinical signs of an inadequate anaesthesia. Different signal-processing methods will be discussed to extract the relevant information from both the spontaneous and the evoked brain electrical activity. In this context well established methods like spectral analysis are investigated in combination with new and more sophisticated methods like bispectral analysis or wavelet decomposition. Since no single-parameter index has been defined for monitoring depth of anaesthesia, a set of EEG parameters may be more useful to take into account intra- and interindividual variability. In parallel to the description of the monitor concept, the investigation of neural nets and fuzzy techniques, in addition to or in substitution of conventional statistical methods, will be introduced. Examples are given for data quality assessment, parameter extraction and re-classification.
W. Nahm, and H. Gehring. Non-invasive in vivo measurement of blood spectrum by time-resolved near-infrared spectroscopy. In Sensors and Actuators B: Chemical, vol. 29(1) , pp. 174-179, 1995
Investigation of rapid near-infrared (NIR) spectroscopy in combination with the fibre optics for biomedical sensing is presented. Modern diode-array technology enables sensitive measurement of changes in tissue absorbance caused by blood pulsation. In order to describe the dynamics of this system a multi-layer model based on pulse wave theory is used. The evaluation of the pulsatile part of tissue absorbance at different wavelengths allows the construction of both pulsatile and static tissue spectra. The absorption monitoring of an injected bolus of indocyanine green is presented of non-invasive measurement of an arterial blood spectrum.
W. Nahm, and G. Gauglitz. Dünne Polymerfilme als Sensoren für Kohlenwasserstoffe.. In GIT Fachz Lab, vol. 7, pp. 889-893, 1990
BACKGROUND: Previous studies suggest that auditory evoked potentials (AEP) may be used to monitor anaesthetic depth. However, during surgery and anaesthesia, the quality of AEP recordings may be reduced by artefacts. This can affect the interpretation of the data and complicate the use of the method. We assessed differences in expert ratings of the signal quality of perioperatively recorded AEPs. METHODS: Signal quality of 180 randomly selected AEP, recorded perioperatively during a European multicentre study, was rated independently by five experts as 'invalid' (0), 'poor' (1), or 'good' (2). Average (n=5) quality rating was calculated for each signal. Differences between quality ratings of the five experts were calculated for each AEP: inter-rater variability (IRV) was calculated as the difference between the worst and best classification of a signal. RESULTS: Average signal quality of 57% of the AEPs was rated as 'invalid', 39% as 'poor', and only 4% as 'good'. IRV was 0 in only 6%, 1 in 62%, and 2 in 32% of the AEP, that is in 32% one expert said signal quality was good, whereas a different expert thought the identical signal was invalid. CONCLUSIONS: There is poor agreement between experts regarding the signal quality of perioperatively recorded AEPs and, as a consequence, results obtained by one expert may not easily be reproduced by a different expert. This limits the use of visual AEP analysis to indicate anaesthetic depth and may affect the comparability of AEP studies, where waveforms were analysed by different experts. An objective automated method for AEP analysis could solve this problem.
BACKGROUND: Middle latency auditory evoked responses (MLAER) as a measure of depth of sedation are critically dependent on data quality and the analysis technique used. Manual peak labeling is subject to observer bias. This study investigated whether a user-independent index based on wavelet transform can be derived to discriminate between awake and unresponsive states during propofol sedation. METHODS: After obtaining ethics committee approval and written informed consent, 13 volunteers and 40 patients were studied. In all subjects, propofol was titrated to loss of response to verbal command. The volunteers were allowed to recover, then propofol was titrated again to the same end point, and subjects were finally allowed to recover. From three MLAER waveforms at each stage, latencies and amplitudes of peaks Pa and Nb were measured manually. In addition, wavelet transform for analysis of MLAER was applied. Wavelet transform gives both frequency and time information by calculation of coefficients related to different frequency contents of the signal. Three coefficients of the so-called wavelet detail level 4 were transformed into a single index (Db3d4) using logistic regression analysis, which was also used for calculation of indices for Pa, Nb, and Pa/Nb latencies. Prediction probabilities for discrimination between awake and unresponsive states were calculated for all MLAER indices. RESULTS: During propofol infusion, subjects were unresponsive, and MLAER components were significantly depressed when compared with the awake states (P < 0.001). The wavelet index Db3d4 was positive for awake and negative for unresponsive subjects with a prediction probability of 0.92. CONCLUSION: These data show that automated wavelet analysis may be used to differentiate between awake and unresponsive states. The threshold value for the wavelet index allows easy recognition of awake versus unresponsive subjects. In addition, it is independent of subjective peak identification and offers the advantage of easy implementation into monitoring devices.
OBJECTIVE: To develop and test a method for standardized calibration of pulse oximeters. METHODS: A novel pulse oximeter calibration technique capable of simulating the behavior of real patients is discussed. It is based on an artificial finger with a variable spectral-resolved light attenuator in conjunction with an extensive clinical database of time-resolved optical transmission spectra of patients fingers in the wavelength range 600-1000 nm. The arterial oxygen saturation of the patients at the time of recording was derived by analyzing a corresponding blood sample with a CO-oximeter. These spectra are used to compute the modulation of the light attenuator which is attached to the artificial finger. This calibration method was tested by arbitrarily playing back recorded spectra to pulse oximeters and comparing their display to the value they displayed when the spectra were recorded. RESULTS: We were able to demonstrate that the calibrator could generate physiological signals which are accepted by a pulse oximeter. We also present some experience of playing back recorded patient spectra. The mean difference between the original reading of the pulse oximeters and the display when attached to the calibrator is 1.2 saturation points (displayed oxygen saturation SpO2) with a standard deviation of 1.9 saturation points. CONCLUSIONS: The tests have shown the capabilities of a spectral light modulator for use as a possible calibration standard for pulse oximeters. If some improvements of the current prototype can be achieved we conclude from the experience with the device that this novel concept for the calibration of pulse oximeters is feasible and that it could become an important tool for assessing the performance of pulse oximeters.
UNLABELLED: The electroencephalogram (EEG) and middle latency auditory evoked responses (MLAER) have been proposed for assessment of the depth of anesthesia. However, a reliable monitor of the adequacy of anesthesia has not yet been defined. In a multicenter study, we tested whether changes in the EEG and MLAER after a tetanic stimulus applied to the wrist could be used to predict subsequent movement in response to skin incision in patients anesthetized with 1 minimum alveolar anesthetic concentration (MAC) isoflurane in N2O. We also investigated whether the absolute values of any of these variables before skin incision was able to predict subsequent movement. After the induction of anesthesia with propofol and facilitation of tracheal intubation with succinylcholine, 82 patients received 1 MAC isoflurane (0.6%) in N2O 50% without an opioid or muscle relaxant. Spontaneous EEG and MLAER to auditory click-stimulation were recorded from a single frontoparietal electrode pair. MLAER were severely depressed at 1 MAC isoflurane. At least 20 min before skin incision, a 5-s tetanic stimulus was applied at the wrist, and the changes in EEG and MLAER were recorded. EEG and MLAER values were evaluated before and after skin incision for patients who did not move in response to tetanic stimulation. Twenty patients (24%) moved after tetanic stimulation. The changes in the EEG or MLAER variables were unable to predict which patients would move in response to skin incision. Preincision values were not different between patients who did and did not move in response to skin incision for any of the variables. MLAER amplitude increased after skin incision. We conclude that it is unlikely that linear EEG measures or MLAER variables can be of practical use in titrating isoflurane anesthesia to prevent movement in response to noxious stimulation. IMPLICATIONS: Reliable estimation of anesthetic adequacy remains a challenge. Changes in spontaneous or auditory evoked brain activity after a brief electrical stimulus at the wrist could not be used to predict whether anesthetized patients would subsequently move at the time of surgical incision.
BACKGROUND: The absorption of irrigation fluid during transurethral resection of the prostate (TURP) is determined primarily by hydrostatic pressure in the bladder and prostatic venous pressure. In comparison to spontaneously breathing patients, patients undergoing mechanical ventilation with positive pressure have a raised central venous pressure and a reduced venous return, both of which can influence intravascular absorption. The purpose of the prospective study was to compare the effects of general (GA) and spinal anaesthetic (SA) techniques on the perioperative absorption of irrigating fluid in patients undergoing TURP. METHODS: Forty patients undergoing TURP were randomised and assigned either to group GA or SA. Irrigating fluid absorption was traced by adding 1.5% (w/v) ethanol to the irrigating fluid. Perioperative blood ethanol concentration (BEC), haemoglobin concentration, haematocrit, serum sodium concentration and central venous pressure (CVP) were measured at 10-min intervals during TURP and at 30-min intervals while patients were recovering. Absorption routes were indexed by the BEC and changes in serum sodium concentrations. Where the BEC was greater than 0.05 mg.mL-1, absorption of irrigating fluid was assumed. For assessing the volume of irrigating fluid absorbed, the maximum BEC, the absorption rate, the area under the BEC curve (AUC), and the volumes calculated according to the Hahn nomogram (Volin) for each patient were taken into consideration. RESULTS: There were 15 cases of irrigating fluid absorption in patients receiving GA (75%), and 11 in those receiving SA (55%). CVP was significantly lower in spontaneously breathing patients with SA as compared to those with GA (P < 0.05). In patients with irrigating fluid absorption the maximum BEC (P < 0.02), as well as the rate of irrigant fluid absorption (P < 0.01), were significantly higher amongst patients receiving SA. In this group, the calculated area under the curve and the absorbed fluid volumes determined with the nomogram were significantly increased (P < 0.05). CONCLUSION: The absorption of irrigation fluid during the TURP is significantly more marked amongst spontaneously breathing patients with regional anaesthesia in comparison to patients undergoing general anaesthesia with positive pressure ventilation. The markedly lower central venous pressure before the start of irrigation should be considered as a possible cause of this effect.
