Facial soft tissue segmentation

The importance of the face for socio-ecological interaction is the cause for a high demand on any surgical intervention on the facial musculo-skeletal system. Bones and soft-tissues are of major importance for any facial surgical treatment to guarantee an optimal, functional and aesthetical result. For this reason, surgeons want to pre-operatively plan, simulate and predict the outcome of the surgery allowing for shorter operation times and improved quality. Accurate simulation requires exact segmentation knowledge of the facial tissues. Thus semi-automatic segmentation techniques are required. This thesis proposes semi-automatic methods for segmentation of the facial soft-tissues, such as muscles, skin and fat, from CT and MRI datasets, using a Markov Random Fields (MRF) framework. Due to image noise, artifacts, weak edges and multiple objects of similar appearance in close proximity, it is difficult to segment the object of interest by using image information alone. Segmentations would leak at weak edges into neighboring structures that have a similar intensity profile. To overcome this problem, additional shape knowledge is incorporated in the energy function which can then be minimized using Graph-Cuts (GC). Incremental approaches by incorporating additional prior shape knowledge are presented. The proposed approaches are not object specific and can be applied to segment any class of objects be that anatomical or non-anatomical from medical or non-medical image datasets, whenever a statistical model is present. In the first approach a 3D mean shape template is used as shape prior, which is integrated into the MRF based energy function. Here, the shape knowledge is encoded into the data and the smoothness terms of the energy function that constrains the segmented parts to a reasonable shape. In the second approach, to improve handling of shape variations naturally found in the population, the fixed shape template is replaced by a more robust 3D statistical shape model based on Probabilistic Principal Component Analysis (PPCA). The advantages of using the Probabilistic PCA are that it allows reconstructing the optimal shape and computing the remaining variance of the statistical model from partial information. By using an iterative method, the statistical shape model is then refined using image based cues to get a better fitting of the statistical model to the patient's muscle anatomy. These image cues are based on the segmented muscle, edge information and intensity likelihood of the muscle. Here, a linear shape update mechanism is used to fit the statistical model to the image based cues. In the third approach, the shape refinement step is further improved by using a non-linear shape update mechanism where vertices of the 3D mesh of the statistical model incur the non-linear penalty depending on the remaining variability of the vertex. The non-linear shape update mechanism provides a more accurate shape update and helps in a finer shape fitting of the statistical model to the image based cues in areas where the shape variability is high. Finally, a unified approach is presented to segment the relevant facial muscles and the remaining facial soft-tissues (skin and fat). One soft-tissue layer is removed at a time such as the head and non-head regions followed by the skin. In the next step, bones are removed from the dataset, followed by the separation of the brain and non-brain regions as well as the removal of air cavities. Afterwards, facial fat is segmented using the standard Graph-Cuts approach. After separating the important anatomical structures, finally, a 3D fixed shape template mesh of the facial muscles is used to segment the relevant facial muscles. The proposed methods are tested on the challenging example of segmenting the masseter muscle. The datasets were noisy with almost all possessing mild to severe imaging artifacts such as high-density artifacts caused by e.g. dental fillings and dental implants. Qualitative and quantitative experimental results show that by incorporating prior shape knowledge leaking can be effectively constrained to obtain better segmentation results

Wireless Power Transfer (WPT) for Electric Vehicles (EVs) - Present and future trends

100 year old gasoline engine technology vehicles have now become one of the major contributors of greenhouse gases. Plug-in Electric Vehicles (PEVs) have been proposed to achieve environmental friendly transportation. Even though the PEV usage is currently increasing, a technology breakthrough would be required to overcome battery related drawbacks. Although battery technology is evolving, drawbacks inherited with batteries such as; cost, size, weight, slower charging characteristic and low energy density would still be dominating constrains for development of EVs. Furthermore, PEVs have not been accepted as preferred choice by many consumers due to charging related issues. To address battery related limitations, the concept of dynamic Wireless Power Transfer (WPT) enabled EVs have been proposed in which EV is being charged while it is in motion. WPT enabled infrastructure has to be employed to achieve dynamic EV charging concept. The weight of the battery pack can be reduced as the required energy storage is lower if the vehicle can be powered wirelessly while driving. Stationary WPT charging where EV is charged wirelessly when it is stopped, is simpler than dynamic WPT in terms of design complexity. However, stationary WPT does not increase vehicle range compared to wired-PEVs. State-of-art WPT technology for future transportation is discussed in this chapter. Analysis of the WPT system and its performance indices are introduced. Modelling the WPT system using different methods such as equivalent circuit theory, two port network theory and coupled mode theory is described illustrating their own merits in Sect. 2.3. Both stationary and dynamic WPT for EV applications are illustrated in Sect. 2.4. Design challenges and optimization directions are analysed in Sect. 2.5. Adaptive tuning techniques such as adaptive impedance matching and frequency tuning are also discussed. A case study for optimizing resonator design is presented in Sect. 2.6. Achievements by the research community is introduced highlighting directions for future research

Wireless Power Transfer (WPT) for Electric Vehicles (EVs)—Present and Future Trends

