IEC 62220-1-3:2008

IEC 62220-1-3
Edition 1.0 2008-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Medical electrical equipment – Characteristics of digital X-ray imaging devices –
Part 1-3: Determination of the detective quantum efficiency – Detectors used in
dynamic imaging
Appareils électromédicaux – Caractéristiques des dispositifs d’imagerie
numérique à rayonnement X –
Partie 1-3: Détermination de l'efficacité quantique de détection – Détecteurs
utilisés en imagerie dynamique

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IEC 62220-1-3
Edition 1.0 2008-06
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
Medical electrical equipment – Characteristics of digital X-ray imaging devices –
Part 1-3: Determination of the detective quantum efficiency – Detectors used in
dynamic imaging
Appareils électromédicaux – Caractéristiques des dispositifs d’imagerie
numérique à rayonnement X –
Partie 1-3: Détermination de l'efficacité quantique de détection – Détecteurs
utilisés en imagerie dynamique

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
V
CODE PRIX
ICS 11.040.50 ISBN 2-8318-9826-9

– 2 – 62220-1-3 © IEC:2008
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 Terms and definitions .8
4 Requirements .10
4.1 Operating conditions .10
4.2 X-RAY EQUIPMENT .10
4.3 RADIATION QUALITY .10
4.4 TEST DEVICE.11
4.5 Geometry .12
4.6 IRRADIATION conditions .14
4.6.1 General conditions .14
4.6.2 AIR KERMA measurement .15
4.6.3 LAG EFFECTS.16
4.6.4 IRRADIATION to obtain the CONVERSION FUNCTION .16
4.6.5 IRRADIATION for determination of the NOISE POWER SPECTRUM and LAG
EFFECTS .16
4.6.6 IRRADIATION with TEST DEVICE in the RADIATION BEAM.17
4.6.7 Overview of all necessary IRRADIATIONS .18
5 Corrections of RAW DATA .18
6 Determination of the DETECTIVE QUANTUM EFFICIENCY .19
6.1 Definition and formula of DQE(u,v).19
6.2 Parameters to be used for evaluation .19
6.3 Determination of different parameters from the images.20
6.3.1 Linearization of data .20
6.3.2 The LAG EFFECTS corrected NOISE POWER SPECTRUM (NPS) .20
6.3.3 Determination of the MODULATION TRANSFER FUNCTION (MTF).24
7 Format of conformance statement .24
8 Accuracy .25
Annex A (informative) Determination of LAG EFFECTS.26
Annex B (informative) Calculation of the input NOISE POWER SPECTRUM .29
Bibliography.30
Index of defined terms .32

Figure 1 – TEST DEVICE .12
Figure 2 – Geometry for exposing the DIGITAL X-RAY IMAGING DEVICE in order to
determine the CONVERSION FUNCTION, the NOISE POWER SPECTRUM and the MODULATION
TRANSFER FUNCTION behind the TEST DEVICE.14
Figure 3 – Image acquisition sequence to determine the NOISE POWER SPECTRUM and
LAG EFFECTS.17
Figure 4 – Geometric arrangement of the ROIs .21
Figure A.1 – Power spectral density of white noise s and correlated signal g (only
positive frequencies are shown).27

62220-1-3 © IEC:2008 – 3 –
Table 1 – RADIATION QUALITY (IEC 61267:1994) for the determination of DETECTIVE
QUANTUM EFFICIENCY and corresponding parameters .11
Table 2 – Necessary IRRADIATIONS .18
Table 3 – Parameters mandatory for the application of this standard .20

– 4 – 62220-1-3 © IEC:2008
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEDICAL ELECTRICAL EQUIPMENT –
CHARACTERISTICS OF DIGITAL X-RAY IMAGING DEVICES –

Part 1-3: Determination of the detective quantum efficiency –
Detectors used in dynamic imaging

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 62220-1-3 has been prepared by subcommittee 62B: Diagnostic
imaging equipment, of IEC technical committee 62: Electrical equipment in medical practice.
The text of this standard is based on the following documents:
FDIS Report on voting
62B/694/FDIS 62B/702/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.

