Note: Descriptions are shown in the official language in which they were submitted.
:~31~371
--1--
IMAGEWISE ACCELERATING EQUILIBRATION
IN ULTRASONOG~APHIC RECORDING
Field of the Invention
This invention relates to an improvement in ultra~
sonography. More specifically this invention relates to an
improvement in obtaining an ultrasonographlc record by
imagewise accelerating diffusion from an ultrasonographic
element to a transport liquid.
Background of the Invention
The terms "ultrasonic radiation" and "ultrasound"
are employed interchangeably in this specification to
designate pressure-rarefaction waves dlffering from sound
waves in exhibiting higher frequencies and shorter wave-
lengths. The term "ultrasonic exposure" is employed to
designate exposure to ultrasonic radiation. The production
of visible images by means of ultrasonic radiation is
referred to in the art as "ultrasonoscopy". The production
by means of ultrasonic radiation of a record which is in,
or can be converted to, a viewable form is referred to as
"ultrasonography". The lnstruments for producing ultra-
sonoscopic images are designated "ultrasonoscopes", and
the ultrasonoscopes which produce ultrasonographic images
are referred to as "sonographic cameras". Elements which
form records of ultrasonic radiation patterns as a result
of being ultrasonically exposed in a sonographic camera
are referred to as "ultrasonographic elements". Instru-
ments which are capable of permitting ultrasonographic
elements to be concurrently exposed in different areas to
different intensities of ultrasound are referred to as
"sonographic sensitometers".
The definitlon of terms as here presented is
believed to be generally consistent with the use of these
terms in the art. Specifically, most of these terms are
suggested by P. J. Ernst in the Journal of the Accoustical
Society of America, ~ol. 22, No. 1, in an article entitled
"Ultrasonography", pp. 80-83, 3anuary 1951.
In Belgian Patent 864,089, dated August 17,
1978, there is disclosed a process for imagewise ultra-
.
~3~'71
--2--sonically exposing an ultrasonographic element while in
contact with a transport liquid to produce an ultrasono-
graphic record which can be converted to a viewable ultra-
~onographic image. Specifically, it is disclosed to employ
as an ultrasonographic element a silver halide photo-
graphic element comprised of a photographic support and a
silver halide emulsion layer. The silver halide emulsion
layer, which functions as an ultrasound recording layer
unit, is placed into contact with a transport liquid, 6uch
as a polar solvent, preferably water or an aqueous 801u-
tion. Following contact, diffusion between the emulsion
layer and the transport liquid begins, tending to bring
the emulsion layer and the transport liquid more closely
into equilibrium. By imagewise ultrasonically exposing
the emulsion layer, the rate of diffusion is accelerated
in imagewise exposed areas. Since diffusion between the
emulsion layer and the transport liquid has the effect of
altering the electromagnetic radiation response of the
emulsion layer, diffusion has the effect of producing in
the emulsion layer a record of the image pattern of ultra-
sonic exposure (that is, an ultrasonographic record) which
can be converted to a viewable ultrasonographic image by
exposure to electromagnetic radiation, typically light,
and subsequent photographic processing.
Although Belgian Patent 864,069, cited above,
employs silver halide photographic elements, ultrasono-
graphic imaging processes are known which employ differ-
ing ultrasonographic elements as well as differing trans-
port liquids in producing an ultrasonographic record.
In U.S. Patent 4,228,230, titled ULTRASOUND
IMAGING OF INTERNALLY FOGGED SILVER HALIDE ELEMENTS~ there
are di6closed internally fogged silver halide emul- sion
layer containing elements useful as ultrasonographic
elements. The process of ultrasonographic exposure dif-
fers from that of Belgian Patent 864,089 in that no light
exposure step is employed during or after ultrasound
exposure in order to produce a viewable ultrasonographic
2~
~$
--3--
image. A solute capable of revealing ~he internal fog in
the emulsion layer is contained in the transport liquid.
In U.S. Patent 4,225,658, titled ULTRASONIC IMAG-
ING WITH CATALYTIC ELEMENTS, ultrasonographic elements are
disclosed containing a catalyst layer. Ultrasonic expo-
sure can be undertaken while the ultrasonographic element
is in contact with a transport liquid containing a cata-
lyst poison. Light exposure is not required for imaging.
In commonly asæigned, copending patent applica-
tion titled ULTRASO~OGRAPHIC ELEMENTS CONTAINING MULTIPLELAYERS AND PROCESS FOR THEIR USE, Serial No. 331,572 filed
June 11, 1979, there are disclosed ultrasonographic ele-
ments which contain in addition to a silver halide emul-
sion layer in the recording layer unit an additional
layer, separated by a barrier layer, which can supplement
the transport liquid in 6upplying or receiving diffusible
ions ~n accelerating equilibration.
Although the above-cited disclosures differ in
their specifics, each is directed to a process of record-
ing an ultrasonic exposure pattern employing an ultrasono-
graphic element comprised of a support and a recording
layer unit. The recording layer unit is contacted with a
transport liquid and imagewise ultrasonically exposed to
accelerate imagewise diffusion between the recording layer
unit and the transport liquid, thereby producing in the
recording layer an ultrasonographic record. The ultra-
sonographic record can itself be viewable or can be con-
verted to a viewable form by subsequent proceseing.
Ultrasonographic recording by the general process
described above is limited by the maximum rate of diffusion
which can be induced by ultrasonic exposure. Although
increasing the ultrasonic exposure itself is a direct
approach to increasing the rate of diffusion, for many
imaging applications it is desirable or even necessary to
operate at very low ultrasound exposure levels. For exam-
ple, where an ultrasonographic image is being produced by
exposing a living sub~ect to ultrasound, it is desirable
to maintain the lowest feasible level of ultrasonic
~'
13 31~71
exposure and guidelines have been establshed for maximum
human exposures. Increasing the rate of spontaneous
diffusion between the ultrasonographic element and the
transport liquid in the absence of ultrasound can have the
effect of permitting higher rates of equilibration to be
obtained by ultrasonic exposure, but this approach is
limited by disadvantages--e.g., background density levels
can become ob~ectionably large, loss of image discrimina-
tion can result and inconveniently short periods of contact
between the ultrasonographic element and the transport
liquid can be required.
Summary of the Invention
.
In one aspect this invention is directed to a
process of recording an ultrasonic exposure pattern employ-
ing an ultrasonographic element comprised of a support anda recording layer unit capable of producing an ultrasono-
- graphic record as a function of diffusion into a transport
liquid, the recording layer unit being beneath the support
and in contact with the transport liquid. This process
comprises imagewise~ultrasonically exposing the record-
ing layer unit through the transport liquid to accelerate
diffusion from the recording layer unit into the transport
liquid in exposed areas, thereby producing in the recording
layer unit an ultrasonographic record. The process is
characterized by the improvement comprising further acceler-
ating diffusion in ultrasonically exposed areas by establish-
ing a temperature differential within the transport liquid
adjacent the recording layer unit so that the transport
liquid remote from the recording layer unit is at a rela-
3 tively lower temperature than the transport liquid contact-
ing the recording layer unit.
In terms of the ultrasonographic images which
have been observed produced by this process, higher maxi-
mum densities in ultrasonically exposed areas are obtained.
Additionally, signlficantly increased image discrimination
(maximum density minus minimum density~ has been observed.
Still further, little or no elevation of minimum den-
sity levels in background areas has been observed.
. ~
1131~371
--5--
Description of Preferred Embodiments
While subheadings are provided for convenience,
to appreciate fully the elements of this invention, it is
intended that this disclosure be read and interpreted as
5 a whole.
Ultrasonic Exposure
This invention is generally applicable to pro-
cesses of producing an ultrasonographic record in which an
ultrasonographic element is comprised of a recording layer
unit coated on a support to form the sole or outermost
layer unit of the element. Ultrasound is conducted
through a transport liquid from an appropriate source to
the element, and the element is oriented so that the
recording layer unit is beneath the support and forms the
interface at which ultrasonic radiation is transferred
~rom the transport liquid to the element. In the areas of
the element exposed to ultrasound, diffusion from the record-
ing layer unit to the transport liquid is accelerated,
thereby producing an ultrasonographic record in the record-
ing layer unit. The recording layer unit consists of at
least a single recording layer and, optionally, a combina-
tion of one or more recording layers and transport liquid
permeable layers which alter the rate of diffusion from
the recording layer unit.
It has been discovered that, in such processes,
the rate of diffusion from the recording layer unit to
the transport liquid in ultrasonographically exposed areas
can be accelerated further without significantly affecting
background or ultrasonically unexposed areas. This is
3 achleved by establishing a temperature differential withln
the transport llquid ad~acent the recording layer unit so
that the transport liquid remote from the recording layer
unit is at a relatively lower temperature than the trans-
port liquid contacting the recording layer unit.
