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Scope

1.1 This test method covers the measurement of the magnetically induced torque produced by the static magnetic field in the magnetic resonance environment on medical devices and the comparison of that torque to the equivalent torque applied by the gravitational force to the implant.

1.2 This test method does not address other possible safety issues which include but are not limited to issues of magnetically induced force due to spatial gradients in the static magnetic field, RF heating, induced heating, acoustic noise, interaction among devices, and the functionality of the device and the MR system.

1.3 The torque considered here is the magneto-static torque due to the interaction of the MRI static magnetic field with the magnetization in the implant. The dynamic torque due to interaction of the static field with eddy currents induced in a rotating device is not addressed in this test method. Currents in lead wires may induce a torque as well.

1.4 The sensitivity of the torque measurement apparatus must be greater than 1/10 the "gravity torque," the product of the device's maximum linear dimension and its weight.

This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

Significance and Use

This test method is one of those required to determine if the presence of a medical device may cause injury during a magnetic resonance examination and in the magnetic resonance environment. Other safety issues which should be addressed include but may not be limited to magnetically induced force (see Test Method F 2052) and RF heating (see Test Method F 2182). The terms and icons in Practice F 2503 should be used to mark the device for safety in the magnetic resonance environment.

If the maximal torque is less than the product of the longest dimension of the medical device and its weight, then the magnetically induced deflection torque is less than the worst case torque on the device due to gravity. For this condition, it is assumed that any risk imposed by the application of the magnetically induced torque is no greater than any risk imposed by normal daily activity in the Earth’gravitational field. This is conservative; it is possible that greater torques would not pose a hazard to the patient.

This test method alone is not sufficient for determining if an implant is safe in the MR environment.

The sensitivity of the torque measurement apparatus must be greater than ¹/₁₀ the “gravity torque,” the product of device weight and the largest linear dimension.

The torque considered here is the magneto-static torque due to the interaction of the MRI static magnetic field with the magnetization in the implant. The dynamic torque due to interaction of the static field with eddy currents induced in a rotating device is not addressed in this test method. Currents in lead wires may induce a torque as well.

Keywords

force, magnetic; implant; metals (for surgical implants); MRI (magnetic resonance imaging); MR safety; torque, magnetic; ICS Number Code 17.220.20 (Measurement of electrical and magnetic quantities)

To find similar documents by ASTM Volume:

13.01 (Medical and Surgical Materials and Devices)

To find similar documents by classification:

17.220.20 (Measurement of electrical and magnetic quantities Including measuring instruments, instrument transformers Electric energy meters in buildings, see 91.140.50)

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