Magnetic resonance imaging of prosthetic cardiac valves in vitro and in vivo
Magnetic Resonance Imaging
Although radiologists do not hesitate to recommend or perform a magnetic resonance imaging (MRI) examination on most patients, there have been reservations-on theoretical grounds-regarding MRI examinations for patients in whom prosthetic cardiac valves have been implanted. It is not known whether MRI is hazardous in the presence of a prosthetic valve. The questions that need to be resolved are whether these valves might malfunction when placed in a strong magnetic field, how much heat might be produced in the valves by radiofrequency pulses, whether induced electric currents might cause arrhythmias and whether unacceptable distortion of adjacent tissue might be generated in the image. Based on the preliminary in vitro work by Soulen et al,1 it seemed that MRI would be safe in patients with prosthetic valves. Other in vitro work by Hassler et al2 and the clinical work by Laakman et al3 in patients with other metallic implants also suggested that MRI in patients with prosthetic valves would be safe as well as display minimal metallic artifact. We undertook a 2-part study to examine the 5 prosthetic valves used at our institution. The valves were evaluated in vitro for heat production, deflection, torque (or a combination of these) that might present a hazard to the patient. Images of the valves were obtained in a saline bath under imaging conditions identical to those used in the in vivo studies. These images demonstrated the kinds of artifacts that would be produced by the valves and formed a baseline with which the patient images could be compared. In vivo, we studied the appearance of the valves and adjacent tissues. Patients were monitored for electrocardiogram changes as well as other symptoms. © 1988.
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