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2007 | Buch

Advances in Medical Engineering

herausgegeben von: Professor Dr. Thorsten M. Buzug, Professor Dr. Dietrich Holz, Professor Dr. Jens Bongartz, Professor Dr. Matthias Kohl-Bareis, Professor Dr. Ulrich Hartmann, Dr. Simone Weber

Verlag: Springer Berlin Heidelberg

Buchreihe : Springer Proceedings in Physics

insite
SUCHEN

Über dieses Buch

In this book, research and development trends of physics, engineering, mathematics and computer sciences in biomedical engineering are presented. Contributions from industry, clinics, universities and research labs with foci on medical imaging (CT, MRT, US, PET, SPECT etc.), medical image processing (segmentation, registration, visualization etc.), computer-assisted surgery (medical robotics, navigation), biomechanics (motion analysis, accident research, computer in sports, ergonomics etc.), biomedical optics (OCT, soft-tissue optics, optical monitoring etc.) and laser medicine (tissue ablation, gas analytics, topometry etc.) give insight to recent engineering, clinical and mathematical studies.

Inhaltsverzeichnis

Frontmatter

Invited Paper

Frontmatter
Modelling and Imaging Electrophysiology and Contraction of the Heart

A computer model of the human heart is presented, that starts with the electrophysiology of single myocardial cells including all relevant ion channels, spans the de- and repolarization of the heart including the generation of the Electrocardiogram (ECG) and ends with the contraction of the heart that can be measured using 4D Magnetic Resonance Imaging (MRI). The model can be used to better understand physiology and pathophysiology of the heart, to improve diagnostics of infarction and arrhythmia and to enable quantitative therapy planning. It can also be used as a regularization tool to gain better solutions of the ill-posed inverse problem of ECG. Movies of the evolution of electrophysiology of the heart can be reconstructed from Body Surface Potential Maps (BSPM) and MRI, leading to a new non-invasive medical imaging technique.

Olaf Dössel, Dima Farina, Matthias Mohr, Matthias Reumann, Gunnar Seemann, Daniel L. Weiss

Medical Imaging

Frontmatter
Influence of Corrections During Image Reconstruction on the Spatial Resolution of ClearPET Neuro

The small-animal PET scanner ClearPET Neuro developed at the Research Centre in Jülich is based on an unconventional scanner geometry. It represents axial and transaxial gaps that lead to sinograms with missing data. Images reconstructed from uncorrected data include artefacts and a high variation of spatial resolution between different slices. Methods to compensate these artefacts are applied by taking the geometrical sensitivity into account. In this work the effects of compensation strategies with regard to the slice by slice variation of spatial resolution are examined.

Christine Steenkamp, Simone Weber, Brigitte Gundlich, Patrick Musmann, Thosten M. Buzug
Dynamic Reconstruction for the ClearPET™ Neuro Using Temporal B-Splines

Dynamic reconstruction methods are studied for the small animal PET (positron emission tomography) scanner ClearPET™ Neuro. In dynamic reconstruction the data are usually sorted into timeframes and reconstructed independently of each other. Using this timeframe approach, an appropriate trade-off between time resolution and noise has to be found. A more advanced method is dynamic reconstruction with temporal basis functions, where voxel values are time dependent modeled as weighted sum of basis functions. In a simulated example list-mode data are generated for the ClearPET™ Neuro and reconstructed with timeframe reconstruction and with dynamic reconstruction using B-Splines as temporal basis functions. Time activity curves are computed for various reconstructions with different timeframes and B-Splines. The example demonstrates the potential of dynamic reconstruction with temporal B-Splines.

Brigitte Gundlich, Patrick Musmann, Simone Weber
Local Compensation for Respiratory Motion in List-mode PET

In this work we present a method to estimate and compensate the local motion of a hot region in a PET list-mode acquisition directly on the measured LORs. The method is applicable for arbitrary motion patterns. Different shapes of the hot regions, different contrast ratios and different count statistics are examined. In a simulated anatomical data set the algorithm has recovered 98% of the true activity in a lung lesion with respiratory motion.

Ralph Brinks, Marc Busch
Hybrid Imaging with SPECT/CT — Presentation of 5 Cases

Combined SPECT/CT imaging in one device is one of the latest developments in medical imaging. Performing SPECT (Single Photon Emission Computed Tomography) and CT (Computed Tomography) one after the other with a single machine can avoid many artifacts due to different patient positioning. To our experience an automatic and precise fusion of the images can be achieved in most cases. Tissue which is moving during the examination (e.g. lungs, heart) still causes artifacts when the data is fused.

S. Berg, B. -I. Börner, H. Rasch, J. Müller-Brand, G. Bongartz
The λ-MLEM Algorithm: An Iterative Reconstruction Technique for Metal Artifact Reduction in CT Images

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.

May Oehler, Thorsten M. Buzug
Quantification of Tissue Microcirculation by Dynamic MRI and CT: Comparative Analysis of Signal-Time Courses Measured in Muscle Tissue

Quantitative analysis of microcirculatory parameters from dynamic MRI data is seriously hampered by the fact that the MR signal is not only affected by the local concentration of the contrast agent administered and the measurement sequence used but also by MR-specific processes, such as proton relaxation enhancement and water exchange between tissue compartments. It was thus the aim of our investigation to assess the reliability of an MRI approach developed by our group by comparing microcirculatory parameters estimated for muscle tissue with those determined from dynamic CT scans. The analysis yielded a good agreement between the tracer-independent parameters estimated from signal-time courses determined by both imaging modalities in muscle tissue.

G. Brix, J. Griebel, S. Delorme, F. Kiessling
A Numerical Investigation of RF Heating Effects on Implants During MRI Compared to Experimental Measurements

A numerical model was developed to examine relationships between energy absorption rate (SAR) and temperature distributions in of a phantom containing a hip prostheses implant during radio frequency deposition in MRI. Calculations of SAR and the resulting temperature increases were performed for different frequencies, i.e. B

0

values of 1T, 1.5T, and 3.0T. Experimental measurements at B

0

=1.5T are compared to the numerical results yielding good qualitative agreement. Attempts to ensure RF safety in MRI often rely on assumptions about local temperature from local SAR levels. In case of patients with implants calculations of temperature may be preferable to calculations of SAR because of the more direct relationship between temperature and safety.

Jens Stenschke, Dan Li, Maike Thomann, Gregor Schaefers, Waldemar Zylka
Real Time Neuronavigation Using 3-D Ultrasound and MRI in Patients with Brain Tumor

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.

