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PubMed2005

The fluorescence bioassay platforms on quantum dots nanoparticles.

In this paper, we present the optical properties and the platforms on fluorescent quantum dots for biological labeling, biomedical engineering and biosensor in molecular imaging. Quantum dots possess several properties that make them very attractive for fluorescent tagging: broad excitation spectrum, narrow emission spectrum, precise tunability of their emission peak, longer fluorescence lifetime than organic fluorophores and negligible photobleaching. We describe how to take such advantages of quantum dots to develop the technology and employ it to build assay platforms. Finally, ultrasensitivity, multicolor, and multiplexing of the technology of semiconductor quantum dots open up promising and interesting possibilities for bioassay platform.

Biotechnology↗
PubMed2006

Optimal wavelets for biomedical signal compression.

Signal compression is gaining importance in biomedical engineering due to the potential applications in telemedicine. In this work, we propose a novel scheme of signal compression based on signal-dependent wavelets. To adapt the mother wavelet to the signal for the purpose of compression, it is necessary to define (1) a family of wavelets that depend on a set of parameters and (2) a quality criterion for wavelet selection (i.e., wavelet parameter optimization). We propose the use of an unconstrained parameterization of the wavelet for wavelet optimization. A natural performance criterion for compression is the minimization of the signal distortion rate given the desired compression rate. For coding the wavelet coefficients, we adopted the embedded zerotree wavelet coding algorithm, although any coding scheme may be used with the proposed wavelet optimization. As a representative example of application, the coding/encoding scheme was applied to surface electromyographic signals recorded from ten subjects. The distortion rate strongly depended on the mother wavelet (for example, for 50% compression rate, optimal wavelet, mean+/-SD, 5.46+/-1.01%; worst wavelet 12.76+/-2.73%). Thus, optimization significantly improved performance with respect to previous approaches based on classic wavelets. The algorithm can be applied to any signal type since the optimal wavelet is selected on a signal-by-signal basis. Examples of application to ECG and EEG signals are also reported.

Algorithms↗
PubMed1989

SWAT team approach to ventricular assistance.

In 1986, the Cardiovascular Research Institute in Sion, Switzerland, created a flying bridge-to-cardiac transplantation team. This team, consisting of two physicians, a physicist, a biomedical engineer, and two intensive care nurses, has participated in 23 bridges to cardiac transplantation in 11 cardiovascular surgery centers in Europe. The cardiac function of all patients was 100% supported by paracorporeal pneumatic biventricular Pierce-Donachy devices. Twenty of the 23 patients have had transplantation, and 11 are alive and well. The bridge-to-cardiac transplantation team, which travels with a transportable driver and the ventricle sets, supervises the bridged patients 24 hours a day until cardiac transplantation is performed.

Adolescent↗
PubMed1975

Metabolic factors in the control of energy stores.

We have examined some of the factors involved in the control of food intake and integrated the data using methods of systems analysis from biomedical engineering. The central hypothesis is that energy stored in the body is a regulated variable. Alterations in the quantity of stored calories initiates changes designed to restore the store of calories to its original level. These responses are both short-term and long-term in nature. They involve integrating data on the quantities of protein, carbohydrate, and lipid stores in the body, probably through such feedback signals as amino acids, glucose, glycerol, and free fatty acids.

Adult↗
PubMed1994

Norwegian standardization effort on medical image interchange.

The Norwegian Computing Center is currently performing a project on standardization in the exchange of medical images and related data, with special emphasis on ultrasound images. The project is performed for Vingmed Sound, a Norwegian manufacturer of ultrasound scanning equipment, and much of the work is done in cooperation with the Department of Biomedical Engineering at the University of Trondheim. In the project, we work in close cooperation with the European Standardization Committee, CEN, and also with the DIGICARE (Digital Imaging in Cardiology) group of the European Society of Cardiology. The main aims of the project are to define, from the viewpoint of ultrasound imaging, the user requirements for medical image exchange standard, and to contribute to the development of such a standard.

Cardiology↗
PubMedDate not supplied

Identification and characterization of biological tissues by NMR. Concerted research project of the European Economic Community. Introduction, objectives, and activities.

