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WS 519-2019: Specification for testing of quality control in X-ray computed tomography
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Specification for testing of quality control in X-ray computed tomography
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WS 519-2019
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(X-ray computed tomography equipment quality control inspection specification)
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Basic data | Standard ID | WS 519-2019 (WS519-2019) | | Description (Translated English) | Specification for testing of quality control in X-ray computed tomography | | Sector / Industry | Health Industry Standard | | Classification of Chinese Standard | C57 | | Classification of International Standard | 13.280 | | Word Count Estimation | 12,130 | | Date of Issue | 2019 | | Date of Implementation | 2019-07-01 | | Issuing agency(ies) | National Health Commission | WS 519-2019: Specification for testing of quality control in X-ray computed tomography---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
Specification for testing of quality control in X-ray computed tomography
ICS 13.280
C 57
WS
People's Republic of China Health Industry Standard
X-ray computed tomography device quality control test
specification
Published on.2019 - 01 - 25
2019 - 07 - 01 implementation
National Health and Wellness Committee of the People's Republic of China
Content
Foreword...II
1 Scope...1
2 Normative references...1
3 Terms and Definitions...1
4 Quality Control Testing Requirements...4
5 Quality Control Testing Projects and Methods...4
Appendix A (Normative Appendix) Quality Control Testing Items and Technical Requirements...8
Foreword
Chapter 4 and Appendix A of this standard are mandatory, and the rest are recommended.
This standard was drafted in accordance with the rules given in GB/T 1.1-2009.
This standard is revised on the basis of GB 17589-2011 "X-ray computed tomography device quality assurance testing specification", and
Compared with GB 17589-2011, the main technical changes are as follows.
-- modified the standard name;
-- increased the number of items;
-- Revised the scope of application of the standard;
-- modified some terms and definitions;
-- Added a chapter on "Quality Control Testing Requirements";
-- Added a description of the method for detecting the tilt accuracy of the gantry using the slope indicator method;
-- Revised the criteria for determining the thickness deviation of the reconstructed layer;
-- Revised the judgment criteria for CTDIw acceptance detection and status detection;
-- Removed the status detection and stability detection requirements of the CTDIw body phantom;
-- Modified noise detection methods and requirements;
-- Modified the stability detection period of noise;
-- Removed the stability detection requirements for high contrast resolution;
-- Removed the state detection requirements for high contrast algorithms in high contrast resolution;
-- Modified the detection method and correction formula for low contrast detectability;
-- Modified the detection method of CT value linearity and deleted the requirement of state detection for linearity of CT value;
-- Further stipulates the diameter requirements of the water mold.
This standard was drafted. China Center for Disease Control and Prevention, Institute of Radiation Protection and Nuclear Safety, Beijing Municipal Center for Disease Control and Prevention, the first
Beijing Tongren Hospital affiliated to the University of Medical Sciences.
The main drafters of this standard. Yue Baorong, Qi Kedao, Xu Hui, Liu Yitao, Jin Yun, Niu Yantao, Wang Jianchao.
The previous versions of the standards replaced by this standard are.
--GB/T 17589-1998.
X-ray computed tomography device quality control test specification
1 Scope
This standard specifies the requirements and methods for quality control testing of X-ray computed tomography (CT).
This standard applies to quality control testing of diagnostic CT, including acceptance testing, CT status detection and stability testing. radiation
In the treatment of simulated positioning CT, CT for nuclear medicine can be implemented with reference to this standard.
This standard does not apply to cone beam CT (CBCT), such as dental CT, breast CT, etc.; also does not apply to mobile CT dedicated to head examination.
2 Normative references
The following documents are indispensable for the application of this document. For dated references, only the dated version applies to this document.
For undated references, the latest edition (including all amendments) applies to this document.
GB/T 19042.5 Evaluation and routine testing of medical imaging systems - Part 3-5. Imaging performance of X-ray computed tomography equipment
Acceptance test
3 Terms and definitions
The following terms and definitions apply to this document.
3.1
X-ray computed tomography; CT
The subject is located between the X-ray tube and the detector, performs multi-directional X-ray scanning, and passes the detected signal through computer processing.
A digital radiological diagnostic device for reconstructing tomographic images.
3.2
CT dose index 100 CT dose index 100; CTDI100
The integral of the dose profile curve from -50 mm to 50 mm along the central axis of the standard cross section, divided by the nominal layer, in a single axial scan
The product of the thickness and the number of layers N is calculated according to equation (1).
