1、CENELEC EN*bL*2b2-7 95 3404583 0173458 053 BRITISH STANDARD Characteristics of electro-optical X-ray imaging intensifiers for medical electrical equipment Part 7. Determination of the modulation transfer function The European Standard EN 61262-7 : 1995 has the status of a British Standard ICs 11.040
2、.50 NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW BS EN 61262-7 : 1996 IEC 1262-7 : 1995 CENELEC EN*bL*Zb2-7 95 H 3404583 0373459 T9T BS EN 61262-7 : 1996 AmdNo. Committees responsible for this British Standard Date Text affected The preparaton of this British Standard was e
3、ntrusted to Technical Committee CW72, X-ray image forming components, upon which the foliowjng bodies were represented: Association of X-ray Equipment Manufacturers (BEAMA Ltd.) Coiiege of Radiographers This British Standard, having been prepared under the direction of the Heaith and Environment sec
4、tor Board, was published under the authority of the Standards Board and comes into effect on 15 June 1996 O BSI 1996 The following BSI references relate to the work on this Standard: Committee reference cw72 DraR for comment 9WM96 JX ISBN O 680 26706 1 CENELEC EN*b1*262-7 95 m 3404583 O373460 701 m
5、BS EN 61262-7 : 1996 Contents Committees responsible National foreword page Inside front cover ii Foreword Text of EN 61262-7 2 3 O BSI 1996 i CENELEC EN*bL*2b2-7 75 3404583 0173461 648 BS EN 61262-7 : 1996 National fore word This British Standard has been prepared by Technical Committee C“2 and is
6、the English language version of EN 61262-7 : 1995 Medical ekcmcal equipment - ChamAWtiCs of electmoptcal X-ray image intermim -Part 7: Deermnation of the modulation cransferfunction published by the European Committee for Electrotechnical Standardization (CENELEC). It is identical with IEC 1262-7 :
7、1995 published by the International Electrotechnid Commission C). Cross-references EN60336: 1995 (IEC 336 : 1993) HD 501 s1: 1988 EN 612624 : 1994 (EC 12624 : 1994) Additional information. The foilowing print types are used in this standard. Requirements, with which compliance can be tested, and def
8、initions: inromantype. Exphnations, advice, general statements, exceptions and references: in smaller type. Test procedures: in italictype. Terms defined in ciause 3 of this standard and in annex A: in SMALL4 CAFTTALS. For the purposes of this British Standard, any references to IEC page numbers in
9、the text should be ignored. Compliance with a British Standard does not of itself confer immunity from legal obligations. hbiication referred to Corresponding British Standard BS EN 60336 : 1995 X-ray tube assemblies for medical d - from the Fourier transform Of the LINE SPREAD FUNCTION; - from the
10、Hankel transform Of the POINT SPREAD FUNCTION; - from scanning a slit image with a spatial filter. Any method is acceptable if performed correctly. For the purpose of simplicity, this standard elaborates on two methods: the Fourier transform of the LINE SPREAD FUNCTION, referred to as the LSF method
11、, and the spatial filter method. Accurate determination of the MODULATION TRANSFER FUNCTION requires specialized EQUIPMENT and does not generally lend itself to be performed at field installations. This standard only specifies methods for measurement of the MODULATION TRANSFER FUNCTION Of X-RAY IMAG
12、E INTENSIFIERS near the CENTRE OF THE ENTRANCE FIELD. CEMELEC EN*b1*262-7 95 3404583 01734b5 293 D Page 4 EN 61262-7 : 1996 MEDICAL ELECTRICAL EQUIPMENT - CHARACTERISTICS OF ELECTRO-OPTICAL X-RAY IMAGE INTENSIFIERS - Part 7: Determination of the modulation transfer function 1 Scope This Internationa
13、l Standard applies to ELECTRO-OPTICAL X-RAY IMAGE INTENSIFIERS for medical use, as components of diagnostic X-RAY EQUIPMENT. This international Standard describes a method of determining the MODULATION TRANSFER FUNCTION Of X-RAY IMAGE INTENSIFIERS. 2 Normative references The following normative docu