In this arrangement the direction of ultrasound
propagation is upward through the transport liquid to the
ultrasonographic element. Typically the ultrasonographic
element is oriented substantially normal to the direction
.971
--6--
of ultrasound propagation. The temperature of the
transport liquid in contact with the recording layer
unit is maintained higher than the temperature of the
transport liquid removed from contact with the record-
ing layer unit. That is, a temperature differential isestablished within the transport liquid ad~acent the
recording layer unit so that the temperature progress-
ively decreases in moving from the surface of the
recording layer unit in contact with the transport
10 liquid to a location within the transport liquid remote
from the recording layer unit.
In the arrangement described above the tem-
perature differential in the transport liquid adjacent
the recording layer unit is such that the temperature
increases in an upward direction as the ultrasonogra-
phic element is approached. Since it is known that the
rate of propagation (i.e., transmission speed) of
ultrasound in a liquid increases with the temperature
of the liquid, it is apparent that the temperature
differential has the effect of accelerating the ultra-
sonic radiation as it passes through the portion of the
transport liquid ad~acent the recording layer unit.
The improvement which this produces in the ultrasono-
graphic record has been described above in terms of
observed improvements in ultrasonographic images. The
mechanism of ultrasonographic record generation is
local acceleration of the rate of diffusion from the
recording layer unit to the transport liquid by image-
wise exposure to ultrasound. The enhancement of the
3 ultrasonographic record is a result of further locally
accelerating this diffusion in ultrasonically exposed
areas.
The demonstratable mechanisms of the ultrasono-
graphic record generation described above do not account
for or in any way predict the observed improvements in the
ultrasonographic records obtained by establishing a tempera-
ture differential in the transport liquid ad~acent the
1~31~71
--7--
recording layer unit so that the temperature increases in
an upward direction~ While only empirically proven by the
results obtained, it appears that the temperature differ-
ential functions to enhance ultrasound induced convection
at the surface of the recording layer unit. In the
absence of convective flow a concentration gradient is
created at the boundary of the transport liquid and the
recording layer unit by diffusion occurring across the
boundary during equilibration. For example, a species
10 diffusing out of the recording layer unit becomes more
concentrated ln the transport liquid at its boundary with
the recording layer unit. The result is to create a
diffusion impedance between the recording layer unit and
the transport liquid. In the presence of convection flow
15 the concentration gradient in the transport liquid at the
recording layer unit boundary is disrupted, and the diffu-
sion lmpedance across the boundary is reduced. In the
absence of convection flow diffusion still occurs, but it
is rate limited by the diffusion impedance at the boundary.
20 It is believed that by maintaining a temperature differen-
tial in the transport liquid ad~acent the recording layer
unit to accelerate the ultrasound in its propagation up-
wardly the convection force which the ultrasonic radiation
can exert on the transport liquid is significantly in-
25 creased. The temperature differential does not directlyinduce a substantial increase in convection in the absence
of ultrasound, since, being uniformly applied, the tem-
perature differential would in such case accelerate diffu-
sion in ultrasonically unexposed areas of the recording
layer unlt, whlch ls at variance with the observed imaging
response.
In addition to explaining the very signlficant
improvements in ultrasonographic imaging obtained by this
process it is believed that the inferiority of alternative
arrangements can also be explained in terms of convection
flow. Ultrasonographic elements which function by equili-
bration between a recording layer unit and a transport
: ' , ;
11315~71
--8--
liquid include both those in which diffusion occurs
from the recording layer unit to the transport liquid
and those in which diffusion occurs from the transport
liquid to the recording layer unit. In the latter case,
the species diffusing into the recording layer unit be-
comes relatively depleted in the transport liquid at its
boundary with the recording layer unit. It is believed
that the reduction in concentration ad~acent the recording
layer unit has the effect of reducing the rate of propaga-
10 tion of ultrasound and reduces the convective force whichthe ultrasound excerts on the transport liquid. It is
believed that the significant advantages of the present
invention are obtained as a result of both concentration
and temperature gradients working to accelerate ultrasound
~5 and increase the convection force it can exert on the
transport liquid. In the practice of the present inven-
tion arrangements are avoided which result in concentra-
tion depletion occuring at the boundary of the recording
layer unit and the transport liquid. Arrangements in
20 which diffusion occurs from the recording layer unit to
the transport liquid or concurrently in both directions
are contemplated. Any known dif~usible species or sub-
stance capable of producing an ultrasonographic record
as a function of its imagewise distribution in the record-
25 ing layer unit can be employed in the practice of thisprocess. In addition, it is specifically contemplated
to load the recording layer unit with substantially
inert diffusible species, such as soluble salts (e.g.,
alkalie nltrates, or sulfates), to provide higher concen-
3 tration gradients favoring an increase in the convectlonforce.
Convection flow effects also explain the orienta-
tion of the ultrasonographic element during ultrasonic
exposure. By positioning the element with the recording
layer unit beneath the support and transmitting ultrasound
upwardly to the element through the transport liquid, the
proper temperature gradient according to this process is
:: .
~131971
-8a-
for the transport liquid to become progressively warmer
in an upward direction approaching the recording layer unit.
By having the warmer, less dense transport liquid above
the cooler, more dense transport liquid, spontaneous
convection apart from that induced by ultrasound is
avoided. In the converse relationship, in which the
cooler transport liquid overlies warmer transport liquid,
spontaneous convection currents are favored, resulting in
reduced image discrimination. The ultrasonic exposure
10 orientation of having the recording layer unlt beneath the
support during ultrasonic exposure has been observed to
produce a superior imaging result.
3o
: :'. '' `
`
11.3~71
The temperature differential in the transport
liquid adjacent the recording layer unit can be obtained
in any convenient manner. The ultrasonographic element is
oriented with the recording layer unit on its surface
nearer the exposing ultrasonic radiation source, and the
transport liquid remote from the recording layer unit is
at a lower temperature than that in contact with the record-
ing layer unit. This can be achieved by heating the
ultrasonographic element to a temperature above that of
the transport liquid so that upon contact thermal con-
duction from the ultrasonographic element to the trans-
port liquid establlshes the desired thermal gradient.
Alternatively, the ultrasonographic element can be main-
tained at ambient temperature and the transport liquid
cooled. Also, the transport liquid can be cooled to a
temperature below ambient temperature and the ultrasono-
graphic element heated to a temperature above ambient
temperature.
From the foregoing it is apparent that the
enhancement in the ultrasonographic record produced by
this invention is a function of a thermal gradient rather
than any specific choice of ultrasonic exposure tempera-
tures. It is contemplated that the ultrasonographic ele-
ments employed in the practice of this process can be
ultrasonically exposed at any temperature at which they
are capable of providing an ultrasonographic record in the
absence of an applied temperature differential.
The ultrasonographic record has been observed to
be enhanced in direct relatlon to the temperature differ-
3 ential established in the transport liquid ad~acent therecording layer unit. It is believed that only the tem-
perature differential within the transport liquid~in
contact with and very near the recording layer unit con-
tributes to the enhancement in results obtained. A practi-
cal approach to establishing and controlling the thermalgradient in the boundary re~ion is to measure the tempera-
ture of the ultrasonographic element surface remote from
the recording layer unit and the bulk temperature of the
,~ .
"
,
1~31971
--10--
transport liquid at a point sufficiently removed from the
ultrasonographic element to be substantially unaffected by
the temperature of the ultrasonographic element. Their
significance in terms of the boundary region thermal
gradient is dependent upon the thermal conduction char-
acteristics of both the particular transport liquid and
ultrasonographic element employed.
Where the transport liquid is distilled water or
an aqueous solution and the ultrasonographic element is
comprised of a recording layer unit coated on a polymeric
film support, it is preferred that the ultrasonographic
element and the transport liquid be within the temperature
range of from about 5 to 80C, more preferably in the range
of from about 10 to 60C, during ultrasonic exposure. The
temperature differential, measured as described above, is
preferably in the range of from about 1 to 75C, most
preferably from 5 to 50C. It is specifically contemplated
to maintain one of the transport liquid and the ultrasono-
graphic element at ambient temperature prior to contact
with the other, although this is by no means essential.
In perhaps the simplest arrangement for ultra-
sonic exposure an ultrasonic transducer is positioned in a
transport liquid containing reservoir, and the ultra-
sonographic element is immersed in the reservoir with its
recording layer unit in contact with the transport liquid
and spaced from the ultrasonic transducer to receive ultra-
sonic radiation. To facilitate convection in the boundary
region with the recording layer unit the transport liquid is
preferably of a viscosity not appreclably higher than about
3 1.5 centipolse. Generally the transport liquid is at a
viscosity in the range of from about 0.5 to 1.5 centipoise.
It is preferred that the ultrasonographic element be
positioned substantially horizontally during ultrasonic
exposure. The recording layer unit forms the lower sur-
face of the element during ultrasonic exposure.
