DIN 6868-157:What, When and How Must Be Checked
Sicherung der Bildqualität in röntgendiagnostischen Betrieben – Teil 157: Abnahme- und Konstanzprüfung nach RöV an Bildwiedergabesystemen in ihrer Umgebung
Sicherung der Bildqualität in röntgendiagnostischen Betrieben – Teil 157: Abnahme- und Konstanzprüfung nach RöV an Bildwiedergabesystemen in ihrer Umgebung
Image quality assurance in diagnostic X-ray departments – Part 157: X-ray ordinance acceptance and constancy test of image display systems in their environment
Assurance de la qualité des images en diagnostic radiographique – Partie 157: Test d´acceptance et contrôle de constance selon RöV des systèmes de visualisation des images dans leur environnemen
DIN 6868-157
November 2014 – WHAT, WHEN and HOW it must be done
Conditions before testing (acceptance and constancy testing):
– The Image Reproduction System (IRS) has to be operated in the medical application, in which it is used later.
– Any modifications to the Image System must be recognizable. Those are for example changes to the application software, the display, the graphics card.
– The displays must be cleaned before starting the test.
– There should be no disturbing reflections on the screenfrom overhead lighting, windows, clothes.
– The room lighting must be stable during the test and when working.
– Before the test, the display must be warmed up according to the manufacturer’s instructions or at least 30 minutes.
– The DICOM curve must be selected or calibrated on all displays with diagnostic quality.
– The test images must match the resolution of the display.
– In case a quality assurance software is used for testing, it must be checked, whether the test images in the application software and in the quality assurance software are equally represented.
– The test shall be performed under the ambient conditions of the room class, which were determined by the radiation protection supervisor.
Test equipment (meters and test images)
Luminance Meters
For acceptance testing a calibrated telescopic luminance meter must be used for distance measurement.
To check consistency, a telescopic luminance meter (distance measurement), a photometer (contact-measurement Puck), a front integrated Meter (front sensor) or a backside integrated instrument can be used.
To measure the illuminance a special illuminance meter must be used.
Test Patterns
The following test patterns must be used and produced in the resolution of the display. A PIXEL of the testpattern must represent a PIXEL on the image reproduction device. AAPM ->
TG 18-OIQ
TG 18-UN80
TG 18-MP
TG 18-LN8-01 to TG 18-LN8-18
TG 18-UN10
TG 18-LPH10
TG 18-LPH50
TG 18-LPH89
TG 18-LPV10
TG 18-LPV50
TG 18-LPV89
Room classes
Room classes are classified depending on use of the IRS. Depending on the room class different limits, testing and inspection intervals may be applied.
In general they are divided into two classes:
1. Image reproduction systems with diagnostic quality
2. Image reproduction systems with re-viewing quality
Furthermore, room classes are classified according to their requirements. The following table summarizes the room classes:
| Room- class | Room | Activity | Cassification | Ambient illuminance |
|---|---|---|---|---|
| RC1 | The radiology viewing room | Diagnosis of radiography and cross-sectional images | Diagnostic quality | ≤ 50 Lx |
| RC2 | Examination rooms with immediate diagnostic | An activity carried out in an examination room, where therapy-related decisions are made. Therefore, the image quality of the IRS must be sufficient for a diagnosis. | Diagnostic quality | ≤ 100 Lx |
| RC3 | Rooms for performing examinations | An examination is made with the help of a dialogue monitor. It is typically used for high contrast objects. | Diagnostic quality | ≤ 500 Lx |
| RC4 | Viewing and treatment rooms | Activities in which a known and evaluated medical diagnosis must be repeatedly retraced (e.g.
repositioning in the operating room, screw removal |
Reviewing quality | ≤ 1000 Lx |
| RC5 | Dental diagnostic workplace | Diagnostics outside the lighting conditions of a dental treatment workplace. | Diagnostic quality | ≤ 100 Lx |
| RC6 | Dental Treatment
Room |
Diagnostic under lighting conditions
of a dental treatment workplace. |
Diagnostic quality | ≤ 1000 Lx |
| The ILLUMINANCE is measured with the switched off image reproduction device and the measurement device
placed perpendicular to the screen surface |
||||
Acceptance test for image reproduction systems with diagnostic quality
The following two tables contain the necessary steps of the acceptance test.
