Apparatus and method for measuring the composition or constitution of a human or animal organ or another object

Abstract

An organ tissue composition or constitution assessment apparatus (10) comprises first and second panel elements (16, 18) disposed in spaced apart and facing relationship. One of the first and second panel elements (16, 17) is adjustable relative to the other in distance. At least one ultrasound emitter (32) is disposed on the second panel element (18). At least one ultrasound receiver (30) is disposed on the first panel element (16), such that the emitter and receiver face another. The panel elements are connected to a support structure (12, 14) and preferably in an arrangement which enables assessment of a patient's body part while the patient is in an upright position. The apparatus includes a processing unit (304) which is configured to determine from the received ultrasound signals a tissue composition or constitution measure associated with the organ tissue to be assessed and preferably an overall tissue composition or constitution measurement across the entire area of the organ tissue to be assessed. The preferred embodiment is able to obtain a measure of an average breast tissue composition or constitution, which can be used as indicative of a medical condition or risk of a medical condition, such as cancer, and as a guide to selection of optimum screening procedures.

Description

[0001]APPARATUS AND METHOD FOR MEASURING THE COMPOSITION ORCONSTITUTION OF A HUMAN OR ANIMAL ORGAN OR ANOTHER OBJECTField of the InventionThe present invention relates to apparatus and a method for obtaining ameasure of the constitution or composition of an organ, such as tissuecomposition or breast density, of a human or animal subject, for example for theassessment of a medical condition, and to a method of identifying a medicalcondition in a subject by use of apparatus or a method as taught herein. Theteachings herein also provide for a method and apparatus for obtaining a measureof acoustic attenuation of or through any other object to determine the compositionor constitution of the object. They may be used, for example, to identify a state orcontents of an object.Background of the InventionBreast density assessment is an important part of personalised breastcancer risk assessment for future risk-adaptive screening services. Existing,measures of breast density assessment, in particular X-Ray Mammography (XRM)and Magnetic Resonance Imaging (MRI) do not meet the criteria set by the UKNational Screening Committee (NSC) for population screening (or pre-screening)because these imaging methods are not simple, safe, precise, or validated tests.Specifically, they are susceptible to characterising women differently betweenreaders or screening occasions. Additionally, existing breast density assessmenttechniques are generally not suitable for younger women who are under thescreening age (40 in the US, and around 50 in Europe).More specifically, the UK National Screening Committee (NSC) considerschanges to screening programmes when there is strong evidence that they couldimprove outcomes. In 2019, the committee considered the use of supplementalscreening for women with dense breasts but found that the identification of thiscohort (by mammographic breast density assessment) could not be doneconsistently, reliably or at scale (https: / / view-health-screening-recommendations.service.gov.uk / document / 465 / download). The NSC Report was accompanied by a consultation (https: / / view-health-screening-recommendations.service.gov.uk / review / breast-cancer-2019 / download-documents / cover_sheet / ) which concluded: "It is essential to establish a safe,consistent and reliable method of measuring breast density before its routine usein clinical procedure could be considered. The current lack of a gold standardmethod must be addressed."Similarly, in the United States in 2023, the FDA published an update to themammography regulations to require, among other things, mammography facilitiesto notify patients about the density of their breasts, in order to strengthen theFDA’s oversight and enforcement of facilities and to help interpreting physiciansbetter categorise and assess mammograms. The update requires allmammographic facilities to comply by 10th September 2024. This will be by way ofa mammographically derived breast density assessment. The intention is thatwomen will be sent one of two Federal density notification statements ("not dense"or "dense") and that the mammogram report sent to referring providers will have toinclude an assessment (more detailed) of the patient's breast density. This followsa grassroots movement, spearheaded Dr Nancy Cappello and her “Are YouDense?” advocacy group, to push for breast density notification in the UnitedStates, as women are needlessly undergoing mastectomies, invasive treatmentand dying after late detection because they were uninformed of breast densityissues. Consistent with this, the American College of Radiology and the Society ofBreast Imaging have recommended that breast cancer risk assessment is firstcarried out by the age 25, so that those at higher risk of developing breast cancercan be identified early and be offered risk management advice and with theprospect of early treatment of any cancer that subsequently develops. While theintention of such early assessment is laudable, breast density assessment cannotcurrently be included in early breast cancer risk assessment becausemammograms are