YY/T 0457.7-2003 Characteristics of optoelectronic X-ray image intensifiers for medical electrical equipment Part 7: Determination of modulation transfer function
Some standard content:
YY/T 0457.7—2003/IEC 61262-7: 1995YY/T0457 "Characteristics of optoelectronic X-ray image intensifiers for medical electrical equipment" is divided into seven parts: Part 1: Determination of human radiation field; Part 2: Determination of conversion coefficient; Part 3: Determination of brightness distribution and brightness non-uniformity; Part 4: Determination of image distortion; Part 5: Determination of detection quantum efficiency; Part 6: Determination of contrast and glare coefficient; Part 7: Determination of modulation transfer function. This part is the 7th part of YY/T0457. The consistency of this part is equivalent to that of IEC61262-7:1995 (English version) (Medical electrical equipment - Characteristics of optoelectronic X-ray image intensifiers - Part 7: Determination of modulation transfer function). The main differences are as follows: some formatting has been modified according to Chinese habits, and some expressions applicable to international standards have been changed to expressions applicable to Chinese standards; the preface of international standards has been deleted;
—IEC788 has been changed to IEC60788
In the original text, the numbers 4.4 and 4.5 were mistakenly written as 4.2 and 4.3, so they were changed to 4.4 and 4.5. Appendices A, B, C and D of this part are all informative appendices. This part was proposed by the State Food and Drug Administration. This part is under the jurisdiction of the National Technical Committee for Standardization of Medical X-ray Equipment and Appliances. The drafting units of this part are Xi'an Aerospace Star Technology Co., Ltd. and Liaoning Medical Device Product Quality Supervision and Inspection Institute. The main drafters of this part are Zou Yuan and Mu Li. YY/T 0457.7—2003/IEC 61262-7:1995 Introduction
Imaging systems are often evaluated using subjective performance measures, such as limiting resolution. These methods do not necessarily adequately describe the performance of the system with respect to imaging tasks relevant to the intended use of the imaging system and are susceptible to interobserver variability.
Linear space-invariant imaging systems can be conveniently analyzed in terms of their transfer functions. The signal transfer of such systems can be explicitly represented by the optical transfer function (OTF). The OTF expresses the response of the system to a sinusoidal wave as a function of the spatial frequency of the system. The modulation transfer function (MTF), the modulus of the optical transfer function, is sufficient to describe the signal transfer of an X-ray image intensifier. A system is called a space-invariant system when the point spread function does not vary with position. It should be noted that an X-ray image intensifier is usually space-invariant only in a limited region, the iso-harbinger region.
The modulation transfer function can be determined by several methods (see Example 1 in Appendix D): by square wave response;
by Fourier transform of line spread function;
——by Hankel transform of point spread function;
——by scanning slit image with the aid of spatial filter. If performed correctly, any of the above methods is acceptable. For simplicity, this part only details two methods: 1. Fourier transform of line spread function, i.e. LSF method mentioned above 2. Spatial filter method. Accurate determination of modulation transfer function requires specialized equipment and is generally not suitable for work in field installation.
This part only specifies the measurement method of modulation transfer function of X-ray image intensifier close to the center of human field. 1 Scope
Medical electrical equipment
YY/T 0457.7—2003/IEC 61262-7:1995 Characteristics of optoelectronic X-ray image intensifiers
Part 7: Determination of modulation transfer function
This part of YY/T0457 applies to optoelectronic X-ray image intensifiers as components of medical diagnostic X-ray equipment. This part describes the method for determining the modulation transfer function of X-ray image intensifiers. 2 Normative references
The clauses in the following documents become clauses of this part through reference in this part of YY/T0457. For any dated referenced document, all subsequent amendments (excluding errata) or revisions are not applicable to this part. However, parties to an agreement based on this part are encouraged to study whether the latest versions of these documents can be used. For any undated referenced document, the latest version of the document applies to this part.
YY/T0063—2000 Focus characteristics of medical diagnostic X-ray tube assemblies (idtIEC60336:1993) YY/T0457.4—2003 Characteristics of electro-optical X-ray image intensifiers for medical electrical equipment Part 4: Determination of image distortion IEC60788:1984 Medical radiology—Terms ISO9334 Optics and optical instruments—Optical transfer functions—Definitions and mathematical relationships 3 Terms
3.1 Definitions
For the purpose of this part, the terms and definitions defined in IEC60788 and the following apply to this part. When there is ambiguity between the definitions, this definition shall prevail.
