# Breakthrough and Challenging Application: Mixed Reality-Assisted Intracardiac Surgery
## 4 Discussion  
The final implementation of Heart Navigation represents a prototype of how cardiac surgery planning could be performed using MR. Feedback from physicians demonstrates how an MR system integrated into the HL2 can drastically reduce procedure execution times, thereby improving accuracy in selecting the appropriate surgical therapy. In fact, as stated in the review [33] about studies concerning congenital heart surgery, MR allowed a significant reduction in time for surgical planning and intraoperative preparation. The spatial representation and visualization of relevant anatomy offered by MR improved depth perception and speeded up intraoperative recognition of structures, resulting in the better processing of pathological structures and surgical phases. However, the segmentation and holographic visualization of intracardiac structures are still a challenge. In fact, the segmentation processes are still in development in order to be more accurate and faster. In this context, the attention has been moved to the deep learning algorithms [34; 35; 36] and to implement a specific dataset of DICOM images useful for the training phase [37]. In this particular case, the patient was 76 years old and was affected by aortic stenosis, which is a chronic disease that occurs over years, and due to its risk factors, it is strongly associated to the atherosclerotic disease. The treatment option, at the severe stage of aortic valve disease, is mainly represented by the aortic valve replacement. In such patients, two options are available to perform the cardiac surgery: the standard surgical or the percutaneous route (TAVR or TAVI). While the standard valve replacement usually requires an open-heart procedure with a surgical access, extracorporeal circulation and, often, heart and great vessels' manipulation. The TAVR or TAVI procedure can be completed through very small openings, or even percutaneousously. This study aims at going beyond the three-dimensional visualization of the cardiac region by accurately illustrating the intracardiac structures. Such a specific visualization is really crucial for preoperative planning in cardiac surgery. Inner organs are as significant as external ones, as they may provide additional or distinct information to experts. Given the patient's condition, focusing on the aortic valve and on the ascending aorta was essential for diagnosis and determining the intervention type. Therefore, the aortic valve was manually segmented and integrated into the 3D model of the heart. In fact, the preoperative planning process and deciding which treatment to adopt are based on an overall assessment of the patient's risks (clinical, procedural, and anatomical risks). The key points are represented by, principally, age and therefore the fragility index of the patient, associated pathologies, degree of atherosclerotic pathology, and the possible involvement of the ascending aorta by the atherosclerotic process. The overall evaluation is based on the clinical visit and, above all, the integration of the information obtained from instrumental tests (chest X-ray, echocardiography, CT angiography). Computed axial tomography images are often analyzed and examined in both axial sections and multiplanar reconstructions. In this specific case, the MR visualization has added some very important elements:  
* Better visualization of the aortic valve and the specific location of the annular calcifications and the valve leaflets;
* An optimal spatial resolution, allowing the surgeon to better visualize and localize aortic calcifications, making surgical intervention and the use of extracorporeal circulation possible, minimizing the risk of peripheral embolism or acute aortic syndromes. Since surgery is based on programming, in order to minimize possible unexpected events, the integration of the information obtained from our model made possible to translate and transform radiological images into a three-dimensional reality that can be cross-examined in every detail, corresponding to the real intraoperative features.