Update Course and Advanced Techniques in MNPS (version 10.36.07, 2019-2020). . Virtual Fiducials Mode Translation into English of the original Portuguese version. MNPS is developed by Mevis Informática Médica, São Paulo, Brazil

1. Update Course and Advanced Techniques in MNPS
(version 10.36.07, 2019-2020)
Working in “Virtual Fiducials Mode”
Armando Alaminos Bouza.
MNPS-CAT3D Development Team.
Mevis Informática Médica LTDA.

2. The “Virtual Fiducials” mode was introduced about several years
ago. So, it's nothing new. The first version of MNPS with “Virtual
Fiducials” was 10.33.03, March 2016.
Due to the importance of this concept, we will come back to it.
Before the introduction of the “Virtual Fiducials” mode we were
required to process image sequences without fiducials using
CAT3D. This solution still exists, but it is no longer the
recommended choice.
CAT3D was not created for neurosurgery, it does not have
important features such as functional neurosurgery tools, atlas
registration, and radiosurgery, and others.

3. The “Virtual Fiducials” mode aims to make the exclusive features of MNPS available to
non-stereotaxic image sequences. Some examples of resources that we can now use
without fiducials and that are not part of CAT3D are:
• Stereotactic atlas for functional neurosurgery.
• Reformat sequences and present AC-PC plane in axial, coronal and sagittal.
• Create “Probe-View” reconstructions.
• Move the cursor in the space of the patient's commissural coordinates.
• Present DBS the and position of their contacts in the patient's anatomy.
• Simulate electric fields and VTA according to DBS specific programming.
• Simulate a radiosurgery plans (SRS) with cylindrical cones.
• Tools for brain fibers (tractography) handling and rendering.
• sEEG electrodes representation.
As we will show, this feature significantly facilitates the pre-planning of radiosurgery and
functional neurosurgery, as well as the post-operative period, particularly in the
evaluation of previously implanted DBS.

4. “Virtual Fiducial” Mode
Before proceeding, it is very important to understand that in the “Virtual Fiducials” mode, the
coordinates that the MNPS presents are not registered with any stereotaxic system. The
coordinates are of a virtual stereotaxic space.
Instead of “Virtual Fiducial mode” some systems use the term “non-localized image set” or
“non-localized dataset” or “set without headframe”.
The coordinates of POIs, ROIs, and trajectories defined in the Virtual Fiducial mode only
become stereotactic after registering, merging, and importing them within a set of
stereotactic images (localized image set).
IMPORTANT:
Never use Virtual Fiducials coordinates in surgery or radiosurgery!

5. How to start a plan with Virtual Fiducials. Recommended way.
Starting from MNPS version 10.33.04, when dragging a DICOM file over the MNPShell shortcut, the dialog
that opens presents three options:
When selecting “For Virtual Fiducials Mode” the Dicom.exe system will invoke the virtual mode when
calling MNPS. In this way the MNPS enters directly into the “Virtual Fiducials” mode.
Selecting “Non-Stereotactic Image Set” will take the traditional way of processing these images with
CAT3D, which is not recommended in general.

6. How to start a plan with Virtual Fiducials. Alternative method
Sometimes the above-mentioned method is not suitable. For example, wanting to create a
new plan from images that were already imported.
In this case open MNPS. From the start menu select “Options” and then select “Virtual
Fiducials”

7. How to start a plan with Virtual Fiducials.
When selecting “Virtual Fiducial” the MNPS asks for confirmation and warns about the risks of
using coordinates of virtual fiducials in surgery. After confirming, we can run FILE and ”NEW
Plan” in virtual fiducials mode.
Never use Virtual Fiducial coordinates in surgery!

8. When in “Virtual Fiducials” (VF) mode, the execution of the “NEW Plan” is different from
the stereotaxic mode. In the case of VF, MNPS does not look for the position of real
fiducials and does not ask the operator for confirmation.
In VF mode the MNPS sets the (X=0,Y=0) of each image plane at the center of the image
pixel matrix. It then creates a set of virtual fiducials for each plane based on the ideal
design of the fiducial. The position of virtual fiducials is shown with small red crosses.
Some, or all, virtual fiducials may be hidden, it depends on whether they enter the “Field
Of View” of the image.

9. The MNPS continually reports that it is in
Virtual Fiducials mode.
Displays a WARNING in the window caption
(text at the top of the window).
Next to the regions with X, Y, Z values, the
virtual mode message appears in red.
Never use Virtual Fiducial coordinates in
surgery or radiosurgery!

10. Are we required to use axial sequences? MRI sequences are often sagittal:

11. MRI sequences can also be coronal.

12. To comfortably use non-axial sequences the MNPS has a very simple solution.
Define the position of the points AC (anterior commissure), PC (posterior commissure) and IHP (point
in the interhemispheric plane, away from the AC-PC line).

13. After defining AC, PC, IHP, we can reconstruct the axial AC-PC plane with the keyboard command
ALT-F6 or by navigating through the help menu (F1) .
We can now navigate the planes
parallel to the axial AC-PC using
<Page-Up> and <Page-Down>.
In these reformatted images we can
define POIs, for all possible purposes,
such as functional neurosurgery and
radiosurgery. We can also draw ROIs.

14. Auxiliary images on the right of the screen continue with an unusual orientation

15. But when activating maps with F6, auxiliary images revert to normal orientation

16. If the operator of MNPS does not want to work over a Coronal or Sagittal, MNPS can reformat the original
sequence into a secondary Axial sequence. Note that this tool is only available for Virtual Fiducial mode
containing Coronal or Sagittal series.
After opening the non-axial series, go to the initial menu of MNPS. Click in Options. Select “Create Axial Series”

17. The following windows will be shown.
Adjust the region that you need to be
included in the reformatted secondary
series. The desired region should be inside
the red rectangle.

18. When the desired reconstruction region is
defined press the <ENTER> key to start the
reconstruction process.

19. After MNPS creates the secondary axial series, it informs the number of slices and waits for any key to
continue.
Following that, MNPS asks permission to create a new plan with the newly created axial series, it is
recommended to accept by clicking [YES].

20. All MNPS features in stereotaxic mode can be used in “Virtual Fiducials” mode.
We just have to remember that the coordinates are not stereotaxically located.
The simulations we created in VF mode can be imported into a stereotaxic
sequence after registration and merging. Once we are satisfied with the quality
of the registration, we can import all POIs, ROIs and Brain Fibers created in the
simulation into the localized sequence.
Note that POIs with names that already exist in the stereotaxic plane are not
imported, to avoid overwriting.

21. Simulation example for radiosurgery in Virtual Fiducials mode.

22. In the case of tractography, we
are obliged to use the Virtual
Fiducials mode as the entry
point for brain fiber into the
planning.
Stereotactic sequences can only
incorporate tractography after
fusion with DWI in Virtual
Fiducials mode.

23. PET – CT in virtual fiducials mode and with registered atlas

24. In VF mode some tables that contain coordinates cannot be printed, to avoid
misuse. For example, tables with POI coordinates and radiosurgery treatment
protocols.
Remember: Never use Virtual Fiducials coordinates in surgery or radiosurgery!

25. Conclusion: The “Virtual Fiducials” mode is of great help for pre-planning stereotaxy
in general and for making post-operative assessments. We just have to remember that
the coordinates of this mode are not stereotactic.
MNPS in VF mode to pre-plan DBS implantation.