1、Designation:F218209 Designation: F2182 11Standard 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 o
2、foriginal adoption 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 frequency (RF
3、) induced heating on or near a passive medical implant andits surroundings during magnetic resonance imaging (MRI).1.2 This test method is one of those required to determine if the presence of a passive implant may cause injury to the patientwith the implant during an MR procedure. Other safety issu
4、es that should be addressed include magnetically induced displacementforce and torque.1.3 The amount of RF-induced temperature rise for a given specific absorption rate (SAR) will depend on the RF frequency,which is dependent on the static magnetic field strength of the MR system. Because of possibl
5、e additional heating, particularlywhen implant dimensions approaches or exceeds one quarter of the wavelength of the RF field inside the phantom, conclusionsfrom measurements made at one static magnetic field strength do not apply to other field strengths and frequencies. While the focusin this test
6、 method is on 1.5 T or 3 Tesla cylindrical bore MR systems, the RF-induced temperature rise for an implant in openMR systems can be evaluated by suitable modification of the method described herein.1.4 This test method assumes that testing is done on devices that will be entirely inside the body. Fo
7、r other implantationconditions (for example, external fixation devices, percutaneous needles, catheters or tethered devices such as ablation probes),modifications of this test method are necessary.1.5 This test method applies to whole body magnetic resonance equipment, as defined in section 2.2.103
8、of the IEC Standard60601-2-33, Ed. 2.0, with a whole body RF transmit coil as defined in section 2.2.100. The RF coil is assumed to have quadratureexcitation.1.6 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.7 This standar
9、d does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatorylimitations prior to use.2. Referenced Documents2.1 ASTM S
10、tandards:2F2052 Test Method for Measurement of Magnetically Induced Displacement Force on Medical Devices in the MagneticResonance EnvironmentF2119 Test Method for Evaluation of MR Image Artifacts from Passive ImplantsF2213 Test Method for Measurement of Magnetically Induced Torque on Medical Device
11、s in the Magnetic ResonanceEnvironmentF2503 Practice for Marking Medical Devices and Other Items 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 ResonanceEquipment for Medical
12、 Diagnosis, 20021This test method is under the jurisdiction of ASTM Committee F04 on Medical and Surgical Materials and Devices and is the direct responsibility of SubcommitteeF04.15 on Material Test Methods.Current edition approved Nov. 15, 2009. Published January 2010. Originally approved in 2002.
13、 Last previous edition approved in 2002 as F218202a. DOI:10.1520/F2182-09.Current edition approved March 1, 2011. Published March 2011. Originally approved in 2002. Last previous edition approved in 2009 as F2182 09. DOI:10.1520/F2182-11.2For referenced ASTM standards, visit the ASTM website, www.as
14、tm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3Available from the International Electrotechnical Commission (IEC), 3 rue de Varembe, Case postale 131, CH-1211 Geneva 2
15、0, Switzerland.1This 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. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users c
16、onsult prior editions as appropriate. In all cases only the current versionof the standard as published by ASTM is to be considered the official document.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.2.3 NEMA Standard:4NEMA MS 82008
17、 Characterization of the Specific Absorption Rate for Magnetic Resonance Imaging Systems3. Terminology3.1 Definitions:3.1.1 gelled salinephantom medium consisting of sodium chloride and polyacrylic acid or sodium chloride and hydroxy-ethylcellulose in water as specified in this test method.3.1.2 imp
18、lant, nin medicine, an object, structure, or device intended to reside within the body for diagnostic, prosthetic, orother therapeutic purposes.3.1.3 isocentergeometric center of the gradient coil system, which generally is the geometric center of a scanner with acylindrical bore.3.1.33.1.4 local SA
19、Rspecific absorption rate (SAR) averaged over any 10 g of tissue of the patient body and over a specified time.60601-2-33, Ed. 2.03.1.43.1.5 magnetic resonance (MR) environmentvolume within the 0.50 mT (5 gauss (G) line of an MR system, which includesthe entire three dimensional volume of space surr
