Coronary Artery Segmentation and Motion Modelling

Conventional coronary artery bypass surgery requires invasive sternotomy and the use of a cardiopulmonary bypass, which leads to long recovery period and has high infectious potential. Totally endoscopic coronary artery bypass (TECAB) surgery based on image guided robotic surgical approaches have been developed to allow the clinicians to conduct the bypass surgery off-pump with only three pin holes incisions in the chest cavity, through which two robotic arms and one stereo endoscopic camera are inserted. However, the restricted field of view of the stereo endoscopic images leads to possible vessel misidentification and coronary artery mis-localization. This results in 20-30% conversion rates from TECAB surgery to the conventional approach. We have constructed patient-specific 3D + time coronary artery and left ventricle motion models from preoperative 4D Computed Tomography Angiography (CTA) scans. Through temporally and spatially aligning this model with the intraoperative endoscopic views of the patient's beating heart, this work assists the surgeon to identify and locate the correct coronaries during the TECAB precedures. Thus this work has the prospect of reducing the conversion rate from TECAB to conventional coronary bypass procedures. This thesis mainly focus on designing segmentation and motion tracking methods of the coronary arteries in order to build pre-operative patient-specific motion models. Various vessel centreline extraction and lumen segmentation algorithms are presented, including intensity based approaches, geometric model matching method and morphology-based method. A probabilistic atlas of the coronary arteries is formed from a group of subjects to facilitate the vascular segmentation and registration procedures. Non-rigid registration framework based on a free-form deformation model and multi-level multi-channel large deformation diffeomorphic metric mapping are proposed to track the coronary motion. The methods are applied to 4D CTA images acquired from various groups of patients and quantitatively evaluated

Medical Robotics

The first generation of surgical robots are already being installed in a number of operating rooms around the world. Robotics is being introduced to medicine because it allows for unprecedented control and precision of surgical instruments in minimally invasive procedures. So far, robots have been used to position an endoscope, perform gallbladder surgery and correct gastroesophogeal reflux and heartburn. The ultimate goal of the robotic surgery field is to design a robot that can be used to perform closed-chest, beating-heart surgery. The use of robotics in surgery will expand over the next decades without any doubt. Minimally Invasive Surgery (MIS) is a revolutionary approach in surgery. In MIS, the operation is performed with instruments and viewing equipment inserted into the body through small incisions created by the surgeon, in contrast to open surgery with large incisions. This minimizes surgical trauma and damage to healthy tissue, resulting in shorter patient recovery time. The aim of this book is to provide an overview of the state-of-art, to present new ideas, original results and practical experiences in this expanding area. Nevertheless, many chapters in the book concern advanced research on this growing area. The book provides critical analysis of clinical trials, assessment of the benefits and risks of the application of these technologies. This book is certainly a small sample of the research activity on Medical Robotics going on around the globe as you read it, but it surely covers a good deal of what has been done in the field recently, and as such it works as a valuable source for researchers interested in the involved subjects, whether they are currently “medical roboticists” or not

Vessel recognition in ultrasound images using machine learning techniques

Purpose: Ultrasound is an imaging modality that is commonly used during cardiovascular surgeries globally. The purpose of this thesis is to investigate how machine learning techniques can be used to identify vessel properties and probe orientation in cardiac ultrasound images. The ultimate goal is developing a machine learning algorithm that can automatically recognize vessels in the region of interest with high mean average precision, identify vessel orientation, and run in near real-time. Method: This thesis present a thoroughly data exploration of ultrasound images acquired from a multicenter study. A pilot study of three different object detection models; Yolo, RetinaNet and EfficientDet, was done to find the best model fit for the dataset in the thesis. The three object detection models were trained, tuned and evaluated on the ultrasound data. The object detection model that performed the best after the pilot study was explored further. Yolo outperformed the other models and was therefore chosen as the object detection model for the final study. To overcome the dataset's class imbalance and size problem, data augmentation, resizing and upscaling of the ultrasound images were employed. The resulting data was used to train multiple yolo models with varying hyperparameter tunings. Model selection was then performed on these trained models, and the final model was evaluated on test data. Results: The final model achieved an overall mean average precision at 50\% at 71.77\%. The vessel orientation achieved a mean average precision at 64.6\% for the longitudinal orientation and 75.8\% for the transversal orientation. The model found it easier to locate the aorta compared to the anastomosis, which proved to be more challenging. The speed of the inference of all of these task was 5.6 milliseconds. Although the overall mean average precision was lower than the objective in this thesis, the model excelled in terms of speed. Conclusion: In conclusion, this thesis explored the application of machine learning techniques on ultrasound data for vessel recognition and orientation. Although the final model did not improve the state of the art, the research from this master thesis can serve as a starting point for future reasearch in the field. It represents pioneering work in utilizing a multicenter dataset for machine learning on ultrasound images, providing valuable groundwork and shedding light on the feasibility and potential of machine learning in intraoperative ultrasound.Masteroppgave i medisinsk teknologiMTEK39