Martin Engelhardt, Christian Hansen, Bernhard Brendel, Stephanie Hold, Christopher Brenke, Ioannis Pechlivanis, Albrecht Harders, Helmut Ermert, Kirsten Schmieder
Vasodynamics of the Murine Arteria Saphena by Optical Coherence Tomography

To investigate the pathogenesis of arteriosclerosis and its negative effects on the vasodynamics,

in vitro

experiments on isolated blood vessels as well as

in vivo

experiments are essential. The isometric force measurement commonly used to analyse the vasoconstriction of isolated blood vessels can not be applied in the

in vivo

situation. In contrast Optical Coherence Tomography (OCT) allows the acquisition of 2D cross sectional images und 3D cross sectional image stacks of vessel sections. We demonstrate that our two Fourier domain OCT-systems with their automated image analysis are suitable investigative tools for studying the stage of arteriosclerotic plaque formation as well as for examining the response of the blood vessel to vasomotor stimuli in the mouse model.

Julia Walther, Sven Meißner, Gregor Müller, Alexander Krüger, Henning Morawietz, Edmund Koch
An Imaging System in the Sub Millimeter Area

The millimeter wave frequency range was pushed through test systems for production lines in the last years. Non destructive test systems for quality control need more powerful sensors to detect non-metallic pollutions inside packages. The millimeter wave frequency range up to the lower terahertz frequencies (T-ray imaging) offers the opportunity to look through many packages. Alternative applications are the detection of non metallic and/or under cloth wearied weapons. Other fields of interest for this frequency range are medical applications, especially the detection of skin cancer.

Christian Krebs, Thorsten M. Buzug, Dirk Nüßler
Mutual Attraction of Oscillating Microbubbles

The driving of contrast microbubbles towards a boundary by means of primary radiation forces has been of interest for ultrasound-assisted drug delivery. Secondary radiation forces, resulting from oscillating microbubbles under ultrasound insonification, may cause the mutual attraction and subsequent coalescence of contrast microbubbles. This phenomenon has been less studied. Microbubbles with a negligible shell can be forced to translate towards each other at relatively low mechanical indices (MI). Thick-shelled microbubbles would require a higher MI to be moved. However, at high MI, microbubble disruption is expected. We investigated if thick-shelled contrast agent microbubbles can be forced to cluster at high-MI. The thick-shelled contrast agent M1639, inserted through a cellulose capillary, was subjected to 3 MHz, high-MI pulsed ultrasound from a commercial ultrasound machine, and synchronously captured through a high numerical aperture microscope. The agent showed the ultrasound-induced formation of bubble clusters, and the translation thereof towards the capillary boundary. Hence, forced translation and clustering of thick-shelled contrast microbubbles is feasible. The phase difference between the excursion of the oscillating bubble and the incident sound field was computed for free and encapsulated bubbles. There is a transition in phase difference for encapsulated bubbles, owing to the friction of the shell. Therefore, approach velocities of encapsulated bubbles may not be comparable to those of free gas bubbles.

Michiel Postema, Michał Mleczko, Georg Schmitz
A new Imaging Data Fusion System for Application in Neurosurgery and Multimodality Phantoms for System Evaluation

A new system has been developed to register imaging data from different modalities (CT, MRI, ultrasound, angiography, DTI, fMRI, and others) and afterwards to process and to visualise these data on an autostereoscopic 3D-display with the possibility to navigate interactively with a 3D-mouse in the virtual data space. The system shall be used in operation planning and intraoperative navigation in neurosurgery. To determine the precision of the image processing, the visualisation and the navigation processes, a deformable head phantom with simulated tumour objects for multimodality imaging is developed.

Julia Oestreich, Falk Uhlemann, Tobias Meyer, Annett Werner, Matthias Kirsch, Ute Morgenstern
CCD-Video Endoscope Subjected to X-Ray

In minimally invasive surgery video endoscopes show salt-and-pepper artifacts when used together with an X-ray device. Since the semiconductor material of the CCD chip interacts with the X-ray photons via photoelectric absorption and Compton scattering, it is not clear if these interactions produce irreversible damages within a typical working window in all day use in a clinical environment. The present study was accomplished at the X-ray Lab of the RheinAhrCampus Remagen in the period between March and July 2006. It deals with the question if a CCD chip of a modern medical endoscope undergo irreversible alterations during a 28 hour radiation load using a commercial C-arm. The report describes the experimental set-up and the characteristic properties for CCD quality assessment, i.e. temporal behaviour of background noise and statistics of X-ray affected pixels of the CCD chip. We do not find any indication of a permanent quality degradation of the CCD chip after 28 hour X-ray exposure.

Lucas Pfaffmann, Ronny Hübl, Thorsten M. Buzug
MRI Based Attenuation Correction for Brain PET Images

This work describes a procedure to yield attenuation maps from MR images which are used for the absorption correction (AC) of brain PET data. Such an approach could be mandatory for future combined PET and MRI scanners, which probably do not include a transmission facility. T1-weighted MR images were segmented into brain tissue, bone, soft tissue, and sinus; attenuation coefficients corresponding to elemental composition and density as well as to 511 keV photon energy were respectively assigned. Attenuation maps containing up to four compartments were created and forward projected into sinograms with attenuation factors which then were used for AC during reconstruction of FDG-PET data. The commonly used AC based on a radioactive (

68

Ge) transmission scan served as reference. The reconstructed radioactivity values obtained with the MRI-based AC were about 20% lower than those obtained with PET-based AC if the skull was not taken into account. Considering the skull the difference was still about 10%. Our investigations demonstrate the feasibility of a MRI-based AC, but revealed also the necessity of a satisfying delineation of bone thickness which tends to be underestimated in our first approach of T1-weighted MR image segmentation.

Elena Rota Kops, Peng Qin, Mattea Müller-Veggian, Hans Herzog
Integration of Functional Data (PET) into Brain Surgery Planning and Neuronavigation

There are distinct advantages of including functional data from PET into surgery planning and neuronavigation: tumor delineation and localization of functional areas. Preoperative intervention planning in brain tumours poses many additional challenges if the goal is to include functional data from PET for neuronavigation: co-registration of multimodal image data (MRI and PET) is conceptually the most demanding task. However, we find that associated problems of visualization, data transfer, documentation and, in general terms, quality assurance are often underestimated. We address some of these problems, including visual inspection of co-registration accuracy, preparation of image data, DICOM capabilities and “electronic documentation” [1].

Stefan Vollmar, Jürgen A. Hampl, Lutz Kracht, Karl Herholz
Comparison of long-T2 Suppression Techniques for 3D Ultrashort Echo-Time Imaging

In this study two different approaches for long-T

2

component suppression in ultrashort TE (UTE) imaging haven been investigated. The aim was to improve depiction of short-T

2

components by means of the UTE technique.

A “dual-echo” and a magnetization-preparation technique were implemented on clinical scanners operating at 1.5T and 3.0T field strength. 3D images obtained in healthy volunteer examinations using both approaches were compared with respect to short-T

2

SNR, long-T

2

suppression quality as well as scan efficiency. A quantitative SNR evaluation was performed using ankle scans of six volunteers. T

2

suppression profiles were simulated for both approaches to facilitate interpretation of the observations.