( )
Mm
Mm
CTDI D z dz
NT
...(1)
In the formula.
N - the number of layers produced by a single axial scan;
T -- nominal layer thickness;
( ) D z -- dose profile distribution along the central axis of the standard cross section.
Note. This formula applies when the NT is not more than 40 mm.
3.3
Weighted CT dose index weighted CT dose index; CTDIw
The value of the weighted summation of the CTDI 100 measured at the center point of the phantom and the average value of the CTDI 100 measured at the peripheral points is calculated according to the formula (2).
100, 100,
Wc pCTDI CTDI CTDI ...(2)
In the formula.
100, CCTDI - CTDI100 for the center point measurement of the phantom;
100, pCTDI - The average of CTDI100 measured at various points around the phantom.
3.4
CT value CT number
The amount used to represent the average of the X-ray attenuation associated with the region corresponding to each pixel of the X-ray CT image. Usually in Hounsfield units
Representation, referred to as HU. The expression of the CT value is shown in equation (3).
1000CT
material water substance
...(3)
In the formula.
物质 Substance--the linear attenuation coefficient of the material in the region of interest;
Water - the linear attenuation coefficient of water.
The CT value is defined according to the above scale, the CT value of water is 0 HU, and the CT value of air is -1 000 HU.
3.5
Region of interest; ROI
The area of interest (such as a circle or rectangle) defined in the image.
3.6
Average CT value mean CT number
The average of the CT values of all pixels in a particular region of interest in a CT image.
3.7
CT noise CT noise
Refers to the variation of the CT value of a given area in a uniform material image. The value can be used as the standard for the CT value of the homogeneous substance in the region of interest.
The difference is divided by the contrast scale.
3.8
Uniformity
Consistent CT image values of uniform material images throughout the scanning field.
3.9
Dose profile distribution profile
In the CT patient dose description, the dose distribution curve along a straight line is taken as a function of position.
3.10
Sensitivity profile
A profile of the relative response values of the CT as a function of position along a line perpendicular to the plane of the body layer.
3.11
Full width at half-maximum; FWHM
In the CT scan, the sensitivity profile distribution curve and the dose profile distribution curve have a height on the ordinate that is half of the maximum value.
The distance traveled on the abscissa.
3.12
Nominal tomography
The layer thickness selected and indicated on the CT control panel.
3.13
Reconstructed slice thickness
The full width at half maximum of the imaging sensitivity profile distribution curve at the center of the scan.
3.14
High-contrast resolution
Spatial resolution
When the difference in attenuation coefficient between different objects is sufficiently large compared to the background noise (usually considered to be at least 100 HU), the CT image displayed
The ability to distinguish between different objects.
3.15
Low contrast detectability
The smallest size of the low contrast detail can be identified in the CT image.
3.16
Acceptance test
Quality control after the X-ray diagnostic equipment is installed or the equipment is majorly repaired to verify that its performance indicators meet the agreed values
Detection.
3.17
Status test
For the X-ray diagnostic equipment in operation, the quality control test is carried out periodically to evaluate whether the performance indicators meet the relevant standards.
3.18
Stability test
To determine whether the value of the X-ray diagnostic equipment under a given condition changes with respect to an initial state, it is determined by the control standard.
Quality control testing conducted during the period.
3.19
Baseline value
The reference value of the device performance parameter. The baseline value is usually established by the value obtained by the acceptance test, or the value given by the corresponding standard.
4 Quality control testing requirements
4.1 After CT installation and major maintenance, acceptance inspection should be carried out. The CT in use should be tested annually and regularly stabilized.
Detection.
4.2 Acceptance test and condition test shall be entrusted to a qualified technical service organization, and the stability test shall be carried out by the medical institution.
Or entrust a competent technical organization.
4.3 The CT test items and technical requirements shall comply with the requirements of Table A.1 of Appendix A, and the functions that are not available or cannot meet the test conditions.
The inspection equipment should be described in the test report.
4.4 The acceptance test results of the newly installed CT shall comply with the product performance indicators listed in the random documents, the technical terms of the contract or agreement of the parties, but
Must not be lower than the requirements of this standard. Items not specified by the supplier shall comply with the requirements of this standard. Quality control test results meet or exceed this standard
The value of the indicator specified in the quasi-middle is qualified.
