Biomedizinische Technik/Biomedical Engineering

Published by De Gruyter
Online ISSN: 1862-278X
Print ISSN: 0013-5585
Publications
Evaluation of models describing computer based technology is crucial for further evolution of medical progress. In this project, the research sites of the Sonderforschungsbereich 414 "Computer and sensor aided surgery" were linked for evaluation purposes. Topics of flow, morphology, function, and robotics in the field of cardiac and oromaxillofacial surgery are addressed. Key methods are animal models, phantoms, image processing and clinical studies in the setting of exactly defined circumstances. As an example, 3D evaluation of myocardial edema is presented. Heterogeneity of 3D distribution of induced myocardial edema was validated. Temporal dynamics of edema is described as an example. Based on such models, diagnostic and operation relevant planning data are offered to cardiac surgeons.
 
OR's are the most profitable units in hospitals, and also the most expensive. They often generate 60-65% of the hospital's revenue and 45% of its costs. In surgery, long turnover and setup times cause delays that result in the suboptimal utilization of resources, especially OR's. Therefore, during scheduling, the availability of all resources, as well as the individual patient characteristics must be taken into account. This type of planning is one of the most complex tasks in the clinical routine, but in practice, such plans are often made manually, which constitutes a heavy source of errors. Thus, hospitals can benefit from using software for automated resource planning and increase the number of surgeries performed. Furthermore, hospitals often lack effective tools for detecting deviations from the schedule at an early stage. The integration of unexpected events, often leads to delays and cancellations. In such situations, the re-assignment of resources and the rapid adjustment of tasks are important for clinical workflows to be performed on time and for the OR's to be optimally utilized. Modern system solutions support hospitals in monitoring and steering surgical workflows. Using localization data, they provide an overview of resources and of the status of treatment processes, and they automatically detect deviations. Besides planning and steering processes, supporting activities like the instrument management should not be disregarded. Problems with instrument trays frequently involve inadequately maintained instruments, or trays that do not contain the right instruments and are returned to the OR with items missing. This leads to intraoperative delays, which may in turn delay the surgical schedule and put patients at risk. The mentioned approaches for an effective usage of OR's require certain construction preconditions to ensure an unproblematic patient and resource flow. These preconditions should be an essential part of each planning process and can be supported by corresponding simulation tools.
 
To compare technical parameters and clinically relevant aspects of on- and off-resonance MTC sequences in mid- and high-field MR systems. Both on- and off-resonance techniques were combined with an FFE sequence using 0.5 and 1.5 Tesla superconducting systems. Parameters were systematically measured by scanning a cadaveric knee joint. Signal-to-noise ratios and MT ratios for fat, cartilage and reference solution (copper sulphate) were determined. Minimal TR and the energy absorption rate were also compared. The MT effect at 1.5 T was more pronounced. However, using optimized parameters, clinically adequate MT contrast was achieved with both techniques and both MT units. The most important parameters for the off-resonance method are pulse angle and off-centre frequency; for the on-resonance method, pulse angle and number of composite pulse elements. Energy absorption was below 2 W/kg. Minimal TR was prolonged by up to 400%. In order to produce MTC images, optimized parameters should be applied. Using optimized pulse parameters, adequate MTC imaging is achievable with mid- and high-field systems using on- and off-resonance techniques. To ensure comparability of MTC studies, the pulse parameters need to be given, and, ideally, standardized.
 
Objectives: A non-contrast-enhanced 2D time-of-flight magnetic resonance angiography (TOF-MRA) protocol was compared with the gold standard of planar digital subtraction angiography (DSA) by calculating correlations of vessel diameters. Methods: A total of 1134 vascular diameters in 81 corresponding sites were prospectively measured by TOF-MRA and DSA in seven patients (four women, three men; mean age, 68 years). For a total of 162 vascular segments per patient, 81 Spearman's ρ correlation coefficients were calculated, consolidated to 41 due to consideration of symmetry (right/left), and assessed by correlation quality. Results: In the 41 consolidated segments, correlations were good, very good, and excellent in 25 segments (n=10>0.5, n=4>0.7, and n=11>0.8), moderate to poor in seven segments (n=4>0.3 and 0<n=3≤0.3), without in two, inverse in three, and nonmeasurable in four segments. Correlations were best for the main arteries above the knee, and these arteries were most consistently visualized. Conclusion: The TOF-MRA protocol presented here can be performed in an open 1.0-T MRI system in 60-90 min. Visualization is degraded when the target artery leaves the plane orthogonal to the imaging plane (1) or signal yield is poor due to small caliber (2).
 
