Clarification on where to store PET angiography

1

Where should PET angiography be stored in BIDS?

I am converting a PET dataset into BIDS and have an image referred to as “PET angiography.” According to the study team, this image was created during PET reconstruction from the first few seconds of the dynamic PET scan. The frame with the peak vascular signal was selected visually, and the resulting image is used to help calculate cerebral blood flow.

Because this image is reconstructed or extracted from the original dynamic PET data, I believe it may be considered a derivative rather than raw PET data. However, I am unsure how it should be represented in BIDS.

Would it be appropriate to store this image under a pipeline-specific derivatives directory, such as:

derivatives/pet-reconstruction/sub-01/ses-01/pet/

If so, what suffix and entities would be most appropriate? For example, should it retain the _pet suffix with a descriptive entity such as _desc-angiography_pet.nii.gz, or is there another recommended way to represent an early-frame vascular or angiographic PET image?

I would also appreciate clarification on whether this type of image could ever be included in the raw BIDS dataset when it is exported directly by the scanner or reconstruction software.

2

What counts as raw or preprocessed is still debated in the community.

For storing it as raw, multiple reconstructions can be loaded on to the rec- entity by following the reconstruction type with an integer. How to identify the file as a single frame that was manually selected in the metadata isn’t clear to me.

As annoying it is for the curator the derivatives approach is, I like it because it gives you the opportunity to explain the file in the derivative readme or dataset_description.md. _desc-angiography_pet.nii.gz makes sense to me. Given the manual intervention of selecting the particular frame is another argument for it being a derivative.

I did not notice this use case being covered by PET derivatives BEP023 after a cursory look.

@bendhouseart @mnoergaard Do you have any familiarity with these kinds of files and where might be best to store them?