ASTM F2213-17
(Test Method)Standard Test Method for Measurement of Magnetically Induced Torque on Medical Devices in the Magnetic Resonance Environment
Standard Test Method for Measurement of Magnetically Induced Torque on Medical Devices in the Magnetic Resonance Environment
SIGNIFICANCE AND USE
5.1 This test method is one of those required to determine if the presence of a medical device may cause injury 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 F2052), RF heating (see Test Method F2182), and image artifact (see Test Method F2119). ISO TS 10974 addresses hazards produced by active implantable medical devices in the MR Environment.
5.2 The terms MR Conditional, MR Safe, and MR Unsafe together with the corresponding icons in Practice F2503 shall be used to mark the device for safety in the MR environment.
5.3 The acceptance criterion associated with this test shall be justified. If the maximum magnetically induced torque is less than the product of the longest dimension of the medical device and its weight, then the magnetically induced 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's gravitational field. This is conservative. It is possible that greater torques also would not pose a hazard. (For example, device position with respect to adjacent tissue, tissue ingrowth, or other mechanisms may act to prevent device movement or forces produced by a magnetically induced torque that are greater than the torque due to gravity from causing harm to adjacent tissue.)
5.4 This test method alone is not sufficient for determining if an implant is safe in the MR environment.
5.5 The magnetically induced torque considered in this standard 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...
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 a user-specified acceptance criterion.
1.2 This test method does not address other possible safety issues which may include, but are not limited to, magnetically induced deflection force, tissue heating, device malfunction, imaging artifacts, 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 of 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. Torque induced by currents in lead wires is not addressed by this standard.
1.4 The methods in this standard are applicable for MR systems with a horizontal magnetic field. Not all of the methods described in this standard are applicable for use in an MR system with a vertical magnetic field. The Suspension Method and the Low Friction Surface Method require gravity to be orthogonal to the magnetically induced torsion and may not be performed using a vertical magnetic field. The Torsional Spring and Pulley Methods can be adapted to work in a vertical magnetic field, however the example apparatus are not appropriate for use in a vertical magnetic field. The Calculation Based on Measured Displacement Force Method is independent of the MR system and thus could be used for an MR system with a vertical magnetic field.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the u...
General Information
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Standards Content (Sample)
This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: F2213 − 17
Standard Test Method for
Measurement of Magnetically Induced Torque on Medical
Devices in the Magnetic Resonance Environment
This standard is issued under the fixed designation F2213; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision.Anumber in parentheses indicates the year of last reapproval.A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope 1.6 This standard does not purport to address all of the
safety concerns, if any, associated with its use. It is the
1.1 This test method covers the measurement of the mag-
responsibility of the user of this standard to establish appro-
netically induced torque produced by the static magnetic field
priate safety, health, and environmental practices and deter-
inthemagneticresonanceenvironmentonmedicaldevicesand
mine the applicability of regulatory limitations prior to use.
the comparison of that torque a user-specified acceptance
1.7 This international standard was developed in accor-
criterion.
dance with internationally recognized principles on standard-
1.2 This test method does not address other possible safety
ization established in the Decision on Principles for the
issues which may include, but are not limited to, magnetically
Development of International Standards, Guides and Recom-
induced deflection force, tissue heating, device malfunction,
mendations issued by the World Trade Organization Technical
imaging artifacts, acoustic noise, interaction among devices,
Barriers to Trade (TBT) Committee.
and the functionality of the device and the MR system.
1.3 The torque considered here is the magneto-static torque
2. Referenced Documents
due to the interaction of the MRI static magnetic field with the
2.1 ASTM Standards:
magnetization of the implant. The dynamic torque due to
F2052Test Method for Measurement of Magnetically In-
interaction of the static field with eddy currents induced in a
duced Displacement Force on Medical Devices in the
rotating device is not addressed in this test method. Torque
Magnetic Resonance Environment
induced by currents in lead wires is not addressed by this
F2119Test Method for Evaluation of MR Image Artifacts
standard.