Visual inspections
| Testequipment (Test pattern) | Test | Partial test |
|---|---|---|
| TG18-OIQ | Overall image quality | unaltered visibility of line pair grid without streaks, smudges or erasures and visibility of the two PIXEL wide line pair grid with low CONTRAST in the center and in the four corners of the test pattern (test image
element 1) |
| RC5 (≤ 100 lx) and RC6 (≤ 1 000 lx): Visibility of 5 %- and 95 %- fields (test image element 2); | ||
|
Visibility of the letters with low CONTRAST (”QUALITY CONTROL” test image element 3); 1) in the white and gray box: “QUALITY CONTROL” for all room classes; 2) in the black field: i) Mammography (RC 1): „QUALITY CONTROL“ ii) RC1 (≤ 50 lx): „QUALITY CONTRO“ iii) RC2 (≤ 100 lx): „QUALITY CONT“ iv) RC3 (≤ 500 lx): „QUALITY CON“ To calculate the maximum allowed defective pixels, multiply the horizontal number of PIXELs of image reproduction device with the vertical number of PIXELs and divide by 1,048,576 (equivalent to 1024×1024 pixels) This result should be multiplied by the value specified in the table of limit values and rounded off to the nearest whole number. |
||
| CLINICAL REFFERENCE IMAGES | Test based on CLINICAL reference images.
Not applicable for RC5 und RC6 |
For this test CLINICAL REFERENCE IMAGES are to be selected that have sufficient quality and image content in order to evaluate correctly the image quality of the display. |
|
TG18-LPH10, -LPH50 und -LPH89 (horizontal Lines); TG18-LPV10, -LPV50 und -LPV89 (vertikal Lines.) |
The visibility of the line structures in the test pattern 6. Required only
for RC1 and Mammography |
The visibility of the line structures in the test pattern 6 must be checked for RC 1.
TG18-LPH10, TG18-LPH50 und TG18-LPH89 (horizontal Lines) TG18-LPV10, TG18-LPV50 und TG18-LPV89 (vertikal Lines) |
Metrological (measurement) tests for acceptance testing
| Testequipment (Test pattern) | Test image and Method of measurement | Test | Test Description |
|---|---|---|---|
| Luminance
Meter (Distance measurement) |
TG18-LN8-01 | Minimum
Luminance |
The minimum luminance L min is measured on the screen center with a telescopic measuring device. |
| TG18-LN8-18 | Maximum
Luminance |
The maximum luminance L’max is measured on the screen center with a telescopic measuring device. | |
| Luminance measurement. Measured with
the switched off display |
Veiling
Luminance |
The veiling luminance Lamb is measured on the screen center with a telescopic measuring device. The display must be switched off. | |
| Luminance Meter (Contact measurement) | TG18-UN80 and TG18-UN10 | Homogeneity
of the display |
It must be measured (for 8 bit corresponding DDL DDL 26 and 204) in essay measurement at five points or a screen diagonal of ≥ 23 inches at nine points in the luminance of 10% and 80% of the maximum DDL. The UNIFORMITY H is calculated as the percentage difference between the highest (Lhighest) and lowest (Llowest) values of the measured LUMINANCE with respect to its mean as follows: H = 200 ×(Lhighest – Llowest)/(Lhighest + Llowest) |
| TG18-UN10 | Homogeneity of multiple
displays |
It is measured in the screen center (z) of all the displays connected to the same workstation in order to determine the uniformity between the displays. The UNIFORMITY of multiple display devices is calculated as the percentage difference between the highest and lowest values of the luminance in relation to their mean value: H = 200 × (Lhighest – Llowest)/(Lhighest + Llowest) |
|
| TG18-LN8-01 to
TG18-LN8-18 |
Luminance Responce Curve – DICOM GSDF | The LUMINANCE RESPONSE CURVE is determined by representing the 18 test pattern TG18-LN8-01 to
TG1-LN8-18 and measurement on the screen center. The evaluation of the measurements must be made with a suitable software tool. The veiling luminance must be considered while calculating. |
|
| Illuminance meter | With a switched off display, perpendicular to the screen surface
(screen center) |
Illuminance | The illuminance is measured while the image reproduction device is switched off and the measurement device placed perpendicular to the screen surface. |
Minimum requirements for image display devices (excluding mammography)
| The body region/ methods | Max Display Luminan- ce cd/m2 | Max Lumi- nance ratio r’= L’max/ L’min | Matrix/ resolu- tion of the display | Lumi- nance respon- ce curve deviation from the DICOM GSDF curve | Homo- genity within the display | Homo- genity bet- ween several displays | Pixel- errors (per 1024x 1024) depen- ding on the error type) | Minimal Luminance cd/m2 | Minimal pixel size |
|---|---|---|---|---|---|---|---|---|---|
|
Projection radiology (Thorax,
skeleton, abdomen) |
≥ 250 | ≥ 250 | ≥ 1600
x ≥ 1200 |
GSDF
± 10% |
<25% | <20% |
A ≤ 1 B ≤ 5 C ≤ 5 D≤ 1 |
≤ 1.1 x Lam | 140 micro meter |
| Fluoroscopy,
all applica- tions |
≥ 150 | ≥ 100 | ≥ 1024 x
≥ 1024 |
GSDF
± 15% |
<25% | <20% | |||
| Computed tomog- raphy(CT) | ≥ 150 | ≥ 100 | ≥ 1024 x
≥ 1024 |
GSDF
± 15% |
<25% | <20% | |||
|
