A. Naber, D. Berwanger, G. K. Steinberg, and W. Nahm. Spatial gradient based segmentation of vessels and quantitative measurement of the inner diameter and wall thickness from ICG fluorescence angiographies. In SPIE Photonics West, vol. 11229 1122916-2, 2020
During neurovascular surgery the vascular function can be checked intraoperatively and qualitatively by observing the blood dynamics inside the vessel via Indocyanine Green (ICG) Fluorescence Angiography. This state-of-the- art method provides the surgeon with valuable semi-quantitative information but needs to be improved towards a quantitative assessment of vascular volume flow. The precise measurement of volume flow rely on the assumption that both the inner geometry of the blood vessel and the blood flow velocity can be precisely obtained from Fluorescence Angiography. The correct reconstruction of the inner diameter of the vessel is essential in order to minimize the propagated error in the flow calculation. Although ICG binds specifically on blood plasma proteins the fluorescence light radiates also from outside the inner vessel volume due to multiple scattering in the vessel wall, causing a fading edge intensity contrast. A spatial gradient based segmentation method is proposed to reliably estimate the inner diameter of cerebral vessels from intraoperative Fluorescence Angiography images. As result the minimum of the second deviation of the intensity values perpendicular to the vessels edge was identified as the best feature to assess the inner diameter of artificial vessel phantoms. This method has been applied to cerebrovascular vessel images and the results, since no ground truth is available, comply with literature values.
A. Naber, D. Berwanger, and W. Nahm. In Silico Modelling of Blood Vessel Segmentations for Estimation of Discretization Error in Spatial Measurement and its Impact on Quantitative Fluorescence Angiography. In 41st Annual International Conference of the IEEE Engineering in Medicine and Biology Society (EMBC), pp. 4787-4790, 2019
Today the vascular function after interventions as Bypass surgeries are checked qualitatively by observing the blood dynamics inside the vessel via Indocyanine Green (ICG) Fluorescence Angiography. This state-of-the-art should be upgraded and has to be improved and converted towards a quantitatively measured blood flow. Previous approaches show that the blood flow measured from fluorescence angiography cannot be easily calibrated to a gold standard reference. In order to systematically address the possible source of error we investigate as a first step the discretization error in a camera-based measurement of the vessel’s geometry. In order to generate an error-free ground truth, a vessel model has been developed based on mathematical functions. This database is then used to determine the error in discretizing the centerline of the structure and estimate its effects on the accuracy of the flow calculation. As result the model is implemented according to the conditions which are set up to ensure transferability on camera-based segmentations of vessels. In this paper the relative discretization error for estimating the centerline length of segmented vessels could be calculated in the range of 6.3%. This would reveal significant error propagated to the estimation of the blood flow value derived by camera-based angiography.
A. Naber, and W. Nahm. Bi - Domain Intraoperative Registration of Vessels. In Current Directions in Biomedical Engineering, vol. 4(1) , pp. 25-28, 2018
The segmentation and registration of structures are gaining importance due to the increasing demand of auto- mated image enhancement and understanding. Especially in medicine and life science, assistance systems could have a large impact on diagnosis, treatment and quality control. Dye driven procedures, such as uorescence imaging with Indocya- nine green (ICG), are nowadays indispensable because they enhance contrast, reveal structures and deliver the operator with important information. The contact free ICG angiography is providing the surgeon spatial and temporal information on blood ow w ithin a v essel. T he p rocessing o f t hose informa- tion is done manually or semi automated but is very helpful for the surgeon. Extending the degree of automatism, the amount of information processed and even augment or transfer it into another domain could deliver the operator useful support and improve surgical work ow. Using, analyzing and transferring those information from ICG-IR domain into the RGB domain is the focus of this project. We are introducing a vessel regis- tration method in the RGB domain driven by the spatial u- orescence behavior of the vessel in the ICG-IR domain. The method includes Superpixel based segmentation of the vessel in the ICG-IR domain, the spatial gradient based transfer and registration in the RGB domain and the continuous segmen- tation of the vessel in a RGB video. This paper show a proof of concept of the method. The results show an successful in- ter domain information transfer and registration of the vessel. Further tracking of the vessel over all frames is possible. Nev- ertheless limitations are revealed and discussed.
