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ABSTRACT: Carbon monoxide (CO) detection in human breath is the focus of much research because of CO's possible use as a marker molecule for different diseases. Detecting CO in human breath remains a tough challenge because of the low concentrations of CO (ppm range) that must be detected. Another problem is that many other molecules, which can be found in human breath, can interfere in these measurements. Additionally, a time resolution of less than 1 s is needed to resolve the CO curve of an exhalation. In this study (13)CO instead of (12)CO concentration is measured. The measurements are performed with a cavity leak-out spectroscopy system. The system's properties match the above-mentioned specifications for measurements, even of the rare isotopologue with high specificity, a time resolution of less than 1 s and a detection limit of 7 ppb Hz(-1/2). Two investigations are presented here. The first is a measurement showing intraday changes between 9.5% and 23.3% of the exhaled CO level due to vigorous exercise. The second shows a long-term observation of the CO base level revealing natural variations in the recorded CO concentration. The covered time period is 25 weeks during which the differences between the minimum and maximum CO levels for each test case reached 84%.
Journal of Breath Research 12/2010; 4(4):047101. · 2.54 Impact Factor
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ABSTRACT: For medical applications, erbium lasers are usually equipped with articulated mirror arms or special glass fibers. However, only with mirror arms is it so far possible to transmit high average powers or pulse energies in the region of 1 J to achieve suitable energy densities for fast tissue preparation. An alternative to the glass fiber systems mentioned above are liquid-core light guides. An extremely flexible liquid-core light guide was used to connect a dental Er:YAG laser system to an especially adapted dental laser applicator. The core liquid was continuously circulated during laser irradiation to transmit pulse energies up to 1.1 J. A modified laser handpiece was used for exemplary clinical treatment. The experimental setup with the highly flexible light guide was completed successfully, and its ease of handling for a dental surgeon was demonstrated in the clinical treatment of leukoplakia of the oral cheek mucosa. Complete ablation of the epithelium with the laser was performed. One year postoperatively, the patient remains disease-free. This article describes the technical realization of a liquid-core light guide system for medical applications. We report about the first successful clinical treatment of oral hyperkeratosis using this new light guide technology.
Lasers in Medical Science 09/2010; 25(5):669-73. · 2.00 Impact Factor
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ABSTRACT: The aim of the study was to compare the histological results after complete osteotomies of the sheep tibia using either the prototype carbon dioxide (CO(2)) laser osteotome 'OsteoLAS' (n = 12) or an oscillating saw (n = 12). The laser parameters were as follows: wavelength 10.6 microm; energy of laser pulses 75-85 mJ; pulse duration 80 mus; pulse repetition rate 200 Hz; spot diameter 460 mum (1/e(2) level); radiant exposure 45-51 J/cm(2); peak irradiance 0.56-0.64 MW/cm(2). Both groups were divided into two subgroups (n = 6), and the animals were killed after 4 weeks or 12 weeks, respectively. Light and fluorescence microscopy with semiquantitative analysis and histomorphometry were performed to compare bone healing. Charring-free laser osteotomies were possible up to a depth of 20 mm with the short-pulsed CO(2) laser. The laser, however, required a significantly longer time to perform, and a wedge-shaped gap was present on the cis-cortex. After 4 weeks the osteotomy gaps were almost unchanged in both groups and filled with connective tissue. After 12 weeks the gaps were filled with newly formed bone in both groups. Primary gap healing was predominant in the laser group and longitudinal cortical remodelling in the control group. On a cellular level, no fundamental differences were observed for early and late stages of bone healing. Further research has to be focussed on improving the CO(2) laser ostetome in order to reduce the long duration of the laser osteotomy and the necessity of creating a wedge-shaped cut in thick bones.
