ISO 9236-1:2004

INTERNATIONAL ISO
STANDARD 9236-1
Second edition
2004-02-01


Photography — Sensitometry of
screen/film systems for medical
radiography —
Part 1:
Determination of sensitometric curve
shape, speed and average gradient
Photographie — Sensitométrie des ensembles film/écran pour la
radiographie médicale —
Partie 1: Détermination de la forme de la courbe sensitométrique, de la
sensibilité et du contraste moyen




Reference number
ISO 9236-1:2004(E)
©
ISO 2004

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ISO 9236-1:2004(E)
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ISO 9236-1:2004(E)
Contents Page
Foreword. iv
Introduction . v
1 Scope. 1
2 Normative references . 1
3 Terms and definitions. 1
4 General requirements. 2
4.1 Storage and handling conditions. 2
4.2 Safelights . 2
4.3 X-ray equipment . 3
4.4 Air kerma meter. 3
4.5 Processing. 3
4.6 Densitometry . 4
5 Determination of sensitometric curve shape. 4
5.1 General. 4
5.2 Beam qualities. 5
5.3 Geometry for curve shape determination. 5
5.4 Exposure. 8
5.5 Evaluation . 8
6 Determination of average gradient. 8
7 Determination of speed . 10
7.1 Definition. 10
7.2 Beam qualities. 10
7.3 Geometry . 13
7.4 Exposure. 13
7.5 Evaluation . 13
8 Speed and average gradient determination without sensitometric curve. 16
9 Uncertainty . 16
10 Test report . 17
Annex A (informative) Rationale .18
Bibliography . 20




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ISO 9236-1:2004(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies
(ISO member bodies). The work of preparing International Standards is normally carried out through ISO
technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
Attention is drawn to the possibility that some of the elements of this document may be the subject of patent
rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 9236-1 was prepared by Technical Committee ISO/TC 42, Photography.
This second edition cancels and replaces the first edition (ISO 9236-1:1996), which has been technically
revised to incorporate the following technical and major editorial changes:
 a spherical ionization chamber, or an equivalent detector, is required for dosimetry;
 only high frequency or 12-pulse high-voltage generators are allowed, 6-pulse high-voltage generators are
excluded;
 the allowed uncertainty for the density measurement has been increased in order to comply with the other
parts of the ISO 9236 series;
 the exposure times for the determination of speed and sensitometric curve shape have been reduced to
match the current state of the art;
 the phantom of Technique IV has been changed (leaving the beam quality unchanged) in order to reduce
the air kerma rate;
 the distances between the focal spot of the x-ray tube and the screen-film combination when determining
speed and average gradient may now be in the range from 1,5 m to 4,0 m;
 the use of a monitoring detector is no longer mandatory, because the precision of modern x-ray tubes and
high-voltage generators is often superior to that of monitoring detectors;
 the total uncertainty which can be reached has been changed;
 an informative annex has been added in order to describe the background of speed and curve shape
measurements, the choice of phantoms, and the energy dependence of speed values.
ISO 9236 consists of the following parts, under the general title Photography — Sensitometry of screen/film
systems for medical radiography:
 Part 1: Determination of sensitometric curve shape, speed and average gradient
 Part 3: Determination of sensitometric curve shape, speed and average gradient for mammography
The following part is under preparation:
 Part 2: Method for determining modulation transfer function (MTF)
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ISO 9236-1:2004(E)
Introduction
This part of ISO 9236 provides methods for determining the sensitometric curve shape, the average gradient
and the speed of radiographic screen/film/filmholder/processing systems used in medical radiography, except
in mammography and dental radiography.
The sensitometric curve shape, which is also needed for the determination of other properties (as, for
example, the modulation transfer function), is measured under low scatter conditions via intensity scale X-ray
sensitometry, preferably using an inverse square sensitometer. For the determination of the sensitometric
curve shape, as well as for a subsequent determination of the average gradient from the measured curve, but
not for speed, the irradiation of the screen/film/filmholder combination need to be measured only in relative
units.
Speed is measured in a separate way, under exposure conditions which simulate medical practice more
closely, including realistic fractions of scattered radiation. Different types of medical exposures are simulated
by using appropriate phantoms and X-ray tube voltages, and the screen/film/filmholder combination is
exposed behind the respective phantom. The irradiation is measured in absolute units of air kerma (gray, Gy)
in order to determine the speed.
Four different techniques are defined, differing in beam quality and fraction of scattered radiation, simulating
the imaging of extremities, skull, lumbar spine and colon, and chest. Speed may be measured for each
technique of interest. Owing to its dependence on X-ray energy and scatter, screen/film system speed varies
widely in medical practice. The four measurement conditions described in this part of ISO 9236 provide values
that are representative of those found under practical conditions.
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INTERNATIONAL STANDARD ISO 9236-1:2004(E)