BACKGROUND: The most common complication during percutaneous nephrolithotripsy (PNL) is the destruction of organ structures with extravasation of the irrigation fluid into the retroperitoneal space. Consequently, there is an increased risk of a urosepsis and a complicated therapeutic course. In this study we aimed to show that extravascular absorption could be differentiated from intravascular absorption due to their unique absorption characteristics, and that these characteristics enable a prediction of possible post-operative complications. METHODS: In a prospective study of 31 patients with PNL, ethanol was added to the irrigating fluid and blood ethanol concentration (BEC) was measured by gas chromatography during the endoscopic procedure and in the recovery room. Following the guidelines of Hahn, patients were divided into two groups: group EVA, in whom extravasation had occurred with subsequent absorption; group IVA, those with intravascular absorption. Patients' post-operative progress along with diagnoses of renal perforations or bleeding, or signs of infection or sepsis, were comprehensively listed. RESULTS: EVA was diagnosed in 19 cases, and IVA in 12 cases. Maximum BEC levels were achieved after 20 min (median) in the IVA group, and 75 min in the EVA group (P < 0.05). Apart from their significantly higher demand for opioids (P < 0.05), EVA patients had been hospitalised for a substantially and significantly longer period of time (P < 0.01). Although without statistical significance, there was a higher rate of peri-operatively confirmed complications and prolonged intensive therapeutic treatment in the extravasation group. CONCLUSION: Retroperitoneal extravasation can be identified by using ethanol monitoring during and after PNL. Afflicted patients require considerably longer hospitalisation, probably because of the additional injury to surrounding organ structures.
R. T. Frankenberger, O. Bussmann, W. Nahm, E. Konecny, and L. Gortner. Messung seitlicher Haupttemperaturprofile von Frühgeborenen in Inkubatoren mittels Thermograhpie - Measuring lateral skin temperature profile of premature infants in incubators with thermography. In Biomedizinische Technik. Biomedical Engineering, vol. 43(6) , pp. 174-178, 1998
Thermography enables the measurement of patients skin temperature profiles without stress caused by direct contact of probes to the skin. In previous incubator studies, frontal recordings were made through a hole in the top wall of the incubator hood. Using this method it is not possible to record the lateral temperature gradient from the back to the abdomen of the infant (in supine position), which is due to very limited heat loss near the incubator mattress. In this study temperature recordings were made from a lateral position. For this purpose a new front door of the incubator (Draeger 8000) was designed, which replaced the standard front door during measurements. In a clinical study thermography was compared to temperature measurements by standard thermistors. The mean difference between thermography and thermistors was 0.16 degree C. These results verify the use of thermography for measuring skin temperature of preterm infants in incubators.
A prerequisite for the further improvement in the quality of warming therapy is an accurate knowledge of the interactions between the microclimate in warming therapy devices and the thermal balance of the infant. For generating this knowledge, thermal manikins can be helpful. Suitable models capable of also simulating evaporative heat loss in preterm infants have, however, not been available to date. A thermal manikin representing an infant weighing 530 g and capable of simulating convective, radiative and also evaporative heat loss has now been developed. It comprises an outer shell made of porous, anatomically shaped clay, and is divided into six compartments each of which can be heated individually. Water-filled Gore-Tex bags located immediately beneath the shell are provided to simulate evaporation. In a clinical study, temperature profiles of 8 very small preterm infants were measured thermographically. Measurements in the manikin showed that highly comparable temperature profiles with only minor differences could be obtained. Total heat and water losses by the manikin were in good agreement with clinical values. Using the model described here it is possible to simulate the heat exchange of premature infants under extreme and accurately reproducible environmental conditions. This manikin may thus serve as a tool for comparative studies, for the development of warming therapy equipment, or for training purposes.
The present paper examined the question as to the extent to which the taking of gas samples for the purpose of measuring the breath alcohol concentration (BAC) in the expired air of patients on artificial respiration is influenced by temperature and humidity. For this purpose a lung model standardized at different alcohol concentrations was used, in which the temperature (T: 25, 30 and 35 degrees C) and the relative humidity (RH: 50, 75 and 95%) were varied.
PURPOSE: There is controversy about relevant EEG signal changes indicating adequate or inadequate anaesthesia. Differences of drug-induced and nociceptive mediated signal changes have not been studied in detail. The present study investigates whether signal changes during decreases of depth of anaesthesia due to surgical stimulation depend on different isoflurane concentrations during sufentanil anaesthesia. METHODS: Following IRB approval and written informed consent 28 patients (ASA: I; age 43 +/- 11 y) scheduled for elective abdominal surgery were included in the study. Anaesthesia: propofol (2.0 mg/kg) and sufentanil (1.0 micrograms/kg). Following endotracheal intubation (vecuronium 0.1 mg/kg) patients were normoventilated (P(ET)CO2: 36-38 mmHg). Randomly assigned to steady-state anaesthesia (group 1: P(ET)Isoflurane 0.2%, (14n); group 2: P(ET)Isoflurane 0.6%, (14n) during the start of surgery. Monitoring: heart rate (HF), mean arterial blood pressure (MAP), P(ET)CO2, arterial oxygen saturation and rectal temperature. EEG (16 channels referenced to Cz; CATEEM, Medisyst, Linden) recorded 5 min before until 10 min after the start of surgery. EEG-analysis (FFT: 4s, 256/s, 0.45-35.0 Hz): topographical distribution of power spectral densities (delta, theta, alpha 1, and alpha 2). Artifact control: ECG and EOG. RESULTS: Surgical stimulation resulted in increases of MAP in both groups (p < 0.05 vs BL), whereas HR was only slightly affected in group 2 when compared with BL. Other variables except of EEG data did not change over time. In group 1 (0.2% isoflurane) surgical stimulation resulted in decreases of delta over the whole cortex (F2, C3, P3, O1) and in marked increases of alpha predominantly at central leads (C3)(p < 0.05 vs BL). In group 2 (0.6% isoflurane) nociceptive stimulation was associated with decreases of faster waves (alpha: F3)(p < 0.05 vs BL) and increases in delta at fronto-central areas (F3, C3)(p < 0.05 vs BL). CONCLUSIONS: EEG recordings are useful in assessing pharmacodynamic drug effects. In contrast, intraoperative EEG recordings have a low correlation to clinical signs of changes in the anaesthetic state. Previous studies demonstrate paradoxical EEG-arousal reactions during isoflurane anaesthesia. The present data suggest that classical or even paradoxical EEG arousal due to nociceptive stimulation may depend on the isoflurane concentration. It seems reasonable that the ascending reticular formation is functionally blocked by isoflurane in a dose-dependent manner.
UNLABELLED: When looking for the possible cause of distortions in values measured for the determination of breath ethanol concentration (BEC) in artificially respirated patients, consideration must be given to the humidity and temperature of the gas examined. In the present study, the effects of humidified and warmed and of dry and cold air on the accuracy of a newly developed BEC measuring device, as compared to a reference model and to a conventional system, were examined in a lung model. METHODS: A temperature-regulated pediatric incubator was used containing a 10 I gas reservoir and a breath humidifier with temperature regulated water bath. This setup provided constant temperature and humidity in the gas examined during measurement period. In the 'expiration' the air was directed from the breath humidifier through a measuring unit via a 'mouthpiece' into the reference system (Alcotest 7110, Dräger Inc., Lübeck) and then out. The measuring unit consisted of sensors for the temperature and relative humidity, and of a connector for the three sample extraction systems (PES). PES I was the conventional system with a 100-cm gas-sample pipe (Alcomed 3010), PES II the newly developed system (AlcoMed 3011, both from Envitec, Wismar) with a 10-cm gas-sample pipe, and PES III with a 20-cm heated gas-sample pipe. During 'inspiration' 2 l of air was fed into the system to rinse the measuring unit and to fill the reservoir. 61 measurements were performed with dry and cold air, and 71 with humidified and warmed air, in the course of which the ethanol concentration was increased from 0 to 1.5/1000. Data were evaluated using regression analysis and the Bland & Altman method. RESULTS AND CONCLUSIONS: The constancy of the values set for temperature, relative humidity and absolute humidity in the lung model was given for all measurements. In the dry and cold air, the results from all three test systems coincided almost perfectly with the reference values. The measured BEC in the humidified and warmed air using sample-extraction systems II and III corresponded to a high degree with the reference, while in the case of PES I, only a moderate linear correlation was achieved. The temperature and humidity of the expired gas during artificial respiration influence the gas samples extracted for the purposes of BEC measurement. Newly developed sample-extraction systems II and III coincide with the reference system, even under respiration-simulated gas conditions.
