Clarify #031245 Will 9.1 Base Horizon Systems with Active Shield Magnet with Uncompensated VLTC's and Failing SPT FGRE S…

Will 9.1 Base Horizon Systems with Active Shield Magnet with Uncompensated VLTC's and Failing SPT FGRE Stability Pass IBIS? See Long Description. SPT on Base Horizon 9.1 systems with active shielded magnets may have "severe" FGRE failures. The plots will show linear ramps in the constant phase. This is due to uncompensated VLTC eddy comp. This was corrected with the older LX software (8.3 and earlier) so it didn't cause a failure in FGRE. With the newer software (ASP2 and above), we no longer correct the stability plots so FGRE stability will fail if VLTC comp is not done on systems with active shield magnets. Unfortunately, we don't have the ability to compensate for VLTC eddy currents on systems with SR20 Base gradients configuration (8645 or SGD Base). The problem is that with these configurations all of the eddy current compensation is done with the WARP processor on the IPG. There is not enough available on the WARP to compensate the linear long and cross term eddy comp and long B0 and VLTC eddy currents. With this limitation in the hardware, something had to be dropped. So VLTC cannot be run on systems with Base gradient configuration due to IPG hardware limitations. The benefit with the configurations that have a Gram Digital Tuning Board (HiSpeed and EchoSpeed and all ACGD configurations) is that the linear long and cross term compensation is taken off of the IPG WARP and done on the GRAM Digital Tuning board, which then allows for the ability on IPG WARP to compensate for VLTC. So the thing to be aware of here is that the SPT FGRE stability will always fail with linear ramps in the constant phase plots on systems with Base gradient configuration and an Active shielded magnet. The older magnets without active shielding in the magnet do not have this signature so this shouldn't be a problem even with base gradients. But will this type system pass IBIS with failing SPT FGRE Stability, that we can't correct?