 Welcome to this video tutorial about Mitral Valve Segmentation with 3D Slicer. Slicer is a free and open-source package for image analysis and scientific visualization. In order to perform the segmentation, we'll use the cardiac models developed by Andras Lasso and Matt Jolly. The first thing to do is to upload a daikon file. It is important to remember that the file should be a Cartesian daikon with the extension dot and rdd. Now we can open the Valve Anulus Analysis module. We create a new Valve and label it Mitral and Sistly. Then we select the Proposition where the volume was acquired. As you noticed in the top left panel, the Mitral Valve is open. Therefore, we should look for the anti-systolic frame. By definition, the frame just before, the Mitral Valve opening. It is possible to regulate contrast and brightness for the image by clicking on the panel and while holding, moving left and right and up and down respectively. The next task is to align the red plane parallel to the Anulus plane. Scrolling the mouse wheel while the mouse cursor is on a panel will cause the movement of the corresponding plane. While the controls on the sidebar can be used to define to an orientation of the image. Now open the contouring menu, click on Mark Anulus and start placing the 24 reference points starting from the Mitral Arctic continuity. After each click, the next rotational plane will be automatically shown. Remember to place all the mark on the same side of the Anulus. It is always wise to check the placement before proceeding. If needed, every point can be overwritten. We can see a preview of the Anulus and then proceed by clicking on the Apply button. Now it's time for leaflet segmentation. First, an editing mask shall be created. As closer the mask is to the Anulus borders, as easier the segmentation will be. Now we erase all the unnecessary labels. We select Show3D and we select the paint. By clicking on the sphere brush, we'll use a 3D paint brush, allowing to draw more than one slice at the same time. After selecting an appropriate size, we can start painting the leaflets and we can scroll through the slices using the mouse wheel. Another option is to use the threshold paint. We set an appropriate lower threshold to get rid of the noise and confirm the choice by clicking on Use for Masking. This way, the brush will paint only the pixels within the thresholds, and we can use a bigger brush. This will allow us to complete the work in less time. Now that the biggest part of the segmentation is gone, we can get rid of the lower threshold and use a smaller brush for the details, like small dropout of the image or the co-optation surface, that requires a higher precision. By clicking on Edit in 3D, we can paint directly on the 3D model. We suggest not to overuse this option, because while it is useful to fill small gaps, at the same time can lead to massive errors. We can now smooth the manual segmentation. There is more than one option, but we usually use joint smoothing with a coefficient of 0.35. At last, we can proceed to the measures. We create a new set of measures, we select Mitral Valve, and we place all the reference points. By clicking on the I button, a table with all the measures will appear. The table can be copied and pasted to an Excel file. By clicking on the I button of each variable, a graphic representation will appear. All the segmented components of the valve can be saved independently, or as a single file by clicking on the pack button. That's all for this video. We hope you enjoyed. Thanks for watching!