H. Gehring, W. Nahm, J. Baerwald, E. Konecny, and P. Schmucker. Atem-Alkoholmeßgeräte mit elektrochemischem Sensor - Meßgenauigkeit bei Beatmung am Lungenmodell - Breath alcohol analyzers with electrochemical sensory--accuracy of measurements in lung model ventilation. In Biomedizinische Technik. Biomedical Engineering, vol. 41(3) , pp. 54-9, 1996
Absorption of irrigating fluid by blood vessels during endoscopic urological surgery may result in cardiac insufficiency, impairment of electrolyte metabolism and neurological disorders. For detection and quantification of the volume absorbed, ethanol is added to the irrigating fluid. The resulting blood alcohol concentration can be obtained by measuring the alcohol concentration in the expired air. For artificially ventilated patients receiving a general anesthetic, electrochemical sensors that remain uneffected by volatile anaesthetics are used. In the present study, the measuring accuracy of three different alcohol analyzers using electrochemical sensors was tested against an infrared reference sensor during simulated ventilation in a lung model, and the optimal trigger time point for sampling determined. All three devices tested show the same degree of accuracy as the reference. For manual endexpiratory triggering devices with short sampling times are best suitable. Portable devices powered by rechargeable batteries and usable with both spontaneously breathing and ventilated patients are recommended for clinical application.
H. Gehring, W. Nahm, K. F. Klotz, A. Knipper, K. Zimmermann, J. Baerwald, and P. Schmucker. Messung der Atem-Alkoholkonzentration mit einem neuen elektronischen Sensor. Modelluntersuchung zur Querempfindlichkeit gegenüber volatile Anästhetika und klinische Anwendung - Measurement of expired alcohol concentrations with a new electrochemical sensor. A model investigation to determine interference with volatile anesthetics and clinical application. In Der Anaesthesist, vol. 45(2) , pp. 154-62, 1996
UNLABELLED: Absorption of irrigating fluid in transurethral prostatic resection (TURP) and percutaneous nephrolitholapaxy (PNL) into veins or delayed absorption due to fluid extravasation may result in a TURP syndrome. The measurement of end-tidal breath alcohol concentration (et AC) as a monitor of absorption of irrigating fluid labelled with 2% ethanol is limited by the disturbance of infrared sensors by volatile anaesthetics and nitrous oxide (N2O) (Fig. 2). An electrochemical sensor is acceptable for this method. The aim of the present study was the evaluation of breath alcohol measurements using an electrochemical sensor device (Alcomed 3010, Envitec). The stability of the sensor in the presence of volatile anaesthetics was examined using a lung model. In a clinical investigation, the device was then applied to spontaneously breathing or mechanically ventilated patients inhaling volatile anaesthetics during endoscopic urological surgery. METHOD: A two-chamber lung model filled with water for performing noninvasive measurements at the mouth of a patient has already been introduced by Brunner et al. (Fig. 1). With the addition of different amounts of ethanol to the temperature-controlled water, a constant ethanol concentration is achievable in the air above the water that is dependent on adjustments of the ventilator. Increasing concentrations of volatile anaesthetics (isoflurane, enflurane, halothane, and sevoflurane) were added to the fresh gas flow (2 l O2/3 l N2O) and etACs were measured using the manually triggered self-absorbent electrochemical sensor. First, regression equations were established between breath alcohol concentrations and increased volatile anaesthetic concentrations. Regression equations were then established between end-tidal anaesthetic gas concentrations and vaporizer adjustments in order to rule out an influence of ethanol on the anaesthetic gas monitor Ultima V (Datex). In the clinical investigation, 53 intubated and ventilated patients (33 undergoing PNL, 20 undergoing TURP) and 48 patients breathing spontaneously (32 with inhalation anaesthesia, 16 with spinal anaesthesia) were investigated. The etAC was measured with the Alcomed 3010 and compared with gas-chromatographically registered blood alcohol concentrations (BAC). The study had previously been approved by the Ethical Committee of the Medical University of Luebeck. Patients with liver disease and a history of toxic abuse were excluded. Only one value per patient (maximum BAC) was included in the statistics in order to avoid a cluster effect. RESULTS: The lung model experiments demonstrated that the measurement of etAC with an electrochemical sensor is free of interference by volatile anaesthetics (Table 1). The slope of the regression between the measured alcohol concentration and increased concentrations of anaesthetics did not differ significantly from baseline values. The measurement of end-tidal anaesthetic concentrations was not significantly different from vaporizer adjustments in the presence of increased alcohol concentrations (Table 2). During the clinical investigation, a regression between etAC and BAC was determined for both groups. For the group of patients breathing spontaneously, the correlation coefficient was 0.961 and the regression equation revealed etAC = 0.5677*BAC-0.1303 (Fig. 5). However, in the group of ventilated patients a biphasic course was shown that was dependent on BAC (Fig. 6). At BAC < 0.4%, a similar correlation (r = 0.856) to the spontaneously breathing group could be seen (regression equation: etAC = 0.617*BAC-0.020). Above 0.4% BAC there was no acceptable correlation (r = 0.444, regression equation: etAC = 0.202*BAC+0.104). CONCLUSIONS: The tested electrochemical sensor does not interfere with volatile anaesthetics and N2O as demonstrated by a lung model. There is a good correlation between etAC and BAC measurements in patients breathing spontaneously with special regard to the slope of the regression (s = 0.57).
One way of determining pulmonary CO2 elimination during anaesthesia is the breath-by-breath method. With this technique, CO2 analysis is carried out using either the mainstream method (MSM), that is, directly in the expired air flow, or in samples of expired air. A disadvantage of MSM is the lack of sensor signal correction for changes in the composition of the gas mixture and barometric pressure. Sidestream Systems (SSM) measure respiratory gas flow and gas con- centration with adequate accuracy, and also correct the measured values for gas composition and ambient parameters. Disadvantages of breath-by-breath analysis are the SSM-system-rela- ted delay and distortion of the CO2 curves. In the present study, a computer-assisted comparati- ve analysis of CO, elimination measurement by the sidestream and mainstream methods was carried out using ctiff erent mixtures of gases in a lung model. Under the selected conditions simulated in the lung model, evaluation of CO2 elimination using SSM and MSM is possible with an error of between 0 and 10 % versus reference Systems.Measu- ring accuracy of the MSM System in particular is found to depend directly on the composition of the gas mixture. Using the method described here, the measuring error of an SSM System in terms of delay and response time can be compensated with adequate accuracy.
H. Gehring, W. Nahm, K. F. Klotz, O. Zais, R. Schreiber, and P. Schüren. Plasmavolumenbestimmung mit dem Farbstoff ICG bei Änderung des intravasalen Volumens - Plasma volume determination with ICG dye in changes of intravascular volume. In Infusionstherapie und Transfusionsmedizin, vol. 23, pp. 86-91, 1996
Ziel: Die Messung des aktuellen intravasalen Volumens mit Hilfe der Indikator-Verdünnungsmethode ist sowohl von klini-schem als auch von wissenschaftlichem Interesse. Bei der Ver-wendung des rasch eliminierten Farbstoffes Indocyanin-Grün (ICG) sind wiederholte Messungen und damit Verlaufskontrollen möglich. In der vorliegenden Studie sollten folgende Fragen geprüft werden: 1. Stimmen die von uns mit der ICG-Methode bei gesunden Probanden bestimmten Werte mit den in der Literatur angegebenen Kontrollwerten überein, und ist somit die Grundlage für die Durchführung weiterer klinischer Studien gegeben, und 2. Stimmen die Differenzen der vor und nach Eigenblutentnahme bzw. Retransfusion bestimmten Werte für das Plasmavolumen mit den tatsächlich entnommenen bzw. retransfundierten Volumina überein? Design: Prospektive Studie (an je 20 gesunden weiblichen bzw. männlichen Probanden). Rahmen: Forschungslabor einer anästhesiologischen Universitätsklinik. Teilnehmer: Je 20 gesunde weibliche bzw. männliche Probanden. Interventionen: Plasmavolumenbestimmung mit ICG vor und nach Entnahme von 10% des ge-schätzten Blutvolumens und nach Retransfusion. Ergebnisse: In der Gruppe der Frauen betrug das Plasmavolumen pro Körperoberfläche (PV/KO) 1639 ± 198 und bei den Männern 1687 ± 224 ml/m2 (Mittelwert ± SD). Durch die Eigenblutspende wurde den Frauen 188 ± 23 und den Männern 149 ± 26 ml/m2 PV entzogen. Die PV-Messung mit ICG ergab für diesen Ent-zug einen Wert von 198 ± 174 bzw. 171 ± 158 ml/m2 und für die Retransfusion 190 ± 169 bzw. 142 ± 154 ml/m2. Schluβfolgerungen: Die Kontrollwerte liegen in dem in der Literatur be-schriebenen Normbereich. Die gemessenen Differenzen der Plasmavolumina vor und nach Eigenblutspende bzw. nach Retransfusion stimmen mit den tatsächlich entnommenen Plasmavolumina im Mittel gut überein. Bei der klinischen Beurteilung im Einzelfall ist die methodisch bedingte hohe Standardabweichung zu berücksichtigen.
Oligomers with a dimethylsiloxane backbone coated as thin films on different substrate surfaces were thermally as well as photochemically cross-linked. The structure and the degree of cross-linking were examined spectroscopically. Diffusion of different gases in the thin polymer films was measured by time resolved infrared ATR-spectroscopy. The process of diffusion is almost immediately followed by a swelling of the polymer proportional to gas concentration. Therefore diffusion may also be measured by spectral interferometry, giving a very sensitive device for optical sensing of hydrocarbons. Furthermore, diffusion in polymers may be measured very accurately by spatially resolved UV/Vis-spectroscopy. Diffusion coefficients may also be determined indirectly from the equilibrium of monomers and excimers indicated by the fluorescence intensities. This method allows the in situ observation of the cross-linking process.