Photography — Sensitometry of screen/film systems for
medical radiography —
Part 1:
Determination of sensitometric curve shape, speed and average
gradient
1 Scope
This part of ISO 9236 specifies methods for the determination of the sensitometric curve shape, average
gradient and speed of a single sample of a screen/film/filmholder/processing system for medical radiography.
It is not applicable to special radiographic applications such as mammography, dental radiography and direct-
[3]
exposing medical radiographic systems (see for example ISO 5799 ).
The filmholder can be any means that ensures close screen/film contact and prevents the film from being
exposed to ambient light. In particular, the filmholder can be a light-tight vacuum bag, as often used in the
laboratory, or a radiographic cassette as used in medical radiography.
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.
ISO 5-2:2001, Photography — Density measurements — Part 2: Geometric conditions for transmission
density
ISO 5-3:1995, Photography — Density measurements — Part 3: Spectral conditions
ISO 554:1976, Standard atmospheres for conditioning and/or testing — Specifications
IEC 60522:1999, Determination of the permanent filtration of X-ray tube assemblies
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
screen/film system
radiographic imaging system consisting of screen(s), film, filmholder and film processing
NOTE Hereafter, screen/film/filmholder combinations will be referred to as “combinations” and will be referred to as
“systems” when the processing is included.
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ISO 9236-1:2004(E)
3.2
air kerma
K
sum of the initial kinetic energies of all charged particles (e.g., electrons) liberated by uncharged particles
(e.g., X-ray photons) from air molecules, divided by the mass of air in that volume where the charged particles
are liberated
NOTE The unit is the gray (Gy).
3.3
sensitometric curve
plot of the density of a processed photographic film as a function of the logarithm to the base 10 of the
exposure
3.4
speed
S
quantitative measure of the response of the screen/film system to radiant energy for the specified conditions
of exposure, processing and density measurement
3.5
average gradient
G