4.5 The basic content of the test report shall include. basic information of the entrusting unit, equipment information, test items, corresponding test requirements, and test results.
And its corresponding standard requirements.
5 Quality Control Testing Projects and Methods
5.1 Diagnostic bed positioning accuracy
5.1.1 A ruler with a minimum precision of 1 mm and an effective length of not less than 300 mm is placed close to the moving bed surface of the diagnostic bed and secured.
Parallel to the direction of motion of the bed, then make a marker on the bed that indicates the scale of the ruler.
5.1.2 When testing, ensure that the bed load is about 70 kg.
5.1.3 Give instructions for “into 300 mm” and “return 300 mm” for the diagnostic bed.
5.1.4 Record the indication values of the start and stop start points and end points on the ruler, and record the bed position indication value on the rack to calculate the positioning error and return.
Bit error.
5.2 Positioning light accuracy
5.2.1 Mould detection method
5.2.1.1 The test phantom adopts a clear and clear positioning mark on the surface, and an object with a specific shape embedded therein, the shape and position of the object
The accommodating has a strict spatial geometric relationship with the phantom surface positioning mark.
5.2.1.2 Place the test phantom on the center line of the scanning field, the axis of the phantom is perpendicular to the scanning cross section, and fine-tune the phantom to make all the tables
The face mark coincides with the positioning light.
5.2.1.3 Use a common head exposure condition, appropriate beam collimation width, single axial scan to obtain internal positioning light mark
The image of the layer, comparing the shape and positional relationship of the specific object in the image with the standard level. If they are consistent, the internal positioning level is specified.
Indeed.
5.2.1.4 If the two are inconsistent in 5.2.1.3, fine-tune the phantom before and after the axis perpendicular to the scanning plane, in accordance with 5.2.1.3
Scanning conditions, finally obtaining an image consistent with the nominal level, and determining the degree of deviation of the positioning light according to the distance adjusted by the phantom along the axis.
5.2.2 Film inspection method
5.2.2.1 Raise the bed to the head scanning position, and place the film with the side length of not less than 15 cm flat on the beam of the positioning lamp on the bed panel.
Inside the circle, the center axis of the film coincides with the center of rotation of the CT harness.
5.2.2.2 Use the needle along the center line of the beam to place a number of small holes on the film as the beam position mark. The diameter of the hole should be as small as possible and straight.
The maximum diameter should not exceed 1 mm.
5.2.2.3 Select the appropriate exposure conditions, the minimum nominal layer thickness, and scan using a single layer axial scan.
5.2.2.4 Read the film image and measure the scan line corresponding to the positioning light. The image on the film and the mark hole are connected to the line between the rotation center axes.
The spacing on the line, which is the degree of deviation of the internal positioning light.
5.3 Scanner tilt accuracy
5.3.1 Mould detection method
5.3.1.1 Using the cuboid with a clearly marked cuboid in the center, the center point of the phantom coincides with the center point of the scanning field, and is fixed horizontally.
The position of the entire phantom, the scanning plane is determined such that the scanning plane passes through the center of the phantom.
5.3.1.2 Scan using clinically common head scan conditions.
5.3.1.3 The mold body is fixed, the frame is tilted by 15°~20°, and scanned again according to the conditions in 5.3.1.2.
5.3.1.4 Using the ranging software in the workstation, measure the vertical scan and the rack tilt angle after the upper and lower edges of the cross-sectional image of the phantom
The distance between them is recorded as L1 and L2, respectively. It is necessary to ensure that the window width and window level are consistent for two measurements.
5.3.1.5 Calculate the actual value of the tilt angle of the gantry by using equation (4), and compare with the set value to determine the accuracy of the tilt angle of the gantry.
Arccos
...(4)
In the formula.
-- the size of the tilt of the gantry;
L1 -- the distance between the upper and lower edges of the cross-sectional image of the phantom during vertical scanning, in millimeters (mm);
L2 -- Rack tilt The distance between the upper and lower edges in the cross-sectional image of the phantom after angle, in millimeters (mm).
5.3.2 Slope indicator method
5.3.2.1 First adjust the tilt angle of the gantry to 0°, fix a slope indicator to the appropriate position of the CT frame, and record the slope indicator reading.
