Edmund Koch

Automatic Lung Segmentation of Helical-CT Scans in Experimental Induced Lung Injury

We present a knowledge-based approach for the automatic segmentation of lungs in 3D thoracic CT images.

Imaging the tympanic membrane oscillation ex vivo with Doppler optical coherence tomography during simulated Eustachian catarrh

Recently, optical coherence tomography (OCT) was utilized in multiple studies for structural and functional imaging of the middle ear and the tympanic membrane. Since Doppler OCT allows both, the spatially resolved measurement of the tympanic membrane oscillation and high-resolution imaging, it is regarded as a promising tool for future in vivo applications. In this study, Doppler OCT is utilized for the visualization of the tympanic membrane oscillation in temporal bones with simulated Eustachian catarrh, which was realized by generating a depression in the tympanic cavity. The transfer function, meaning the oscillation amplitude normalized to the applied sound pressure, is measured frequency resolved in the range from 0.5 kHz to 6 kHz and with a lateral spatial resolution of 0.4 mm. Typical oscillation patterns could be observed in case of ambient pressure in the tympanic cavity. Under depression the characteristic oscillation patterns were observed with widely congruent appearance but at higher frequencies.

Three-dimensional Fourier-domain optical coherence tomography of alveolar mechanics in stepwise inflated and deflated isolated and perfused rabbit lungs

Fourier domain optical coherence tomography (FD-OCT) was used to acquire three-dimensional image stacks of isolated and perfused rabbit lungs (n = 4) at different constant pulmonary airway pressures (CPAP) and during vascular fixation. After despeckling and applying a threshold, the images were segmented into air and tissue, and registered to each other to compensate for movement between CPAP steps. The air-filled cross-sectional areas were quantified using a semi-automatic algorithm. The cross-sectional area of alveolar structures taken at all three perpendicular planes increased with increasing CPAP. Between the minimal CPAP of 3 mbar and the maximum of 25 mbar the areas increased to about 140% of their initial value. There was no systematic dependency of inflation rate on initial size of the alveolar structure. During the perfusion fixation of the lungs with glutaraldehyde morphometric changes of the alveolar geometry measured with FD-OCT were negligible.

Magnetomotive imaging of iron oxide nanoparticles as cellular contrast agents for optical coherence tomography

Recent studies in animal models provided proof-of-principle evidence for cell transplantation as a potential future therapeutic approach for retinal pathologies in humans such as Retinitis pigmentosa or age-related macular degeneration. In this case, donor cells are injected into the eye in order to protect or replace degenerating photoreceptors or retinal pigment epithelium. However, currently there is no three-dimensional imaging technique available that allows tracking of cell migration and integration into the host tissue under in vivo conditions. Therefore, we investigate about magnetomotive optical coherence tomography (OCT) of substances labeled with iron oxide nanoparticles as a potential method for noninvasive, three-dimensional cell tracking in the retina. We use a self-developed spectral domain OCT system for high-resolution imaging in the 800 nm-wavelength region. A suitable AC magnetic field for magnetomotive imaging was generated using two different setups, which consist of an electrically driven solenoid in combination with a permanent magnet, and a mechanically driven all-permanent magnet configuration. In the sample region the maximum magnetic flux density was 100 mT for both setups, with a field gradient of 9 T/m and 13 T/m for the solenoid and the allpermanent magnet setup, respectively. Magnetomotive OCT imaging was performed in elastic tissue phantoms and single cells labeled with iron oxide nanoparticles. Particle-induced sub-resolution movement of the elastic samples and the single cells could successfully be detected and visualized by means of phase-resolved Doppler OCT analysis. Therefore, this method is a potential technique to enhance image contrast of specific cells in OCT.

Four-dimensional optical coherence tomography imaging of total liquid ventilated rats

Optical coherence tomography (OCT) can be utilized for the spatially and temporally resolved visualization of alveolar tissue and its dynamics in rodent models, which allows the investigation of lung dynamics on the microscopic scale of single alveoli. The findings could provide experimental input data for numerical simulations of lung tissue mechanics and could support the development of protective ventilation strategies. Real four-dimensional OCT imaging permits the acquisition of several OCT stacks within one single ventilation cycle. Thus, the entire four-dimensional information is directly obtained. Compared to conventional virtual four-dimensional OCT imaging, where the image acquisition is extended over many ventilation cycles and is triggered on pressure levels, real four-dimensional OCT is less vulnerable against motion artifacts and non-reproducible movement of the lung tissue over subsequent ventilation cycles, which widely reduces image artifacts. However, OCT imaging of alveolar tissue is affected by refraction and total internal reflection at air-tissue interfaces. Thus, only the first alveolar layer beneath the pleura is visible. To circumvent this effect, total liquid ventilation can be carried out to match the refractive indices of lung tissue and the breathing medium, which improves the visibility of the alveolar structure, the image quality and the penetration depth and provides the real structure of the alveolar tissue. In this study, a combination of four-dimensional OCT imaging with total liquid ventilation allowed the visualization of the alveolar structure in rat lung tissue benefiting from the improved depth range beneath the pleura and from the high spatial and temporal resolution.