G. Gauglitz, A. Brecht, G. Kraus, and W. Nahm. Chemical and biochemical sensors based on interferometry at thin (multi-) layers. In Sensors and Actuators B: Chemical, vol. 11(1) , pp. 21-27, 1993
Spectral interferometry is presented as a tool to monitor the swelling of polymers caused by organic gases or hydrocarbons in waste water as well as the adsorption and interaction of antigens and antibodies in immunoreactions. Modern diode-array technology allows the consequent observation of changes in optical pathlength on a fractional nanometer scale with subsecond repetition times. The theory of multiple-reflection principles in white-light interferometry determines the possibilities and limitations of this method. The optical set-up and some applications in gas sensing and label-free immunosensing are discussed with respect to the sensitivity, selectivity and limits of detection at present.
The principle of interferometry has been applied to thin polymer films as they swell by sorption of gases or as they interact with biochemical material. Modern diode array technology allows the monitoring of changes in optical path-length at a fractional nanometre scale. Observation of the interference spectra makes discrimination between thickness and Fresnel refractive index effects possible. Thus, very sensitive sensors can be developed for measuring concentrations of gaseous and liquid organic solvents as well as specific antigen-antibody interactions.
G. Gauglitz, and W. Nahm. Observation of spectral interferences for the determination of volume and surface effects of thin films. In Fresenius Journal of Analytical Chemistry, vol. 341(3-4) , pp. 279 283, 1991
The application of a rapid scanning diode array spectrometer allows the time-resolved observation of the interferences caused by multiple reflections at the interfaces of thin films. This spectral interferometry enables the observation of changes in optical pathlengths and allows to separate volume-effects like polymer swelling from surface-effects like adsorption or deposition. Polymer/solvent interactions will give an example for an application of this method.
G. Gauglitz, and W. Nahm. Rapid optical sensors for the detection of organic solvent vapors. In Proc ACHEMA, pp. 3-4, 1991
Der Effekt von Temperatur und Luftfeuchtigkeit auf die Gasprobenentnahme zur Messung der Atem-Alkoholkonzentration (AAK) wurde zwischen 0 und 1,5‰ in einem Lungenmodell bei Messungen sowohl in trockener und kühler als auch in feuchter und angewärmter Luft untersucht. Methodik: Neben dem herkömmlichen Probenentnahmesystem (PES) mit einem 100 cm langen Schlauch (Alcomed 3010®, PES I) wurde ein weiterentwickeltes Gerät mit verbessertem Gasprobentransport (AlcoMed 3011®, beide Fa. Envitec, Wismar) und 10 cm kurzem (PES II) sowie 20 cm kurzem und auf 36°C beheiztem Gasprobenschlauch (PES III) gegenüber einem Referenzsystem mit Infrarot-Sensor (Alcotest 7110®, Fa. Dräger, Lübeck) eingesetzt. Ergebnisse: In der trockenen und kühlen Luft entsprachen die Meßergebnisse aller 3 Testsysteme fast idealerweise den Referenzwerten. Bei den Messungen in feuchter und angewärmter Luft bestand diese Übereinstimmung für das PES II und III, während das PES I keinen linearen Zusammenhang mit den Referenzwerten zeigte. Schlußfolgerung: Die Temperatur und die Luftfeuchtigkeit hat einen erheblichen Einfluß auf die AAK-Messung bei beatmeten Patienten und ist bei der Probenentnahme zu berücksichtigen.
E. Konecny, and W. Nahm. Physikalische Messtechniken in der Medizin. Zentrum für Fernstudien & universitäre Weiterbildung, UNI Kaiserslautern, 1996.
Book Chapters (3)
J. Petersen, G. Stockmanns, and W. Nahm. EEG Analysis for Assessment of Depth of Anaesthesia. In Fuzzy Systems in Medicine, P. Szczepaniak, P. Lisboa, J. Kacprzyk (eds), Physica-Verlag, Heidelberg, pp. , 2000
Up to now one unsolved challenge in anaesthesia is the assessment of depth of anaesthesia during surgery. No general purpose on-line monitoring system predicting depth or quality of anaesthesia exists. The analysis of spontaneous (EEG) and evoked electrical brain activities (AEP) leads to methods assessing depth of anaesthesia. A monitor concept was developed consisting of the three functional components EEG recorder, pre-processor and knowledge based discriminator including an inductive learning algorithm generating fuzzy decision trees. By their statistical evaluation feature vectors for training Kohonen networks are selected aplied for re-classification tests of clinical study data.
J. Abke, W. Nahm, and E. Konecny. Implementierung einer Bispektralanalyse in LabVIEW zur Beurteilung von Narkosetiefe über das EEG. In Virtuelle Instrumente in der Praxis - Meßtechnik, R. Jamal, H. Jaschinski (eds), VDE-Verlag, pp. 256-264, 1998
M. Daumer, W. Nahm, M. Scholz, and F. Danneger. Online Monitoring mit virtuellen Instrumenten. In Virtuelle Instrumente in der Praxis - Meßtechnik, R. Jamal, H. Jaschinski (eds), VDE-Verlag, pp. 265-270, 1998
W. Nahm, G. Stockmanns, M. Daumer, J. Abke, and E. Konecny. Automatische EEG-Datenvorverarbeitung in einer Multicenterstudie - Automatic EEG data processing in a multicenter study. In Biomedizinische Technik/Biomedical Engineering, vol. 43(s1) , pp. 146-147, 1998
W. Nahm, H. Gehring, and C. W. Du. Nichtinvasive Messung der Konzentration von Indocyanin-Grün im arteriellen Blut durch spektrale Photoplethysmonographie. In Biomedizinische Technik / Biomedical Engineering, vol. 39(s1) , pp. 66-67, 1994
W. Nahm, H. Gehring, E. Konecny, and P. Schmucker. Messung der Atemalkoholkonzentration zur Beurteilung des Einschwemmsyndroms bei urologischen Eingriffen unter Vollnarkose.. In Biomedizinische Technik / Biomedical Engineering, vol. 38(s1) , pp. 423-424, 1993
W. Nahm, and G. Gauglitz. Optische Sensoren für Kohlenwasserstoffe in Wasser und Luft. In Proc. Sensor '91, vol. 3, pp. 7-18, 1991
K. Sieler, A. Naber, and W. Nahm. An Evaluation of Image Feature Detectors Based on Spatial Density and Temporal Robustness in Microsurgical Image Processing. In Current Directions in Biomedical Engineering, vol. 5(1) , pp. 273-276, 2019
Optical image processing is part of many applications used for brain surgeries. Microscope camera, or patient movement, like brain-movement through the pulse or a change in the liquor, can cause the image processing to fail. One option to compensate movement is feature detection and spatial allocation. This allocation is based on image features. The frame wise matched features are used to calculate the transformation matrix. The goal of this project was to evaluate different feature detectors based on spatial density and temporal robustness to reveal the most appropriate feature. The feature detectors included corner-, and blob-detectors and were applied on nine videos. These videos were taken during brain surgery with surgical microscopes and include the RGB channels. The evaluation showed that each detector detected up to 10 features for nine frames. The feature detector KAZE resulted in being the best feature detector in both density and robustness.
A. Naber, D. Berwanger, and W. Nahm. In Silico Modelling of Blood Vessel Segmentations for Estimation of Discretization Error in Spatial Measurement and its Impact on Quantitative Fluorescence Angiography. In 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), pp. 4787-4790, 2019
Today the vascular function after interventions as Bypass surgeries are checked qualitatively by observing the blood dynamics inside the vessel via Indocyanine Green (ICG) Fluorescence Angiography. This state-of-the-art should be upgraded and has to be improved and converted towards a quantitatively measured blood flow. Previous approaches show that the blood flow measured from fluorescence angiography cannot be easily calibrated to a gold standard reference. In order to systematically address the possible source of error we investigate as a first step the discretization error in a camera-based measurement of the vessel’s geometry. In order to generate an error-free ground truth, a vessel model has been developed based on mathematical functions. This database is then used to determine the error in discretizing the centerline of the structure and estimate its effects on the accuracy of the flow calculation. As result the model is implemented according to the conditions which are set up to ensure transferability on camera-based segmentations of vessels. In this paper the relative discretization error for estimating the centerline length of segmented vessels could be calculated in the range of 6.3%. This would reveal significant error propagated to the estimation of the blood flow value derived by camera-based angiography.
A. Wachter, A. Mohra, and W. Nahm. Development of a real-time virtual reality environment for visualization of fully digital microscope datasets. In Proceedings of SPIE, vol. 10868, pp. 108681F1-9, 2019
Current surgical microscope systems have excellent optical properties but still involve some limitations. A future fully digital surgical microscope may overcome some major limitations of typical optomechanical systems, like ergonomic restrictions or limited number of observers. Furthermore, it can leverage and provide the full potential of digital reality. To achieve this, the frontend, the reconstruction of the digital twin of the surgical scenery, as well as the backend, the 3-D visualization interface for the surgeon, need to work in real-time. To investigate the visualization chain, we developed a virtual reality environment allowing pretesting this new form of 3-D data presentation. In this study, we wanted to answer the following question: How must the visualization pipeline look like to achieve a real-time update of the 3-D digital reality scenery. With our current approach, we were able to obtain visualizations with a frame rate of 120 frames per second and a 3-D data update rate of approximately 90 datasets per second. In a further step, a first prototype of a real-time mixed-reality head mounted visualization system could be manufactured based on the knowledge gained during the virtual reality pretesting.