Instead of employing a single transport liquid,one transport liquid can be in contact with the trans-
ducer, and a second transport liquid can be in contact with
'
:-:
--ll--
the recording layer unit. The two liquids can be in direct
contact or separated by an ultrasonically conducting member,
such as a membrane. Since the second transport liquid is
not in contact with the ultrasonographic element and does
not participate in equilibration with the element, i~t is
apparent that any transport liquid can be employed which
is capable of conducting ultrasound. In fact, a gaseous
transport medium can be substituted for the second trans-
port liquid where the ultrasound attenuation is not objec-
tionable. The first transport liquid can actually be con~tained within and, along with the membrane, form a part
of the ultrasonographic element, if desired.
In choosing among otherwise comparable transport
liquids, whether they directly contact the recording layer
unit to be exposed or are remote or external, considera-
tion can be given to the ultrasonic absorption coefficient
of the transport liquid. Water at an ultrasonic frequency
of 5 megahertz and at a temperature of 20C has an ultra-
sonic absorption attenuation coefficient of 6 X 10 3
cm 1. The ultrasonic absorption attenuation coefficients
for liquids range from about two orders of magnitude
higher than that of water to about two orders of magnitude
lower than that of water. The advantage to be achieved by
a low ultrasonic absorption coefficient is reduced dissi-
pation of ultrasonic energy in the transport liquid.Lower ultrasonic attenuation coefficients are particularly
preferred for the transport liquids external to the ultra-
sonographic element or remote from the recording layer unit.
It is believed that higher ultrasonic absorption coeffi-
cients for transport liquids which contact the recordinglayer unit can contrlbute to improving thelr response to
ultrasound.
Ultrasonic absorption coefficients of transport
liquids can be ascertalned by reference to published
values. For example, values are published by Kinsler and
Frey, Fundamentals of Acoustics, Wiley, N.Y., 1950; Hueter
and Bolt, Sonics, Wiley, N.Y., 1955; and Herzfeld and
Litovitz, Absorption and Dispersion of Ultrasound Waves,
Academic Press, N.Y., 1959.
~ '
~13~71
-12-
Ultrasonic exposure of the recording layer unit
of the ultrasonographlc element while ln contact with the
transport liquid and while a temperature dif~erential is
established in the transport liquid as described above can
be undertaken by techniques otherwise identical to those
known in the art. For example, the teachings of Belgian
Patent 846,o6~, cited above, are considered sufficiently
detailed to enable a person skilled in the art to practice
this process step. Nevertheless, the ultrasonic exposure
step of this process is summarized below.
The ultrasonographic element can be imagewise
exposed to ultrasonic radiation using any conventional
sonographic camera which is capable of impinging ultra-
sonic radiation on a ultrasonographic element as an image
receptor. In such a sonographic camera an ultrasound
source or transducer (i.e., an emitter of ultrasonic
radiation? and the ultrasonographic element are spatially
related so that the ultrasonic radiation, unless absorbed,
can impinge on the recording layer unit to be imagewise
exposed. Between the ultrasound transducer and the ultra-
sonographic element is interposed any means which will
imagewise modulate the ultrasonic radiation as it is
received by the recording layer unit. In a simple form
this can take the form of an apertured template which
absorbs or reflects the ultrasonic radiation which strikes
it and allows a portion of the ultrasonic radiation to
pass through the aperture to the ultrasonographic element.
Alternatively the reflected ultrasonic radiation can be
caused to impinge on the ultrasonographic element. In a
3 more sophisticated ~orm the lmaglng means can include
combinations o~ sonic lenses and re~lectors for ~ocusing
and dlrecting the ultrasonic radlatlon. In one appllca-
tion of thls process an ob~ect whose ultrasonic modulation
characterlstlc ls desired to be recorded is placed in the
sonographlc camera so that it intercepts ultrasonic radia-
tion passing from the ultrasound transducer to the ultra-
sonographic element. For example, the ultrasonoscope of
Brenden U.S. Patent 3,765,403 can be readily adapted ~or
: .
.
1131~71
.
-13-
use as a sonographic camera in the practice of this inven-
tion merely by locating the ultrasonographic element in
one of the water tanks so that it is impinged by the
ultrasonic radiation which has passed through or been
reflected by the object under examination. A preferred
ultrasonographic exposure apparatus is disclosed in com-
monly assigned, copending patent application titled ULTRA-
SONOGRAPHIC EXPOSURE APPARATUS, U.S. Patent 4,232,555.
Except where rapid diffusion from the ultraRono-
graphic element as a function of contact with the trans-
port liquid prohiblts, it is usually preferred to allow
the ultrasonographic element at least a few seconds, pref-
erably at least about 10 seconds, of contact with the
transport liquid before initiating ultrasonic exposure.
Delaying ultrasonic exposure after initial contact with
the transport liquid can be used to enhance the ultrasono-
graphic response. The optimum delay period for a particu-
lar element can be correlated to the transport liquid con-
tact period at which incipient alteration of the recording
characteristics of the element is observed. For some ele-
ments observable alteration begins immediately upon con-
tact with the transport liquid, and there is no advantage
to delaying the ultrasonic exposure.
Imagewise exposure of the ultrasonographic ele-
ment in the 60nogrsphic camera is at an intensity and for
a duration which is known in the art to be 6ufficient to
accelerate imagewise diffusion to the tran6port liquid
from the recording layer unit. Although both high and low
levels of ultrasound exposure are possible, lt is gener-
ally preferred to employ low levels of ultrasound expo-
sure, particularly where living sub~ects are being
exposed. Successful imaging is readily achieved with pre-
ferred ultrasonographic elements, such as those in Belgian
Patent 864,089 and patent application Serial No. 331,572,
cited above, at ultrasonic exposures below 100 watt-
sec/cm2 by this process.
,
,
-14-
Different ultrasonographic elements exhibit
different threshold sensitivities to ultrasonic radiation.
By exposing ultrasonographic elements to differing ultra-
sonic intensities and then converting the ultrasonographic
record to a viewable form, the optimum ultrasonic exposure
for a given ultrasonographic element can be readily
determined. In a manner analogous to photographic sensi-
tometry using a step tablet, it is possible to expose an
ultrasonographic element simultaneously in lateral areas
with an array o~ laterally spaced ultrasound transducers
which are calibrated to transmit ultrasonic radiation at
predetermined stepped levels of intensity. Densities
produced directly or following processing by each ultra-
sound transducer can be plotted against ultrasonic exposure.
This generates an ultrasonic characteristic curve for the
particular ultrasonographic element from which the optimum
intensity of ultrasonic exposure can be readily determined.
The determination can be repeated using differ-
ing durations of ultrasonic exposure, if desired, although
this is not usually necessary. In using photographic
cameras varied shutter speeds (exposure times) and f-stop
settings (exposure intensities) are available to the
photographer to achieve a given exposure, since exposure
is recognized to be the mathematical product of exposure
time and intensity. The proposition that equal photo-
graphic exposures differing in intensity and duration
produce similar photochemical response is referred to as
the photographic reciprocity law, and this law is gen-
erally relled upon in photography in varylng exposure
3 times and lntensities, although it is recognized that many
photographic elements exhlbit signi~icant reciprocity law
fallure. By analogy to photography, various combinations
o~ ultrasonic exposures as a mathematical product can be
relied upon in a general way in accordance with a reci-
procity law of ultrasonic exposure which is analogous tothe photographic reciprocity law.
A significant ultrasonic exposure reciprocity
law departure discussed in Belgian Patent 846,069 can
' : -
3~ ~ 7
-15-
be put to favorable use. At equal exposures differing in
intensity and duration the ultrasonographic speeds observed
progressively increase as a function of the shortening of
the exposure duration~ Viewed another way, by using shorter
durations of ultrasonic exposure, less than expected
increases in intensity are required to achieve a particular
ultrasonographic speed. This is particularly advantageous,
since many ob;ects which might be ultrasonographically
examined are limited in both the intensity and duration of
the ultrasonic radiation which they can withstand safely
without risk of degradation. Generally the longer the dura-
tion of exposure above a threshold minimum level of intensity
the lower the intensity must be to avoid degradation. The
favorable ultrasonic exposure reciprocity law departure
allows the use of lower than the expected intensities with
decreased duration of exposure, thereby avolding degradation
without sacrificing ultrasonographic speed.
Any ultrasonic frequency heretofore employed in
ultrasonography can be applied to the practice of this
process. For a given transmission medium the wavelength
of the ultrasonic radiation is reciprocally related to
its frequency. Since best imaging results in ultra-
sonography and ultrasonoscopy are recognized to be
obtainable when the wavelength of the ultrasonic imaging
radiation is substantially shorter than the dimension of
the ob~ect or ob~ect feature to be imaged, it is
generally preferred to operate at shorter wavelengths and
hence higher frequencies. For example, at a ~requency of
l megahertz ultrasonic radiation transmitted in water
3 exhibits a wavelength in the order of 1.5 millimeters.
