Feature Lines for Illustrating Medical Surface Models: Mathematical Background and Survey

This paper provides a tutorial and survey for a specific kind of illustrative visualization technique: feature lines. We examine different feature line methods. For this, we provide the differential geometry behind these concepts and adapt this mathematical field to the discrete differential geometry. All discrete differential geometry terms are explained for triangulated surface meshes. These utilities serve as basis for the feature line methods. We provide the reader with all knowledge to re-implement every feature line method. Furthermore, we summarize the methods and suggest a guideline for which kind of surface which feature line algorithm is best suited. Our work is motivated by, but not restricted to, medical and biological surface models.Comment: 33 page

Sliding to predict: vision-based beating heart motion estimation by modeling temporal interactions

Purpose: Technical advancements have been part of modern medical solutions as they promote better surgical alternatives that serve to the benefit of patients. Particularly with cardiovascular surgeries, robotic surgical systems enable surgeons to perform delicate procedures on a beating heart, avoiding the complications of cardiac arrest. This advantage comes with the price of having to deal with a dynamic target which presents technical challenges for the surgical system. In this work, we propose a solution for cardiac motion estimation. Methods: Our estimation approach uses a variational framework that guarantees preservation of the complex anatomy of the heart. An advantage of our approach is that it takes into account different disturbances, such as specular reflections and occlusion events. This is achieved by performing a preprocessing step that eliminates the specular highlights and a predicting step, based on a conditional restricted Boltzmann machine, that recovers missing information caused by partial occlusions. Results: We carried out exhaustive experimentations on two datasets, one from a phantom and the other from an in vivo procedure. The results show that our visual approach reaches an average minima in the order of magnitude of 10-7 while preserving the heart’s anatomical structure and providing stable values for the Jacobian determinant ranging from 0.917 to 1.015. We also show that our specular elimination approach reaches an accuracy of 99% compared to a ground truth. In terms of prediction, our approach compared favorably against two well-known predictors, NARX and EKF, giving the lowest average RMSE of 0.071. Conclusion: Our approach avoids the risks of using mechanical stabilizers and can also be effective for acquiring the motion of organs other than the heart, such as the lung or other deformable objects.Peer ReviewedPostprint (published version

End-points of Decompression of in Lumbar Transforaminal Endoscopic Spine Surgery: A Narrative Review of Objective and Subjective Criteria to Prevent Failures

Objective Executions of indications/extended indications are associated with higher than normal rates of symptomatic recurrences and treatment failures, especially for novice surgeons incorporating Percutaneous Transforaminal endoscopic lumbar discectomy/decompression (PTELD) techniques. Causes of failures can be manifold and can occur because of a residual or a complete fragment causing persistent compression or associated unaddressed stenosis. To prevent this problem, proper training, multiple instrument inventory, variable techniques are needed with progressive learning. Authors aim to suggest objective and subjective criteria to define end-points/adequacy of decompression (EPD). Methods PubMed database search was limited to locate only adequacy of decompression of PTELD and thus included specific keywords: “ENDPOINT” OR “ADEQUATE” AND “DECOMPRESSION” AND “TRANSFORAMINAL” AND “ENDOSCOPY”. Authors added their experience to refine and define multiple EPD. Results In the search we found 12 articles total. Upon reviewing these, we found 7 articles matching our criteria. Cross references of included articles were searched, 5 additional articles were included. EPD were described in only 9 articles. Author’s experience with other relevant references were added to complete the viewpoint (EPD, n=29). Direct observed/provoked EPD and inferred EPD were defined separately. Videos, illustrations and descriptions of each EPD are illustrated to provide the ideation. Conclusion EPD are variable and not all signs may be elicited in every case and may change with surgeon experience. The ability to recognize EPD is the crux for successful outcomes and maximum possible EPD’s should be aimed in every surgery to avoid failures

Minimally invasive thoracoscopic approach for anterior decompression and stabilization of metastatic spine disease