Building a better bypass with emphasis on bilateral internal mammary grafting

Abstract The goals for this thesis are 1) to encourage the use of bilateral internal mammary artery (BIMA) grafting more frequently so that many more patients receive the ‘BIMA benefit’ and 2) to ensure that an increase in bilateral IMA grafting is achieved with accuracy and no greater morbidity than that which is achieved with one IMA and the rest of bypasses with a saphenous vein. Revascularization of diseased coronary arteries may be accomplished in one of two ways: by percutaneous coronary intervention (PCI) or by coronary artery bypass graft surgery (CABG). The principal difference between the two procedures involves the length of coronary artery needed to be addressed to improve blood flow to the heart. PCI with placement of stents must open all significantly obstructed areas along a coronary artery whereas in CABG, a surgeon needs only a ‘postage-stamp’ size of disease-free artery in order to perform an anastomosis. However as with everything in life, there are pros and cons to both approaches. PCI is quicker and requires no surgical incision from which a patient must recover. CABG is a major surgical procedure with all the inherent risks associated with a median sternotomy and the use of a heart-lung machine (or not, in the case of off-pump CABG). Patients are naturally drawn to the less invasive PCI but recent publications, most notably the recent 5 year SYNTAX trial (Ref1) results have clearly shown an advantage for CABG for the majority of patients needing revascularization. ‘Pay me now or pay me later’ is a saying that comes to mind… Coronary artery bypass grafting (CABG) has remained the cornerstone treatment for obstructive coronary artery disease for more than 50 years. Chapters 3 and 4 outline the past and the present/future of the CABG procedure, respectively. Chapters 5 and 6 are commentary articles on the benefit of bilateral IMA grafting. Chapter 7 addresses the possibility of an age cut-off as to the survival benefit of BIMA use. BIMA grafting is technically more challenging – all the more reason to use an intra-operative assessment of graft function to ensure bypasses are functioning to the best of a surgeon’s ability before the patient leaves the operating room. (Chapter 8) Operative revascularization is more invasive compared to that with PCI but cementing a sternum solid within 24 hours of operation may possibly reduce the relative invasiveness of CABG, especially when the revascularization rate for CABG is so much lower than PC I (Chapter 9) BIMA grafting is definitely associated with an increase in deep sternal wound infection, one of the most dreaded complications of CABG surgery and commonest reason for not performing BIMA grafting. However if many preventive measures/procedures are used meticulously and consistently on every patient, the risk for this complication can be reduced to almost zero. (Chapter 10) Complete revascularization has been found to improve the survival of patients undergoing CABG surgery; however it is not always possible to completely revascularize a patient. For example if coronary arteries are very small, diffusely diseased or are mostly in scar tissue it may not be possible or even advisable to perform bypasses to such arteries. We have shown that if total arterial grafting (with the majority of arterial grafts of internal mammary artery origin) is used, there is no difference in midterm survival if a patient is incompletely revascularized by inability to bypass one of three artery systems. This is a valuable point as there is only a finite amount of arterial conduit available and there may not be enough to perform all bypasses desired. (Chapter 11 and 12) BIMA grafting does take increased operative time but harmonic ultrasound technology used to skeletonize IMAs helps shorten this time. (Chapter 13 and 14) Chapter15 discusses sequential bypass grafts and the inherent risk of losing the second anastomosis in preference to the first, a serious problem if the second anastomosis is to the more important artery. Chapter 16 presents a rare complication of CABG surgery but from this problem, an operative technique has been developed that is applicable to similar patients with prohibitively calcified coronary arteries. To summarize: It is the author’s wish to 1) refute every reason used as to why BIMA grafting is not performed more frequently and 2) to establish credible studies and guides to encourage their use

