LOW-FIELD MAGNETIC-RESONANCE-IMAGING IN THE EVALUATION OF MECHANICAL AND BIOLOGICAL HEART-VALVE FUNCTION

Magnetic resonance imaging (MRI) has been frequently considered unsafe for patients with ferromagnetic implants: risks to be considered incl ude induction of electric current, heating and dislocation of the pros thesis. Previous in vitro and in vivo studies have indicated the possi bility of performing MRI examinations on patients with prosthetic hear t valves. The aim of our study was to verify the presence of artifacts at the level of the prosthetic heart valve in vivo using a low-field MR unit (0.2 T) and to define the possibility of a functional analysis of the valve in patients with biomedical or mechanical prostheses. We evaluated 14 patients surgically treated for implantation of nine bio logical and seven mechanical aortic and mitral valves. A low-field MR unit (0.2 T) was employed using cine-MR technique on long- and short-a xis view. The images were acquired on planes parallel and perpendicula r to the valvular plane. Semiquantitative analysis with double-blind e valuation for definition of the extent of the artifact was performed. Three classes of artifacts were distinguished from minimal to signific ant. The examinations showed the presence of minimal artifacts in all biological heart valves and moderate artifacts in mechanical valves gi ving good qualitative data on blood flow near the valve. Analysis of t he flow behind the valve showed signs of normal function in 13 prosthe ses and pathological findings in the remaining three. In these latter cases, MRI was able to define the presence of a pathologic aortic pres sure gradient, mitral insufficiency and malpositioning of the mitral v alve causing subvalvular turbulence. Nevertheless, we believe that the application of velocity-encoding cine-MR is more promising than semiq uantitative analysis of artifacts.