A *.btc file stores estimated ROI beta values over time in Turbo-BrainVoyager. It is a plain text log file that is written incrementally while data are processed.
The file contains ROI-level beta estimates, not voxel-by-voxel beta values. For each logged time point, the file stores the available condition beta values for each ROI.
When is a BTC file created?
A BTC file is created when logging of estimated ROI betas is enabled in TBV, for example via the option:
Log Estimated ROI Betas (BTC)
The file is typically saved in the target/output directory using the current run name, followed by:
_ROI_betas.btc
Example:
Run01_ROI_betas.btc
General structure
A .btc file starts with a short header:
FileVersion: 1 BetaMode: PercentToBaseline
After the header, the file contains repeated blocks, one block per logged time point.
Example:
TimePoint: 1 NrOfROIs: 2 ROI: 1 NrOfVoxels: 125 NrOfCondBetas: 3 0.432 -0.081 1.204 ROI: 2 NrOfVoxels: 98 NrOfCondBetas: 3 -0.025 0.744 0.318
A later time point is appended as another block:
TimePoint: 2 NrOfROIs: 2 ROI: 1 NrOfVoxels: 125 NrOfCondBetas: 3 0.455 -0.076 1.188 ROI: 2 NrOfVoxels: 98 NrOfCondBetas: 3 -0.018 0.701 0.337
Field descriptions
| Field | Description |
|---|---|
FileVersion | File format version. |
BetaMode | Indicates how beta values are represented. PercentToBaseline means the beta values are expressed relative to the baseline level. |
TimePoint | Logged time point. Time points are written as 1-based values. |
NrOfROIs | Number of ROIs available for the current time point. |
ROI | Index of the ROI in the current TBV session. |
NrOfVoxels | Number of voxels included in the ROI estimate. |
NrOfCondBetas | Number of condition beta values written for the ROI. |
| Beta value row | One row containing the beta values for the ROI, with one value per condition. |
Interpreting the beta values
The beta value row contains one value per condition:
beta_condition_1 beta_condition_2 beta_condition_3
The order of the values follows the order of the condition predictors used by TBV for the current protocol/design. The .btc file itself does not store the condition names, so the protocol/design information should be used to interpret which value belongs to which condition.
For example, if the condition predictor order is:
Faces, Houses, Objects
then a BTC row such as:
0.432 -0.081 1.204
should be interpreted as:
Faces: 0.432 Houses: -0.081 Objects: 1.204
Important notes
A .btc file stores ROI beta estimates over time. It should not be confused with voxel-level time-course logging files.
The values are written as percent-to-baseline beta estimates. This makes the values easier to compare across ROIs than raw beta estimates.
The number of beta values in each ROI block should match NrOfCondBetas.
If an ROI contains no voxels, or if the required beta estimate is not available at a given time point, the beta value row may be missing for that ROI/time point.
Because the file is written incrementally during processing, it can be inspected while a run is ongoing, but it is safest to analyze the complete file after the run has finished.