Both techniques provide comparable results at 1.5T regarding the suppression of long-T

2

species and fat. At 3T however the magnetization preparation suffers from stronger off-resonance effects. The magnetization preparation approach is more sensitive to magnetic field inhomogeneities due to the application of narrow band RF pulses and requires more shimming effort. The “dual echo” approach needs an additional post-processing step to calculate the subtraction image of two data sets acquired with different echo times. The signal-to-noise ratio in image areas with short-T

2

components is superior in the “dual-echo” approach.

In conclusion, both techniques provide good suppression of long-T

2

species with comparable short-T

2

SNR. The “dual-echo” approach offers better scan efficiency and is less sensitive to field inhomogeneity.

Ulrike Blume, Jürgen Rahmer, Peter Börnert, Dietrich Holz
Scatter Analysis of the ClearPET™ Neuro Using Monte Carlo Simulations

Scatter reduces the image quality in Positron Emission Tomography (PET). In this paper we discuss a) methods to estimate the scatter fraction in the raw data set as well as b) analysis of the different scatter components (e.g. phantom scatter, gantry scatter) arising from activity outside the field of view (OFOV). The PET detection system does not allow a discrimination of scattered events, thus Monte Carlo Simulations were used. The accuracy of the different scatter estimation methods was analyzed. Simulations with OFOV activity showed that small animal PET systems are indeed sensitive to random and scattered events from OFOV.

Anna M. Fulterer, Stephan Schneider, Brigitte Gundlich, Patrick Musmann, Simone Weber, Thorsten M. Buzug
Multi-Modality-Imaging for Radiosurgery Planning of Arteriovenous Malformations

For arteriovenous malformations (AVMs) radiosurgery (RS) is a well-established treatment option. The needed high precise dose application is depending on the availability of imaging data sets with superior image quality that can be superimposed using an image fusion algorithm. Digital subtraction angiography (DSA) has to be integrated because it is a mandatory tool for RS planning procedure. In 34 patients suffering from an AVM various MR data sets including T1-weighted series and TOF angiographies (time of flight) were used together with the stereotactically localized CT and DSA data sets radiosurgery planning. All available image data sets were fused onto the CT data set using an automatic image fusion algorithm, in order to define the AVM nidus very precisely. The nidus was outlined in both localized DSA projections resulting in a DSA volume. Subsequently this DSA volume of the AVM has been adapted by inclusion of all available CT and MRI informations slice by slice resulting in the final target volume. We investigate in which cases the DSA volume and the finally treated target volume of the AVM were in agreement. The used thin-slice MR data sets (1–2 mm slice width) have been precisely fused onto the stereotactically localized treatment planning CT. The finally treated target volume was compared with the DSA volume of the AVM nidus as follows: In 19 cases the final target volume was larger than the DSA volume, in 6 it was smaller and 5 it was approximately equal. The difference was significant (Wilcoxon test: difference<0.0001; t-test: t=3.01, p>0.005). In 4 cases outlining the AVM was not possible without DSA. In 5 patients a two- or three-vessel DSA was needed, since there were different AVM compartments. In cases where previously a partial embolization had been undergone, the use of superimposed CT sets with, and without, contrast medium was important in order to define the completely embolized partial volumes that were not subject to treatment. The inclusion of the DSA images enabled a better identification of those arterialized veins that did not belong to the nidus. The exact 3-dimensional definition of the AVM nidus has been realized safely by integrating all available imaging modalities. The stereotactic DSA data acquisition remains a crucial tool for safe nidus definition in radiosurgery treatment planning.

Klaus-D. Hamm, Cornelia Eger, Gunnar Surber, Gabriele Kleinert, Rene Aschenbach, Joachim Klisch
Image Based Analysis of Bone Graft Samples made by 3D Printing Using Conventional and Synchrotron-Radiation-Based Micro-Computed Tomography

Rapid Prototyping and especially the 3D printing, allows generating complex porous ceramic scaffolds directly from powders. Furthermore, these technologies allow manufacturing patient-specific implants of centimeter size with an internal pore network to mimic bony structures including vascularization. The non-destructive analysis of the internal structure of such 3D printed scaffolds provides important information. We used computed-microtomography as investigation method. Conventional and Synchrotron radiation based methods were tested and compared.

S. H. Irsen, B. Leukers, C. Tille, F. Beckmann, B. Müller, T. M. Buzug, H. Seitz
SPECT-CT in Maxillofacial Surgery

Bone scintigraphy and SPECT (Single Photon Emission Computer Tomography) imaging with

99m

Tc-DPD (

99m

Tc-dicarboxypropane-diphosphonate) is a routine procedure to detect Osteitis. Until now, the technique was of limited use in craniofacial surgery due to low spatial resolution and lack of anatomical detail. We present two cases in which bone scintigraphy with

99m

Tc-DPD and SPECT-CT imaging (Symbia®, Siemens) was performed. With SPECT/CT accurate image fusion is achieved automatically and complex anatomical regions can be investigated. Automatic image fusion matched precisely. The areas of increased bone turnover were clearly marked. No artefacts occurred due to patient’s movement. SPECT/CT is a promising tool for the follow-up imaging of osteitis because of precise localisation and extension of the bone changes.

B. -I. Boerner, S. Berg, P. Juergens, A. Robertson, K. Schwenzer-Zimmerer

Medical Image Processing

Frontmatter
High Performance 2D/3D-Registration for Patient Positioning in Radiotherapy

The precise and repeatable positioning of patients is one of the key elements of successful radiation therapy. Our aim is to develop an automated system, which determines the exact position of the patient. We use volume rendering based on 3D-textures to generate a 3D-model of the region of interest from pre-treatment CT-data. The idea is to generate before each treatment session additional x-ray images from orthogonal positions. These x-ray images represent the current position of the patient. With the help of projection images of the 3D-model, so-called digitally reconstructed radiographs (DRRs), we determine the rigid transformation between the 2D-x-ray images and the 3D CT data via an intensity based 2D/3D registration process. This represents the misalignment between the current position and the position in the treatment plan. For our simulation results we used as a first step ray-casting images instead of real x-ray images. Because of the high performance of our approach, we were able to investigate, which optimization methods and which number of orthogonal x-ray tubes give best results.

Frank Heinze, André Kupetz, Jürgen Roßmann
Modelling Tumour Growth Patterns with Non-Rigid Image Registration

We present a registration-based approach to model growth of glioma tumours seen in serial magnetic resonance imaging. Two state-of-the-art intensity-based non-rigid registration methods are investigated for their ability to compensate for the mass effect of the tumour. Both methods perform well and volume change estimates correlate well with manual delineation. However the complex structural and functional changes in glioma cannot be fully resolved by intensity-based methods due to the profound changes in morphology and appearance associated with glioma progression.