from Passive Implants
1.4 The methods in this standard are applicable for MR
F2182Test Method for Measurement of Radio Frequency
systems with a horizontal magnetic field. Not all of the
Induced Heating On or Near Passive Implants During
methods described in this standard are applicable for use in an
Magnetic Resonance Imaging
MR system with a vertical magnetic field. The Suspension
F2503Practice for Marking Medical Devices and Other
Method and the Low Friction Surface Method require gravity
Items for Safety in the Magnetic Resonance Environment
to be orthogonal to the magnetically induced torsion and may
2.2 Other Standards:
notbeperformedusingaverticalmagneticfield.TheTorsional
IEC 60601-2-33Medical electrical equipment - Part 2-33:
SpringandPulleyMethodscanbeadaptedtoworkinavertical
Particular requirements for the basic safety and essential
magnetic field, however the example apparatus are not appro-
performance of magnetic resonance equipment for medi-
priate for use in a vertical magnetic field. The Calculation
cal diagnosis
Based on Measured Displacement Force Method is indepen-
ISO 13485Medical devices -- Quality management systems
dent of the MR system and thus could be used for an MR
-- Requirements for regulatory purposes
system with a vertical magnetic field.
ISO TS 10974Assessment of the safety of magnetic reso-
1.5 The values stated in SI units are to be regarded as
nance imaging for patients with an active implantable
standard. No other units of measurement are included in this
medical device
standard.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
ThistestmethodisunderthejurisdictionofASTMCommitteeF04onMedical contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
andSurgicalMaterialsandDevicesandisthedirectresponsibilityofSubcommittee Standards volume information, refer to the standard’s Document Summary page on
F04.15 on Material Test Methods. the ASTM website.
Current edition approved Sept. 1, 2017. Published October 2017. Originally Available fromAmerican National Standards Institute (ANSI), 25 W. 43rd St.,
approved in 2002. Last previous edition approved in 2011 as F2213–06(2011). 4th Floor, New York, NY 10036, http://www.ansi.org.
DOI: 10.1520/F2213-17. Specifically, definition 3.11.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2213 − 17
3. Terminology intended by the manufacturer to be used, alone or in
combination, for human beings for one or more of the specific
3.1 Definitions:
purpose(s) of:
3.1.1 diamagnetic material, n—a material whose relative
(1) diagnosis, prevention, monitoring, treatment, or alleviation of disease;
permeability is less than unity.
(2) diagnosis, monitoring, treatment, alleviation of, or compensation for an
injury;
3.1.2 ferromagnetic material, n—amaterialwhosemagnetic
(3) investigation, replacement, modification, or support of the anatomy or of
moments are ordered and parallel producing magnetization in
a physiological process;
one direction.
(4) supporting or sustaining life;
(5) control of conception;
3.1.3 magnetic induction or magnetic flux density (B in T),
(6) disinfection of medical devices; and
n—that magnetic vector quantity which at any point in a
(7) providing information for medical purposes by means of in vitro exami-
nation of specimens derived from the human body, and which does not
magnetic field is measured either by the mechanical force
achieve its primary intended action in or on the human body by
experiencedbyanelementofelectriccurrentatthepoint,orby
pharmacological, immunological, or metabolic means, but which may be
the electromotive force induced in an elementary loop during
assisted in its function by such means.
ISO 13485
any change in flux linkages with the loop at the point. The
magnetic induction is frequently referred to as the magnetic
3.1.14 paramagnetic material, n—a material having a rela-
field. B isthestaticfieldinanMRsystem.Plaintypeindicates
0 tive permeability which is slightly greater than unity, and
a scalar (for example, B) and bold type indicates a vector (for
which is practically independent of the magnetizing force.
example,B).
3.1.15 passive implant, n—an implant that serves its func-
3.1.4 magnetic field strength (H in A/m), n—strength of the
tion without the supply of electrical power.
applied magnetic field.
3.1.16 tesla, (T), n—the SI unit of magnetic induction equal
3.1.5 magnetic resonance (MR), n—resonant absorption of
to 10 gauss (G).
electromagnetic energy by an ensemble of atomic particle
4. Summary of Test Method
situated in a magnetic field.
