Iso-contours are often very helpful to verify that the spatial alignment of studies is acceptable, or to overlay the location of an anatomical structure in the fusion image.
The fourth tab
is used to overlay iso-contour lines onto the images. A histogram of the pixel values is shown, and the value at which the iso-contour lines are drawn can be adjusted by entering a numerical value, or by dragging the marker highlighted in the graphics above. The selection on the right allows to choose among several colors for the contour lines.
Per default, the iso-contour lines are shown as long as the iso-contour tab is selected. If another tab is selected, they disappear. To make them appear permanently in the images the pin button 
can be fixed to 
.
The display of contours in the fusion image is independent of the display in the source image. It is controlled by the the Contours radio box.