ISO 9236-1:1996
(Main)Photography — Sensitometry of screen/film systems for medical radiography — Part 1: Determination of sensitometric curve shape, speed and average gradient
Photography — Sensitometry of screen/film systems for medical radiography — Part 1: Determination of sensitometric curve shape, speed and average gradient
Methods for the determination of the sensitometric curve shape, average gradient and speed of a single sample of a screen/film/filmholder system in medical radiography. Does not apply for special radiographic applications such as mammographie and dental radiography.
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
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INTERNATIONAL
STANDARD
First edition
1996-l l-01
Photography - Sensitometry of
screen/film systems for medical
radiography -
Part 1:
Determination of sensitometric curve shape,
speed and average gradient
Photographie - Sensitom&rie des ensembles film/&ran pour la
radiographie mgdicale -
Partie 7: Dktermination de la forme de la courbe sensitom&rique, de la
sensibilit6 et du con traste moyen
Reference number
IS0 9236-l : 1996(E)
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Foreword
IS0 (the International Organization for Standardization) is a worldwide
federation of national standards bodies (IS0 member bodies). The work of
preparing International Standards is normally carried out through IS0
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. IS0
collaborates closely with the International Electrotechnical Commission
(IEC) on all matters of electrotechnical standardization.
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.
International Standard IS0 9236-l was prepared by Technical Committee
ISO/TC 42, Photography.
IS0 9236 consists of the following parts, under the general title
Photography - Sensitome try of screen/film sys terns for medical
radiography:
- Part I: Determination of sensitometric curve shape, speed and
average gradient
- Part 2: Determination of the modulation transfer function (MTF)
- Part 3: Mammography
Annex A of this part of IS0 9236 is for information only.
0 IS0 1996
Ail rights reserved. Unless otherwise specified, no part of this publication may be
reproduced or utilized in any form or by any means, electronic or mechanical, including
photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case Postale 56 l CH-1211 Geneve 20 l Switzerland
Printed in Switzerland
ii
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@ IS0 IS0 9236=1:1996(E)
This part of IS0 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, 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. Since it is
unlikely that the curve shape will be energy dependent within the kilovolt
range covered by this part of IS0 9236, any one of the four beam qualities
corresponding to those used for speed determination may be used for
determining curve shape. For the determination of the sensitometric curve
shape, the irradiation of the screen/fiIm/fiImhoIder combination need be
measured only in relative units.
While the average gradient is determined from the sensitometric curve
shape, speed must be measured in a separate way, since the exposure
conditions should simulate as closely as possible those which are used in
practice. Therefore, scattered radiation is included, accompanied by a
slight change of beam quality compared to the beam quality used for
intensity scale sensitometry. The exposure is simulated by using
appropriate phantoms and tube voltages. The screen/fiIm/filmholder
combination is exposed behind the phantom. The exposure is measured in
absolute units (gray, Gy) in order to determine the speed.
Speed is generally dependent on X-ray energy and the amount of
scattered radiation emerging from the patient. Therefore, a wide variety of
speed values may be expected under practical conditions. The four
measurement conditions described in this part of IS0 9236 provide values
for speed and average gradient which are representative of those found
under practical conditions.
Four different techniques are offered, differing in beam quality and fraction
of scattered radiation. These techniques simulate four different scenarios
of the practice: imaging extremities; skull; lumbar spine and colon; and
chest. Speed may be measured for each technique of interest.
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INTERNATIONAL STANDARD @ IS0 IS0 92364:1996(E)
Sensitometry of screen/film systems for medical
Photography -
radiography -
Part 1:
Determination of sensitometric curve shape, speed and average gradient
1 Scope
This part of IS0 9236 specifies methods for determination of the sensitometric curve shape, average gradient and speed
of a single sample of a screen/film/filmholder/processing system in medical radiography. Special radiographic applications
such as mammography, dental radiography and direct-exposing medical radiographic systems (see for example IS0 5799)
are excluded.
The filmholder may be any means which ensures close screen/film contact and prevents the film from being
exposed to ambient light. In particular, the filmholder may be a light-tight vacuum bag, as often used in the
laboratory, or a radiographic cassette as used in medical radiography.
NOTE - Hereafter, screen/fiIm/filmholder combinations will be referred to as “combinations” and will be referred to as
“systems” when the processing is included.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this part
of IS0 9236. At the time of publication, the editions indicated were valid. All standards are subject to revision, and
parties to agreements based on this part of IS0 9236 are encouraged to investigate the possibility of applying the
most recent editions of the standards indicated below. Members of IEC and IS0 maintain registers of currently
valid International Standards.
IS0 5-2: 1991, Photography - Density measurements - Part 2: Geometric conditions for transmission density.
IS0 5-3: 1995, Photography - Density measurements - Part 3: Spectral conditions.
IS0 554: 1976, Standard atmospheres for conditioning and/or testing - Specifications.