4.1 The static magnetic field associated with an MR system
3.1.6 magnetic resonance (MR) environment, n—volume
within the 0.50 mT(5 gauss (G)) line of an MR system, which producesatorqueonadevicethatactstoalignthelongaxisof
includes the entire three-dimensional volume of space sur- the object with the direction of the magnetic field. Five
rounding the MR scanner. For cases where the 0.50 mT line is methods for measurement or assessment of magnetically in-
contained within the Faraday shielded volume, the entire room duced torque are given in this standard: the Suspension
shall be considered the MR environment. Method, the Low Friction Surface Method, the Torsional
Spring Method, the Pulley Method, and the Calculation Based
3.1.7 magnetic resonance equipment, n—medical electrical
on Measured Displacement Force Method.
equipment which is intended for magnetic resonance examina-
tion of a patient. The MR equipment comprises all parts in 4.2 The Suspension Method and the Low Friction Surface
hardware and software from the supply mains to the display
Method are not appropriate for devices for which the magneti-
monitor. The MR equipment is a Programmable Electrical cally induced torque is expected to be greater than the torque
Medical System (PEMS). IEC 60601-2-33
due to gravity.
3.1.8 magnetic resonance imaging (MRI), n—imaging tech-
4.3 The Low Friction Surface Method is performed by
nique that uses static and time-varying magnetic fields to
placing the device on a low friction non-metallic, non-
provide images of tissue by the magnetic resonance of nuclei.
conductive surface as near as practical to the isocenter of the
MR system. The device is then rotated in defined angular
3.1.9 magnetic resonance system (MR System),
increments while alignment or rotation of the device with the
n—ensemble of MR equipment, accessories including means
staticmagneticfieldisobserved.Ifrotationofthedeviceisnot
for display, control, energy supplies, and the MR environment.
observed, an upper bound on the magnetically induced torque
IEC 60601-2-33
is estimated using the coefficient of friction between the
3.1.10 magnetically induced displacement force, n—force
surface and the device and the weight of the device. If
produced when a magnetic object is exposed to the spatial
alignment or rotation of the device is observed, then either the
gradient of a magnetic field. This force will tend to cause the
Torsional Spring Method or the Pulley Method shall be
object to translate in the gradient field.
performed. The coefficient of friction is calculated from the
3.1.11 magnetically induced torque, n—torque produced
device weight and the angle of repose (the angle in which the
when a magnetic object is exposed to a magnetic field. This
implant is on the verge of sliding off the low friction surface)
torque will tend to cause the object to align itself along the
which is measured outside the MR environment.
magnetic field in an equilibrium direction that induces no
4.4 TheTorsionSpringMethoddeterminesthemagnetically
torque.
inducedtorqueusingatorsionpendulum.Adeviceisplacedon
3.1.12 magnetization (M in T), n—magnetic moment per
aholdersuspendedbyatorsionspring.Theapparatusisplaced
unit volume
in the center of the magnetic resonance equipment magnet
3.1.13 medical device, n—any instrument, apparatus, where the magnetic field is uniform. The torque is determined
implement, machine, appliance, implant, in vitro reagent or from the measurement of the deflection angle of the holder
calibrator,software,material,orothersimilarorrelatedarticle, fromitsequilibriumposition.Theframeholdingthespringand
F2213 − 17
holderassemblyisrotatedandthetorqueasafunctionofangle devicepositionwithrespecttoadjacenttissue,tissueingrowth,
of the implant is determined. The maximal magnetic torque is or other mechanisms may act to prevent device movement or
compared to the worst case gravitational torque, defined as the forces produced by a magnetically induced torque that are
productofthemaximumlineardimensionofthedeviceandthe greater than the torque due to gravity from causing harm to
device weight. adjacent tissue.)
4.5 The Pulley Method allows determination of the maxi- 5.4 This test method alone is not sufficient for determining
mum magnetically induced torque of the device using a low if an implant is safe in the MR environment.
friction pulley attached to a rotating platform. The device is
5.5 The magnetically induced torque considered in this
fixed on the platform while positioning the device to be
standard is the magneto-static torque due to the interaction of
centered as near as practical to isocenter of the MR system.
the MRI static magnetic field with the magnetization in the
Using a lightweight string attached to the pulley and a force
implant. The dynamic torque due to interaction of the static
gauge, the platform is rotated by pulling the force gauge in a
field with eddy currents induced in a rotating device is not
direct line away from the torque fixture. The maximum torque
addressed in this test method. Currents in lead wires may
is determined by using the maximum reading from the force
induce a torque as well.
gauge.