Different techniques for magnetic resonance-guided lumbar interventions have been introduced in recent years. Appropriate pulse sequence design is crucial since high spatial resolution often comes at the cost of lower temporal resolution. The purpose of this study was to evaluate the value of accelerated reduced field of view (ZOOM)-based imaging sequences for lumbar interventions. ZOOM imaging was used in 31 interventions (periradicular, facet joint, epidural infiltrations, and discography) performed in 24 patients (10 women, 14 men; age 43±13.3 years). Signal-to-noise ratio and contrast-to-noise ratio (CNR) were determined and retrospectively compared with standard preinterventional (T2 weighted), peri-interventional (proton density), and postinterventional (spectral presaturation with inversion recovery [SPIR]) imaging. Needle artifacts were assessed by direct measurement as well as with parallel and perpendicular needle profiles. Puncture times were compared to similar interventions previously performed in our department. No significant differences in signal intensities (standard/ZOOM: 152.0/151.6; p=0.136) and CNR values (2.0/4.0; p=0.487) were identified for T2-weighted sequences. The needle artifact signal intensity was comparable (648.1/747.5; p=0.172) for peri-interventional imaging. Standard interventional (fat needle: 43.8/23.4; p<0.001; muscle needle: 6.2/2.4; p<0.001) and SPIR sequences (43.3/13.9; p=0.010) showed a higher CNR than corresponding ZOOM sequences did. Needle artifacts were larger in ZOOM (2.4 mm/2.9 mm; p=0.005). The profiles revealed that ZOOM imaging delivers more overall signal intensity. The turning points of both profiles were comparable. ZOOM reduced intervention times significantly (329.1 s/228.5 s; p=0.026). ZOOM imaging is a feasible interactive sequence for lumbar interventions. It ameliorates the tradeoff between image quality and temporal resolution. Moreover, the sequence design reduces intervention times significantly.
 
Purpose: To report our initial clinical experience with a new magnetic resonance imaging (MRI) quadrupole coil that allows interventions in prone position. Materials and methods: Fifteen patients (seven women, eight men; average age, 42.8 years) were treated in the same 1.0-Tesla Panorama High Field Open (HFO) MRI system (Panorama HFO) using a quadrupole butterfly coil (Bfly) and compared with 15 patients matched for sex, age, and MR intervention using the MultiPurposeL coil (MPL), performed in conventional lateral decubitus position (all, Philips Medical Systems, Best, The Netherlands). All interventions were performed with a near-real-time proton density turbo spin echo (PD TSE) sequence (time to repeat/time to echo/flip angle/acquisition time, 600 ms/10 ms/90°/3 s/image). Qualitative and quantitative image analyses were performed, including signal intensity, signal-to-noise and contrast-to-noise ratio (SNR, CNR), contrast, and full width at half maximum (FWHM) measurements. Results: Contrast differed significantly between the needle and muscles (Bfly 0.27/MPL 0.17), as well as the needle and periradicular fat (0.13/0.24) during the intervention (both, p=0.029), as well as the CNR between muscles and the needle (10.61/5.23; p=0.010), although the FWHM values did not (2.4/2.2; p=0.754). The signal intensity of the needle in interventional imaging (1152.9/793.2; p=0.006) and the postinterventional SNR values of subcutaneous fat (15.3/28.6; p=0.007), muscles (6.6/11.8; p=0.011), and the CNR between these tissues (8.7/17.5; p=0.004) yielded significant differences. Conclusion: The new coil is a valid alternative for MR-guided interventions in an open MRI system at 1.0 tesla, especially if patients cannot (or prefer not to) be in a lateral decubitus position or if prone positioning yields better access to the target zone.
 