14、ments contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All normative documents are subject to revision, and parties to agreements based on this International Standard are enc
15、ouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. Members of IEC and IS0 maintain registers of currently valid International Standards. IEC 336: 1993, X-ray tube assemblies for medical diagnosis - Characteristics of focal spots IE
16、C 788: 1984, Medical radiology - Terminology IEC 1262-4: 1994, Medical electrical equipment - Characteristics of electro-optical X-ray image intensifiers - Part 4: Determination of the image distortion - ISO/DIS 9334, Optics and optical instruments - Optical transfer function - Definitions and ma th
17、ema tical rela tionships 3 Terminology 3.1 Definitions For the purposes of this International Standard, the following definitions apply together with those given in IEC 788. The definitions given below take preference over those given in IEC 788 when differences occur. 3.1 .I XRII: An abbreviation f
18、or ELECTRO-OPTICAL X-RAY IMAGE INTENSIFIER. 3.1.2 ENTRANCE puNf: The plane perpendicular to the axis of symmetry of the XRII and grazing the part of the XRII, including its housing, that protrudes most in the direction of the RADIATION SOURCE. - CENELEC EN*bl*262-7 95 = 3404583 OL734bb L2T = Page 5
19、EN 61262-7 : 1995 3.1.3 ENTRANCE FIELD: For an XRII, the area in the ENTRANCE PLANE that can be used for the TRANSMISSION Of an X-RAY PATTERN under Specific conditions. 3.1.4 ENTRANCE FIELD SIZE: For an XRII, the diameter of the field in the ENTRANCE PLANE that can be used at a specified SED for the
20、 TRANSMISSION of an X-RAY PATTERN. For an XRII with more than one magnification mode, the ENTRANCE FIELD SIZE for each of the magnification modes shall correspond to the same diameter of the XRII OUTPUT IMAGE occurring with the largest ENTRANCE FIELD SIZE. . 3.1.5 SOURCE To ENTRANCE PLANE DISTANCE (
21、abbreviation SED): The distance between the FOCAL SPOT Of the X-RAY TUBE and the ENTRANCE PLANE of the XRII. 3.1.6 CENTRE OF THE OUTPUT IMAGE: The centre of the smallest circle circumscribing the OUTPUT IMAGE. 3.1.7 CENTRE OF THE ENTRANCE FIELD: That point in the ENTRANCE PLANE which is imaged at th
22、e CENTRE OF THE OUTPUT IMAGE. 3.1.8 CENTRAL AXIS: The line perpendicular to the ENTRANCE PLANE passing through the CENTRE OF THE ENTRANCE FIELD. 3.1.9 CENTRAL MAGNIFICATION: As a characteristic of XRIIs, the ratio of the length in the symmetrically about the CENTRAL AXIS. OUTPUT IMAGE to the actual
23、length Of a Small object placed in the ENTRANCE PLANE 3.1.1 O POINT SPREAD FUNCTION (abbreviation PSF): Normalized distribution of irradiance in the image of a point source, see ISO/DIS 9334. 3.1.1 1 /SOPLANATIC REGION: Region where the form Of the POINT SPREAD FUNCTION is COnStant within specified
24、accuracy. 3.1.12 LINEARITY: Property of an imaging system in that the image of a weighted sum of objects is identical to the similarly weighted sum of images of individual objects. 3.1.13 LINEARITY within specified accuracy, see ISO/DIS 9334. LINEAR RANGE: Range of input signals within which the ima
25、ging system exhibits NOTE - The range Of input signals indicating the LINEAR RANGE Of the imaging SyStem Should be specified by minimum and maximum levels. 3.1.1 4 OPTICAL TRANSFER FUNCTION (abbreviation OTF): Two-dimensional Fourier transform of the imaging SyStemS POINT SPREAD FUNCTION, See ISO/DI
26、S 9334. NOTE - For the OPTICAL TRANSFER FUNCTION to have significance, it is essential that the imaging system is working in its LINEAR RANGE, and that an ICOPLANATIC REGION iS considered. 3.1 .I 5 OPTICAL TRANSFER FUNCTION through the Origin in a given Orientation. ONE-DIMENSIONAL OPTICAL TRANSFER