3 Definitions
For the purposes of this part of IS0 9236, the following definitions apply.
3.1 air kerma, K: That energy which is transferred by ionizing radiation (for instance X-rays) to air molecules
divided by the mass of air in that volume where the energy is released. The unit is the gray (Gy).
3.2 sensitometric curve: Plot of the density of a processed photographic film as a function of the logarithm of
the exposure.
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@ IS0
IS0 9236=1:1996(E)
3.3 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.
3.4 average gradient, G: The slope of the straight line joining two specified points on a sensitometric curve.
3.5 net density, D: Density of an exposed and processed film minus the density of an unexposed and processed
sample of that film.
4 General requirements
4.1 Storage and handling conditions
The film and screens shall be stored according to the manufacturers recommendations. Before and during
exposures, the temperatures of the films and screens shall be maintained at 23 “C & 2 “C (see IS0 554) and the
moisture content of the film shall be such that it will be in equilibrium at a relative humidity of (50 k 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.
43 . X-ray equipment
For all tests described in this part of IS0 9236, a 6-pulse, 12-pulse or a high frequency (multipulse) generator shall
be used.
For the dose measurement, calibrated detectors shall be used. The accuracy of readings shall be better than + 5 %
for collimated beams without scatter, and better that + 7 % for radiation measurements behind the phantom when
scattered radiation is included.
NOTE - A spherical ionization chamber is recommended for measurements where scattered radiation is involved. 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 focus direction. If a cylindrical chamber is used, the ratio of diameter to height should be at least 4 to 1.
4.4 Processing
Screen/film systems, including either manual or automatic processing, may be tested in accordance with this part
of IS0 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 IS0 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,
temperatures, agitation, equipment and procedures used for each of the processing steps, and any
times,
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 IS0 9236 are, in any case, part of the system being tested. Different speeds for a
particular film may be achieved by varying the processes, but the user should be aware that other changes may
accompany the speed 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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0 IS0 IS0 9236=1:1996(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 IS0 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 IS0 9236, a time
delay of 5,0 min is used for computing speed.
NOTES
1 The information about the necessary correction may easily be gained by exposing film strips in a light sensitometer and
varying the time between exposure and processing. Care should be taken that both front and back emulsions are exposed
equally by the sensitometer.
2 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 required. 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:
trade designations of all chemicals, if proprietary; otherwise, the formulae;
a)
temperature of the developer to within k 0,3 “C;
b)
d temperature of other solutions to within + 2 “C;
immersion times in the developer solution to within 3 %I;
d)
whether the developer is fresh or “seasoned” (if “seasoned”, the type and amount of film used for
e)
seasoning), the density of the processed film and the replenishment procedure;
agitation specifications, in terms of volume of solution recirculated or rate at which a gas is used;
f 1
drying temperature to within + 5 “C;
9)
trade designation of processing equipment.
h)
NOTE - The term “seasoned developer” means that the developer is no longer unused or fresh, but is already used and in a
“normal working condition”.
4.5 Densitometry
IS0 standard visual diffuse transmission density of the processed images shall be measured using a densitometer
complying with the geometric conditions specified in IS0 5-2 and spectral conditions specified in IS0 5-3. Readings
shall be made in a uniform area of the image. The densities, D, shall be measured with an accuracy of
AD/D = rf: 0,Ol or m = t O,Ol, whichever is the greater.
5 Determination of sensitometric curve shape
In this part of IS0 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.
5.1 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 7.2.5 and figure 5).
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IS0 9236=1:1996(E)
Table 1 - Beam qualities for the determination of the sensitometric curve shape
1) The tolerance for the HVL is k 2 %.
The aluminium used as filter material shall have a purity of at least 99,4 % and the copper a purity of at least
NOTE -
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.
5.2 Geometry for curve shape determination
The geometrical set-up of the measuring arrangement shall comply with figures 1 and 2. The diaphragm Bl and the
added filter(s) shall be positioned near the radiation source. The diaphragms Bl and B2 and the added filter(s) shall
be in a fixed relation to the radiation source. The diaphragm B3 and the screen/fiIm/fiImhoIder combination or the
radiation detector R2 shall be in a fixed relation 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 84, 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,l %. The radiation aperture of the diaphragm Bl
shall be large enough so that the penumbra of the radiation beam will be outside the sensitive volume of the
monitoring detector RI 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
100mm~10mm.
A monitoring detector RI 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 adiation detector R2 and the protective barrier shall contain nothing but air.
5.3 Exposure
Each exposure of the combination shal be achieved in one uninterrupted irradiation. The exposure time shall be in
the range 20 ms +_ 10 ms to 200 ms & 100 ms and shall be kept constant for all exposures.
NOTE - With the use of intensifying screens, reciprocity law failure and the intermittency effect may 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
required 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
maximum increments of log exposure shall not be greater than 0,l.
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IS0 9236-l :1996(E)
Dimensions in metres
vag
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