For RC 5: Dental digital volume tomography, intraoral x-ray diagnos tic with dental x- ray tube heads, panoramic radiographs, cephalometric radiographs of the skull, dental skull plain films, hand- held shooting for skeletal growth determination |
≥ 200 | ≥ 100 | ≥ 1024 x
≥ 768 |
only visual test
with the test image TG18-O IQ and the test image elements e a), b), c), e) and g) |
<30% | <30% | |||
|
For RC 6: Intraoral X-ray diagnos tics with dental x- ray tube heads, panoramic radiographs, cephalometric radiogr phs of the skull, dental skull plain films, hand- held shooting for skeletal growth determination |
≥ 300 | ≥ 100 | ≥ 1024 x
≥ 768 |
only visual tests with
the test image TG18-O IQ and the test image elements e a), b), c), e) and g) |
<30% | <30% |
Minimum requirements for image display devices for the mammography. In addition the following test patterns must be
checked for the visibility of the line structures: TG18-LPH10, -LPH50 und -LPH89 (horizontal Lines) TG18-LPV10, -LPV50 und -LPV89 (vertical Lines)
| The body region/ methods | Max Display Luminan- ce cd/m2 | Max Lumi- nance ratio r’= L’max/ L’min | Matrix/ resolu- tion of the display | Lumi- nance respon- ce curve deviation from the DICOM GSDF curve | Homo- genity within the display | Homo- genity bet- ween several displays | Pixel- errors (per 1024x 1024) depen- ding on the error type) | Minimal Luminance cd/m2 | Minimal Luminance cd/m2 |
|---|---|---|---|---|---|---|---|---|---|
| Mammo
graphy |
≥ 250 | ≥ 250 | ≥ 2048 x
≥ 2048 |
GSDF
± 10% |
<25% | <10% |
A ≤ 1 B ≤ 5 C ≤ 5 D≤ 1 |
≤ 1.1 x Lam | 140 micro meter |
| Mammo
graphic Stereota- xy |
≥ 200 | ≥ 100 | ≥ 1024 x
≥ 1024 |
GSDF
± 15% |
<25% | <20% |
Reference values for constancy tests
If the acceptance test passed, the measured values must be stored as reference values for constancy tests.
In case of a deviation of the measured values by more than 20% from the
reference values of the ACCEPTANCE TEST it is recommended to take an appropriate action in order to prevent further deviations. In case of deviations of the measured values by more than 30%, it is required to correct the errors.
After the error has been removed, a CONSTANCY or an ACCEPTANCE TEST is
required. If the significant changes had been made to the image reproduction device during troubleshooting, an acceptance testing is mandatory.
Constancy tests at workplaces with diagnostic quality
The constancy tests must be carried out at the intervals indicated below or after significant changes in the workstation.
If the veiling luminance is less than 0.15 cd /m2, a negative deviation from the reference value must not be considered.
| Visual steps for constancy tests | Interval | ||
|---|---|---|---|
|
Test equipment (Test Image) |
Test |
Test Description |
|
| TG18-OIQ | Overall image quality | Unaltered visibility of line pair grid without streaks, smudges or cancellations and visibility of the two pixel wide line pair grid with low contrast in the center and in the four corners of the TEST IMAGE (test pattern element 1) | Daily |
| RC5 (≤ 100 lx) and RC6 (≤ 1000 lx): In the test pattern element 2 (5% – and 95% field) the low-contrast squares must be recognizable. | |||
|
Visibility of the letters with low CONTRAST (“QUALITY CONTROL” test image element 3); 1)In the white and gray box: “QUALITY CONTROL” for all room classes 2) in the black field: i) Mammography (RC1): „QUALITY CONTROL“ ii) RC1 (≤ 50 lx): „QUALITY CONTRO“ iii) RC2 (≤ 100 lx): „QUALITY CONT“ iv) RC3 (≤ 500 lx): „QUALITY CON“ |
|||
| The following applies for room class 5 and 6: At the test pattern element 3 at least in the mid gray box the words ”QUALITY CONTROL” must be visible. | |||
| Continuity of the appearance of the progress bar (test image element
7); |
|||
| TG18-UN80 | Luminance uniformity | Visual assessment of the test pattern for interfering irregularities from the center to the edges. | Semi-
annually |
| Color appearan-
ce and uniformity |
The color uniformity over the screen of the displayed test pattern is to be verified. The test must be performed on multiple image display devices of the same type that are connected to the same image display system and are installed next to each other. This is to test for perceptual color differences between the individual IMAGE DISPLAY DEVICES. | ||
Metrological (measurement) tests for constancy tests. The same limits as for the acceptance test must be applied
Interval: Semi-annual
| Test Equipment | Test image and method of measurement | Test | Test Description |
|---|---|---|---|
| Luminance Meter (Contact measurement and distance measurement) | TG18-LN8-01 | Minimum
Luminance |
The minimum luminance L min is measured on the screen center with a telescopic measuring device. |
| TG18-LN8-18 | Maximum
Luminance |
The maximum luminance L’max is measured on the screen center with a telescopic measuring device. | |
| Luminance measurement. Measured with
the switched off display |
Veiling
Luminance |
The veiling luminance Lamb is measured on the screen center with a telescopic luminace meter with the display turned off. The test is only required if there were differences in the minimum luminance.
