5. (optional) Reconstruction of Electrode Trajectories
You are almost done! Once volumes are coregistered and optionally normalized, you can run
pre-reconstruct of the electrode trajectories and Localize DBS electrodes, which is the actual electrode reconstruction step.
For the automatic pre-reconstruction step to take place, check the box
[] pre-Reconstruct, choose the preferred parameters for obtaining the images, and press Run. Depending on the postop images, Lead-DBS selects a method automatically, i.e., Refined TRAC/CORE for postop MR and PaCER for postop CT. For more information on PaCER, read Andreas Husch's site.For TRAC/CORE, Lead-DBS performs an automatic search of the artifacts caused by the electrode leads. This can be modified using the following parameters:
- Entry point: set
STN, GPi, or ViM,Cg25orManual. If set to Manual, you are prompted to select the starting point of the artifact for each side. The latter is important for troubleshooting but also if you try to reconstruct electrodes at uncommon DBS targets. - Axis: Several “preprocessing”-options can be selected to optimize the imaging data you want to use for the reconstruction here.
- Mask window size: either set a concrete value (the range of 5 to 20 might improve results) or set the value to “auto”. This option is only important for MR images, in CT imaging, a large mask size (e.g. 20) can be used but “auto” should work as well. If performing reconstructions based on MR images, please use a larger mask value if there is a lot of edema around the electrode and a smaller value if the images are rather noisy. Smaller values will prevent the algorithm to “lose track” but might stop to soon if the artifacts are rather large.
The goal of this step is to refine the localization of the electrode and contact templates within the artifact, in order to place it as accurately as possible.
When the option is checked, Lead-DBS shows a window where you can visualize and modify the position and orientation of the electrodes. This should always be done to obtain a meaningful reconstruction. Moreover, this is probably the most difficult step in the standard processing pipeline of Lead-DBS, it needs some anatomical insight and experience with interpretation of postoperative images. We recommend to watch the walkthrough tutorial (around 00:40 minutes) to better understand this crucial processing step.
In this window, the user visualizes the position of the electrode trajectory with respect to the artifacts of the MR or CT images. Lead-DBS places within these artifacts the built-in templates for the electrodes, represented as straight lines that run along the artifacts. The contacts are represented as a set of circles on the electrode lead lines (4 or 8 circles, depending on the electrode model chosen). First, the user adjusts the position of the right electrode, then the left electrode for a bilaterally implanted patient.
Manual refinement window to localize the electrode on a postop CT image.
If no contact is selected, the up and down arrow keys move the whole electrodes up or down in the axial plane. Pressing
Shift together with the arrow keys moves the electrode in bigger steps.For easier adjustment, specific contacts can be selected and their changes checked in their respective transversal views. Contacts are selected by clicking on the little
0 or 3 icon in the menu bar or by pressing 0 or 3 on the keyboard.With a specific contact the arrow keys up, down, left and right adjust the position within the axial and coronal planes. The goal is to center the trajectory on the artifact (white in the CT image above).
To detect the orientation of directional leads such as Boston Vercise Directional, see the subpages by Till Dembek.
To save the adjustments and move to the next electrode, press the
SPACE bar. To read more about how these reconstruction are stored, open this subpage.