Accurate and fast understanding of the patient's anatomy is crucial in surgical decision making and particularly important in visceral surgery. Sophisticated visualization techniques such as 3D Volume Rendering can aid the surgeon and potentially lead to a benefit for the patient. Recently, we proposed a novel volume rendering technique called Adaptive Volumetric Illumination Sampling (AVIS) that can generate realistic lighting in real-time, even for high resolution images and volumes but without introducing additional image noise. In order to evaluate this new technique, we conducted a randomized, three-period crossover study comparing AVIS to conventional Direct Volume Rendering (DVR) and Path Tracing (PT). CT datasets from 12 patients were evaluated by 10 visceral surgeons who were either senior physicians or experienced specialists. The time needed for answering clinically relevant questions as well as the correctness of the answers were analyzed for each visualization technique. In addition to that, the perceived workload during these tasks was assessed for each technique, respectively. The results of the study indicate that AVIS has an advantage in terms of both time efficiency and most aspects of the perceived workload, while the average correctness of the given answers was very similar for all three methods. In contrast to that, Path Tracing seems to show particularly high values for mental demand and frustration. We plan to repeat a similar study with a larger participant group to consolidate the results.

Due to the highly industrialized manufacturing process of printed-circuit-boards, PCB-based axial flux machines are the center of interest. The thermal utilization, and thus the current carrying capability, of such machines is crucial for their design and is therefore one of the main design critera. A new motor winding design is presented using thermal Vertical Interconnect Accesses (VIA) to improve the thermal conductivity to the heat sink, where the operating temperature and the specific electrical resistance of copper mutually interact with each other. The VIAs also implement electrical interconnects between the layers and shorten the total length of the end windings. Finite element simulations were performed for a given PCB layer stack design with variations of the vertical interconnect access pitch and different conductor currents. Because of the complex structure of the winding system, a parametric study was performed to demonstrate the effectiveness of thermal VIAs depending on the VIA pitch. The finite element simulations and measurements show that VIAs can be integrated into winding systems and confirms the superior effectiveness of the proposed cooling strategy.

In this paper an enhanced cooling strategy for PCB motor windings is presented. It is proposed that using thermal vias for a parallel multilayer PCB winding system can achieve a higher current carrying capacity. Experimental measurements were performed under strict thermal boundary conditions. The results show a significant increase in current carrying capacity while using thermal vias in combination with a heat sink. Further optimization possibilities in respect to axial flux machines are discussed.

In this paper, a novel 42 slot, 20 pole ironless winding for use in an axial-flux machine is presented. The proposed design improves the utilization of the available air gap area and is based on the implementation of the winding as a printed circuit board (PCB). Besides, it is compared with a conventional 21 slot, 20 pole ironless axial-flux winding regarding the criteria: torque generation and induced voltage at constant speed. The comparison is based on analytical calculated results, which were obtained by using the winding function theory and an exponential function approach for the magnetic flux density produced by the permanent magnets. The analytical description of the MMF is derived from the geometry whereas the torque and the induced EMF are calculated by using complex Fourier series. Furthermore, a special case of Parseval's theorem is used to get the torque and voltage from the Fourier coefficients in a very simple way. The analytical calculated results are compared to those obtained by FEM.

Percutaneous radiofrequency ablation (RFA) is becoming a standard minimally invasive clinical procedure for the treatment of liver tumors. However, planning the applicator placement such that the malignant tissue is completely destroyed, is a demanding task that requires considerable experience. In this work, we present a fast GPU-based real-time approximation of the ablation zone incorporating the cooling effect of liver vessels. Weighted distance fields of varying RF applicator types are derived from complex numerical simulations to allow a fast estimation of the ablation zone. Furthermore, the heat-sink effect of the cooling blood flow close to the applicator's electrode is estimated by means of a preprocessed thermal equilibrium representation of the liver parenchyma and blood vessels. Utilizing the graphics card, the weighted distance field incorporating the cooling blood flow is calculated using a modular shader framework, which facilitates the real-time visualization of the ablation zone in projected slice views and in volume rendering. The proposed methods are integrated in our software assistant prototype for planning RFA therapy. The software allows the physician to interactively place virtual RF applicator models. The real-time visualization of the corresponding approximated ablation zone facilitates interactive evaluation of the tumor coverage in order to optimize the applicator's placement such that all cancer cells are destroyed by the ablation.

Abstract Percutaneous radiofrequency (RF) ablation is a minimally invasive, image‐guided therapy for the treatment of liver tumors. The assessment of the ablation area (coagulation) is performed to verify the treatment success as an essential part of the therapy. Traditionally, pre‐ and post‐interventional CT images are used to visually compare the shape, size, and position of tumor and coagulation. In this work, we present a novel visualization as well as a navigation tool, the so‐called tumor map. The tumor map is a pseudo‐cylindrical mapping of the tumor surface onto a 2D image. It is used for a combined visualization of all ablation zones of the tumor to allow a reliable therapy assessment. Additionally, the tumor map serves as an interactive tool for intuitive navigation within the 3D volume rendering of the tumor vicinity as well as with familiar 2D viewers.

Expressive and efficient visualizations of complex vascular structures are essential for medical applications, such as diagnosis and therapy planning. A variety of techniques has been developed which provide smooth high-quality visualizations of vascular structures based on rather simple model assumptions. For diagnostic applications, these model assumptions and the resulting deviations from the actual vessel surface are not acceptable. We present a model-free approach which employs the binary result of a prior vessel segmentation as input. Instead of directly converting the segmentation result into a surface, we compute a point cloud which is adaptively refined at thin structures, where aliasing effects are particularly obvious and artifacts may occur. The point cloud is transformed into a surface representation by means of MPU Implicits, which provide a smooth piecewise quadratic approximation. Our method has been applied to a variety of datasets including pathologic cases. The generated visualizations are considerably more accurate than model-based approaches. Compared to other model-free approaches, our method produces smoother results.