not recommended for young women in light of the health risksthey entail.Similarly, in the “Report of The Independent Review of AdultScreening Programmes in England” of October 2019, Sir Michael Richardshighlighted targeted risk-based screening as the main opportunity to furtherimprove the uptake, coverage and functioning of breast screening programme.In light of all these recommendations and regulations seeking to establishscreening of breast density particularly in younger women in order to identify earlywomen at risk, in March 2023, the UK National Screening Committee gatheredexperts to discuss models for personalised breast screening based on risk(https: / / nationalscreening.blog.gov.uk / 2023 / 03 / 28 / experts-discuss-models-for- personalised-breast-screening-based-on-risk / ) There is therefore a healthcare need and push to provide for quantitativebreast density assessment for early detection of people at risk of developingbreast cancer, even though no reliable system that is safe to be used particularlyon younger women exists.In order to avoid X-ray and magnetic resonance imaging, the use ofultrasound imaging has been proposed, which is safe and can be appliedrepeatedly even in younger people.While ultrasound is a suitable candidate technology, traditional handheldscanners are heavily operator dependant and are not capable of consistent andreliable breast density assessment. Ultrasound computed tomography scannersin development are less dependant on the skill of the operator and are capable ofbreast density assessment. However, they are complex devices designed forbreast screening and require thousands of ultrasound emitters and receivers toreconstruct images and map breast composition. Breast density assessmentwould be an adjunct to their primary use of breast screening.Furthermore, quantitative acoustic attenuation measurement of aheterogeneous tissue structure, such as breast tissue, is difficult in vivo due tocomplex ultrasound-tissue interactions, including refraction and phase cancellationeffects, which cause significant measurement errors.To date there has not been proposed any ultrasound based system that canprovide a reliable indication of breast density.As a consequence, mammography remains the only currently acceptedmethod for breast density assessment. However, as mammography uses ionisingradiation, this limits the frequency of assessment, as well as requiring specialistfacilities and operating personnel. Mammography is also an uncomfortableprocedure which necessitates painful compression of the breast. Ultrasoundtomography systems that have been proposed in the literature require watercoupling to facilitate ultrasound propagation between a hemisphere / ring ofultrasound elements and the breast, which again is not an ideal solution.While there has been much focus by the health authorities in seeking todetect early the risk of a woman developing breast cancer, especially in youngerwomen, there are more general clinical needs to early assessment of othermedical conditions. These can include, for example, other cancers or the risk ofdeveloping cancer in other parts of the body and other benign growths. There isalso a need for identifying early the risk or actual early onset of other changes tothe condition of a person’s organs, including for example bone tissue and possibleonset of osteoporosis, for instance. While X-ray and magnetic resonance imagingare capable to detecting such conditions, they are not routinely practiced out on aperson until actual symptoms develop, which typically occurs only once thecondition is advanced. This frustrates attempts for early detection andconsequential management and early treatment of such conditions.The teachings herein are also applicable to non-medical applications, forinstance in the assessment of a composition or condition of an object, anycontents thereof and so on.Summary of the Present InventionThe present invention seeks to provide apparatus and a method forobtaining a measure of organ composition or constitution of a human or animal,particularly for the assessment of risk of developing or early onset of medicaldisorders. The preferred embodiments are configured to obtain a measure oftissue composition, useful for example in the determination of onset or risk ofonset of disease such as cancer, osteoporosis and so on. The present inventioncan also provide apparatus and a method for obtaining a measure of attenuationof or through inanimate objects.According to an aspect of the present invention, there is provided an objectcomposition or constitution assessment apparatus comprising:first and second panel elements disposable in spaced apart and facingrelationship, at least one of the first and second panel elements being adjustablerelative to the other in separation;at least one ultrasound emitter disposed at or on one of the first and secondpanel elements;at least one ultrasound receiver disposed at or on the other of the first andsecond panel elements, whereby the at least one ultrasound emitter and the atleast one ultrasound receiver face one another;a support structure to which the first and second panel elements areattached; anda processing unit coupled to the at least one ultrasound transmitter andreceiver and configured to determine the received ultrasound signal which isproportional to the acoustic power transmitted through the object representative ofthe total acoustic attenuation through the object assessed, and to determinetherefrom an object composition or