BACKGROUND OF THE INVENTION
[0001] The incidence of breast cancer carcinoma among women continues to increase, posing
a serious health problem throughout the world. The mortality rate from breast cancer
can be decreased significantly by early detection using the radiological mammography
technique. With this technique the compressed breast is irradiated with soft X-rays
emitted from an X-ray generating device and modulated X-rays are detected with a radiographic
X-ray conversion screen, also called intensifying screen, fluorescent screen or phosphor
screen. The X-ray conversion screen comprises a luminescent phosphor which converts
the absorbed X-rays into visible light and the emitted visible light exposes a silver
halide film that is brought into contact with said X-ray conversion screen. After
film processing, comprising the steps of developing, fixing, rinsing and drying, a
mammogram is obtained which can be read on a light box.
[0002] No other field of medical radiology demands such a high level of image quality as
mammography and the ability of the mammogram to portray relevant diagnostic information
is highly determined by the image quality of the screen-film system. Image quality
is manifested by a number of features in the image including sharpness, noise, contrast,
silver image colour and skin line perceptibility. It is common practice to set the
amount of X-ray exposure so that the tissues on the inside of the breast are depicted
at medium optical density values, i.e. in the optical density range from [Dmin+1.0]
to [Dmin+2.5], Dmin being defined as the [base+fog]-density obtained after processing
the unexposed film, and the diagnostic perceptibility of small, potentially malignant
lesions in these tissues is highly determined by the contrast of the mammography film
within said density range. A quantitative measure of the film contrast is the so-called
average gradation, defined as the slope of the line drawn by connecting both points
of the sensitometric curve of optical density vs. logarithmic exposure at which the
optical density is equal to [Dmin+1.0] and [Dmin+2.5].
[0003] Conventional mammography films can roughly be classified in low and high contrast
types according to the value of their average gradation as defined above. The low
contrast type can be characterized by a relatively low average gradation ranging from
2.0 to 2.5, whereas the average gradation of the high contrast type may range from
3.0 to 3.5. Often, high contrast films are preferred because of the higher ability
to detect tiny cancers deep in the glandular tissue of the breast. If the contrast
is too high, however, it may preclude visualization of both thin (i.e. the skin line)
and thick tissues (i.e. the inside of the breast) in the same image due to lack of
exposure latitude. Therefore, some radiologists prefer low contrast mammography films.
When the contrast is low, skin line perceptibility is excellent, but then the chance
of missing possibly malignant breast lesions is high. Thus a balance has to be found
between contrast and exposure latitude and an example of this approach is described
in US-A 5,290,665.
[0004] In order to extend the exposure latitude some manufacturers have introduced high
contrast mammography films characterized by a higher maximum density (hereinafter
referred to as Dmax) than conventional high contrast films, e.g. a Dmax equal to at
least 3.7, preferably even higher than 4.0. However, a film characterized by a higher
"Dmax" is only a minor improvement with regard to better skin line perceptibility,
since the background density is too high for the skin line to be clearly visible.
Indeed at optical density values above 3.5, the local gradient, i.e. the slope of
the sensitometric curve, must be very high in order to guarantee a reasonable perceptibility
as described in the well-known article titled "Determination of optimum film density
range for röntgenograms from visual effect" by H. Kanamori (Acta Radiol. Diagn. Vol.4,
p. 463, 1966). Nevertheless, processed mammography films showing a higher maxmum density
are appreciated by a growing number of radiologists because of the wider dynamic range,
i.e., the density range [Dmax-Dmin] of the mammogram.
[0005] To summarize: it remains difficult to obtain mammograms with high contrast and high
maximum density, moreover clearly depicting thin tissue such as the skin line of the
breast. Some improvements have been obtained by modifying the X-ray generating device,
such as the scanning mammography system described in US-A 5,164,976. These solutions
however require the replacement of the conventional X-ray apparatus by a completely
new system with a much higher technical complexity. Maintaining the image quality
constant is becoming another requirement of facilities performing mammography. Accordingly,
quality control tests are executed on a regular basis in order to monitor the consistency
of the performance of the X-ray equipment, the image receptors and the film processor.
To minimize the influence of varying film processing time, temperature, chemistry
and replenishment, a preferred mammography film requires a stable speed and contrast
with respect to these processing parameters.
[0006] In addition, there is a general trend in the field of radiology to shorten the film
processing time and likewise in the field of mammography, the interest has focused
on rapid access of mammograms. As a consequence mammography films are preferred which
comprise silver halide crystals that can be processed rapidly and consistently in
a dry-to-dry processing cycle of 90 seconds or less and therefore, most mammography
films today comprise good developable cubic silver halide crystals. As described in
EP-A 0 712 036, such cubic crystals show a stable speed and contrast upon varying
processing parameters. Cubic emulsions however are characterized by a very high contrast,
resulting in a poor skin line perceptibility. On the other hand tabular silver halide
emulsion crystals, also being rapidly processable, are characterized by a much lower
contrast than cubic silver halide emulsions and thus are only applicable for manufacturing
low contrast mammography films. Another drawback of these tabular emulsions is the
residual color after processing: due to the larger specific area of the tabular grains
compared e.g. with cubic crystals having the same crystal volume, these tabular grains
require higher amounts of spectrally sensitizing dye(s), which may leave dye stain
after the short processing cycle. Also the brownish color of the developed silver
image of thin tabular grains, resulting in an undesired image tone, is a disadvantage
for mammography making use of the said tabular grains.
[0007] Nowadays most of the single-side coated film materials for mammography have an amount
of coated silver halide, expressed as an equivalent amount of silver nitrate, in the
range from 6.0 up to less than 8.5 g/m2. A disadvantage related with such high coating
amounts is the presence of high amounts of coated gelatin, present as protective colloid
of the silver halide crystals and as hydrophilic binder of the coated layers, which
results in absorption of high amounts of water at one side of the support and long
drying times in the processing. A high pressure sensitivity as coated minimum amounts
of hydrophilic colloidal binder are envisaged on one hand and questionable archivability
as a consequence of long fixing times, shortened in order to provide ending processing
within shortened rapid processing cycles at the other hand, clearly lay burden on
the most critical feature in mammography, being "image quality", and more particularly
"sharpness".
[0008] As mammographic and similar soft tissue imaging medical diagnostic films are coated
in a single-sided format in order to maximize image sharpness and uniformity, higher
rates of rapid access processing finding increasing use in processing dual-coated
radiographic films are questionable. A first attempt has been made by Luckey et al,
US-A 4,710,637 in order to provide mammographic film in dual-coated format. However
this film was ultimately rejected by radiologists as failing to provide images of
acceptably high sharpness and low mottle. No medical diagnostic radiographic film
for imaging soft tissue, such as mammographic film, has heretofore been available
combining high levels of image sharpness and uniformity and the capability of accelerated
rates of rapid access processing attainable with dual-coated radiographic films. Another
attempt has been made in US-A 5,759,754, wherein it was a purpose to maintain acceptably
high levels of image sharpness and low levels of mottle. In one aspect that invention
was directed to a radiographic film for recording medical diagnostic images of soft
tissue through
(a) exposure by a single intensifying screen located to receive an image bearing source
of X-radiation and
(b) processing, including development, fixing and drying, in 90 seconds or less comprised
of a transparent film support (transparent to radiation emitted by the intensifying
screen) and having opposed front and back major faces and an image-forming portion
for providing, when imagewise exposed by the intensifying screen and processed, an
average contrast in the range of from 2.5 to 3.5, measured over a density above fog
of from 0.25 to 2.5, wherein the image-forming portion is comprised of (i) a processing
solution permeable front layer unit coated on the front major face of the support
capable of absorbing up to 60 percent of the exposing radiation and containing less
than 3 g/m2 of hydrophilic colloid and less than 3g/m2 silver in form of radiation-sensitive
silver halide grains, and (ii) a processing solution permeable back layer unit coated
on the back major face of the support containing less than 4 g/m2 of hydrophilic colloid,
silver in the form of radiation-sensitive silver halide grains accounting for from
40 to 60 percent of the total radiation-sensitive silver halide present in the film,
and a dye capable of providing an optical density of at most 0.40 in the wavelength
region of the exposing radiation intended to be recorded and an optical density of
less than 0.1 in the visible spectrum at the conclusion of film processing. In a preferred
embodiment said radiation-sensitive silver halide grains in the front and back layer
units were provided by a tabular grain silver halide emulsion containing more than
70 mole % of bromide and less than 4 mole % of iodide, based on the total amount of
silver present. Another attempt has been proposed in US-A 6,037,112 wherein part of
the density of the exposed film after processing, more particularly in the high-density
region, has been built-up by silver, generated by reducing thin tabular silver halide
emulsion crystals, coated in the backing layer. Said tabular grains or crystals having
an average thickness of less than 0.3 µm and an average aspect ratio of more than
5:1 provide high covering power. Apart from the resulting brownish-red colour of the
processed thin tabular grains, which is clearly observed in reflectance, the morphological
difference between cubic crystals at the front side of the support, exposed in contact
with the intensifying screen, and the thin tabular grains present at the side of the
backing layer, lays burden on sensitometrical consistency when making use of developer
and fixer solutions having differing or varying compositions.
