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Filtered backprojection (FBP) is an inadequate method to cope with inconsistencies in Radon space and, consequently, leads to artifacts in reconstructed CT images. A solution to this problem is given by statistical reconstruction methods like the Maximum-Likelihood Expectation-Maximization (MLEM) algorithm. The advantage of MLEM is that it allows to weight raw projection data during reconstruction. The method presented here consists of two steps. In a first step, inconsistent data in the Radon space were bridged using a directional interpolation scheme. Since these surrogate data are contaminated with residual inconsistencies, in a second step, the image is reconstructed using a weighted MLEM algorithm. In this work, the modified MLEM algorithm for metal artifact reduction in CT is presented for clinical hip prosthesis data. On the basis of image entropy the reconstruction success is evaluated. [ABSTRACT FROM AUTHOR]

The loss of accuracy during neuronavigation, caused by intraoperative changes of intracranial masses after trepanation, is one of the major problems in neurosurgery. It usually affects the planning and performing of surgery as both is conventionally based on preoperative patient data sets. Thus, an online acquisition and processing of data during surgery is needed to increase navigational accuracy. Beside cost-intensive solutions like intraoperative CT or MRI scanners, an ultrasound guided navigation is applicable and demonstrates online guidance in real-time. This study describes a development to provide the best possible support for neurosurgeons intraoperatively, concerning data presentation and ergonomic aspects in the operation theatre. Patients underwent MRI examination for a conventional neuronavigation preoperatively. Intraoperatively, ultrasound volume data sets were acquired by means of a tracked ultrasound probe and related to this preoperative MRI. The intraoperative ultrasound imaging was possible in all cases whereat ultrasound images were displayed beside the corresponding MRI images. Brain shift was presentable and the possibility of online navigation with ultrasound and preoperative MRI was helpful for the surgeon. [ABSTRACT FROM AUTHOR]

For capturing facial surfaces, different commercial systems are available. These conventional systems can be mainly divided into white-light-scanners, linear laser scanners and photogrammetric devices. The latest developments are based on holographic image acquisition. With all these devices shadowing effects will occur. These effects might be avoided by the use of a hand-held laser scanner with simultaneous registration. The T-Scan (Fa. Steinbichler, Germany [1]) is such a tracked scanning device. To assess the suitability of this scanner, a total of 16 scans (two infants with a lip-alveolus-palate cleft) were acquired by the same surgeon. Data sets with an accuracy of less than a millimetre were acquired. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

This article shows the development of a concept for a Thulium (Tm) laser scalpel at the emitting wavelength of 1.92 µm with a maximum output power of 60 W. The system is currently developed at the Medical Laser Center in Luebeck for a clinical investigation in minimal invasive surgery, e. g. to be used on liver and kidney. The concept includes technical construction as well as the design and usability referring to standards in medical engineering. The required documentation, design and the software were part of two diploma theses at the Institute of Biomedical Optics/University of Luebeck, Germany. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

A Laser-Scalpel system (StarMedTec, GmbH, Starnberg, Germany) emitting a wavelength at 1,94µm and a laser power at 16 W (cw mode) was used for partial resection of the porcine kidney in comparison to standard HF dissection device (Elektrotom 505, Berchtold, Tutlingen, Germany). Partial resection were performed on 6 kidneys, three with the Laser-Scalpel and three with the HF dissection device respectively. Blood lost was 11±10 ml with the Laser-Scalpel and 170±121 ml with the HF Dissector. Total resection time including haemostasis of the remaining tissue was 8,7±1,5 min with the Laser-Scalpel and 13,7±5,8 min with the HF dissection device. During resection with the Laser-Scalpel no occlusion of the blood supply of the kidney was needed compared to 6±2,2 min ischemic time by the use of the Elektrotom. In conclusion, the first experiments show that the 1,94 µm Laser-Scalpel is a very promising device for bloodless and fast kidney resection. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

We present an experimental setup for the goniometric measurement of non rotational symmetric phase functions in the whole solid angle. These asymmetric phase functions are usually found in biological tissues with an aligned microstructure like muscle, skin, tooth and various other tissues. A method for the measurement of thin slabs of tissue samples was developed. We present goniometric measurements of pork muscle und compare them with microscopic images. [ABSTRACT FROM AUTHOR]

In prosthetic dentistry many different prefabricated attachments are used for non-permanent fixation of dentures. A numerical model to evaluate the loading behavior of such a system in a realistic environment under different typical clinical loading situations was developed using Finite Element Analysis (FEA). The model was used to investigate the mechanical properties of one selected attachment system. [ABSTRACT FROM AUTHOR]

