Acquisition Entity MRI vs PET

1

Dear all,

I’ve been working before with BIDS for MRI, but now I’m starting to use it in PET too. However, I’ve run into some limitations, so I’d like to ask for advice:

In MRI when you repeat the same acquisition varying slightly any of the acquisition parameters you can have the entity: acq- which is a custom label the user MAY use to distinguish a different set of parameters used for acquiring the same modality. However, according to the PET standard (Positron Emission Tomography - Brain Imaging Data Structure v1.8.0) there is nothing similar there, and so the only option seems to be to include the entity run-.
As a result the bids validator raise the following warning: [WARN] Not all subjects/sessions/runs have the same scanning parameters. (code: 39 - INCONSISTENT_PARAMETERS)

Is this correct? How can I overcome it and still be compliant with BIDS?

I know, if there are different reconstruction methods we can add the run entity within the rec entity. But with this post I’m referring to any other kind of parameter.

Best and thank you very much in advance.
Óscar

2

Will ping some of the PET experts to help you with this.

3

Dear Oscar,

thanks for bringing this up. Indeed we didn’t talk about different acquisitions in PET back then.

I think this was not discussed, since basically you cannot really change the acquisition in PET, but only the reconstruction. In MRI I actively excite the spins to get the image I want to get out - so I actively want to to influence my acquisition. In PET I inject radioactivity and just watch the decay aka do passively recording. After measuring the decay, you can then bin the scan differently, smooth differently and reconstruct differently.

So could you explain what you exactly are doing different between the two runs?

Kind regards,
Melanie