OBJECTS OF THE INVENTION
[0009] It is therefore a first object of the present invention to provide a photographic
material for mammography which is not only characterized by a high diagnostic quality,
a large dynamic range and a high contrast so that small lesions deep in the glandular
tissue are accurately detected without disturbing sites or strikes, present as a consequence
of pressure sensitivity of the coated silver halide emulsion crystals, but which moreover
clearly depicts thin tissue such as the skin line of the breast.
[0010] It is another object of the present invention to provide a photographic material
comprising silver halide emulsion crystals which are rapidly processable, more particularly
with respect to a reduced drying time, and to provide a neutral silver image color
without leaving residual sensitizing dye after processing.
[0011] It is still another object of the present invention to guarantee perfect archivability
of the images obtained, by complete fixation of the processed image within a short
processing time cycle of at most 120 seconds, and, more preferably, within a time
cycle of 90 seconds dry-to-dry.
[0012] It is even a further object of the present invention to provide a radiological method
using the photographic material according to the present invention for obtaining a
suitable diagnostic image for mammography in differing developer compositions, in
that an optimized sensitometric profile is attained in strongly differing processing
conditions.
[0013] Further objects and advantages of this invention, which may be obtained by specific
embodiments, will become apparent from the description hereinafter.
SUMMARY OF THE INVENTION
[0014] In order to fully reach the objects of the present invention, a radiographic film
material has been provided for recording medical diagnostic images of soft tissue
through exposure to light, emitted by a single intensifying screen, after having been
subjecting to exposure with X-rays, emitted from an X-ray generating device with a
tube voltage of 20 kV to 40 kV, and processing, including development, fixing and
drying, within a time of 120 seconds (and more preferably 90 seconds or less), wherein
said film is comprised of a transparent film support, front and back major faces and
an image-forming portion for providing, when imagewise exposed by light emitted by
said intensifying screen and processed, an average contrast or gradient in the range
from 3.0 up to 4.5, measured over a density above fog in the range of from 0.25 to
2.00, and wherein said image-forming portion is comprised of layer units permeable
for aqueous processing solutions, said layer units being
- a hydrophilic front layer unit (unit more close to the intensifying screen during
exposure to X-rays) coated on the said front major face of the support wherein the
front layer unit is capable of reaching a maximum density of more than 3.00;
- a hydrophilic back layer unit (unit farther from the intensifying screen during exposure
to X-rays) coated on the said back major face of the support; wherein sensitivity
(speed), measured at a density of 0.50 above fog, is higher for the front layer unit
than for the back layer unit in an amount of from 0.70 up to 1.70 log (Exposure) [differences
calculated before and after washing off the backing layer unit from the material,
processed after exposure to X-rays of the said material, being in intimate contact
with an intensifying screen at the front layer side thereof] ;
characterized in that both the front layer unit and the back layer unit have one
or more light-sensitive silver halide emulsion layer(s) coated with emulsion crystals,
essentially having a cubic crystal habit.
[0015] A process for obtaining a medical diagnostic image of soft tissue is further claimed,
said process comprising the steps of
mounting a radiographic film as claimed adjacent to a single intensifying screen,
exposing the intensifying screen to an image pattern of X-radiation that has passed
through the soft tissue to provoke light emission by the intensifying screen that
imagewise exposes the radiographic film, and
processing the radiographic film, including development, fixing and drying in less
than 120 (and more preferably 90) seconds.
DETAILED DESCRIPTION OF THE INVENTION
[0016] As has been disclosed in the statement of the present invention a radiographic film
for recording medical diagnostic images of soft tissue, and more in particular for
mammographic applications, is thus characterized by the presence, at both sides of
a transparent film support, of light-sensitive silver halide emulsion layers, wherein
the silver halide emulsions essentially have cubic emulsion crystals. The term "essentially
cubic" is indicative for the presence, in an amount of at least 90, more preferably
at least 95 and even more preferably at least 99 % by number of crystals having a
{100} crystal habit and thus (100) crystal faces, wherein edges may be sharp or rounded-off
(e.g. due to preparation methods wherein silver solubilizing growth accelerators are
used such as ammonia or methionine, a thioether compound, thazolidine-2-thione, tetra-substituted
thiourea, potassium or ammonium rhodanide and an amine compound may be present during
grain precipitation in order to adjust the average grain size) and wherein it is even
not excluded that cubo-octaeders are present, provided that (111) crystal faces therein
represent not more than 10 %, more preferably not more than 5 % and even more preferably
not more than 1 % of the total projective area of all crystal faces present, and wherein
(100) faces are clearly representing the majority of the crystal faces present in
the emulsions. The class of so-called cubic grains embraces (a) perfectly cubic crystals,
or (b) cubic crystals with rounded corners, or (c) cubic crystals with small (111)
faces at the corners (also known as tetradecahedrical grains), the total area of these
(111) faces however being small compared to the total area of the (100) faces. Presence
of cubo-octahedral shapes which are not excluded depends on the pAg values applied
during the precipitation. So preferred methods for the precipitation of cubic grains
are the pAg-balanced double- or triple-jet methods as described in EP-A's 0 712 036
and 0 610 609, since these methods provide monodispersed emulsions characterized by
a narrow grain size distribution defined in that at least 95 % by weight or number
of the grains have a diameter within about 40 %, preferably within about 30 % of the
average grain size and more preferably within about 10% to 20%. The variation coefficient
of the emulsion grains according to this invention has preferably a low value of between
0.15 and 0.20, and still more preferably of 0.10, said variation coefficient being
defined as the ratio between the standard deviation of the grain size and the average
grain size. This is particularly desired as a high contrast is envisaged for the mammographic
image after processing of the material according to the present invention. The silver
halide grains are obtained by conventional precipitation techniques which are well
known in the art and consist of the addition of aqueous solutions of silver and halide
salts, e.g. silver nitrate and sodium, potassium or ammonium halide to a solution
comprising a protective colloid. In order to get controlled growth use is often made
of variable flow rates in order to provide (and controll) crystal growth to be performed
at a higher rate and to perform precipitation in more concentrated reaction vessels
which may even lead to variability coefficients over the grain distributions in the
range from 0.10 up to 0.20. It may however be recommended, in favour of fine-tuning
desired gradations at differing densities or sensitivity points of the sensitometric
curve, to have a broader emulsion grain distribution. Apart for growing the cubes
in a reaction vessel at slightly higher pAg values, it is also possible and, in favour
of addition of other ingredients - such as chemical and spectral sensitizers - to
more uniform crystals, even recommended to prepare the most suitable cubic grain emulsion
from more than one chemically and spectrally sensitized emulsion having a very narrow
grain distribution. This is recommended more particularly for the light-sensitive
emulsion layer in the back layer unit, which, in favour of skin line perceptibility,
should contribute to the total density of the processed material, wherein the back
layer unit should exhibit an optical density of at least 1.00 in the wavelength region
of the exposing radiation.
[0017] The grain size of the cubic grain emulsions can be determined using conventional
techniques, e.g. as described by Trivelli and Smith, The Photographic Journal, vol.
69, 1939, p.330-338, Loveland "ASTM symposium on light microscopy" 1953, p.94-122
and Mees and James "The Theory of the photographic process" (1977), Chapter II.
[0018] According to the present invention the material is coated with light(radiation)-sensitive
emulsion layers having cubic emulsion grains in the front and in the back layer unit,
wherein the radiation-sensitive silver halide grains are containing more than 50 mole
% of silver bromide and less than 3 mole % of silver iodide, more preferably less
than 2 mole % based on total molar silver amounts. In a more preferred embodiment
the said radiation-sensitive silver halide grains are silver bromide or silver bromoiodide
grains, containing up to at most 1 mole % of silver iodide, based on silver. Differences
in silver iodide content, if present, between front and back layer units, are preferably
directed to a lower iodide content in the back layer unit, in that less than 1 mole
% of iodide, and more preferably about 0.5 mole % of iodide is present, based on silver.