constitution measure associated with the objectassessed. In practical terms, the processing unit determines what the signals arerepresentative of, acoustic attenuation of the beam energy and therefrom thecomposition or constitution of the object located between the emitters and thereceiver. Preferably, the processing unit is configured to determine the insertion lossfrom each of a plurality of emitters and therefrom a bulk or volume averageacoustic attenuation across a determined area of the object assessed.In practice, the processing unit is configured to determine from the signals:(i) the peak voltage response from the sensor which is proportional to the incidentacoustic power, (ii) the acoustic insertion loss relative to water (a calibrationcoefficient) (iii) the acoustic attenuation coefficient (measured to a calibrated valueand on the basis of the emitter and receiver separation).The advantage of the apparatus and method taught herein is that they canobtain an indication of the overall condition of an object or organ of a patient, suchas tissue, in a process that does not require ionising radiation, which is thereforesafe, and which can provide an indication of possible issues and therefrom arecommendation form further investigations, typically more intrusive such as x-rays, MRI or the like. The system and method taught herein can provide anindication of potential risk of developing a disease, for instance.Advantageously, the apparatus is configured to determine the compositionor constitution of as body part of a human or animal. The body part maycomprises an organ such as tissue.Preferably, the support structure and panel elements permit a subject toundergo tissue composition assessment of a body part of that subject while in agenerally upright position, advantageously standing or seated.At least one of the first and second panel elements preferably comprises anadjustment element with an object or patient facing plate orientable relative to theassociated first or second panel element and relative to a part of an object orpatient’s body to be assessed.The adjustment element is advantageously configured to reduce orminimise air gaps between the transmitter and receiver elements and the object orpart of a patient’s body to be assessed. The adjustment element may be coupledto at a respective one of the first and second panel elements by a hinge or pivotand configured to rotate thereabout.Preferably, the adjustment element comprises a compliant mechanismdisposed at an object or patient remote side of the object or body part facing paneland configured to allow adjustment of an angle of tilt of the object or patient facingpanel. The compliant mechanism may comprise a bladder selectively fillable witha fluid, and preferably a fluid source, a pump coupled to the source and a pressureor volume sensor, the fluid source being coupled to the bladder for filling thebladder with fluid to a determined pressure or volume.The compliant mechanism may be made of an acoustically transmissiblematerial, wherein the at least one ultrasonic emitter or the at least one ultrasonicreceiver is disposed behind the compliant mechanism relative to the object orpatient facing surface such that in use ultrasonic beams pass through the materialof the compliant mechanism.Advantageously, the at least one ultrasound receiver is shaped and sized tobe at least as large as an area expected to be covered by an object or person’sbody part to be assessed when placed between the lower and upper panelelements. There is preferably provided an array of ultrasound emitters, the arrayadvantageously being shaped and sized to be at least as large as an areaexpected to be covered by an object or person’s body part to be assessed whenplaced between the lower and upper panel elements.The at least one ultrasound emitter may be adjustable and / or movablerelative to the at least one receiver so as to be able to emit an adjustable ormovable ultrasonic beam towards the at least one emitter. The at least oneultrasound emitter may have an adjustable ultrasonic beam angle.Preferably, the at least one ultrasonic receiver's output is proportional to thetotal acoustic power of ultrasound incident on its surface.In the preferred embodiments, the processing unit is configured todetermine on the basis of an ultrasonic signal sensed at the at least one ultrasonicreceiver and of the detected distance between the at least one ultrasonic emitterand the at least one ultrasonic receiver an attenuation of the ultrasonic energy andto determine therefrom a measure of composition or constitution of the object ororgan. Advantageously, the processing unit is configured to determine on the basisof a thickness of compliant and / or other material between the at least oneultrasonic emitter and / or the at least one ultrasonic receiver and the or an object ortissue contact panel of the apparatus a lost ultrasonic attenuation from thecompliant and other material and to adjust the measured attenuation on the basisof the determined lost ultrasonic attenuation.The processing unit is preferably configured to calculate thickness ofcompliant and / or other material on the basis of a measured angle of the object ortissue facing surface relative to the at least one ultrasonic emitter or receiver, or onthe basis of volume of fluid in the or a fillable bladder. It may be configured todetermine attenuation across substantially the whole area of an object or body partand to determine an average attenuation through the