1、Designation: F2182 09Standard 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 o
2、r, 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 o
3、n or near a passive medicalimplant and its surroundings during magnetic resonance imag-ing (MRI).1.2 This test method is one of those required to determine ifthe presence of a passive implant may cause injury to thepatient with the implant during an MR procedure. Other safetyissues that should be ad
4、dressed include magnetically induceddisplacement force and torque.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 static magnetic fieldstrength of the MR system. Because of possible additionalheating,
5、 particularly when implant dimensions approaches orexceeds onequarter of the wavelength of the RF field inside thephantom, conclusions from measurements made at one staticmagnetic field strength do not apply to other field strengths andfrequencies. While the focus in this test method is on 1.5 T or3
6、 Tesla cylindrical bore MR systems, the RF-induced tempera-ture rise for an implant in open MR systems can be evaluatedby suitable modification of the method described herein.1.4 This test method assumes that testing is done on devicesthat will be entirely inside the body. For other implantationcond
7、itions (for example, external fixation devices, percutane-ous needles, catheters or tethered devices such as ablationprobes), modifications of this 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
8、-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 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 addre
9、ss all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2F2052 Test Meth
10、od for Measurement of Magnetically In-duced Displacement Force on Medical Devices in theMagnetic Resonance EnvironmentF2119 Test Method for Evaluation of MR Image Artifactsfrom Passive ImplantsF2213 Test Method for Measurement of Magnetically In-duced Torque on Medical Devices in the Magnetic Reso-n
11、ance EnvironmentF2503 Practice for Marking Medical Devices and OtherItems for Safety in the Magnetic Resonance Environment2.2 IEC Standard:360601-2-33, Ed. 2.0 Medical Electrical EquipmentPart 2:Particular Requirements for the Safety of Magnetic Reso-nance Equipment for Medical Diagnosis, 20022.3 NE
12、MA Standard:4NEMA MS 82008 Characterization of the Specific Ab-sorption Rate for Magnetic Resonance Imaging Systems3. Terminology3.1 Definitions:3.1.1 gelled salinephantom medium consisting of sodiumchloride and polyacrylic acid or sodium chloride and hydroxy-ethylcellulose in water as specified in
13、this test method.3.1.2 isocentergeometric center of the gradient coil sys-tem, which generally is the geometric center of a scanner witha cylindrical bore.1This test method is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devices and is the direct responsibility o
14、f SubcommitteeF04.15 on Material Test Methods.Current edition approved Nov. 15, 2009. Published January 2010. Originallyapproved in 2002. Last previous edition approved in 2002 as F2182 02a. DOI:10.1520/F2182-09.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Cus
15、tomer 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.4Available fro
16、m 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.3.1.3 local SARspecific absorption rate (SAR) averagedover any
17、 10 g of tissue of the patient body and over a specifiedtime. 60601-2-33, Ed. 2.03.1.4 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 0.50 mT li
18、ne iscontained within the Faraday shielded volume, the entire roomshall be considered the MR environment.3.1.5 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.3.1.6 magnetic resonance
19、system (MR system)ensembleof MR equipment, accessories including means for display,control, energy supplies, and the MR environment.60601-2-33, Ed. 2.03.1.7 medical implanta structure or device that is placedwithin the body of the patient for medical diagnostic ortherapeutic purposes.3.1.8 MR Condit
20、ionalan item that has been demonstratedto pose no known hazards in a specified MR environment withspecified conditions of use. 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) fi
21、elds, and specific absorption rate (SAR).Additional conditions, including specific configurations of theitem, may be required.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 b
22、e determined to be MR Safe byproviding a scientifically based rationale rather than test data.3.1.10 MR test systemMR system 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 ma
23、gnetic items such as a pair offerromagnetic scissors.3.1.12 passive implantan implant that serves its functionwithout supply 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
24、 the gyromagneticconstant, 42.56 MHz/T for protons, and B0is the staticmagnetic field in Tesla.3.1.14 specific absorption rate (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
25、 placed in a phantom materialthat simulates the electrical and thermal properties of thehuman body. The implant is placed at a location with wellcharacterized exposure conditions. The local SAR is assessedto characterize the exposure conditions at that location. Thephantom material is a gelled salin
26、e consisting of a salinesolution and a gelling agent. Fiberoptic temperature probes areplaced at locations where the induced implant heating isexpected to be the greatest (this may require pilot experimentsto determine the proper placement of the temperature probes).The phantom is placed in an MR sy
27、stem or an apparatus thatreproduces the RF field of such an MR system. An RF fieldproducing a whole body averaged SAR of about 2 W/kgaveraged over the volume of the phantom is applied forapproximately 15 min, or other time sufficient to characterizethe temperature rise and the local SAR.4.2 The meas