Silver iodide present in lower amounts than silver bromide can be distributed in a
homogeneously (continuously) or heterogeneously (for so-called "core-shell emulsions"
having a core wherein iodide concentrations are lower or higher than in the shell
or shells adjacent thereto). In another embodiment pure silver bromide cubes may still
be "doped" with silver iodide by application of the so-called "conversion"-technique,
wherein silver iodide is formed by conversion at the grain surface after addition
of organic or inorganic compounds relasing iodide ions, such as potassium iodide or
the iodide releasing compounds described in EP-A's 0 563 701, 0 563 708 and 0 651
284. In still another embodiment silver iodide is added in form of ultrafine silver
iodide grains of about 0.050 µm or even smaller (also called "micrate emulsions")
after stopping precipitation in the precipitation method or after having ended precipitation,
so that silver iodide is located at dedicated sites in the cubic grains.
[0019] Precipitation of silver halide crystals suitable for use in emulsion layers according
to the present invention is performed in the presence of a protective, hydrophilic
colloid, which should be chosedn with care: e.g. conventional lime-treated or acid
treated gelatin can be used, but also oxidized gelatin (generally known as gelatin
having less than 30 p.p.m. of methionine) or a synthetic peptizer. The preparation
of such modified gelatin types has been described in e.g. "The Science and Technology
of Gelatin", edited by A.G. Ward and A. Courts, Academic Press 1977, page 295 and
next pages. The gelatin may also be an enzyme-treated gelatin as described in Bull.
Soc. Sci. Phot. Japan, No. 16, page 30 (1966). Before and during formation of the
silver halide grains it is common practice to establish a gelatin concentration of
from about 0.05 % to 5.0 % by weight in the dispersion medium. Cubic silver halide
grains may also be precipitated in absence of gelatin, e.g. by making use of colloidal
silica as a protective colloid in the presence of an onium compound, as described
in EP-A's 0 677 773 and 0 649 051; or in the alternative by making use of cationic
oxidized starch as has been disclosed e.g. in EP-A 0 758 759.
[0020] At the end of the precipitation the emulsion is made free from excess of soluble
inorganic salts by a conventional washing technique e.g. flocculation by ammonium
sulphate or polystyrene sulphonate, followed by one or more washing and redispersion
steps.
[0021] Conventional washing techniques can be found in Research Disclosure, Item 38957,
Section III. Emulsion washing.Another well-known washing technique is ultrafiltration
as described e.g. in EP-A 0 794 455. Finally, in order to prepare the emulsion for
further sensitization actions extra gelatin or another binder material can be added
to the emulsion in order to obtain a gelatin to silver ratio wherein the emulsion
remains colloidally stable during said further actions. So in order to enhance speed
of the cubic silver halide emulsion grains chemical sensitization is applied thereto
according to the procedures described in e.g. "Chimie et Physique Photographique"
by P. Glafkides, in "Photographic Emulsion Chemistry" by G.F. Duffin, in "Making and
Coating Photographic Emulsion" by V.L. Zelikman et al, and in "Die Grundlagen der
Photographischen Prozesse mit Silberhalogeniden" edited by H.Frieser and published
by Akademische Verlagsgesellschaft (1968). As described in the above mentioned literature,
chemical sensitization can be carried out by effecting the ripening in the presence
of small amounts of compounds containing sulphur,selenium or tellurium e.g. thiosulphate,
thiocyanate, thiourea, selenosulphate, selenocyanate, selenoureas, tellurosulphate,
tellurocyanate, sulphites, mercapto compounds, and rhodamines. In a preferred embodiment,
these compounds or combinations thereof are applied in combination with a noble metal
salt, preferably a gold complex salt, but also salts of platinum, palladium and iridium
as described in US-A 2,448,060 and GB-A 618,061 may be used. Description of chemical
sensitization techniques can be found in Research Disclosure, Item 38957, Chapter
IV. The amount of gold, used in the chemical ripening of emulsions according to the
present invention, is preferably in the range of 25 to 45 p.p.m. vs. the amount of
metallic silver. Additions of sulphur and/or selenium and/or tellurium and gold may
be carried out consecutively or simultaneously. In the latter case the addition of
goldthiosulphate, goldselenosulphate or goldtellurosulphate compounds may be recommended.
Optionally, small amounts of dopants in form of complexing agents of Rh, Ru, Os, Pt
or Ir, can be added if not yet performed in the course of grain precipitation in order
to get grain occlusions other than silver and halide as disclosed in Research Disclosure,
Item 38957, Section I; or in more general terms of transition metal hexacoordination
complexes as dopants for increasing imaging speed by providing or as so-called SET's
(shallow electron trapping agents as described in Research Disclosure, Vol. 367, Nov.
1994, Item 36736. Also reductors may be added as chemical sensitizers as e.g. tin
compounds as described in GB-A 789,823, amines, hydrazine derivatives, formamidine-sulphinic
acids, and silane compounds. The chemical sensitization can also proceed in the presence
of phenidone and/or its derivatives, a dihydroxybenzene as hydroquinone, resorcinol,
catechol and/or a derivative(s) thereof, one or more stabilizer(s) or antifoggant(s),
one or more spectral sensitizer(s) or combinations of said ingredients.
[0022] The silver halide emulsions may be chemically sensitized according to the procedures
described in e.g. "Chimie et Physique Photographique" by P. Glafkides, in "Photographic
Emulsion Chemistry" by G.F. Duffin, in "Making and Coating Photographic Emulsion"
by V.L. Zelikman et al, and in "Die Grundlagen der Photographischen Prozesse mit Silberhalogeniden"
edited by H. Frieser and published by Akademische Verlagsgesellschaft (1968). As described
in the above mentioned literature, chemical sensitization can be carried out by effecting
the ripening in the presence of small amounts of compounds containing sulphur,selenium
or tellurium e.g. thiosulphate, thiocyanate, thiourea, selenosulphate, selenocyanate,
selenoureas, tellurosulphate, tellurocyanate, sulphites, mercapto compounds, and rhodamines.
[0023] In a preferred embodiment, these compounds or combinations thereof are applied in
combination with a noble metal salt, preferably a gold complex salt, but also salts
of platinum, palladium and iridium as described in US-A 2,448,060 and 5,759,760 and
in GB-A 618,061 may be used. Amounts of gold, used in the chemical ripening of emulsions
in order to get the most preferred contrast in the toe portion of the sensitometric
curve have been disclosed e.g. in EP-A's 0 610 609 and 0 712 036. Additions of sulphur
and/or selenium and/or tellurium and gold may be carried out consecutively or simultaneously.
In the latter case the addition of goldthiosulphate, goldselenosulphate or goldtellurosulphate
compounds may be recommended. Optionally, small amounts of compounds (complexing agents)
of Rh, Ru, Os or Ir can be added. Also reductors may be added as chemical sensitizers
as e.g. tin compounds as described in GB-A 789,823, amines, hydrazine derivatives,
formamidine-sulphinic acids, and silane compounds. The chemical sensitization can
also proceed in the presence of phenidone and/or its derivatives, a dihydroxybenzene
as hydroquinone, resorcinol, catechol and/or a derivative(s) thereof, one or more
stabilizer(s) or antifoggant(s), one or more spectral sensitizer(s) or combinations
of said ingredients.
