Segmentation, separation and pose estimation of prostate brachytherapy seeds in CT images.

International audienceIn this paper, we address the development of an automatic approach for the computation of pose information (position + orientation) of prostate brachytherapy loose seeds from 3D CT images. From an initial detection of a set of seed candidates in CT images using a threshold and connected component method, the orientation of each individual seed is estimated by using the principal components analysis (PCA) method. The main originality of this approach is the ability to classify the detected objects based on a priori intensity and volume information and to separate groups of closely spaced seeds using three competing clustering methods: the standard and a modified k-means method and a Gaussian mixture model with an Expectation-Maximization algorithm. Experiments were carried out on a series of CT images of two phantoms and patients. The fourteen patients correspond to a total of 1063 implanted seeds. Detections are compared to manual segmentation and to related work in terms of detection performance and calculation time. This automatic method has proved to be accurate and fast including the ability to separate groups of seeds in a reliable way and to determine the orientation of each seed. Such a method is mandatory to be able to compute precisely the real dose delivered to the patient post-operatively instead of assuming the alignment of seeds along the theoretical insertion direction of the brachytherapy needles

Dynamic Image Processing for Guidance of Off-pump Beating Heart Mitral Valve Repair

Compared to conventional open heart procedures, minimally invasive off-pump beating heart mitral valve repair aims to deliver equivalent treatment for mitral regurgitation with reduced trauma and side effects. However, minimally invasive approaches are often limited by the lack of a direct view to surgical targets and/or tools, a challenge that is compounded by potential movement of the target during the cardiac cycle. For this reason, sophisticated image guidance systems are required in achieving procedural efficiency and therapeutic success. The development of such guidance systems is associated with many challenges. For example, the system should be able to provide high quality visualization of both cardiac anatomy and motion, as well as augmenting it with virtual models of tracked tools and targets. It should have the capability of integrating pre-operative images to the intra-operative scenario through registration techniques. The computation speed must be sufficiently fast to capture the rapid cardiac motion. Meanwhile, the system should be cost effective and easily integrated into standard clinical workflow. This thesis develops image processing techniques to address these challenges, aiming to achieve a safe and efficient guidance system for off-pump beating heart mitral valve repair. These techniques can be divided into two categories, using 3D and 2D image data respectively. When 3D images are accessible, a rapid multi-modal registration approach is proposed to link the pre-operative CT images to the intra-operative ultrasound images. The ultrasound images are used to display the real time cardiac motion, enhanced by CT data serving as high quality 3D context with annotated features. I also developed a method to generate synthetic dynamic CT images, aiming to replace real dynamic CT data in such a guidance system to reduce the radiation dose applied to the patients. When only 2D images are available, an approach is developed to track the feature of interest, i.e. the mitral annulus, based on bi-plane ultrasound images and a magnetic tracking system. The concept of modern GPU-based parallel computing is employed in most of these approaches to accelerate the computation in order to capture the rapid cardiac motion with desired accuracy. Validation experiments were performed on phantom, animal and human data. The overall accuracy of registration and feature tracking with respect to the mitral annulus was about 2-3mm with computation time of 60-400ms per frame, sufficient for one update per cardiac cycle. It was also demonstrated in the results that the synthetic CT images can provide very similar anatomical representations and registration accuracy compared to that of the real dynamic CT images. These results suggest that the approaches developed in the thesis have good potential for a safer and more effective guidance system for off-pump beating heart mitral valve repair