4.6 The Suspension Method is a qualitative method that is
6. Test Specimens
performed by suspending the device by a lightweight string in
6.1 For purposes of device qualification, the device evalu-
a location as near as practical to the isocenter of the MR
ated according to this test method should be representative of
system. The device is then rotated in defined angular incre-
manufactured devices. The device should be sterilized, unless
ments while movement or rotation of the device to align with
sterilization is not expected to affect the relevant properties of
thestaticmagneticfieldisobserved.Ifrotationofthedeviceis
the device (for example: magnetic susceptibility, weight)
not observed, the magnetically induced torque is small and no
6.2 Forpurposesofdevicequalification,anyalterationfrom
further evaluation is required. If rotation of the device is
the finished condition should be reported. For instance, if
observed,thentheLowFrictionSurfaceMethod,theTorsional
sections are removed from the device for testing or if the
Spring Method, or the Pulley Method shall be performed.
device has not been sterilized, this should be reported.
4.7 The Calculation Based on Measured Displacement
Force Method provides an upper bound for the magnetically
7. Procedure
induced torque based on magnetically induced displacement
7.1 Selection of Test Device:
force measurements using Test Method F2052. This method is
most appropriate for devices which are composed of only one 7.1.1 The test sample shall be worst case for the device
under test. Provide a rationale for the selection of the test
material; however it may also be used with devices composed
of multiple materials (see 7.8.2.2). This method is not appro- sample as worst case. For instance, for devices that are
available in multiple sizes and/or configurations, provide a
priate for devices that contain magnets or ferromagnetic
material. rationale supporting the chosen test sample as worst case for
the entire range of device sizes and/or configurations.
5. Significance and Use
7.1.1.1 It might be appropriate to test only a relevant
sectionofadevice(forexample,foraflexibledevicewithonly
5.1 Thistestmethodisoneofthoserequiredtodetermineif
a small metallic portion, test only the metallic portion of the
the presence of a medical device may cause injury in the
device). A justification for the selected portion of the device
magnetic resonance environment. Other safety issues which
shall be provided. M
...
This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: F2213 − 06 (Reapproved 2011) F2213 − 17
Standard Test Method for
Measurement of Magnetically Induced Torque on Medical
Devices in the Magnetic Resonance Environment
This standard is issued under the fixed designation F2213; 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 (´) indicates an editorial change since the last revision or reapproval.
1. 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.a user-specified acceptance criterion.
1.2 This test method does not address other possible safety issues which include may include, but are not limited to issues of
magnetically induced force due to spatial gradients in the static magnetic field, RF heating, induced heating, to, magnetically
induced deflection force, tissue heating, device malfunction, imaging artifacts, 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 inof 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 Torque induced by currents in lead wires may induce a torque as well.is not
addressed by this standard.
1.4 The sensitivity of the torque measurement apparatus must be greater thanmethods in this standard are applicable for MR
systems with a horizontal magnetic field. Not all of the methods described in this standard are applicable for use in an MR system
with a vertical magnetic field. The Suspension Method and the Low Friction Surface Method require gravity to be orthogonal to
the magnetically induced torsion and may not be performed using a vertical magnetic field. The Torsional Spring and Pulley
Methods can be adapted to work in a vertical magnetic field, however the example apparatus are not appropriate for ⁄10 the “gravity
torque,” the product of the device’s maximum linear dimension and its weight.use in a vertical magnetic field. The Calculation
Based on Measured Displacement Force Method is independent of the MR system and thus could be used for an MR system with
a vertical magnetic field.
1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.6 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 safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
F2052 Test Method for Measurement of Magnetically Induced Displacement Force on Medical Devices in the Magnetic
Resonance Environment
F2119 Test Method for Evaluation of MR Image Artifacts from Passive Implants
F2182 Test Method for Measurement of Radio Frequency Induced Heating On or Near Passive Implants During Magnetic
Resonance Imaging
This test method is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility of Subcommittee
F04.15 on Material Test Methods.
