1、NEMA Standards PublicationNational Electrical Manufacturers AssociationNEMA XR 15-1991 (R2001)Test Standard for the Determination of the Visible Entrance Field of an X-Ray Image Intensifier SystemNEMA Standards Publication No. XR 15-1 991 (RI 996, R2001) Test Standard for the Determination of the Vi
2、sible Entrance Field of an X-Ray Image Intensifier System Published by: National Electrical Manufacturers Association 1300 North 17th Street, Suite 1847 Rosslyn, VA 22209 O Copyright 2001 by the National Electrical Manufacturers Association. All rights including translation into other languages, res
3、erved under the Universal Copyright Convention, the Berne Convention for the Protection of Literary and Artistic Works, and the International and Pan American Copyright Conventions. 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. STDONEMA XR 15-ENGL 19
13、9L 6470247 0527330 548 6 TABLE OF CONTENTS Page FOREWORD U INTRODUCTION . u1 SCOPE . u1 REFERENCED STANDARDS AND TERMINOLOGY Referenced Standards 1 Degree of Requirements . . - . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Definitions 1 TESTEQUIPMENT . . . . . . . . . . . . . . . .
14、 . . . . . . . . . . . . . -. . . . . . . 3 General Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Source to Enme Plane Distance (SED) . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Measurement Procedures . . . . . . . . . . . . . . . . . . . . . . . .
15、. . . . . . . . . . 7 Presentation of Results . . . . . . . . . . . . . . . . . . . . - . . . . . . . . . . . . . . . 7 STATEMENT OF COMPLIANCE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Figure 2- 1 image Position Calibration Template . . . . . . . . . . . . . . . . . . . . . 3 . .
16、SECTION 1 SECTION2 SECTION 3 STANDARD TEST CONDIONS SECTION 4 DETERMINATION SECTION 5 FIGURE i Foreword This NEMA Standards Publication is one of a series of test standards developed by the X-ray imaging products Section and the medical diagnostic imaging industry for the measurement of performance
17、characteristics governing the image quality of X-ray image intensifier (XRIi) systems. These test standards are intended for the use of equipment manufacturers, prospective purchasers, and users dike. Manufacturers may find these standards useful in establishing standard test conditions for the dete
18、rmination of system performance specifications. prospeCtive equipment purchasers may benefit drom these standards as the employment of standard test conditions and methods enables meaningful comparisons to be made of NEMA-referencexk competitive, equipment performance speci- fications. Users may als
19、o benefit hm these standards through a better appreciation of the Characterizing the parameters that govern image quality is a non-trivial task. The assess- ment of image quality lies in the eye of the beholder and so is a somewhat subjective measure influenced by the spatial, temporal, conhast, and
20、 noise characteristics of the image. Histon- cally, many techniques have been developed employing varying degrees of sophistication to establish subjective and objective measures of these parameters, and the following nonexhaustive list of parameters can be considered as relevant to image quality: p
21、erformance of XRII systems. Conmt Ratio Detective Quantum Efficiency (DQE) Fixed Pattern Noise Gain image Signal Uniformity Lag Limiting Spatial Resolution Modulation Transfer Function 0 Noise Power Spectrum Radiai Image Distortion Signal to Noise Ratio Visible Entrance Field Size These parameters a
22、re not ail independent and some of them may partiaiiy overlap in assessing the image quality. Moreover, it must be recognized that not aii of these parameters lend themselves to measurement at the installation site. Some parameters require instrumen- tation better suited to factory measurements whil
23、e others require the facilities of an instru- mentation laboratory to assure the stable test conditions necessary for reliable measurements. The NEMA X-ray image Intensifier Systems Subcornminee intends to makea selection from the above-mentioned list of parameters where practical and technically fe
24、asible measure- ments can be made at the system level and to prepare a set of NEMA standards. This publication has been prepared by the X-Ray Imaging Products Section of NEMA which periodically reviews it for revisions necessary to keep it up to date with advancing technology. Comments or proposed r
25、evisions are welcomed and should be submitted to: Vice-President, Engineering Department National Electrical Manufacturers Association 2101 L Street, N.W., Suite 300 Washington, D.C. 20037 STD*NEMA XR 15-ENGL 1991 9 6470247 0527332 3LO introduction This document defuies the NEMA test standard method
26、 for the determination of the visible entrance field size of an X-ray image intensifier (XRII) system. These systems include direct viewing systems, video systems, photofluorographic film recording systems, and cine film recording and projection systems. The visible entrance field size is a measure
27、of the area imaged by an X-ray image intensifier system. Scope Ihe procedures in this standard determine the visible entrance field size of an X-ray image intensifier system. . u1 XR 15-1991 Page 1 Section 1 REFERENCED STANDARDS AND TERMINOLOGY 1.1 REFERENCED STANDARDS None 1.2 DEGREE OF REQUIREMENT
28、S A statement incorporating the auxiliary verb “shall“ indicates that compliance with a requirement is mandatory for compliance with the standard. Statements incorporating other auxiliary verbs such as “should,“ “may,“ etc., refer to authorized engineering in- fonnation and not to procedures require
29、d for compliance with the standard. 1.3 DEFINITIONS 1.3.1 Actual Focal Spot cepts the beam of electrons. 1.3.2 Center of the Image That point in the entrance plane of the Mu1 system which corresponds to the center of the smallest circle circumscribing the image. 1.3.3 Central Axis of the X-ray Field
30、 The line perpendicular to the entrance piane of the xrii system passing through the center of the actual focal spot Area on the surface of the X-ray tube target that inm- NEMA Standard 8-28-1991. NEM Standard 8-28-1991. NEMA Standard 8-28-1991. 1.3.4 Entrance Plane of the XRII System The plane perp
