Keywords:
Physics in Medical Imaging, MR physics, MR, Physics, Safety, Quality assurance, Not applicable, Experimental, Performed at one institution
Authors:
A. Heinrich, C. Riedel, M. Engler, F. Güttler, U. K. M. Teichgräber; Jena/DE
DOI:
10.26044/ecr2020/C-10279
Methods and materials
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.
Fig. 1: MR-safe structure with (a) display of measurement value, (b) test object platform, (c) force sensor, (d) locking screw, (e) protractor and (f) Fixation of a test object with cable ties and performing a measurement in a MR scanner.
References: Heinrich, A., et al., Development of an apparatus for digital measurement of magnetically induced torque on medical implants to facilitate the application of the ASTM F2213 standard. IEEE Transactions on Biomedical Engineering, 2019: p. 1-1.
The measured value is indicated on the display of the precision balance. The force sensor and the computer unit with the display form a closed system. External influences that might affect the measurement results are automatically corrected during the taring process. The computer unit with the display is placed outside the 200 gauss line of an MR system and is connected with an MR-compatible wire to the MR-safe structure. A protractor (15 cm L09010, Helix Trading Ltd, Great Britain) and a locking screw are provided to exactly align the test object with B0.
Fig. 2: A schematic representation of the MR-safe structure is shown. The force sensor (above), force transfer unit (bottom left) and ball-bearings (bottom right) are highlighted in green.
References: Heinrich, A., et al., Development of an apparatus for digital measurement of magnetically induced torque on medical implants to facilitate the application of the ASTM F2213 standard. IEEE Transactions on Biomedical Engineering, 2019: p. 1-1.
The evaluation was performed with a neurostimulator (LibraXP, St. Jude Medical) in the magnetic field center of a 1.5T and 3T MRI. The torque was measured at 10-degree increments as the implant was rotated relative to the static magnetic field. Additionally, a conductor loop and a straight conductor (length 100 mm) was added to the neurostimulator to investigate currents in lead wires. The current was increased from 0 to 2 A with a step size of 0.1 A.