The frail patient undergoing cardiac surgery: lessons learned and future perspectives

Frailty is a geriatric condition characterized by the reduction of the individual's homeostatic reserves. It determines an increased vulnerability to endogenous and exogenous stressors and can lead to poor outcomes. It is an emerging concept in perioperative medicine, since an increasing number of patients undergoing surgical interventions are older and the traditional models of care seem to be inadequate to satisfy these patients' emerging clinical needs. Nowadays, the progressive technical and clinical improvements allow to offer cardiac operations to an older, sicker and frail population. For these reasons, a multidisciplinary team involving cardiac surgeons, clinical cardiologists, anesthesiologists, and geriatricians, is often needed to assess, select and provide tailored care to these high-risk frail patients to optimize clinical outcomes. There is unanimous agreement that frailty assessment may capture the individual's biological decline and the heterogeneity in risk profile for poor health-related outcomes among people of the same age. However, since commonly used preoperative scores for cardiac surgery fail to capture frailty, a specific preoperative assessment with dedicated tools is warranted to correctly recognize, measure and quantify frailty in these patients. On the contrary, pre-operative and post-operative interventions can reduce the risk of complications and support patient recovery promoting surgical resilience. Minimally invasive cardiac procedures aim to reduce surgical trauma and may be associated with better clinical outcome in this specific sub-group of high-risk patients. Among postoperative adverse events, the occurrence of delirium represents a risk factor for several unfavorable outcomes including mortality and subsequent cognitive decline. Its presence should be carefully recognized, triggering an adequate, evidence based, treatment. There is evidence, from several cross-section and longitudinal studies, that frailty and delirium may frequently overlap, with frailty serving both as a predisposing factor and as an outcome of delirium and delirium being a marker of a latent condition of frailty. In conclusion, frail patients are at increased risk to experience poor outcome after cardiac surgery. A multidisciplinary approach aimed to recognize more vulnerable individuals, optimize pre-operative conditions, reduce surgical invasivity and improve post-operative recovery is required to obtain optimal long-term outcome

An Appraisal of Developments in Surgical and Catheter-based Cardiovascular Therapy

After a few decades of limited experience in treating congenital heart defects, the introduction of cardiopulmonary bypass in 1954 provided the opportunity to advance cardiac surgery into an adult patient population. In the 1960s this resulted in the first aortic and mitral valve procedures to treat patients with valvular stenosis and/or regurgitation. Evolving from ball-caged valves to stentless porcine bioprosthetic valves, tens of millions of patients have undergone aortic, mitral, or combined valve replacements with excellent short- and long-term valve durability and survival, even with the earliest generation of mechanical valves. Ischemic heart disease was the leading cause of death in the general population (Figure 1), and the only treatment available at that time -- medical therapy -- fell short to reduce early mortality. Despite the pioneering work of Arthur M. Vineberg to induce coronary anastomosis of an internal mammary artery graft by burrowing it in the myocardium, surgical revascularization did not take off until in the mid-1960s when coronary artery bypass grafting (CABG) through surgical anastomosis was introduced. Its wide-spread adoption caused CABG to rapidly evolve as the standard of care for patients suffering from coronary artery disease

Decision Making in Patients Undergoing Coronary Artery Revascularization : A New Era in Clinical Trial Design and Evidence-Based Practice

The clinical goals for the care of each patient with complex coronary artery disease are to ensure that the most appropriate treatment is selected, and the best available evidence is used to guide procedural techniques and modify risk factors that could impact life expectancy and health-related quality of life. In this thesis, ef