slope of the straight line joining two specified points on a sensitometric curve
3.6
net density
D
density of an exposed and processed film minus the density of an unexposed and processed sample of that
film
3.7
coverage factor
k
numerical factor, used as a multiplier of the combined standard uncertainty in order to obtain an expanded
uncertainty
[8]
NOTE The coverage factor is explained in the Guide to the expression of uncertainty in measurement . Its value is
typically in the range of 2 to 3. The coverage factor is chosen based on the level of confidence desired. A coverage factor
(k) of 2 generally will result in a level of confidence of approximately 95 %, and a coverage factor of 3 generally will result
in a level of confidence of approximately 99 %. This association of confidence level and coverage factor is based on an
assumption regarding the probability distribution of measurement results.
4 General requirements
4.1 Storage and handling conditions
The film and screens shall be stored according to the manufacturer's recommendations. Before and during
exposures, the temperatures of the films and screens shall be maintained at 23 °C ± 2 °C (see ISO 554) and
the moisture content of the film shall be such that it will be in equilibrium at a relative humidity of (50 ± 20) %.
4.2 Safelights
To eliminate the possibility of safelight illumination affecting the sensitometric results, all films shall be kept in
total darkness during handling, exposure and processing.
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ISO 9236-1:2004(E)
4.3 X-ray equipment
For all tests described in this part of ISO 9236, high frequency (multipulse) high voltage generators or at least
12-pulse high voltage generators shall be used.
For all tests described in this part of ISO 9236, X-ray tubes equipped with fixed anodes or rotating anodes
may be used. In either case, the target material shall be tungsten or a tungsten-based alloy.
NOTE 1 The target is that part of the anode onto which the electron beam is directed to produce X-radiation. For
technological reasons it is common practice to use alloys of tungsten with up to 10 % rhenium for the target, while other
parts of the anode can consist of other materials (e.g. molybdenum).
The permanent filtration of the X-ray tube and its housing, as defined in IEC 60522, shall be equivalent to
2,5 mm ± 0,2 mm of aluminium.
NOTE 2 The permanent filtration of the X-ray tube and its housing is effected by permanently fixed materials
intercepting the X-ray beam, which are not intended to be removed for any application. As the permanent filtration is
usually stated on the X-ray tube housing and in the accompanying documents, its measurement, as described in
IEC 60522, is not necessary.
4.4 Air kerma meter
For the air kerma measurement, calibrated detectors shall be used. The uncertainty of air kerma
measurement (level of confidence 95 %) shall be less than 3 % for collimated beams without scatter, and less
than 5 % for radiation measurements behind the phantom when scattered radiation is included.
3 3
A spherical ionization chamber of 30 cm to 100 cm volume should be used for measurements where
scattered radiation is involved. The chamber shall be calibrated for the beam qualities given in Table 2,
including scattered radiation. The centre of the spherical chamber is to be considered the reference point; the
stem of the spherical chamber should point in a direction opposite to the radiation source.
NOTE During calibration of the air kerma meter and during usage, scattered radiation originating not from the
phantom but from, for example, the stem of the chamber, can be minimized in order to meet the specified uncertainty
requirement.
4.5 Processing
Screen/film systems, including either manual or automatic processing, may be tested in accordance with this
part of ISO 9236. Processing should be carried out in accordance with the film manufacturer's
recommendations. Nothing shall be construed to require the disclosure of proprietary information.
No processing specifications are described in this part of ISO 9236 in recognition of the wide range of
chemicals and equipment used. Speed and average gradient values provided by film manufacturers generally
apply to the system when the film is processed in accordance with their recommendations so that the
photographic characteristics specified for the process are produced. Processing information shall be provided
by the film manufacturer or others who quote speed and average gradient values and shall specify the
processing chemicals, times, temperatures, agitation, equipment and procedures used for each of the
processing steps, and any additional information required to obtain the sensitometric results described. The
values for speed and average gradient obtained using other processing procedures may differ significantly.
The processing conditions selected by a person using this part of ISO 9236 are, in any case, part of the
system being tested.
NOTE 1 Different speeds for a particular film can be achieved by varying the processes. However, these variations to
the processes can cause other undesirable changes.
In order to minimize any effects due to latent-image instability or process variability, all film samples shall be
processed together, neither less than 30 min nor more than 4 h after exposure. Between exposure and
processing, the temperature of the film shall be maintained at 23 °C ± 2 °C and its moisture content shall be
such that the film will be in equilibrium at a relative humidity of (50 ± 20) %.
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ISO 9236-1:2004(E)
Since films are generally processed in practice a few minutes after exposure, the speed observed in practice
may differ from that determined by this part of ISO 9236 due to latent-image fading of some films. Therefore,
the speed measured with a time delay of 30 min to 4 h between exposure and processing shall be corrected
to the value one would obtain if the film were processed soon after exposure. For the purposes of this part of
ISO 9236, a time delay of 5,0 min is used for computing speed.
NOTE 2 One means of obtaining the information about the necessary correction is by exposing film strips in a light
sensitometer and varying the time between exposure and processing. In this case, both front and back emulsions are
exposed equally by the sensitometer.
NOTE 3 Since the time required for the many individual exposures to obtain the sensitometric curve is comparatively
long, a time delay of at least 30 min between exposure and processing is necessary. This time delay is considered to be
sufficient to minimize any differences in latent-image fading for the individual exposures.
The following processing information and accuracies shall be specified:
a) trade designations of all chemicals, if proprietary; otherwise, the formulae;
b) temperature of the developer to within ± 0,3 °C;
c) temperature of other solutions to within ± 2 °C;
d) immersion times in the developer, fix and washing solutions to within the greater of 3 % or 1 s; these
times shall be measured from the time the leading edge enters the solution until the leading edge exits
the solution;
e) whether the developer is fresh or “seasoned” (if “seasoned”, the type and amount of film used for
seasoning), the density of the processed film and the replenishment procedure;
f) agitation specifications, in terms of volume of solution recirculated or rate at which a gas is used, if used
at all;
g) drying temperature to within ± 5 °C and drying time within the greater of 3 % or 1 s; the drying time shall
be measured from the time the leading edge enters this stage until the leading edge exits this stage;
h) trade designation of processing equipment.
NOTE 4 The term “seasoned developer” means that the developer is no longer unused or fresh, but is already used
and in a “normal working condition”.
4.6 Densitometry
ISO standard visual diffuse transmission density of the processed images shall be measured using a
densitometer complying with the geometric conditions specified in ISO 5-2 and spectral conditions specified in
ISO 5-3. Readings shall be made in a uniform area of the image. The optical density shall be measured such
that the expanded uncertainty U (level of confidence 95 %) associated with the result of measurement D, is
U = 0,02, or that the relative expanded uncertainty is U/D = 0,02, whichever is the greater.
5 Determination of sensitometric curve shape
5.1 General
In this part of ISO 9236, intensity scale sensitometry is used to determine curve shape. The intensity is
modified according to the inverse-square law by a change of the distance between the radiation source and
the combination. As a consequence of filters and other secondary radiation sources in the beam, the
relationship between exposure and distance may not obey the inverse-square law. Therefore that relationship
shall be calibrated.
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ISO 9236-1:2004(E)
5.2 Beam qualities
For the determination of the sensitometric curve shape, any of the four beam qualities specified in Table 1
may be used. The beam qualities can be achieved by an iterative procedure of half-value layer (HVL)
measurements using the specified added filtration. The approximate X-ray tube voltages are recommended as
starting values for this procedure (see 7.2.6).
Table 1 — Beam qualities for the determination of the sensitometric curve shape
Beam quality Approximate X-ray Half-value layer