A. Naber, and W. Nahm. Bi - Domain Intraoperative Registration of Vessels. In Current Directions in Biomedical Engineering, vol. 4(1) , pp. 25-28, 2018
The segmentation and registration of structures are gaining importance due to the increasing demand of auto- mated image enhancement and understanding. Especially in medicine and life science, assistance systems could have a large impact on diagnosis, treatment and quality control. Dye driven procedures, such as uorescence imaging with Indocya- nine green (ICG), are nowadays indispensable because they enhance contrast, reveal structures and deliver the operator with important information. The contact free ICG angiography is providing the surgeon spatial and temporal information on blood ow w ithin a v essel. T he p rocessing o f t hose informa- tion is done manually or semi automated but is very helpful for the surgeon. Extending the degree of automatism, the amount of information processed and even augment or transfer it into another domain could deliver the operator useful support and improve surgical work ow. Using, analyzing and transferring those information from ICG-IR domain into the RGB domain is the focus of this project. We are introducing a vessel regis- tration method in the RGB domain driven by the spatial u- orescence behavior of the vessel in the ICG-IR domain. The method includes Superpixel based segmentation of the vessel in the ICG-IR domain, the spatial gradient based transfer and registration in the RGB domain and the continuous segmen- tation of the vessel in a RGB video. This paper show a proof of concept of the method. The results show an successful in- ter domain information transfer and registration of the vessel. Further tracking of the vessel over all frames is possible. Nev- ertheless limitations are revealed and discussed.
A. Wachter, J. Kost, and W. Nahm. MATLAB Simulation Environment for Estimating the Minimal Number and Positions of Cameras for 3D Surface Reconstruction in a Fully-Digital Surgical Microscope. In Current Directions in Biomedical Engineering, vol. 4(1) , pp. 517-520, 2018
Contemporary surgical microscope systems have excellent optical properties but some desirable features re- main unavailable. The number of co-observers is currently re- stricted, by spatial and optical limitations, to only two. More- over, ergonomics poses are a problem: Current microscope systems impede free movement and sometimes demand that surgeons take uncomfortable postures over long periods of time. To rectify these issues, some companies developed surgi- cal microscope systems based on a streaming approach. These systems remove some of the limitations. Multi-observer po- sitions, for example, are not independent from each other, for example. In order to overcome the aforementioned limitations, we are currently developing an approach for the next genera- tion of surgical microscope: Namely the fully digital surgi- cal microscope, where the current observation system is re- placed with a camera array, allowing real-time 3D reconstruc- tion of surgical scenes and, consequently, the rendering of al- most unlimited views for multiple observers. These digital mi- croscopes could make the perspective through the microscope unnecessary allowing the surgeon to move freely and work in more comfortable postures. The requirements on the camera array in such a system have to be determined. For this purpose, we propose of estimation the minimal number of cameras and their positions needed for the 3D reconstruction of microsurgi- cal scenes. The method of estimation is based on the require- ments for the 3D reconstruction. Within the MATLAB simu- lation environment, we have developed a 3D model of a mi- crosurgical scene, used for the determination of the number of required cameras. In a next step a small, compact and cost- ef cient s ystem w ith f ew o pto-mechanical c omponents could be manufactured.
T. Wirth, A. Naber, and W. Nahm. Combination of Color and Focus Segmentation for Medical Images with Low Depth-of-Field. In Current Directions in Biomedical Engineering, vol. 4(1) , pp. 345-349, 2018
Image segmentation plays an increasingly important role in image processing. It allows for various applications including the analysis of an image for automatic image understanding and the integration of complementary data. During vascular surgeries, the blood flow in the vessels has to be checked constantly, which could be facilitated by a segmentation of the affected vessels. The segmentation of medical images is still done manually, which depends on the surgeon’s experience and is time-consuming. As a result, there is a growing need for automatic image segmentation methods. We propose an unsupervised method to detect the regions of no interest (RONI) in intraoperative images with low depth-of-field (DOF). The proposed method is divided into three steps. First, a color segmentation using a clustering algorithm is performed. In a second step, we assume that the regions of interest (ROI) are in focus whereas the RONI are unfocused. This allows us to segment the image using an edge-based focus measure. Finally, we combine the focused edges with the color RONI to determine the final segmentation result. When tested on different intraoperative images of aneurysm clipping surgeries, the algorithm is able to segment most of the RONI not belonging to the pulsating vessel of interest. Surgical instruments like the metallic clips can also be excluded. Although the image data for the validation of the proposed method is limited to one intraoperative video, a proof of concept is demonstrated.
E. Dicke, A. Wachter, and W. Nahm. Estimation of the interpolation error of a three-step rotation algorithm using recorded images with rotated test pattern as ground truth. In Current Directions in Biomedical Engineering, vol. 3(2) , pp. 555-558, 2017
Nowadays, the surgical microscope is the goldstandard for microsurgical procedures. Additional functionalities such as surgical navigation, data injection or imageoverlay are providing additional valuable information to the surgeon. For substituting the conventional optical system by a fully-digital multi-camera setup the three dimensional (3D) reconstruction of the scenery in the field of view is required. However, for in camera-based systems, an exact alignment of the cameras is a challenging task. Therefore, a final adjustment through a digital image rotation becomes necessary. Even though the digital rotation is a commonly used procedure, it leads to unavoidable errors because of the discretized grid of the image. Previous research reported in literature has demonstrated that the method of digitally rotating the images combined with the Fourier interpolation delivers the results of best quality. Nevertheless, the performance evaluation of this algorithm was carried out rotating an image in multiple threestep rotations to a total of 90 or 180 degrees and comparing it to the original image rotated in one step. This is a valid approach because a rotation of 90 or 180 degrees does not produce rotation artifacts. In this research project, we verify the performance of the three-step rotation algorithm using recorded images for which the test pattern was rotated as ground truth. A series of photographs with a rotation angle of 3 to 45 degrees was created. The advantage of this setup is that the result of the digital rotation can be directly compared to the recorded image. In addition, with the knowledge obtained about the interpolation error, we can improve pixel matching in the further triangulation used for 3D reconstruction. By doing so, the estimation of the interpolation error helps to reduce the triangulation error.
C. Marzi, A. Wachter, and W. Nahm. Design of an experimental four-camera setup for enhanced 3D surface reconstruction in microsurgery. In Current Directions in Biomedical Engineering, vol. 3(2) , pp. 539542, 2017
Future fully digital surgical visualization systems enable a wide range of new options. Caused by optomechanical limitations a main disadvantage of todays surgical microscopes is their incapability of providing arbitrary perspectives to more than two observers. In a fully digital microscopic system, multiple arbitrary views can be generated from a 3D reconstruction. Modern surgical microscopes allow replacing the eyepieces by cameras in order to record stereoscopic videos. A reconstruction from these videos can only contain the amount of detail the recording camera system gathers from the scene. Therefore, covered surfaces can result in a faulty reconstruction for deviating stereoscopic perspectives. By adding cameras recording the object from different angles, additional information of the scene is acquired, allowing to improve the reconstruction. Our approach is to use a fixed four-camera setup as a front-end system to capture enhanced 3D topography of a pseudo-surgical scene. This experimental setup would provide images for the reconstruction algorithms and generation of multiple observing stereo perspectives. The concept of the designed setup is based on the common main objective (CMO) principle of current surgical microscopes. These systems are well established and optically mature. Furthermore, the CMO principle allows a more compact design and a lowered effort in calibration than cameras with separate optics. Behind the CMO four pupils separate the four channels which are recorded by one camera each. The designed system captures an area of approximately 28mm × 28mm with four cameras. Thus, allowing to process images of 6 different stereo perspectives. In order to verify the setup, it is modelled in silico. It can be used in further studies to test algorithms for 3D reconstruction from up to four perspectives and provide information about the impact of additionally recorded perspectives on the enhancement of a reconstruction.
A. Naber, and W. Nahm. Video magnification for intraoperative assessment of vascular function. In Current Directions in Biomedical Engineering, vol. 3(2) , pp. 175-178, 2017
In neurovascular surgery the intraoperative fluorescence angiography has been proven to be a reliable contact-free optical imaging technique to visualize vascular blood-flow. This angiography is obtained by injecting a fluorescence dye e.g. indocyanine green and using an infrared camera system to visualize the fluorescence inside the vessel. Obviously this requires a medical approved dye and an additional camera setup and therefore generating risks and costs. Hence, the aim of our research is to develop a comparable technique for assessing the vascular function. This approach would not require dye nor an additional infrared camera setup. It is achieved by first preprocessing the video data of a camera that records only the visible spectrum and then filter it spatially as well as temporally. The prepared data is again processed to extract information about the vascular function and visualize it. This method would provide an option to compute and visualize the vascular function using the data recorded in the visible spectrum by the surgical microscopes. Given this contact-free optical imaging system, physiological information can be easily provided to the surgeon without an additional setup. In the case of comparable results with the state-of-the-art, this technique provides a straightforward optical intraoperative angiography. Further no drug approval is needed since no dye is injected.
