RF aitifacts caused by metallic implants or instruments which get more prominent at 3 T: an in vitro study

Metallic devices with high electrical conductivity inside or adjacent to the body might lead to marked alterations of the RF amplitude B-1 in the tissue under investigation, especially at increased RF frequency, and if specific conditions for electromagnetic resonance are fulfilled. RF-metal interaction effects were investigated systematically at B-0=0.2, 1.5 and 3 T analyzing correlated image artifacts for copper wires (d=1 mm, L=53 and 27 cm), and for following instruments and implants made of titanium or nitinol: biopsy needles, hip prostheses, vascular stents and aneurysm clips. The samples were examined in Gd-DTPA-doped 140 mM NaCl solution using spin-echo (SE) sequences with high readout bandwidth. Automatic transmitter adjustment V-T,V-auto and manually reduced transmitter voltage V-T were applied in order to detect B-1 enhancement. At 0.2 T, beyond the shielding of the luminal region of the stents, no RF effects were observed. At 1.5 T, the copper wires caused distinct RF artifacts. At 3 T, RF artifacts also appeared for the hip prostheses and the biopsy needles. Stents with pronounced luminal shielding at lower field strength revealed marked B, enhancement close to their outer surface. © 2005 Elsevier Inc. All rights reserved.