YY/T 0987.5-2016Magnetic resonance compatibility for surgical implants - Part 5: Test method for magnetically induced torque (English PDF)

1 Scope

This Part of YY/T 0987 includes test method for magnetically induced torque generated by medical devices as a result of static magnetic field in magnetic resonance environment; a comparison of magnetically induced torque and medical devices' gravity moment.

This Part does not involve other possible safety questions. These safety questions include, but are not limited to, magnetically induced displacement force generated by the spatial gradient of magnetic field, radio frequency heating and radio frequency induced heating, noise, interaction among medical devices, functions of medical devices and magnetic resonance system.

In this Part, torque refers to static magnetic torque generated by MRI static magnetic field and implant's magnetic moment. This Part does not include dynamic torque generated by the rotation of medical device as a result of the interaction between the static magnetic field and eddy current. Current in the wires might also generate torque.

The sensitivity of torque measurement device shall be more than 1/10 of gravity moment; gravity moment equals the arithmetic product of the maximum linear size and the weight of medical device.

This Part does not attempt to elaborate all the involved safety questions, even though those safety questions are related with the usage. Determining appropriate safety and health specifications and clarifying the applicability of management limit before application is the responsibility on the users of this Standard.

2 Normative References

The following documents are indispensable to the application of this Standard. In terms of references with a specified date, only versions with a specified date are applicable to this Standard. The latest version (including all the modifications) of references without a specified date is also applicable to this Standard.

YY/T 0987.1 Implants for Surgery - Magnetic Resonance Compatibility - Part 1. Safety Marking

YY/T 0987.2 Implants for Surgery - Magnetic Resonance Compatibility - Part 2. images and/or spectrograms, other physical parameters can also be obtained.

3 Terms and Definitions

5 Significance and Application

The test method in this Part is is one of the test methods of determining whether the existence of medical devices would lead to patients' injury in MR examination or MR environment. Other safety questions that need to be described include, but are not limited to, magnetically induced displacement force (refer to YY/T 0987.2) and radio frequency induced heating (refer to YY/T 0987.4). In order to guarantee the safety of medical devices in magnetic resonance environment, terms and markings stipulated in YY/T 0987.1 shall be applied to the marking of medical devices.

If the maximum torque is less than the arithmetic product of medical device's maximum size and weight, then, magnetically induced torque is less than the severest gravity moment generated by gravity. Under this circumstance, it can be deemed that the risk of magnetically induced torque is not higher than risks of daily activities in the earth's gravity field. This is merely conservative estimation; it is possible that a larger torque also would not bring any hazard to patients.

This test is insufficient to prove medical devices' safety in magnetic resonance environment.

The sensitivity of torque measurement device shall be more than 1/10 of gravity moment; gravity moment equals the arithmetic product of the maximum linear size and the weight of medical device.

In this Part, torque refers to static magnetic torque generated by MRI static magnetic field and implant's magnetic moment. This Part does not include dynamic torque generated by the rotation of medical device as a result of the interaction between the static magnetic field and eddy current. Current in the wires might also generate torque.

6 Instruments and Equipment

Test device is shown in Figure 1. The device is constituted of a solid structure, including a loading tray supported by torsional spring. The device is completely made of non-ferromagnetic materials. Test sample shall be pasted or bundled on the loading tray. A protractor (division value. 1°) shall be fixated on a supporting structure. There is a marking on the loading tray, through which, the included angle of the loading tray and above test process.

In terms of conductors, try to place them in accordance with the physical configuration in vivo. If it is feasible, conductors shall load the electric current during the application in vivo.

9 Calculation

Torque. signifies the loading tray's deflection angle relative to the equilibrium position. The equilibrium position is the loading tray's deflection angle relative to the fixed pedestal in magnetic field-free area. signifies the torsional spring's elastic coefficient.

10 Report

In terms of each test sample, report shall include the following content.

a) Description of test product, including dimension figures or photos (with scale) of medical devices;

b) Sketch maps or photos of three sample configurations in tests;

c) Medical devices' product identification (such as batch, batch number, model number, version number, serial number and date of production);

d) Materials (stipulated materials or others);

e) Quantity of test samples and dimensional specification of selected samples;

f) The mass of sample;

g) Dimension drawings or photos of medical devices (with scale);

h) Type of magnetic object; magnetic field strength B0 of static magnetic field;

i) Take the central point of magnetic object as the original point; use Cartesian coordinates (x, y, z) of the gravity center of the medical device, which is determined through right-hand screw rule; including a sketch map of magnetic resonance system and coordinate axis;

j) Sketch map or photo of test device, including torsional spring's elastic coefficient;

k) Draw sketch maps of torque (unit. N-m) angle; the angle is the deflection angle of medical device's principal axis relative to the direction of static magnetic field;

Appendix A (Informative) Fundamental Principle