object or body part; such asacoustic attenuation across a plurality of select areas of an object or organ and todetermine an ultrasound attenuation map across the areas of the object or organ.In practice, this is an average determined at a number of discrete positionsover the object being investigated.The processing unit may be configured to apply a calibration value to theacoustic energy signals received at the receiver to take into account factorsincluding: sensor spacing, lost emitter energy through intervening materials of theapparatus. Advantageously, the calibration value includes one or more of: measurementsmade through reference materials, data relevant to a particular organ or object to beexamined, nature or characteristics of a patient or object undergoing examination, spacingof the emitter and receiver assemblies from one another, the amount of attenuationmaterial other than body part between the emitter and receiver assemblies.Preferably, the processing unit is configured to operate the at least onetransmitter at different frequencies, for the analysis of different tissue types and / orfor different assessment specificity, in other embodiments the apparatuscomprising transmitters operable at different frequencies in the array, such as 50%being 2 MHz emitters and 50% being 4 MHz emitters.The processing unit is optionally configured to determine a measure oftissue composition or constitution of a selected tissue type within a body part beingtested. In embodiments, one or both of the first and second panel elementscomprises a pivot or hinge configured to tilt at least a part of the panel element.The apparatus is preferably configured to obtain a determination of objector tissue composition or constitution in a plurality of planes by adjustment of theorientation and / or disposition of the transmitter and receiver elements relative toan object or body part being analysed.There may be provided a gimbal mechanism coupled to the panel elementsand operable to adjust the orientation of the first and second panel elements.Preferably, the apparatus is configured to assess breast tissue compositionor constitution.In the preferred embodiments, the at least one receiver has a size and areaat least as large as a size and area of the ultrasonic beam or beams emitted bythe emitter or emitters in free air. The at least one receiver may have a size andarea at least 10% larger than a size and area of the ultrasonic beam or beamsemitted by the emitter or emitters in free air.According to another aspect of the present invention, there is provided amethod of assessing the composition or constitution of an object comprising:disposing first and second panel elements in spaced apart and facingrelationship, at least one ultrasound emitter being disposed at or on one of the firstand second panel elements and at least one ultrasound receiver disposed at or onthe other of the first and second panel elements, whereby the at least oneultrasound emitter and the at least one ultrasound receiver face one another;and determining the received ultrasound signal which is proportional to theacoustic power transmitted through the object representative of the total acousticattenuation through the object assessed, and to determine therefrom an objectcomposition or constitution measure associated with the object assessed.Preferably, an overall object composition or constitution measurement isdetermined across an area of the object assessed.Advantageously, the method is carried out to determine the composition orconstitution of an organ or tissue of human or animal patient. Preferably, themethod is practiced on an organ of a person while in a generally upright position,advantageously standing or seated.At least one of the first and second panel elements may comprise anorientation adjustable object or patient facing plate, wherein the method comprisesadjusting the orientation of the plate relative to the associated first or second panelelement and relative to an object or part of a patient’s body to be assessed.The method may comprise adjusting the orientation of the object or patientfacing plate to reduce or minimise air gaps between the transmitter and receiverelements and the object or part of a patient’s body to be assessed.There may be provided the step of comprising operating a compliantmechanism disposed at a remote side of the object or patient facing panel to allowadjustment of an angle of tilt of the object or patient facing panel. This maycomprise selectively filling with a fluid a bladder of the compliant mechanism byoperating a fluid source with a pump coupled to the source and a pressure orvolume sensor, and selectively filling the bladder to a determined pressure orvolume. The method may apply a calibration value to the acoustic energy signalsreceived at the receiver to take into account factors including: sensor spacing, lostemitter energy through intervening materials of the apparatus.Advantageously, the calibration value includes one or more of: measurementsmade through reference materials, data relevant to a particular organ or object to beexamined, nature or characteristics of a patient or object undergoing examination, spacingof the emitter and receiver assemblies from one another, the amount of attenuationmaterial other than body part between the emitter and receiver assemblies.The method preferably comprises receiving ultrasonic signals across anarea at least as large as an area covered by an object or person’s body part to beassessed. It may