A Novel Method For Measuring The Torque Acting On Cardiovascular Implants In NMR Scanners

• Published in: International journal of artificial organs 2005-09, Vol.28 (9), p.919-919
• Main Authors: Tedesco, A, Pallotti, G, Pallotti, M C, Pallotti, M G, D'Avenio, G, Canese, R, Podo, F, Grigioni, M
• Format: Article
• Language: English
• ISSN: 0391-3988

Background/Aim: The use of NMR techniques is widespread in the clinical field and is becoming a tool also in the study of pathologies of heart and large vessels. The growing need for high resolution in very short time in MR investigation calls for increasing static fields. Moreover, magnetic fields up to 3.0T are becoming commonplace in hospitals and the installation of systems at > 3T is increasing in research institutes. The question arises if cardiovascular implants such as mechanical heart valve prostheses can withstand such increasing static fields. We propose a novel method for measuring the torque acting on prosthetic implants subjected to the high static magnetic fields of NMR scanners. Methods: The torque measurements have been performed with a torsion balance, realized with a thin copper wire (whose diamagnetic properties render it suitable for this task), mounted on the scanner's cradle. The contact between valve and torsion wire is ideally point-like, so that the global torque is the sum of the contributions of two torsion bars. The deflection angle is calculated from the laser spot projected on a graduated scale by the device under test. The torque is readily calculated from the deflection angle and the geometrical parameters of the set-up. Mechanical valves of different type and brand have been tested in the small bore system Varian (nova 200/183 operating at 4.7 T. Results: The method has proved to be very sensitive, with respect to the other approaches followed in this type of characterization of prosthetic implants. A series of measurements on the same valve, repeated with different torsion wire diameters, has confirmed that the method is reliable and yields repeatable results. In general, the measurements have confirmed the safety of the tested valves, previously reported at smaller magnetic fields. Conclusion: The proposed method for torque measurements is capable of providing a quantitative evaluation of the interaction between prosthetic device and NMR scanner's magnetic field. Such information, besides being valuable for confirming the safety of a diagnostic investigation at a given magnetic field on an implanted patient, can be used for deriving functional parameters for the prediction of the device-field interaction that could occur at higher static levels.