English abbreviation of electro-optical X-ray image intensifier. 3.1.2
Entrance plane
The plane perpendicular to the axis of symmetry of the XRII and tangent to the most protruding part of the XRII in the direction of the radiation source (including the protective shell of the XRII).
Entrance field
For XRII, the area in the entrance plane that can be used for X-ray pattern transmission under specific conditions. 3.1.4
Entrance field sizeFor XRII, the diameter of the area in the entrance plane that can be used for X-ray pattern transmission at a specified source plane distance (SED). For XRII with more than one magnification mode, the corresponding output image diameter for each magnification mode shall be consistent with the output image diameter of the XRII at the maximum entrance plane size. 3.1.5
Source to entrance plane distance(SED)1
YY/T 0457.7—2003/IEC 61262-7:1995The distance between the focus of the X-ray tube and the entrance plane of the XRI. 3.1.6
Centre of the output imagecentre of the smallest circle circumscribing the output image.
centre of the entrance fieldcentre of the entrance fieldpoint on the incident plane imaged at the centre of the output image. 3.1.8
central axis
the straight line passing through the centre of the incident field and perpendicular to the incident plane. 3.1.9
central magnificationXRIIa property of a small object placed symmetrically about the central axis on the entrance plane, the ratio of the length of the output image to the actual length. 3.1.10
point spread function (PSF)normalised distribution of the irradiance of a point source image, see ISO 9334. 3.1.11
isoplanatic region
the region where the point spread function is constant within a specified accuracy range. 3.1.12
linearity
a property of an imaging system. In an imaging system with this property the image of the weighted sum of all objects is equal to the equally weighted sum of the images of its individual objects.
Linear rangelinear range
The range of the input signal. Within this range the imaging system is linear within a specified accuracy, see ISO 9334. NOTE: The input signal range that describes the linear range of the imaging system should be stated using maximum and minimum values. 3.1.14
optical transfer function (OTF)Optical transfer function
The two-dimensional Fourier transform of the point spread function of the imaging system, see ISO 9334. NOTE: In order for the optical transfer function to be meaningful, it is a basic requirement that the imaging system operates within the linear range and that the isoplanets are taken into account. 3.1.15
One-dimensional optical transfer functionone- dimensional optical transfer function (1-OTF)The cross section of the optical transfer function through the origin in a given direction. 3.1.16
Line spread function (LSF)The normalized distribution of the image irradiance of an incoherent linear radiation source. The line spread function exists only within the isoplanets, see ISO 9334. Note: The Fourier transform of the line spread function is the one-dimensional optical transfer function perpendicular to the direction of the line light source. 3. 1.17
modulation transfer function (MTF) modulation transfer function
the modulus of a one-dimensional optical transfer function.
