A comparison of shimming techniques for optimizing fat suppression in MR mammography

We evaluated the degree of inhomogeneities of fat suppression using the fully automated three-dimensional breast shimming technique (Image Based-Smart: IB-Smart) and manual setting of a rectangular parallelepiped shim (volume shimming) in MR mammography. Information on breast shape was collected from 9 patients whose images were insufficiently fat-suppressed. A breast phantom made of a thermoplastic sheet was used. Shimming of the magnetic field was done with IB-Smart and various dimensions of volume shims: the anterior to posterior/right to left/head to foot directions were set to 75-150/150-350/50-150 mm. The volumes of inhomogeneously suppressed fat were measured. The calculated volume with inhomogeneous fat suppression with use of IB-Smart was 13.3 × 10 ⁴ mm³. The smallest volume of inhomogeneous fat suppression with volume shimming was 5.4 × 10⁴ mm³ when the anterior-posterior/right-left/head-foot directions were set to 75/350/50 mm. Our results show that using optimized dimensions of volume shims enables better fat suppression than does IB-Smart.