NEMA MS 8-2016 Characterization of the Specific Absorption Rate (SAR) for Magnetic Resonance Imaging Systems.pdf

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1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA MS 8-2016Characterization of the Specific Absorption Rate (SAR) for Magnetic Resonance Imaging SystemsNEMA Standards Publication MS 8-2016 Characterization of the Specific Absorption Rate (SAR) for Magnetic Resonance Imaging

2、 Systems Published by: National Electrical Manufacturers Association 1300 North 17thStreet, Suite 900 Rosslyn, Virginia 22209 www.nema.org 2016 National Electrical Manufacturers Association. All rights including translation into other languages, reserved under the Universal Copyright Convention, the

3、 Berne Convention for the Protection of Literary and Artistic Works, and the International and Pan American Copyright Conventions. 2016 National Electrical Manufacturers Association NOTICE AND DISCLAIMER The information in this publication was considered technically sound by the consensus of persons

4、 engaged in the development and approval of the document at the time it was developed. Consensus does not necessarily mean that there is unanimous agreement among every person participating in the development of this document. NEMA standards and guideline publications, of which the document containe

5、d herein is one, are developed through a voluntary consensus standards development process. This process brings together volunteers and/or seeks out the views of persons who have an interest in the topic covered by this publication. While NEMA administers the process and establishes rules to promote

6、 fairness in the development of consensus, it does not write the document and it does not independently test, evaluate, or verify the accuracy or completeness of any information or the soundness of any judgments contained in its standards and guideline publications. NEMA disclaims liability for any

7、personal injury, property, or other damages of any nature whatsoever, whether special, indirect, consequential, or compensatory, directly or indirectly resulting from the publication, use of, application, or reliance on this document. NEMA disclaims and makes no guaranty or warranty, express or impl

8、ied, as to the accuracy or completeness of any information published herein, and disclaims and makes no warranty that the information in this document will fulfill any of your particular purposes or needs. NEMA does not undertake to guarantee the performance of any individual manufacturer or sellers

9、 products or services by virtue of this standard or guide. In publishing and making this document available, NEMA is not undertaking to render professional or other services for or on behalf of any person or entity, nor is NEMA undertaking to perform any duty owed by any person or entity to someone

10、else. Anyone using this document should rely on his or her own independent judgment or, as appropriate, seek the advice of a competent professional in determining the exercise of reasonable care in any given circumstances. Information and other standards on the topic covered by this publication may

11、be available from other sources, which the user may wish to consult for additional views or information not covered by this publication. NEMA has no power, nor does it undertake to police or enforce compliance with the contents of this document. NEMA does not certify, test, or inspect products, desi

12、gns, or installations for safety or health purposes. Any certification or other statement of compliance with any health or safety-related information in this document shall not be attributable to NEMA and is solely the responsibility of the certifier or maker of the statement. NEMA MS 8-2016 Page i

13、2016 National Electrical Manufacturers Association. CONTENTS Preamble iii Foreword iv Introduction . v Scope . vi Equivalence . vi Uncertainty of the Measurements . vi Section 1 References and Definitions 1 1.1 References 1 1.2 Definitions 1 1.2.1 B1 and B1+ 1 1.2.2 Body coil current sense . 1 1.2.3

14、 Equivalent loading . 2 1.2.4 Equivalent mass Mbod2 1.2.5 Landmark . 2 1.2.6 Phantom 1: Unloaded Tip Angle Calibration Phantom 2 1.2.7 Phantom 2: Pulse-Energy Device under Test (Human or Phantom to be tested) 2 1.2.8 Phantom 3: Calorimetric Test Phantom 3 1.2.9 Pforward_loaded , unloaded. 4 1.2.10 P

15、other_loaded , unloaded. 4 1.2.11 Preflected_loaded, unloaded4 1.2.12 PCPL_loaded ,unloaded. 5 1.2.13 Pphantom_2. 5 1.2.14 Phuman. 5 1.2.15 Whole body Specific Absorption Rate (SAR) 5 1.2.16 Tip Angle . 5 1.2.17 Vflux_loop_loaded. 5 1.2.18 Vflux_loop_unloaded5 Section 2 Pulse Energy Method 6 2.1 Ove

16、rview 6 2.2 Test Hardware . 6 2.3 Hardware Setup . 7 2.4 General Measurement Procedure . 10 2.5 Pulse Energy Sar Measurement Evaluation 10 Section 3 Calorimetry Method . 14 3.1 Test Hardware . 14 3.2 Hardware Setup . 14 3.3 Sar Measurement Procedure 14 Section 4 Results 16 4.1 Reporting Sar Results