28、urement is divided into two parts: In Step 1,the implant heating is measured and the RF energy is assessedby measuring the local SAR at a temperature reference probe.The temperature rise on or near the implant at several locationsis measured using fiber-optic thermometry probes duringapproximately 1
29、5 min of RF application. In Step 2, the implantis removed and the local SAR is assessed at the same positionswhere the implant heating was measured in Step 1 and at thelocation of the temperature reference probe. All measurementsshall be done with the implant holders in place. The local SARvalue at
30、the temperature reference probe is calculated and isused to verify 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 sp
31、ecific frequency of RF irradiation ofan implant. The heating measurements 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 If there is a signific
32、ant temperature rise associated withthe implant, the results may be used as an input to acomputational model for estimating temperature rise in apatient. The combination of the test results and the computa-tional model results may then be provided to regulatory bodiesand physicians to assess the saf
33、ety of a patient with the implantduring an MR scan.6. Apparatus6.1 Test ApparatusThe test apparatus consists of a suit-able phantom and an MR test system for production of the RFfield. The phantom, implant, and MR test system are utilized toapproximate the electrical and physical environment that th
34、epatient and device experience during an MR procedure. Thephantom, implant, and MR test system are utilized to establishthe heating behavior of a device in a known RF field in astandardized phantom.6.2 Temperature SensorA suitable temperature measuringdevice, usually a fiberoptic thermometry probe,
35、is used tomeasure temperature versus time of RF exposure on or in thevicinity of the implant. The temperature sensor will have aresolution of no worse than 0.1C and a spatial resolution notto exceed 1 mm in any direction.NOTE 3Fluoroptic temperature probes have been found to be satis-factory for thi
36、s purpose.7. Test Specimens7.1 For purposes of device qualification, the implant evalu-ated according to this test method shall be representative of aF2182 092finished device in the as-implanted condition; for example,balloon expandable stents should be balloon expanded.7.2 For purposes of device qu
37、alification, implants shall notbe altered in any manner prior to testing other than positioning/coiling of the implant in order to orient it in the anticipatedworst case scenario for that device/scanner frequency.7.3 This test method may be used on prototype devicesduring product development.8. Proc
38、edure8.1 Phantom MorphologyThe phantom container and allits parts should be made of material that is an electricalinsulator and is non-magnetic and non-metallic. The phantomcontainer should be constructed so that the phantom gelled-saline material is of the dimensions shown in Fig. 1.8.2 Phantom Mat
39、erialPhantom 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 at 64 MHz and 128MHz.NOTE 4The conductivity at the test temperature was selected to matchthe average conductiv
40、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 at the lower frequencies specified in 8.3.1. (SeeStuchly et al. (1)5for data on tissue electrica
41、l properties and Athey et al.(2) for procedures for measurement of electrical properties.)8.2.2 Dielectric ConstantDielectric constant shall be 60to 100 at 64 MHz and 128 MHz.8.2.3 Thermal ParametersThe phantom material shallhave thermal properties similar to those of the body which hasdiffusivity o
42、f about 1.3 3 10-7m2/s and heat capacity close tothat of water, 4160 J/kgC.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 achieved by inclusion of agelling agent.NOTE 5The amount of aqueous solu
43、tion absorbed decreases withincreasing salt concentrations.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/man
44、d viscosity is sufficient to prevent convective heat transport.NOTE 6Another formulation can be made with NaCl and hydroxy-ethyl cellulose (HEC) in water. See X1.4. Comparative testing betweenPAAand HEC gels has not been performed prior to publication of this testmethod.8.3.1 It is essential to stri
45、ctly 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 of0.40 to 0.60 S/m at temperatures between 20 and 25Cmeasured at frequencies lower t
46、han 15 kHz. The specific heatof the gel is 4160 J/(kg k) at 21C and there is a linear rise of2.35 J/(kg K) per degree kelvin in the specific heat from 20 to40C. The gelled saline should have a shelf life of two months.However, a new batch of gelled saline is needed when there isa change in any prope
47、rty, such as volume, conductivity, color,or viscosity. The phantom should be sealed in an airtightcontainer whenever possible to prevent evaporation and/orcontamination. Evaporation will alter the gelled saline proper-ties.NOTE 7The objective is to have a resulting gel with a conductivity of0.47 S/m
48、 at frequencies of 64 and 128 MHz, however, the ability to makea precise formulation of the material exceeds the ability to preciselymeasure its complex permittivity at these frequencies using readilyavailable methods. As such, care must be taken in following theinstructions, and it is suggested to
49、measure the conductivity with a simpledevice at low frequencies (between approximately 1 and 15 kHz) in orderto check that the recipe was made without large errors or deviations.8.3.1.1 Ingredients of PAA gelled saline:Waterdeionized or distilled water, conductivity less than1 mS/m.NaClreagent grade, 99 % pure.Polyacrylic acidAldrich product number 436364, Poly-acrylic acid partial sodium salt, CAS no. 76774-25-9.6SeeNote 8.5The boldface numbers in parentheses refer to a list of references at the end ofthis standard.6The sole source of sup