b
Added filtration
a
number tube voltage HVL
kV mm Al mm Al mm Cu + mm Al
I 50 3,0 5,0 0,10 + 1,5
II 70 5,7 12,0
0,25 + 2,5
III 90 7,4 13,0 0,25 + 3,5
IV 120 8,5 10,0 0,20 + 2,5
a
The tolerance for the HVL is ± 2 %.
b
The added filter, consisting of copper plus aluminium, is an alternative to that filter, which consists of aluminium only. The
aluminium used as filter material shall have a purity of at least 99,4 % and the copper a purity of at least 99,5 %. If a mixed filter is used,
the last layer towards the detectors shall be aluminium. The inherent tube filtration is assumed to correspond to 2,5 mm of aluminium.

5.3 Geometry for curve shape determination
The measurement geometry shall comply with Figures 1 and 2. The diaphragm B1 and the added filter(s) shall
be positioned near the radiation source. The diaphragms B1 and B2 and the added filter(s) shall be in a fixed
relation to the radiation source. The diaphragm B3 and the screen/film/filmholder combination or the radiation
detector R2 shall be in a fixed relation to each other at each distance from the radiation source. The incident
face of diaphragm B3 shall be 100 mm in front of the plane of the radiographic film. If it has been confirmed
that scattered radiation from walls, equipment, etc. does not influence the results, the diaphragm B3 may be
omitted. To this end, the radiation aperture of diaphragm B2 may be made variable so that the beam remains
tightly collimated as distance is changed.
A diaphragm B4, whose shortest dimension shall be at least 15 mm, may be positioned directly in front of the
combination in order to limit the area of the exposure.
The attenuating properties of the diaphragms shall be such that their transmission into shielded areas does
not contribute to the results of the measurements by more than 0,1 %. 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 monitoring detector R1 and the radiation aperture of diaphragm B2.
The radiation aperture of diaphragm B2 shall be smaller than 100 mm; that of B3 shall have a diameter of
100 mm ± 10 mm.
A monitoring detector R1 may be inside the beam that exposes the combination if it is suitably transparent and
free of structure, otherwise it shall be placed outside the beam. The precision of the monitoring detector shall
be better than ± 2 %.
An attenuating protective barrier shall be at least 450 mm beyond the last area involved in the measurement.
The space between the combination or the radiation detector R2 (see Figures 1 and 2) and the protective
barrier shall contain nothing but air.
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ISO 9236-1:2004(E)
Dimensions in metres

Key
1 beam diaphragms 3 monitoring detector (R1)
2 added filter 4 film plane
5 lead shield
D variable distance
Figure 1 — Geometric set-up of the inverse-square-law sensitometer
for exposure of the screen/film combination
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ISO 9236-1:2004(E)
Dimensions in metres

Key
1 beam diaphragms
2 added filter
3 monitoring detector (R1)
4 measuring detector (R2)
5 lead shield
D variable distance
Figure 2 — Geometric set-up for calibration of the inverse-square-law sensitometer
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ISO 9236-1:2004(E)
5.4 Exposure
Each exposure of the combination shall be achieved in one uninterrupted irradiation. The exposure time shall
be in the range (15 ± 5) ms to (60 ± 30) ms and shall be kept constant for all exposures.
NOTE 1 With the use of intensifying screens, reciprocity law failure and the intermittency effect can occur. In order to
avoid the influence of these effects, a single irradiation with a constant irradiation time in the specified range of irradiation
times is necessary for each exposure.
The different values of air kerma shall be obtained exclusively by varying the distance from the radiation
source to the plane of the radiographic film, with the exposure time and all other conditions of exposure
constant. The increments of logarithmic (to the base 10) exposure shall not be greater than 0,1.
For determination of the sensitometric curve, 20 different exposures or more shall be made, equally
distributed on a logarithmic scale, that produce net densities from 0,1 to at least 2,1. To define accurately the
curve at low densities, at least three exposures producing net densities between 0,1 and 0,25 shall be made.
The time interval between the different exposures should not exceed 30 s, but shall not exceed 2 min.
NOTE 2 An automated procedure such as that described in reference [4] in Bibliography can be used to manage the
operation of moving the filmholder, changing the distance and verifying the monitor reading within the time period.
If one wishes to determine the shape of the sensitometric curve at much higher densities than 2,1 and the
required intensity increase is not possible via decrease of distance, the exposure should be increased by an
increase of the tube current, but it shall be verified that the higher tube current does not change the beam
quality.
5.5 Evaluation
The density is plotted against the corresponding logarithmic (to the base 10) air kerma values. Through the
points, a smooth curve is drawn either by han
...