17、. 16 Appendix A Basic Flux Loop Design 19 Appendix B Document Changes . 23 NEMA MS 8-2016 Page ii 2016 National Electrical Manufacturers Association Figures Figure 1-1 Examples Of Test Phantoms . 4 Figure 2-1 Possible Arrangements for Measuring Radiofrequency Power Absorption in Linear Transmit Coil

18、 7 Figure 2-2 Possible Arrangements for Measuring Radiofrequency Power Absorption in Quadradture Transmit Coils 8 Figure 2-3 Method to Find Average Power Per TR Using Coupler Forward Power Port and an Oscilloscope Capable of Finding Peak and Rms Levels of the Waveform . 9 NEMA MS 8-2016 Page iii 201

19、6 National Electrical Manufacturers Association. Preamble This is one of a series of test standards developed by the medical diagnostic industry for the measurement of performance parameters related to the safety of Magnetic Resonance Imaging systems. These test standards are intended for the use of

20、 equipment manufacturers, prospective purchasers, and users alike. Manufacturers are permitted to use these standards for the determination of system performance specifications. This standardization of performance specifications is of benefit to the prospective equip-ment purchaser, and the paramete

21、rs supplied with each NEMA measurement serve as a guide to those factors that can influence the measurement. These standards can also serve as reference procedures for acceptance testing and periodic quality assurance. It must be recognized, however, that not all test standards lend themselves to me

22、asurement at the installation site. Some test standards require instrumentation better suited to factory measurements, while others require the facilities of an instrumentation laboratory to assure the stable test conditions necessary for reliable measurements. The NEMA test procedures are carried o

23、ut using the normal clinical operating mode of the system. For example, standard calibration procedures, standard clinical sequences, and standard reconstruction processes shall be used. No modifications to alter test results shall be used unless otherwise specified in these standards. NEMA MS 8-201

24、6 Page iv 2016 National Electrical Manufacturers Association Foreword Unless otherwise noted, this publication has been approved as a NEMA standard. It describes the test conditions and parameters that ensure accurate measurement of the Specific Absorption Rate (SAR). This Standard does not attempt

25、to establish relationships between SAR and body temperature. This standards publication was developed by the Magnetic Resonance Section of the National Electrical Manufacturers Association. Section approval of the standard does not necessarily imply that all section members voted for its approval or

26、 participated in its development. At the time it was approved, the section was composed of the following members: Computer Imaging Reference Systems Norfolk, VA. GE Healthcare, Inc. Milwaukee, WI. Hitachi Medical Systems America, Inc. Twinsburg, OH. Invivo Gainesville, FL. Medipattern Corporation To

27、ronto, Ontario Medtronic Navigation Yokneam, Israel Philips Healthcare Bothell, WA. Siemens Medical Solutions, Inc. Malvern, PA. Toshiba America Medical Systems Tustin, CA. AllTech Medical Systems America Solon, OH. User needs have been considered throughout the development of this publication. Prop

28、osed or recommended revisions should be submitted to: Executive Director, Medical Imaging either method may be chosen. The pulse energy method permits the use of low duty cycle scans for the test. The results from either method may then be extrapolated to other scan parameters and even to other wave

29、forms. Local SAR measurements are important for assessing localized heating. The local average SAR is the total power divided by the exposed mass. The (spatial) peak SAR is the SAR in the highest SAR occurring in any 10 grams of tissue. While peak and local SAR levels are important in localized heat

30、ing, they are difficult to measure directly in living patients. For this reason, determinations of peak and local SAR levels are beyond the scope of this document. An addition has been made to this standard that takes into account variations in coil power loss that have been observed since the last

31、publication of the standard. Note that the variation is higher for the relatively newly introduced 70 cm and 3T systems compared to the old standard 1.5T systems. This variation affects directly the SAR estimate because the transmit coil power loss is not constant. Additionally, the calorimetric SAR

32、 verification is affected because of the necessary step of finding the patient equivalent mass of phantom 2. NEMA MS 8-2016 Page vi 2016 National Electrical Manufacturers Association Scope This NEMA Standards Publication describes two measurement procedures for whole-body SAR measurements, the calor

33、imetric method and the pulse-energy method. Extrapolation of these data to pa-tient temperature rise is beyond the scope of this document. This document does not apply to gradient (low-frequency time-varying magnetic fields) safety where nerve and cardiac excitation are the primary safety issues. Ne

34、ither is it intended to apply to spatial peak or local average SAR nor does it address other factors involved with patient heating. The tests specified are only for volume RF transmit coils that produce relatively homogeneous RF fields. Equivalence It is intended and expected that manufacturers or o

