tSNR changes across time
I got interested in gradient temperature because of the weird effect that tSNR seemed to increase over time.
Upon posing this effect on Twitter, PracitalfMRI and Ben Poser suggested that it might be due to gradient temperature. So I learned how to track it with as described below.
The gradient temperature
The gradient temperature can be checked on the scanner as follows.
- Options -> Service -> Local Service
- Login (Password is the string after)
- Magnet and cooling
- Cooling Status
The effect of drifting signal and drifting tSNR is not necessarily only caused by the gradient temperature. the gradients can also have an effect on other system components. iIn fact, it’s likely not the heating of the gradients themselves, rather due to eddy-induced warming in other parts of the system (shim plates, cryo shields, RF coil).
For me with a conventional high-res pipeline, the temperature ACS temperature increases up to 25dec C.
Ben Poser suggested that the gradient temperature alone might not be the solely reason for the instable tSNR. Instead, the usage of the gradients can also heat up the magnet itself and the RF coils.