Andreas Mang, William R. Crum, Oscar Camara, Julia A. Schnabel, Gisele Brasil Caseiras, Thorsten M. Buzug, Hans R. Jäger, Tarek A. Yousry, David J. Hawkes
Segmentation and Navigation Support of Clinical Data Sets to Simulate the Bronchoscopy and Rhinoscopy

A training and simulation system for therapy planning is developed based on patient specific imaging data. A real endoscope is used for navigation through the virtual patient. For this purpose sensors were built in the endoscope in order to track the translation, rotation and the angle of the distal end. Pre-processing (segmentation, tissue characterization) speeds-up the volume rendering up to real-time. Collision detection enables a realistic fly through the virtual patient.

Christian Dold, Ulrich Bockolt, Marcus Roth, Claus Peter Heussel, Jan Gosepath, Georgios Sakas
Analysis of Body Surfaces in a Body-Fixed Coordinate System

Visualisation of shape and shape change e.g. by contour lines depends on the selection of the coordinate system of the contour levels. This is elucidated by using the plaster cast of a scoliotic back being rotated in front of a 3-D measurement and analysis system. Axial rotation through an axis parallel to the contour planes results in a dramatic change of the contour patterns on the back. This is in contrast to the expectation of the ingenuous viewer interpreting the contour line pattern like a fingerprint. To meet this attitude shape analysis must be referenced to a body fixed coordinate system, which may be defined by anatomical landmarks. It is shown, that vertebra prominens and the lumbar dimples provide anatomical landmarks capable for this purpose.

Burkhard Drerup, Stefan Kraneburg
Deconvolution of Medical Ultrasound Data with Consideration of the Pressure Field, the Excitation Pulse and Focussing

Medical ultrasound data suffers from blur caused by the volume expansion of the pressure field of the mechanical wave. This blur is dependent on the used excitation signal and focussing of the ultrasonic wave and can therefore be examined and manipulated to compute a set of better parameters for deconvolution on the data in order to improve overall system resolution. Looking at the ultrasound transfer function we can focus on the examination of the “point spread function” and ways to influence its size especially in the lateral and elevational direction. Furthermore the combination of several measurements from different directions is analyzed to compensate the worse elevational resolution with the lateral resolution of measurements from other directions.

Holger J. Hewener, Robert Lemor
Evaluation and Enhancement of a Procedure for Generating a 3D Bone Model Using Radiographs

Volumetric information about the patient’s anatomy is quite valuable for medical diagnosis. Computed tomography (CT) is the common imaging modality for 3D visualization of bone tissue but rising costs in health care system demand for new approaches. A promising one is to use a 3D model being deformable under the constraint of statistical plausibility. The model is adapted to the patient’s anatomy by extracting the specific bone features from several conventional radiographs (2D–3D registration). These have to be acquired under different angles thus providing the features’ 3D position by means of which the model is deformed. The resulting bone representation may then be used for medical diagnosis instead of using CT data. Present work validates accuracy of the resulting bone shape and thus of the diagnosis relying thereon. Results are starting point for further implementations and modifications in order to reduce remaining errors.

Sebastian Gollmer, Rainer Lachner, Thorsten M. Buzug
High-Speed-Camera Recordings and Image Sequence Analysis of Moving Heart-Valves: Experiments and First Results

Heart valve prosthesis and related reconstruction develop problems during clinical course in patients, due to calcification. To analyse and quantify these effects, heart valves of pigs are filmed during motion using a high-speed camera, whereas the resulting image sequences are analyzed by motion analysis methods based on dynamic active contours. In this contribution we present first experiments and results for both, recording and motion analysis. The far-goal of our work is an analysis and understanding of the heart valve motion in the context of automatic quality assurance for the production of heart valves.

Thomas Wittenberg, Robert Cesnjevar, Stephan Rupp, Michael Weyand, Markus Kondruweit
Stereoscopic 4D-Visualization of Craniofacial Soft Tissue based on Dynamic MRI and 256 Row 4D-CT

For soft tissue organs, standard 3D-reconstructions can only provide a snapshot of a dynamically deforming structure. A reasonable possibility to overcome this drawback is the transition forward from 3D-reconstruction to 4D-visualization, i. e. rendering time dependent behavior based on dynamical radiological data sets. This article is dedicated to dynamical visualization of craniofacial soft tissue, namely human eye movement (MRI) and real time visualization of the downward movement of a volunteer’s mandible (256 row 4D-CT, NIRS, Chiba, Japan). Within several considered approaches for presentation of the results, stereoscopic realization of the 4D-visualization was regarded as providing best diagnostic impact and acceptance.

Cornelia Kober, Britt-Isabelle Boerner, Shinichiro Mori, Carlos Buitrago Tellez, Markus Klarhöfer, Klaus Scheffler, Robert Sader, Hans-Florian Zeilhofer
Analysis of Tumor-Influenced Respiratory Dynamics Using Motion Artifact Reduced Thoracic 4D CT Images

Respiratory motion represents a major problem in radiation therapy of thoracic tumors. Methods for compensation require comprehensive knowledge of underlying dynamics. In this study, motion of thoracic anatomical and pathological structures in lung cancer patients was analyzed using motion artifact reduced 4D CT data sets of high temporal and spatial resolution. Motion artifact reduction was achieved by applying an optical flow based 4D CT reconstruction method. Motion analysis especially focuses on inner organ and tumor mobility and the interrelation between tumor / inner organ motion and chest wall motion. Trajectories of tumor mass centers and organ specific landmarks were determined and analyzed. To study chest wall motion a non-linear registration based point tracking scheme was applied to compute trajectories of points on the chest wall skin. The interrelation of chest wall and tumor / inner organ motion was investigated using methods of multivariate statistics. Results show that, for instance, tumor motion patterns differ noticeably between the patients; a dependency between tumor motion and tumor location seems apparent. The correlation of tumor motion and motion of chest wall points depends on the patient breathing pattern (e.g. abdominal or chest wall breathing). Thus, skin regions which are suitable for prediction of tumor motion differ between the patients.

René Werner, Jan Ehrhardt, Thorsten Frenzel, Wei Lu, Daniel Low, Heinz Handels
3D-CSC: A General Segmentation Technique for Voxel Images with Application in Medicine

The successful 2d segmentation method CSC has recently been generalized to 3d. We shortly introduce the concept of both 2D- and 3D-CSC and present two use cases (classification of MR brain data and CT bone data) which demonstrate that analysis of segments generated by the CSC allows high quality classification of 3d data by relatively easy means.

