Abstract:

Fluorescence video angiography is used in neurosurgery to intraoperatively monitor the vascular func-tion, namely the blood flow. This is done by injecting the dye Indocyanine green (ICG) intravenously. After excitation by a near-infrared light source, the fluorescence signal is captured by a camera system. The recorded signal is used to qualitatively assess the vascular function during the intervention. This provides the surgeon with an immediate feedback of the quality of his surgery. Nevertheless, this qualitative assessment needs to be extended and a quantitative value should be calculated to assist the surgical staff. This step requires a standardized and validated test setup mimicking cerebral vessels for studies, such as measurement of the flow and flow profile. This includes the confirmation of the suita-bility of the investigation site in the phantom. Therefore, a flow phantom is designed according to the requirements and set up. The requirements include a variable diameter of the vessel mimicking tubes, variable flow range within the clinical relevant range, a handy and precise injection system with an ini-tial ICG concentration which minimizes quenching effects, a non-toxic and low cost blood analogue with similar viscosity as human blood and finally a last requirement which need more explanation. Re-al blood should not be used due to the contamination of the pump, so water is used as flow media. But the ICG is dissolved in a protein solution and should be surrounded by a protein solution to ensure mixing and diffusion into the same solution media, so the ICG should not get into touch with the flow media water. The investigation sites are given in the ranges which are confirmed to be suitable. The flow phantom provides a consistent testing environment and will be used to conduct studies analyzing the suitability of different methods to assess the flow by fluorescence imaging.

Abstract:

This topic was embedded in the project of measuring blood flow intraoperativly with an optical system (surgical microscope). Measuring blood flow is important to assess the tissues perfusion. In case of hypoperfusion, the function of the tissue cannot be maintained and irreversible damages are possible. To visualize the flow dynamics in the blood, the fluores- cence dye Indocyanine Green (ICG) is injected intravenously and the dyes’ fluorescence is captured with a NIR camera. The performance of methods which assess the blood flow dynamics cannot be determined on living subjects. To facilitate the performance testing, a blood flow phantom was set up within the scope of this thesis. The main goals of this thesis were the design and the installation of the injection mimicking setup and its validation. Since no detailed flow profile of the fluids’ dynamic was available, an in-silico simulation of the flow phantom was implemented via COMSOL Multiphysics. In comparison to previous theses, the focus was on the diffusion and and convection processes of the fluorescence dye for different dimensioning of the ICG dyed bolus. The spatio-temporal morphology of the fluorescence signal depends with some constraint on the volume flow of the liquid media. For the design of the flow phantom, blood analogs were researched to obtain the flow behavior of whole blood, to support the fluorescence of ICG and to avoid impairment of the optical detection. With an ICG concentration of 0.005 g , l the optical detection of the ICG bolus was successful. The in-silico simulation of the flow dynamics and the distribution of the ICG dye showed similar results: the first but not the second boundary of the ICG bolus was detectable for a chosen dimensioning of the ICG dyed bolus. The technical model developed within the scope of this thesis shows promising results for further research. The propagation of the excitation and the fluorescence light can be calculated based on the calculated ICG distribution within the given geometry. With the optical part of the modeling, the distribution of ICG will be better understood and the development of methods which assess the blood flow will be supported.