Towards Image-Guided Pediatric Atrial Septal Defect Repair

Congenital heart disease occurs in 107.6 out of 10,000 live births, with Atrial Septal Defects (ASD) accounting for 10\% of these conditions. Historically, ASDs were treated with open heart surgery using cardiopulmonary bypass, allowing a patch to be sewn over the defect. In 1976, King et al. demonstrated use of a transcatheter occlusion procedure, thus reducing the invasiveness of ASD repair. Localization during these catheter based procedures traditionally has relied on bi-plane fluoroscopy; more recently trans-esophageal echocardiography (TEE) and intra-cardiac echocardiography (ICE) have been used to navigate these procedures. Although there is a high success rate using the transcatheter occlusion procedure, fluoroscopy poses radiation dose risk to both patient and clinician. The impact of this dose to the patients is important as many of those undergoing this procedure are children, who have an increased risk associated with radiation exposure. Their longer life expectancy than adults provides a larger window of opportunity for expressing the damaging effects of ionizing radiation. In addition, epidemiologic studies of exposed populations have demonstrated that children are considerably more sensitive to the carcinogenic effects radiation. Image-guided surgery (IGS) uses pre-operative and intra-operative images to guide surgery or an interventional procedure. Central to every IGS system is a software application capable of processing and displaying patient images, registration between multiple coordinate systems, and interfacing with a tool tracking system. We have developed a novel image-guided surgery framework called Kit for Navigation by Image Focused Exploration (KNIFE). This software system serves as the core technology by which a system for reduction of radiation exposure to pediatric patients was developed. The bulk of the initial work in this research endevaour was the development of KNIFE which itself went through countless iterations before arriving at its current state as per the feature requirements established. Secondly, since this work involved the use of captured medical images and their use in an IGS software suite, a brief analysis of the physics behind the images was conducted. Through this aspect of the work, intrinsic parameters (principal point and focal point) of the fluoroscope were quantified using a 3D grid calibration phantom. A second grid phantom was traversed through the fluoroscopic imaging volume of II and flat panel based systems at 2 cm intervals building a scatter field of the volume to demonstrate pincushion and \u27S\u27 distortion in the images. Effects of projection distortion on the images was assessed by measuring the fiducial registration error (FRE) of each point used in two different registration techniques, where both methods utilized ordinary procrustes analysis but the second used a projection matrix built from the fluoroscopes calculated intrinsic parameters. A case study was performed to test whether the projection registration outperforms the rigid transform only. Using the knowledge generated were able to successfully design and complete mock clinical procedures using cardiac phantom models. These mock trials at the beginning of this work used a single point to represent catheter location but this was eventually replaced with a full shape model that offered numerous advantages. At the conclusion of this work a novel protocol for conducting IG ASD procedures was developed. Future work would involve the construction of novel EM tracked tools, phantom models for other vascular diseases and finally clinical integration and use

Biplanar Fluoroscopic Analysis of in vivo Hindfoot Kinematics During Ambulation

The overall goal of this project was to develop and validate a biplanar fluoroscopic system and integrated software to assess hindfoot kinematics. Understanding the motion of the foot and ankle joints may lead to improved treatment methods in persons with foot and ankle pathologies. During gait analysis, skin markers are placed on the lower extremities, which are defined as four rigid-body segments with three joints representing the hip, knee and ankle. This method introduces gross assumptions on the foot and severely limits the analysis of in depth foot mechanics. Multi-segmental models have been developed, but are susceptible to skin motion artifact error. Intra-cortical bone pins studies provide higher accuracy, but are invasive. This dissertation developed and validated a noninvasive biplane fluoroscopy system to overcome the skin motion artifacts and rigid-body assumptions of conventional foot motion analysis. The custom-built biplane fluoroscopy system was constructed from two fluoroscopes separated by 60°, attached to a custom walkway with an embedded force plate. Open source software was incorporated to correct the image distortion and calibrate the capture volume. This study was the first that quantified the cross-scatter contamination in a biplane fluoroscopic system and its effects on the accuracy of marker-based tracking. A cadaver foot study determined the static and dynamic error of the biplane fluoroscopic system using both marker-based and model-based tracking algorithms. The study also developed in vivo 3D kinematic models of the talocrural and subtalar joints during the stance phase of gait. Cross-scatter degradation showed negligible effects in the smallest phantom, suggesting negligible motion tracking error due to cross scatter for distal extremities. Marker-based tracking error had a maximum absolute mean error of 0.21 (± 0.15) in dynamic trials. Model-based tracking results compared to marker-based had an overall dynamic RMS average error of 0.59 mm. Models were developed using custom algorithms to determine talocrural and subtalar joint 3D kinematics. The models offer a viable, noninvasive method suitable for quantifying hindfoot kinematics. Patients with a variety of adult and pediatric conditions which affect foot and ankle dynamics during walking may benefit from this work

