Tracing Anatomic Structures
Before you trace, you should define the structure.
You can trace a structure as follows:
- Go to a plane where the structure is visible (use the "-" or "+" buttons on the control
panel at the bottom of the main window or type a plane number into the box between these buttons).
- Depending on whether you want traces to be open or closed (i.e., whether the trace should
connect back to its starting point, from the "Contours" menu, select the "Style" item and then
pick "Open" or "Closed" from the submenu. The contous style has no effect on the contours that
are saved (you can switch back and forth even once the trace is drawn), but it is disconcerting
to see and open trace when you expect a closed one and vice versa. When the polygon drawing mode
(see below) is used, "Vertices" can be selected from the "Style" menu and will show the
individual points, connected using the "open" style.
- Using the popup menu at the top of the control panel at the bottom of the main window,
select the name of the structure you want to trace.
- If MultiTracer is not currently in tracing mode (indicated by red text on the "Trace" button on
the control panel), click on the "Trace" button to activate tracing mode.
- Make sure that the magnification is appropriate and that the entire structure is currently
visible by adjusing the magnification and scroll bars.
- Without pressing the mouse button, move the mouse around on the image in the main window to
explore and review the anatomy in the orthogonal views and confirm where you should trace
If you have not already done so, choose the drawing mode that you would like to use. Three
drawing modes are available and can be chosen from the "Select Drawing Mode"
submenu from the "Contours" Menu. Each drawing mode has a distinct way that mouse clicks and
movements start, continue or end traces:
Note that keyboard shortcuts can be used to change the drawing mode. This can be done even
in the middle of a trace for certain changes.
- Freehand drawing mode (default)
Press and release the mouse button to start tracing at the anatomically defined
starting point and press and release the mouse button a second time to stop tracing
- Tablet drawing mode (suitable for stylus and tablet based tracing)
Press and hold the mouse button to start tracing at the anatomically defined
starting point and release the mouse button to stop tracing
- Polygon drawing mode (connect-the-dot tracing)
Press and release the mouse button to define the first point and continue to press
and release to define subsequent points to be joined by straight lines. Click while
holding the ALT-key (Windows) or Option-key (Macintosh) to end the trace.
- Move the mouse to the anatomically defined starting point of the structure. Start tracing
at this point as appropriate for the selected drawing mode.
- Move the mouse in the direction defined in your anatomic protocol along the anatomic
structure. Don't worry about small errors; you can fix them later. If you make a grotesque error,
you can "shrug off" the bad trace immediately by moving the mouse outside of the main window
before you end the trace.
- Continuous updating of the orthogonal views is suspended while traces are being drawn.
However, you can apply the keyboard shortcut for the "Slice" menu's "Update Ortho Views" item
while you are tracing to get an updated view corresponding to the current mouse position.
- When the trace is complete, end it as appropriate for the selected drawing mode.
- If you want to improve the trace, you can modify it.
- You can procede to another plane, or change to another structure to trace on the current
Since anatomic protocols often forbid multiple traces for the same structure on a given
plane, MultiTracer will warn you if you complete additional traces using the same structure
name. To prevent this warning from being displayed, click the checkbox labelled "Don't show
this message again". The message will be suppressed until the next time you launch MultiTracer.
If you choose to allow more than one trace for a given structure on the same plane, you should
be careful to assure that the different traces do not overlap--areas and volumes will be computed
as if the structures were not overlapping, so overlaps will result in overestimates of areas and
©2001-2004 Roger P. Woods, M.D.
Modified: August 23, 2004