A. Naber, and W. Nahm. Video magnification for intraoperative assessment of vascular function. In Current Directions in Biomedical Engineering, vol. 3(2) , pp. 175-178, 2017
In neurovascular surgery the intraoperative fluorescence angiography has been proven to be a reliable contact-free optical imaging technique to visualize vascular blood-flow. This angiography is obtained by injecting a fluorescence dye e.g. indocyanine green and using an infrared camera system to visualize the fluorescence inside the vessel. Obviously this requires a medical approved dye and an additional camera setup and therefore generating risks and costs. Hence, the aim of our research is to develop a comparable technique for assessing the vascular function. This approach would not require dye nor an additional infrared camera setup. It is achieved by first preprocessing the video data of a camera that records only the visible spectrum and then filter it spatially as well as temporally. The prepared data is again processed to extract information about the vascular function and visualize it. This method would provide an option to compute and visualize the vascular function using the data recorded in the visible spectrum by the surgical microscopes. Given this contact-free optical imaging system, physiological information can be easily provided to the surgeon without an additional setup. In the case of comparable results with the state-of-the-art, this technique provides a straightforward optical intraoperative angiography. Further no drug approval is needed since no dye is injected.
K. Sieler, A. Naber, and W. Nahm. An Evaluation of Image Feature Detectors Based on Spatial Density and Temporal Robustness in Microsurgical Image Processing. In Current Directions in Biomedical Engineering, vol. 5(1) , pp. 273-276, 2019
Optical image processing is part of many applications used for brain surgeries. Microscope camera, or patient movement, like brain-movement through the pulse or a change in the liquor, can cause the image processing to fail. One option to compensate movement is feature detection and spatial allocation. This allocation is based on image features. The frame wise matched features are used to calculate the transformation matrix. The goal of this project was to evaluate different feature detectors based on spatial density and temporal robustness to reveal the most appropriate feature. The feature detectors included corner-, and blob-detectors and were applied on nine videos. These videos were taken during brain surgery with surgical microscopes and include the RGB channels. The evaluation showed that each detector detected up to 10 features for nine frames. The feature detector KAZE resulted in being the best feature detector in both density and robustness.
T. Wirth, A. Naber, and W. Nahm. Combination of Color and Focus Segmentation for Medical Images with Low Depth-of-Field. In Current Directions in Biomedical Engineering, vol. 4(1) , pp. 345-349, 2018
Image segmentation plays an increasingly important role in image processing. It allows for various applications including the analysis of an image for automatic image understanding and the integration of complementary data. During vascular surgeries, the blood flow in the vessels has to be checked constantly, which could be facilitated by a segmentation of the affected vessels. The segmentation of medical images is still done manually, which depends on the surgeon’s experience and is time-consuming. As a result, there is a growing need for automatic image segmentation methods. We propose an unsupervised method to detect the regions of no interest (RONI) in intraoperative images with low depth-of-field (DOF). The proposed method is divided into three steps. First, a color segmentation using a clustering algorithm is performed. In a second step, we assume that the regions of interest (ROI) are in focus whereas the RONI are unfocused. This allows us to segment the image using an edge-based focus measure. Finally, we combine the focused edges with the color RONI to determine the final segmentation result. When tested on different intraoperative images of aneurysm clipping surgeries, the algorithm is able to segment most of the RONI not belonging to the pulsating vessel of interest. Surgical instruments like the metallic clips can also be excluded. Although the image data for the validation of the proposed method is limited to one intraoperative video, a proof of concept is demonstrated.
A miniaturized ceramic atmospheric plasma source for the utilization in life sciences has been developed. It is manufactured in LTCC-technology (low temperature cofired ceramic). The plasma generation is based on buried electrodes which lead to a Dielectric Barrier Discharge (DBD). The employed technology allows small feature sizes (electrode width 150 μm, barrier thickness 40μm etc.) as well as precision in the μm range, resulting in a very low power consumption of the system (approx. 5 W). Thus, the maximum temperature at the point of use can be kept below 40 °C. The flexibility of the manufacturing process (layer lamination, screen printing, patterning with picosecond laser etc.) offers additional features like robust fluidic structures (channels, chambers, gas distribution etc.) as well as the direct implementation of electronic components. The technology concept as well as the design of the ceramic parts and the handhold matched to the multi-well plate format is demonstrated. The plasma of the system can be tuned depending on the assembly of the system and the electric excitation. To prove the biocompatibility and the experimental compatibility with cell cultures (low temperature at the point of use), a method for temperature measurements on the bottom of a multi-well plate was developed. First results of the impact of the plasma source on cell cultures are presented. The effects occurring in the plasma, as well as their effects on the cell cultures (ozone formation, ultraviolet radiation etc.) are separately considered. Furthermore, the cell tolerability of the treatment with the micro-plasma source is investigated with L929 fibroblast cells.