Lasers in Medical Science 09/2009; 25(2):239-49. · 2.00 Impact Factor
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ABSTRACT: Facial reconstruction can be used as a forensic technique to identify a person, when no other identification method is applicable. The facial soft tissue thickness applied to the skull is crucial when performing an accurate facial reconstruction. Historically, scientists developed several techniques to measure the soft tissue of the face. It was their aim, to build a database of a unique point-set, differentiated by gender, age, ethnic origin, BMI. All used a limited number of landmarks and an inaccurate measuring technique. We developed a contact-free and precise measuring technique, using low-dose CT and holographic data. Due to the extremely short exposure time, the holographic measurement is very precise. We lay out our first experiences to create a facial soft tissue layer map of the face.
Forensic Science Medicine and Pathology 05/2009; 5(1):11-6. · 1.44 Impact Factor
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ABSTRACT: This paper presents a shape-from-focus method, which is improved with regard to the mathematical operator used for contrast measurement, the selection of the neighborhood size, surface refinement through interpolation, and surface postprocessing. Three-dimensional models of living human faces are presented with such a high resolution that single hairs are visible.
IEEE Transactions on Image Processing 02/2009; 18(1):151-7. · 3.04 Impact Factor
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ABSTRACT: A precise cochleostomy is a crucial step in cochlear implantation, particularly if residual hearing is to be preserved. A contactless ablation of the promontory bone by a pulsed CO(2) laser system seems to be a promising approach. The bone is removed by a scan head controlled laser beam in sequential scan cycles with a pulse rate of 50-100 mus. Digital picture analysis and pattern detection are used to identify the membranous lining of the cochlea. We achieved a bone ablation in a micrometer range per scan cycle with the laser. A perforation of the promontory bone could be detected by automatic pattern detection. The enhancement of automatic pattern detection can lead to a minimally invasive, function-preserving laser cochleostomy.
Cochlear implants international 02/2009; 10 Suppl 1:58-62.
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ABSTRACT: Accurate characterization of the biochemical pathways of nitric oxide (NO) is essential for investigations in the field of NO research. To analyze the different reaction pathways of enzymatic and non-enzymatic NO formation, determination of the source of NO is crucial. Measuring NO-related products in biological samples distinguishing between (14)NO and (15)NO offers the opportunity to specifically analyze NO signaling in blood and tissue. The aim of this study was to establish a highly sensitive technique for the specific measurement of NO in an isotopologue-selective manner in biological samples. With the cavity leak-out spectroscopy setup (CALOS) a differentiation between (14)NO and (15)NO is feasible. We describe here the employment of this method for measurements in biological samples. Certified gas mixtures of (14)NO/N(2) and (15)NO/N(2) were used to calibrate the system. (14)NO2- and (15)NO2- of aqueous and biological samples were reduced in a triiodide solution, and the NO released was detected via CALOS. Gas-phase chemiluminescence detection (CLD) was used for evaluation. The correlation received for both methods for the detection of NO in the gas phase was r=0.999, p<0.0001. Results obtained using aqueous and biological samples verified that CALOS enables NO measurements with high accuracy (detection limit for (14)NO2- 0.3 pmol and (15)NO2- 0.5 pmol; correlation (14)NO: p<0.0001, r=0.975, (15)NO: p<0.0001, r=0.969). The CALOS assay represents an extension of NO measurements in biological samples, allowing specific investigations of enzymatic and non-enzymatic NO formation and metabolism in a variety of samples.
Nitric Oxide 08/2008; 19(1):50-6. · 3.55 Impact Factor
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ABSTRACT: Comparison of two different methods for the measurement of ethane at the parts-per-billion (ppb) level is reported. We used cavity leak-out spectroscopy (CALOS) in the 3 microm wavelength region and gas chromatography-flame ionization detection (GC-FID) for the analysis of various gas samples containing ethane fractions in synthetic air. Intraday and interday reproducibilities were studied. Intercomparing the results of two series involving seven samples with ethane mixing ratios ranging from 0.5 to 100 ppb, we found a reasonable agreement between both methods. The scatter plot of GC-FID data versus CALOS data yields a linear regression slope of 1.07 +/- 0.03. Furthermore, some of the ethane mixtures were checked over the course of 1 year, which proved the long-term stability of the ethane mixing ratio. We conclude that CALOS shows equivalent ethane analysis precision compared to GC-FID, with the significant advantage of a much higher time resolution (<1 s) since there is no requirement for sample preconcentration. This opens new analytical possibilities, e.g., for real-time monitoring of ethane traces in exhaled human breath.