Accordingly in obtaining ultrasonographs of ob~ects or
ob;ect features of about 1.5 millimeters in dimension it
is preferred to operate substantially above 1 megahertz,
typically in the range of 2.5 to lO0 megahertz.
Frequencies in the order of gigahertz are known in the
art and can be employed, particularly when microscopic
image definition is required. The high operating
3~
-16-
frequencies are, of course, advantageous since they
effectively define both large and small ob~ects and
object features, although increased absorptivity of many
materials at higher frequencies requires thinner ob~ect
samples.
The ultrasonic exposure of the ultrasono-
graphic element can be constant in intensity for the
duration of exposure or it can be varied in intensity.
An increase in response for a given ultrasonographic
element can be achieved if the ultrasonic exposure is
pulsed. Pulsing of the ultrasonic exposure can be
achieved by continuously modulating the intensity of
exposure or, preferably, interrupting ultrasonic
exposure so that ultrasonic exposure is divided into
separate bursts or discrete pulses. It is preferred to
employ discrete pulses wherein the duration of the
pulses and the interval therebetween is less than a
tenth of a second. The response of the ultrasonographic
element can be increased further by employing higher
frequencies of pulsing. The duration of the ultrasonic
pulse and the interval between pulses can be varied
independently, if desired.
Upon completion of the ultrasonic exposure an
ultrasonographic record is present in the recording
layer unit of the ultrasonographic element. The ultra-
sonographic record can itself be viewable or subsequent
processing can be employed to produce a viewable image,
either in the ultrasonographic element or ln a separate
element, such as a recelver. The processing steps, if
3 any, following ultrasonographic recording according to
this invention can be conducted by procedures well known
in the art. Such procedures are, of course, chosen for
the particular ultrasonographic element and transport
liquid composltion employed.
In perhaps the simplest approach to producing
an ultrasonographic image according to this invention
the ultrasonographic record can itself be viewable as
il31971
-17-
formed. For example, in a simple form the recording
layer unit can be a liquid permeable layer, such as
a hydrophilic colloid layer, the transport liquid
can be water or an aqueous solution and the record-
ing layer unit can initially contain a diffusibledye. A variety of diffusible dyes suitable for this
purpose are known in photography, such as azo, azo-
methine, azopyrazolone, indoan~line, indophenol,
anthraqu~none, triarylmethane, alizarin, merocya-
nine, nitro, quinoline, cyanine, indigo, andphthalocyanine dyes. Following contact between the
transport liquid and the recording layer unit ultra-
sound accelerated diffusion according to this inven-
tion as described above produces an imagewise dis-
tribution of dye in the recording layer unit which
at once forms both an ultrasonographic record and a
viewable image. The dye density is perceptibly
reduced in the ultrasonically exposed areas of the
recording layer unit.
To minimize diffusion in background areas
which can tend to reduce image discrimination the
ultrasonographic element is removed from contact
with the transport liquid following ultrasonic expo-
sure. In some instances an enhancement in the
ultrasonographic record is obtained if the ultra-
sonographic element is allowed to remain undisturbed
for a few seconds following ultrasound exposure. As
described below, silver halide photographic elements
sre allowed to remain undisturbed in contact with
the transport liquid until after light expo~ure.
Ultrasonographic Imagin8 with Sil-
ver Halide Photographic Elements
In a specifically preferred form of the
invention the ultrasonographic elements employed are
silver halide photographic elements. Processes for
producing ultrasonographic images employing such
elements are disclosed in Belgian Patent 864,069.
~'
.
1~31~71
--18--
Upon formation of an ultrasonographic record in one or
more of the silver halide emulsion layers of the
photographic elements the next step of the process is to
convert the ultrasonographic record into a photographic
latent image. This is done by nonimagewise exposing the
photographic element to electromagnetic radiation,
typically light. Thereafter the latent image can be
converted into a viewable image by conventional photo-
graphic processing.
In a specifically preferred form of this
process the photographic silver halide element to be
imagewise exposed contains a silver halide emulslon
recording layer unit in contact with a polar solvent
acting as a transport liquid. The function of the polar
solvent is to provide a medium in which ionic diffusion
can occur.
Any conventional technique for contacting the
polar solvent with the recording layer unit can, of
course, be employed. The photographic element can be
immersed in a polar solvent reservoir, or the photo-
graphic element can be sprayed, swabbed, bathed or
otherwise analogously contacted with the polar solvent.
Water is a preferred polar solvent for use in
the practice of this process; however, any polar solvent
or combination of polar solvents known to be compatible
with the photographic elements to be exposed can be
employed. Exemplary useful polar solvents in addition
to water include water-miscible alcohols, ketones and
amides (e.g., acetone, phenol, ethyl alcohol, methyl
alcohol, lsopropyl alcohol, ethylene glycol, N,N-di-
methylformamide, N-methylacetamide, N,N-dimethyl~
acetamide, methyl ethyl ketone), tetrahydrofuran, N-
methyl-2-pyrrolidone, dimethylsulfoxide and mixtures of
the above, with or without water. Any polar solvent
which is compatible with the photographic element and
which is sufficiently polar to permit ions, particularly
halide ions, silver ions and/or hydrogen ions, to be
~ ' ' ,., . ' ' '
.
11319~71
--19--
diffusible therein can be employed in combination with
silver halide photographic elements.
While polar solvents are preferred transport
liquids for contact with silver halide emulsion record-
ing layer units, particularly those containing a hydro-
philic vehicle, such as hydrophilic colloid (e.g.,
gelatin or a gelatin derivative), it is recognized that
other transport liquids capable of providing a diffusion
medium can also be employed. The transport liquid which
contacts the silver halide emulsion recording layer unit
of the photographic element can be any chemically com-
patible liquld which provides a diffusion path to or
from the silver halide grain surfaces for a species
capable of altering their electromagnetic exposure
reSponse-
Electromagnetic exposure of the photographicelement is undertaken as well as ultrasonic exposure.
It is preferred to employ visible light during elec-
tromagnetic radiation exposure, and the description of
electromagnetic radiation exposure is discussed in terms
of light exposure. However, it is to be appreciated
that the utility of this process is not limited
to use with any particular portion of the electro-
magnetic spectrum, but can employ electromagnetic radiation
3o
.
.,.. , . . ,, ~,
,~: , -
~ ;
113~
-20-
of any wavelength heretofore known to be useful ln photog-
raphy, including ultraviolet and visible light, as well as
infrared radiation, unless otherwise speciflcally qualified
below.
In using an ultrasonographically negative-
working photographic element (that is, one which is
initially relatively insensitive to light exposure and
which becomes more responsive as a result of ultrasonic
exposure) it is only necessary that the light exposure
strike those areas of the photographic element that are
ultrasonically exposed. In other words, a light image
which is a duplicate or approximation of the imagewise
ultrasonic exposure can be employed. It is usually more
convenient to expose in a nonimagewise manner, preferably
uniformly, the photographic element to light so that
registration of the two exposures is not required. For
ultrasonographically negative-working elements light
exposure can usefully occur at any stage following the
onset of ultrasonic modification of the photographic
element--i.e., either during or after ultrasonic exposure.
Since the ultrasonographically negative-working photo-
graphic elements are initially relatively light-insensitive,
light exposure of the photographic element before ultra-
sonic exposure can be permitted, but it is not responsible
for latent image formation.
In using an ultrasonographically positive-
working photographic element (that is, one which is
initially sensitive to light exposure and becomes less
responsive as a result of ultrasonic exposure~, light
3 exposure is required ln those areas which are not initially
imagewise ultrasonically exposed, and, as a practical
matter, nonimagewise light exposure, usually uni~orm light
exposure, is generally most convenient. It is generally
preferred to avoid light exposure before or during ultra-
sonic exposure and to defer light exposure until afterultrasonlc imagewise desensitization of the photographic
element has been accomplished. Light exposure while
ultrasonic exposure ls still occurring is specifically
,
. ~ .
~ ~ ,. . .
!
' ~ ''~"' ' "' ' ' ' '
11319~7~
-21-
contemplated, although not preferred. Further, prior to
ultrasound exposure, the silver halide photographic ele-
ment can be given a nonimagewise, preferably uniform,
light exposure of any type which does not destroy its
photographic imaging capability. For example, it is
known in photography that a uniform light pre-exposure
of a photographic element can have the effect of revers-
ing the photographic image obtained following subsequent
imagewise exposure and processing. This effect is
10 commonly referred to as solarization and is further
discussed below.
