Thank you for your question to the ADNI MRI Core.
Not sure if this is what you are referring to but for GE specifically.
MR750 is the XRM gradient set.
MR750W is the 70 cm bore version of the XRM (no dedicated name)
Signa HDxt uses the TRM gradient set.
For the other manufacturers the gradient set is equivanlant to the Scanner type. (Siemens = TRIO/Verio/Skyra etc. - Philips = Acheiva,Ingenia etc.)
Thank you
ADNI MRI Core