Analytical Chemistry 04/2008; 80(8):2768-73. · 5.86 Impact Factor
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ABSTRACT: The purpose of this study was to examine for the first time the feasibility of performing complete osteotomy of sheep tibia using a computer-guided CO2-laser osteotome, and to examine bone healing under functional loading.
Bone cutting without aggravating thermal side effects has been demonstrated with scanning CO2-laser osteotomy. Further research is necessary to develop a clinically usable laser osteotome, which may allow new types of bone surgical procedures.
The scanning parameters for performing tibial osteotomies were determined in preliminary ex vivo trials. Osteotomies were performed in the mid-diaphysis of sheep tibia using either the prototype laser osteotome (osteoLAS, study group; n = 12), or an oscillating saw (control group; n = 12). Both groups were divided into two subgroups each (n = 6), and the two groups were sacrificed after 4 and 12 wk. Radiographs were taken postoperatively and after 4, 8, and 12 wk to compare the course of bone healing.
Laser osteotomies of sheep tibia up to a depth of 20 mm were possible without visible thermal damage to the bone. A sequential PC-controlled cut geometry with artificial widening of the osteotomy gap was required for a complete osteotomy. Both clinically and radiologically, the laser and control groups showed undisturbed primary gap healing. Bone healing was similar and undelayed after both laser osteotomy and osteotomy done by mechanical saw.
Osteotomy of multi-layered bones with a scanning CO2-laser demonstrates clinical and radiological healing patterns comparable to those seen with osteotomy done by standard mechanical instruments. It is, however, a technically demanding procedure, and complete laser osteotomies of long bones are only reasonable in bones with a diameter <20 mm, which will likely restrict the use of this technique to bones 7-10 mm thick. Through the use of computer guidance, extremely precise osteotomies and sophisticated cut geometries are possible using this technique. For practical applications, precise control of the depth of laser cutting and easier manipulation of the osteotome are required.
Photomedicine and Laser Surgery 04/2008; 26(2):129-36. · 1.25 Impact Factor
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ABSTRACT: This review describes the merits of laser-assisted analytical instrumentation for biomedical diagnostics. In particular, we
present an overview of the recent progress on spectroscopic online monitoring of exhaled breath with mid-infrared coherent
sources. The current detection limits of laser spectroscopic approaches are in the picomolar to nanomolar range, depending
on the molecular compound. The time resolution of the measurements is down to the sub-second range. This very high sensitivity
and time resolution open up exciting perspectives for novel analytical tasks in biomedical research and clinical diagnosis.
Keywords: laser absorption spectroscopy; trace gas monitoring; cavity ring-down; exhaled breath
12/2007: pages 535-555;
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ABSTRACT: Despite the growing number of reports on breath CO measurements, the development of rapid and sensitive analysis techniques for measurements of this breath constituent still remains a challenge. We demonstrate the application of infrared laser spectroscopy for exhaled CO analysis. The breath samples are analyzed in real-time during single exhalations by means of cavity ring-down spectroscopy. This is an ultra-sensitive laser-based method for the analysis of trace gases with precision on the ppb level (parts per billion). The noise-equivalent CO level of this method is 7 ppb Hz(-1/2); the time resolution is around 1 s. The expirograms were recorded with exhalation flow rates varying from 4 l min(-1) up to 50 l min(-1). Alveolar phase (phase III) of expiration shows a remarkable flow-rate dependence. Also, expirograms were recorded after a breath holding time between 0 s and 60 s. The normalized slope of the alveolar plateau (S(n)) was determined, which is between 0.004 l(-1) and 0.15 l(-1).