Frank Schmitt, Patrick Sturm, Lutz Priese
An Algorithm for Automatic Stitching of CR X-ray Images

Stitching of X-ray images is of interest in cases of disease patterns like scoliosis

Markus Gramer, Wilfried Bohlken, Bernd Lundt, Thomas Pralow, Thorsten M. Buzug
Topology Correction in Brain Segmentation Using a Multiscale Algorithm

This is a new method for automatically correcting the spherical topology of a human brain segmentation under any digital connectivity. Topological correctness is important because it is an essential prerequisite for brain atlas deformation and surface flattening. A morphological multiscale approach which acts on foreground and background simultaneously divides the segmentation into several connected components, and subsequent region growing guarantees convergence to the correct spherical topology. In addition to existing graph-based procedures, this provides an alternate approach which has several advantages, including high speed and ease of operation without graph analysis and changing as few voxels as possible.

Lin Chen, Gudrun Wagenknecht
Intensity-Modulated Radiation Therapy — Quality Assurance with the Mutual Information Index (MI)

Radiation therapy is an important method of treating neoplastic diseases with ionizing radiation. For this treatment electromagnetic or corpuscular (electrons, protons, neutrons) radiation is used which causes ionization and excitation in the energy absorbing tissue [1]. The conventional radiation therapy applies beams with a homogeneous dose distribution or uses wedges to optimize the dose to the cancerous volume and prevents high doses in organs of risk (e.g. rectum, eye). The individual treatment plan is developed by the physicist who sets the beams in a treatment planning system which calculates the dose distribution. With the objective of ideal adjustment to the cancerous volume it is advantageous to use the “inverse treatment planning” and the intensity-modulated radiation therapy (IMRT) especially for concave volumes. Therefore, the dose distribution is designated by the physicist and the individual treatment plan is developed including the number and direction of beams and the multi-leaf collimators’ position. Due to the fact that the leaf collimator conforms the dose to the tumor volume IMRT protects the adjacent tissue as good as possible. Before an application of IMRT starts a quality assurance is important. It is especially necessary to check the accuracy of the system including the data of the planning software.

Astrid Brendemühl, Stefan Ostrowitzki, Uwe Altenburger, J. Christoph Haller, Jürgen Ruhlmann, Thorsten M. Buzug
Image Registration of Structural and Physiological MR Images of Abnormal Anatomy

This study applies image registration techniques to combine functional and structural information derived from multi-modal magnetic resonance imaging in patients diagnosed with brain gliomas. The images vary substantially in resolution, signal-to-noise ratio, information content and field of view and therefore pose a challenging registration problem. Specific protocols have been designed for each registration task, with careful selection of critical parameters and appropriate pre-processing. In addition, we have developed a visual assessment protocol to evaluate the accuracy of the proposed methods. Preliminary results suggest that registrations errors are below the functional image resolutions, thus achieving sub-voxel accuracy.

Andreas Mang, Oscar Camara, Gisele Brasil Caseiras, William R. Crum, Julia A. Schnabel, Thorsten M. Buzug, John Thornton, H. Rolf Jäger, David J. Hawkes

Computer-Assisted Surgery (MRNV Workshop)

Frontmatter
Video Camera Based Navigation of a Laser Beam for Micro Surgery Bone Ablation at the Skull Base — Setup and Initial Experiments

The protection of soft tissue structures behind the ablated bone in skull base surgery is mandatory. As the destruction of the membrane lining the inner ear can lead to a damage of organ functions (e.g. deafness or vertigo) a precise bone tissue removal by a laser ablation setup is investigated. For the detection of the boundary between soft tissue and bone the ablation area and rate are monitored by a video camera. Through this the laser is guided across the ablation area by image processing technologies. An aim of this project is a defined, navigated-controlled and laser based bone removal for the future buildup of a robot based surgical laser instrument. This publication describes the setup of our video controlled laser ablation system, initial experiments and results.

L. A. Kahrs, M. Werner, F. B. Knapp, S. -F. Lu, J. Raczkowsky, J. Schipper, M. Ivanenko, H. Wörn, P. Hering, Th. Klenzner
Ultrasound Based Navigation System for Minimal Invasive Surgery at the Lumbar Spine within OrthoMIT

We present a system to register three-dimensional ultrasound datasets with preoperative CT datasets to support navigated surgery at the lumbar spine, using a registration algorithm based on bone structures. The registration of the coordinates of the patient and the image data is divided into two steps: a rough point-to-point pre-registration and an ultrasound based volume-surface registration. We evaluated three different methods for a pre-registration process in simulation and

in vitro

. The orthogonal

Procrustes

method was compared to the

Downhill Simplex method

with six and four degrees of freedom. The

Downhill Simplex method

with six degrees of freedom provided a precise and robust registration considering misplacements of landmarks on the phantom of up to 56 mm.

Karin Hensel, Stephanie Hold, Susanne Winter, Claudia Dekomien, Markus Mildenstein, Bernhard Brendel, Helmut Ermert, Georg Schmitz
Optimization and Quantification of Aaccuracy for Rigid Point Based Registration for Computer Aided Surgery

When conducting complex neurosurgical interventions on the brain, surgeons are often assisted by planning systems and neuronavigation. To position the instruments in relation to the preoperatively acquired image datasets, rigid registration between the coordination systems of the patient and the corresponding diagnostic images is performed using fiducial markers or screws attached to the patient’s head. In this work a registration-framework was implemented, which allows the easy integration of different point based registration algorithms as well as the estimation of registration accuracy. To perform the registration, two algorithms were implemented and tested using simulation as well as real world measurements. The target registration error (TRE) is predicted by a method introduced from Fitzpatrick. Two different approaches were implemented and both achieve better results than the RMS Error (“Root Mean Square”) widely used in clinical applications. To provide the surgeon with an intuitive understanding of the accuracy, a graphical representation of the estimator was developed and integrated into the existing MOPS 3D planning system. Additionally an iterative marker selection method was developed for identifying markers which would contribute to a higher registration error. The described registration framework is developed in C++ using MS Visual Studio and is easy to integrate in different medical applications.

Philip Oberhammer, Urs Eisenmann, Roland Metzner, Dimitrios Paraskevopoulos, Christian R. Wirtz, Hartmut Dickhaus
Virtual Reality Based Training of Lumbar Punctures Using a 6DOF Haptic Device

The lumbar puncture is performed by inserting a needle into the spinal chord of the patient to inject medicaments or to extract liquor. This procedure is usually trained on the patient guided by experienced supervisors. A virtual reality lumbar puncture simulator has been developed in order to enhance the training by providing new insight into a virtual patient and in order to minimize the patient’s risk. We use a haptic device with six degrees of freedom (6DOF) to feedback forces that resist needle insertion and rotation. An improved haptic volume rendering approach is used to calculate the forces for the haptic feedback. A real time 3D visualization with optional stereo view gives an overview of the punctured region. 2D visualizations of orthogonal slices enable a detailed impression of the anatomical context. In a first evaluation the visible human male data has been used to generate the virtual body. Several users with different medical experience tested the lumbar puncture trainer. The simulator gives a good haptic and visual impression of the needle insertion and the haptic volume rendering technique enables the feeling of segmented and unsegmented structures.