comprise emitting ultrasonic signals across an area at least aslarge as an area covered by an object or person’s body part to be assessed.The method may include adjusting and / or moving the at least oneultrasound emitter relative to the at least one receiver so as to emit an adjustableor movable ultrasonic beam towards the at least one emitter. It may includeadjusting an ultrasonic beam angle of the at least one ultrasound emitter.Advantageously, the method includes determining on the basis of anultrasonic signal sensed at the at least one ultrasonic receiver and of the detecteddistance between the at least one ultrasonic emitter and the at least one ultrasonicreceiver an attenuation of the ultrasonic energy and to determine therefrom ameasure of object or organ composition or constitution.The method may include determining on the basis of a thickness ofcompliant and / or other material between the at least one ultrasonic emitter and / orthe at least one ultrasonic receiver and the or an object or body part contact panelof the apparatus a lost ultrasonic attenuation from the compliant and other materialand to adjust the measured attenuation on the basis of the determined lostultrasonic attenuation. It preferably includes calculating a thickness of compliantand / or other material on the basis of a measured angle of the object or patientfacing surface relative to the at least one ultrasonic emitter or receiver, or on thebasis of volume of fluid in the or a fillable bladder.Advantageously, there is provided the step of determining an attenuationacross substantially the whole area of an object or organ and determining anaverage attenuation through the object or organ; and / or determining anattenuation across a plurality of select areas of an object or body part and anattenuation map across the areas of the object or body part.The method may include the step of operating the at least one transmitter atdifferent frequencies, for the analysis of different object or tissue types. It mayinclude determining a measure of tissue composition of a selected tissue typewithin a body part being tested.Preferably, the method includes obtaining a determination of object ororgan composition or constitution in a plurality of planes by adjustment of theorientation of the transmitter and receiver elements relative to an object or bodypart being analysed.According to another aspect of the present invention, there is providedapparatus or a method as specified herein for the assessment of at least one of:a) risk of developing cancer;b) assessment of an appropriate screening modalityc) the existence of a potential cancerous growth;d) an acute or chronic muscle condition;e) the existence or risk of muscular dystrophy;f) an acute or chronic bone condition;g) the existence or risk of osteoporosis.According to another aspect of the present invention, there is provided amethod of identifying a medical condition in a patient by use of apparatus or amethod as specified herein.The method may be for the assessment of at least one of:a) risk of developing cancer;b) assessment of an appropriate screening modalityc) the existence of a potential cancerous growth;d) an acute or chronic muscle condition;e) the existence or risk of muscular dystrophy;f) an acute or chronic bone condition;g) the existence or risk of osteoporosis.As described above, the apparatus may comprise an array of ultrasoundemitters, the array advantageously being shaped and sized to be at least as largeas an area expected to be covered by a person’s body part to be assessed whenplaced between the lower and upper panel elements. In practical terms, as withthe receiver, it is not essential for the emitter or emitters to have an area biggerthan the body part under investigation, as it / they just need(s) to be of a size andshape to transmit acoustic energy transmitted through the entire body part underinvestigation. According to another aspect of the present invention, there is provided atissue composition or constitution assessment apparatus comprising:first and second panel elements disposable in spaced apart and facingrelationship, at least one of the first and second panel elements being adjustablerelative to the other in separation;at least one ultrasound emitter disposed at or on one of the first and secondpanel elements;at least one ultrasound receiver disposed at or on the other of the first andsecond panel elements, whereby the at least one ultrasound emitter and the atleast one ultrasound receiver face one another;a support structure to which the first and second panel elements areattached; anda processing unit coupled to the at least one ultrasound transmitter andreceiver and configured to determine from received ultrasound signals a tissuecomposition or constitution measure associated with the organ tissue assessed.Preferably, at least one of the first and second panel elements comprisesan adjustment element with a tissue facing plate orientable relative to theassociated first or second panel element and relative to a part of a patient’s bodyto be assessed. The adjustment element may be configured to reduce orminimise air gaps between the transmitter and receiver elements and the part of apatient’s body to be assessed. Preferably, the adjustment element is coupled to ata respective one of the first and second panel elements by a hinge or pivot andconfigured to rotate thereabout. For this purpose, the adjustment element maycomprise a compliant mechanism disposed at a tissue remote side of