31、endicular to the axis of the XRII and grazing that part of the XRII, including its housing, which protrudes most in the direction of the radiation source. The following components shail not be considered elements of the XRII housing: Antiscatter grid Collision sensors Ionization chambers Protective
32、cover Removable magnetic shields and coils Spot film device NEMA Standard 8-28-1991. 1.3.5 Geometric Magnification Magnification of an object in the X-ray field amibutable to the relative distances of the object and the enIrance plane of the XEI om the actuai focai spot. 1.3.6 Output Image of the XR
33、II System The image produced by the XRII system that is visually perceivable by a human observer. Output image channels of the system include: NEM4 Standard 8-28-1 991. a processed photofluorographic film b. processedcinefilm c. television monitor display screen d direct viewing system. NEM4 Standar
34、d 8-28-1991. 1.3.7 SourceTo-Entrance Plane Distance (SED) The distance hm the actual focai spot to the entxance piane of the XRII system measured along the central axis of the X-ray field. 1.3.8 Visible Entrance Field Sue NEMA StandaK18-28-1991. The dimensions in the entrance piane of the XRII syste
35、m of the field that is used for transmission of the X-ray paneni measured dong two specified axes. NEMA Standard 8-28-1991. 1.3.9 X-ray Image Intensifier (XRII) Systems That portion of an X-ray imaging system consisting of the XRII with its housing and the subsequent components of the imaging chain
36、responsible for transmitting and displaying the detected X-ray panerns. The following components shall not be considered elements of the XRII SYSTEM: antiscatter grid, spotfilm device, collision sen- SOTS. removable magnetic shields and coils. STD-NEMA XR 15-ENGL 1991 b470247 O527334 193 XR 15-1991
37、Page 3 Section 2 TEST EQUIPMENT-IMAGE CALIBRATION TEMPLATE An image position calibration template is used to locate the center of the image and to measure the visible enhance field size. A suggested template is shown in Figure 2-1 consisting of a thin X-ray hamparent panel with X-ray absorbing demar
38、cations dong which distance measm- ments are made. The overall size of the template shaii be iarger than the visible entrance field size to be measured. Figure 2-1 Image Position Calibration Template STD*NEflA XR 15-ENGL 1991 A b470247 0527335 UZT m XR 15-1991 Page 5 Section 3 STANDARD TEST CONDITIO
39、NS 3.1 GENERAL REQUIREMENTS The system shall be set up according to the specifications of the manufacturer, except as noted in paragraphs below. During the test, except where explicitly permiaed, no change shall be made to the system setup. This includes, but is not limited to, adjusunent of the X-r
40、ay image inten- sifier and video camera, as well as the focus of the Mu1 and any lenses and video cameras. It is recognized that under some Conditions it will be necessary to remove a grid or disassemble a window covering to satisfy the test conditions. Deviations iom the standard test conitions are
41、 permitted only where it is impractical to meet thoseconditions. Such deviations must be explicitly stared in the Presentation of Results. NEMA Standad 8-28-1 991. 3.2 SOURCE TO ENTRANCE PLANE DISTANCE (SED) The standard SED shail be 100 i 1 cm. Equipment of fixed SED or whose adjustment range does
42、not span the standard SED shaii be tested at the spacing recommended by the manufacm and such spacing shali be reported in the Presentation of Results. NEM4 Standard 8-28-1991. STD-NEMA XR 15-ENGL 1791 6470247 052733b Tbh XR 15-1 991 Page 7 Section 4 DETERMINATION 4.1 MEASUREMENT PROCEDURES 4.1.1 Th
43、e visible entrance field size shall be measured along two axes, as specified below, which are orthogonal in the entrance plane of the XRiI system and intersect at the center of the image. 4.1.2 The image position calibration template shaii be placed as close as possible to the entrance plane of the
44、XRII system. If necessary, objects shail be removed between the X-ray source and the entrance plane of the XRII system such as grid holders, cones, compression devices and the like. If it is impossible to place the calibration template at the entrance plane of the XRII system, the distance from the
45、template to the entrance plane of the XRiI shall be stated and the data corrected for the geomemc magnifica- tion introduced 4.1.3 Video System NEM4 Standad 8-28-1991. NEM4 Standad 8-28-1991. a. The kV and mA as well as the monitor controls shall be adjusted so that the calibration template is clear
46、ly viewed. b. One of the two orthogonal axes shall be parallel to the video raster lines. Using the template, the lengths shall be measured along both axes in the entrance plane of the XRII system which are visualized in the image. NEM4 Standard 8-28-1991. 4.1.4 Photofluorographic and Cine Cameras b
47、. One of the two orthogonal axes shall be parallel to the longer edge of the film frame. For a square image rame, the reference edge shall be speci- fied in the Presentation of Results. Using the template, the lengths shail be measured along both axes in the entrance plane of the XRII system which a
48、re visualized in the image along these axes. NEMA Standard 8-28-1 99 1. 4.1.5 Direci Viewing System a. Adjust the kV and mA of the system shall be adjusted such that the calibration template can be clearly viewed. b. One of the wo Orthogonal axes shaii be paraiiel to the maximum image dimension. Usi
49、ng the template, the lengths shall be measured along both axes in the entrance plane of the XRII system which are visualized in the image. If the image is circular, then only the diameter shall be reported. NEM4 Standard 8-28-1991. 4.2 PRESENTATION OF RESULTS The Presentation of Results shall specify the following: a. XRII system identification b. Output channels measured c. The dimensions in centimeters along the two orthogonal axes as specified in Section 4.1.4 (or the diameter in the special case of a circular image) for each system outpur image. A state- a. The kV,
