1、Designation: F2182 11aStandard Test Method forMeasurement of Radio Frequency Induced Heating On orNear Passive Implants During Magnetic ResonanceImaging1This standard is issued under the fixed designation F2182; the number immediately following the designation indicates the year oforiginal adoption
2、or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This test method covers measurement of radio fre-quency (RF) induced heating
3、on or near a passive medicalimplant and its surroundings during magnetic resonance imag-ing (MRI).1.2 This test method is one required to determine if thepresence of a passive implant may cause injury to the patientwith the implant during an MR procedure. Other safety issuesthat should be addressed
4、include magnetically induced dis-placement force and torque, as well as proper device functionwhile in various configurations in the MR environment.1.3 The amount of RF-induced temperature rise for a givenspecific absorption rate (SAR) will depend on the RF fre-quency, which is dependent on the stat
5、ic magnetic fieldstrength of the MR system. While the focus in this test methodis on 1.5 Tesla (T) or 3 Tesla cylindrical bore MR systems, theRF-induced temperature rise for an implant in MR systems ofother static magnetic field strengths or magnet designs can beevaluated by suitable modification of
6、 the method describedherein.1.4 This test method assumes that testing is done on devicesthat will be entirely inside the body. For other implantationconditions (for example, external fixation devices, percutane-ous needles, catheters or tethered devices such as ablationprobes), modifications of this
7、 test method are necessary.1.5 This test method applies to whole body magneticresonance equipment, as defined in section 2.2.103 of the IECStandard 60601-2-33, Ed. 2.0, with a whole body RF transmitcoil as defined in section 2.2.100. The RF coil is assumed tohave quadrature excitation.1.6 The values
8、 stated in SI units are to be regarded asstandard. No other units of measurement are included in thisstandard.1.7 This standard does not purport to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safet
9、y and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2F2052 Test Method for Measurement of Magnetically In-duced Displacement Force on Medical Devices in theMagnetic Resonance EnvironmentF2119 Test Method for Evaluat
10、ion of MR Image Artifactsfrom Passive ImplantsF2213 Test Method for Measurement of Magnetically In-duced Torque on Medical Devices in the Magnetic Reso-nance EnvironmentF2503 Practice for Marking Medical Devices and OtherItems for Safety in the Magnetic Resonance Environment2.2 IEC Standard:360601-2
11、-33, Ed. 2.0 Medical Electrical EquipmentPart 2:Particular Requirements for the Safety of Magnetic Reso-nance Equipment for Medical Diagnosis, 20022.3 NEMA Standard:4NEMA MS 82008 Characterization of the Specific Ab-sorption Rate for Magnetic Resonance Imaging Systems3. Terminology3.1 Definitions:3.
12、1.1 gelled salinephantom medium consisting of sodiumchloride and polyacrylic acid or sodium chloride and hydroxy-ethylcellulose in water as specified in this test method.1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devices and is the direct r
13、esponsibility of SubcommitteeF04.15 on Material Test Methods.Current edition approved April 15, 2011. Published August 2011. Originallyapproved in 2002. Last previous edition approved in 2011 as F2182 11. DOI:10.1520/F2182-11A.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orc
14、ontact ASTM Customer Service at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from the International Electrotechnical Commission (IEC), 3 rue deVarembe, Case postale 131, CH-1211 Geneva 20, Switzerland
15、.4Available from National Electrical Manufacturers Association (NEMA), 1300N. 17th St., Suite 1752, Rosslyn, VA 22209, http:/www.nema.org.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.3.1.2 implant, nin medicine, an object, structu
16、re, or de-vice intended to reside within the body for diagnostic, pros-thetic, or other therapeutic purposes.3.1.3 isocentergeometric center of the gradient coil sys-tem, which generally is the geometric center of a scanner witha cylindrical bore.3.1.4 local SARspecific absorption rate (SAR) average
17、dover any 10 g of tissue of the patient body and over a specifiedtime. 60601-2-33, Ed. 2.03.1.5 magnetic resonance (MR) environmentvolumewithin the 0.50 mT (5 gauss (G) line of an MR system, whichincludes the entire three dimensional volume of space sur-rounding the MR scanner. For cases where the 0
18、.50 mT line iscontained within the Faraday shielded volume, the entire roomshall be considered the MR environment.3.1.6 magnetic resonance imaging (MRI)imaging tech-nique that uses static and time varying magnetic fields toprovide images of tissue by the magnetic resonance of nuclei.3.1.7 magnetic r