62220-1-3 © IEC:2008 – 5 –
A list of all parts of the IEC 62220 series, published under the general title Medical electrical
equipment – Characteristics of digital X-ray imaging devices, can be found on the IEC
website.
In this standard, terms printed in SMALL CAPITALS are used as defined in IEC 60788, in Clause
3 of this standard or in other IEC publications referenced in the Index of defined terms. Where
a defined term is used as a qualifier in another defined or undefined term it is not printed in
SMALL CAPITALS, unless the concept thus qualified is defined or recognized as a “derived term
without definition”.
NOTE Attention is drawn to the fact that, in cases where the concept addressed is not strongly confined to the
definition given in one of the publications listed above, a corresponding term is printed in lower-case letters.
In this standard, certain terms that are not printed in SMALL CAPITALS have particular
meanings, as follows:
– "shall" indicates a requirement that is mandatory for compliance;
– "should" indicates a strong recommendation that is not mandatory for compliance;
– "may" indicates a permitted manner of complying with a requirement or of avoiding the
need to comply;
– "specific" is used to indicate definitive information stated in this standard or referenced in
other standards, usually concerning particular operating conditions, test arrangements or
values connected with compliance;
– "specified" is used to indicate definitive information stated by the manufacturer in
accompanying documents or in other documentation relating to the equipment under
consideration, usually concerning its intended purposes, or the parameters or conditions
associated with its use or with testing to determine compliance.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in
the data related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
– 6 – 62220-1-3 © IEC:2008
INTRODUCTION
DIGITAL X-RAY IMAGING DEVICES are increasingly used in medical diagnosis and will widely
replace conventional (analogue) imaging devices such as screen-film systems or analogue X-
RAY IMAGE INTENSIFIER television systems in the future. It is necessary, therefore, to define
parameters that describe the specific imaging properties of these DIGITAL X-RAY IMAGING
DEVICES and to standardize the measurement procedures employed.
There is growing consensus in the scientific world that the DETECTIVE QUANTUM EFFICIENCY
(DQE) is the most suitable parameter for describing the imaging performance of an X-ray
imaging device. The DQE describes the ability of the imaging device to preserve the signal-to-
NOISE ratio from the radiation field to the resulting digital image data. Since in X-ray imaging,
the NOISE in the radiation field is intimately coupled to the AIR KERMA level, DQE values can
also be considered to describe the dose efficiency of a given DIGITAL X-RAY IMAGING DEVICE.
NOTE 1 In spite of the fact that the DQE is widely used to describe the performance of imaging devices, the
connection between this physical parameter and the decision performance of a human observer is not yet
1)
completely understood [1], [3].
NOTE 2 IEC 61262-5 specifies a method to determine the DQE of X-RAY IMAGE INTENSIFIERS at nearly zero
SPATIAL FREQUENCY. It focuses only on the electro-optical components of X-RAY IMAGE INTENSIFIERS, not on the
imaging properties as this standard does. As a consequence, the output is measured as an optical quantity
(luminance), and not as digital data. Moreover, IEC 61262-5 prescribes the use of a RADIATION SOURCE ASSEMBLY,
whereas this standard prescribes the use of an X-RAY TUBE. The scope of IEC 61262-5 is limited to X-RAY IMAGE
INTENSIFIERS and does not interfere with the scope of this standard.
The DQE is already widely used by manufacturers to describe the performance of their
DIGITAL X-RAY IMAGING DEVICE. The specification of the DQE is also required by regulatory
agencies (such as the Food and Drug Administration (FDA)) for admission procedures.
However, there is presently no standard governing either the measurement conditions or the
measurement procedure, with the consequence that values from different sources may not be
comparable.
This standard has therefore been developed in order to specify the measurement procedure
together with the format of the conformance statement for the DETECTIVE QUANTUM EFFICIENCY
of DIGITAL X-RAY IMAGING DEVICES.
In the DQE calculations proposed in this standard, it is assumed that system response is
measured for objects that attenuate all energies equally (task-independent) [5].
This standard will be beneficial for manufacturers, users, distributors and regulatory agencies.
It is the third document out of a series of three related standards:
• Part 1, which is intended to be used in RADIOGRAPHY, excluding MAMMOGRAPHY and
RADIOSCOPY.
• Part 1-2, which is intended to be used for MAMMOGRAPHY.
• the present Part 1-3, which is intended to be used for dynamic imaging detectors.
These standards can be regarded as the first part of the family of IEC 62220 standards
describing the relevant parameters of DIGITAL X-RAY IMAGING DEVICES.
———————
1)
Figures in square brackets refer to the bibliography.