20、ounding the MR scanner. For cases where the 0.50 mT line is contained withinthe Faraday shielded volume, the entire room shall be considered the MR environment.3.1.53.1.6 magnetic resonance imaging (MRI)imaging technique that uses static and time varying magnetic fields to provideimages of tissue by
21、 the magnetic resonance of nuclei.3.1.63.1.7 magnetic resonance system (MR system)ensemble of MR equipment, accessories including means for display, control,energy supplies, and the MR environment.60601-2-33, Ed. 2.03.1.7medical implanta structure or device that is placed within the body of the pati
22、ent for medical diagnostic or therapeuticpurposes.3.1.8 MR Conditionalan item that has been demonstrated to pose no known hazards in a specified MR environment withspecified conditions of use. Field conditions that define the specified MR environment include field strength, spatial gradient, dB/dt(t
23、ime rate of change of the magnetic field), radio frequency (RF) fields, and specific absorption rate (SAR). Additional conditions,including specific configurations of the item, may be required.3.1.9 MR Safean item that poses no known hazards in all MR environments.NOTE 1MR Safe items include noncond
24、ucting, nonmagnetic items such 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 or an apparatus that reproduces the RF field of this type of system.3.1.11 MR Unsafean item that is known
25、to pose hazards in all MR environments.NOTE 2MR Unsafe items include magnetic items such as a pair of ferromagnetic scissors.3.1.12 passive implantan implant that serves its function without supply of electrical power.3.1.13 radio frequency (RF) magnetic fieldthe magnetic field in MRI that is used t
26、o flip the magnetic moments. The frequencyof the RF field is gB0where g is the gyromagnetic constant, 42.56 MHz/T for protons, and B0is the static magnetic field in Tesla.3.1.14 specific absorption rate (SAR)the mass normalized rate at which RF energy is deposited in biological tissue. SAR istypical
27、ly indicated in W/kg.4. Summary of Test Method4.1 The implant to be tested is placed in a phantom material that simulates the electrical and thermal properties of the humanbody. The implant is placed at a location with well characterized exposure conditions. The local SAR is assessed to characterize
28、the exposure conditions at that location. The phantom material is a gelled saline consisting of a saline solution and a gelling agent.Fiberoptic temperature probes are placed at locations where the induced implant heating is expected to be the greatest (this mayrequire pilot experiments to determine
29、 the proper placement of the temperature probes). The phantom is placed in an MR systemor an apparatus that reproduces the RF field of such an MR system. An RF field producing a whole body averaged SAR of about2 W/kg averaged over the volume of the phantom is applied for approximately 15 min, or oth
30、er time sufficient to characterize thetemperature rise and the local SAR.4.2 The measurement is divided into two parts: In Step 1, the implant heating is measured and the RF energy is assessed bymeasuring the local SAR at a temperature reference probe. The temperature rise on or near the implant at
31、several locations is4Available from National Electrical Manufacturers Association (NEMA), 1300 N. 17th St., Suite 1752, Rosslyn, VA 22209, http:/www.nema.org.F2182 112measured using fiber-optic thermometry probes during approximately 15 min of RF application. In Step 2, the implant is removedand the
32、 local SAR is assessed at the same positions where the implant heating was measured in Step 1 and at the location of thetemperature reference probe. All measurements shall be done with the implant holders in place. The local SAR value at thetemperature reference probe is calculated and is used to ve
33、rify that the same RF exposure conditions are applied during Steps 1and 2.5. Significance and Use5.1 This test method describes a test procedure for evaluating the RF-induced temperature rise associated with an MR procedureinvolving a specific frequency of RF irradiation of an implant. The heating m
34、easurements are made twice, once with the implantand then repeated at the same location without the implant. These two measurements estimate the local SAR and the localadditional temperature rise with the implant.5.2 If there is a significant temperature rise associated with the implant, the results
35、 may be used as an input to a computationalmodel for estimating temperature rise in a patient. The combination of the test results and the computational model results maythen be provided to regulatory bodies and physicians to assess the safety of a patient with the implant during an MR scan.6. Appar