NMR offers, in the complex proton relaxation properties of biological tissues, a unique and potentially powerful tool of tissue characterization. The difficulties encountered so far in comparing the results of in vitro and in vivo NMR studies carried out in different laboratories inhibit NMR methodologies from fully expressing their content of physiopathological information, as well as their potential for therapeutic monitoring. Moreover, obtaining accurate data on proton relaxation in vivo requires accurate location of the anatomical region under study. The acquisition of acceptable information about location and effects is dependent on the establishment of agreed procedures for tests, as well as on the use of appropriate test objects and test substances. A concerted research project entitled "Identification and Characterization of Biological Tissues by NMR" was activated in 1984 by the European Economic Community as part of the Third Medical Research Program, under the auspices of the Biomedical Engineering Concerted Action Committee. A series of papers is presented here which illustrates objectives and scientific programs of this project, the protocols adopted for multi-center comparison of in vitro and in vivo studies, and the results of validating trials, as well as problems of reference substances.

European Union↗
PubMed1993

Tissue characterization by magnetic resonance spectroscopy and imaging: Results of a concerted research project of the European Economic Community. Introduction, objectives, and activities.

The multi-parameter dependence of magnetic resonance (MR) images allows a unique flexibility of soft tissue contrast and gives access to peculiar sources of in vivo tissue characterization, mainly associated with magnetic relaxation properties. However, MR methodologies have not yet expressed their full potential in terms of tissue characterization for several reasons: a) problems of quality control and quantitation have generally not been addressed by centers using MRI equipment, nor in most of the published literature; and b) data scattering of quantitative measurements obtained from tissues in vitro and in vivo appear to be a major factor in inhibiting or limiting the clinical utility of MRI, for a possible in vivo characterization of pathological tissues. An international project, aimed at evaluating the clinical significance of tissue characterization by MR, was activated in 1984 by the Biomedical Engineering Advisory Committee of the European Communities (EC COMAC-BME) within the 3rd EC Medical and Health Research Programme (MHRP). The scientific achievements of this first project (Magn. Reson. Imaging, 6:171-222; 1988) represented the basis for launching and performing a second Concerted Action, in the frame of the 4th MHRP (1988-1992). Main areas of research of this second project were: a) development of standard methodologies for quantitative measurements of MR parameters and correlation with histo- and physiopathology; b) performance assessment and calibration of MR clinical equipment; c) harmonization of test procedures with other centers and industry; and d) pilot multi-center collections of data.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Quality assessment in in vivo NMR spectroscopy: I. Introduction, objectives, and activities.

By enabling noninvasive measurements of tissue biochemistry, nuclear magnetic resonance spectroscopy (MRS) provides a unique means of characterizing tissues. Differences in equipment, techniques, and methodology between different laboratories cause major difficulties when comparing results, whether from measurements of tissue metabolism, or from the effects of different therapies. This is of concern in critically evaluating work from different laboratories and centres, causing potential difficulties in reproducing results, limiting the establishment of MRS as a standard method of diagnosis and of characterising disease and response to therapy in the laboratory and clinic. It also poses particular problems in establishing the multicentre clinical trials of MRS that are now required to provide adequate statistical power in confirming the encouraging preliminary clinical observations. These difficulties arise principally from imperfect localization of signal from selected regions of interest in the body, and from the subsequent analyses of the MRS spectra. Improvement is possible by establishing agreed procedures for test measurements and for data analysis, and by using appropriate test objects and test substances to establish the quality of measurements. A concerted research project on characterisation of biological tissues by NMR, principally concerned with MR imaging (MRI), was activated in 1984 by the European Economic Community as part of its third Medical and Health Research Programme, under the auspices of the Biomedical Engineering Concerted Actions' Committee (COMAC-BME). In 1988, this project was prolonged for 5 years, when the programme was expanded to encompass MRS.(ABSTRACT TRUNCATED AT 250 WORDS)

Humans↗
PubMed2005

Ultrahigh resolution optical coherence tomography in macular dystrophy.