35、thers who claim compliance with these NEMA standard test procedures for the determination of image quality parameters shall have carried out the tests in accordance with the procedures in the published standards. In those cases where it is impossible or impractical to follow the literal prescription

36、 of a NEMA test procedure, a complete description of any deviation from the published procedure must be included with any measurement claimed to be equivalent to the NEMA standard. The validity or equivalence of the modified procedures will be determined by each reader. Uncertainty of the Measuremen

37、ts The measurement uncertainty of the parameter determined using this standard is to be reported, together with the value of the parameter. Justification for the claimed uncertainty limits shall also be provided by a listing and discussion of sources and magnitudes of error. NEMA MS 8-2016 Page 1 20

38、16 National Electrical Manufacturers Association. Section 1 References and Definitions 1.1 References 1. Goldman, R.F., E.B. Green, and P.F. Lampietro, 1965, “Tolerance of Hot Wet Environments by Resting Men,“ J. Appl. Physiol., 20:271-277. 2. Wyndham, C.H., N.B. Strydom, J.F. Morrison, C.G. William

39、s, G.A.G. Bredell, J.S. Maritz, and A. Munro, 1965, “Criteria for Physiological Limits for Work in Heat,“ J. Appl. Physiol., 20: 27-45. 3. Department of Health and Human Services, Food and Drug Administration. Magnetic Resonance Diagnostic Device; Panel Recommendation and Report on Petitions for MR

40、Reclassification, Docket nos. 87P-0214/CP through 87P-0214/CP0013. Fed Reg 1988; 53:7575-7579. 4. Department of Health and Human Services, Food and Drug Administration. Recommendation and Report on Petitions for Magnetic Resonance Reclassification and Codification, Final Rule, 21 CFR Part 892. Fed R

41、eg 1989; 54: 5077-5088. 5. Adair, E.R. and L.G. Berglund, “On the Thermoregulatory Consequences of NMR Imaging,“ Magnetic Resonance Imaging, 1986; 4, 321-333. 6. Adair, E.R. and L.G. Berglund, “Thermoregulatory consequences of cardiovascular impairment during NMR imaging in warm/humid environments,“

42、 Magnetic Resonance Imaging, 1989; 7: 25-37. 7. F 2182, Standard Test Method for Measurement of Radio Frequency Induced Heating Near Passive Implants During Magnetic Resonance Imaging, ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States. 8. Vaughan

43、, J.T., J.R. Griffiths, “RF Coils for MRI” ISBN 978-0-470-77076-4 John Wiley i.e., the RF power delivered to the coil that is not absorbed by the subject positioned inside the coil 1.2.13 Pphantom_2The net peak, average power absorbed by phantom 2. 1.2.14 PhumanThe net peak, average power absorbed b

44、y human subject. 1.2.15 Whole body Specific Absorption Rate (SAR) The whole body SAR is the average RF power absorbed by the object in watts divided by the mass of the object in kilograms. 1.2.16 Tip Angle The tip angle is the angle through which the macroscopic magnetization vector is nutated by an

45、 RF pulse. 1.2.17 Vflux_loop_loadedThe peak voltage from body coil flux loop when the RF coil is loaded with phantom 2, or other test object. 1.2.18 Vflux_loop_unloadedThe peak voltage from Body coil flux loop when the RF coil is loaded with phantom 1. NEMA MS 8-2016 Page 6 2016 National Electrical

46、Manufacturers Association Section 2 Pulse Energy Method 2.1 Overview Whole-body SAR is defined as the ratio of the absorbed RF power to the mass of the whole body. Therefore the primary task is the determination of the RF power absorbed by the subject; i.e. the loading phantom in this test. The whol

47、e-body-SAR is simple division of the absorbed RF power by the registered weight. The Pulse Energy Method describes a procedure for measuring the RF power absorption utilizing directional couplers in the RF transmission path to the body coil. To excite spins in an MRI experiment RF power is applied d

48、uring multiple pulses. Therefore, the time average RF power is the sum of all pulse-energy-values applied during the sequence divided by the scan time. Total pulse energy can be measured either by RF power meter with averaging capability, or via measurement of the pulse-peak-power and subsequent cal

49、culation of the pulse energy utilizing knowledge about the pulse shape. In case of rectangular shaped RF pulse the pulse energy simply results by the multiplication of the pulse-peak-power with the length of the RF pulse. The pulse-peak-power can be measured either by peak reading RF power meter or an oscilloscope. The knowledge of the pulse shape could come from analysis of the pulse shape, by measurement, or from a prior knowledge of the radiofrequency waveform (e.g. from the system pulse programmer). In order to determine the RF power abso