ABSTRACT
PURPOSE: To determine which sequence for frequently used general contrast-enhanced brain MRI shows the least radiofrequency shielding effect of a titanium mesh in cranioplasty using a phantom. METHODS: A 1.5T MRI scanner was used. Frequently used general 2D and 3D spin-echo sequences (SE) and T1 spoiled gradient echo sequences (GRE) used for MRI in clinical settings were adopted in this study. A titanium mesh was placed above a cubic phantom containing manganese chloride tetrahydrate and sodium chloride. The signal attenuation ratio and normalized absolute average deviation (NAAD) were calculated. Moreover, the flip angle (FA) dependency in SE and area of excitation dependency in 3D sequences were analyzed using NAAD. RESULTS: The signal attenuation ratio at the position nearest to the titanium mesh for 2D SE was 71.8% larger than that at the position nearest to the titanium mesh for 3D GRE. With regard to NAAD, 3D GRE showed the highest values among the sequences. When FA was increased, radiofrequency shielding effect was improved. There were no significant differences between the narrow and wide area of excitation. 3D GRE showed the least radiofrequency shielding effect, and it was considered as the optimal sequence for MRI in the presence of a titanium mesh. CONCLUSION: 3D GRE shows the least radiofrequency shielding effect of a titanium mesh after cranioplasty among frequently used general sequences for contrast-enhanced brain MRI.
Subject(s)
Brain/diagnostic imaging , Image Processing, Computer-Assisted/methods , Magnetic Resonance Imaging/methods , Phantoms, Imaging , Radio Waves/adverse effects , Surgical Mesh/adverse effects , Titanium , Adult , Aged , Aged, 80 and over , Brain/pathology , Female , Humans , Image Processing, Computer-Assisted/instrumentation , Magnetic Resonance Imaging/instrumentation , Male , Middle Aged , Prostheses and ImplantsABSTRACT
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) mm(3). The smallest volume of inhomogeneous fat suppression with volume shimming was 5.4 × 10(4) mm(3) 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.