62220-1-3 © IEC:2008 – 7 –
MEDICAL ELECTRICAL EQUIPMENT –
CHARACTERISTICS OF DIGITAL X-RAY IMAGING DEVICES –

Part 1-3: Determination of the detective quantum efficiency –
Detectors used in dynamic imaging

1 Scope
This part of IEC 62220 specifies the method for the determination of the DETECTIVE QUANTUM
EFFICIENCY (DQE) of DIGITAL X-RAY IMAGING DEVICES as a function of AIR KERMA and of SPATIAL
FREQUENCY for the working conditions in the range of the medical application as specified by
the MANUFACTURER. The intended users of this part of IEC 62220 are manufacturers and well
equipped test laboratories.
This Part 1-3 is restricted to DIGITAL X-RAY IMAGING DEVICES that are used for dynamic imaging
such as, but not exclusively, direct and indirect flat panel-detector based systems.
It is not recommended to use this part of IEC 62220 for digital X-RAY IMAGE INTENSIFIER-based
systems.
NOTE 1 This negative recommendation is based on the low frequency drop, vignetting and geometrical distortion
present in these devices which may put severe limitations on the applicability of the measurement methods
described in this standard.
This part of IEC 62220 is not applicable to:
– DIGITAL X-RAY IMAGING DEVICES intended to be used in mammography or in dental
radiography;
– COMPUTED TOMOGRAPHY; and
– systems in which the X-ray field is scanned across the patient.
NOTE 2 The devices noted above are excluded because they contain many parameters (for instance, beam
qualities, geometry, time dependence, etc.) which differ from those important for dynamic imaging. Some of these
techniques are treated in separate standards (IEC 62220-1 and IEC 62220-1-2).
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60336, Medical electrical equipment – X-ray tube assemblies for medical diagnosis –
Characteristics of focal spots
IEC TR 60788:2004, Medical electrical equipment – Glossary of defined terms
2)
IEC 61267:1994, Medical diagnostic X-ray equipment – Radiation conditions for use in the
determination of characteristics
ISO 12232:1998, Photography – Electronic still-picture cameras – Determination of ISO speed
———————
2)
Although a second edition (2005) of IEC 61267 exists, reference to the first edition (IEC 61267:1994) is
expressly retained throughout this standard for reasons of harmonization within the IEC62220 family. (See 4.3,
Note 1.)
– 8 – 62220-1-3 © IEC:2008
3 Terms and definitions
For the purpose of this document, the terms and definitions given in IEC 60788 and the
following apply.
3.1
CENTRAL AXIS
ENTRANCE PLANE passing through the centre of the entrance field
line perpendicular to the
[IEC 62220-1:2003, definition 3.1]
3.2
CONVERSION FUNCTION
plot of the large area output level (ORIGINAL DATA) of a DIGITAL X-RAY IMAGING DEVICE versus
the number of exposure quanta per unit area (Q) in the DETECTOR SURFACE plane
[IEC 62220-1:2003, definition 3.2]
NOTE 1 Q is to be calculated by multiplying the measured AIR KERMA excluding back scatter by the value given in
column 2 of Table 3.
NOTE 2 Many calibration laboratories, such as national metrology institutes, calibrate RADIATION METERS to
measure AIR KERMA.
3.3
DETECTIVE QUANTUM EFFICIENCY
DQE(u,v)
ratio of two NOISE POWER SPECTRUM (NPS) functions with the numerator being the NPS of the
input signal at the DETECTOR SURFACE of a digital X-ray detector after having gone through the
deterministic filter given by the system transfer function, and the denominator being the
measured NPS of the output signal (ORIGINAL DATA)
NOTE Instead of the two-dimensional DETECTIVE QUANTUM EFFICIENCY, often a cut through the two-dimensional
DETECTIVE QUANTUM EFFICIENCY along a specified SPATIAL FREQUENCY axis is published.
[IEC 62220-1:2003, definition 3.3]
3.4
DETECTOR SURFACE
accessible area which is closest to the IMAGE RECEPTOR PLANE
NOTE After removal of all parts (including the ANTI-SCATTER GRID and components for AUTOMATIC EXPOSURE
CONTROL, if applicable) that can be safely removed from the RADIATION BEAM without damaging the digital X-ray
detector.
[IEC 62220-1:2003, definition 3.4]
3.5
DIGITAL X-RAY IMAGING DEVICE
device consisting of a digital X-ray detector including the protective layers installed for use in
practice, the amplifying and digitizing electronics, and a computer providing the ORIGINAL DATA
(DN) of the image
[IEC 62220-1:2003, definition 3.5]
3.6
IMAGE MATRIX
arrangement of matrix elements preferentially in a Cartesian coordinate system
[IEC 62220-1:2003, definition 3.6]

