1、Designation: F 2182 02aStandard Test Method forMeasurement of Radio Frequency Induced Heating NearPassive Implants During Magnetic Resonance Imaging1This standard is issued under the fixed designation F 2182; the number immediately following the designation indicates the year oforiginal adoption or,
2、 in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon (e) 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 ne
3、ar a passive medical implantand its surroundings during Magnetic Resonance Imaging(MRI).1.2 This test method is one of those required to determine ifthe presence of a passive implant may cause injury to theperson with the implant during an MRI procedure. Other safetyissues that should be addressed i
4、nclude 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 proportional to the static magnetic fieldstrength. Because of possible additional heating, particularlywhen devi
5、ce dimensions exceed a quarter wavelength, conclu-sions from measurements made at one frequency may notapply to other frequencies. While the focus in this test methodis on 1.5 T cylindrical bore imagers, the RF-induced tempera-ture rise in the open MRI systems can be evaluated by suitablemodificatio
6、n of the methods described here.1.4 This test method assumes that testing is done on devicesthat will be entirely inside the body.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 transmi
7、tcoil as defined in section 2.2.100. The RF coil is assumed tohave quadrature excitation.1.6 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 safety and health practice
8、s and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:A 340 Terminology of Symbols and Definitions Relating toMagnetic Testing2F 2052 Test Method for Measurement of Magnetically In-duced Displacement Force on Medical Devices in theMagneti
9、c Resonance Environment3F 2119 Test Method for Evaluation of MR Image Artifactsfrom Passive Implants32.2 IEC Standard:460601-2-33, Ed. 2.0 Medical Electrical EquipmentPart 2:Particular Requirements for the Safety of Magnetic Reso-nance Equipment for Medical Diagnosis, 20023. Terminology3.1 Definitio
10、nsFor the purposes of this test method, thedefinitions in 3.1.1-3.1.10 shall apply.3.1.1 isocentergeometric center of the gradient coil sys-tem, which generally is the geometric center of a scanner witha cylindrical bore.3.1.2 magnetic resonance imaging (MRI)diagnostic im-aging technique that uses s
11、tatic and time varying magneticfields to provide images of tissue by the magnetic resonance ofnuclei.3.1.3 magnetic resonance (MR) environmentarea withinthe 5 G line of an MR system.3.1.4 magnetic resonance system (MR System)ensembleof MR equipment, accessories including means for display,control, e
12、nergy supplies, and the MR environment.3.1.5 medical implanta structure or device that is placedwithin the body of the patient for medical diagnostic ortherapeutic purposes.3.1.6 MR safethe device, when used in the MR environ-ment, has been demonstrated to present no additional risk to1This test met
13、hod is under the jurisdiction of ASTM Committee F04 on Medicaland Surgical Materials and Devices and is the direct responsibility of SubcommitteeF04.15 on Material Test Methods.Current edition approved Nov. 10, 2002. Published December 2002. Originallyapproved in 2002. Last previous edition approved
14、 in 2002 as F 2182 02.2Annual Book of ASTM Standards, Vol 03.04.3Annual Book of ASTM Standards, Vol 13.01.4Available from the International Electrotechnical Commission (IEC), 3 rue deVarembe, Case postale 131, CH-1211 Geneva 20, Switzerland.1Copyright ASTM International, 100 Barr Harbor Drive, PO Bo
15、x C700, West Conshohocken, PA 19428-2959, United States.the patient or other individuals, but may affect the quality ofthe diagnostic information. The MR conditions in which thedevice was tested should be specified in conjunction with theterms MR safe and MR compatible since a device which is safeor
16、 compatible under one set of conditions may not be found tobe so under more extreme MR conditions.3.1.7 MR compatiblethe device, when used in the MRenvironment, is MR safe and has been demonstrated to neithersignificantly affect the quality of the diagnostic information norhave its operations affect
17、ed by the MR device. The MRconditions in which the device was tested should be specifiedin conjunction with the terms MR safe and MR compatiblesince a device which is safe or compatible under one set ofconditions may not be found to be so under more extreme MRconditions.3.1.8 passive implantan impla
18、nt that serves its functionwithout supply of electrical power.3.1.9 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 fiel