Note: In ISO 9334, the modulation function is defined as the modulus of an optical transfer function. For the purpose of this standard, the definition in 3.1.17 is more appropriate. 2
MTF analyserMTF analyser
An instrument capable of making modulation transfer function measurements, including the optical system and software. 3.1.19
best focusbest focus
YY/T 0457.7--2003/IEC 61262-7:1995 The setting of the focus voltage that maximizes the integrated area under the MTF curve for a given slit orientation. Note: The focus voltage setting is chosen to reduce blur and may deviate slightly from the setting in actual use of XRI. 3.1.20
Low-frequency drop (LFD) The difference between 1 (unity) and the value of the modulation transfer function near zero spatial frequency. NOTE: All XRIs known today exhibit significant glare. This is manifested as a steep drop in the MTF curve slightly above zero spatial frequency. For the purpose of this standard, the point at which the spatial frequency is 0.1 mm-1 is selected for the determination of the LFD. 3.1.21
Light detector light detector
A radiation detector sensitive to visible radiation (light). 3.2 Degree of requirement
Auxiliary verbs in this standard:
_ "shall" indicates that compliance with a requirement is necessary. "should" indicates that compliance with a requirement is highly recommended but not mandatory. _ "may" indicates that compliance with a requirement is permitted to be accomplished in a special manner in order to comply with this standard. The following words have the following meanings:
- "specific" when used with a parameter or condition: refers to a particular value or standardized arrangement, usually those required by IEC standards or by law; see IEC 60788, rm-74-01. - "specified" when used with a parameter or condition: a value or arrangement usually indicated in the accompanying documents or selected with regard to the intended purpose, see IEC 60788, rm-74-02. - "designed for" when used in a standard to describe the characteristics of equipment, components, parts or arrangements: indicates the intended and usually obvious application or use of the product. 4 Requirements
The methods for determining the modulation transfer function of the XRII described in this standard involve slit image analysis. In the first method, the image is scanned with a (one-dimensional) spatial filter, resulting in a direct determination of the modulation transfer function. The second method, the LSF method, uses a two-dimensional camera to obtain the line spread function, which is then derived from the Fourier transform of the line spread function. A special test setup is required for the determination, including an MTF analyzer (see Figure 1). 3
YY/T0457.7--2003/IEC61262-7:1995
4.1 Test setup
a) SED should be 100cm±1cm;
b) The focus of the X-ray tube should be located on the central axis; Figure 1 Measurement layout
c), d), e) The combination of the three should not affect the measurement results more than the overall measurement accuracy (see 5.5); Magnetic and electric stray fields. Effectively shielded and non-magnetic materials should be used in the construction of the test setup; c)
Stray light;
Mechanical instability of the test device. Vibration with an amplitude of 10um can deteriorate the test results. 4.2 X-ray image intensifier - working conditions YY/T0457.7-2003/IEC 61262-7:1995a) In addition to the focus voltage of the XRII, the XRII should be operated under the normal use conditions specified by the manufacturer. The focus voltage should be set to the value that allows the center of the XRII to be optimally focused. b) No anti-scatter grid or protective cover should be used; for multi-field XRII, the maximum incident field should be measured, and for other incident fields, the measurement should be optional; the ripple factor of the voltage applied to the XRII electrode should not exceed 0.1%. d) The XRII should operate within its linear range.
4.3 Input Radiation
a) The X-ray tube should have a peak voltage of 50kV ± 2kV and a radiation quality of 2.0mm ± 0.2mm aluminum (purity 99.9%); this is equivalent to a total filtration of about 3mm aluminum. b) The focal point nominal value, in accordance with the provisions of YY/T0063, should not be greater than 0.6. c) The influence of X-ray intensity fluctuations on the measurement results should not exceed 2%. 4.4 Test Device
a) The test device includes a slit. The width of the slit should be less than or equal to 0.5×fml, where f is the maximum spatial frequency value to be analyzed, in mm-1.
The variation of the slit width over the entire slit length should not exceed 5%. b)
The slit length should not exceed the range of the isohaloic zone. The practical length is usually 10mm. c
d) The energy of the X-radiation received by the XRII outside the projection area of the slit should be less than 1% of the total X-radiation energy received by the XRII; see Appendix B.
4.5 Measurement equipment
a) In order to correctly determine the low-frequency part of the MTF, the entire image on the output screen should be analyzed using an MTF analyzer; b) If more than one lens or lens group is used, at least one of the lenses or lens groups should meet the requirements of a); Note: Multiple lenses can be used to increase the number of readings or expand the frequency range of the MTF. c)
The MTF analyzer should allow rotational collimation of the slit image; the input device of the MTF analyzer should have a linear response. For the spatial filter method, the input device is a light detector, such as a photomultiplier. For the LSF method, the input device is a two-dimensional camera, such as a CCD camera; e) The LSF method should be able to measure a brightness range covering six orders of magnitude. If the input device of the MTF analyzer cannot cover the above dynamic range, the measurement should be carried out step by step. And make corrections. If dark current exists, it should be measured and corrected separately. If a CCD camera is used, it is strongly recommended to use a cooled sensor to reduce noise and obtain a wider dynamic range.
