VOI Level Properties

The List tab illustrated below is used to work with contour VOIs and define their properties.

VOI List Tab

The VOIs section contains the list of defined contour VOIs, and VOIs which are in the progress of outlining. New VOI creates a new list entry, with the plane direction P according to the currently selected plane (Z = axial for all VOIs in the example above). The selected VOI can be removed using the Remove button. The button removes all VOIs at once. The arrow buttons on top of the list allow changing the location of the selected VOI in the list.

In addition to the plane orientation a VOI has several properties, which can be changed using the button. It shows the VOI properties dialog window illustrated below.

The window allows changing the properties, and immediately updates the display for providing a visual feedback. The property elements have the following meaning:

/	Static VOI : This property is only relevant for dynamic series. If a VOI is static, the same VOI definition is applied and shown at all times. Dynamic VOI : This property is only relevant for dynamic series. For dynamic VOIs, a different VOI definition can be used at different times. Note that a dynamic VOI is only shown when viewing the images of the time frame it was defined on. As long as only one VOI is defined, statistics calculation will apply this VOI at all times as with a static VOI. However, as soon as VOIs have been defined at more than one time, it is required that VOIs are defined at all times. Here the VOI propagate functionality may be helpful.
/	Filled VOI : All pixels inside the contours belong to the VOI. Tape VOI : The contour is interpreted as the center line of a VOI which includes pixels inside a band along the contour. The number of pixels inside and outside can be specified. This type of VOI was introduced for myocardium VOIs.
/	Full VOI : Uses pixels from all directions. Sector VOI : Only the pixels in a defined angular sector will be considered. The sector angle can be defined in the VOI Action Mode using the handles at the angle corners. This type of VOI was introduced for myocardium VOIs.
Location	X, Y and Z position of the VOI relative to the origin in [mm]. The location can be changed by entering new coordinates or using the incrementing arrow buttons.
Size	Size of the VOI bounding box in mm. The sizes can be changed and result in a proportional scaling in the corresponding direction. The sizes can be edited or incremented by the arrow buttons. Note that for contour VOIs consisting of planar ROIs the scaling is only supported within the ROI planes, not orthogonal to it. Object VOIs can be scaled in all directions.
Rotation	The VOI can be rotated in space. Note that for contour VOIs consisting of planar ROIs rotation is only supported around the axis orthogonal to the ROI plane. Object VOIs can be rotated around all directions. The angles can be numerically specified in degrees, or incremented using the arrow buttons.
	Color Palette. Allows changing the contour color. All contours belonging to a VOI have the same color.

The illustration below illustrates the effect of the different properties on the pixels used for VOI statistics.

Sector VOI

The + and - buttons to the right set all contours of the selected VOI to + and - respectively.

ROI and Contour Level Properties

The Contours section contains the list of the contours defined in the current slice of the image series for the VOI selected in the VOIs list. All contours belonging to a VOI in a single plane form together the planar ROI.

The arrow buttons on top of the list allow changing the location of the selected contour in the list.

Each contour has properties, which can be changed with the buttons on the right of the list.

Plus Contour: This buttons sets all contours selected in the list to + in the operation column O. The meaning of a + contour is that the pixels defined by the contour are included in the statistics. This operation mode is equivalent to the OR set operation.

Minus Contour: This buttons sets all contours selected in the list to -. The meaning of a - contour is that the pixels defined by the contour are excluded from the statistics. This operation mode is equivalent to the AND NOT set operation.

Cardiac example illustrating how a negative inner contour can be used to create a hollow VOI.

CAUTION: The first contour in the list should be the + contour.

Toggle
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Closed Contour : The last vertex is connected to the first vertex, so that a closed trajectory is formed.

Line Contour : Only the pixels along the trajectory from the first to the last contour vertex are included into the VOI.

Similar to the VOI level, the size and angle can be changed on the contour level by two approaches.

ROI Properties

All contours belonging to a VOI in a single plane form together the planar ROI. The properties of all ROI contours can be changed at once by the button, which shows the dialog window below. It allows changing the Location, Size and Rotation angles of the ROIs. The translation and scaling operations are restricted within the contour plane plane, and the to rotation around the orthogonal.

Contour Properties

The properties of individual contours can be changed by the button, which works similar as the button. It additionally offers changing the Contour name.

Contour Display Properties

In the lower right, there are some properties defining how the VOIs are displayed in the image overlay.

VOI Display Properties

The following properties can be configured in the option menu:

Show Names	Shows the VOI names next to the contours in the image overlay. Note: The location of the names can not be changed.
View Name (by mouse)	Shows the names of the VOIs below the cursor in a separate section at the top of the image. Overlapping regions are shown as a list of names.
Hide Move Overlay	Hides the handle for moving the VOI to avoid obstructing the view with small VOIs. The VOI shifting/rotation operations have to be performed with the keyboard arrow cursors.
Data driven display	Determines the behavior of the image layout when switching between different series. If the box is checked, each image has its own properties such as layout, zoom, color etc. Otherwise, the images are shown with the same layout properties.

Usually contours are outlined on images displayed with interpolation, often combined with image zooming. In such a representation the images look smooth, even if the original pixels are big as with modalities suffering from low spatial resolution relative to the structure being outlined. To make sure that the right pixels are included in the VOI it is recommended - especially for small structures - to examine the VOI pixels as follows:

Check the S box. The display shows only the contours of the currently selected VOI to avoid confusion in the presence of multiple VOIs.
Check the P box. The VOI is drawn in all planes if orthogonal layout is set. When the P box is unchecked the VOI is drawn in continuous line mode only in the active plane.
Check that the squares which indicate the polygon vertex location from the image overlay are ON .
Check the Fill box. The display now shows a raster outlining the VOI pixels (G). The raster can also be filled by setting the radio button to A (opaque filling). The degree of opacity can be change using the UP arrow next to the radiobutton A. The 100% value indicates full opacity.
Disable image smoothing by disabling the

button in the image control section.
Modify the VOI contours while the Fill box is still checked, for instance by moving a vertex. The raster is updated as soon as the changes are completed.

ROI Filling

Note: PMOD only considers the entire pixels for the statistics calculation which are visualized with the Fill functionality.