PURPOSE: To visualize and investigate intraretinal changes in macular dystrophies with ultrahigh resolution optical coherence tomography (UHR OCT). DESIGN: Prospective observational case series. METHODS: setting: Department of Ophthalmology and Center for Biomedical Engineering and Physics, Christian Doppler Laboratory, Medical University of Vienna, Vienna, Austria. patients: Thirteen patients (23 eyes) with adult-onset foveomacular vitelliform dystrophy (AOFVD) and 14 patients (27 eyes) with Stargardt's disease (SD) or fundus flavimaculatus (FF). OBSERVATIONS: Imaging using a compact, new generation UHR OCT system, achieving considerably improved visualization of intraretinal layers, especially the photoreceptor layer. main outcome measures: UHR OCT tomograms visualizing intraretinal differences in morphology of AOFVD and SD/FF as location and extension of deposits and loss of photoreceptors. Central foveal thickness defined as distance between internal limiting membrane and photoreceptors/retinal pigment epithelium interface. RESULTS: Patients with AOFVD had a mostly intact photoreceptor layer, a central foveal thickness of 142 +/- 23 microm as well as subretinal deposits. Patients with SD generally had a diffuse degenerative change with a visible reduction in thickness of all intraretinal layers, resulting in a corresponding reduction of central foveal thickness (94 +/- 38 microm) and central loss of photoreceptors (PRs). Comparative central foveal thickness of patients with AOFVD and SD/FF was significantly different (P < .001). Patients with FF had pigment epithelial deposits and paracentral focal photoreceptor loss. CONCLUSIONS: UHR OCT is a clinically feasible tool for examining intraretinal changes, in particular photoreceptor atrophy in macular dystrophies and, therefore, has the potential to be an adequate imaging system for monitoring the course of disease.

Adult↗
PubMed2005

Variations in the output power and surface heating effects of transducers in therapeutic ultrasound.

OBJECTIVE: To determine the real emitted output power and maximum surface heating of commercial therapeutic ultrasound transducers emitting in air for various therapeutic regimens. DESIGN: Surface temperatures of ultrasound transducers with frequencies of .05 to 3 MHz were detected over 5 minutes by using a calibrated infrared thermographic camera; additionally, the indicated output power was checked with a radiation force balance. SETTING: University center for biomedical engineering and physics and medical school for physical medicine and rehabilitation. PARTICIPANTS: Not applicable. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Power variations and surface temperatures of clinical devices were analyzed to determine whether they comply with obligatory limits given in International Electrotechnical Commission standard 60601-2-5. RESULTS: Depending on the operation mode and the output power, surface temperatures ranged between 24.2 degrees to 80 degrees C within 5 minutes. Differences between measured and displayed power output (limit, +/-20%) ranged between -32% and 28%. CONCLUSIONS: The effectiveness of treatment is lowered if the value of emitted power is not known reliably. In the worst case, damage or irritation of the skin is possible, particularly in patients with sensory compromised skin. Damage may be caused by hot surfaces if the threshold level required to activate the device is lowered or if the device is defective. Improved thermal control units are necessary to prevent potential thermal hazards. Regular checks of transducer emission should be obligatory to ensure correct and precise function of the clinical devices.

Temperature↗
PubMed2006

High-resolution imaging of proteins in human teeth by scanning probe microscopy.

High-resolution studies of dental tissues are of considerable interest for biomedical engineering and clinical applications. In this paper, we demonstrate the application of piezoresponse force microscopy (PFM) to nanoscale imaging of internal structure of human teeth by monitoring the local mechanical response to an electrical bias applied via a conductive tip. It is shown that PFM is capable of detecting dissimilar components of dental tissues, namely, proteins and calcified matrix, which have resembling morphology but different piezoelectric properties. It is demonstrated that collagen fibrils revealed in chemically treated intertubular dentin exhibit high piezoelectric activity and can be visualized in PFM with spatial resolution of 10 nm. Evidence of the presence of protein inclusions of 100-200 nm wide and several micrometers long in tooth enamel has been obtained. Furthermore, it is found that the peritubular dentin and intertubular dentin exhibit different piezoelectric behavior suggesting different concentration of collagen fibrils. The obtained results demonstrate a high potential of PFM in providing an additional insight into the structure of dental tissues. It is suggested that the PFM approach can be used to study the structure of a wide range of biological materials by monitoring their electromechanical behavior at the nanoscale.