Journal of Breath Research 09/2007; 1(1):014002. · 2.54 Impact Factor
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ABSTRACT: Digital sensors and fast digital image processing facilitate the use of pulsed holography for 3D surface measurement of moving objects. The real image of a hologram is reconstructed optically. A sequence of high-resolution projection images of the real image with a varying distance to the hologram is recorded digitally. Focus detection in this image sequence by digital image processing yields the shape of the recorded object. The image intensity serves as a precise pixel-matching texture. An application of this concept is the generation of a textured 3D computer model of a facial surface from a portrait hologram.
Applied Optics 05/2007; 46(11):1986-93. · 1.41 Impact Factor
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ABSTRACT: For medical application in the field of maxillofacial surgery, a highly resolved 3D digital representation of the human face
is needed. Especially moving objects, i.e. infant patients are hard to capture with conventional systems. We eliminated moveable
artifacts systematically by using eye safe holographic recording with short pulsed lasers (Nd:YLF laser, 526.5 nm wavelength).
With a single pulse (35 ns, 1,4 J energy), surface data are recorded. Our conventional system uses an analogue process, where
the hologram is reconstructed optically and digitized slice-by-slice.
We explored the possibility for a complete digital process. The conventional analogue recording material is replaced by a
CCD-sensor with significantly lower pulse energy (0.1 mJ) for exposure. Numerical reconstruction of the real image is performed
on a computer using appropriate algorithms. Surface calculations can follow immediately. Using this digital holographic approach
to measure 3D surfaces means, that processing time, costs and effort can be reduced. However, in terms of resolution, digital
technology lags behind the capabilities of our current analogue method for 3D surface detection. This involves inherent limitations
at the current technological state of sensor technology. Nevertheless first applications are already possible.
12/2006: pages 435-440;
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ABSTRACT: Thermal side effects are the main problems concerning laser osteotomy. Data of the temperature increase in the vicinity of
the laser cut for different irradiation conditions are important for understanding and optimisation of the laser ablation
process. The first temperature measurements were done with an IR-camera (Flir SC 3000, spectral sensitivity 7.5 – 10 µm) from
the back side of a bone plate (compact bone of bull femur) during drilling. The ablation is carried out with a TEA CO2 laser (λ = 10.6 µm, pulse duration 1 µs and focus diameter 230 µm (1/e2 level)). In another series of experiments the temperature was monitored during multi-pass cutting with the same laser. The
temperature was investigated depending on the laser pulse energy, pulse repetition rate and beam scanning velocity and the
settings of the cooling spray. Room temperature was amounted to 23 °C. The temperature during the laser drilling (50 Hz, 30
mJ) grows up to 400°C (5 min, pressurised air jet cooling) respectively to 120 °C (3 min.) with a water spray cooling. During
the laser multi-pass bone cutting with the use of a water spray and a scanning velocity of 2 mm/s the temperature reaches
only 30 °C. These examinations emphasise that laser cutting is not dangerous for living bone cells under optimal conditions.
The results of the temperature measurements during laser ablation are compared to the test results during mechanical abrasion.
They underline that laser cutting of bones and mechanical abrasion show temperatures of an equal level. One strong advantage
of laser cutting of bone is the nearly arbitrary cut geometry which could lead to an improvement in surgery.
12/2006: pages 419-424;
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ABSTRACT: We present an overview of the recent progress on spectroscopic online monitoring of exhaled breath with mid-infrared coherent
sources. The current detection limits of laser spectroscopic approaches are in the picomolar to nanomolar range, depending
on the molecular compound. The time resolution of the measurements is down to the sub-second range. This very high sensitivity
and time resolution open up exciting perspectives for novel analytical tasks in biomedical research and clinical diagnosis.