[0024] The silver halide grains present in a mammography film are spectrally sensitized
in order to optimally detect the light emitted from the X-ray conversion screen. A
preferred mammography film is characterized by a spectral sensitivity ranging from
5 to 130 µJ/m
2 measured at the emission maximum of the X-ray conversion screen, said spectral sensitivity
being defined herein as the amount of exposure to light of a given wavelength required
to obtain an optical density Dmin + 1.0 after processing. The silver halide emulsion
are spectrally sensitized by adding one or several cyanine dyes, merocyanine dyes,
complex, cyanine dyes, complex merocyanine dyes, hemicyanine dyes, styryl dyes and
hemioxonol dyes. Preferred examples of suitable orthochromatic (J-aggregating) spectral
sensitizers are 5,5'-dichloro-3,3'-bis(SO3-R)-9-ethylbenzoxacarbo-cyanines with R
being n-propylene or n-butylene. Furthermore green-light absorbing spectral sensitizers
according to the formulae given in JP-A's 06-35104, 06-35101, 06-35102, 62-191847,
63-249839, 01-312536, 03-200246, US-A's 4,777,125 and DE 3,819,241 may be used. The
right choice of said sensitizers or combinations thereof is always related to the
goal of attaining the highest possible photographic speed while reducing dye stain
after processing. Another survey of useful chemical classes of spectral sensitizers
has been given by F.M. Hamer in "The Cyanine Dyes and Related Compounds", 1964, John
Wiley & Sons. A more recent disclosure has been given in EP-A 0 757 285. Techniques
in order to perform optimized spectral sensitization have been described in Research
Disclosures, Item 18431, Section X and Item 38957, Section V.
[0025] The silver halide grains present in a mammography film are spectrally sensitized
in order to optimally detect the light emitted from the X-ray conversion screen. A
preferred mammography film is characterized by a spectral sensitivity ranging from
5 to 130 µJ/m
2 measured at the emission maximum of the X-ray conversion screen, said spectral sensitivity
being defined herein as the amount of exposure to light of a given wavelength required
to obtain an optical density Dmin + 1.0 after processing.
[0026] It is clear that in the present invention the light-sensitive emulsion layers at
both sides of the transparent support, which is typically a blue coloured polyethylene
terephtalate (PET) film having a thickness of 175 µm, are not symmetrically coated:
according to the present invention the radiographic material is coated with a hydrophilic
front layer unit coated on the front major face of the support (to be contacted with
the sole intensifying screen when exposed to "soft" X-rays, generated from a device
with a tube voltage of 20 kV to 40 kV, as is typical for mammographic applications)
wherein the front layer unit is capable of reaching a maximum density of more than
3.00, and even more preferably more than 3.5, after processing and wherein sensitivity
(speed), measured at a density of 0.50 above fog, is higher for the front layer unit
than for the back layer unit in an amount of from 0.70 up to 1.70 log (Exposure) and
in a more preferred embodiment the back layer unit has a speed ranging from 1.00 log
E to 1.50 log E slower than the front layer unit.
[0027] So according to a preferred embodiment the front layer is coated with cubic silver
halide emulsion crystals in an amount, expressed as equivalent amount of silver nitrate,
of less than 8.5 g/m2 and more preferably in the range from 6.0 to 7.0 g/m2, but always
more than 4.0 g/m2. The radiation-sensitive cubic silver halide emulsion grains therein
have an average grain size in the range of from 0.45 µm up to 0.85 µm. Coating amounts
of hardenable hydrophilic colloid, composing the front layer unit are, in a preferred
embodiment, limited to less than 5.0 g/m2 and, more preferably to less than 4.0 g/m2,
and coating amounts of non-hardenable hydrophilic colloid are limited to less than
60 weight % thereof; in order to provide the desired sensitometric and drying properties
within the short running time (within 120 seconds, and more preferably less than 90
seconds) of the processing cycle as will be described hereinafter.
[0028] In order to provide the desired speed difference between the front layer unit and
the back layer unit, the said back layer unit is coated with radiation-sensitive cubic
silver halide grains accounting for less than 40 % (but not less than 1/5) of the
total radiation-sensitive silver halide present in the film, preferably in an amount
of not more than 3 g/m2, expressed as equivalent amount of silver nitrate, wherein
said cubic grains having an average grain size in the range from 0.40 up to 0.60 µm.
The hydrophilic backing layer unit coated on the back major face of the support further
contains hardenable hydrophilic colloid limited to less than 4.0 g/m2, (more preferably
in the range from 2.0 up to 3.0 g/m2) and non-hardenabe hydrophilic colloid limited
to less than 60 weight % thereof.
[0029] A total amount of silver halide coated in the material (sum of coating amounts at
both sides for both - front and back - layer units), expressed as equivalent amount
of silver nitrate again, should be in the range from 6.0 up to 10.0 g/m2.
[0030] In favour of attaining that speed difference the image-forming portion in the material
according to the present invention is, as a consequence of its composition, as disclosed
hereinbefore, further comprised of a hydrophilic front layer unit coated on the front
major face of the support capable of absorbing up to at least 60 %, and more preferably
even more than 70 %, of the exposing radiation.
[0031] The cubic grains in the back layer unit, exhibiting a speed that ranges from 0.3
log E to 1.0 log E slower than in the front layer unit, provide facilitating visualization
of anatomical features in the region of the skin-line. Said "E" stands for "Exposure"
and speed (sensitivity) is measured at a density of 1.0 above fog for the front as
well as for the back layer unit.
[0032] In a preferred embodiment according to the present invention, hardenable hydrophilic
colloid in the whole back layer unit should be limited to less than or at most 3.0
g/m2, and should, more preferably, be situated in the range from 2.0 to 2.5 g/m2,
whereas in the whole front layer unit it should be limited to less than 4.0 g/m2,
more preferably be situated in the range from 3.5 to 3.9 g/m2.
[0033] In the back layer unit the non-hardenabe hydrophilic colloid, the presence of which
is preferably limited to the light-sensitive emulsion layer thereof, should be limited
to less than 10 wt %, but more than 5 wt %, versus the total amount of hardenable
hydrophilic colloid present in the whole back layer unit.
[0034] Opposite thereto in the front layer unit the non-hardenabe hydrophilic colloid is
present in the light-sensitive emulsion layer thereof in an amount of more than 50
wt % and even up to 60 wt %, versus the amount of hardenable hydrophilic colloid present
in the light-sensitive layer, which means that in the whole front layer unit the said
non-hardenable hydrophilic colloid is present in an amount of about 30 wt% (preferably
in the range from 25 up to 35 wt%).
[0035] With respect to the terminology "whole back layer unit" it is understood that, according
to the present invention, besides the subbed support a density providing layer is
present, situated farther from the said support, and adjacent thereto the emulsion
layer is present, further covered by an outermost protective antistress layer as a
topcoat layer, whereas the terminology "whole front layer unit" is indicative, according
to the present invention, besides the subbed support, for a light-sensitive emulsion
layer adjacent to the said subbed support, and wherein said emulsion layer is covered
by an outermost protective antistress layer as a topcoat layer, wherein this protective
layer must be hardened to an extent in order to avoid scratches due to contact made
with the intensifying screen during exposure.
[0036] With respect to the subbing layers coated directly on the thus provide subbed support,
it is clear that these layers are coated (preferably during stretching the polyester
in order to get the support of the desired thickness) in order to improve the adhesion
of the radiation-sensitive emulsion layer of the front layer unit and the non-radiation
sensitive dye containing layer of the back layer unit to the support.
[0037] In addition an undercoat layer between the emulsion and subbing layer(s) and a protective
layer on top of the emulsion layer(s) is present. Additional non light-sensitive intermediate
layers are optional.
[0038] The layer arrangements of the whole front and back layer units described hereinbefore
should further be constructed in such a way that after processing (inclusive for the
drying step) no curl of the processed film material occurs, as examination of the
image would become more problematic. A solution therefore has been described in EP-Application
No. 00201286.2 filed April 10, 2000.
[0039] In that invention a single-side coated light-sensitive silver halide photographic
film material has been described, comprising, on one side of a subbed support, one
or more light-sensitive silver halide emulsion layer(s) overcoated with an outermost
protective layer; said emulsion layer(s) having silver halide grains dispersed in
binder, wherein said silver halide is coated in a total amount, expressed as an equivalent
amount of silver nitrate of more than 5 g per m
2, a latex polymer present in an amount of less than 30 % by weight versus said binder,
and, at the other side of said support, a backing layer, covered with a protective
outermost layer, characterized in that at least said backing layer is provided in
at least one layer thereof, besides a cross-linked or cross-linkable first binder,
with an organic component as a second binder, wherein said organic component is free
from cross-linking upon reaction with a hardener and wherein said organic component
is a polymer selected from the group consisting of dextran having a molecular weight
of not more than 20000 and polyacrylamide having a molecular weight not more than
20000. Said organic component free from cross-linking upon reaction with a hardener
is present therein in an amount of more than 50 % by weight of a total binder amount
calculated as sum of said first and second binder.
