InMagnetic resonance imaging (MRI), strong magnetically induced torques may act on implanted ferromagnetic medical devices. These forces are liable to restrict the function of the device, damage it, or cause severe, sometimes life-threatening accidents[1-3]. The ASTM F2213 standard[4]describes the measurement of magnetically induced torques using a torsional spring method. As this method is very complex[5,6], it has been rarely ever employed. Also, this standard is not suitable for measuring torque induced by currents in lead wires.Instead, one frequently uses qualitative assessments according to a scale...

A MR-safe structure(Fig. 1 and Fig. 2,[12])was developed, consisting of polyvinyl chloride (PVC) and polyoxymethylene (POM). A completely ceramic zirconium oxide (ZrO2) ball-bearing (608-2RSR FAG, Schaeffler Technologies AG & Co. KG, Germany) permits a 360° rotation of the platform holding the test object unless the force sensor is fitted. The force sensor, originally integrated in a precision balance (PCB 1600-2, Kern & Sohn GmbH, Germany), was fixed directly to the test object platform via a force transfer unit. The measured value is indicated on the...

The data obtained in repeated measurements and with different MR systems of equal field strengths were always reproducible.The neurostimulator had a maximum torque of 63 ± 1 N·mm (Fig. 3).At the center of the magnetic field, the magnetically induced torques vary with the orientation of the object axis relative to B0.The highest values were measured at angles of about 45°, 135°, 225° and 315°. Zero passages were observed with orientations of the longitudinal axis of the test object parallel (0°, 180°) and normal (90°, 270°)...

In summary, it can be said that ferromagnetic medical implants may be affected by strong magnetically induced torques, the strength of which varies with the material and dimension of the implant.Currents in lead wires can increased the maximum torque. To measure very small currents, a force sensor with a sufficiently high resolution must be selected. The measurement apparatus proposed enables reproducible, fast and precise measurements possible, which allow the ASTM F2213 standard measurement method to be performed with greater ease, at greater speed and with...

Andreas Heinrich, medical physicists Department of Radiology, University Hospital Jena, Friedrich Schiller University, Germany Am Klinikum 1 07747 Jena, Germany e-mail: [email protected] A. Heinrich; Jena/DE - nothing to disclose C. Riedel; Jena/DE - nothing to disclose U. K. M. Teichgräber; Jena/DE - nothing to disclose M. Engler; Jena/DE - nothing to disclose F. Güttler; Jena/DE - nothing to disclose

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