12/2006: pages 441-446;
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ABSTRACT: Non-contact laser osteotomy offers new opportunities in various surgical fields, since it allows very precise pre-programmed
incisions with completely free geometry. However laser osteotomy is a demanding task, because bone is a tough composite material,
which is at the same time a living tissue and sensitive to temperature increases. Besides thermal side effects, practical
laser applicability was limited until now because of very low cutting rates and limited incision depths. We discuss how to
overcome these disadvantages by means of an optimal arrangement of thermo-mechanical ablation with a pulsed CO2 laser and with a water-spray as an assisting media. To this arrangement belong optimal pulse duration, irradiance and radiant
exposure of the laser pulses, as well as multi-pass cutting procedures. Effective ablation of hard bone tissue with minimal
thermal damage is possible with relatively long CO2 laser pulses of 80 µs duration and an average laser power of up to 40 W. To overcome the depth limitation special scanning
techniques, which allow deep incisions even in thick multi-layer bones in feasible irradiation times, were developed in our
group.
12/2006: pages 453-457;
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ABSTRACT: The advantages of laser osteotomy are free cut geometry and minimal thermal damage. Due to the lack of haptic feedback there
is need for an alternate feedback method for accurate Laser Osteotomy. Based on the frequency analysis of the acoustic signal,
generated by the ablation process, we are developing a feedback system to obtain in situ information on the ablation and for
differentiation between different sorts of biological tissue. We used a pulsed slab CO2-laser (wavelength 10.6 µm, pulse length 80 µs) and piezoelectric sensors for sound detection. We studied the correlation
of the ablation signal of different kinds of tissue in the frequency domain.
12/2006: pages 425-430;
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ABSTRACT: We present an overview of our recent progress on spectroscopic trace gas detection for biomedical applications. The latest developments of cavity-enhanced spectroscopy as well as magnetic rotation spectroscopy lead to unprecedented sensitivity and specificity. The current detection limits of our laser spectroscopic approaches are in the picomolar to nanomolar range, depending on the molecular compound. The time resolution of the measurements is down to the sub-second range. This very high sensitivity and time resolution open up exciting perspectives for novel analytical tasks in biomedical research and clinical diagnosis.
Spectrochimica Acta Part A Molecular and Biomolecular Spectroscopy 05/2006; 63(5):963-9. · 2.10 Impact Factor
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ABSTRACT: We present a ring-down absorption spectrometer based on a continuous-wave CO laser in the mid-infrared spectral region near lambda = 5 microm. Using a linear ring-down cavity (length: 0.5 m) with high reflective mirrors (R = 99.988 %), we observed a noise-equivalent absorption coefficient of 3 x 10(-10) cm(-1)Hz(-1/2). This corresponds to a noise-equivalent concentration of 800 parts per trillion (ppt) for (14)NO and 40 ppt for (15)NO in 1 s averaging time. We achieve a time resolution of 1 s which allows time resolved simultaneous detection of the two N isotopes. The delta(15)N value was obtained with a precision of +/-1.2 per thousand in a sample with a NO fraction of 11 ppm. The simultaneous detection enables the use of (15)NO as a tracer molecule for endogenous biomedical processes.
Isotopes in Environmental and Health Studies 01/2006; 41(4):303-11. · 0.90 Impact Factor
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ABSTRACT: We report first results of animal trials using an improved laser osteotomy technique. This technique allows effective bone cutting without the usual thermal tissue damage.
A comparative in vivo study on mandibles of seven canines was done with a mechanical saw and a CO(2) laser based osteotome with a pulse duration of 80 microseconds. The laser incisions were performed in a multipass mode using a PC-controlled galvanic beam scanner and an assisting water spray.
A complete healing through a whole bony rearrangement of the osteotomy gap with newly build lamellar Haversian bone was observed 22 days after the laser operations under optimal irradiation conditions.
An effective CO(2) laser osteotomy without aggravating thermal side effects and healing delay is possible using the described irradiation technique. It allows an arbitrary cut geometry and may result in new advantageous bone surgery procedures.
Lasers in Surgery and Medicine 09/2005; 37(2):144-8. · 2.75 Impact Factor
