ASTM F2052-00

NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
Designation: F 2052 – 00
Standard Test Method for
Measurement of Magnetically Induced Displacement Force
on Passive Implants in the Magnetic Resonance
Environment
This standard is issued under the fixed designation F 2052; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.
1. Scope experienced by an element of electric current at the point, or by
the electromotive force induced in an elementary loop during
1.1 This standard test method covers the measurement of
any change in flux linkages with the loop at the point. The
the magnetically induced displacement force produced by the
magnetic induction is frequently referred to as the magnetic
spatial gradients of a magnetic field on passive implants
field. B is the static field in an MR scanner.
o
(implants that function without the supply of electrical power)
3.1.5 magnetic resonance diagnostic device—a device in-
and the comparison of that force to the weight of the implant.
tended for general diagnostic use to present images which
1.2 This method does not address the issues of magnetically
reflect the spatial distribution and/or magnetic resonance spec-
induced torque or RF heating.
tra which reflect frequency and distribution of nuclei exhibiting
1.3 This method is intended for devices that can be sus-
nuclear magnetic resonance. Other physical parameters derived
pended from a thin string. Devices which cannot be suspended
from the images and/or spectra may also be produced.
from a thin string are not covered by this test method.
3.1.6 magnetic resonance (MR) environment—refers to the
1.4 The weight of the thin string from which the device is
electromagnetic environment present in the vicinity of an MR
suspended during the test must be less than 1% of the weight
scanner within the 5 gauss line.
of the tested device.
3.1.7 magnetic resonance imaging (MRI)—imaging tech-
1.5 This method is applicable only to magnet systems in
nique that uses static and time varying magnetic fields to
which the direction of the magnetic field (and the direction of
provide images of tissue by the magnetic resonance of nuclei.
the magnetically induced deflection force) is horizontal.
3.1.8 magnetically induced displacement force— force pro-
2. Referenced Documents
duced when a magnetic object is exposed to the spatial gradient
of a magnetic field. This force will tend to cause the object to
2.1 ASTM Standards:
translate in the gradient field.
A 340 Standard Terminology of Symbols and Definitions
3.1.9 paramagnetic material—a material having a relative
Relating to Magnetic Testing
permeability which is slightly greater than unity, and which is
F 1542 Standard Specification for the Requirements and
practically independent of the magnetizing force.
Disclosure of Self-Closing Aneurysm Clips
3.1.10 passive implant—an implant that serves its function
3. Terminology
without the supply of electrical power.
3.1.11 tesla, (T)—the SI unit of magnetic induction equal to
3.1 Definitions:
10 gauss.
3.1.1 diamagnetic material—a material whose relative per-
meability is less than unity.
4. Summary of Test Method
3.1.2 ferromagnetic material—a material whose magnetic
4.1 An implant is suspended by a fine string at the point in
moments are ordered and parallel producing magnetization in
a magnetic field that will produce the greatest magnetically
one direction.
induced deflection. The angular deflection of the string from
3.1.3 magnetic field strength (H in A/m)—strength of the
the vertical is measured. If the implant deflects less than 45°,
applied magnetic field.
then the magnetically induced deflection force is less than the
3.1.4 magnetic induction or magnetic flux density (B in
force on the implant due to gravity (its weight).
T)—that magnetic vector quantity which at any point in a
magnetic field is measured either by the mechanical force
5. Significance and Use
5.1 This test is one of those required to determine if the
1 presence of a passive implant may cause injury to the person
This test method is under the jurisdiction of ASTM Committee F04 on Medical
with the implant during an MRI scan and in the vicinity of the
& Surgical Materials & Devices and is the direct responsibility of Subcommittee
F04.15 on Materials Test Methods.
MRI scanner. Other safety issues which should be addressed
Current edition approved July 10, 2000. Published September 2000.
Copyright © ASTM, 100 Barr Harbor Drive, West Conshohocken, PA 19428-2959, United States.