Fluorescence video angiography has recently been introduced in neurosurgery. Such videos are analysed by a new software to allow quantitative characterization of the blood flow during neurovascular operations (clipping an aneurysm, treatment of an angioma). For these purposes the fluorescence dye Indocyanin Green is given intravenously. After activation by a near-infrared light source the fluorescence signal is evaluated by the software. Reference measurements by using a flow phantom were performed to verify the quantitative blood flow results of the software and to validate the software algorithms. The analysis of intraoperative videos provided characteristic biological parameters allowing their implementation in the flow phantom. Under certain conditions the experiments with the help of the flow phantom showed, the results of the software parameter identification algorithmus are within the range of parameter accuracy by the reference method.
G. Stockmanns, E. Kochs, W. Nahm, and M. Brunner. Automatic analysis of auditory evoked potentials by means of wavelet analysis. In Memory and Awareness in Anaesthesia IV, Proc. 4th International Symposium, pp. 117-131, 2000
M. Daumer, W. Nahm, M. Scholz, F. Dannegger, G. Morfill, E. Kochs, and A. Neiss. Konzept für eine Internet-basierte Datenbank zur Unterstützung von Projekten auf dem Gebiet der Biosignalanalys - Concept for an internet-based databank for supporting projects in the area of biosignal analysis. In Biomedizinische Technik. Biomedical Engineering, vol. 43 s3, pp. 23-26, 1998
M. Kelling, Z. Hussein, W. Nahm, and E. Konecny. Experimenteller Aufbau zur nicht-dispersiven Messung des Isotopenverhältnisses 13C/12C in Gasen - Experimental development of non-dispersive measurement of 13C/12C isotope relations in gases. In Biomedizinische Technik. Biomedical Engineering, vol. 43 Suppl, pp. 280-1, 1998
P. Knoop, C. Hornberger, W. Nahm, and E. Konecny. Entwicklung eines optischen Kalibrators für kommerzielle Pulsoximeter: Erste Erfolge - Development of an optical calibrator for commercial pulse oximeters: initial successes. In Biomedizinische Technik. Biomedical Engineering, vol. 43 s1, pp. 128-129, 1998
O. Bussmann, W. Nahm, and E. Konecny. Modell zur Simulation der Wärmeabgabe und Thermoregulation Frühgeborener - A Model for simulating heat transfer and thermoregulation of premature infants. In Biomedizinische Technik/Biomedical Engineering, vol. 43(s1) , pp. 300-301, 1998
H. Gehring, W. Nahm, D. Hufker, A. Schmitz, W. Mertins, and E. Konecny. Messung der Atem-Alkoholkonzentration während der Beatmung. Modelluntersuchungen zum Einfluß der Temperatur und Luftfeuchtigkeit auf die Reproduzierbarkeit der Messung verschiedener Probenentnahmesystem - Measuring breath alcohol concentration during artificial ventilation. Model studies of the effect of temperature and humidity on the reproducibility of measurements of various sampling systems].. In Biomedizinische Technik. Biomedical Engineering, vol. 42 Suppl, pp. 356-7, 1997
C. Hornberger, W. Nahm, P. Knoop, H. Gehring, P. Wouters, and E. Konecny. Nicht-invasive Erfassung von Blutspektren durch zeitaufgelöste in vivo Spektroskopie - Noninvasive detection of blood spectra by time resolved in vivo spectroscopy. In Biomedizinische Technik. Biomedical Engineering, vol. 42 s2, pp. 217-8, 1997
M. Kelling, W. Nahm, and E. Konecny. Absorptions-spektroskopische Methode zur Messung des Istopenverhältnisses 13C/12C - Absorption spectroscopy method for measuring 13C/12C isotope relations. In Biomedizinische Technik. Biomedical Engineering, vol. 42 Suppl, pp. 315-6, 1997
R. Sevcik, W. Nahm, E. Konecny, O. Petrowicz, H. Borgolte, and D. Nolte. Analyse diskontinuierlicher Lungengeräusche durch die Wavelet-Transformation und die Illustration selten auftretender kontinuierlicher Oszillationen - Analysis of discontinuous lung sounds by wavelet transformation and illustration of rare continuous oscillations. In Biomedizinische Technik. Biomedical Engineering, vol. 42 s2, pp. 297-8, 1997
G. Stockmanns, W. Nahm, J. Petersen, C. Thornton, and H. D. Kochs. Wavelet-Analyse akustisch evozierter Potentiale während wiederholter Propofol-Sedierung - Wavelet analysis of acoustically evoked potentials during repeated propofol sedation. In Biomedizinische Technik. Biomedical Engineering, vol. 42 Suppl, pp. 373-374, 1997
G. Stockmanns, J. Abke, and W. Nahm. Extraktion relevanter Parameter aus wavelet-transformierten akustisch evozierten Potentialen zur Bestimmung inadäquater Anästhesie mit Hilfe des Kohonen-Netzes. In Biomedizinische Technik / Biomedical Engineering, vol. 41(s1) , pp. 234-235, 1996
C. Du, W. Nahm, H. Gehring, and E. Konecny. Quantification of NIRS data of a blood phantom by spectral multicomponent analysis. In Proceedings of the SPIE, vol. 2626, pp. 130-140, 1995
In order to quantify the chromophore components from in vivo blood NIRS, a blood- equivalent phantom has been developed which consists of properly diluted intralipid and ICG dye. The reflection and transmission near infrared spectroscopy (NIRS) of the phantoms with different scattering backgrounds and ICG concentrations are measured and analyzed by the spectral multicomponent analysis (MCA) method to extract ICG concentration. The experimental results show that the MCA method can be used to quantify absolute ICG concentrations in scattering media if the average path lengths are known. Moreover, it was found by the experiments that both the water absorption peak at 970 nm and the ICG absorption peak at 800 nm show similar behavior during the change of the scattering background. Thus the ratio of the MCA-estimated concentration factor of ICG to water is independent of the blood-phantom scattering.
C. Du, and W. Nahm. Influence of multiple scattering effects on in vivo NIR spectroscopy. In Proceedings of the SPIE, vol. 2326, pp. 307-318, 1995
On the basis of both homogeneous and layered skin models this paper analyzes the influences of multiple scattering of skin on the measurements of NIR spectroscopy. Emphasis is laid on the wavelengths of 660, 805, and 940 nm which are used in clinical monitoring systems. The results of Monte-Carlo simulation show that the overwhelming scattering of tissue leads to a nonlinearity in the Lambert-Beer's relation between optical density and chromophore concentration. The consequences of this effect shall be discussed using as an example the non invasive measurement of Indocyanine Green (ICG) in the blood. In this case the multiple scattering of skin causes substantial non-linear relation between the optical density at 805 nm and the concentration of an injected NIR dye in the blood if the concentration of ICG exceeds 10 mg/l. This leads to a significant distortion of the ICG clearance curve and in consequence to a systematic error in the determination of physiological parameters. For multi-wavelength spectroscopy the wavelength dependency of scattering coefficients has to be noticed. The consequence of this effect is demonstrated for blood oxygen saturation (SaO2) measurements.
H. Frankenberger, and W. Nahm. Meßdatenerfassung in der Medizin-Entwicklung eines Neugeborenen-Intensiv-Meßplatzes. In Proc. MessComp (MC), vol. 9, pp. 348-351, 1995
H. Gehring, and W. Nahm. Ein neues elektrochemisches Meßgerät für Atemalkohol zur Erkennung eingeschwemmter Flüssigkeit bei beatmeten und spontanatmenden Patienten. In Biomedizinische Technik / Biomedical Engineering, vol. s1, pp. 286-287, 1994
This disclosure generally relates to medical systems and methods. In one aspect of the invention, a method includes determining a fluorescent light intensity at one or more points on each of multiple recorded images, and producing an image based on the determined fluorescent light intensity at the one or more points.
W. Nahm. Positionierungsvorrichtung für ein chirurgisches Gerät. DE 102013013492 A1, 2015.
Eine Positionierungsvorrichtung (100) für ein chirurgisches Gerät, insbesondere ein Operationsmikroskop (3), umfasst: – ein erstes Element (102), welches an einem Körperteil eines Benutzers des chirurgischen Geräts anbringbar ist; – ein zweites Element (101), welches an dem chirurgischen Gerät angebracht ist; und – eine Kupplung, welche das erste und das zweite Element (101, 102) lösbar miteinander verbindet, so dass ein Benutzer mittels der Positionierungsvorrichtung (100) eine Kraft zum Positionieren des chirurgischen Geräts von seinem Körperteil auf das chirurgische Gerät übertragen kann.
W. Nahm. Arrangement and method for quantitatively determining the blood flow within blood vessels. US 8483796 B2, United States Patent, 2013.
An arrangement quantitatively determines the blood flow within blood vessels through which blood flows in a volume of a tissue defining a surface. Three-dimensional first image data of a first volume portion of the volume is detected and optical second image data is detected continuously in time of a first surface portion of the surface. A calibrating unit of the arrangement calibrates the relative value of the flow speed and/or the volumetric flow of the blood flowing through the blood vessels disposed directly below the first surface portion based on the absolute values of the flow speed and/or of the volumetric flow of the blood. An output unit outputs the absolute values of the flow speed and/or the volumetric flow of the blood flowing through the blood vessels arranged directly below the first surface portion.