Journal ArticleObject. The choices available in the management of metastatic spine disease are complex, and the role of surgical therapy is increasing. Recent studies have indicated that patients treated with direct surgical decompression and stabilization before radiation have better functional outcomes than those treated with radiation alone. The most common anterior surgical approach for direct spinal cord decompression and stabilization in the thoracic spine is open thoracotomy; however, thoracotomy for spinal access is associated with morbidity that can be avoided with minimally invasive techniques like thoracoscopy. Methods. A minimally invasive thoracoscopic approach was used for the surgical treatment of thoracic and thoracolumbar metastatic spinal cord compression. This technique allows ventral decompression via corpectomy, interbody reconstruction with expandable cages, and stabilization with an anterolateral plating system designed specifically for minimally invasive implantation. This technique was performed in 5 patients with metastatic disease of the thoracic spine, including the thoracolumbar junction. Results. All patients had improvement in preoperative symptoms and neurological deficits. No complications occurred in this small series. Conclusions. The minimally invasive thoracoscopic approach can be applied to the treatment of thoracic and thoracolumbar metastatic spine disease in an effort to reduce access morbidity. Preliminary results have indicated that adequate decompression, reconstruction, and stabilization can be achieved with this technique

직접 볼륨 렌더링에서 점진적 렌즈 샘플링을 사용한 피사계 심도 렌더링

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·컴퓨터공학부, 2021. 2. 신영길.Direct volume rendering is a widely used technique for extracting information from 3D scalar fields acquired by measurement or numerical simulation. To visualize the structure inside the volume, the voxels scalar value is often represented by a translucent color. This translucency of direct volume rendering makes it difficult to perceive the depth between the nested structures. Various volume rendering techniques to improve depth perception are mainly based on illustrative rendering techniques, and physically based rendering techniques such as depth of field effects are difficult to apply due to long computation time. With the development of immersive systems such as virtual and augmented reality and the growing interest in perceptually motivated medical visualization, it is necessary to implement depth of field in direct volume rendering. This study proposes a novel method for applying depth of field effects to volume ray casting to improve the depth perception. By performing ray casting using multiple rays per pixel, objects at a distance in focus are sharply rendered and objects at an out-of-focus distance are blurred. To achieve these effects, a thin lens camera model is used to simulate rays passing through different parts of the lens. And an effective lens sampling method is used to generate an aliasing-free image with a minimum number of lens samples that directly affect performance. The proposed method is implemented without preprocessing based on the GPU-based volume ray casting pipeline. Therefore, all acceleration techniques of volume ray casting can be applied without restrictions. We also propose multi-pass rendering using progressive lens sampling as an acceleration technique. More lens samples are progressively used for ray generation over multiple render