19、d in Tesla.3.1.10 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 placed in a phantom materialthat simulates the electrical and thermal properties of
20、 thehuman body. The phantom material will include saline solutionand a gelling agent. Fiber optic temperature probes are placedat locations where the induced heating is expected to begreatest. The phantom is placed in an MR system with acylindrical bore or an apparatus that reproduces the RF field o
21、fthis type of system. An RF field with SAR of at least 1 W/kgaveraged over the volume of the phantom is applied. Thetemperature rise at the sensors is measured during the approxi-mately 15 min of RF application, or other appropriate period,depending on the mass and thermal conductivity of criticalpa
22、rts of the device. Temperature measurements at one or morelocations away from the device serve as the control.5. Significance and Use5.1 This test method describes a test procedure for evaluat-ing the RF-induced temperature rise in MRI in the vicinity ofan implanted medical device. The actual temper
23、ature rise in thepatient will depend on a variety of factors beyond the SAR andtime of RF application. The conditions and results of thetesting should be included in the device labeling so that theattending physician can make the decision of whether to allowthe patient with the implant to undergo an
24、 MRI procedure.6. Apparatus6.1 Test ApparatusThe test apparatus consists of a suit-able phantom and an MR imager for production of the RF field.The phantom, implant and MR imager are to simulate theelectrical and physical environment that the patient and deviceexperience during an MRI procedure.6.2
25、Temperature SensorA suitable temperature measuringdevice, usually a fiber optic probe, is used to measure tempera-ture versus time of RF exposure in the vicinity of the implant.The temperature sensor will have a resolution of 0.1C and asensitive volume not to exceed 1 mm in radius. Fluoroptictempera
26、ture probes have been found to be satisfactory for thispurpose.57. Test Specimens7.1 For purposes of device qualification, the implant ordevice evaluated according to this test method shall be repre-sentative of a finished sterilized device. For the purposes ofdevice qualification, the device evalua
27、ted according to this testmethod should be a finished sterilized device.NOTE 1The device does not have to be sterile at the time of testing.However, it should have been subjected to all processing, packaging, andsterilization steps before testing because any of these steps may affect themagnetic pro
28、perties of the device.7.2 For purposes of device qualification, implant devicesshall not be altered in any manner prior to testing.7.3 This test method may be used on prototype devicesduring product development.8. Procedure8.1 Phantom MorphologyUse a phantom geometry thatreflects how the implant is
29、placed in the body. The phantomcontainer needs to be large enough to allow the device to beplaced in a position representative of where it would be in thebody. The container and all its parts should be made of materialthat is an electrical insulator and is non-magnetic. A wholebody phantom should si
30、mulate the RF loading that would occurwith a patient. The phantom should have the general shape ofa patient (Fig. 1) but a rectangular phantom (Fig. 2) is alsoacceptable.6For application of RF by the body coil, thephantom should contain at least 30 kg of phantom material. Foran implant inserted enti
31、rely in the head, a spherical phantomwith dimensions similar to those of the human head may beappropriate. Generally, a homogeneous phantom will suffice,but in certain cases it may be appropriate to incorporatematerials of different conductivity within the phantom.8.2 Phantom MaterialPhantom materia
32、ls simulating tis-sue for the RF heating test during MRI shall meet the followingcriteria.8.2.1 ConductivityConductivity shall be 0.4 to 0.8 S/m at64 MHz, depending on the tissue to be modeled. (See Stuchlyet al. (1)7for data on tissue electrical properties and Athey etal. (2) for procedures for mea
33、surement of electrical properties.)Electrical conductivity at low frequency will be less than at 64MHz. The phantom conductivity should be 0.2 to 0.4 S/m formeasurements made at a frequency of 1 kHz. (Stuchly andStuchly (3).5Particularly suitable are the Luxtron (Luxtron Corporation, Santa Clara, CA
34、,USA) Models 790, 3000, and 3100 Fluoroptic Thermometer Systems and the 0.6mm diameter SFF-10 probe.6The phantom in Fig. 2 may be purchased from Fab Lab Inc., Suite 1501325Armstrong Rd., Northfield, MN 55057, .7The boldface numbers in parentheses refer to the list of references at the end ofthis sta