5.3.2.2 Tilt the rack 15°~20° and read the slope indicator reading.
5.3.2.3 Calculate the tilt error of the gantry.
5.4 Reconstruction layer thickness deviation
5.4.1 The phantom used for axial scanning layer thickness deviation measurement is embedded with a marker that is highly contrasted with a homogeneous background, and the marker has certain
The geometric position, through its geometric position, can reflect the image reconstruction layer thickness.
5.4.2 Place the axis of the phantom perpendicular to the scanning plane and place it in the center of the scanning field.
5.4.3 Single-axis axial scanning is performed using the commonly used head exposure conditions in clinical practice and using the nominal thickness of the commonly used clinical reconstruction layer.
5.4.4 Adjust the image window width window position according to the observation conditions in the model specification, and record to obtain the measured value of the reconstructed layer thickness.
5.4.5 Under the appropriate window width window position, measure the CT value of the background near the marker, which is CTbackgroud; adjust the window width to the minimum, change
Change the window position until the marker image just disappears completely, and record the CT value at this time, which is CTmax. Then the half height of the CT value is the above two CTs
Half of the sum of the values is recorded as CThm, and then the window level is re-adjusted to CThm, and the length of the marker at this time, that is, the full width at half maximum (FWHM), is measured.
The measured values of the reconstructed layer thickness are calculated using the fixed geometric relationship of the markers.
5.5 CTDIw
5.5.1 A homogenous cylindrical mold body of polymethyl methacrylate (PMMA) with a head mold diameter of 160 mm and a phantom diameter of 320 mm.
The length of the body is about 15 cm. There are holes for the dosimeter detector at the center and 10 mm from the surface of the mold body. The dose measuring instrument has been obtained.
To check or calibrate.
5.5.2 Place the head mold or phantom in the center of the scanning field. The axis of the cylinder is perpendicular to the scanning plane. The effective detection center of the detector is located in the sweep.
At the center of the trace, the unmeasured probe placement holes are filled with the same material filling rods of the phantom.
5.5.3 Perform a single axial scan according to typical adult head conditions and body conditions given in the manufacturer's instructions, or use clinical
A single axial scan is performed using common head and body conditions.
5.5.4 Record the dosimeter readings and calculate the measured values of CTDI100 and CTDIw according to equations (1) and (2).
5.6 CT value (water), noise and uniformity
5.6.1 A cylindrical homogeneous water mold body with an inner diameter of 18 cm~22 cm is used.
5.6.2 Align the cylinder axis of the water phantom with the scanning plane and at the center of the scanning field to scan the intermediate layer of the water phantom.
5.6.3 Scanning is performed using head scan conditions, and the dose CTDIw for each scan should be no more than 50 mGy.
5.6.4 Select an ROI with a diameter of approximately 10% of the diameter of the test phantom image in the center of the image, and measure the average CT value of the ROI as the water CT value.
Measurements.
5.6.5 Select an ROI with a diameter of approximately 40% of the diameter of the test phantom image in the center of the image, and measure the standard deviation of the CT value in the ROI.
The quasi-bias is divided by the contrast scale as the measured value n of the noise, and the calculation is given by equation (5).
100%n
CT CT
Water air
...(5)
In the formula.
水--standard deviation measured in water model ROI;
CT water--the CT value of water;
CT air--the CT value of the air;
CT CT water--contrast scale, take 1000 HU.
5.6.6 The detection and evaluation of noise should be carried out with a layer thickness of 10 mm. For CTs with a layer thickness not set to 10 mm,
The noise can be corrected according to equation (6).
Nn ...(6)
In the formula.
10n -- noise when the layer thickness is 10 mm;
Tn -- the measured value of the noise when the actual layer thickness is T;
T -- Preset layer thickness in millimeters (mm).
5.6.7 In addition, the circumference of the image is equivalent to the direction of the clock hour, point 3, 6 o'clock, 9 o'clock, 12 o'clock, about 10 mm from the edge of the image image.
Select an ROI with a diameter of approximately 10% of the diameter of the test phantom image, and measure the average CT values of the four ROIs, respectively, in the image with 5.6.4
The maximum difference in the mean ROI of the cardiac ROI is taken as a measure of uniformity.
5.7 High contrast resolution
5.7.1 Using a phantom that can be evaluated by direct observation of the image or using a modulated transfer function (modulated transfer)
Function, MTF) Evaluation of high contrast resolution, calculation of MTF phantom description and its corresponding high contrast resolution measurement method with reference to GB/T
19042.5.