The cytotoxicity of Degutan surfaces with different degrees of roughness, and the effect of surface structures on osteoblast proliferation and differentiation, was investigated with standardised cell culture systems. Fibroblast cell lines (BALB/3T3) and osteoblast cell lines (hFOB 1.19) were used. The number and variability of the cells were determined for assessment of proliferation and alkaline phosphatase activity, collagen I and osteocalcin production were used as parameters for differentiation. In the early phase, the largest numbers of cells and greatest proliferation were measured on polished Degutan surfaces. In the late phase, however, larger numbers of cells and a greater degree of proliferation were to be seen on sandblasted and sandblasted/heat-treated Degutan surfaces. No differences were found for collagen I, osteocalcin production or alkaline phosphatase activity. Neither the osteoblasts nor the fibroblasts revealed a toxic effect of Degutan. The results for osteoblast differentiation correlate with recent studies on identical structured titanium surfaces. In view of the immeasurable amount of ion release, Degutan may be considered an ideal model for an inert material surface.
 
This paper presents the results of an experimental investigation with two different rotatory piezomotors in a closed 1.5 Tesla high-field MRI. The focus of the investigation was on testing the functionality of these motors within the MRI and to determining the image interference they caused. To obtain a differentiated estimate of the interference the motors were tested in both the passive (turned off, i.e. without current flow) and active (turned on, i.e. with current flow) state during MRI scanning. Three different types of sequences were used for the test: Spin-Echo (SE), Gradient-Echo (GE) and Echo-Planar Imaging (EPI). A plastic container filled with a gadolinium-manganese solution was used for representation of the artefacts. The motors investigated were placed parallel to the container at predetermined distances during the experiment. The results show that the motors investigated suffered no functional limitations in the magnetic field of the MRI but, depending on the type of motor, the measurement distance and the state of the motor, the motors had different effects on the sequence images. A motor in the off-state placed immediately next to the object to be measured mainly causes artefacts because of its material properties. If, on the other hand, the piezomotor is in the on-state images with strong noise result when the motor is immediately next to the object being measured. The images regain their normal quality when the motor is approximately at a distance of 1 m from the object being investigated. Driving the motor inside the MRI, therefore, is only to be recommended during the pauses in scanning: this delivers artefact-free images if minimal, motor-specific distances are kept to. With regard to the three different types of sequences it was determined that the SE sequence was the least sensitive and the EPI sequence the most sensitive to disturbance. The GE sequence showed only minimal differences to the SE sequence with regard to signal-to-noise ratios. Since it requires considerably shorter scan-times it can be considered to be the most effective type of sequence under these conditions.
 
This article shows the results of an experimental investigation of the interference by paramagnetic and diamagnetic materials on imaging in a closed 1.5 Tesla high field magnetic resonance imaging system (MRI). For different types of sequences (SE, GE, EPI) the effects of metal and non-metal profiles in producing artefacts were investigated. A phantom (plastic trunk) filled with Gd-Mn-solution was used for representation of the artefacts. The materials analysed were placed parallel to the phantom at predetermined distances. The images were obtained in transverse and sagittal planes and analysed with respect to the resulting artefacts. The results show that aluminum and polymer profiles produce the weakest artefacts, even when the material is positioned close to the phantom. A comparison of the sequence types shows that the SE-sequence has a low sensitivity to artefacts, despite the great profile variation in size and shape. The SE-sequence accordingly showed a higher imaging stability as compared with the GE- and EPI-sequences. Steel and copper produced the strongest artefacts. The examination was begun after an intensive study of the literature (Internet, Medline, Meditec). So far have been few publications on this subject.
 
Composite tablets of human recombinant bone morphogenetic protein 2 (rhBMP-2) and poly-(D,L)-lactide (PDLLA) (1-2 mg rhBMP-2/g PDLLA) were prepared by foaming of PDLLA with supercritical CO 2. Release kinetics of rhBMP-2 were measured by a continuous flow and a batch dilution method at 22°C and 50 °C respectively. In both cases a two-phase first-order release was found. Release half-lives of the sustained release phases (87-90% of total) decreased significantly from 348 days at 22°C to 86 days at 55 °C i.e. by a factor of 4 indicating a coupling with PDLLA hydrolysis. The released rhBMP-2 was biologically active.
 