Adult↗
PubMed2006

Local film thinning due to concentration gradient of an insoluble surfactant at an interface.

The local thinning of a viscous liquid film on a substrate driven by a surface (or interfacial) tension gradient due to a concentration gradient of a monolayer of an insoluble surfactant initially non-uniformly distributed at a liquid interface relevant to chemical engineering, biomedical and other applications is investigated. A simple model is presented for the temporal evolution of the profiles of radial variation in the thickness of a thin liquid film, the effects of gravity and capillarity due to deformation of the interface in slowing down the film thinning process being allowed. As time increases, the surfactant spreads and the radius of its front increases inversely with decrease in the two-third power of the film thickness at the center. The model describes well not only the published experimental results but also those obtained by other authors using numerical simulations of a set of coupled partial differential equations.

Journal Article↗
PubMed2004

Wavefront-optimized ablation profiles: theoretical background.

PURPOSE: To describe a method for calculating wavefront-optimized ablation profiles to precompensate for the spherical aberration and higher-order astigmatism induced by myopic, hyperopic, and astigmatic corneal laser corrections. SETTING: IROC-Institut für Refraktive und Ophthalmo-Chirurgie, and Institute for Biomedical Engineering, Swiss Federal Institute of Technology, Zürich, Switzerland. METHODS: The basic ablation profile for myopic, hyperopic, and astigmatic correction is derived from the 2nd-order Zernike representation of wavefront aberrations. Including 4th-order spherical aberration and higher-order astigmatism in the theoretical calculation of the ablation profile allows precompensation for the expected amount of higher-order aberrations (HOAs). The shapes of wavefront-optimized ablation profiles are compared with the shapes of "classic" ablation profiles for myopic and astigmatic corrections. RESULTS: The introduction of precompensating spherical aberration and higher-order astigmatism leads to a more aspheric ablation profile with a significant increase in ablation depth (up to 35%) in the midperiphery of the optical zone. The central ablation depth remains unchanged in the myopic correction but increases by 3% in cylinder correction. CONCLUSIONS: Wavefront-optimized ablation profiles provide a simple method to precompensate for the expected 4th-order spherical aberration and higher-order astigmatism in the average eye. Further clinical studies must be performed to prove the theoretical results; demonstrate the reduction in HOAs; and predict safety, predictability, and stability of wavefront-optimized ablation profiles.

Algorithms↗
PubMed2005

Influence of corneal biomechanical properties on intraocular pressure measurement: quantitative analysis.

PURPOSE: To understand and quantify intraocular pressure (IOP) measurement errors introduced by corneal variables during applanation tonometry using a cornea biomechanical model. SETTING: Department of Ophthalmology, Biomedical Engineering Center, The Ohio State University, Columbus, Ohio, USA. METHODS: The model assumed an overall resultant pressure that was based on the summation of the applanation pressure, the true IOP, and the surface tension caused by the tear film to determine the final deformation of the corneal apex during IOP measurement. Corneal resistance was varied according to the cornea's biomechanical properties, thickness, and curvature, and the effect of each variable on the accuracy of IOP tonometry readings was examined quantitatively. RESULTS: The model demonstrated that tonometry readings do not always reflect true IOP values. They deviate when corneal thickness, curvature, or biomechanical properties vary from normal values. Based on the model, predicted IOP readings have a 2.87 mm Hg range resulting from the variation in the corneal thickness in the normal population and a 1.76 mm Hg range from the variation in the corneal radius of curvature. Considering that Young's modulus of the corneal varies from 0.1 to 0.9 MPa in the normal population, the model predicts tonometry IOP readings will have a range of 17.26 mm Hg because of the variation in this corneal biomechanical parameter alone. CONCLUSIONS: The simulation based on the model demonstrated quantitatively that variations in each corneal variable cause errors in tonometry IOP readings. The simulation results indicate that differences in corneal biomechanics across individuals may have greater impact on IOP measurement errors than corneal thickness or curvature.