27、FUNCTION (abbreviation I-OTF): Section Of the CEMELEC EN*b3*2b2-7 75 3404583 0373467 Ob6 Page 6 EN 61262-7 : 1995 3.1.1 6 LINE SPREAD FUNCTION (abbreviation LSF): Normalised distribution of irradiance in the image of an incoherently radiating line source. The LINE SPREAD FUNCTION only exists in an I
28、SOPLANATIC REGION, see ISO/DIS 9334. NOTE - The Fourier transform Of the LINE SPREAD FUNCTION is the ONE-DIMENSIONAL OPTICAL TRANSFER FUNCTION for the orientation perpendicular to the direction of the line source. 3.1.1 7 OPTICAL TRANSFER FUNCTION. MODULATION TRANSFER FUNCTION (abbreviation MTF): Mo
29、dulus Of the ONE-DIMENSIONAL NOTE - The MTF is defined in ISO/DIS 9334 as the modulus of the OPTICAL TRANSFER FUNCTION. For the purpose of this International Standard, definition 3.1 .I 7 is more appropriate. 3.1.18 MTF ANALYSER: Instrument, including relay optics and software, capable of performing
30、 IneaSUrementS Of the MODULATION TRANSFER FUNCTION. 3.1.1 9 BEST FOCUS: Setting of focusing potentials resulting in maximum integrated area under the MTF curve for the given slit orientation. NOTE - This setting of focusing potentials is chosen to reduce ambiguity and may slightly deviate from setti
31、ngs in practical use of the XRII. 3.1.20 LOW-FREQUENCY DROP (abbreviation LFD): Difference between unity and the value of the MODULATION TRANSFER FUNCTION Close to zero Spatial frequency. NOTE -With currently known XRlls, significant veiling glare is present. This is apparent as a steep drop in the
32、MTF curve slightly above zero spatial frequency. For the purpose of this International Standard the spatial frequency at which the LFD is to be determined, is chosen to be 0,l mm-. 3.1.21 LIGHT DETECTOR: RADIATION DETECTOR SenSitiVe to VISIBLE RADIATION (light). 3.2 Degree of requirements and readin
33、g instructions In this International Standard the auxiliary verb: - shall“ - should“ implies that compliance with a requirement is mandatory for compliance with the standard; implies that compliance with a requirement is strongly recommended but is not mandatory for compliance with the standard; - m
34、ay implies that compliance with a requirement is permitted to be accomplished in a particular manner, for compliance with the standard; and the following words have the meaning: - specific - specified“ - “designed for“ when used in combination with parameters or conditions: refers to a particular va
35、lue or standardized arrangement, usually to those required in an IEC sandard or a legal requirement; see IEC 788, rm-74-01. when used in combination with parameters or conditions: refers to a value or arrangement to be chosen for the purpose under consider-ationand indicated usually in ACCOMPANYING
36、DOCUMENTS; see IEC 788, rm-74-02. when used in standards to characterize equipment, devices, com-ponents or arrangements: designates an intended and usually apparent purpose or use for the product. CENELEC EN*b1*2b2-7 95 M 3404583 0373468 TT2 Page 7 EN 61262-7 : 1995 4 Requirements The methods for d
37、etermining the MODULATION TRANSFER FUNCTION of an XRII described in this International Standard incorporate analyzing a slit image. In one method, the image is scanned with a (one-dimensional) spatial filter, directly resulting in the MTF. With the second method, called the LSF method, the LINE SPRE
38、AD FUNCTION is obtained by using a two-dimensional camera. Fourier transform of the LSF then gives the MTF. A special test set-up is required including an MTF ANALYSER, see figure 1. 4.1 Test set-up a) The SED shall be 100 cm k 1 cm. b) The FOCAL SPOT of the X-RAY TUBE shall be on the CENTRAL Axis.
