VR-Render 2D Multi-Planar Rendering (MPR): the standard image viewer

The 2D MPR visualization is the default visualization mode. It corresponds to the most standard visualization techniques developed and used on professional medical imaging workstations. The multi-planar rendering corresponds to three different views of the medical image in Axial, Frontal and Sagittal views. Each window is called Negato. VR-Render provides such a 2D MPR view in one big left window (Negato1) and two smaller right windows (Negato2 and Negato 3). Each Negato contains the same set of buttons located in the button of the windows and allowing respectively to select the visualized axe (axial, frontal or sagittal), to take a picture of the window, to select the slice thanks to a slider and to compute distances (see next image).

It also indicates the minimum and maximum screened density [min,max], the standard density windowing size W and the middle density of the windowing L. Indeed, it is possible to improve the visualized grey-level by modifying the screened windowing. The parameterization of the visualized grey level window is done via the same technique as developed in all existing radiological software tools. When pressing the right mouse button in the image, it is possible to decrease or increase the center of the grey level window and the grey level window size with up (decrease) or down (increase) and left (decrease) or right (increase) movements of the mouse (see next image)..

Finally each Negato indicates the last selected voxel (voxel = volumic pixel), the coordinates (x,y,z) and the density of this voxel being indicated on the last line. Such a selection is performed by a simple left click in the image. Pressing (or clicking) the middle button provides the same information but adds an automatic synchronization of all views (see image F1-Info-Synchro.jpg). When pressing the button, a full red cross centered on the selected voxel appears on all views while pressing the button.

After letting go the middle button, a visible cross can remain visible. Indeed, three options are available: hide cross, normal cross or full cross. Hide cross removes the position cross, Normal cross partially shows the position and Full cross shows the complete position, the default mode being the Normal one (see image F1-CROSS.jpg). The selection of the cross mode is performed by using the window menu “Hide cross”, “Show normal cross” and “Show full cross”.

It is easy to change the visualized axis of the Negato by using the axis selection menu. As shown on the image (F1-AXES.jpg), the visualized axes are automatically synchronized in order to keep the three Axial, Frontal and Sagittal views in three different windows.

It is also possible to zoom and to translate the image on each Negato in order to focus the attention on a part of the image. After a left click in the selected Negato, you can ZOOM with the mouse SCROLLER or by using the combination of the SHIFT key and pressing the RIGHT button. A movement from bottom to top increases the zoom, and a movement from top to bottom decreases the zoom. The TRANSLATION is performed by using the combination of the SHIFT key and pressing the LEFT button anywhere in the image. In this case, a movement in any direction creates a translation in the same direction. The reset of translations and zooms is performed with the R key.

VR-Render offers the possibility to compute distances in 3D on all Negatos. Distance computation is activated by using the “distance button” located in the bottom right part of each Negato. A single click adds a colorized distance segment in the Negato view. Each new click adds such a distance segment with each time a new color. Distances are computed between two 3D spheres that can be moved in the Negato by simply selecting it by pressing on the mouse left button, and by moving it in the view by keeping the left button pressed and releasing it in the wanted location (see image F1-DISTANCES.jpg).

From VR-Render 0.8, distances are computed in 3D. It is thus possible to position the two spheres on two different slices (slice selection being performed thanks to the slider). In order to simplify such positioning, the distance segment always appears in the Negato. The sphere representation then allows to know if the sphere is on (normal grey sphere), under (no sphere) or above (grey sphere surrounded by a yellow disk) the visualized slice as show on the image F1-DISTANCE.jpg.

Each distance segment can be removed by a simple right button click on one of its two distance spheres. Another way to remove distance segments consists in using the Window “Remove distance” menu. Two options are then proposed: remove all distances or remove a selected distance.

In order to label specific position in the medical image, VR-Render 0.8 also integrates a 3D landmarks positioning system that is started by using the Window “new landmark” menu. This action open a small windows allowing to name the landmark. The landmark then appears and can be moved in the Negato view exactly like a distance control sphere.

The last option of the Negato is the snapshot allowing to save the 2D-Slicer view. The snapshot is activated by a left button click on the snapshot icon located in the bottom left part of the Negato window.