BrainVoyager version: 22.4.6
Dataset used: Getting Started Guide data

This document shows in a step by step example how to transform a ROI to a VOI and how to transform a VOI back to a ROI.

ROI to VOI

To start, we open an FMR document, in this case the preprocessed dataset of sub-01.

In a next step we compute a single-subject GLM and define a contrast to identify regions that respond stronger to stimuli in the left visual field:

After zooming into slice 19, we select a significant functional cluster. 

After the 'ROI Signal Time Course' dialog has been extended by clicking with the left mouse button in the time course of the ROI, you can check the ROI details by clicking on 'Options'.

Now we can define this region as ROI using the menu 'Analysis -> Region-of-Interest Analysis..'. 

After the ROI has been saved, we can start to convert the ROI to a VOI by clicking on 'Convert to VOIs...'

In the invoked dialog we can choose to convert the ROI to a VOI in different reference spaces:

• either to a Native VOI, in this case only the coregistration TRF files have to be specified or
• to ACPC space, which additionally asks for the ACPC TRF file or
• to Talairach space, which also requires a TAL file or
• to MNI space, which requires the coregistration TRF files as well as the MNI transformation file

In the current example we choose to convert the ROI to a VOI file in Native VMR space. After having specified the required transformation files, we can start the transformation by clicking on 'GO':

As a final step BrainVoyager will ask for the Native Space VMR:

You can check whether the conversion has been performed correctly by opening the Native Space VMR and loading the resulting VOI file in the 'Volumes-Of-Interest' dialog.

The screenshot below shows the loaded converted VOI displayed on the Native VMR together with a statistical map of the same contrast that we had computed before on the FMR ([Faces_LVF +1] + [Houses_LVF +1] ≠ [Houses_RVF -1] + [Faces_RVF -1]):

VOI to ROI

You can also perform this transformation backward, i.e. convert a VOI to an ROI. Please note that this is only possible for VOIs in Native space. If you would like to use an ACPC- / Talairach- or MNI-VOI, you need to back-transform it first to Native Space and then use the resulting Native VOI to transform it to an ROI. In the current example we will use the newly converted Native VOI and transform it back to an ROI.

To start this process, first load your Native VOI in the Volumes-Of-Interest dialog and click on 'Options..' 

Note: Please be certain that the Native VOI that you have loaded fits the hosting Native VMR file.

In the 'VOI Analysis Options' switch to the 'Transformations' tab and click on 'Convert..' in the 'Convert VOIs to ROIs (e.g. for Turbo-BrainVoyager)' field.

In the appearing dialog, you need to specify the hosting FMR and the coregistration TRF files:

Start the conversion by clicking on 'GO'.

Now you can check whether the ROI has been successfully created by opening the host FMR and loading the ROI file via the menu 'Analysis -> Region-of-Interest Analysis..'.

You might notice that the resulting ROI seems close but not absolutely identical to the initial ROI that we have selected above. 
However, when you open both ROI files in a text editor and compare the included voxels in both files, you will notice that this is only a difference in the displayed rectangle, but not in the content of the ROI.