When ultrasonic and light exposures are con-
currently undertaken, or at least undertaken in over-
lapping time periods, it is necessary to light expose
15 the photographic element while it is still in contact
with the transport liquid. For example, if the photo-
graphic element is immersed in a polar solvent or other
transport liquid medium during ultrasonic exposure,
light exposure can also be undertaken through this
20 medium. Conveniently the ultrasonic transport liquids
are most commonly substantially transparent (specularly
transmissive to light over at least a portion oP the
visible spectrum~. Where ultrasonic and light expo-
sures are undertaken consecutively, it is possible to
remove the photographic element from the environment of
ultrasonic exposure--e.g., contact with the transport
liquid--before light exposure is undertaken. However,
it is preferred to light expose the photographic
element after ultrasonic exposure without moving the
3 element wlth respect to the transport liquid contacting
the silver halide emulsion recording layer unlt, and
thus risklng degradatlon of image definition.
According to a preferred technique for practicing
this process, ultrasonic and light exposures are consecu-
tive, rather than concurrent or overlapping. A signifi-
cant increase in the imaging sensitivity of the ultrasono-
graphic element occurs if light exposure follows ultrasonic
` ` 1131~71
--22--
exposure. Specifically, signiflcant enhancement ln density
dlfferences between ultrasonlcally exposed and background
areas are observed when llght exposure ls delayed from
about 10 to 200 seconds Coptimally from about 15 to 50
seconds) followlng ultrasonic exposure at ordinary room
temperatures (20 to 25C). This enhancement of the ultra-
sonographic image ls attrlbuted to a furtherance durlng
the delay perlod of the alteratlons of the photographic
element initlated by ultrasonic exposure. It is preferred
not to disturb the photographic element between ultrasonic
and light exposure.
For ultrasonographically positive-working photo-
graphic elements conventional speed ratlngs for the photo-
graphic elements can be employed as an approximate guide
for light exposure. To more precisely determine the
exposure properties of an ultrasonographically positive-
working photographic element a series of exposures, with
different samples Gr using a step tablet, can be made
under the conditions of actual use to ldentify optlmum
levels of electromagnetic radiatlon exposure. For example,
the minimum level of light which produces a maximum density
as well as the maximum level of light which produces a
minlmum density can be determined as well as exposures
which produce intermediate density levels under the con-
templated conditions of photographic processing. It lspreferred to employ a light exposure in excess o~ that
requlred to produce a maxlmum denslty ln subsequent pro-
cessing. However, low levels o~ llght exposure whlch
produce a density at least 0.1 above the minlmum density
3 (preferably 0.5 above minimum density~ can be employed.
For ultrasonographically negative-working photo-
graphic elements, optimum levels of light exposure cannot
be determined from the normal photographic speed ratings
of the elements, since they are typlcally initially rela-
tively insensitive to light. The optimum exposure forsuch negative-working photographic elements can be ascer-
tained by contactlng the photographic element with the
,
. :
1131~371
--23--
transport liquid to be placed in contact with it during
ultrasonic and light exposure and then variably light
exposing the element, using different samples or a step
tablet, after the ultrasonographically negative-working
photographic element has approached its maximum light
sensitivity.
In determining the optimum levels of light
exposure as described above, the photographic elements are
photographically processed in accordance with the tech-
niques to be employed in this process. Once usable lightexposure levels have been identified, intensity and dura-
tion of light exposure can be varied in accordance with
the photographic reciprocity law.
It is recognized in photography that the inte-
grated sum of intermittent light exposures can produce ahigher density than a corresponding continuous light expo-
sure when the average intensity of exposure is less than
the intensity (referred to herein as the transition inten-
sity) at the nadir of a plot of log continuous exposure
versus log intensity (referred to in the art as a reci-
procity curve~ for a photographic element. The density
difference observed is referred to in the art as an inter-
mittency effect. It is known in the art that the effect
of increasing the frequency of intermittent light exposures
at an average intensity level below the transition inten-
sity, holding the integrated sum of the exposures constant,
causes the densities obtained to increase until a critical
frequency is reached. Above the critical frequency no
further increase in density occurs.
An unexpected increase in density difference
between high density and low density areas of ultrasonographs
formed by this process can be achieved by employing pulsed--
that is, varied intensity, preferably intermittent, light
exposures. This effect can be achieved employing nonimage-
wise or uniform light exposures of both high and low
density rendering areas of the photographic elements in
direct contrast with the necessarily differential Ce~g.,
imagewise) light exposures of high and low density areas
~131~7~
--24--
in obtaining photographic intermittency effects. Specif-
ically, maximum obtalnable densitles can be increased
signifiantly by nonimagewise or uniform, intermittent
light exposures of photographic elements without the same
increases in minimum densities occurring. In considering
pulsed light exposure, such variants as synchronizing the
pulsed light exposure with the ultrasound exposure and
also varying the fre~uency of light pulsing are contem-
plated. Since the speed of light is much faster than the
rate of pressure-rarefaction wave propagation, synchronized
delay of light pulses is contemplated so that each light
pulse reaches the element being exposed concurrently with
or following after a time delay each ultrasound pulse.
The duration of the delay of the light pulses with respect
to the ultrasound pulses can be chosen to take optimum
advantage of the chemical or physical alteration set in
motion by the preceding ultrasound pulse or pulses.
As is well understood by those skilled in the
art of photography, if silver halide emulsion imaging
layers are given progressively greater exposures substan-
tially in excess of those required to produce a maximum
density, the densities produced typically plateau at the
maximum density and then decline, in many instances, to
approach the initial minimum density level (or less) at
very high levels of exposure. This photographic effect is
referred to in the art as solarization. Solarization is
occasionally used in photography to reverse the sense of a
photographic image. For example, solarization will produce
a positive image using a normally negative-working photo-
graphic element.
Unlike conventional photography, the ultrasono-
graphic images obtained with this process exhibit no
reversal of the sense of the ultrasonographic image when
operating at high levels of exposure approaching solariza-
tion. Accordingly, the maximum light exposures which areemployed in the practice of this process can be at any
level below that which will completely solarize the photo-
graphic element. For purposes of providing a point of
~ ~ ' '~ ` ' , ;
~ :
1~1971
--25--
reference !'completely solarizing light exposure" is herein
defined as that light exposure which produces a denslty
after processing equal to the denslty produced in ultra-
sonlcally unexposed areas after processlng in the absence
of light exposure. It is contemplated to employ maxlmum
light exposures which produce a density of at least 0.1
(preferably at least 0. 5~ above that produced by a com-
pletely solarizing light exposure.
I~ samples of a photographic element are pro-
cessed according to this process, but not ultrasonically
exposed, and each light exposed at a different llght
exposure level ranging up to some maximum exposure, such
as a completely solarlzing light exposure level, a char-
acteristic curve can be plotted--that is, a curve can be
formed by plotting observed density versus light exposure.
If another set of samples are simllarly processed, but
wlth a fixed ultrasonlc level of exposure, a second char-
acteristic curve can be plotted. The density difference
between the characteristic curves at a reference light
exposure level is the difference between maximum and
minimum densities obtained by the practice of this inven-
tion in the course of processing that photographic element
under those process conditions. The maximum density
difference can occur before the light exposure level is
reached which produces a maximum density or at a higher
light exposure level. For this reason it is in some
instances unexpectedly advantageous to employ light expo-
sure levels which are higher than those which produce a
maximum density.
3 Once ultrasonic and llght exposures of the
photographic element have occurred, a selectively devel-
opable latent image has been formed in the exposed silver
halide emulsion layer or layers of the element. The
latent image can be subsequently converted to a visible
image employing solutions and procedures which are conven-
tionally employed in photographic processing. The term
"photographic processing" is employed in its art recog-
nized sense as designating those processing steps conven-
1131~371
-26-
tionally employed in photography to form a visible image
corresponding to a latent image contained in a silver
halide emulsion layer of a photographic element. Photo-
graphic processing useful in the practice of this procesæ
is disclosed, for example, in Product Licensin~ Index,
Vol. 92, December 1971, publication 9232, paragraph XXIII,
Processing, page 110, and Research Disclosure, Vol. 176,
December 1978, publication 17643, paragraph XIX, Process-
ing, page 28. Research Disclosure and Product Licensin~
Index are published by Industrial Opportunities Ltd.,
Homewell, Havant, Hampshire, PO9, lEF, United Kingdom.
The photographic elements employed in the prac-
tice of this process typically include a support or sub-
strate. The support can conveniently take the form of a
conventional photographic support, such as disclosed in
Research Disclosure, Paragraph XVII, Supports, Item 17643,
cited above.
In a simple form, the photographic element can
consist of the support as described above and, coated
thereon, a single silver halide emulsion layer. The emul-
sion can be formed by dispersed silver halide grains and a
conventional photographic emulsion vehicle, such as a
hydrophilic colloid or other suitable vehicle. The silver
halide grains in the emulsion layer can be of any conven-
tional type which can form a latent image predominantly on
the surface of the silver halide grains or predominantly
on the interior of the silver halide grains. Conventional
photographic silver halide emulsions useful in the prac-
tice of this process are disclosed in Research Disclosure,
30 Paragraph I, Item 17643, cited above.
To illustrate A simple mode of practicing this
invention, surface latent image silver halide grain~ are
employed capable of forming a photographic negative image
when light expoQed in a conventional imaging silver halide
emulsion layer; however, the emulsion in which they are
incorporated in the practice of this process is modified
~.