the tissuefacing panel and configured to allow adjustment of an angle of tilt of the tissuefacing panel.This aspect may include any or all of the features and characteristics of theother aspects and embodiments disclosed herein.Other aspects and advantages of the present invention will becomeapparent to the person skilled in the art having regard to the disclose of thepreferred embodiments which follows.Brief Description of the DrawingsEmbodiments of the present invention are described below, by way ofexample only, with reference to the accompanying drawings, in which:Figure 1 is a side elevational view of a preferred embodiment of tissuecomposition or constitution assessment apparatus according to the presentinvention; Figure 2 is a front elevational view of the embodiment of apparatus ofFigure 1;Figure 3 is a side elevational view of a part of the transducer plates of theembodiment of apparatus of Figure 1;Figure 4 is a front elevational view of the part of the transducer plates ofFigure 3;Figure 5 is a side elevational view of the embodiment of apparatus of Figure1 in use;Figure 6 is a front elevational view of a part of the apparatus of Figure 1 inuse;Figure 7 is a front elevational view of a part of the embodiment of apparatusof Figure 1 showing the operation of a gimbal of the apparatus;Figure 8 shows front and side elevational views of a rendered casing for theapparatus of Figure 1;Figure 9 is a side perspective view from above of the rendered casing ofFigure 8;Figure 10 is a side perspective view of the transducer plates of therendered casing of Figure 8;Figure 11 is a side elevational view of the transducer plates of Figure 10;Figure 12 is a schematic representation of a sensor plate of theembodiment of apparatus of Figure 1;Figure 13 is a schematic representation of the sensor plate of Figure 12 inan example mode of operation;Figure 14 is a schematic diagram of the electronic circuitry of theembodiment of apparatus of Figure 1;Figure 15 is a schematic diagram of a part of the electronic circuitry ofFigure 14;Figure 16 is a schematic diagram showing and alternative implementationof a part of the apparatus circuit apparatus of Figure 14;Figure 17 illustrates a case where there are multiple ultrasound emitters,and which emitters contribute to the assessment of tissue composition given thecontact area;Figures 18 to 21 show four flow charts showing the steps of the preferredembodiments performed by the system and method taught herein;Figure 22 is a schematic diagram of the preferred structure of ultrasonicreceiver for the apparatus disclosed herein;Figure 23 is a graphical illustration of a simulation of the intensity of anultrasound field produced by an ideal plane-piston transducer;Figure 24 is a graph showing the frequency dependence of ultrasoundattenuation and backscatter in breast tissue;Figures 25 to 27 are schematic representations of a receiver array showingtransducer coupling to the object of interest;Figures 28 to 30 are schematic representations of a receiver array showingthe effect of selecting only transducers positioned over the region of interest;Figure 31 is a series of graphs depicting pyroelectric voltage output of thesensor electronics when the sensor is exposed to ultrasound;Figure 32 shows the pyroelectric voltage output of the sensor electronicswhen the sensor is exposed to ultrasound in conditions of poor signal of noise. ;Figure 33 is a graph depicting the effect of measurements performed inquick succession when the sensor does not have time to return to the “rest” state;Figure 34 is an example acoustic simulation through a computational breastphantom; Figure 35 this shows the result of multiple acoustic simulations;Figure 36 is a schematic side elevational view of transducer plates of theapparatus with no compliant coupling provided;Figure 37 is a schematic side elevational view of transducer plates of theapparatus with compliant coupling provided;Figure 38 is a graph of simulated measurements of attenuation through thesame 70 mm pathlength of tissue showing how attenuation is directly proportionalto acoustic attenuation in the example shown.Description of the Preferred EmbodimentsThe disclosures herein relate to the measurement of the composition orconstitution of an organ, such as tissue, of a human or animal subject, for theassessment of the condition of the subject. While the disclosures focus on breastdensity assessment as one example implementation of the teachings herein, it isto be understood, and it is disclosed herein, that the method and apparatus taughtcan be used to the detection of conditions in other parts of the body and also othermedical conditions. The method and apparatus can be used for the determinationof risk of a patient to develop breast cancer, for example. They can equally beused to determine cancerous growths in other parts of the body, including partsmade up of different tissue types such as muscle, fatty tissue, bone and so on.They can equally be used to detect other conditions or the risk of developing otherconditions, such as osteoporosis and the like. Examples are described below.In other medical applications the apparatus and method taught herein canbe used to determine tissue constitution or composition, such as bone density,vascular occlusions and so on.In more general terms, the disclosures herein relate to the measurement ofattenuation of or through an object or part of an object to obtain an indication ofthe composition or condition of the object or object part, in