19、esonance system (MR system)ensembleof MR equipment, accessories including means for display,control, energy supplies, and the MR environment.60601-2-33, Ed. 2.03.1.8 MR Conditionalan item that has been demonstratedto pose no known hazards in a specified MR environment withspecified conditions of use
20、. Field conditions that define thespecified MR environment include field strength, spatial gra-dient, dB/dt (time rate of change of the magnetic field), radiofrequency (RF) fields, and specific absorption rate (SAR).Additional conditions, including specific configurations of theitem, may be required
21、.3.1.9 MR Safean item that poses no known hazards in allMR environments.NOTE 1MR Safe items include nonconducting, nonmagnetic itemssuch as a plastic petri dish. An item may be determined to be MR Safe byproviding a scientifically based rationale rather than test data.3.1.10 MR test systemMR system
22、or an apparatus thatreproduces the RF field of this type of system.3.1.11 MR Unsafean item that is known to pose hazardsin all MR environments.NOTE 2MR Unsafe items include magnetic items such as a pair offerromagnetic scissors.3.1.12 passive implantan implant that serves its functionwithout supply
23、of electrical power.3.1.13 radio frequency (RF) magnetic fieldthe magneticfield in MRI that is used to flip the magnetic moments. Thefrequency of the RF field is gB0where g is the gyromagneticconstant, 42.56 MHz/T for protons, and B0is the staticmagnetic field in Tesla.3.1.14 specific absorption rat
24、e (SAR)the mass normalizedrate at which RF energy is deposited in biological tissue. SARis typically indicated in W/kg.4. Summary of Test Method4.1 The implant to be tested is placed in a phantom materialthat simulates the electrical and thermal properties of thehuman body. The implant is placed at
25、a location with wellcharacterized exposure conditions. The local SAR is assessedto characterize the exposure conditions at that location. Thephantom material is a gelled saline consisting of a salinesolution and a gelling agent. Temperature probes are placed atlocations where the induced implant hea
26、ting is expected to bethe greatest (this may require pilot experiments to determinethe proper placement of the temperature probes). The phantomis placed in an MR system or an apparatus that reproduces theRF field of such an MR system. An RF field producing asufficient whole body averaged SAR of abou
27、t 2 W/kg averagedover the volume of the phantom is applied for approximately15 min, or other time sufficient to characterize the temperaturerise and the local SAR.4.2 The test procedure is divided into two steps. In Step 1,the temperature rise on or near the implant at several locationsis measured u
28、sing fiber-optic thermometry probes (or equiva-lent technology) during approximately 15 min of RF applica-tion. Temperature rise is also measured at a reference locationduring Step 1. In Step 2, the implant is removed and the sameRF application is repeated while the temperature measurementsare obtai
29、ned at the same probe locations as in Step 1. Allmeasurements shall be done with the implant holders in place.The local SAR is calculated from the temperature measure-ments for each probe location, including the reference location.The local SAR value at the temperature reference probe is usedto veri
30、fy that the same RF exposure conditions are appliedduring Steps 1 and 2.5. Significance and Use5.1 This test method describes a test procedure for evaluat-ing the RF-induced temperature rise associated with an MRprocedure involving a specific frequency of RF irradiation ofan implant. The heating mea
31、surements are made twice, oncewith the implant and then repeated at the same location withoutthe implant. These two measurements estimate the local SARand the local additional temperature rise with the implant.5.2 The results may be used as an input to a computationalmodel for estimating temperature
32、 rise due to the presence ofthat implant in a patient. The combination of the test results andthe computational model results may then be used to helpassess the safety of a patient with the implant during an MRscan.6. Apparatus6.1 Test ApparatusThe test apparatus consists of a suit-able phantom and
33、an MR system or MR test system forproduction of the RF field. The phantom, implant, and MR testsystem are utilized to approximate the electrical and physicalenvironment that the patient and device experience during anMR procedure. The phantom, implant, and MR test system areutilized to establish the
34、 heating behavior of a device in a knownRF field in a standardized phantom.6.2 Temperature SensorA suitable temperature measuringdevice, usually a fiberoptic or fluoroptic thermometry probe, isused to measure temperature versus time during the RFexposure on or in the vicinity of the implant. The tem
