Radiofrequency-shielding Effect of a Titanium Mesh Implanted for Cranioplasty.

Abstract

After cranioplasty with a titanium mesh, radiofrequency (RF)-shielding images appear during magnetic resonance (MR) imaging. To clarify their influence, we evaluated the effect of mesh position, phase-encoding direction, and type of coil employed. On a 1.5-tesla MR imager, we placed a titanium mesh board (100 × 100 × 0.8 mm) on the surface of a cubic phantom to mimic a human brain and used a quadrature coil and an 8-channel neurovascular coil to measure nonuniformity, signal decay ratio, and the B1 map. Nonuniformity was 6.7 times higher at the quadrature head coil and 1.6 times higher at the neurovascular coil when the mesh was on the phantom's right side or anterior to it than when it was on its superior end or absent. The profile of the signal decay ratio increased by 1.9% mm(-1) from 0 to 40 mm from the mesh side to the base value at the quadrature head coil when the mesh was on the phantom's right side and 0.9% mm(-1) from 0 to 80 mm at the neurovascular coil when the mesh was on the phantom's right side or anterior to it. The quadrature head coil showed greater incline of the profile when the mesh was on the right in coronal and axial views and no notable change in the profile in coronal and sagittal views when the mesh was on the superior end. In the B1 map, the flip angle was lower when the mesh was nearer. The response to the RF-shielding effect from a titanium mesh depends on the location of the mesh and the RF coil used but not on the phase-encoding direction.