39、The influences of c) d) and e), combined, shall not affect measurement results by more than the overall measurement accuracy (see 5.5). c) Magnetic and electric stray fields. Effective shielding and non-magnetic materials should be used in the construction of the test Set-up. d) Stray light. e) Mech
40、anical instability of the test Set-up. Vibrations with amplitudes as small as 10 pm may degrade results. 4.2 X-RAY IMAGE INTENSIFIER - Operating conditions a) The XRII shall be operated under the conditions for NORMAL USE as specified by the MANUFACTURER, except for the focusing potential of the XRI
41、I, which shall be set to achieve BEST FOCUS at the centre of the XRII. b) No ANTI-SCATTER GRID or protective cover shall be used. c) In the case of multiple field XRlls, the measurement shall be done for the largest d) The ripple in the electrode potentials applied to the XRII shall not exceed 0,l %
42、. specified ENTRANCE FIELD. Measurements for other ENTRANCE FIELDS are Optional. e) The XRII shall be operating in its LINEAR RANGE. 4.3 Input radiation a) The RADIATION QUALITY shall be that Of an X-RAY TUBE, operated at a peak X-RAY TUBE VOLTAGE Of 50 kV f 2 kV, and a HALF-VALUE LAYER Of 2,0 mm i
43、0,2 mm Of aluminium (99,9% purity); this corresponds to a TOTAL FILTRATION of approximately 3 mm of aluminium equivalent. b) The NOMINAL FOCAL SPOT VALUE, specified according to IEC 336, shall be 0,6 or less. If this condition cannot be met, for example due to too low signals, correction for the MTF
44、 of actually used shall be included in the presentation of the results. c) The fluctuations of the intensity of X-RADIATION should not influence the measurement results by more than 2 % relative. the FOCAL SPOT actually used shall be made. in Such case, the NOMINAL FOCAL SPOT VALUE CENELEC EN*bL*2b2
45、-7 95 340Li583 0373Vb9 939 Page 8 EN 61262-7 : 1996 4.2 Test device a) The TEST DEVICE contains a slit, the width of which shall be less than or equal to 0,5 x fm-l, where fm is the maximum spatial frequency to be analysed, expressed in mm-1. b) The width of the slit shall not vary by more than 5 70
46、 over its entire length. c) The length of the slit shall not exceed the extent of the ISOPLANATIC REGION. A length of 1 O mm is generally practicable. d) The energy of X-RADIATION received by the XRII outside the projected area of the slit shall be less than 1 % of the total energy ,of X-RADIATION r
47、eceived by the XRII; see annex B. 4.3 Measurement equipment a) The entire image at the OUTPUT SCREEN shall be analysed by the MTF ANALYSER, to enable correct determination of the low-frequency part of the MTF. b) if more than one relay lens or relay lens system is used, the requirement of item a) sh
48、all be met by at least one of the lenses or lens systems. NOTE - More than one relay lens may be used to increase the number of readings or the frequency range of the MTF. c) The MTF ANALYSER shall allow for rotational alignment with respect to the slit image. d) The input device of the MTF ANALYSER
49、 shall have a linear response. For the spatial filter method, the input device is a LIGHT DETECTOR, e.g. a photomultiplier. For the LSF method, the input device is a two-dimensional camera, e.g. a CCO camera. e) The LSF method shall be capable of measuring luminance levels at least six orders of magnitude apart. If such a dynamic range is not covered by the input device of the MTF ANALYSER, the measurement shall be done in more than one step. If dark current signals are present, they should be measured separately, and corrected. If a CCD camera is used, it is strongly adv
