The IVUS tools are available when viewing IVUS data, the cross-cut tool is for IVUS exclusive, the axis-cross can be used on other modalities as well.
Left, non IVUS image: axis cross. Right, IVUS data: IVUS tools
The IVUS cross-cut tool indicates the cut-line, used to draw the longitudinal view in a separate window. Select the tool and click anywhere on the IVUS image to show and set the cut-line. Make sure the longitudinal view is visible, otherwise the cross-cut tool is disabled. See the image below.
Go to the help file of the longitudinal viewer for further explanation.
The cross-cut used to calculate the longitudinal view
The axis tool is available for all modalities and can be set anywhere on the image. The cross consists of 12 lines, 30 degrees apart.
The axis-cross assigned to the left mouse button, set in the middle of the image