some examples objectmaterial density.Non-medical applications include, but are not limited to:(i) fluid flow monitoring systems (such as in a pipe example) for in-lineassessment (mainly of two-phase fluids);(ii) quality assurance of rubbers and gels. Acoustic attenuationmeasurements that fall outside an acceptable window may indicate things likecontamination of the sample or discontinuities like air pockets ;(iii) assessment of the composition of colloids (in particular foams,emulsions, sols and gels);(iv) foreign-body detection in foodstuffs / cosmetics and so on (such as solidcontaminants in liquids / gels);(v) verifying the presence of something intended (because of its acousticsignature). This could be, for example, a security feature, ID tag and so on.The person skilled in the art will appreciate how to configure the apparatusand method disclosed herein to be able to assess an object including inconnection with the above described non-medical examples.Breast density is a measure of the relative proportion of fat tofibro-glandular tissue in the breast and is a key indicator of breast cancer risk andmammographic sensitivity. Fat and fibro-glandular tissue differ in their ultrasonicpropagation properties. In the preferred embodiments of the present invention, aseries of through-transmission ultrasound measurements of the breast at severalpositions are taken and used to determine the bulk / volume-averaged acousticattenuation of the breast, which can act as a surrogate measure of mammographicbreast density.The quantitative through-transmission ultrasound measurement byphase-insensitive detection as disclosed in the embodiments of the inventiondescribed below can overcome these challenges and meet regulatory criteria byproviding: 1) simple ultrasound-based through-transmission measurements in thepreferred embodiments only requiring a single emitter and receiver pair which aredirectly-coupled to the patient (that is not through water), and in which imaging isavoided so as to avoid complex reconstruction computations;2) safe non-ionising diagnostic ultrasound conditions, which can incurreduced and preferably no compression of the breast or other body part and withdirect-coupling thereby avoiding water-based signal cross-contamination;3) precise quantitative measurements which can be largely operatorindependent, and which can provide high contrast.Technical benefits of the disclosed apparatus and method in the field ofbreast density assessment and in other fields include the following:1) in comparison to conventional mammography: avoidance of non-ionisingradiation, quantitative measurement, and avoidance of compression of thepatient’s breasts;2) in comparison to ultrasound computed tomography: a simpler andcheaper technology which requires less computation and fewer ultra-soundelements; faster signal processing and determination (no complex reconstructionalgorithm is required); and the avoidance of water coupling;2) in comparison to hand held ultrasound: a quantitative determination andwhich is largely operator independent.Quantitative, traceable measurements attainable by the system and methodtaught herein can provide confidence and assurance in the assessment forpatients and clinicians. Quantitative data can more readily allow for theintercomparison of density across patients and also (or in the alternative) overtime, which will provide great value for national screening programmes and theknowledgebase of breast density.The configuration of the apparatus and the method for ultrasound breastdensity assessment are safe, affordable and can be automated, which can enableprocedures to be performed outside a typical hospital setting, for instance, inpharmacies, general doctor surgeries and private breast cancer risk clinics.In one aspect, the teachings herein can provide ultrasound breast densityassessment for comprehensive personalised breast cancer risk assessment(optionally combining with information on lifestyle, familial history, genetics, and soon) which can be used to inform risk stratified screening. These new screeningrequirement strategies can be used to notify individuals of optimum screeningrecruitment including, for example: within an age range (such as: 50-70, 40-70…),at a certain frequency (such as every 1, 2, or 3 years), recommended imagingmodality (such as: mammography-only, mammography plus handheld ultrasound,MRI-only, as so on), refinement of existing risk stratification for high-riskindividuals. It can also be used as a research tool for pharmaceutical companiesdeveloping risk-reducing medicines, such as TamoxifenTM used to reduce breastdensity. Other example applications include providing through-transmission acousticattenuation measurements of large muscle masses (such as quadricep, calf, bicepand so on) for example for use by sports scientists.The preferred embodiments disclosed herein make use of phase-insensitivepyroelectric sensors for obtaining quantitative ultrasound determinations, althoughembodiments are envisaged that could use other sensor types. Examples of suchsensors have been disclosed by the applicant in, for example, EP-3,588,023, WO-2010 / 084319. As these sensors are known in the art and described in detail inthese patent publications, they are not described in further detail herein. Should itbe deemed necessary, for the avoidance of doubt, the disclosures in these patentpublications are incorporated herein by reference.While these patent publications relate to quantitative acoustic