~,~
1131~71
by halide ion ad~ustment so that it is substantially desen-
sitized to light exposure. That is, the pAg o~ the emul-
sion is ad~usted with halide ion addition so that the
maximum density obtainable with the element without ultra-
sonic activation at 30 seconds of immersion in a polarsolvent is less than 1.0, preferably less than 0.5.
As is well understood by those skilled in the
art, pAg is the negative logarithm (hereinafter designated
log) of the silver ion concentration expressed in normality
units (which for monovalent ions corresponds to moles/liter).
The relationship of the silver ion concentration, expressed
as pAg and the concentration of bromide ion, for example,
in a silver bromide emulsion can be illustrated by the
following equation:
-log Ksp = pBr ~ pAg
where
pAg is the negative log silver ion concentra-
tion, expressed in normality units,
pBr is the negative log bromide ion concentra-
tion, expressed in normality units, and
Ksp is the solubility product constant.
As is well appreciated in the art, Ksp values are a function
of both temperature and the specific halide or mixture of
halides chosen.
From the foregoing, it is apparent that to ele-
vate the pAg of the emulsion to a substantially desensitiz-
ing level, a higher concentration of halide ions (e.g., a
lower pBr) is required in the emulsion layer. The pAg of
the emulsion is preferably increased by bringing the emul-
slon lnto contact wlth a source of hallde lons, such as
alkali halide solutlon, whlle the emulsion ls in the form
of a melt before coating. Alternatively, the pAg of the
sllver halide emulsion can be regulated as it is formed.
pAg is a commonly employed photographic emulsion making
measuring approach whlch provides an indirect measure o~
halide ion concentration. It is, of course, recognized
that the presence of emulslon constituents other than
halide ions can also affect silver ion concentrations.
'
' ~
113~
-28-
Accordingly, pAg measurements must be carefully related to
the emulsions with which they are being employed. Optimum
halide ion levels to desensitize an imaging silver halide
emulsion layer can be established by coating otherwise
comparable emulsion layers at differing halide ion adjusted
pAg levels. It is, of course, within the skill of the art
to measure desensitizing halide ion levels directly rather
than indirectly through the measurement of pAg.
The above-described desensitized photographic
elements are ultrasonographically negative-working in this
process. It appears that ultrasonic exposure of the
above-described, high pAg ultrasonographic elements has the
effect of accelerating the release of halide ions from the
surface of the silver halide grains in the presence of a
polar solvent with the result of lowering the pAg in the
immediate vicinity of the silver halide grain surfaces.
These grains are then no longer desensitized and will
respond when subsequently exposed to light and further
processed.
It is further recognized that ultrasonic exposure
can concurrently stimulate ionic diffusion both into and
out of the silver halide emulsion layer being exposed.
For example, an ultrasonographically negative-working
element useful in the practice of this process can be
initially desensitized to light by imbibing bromide ions
into the silver halide emulsion layer, as described above,
and imagewise ultrasonically exposing the emulsion layer
while it is in contact with a polar solvent containing
silver ions dissolved therein. In this instance both
3 bromide ion dlffusion out of the emulslon layer and silver
ion diffusion into the emulsion layer contribute to image-
wise sensitizing the silver halide gralns of the emulsion
layer to light exposure. In a converse mode of practicing
this process~ the photographic element can be ultrasono-
graphically positive-working, initially containing the
silver ions imbibed in the emulsion layer while the bromide
ions are dissolved in the polar solvent in contact there-
` ~ ,
113~71
--29--
with. In this instance, it is silver ion diffusion out of
the emulsion layer and bromide lon diffusion into the
emulsion layer that relatively desensitizes the silver
halide grains to llght exposure.
The foregoing modes of practicing this process
with sllver halide photographic elements are descrlbed by
reference to surface latent image-forming silver halide
grains which are desensitized to light exposure as a
function of pAg. Silver halide grains which contain an
internal latent image are not developable in surface
developers and therefore yield photographic responses in
surface developers similar to surface latent image-forming
silver halide grains which have been desensitized--that
is, which contain no or few latent image centers. Con-
ventional silver halide grains and emulsions can then beused in the foregoing modes of practicing this process
which exhibit a balance of internal and surface latent
image-forming efficiencies which can be shifted as a
function of pAg ad~ustment. The references herein to
silver halide grains and emulsions which have been desensi-
tized include as a species thereof silver halide grains
and emulsions which under the pAg conditions of light
exposure form internal latent images, but which can form
surface latent images at a different pAg.
To illustrate specifically useful embodiments of
this type, what are known in the art as converted-halide
type silver halide grains exhibit a balance of internal
and external latent image-forming capabilitles. In the
form employed by Davey and Knott U.S. Patent 2,592,250 and
Motter U.S. Patent 3,703,584, the internal and external
latent image-forming efficiencies of the converted-halide
type silver halide grains are weighted in favor of forming
an internal latent image. However, in Evans U.S. Patent
3,622,318, issued November 23, 1971, the converted-halide
type silver halide grains are surface chemically sensitized
to a degree to balance the internal and external latent
image-forming efficiencies in favor of the formation of a
surface latent image. In Motter, cited above, surface
:: :
.
1131971
-30-
latent images can be similarly formed if surface chemical
sensitization is undertaken to the same degree. Evans
U.S. Patent 3,761,276, cited above, is an illustration of
internally doped and surface chemically sensitized silver
halide gralns exhibiting a balance of internal and surface
latent image efficiencies, which under the contemplated
conditions of photographic use disclosed therein, are
predisposed to form an interna] latent image. Evans and
Atwell U.S. Patent 4,035,185, cited above, illustrates a
blended emulsion of the type disclosed by Evans ('276~
wherein the silver halide grains are internally doped with
a combination of a noble metal and a middle chalcogen
sensitizer.
The photographic elements of Davey and Knott,
Motter, Evans ('276) and Evans and Atwell are useful as
ultrasonographically negative-working elements in the
practice of this process, since they are initially incapable
of forming a surface latent image when exposed to light, but
can be made capable of forming a surface latent image by
lowering the pAg at the silver halide grain surface. The
photographic elements of Evans ('318) can be employed in
this process as ultrasonographically positive-working ele-
ments, since they are initially capable of forming a sur-
face latent image upon exposure to light, but can be con-
verted to a form in which an internal latent image isformed by increasing the pAg ad~acent the surface of the
silver halide grains. It is recognized that the pAg of
the photographic elements of these patents can be altered
uniformly before ultrasonic exposure so that the negative-
3 working elements are converted to positlve-worklng ele-
ments and vice versa.
The term "surface developer" is used in its art
recognized sense and encompasses those developers which
will reveal the surface latent image on a silver halide
grain, but will not reveal substantial internal latent
image in an internal image-forming emulsion, under condi-
tions generally used to develop a surface-sensitive silver
halide emulsion. The surface develo~ers can generally
:1 131~371
-31-
utilize any of the silver halide developing sgent6 or
reducing agent~, but the developing bath or composition is
generally substantially free of a silver halide solvent
(such as w~ter-soluble thiocyanates, water-soluble thio-
ether~, thiosulfates, ammonia and the like) which willdisrupt or dissolve the grain to reveal subætantial inter-
nal image. Low amounts of excess halide are sometimes
desirable in the dveloper or incorporated in the emul~ion
as halide-releasing compounds, but high amounts are gener-
ally avoided to prevent substantial disruption of thegrain, especially with respect to iodide-relea~ing com-
pounds.
In photographic proce6ses for producing direct-
positive images employing conventional slver halide emul-
sions exhibiting a balance of internal and surfAce latentimage-forming efficiencies, the use of fogging or nucleat-
ing agent~ in the element or developer is common. These
fogging or nucleating agents can be employed in the prac-
tice of this process~ but they are not required, since the
nonimagewise or uniform light exposure step of this pro-
cess simultaneously performs functions similar to both the
imagewise light exposure step and the fogging or nucleat-
ing step of direct-positive photographic imaging. It is
recognized, of course, that light exposure can be confined
selectively to only those areas of the ultrasonographic
element which are intended to form an internal latent
image and, instead of light exposing areaæ to form a sur-
face latent image, the direct-po6itive photographic
nucleating procedure can be relied upon.
The patents of Davey and Knott, Motter, Evan~
('276) and Evans ('318), cited above, illustrate further
details of silver halide grains and emulsions exhibiting
balanced internal and surface latent image-forming effi-
ciencies as well as the techniques for their processing
and to define and illustrate the terms of art, such a6
"converted-halide", "surface developer", "internal latent
image" and the like, which are well known and understood
by tho~e 6killed in the art of photography.