5.7.2 The phantom used for direct observation of the image for evaluation should have periodic details. The spacing between such periodic structures should be a single week.
The difference between the CT values caused by the difference between the effective attenuation coefficient of the periodic detail and the effective attenuation coefficient of the homogeneous background
Should be greater than 100 HU.
5.7.3 Place the phantom in the center of the scan field with the cylinder axis perpendicular to the scanning plane.
5.7.4 According to the clinical common head conditions, set the thin layer thickness, standard reconstruction mode, and perform axial scanning. Dosage CTDIw per scan
It should be no more than 50 mGy.
5.7.5 Adjust the image observation conditions according to the template specification or reach the clearest state that the observer thinks, but the window position must not be larger than
The difference between the CT value of the section and the background CT value.
5.7.6 Record the size of the smallest periodic detail that can be resolved or record the spatial frequency value corresponding to 10% on the MTF curve as spatial resolution
Measured value.
5.7.7 If the high contrast resolution obtained by a special algorithm is used, the high contrast corresponding to the special algorithm should be recorded first according to the method in 5.7.6.
For the measurement of the resolution, the scanned image in 5.7.5 should be reconstructed according to this special algorithm.
5.8 Low contrast detectability
5.8.1 The size of the phantom is usually between 2 mm and 10 mm, and the contrast ratio with the background is between 0.3% and 2%.
The diameter shall not be greater than 2.5 mm and the minimum contrast shall not be greater than 0.6%.
5.8.2 Place the phantom in the center of the scanning field with its axis perpendicular to the scanning plane.
5.8.3 According to the clinical common head axial scanning conditions, the standard reconstruction mode, set the layer thickness to 10 mm, when the less than 10 mm, select the most
The layer thickness of nearly 10 mm, the CTDIw of each scan should be no more than 50 mGy, as close as possible to 50 mGy.
5.8.4 Adjust the image viewing conditions according to the template instructions or reach the clearest state that the observer thinks.
5.8.5 Record the minimum diameter that can be observed for each nominal contrast detail, then multiply by the nominal contrast, with different nominal contrast
The average of the detail product is used as the detection value of the low contrast detectability.
5.9 CT value linearity
5.9.1 The phantom with more than 3 different CT value modules is used, and the difference between the CT values of the modules should be greater than 100 HU.
5.9.2 Use the phantom instructions to specify the scanning conditions or scan separately using clinically common head and body scanning conditions.
5.9.3 Select an ROI with a diameter of approximately 80% of the module diameter at the center of the different modules and measure the average CT value.
5.9.4 Attenuation coefficient of each attenuation module marked in the model specification according to the corresponding ray quality conditions and the nominal CT of each module
Value, and then calculate the difference between the nominal CT value and the measured average CT value of the module in each CT value module. The largest difference is recorded as the CT value line.
Sexual evaluation parameters.
Appendix A
(normative appendix)
Quality control testing items and technical requirements
CT test items and requirements are shown in Table A.1.
Table A.1 CT test items and requirements
Test item inspection requirements
Acceptance detection state detection stability detection
Judgment standard judgment standard judgment standard period
Diagnostic bed positioning
Positioning within ±2 mm within ±2 mm within ±2 mm
One month
Hom within ±2 mm within ±2 mm within ±2 mm
2 Positioning light accuracy within ±2 mm within ±2 mm of positioning light -
Scanning frame
Cuboid phantom or dip
Within ±2 o - - -
4 reconstruction layer thickness deviation
a > within 2 mm ±1 mm within ±1 mm
Difference from baseline value ±
Within 20% or ±1 mm,
The larger one controls one year
2 mm ≥ s ≥ 1 mm ± 50% within -
s< 1 mm ±0.5 mm -
5 CTDIw
Head phantom
And manufacturer's specification indicators
Within ±15% of the difference
Difference with manufacturer's specification index
Within 20%, if there is no technical specification
Standard reference, should be ≤50 mGy
Difference from baseline value ±
Within 15%
One year
Body phantom
And manufacturer's specification indicators
Within ±15% of the difference
- -
6 CT value (water)
Water mold body inner diameter 18
Cm~22 cm, CTDIw
No more than 50 mGy, noise
Acoustic detection layer thickness 10 mm
Within ±4 HU within ±4 HU
Difference from baseline value
Within ±4 HU
One month
7 Uniformity ±5 HU...
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