passes. Each pixel has a different final render pass depending on the predicted maximum blurring size based on the circle of confusion. This technique makes it possible to apply a different number of lens samples for each pixel, depending on the degree of blurring of the depth of field effects over distance. This acceleration method reduces unnecessary lens sampling and increases the cache hit rate of the GPU, allowing us to generate the depth of field effects at interactive frame rates in direct volume rendering. In the experiments using various data, the proposed method generated realistic depth of field effects in real time. These results demonstrate that our method produces depth of field effects with similar quality to the offline image synthesis method and is up to 12 times faster than the existing depth of field method in direct volume rendering.직접 볼륨 렌더링(direct volume rendering, DVR)은 측정 또는 수치 시뮬레이션으로 얻은 3차원 공간의 스칼라 필드(3D scalar fields) 데이터에서 정보를 추출하는데 널리 사용되는 기술이다. 볼륨 내부의 구조를 가시화하기 위해 복셀(voxel)의 스칼라 값은 종종 반투명의 색상으로 표현된다. 이러한 직접 볼륨 렌더링의 반투명성은 중첩된 구조 간 깊이 인식을 어렵게 한다. 깊이 인식을 향상시키기 위한 다양한 볼륨 렌더링 기법들은 주로 삽화풍 렌더링(illustrative rendering)을 기반으로 하며, 피사계 심도(depth of field, DoF) 효과와 같은 물리 기반 렌더링(physically based rendering) 기법들은 계산 시간이 오래 걸리기 때문에 적용이 어렵다. 가상 및 증강 현실과 같은 몰입형 시스템의 발전과 인간의 지각에 기반한 의료영상 시각화에 대한 관심이 증가함에 따라 직접 볼륨 렌더링에서 피사계 심도를 구현할 필요가 있다. 본 논문에서는 직접 볼륨 렌더링의 깊이 인식을 향상시키기 위해 볼륨 광선투사법에 피사계 심도 효과를 적용하는 새로운 방법을 제안한다. 픽셀 당 여러 개의 광선을 사용한 광선투사법(ray casting)을 수행하여 초점이 맞는 거리에 있는 물체는 선명하게 표현되고 초점이 맞지 않는 거리에 있는 물체는 흐리게 표현된다. 이러한 효과를 얻기 위하여 렌즈의 서로 다른 부분을 통과하는 광선들을 시뮬레이션 하는 얇은 렌즈 카메라 모델(thin lens camera model)이 사용되었다. 그리고 성능에 직접적으로 영향을 끼치는 렌즈 샘플은 최적의 렌즈 샘플링 방법을 사용하여 최소한의 개수를 가지고 앨리어싱(aliasing)이 없는 이미지를 생성하였다. 제안한 방법은 기존의 GPU 기반 볼륨 광선투사법 파이프라인 내에서 전처리 없이 구현된다. 따라서 볼륨 광선투사법의 모든 가속화 기법을 제한없이 적용할 수 있다. 또한 가속 기술로 누진 렌즈 샘플링(progressive lens sampling)을 사용하는 다중 패스 렌더링(multi-pass rendering)을 제안한다. 더 많은 렌즈 샘플들이 여러 렌더 패스들을 거치면서 점진적으로 사용된다. 각 픽셀은 착란원(circle of confusion)을 기반으로 예측된 최대 흐림 정도에 따라 다른 최종 렌더링 패스를 갖는다. 이 기법은 거리에 따른 피사계 심도 효과의 흐림 정도에 따라 각 픽셀에 다른 개수의 렌즈 샘플을 적용할 수 있게 한다. 이러한 가속화 방법은 불필요한 렌즈 샘플링을 줄이고 GPU의 캐시(cache) 적중률을 높여 직접 볼륨 렌더링에서 상호작용이 가능한 프레임 속도로 피사계 심도 효과를 렌더링 할 수 있게 한다. 다양한 데이터를 사용한 실험에서 제안한 방법은 실시간으로 사실적인 피사계 심도 효과를 생성했다. 이러한 결과는 우리의 방법이 오프라인 이미지 합성 방법과 유사한 품질의 피사계 심도 효과를 생성하면서 직접 볼륨 렌더링의 기존 피사계 심도 렌더링 방법보다 최대 12배까지 빠르다는 것을 보여준다.CHAPTER 1 INTRODUCTION 1 1.1 Motivation 1 1.2 Dissertation Goals 5 1.3 Main Contributions 6 1.4 Organization of Dissertation 8 CHAPTER 2 RELATED WORK 9 2.1 Depth of Field on Surface Rendering 10 2.1.1 Object-Space Approaches 11 2.1.2 Image-Space Approaches 15 2.2 Depth of Field on Volume Rendering 26 2.2.1 Blur Filtering on Slice-Based Volume Rendering 28 2.2.2 Stochastic Sampling on Volume Ray Casting 30 CHAPTER 3 DEPTH OF FIELD VOLUME RAY CASTING 33 3.1 Fundamentals 33 3.1.1 Depth of Field 34 3.1.2 Camera Models 36 3.1.3 Direct Volume Rendering 42 3.2 Geometry Setup 48 3.3 Lens Sampling Strategy 53 3.3.1 Sampling Techniques 53 3.3.2 Disk Mapping 57 3.4 CoC-Based Multi-Pass Rendering 60 3.4.1 Progressive Lens Sample Sequence 60 3.4.2 Final Render Pass Determination 62 CHAPTER 4 GPU IMPLEMENTATION 66 4.1 Overview 66 4.2 Rendering Pipeline 67 4.3 Focal Plane Transformation 74 4.4 Lens Sample Transformation 76 CHAPTER 5 EXPERIMENTAL RESULTS 78 5.1 Number of Lens Samples 79 5.2 Number of Render Passes 82 5.3 Render Pass Parameter 84 5.4 Comparison with Previous Methods 87 CHAPTER 6 CONCLUSION 97 Bibliography 101 Appendix 111Docto

