3D shape instantiation for intra-operative navigation from a single 2D projection

Unlike traditional open surgery where surgeons can see the operation area clearly, in robot-assisted Minimally Invasive Surgery (MIS), a surgeon’s view of the region of interest is usually limited. Currently, 2D images from fluoroscopy, Magnetic Resonance Imaging (MRI), endoscopy or ultrasound are used for intra-operative guidance as real-time 3D volumetric acquisition is not always possible due to the acquisition speed or exposure constraints. 3D reconstruction, however, is key to navigation in complex in vivo geometries and can help resolve this issue. Novel 3D shape instantiation schemes are developed in this thesis, which can reconstruct the high-resolution 3D shape of a target from limited 2D views, especially a single 2D projection or slice. To achieve a complete and automatic 3D shape instantiation pipeline, segmentation schemes based on deep learning are also investigated. These include normalization schemes for training U-Nets and network architecture design of Atrous Convolutional Neural Networks (ACNNs). For U-Net normalization, four popular normalization methods are reviewed, then Instance-Layer Normalization (ILN) is proposed. It uses a sigmoid function to linearly weight the feature map after instance normalization and layer normalization, and cascades group normalization after the weighted feature map. Detailed validation results potentially demonstrate the practical advantages of the proposed ILN for effective and robust segmentation of different anatomies. For network architecture design in training Deep Convolutional Neural Networks (DCNNs), the newly proposed ACNN is compared to traditional U-Net where max-pooling and deconvolutional layers are essential. Only convolutional layers are used in the proposed ACNN with different atrous rates and it has been shown that the method is able to provide a fully-covered receptive field with a minimum number of atrous convolutional layers. ACNN enhances the robustness and generalizability of the analysis scheme by cascading multiple atrous blocks. Validation results have shown the proposed method achieves comparable results to the U-Net in terms of medical image segmentation, whilst reducing the trainable parameters, thus improving the convergence and real-time instantiation speed. For 3D shape instantiation of soft and deforming organs during MIS, Sparse Principle Component Analysis (SPCA) has been used to analyse a 3D Statistical Shape Model (SSM) and to determine the most informative scan plane. Synchronized 2D images are then scanned at the most informative scan plane and are expressed in a 2D SSM. Kernel Partial Least Square Regression (KPLSR) has been applied to learn the relationship between the 2D and 3D SSM. It has been shown that the KPLSR-learned model developed in this thesis is able to predict the intra-operative 3D target shape from a single 2D projection or slice, thus permitting real-time 3D navigation. Validation results have shown the intrinsic accuracy achieved and the potential clinical value of the technique. The proposed 3D shape instantiation scheme is further applied to intra-operative stent graft deployment for the robot-assisted treatment of aortic aneurysms. Mathematical modelling is first used to simulate the stent graft characteristics. This is then followed by the Robust Perspective-n-Point (RPnP) method to instantiate the 3D pose of fiducial markers of the graft. Here, Equally-weighted Focal U-Net is proposed with a cross-entropy and an additional focal loss function. Detailed validation has been performed on patient-specific stent grafts with an accuracy between 1-3mm. Finally, the relative merits and potential pitfalls of all the methods developed in this thesis are discussed, followed by potential future research directions and additional challenges that need to be tackled.Open Acces

Group Differences Among Nongmingong: A Follow-up Ethnographic Case Study

This study probes the differences between two generations of nongmingong by presenting and analyzing the ethnographic fieldwork data collected in a labor-intensive enterprise. In the article the authors tend to stress two points. The first is about the attitude to the choice of “reflux” and “job-hopping”. It is suggested that “reflux” and “job-hopping” are two different practices and attempts for both new and old nongmingong when confronted with future development, which may be viewed an opportunity for them. It also suggests that “reflux” and “job-hopping” may represent the needs for self-actualization, strategies and means of mobility or even the different ways of worldview between rural and urban residents of the new and old nongmingong. The second point is about the process of self-categorization of the nongmingong, which illustrates how they are divided by the ideas and options. The authors will explain the process of internal alteration by analysis of their mutual evaluation and definition, interaction, and even conflic

PET imaging of adenosine A2A receptors

This thesis describes the development and evaluation of [11C]preladenant as a novel radioligand for in vivo imaging of adenosine A2A receptors in the brain with positron-emission tomography (PET). The 11C-labeled drug [11C]preladenant was produced with high radiochemical yield and specific activity. The tracer uptake was in accordance with A2A receptor distribution in the brain. [11C]preladenant displayed favorable pharmacokinetics and radiation dosimetry and proved to be a suitable tracer for the in vivo quantification of striatal A2A receptors in rat and monkey brain. [11C]preladenant-PET was also used to investigate A2A receptor availability in a rat model for Parkinson’s disease. We demonstrated that [11C]preladenant-PET is able to show changes of A2A receptor availability during the course of Parkinson’s disease, and that A2A receptor availability positively correlated with dopamine D2 receptor availability in rats with levodopa-induced dyskinesia. These findings could contribute to our knowledge about the molecular mechanisms underlying Parkinson’s disease. Thus, this study provides a useful tool to map A2A receptors in the living brain, which could be of help in exploring the functions of A2A receptors in physiological and pathological conditions. [11C]preladenant-PET could facilitate linking changes in A2A receptor availability with clinical symptoms, measuring drug-related A2A receptor occupancy in drug development and determining the best regimen of A2A receptor-targeting treatment. Now this tracer is ready for validation in human subjects. If the validation is successful, [11C]preladenant-PET can be applied to study the behavior and functions of A2A receptors in the human brain in various conditions

A Case of Cutaneous Nocardiosis with Involvement of the Trachea, Anterior Mediastinum and Sternum

Nocardiosis is a rare infectious disease due to Nocardia infections. In this report, we present a rare case of cutaneous nocardiosis with involvement of the trachea, anterior mediastinum and sternum. The strain of Nocardia has been isolated from bacterial culture of infected tissue. 16s rRNA sequencing confirmed that it contained the Nocardia genus. The patient was successfully treated with Co-SMZ