It is also advisable to use a camera with at least 1000 pixels per line. 5 Determination of modulation transfer function
5.1 Preparation
a) The test device should be placed on a plane that is as close to the incident plane as possible, but the distance between them is not more than 10mm, and parallel to the incident plane;
Note: The rotational symmetry of modern XRI means that there is no requirement for the orientation of the test device used. b) The central magnification should be measured with an accuracy of 1% or higher: Note: A method for determining the central magnification is given in YY/T0457.4. c) The center of the test device should be on the central axis. 5.2 Measurement
a) Spatial filter method
YY/T 0457.7—2003/IEC 61262-7:1995 The image on the output screen is projected through a lens or lens group onto the analyzer plane containing the spatial filter of the MTF analyzer. The spatial filter is adjusted so that its arrangement direction is parallel to the long axis of the slit image. The light intensity transmitted through the spatial filter is measured by a light detector, such as a photomultiplier tube. The filter is moved on the analyzer plane in a direction perpendicular to the long axis of the slit image for at least one revolution, and the maximum and minimum values of the light intensity are recorded.
Assuming that the spatial filter is sinusoidal and changes from completely transparent to completely opaque during transmission, the measured MTF expressed in terms of the filter frequency f: is determined by the following formula:
INTmax -INTmin
MTFM(f.)-1
INTmax + INTmin
where:
INT-light intensity.
The above measurement should be repeated for all required frequencies. Note: Instead of multiple filters with different spatial frequencies, a filter with adjustable spatial frequency can be used to measure the MTF at different frequencies. b) LSF method
The image on the output screen is projected onto the target surface of a two-dimensional camera through a lens or lens group. Relative to the camera, the direction of the slit should be such that the slit image is parallel to the vertical direction of the camera. With the help of a two-dimensional camera, the content of all image pixels in the area projected on the output image is accumulated in the vertical direction to obtain a digitized image and then derive the line spread function. For a circular image, this means that a smaller number of pixels at the edge of the image contribute to the LSF than at the center of the image. If the dynamic range of the input instrument of the MTF analyzer is limited, see 4.5e), the LSF should be determined by more than one measurement, for example with different intensities. The measurement results can be combined by conversion. NOTE 1: For the measurement of the low frequency portion of the MTF, it is advantageous to use a wider slit than that used in the measurement of the high frequency portion of the MTF (see 4.4a). When recording the smear value of the MTF, a narrow neutral density filter can be used to block the strongest part in the center of the output image.
NOTE 2: When dark current correction is required, see 4.5e), negative values may appear in the smear value of the LSF result. Negative values should be eliminated by spatial smoothing.
The measured modulation transfer function, MTFM, is obtained by Fourier transforming the LSF. The spatial frequency resolution, ∆f, for the measurement is given by:∆f = (N× X)-1 mm-1
:fmin =(EFS)-1 mm-1
fmax = (4 XX)-1 mm-1
where:
N – number of measurement points per line (pixels);
X – sampling interval [in millimeters (mm) and related to the entrance plane];fmin – minimum visible spatial frequency;
EFS – field size [in millimeters (mm)];fmax – maximum useful spatial frequency (half the Nyquist frequency). If the MTFm value at fmax exceeds 0.02, the slit image is not sampled properly, for example due to limited camera resolution, and a second measurement should be performed at a higher optical magnification. c) The spatial frequency calibration should be referenced to the entrance plane of the XRII. Where necessary, the spatial frequency calibration shall be recalibrated using the central magnification and lens magnification.
d) The MTF value at zero spatial frequency is defined as 1.00. 5.3 Correction
The measured modulation transfer function MTFM is affected by the modulation transfer function MTFr of the test device, the modulation transfer function MTFA of the optical system and the MTF analyzer. The modulation transfer function MTFs of the focus may also affect the measured modulation transfer function. In order to obtain the modulation transfer function MTFx of XRII, these effects shall be corrected. a) MTFx shall be calculated as follows:
MTF× = MTF+ MTF^X MTF
b) The MTF of the test device is given by:sin(πXd X f)
MTF(f)
π×d×f
where:
f – spatial frequency;
d – slit width.
