A question about brain dataset

I have a question about the brain dataset.
There are some data which consist of 2 or 4 coils, of which SNR is very high.
Also, there is no coil information on the ismrmrd_header of the data.
It seems like some process (like coil compression) was performed to this data.
Could you explain what was performed in detail?
Thanks in advance.

This is related to the machine that the samples were acquired on, we haven’t done any explicit coil compression after acquisition.

If you can find the specification of the machine used, it may have more information. Machine information can be found in the header.