[0040] In the present invention use is thus made again of a first cross-linkable binder,
called hardenable hydrophilic colloid in the present invention and present in amounts
in the front layer unit and in the back layer unit as disclosed hereinbefore, besides
a second binder, called herein "non-hardenable hydrophilic colloid", being a polymer
selected from the group consisting of dextran having an average molecular weight from
1000 up to 100000, polyacrylamide having an average molecular weight from 1000 up
to 100000, polyvinyl-pyrrolidone, polyvinyl alcohol and gelatin of the type which
is free from cross-linking upon reaction with a hardener, more preferably a polymer
selected from the group consisting of dextran having a molecular weight of not more
than 20000 and polyacrylamide having a molecular weight not more than 20000. Amounts
at both sides of the support are differing from those disclosed in the cited EP-Application
as an equilibrium in order to prevent the processed material from curling had to be
sought, due to the presence of light-sensitive emulsion layers at both sides of that
support now, moreover being complicated by the presence of coating amounts of silver
(expressed as equivalent amount of silver nitrate) at both sides, clearly differing
from each other. Apart from differing amounts of coated silver halide, differing total
amounts of hydrophilic polymer at both sides of the support are present in that the
topcoat layer of the front layer unit is coated from an amount of gelatin of about
1.0 up to 1.2 g/m2, corresponding with a coating amount twice as high as coated in
the topcoat layer of the back layer unit, and wherein, even when the "density providing
layer" in the back layer unit contains about 0.5 g/m2 of gelatin amounts of gelatin
in the back layer unit are not exceeding 60 wt% of the total amount of gelatin coated
in the whole front layer unit.
[0041] Therefore amounts of hardener should be added to the respective layer units in order
to get a perfect balance for the material when leaving the processor as a dried film
material bearing the image to be examined. As a consequence amounts of water absorption
before processing should be different at the front layer unit side versus at the back
layer unit side due to the required differences in hardening degrees, but should become
about equal after processing: as dextran is a non-hardenable polymer binder, present
in higher amounts in the emulsion layer(s) of the front layer unit - more than 0.5
g/m2, more preferably more than 1.0 g/m2 and even more preferably more than 1.5 g/m2)
in an amount of about 10 times the amounts in the emulsion layer(s) of the back layer
unit, the highest amounts will leave the photographic material from the front layer
unit during processing, and more particularly during the rinsing step, the better
for dextran having a lower molecular weight (M.W. of 10000 even being more preferred
than a M.W. of 20000; differentiation in M.W. in front and back layer unit moreover
leaving further degrees of freedom in optimizing the layer built-up of the material
of the present invention). After the drying step a processed material without ennoying
curl properties is thus attained thanks to a suitable balance of hydrophilic colloid
gelatin binder in front and back layer unit.
[0042] As a hardenable hydrophilic colloid binder of the layers, gelatin is used as a preferred
polymer binder material, which can be forehardened with appropriate hardening agents
such as those of the epoxide type, those of the ethylenimine type, those of the vinylsulfone
type, e.g. 1,3-vinylsulphonyl-2-propanol or di-(vinylsulphonyl)-methane, vinylsulphonyl-ether
compounds, vinylsulphonyl compounds having soluble groups, chromium salts like e.g.
chromium acetate and chromium alum, aldehydes as e.g. formaldehyde, glyoxal, and glutaraldehyde,
N-methylol compounds as e.g. methylolurea and methyloldimethylhydantoin, dioxan derivatives
e.g. 2,3-dihydroxy-dioxan, active vinyl compounds e.g. 1,3,5-triacryloyl-hexahydro-s-triazine,
active halogen compounds e.g. 2,4-dichloro-6-hydroxy-s-triazine, and mucohalogenic
acids e.g. mucochloric acid and mucophenoxychloric acid. These hardeners can be used
alone or in combination. The binder can also be hardened with fast-reacting hardeners
such as carbamoylpyridinium salts as disclosed in US-A 4,063,952 and with onium compounds
as disclosed in EP-A 0 408 143.
[0043] Topcoat layers present as outermost layers at both sides of the material according
to the present invention have a protective function and are coated from hydrophilic
colloid in an amount of from about 1.1 g/m2 and 0.5 g/m2 in the front and in the back
layer unit respectively, wherein those amounts are not to be considered as being limitative
as amounts differing therefrom may be applied.
[0044] According to the present invention a density providing layer is present as an additional
layer in the back layer unit: situated in a layer farther from the support than the
emulsion layer(s), it represents a layer containing a dye in an amount in order to
provide a density of at most 0.40 (about 0.40 in green light; about 0.30 in white
light) before, and less than 0.10 after processing, due to decolorization of said
dye in an alkaline developer. In a further embodiment the dye exhibits a half peak
absorption bandwidth over the spectral region of peak emission by the intensifying
screen. Accordingly preferred dyes suitable for use in the density providing layer
have been described in EP-A's 0 489 973, 0 586 748, 0 587 229, 0 587 230, 0 656 401,
0 786 497 and 0 781 816, as well in the US-A's corresponding therewith. Especially
preferred is the dye according to the formula (I) hereinafter, the preparation method
of which has been described in US-A 5,344,749.

[0045] Methods in which dye dispersions can be prepared have been described in EP-A's 0
549 486, 0 602 428, 0 724 191, 0 756 201, 0 762 193 and 0 762 194. Examples of typical
so-called ultrafine (less than 1 µm) "solid particle dispersions" and the method of
preparing them can be found in EP-A's 0 299 435, 0 323 729, 0 351 593, 0 387 923,
0 524 498, and in US-A 4,988,611; without however being limited thereto. Said dyes
can also be added in the form of a solid silica particle dispersion as disclosed in
EP-A 0 569 074. Still another technique to obtain ultra fine dye dispersions consists
in acidifying a slightly alkaline coating composition "in situ" just before coating
it onto the supporting layer. Further useful information about dyes having decolorizing
characteristics in alkaline processing solutions can be found in Research Disclosure,
Item 38957, Chapter VIII. Presence of such dye(s) in adapted amounts is not only recommended
to adjust the sensitivity of the different emulsion layers and eventually the required
contrast, but also in order to reduce scattering of exposure radiation and thus to
enhance sharpness.
[0046] Apart from the said dye or dyes providing a density of at most 0.40 in the back layer
unit, the radiographic material according to the present invention has a spectral
sensitivity maximum by the adsorption of spectral sensitizers disclosed hereinbefore,
absorbing light from the phosphors prompt emitting light in the wavelength range from
540 to 555 nm after having been irradiated with X-rays, said maximum corresponding
with an exposure amount from 5 to 130 µJ per m2 required in order to obtain an optical
density of Dmin+1.0 after processing.
[0047] Other dyes, which per se do not have any spectral sensitization activity, or certain
other compounds, which do not substantially absorb visible radiation, can have a supersensitization
effect when they are incorporated together with spectral sensitizing agents into the
emulsion. Suitable supersensitizers are e.g. heterocyclic mercapto compounds containing
at least one electronegative substituent as described e.g. in US-A 3,457,078, nitrogen-containing
heterocyclic ring-substituted aminostilbene compounds as described e.g. in US-A's
2,933,390 and 3,635,721, aromatic organic acid/for-maldehyde condensation products
as described e.g. in US-A 3,743,510 as well as cadmium salts, although nowadays to
be avoided, due to ecological considerations, and azaindene compounds.
[0048] The silver halide emulsions suitable for use in hydrophilic layers of the film material
according to the present invention may also comprise compounds preventing the formation
of a high minimum density or stabilizing the photographic properties during the production
or storage of photographic materials or during the photographic treatment thereof.
Many known compounds may be added as fog-inhibiting agent or stabilizer to the silver
halide emulsion. Suitable examples are i.a. the heterocyclic nitrogen-containing compounds
such as benzothiazolium salts, nitroimidazoles, nitrobenzimidazoles, chlorobenzimidazoles,
bromobenzimidazoles, mercaptothiazoles, mercaptobenzothiazoles, mercaptobenzimidazoles,
mercaptothiadiazoles, aminotriazoles, benzotriazoles (preferably 5-methyl-benzotriazole),
nitrobenzotriazoles, mercaptotetrazoles, in particular 1-phenyl-5-mercapto-tetrazole,
mercaptopyrimidines, mercaptotriazines, benzothiazoline-2-thione, oxazoline-thione,
triazaindenes, tetrazaindenes and pentazaindenes, especially those described by Birr
in Z. Wiss. Phot. 47 (1952), pages 2-58, triazolopyrimidines such as those described
in GB-A 1,203,757, GB-A 1,209,146, JP-B 77/031738 and GB-A 1,500,278, and 7-hydroxy-s-tria-zolo-[1,5-a]-pyrimidines
as described in US-A 4,727,017, and other compounds such as benzenethiosulphonic acid,
benzenethiosulphinic acid and benzenethiosulphonic acid amide. Other compounds which
can be used as fog-inhibiting compounds are those described in Research Disclosure
No. 17643 (1978), Chapter VI; in Research Disclosure, Item 38957, Chapter VII and
in Item 18431, Chapter II. These fog-inhibiting agents or stabilizers may be added
to the silver halide emulsion prior to, during, or after the ripening thereof and
mixtures of two or more of these compounds can be used.