M. Färber, J. Heller, F. Hummel, C. Gerloff, H. Handels
Robot-Assisted 3D-Ultrasound Volume Registration for Skull Bone Surgery

Surgical procedures with navigation or robot system support usually require some pre-operative planning data. This data can be acquired by traditional imaging modalities like e.g. computed tomography (CT), the current gold standard due to its high precision. With such imaging data, access trajectories, implant positions, individual milling paths etc. can be computed. We present an ultrasound-based method to generate 3D image data which is equally suited for many interventions, but less costly than CT and real time. The method’s feasibility is demonstrated for robot-based implant bed milling in the lateral skull base.

Philipp J. Stolka, Steffen H. Tretbar, Michel Waringo, Philipp A. Federspil, Peter K. Plinkert, Dominik Henrich
Recent Significance of Mechatronic Support Systems in General Surgery

With an opinion and application poll in Swiss, Austria and Germany, the recent significance of mechatronic support systems was analyzed. Various advantages were reported by users. Advantages for surgery account for automation and limitation of surgical manipulations and increased instrumental skill, but the application of theses support systems are still very limited, due to negative cost-value ratio.

Siegfried Beller, Felix Härtl
Registration of Intraoperative 3D Ultrasound with MR Data for the Navigated Computer Based Surgery

Computer based navigated surgery assists the spatial orientation of the surgeon. Our system registers preoperative data like CT or MR with intraoperative ultrasound data to get the coordinate transformation between the preoperative and the intraoperative data. With a surface volume registration we avoid a difficult surface segmentation in the ultrasound data. To prevent radial exposure and to get more details in the soft tissue the use of MR data for the operation planning is common. Extracting the bone surface in MR data is more difficult than in CT data because MR data has no normalized gray values. To register the ultrasound with the MR data at the knee we detected distinctive anatomic regions in the ultrasound data. We selected an adequate MR sequence in which we could segment the bone surface at the specific region. We evaluate the registration with 1000 random starting positions. 99.2% of the 1000 trails reached the optimum with an error less than 1 mm.

Claudia Dekomien, Markus Mildenstein, Karin Hensel, Stephanie Hold, Susanne Winter
Measuring the Fat Content of the Liver for Transplantation Medicine

For a successful transplantation the fat content of the liver is an important parameter for the suitability of the graft. In a cooperation between the university hospitals Essen and Cologne and the RheinAhrCampus Remagen of the University of Applied Sciences Koblenz, the potentialities of electrical measurement of the liver fat content were investigated.

Jörg Himmel, Manfred Nagelschmidt, Jürgen Treckmann, Christian Sehestedt, Sidi Mohamed Ait Sghir, Stephan Sehestedt

Biomechanics

Frontmatter
Influence of Modern Above-Knee Prostheses on the Biomechanics of Gait

The advent of modern knee prostheses has opened up a new quality in the provision of above-knee amputees. This can be demonstrated by means of kinetic and kinematic measurements. Amputees achieve significantly more security combined with sufficient dynamics.

J. Wühr, U. Veltmann, L. Linkemeyer, B. Drerup, H. H. Wetz
Spinal-Load Analysis of Patient-Transfer Activities

Selected care-activities with patient transfers, which are classified as “definitely being endangering” with respect to the corresponding German occupational disease, were analyzed regarding the corresponding (bio-)mechanical load on the lumbar spine. In a laboratory study, the postural data of a health-care worker were recorded optoelectronically and via video documentation, the nurse’s action-forces were captured via force sensors at a specifically modified bed, chair, or floor. The analyses of about 100 transfers show that patient transfers result in intensive lumbar load, which may exceed lumbar-load limits recommended for work design. Application of optimized transfer techniques resulted in diminished biomechanical load for the low-back.

Matthias Jäger, Claus Jordan, Andreas Theilmeier, Alwin Luttmann, DOLLY Group
Investigation of the Influence of Interbody Fusion on Biomechanics of the Cervical Spine Using a Computer Model

Anterior cervical fusion alters the physiologic motion of the adjacent intervertebral joints. Using a computer model the changes in motion within the biological structures are investigated in dynamic loading situations. A multibody system of the cranial part of the upper spine (T3 to C1), clavicle, sternum, and cranium includes the exact geometry of the bony structures, the validated description of the material behavior of the passive soft tissue structures, and control elements simulating the active muscle structures.

Stefan Lehner, Ulrich Schreiber
Design and Testing of an Autonomous Computer Controlled Loading Device to Study Tissue Adaptation around Immediately Loaded Implants in the Reindeer Antler

The investigation of bone remodeling phenomena around immediately loaded dental implants with regard to clinical, histological and biomechanical aspects is of great importance. The main interest is directed towards the time-dependant behavior of the bone around the implants. The aim of this work was to develop an autonomous loading device that has the ability to load any inserted implant with a defined force for predetermined time slices. For the execution of the experimental studies a novel animal model will be established. For this task, the reindeer antler will be used as a reference model for bone remodeling processes as implant bed. For loading the implants, an autonomic simulator for the application of occlusal forces has been developed. The mechanical part of this device can be attached to the antler and it is capable of cyclically loading the implant with forces of up to 100 N. The loading device was subsequently tested with a biomechanical measuring system. The calibration of devices such as using a force/torque transducer with a range of 80N was done. This exhibit A logarithmic force/current relationship.

Alireza Rahimi, Marcus Abboud, Gerhard Wahl, Ludger Keilig, Ingo Hensch, Christoph Bourauel
Numerical Simulation of the Biomechanical Properties of a Prefabricated Attachment System for Use in Prosthetic Dentistry

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.

Susanne Reimann, Christoph Bourauel, Ludger Keilig, Andreas Jäger, Helmut Stark, Mathias Strazza
Experimental and Numerical Analysis of the Mobility of Immediately Loaded Dental Implants Using a Pig Model

The aim of this study was to model a system of implant and bone using the finite elements analysis (FEA). For this purpose immediately loaded dental implants were used. In an experimental analysis of preparations from pig jaws the force-displacement behaviour was measured using a self development set-up. With the aid of a micro computer tomograph (µCT) three dimensional surface models were reconstructed. These surface models were imported into the finite elements (FE) software package Marc/Mentat. Then the three dimensional surface models were transformed into FE-models, that mirror the geometry of implant and bone in detail. Comparison of the experimental achieved data and the numerical calculated data showed the magnitude of relative movements between implant and bone.

Alex Meier, Alireza Rahimi, Christoph Bourauel, Thorsten M. Buzug, Susanne Reimann, Dennis Giantoro
Measuring System for the Comparative Ergonomic Study of Office Chairs

Working in static sitting postures at office workstations can cause musculoskeletal disorders (MSD). In the paper a measuring system for the comparative ergonomic study of office chairs is presented. With the system different concepts of dynamic office chairs that promote dynamic sitting and therefore prevent MSD, can be analyzed. Exemplary results of a laboratory study with different office chairs are described.