62220-1-3 © IEC:2008 – 9 –
3.7
LAG EFFECT
influence from a previous image on the current one
[IEC 62220-1:2003, definition 3.7]
3.8
LINEARIZED DATA
ORIGINAL DATA to which the inverse CONVERSION FUNCTION has been applied
[IEC 62220-1:2003, definition 3.8]
NOTE The LINEARIZED DATA are directly proportional to the AIR KERMA.
3.9
MODULATION TRANSFER FUNCTION
MTF(u,v)
modulus of the generally complex optical transfer function, expressed as a function of SPATIAL
FREQUENCIES u and v
[IEC 62220-1:2003, definition 3.9]
3.10
NOISE
fluctuations from the expected value of a stochastic process
[IEC 62220-1:2003, definition 3.10]
3.11
NOISE POWER SPECTRUM
NPS
W(u,v)
modulus of the Fourier transform of the NOISE auto-covariance function. The power of NOISE,
contained in a two-dimensional SPATIAL FREQUENCY interval, as a function of the two-
dimensional frequency
NOTE In literature, the NOISE POWER SPECTRUM is often named “Wiener spectrum” in honour of the mathematician
Norbert Wiener.
[IEC 62220-1:2003, definition 3.11]
3.12
ORIGINAL DATA
DN
RAW DATA to which the corrections allowed in this standard have been applied
[IEC 62220-1:2003, definition 3.12]
3.13
PHOTON FLUENCE
Q
mean number of photons per unit area
[IEC 62220-1:2003, definition 3.13]
3.14
RAW DATA
pixel values read directly after the analogue-digital-conversion from the DIGITAL X-RAY IMAGING
DEVICE or counts from photon counting systems without any software corrections
[IEC 62220-1:2003, definition 3.14]

– 10 – 62220-1-3 © IEC:2008
3.15
SPATIAL FREQUENCY
u or v
inverse of the period of a repetitive spatial phenomenon. The dimension of the SPATIAL
FREQUENCY is inverse length
[IEC 62220-1:2003, definition 3.15]
4 Requirements
4.1 Operating conditions
The DIGITAL X-RAY IMAGING DEVICE shall be stored and operated according to the
MANUFACTURER’S recommendations. The warm-up time shall be chosen according to the
recommendation of the MANUFACTURER. The operating conditions shall be the same as those
intended for clinical use including the frame rate and shall be maintained during evaluation as
required for the specific tests described herein.
DIGITAL X-RAY IMAGING DEVICE is operated
Ambient climatic conditions in the room where the
shall be stated together with the results.
4.2 X-RAY EQUIPMENT
For all tests described in the following subclauses, a CONSTANT POTENTIAL HIGH-VOLTAGE
GENERATOR shall be used (IEC 60601-2-7). The PERCENTAGE RIPPLE shall be equal to, or less
than, 4.
The NOMINAL FOCAL SPOT VALUE (IEC 60336) shall be not larger than 1,2.
For the measuring of AIR KERMA, calibrated RADIATION METERS shall be used. The uncertainty
(coverage factor 2) [2] of the measurements shall be less than 5 %.
NOTE 1 “Uncertainty” and “coverage factor” are terms defined in the ISO/IEC Guide to the expression of
uncertainty in measurement [2].
NOTE 2 RADIATION METERS to read AIR KERMA are, for instance, calibrated by many national metrology institutes.
4.3 RADIATION QUALITY
The RADIATION QUALITIES shall be one or more out of four selected RADIATION QUALITIES
specified in IEC 61267:1994 (see Table 1). If only a single RADIATION QUALITY is used,
RADIATION QUALITY RQA5 should be preferred.
For the application of the RADIATION QUALITIES, refer to IEC 61267:1994.
NOTE 1 Although a more recent edition of IEC 61267 is available, this standard will keep its reference to
IEC 61267:1994 for reasons of harmonization within the IEC 62220 family. In addition, IEC 61267:2005 puts severe
requirements on the practical realization of the RADIATION QUALITIES. These requirements are not necessary for the
intended use in this standard.
According to IEC 61267:1994, RADIATION QUALITIES are defined by a fixed ADDITIONAL FILTRATION and a
NOTE 2
HALF-VALUE LAYER that is realized with this filtration by a suitable adaptation of the X-RAY TUBE VOLTAGE, starting
from the approximate X-RAY TUBE VOLTAGE (Table 1).