Organization and dynamics of cell membranes have a large impact on cellular uptake and release of various metabolites or pharmaceutical agents. Membranes of living cells are characterized using the membrane marker 6-dodecanoyl-2-dimethylamino naphthalene (Laurdan). Membranes are assessed by laser-assisted fluorescence microscopy, in particular a combination of microspectrofluorometry and total internal reflection fluorescence microscopy (TIRFM). Previously Membrane stiffness was related to spectral properties and expressed by the generalized polarization (GP), which depends on the phase of membrane lipids. GP generally decreased with temperature, and was always higher for the plasma membrane than for intracellular membranes. In addition, membrane fluidity was assessed by measurements of steady-state and time-resolved fluorescence anisotropy r(t), since with increasing viscosity, i. e. decreasing fluidity of the environment, the rotation of an excited molecule is impeded. The parallel and perpendicular components of the fluorescence emission from the sample were measured simultaneously using an imaging device with polarization sensitivity. In addition to GP, fluorescence anisotropy r(t) proved to be an independent measure for characterizing membrane dynamics. So far, membrane dynamics depended on temperature, growth phase as well as the on the intracellular amount of cholesterol. [ABSTRACT FROM AUTHOR]

Neurological impairments following cardio-pulmonary bypass (CPB) during open heart surgery can result from microembolism and ischaemia. Here we present results from monitoring cerebral hemodynamics during CPB with near infrared spatially resolved spectroscopy. In particular, the study has the objective (a) to monitor oxy- and deoxyhemoglobin concentrations (oxy-Hb, deoxy-Hb) and their changes during CPB surgery and (b) to develop and test algorithms for the calculation of these parameters from broad band spectroscopy. For this purpose a detection system was developed based on a lens imaging spectrograph designed to optimise sensitivity of recorded reflectance spectra for wavelengths between 600 and 1000 nm. Two independent detector channels for both cerebral hemispheres each with three source-detector distances are used. It is demonstrated that the system does record cerebral oxygenation parameters during CPB in infants with a significant decrease in oxygen saturation SO2 during cardiac arrest. The methodological focus is on an error estimation of the haemoglobin concentrations and separation of cerebral from skin signals. The depth sensitivity profile of the set-up is estimated with a layered structure model of tissue and Monte Carlo methods for the description of the photon propagation. [ABSTRACT FROM AUTHOR]

We have implemented a parallel two-dimensional finite difference time domain (FDTD) method to investigate the propagation of light in biological tissue. In particular we want to examine the dependence of the light propagation on the microstructure of tissue containing cylindrical scatterers. Therefore we performed simulations for a series of various tissue models of randomly distributed cylinders embedded in dielectric media with varying cylinder concentrations and tissue probe thickness. [ABSTRACT FROM AUTHOR]

Intraoperative optical imaging in neurosurgery has the potential to reduce morbidity during tumour resection. This method for identifying active functional areas of the cortex has been tested experimentally. In this work an equipment configuration for intraoperative use of optical imaging was developed. On the basis of phantom tests parameters for intraoperative data acquisition were determined. First clinical tests during tumour resection show that it is possible to acquire significant information with high spatial resolution about the activation of cortical tissue. [ABSTRACT FROM AUTHOR]

The measurement of skeletal muscle oxygenation by NIRS methods is obstructed by the subcutaneous adipose tissue which might vary between < 1 mm to more than 12 mm in thickness. A new algorithm is developed to minimize the effect of this lipid layer on the calculation of muscle haemoglobin / myoglobin concentrations. First, we demonstrate by comparison with ultrasound imaging that the optical lipid signal peaking at 930 nm is a good predictor of the adipose tissue thickness (ATT). Second, the algorithm is based on measurements of the wavelength dependence of the slope ΔA/Δρ of attenuation A with respect to source detector distance ρ and Monte Carlo simulations which estimate the muscle absorption coefficient based on this slope and the additional information of the ATT. This method is tested on experimental data measured on the vastus lateralis muscle of volunteers during an incremental cycling exercise during normal and hypoxic conditions (corresponding to 0, 2000 and 4000 m altitude). The experimental setup uses broad band detection between 700 and 1000 nm at six source-detector distances. We demonstrate that the description of the experimental data is improved and the calculated changes in oxygen saturation are markedly different when the ATT correction is included. [ABSTRACT FROM AUTHOR]

Since optical vibrational spectroscopy is exquisitely sensitive to the biochemical composition of the sample and variations therein, it is possible to monitor metabolic processes and biochemical states in tissue and cells. The chances of identifying spectral indicators of diseases are much more favourable when spectroscopic imaging methods are used. Such images permit a direct correlation between the spectroscopic information and the sample histopathology. The spectroscopic imaging methods, which are barely ten years old at this point in time, become now a valuable technique for biomedical applications. In this contribution we illustrate the capability and versatility of spectroscopic imaging on the example of identification and visualization of brain tumors. [ABSTRACT FROM AUTHOR]