100 year old gasoline engine technology vehicles have now become one of the major contributors of greenhouse gases. Plug-in Electric Vehicles (PEVs) have been proposed to achieve environmental friendly transportation. Even though the PEV usage is currently increasing, a technology breakthrough would be required to overcome battery related drawbacks. Although battery technology is evolving, drawbacks inherited with batteries such as; cost, size, weight, slower charging characteristic and low energy density would still be dominating constrains for development of EVs. Furthermore, PEVs have not been accepted as preferred choice by many consumers due to charging related issues. To address battery related limitations, the concept of dynamic Wireless Power Transfer (WPT) enabled EVs have been proposed in which EV is being charged while it is in motion. WPT enabled infrastructure has to be employed to achieve dynamic EV charging concept. The weight of the battery pack can be reduced as the required energy storage is lower if the vehicle can be powered wirelessly while driving. Stationary WPT charging where EV is charged wirelessly when it is stopped, is simpler than dynamic WPT in terms of design complexity. However, stationary WPT does not increase vehicle range compared to wired-PEVs. State-of-art WPT technology for future transportation is discussed in this chapter. Analysis of the WPT system and its performance indices are introduced. Modelling the WPT system using different methods such as equivalent circuit theory, two port network theory and coupled mode theory is described illustrating their own merits in Sect. 2.3. Both stationary and dynamic WPT for EV applications are illustrated in Sect. 2.4. Design challenges and optimization directions are analysed in Sect. 2.5. Adaptive tuning techniques such as adaptive impedance matching and frequency tuning are also discussed. A case study for optimizing resonator design is presented in Sect. 2.6. Achievements by the research community is introduced highlighting directions for future research

Tunable metamaterials for optimization of wireless power transfer systems

Metamaterials (MMs) have been proposed to improve the performance of wireless power transfer (WPT) systems. The performance of identical unit cells having the same transmitter and receiver self-resonance is presented in the literature. This paper presents the optimization of tunable MM for performance improvement in WPT systems. Furthermore, a figure of merit (FOM) is proposed for the optimization of WPT systems with MMs. It is found that both transferred power and power transfer efficiency can be improved significantly by using the proposed FOM and tunable MM, particularly under misaligned conditions

Tunable metamaterials for optimization of wireless power transfer systems

<i>Metamaterials</i> (MMs) have been proposed to improve the performance of <i>wireless power transfer</i> (WPT) systems. The performance of identical unit cells having the same transmitter and receiver self-resonance is presented in the literature. This paper presents the optimization of tunable MM for performance improvement in WPT systems. Furthermore, a <i>figure of merit</i> (FOM) is proposed for the optimization of WPT systems with MMs. It is found that both transferred power and power transfer efficiency can be improved significantly by using the proposed FOM and tunable MM, particularly under misaligned conditions

Optimization of double spiral metamaterial for wireless power transfer

Metamaterials (MMs) have been proposed to improve the performance of wireless power transfer (WPT) systems. However, optimization of WPT systems with MM using complex electromagnetic analytical methods and slow finite element simulation methods have become increasingly tedious. A simple analytical approach using equivalent circuit method to optimize WPT systems with MMs is proposed in this paper. A Double spiral metamaterial (DSM) is introduced and analyzed using the proposed approach. Furthermore, a detailed optimization process is presented considering system level performance indices (efficiency and transferred power) and application level requirements (transfer distance, maximum misalignment and probability of alignment). A novel figure-of-merit is introduced to achieve better compromise between system level performance indices and application level requirements. The proposed optimization strategy is validated with the experimental results

Repeater tuning against load variation for wireless power transfer

The incorporation of a repeater with a wireless power transfer (<i>WPT</i>) system for the performance improvement is investigated in this paper. Tuning of the self-resonance frequencies of transmitter, receiver and repeater coils is investigated as a promising approach to improve the performance against load variation. Theoretical analysis is presented using equivalent circuit method, and the 2-coil equivalent of WPT system with a repeaters is explored. Numerical results are presented along with experimental results to validate the proposed method

Repeater tuning against load variation for wireless power transfer

The incorporation of a repeater with a wireless power transfer (WPT) system for the performance improvement is investigated in this paper. Tuning of the self-resonance frequencies of transmitter, receiver and repeater coils is investigated as a promising approach to improve the performance against load variation. Theoretical analysis is presented using equivalent circuit method, and the 2-coil equivalent of WPT system with a repeaters is explored. Numerical results are presented along with experimental results to validate the proposed method

Efficiency enhancement for dynamic wireless power transfer system with segmented transmitter array

Achieving high efficiency with improved power transfer distance and misalignment tolerance is the major design challenge in realizing dynamic wireless power transfer (D-WPT) systems. This paper provides an analysis on designing D-WPT systems. Design parameters such as number of Tx coils, separation between Tx, operating frequency, and load characteristics are analyzed with respect to efficiency for the D-WPT system with segmented transmitter array. A double-spiral repeater (DSR) is proposed for improving efficiency, enhancing transfer distance, and misalignment tolerance. Experimental results of the proposed topology with DSRs show efficiencies of 81% and 60% at normalized transfer distances (normalized to geometric mean of Tx and Rx sizes) of 0.74 and 2.2, respectively. The proposed topology can be effectively used to alleviate efficiency deterioration against transfer distance and misalignment in D-WPT systems