Current edition approved Oct. 1, 2011Sept. 1, 2017. Published October 2011October 2017. Originally approved in 2002. Last previous edition approved in 20062011 as
F2213 – 06.F2213 – 06 (2011). DOI: 10.1520/F2213-06R11.10.1520/F2213-17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
F2213 − 17
F2503 Practice for Marking Medical Devices and Other Items for Safety in the Magnetic Resonance Environment
2.2 Other Standards:
IEC 60601-2-33 Ed. 2.0 Medical Electrical Equipment—Part 2: Particular Requirements for the Safety of Magnetic Resonance
Equipment for Medical Diagnosis, 2002Medical electrical equipment - Part 2-33: Particular requirements for the basic safety
and essential performance of magnetic resonance equipment for medical diagnosis
ISO 13485:2003(E)13485 Medical Devices—Quality Management Systems—Requirements for Regulatory Purposes, definition
3.7devices -- Quality management systems -- Requirements for regulatory purposes
ISO TS 10974 Assessment of the safety of magnetic resonance imaging for patients with an active implantable medical device
3. Terminology
3.1 Definitions—Definitions:For the purposes of this test method, the definitions in 3.1.1 – 3.1.18 shall apply:
3.1.1 diamagnetic material—material, n—a material whose relative permeability is less than unity.
3.1.2 ferromagnetic material—material, n—a material whose magnetic moments are ordered and parallel producing magneti-
zation in one direction.
3.1.3 magnetic induction or magnetic flux density (B in T)—T), n—that magnetic vector quantity which at any point in a
magnetic field is measured either by the mechanical force experienced by an element of electric current at the point, or by the
electromotive force induced in an elementary loop during any change in flux linkages with the loop at the point. The magnetic
induction is frequently referred to as the magnetic field. B is the static field in an MR system. Plain type indicates a scalar (for
example, B) and bold type indicates a vector (for example, B).
3.1.4 magnetic field strength (H in A/m)—A/m), n—strength of the applied magnetic field.
3.1.5 magnetic resonance (MR)—(MR), n—resonant absorption of electromagnetic energy by an ensemble of atomic particle
situated in a magnetic field.
3.1.6 magnetic resonance diagnostic device—a device intended for general diagnostic use to present images which reflect the
spatial distribution or magnetic resonance spectra, or both, which reflect frequency and distribution of nuclei exhibiting nuclear
magnetic resonance. Other physical parameters derived from the images or spectra, or both, may also be produced.
3.1.6 magnetic resonance (MR) environment—environment, n—volume within the 0.50 mT (5 gauss (G)) line of an MR system,
which includes the entire three dimensional three-dimensional volume of space surrounding the MR scanner. For cases where the
0.50 mT line is contained within the Faraday shielded volume, the entire room shall be considered the MR environment.
3.1.7 magnetic resonance equipment—equipment, n—medical electrical equipment which is intended for in-vivomagnetic
resonance examination of a patient. The MR equipment comprises all parts in hardware and software from the supply mains to
the display monitor. The MR equipment is a Programmable Electrical Medical System (PEMS). IEC 60601-2-33
3.1.9 magnetic resonance examination (MR Examination)—process of acquiring data by magnetic resonance from a patient.
3.1.8 magnetic resonance imaging (MRI)—(MRI), n—imaging technique that uses static and time varying time-varying
magnetic fields to provide images of tissue by the magnetic resonance of nuclei.
3.1.9 magnetic resonance system (MR System)—System), n—ensemble of MR equipment, accessories including means for
display, control, energy supplies, and the MR environment.
IEC 60601–2–3360601-2-33
3.1.10 magnetically induced displacement force—force, n—force produced when a magnetic object is exposed to the spatial
gradient of a magnetic field. This force will tend to cause the object to translate in the gradient field.
3.1.11 magnetically induced torque—torque, n—torque produced when a magnetic object is exposed to a magnetic field. This
torque will tend to cause the object to align itself along the magnetic field in an equilibrium direction that induces no torque.
3.1.12 magnetization (M in T)—T), n—magnetic moment per unit volume.volume
3.1.13 medical device—device, n—any instrument, apparatus, implement, machine, appliance, implant, in vitro reagent or
calilbrator,calibrator, software, material, or other similar or related article, intended by the manufacturer to be used, alone or in
combination, for human beings for one or more of the specific purpose(s) of:
(1) diagnosis, prevention, monitoring, treatment, or alleviation of disease,
(2) diagnosis, monitoring, treatment, alleviation of, or compensation for an injury,
(3) investigation, replacement, modification, or support of the anatomy or of a physiological process,
(4) supporting or sustaining life,
(5) control of conception,
(6) disinfection of medical devices, and
(7) providing information for medical purposes by means of in vitro examination of specimens derived from the human body, and which does not achieve
its primary intended action in or on the human body by pharmacological, immunological, or metabolic means, but which may be assisted in its function
by such means.