We used a recently described all-dry silicon etch process for SOI wafers to fabricate 64-site electrode arrays in stereotrode arrangement for acute cortical recordings. The fork-like probes are connected to preamplification units by flexible, Y-shaped interconnects. This facilitates maximal experimental flexibility for simultaneously recording from all available channels from the cortex of anaesthetised rats. Preconditioned signals are amplified by a novel modular main amp, which may be software or dial controlled. Signals are 16bit digitized, recorded, analyzed, stored and processed on a DSP-based modular data acquisition system. Digital data is processed, filtered and denoised on all up to (4*32) 128 channels based on an extremely fast wavelet transformation framework.
 
In a previous article the author has demonstrated regular 13-Hz oscillations of the bellies of the arm muscles during isometric contractions. In this research these experiments were extended with the study of physiological tremor by application of an accelerometer on the wrist. During repeated isometric and faradic contractions of the arm muscles, an harmonic relation between this physiological tremor and the 13-Hz oscillations was proved. Also it is plausible to consider these 13-Hz oscillations as the primary origin of the physiological tremor.
 
We evaluated two user-friendly, commercially available transcranial cerebral oximeters (TOS 96, Tostec, Tokyo, Japan and INVOS 3100, Somanetics, Troy, USA) for use in adults. We compared the absolute values (%) of regional cerebral oxygen saturation (rSO2) from 108 measurements in 54 healthy volunteers (31 women, mean age 35.8 +/- 16.3 years and 23 men, mean age 35.4 +/- 9.2 years). The mean rSO2 values obtained by the TOS 96 and INVOS 3100 systems were 72.3 +/- 8.4 % and 72.6 +/- 7.2% respectively. Significant differences (p < 0.01) were found between females and males with the INVOS equipment. The study shows that anatomical (thickness of the skull) and technical (calibration) aspects have to be taken into consideration when interpreting absolute rSO2 values.
 
The continuing development of new, highly sophisticated materials for the articulating surfaces of total hip endoprostheses involves the need for testing, not only of biocompatibility and dynamic loadability, but also of tribological properties (friction, wear, lubrication). For decades, the wear resistance of these materials has been tested in wear simulators. In consequence of the currently often widely differing test methods, the technical committee (TC 150) of the ISO (International Organization for Standardization) has been concerned to develop an International Standard (ISO/FDIS 14242 1 and 2: Implants for Surgery--wear of total hip joint prostheses--on the basis of kinetic and kinematic data from gait analysis. This new standard will be the basis for ensuring the comparability of scientific data obtained from tribological testing of total hip endoprothesis. The new hip simulator, E-SIM, presented in this paper, complies with the currently published FDIS (Final Draft International Standard), and enables testing in accordance with these specifications.
 
We describe a newly developed multi-function video image analysis system for the computer-aided evaluation of capillaroscopic findings in microcirculation research. The Cap image analysis system comprises an IBM-compatible PC with a Matrox image processing card and real-time video tape digitalization. The video recorder is driven by a personal computer to which it is connected via an RS-232 interface. In contrast to currently available systems, the program presented here makes it possible to select any of several integrated image analysis functions, depending on the quality of the video image. Some examples of the analysis functions available are measurements of erythrocyte flow velocity using the line shift diagram method, the spatial correlation method, and the auto flying spot method. The standard features of the new program include a number of special functions and automatic movement correction. The system thus makes it possible not only to measure numerous morphological parameters such as capillary diameter, length, torquation index and capillary density, but also to perform video densitometric analysis, for example using fluorescent dyes.
 
The efficacy of cardiac resynchronization therapy through biventricular pacing (BVP) has been demonstrated by numerous studies in patients suffering from congestive heart failure. In order to achieve a guideline for optimal treatment with BVP devices, an automated non-invasive strategy based on a computer model of the heart is presented. The presented research investigates an off-line optimization algorithm regarding electrode positioning and timing delays. The efficacy of the algorithm is demonstrated in four patients suffering from left bundle branch block (LBBB) and myocardial infarction (MI). The computer model of the heart was used to simulate the LBBB in addition to several MI allocations according to the different left ventricular subdivisions introduced by the American Heart Association. Furthermore, simulations with reduced interventricular conduction velocity were performed in order to model interventricular excitation conduction delay. More than 800,000 simulations were carried out by adjusting a variety of 121 pairs of atrioventricular and interventricular delays and 36 different electrode positioning set-ups. Additionally, three different conduction velocities were examined. The optimization measures included the minimum root mean square error (E(RMS)) between physiological, pathological and therapeutic excitation, and also the difference of QRS-complex duration. Both of these measures were computed automatically. Depending on the patient's pathology and conduction velocity, a reduction of E(RMS) between physiological and therapeutic excitation could be reached. For each patient and pathology, an optimal pacing electrode pair was determined. The results demonstrated the importance of an individual adjustment of BVP parameters to the patient's anatomy and pathology. This work proposes a novel non-invasive optimization algorithm to find the best electrode positioning sites and timing delays for BVP in patients with LBBB and MI. This algorithm can be used to plan an optimal therapy for an individual patient.
 