Selection Criteria for Competing Models of Respiratory Mechanics

Mathematical models of respiratory mechanics are useful for assessing the mechanical properties of the respiratory system. The application of models in therapy requires robust identification methods and criteria to quantify the quality of the estimated model parameters. These criteria should support the selection of the best model amongst a collection of competing models to describe the given mechanical behaviour. In this work, three selection criteria were tested on two respiratory mechanics models in various lung conditions using experimental data of 11 mechanically ventilated subjects. Different lung conditions lead to different model preferences as indicated by the Coefficient of Determination, Akaikes Information Criterion and reported confidence intervals. The combination of the presented selection criteria provides a clear preference to select an appropriate model for a given situation to be implemented in a model-based ventilation monitoring.

Methods for determining the blood flow velocity in cerebral vessels using intraoperative Indocyanine Green fluorescence video angiography

Objective nFluorescence video angiography has recently been introduced to neurosurgery. For intraoperative control, blood flow in the brain vessels can be visualized by means of near-infrared fluorescence dye Indocyanine Green. Until now the sufficiency of the blood flow has to be assessed qualitatively by the surgeon. Therefore, an objective quantification of the blood flow by means of video analysis is desirable.

Multimodal imaging of lung tissue dynamics in mechanically ventilated rats with optical coherence tomography and intravital microscopy (Conference Presentation)

The understanding of alveolar mechanics is an essential step towards new and more protective ventilation strategies which are of dare need for the treatment of diseases of lung tissue and the airways. Such ailments become a major task for medical care and health care systems in modern industrial countries in the future. Besides the obvious importance as life-saving intervention, the mechanical strain and processes on the level of gas exchange are still insufficiently understood. Therefore, it is of great interest to characterize lung tissue and tissue dynamics during artificial ventilation at the alveolar level. 4D Optical coherence tomography (OCT) in combination with high-speed video microscopy (IVM) are promising tools for the investigation and characterization of lung tissue with a high spatial and temporal resolution in artificially ventilated rats. Optical access to the subpleural alveoli is achieved by removing the skin and tissue between the ribs. For IVM, a tunable focus lens is used to track axial motion and keep the tissue in focus and 4D OCT is performed using a gated scanning algorithm for image acquisition. The movement of alveolar tissue during uninterrupted ventilation was visualized during one ventilation cycle using these image acquisition techniques. The alveolar structures are clearly visible and can be segmented and measured regarding volume and volume changes. The measurement of three-dimensional volume changes during uninterrupted ventilation from OCT data and the comparison with two-dimensional information from IVM promote the understanding of alveolar mechanics and the effort for the development of more protective ventilation strategies.

4D optical coherence tomography for imaging aortic valve dynamics ex vivo (Conference Presentation)

The mechanical components of the heart, especially the valves, are enormously stressed during lifetime and undergo different pathophysiological tissue transformations, which affect cardiac output and in consequence living comfort of affected patients. Calcific aortic valve stenosis (AVS) is the most common valve disease in modern industrial countries but the pathogenesis and progression of this disease is still unknown. Therefore, animal models, especially mouse models, are a powerfull tool to investigate this disease in more detail with high resolution imaging techniques like optical coherence tomography and video microscopy.nA custom-made pump was used for artificial stimulation of aortic valves ex vivo of 17-week-old wildtype and 12-month-old ApoE knockout mice. Image acquisition and viszualization of tissue dynamics was perfomed by using a multimodal imaging system for time-resolved 3D OCT and high-speed microscopy.nExemplary findings will be presented showing the differences in tissue behaviour and dynamics of the aortic valves, which were visualized under same conditions of artificial stimulation with 4D OCT and high speed mi-croscopy. Furthermore, clinically relevant parameters like maximum opening area and slope time of the valve movement can be measured from these time-resolved image data.nThe presented results show that optical coherence tomography and high-speed video microscopy are prom-ising tools for the investigation of dynamic behavior and its changes in calcific aortic valve stenosis disease models in mice. OCT offers an easy access to the morphology in 3D and the measurement of tissue parameters like tissue thickness without any sample preparation like staining or cutting.

4D optical coherence tomography of aortic valve dynamics in a murine mouse model ex vivo

The heart and its mechanical components, especially the heart valves and leaflets, are under enormous strain during lifetime. Like all highly stressed materials, also these biological components undergo fatigue and signs of wear, which impinge upon cardiac output and in the end on health and living comfort of affected patients. Thereby pathophysiological changes of the aortic valve leading to calcific aortic valve stenosis (AVS) as most frequent heart valve disease in humans are of particular interest. The knowledge about changes of the dynamic behavior during the course of this disease and the possibility of early stage diagnosis could lead to the development of new treatment strategies and drug-based options of prevention or therapy. ApoE-/- mice as established model of AVS versus wildtype mice were introduced in an ex vivo artificially stimulated heart model. 4D optical coherence tomography (OCT) in combination with high-speed video microscopy were applied to characterize dynamic behavior of the murine aortic valve and to characterize dynamic properties during artificial stimulation. OCT and high-speed video microscopy with high spatial and temporal resolution represent promising tools for the investigation of dynamic behavior and their changes in calcific aortic stenosis disease models in mice.