35、ndard.F 2182 02a28.2.2 Dielectric ConstantDielectric constant shall be 60to 100 at 64 MHz.8.2.3 Thermal ParametersThe phantom material shallhave thermal properties similar to those of the body which hasFIG. 1 Diagram of Apparatus for Testing of RF Heating Near an Implant During MR ImagingNOTEThe dep
36、th is 26.5 cm and 30 L of phantom material fills the phantom to a depth of 9 cm.FIG. 2 Sample Rectangular Phantom to Model the Human Trunk and Head for Use in a Cylindrical Bore ImagerF 2182 02a3diffusivity of about 1.3 3 10-7m2/s and heat capacity close tothat of water, 4184 J/kg C.8.2.4 ViscosityT
37、he viscosity shall be sufficient so that thephantom material does not allow bulk transport or convectioncurrents. Generally, this is achieved by inclusion of a gellingagent.8.3 Phantom FormulationA suitable gelled phantom(Rezai (4) can be made with 0.8 g/L NaCl and 5.85 g/LPolyacrylic acid8into dist
38、illed water. This formulation has aroom temperature conductivity of about 0.25 S/m and aviscosity sufficient to prevent convective heat transport. Anumber of other phantom formulations may be appropriate andsome are described in the rationale.NOTE 2Note that the amount of aqueous solution absorbed d
39、ecreaseswith increasing salt concentrations.8.4 Device PlacementA representative experimental ap-paratus is depicted in Fig. 1. First, stir the phantom material tohomogenize it. Place the device in the phantom in the locationwhere it would be in a patient. If the device has longconducting wires, giv
40、e consideration to possible resonanteffects. Arrange wires in the worst case situation that would beexperienced clinically. For example, long wires should beplaced near the edge of the phantom in order to maximizereception of the induced electric field. Coil the leads accordingto the usual clinical
41、technique. More than one run may need tobe done to cover the clinically relevant situations. Cover thephantom with a cover or plastic sheet after the device is inplace in order to minimize effects of air flow on the tempera-ture measurements.8.5 Temperature Probe PlacementPlace at least threetempera
42、ture probes on and near device parts that are expectedto generate the greatest heating. Some experimentation may berequired to determine the best probe placement. For example,for an elongated implant the greatest heating will likely occurnear the end. One probe could be at the end (probe 1 in Fig. 1
43、),another (probe 2) 5 mm from the end, a third at the other endof the implant (probe 4). Be sure there are no air bubbles at theprobe tips. To provide confirmation of the whole body aver-aged SAR, place a probe (probe 3) at the side of the phantomwhere the heating is expected to be greatest.8.6 RF F
44、ield ApplicationUse an imaging protocol pro-ducing an intensive RF field. The whole-body averaged SARshould be at least 1 W/kg for a 50 kg patient and 2 W/kg isdesirable. A sample protocol for a 1.5 T (64 MHz) scanner isprovided in Table 1. Note that the key parameter for a highSAR is to maximize th
45、e number of 180 RF pulses per second.The protocol in Table 1 generates 48 180 pulses per secondand a whole body averaged SAR of 1.14 W/kg for a 50-kgpatient. Use a protocol duration of at least 15 min in order toachieve adequate signal to noise in evaluation of the rate oftemperature rise.8.7 RF Fie
46、ld MonitoringRecord the applied whole bodyaveraged SAR reported by the MR system software. Check thatthe temperature rise at the reference location is consistent withthe reported SAR. Record the flip angle and bandwidth of theRF pulses, as well as the number of RF pulses applied per unittime. If the
47、 scanner software provides it, record the RMSaverage applied B1field and the total average power depositedin the patient.8.8 Thermal Equilibrium of Phantom with SurroundingsMonitor temperature in the phantom for at least 10 min prior tothe application of the RF. There must be sufficient thermalequil
48、ibrium between the phantom and surroundings that thetemperature of the phantom does not change by more than0.2C during the observation time. The temperature within thescan room should be 23 6 3C and should be stable to 61Cper h.8.9 Recording of Temperature versus TimeRecord thetemperature at least 5
49、 times per min. Begin recording at least 2min prior to the start of the scan. This will allow evaluation ofwhether or not the temperature reaches steady state during thescan. After the RF is turned off, monitor and record thetemperature for at least 2 additional min. The fan inside thebore is to be turned off while performing the temperaturemeasurements.8.10 Control Measurements (optional)Take the implantout, and with temperature probes in the same locations as forthe test, repeat the temperature measurements to determine theb