W. Nahm, and H.-J. Miesner. Anordnung und Verfahren zur Registrierung von Gewebeverschiebungen. WO 2013/087210 A1, WIPO, 2013.
This disclosure generally relates to medical systems and methods. In one aspect of the invention, a method includes determining a fluorescent light intensity at one or more points on each of multiple recorded images, and producing an image based on the determined fluorescent light intensity at the one or more points.
Es wird eine sekundäre Lichtquelle einer schmalbandiges Licht emittierenden schmalbandigen Lichtquelle (11) als einer primären Lichtquelle, einem Lichtleiter (5) mit einem proximalen und einem distalen Ende (9), einer am proximalen Ende (7) des Lichtleiters (5) angeordneten Einkopplungsvorrichtung (13) zum Einkoppeln des schmalbandigen Lichts in den Lichtleiter (5) und einem an oder vor dem distalen Ende (9) des Lichtleiters (5) vorhandenen Leuchtstoffbereich (19), der mit einem Konverter-Leuchtstoff versehen ist, zur Verfügung gestellt. Der Konverter-Leuchtstoff des Leuchtstoffbereiches (19) ist derart im Bezug auf das von der schmalbandigen Lichtquelle (11) emittierte schmalbandige Licht gewählt, dass die W
W. Nahm, and K. Stree. Verfahren zur Personenerkennung bei einer Personenwaage und Personenwaage. DE 10338931 B4, 2009.
Verfahren zur Personenerkennung bei einer Personenwaage, wobei das Gewicht und eine zweite physikalische oder physiologische Größe einer zu erkennenden Person gemessen werden, wobei die beiden mittels der Messungen erhaltenen Messwerte von Gewicht und zweiter Größe verglichen werden mit in einem Speicher abgelegten, einer bestimmten Person zugeordneten Vergleichswerten von Gewicht und zweiter Größe, wobei zumindest einer der Vergleichswerte der Mittelwert aus vorangegangenen Messungen des Gewichts und/oder der zweiten Größe der Person ist, wobei die beiden Messwerte bei Übereinstimmung mit den Vergleichswerten der Person zugeordnet werden, und wobei der Mittelwert gewichtet wird.
W. Nahm. Personal scale with support, at least one power storage units, at least one electrodes, electron and display unit. KP 1020040103107 A, Korean Intellectual Property Office, 2004.
PURPOSE: A personal electrode is provided to maintain every option for a harmonic design, to secure the quality and the function and to make a mass-production by having a glass support. CONSTITUTION: A support(3) is formed for strip conductors(5~12) to be combined through a power combination method and/or an electrode formed by a conductive film metal. Thereby, every option for a harmonic design is maintained, the quality and the function are secured and a chip mass-production is possible.
W. Nahm. Measuring device for body analysis scale, including electrodes arranged on food-step plate on body analysis scale. KP 1020040103106 A, Korean Intellectual Property Office, 2004.
PURPOSE: A measuring device is provided to achieve improved use convenience and accuracy of measurement by arranging electrodes on a foot-step plate on a body analysis scale. CONSTITUTION: A measuring device comprises electrodes(2a,2b,3a,3b) arranged on a foot-step plate(1) such that the electrodes serve as a measurement electrodes and function switches. The electrodes are shaped as a comb engaged with each other.
W. Nahm. Method for displaying measurement result of body analysis scale, by displaying combination of physiological parameter and anthropological parameter on analytic graphic display. KP 1020040103104 A, Korean Intellectual Property Office, 2004.
PURPOSE: A method is provided to allow a user to easily evaluate the measurement result even without checking a table and/or a brochure. CONSTITUTION: A method is characterized in that a combination of at least one physiological parameter and at least anthropological parameter is displayed on an analytic graphic display through a transponder. The graphic display is divided into at least three groups. First and third groups of the graphic display are arranged to display a rising representation, and the intermediate group is arranged to display a constant representation.
W. Nahm. Vorrichtung zur plethysmographischen Bestimmung der Wiederauffüllzeit der Beinvenen. EP 1442702 A1, Europäisches Patentamt, 2004.
Eine Vorrichtung dient zur Bestimmung der Lichtreflexion, insbesondere zur Bestimmung der Wiederauffüllzeit der Beinvenen. Eine verbesserte Vorrichtung dieser Art umfaßt einen Sensor (1) zum Erfassen der Lichtreflexion zu verschiedenen Zeitpunkten und eine Signalauswerteeinrichtung (10) zum Bestimmen des Zeitraums zwischen einem Ausgangszeitpunkt und einem Endzeitpunkt (Fig. 1).
W. Nahm. Messvorrichtung, insbesondere für medizinische oder physiologische Messgrössen. EP 1443613 A1, Europäisches Patentamt, 2004.
Eine Meßvorrichtung, insbesondere für eine oder mehrere medizinische oder physiologische Meßgrößen, besteht aus einem Bedienteil (8), das ein Gehäuse (1) umfaßt und mindestens einem Sensorgehäuse (2), das mit dem Bedienteil (8) durch ein flexibles Kabel (3) verbunden ist. Um eine derartige Meßvorrichtung zu verbessern ist in dem Gehäuse (1) eine Nut (4) zur Aufnahme des flexiblen Kabels (3) vorgesehen (Fig. 1).
W. Nahm. Vein function monitor. US 00481459 S, United States Design Patent, 2003.
W. Nahm. Verfahren zur Personenkennung bei einer Körperanalysewaage. DE 10239267 A1, Deutsches Patentamt, 2003.
Die Erfindung betrifft ein Verfahren zur Personenerkennung bei einer Körperanalysewaage sowie eine Meßvorrichtung zur Durchführung dieses Verfahrens. Bezüglich des Verfahrens wird vorgeschlagen, daß die Messung von zumindest zwei physiologischen und/oder anthropometrischen Parametern erfolgt, wobei wenigstens einer der Meßparameter dem physiologischen Bereich und ein zweiter Meßparameter dem anthropometrischen Bereich der zu erkennenden Person zugeordnet ist. Die Meßvorrichtung zeichnet sich dadurch aus, daß eine Trittplatte 2 zum einen mit Sensoren 3 zur Erfassung zumindest eines physiologischen Parameters und zum anderen mit zumindest einem Kraftaufnehmer 4 zur Erfassung eines anthropometrischen Parameters versehen ist, wobei die Sensoren 3 und der beziehungsweise die Kraftaufnehmer 4 mit einer Auswerteeinheit 10 verbunden sind, die aus dem Parameter die Kenngröße zur Personenerkennung ermittelt.
W. Nahm. Darstellung des Mess-Ergebnisses eines Körperfettmessgeräts. EP 1338245 A2, Europäisches Patentamt, 2003.
Die Erfindung betrifft ein Verfahren zur Darstellung des Meßergebnisses eines Körperanalysegerätes, insbesondere einer Körperanalysewaage. Zur Bewertung des Meßergebnisses wird vorgeschlagen, daß die Kombination aus zumindest einem physiologischen und zumindest einem anthropometrischen Parameter über einen Transponder in einer in zumindest drei Gruppen unterteilten, interpretierenden Grafikanzeige dargestellt ist.
W. Nahm. Personenwaage. EP 1336826 A2, Europäisches Patentamt, 2003.
Die Erfindung betrifft eine Personenwaage mit einer Trittplatte aus Glas, zumindestest einem einer Kraftaufnehmer und/oder zumindest einer Elektrode und einer mit diesem beziehungsweise diesen über Leiterbahnen verbundenen Elektronik- und Anzeigeeinheit 2. Für eine kostengünstige Großserienfertigung wird vorgeschlagen, daß die Trittplatte 3 als Träger für die mit dieser kraftschlüssig verbundenen Leiterbahnen 5 und/oder Elektroden aus einem leitenden Dünnschichtmaterial ausgebildet ist.
W. Nahm. Messvorrichtung für eine Körperanalysewaage. EP 1336825 A2, Europäisches Patentamt, 2003.
Die Erfindung betrifft eine Meßvorrichtung für eine Körperanalysewaage mit Meßelektroden auf der Trittplatte 1 und mit personen- und funktionsbezogenen Schaltem. Für eine erleichterte Nutzung, kostengünstigere Fertigung und vereinfachte Bedienung wird vorgeschlagen, daß Elektroden 2a, 2b; 3a, 3b auf der Trittplatte 1 angebracht sind, die sowohl als Meßelektroden als auch als personenund funktionsbezogene Schalter ausgeführt sind.
W. Nahm. Verfahren und Anzeigevorrichtung zur Darstellung eines durch mehrere Grössen definierten physiologischen Zustands eines Lebewesens. EP 1197179 A2, Europäisches Patentamt, 2002.
Anzeigevorrichtung (1) zur Darstellung eines durch mehrere Größen definierten physiologischen Zustands (91, 92, ..., 99) eines Lebewesens. Um eine eindeutige, leicht verständliche und schnell erfassbare Darstellung des physiologischen Zustands (91, 92, ..., 99) zu ermöglichen, wird vorgeschlagen, dass die Größen jeweils einer Achse (3, 4) eines mehrdimensionalen kartesischen Koordinatensystems zugeordnet werden, dass eine Zeitbasis zur Darstellung des Zustands (91, 92, ..., 99) des Lebewesens vorgegeben wird und dass der Zustand (91, 92, ..., 99) des Lebewesens auf Grundlage der Zeitbasis in Abhängigkeit von den Werten der Größen in dem Koordinatensystem dargestellt wird. Es wird weiter vorgeschlagen, den Ursprung (8) des Koordinatensystems in den Idealzustand des Lebewesens zu legen.