[0049] The photographic material according to the present invention may further comprise
various kinds of surface-active agents in the light-sensitive emulsion layer(s) or
in at least one other hydrophilic colloid layer. Suitable surface-active agents include
non-ionic agents such as saponins, alkylene oxides, e.g., polyethylene glycol, polyethylene
glycol/polypropylene glycol condensation products, polyethylene glycol alkyl ethers
or polyethylene glycol alkylaryl ethers, polyethylene glycol esters, polyethylene
glycol sorbitan esters, polyalkylene glycol alkylamines or alkylamides, siliconepolyethylene
oxide adducts, glycidol derivatives, fatty acid esters of polyhydric alcohols and
alkyl esters of saccharides, anionic agents comprising an acid group such as a carboxyl,
sulpho, phospho, sulphuric or phosphoric ester group; ampholytic agents such as aminoacids,
aminoalkyl sulphonic acids, aminoalkyl sulphates or phosphates, alkyl betaines, and
amine-N-oxides; and cationic agents such as alkylamine salts, aliphatic, aromatic,
or heterocyclic quaternary ammonium salts, aliphatic or heterocyclic ring-containing
phosphonium or sulphonium salts. Such surface-active agents can be used for various
purposes, e.g. as coating aids, as compounds preventing electric charges, as compounds
improving film transport in automatic film handling equipment, as compounds facilitating
dispersive emulsification, as compounds preventing or reducing adhesion, and as compounds
improving photographic properties such as higher contrast, sensitisation and development
acceleration.
[0050] Especially when rapid processing conditions are important, development acceleration
may be useful, which can be accomplished with the aid of various compounds, preferably
polyoxyalkylene derivatives having a molecular weight of at least 400 such as those
described in e.g. US-A's 3,038,805; 4,038,075 and 4,292,400. Especially preferred
developing accelerators are recurrent thioether groups containing polyoxyethylenes
as described in DE 2,360,878, EP-A's 0,634,688 and 0,674,215, which are incorporated
herein by reference. The same or different or a mixture of different developing accelerators
may be added to at least one of the hydrophilic layers at the emulsion side. It may
be advantageous to partially substitute the hydrophilic colloid binder, preferably
gelatin, of the light-sensitive silver halide emulsion layer or of an hydrophilic
colloid layer in water-permeable relationship therewith by suitable amounts of dextran
or dextran derivatives to improve the covering power of the silver image formed and
to provide a higher resistance to abrasion in wet condition.
[0051] The photographic material of the present invention may further comprise various other
additives such as compounds improving the dimensional stability of the photographic
material, UV-absorbers, spacing agents, lubricants, plasticizers, antistatic agents,
etc. as those described in Research Disclosure, Item 38957, Chapter IX, particularly
referring to coating physical property modifying addenda, as coating aids (A), plasticizers
and lubricants (B), antistatic agents (C), and matting agents (D). Suitable additives
for improving the dimensional stability are i.a. dispersions of a water-soluble or
hardly soluble synthetic polymer e.g. polymers of alkyl (meth)acrylates, alkoxy(meth)acrylates,
glycidyl (meth)acrylates, (meth)acrylamides, vinyl esters, acrylo-nitriles, olefins
and styrenes, or copolymers of the above with acrylic acids, methacrylic acids, α-β-unsaturated
dicarboxylic acids, hydroxyalkyl (meth)acrylates, sulphoalkyl (meth)acrylates, and
styrene sulphonic acids.
[0052] Suitable UV-absorbers are e.g. aryl-substituted benzotriazole compounds as described
in US-A 3,533,794, 4-thiazolidone compounds as described in US-A's 3,314,794 and 3,352,681,
benzophenone compounds as described in JP-A 2784/71, cinnamic ester compounds as described
in US-A's 3,705,805 and 3,707,375, butadiene compounds as described in US-A 4,045,229,
and benzoxazole compounds as described in US-P 3,700,455.
[0053] In general, the average particle size of spacing agents is comprised between 0.2
and 10 µm. Spacing agents can be soluble or insoluble in alkali. Alkali-insoluble
spacing agents usually remain permanently in the photographic material, whereas alkali-soluble
spacing agents usually are removed in an alkaline processing bath. Suitable spacing
agents can be made i.a. of polymethyl methacrylate, of copolymers of acrylic acid
and methyl methacrylate, and of hydroxypropylmethyl cellulose hexahydrophthalate.
Other suitable spacing agents have been described in US-A 4,614,708. Compounds which
can be used as a plasticizer for the hydrophilic colloid layers are acetamide or polyols
such as trimethylolpropane, pentanediol, butanediol, ethylene glycol and glycerine.
Further, a polymer latex is preferably incorporated into the hydrophilic colloid layer
for the purpose of improving the anti-pressure properties, e.g. a homopolymer of acrylic
acid alkyl ester or a copolymer thereof with acrylic acid, a copolymer of styrene
and butadiene, and a homopolymer or copolymer consisting of monomers having an active
methylene group.
[0054] The photographic material may comprise an antistatic layer to avoid static discharges
during coating, processing and other handling of the material. Such antistatic layer
may be an outermost coating like the protective layer or an afterlayer or a stratum
of one or more antistatic agents or a coating applied directly to the film support
or other support and overcoated with a barrier or gelatin layer. Antistatic compounds
suitable for use in such layers are e.g. vanadium pentoxide soles, tin oxide soles
or conductive polymers such as polyethylene oxides or a polymer latex;, polythiopene
(and more particularly PEDT) and the like.
[0055] Non-neutral silver image colours obtained after processing, due to the colour of
the silver thus formed, can be corrected by increasing the optical density in the
red region of the visible spectrum by adding suitable dyes to the support or any coated
layer. This non-image wise colour correction method has been disclosed in references
as e.g. JP-A's 03-100645, 01-029838, 01-312536, 03-103846, 03-094249, 03-255435, 61-285445;
issued EP-A 0 271 309 and US-A 4,861,702. This method however may result in an excessive
base + fog density of the photographic material and therefore, an alternative way
consists in an image-wise colour correction by using colour-forming developers, which
are blue coloured in their oxidized form. Examples thereof have been summarized in
JP-A's 03-153234, 03-154043 and 03-154046. In JP-A's 03-156447 and 03-157645 the adsorption
of a blue coloured dye as a function of exposure has further been disclosed.
[0056] According to the present invention the processing of the exposed material includes
the steps of developing, fixing and drying, is performed within 120 seconds or less
and more preferably within 90 seconds or less. An important advantage of the dual-
or double-side coated radiographic elements for soft tissue imaging is that they are
much better suited for rapid processing applications than radiographic elements containing
a single emulsion layer unit. This suitability for rapid processing is particularly
due to the fact that high amounts of silver are not restricted to presence in only
one radiation-sensitive emulsion layer and to the fact that, opposite to duplitized
films as for chest imaging in radiology, low cross-over can only be attained the presence
of two antihalation layers, interposed between the support and each emulsion layer
unit. This allows the amount of hydrophilic colloid coated on each side of the support
to be decreased further if compared with amount spresent in the said duplitized films.
Rapid processing in mammographic applications, more preferably related with hardener-free
processing solutions although not limited thereto, has been described in EP-A's 0
610 609, 0 712 036 and 0 874 275 and is perfectly suitable for use in the present
application.