.
.. .
1131971
-32-
Although-light exposure of the silver halide emul-
sion layer can be confined to the portion of the spectrum to
which the imaging grains possess a native sensitivity, it is
contemplated to sensitize spectrally the silver halide
grains so that they respond also to other portions of the
electromagnetic spectrum. Spectral sensitization can be
undertaken using the dyes and techniques which are conven-
tional in preparing spectrally sensitive photographic
elements.
Sensitizing dyes useful in sensitizing silver
halidè emulsions are described for example, in Brooker
et al U.S. Patent 2,526,632, Sprague U.S. Patent 2,503,776,
Brooker et al U.S. Patent 2,493,748 and Taber et al U.S.
Patent 3,384,486. Spectral sensitizers which can be used
include the cyanines, merocyanines, complex (tri-or tetra-
nuclear) cyanines, holopolar cyanines, styryls, hemicyan-
ines (e.g., enamine hemicyanines~, oxonols and hemioxonols.
Dyes of the cyanine classes suitable for sensi-
tizing silver halide can contain such basic nuclei as the
thiazolines, oxazolines, pyrrolines, pyridines, oxazoles,
thiazoles, selenazoles and imidazoles. Such nuclei can
contain alkali, alkylene, hydroxyalkyl, sulfoalkyl, car-
boxyalkyl, aminoalkyl and enamine groups and can be fused
to carboxylic or heterocyclic ring systems either unsubsti-
tuted or substituted with halogen, phenyl, alkyl, halo-
alkyl, cyano, or alkoxy groups. The dyes can be symmetri-
cal or unsymmetrical and can contain alkyl, phenyl,
enamine or heterocyclic substituents on the methine or
polymethine chain.
The merocyanine dyes can contain the basic
nuclei mentioned above as well as acid nuclei such as
thiohydantoins, rhodanines, oxazolidenediones, thiazoli-
denediones, barbituric acids, thiazolineones, and malono-
nitrile. These acid nuclei can be appropriately substi-
tuted with alkyl, alkylene, phenyl, carboxyalkyl, sulfo-
alkyl, hydroxyalkyl, alkoxyalkyl, alkylamino groups, or
heterocyclic nuclel. Combinations of these dyes can be
used, if desired. In addition, super-sensitizlng addenda
:, , :
L
``"`~ il31971
-33-
which do not abæorb visible light can be included, for
instance, ascorbic acid derivatives, azaindenes, cadmium
salts, and organic sulfon~c acids as described in McFall
et al U.S. Patent 2,933,390 and Jones et al U.S. Patent
5 2,937,089.
It is known in the art that spectral sen6itizing
dyes in addition to extending the spectral response of the
silver halide grains can have a definite desensitizing
effect on the grains. The degree of desensitization
exhibited is a function of parameters such as the concen-
tration of the dye incorporated, the oxidation and reduc-
tion potentials of the dye and the pAg of the æilver
halide emulsion layer into which it is incorporated. By
employing sensitizing dyes as desensitizer6, it is possi-
ble to reduce the background or minimum densities ofnegative-working ultrasonographic elements, since the
desensitizing action of the dye supplements the desensiti-
zation effect attributable solely to the high initial pAg
of the emulsion layer. By employing desensitizers which
become less effective at lower pAg's, it i6 pos6ible to
avoid desensitization in ultrasonically exposed areas of
the ultrasonographic element. Large differences in den-
sity can be obtained between ultrasonically exposed and
unexposed areas of ultrasonographically negative-working
elements using selected desensitizers.
It is contemplated to employ in the practice of
this process any conventional silver halide emulsion
desensitizer. It is preferred to employ desensitizers
which exhibit a variation in desensitization a6 a function
of pAg and, in ultrasono~raphically negative-working ele-
ments, it is preferred to employ desensitizers which
become less effective at lowered pAg values~
Specifically preferred desensitizers are dyes,
such as cyanine and merocyanine dyes, and compounds which
are dyes which exhibit a strong desensitizing effect on
photographically negative-working silver halide emulsions
disclosed in Research Disclosure, Paragraph IV, Item
17643, cited above.
.~
I~ ~
, . . . .
-34-
While simple photographic elements are described,
it is apparent that this process is generally useful with
any conventional photographic element, the imaging silver
halide emulsion layer or layers of which have been desensi-
tized through the use of a high pAg, preferably halide ionadjusted high pAg. Stated still more generally, it is
apparent that any conventional photographic element which
exhibits a speed dependence on the pAg of the silver halide
imaging layer or layers can be employed in the practice of
this process. The halide ions employed for adJusting the
pAg can correspond to the halides forming the silver
halide grains. It is preferred to employ soluble bromide
salts, such as alkali metal bromides, to raise pAg. It is
preferred to employ water soluble silver salts for lowering
pAg, such as silver nitrate.
While the above modes of practicing this process
employ a photographic element which exhibits an alteration
in sensitivity as a function of halide ion ad~usted pAg, it
is appreciated that this process can be practiced using
still other mechanisms of sensitization or desensitization.
For example, in the practice of this process any conventional
photographic element having at least one silver halide
emulsion layer can be employed which contains a protonated
dye which can be deprotonated to a light-absorbing, spec-
tral sensitizing form.
Where the spectral sensitizing dye is of a typewhich can be converted from an initially colorless form to
a light-absorbing form by deprotonation, it is apparent
that the above-described process can be readily adapted to
formlng negative ultrasonographic images. In thls instance,
the dye in ~ts protonated form is incorporated in the
imaging silver halide emulsion layer. The polar solvent
to be contacted with the element is then chosen so that it
is of a higher pH than the emulsion layer so that the
element when immersed in the polar solvent experiences a
deprotonation of the dye to its chromophoric form in from
10 seconds to 10 hours. By practicing the process as
described above, it produces an ultrasonographic negative
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image, and the element, since it goes from an initially
light-insensitive form to a light-sensitive form, is
ultrasonographically negative-working, as that term has
been defined above.
Exemplary of conventional spectral sensitizing
dyes which are known to be protonatable to a colorless form
and/or deprotonated to generate the dye chromophore are
those disclosed by A. H. Herz, Photograhic Science and
Engineering, Vol. 18, No. 2, March-April 1974, pages 207
10 through 215 and VanLare U.S. Patent 3,482,981. Preferred
spectral sensitizing dyes of this type are benzimidazole
carbocyanine dyes. By proper choice of nuclei substituents
such dyes can be made to exhibit absorption maxima at wave-
lengths within the blue, green, red and infrared portions
of the electromagnetic spectrum.
In addition to spectral sensitizing dyes whose
effectiveness can be modified by pH, desensitizers having
p~ dependence are also known in the art. For example, Itoh,
J. Soc. Sci. Photo., Vol. 32, page 18, 1969, discloses that
adenine, a known desensitizer, will adsorb to silver halide
grains at a pH of 6, but not at a pH of 2. Similarly, E. J.
Birr, Z. Wiss. Phot., Vol. 49, page 261, 1954, Volume 50,
page 107, 1955 and Volume 50, page 124, 1955, discloses the
pH dependence of adsorption of tetraazindenes. E. J. Birr
in his book Stabilizati _ of Photographic Silver Halide
Emulsions, Focal Press, 1974, page 175, discloses that the
desensitizers nitrobenzimidazole, mercaptobenzimidazole,
mercaptobenzimidzole sulfonic acid, benzotriazole and
phenylmercaptotetrazole are selectively adsorbed by silver
3 halide grains at higher pH.
It 18 apparent that the ul~ra~onographic elements
discussed immediately above lllustrate that ultrasonic
radiation can be employed to modlfy locally the pH of an
imaging silver halide emulsion layer so that its light
response is also locally modified. This ultrasonically
induced modification of the element can be used to generate
a viewable ultrasonographic image. Since the component of
the emulsion layer in this instance being acted upon is the
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sensitizer or desensitizer, it is apparent that any con-
ventional photograhic element comprised of at least one
imaging silver halide emulsion layer compatible with such a
pH modifiable sensitizer or desensitizer can be employed.
The photographic elements described above as being
pAg or pH modifiable in their photographic response through
the use of ultrasonographic radiation can, of course, con-
tain a variety of conventional photographic silver halide
emulsion addenda. The silver halide photographic elements
can be chosen from among those particularly adapted for
various photographic applications, such as thermal pro-
cessing, image transfer, multicolor imaging and the like.
For example, any of the conventional photographic features
disclosed in Research Disclosure, Item 17643, and Product
Licensing Index, Item 9232, both cited above, not incom-
patible with obtaining the desired pAg and pH modifica-
tion effects, can be used in the practice of this process.
