# A Prostate MRI Segmentation Tool Based on Active Contour Models Using a Gradient Vector Flow
## 3 Experimental Case of Use for Demonstration  
In this section a case of use for demonstration is presented. Previously, the proposed GUI has been explained in Section 2.2. A detailed definition of this algorithm and the introduced improvements have been explained in Sections 2.3 and 2.4. The following study case demonstrates how an user can use the proposed tool to manage and segment a real prostate image. First, the user must load an image in DICOM format. For this application, the snake initialization is required; an example of the initial contours for a study is shown in Figure 8. In the area of the GUI that corresponds to the initialization of the snake, the three first buttons are used for selecting the different zones of the prostate, whereas the fourth one gives the possibility of selecting a tumor. Located below these buttons, there are two radio buttons, enabling to choose the shape of the initial contour, which can be circular or manual. The first option corresponds to an initial contour with a shape of a circle whose radius can be specified with the spin box located at the end of this area. The possible values are between 1 and 30 pixels. The manual input enables the user to enter a random polygon as initial contour. If selected, the user just has to make a click with the mouse in the vertices of the desired polygon. There are no limits for the amount of points, or the shape of the polygon. The steps required to initialize the snake for any of the prostate areas are the following:  
1. Select the type of contour to enter, circular or manual. In case of circular, enter also the radius. 2. Select an area: TZ, PZ, CZ or Tumour. 3. Create the initial contour for the snake in the left image. If it is a circle, the mouse cursor must be placed in the center of the area of interest, and click with the left button of the mouse. If manual contour has been chosen, the mouse must be placed in the point where the user wishes to start the contour and make click with the left button. Then move the cursor until the next point, make a left click and go to the next point. More than 2 points are required. 4. In manual mode, once the contour is finished, press the \"Ok\" button. If not, go to step 5. 5. A message box will appear informing if the contour has been correctly added or not. The user can repeat the same procedure for all the zones, or just some of them. In order to differentiate the various selected areas, each initial contour will be drawn with a different color. There are no constraints about the type of contours to use. All the contours can be manual, all of them can be circles or they can be a combination of them. The following area of the control panel is used for triggering the segmentation. This section is depicted in Figure 9. After an image has been loaded, at least one initial contour has been entered, then the segmentation process will start after pressing the \(Run\) button. The segmentation method will be triggered as many times as initial contours have been entered, and they will be executed sequentially. During this process, the user can cancel the segmentation at any moment, pressing the \(Cancel\) button. Once the algorithm had finished, the results will be shown in the right image. Additionally, the color code of the contours is the same for both, left and right images. For instance, the resulting contour of color blue in the right image has as initial contour the blue snake from the left image. If some results have been produced, then a 3D representation of them can be visualized if the user presses the button \(Show\)\(3D\)\(model\). This representation consists only of the resulting contours, replicated several times along the Z axis. It is an extra option for users to visualize the main structure of the segmentation in a 3D model. In fact, this option should be improved using better visualization techniques, but it is out of scope of this work for the moment. The amount of repetitions has been set to 50.