CA1131971A - Imagewise accelerating equilibration in ultrasonographic recording - Google Patents

Abstract

IMAGEWISE ACCELERATING EQUILIBRATION
IN ULTRASONOGRAPHIC RECORDING
Abstract of the Disclosure A process is disclosed for recording an ultrasonic exposure pattern employing an ultrasonographic element containing a support and a recording layer unit. The re-cording layer unit is placed into contact with a transport liquid and imagewise ultrasonically exposed to accelerate imagewise diffusion from the recording layer unit to the transport liquid, thereby producing in the recording layer unit an ultrasonographic record. Diffusion is further accelerated imagewise by establishing a temperature differ-ential within the transport liquid adjacent the recording layer unit.

Description

:~31~371 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

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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.

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1131~371 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 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 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 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.

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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 ,~ .

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, 1~31971 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 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 : .

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1131~71 .

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.

, , 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 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~

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 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.

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1~31~71 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 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 .

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113~

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 , . ~ .
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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 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 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~

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 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 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~

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 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 :: :
.

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 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.

.

.. .

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 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~ ~
, . . . .

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 - : :
.~ , .

3i 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 .

;. .,.. ,: ~

~ ~ 31 ~ 71 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-: ~

1131~7 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.

~ , , 1~31971 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 '` :

31 ~ 7 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.

3o ~, ;

Claims (10)

WHAT IS CLAIMED IS

1. In a process of recording an ultrasonic exposure pattern employing an ultrasonographic element comprised of a support and a recording layer unit capable of producing an ultrasonographic record as a function of diffusion to a transport liquid, the recording layer unit being beneath the support and in contact with the transport liquid, said process comprising imagewise ultrasonically exposing the recording 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 improvement comprising further accelerating diffusion in ultrasonically exposed areas by establishing 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 relatively lower temperature than the transport liquid contacting the recording layer unit.

2. An improved process according to claim 1 additionally including the step of converting the ultra-sonographic record to a viewable ultrasonographic image.

3. An improved process according to claim 2 in which the recording layer unit is ultrasonographically negative-working and a maximum density is produced in the ultrasonographic image corresponding to ultrasonically exposed areas of the recording layer unit.

4. An improved process according to claim 1 in which the ultrasonographic element and the transport liquid are maintained within a temperature range of from about 5 to 80°C.

5. An improved process according to claim 4 in which the ultrasonographic element and the transport liquid are maintained within a temperature range Or from about 10 to 60°C.

6. An improved process according to claim 1 in which the support and the transport liquid remote from the recording layer unit exhibit a temperature differential in the range of from about 1 to 75°C.

7. An improved process according to claim 6 in which the support and the transport liquid remote from the recording layer unit exhibit a temperature differential in the range of from about 5 to 50°C.

8. An improved process according to claim 1 in which the transport liquid exhibits a viscosity in the range of from abot 0.5 to 1.5 centipoise.

9. An improved process according to claim 1 in which the ultrasonographic element is substantially hori-zontally positioned during ultrasonic exposure.

10. An improved process according to claims 1, 5, or 7 in which the recording layer unit includes a silver halide emulsion layer.