Fetal Interventions: A Closer Look at Fetoscopic Laser Surgery: A Literature Review

Over the past decades, due to the advances in imaging methods, prenatal diagnosis of congenital malformations has become widely available. Simultaneously with the improvement of surgical techniques and the development of instrumentation technology, fetal treatment of these pathologies became possible, arising as an alternative to the standard postnatal therapy, aiming to improve fetal outcomes and optimize the transition into neonatal life. Thus, fetal surgery emerges, comprising open interventions and minimally invasive procedures, such as fetoscopy. Fetoscopic surgery, or fetal endoscopic surgery, is a technique that uses endoscopic technology to correct structural and/or functional fetal anomalies in utero, under continuous ultrasound guidance. Fetoscopy is mainly performed percutaneously and allows direct visualization of the fetus and adjacent structures. Nowadays, fetal surgery is most commonly indicated in the treatment of twinto-twin transfusion syndrome, a complication of monochorionic twin pregnancies, using laser coagulation. However, fetoscopic laser surgery can also be performed for the management of other conditions affecting monochorionic pregnancies, such as twin anemia polycythemia sequence and twin reversed arterial perfusion sequence, as well as several other pathologies including amniotic band syndrome, lower urinary tract obstruction, congenital high airway obstruction syndrome, chorioangiomas, and sacrococcygeal teratomas. The aim of this literature review is to provide a brief overview of the most common fetal interventions and to describe fetoscopic laser surgery, covering its indications, techniques, and outcomes following fetal treatment.Nas últimas décadas, a evolução da técnica imagiológica permitiu o diagnóstico pré-natal de um maior número de malformações congénitas. Simultaneamente com os avanços da técnica cirúrgica e dos próprios instrumentos utilizados, o tratamento fetal destas patologias surge como uma alternativa às opções terapêuticas pós-natais, de modo a melhorar o prognóstico neonatal e otimizar a transição do feto à vida extrauterina. Deste modo, a cirurgia fetal torna-se uma realidade, abrangendo procedimentos por via aberta e intervenções minimamente invasivas, como a fetoscopia. A cirurgia fetoscópica, ou cirurgia endoscópica fetal, consiste na utilização de técnicas de endoscopia para a correção de anomalias estruturais e/ou funcionais do feto, com o auxílio de monitorização ecográfica contínua. A fetoscopia é uma intervenção realizada maioritariamente por abordagem percutânea, permitindo a visualização direta do feto e estruturas adjacentes. Atualmente, a cirurgia fetal mais frequentemente realizada tem como indicação a síndrome de transfusão feto-fetal, complicação da gravidez gemelar monocoriónica, recorrendo à fetoscopia com coagulação a laser. A cirurgia fetal a laser pode também ser uma opção terapêutica noutras complicações das gestações gemelares monocoriónicas, como na sequência anemia-policitemia gemelar e na sequência de perfusão arterial reversa gemelar. Além destas patologias, o tratamento fetoscópico a laser foi também descrito na síndrome da banda amniótica, uropatia obstrutiva, síndrome de obstrução congénita das vias aéreas superiores, corioangioma e teratoma sacrococcígeo. Esta revisão bibliográfica pretende explorar os diferentes tipos de cirurgia fetal, focando-se na descrição da técnica da cirurgia fetoscópica a laser, bem como nas suas indicações e diferentes prognósticos após a intervenção fetal