62220-1-3 © IEC:2008 – 11 –
Table 1 – RADIATION QUALITY (IEC 61267:1994) for the determination
of DETECTIVE QUANTUM EFFICIENCY and corresponding parameters
Approximate
RADIATION HALF-VALUE ADDITIONAL
X-RAY TUBE
QUALITY No. LAYER (HVL) FILTRATION
VOLTAGE
mm Al mm Al
kV
RQA 3 50 4,0 10,0
RQA 5 70 7,1 21,0
RQA 7 90 9,1 30,0
RQA 9 120 11,5 40,0
NOTE 3 The additional filtration is the filtration added to the inherent filtration of the X-RAY TUBE.
NOTE 4 The capability of X-RAY GENERATORS to produce low AIR KERMA levels may not be sufficient, especially for
RQA9. In this case, it is recommended that the distance FOCAL SPOT to DETECTOR SURFACE be increased.
4.4 TEST DEVICE
The TEST DEVICE for the determination of the MODULATION TRANSFER FUNCTION shall consist of a
1,0 mm thick tungsten plate (purity higher than 90 %) 100 mm long and at least 75 mm wide
(see Figure 1). Inadequate purity of tungsten shall be compensated by increased thickness.
The tungsten plate is used as an edge TEST DEVICE. Therefore, the edge which is used for the
test IRRADIATION shall be carefully polished straight and at 90° to the plate. If the edge is
irradiated by X-rays in contact with a screenless film, the image on the film shall show no
ripples on the edge larger than 5 μm.
The tungsten plate shall be fixed on a 3 mm thick lead plate (see Figure 1). This arrangement
is suitable to measure the MODULATION TRANSFER FUNCTION of the DIGITAL X-RAY IMAGING
DEVICE in one direction.
– 12 – 62220-1-3 © IEC:2008
3 mm
Pb (2)
b
W (1)
X-ray
a
e
b
c
1 mm
d
f
IEC  840/08
NOTE The TEST DEVICE consists of a 1,0 mm thick tungsten plate (1) fixed on a 3 mm thick lead plate (2).
Dimension of the lead plate: a: 200 mm, d: 70 mm, e: 90 mm, f: 100 mm.
Dimension of the tungsten plate: 100 mm × 75 mm.
The region of interest (ROI) used for the determination of the MTF is defined by b × c, 50 mm × 100 mm (inner long
dashed line).
The irradiated field on the detector (outer dashed line) is at least 160 mm × 160 mm.
Figure 1 – TEST DEVICE
4.5 Geometry
The geometrical set-up of the measuring arrangement shall comply with Figure 2. The X-RAY
EQUIPMENT is used in that geometric configuration in the same way as it is used for normal
diagnostic applications. The distance between the FOCAL SPOT of the X-RAY TUBE and the
DETECTOR SURFACE should be not less than 1,50 m. If, for technical reasons, the distance
cannot be 1,50 m or more, a smaller distance can be chosen but has to be explicitly declared
when reporting results.
The REFERENCE AXIS shall be aligned with the CENTRAL AXIS.
The TEST DEVICE is placed immediately in front of the DETECTOR SURFACE. The centre of the
edge of the TEST DEVICE should be aligned to the REFERENCE AXIS of the X-ray beam.
Displacement from the REFERENCE AXIS will lower the measured MTF. The REFERENCE AXIS can
be located by maximizing the MTF as a function of TEST DEVICE displacement.