This approximation assumes that the slit width is less than its length. The modulation transfer function of the MTF analyser, including the optical system, can be obtained from the specifications in the random file of the MTF analyser. e
On the other hand, MTF^ can be determined by separate measurements (see Annex C). d) If the MTF has been measured in more than one frequency range, for example a low frequency band and a high frequency band, the results of the various bands shall be combined after correction of the MTFA for each band. The conversion (calibration) from high frequency band to low frequency band shall be carried out at a frequency or frequency range between the limits of each frequency band. If correction of MTFs is required, the MTF of the actual focus shall be determined in accordance with YY/T0063, see 4.3b). No e)
then the MTFs shall be 1.00.
f) The calibration of spatial frequency shall be based on the XRII's incident surface (see 5.2b). g) The product of all modulation transfer functions used for correction shall be greater than 0.5 over the entire range of spatial frequencies considered. 5.4 Determination of low frequency drop
The low frequency drop is calculated by the following formula:
LFD = [1.00- MTF(0. 1 mm-)
5.5 Overall accuracy of measurement
The resulting modulation transfer function shall be measured with an accuracy of 0.02 or better over the entire range of frequencies considered. Note: Please refer to the ISO/TC172/SC1 document [2] on the accuracy of (TF measurement. 6 Expression of modulation transfer function
a) The expression of MTF should include the following points: - XRII identification, such as category, model or number; - MTF including LFD are expressed as a double line graph on a double coordinate axis starting from zero. The expression of spatial frequency in units of mm-1 (or cm-) should be based on the value on the XRII incident surface; - ILFD value.
b) Unless otherwise specified, the data expressed should be based on the maximum incident field size. 7 Declaration of conformity
If it is to be declared that the determination of the modulation transfer function of the X-ray image intensifier complies with this standard, it should be expressed in the following form: - Modulation transfer function: YY/T 0457.7—2003 or
-MTF YY/T 0457.7--2003.
YY/T 0457.7-—2003/IEC 61262-7: 1995IEC60788
Unit names in the International System of Units
Undefined derived terms
Undefined terms
Early unit names
Abbreviations…
3 in YY/T0457.7.1
Accompanying documents
actul focal spot
anti-scatter gridbest focus
central axis
central magnificationAppendix A
(Informative)
Term index
centre of the entrance field axiscentre of the output imagedaiphragm
electro-optical X-ray image intensifierentrance field
entrance field sizeentrance field plane
focal spot
half-value layerhalf-value layer
isoplanatic region
light detector
linespread functionLSFlinear range·
Linearity
Low frequency droplowfrequencydrop
Manufacturer
Manufacturer
Manufacturer
Modulation transfer functionModulation transfer function MTFanalyserNominal focal spotvalueNormal use
Bone fruit bone bone
One-dimensional optical transfer functionone-dimensional optical transfer functionoptical transfer functionl
rm-82-01
rm-20-12
rm-32-06
rm-37-29
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point spread functionDSFradiation
radiation detectorradiation quality
radiation source
source to entrance plane distancespecific
specified
target
test device.
total filtration
transfer
transmission
visible radiation
visible radiation
X-ray radiation
X-ray equipmentX-ray equipment
X-ray image intensifierX-ray tubeX-ray tube·
X-ray tube voltageX-ray graphicsX-ray pattern
Photoelectric X-ray image intensifier
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YY/T0457.7—2003/1EC61262-7:1995 Appendix B
(Informative Appendix)
Construction of test device
For the construction of the test device, it is recommended to use one or more layers of heavy elements such as tungsten, platinum, uranium, etc. In order to fully block X-rays, the thickness of the test device depends on the composition of the test device and the elements used. The thickness is usually 1.0 mm or thicker. 10eiea
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YY/T0457.7—2003/1EC61262-7:1995 Appendix B
(Informative Appendix)
Test Device Construction
For the test device construction, it is recommended to use one or more layers of heavy elements such as tungsten, platinum, uranium, etc. In order to fully block X-rays, the thickness of the test device depends on the test device construction and The element used. The thickness is usually 1.0mm or thicker. 10eiea
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YY/T0457.7—2003/1EC61262-7:1995 Appendix B
(Informative Appendix)
Test Device Construction
For the test device construction, it is recommended to use one or more layers of heavy elements such as tungsten, platinum, uranium, etc. In order to fully block X-rays, the thickness of the test device depends on the test device construction and The element used. The thickness is usually 1.0mm or thicker. 10
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