[0057] After image-wise exposure by light emitted by the intensifying screen and processing
the image thus obtained, an average contrast or gradient in the range from 3.0 up
to 4.5, measured over a density above fog in the range of from 0.25 to 2.00, is thus
attained, wherein said image-forming portion is comprised of layer units permeable
for aqueous processing solutions, said layer units being a hydrophilic front layer
unit coated on the front major face of the support wherein the front layer unit is
capable of reaching a maximum density of more than 3.00 and a hydrophilic back layer
unit coated on the back major face of the support, wherein sensitivity (speed), measured
at a density of 0.50 above fog, is higher for the front layer unit than for the back
layer unit in an amount of from 0.70 up to 1.70 log (Exposure), thanks to the presence
in both, the front layer unit and the back layer unit, of the presence of one or more
light-sensitive silver halide emulsion layer(s) coated with emulsion crystals, essentially
having a cubic crystal habit.
[0058] According to the present invention a radiological method for obtaining a diagnostic
image for mammography is provided, comprising the steps of mounting a film-screen
system by bringing a photographic material as disclosed herein into contact with a
radiographic X-ray conversion screen; and processing said photographic material in
a total dry-to-dry processing time of from 38 seconds up to less than 120 seconds,
and, more preferably, in a dry-to-dry processing time of from 45 up to 90 seconds.
Sensitometric curves of processed film materials are known to show the plot of optical
density (D) as a function of relative logarithmic exposure (logE). Important characteristics
of mammographic film materials in particular, besides the preferably low fog and high
speed (defined as the log E(xposure) at which the optical density is equal to minimum
density Dmin + 1.0) and contrast are the skin line point (SL) being defined herein
as the point of the sensitometric curve where log E equals the "Speed Point"+ 0.8.
[0059] A practical mammogram is normally obtained by subjecting a film-screen system to
X-ray exposure. In diagnostic image formation any commercially available X-ray generating
device may be used, providing an exposure to soft X-rays with a tube voltage of 20
to 40 kV. A preferred luminescent phosphor coated in the X-ray conversion screen is
Gd2O2S:Tb, which emits green light in the wavelength range from 540 tot 555 nm. Said
phosphor and its use in intensifying screens have been described extensively in patent
literature, e.g. in US-A's 3,872,309; 4,130,429; 4,912,333; 4,925,594; 4,994,355;
5,021,327; 5,107,125 and 5,259,016 and in GB-A 1,489,398. The thickness of the phosphor
layer depends on the amount of coated phosphor required in order to obtain the desired
screen speed. A preferred intensifying screen used in combination with the film material
according to this invention is characterized by a phosphor coating weight of at least
45 mg/cm
2 and a phosphor to binder ratio of at least 97:3 as described in EP-A 0 712 036.
[0060] While the present invention will hereinafter be illustrated by working examples representing
preferred embodiments thereof, it will be understood that it is not intended to limit
the invention to those embodiments.
EXAMPLES
[0061] The following Examples will illustrate the invention, without however limiting it
thereto.
Layer arrangement of the coated Film Materials:
[0062]
Side |
Film A
(Comparative I) |
Film B
(Invention) |
Film C
(Comparative II) |
Front
Layer Unit |
Protective layer I
Emulsion layer I (cubes)
Emulsion layer II (cubes)
Support* |
Protective layer I
Emulsion layer I (cubes)
Support* |
Protective layer I
Emulsion layer I (cubes)
Support* |
|
Back Layer
Unit |
Antihalation layer I
Protective layer II |
Emulsion layer II (cubes)
Antihalation layer II
Protective layer I |
Emulsion layer III (tabs)
Antihalation layer II
Protective layer I |
* thickness: 175 µm blue tinted polyester support |
Detailed description of the layer compositions:
Protective layer I (amounts in g/m2)
[0063]
- gelatin: 1.1
- polymethyl methacrylate spacing agent (average particle size: 3 µm) 0.018
- chromium acetate: 0.005
- 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene: 0.082
- CF3(CF2)6 COOH.NH3 : 0.007
- CF3(CF2)6 CONH (CH2CH2O)17-20 : 0.019
- Phenol: 0.003
- Mobilcer Q (a paraffin wax, trade name product from MOBIL OIL): 0.025
- formaldehyde (added just before coating): 0.18
Protective layer II (amounts in g/m2):
[0064]
- gelatin: 0.56
- CF3(CF2)6COOH.NH3: 0.002
- glyoxal: 0.17
- polymethyl metacrylate particles (av. part. size: 7µm): 0.023
Emulsion layer I (amounts in g/m2) :
[0065]
- AgBr(I) emulsion having cubic grains*(1 mole% AgI/ 99 mole% AgBr) in weight amount
expressed as equivalent amount of AgNO3 6.4
- gelatin: 2.56
- 5,5'-dichloro-3,3'-bis(n-propyl-4-sulphonate)- ethylbenzoxacarbocyanine (anhydrous
triethylammonium salt) 0.014
- 4-hydroxy-6-methyl-1,3,3a,7- tetraazaindene 0.029
- sorbitol 0.45
- polyethylacrylate, latex as a plasticizer 0.45
- resorcinol 0.10
- potassium bromide 0.007
- dextran (M.W. = 10000) 1.50
Emulsion layer II (amounts in g/m2):
[0066]
- AgBr(I) emulsion having cubic grains** (1 mole% AgI/99 mole% AgBr) in weight amount
expressed as equivalent amount of AgNO3 2.4
- Gelatin 1.2
- 5,5'-dichloro-3,3'-bis(n-propyl-4-sulphonate)- ethylbenzoxacarbocyanine anhydrous
triethylammonium salt 0.003
- 4-hydroxy-6-methyl-1,3,3a,7- tetraazaindene 0.001
- sorbitol 0.17
- polyethylacrylate, latex as a plasticizer 0.17
- resorcinol 0.04
- potassium bromide 0.002
- dextran (M.W. = 10000) 0.21
* cubic crystals having mean grain size(edge length) of 0.70 µm (average diameter,
calculated from spheres having equivalent volume; precipitation and chemical ripening
described below)
** mixture of cubic crystals (55 wt% having average grain size of 0.57 µm and 45 wt%
having average grain size of 0.38 µm (average diameters, calculated from spheres having
equivalent volume; precipitation and chemical ripening described below)
Emulsion layer III(amounts in g/m2):
[0067]
- AgBr(I) emulsion having tabular grains***(1 mole% AgI/99 mole% AgBr); expressed as
equivalent amount of AgNO3 2.4
- Gelatin 1.2
- 5,5'-dichloro-3,3'-bis(n-propyl-4- sulphonate)- ethylbenzoxacarbocyanine anhydrous
triethylammonium salt 0.01
- 4-hydroxy-6-methyl-1,3,3a,7-tetraazaindene 0.004
- sorbitol 0.17
- polyethylacrylate latex (as a plasticizer) 0.17
- resorcinol 0.04
- potassium bromide 0.002
- dextran (M.W. = 10000) 0.21
*** tabular crystals having an average diameter of 0.70 µm and an average grain thickness
of 0.10 µm (calculated as equivalent circular diameter, obtained from shadowed electron
microscopic replicas, as well as thickness of the grains; precipitation and chemical
ripening described below)
Antihalation layer I (amounts in g/m2):
Antihalation layer II(amounts expressed in g/m2) :
[0068]
- gelatin 1.4
- dye II (see dye according to the formula (I) in the detailed description in form of
a dispersion having average particle size of 1 µm) being decolorized in the processing
solution: 0.190
Emulsion preparation of emulsions having cubic/tabular crystals respectively:
[0069] Preparation of AgBr(I) Cubic Grain Emulsion (0.70 µm)
Precipitation scheme:
[0070] To 1 l of a solution, containing 15 g of methionine and 50 g of gelatin, adjusted
to a pH of 5.8, were added, at 60° C, by double jet addition, a 2.94 M solution of
AgNO
3 at a constant flow rate of 5.7 ml/min during 5 minutes and a solution of a mixture
of 2.91 M of KBr and 0.03 M of KI at a flow rate controlled in order to maintain pAg
constant at 7.8.
[0071] Then the flow rate of the AgNO
3 solution was increased linearly up to 21 ml/min during 72 minutes and 46 seconds.
Cubic grains thus prepared having as a composition 99 mole% AgBr and 1 mole% AgI,
based on silver, showed an average grain size (edge length, calculated from equivalent
sphere volumes) of 0.70 µm.
Chemical ripening:
[0072] At a pH of 6.0, optimized amounts of sodium thiosulphate, chloro auric acid, ammonium
thiocyanate, sodium toluene thiosulphonate and sodium sulphite were added in order
to provide the best available fog/speed ratio.
Preparation of AgBr(I) Cubic Grain Emulsion (0.57 µm)
Precipitation scheme:
[0073] Same as the scheme in order to prepare the cubic grain emulsion of 0.70 µm described
hereinbefore, but with a flow rate of 10.6 instead of 5.7 ml/min during the first
5 minutes.