62220-1-3 © IEC:2008 – 13 –
The recommended procedure is that the TEST DEVICE and the X-ray field be centred on the
detector. If this is not done, the position of the centre of the X-ray field and of the TEST DEVICE
needs to be stated.
In the set-up of Figure 2, the DIAPHRAGM B1 and the ADDED FILTER shall be positioned near the
FOCAL SPOT of the X-RAY TUBE. The diaphragms B2 and B3 should be used, but may be
omitted if it is proven that this does not change the result of the measurements. The
DIAPHRAGMS B1 and - if applicable - B2 and the ADDED FILTER shall be in a fixed relation to the
position of the FOCAL SPOT. The DIAPHRAGM B3 - if applicable - and the DETECTOR SURFACE
shall be in a fixed relation at each distance from the FOCAL SPOT. The square DIAPHRAGM B3 –
if applicable – shall be 120 mm in front of the DETECTOR SURFACE and shall be of a size to
allow an irradiated field at the DETECTOR SURFACE of at least 160 mm × 160 mm. The
RADIATION APERTURE of DIAPHRAGM B2 may be made variable so that the beam remains tightly
DETECTOR SURFACE shall be
collimated as the distance is changed. The irradiated field at the
at least 160 mm × 160 mm.
The attenuating properties of the DIAPHRAGMS shall be such that their transmission into
shielded areas does not contribute to the results of the measurements. The RADIATION
APERTURE of the DIAPHRAGM B1 shall be large enough so that the PENUMBRA of the RADIATION
BEAM will be outside the sensitive volume of the monitor detector R1 and the RADIATION
APERTURE of DIAPHRAGM B2 – if applicable.
A monitor detector should be used to assure the precision of the X-RAY GENERATOR. The
monitor detector R1 may be inside the beam that irradiates the DETECTOR SURFACE if it is
suitably transparent and free of structure; otherwise, it shall be placed outside of that portion of
the beam that passes aperture B3. The precision (standard deviation 1σ) of the monitor detector
shall be better than 2 %. The relationship between the monitor reading and the AIR KERMA at
the DETECTOR SURFACE shall be calibrated for each RADIATION QUALITY used (see also 4.6.2).
To minimize the effect of back-scatter from layers behind the detector, a minimum distance of
500 mm to other objects should be provided.
NOTE The calibration of the monitor detector may be sensitive to the positioning of the ADDED FILTER and to the
adjustment of the shutters built into the X-RAY SOURCE. Therefore, these items should not be altered without re-
calibration of the monitor detector.
This geometry is used either to irradiate the DETECTOR SURFACE uniformly for the
determination of the CONVERSION FUNCTION and the NOISE POWER SPECTRUM or to irradiate the
DETECTOR SURFACE behind a TEST DEVICE (see 4.6.6). For all measurements, the same area of
the DETECTOR SURFACE shall be irradiated. The centre of this area, with respect to either the
centre or the border of the digital X-ray detector, shall be recorded.
All measurements shall be made using the same geometry.
For the determination of the NOISE POWER SPECTRUM and the CONVERSION FUNCTION, the TEST
DEVICE shall be moved out of the beam.