Biomechanical Phenomena↗
PubMed2005

Prediction of flap response.

PURPOSE: To find predictors of the induced biomechanical and optical effects of lamellar flap creation on the cornea. SETTING: Optimed Eye and Laser Clinic, Pretoria, South Africa, and the Department of Ophthalmology and Biomedical Engineering Center, The Ohio State University, Columbus, Ohio, and Bausch & Lomb Vision Research Laboratory, Rochester, New York, USA. METHODS: This prospective study monitored the refractive, wavefront aberration, and corneal topographic changes in 29 eyes of 15 patients for 3 months after the creation of a corneal lamellar flap. The main outcome measures for statistical analysis were refraction, total corneal thickness, residual corneal bed thickness, horizontal white-to-white corneal diameter, horizontal flap diameter, topography data, and wavefront data. RESULTS: Statistically significant changes were seen in the autorefraction mode. Wavefront data showed significant change in 4 Zernike modes-90/180-degree astigmatism, vertical coma, horizontal coma, and spherical aberration. The topography data indicated the corneal biomechanical response was significantly predicted by stromal bed thickness in the early follow-up period and by total corneal pachymetry and flap diameter in a 2-parameter statistical model in the late follow-up period. CONCLUSIONS: Uncomplicated lamellar flap creation is responsible for systematic changes in corneal topography and induction of higher-order optical aberrations. Predictors of this response include stromal bed thickness, flap diameter, and total corneal pachymetry.

Adult↗
PubMed2005

Treatment-induced shifts of ocular reference axes used for measurement centration.

PURPOSE: To determine the shifts of the main corneal reference points in dependence of the chosen centration axis for the treatment. SETTING: Federal Institute of Technology Zurich, Institute of Biomedical Engineering, Zurich, Switzerland. METHODS: Computer simulations were performed on several variants of the Gullstrand-Emsley schematic eye, which was modified by an off-axis fovea. Refractive corrections were simulated by centering Munnerlyn's formula on each of the 4 corneal reference points determined in the preoperative eye: the optical axis, the line of sight, the visual axis, and the first corneal reflex. Subsequently, the postoperative locations of these axes were determined and compared with the preoperative values. RESULTS: The postoperative line of sight was found to depend least on the choice of the preoperative centration axis for both myopic and hyperopic treatments. It undergoes a maximum movement of 0.040 mm when centering a +5 diopter correction on the preoperative line of sight, whereas the corneal reflex, which is used for centering most topography systems, can move by more than 0.10 mm. CONCLUSIONS: Centration of the correction on the preoperative line of sight enabled good comparability between preoperative and postoperative measurements that use the line of sight as a reference axis. Yet, centration of the treatment on the preoperative line of sight does not ensure comparability between preoperative and postoperative measurements that use the corneal reflex as a reference axis such as most corneal topography systems. Axis shifts might lead to misinterpretation of data such as a wrong diagnosis of a decentered ablation or changes in the Zernike representation.

Computer Simulation↗
PubMed2006

Psychometric properties of measurement tools for quantifying knee joint position and movement: a systematic review.

This systematic review critically evaluates literature on the reliability and validity of measurement tools for quantifying knee joint angles and knee movement. A search was conducted of seven medical databases and one biomedical engineering database, yielding 43 articles that reported reliability or validity. Tools for quantifying knee joint angles included standard handheld goniometers, fluid-based goniometers, gravity-based goniometers, photographs and two dimensional (2-D) motion analysis. Knee movement was measured with electrogoniometers, 2-D and three dimensional (3-D) motion analysis. Intraclass correlation coefficients for testing knee angles ranged from 0.51-1.00 for intratester reliability and 0.43-0.99 for intertester reliability. For quantifying knee position, sequential MRI and 2-D had the least error of measurement, followed by hand held goniometers and photographs. For dynamic measurements, electrogoniometers and 3-D motion analysis were most reliable and had low error of measurement. Strong concurrent validity was found between hand held goniometers and radiographs, as well as between hand held goniometers and 3-D motion analysis.

Arthrometry, Articular↗