W. Nahm, G. Gauglitz, and W. Hofmann. Verfahren und Vorrichtung zum optischen Nachweis einer An- oder Einlagerung mindestens einer stofflichen Spezies in oder an mindestens einer dünnen Schicht. DE 4200 088 C2, Deutsches Patentamt, 1997.
The invention relates to a system for visualizing characteristic tissue with a colorant in a surgical region. The system contains a detection unit which detects light from at least one object point in the surgical region. The system has a computer unit which is connected to the detection unit and drives a visualization unit which displays an image of an area in the surgical region. The computer unit determines the color coordinate in a color space with respect to the light from a point from the object point in the surgical region. Depending on the position of the color coordinate determined with respect to the object point, the computer unit calculates a color coordinate information ("0", "1") for controlling the visualization unit by comparing information concerning the determined color coordinate of the object point with information concerning a characteristic reference color coordinate.
An imaging apparatus and method are provided. The probe for an imaging apparatus includes a manually manipulable proximal portion; a straight distal portion with a distal tip for locating at a site to define an observational field; and a curved portion between the proximal portion and the distal portion. The imaging method includes the steps of locating a distal tip of an imaging probe at a site to define an observational field; irradiating the observational field from the distal tip; and collecting a return signal at the distal tip; wherein the probe comprises a manually manipulable proximal portion. The apparatus and method provided herein are useful for various applications including but not limited to endomicroscopy and other microsurgical procedures performed under optical stereoscopic magnified visualization, such as neurosurgery, ENT/facial surgery and spinal surgery.
H. Jess, D. Quendt, W. Nahm, and J. Steffen. Chirurgisches Mikroskop zur Beobachtung einer Infrarot-Fluoreszenz und entsprechendes Verfahren. EP 2199842 B1, Europäisches Patentamt, 2015.
In a system and a method for examining an object containing a fluid liquid, the object is illuminated with measuring light and images are temporarily shortly subsequently recorded. The images are evaluated per pixel to determine perfusion data from a high frequency portion above 1 kHz and to determine further information about properties of the object from a low frequency portion below 100 Hz, such as a degree of oxygenation of hemoglobin, a concentration of hemoglobin or a concentration of ICG. This information determined by evaluation is displayed in a form of an image in superposition with a white light image of the object.
Verfahren zur quantitativen Darstellung des Blutflusses in einer Gewebe- oder Adernregion basierend auf einem Signal eines in das Blut injizierten Kontrastmittels, wobei – zu aufeinander folgenden Zeitpunkten mehrere Einzelbilder (4) des von der Gewebe- oder Adernregion abgegebenen Signals aufgenommen und gespeichert werden, – für Bildpunkte von Einzelbildern (4) jeweils anhand des Signals eine für den Blutfluss charakteristische Größe und pro Bildpunkt eine weitere, für die Position der Adern charakteristische Größe aus dem Signal bestimmt wird, – diese Größen jeweils für die Bildpunkte bildpunktweise überlagert dargestellt (14) werden, – auf die Einzelbilder (4) vor der Bestimmung der Zeitpunkte eine Bewegungskompensation (7) angewandt wird, – zur Bewegungskompensation (7) über ein Kantendetektionsverfahren Kantenbilder von Einzelbildern (4) erzeugt werden, – Kantenbilder miteinander korreliert werden, um einen Verschiebungsvektor zu bestimmen und – die Korrelation des Kantenbildes eines Einzelbildes (4) jeweils mit einem Referenzbild erfolgt, welches weiterentwickelt wird, indem die Kantenbilder zweier miteinander korrelierter und verschobener Einzelbilder (4) im Referenzbild ergänzt werden.
Verfahren zum Ableiten medizinischer Größen aus einer Bildfolge medizinischer Bilddaten welche mit einer Kamera (4) aufgenommen werden, wobei Einzelbilder (11) der Bildfolge gespeichert werden und aus mehreren Einzelbildern (11) jeweils mindestens eine medizinische Größe abgeleitet und dargestellt wird, wobei bei der Aufnahme der Bildfolge Metadaten (17) aufgezeichnet werden, welche Aufschluss über die Aufnahmebedingungen geben und den Einzelbildern (11) zugeordnet werden und solche Daten als Metadaten (17) aufgezeichnet werden, welche sich auf die Helligkeit der Bilddaten auswirken, dadurch gekennzeichnet, dass als Metadaten (17) für die Helligkeitskorrektur (13) eingestellte Verstärkungsfaktoren einer die Bildfolge aufnehmenden Kamera (4) und Zeitpunkte, an denen sie geändert wurden, aufgezeichnet werden und als medizinische Größe ein Blutfluss in einem Gewebe- oder Aderngebiet aus der Bildfolge abgeleitet wird und die Kamera (4) durch unterschiedliche Verstärkungsfaktoren an eine unterschiedlich starke Fluoreszenz eines aufzunehmenden Gewebe- oder Aderngebiets angepasst wird, in welches zur Bestimmung des Blutflusses ein Fluoreszenzfarbstoff appliziert wird.
Die Erfindung betrifft eine ophthalmologische Vorrichtung, aufweisend – ein Leistungsmodul zum Bereitstellen von Leistung für ein ophthalmologisches Handstück, – ein Sicherheitsmodul zum Begrenzen der Leistung, wobei das Sicherheitsmodul mit dem Leistungsmodul gekoppelt ist, – eine Kopplungseinheit zum Ankoppeln des Handstückes, wobei die Kopplungseinheit mit dem Sicherheitsmodul oder Leistungsmodul gekoppelt ist, – einen Informationsgeber, welcher eine Information über den Status der Kopplungseinheit abgibt und mit dem Sicherheitsmodul verbunden ist.
Systems and methods are described for imaging an eye portion or for treating glaucoma in an eye of a patient. In a first step an optical microscopic image of a portion of the eye is acquired. In the optical microscopic image a distinguishable anatomical structure is identified to predict a location of a volume portion to be imaged three-dimensionally. Three-dimensional imaging of the located volume portion is performed by acquiring an optical coherence tomography image of the located volume portion. The volume portion is treated by either directing a laser beam to the volume portion or inserting an implant based on the OCT-image.
Imaging systems and methods are provided herein. An imaging system for imaging a surgical site, may include a macroscopic visualization system; and an imaging apparatus with a probe, the imaging apparatus being adapted to image the observational field and generate second image data; wherein the system is operable to control the macroscopic visualization system and the imaging apparatus to image the site and the observational field respectively at substantially the same time, and to associate the first image data and the second image data. Imaging methods provided herein may include the steps of: imaging the site with a macroscopic visualization system and generating first image data; imaging at substantially the same time an observational field with an imaging apparatus and generating second image data; and associating the first image data and the second image data.
A method for the quantitative representation of the blood flow in a tissue or vascular region is based on the signal of a contrast agent injected into the blood. In the method, several individual images of the signal emitted by the tissue or vascular region are recorded at successive points in time and are stored. Based on the respective signal, a quantity characteristic for the blood flow and a quantity characteristic for the position of the blood vessels are determined for image areas of individual images. These quantities are represented superimposed for the respective image areas such that both the blood flow quantity and the position of the fine blood vessels become clearly visible in the representation and can be differentiated from the tissue.
An ophthalmologic surgical work station has a microscope and a foot switch corresponding thereto. The microscope is connected to the foot switch via a console. The microscope and the foot switch are coarsely prepositioned and a change of the relative position between the microscope and the foot switch with respect to each other is only possible via a fine positioning.
A method for the quantitative representation of the blood flow in a tissue or vascular region is based on the signal of a contrast agent injected into the blood. Several individual images of the signal emitted by the tissue or vascular region are recorded and stored at successive points in time. For image areas of the individual images, the respective intensities of different points in time are compared and the maximum intensities of the signals are determined for these image areas. The maximum intensities are represented for these image areas.
A method for the quantitative representation of the blood flow in a tissue or vascular region based on the signal of a contrast agent injected into the blood. In the process, several individual images of the signal emitted by the tissue or vascular region are recorded at successive points in time and are stored. For image areas of stored individual images the respective point in time is determined at which the signal has exceeded a certain threshold value and this point in time is represented for each of the image areas.
A system and a method for examining an object containing a fluid liquid are provided, wherein the object is illuminated with measuring light and images are temporarily shortly subsequently recorded. The images are evaluated per pixel to determine perfusion data from a high frequency portion above 1 kHz and to determine further information about properties of the object from a low frequency portion below 100 Hz, such as a degree of oxygenation of haemoglobin, a concentration of haemoglobin or a concentration of ICG. This information determined by evaluation is displayed in a form of an image in superposition with a white light image of the object.
C. Hauger, and W. Nahm. Method and apparatus for displaying a field of a brain of a patient and navigation system for brain surgery. EP 1982645 A1, European Patent Application, 2008.
A method and an apparatus for displaying a part of a brain of a patient is provided. Laser-Doppler-images are acquired before and after a stimulation. The laser- Doppler-images comprise information about a blood motion or about a perfusion at the acquired part. Then, the blood motion images acquired before and after the stim- ulation are compared to identify areas in the brain of the patient which are related to the stimulation.