– 14 – 62220-1-3 © IEC:2008
B1
ADDED FILTER
Monitor detector R1
B2
1,5 m min.
B3
TEST DEVICE
120 mm
DETECTOR SURFACE
IEC  841/08
NOTE The TEST DEVICE is not used for the measurement of the CONVERSION FUNCTION and the NOISE POWER
SPECTRUM.
Figure 2 – Geometry for exposing the DIGITAL X-RAY IMAGING DEVICE in order to determine
the CONVERSION FUNCTION, the NOISE POWER SPECTRUM and the MODULATION TRANSFER
FUNCTION behind the TEST DEVICE
4.6 IRRADIATION conditions
4.6.1 General conditions
The calibration of the digital X-ray detector shall be carried out prior to any testing, i.e., all
operations necessary for corrections according to Clause 5 shall be effected. The whole
series of measurements shall be done without re-calibration. Offset calibrations are excluded
from this requirement. They can be performed as in normal clinical use.
The AIR KERMA level shall be chosen as that used when the digital X-ray detector is operated
for the intended use in clinical practice. This is called the “normal“ level. At least two
additional AIR KERMA levels shall be chosen, one 3,2 times the normal level and one at 1/3,2 of
the normal level. No change of settings of the DIGITAL X-RAY IMAGING DEVICE (such as gain etc.)
shall be allowed when changing AIR KERMA levels within one Imaging Mode.
NOTE A factor of three in the AIR KERMA above and below the “normal” level approximately corresponds to the
bright and dark parts within one clinical radiation image.

62220-1-3 © IEC:2008 – 15 –
Depending on the intended clinical use of the digital X-ray detector, one or more of the
following Imaging Modes with their corresponding “normal” levels shall be chosen:
Imaging Mode1, Fluoroscopy “normal” level 20 nGy ± 10 %
Imaging Mode2, Cardiac imaging “normal” level 200 nGy ± 10 %
Imaging Mode3, Series exposures “normal” level 2 000 nGy ± 10 %
For each Imaging Mode, the settings of the DIGITAL X-RAY IMAGING DEVICE shall be kept
constant. When another Imaging Mode is selected, other settings of the DIGITAL X-RAY IMAGING
DEVICE may be chosen and shall be kept constant while staying in that Imaging Mode.
Additional “normal” levels may be chosen.
The variation of AIR KERMA shall be carried out by variation of the X-RAY TUBE CURRENT or the
IRRADIATION TIME or both. The IRRADIATION TIME level shall be similar to the conditions for
clinical application of the digital X-ray detector.
The IRRADIATION conditions shall be stated together with the results (see Clause 7).
The RADIATION QUALITY shall be assured when varying the X-RAY TUBE CURRENT or the
IRRADIATION TIME and shall be checked at the lowest AIR KERMA level.
4.6.2 AIR KERMA measurement
The AIR KERMA at the DETECTOR SURFACE is measured with an appropriate RADIATION METER.
For this purpose, the digital X-ray detector is removed from the beam and the RADIATION
DETECTOR of the RADIATION METER is placed behind APERTURE B3 in the DETECTOR SURFACE
plane. Care shall be taken to minimize the back-SCATTERED RADIATION. The correlation
between the readings of the RADIATION METER and the monitoring detector, if used, shall be
noted, and shall be used for the AIR KERMA calculation at the DETECTOR SURFACE when
irradiating the DETECTOR SURFACE to determine the CONVERSION FUNCTION, the NOISE POWER
SPECTRUM and the MODULATION TRANSFER FUNCTION. In this standard a large number of images
shall be exposed. It is therefore recommended to measure the accumulated AIR KERMA
including the stabilization images (see 4.6.5) and divide this value by the number of exposed
images.
NOTE 1 To reduce back-SCATTERED RADIATION, a lead screen of 4 mm in thickness may be placed 450 mm behind
the RADIATION DETECTOR. It has been proven by experiments that, under these conditions, the back-SCATTERED
RADIATION is not more than 0,5 %. If the lead screen is at a distance of 250 mm, the back-SCATTERED RADIATION is
not more than 2,5 %.
If it is not possible to remove the digital X-ray detector out of the beam, the AIR KERMA at the
DETECTOR SURFACE may be calculated via the inverse square distance law. For that purpose,
the AIR KERMA is measured at different distances from the FOCAL SPOT in front of the DETECTOR
SURFACE. For this measurement, radiation, back-scattered from the DETECTOR SURFACE, shall
be avoided. Therefore, a minimum distance between the DETECTOR SURFACE and the
RADIATION DETECTOR of 450 mm is recommended.
If a monitoring detector is used, the following equation shall be plotted as a function of the
distance d between the FOCAL SPOT and the RADIATION DETECTOR:
monitor detector reading
f (d) =
radiation detector reading
By extrapolating this approximately linear curve up to the distance between the FOCAL SPOT
and the DETECTOR SURFACE r , the ratio of the readings at r can be obtained and the AIR
SID SID
KERMA at the DETECTOR SURFACE for any monitoring detector reading can be calculated.