The test is not required for room classes 3, 5 and 6 . |
|
| Luminance Meter
(Contact measurement and distance measurement) |
TG18-UN10 | Homogenity of multiple
displays |
Is is to be measured in the screen center (z) of all the displays connected to the same workstation, in order to determine the uniformity between the displays. The uniformity of multiple displays is calculated as the percentage difference between the highest and lowest values of the measured LUMINANCE taking into account its mean as follows: H = 200 × (Lhighest – Llowest)/(Lhighest + Llowest) The test is not required for RC3, RC5 und RC6. |
| Luminance Meter
(Contact measurement) |
TG18-LN8-01 to
TG18-LN8-18 |
Luminance curve DICOM GSDF |
The LUMINANCE CURVE is determined by representing the 18 TEST PATTERNs TG18 from TG18 to-LN8-01 to LN8-18. Measurements must be taken on the screen center using a contact measurement method. The evaluation of the measurements must be made with a sutable software tool. The veiling luminance must be considered while calculating. The test is not required for RC3, RC5 und RC6. |
| Illuminance meter | with a switched off display measurement device is placed perpendicular to the screen surface (screen center) | Illuminance | The illuminance is measured while the image reproduction device is switched off and the measurement device placed perpendicular to the screen surface. |
Terms and definitions
Acceptance test
Examination of an image display system (workstation), including the image reproduction device (display) immediately after installation and before operating assumption. Measured values are stored as reference values for constancy tests.
Application software
The software that is used to display the medical images.
Artifact
The structures that can be recognized by the viewer but are not part of the image.
Diagnostic quality
Visual quality of the image display systems that are used to allow diagnostic statements and used as the basis of medical decisions
Illuminance
E
The strength of the luminous flux incident on a surface per unit area. Unit: Lux (lx).
Viewing quality
Visual quality of the image reproduction systems that are used in order to view the already diagnosed images to detect image features and content.
IMAGE REPRODUCTION DISPLAY (in the DIN named as “BWG”)
In general, a monitor. Or other displays as projectors.
Image Reproduction System (in the DIN named as “BWS”)
A workstation consisting of the computer graphic card, application software and all connected displays.
Grayscale Standard Display Function GSDF
Function for reproduction of grayscales on a computer display. Generally known as DICOM curve, DICOM GSDF curve Part 14 or Barten curve.
Luminance Uniformity
H
Uniformity of brightness distribution on one or multiple displays.
Clinical reference image
A medical image that is typical for the application of image reproduction system, and contains important image elements that allow conclusions about the quality of the image.
Constancy test
Checks carried out at regular intervals in order to identify and document changes compared to the reference values of the acceptance test.
Luminance
L
The luminance describes the brightness of extended, planar light sources. Unit: cd/m2 (candela per m2)
Luminance coefficient
q
Quotient of the LUMINANCE of the surface element in the given direction and ILLUMINANCE
on the medium.
Maximum display luminance
L’max
Maximum luminance of the display.
Maximum Luminance Ratio
r’
Ratio of MAXIMUM Luminance L’max and MINIMAL LUMINANCE L’min.
r=’ L’max/ L’min
Maximum Luminance
L’max
Maximum luminance in the center of the screen plus veiling luminance L’max= Lmax+ Lamb
Minimal Display Luminance
Lmin
Minimal luminance of the display.
Minimal Luminance
L’max
Minimum luminance in the center of the screen plus veiling luminance.
L’max = Lmax + Lamb
Veiling Luminance
Lamb
Luminance generated by the ambient light on the surface of a display (reflection of ambient light on the display)
QUBYX editorial archive.