Available from American National Standards Institute (ANSI), 25 W. 43rd St., 4th Floor, New York, NY 10036, http://www.ansi.org.
Specifically, definition 3.11.
F2213 − 17
(1) diagnosis, prevention, monitoring, treatment, or alleviation of disease;
(2) diagnosis, monitoring, treatment, alleviation of, or compensation for an injury;
(3) investigation, replacement, modification, or support of the anatomy or of a physiological process;
(4) supporting or sustaining life;
(5) control of conception;
(6) disinfection of medical devices; and
(7) providing information for medical purposes by means of in vitro examination of specimens derived from the human body, and which does not achieve
its primary intended action in or on the human body by pharmacological, immunological, or metabolic means, but which may be assisted in its function
by such means.
ISO 13485
3.1.14 paramagnetic material—material, n—a material having a relative permeability which is slightly greater than unity, and
which is practically independent of the magnetizing force.
3.1.15 passive implant—implant, n—an implant that serves its function without the supply of electrical power.
3.1.16 tesla, (T)—(T), n—the SI unit of magnetic induction equal to 10 gauss (G).
4. Summary of Test Method
4.1 The static magnetic field associated with an MR system produces a torque on a device that acts to align the long axis of
the object with the direction of the magnetic field. Five methods for measurement or assessment of magnetically induced torque
are given in this standard: the Suspension Method, the Low Friction Surface Method, the Torsional Spring Method, the Pulley
Method, and the Calculation Based on Measured Displacement Force Method.
4.2 The Suspension Method and the Low Friction Surface Method are not appropriate for devices for which the magnetically
induced torque is expected to be greater than the torque due to gravity.
4.3 The Low Friction Surface Method is performed by placing the device on a low friction non-metallic, non-conductive surface
as near as practical to the isocenter of the MR system. The device is then rotated in defined angular increments while alignment
or rotation of the device with the static magnetic field is observed. If rotation of the device is not observed, an upper bound on
the magnetically induced torque is estimated using the coefficient of friction between the surface and the device and the weight
of the device. If alignment or rotation of the device is observed, then either the Torsional Spring Method or the Pulley Method shall
be performed. The coefficient of friction is calculated from the device weight and the angle of repose (the angle in which the
implant is on the verge of sliding off the low friction surface) which is measured outside the MR environment.
4.4 The static field in a magnetic resonance system produces a torque on a device that acts to align the long axis of the object
with the magnetic field. The torque is evaluated using a torsional pendulum method. Torsion Spring Method determines the
magnetically induced torque using a torsion pendulum. A device is placed on a holder suspended by a torsionaltorsion spring. The
apparatus is placed in the center of the magnetic resonance equipment magnet where the magnetic field is uniform. The torque is
determined from the measurement of the deflection angle of the holder from its equilibrium position. The frame holding the spring
and holder assembly is rotated and the torque as a function of angle of the implant is determined. The maximal magnetic torque
is compared to the worst case gravitygravitational torque, defined as the product of the maximum linear dimension of the device
and the device weight.
4.5 The Pulley Method allows determination of the maximum magnetically induced torque of the device using a low friction
pulley attached to a rotating platform. The device is fixed on the platform while positioning the device to be centered as near as
practical to isocenter of the MR system. Using a lightweight string attached to the pulley and a force gauge, the platform is rotated
by pulling the force gauge in a direct line away from the torque fixture. The maximum torque is determined by using the maximum
reading from the force gauge.
4.6 The Suspension Method is a qualitative method that is performed by suspending the device by a lightweight string in a
location as near as practical to the isocenter of the MR system. The device is then rotated in defined angular increments while
movement or rotation of the device to align with the static magnetic field is observed. If rotation of the device is not observed,
the magnetically induced torque is small and no further evaluation is required. If rotation of the device is observed, then the Low
Friction Surface Method,
...
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