– 16 – 62220-1-3 © IEC:2008
If no monitoring detector is used, the square root of the inverse RADIATION METER reading is
plotted as a function of the distance between the FOCAL SPOT and the RADIATION DETECTOR.
The extrapolation etc. is carried out as in the preceding paragraph.
NOTE 2 To reduce back-SCATTERED RADIATION, a lead shield of 4 mm thickness may be placed in front of the
DETECTOR SURFACE.
4.6.3 LAG EFFECTS
LAG EFFECTS influence the measurement of the NOISE POWER SPECTRUM. They therefore,
influence the measurement of the DETECTIVE QUANTUM EFFICIENCY.
As LAG EFFECTS will be inherently present during normal clinical use, the digital X-ray detector
shall be operated as in normal clinical use. LAG EFFECTS will be separately determined and the
estimated NOISE POWER SPECTRUM will be corrected for these effects yielding the LAG EFFECT
corrected NOISE POWER SPECTRUM. No separate image acquisitions are necessary for
measuring the LAG EFFECT, it will be combined with the image acquisitions as necessary for
determining the NOISE POWER SPECTRUM. See [11, 12 and 13] for more background
information.
4.6.4 IRRADIATION to obtain the CONVERSION FUNCTION
The settings of the DIGITAL X-RAY IMAGING DEVICE shall be the same as those used when
exposing the TEST DEVICE. The IRRADIATION shall be carried out using the geometry of Figure 2
but without any TEST DEVICE in the beam. The AIR KERMA is measured according to 4.6.2. The
CONVERSION FUNCTION shall be determined from AIR KERMA level zero up to four times the
normal AIR KERMA level.
The CONVERSION FUNCTION for AIR KERMA level zero shall be determined from a dark image,
realized under the same conditions as an X-ray image. The minimum X-ray AIR KERMA level
shall not be greater than one-fifth of the normal AIR KERMA level.
Depending on the form of the CONVERSION FUNCTION, the number of different exposures varies;
if only the linearity of the CONVERSION FUNCTION has to be checked, five exposures, uniformly
distributed within the desired range, are sufficient. If the complete CONVERSION FUNCTION has
to be determined, the AIR KERMA shall be varied in such a way that the maximum increments
of logarithmic (to the base 10) AIR KERMA is not greater than 0,1. The RADIATION QUALITY for all
AIR KERMA levels shall be assured and shall be checked at the lowest AIR KERMA level. In case
of deviations from this requirement, the FOCAL SPOT to DETECTOR SURFACE distance may have
to be increased.
4.6.5 IRRADIATION for determination of the NOISE POWER SPECTRUM and LAG EFFECTS
The settings of the DIGITAL X-RAY IMAGING DEVICE shall be the same as those used when
exposing the TEST DEVICE. The IRRADIATION shall be carried out using the geometry of Figure 2
but without any TEST DEVICE in the beam. The AIR KERMA is measured according to 4.6.2.
A square area of approximately 125 mm × 125 mm located centrally behind the 160 mm
square DIAPHRAGM is used for the evaluation of an estimate for the NOISE POWER SPECTRUM to
be used later on to calculate the DQE.
For this purpose, the set of input data shall consist of at least N consecutive non-exposed
IM
images and N consecutive exposed images each having at least 256 PIXELS in either spatial
IM
direction in the area used for the evaluation of the NOISE POWER SPECTRUM. All individual
images shall be taken at the same RADIATION QUALITY and AIR KERMA. The image acquisition
sequence is shown in Figure 3.
N is defined as the number of images. It shall be at least 64 and shall always be a power of
IM
2.
62220-1-3 © IEC:2008 – 17 –
To avoid transient effects both non-exposed and exposed images are preceded by additional
i
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