Rolf Ellegast, Rene Hamburger, Kathrin Keller, Helmut Berger
3-Dimensional Foot Geometry and Pressure Distribution Analysis of the Human Foot. Visualization and Analysis of two Independent Foot Quantities for Clinical Applications

The purpose of this research was to visualize three dimensional foot scan data simultaneously with pressure distribution information under the foot. Furthermore, simplified pressure distribution analysis software was developed. 382 school children were measured with a 3D - foot laser scanner and a pressure distribution platform during one-legged standing. A visualization program to combine foot geometry with plantar pressure distribution in a single graphical representation (

PressoMorph 1.0

) was developed using MATLAB. The two different data sets from the foot scanner and the pressure distribution device were imported into

PressoMorph 1.0

and matched in orientation, position and size. A positioning of the virtual three-dimensional foot onto the pressure matrix image resulted in a visual combination of both data as a wire-frame image with colour coded pressure isobarographs. Program options include rotations of the image along the three axes and provide a cursor value readout possibility for a user friendly program interface. The combination of 3D foot geometry and plantar pressure distribution data in only a single graphical representation guarantees a fast and easy judgement of foot shape and mechanical foot characteristics in a clinical setting.

Ann-Kathrin Hömme, Ewald M. Hennig, Ulrich Hartmann
Assessment of Ambulatory Activity of Diabetic Patients: A Reliability Test

In preventing the development of foot ulcerations in diabetic patients exposition to excessive plantar pressure is realized as a major risk. Therefore, ambulatory activity is important to know when assessing the risk of ulcerations.

J. Baumeister, R. Ellegast, B. Drerup, A. Koller, H. H. Wetz
MBS-Modeling for Estimation of Stress and Strain in Human Body

Herniated and degenerated intervertebral disk is a painful disease which decreases the patient’s quality of life. Because of the enormous pain every movement of the body is avoided and comprised the risk of clumping nerve cords. While the number of patients increases still no proper method is known to measure forces, pressure and torques in transmitted structures of the spine, especially during motion. The only accurate possibility for measurement is to place a sensor directly into the intervertebral disk, which leads beside the normal risk of surgery also to the risk of paraplegia and dangerous infections. Therefore, a new non-invasive method is developed to estimate the mentioned parameters in spine. This method is based on a computer generated model of the human lumbar spine which reflects geometry, surface and biomechanical features in an accurate way.

Sabine Juchem, Lucas Pfaffmann, Franziska Eckhardt, Dirk Thomsen, Stefan Lehner, Thorsten M. Buzug, Karin Gruber
A Bicycle Simulator Based on a Motion Platform in a Virtual Reality Environment — FIVIS Project

The objective of this project is to develop a real bicycle simulator with the ability to represent real life traffic situations as a virtual scenario within an immersive environment. The bicycle will be fixed onto a motion platform to enable a close to reality simulation of turns and balance situations. The platform is fed with real forces and accelerations that have been logged by a mobile data acquisition system during real bicycle test drives. Thus, using a feedback system makes the movements of the platform match to the virtual environment and the reaction of the driver (e.g. steering angle, step rate).

O. Schulzyk, J. Bongartz, T. Bildhauer, U. Hartmann, B. Goebel, R. Herpers, D. Reinert
Inverse Dynamics in Cycling Performance

Joint reaction forces and moments are of great interest for cyclists, coaches, therapists and medics because they give information about muscular effort and therefore cycling technique. The objective of this study is to examine the influence of pedalling rate and power on joint moments. An own mechanical construction was used to measure pedal forces, kinematic data was recorded and joint moment calculations were solved on a computer for ankle, knee and hip with help of a link segment model. Results show an increase of moments with increase of power and decrease of pedal rate.

Malte Wangerin, Syn Schmitt, Björn Stapelfeldt, Albert Gollhofer

Biomedical Optics

Frontmatter
Determination of Alveolar Geometry by Optical Coherence Tomography to Develop a Numerical Model of the Fluid Dynamics in the Pulmonary Acinus

In this feasibility study a Fourier domain optical coherence tomography (FDOCT) system was used for 3D imaging of sub pleural lung parenchyma in the ventilated and perfused isolated rabbit lung. A series of 3D OCT images during a stepwise increase of pulmonary airway pressure was acquired. Refocusing and repositioning of the OCT scanner head allowed follow the volume changes of a single partial acinus of the lung.

Sven Meißner, Alexander Krüger, Martina Wendel, Lilla Knels, Axel Heller, Thea Koch, Edmund Koch
Combining Optical Coherence Tomography (OCT) with an Operating Microscope

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.

Eva Lankenau, David Klinger, Christian Winter, Asim Malik, Heike Hedwig Müller, Stefan Oelckers, Hans-Wilhelm Pau, Timo Just, Gereon Hüttmann
Measurement of the Epidermal Thickness with Fourier Domain Optical Coherence Tomography in an Occupational Health Study on Natural Sun Protection of the Human Skin

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.

A. Krüger, T. Schwabe, M. Cuevas, P. Knuschke, E. Koch
Multiscale Description of Light Propagation in Biological Tissue

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.

Alwin Kienle, René Michels, Jan Schäfer, Oliver Fugger
The Influence of Heterogeneous Optical Properties upon Fluorescence Diffusion Tomography of Small Animals

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.

Saskia Bjoern, Sachin V. Patwardhan, Joseph P. Culver
Cell Membrane Fluidity Determined by Fluorescence Lifetime and Polarization Screening

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).

Thomas Bruns, Wolfgang S. L. Strauss, Herbert Schneckenburger
Cholesterol Dependence of Cell Membrane Dynamics Proved by Fluorescence Spectroscopy and Imaging

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.

Petra Weber, Michael Wagner, Wolfgang S. L. Strauss, Herbert Schneckenburger
Fast and Objective Classification of Tumor Tissue by Optical Vibrational Spectroscopy

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.

Gerald Steiner, Christoph Krafft, Claudia Beleites, Stephan Sobottka, Gabriele Schackert, Edmund Koch, Reiner Salzer
Algorithms for Muscle Oxygenation Monitoring Corrected for Adipose Tissue Thickness

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 Δ

A

/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.

Dmitri Geraskin, Petra Platen, Julia Franke, Matthias Kohl-Bareis
Establishment of an Optical Imaging Device for Intraoperative Identification of Active Brain Areas

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.

Tobias Meyer, Hans Dietrich, Falk Uhlemann, Stephan B. Sobottka, Matthias Kirsch, Alexander Krüger, Edmund Koch, Ralf Steinmeier, Gabriele Schackert, Ute Morgenstern
Parallel FDTD Simulation of the Scattering of Light in Media Containing Cylindrical Scatterers

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.

