• SIGNA MR355 / SIGNA MR360
  • Service Manual
  • 5856356-3EN Revision 5.0
  • Basic Service Documentation. Copyright General Electric Company.
  • Object ID: 00000018WIA30314F20GYZ
  • Topic ID: id_13106919 Version: 1.1
  • Date: Jul 5, 2019 10:46:04 PM

BRM WB (Whole Body)

Monitor the overall inhomogeneity change from one iteration to the next. If you are seeing no more than a 1-Hz change between iterations, stop shimming. If you are unable to shim the magnet below the specified overall inhomogeneity, you may need to:

  • Check and adjust B0. Refer to the Eddy Current Compensation procedure for details on measuring and adjusting B0.

  • Check for image artifacts, such as zippers, spike noise, etc.

  • Call your Zone Support Engineer or OLC for assistance if the system cannot achieve the magnet shim specifications.

Note:

Most magnets should be able to achieve the “Shim To” values shown. All magnets must meet the “Customer Acceptance” values. As long as the magnet meets the Customer Acceptance values, Gradient LVshim should be sufficient to maintain an acceptable shim quality. When the Customer Acceptance values are exceeded, Main LVshim must be performed to re-establish an acceptable shim quality.

Note:

All Harmonics are Absolute Values and given as Shim to Goal / Customer Acceptance

See Table 1 for 1.5T Specs.

Table 1. 1.5T
DSV = 45 cm
BW = 200 Hz
Values are shown as: Shim to Goal / Customer Acceptance
LCC
STD DEV Hz<50/80
STD DEV PPM<0.6/1.25
Harmonic Name
1,0 (Z1)<10/35
2,0 (Z2)<25/50
3,0 (Z3)<25/50
4,0 (Z4)<50/100
5,0 (Z5)<50/100
6,0 (Z6)<50/100
1, -1 (X)<10/35
1, 1 (Y)<10/35
2, -1 (ZX)<25/50
2, 1 (ZY)<25/50
2, -2 (X2-Y2)<25/50
2, 2 (XY)<25/50
3, -1 (Z2X)<25/50
3, 1 (Z2Y)<25/50
3, -2 (Z(X2-Y2))<25/50
3, 2 (ZXY)<25/50
3, -3 (X3)<25/50
3, 3 (Y3)<25/50