Plural Layer Recording Layer Units
Although the ultrasonographic elements are des-
cribed above in terms of a recording layer unit consisting
of a single layer coated on a support, significant advan-
tages can be obtained in terms of maximum densities and
image discrimination by expanding the recording layer unit
to include also a transport liquid permeable layer in
contact with the recording layer and between the recording
layer and the support. The transport liquid permeable
layer can be formed, for example, of any of the conven-
tional vehicle and vehicle extenders employed in silver
halide emulsion layers. These layers, more specifically
undercoats, are preferably formed of a hydrophilic colloid,
such as gelatln or a gelatin-derivative, as described above.
Undercoat layers of this type are conventional in silver
halide photographic elements.
It is also recognized that further improvements
in maximum densities and image discrimination can be
achieved when a plurality of recording layers are present
as opposed to a single recording layer. In such an arrange-
ment it is preferred that each recording layer be under-
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coated with a transport liquid permeable layer in contact
with the recording and interposed between the recording
layer and the support. Conventional silver halide photo-
graphic elements with vehicle interlayers between ad~acent
emulsion layers illustrate u6eful ultrasonographic ele-
ments of this type. U.S. Patent 4,223,082, titled ULTRA-
SONOGRAPHY, which in part corresponds to Belgian Patent
864,069, cited above, discloses suitable ultrasonographic
elements of this type.
Still another form of multiple layer recording
layer unit useful in the practice of this invention is
disclosed in copending, commonly assigned patent applica-
tion Serial No. 331,572, filed June 11, 1979, titled
ULTRASONOGRAPHIC ELEMENTS CONTAINING MULTIPLE LAYERS AND
PROCESS FOR THEIR USE, cited above.
In one specifically preferred form an outer layer
of the recording layer unit iæ a silver halide emulsion
layer which contains diffusible ions capable of desensi-
tizing the emulsion to light. A layer nearer the æupport
20 i6 a receiving layer for the diffu6ible ions, and a bar-
rier layer separates the emulsion and receiving layers.
When the element is immersed in transport liquid
and imagewise ultrasonically exposed, the diffusible ions
which are initially desen~itizing the silver halide emul-
sion layer in part diffuse into the transport liquid. Aportion of the diffusible ions also enter the barrier
lsyer, since their rate of diffusion in the barrier mate-
rial i8 greatly accelerated by ultrasound. However, since
the diffu6ion paths of the ions are es~entially random, in
the absence of the receiving layer, the diffusible ions
are free, not only to enter the barrier layer, but also to
return.
The presence of the receiving layer can have the
effect of increasing both the image discrimination and the
ultrasonic 6ensitivity of theultrasonographic element.
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The diffusible desensitizing ions leaving the emulsion
layer penetrate the barrier layer and thereby come into
contact with the receiving layer. Upon contact with the
receiving layer the ions are immobilized. Thus, they are
not free to continue their random migration in the presence
of ultrasound, which otherwise results in a portion of the
ions migrating back to the emulsion layer. It is believed
that the enhanced response of the ultrasonographic elements
of this invention in this preferred form can be attributed
to the contribution of the receiving layer in depleting the
desensitizing ions initially within the emulsion layer.
It is specifically contemplated that both the
layer which is the source of diffusible ions (i.e., the
source layer) and the receiving layer can be silver halide
emulsion layers. The two emulsions are preferably chosen
so that the ultrasonically induced migration of a diffusible
ion from one emulsion layer has the effect of sensitizing
it as well. In this specific form the receiving layer is
preferably a silver chloride emulsion layer while the source
layer is a silver bromide emulsion layer which is desensi-
tized by bromide ion ad~ustment as has been described above.
Where the receiving layer is not a silver halide emulsion
layer, it can take the form of a layer containing any
convenient substance for immobilizing the ions diffusing
from the source layer. For example, the receiving layer
can contain a silver salt, such as silver nitrate, to react
with and immobilize bromide ions migrating from a bromide
ion desensitized silver halide emulsion source layer.
The foregolng discussion is considered suffi-
3 clently complete to permit those familiar with the photo-
graphic and ultrasonlc arts to practice this process. To
the extent that specific details and variants of this
process and means for its practice are not explicitly
discussed they can be appreciated by reference to the
photographic and ultrasonic arts. For example, it is
contemplated that the ultrasonic exposure, development and
other processing steps of this process can be practiced
within the temperature ranges conventionally employed in
photography.
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Examples
The invention is further illustrated by the
following examples:
To illustrate a specific preferred embodiment of
the present invention an ultrasonographic element was
prepared in the following manner: A cubic-grained gelatino-
silver bromide emulsion free of surface chemical sensi-
tization and having a mean grain diameter of 0.2 micron,
to which a desensitizing dye 1,1'-diethyl-6,6'-dinitro-
10 thiacyanine chloride has been added at a level of 1.25 XlO 4 mole per mole of silver, was coated on a poly(ethyl-
ene terephthalate) film support to obtain a silver cover-
age of 3.2 grams per square meter and a gelatin coverage
of 2.7 grams per square meter. The pH of the emulsion
15 coating was 6.5 and the pAg 6.o.
During each ultrasound exposure the ultrasono-
graphic element was pressed between two aligned open-ended
cylinders so that it formed a dividing wall separating the
interiors of the cylinders. The cylinders were vertically
20 aligned above an ultrasound transducer in a reservoir con-
taining a distilled water transport liquid so that the
emulsion layer of the ultrasonographic element was on the
surface of the support nearest the transducer. The lower
cylinder was filled with distilled water by immersing it
25 in the transport liquid within the reservoir. The upper
cylinder was filled with distilled water at varied tempera-
tures shown below in Table I.
The emulsion layer was positioned ~lorlzontally
durln~ ultrasonic exposure 7.6 cm above the tlp of the
30 ultrasound transducer. The ultrasound transducer was
driven to provide ultrasound at a peak intensity of 0.57
; watt per square centimeter at the emulsion layer. A
pulsed ultrasound exposure was employed at lO 6 second
pulse width~ lO 4 second pulse period and lO seconds total
elapsed exposure time. Prior to ultrasound exposure the
emulsion layer was in contact with the transport liquid
for lO seconds, and following ultrasound exposure the
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emulsion layer was in contact with the transport liquid
for 40 seconds prior to light exposure.
The light source was an array of 132 tungsten
lamps of one and one-half watt each (commercially avail-
able under the trademark GE 31) equally spaced on apolished metal reflecting surface contained within a
housing 10 by 40 centimeter on an edge. Light exposure of
the element for 8 seconds at 65,000 lux (lumens per square
meter). Following light exposure the ultrasonographic
element was removed from contact with the transport liquid
i` and developed in Kodak Developer D-19, fixed, washed and
dried. Except for the difference in the thermal gradient
each of the elements were identically exposed and pro-
cessed.
Table I
Upper
Reservoir Cylinder Density Image
Tempera- Tempera- Exposed Back- Discrim-
ture (C) ture (C) Areas ground ination
Control 20 20 2.6 1.2 1.4
20 Example l 20 35 3.7 l.l 2.6
Example 2 20 45 5.6 1.6 4.o
In reviewing the results reported in Table I it
can be seen that in the absence of a temperature differ-
ential in the transport liquid immediately ad~acent the
recording layer unit (the emulsion layer) a density of 2.6
was obtained in exposed areas while a density of 1.2 was
obtained in background (ultrasonically unexposed) areas.
This demonstrated that the ultrasound in the absence of
the termal gradlent was able to accelerate equilibration
of the ultrasonographic element and the transport liquid.
The image discrimination was 1.4.
When the temperature of the distilled ~ater in
the upper cylinder contacting the ultrasonographic element
support surface opposite the recording layer unit was
raised to 35C as in Example l, the density obtained in
ultrasonically exposed areas increased significantly to
3.7. On the other hand, the background density remained
at approximately the same level as in the absence of a
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thermal differential. This resulted in an increase in the
image discrimination from 1.4 to 2.6. The effect of being
able to increase the density in ultrasonically exposed
areas without significantly raising density in background
areas is distinctly advantageous for ultrasonographic
imaging.
In Example 2 the temperature of the liquid in
the upper cylinder was raised further from 35C to 45C.
The result was a further increase in density in exposed
areas. A density increase in exposed areas of 3.0 was
observed to result from the thermal gradient employed.
Background density rose slightly to 1.6, a rise of only
0.4. Image discrimination was 4.0 as compared to only
1.4 in the absence of a thermal gradient. The imaging
results continued to improve as the thermal gradient was
increased from 15 to 25C between the support surface of
the ultrasonographic element and the transport liquid
reservoir.
The results of Examples 1 and 2 were qualita-
tively corroborated by additional investigations. Although
densities in exposed areas were in some instances less
than those of Examples 1 and 2, these examples are con-
sidered fairly indicative of results which can be obtained
by the practice of this process.
The invention has been described in detail with
particular reference to preferred embodiments thereof but
it will be understood that variations and modifications
can be effected within the spirit and scope of the invention.
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