Membrane dynamics -including membrane stiffness and fluidity- are important features of living cells. These parameters have a large impact on cellular uptake and release of metabolites or pharmaceutical agents and may be used for in vitro diagnostics. For assessment of these parameters we used a combination of conventional and total internal reflection fluorescence microscopy (TIRFM) as well as fluorescence decay kinetics. Laurdan, a polarity-sensitive fluorescent probe, whose electronic excitation energy is different in polar and non-polar environment proved to be useful for membrane studies, since its generalized polarization (GP, characterizing a spectral shift which depends on the phase of membrane lipids) and fluorescence lifetime (τ) revealed to be appropriate measures for membrane stiffness and fluidity. GP generally decreased with increasing temperatures and was always higher for the plasma membrane than for the intracellular membranes. Furthermore, GP appeared to increase during cell growth and upon aging of the cells. A specific role of cholesterol content on these findings was now examined using defined protocols of cholesterol depletion and enrichment. In addition to the decrease of GP with increasing temperature, the GP values showed a pronounced increase upon enrichment and a decrease upon depletion of cholesterol. Cholesterol content also had a large impact on fluorescence lifetime in the subnanosecond range. GP and τ were determined as integral values of single cells or small cell collectives and were also displayed as images with subnanosecond time resolution. [ABSTRACT FROM AUTHOR]

A novel setup for fluorescence measurements of surfaces of biological samples, in particular the plasma membrane of living cells, is described. The method is based on splitting of a laser beam and multiple total internal reflections (TIR) within the bottom of a microtiter plate, such that up to 96 individual samples are illuminated simultaneously by an evanescent electromagnetic field. In general, two different screening procedures (1) High Throughput Screening (HTS) and (2) High Content Screening (HCS) are distinguished, where in the first case a rapid measurement of large sample numbers, and in the second case a high information content from a single sample is achieved. In particular, a HCS system for the parameters fluorescence lifetime (Fluorescence Lifetime Screening, FLiS) and fluorescence anisotropy (Fluorescence Lifetime Polarization Screening, FLiPS) has been established and integrated into an existing HTS-system. While fluorescence lifetime represents a general measure for the interaction of a marker molecule with its molecular or cellular environment, fluorescence anisotropy corresponds to the time of rotation of this molecule from a position with defined orientation into a position with arbitrary orientation and reflects directly the viscosity of the environment and thus membrane fluidity. For fluorescence lifetime screening (FLiS) and fluorescence lifetime polarization screening (FLiPS) fluorescent membrane markers, intercalating into cell membranes, were applied to an established human glioblastoma cell line (U373-MG). [ABSTRACT FROM AUTHOR]

We evaluated the influence of optical property maps on inversion of fluorescence data from mice. For highly absorbing regions (5x background) of sufficient size, heterogeneous optical property maps provide significant improvements over homogeneous maps. [ABSTRACT FROM AUTHOR]

A multiscale description of the light propagation in biological tissue is presented. The Maxwell's equations, the transport equation, and the diffusion equation are applied for the description on the microscopic, mesoscopic, and macroscopic scale, respectively. The modus operandi of the multiscale approach is illustrated for the case of tendon tissue. It is shown that the aligned microstructure of tendon strongly influences the light propagation in the tissue. [ABSTRACT FROM AUTHOR]

Fourier domain optical coherence tomography (FD-OCT) was used to take cross-sectional images of the skin at the forehead, back of hand and back of volunteers. The aim of the occupational health study was the investigation of the natural sun protection of outdoor workers and in particular the quantification of the UV induced epidermal thickening. A set of manually segmented OCT images was used as a gold standard to evaluate the performance of automatic algorithms for finding the epidermal thickness. The established A-scan averaging method and two newly developed automatic algorithms were compared. The first of the new methods is based on Markov random chains and the second new and best performing algorithm is based on a convolution filter with a trace finding routine with a quadratic cost function. Although the results of all algorithms differ in the absolute values for the epidermal thickness, they all show the same tendencies. There is a strong dependency of epidermal thickness on skin site, a weak dependency on the season of the year and a noticeable epidermal thickening 7 days of recovery after UV induced erythema. [ABSTRACT FROM AUTHOR]

Optical coherence tomography (OCT) is an emerging biomedical imaging technology which gives high-resolution sectional images of light scattering tissue down to a depth of a few millimeter. The objective of this work is to combine OCT with an operation microscope. A spectral domain OCT was adapted via a specially designed scanning optics to the camera port of an operation microscope. This enables a non-contact on-line OCT during different medical applications. Hidden tissue structures were visualized with a resolution below 30 µm. As a first example for an application in otolaryngology we demonstrated that the OCT operation microscope is basically able to reveal parts of the cochlear morphology without opening its enveloping membranes. Thus it may serve as a helpful guide for the surgeon to exactly localize the scala tympani before opening the fluid-filled inner ear for inserting the electrode array of cochlear implants. [ABSTRACT FROM AUTHOR]