SERV-CT: A disparity dataset from cone-beam CT for validation of endoscopic 3D reconstruction

In computer vision, reference datasets from simulation and real outdoor scenes have been highly successful in promoting algorithmic development in stereo reconstruction. Endoscopic stereo reconstruction for surgical scenes gives rise to specific problems, including the lack of clear corner features, highly specular surface properties and the presence of blood and smoke. These issues present difficulties for both stereo reconstruction itself and also for standardised dataset production. Previous datasets have been produced using computed tomography (CT) or structured light reconstruction on phantom or ex vivo models. We present a stereo-endoscopic reconstruction validation dataset based on cone-beam CT (SERV-CT). Two ex vivo small porcine full torso cadavers were placed within the view of the endoscope with both the endoscope and target anatomy visible in the CT scan. Subsequent orientation of the endoscope was manually aligned to match the stereoscopic view and benchmark disparities, depths and occlusions are calculated. The requirement of a CT scan limited the number of stereo pairs to 8 from each ex vivo sample. For the second sample an RGB surface was acquired to aid alignment of smooth, featureless surfaces. Repeated manual alignments showed an RMS disparity accuracy of around 2 pixels and a depth accuracy of about 2 mm. A simplified reference dataset is provided consisting of endoscope image pairs with corresponding calibration, disparities, depths and occlusions covering the majority of the endoscopic image and a range of tissue types, including smooth specular surfaces, as well as significant variation of depth. We assessed the performance of various stereo algorithms from online available repositories. There is a significant variation between algorithms, highlighting some of the challenges of surgical endoscopic images. The SERV-CT dataset provides an easy to use stereoscopic validation for surgical applications with smooth reference disparities and depths covering the majority of the endoscopic image. This complements existing resources well and we hope will aid the development of surgical endoscopic anatomical reconstruction algorithms

Visual Perception and Cognition in Image-Guided Intervention

Surgical image visualization and interaction systems can dramatically affect the efficacy and efficiency of surgical training, planning, and interventions. This is even more profound in the case of minimally-invasive surgery where restricted access to the operative field in conjunction with limited field of view necessitate a visualization medium to provide patient-specific information at any given moment. Unfortunately, little research has been devoted to studying human factors associated with medical image displays and the need for a robust, intuitive visualization and interaction interfaces has remained largely unfulfilled to this day. Failure to engineer efficient medical solutions and design intuitive visualization interfaces is argued to be one of the major barriers to the meaningful transfer of innovative technology to the operating room. This thesis was, therefore, motivated by the need to study various cognitive and perceptual aspects of human factors in surgical image visualization systems, to increase the efficiency and effectiveness of medical interfaces, and ultimately to improve patient outcomes. To this end, we chose four different minimally-invasive interventions in the realm of surgical training, planning, training for planning, and navigation: The first chapter involves the use of stereoendoscopes to reduce morbidity in endoscopic third ventriculostomy. The results of this study suggest that, compared with conventional endoscopes, the detection of the basilar artery on the surface of the third ventricle can be facilitated with the use of stereoendoscopes, increasing the safety of targeting in third ventriculostomy procedures. In the second chapter, a contour enhancement technique is described to improve preoperative planning of arteriovenous malformation interventions. The proposed method, particularly when combined with stereopsis, is shown to increase the speed and accuracy of understanding the spatial relationship between vascular structures. In the third chapter, an augmented-reality system is proposed to facilitate the training of planning brain tumour resection. The results of our user study indicate that the proposed system improves subjects\u27 performance, particularly novices\u27, in formulating the optimal point of entry and surgical path independent of the sensorimotor tasks performed. In the last chapter, the role of fully-immersive simulation environments on the surgeons\u27 non-technical skills to perform vertebroplasty procedure is investigated. Our results suggest that while training surgeons may increase their technical skills, the introduction of crisis scenarios significantly disturbs the performance, emphasizing the need of realistic simulation environments as part of training curriculum