A Computational Model to Predict \u3cem\u3eIn Vivo\u3c/em\u3e Kinetics in Implanted and Non-Implanted Shoulders

The purpose of this study was to develop and implement a computational model designed to input in vivo kinematic and predict in vivo forces and torques for the shoulder, elbow, and wrist in normal, rotator cuff-deficient (RCD), reverse shoulder arthroplasty (RSA) and total shoulder arthroplasty (TSA) shoulder subjects. Twenty subjects, divided evenly amongst the four shoulder types, performed a box-lift activity while under fluoroscopic surveillance. Three dimensional (3D) in vivo kinematics was determined for the subjects using implant models and bone models created from CT (computed tomography) scans in a 2D-to-3D registration process. The kinematics were used as input for an inverse dynamics mathematical model, and the subject-specific kinetics were derived. Average resultant shoulder forces were 78.3N (range: 70.4N to 117N, SD: 5.213), 102N (range: 90.2N to 180.2N, SD: 12.339), 94.9N (range: 84.9N to 149N, SD: 10.02), and 92.5N (range: 87.984N to 95.370N, SD: 1.848), for normal, RCD, RSA, and TSA subjects, respectively. Average resultant shoulder torques were 23.6Nm (range: 8.32Nm to 73.7Nm, SD: 11.227), 29.6Nm (range: 22.892Nm to 71.377Nm, SD: 7.581), 27.2Nm (range: 19.961Nm to 59.352Nm, SD: 6.664), 20.3Nm (range: 11.700Nm to 31.409Nm, SD: 6.496), for normal, RCD, RSA, and TSA shoulders, respectively. This study revealed that RCD subjects exhibited a decreased ROM (range of motion) of the humeral head with respect to the glenoid, as compared to the other groups. This study also showed that subjects having a rotator cuff-deficient shoulder and/or a replaced shoulder tend to use compensatory motions to perform the task of lifting a box, and, as a result, they experience greater forces at the glenohumeral joint. Paradoxically, the RCD subjects experienced the highest joint forces and torques among the different shoulder types

3D Reconstruction of Interventional Material from Very Few X-Ray Projections for Interventional Image Guidance

Today, minimally invasive endovascular interventions are usually guided by 2D fluoroscopy, i.e. a live 2D X-ray image. However, 3D fluoroscopy, i.e. a live 3D image reconstructed from a stream of 2D X-ray images, could improve spatial awareness. 3D fluoroscopy is, however, not used today, since no appropriate 3D reconstruction algorithm is known. Existing algorithms for the real-time reconstruction of interventional material (guidewires, stents, catheters, etc.) are either only capable of reconstructing a single guidewire or catheter, or use too many X-ray images and therefore too much dose per 3D reconstruction. The goal of this thesis was to reconstruct complex arrangements of interventional material from as few X-ray images as possible. To this end, a previously proposed algorithm for the reconstruction of interventional material from four X-ray images was adapted. Five key improvements allowed to reduce the number of X-ray images per 3D reconstruction from four to two: a) use of temporal information in a rotating imaging setup, b) separate reconstruction of different types of interventional material enabled by the computation of semantic interventional material extraction images, c) compensation of stent motion by spatial transformer networks, d) per-projection backprojection and e) binarization of the guidewire extraction images. While previously only single curves could be reconstructed from two newly acquired X-ray images, the proposed pipeline can reconstruct stents and even stent-guidewire combinations. Submillimeter reconstruction accuracy was demonstrated on measured X-ray images of interventional material inside an anthropomorphic phantom with simulated respiratory motion. Measurements of the dose area product rate of the proposed 3D reconstruction pipeline indicate a dose burden roughly similar to that of 2D fluoroscopy