NOTICE: This standard has either been superseded and replaced by a new version or discontinued.
Contact ASTM International (www.astm.org) for the latest information.
F 2052
include magnetically induced torque and RF heating.
5.2 If the implant deflects less than 45°, then the magneti-
cally induced deflection force is less than the force on the
implant due to gravity (its weight). For this condition, it is
assumed that any risk imposed by the application of the
magnetically induced force is no greater than any risk imposed
by normal daily activity in the Earth’s gravitational field.
5.3 A deflection of less than 45° at the location of the
maximum spatial gradient in one MRI scanner does not
preclude a deflection exceeding 45° in a scanner with a higher
field strength or larger spatial gradients.
5.4 This test alone is not sufficient for determining if an
implant is safe in the MR environment.
FIG. 1 Test Fixture Mounted on the Patient Table of an MRI
Scanner
6. Apparatus
6.1 The test fixture consists of a sturdy structure capable of
holding the test device in the proper position without deflection
of the test fixture and containing a protractor with 1° graduated
markings, rigidly mounted to the structure. The 0° indicator on
the protractor is oriented vertically. The test device is sus-
pended from a thin string that is attached to the 0° indicator on
the protractor. In order for the weight of the string to be
considered negligible when compared to the weight of the
device, the weight of the string should be less than 1% of the
weight of the device. The string should be long enough so that
the device may be suspended from the test fixture and hang
freely in space. Motion of the string should not be constrained
by the support structure or the protractor. The string may be
attached to the device at any convenient location.
7. Test Specimens
FIG. 2 Test Device in Magnetic Field
7.1 For purposes of device qualification, the device evalu-
9. Calculations
ated according to this standard test method should be repre-
sentative of manufactured implant devices that are in the 9.1 Calculate the mean deflection angle using the absolute
finished sterilized condition.
values of the 3 values for deflection angle, a, measured in
7.2 For purposes of device qualification, implant devices
Section 8. (It is possible that instead of being attracted to the
should not be altered in any manner prior to testing.
magnet, the device might be repelled by the magnet. Therefore,
7.3 This standard test method may be used on prototype
the absolute value of the deflection angle should be used when
devices during product development.
calculating the mean deflection angle.)
9.2 Calculate the mean magnetically induced deflection
8. Procedure
force for the device using the mean value for the deflection
8.1 Any magnet with a horizontal magnetic field that angle a determined in 9.1 and the following relation (derived
produces a large spatial gradient may be used for the test. Fig.
in Appendix X2): F = mg tana, where m is the mass of the
m
1 shows the test fixture mounted on the patient table of an MRI implant and g is the acceleration due to gravity. If the mean
scanner. The test device is suspended from a thin string value for a is less than 45°, F , the magnetically induced
m
attached to the 0° indicator on the test fixture protractor. deflection force, is less than the force on the device due to
Position the test fixture so that the center of mass of the device gravity (its weight).
is at the location where the deflection is a maximum. Hold the
10. Report
device so that the string is vertical and then release it. Record
10.1 The report shall include the following for each speci-
a, the deflection of the device from the vertical direction to the
men tested:
nearest 0.5° (Fig. 2).
10.1.1 Device product description.
8.2 Repeat the process in 8.1 three times for each device
10.1.2 Device product number.
tested.
10.1.3 Materials of construction (ASTM designation or
NOTE 1—For a paramagnetic, diamagnetic or ferromagnetic device
other).
below saturation, the location of maximum deflection is at the point where
10.1.4 Number of specimens tested with explanation for the
|B| |„B| is a maximum. For a ferromagnetic device above the magnetic
sample size used.
saturation point, the maximum deflection will occur at the location where
10.1.5 Cartesian coordinate (x, y, z) location of the center of
„B is a maximum. If it is not known whether the device is paramagnetic,
diamagnetic or ferromagnetic, perform the test at both locations. mass of the device during the test using a right handed
-------------
...