Jan Schäfer, Alwin Kienle, Alfred Strey
Cerebral Oxygenation Monitoring during Cardiac Bypass Surgery in Babies with Broad Band Spatially Resolved Spectroscopy

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 SO

2

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.

Jan Soschinski, Dmitri Geraskin, Branislav Milosavljevic, Uwe Mehlhorn, Uwe Fischer, Gerardus Bennink, Matthias Kohl-Bareis
Microspectrofluorometry and Polarisation Microscopy of Membrane Dynamics in Living Cells

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.

Michael Wagner, Petra Weber, Herbert Schneckenburger
Goniometrical Measurements of the Phase Function of Microstructured Tissue

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.

René Michels, Alwin Kienle

Medical Laser Engineering

Frontmatter
Comparison of Process Temperature during Laser and Mechanical Cutting of Compact Bone

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 CO

2

laser (λ = 10.6 µm, pulse duration 1 µs and focus diameter 230 µm (1/e

2

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.

Astrid Brendemühl, Martin Werner, Mikhail Ivanenko, Peter Hering, Thorsten M. Buzug
Spectral Analysis of the Acoustic Signal During Ablation of Biological Tissue with Pulsed CO2- Lasers

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 CO

2

-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.

Hendrik Steigerwald, Martin Werner, Manfred Klasing, Mikhail Ivanenko, Daniela Harbecke, Christian Wagner, Peter Hering
Laser-Scalpel for Kidney Resection Based on 1,94 µm Fibre Laser System

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.

Dirk Theisen-Kunde, Söhnke Tedsen, Veit Danicke, Robert Keller, Ralf Brinkmann
Three-Dimensional Surface Measurement Using Digital Holography with Pulsed Lasers

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.

Stephanie Heintz, Sven Hirsch, Andrea Thelen, Peter Hering
Laser Spectroscopic Online Monitoring of Volatile Diseasemarkers in Human Breath

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.

Manfred Mürtz, Sven Thelen, Thomas Fritsch, Peter Hering
Design and Technical Concept of a Tm Laser Scalpel for Clinical Investigation Based on a 60W, 1.92 µm Tm Fiber Laser System

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.

Sebastian Wenk, Stephan Fürst, Veit Danicke, Dirk Theisen Kunde
Laser Osteotomy with Pulsed CO2 Lasers

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 CO

2

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 CO

2

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.

Martin Werner, Mikhail Ivanenko, Daniela Harbecke, Manfred Klasing, Hendrik Steigerwald, Peter Hering
T-Scan: First Experiences with Acquisition of Cleft Morphology

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.

K. Schwenzer-Zimmerer, B. -I. Boerner, A. A. Müller, P. Jürgens, A. Ringenbach, E. Schkommodau

Clinical Post-Deadline Papers

Frontmatter
Accuracy of Translation and Rotation Measurements in Navigated ACL Reconstruction

An accurate tool for a combined pre-, intra-, and postoperative stability measurment for rotation and translation after ACL reconstruction of the tibia is still not in clinical use, although these measurments provide important stability parameters. Navigation has been introduced a few years ago for the evaluation of impingement problems or the drill canal for ACL replacement but the measurement of the tibial translation and rotation is only available for a short time and only available with a few navigation modules. The navigated accuracy is 1 mm/

o

. In this study navigated measurement of tibial rotation and translation were evaluated with a new developed mechanical device and directly compared with a c-arm based navigation modul.

D. Kendoff, M. Citak, R. Meller, P. Bretin, J. Geerling, C. Krettek, T. Hüfner
Stability of Different Attachment Arrays of Reference Bases Against Mechanical Stress

An invasive, rugged fixation of the reference bases is necessary to execute a save and precise navigated operation. In case of dislocation of the reference bases the operation must be stopped and the system must be calibrated again, because already small dislocations mean severe impreciseness during the operation. Aims of that study were to test the stability of some of the reference bases especially how much power is needed to remove them.

M. Citak, D. Kendoff, P. Bretin, J. Geerling, C. Krettek, T. Hüfner
Problems of the Pre- and Postoperativ Determination of the Antetorsionangle of the Femur by Navigation and CT

One Problem of the intramedullary nail osteosynthesis are clinical relevant errors in the torsion of the femur. It can hardly be noticed during the surgery, and often it cannot be avoided. It is necessary to know the antetorsion and the length of the healthful femur in a navigated operation, although there are preoperative CT analysis. There is no way to use invasive reference bases on a healthful extremity, but good working non-invasive technologys are not available at this point of time. Thats why the reference base is placed on the operation table and the leg must be fixed in a good position and may not be moved during the operation. More time is needed, also a high dose x-ray. This study tried to determine the antetorsionangel and the tolerable Differences in a.p.and lateral view of 15 human femurs by using the Brainlab Navigation System and the CT.

M. Citak, D. Kendoff, P. Bretin, J. Geerling, C. Krettek, T. Hüfner
3D-Analyses and Libraries for the Construction of Individual Craniomaxillofacial Alloplastic Implants

Alloplastic CAM-CAM manufactured implants are regularly used to cover bony defects of the skull in craniomaxillofacial surgery. Regarding unilateral “simple” deficiencies, mirroring procedures can be successfully employed for construction. In cases of complex and bilateral defects resp. syndromic malformations, planning can only be performed according to the esthetic understanding of the engineer-doctor team. Especially in the facial region with its high esthetic impact this situation is less preferable. Therefore a study was planned to allow planning of CAD-CAM implants on the basis of reliable data.

Th. Hierl, J. Hendricks, G. Wollny, F. P. Schulze, E. Scholz, G. Berti, J. G. Schmidt, Th. Schulz
Evaluation of Various Ceramic Implants after Immediate Loading

Ceramic implants showed in the past a very nice soft tissue behavior but the clinical success was compromised due to lack of osseointegration in the early stage and mechanical complication like fracture in the long term run. New material like Yttrium stabilized Zirconia ceramics promise a higher mechanical stability. While mechanical stability can be proven by in-vitro-testing the course of osseointegration had to be determined by in-vivo condition. A pilot study on four mongrel dogs was performed to compare the course of osseointegration of root-form and parallel walled one-piece ZrO-ceramic implants in comparison to titanium implants.

J. Neugebauer, B. Nolte, T. M. Buzug, M. Weinländer, V. Lecovic, F. Vizethum, C. Khoury, J. E. Zöller
Backmatter
Metadaten
Titel
Advances in Medical Engineering
herausgegeben von
Professor Dr. Thorsten M. Buzug
Professor Dr. Dietrich Holz
Professor Dr. Jens Bongartz
Professor Dr. Matthias Kohl-Bareis
Professor Dr. Ulrich Hartmann
Dr. Simone Weber
Copyright-Jahr
2007
Verlag
Springer Berlin Heidelberg
Electronic ISBN
978-3-540-68764-1
Print ISBN
978-3-540-68763-4
DOI
https://doi.org/10.1007/978-3-540-68764-1