Aiming at the development of an implantable neuroprosthesis for restoration of hand function in tetraplegic patients (C5/C6), we examined and compared the stimulation performance of two different neural electrode designs. Our studies on the radial nerve of adult pigs proved the feasibility of selective control of different forearm muscles by using only one multichannel nerve cuff electrode. The results gained by applying a 12-polar cuff electrode design were poor, while the potential of an 18-polar design was very encouraging.
 
Due to the high solubility of molecular oxygen in perfluorocabons (PFC), this class of fluorinated compounds has gained wide-spread interest for its biomedical application as temporary blood substitutes and as radiosensitizers. Since the observation that the NMR spin-lattice relaxation times (T1) of some 19F PFC resonances are sensitive to oxygen tension (pO2), this paramagnetic effect has been used to non-invasively probe pO2 in vivo. In this study, combined 19F/1H NMR image data of Copenhagen rats after PFC application were evaluated with the software package MATLAB. The analysis of the 19F NMR data resulted in image matrices with calculated T1 values in each pixel. By using a calibration curve, the corresponding pO2 values were computed. Color overlays of pO2 contour lines on T1-weighted 1H images show a good anatomical-functional correspondence.
 
This study investigates the contribution of central vasopressin receptors in the modulation of systolic arterial pressure (SAP) and heart rate (HR) response to air-jet stress in conscious Wistar rats equipped with a femoral arterial catheter and intracerebroventricular cannula using novel non-peptide and selective vasopressin V(1a) (SR49059) and V(1b) (SSR149415) antagonists. The effects of stress on SAP and HR were evaluated by measuring the maximal response to stress, the latency of the maximal response, the duration of the recovery period, and the increase in the low frequency (LF) short-term variability component. Stress induced a parallel and almost immediate increase in both SAP and HR, followed by enhanced LF SAP variability in the recovery period. Pretreatment of rats with V(1a) antagonist did not affect the maximal increase or the latency of SAP and HR response to acute stress, but shortened the recovery period of SAP and HR and prevented the increase in LF SAP. The V(1b) antagonist reduced the maximal increase in SAP without affecting HR and their latencies, shortened the recovery period of SAP and inhibited the increase in LF SAP variability. These results indicate that both central V(1a) and V(1b) receptors mediate cardiovascular changes induced by air-jet stress in conscious rats.
 
Presence of a brain tumor affects the metabolite concentrations of healthy brain tissue. This study inspects the qualification of MR spectroscopy recordings of this tissue for automatic tumor patient classification with linear discriminant analysis, artificial neural networks and support vector machines. With spectroscopy datasets reduced down to the concentrations of two different metabolites, a classification performance of approximately 80% could still be achieved.
 
For the first time a double turn breast coil has been described which can be used for 1H imaging, 1H spectroscopy and 31P spectroscopy. The paper describes basic technical features of the coil, coil design, B1 field/excitation field distribution for 1H and 31P, sensitivity, and feasibility for 31P spectroscopic in vivo studies. The main advantage of the double frequency tuneable coil is that 1H imaging for tumor localization and 31P spectroscopy for response control can be done without an additional repositioning of the patient.
 
Top-cited authors
Gernot R Müller-Putz
  • Graz University of Technology
Friedhelm Heinemann
  • University of Greifswald
Rüdiger Rupp
  • Universität Heidelberg
Charlotte Scherzinger
  • Klinikum Forchheim
Ralf Ringler
  • Ostbayerische Technische Hochschule Amberg-Weiden, Weiden, Germany