Chemical ripening conditions:
[0074] At a pH of 6.0, optimized amounts of sodium thiosulphate, chloro auric acid, ammonium
thiocyanate, sodium toluene thiosulphonate and sodium sulphite were added in order
to provide the best available fog/speed ratio.
Preparation of AgBr(I) Cubic Grain Emulsion (0.38 µm)
Precipitation scheme:
[0075] Same as the scheme in order to prepare the cubic grain emulsion of 0.70 µm described
hereinbefore, but a flow rate of 35.6 instead of 5.7 ml/min during the first 5 minutes.
Chemical ripening conditions:
[0076] At a pH of 6.0, optimized amounts of sodium thiosulphate, chloro auric acid, ammonium
thiocyanate, sodium toluene thiosulphonate and sodium sulphite were added in order
to provide the best available fog/speed ratio.
Preparation of AgBr(I) Tabular Grain Emulsion (equivalent volume diameter of 0.53
µm, average grain thickness 0.09 µm)
Precipitation scheme:
[0077] In a reaction vessel a solution was prepared of 6.9 g of oxidized gelatin in 3 1
of demineralized water at 51°C, adjusted to a pH of 2.5 by adding H
2SO
4, and said solution was stirred at a rate of 600 r.p.m.. To said solution were added
by a double jet method aqueous solutions of 0.98 M AgNO
3 (hereinafter referred to as A1) and 0.98 M KBr (hereinafter referred to as B1): 25
ml of A1 and 25 ml of B1 were added in a time interval of 30 seconds. When the addition
was completed, the temperature was increased up to 70°C over a period of 30 minutes:
UAg was controlled (expressed in mV versus a Ag/AgCl(sat.) reference electrode and
should be in the range from 44.5 ± 5 mV at a temperature of 70°C ± 1°C. 1 minute later
pH was set to a value of 5.0 ± 0.3 and immediately thereafter a solution of 50 g of
inert gelatin in 500 ml of demineralized water of 70°C was added. 3 minutes later
B1 was added at a rate of 7.06 ml/min. during 120 seconds, while simultaneously adding
by double jet A1 at a rate of 7.5 ml/min.. In a further double jet addition A1 and
B1 were added during 2822 seconds at a linearly increasing rate going from 7.0 up
to 21.11 ml/min. for A1 and from 7.06 up to 21.29 ml/min. in order to maintain a constant
UAg potential of + 40 mV in the reaction vessel. After 5 minutes A1 and B1 were simultaneously
added by double-jet addition during 60 seconds at a rate of 10.0 and 10.04 ml/min.
respectively whereby the UAg value was held at a constant value of 50 mV while increasing
the flow rate up to 46.49 ml/min. and 46.69 ml/min. respectively over a total time
period of 81 min. and 5 seconds.
[0078] After that double-jet addition time period, an amount of an emulsion having ultrafine
(ca. 0.040 µm) 100 % AgI crystals, dissolved in 20 g of demineralized water at 40°C,
was added to the reaction vessel in order to get a total AgI content at the end of
precipitation of 0.1 mole % based on precipitated silver halide.
Chemical ripening conditions:
[0079] At a pH of 6.0, optimized amounts of sodium thiosulphate, chloro auric acid, ammonium
thiocyanate and sodium sulphite were added in order to provide the best available
fog/speed ratio.
Exposure and processing conditions:
[0080] Samples of Film Materials A, B and C, the layer arrangement of which has been given
hereinbefore, were identically exposed from the front-side with green light (filter
Corning 4010) during 2.0 seconds, making use of a continuous wedge.
[0081] The samples were processed in a CURIX 530 , tradename of Agfa-Gevaert N.V., automatic
processing machine.
[0082] Processing sequence and conditions in the said CURIX 530 processing machine were
following (expressed in seconds(sec.), temperature (in °C) added thereto:
loading |
3.4 sec. |
developing |
23.4 sec./35°C in developer |
cross-over |
3.8 sec. |
fixing |
15.7 sec./35°C in fixer G334 |
cross-over |
3.8 sec. |
rinsing |
15.7 sec./20°C |
drying |
32.2 sec. (cross-over time included) |
total time |
98.0 sec. |
Samples of the film materials were processed in an "active" developer and in a "weak"
developer, the weak developer being a model for less optimal development conditions:
1) The "active" developer: G138 : a glutaraldehyde containing hydroquinone/1-phenyl-3-pyrazolidine-1-one("phenidone")
developer marketed by Agfa-Gevaert N.V.
2) Composition of the "weak" developer in grams per liter, ready-for-use:
Potassium sulphite |
23.0 |
Sodium sulphite |
27.0 |
Boric acid |
6.80 |
EDTA (tetra sodium salt) |
1.40 |
HEDP |
0.62 |
Hydroquinone |
16.0 |
Potassium hydroxide |
17.5 |
Phenidone |
0.96 |
Nitro-6-Benzimidazole |
0.06 |
Methyl benzotriazole |
0.048 |
Acetic acid |
9.54 |
Diethyleneglycole |
14.5 |
Glutardialdehyde |
3.50 |
Potassium metabisulphite |
6.00 |
Potassium bromide |
3.20 |
Potassium iodide |
0.008 |
Determination of fog, contrast(gradation) and speed (sensitivity):
[0083] After exposure and procesing under the above described circumstances the optical
density as a function of exposure dose was measured and fog, speed and contrast were
determined as follows:
(i) Fog "F": density "D" at a non-exposed part of the sample, minus density of the
undercoat layer.
(ii) Speed "S": log E(xposure) value at density value of 1.4 + Fog.
(iii) Average contrast "GG": determined as 1.75/((log E at density D = 2.00+F)-(log
E at density D = 0.25+F))
(iv) Contrast "GGSKIN": determined at the higher density part of the sensitometric
curve determined as:

Results:
[0084] Table I shows values of fog "F", speed "S", contrasts "GG" and "GGSKIN" after processing
samples of film materials A (comparative), B (inventive) and C (comparative) in the
active (AD) and weak developer (WD) respectively.
[0085] Differences between the results in both developing processing conditions thus obtained
were calculated and given in the Table I as Δ (AD - WD).
[0086] Figures of fog F have been multiplied by a factor of 1000; all other figures have
been multiplied by a factor of 100.
Table I
Film Matl |
AD |
WD |
Δ (AD - WD) |
|
F |
S |
GG |
GGSKIN |
F |
S |
GG |
GGSKIN |
F |
S |
GG |
GGSKIN |
A |
205 |
138 |
390 |
161 |
198 |
146 |
370 |
141 |
-7 |
-8 |
-20 |
-20 |
B |
211 |
141 |
380 |
153 |
203 |
147 |
350 |
148 |
-8 |
-7 |
-30 |
-5 |
C |
208 |
145 |
369 |
156 |
201 |
151 |
352 |
128 |
-7 |
-6 |
-17 |
-28 |
[0087] As becomes clear from the data summarized in the Table I, all film materials show
a loss in speed S and contrast (GG and GGSKIN) when processed in the weak developer
WD, if compared with the active developer AD.
[0088] In the inventive Film Material B however, a clearly lower loss of contrast Δ GGSKIN
in the high density region has been demonstrated, especially if compared with Film
Material C containing tabular grains on the back-layer side of the material.
[0089] A photographic material having a large dynamic range and a high contrast, so that
lesions deep in the glandular tissue are accurately detected, moreover clearly depicting
thin, soft tissue such as the skin line of the breast, has thus been provided.
[0090] Differences in speed (measured at a density of 0.5 above fog) between the front and
back layer unit for inventive material B were calculated before and after washing
off the front layer unit from the material B, processed in a G138 developer/G334®
fixer combination after exposure to X-rays of the said material, being in intimate
contact with an intensifying mammographic screen Mamoray HD® (trademarketed product
from Agfa-Gevaert N.V., Mortsel, Belgium, at the front layer side thereof: a difference
of 1.30 log E (Exposure) was calculated.
[0091] The film allows rapid processing by good developability within a cycle of at most
120 seconds and provides high levels of image sharpness and a good image tone in processing
cycles having differing activities, thereby showing good archivability and drying
capacity.
[0092] Having described in detail preferred embodiments it is understood that the invention
is not limited thereto as will become apparent from the claims as formulated hereinafter.