Immel Erwin, Gilbert F J, Melzer Andreas
IMSaT, University of Dundee, UK.
Minim Invasive Ther Allied Technol. 2009;18(3):149-55. doi: 10.1080/13645700902921310.
Artificial heart valves comprising metal can cause significant MR image artifacts due to the material (susceptibility artifact) and/or electromagnetic characteristics (RF artifact). The purpose of our study was to examine current commercially available heart valve prostheses, integrate resonant circuits and to produce a prototype self-expanding heart valve for MRI-guided placement. Different types of commercially available heart valves were tested in MRI. Freshly excised porcine heart valves were sutured with 6-0 prolene into a 21 mm Nitinol stent. Resonant circuits were integrated into the heart valves and tuned to the Larmor frequency of the MRI (42.58 MHz for 1.0 T and about 64 MHz for 1.5 T and 128 MHz for 3T). The artifacts caused by the non-ferromagnetic heart valves and the Nitinol stent could be overcome. MRI signal could be enhanced using low flip angles <40 and visualization improved in 1T, 1.5T and 3T MRI. MRI-guided implantation was facilitated. A resonant circuit tuned to the Larmor frequency of the MR tomography can overcome the RF artifacts and thus improve the visualization of prosthetic heart valves.
