ASL BIDS - Background Suppression fields

Hi all,

Is anyone able to provide details on how to obtain the “BackgroundSuppressionPulseTime” and
“BackgroundSuppressionNumberPulses” fields for an ASL BIDS dataset?

I cannot find any details in our imaging protocol or DICOM headers that pertain to these fields. I’m unsure how to derive these values as defined by the BIDS specification.

Thanks
Lachlan

I know of these sources of info for BIDS ASL.

https://bids-specification.readthedocs.io/en/latest/appendices/arterial-spin-labeling.html#arterial-spin-labeling

https://bids-standard.github.io/bids-starter-kit/tutorials/asl.html

Could not find the exact info for this.

@jan-petr maybe you know better

This can be indeed very tricky. Most ASL implementations on Philips show those on the scanner console (number of pulses and timings), and save them to Philips XX file, but not to DICOMs. GE and Siemens, as far as I know, don’t provide the pulse timings on the console, and only very old Siemens even allowed you to turn those ON/OFF. The newest GE and Siemens product doesn’t allow you to change the background suppression or its timing and doesn’t save the information to the DICOM. Certain research implementations of Siemens (notably from Mevis) save information in Phoenix-DICOM field that allows reconstructing the timings if you know the formula.

So overall - unless you have access to Philips scanner, you can’t get the background suppression number of pulses or timings. You would have to contact the vendor or sequence provider to provide you those.

The good news is that in normal use and normal quantification, you don’t need to provide these values. And they are also not REQUIRED, but only RECOMMENDED.

Note that in BIDS, you should provide the timings as a time after the start of labeling, not as a time to readout.