35、peraturesensor will have a resolution of no worse than 0.1C, atemperature probe spatial resolution not to exceed 1 mm alongthe specific axis of measurement in any direction, and atemporal resolution of at least 4 s.F2182 11a2NOTE 3It may be necessary to perform multiple measurements nearthe position
36、 of interest to ensure that the temperature probe is in thelocation of greatest temperature rise.NOTE 4The temperature probe should be transparent to the appliedRF field and must not disturb the local E-field (electric fields) signifi-cantly. It is assumed that probes that are not electrically condu
37、ctive areacceptable.7. Test Specimens7.1 While this test method may be used on prototype orpredicate devices, for purposes of device qualification, theimplant evaluated according to this test method shall berepresentative of a finished device in the as-implanted or in situcondition; for example, bal
38、loon expandable stents should beballoon expanded to the proper diameter.7.2 Other than described as in 7.1, for purposes of devicequalification, implants shall not be altered in any manner priorto testing other than positioning/coiling or otherwise configur-ing the implant in order to orient it in t
39、he anticipated worst casescenario for that device/scanner frequency.8. Procedure8.1 Phantom MorphologyThe phantom container and allits parts should be made of materials that are electricalinsulators and non-magnetic and non-metallic. The phantomcontainer should be constructed so that the phantom gel
40、led-saline material is of the dimensions shown in Fig. 1. Thephantom material shown in Fig. 1 has a volume of approxi-mately 24.6 L. The phantom material including the optionalportion has a volume of approximately 28.2 L. To test largerdevices, it may be necessary to increase the depth of the gelmat
41、erial.8.2 Phantom MaterialPhantom materials simulating tis-sue for the RF heating test meet the following criteria.8.2.1 ConductivityConductivity of the gelled saline at testtemperature shall be 0.47 6 10 % S/m.NOTE 5The conductivity at the test temperature was selected to matchthe average conductiv
42、ity of the human body at body temperature.Electrical conductivity in the MHz range is greater than conductivitymeasured in the kHz range. The conductivity at 64 MHz and 128 MHz isvalid using measurements made at lower frequencies. (See Stuchly et al.(1)5for data on tissue electrical properties and A
43、they et al. (2) forprocedures for measurement of electrical properties.)8.2.2 Dielectric ConstantDielectric constant, or relativeelectric permittivity (r) shall be 80 6 20 at the appropriate testfrequency (64 MHz or 128 MHz).8.2.3 Thermal ParametersThe phantom material shallhave thermal properties s
44、imilar to those of the body which hasdiffusivity of about 1.3 3 10-7m2/s and heat capacity 4150J/kgC. This is close to the heat capacity of water.8.2.4 ViscosityThe viscosity shall be great enough so thatthe phantom material does not allow bulk transport or convec-tion currents. Generally, this is a
45、chieved by inclusion of agelling agent.8.3 Phantom FormulationAsuitable gelled saline that hasthe properties described in 8.2 can be made with 1.32 g/L NaCland 10 g/L polyacrylic acid (PAA) in water. For this formula-tion, room temperature conductivity is approximately 0.47 S/mand viscosity is suffi
46、cient to prevent convective heat transport.NOTE 6The amount of aqueous solution absorbed decreases withincreasing salt concentrations.NOTE 7Another formulation can be made with NaCl and hydroxy-ethyl cellulose (HEC) in water. See X1.4. Comparative testing betweenPAAand HEC gels has not been performe
47、d prior to publication of this testmethod.8.3.1 It is essential to strictly follow the mixing protocol anduse the given ingredients in order to achieve reliable andrepeatable results. The following protocol needs to be followedprecisely. The resulting gel (PAA) should have conductivity of0.47 6 10 %
48、 S/m at temperatures between 20 and 25C. Theconductivity does not need to be measured at 64 MHz or 128MHz. The specific heat of the gel is 4150 J/(kg K) at 21C andthere is a linear rise of 2.35 J/(kg K) per degree kelvin in thespecific heat from 20 to 40C. The gelled saline should have ashelf life o
49、f two months. However, a new batch of gelled salineis needed when there is a change in any property, such asvolume, conductivity, color, or viscosity. The phantom shouldbe sealed in an airtight container whenever possible to preventevaporation and/or contamination. Evaporation will alter thegelled saline properties.NOTE 8The objective is to have a resulting gel with a conductivity of0.47 S/m at frequencies of 64 and 128 MHz, however, the ability to makea precise formulation of the material exceeds the ability to preciselymeasure its complex p