36、atus6.1 Test ApparatusThe test apparatus consists of a suitable phantom and an MR test system for production of the RF field.The phantom, implant, and MR test system are utilized to approximate the electrical and physical environment that the patient anddevice experience during an MR procedure. The
37、phantom, implant, and MR test system are utilized to establish the heatingbehavior of a device in a known RF field in a standardized phantom.6.2 Temperature SensorA suitable temperature measuring device, usually a fiberoptic thermometry probe, is used to measuretemperature versus time of RF exposure
38、 on or in the vicinity of the implant. The temperature sensor will have a resolution of noworse than 0.1C and a spatial resolution not to exceed 1 mm in any direction.NOTE 3Fluoroptic temperature probes have been found to be satisfactory for this purpose.7. Test Specimens7.1 For purposes of device q
39、ualification, the implant evaluated according to this test method shall be representative of a finisheddevice in the as-implanted condition; for example, balloon expandable stents should be balloon expanded.7.2 For purposes of device qualification, implants shall not be altered in any manner prior t
40、o testing other thanpositioning/coiling of the implant in order to orient it in the anticipated worst case scenario for that device/scanner frequency.7.3 This test method may be used on prototype devices during product development.8. Procedure8.1 Phantom MorphologyThe phantom container and all its p
41、arts should be made of material that is an electrical insulator andis non-magnetic and non-metallic. The phantom container should be constructed so that the phantom gelled-saline material is ofthe dimensions shown in Fig. 1.8.2 Phantom MaterialPhantom materials simulating tissue for the RF heating t
42、est meet the following criteria.8.2.1 ConductivityConductivity of the gelled saline at test temperature shall be 0.47 6 10 % S/m at 64 MHz and 128 MHz.NOTE 4The conductivity at the test temperature was selected to match the average conductivity of the human body at body temperature. Electricalconduc
43、tivity in the MHz range is greater than conductivity measured in the kHz range. The conductivity at 64 MHz and 128 MHz is valid usingmeasurements at the lower frequencies specified in 8.3.1. (See Stuchly et al. (1)5for data on tissue electrical properties andAthey et al. (2) for proceduresfor measur
44、ement of electrical properties.)8.2.2 Dielectric ConstantDielectric constant shall be 60 to 100 at 64 MHz and 128 MHz.8.2.3 Thermal ParametersThe phantom material shall have thermal properties similar to those of the body which hasdiffusivity of about 1.3 3 10-7m2/s and heat capacity close to that o
45、f water, 4160 J/kgC.8.2.4 ViscosityThe viscosity shall be great enough so that the phantom material does not allow bulk transport or convectioncurrents. Generally, this is achieved by inclusion of a gelling agent.NOTE 5The amount of aqueous solution absorbed decreases with increasing salt concentrat
46、ions.8.3 Phantom FormulationA suitable gelled saline that has the properties described in 8.2 can be made with 1.32 g/L NaCland 10 g/L polyacrylic acid (PAA) in water. For this formulation, room temperature conductivity is approximately 0.47 S/m andviscosity is sufficient to prevent convective heat
47、transport.NOTE 6Another formulation can be made with NaCl and hydroxyethyl cellulose (HEC) in water. See X1.4. Comparative testing between PAA andHEC gels has not been performed prior to publication of this test method.8.3.1 It is essential to strictly follow the mixing protocol and use the given in
48、gredients in order to achieve reliable and repeatableresults. The following protocol needs to be followed precisely. The resulting gel (PAA) should have conductivity of 0.40 to 0.605The boldface numbers in parentheses refer to a list of references at the end of this standard.F2182 113S/m at temperat
49、ures between 20 and 25C measured at frequencies lower than 15 kHz. The specific heat of the gel is 4160 J/(kgk) at 21C and there is a linear rise of 2.35 J/(kg K) per degree kelvin in the specific heat from 20 to 40C. The gelled saline shouldhave a shelf life of two months. However, a new batch of gelled saline is needed when there is a change in any property, such asvolume, conductivity, color, or viscosity. The phantom should be sealed in an airtight container whenever possible to preventevaporation and/or contamination. Evaporation will