attenuationtomography (imaging) of breast tissue and use cases of this quantitative imagingtechnology for neo-adjuvant therapy response monitoring and breast cancerdiagnosis, the apparatus and method disclosed herein use such sensors in adifferent manner, as described in detail below.The preferred embodiments determine a bulk acoustic attenuationmeasurement, preferably using phase-insensitive pyroelectric sensors, byobtaining simple through-transmission ultrasound measurements in a modifiednon-imaging configuration. The measurement can be of an entire body part, or asection of a body part or targeted to a specific tissue type.The preferred embodiments provide apparatus and a process which:1) enables a patient to remain upright during the procedure,2) provides direct coupling of the sensors to the patient avoiding passagethrough water,3) provides signal pathlengths which can be readily determined from plateseparation distance and compliance mechanism angle, and4) reduces the amount of body part compression required compared totraditional imaging systems.Figures 8 to 11 are different views depicting an example of tissuecomposition or constitution assessment device in what could be described as afinal implemented form. The device 200 comprises the components of theembodiment shown in Figures 1 to 7. The device 200 includes a main casing 202which in this example is intended to be floor standing, and a frame component 204which includes first and second arms 206, 208 extending substantially horizontallyfrom the frame 204 and which support the transducer plates 210, 212. The arm206 is able to move upwardly and downwardly, that is to bring the transducerplates 210 further away or closer together. The lower arm 208 is typically fixed tothe frame 204, although the frame 204 can itself move upwardly and downwardlyand also rotate in a manner similar to that shown in Figure 7.The upper transducer element, in this example, comprises a conformancemechanism 220, which includes an inflatable bladder 220 and a contact plate 222,which are equivalent to the conformance mechanism 40 described above.The skilled person will appreciate that this is just one example of finalimplementation of the apparatus taught herein and that it can take different forms,for example to assess other body parts. It is to be understood that the bladderassembly taught herein is a preferred element of the apparatus but not essential inall cases. Whether or not a balder is used, in preferred embodiments there isprovided a conformable coating or layer on the transducer plates to optimisecontact with tissue or other object. This may be standard acoustic coupling gel butmore preferably of a material that does not remain on the patient or object.Examples include a semi-rigid material, such as silicone or rubber or any othersuitable material. In cases where the material is compressible, the calibration datawill take into account changes in acoustic attenuation through the material in anon-compressed state as well as when in a compressed state. In this regard, theapparatus and method are preferably configured to be able to determine thecompressed thickness of the material under a variety of operating conditions andto determined therefrom an accurate path length through an object under test. Thiscan be accomplished, as an example only, by using a pulse-echo response fromthe emitters to measure distance to the object material interface.The example shown in Figures 8 to 11 is designed specifically for breasttissue composition or constitution (especially breast density) assessment and it isconsidered that the form shown in this example is a material improvement overexisting imaging system devices.For example, it is envisaged that in some embodiments the emitter andreceiver plates could be set at an angle to one another, while still facing oneanother, for example to present an inwardly tapering form. In such embodiments itmay not be necessary to have a mechanism to rotate one or both of the emitterand receiver plates, although it is envisaged that the assembly will in any eventcomprise the configurable bladder.Additionally or alternatively, the apparatus may include a frame in which atleast one of the emitter and receiver comprises a holder fixed in separationposition, and in which one of the emitter and receiver units is movable relative toits holder so as to provide separation adjustability between the emitter andreceivers, as disclosed above.Referring now to Figures 12 and 13, these show schematic representationsof the transducer plate 32 of the embodiment of Figures 1 to 7 (and equally of theembodiment of Figures 8 to 11). It will be appreciated that the images of Figures12 and 13 could relate to an embodiment comprising an array of transmitters or anarray of receivers. While the mechanism will be different, the principle remains thesame.Referring first to Figure 12, this shows a silhouette of a breast 100 locatedadjacent the transducer plate 32. Typically, and in order to ensure that theapparatus is able to assess the entirety of a breast, in this example, the transducerarray 32 is generally larger than the area of the breast 100, such that there is atransducer aligned at every location of the breast 100 (or other body part). It willbe appreciated that some of the transducers will fall outside the area of the breast100 or other body part and that therefore any signal that is generated as aconsequence of those outlying transducer elements will in practice need to bediscounted. The preferred embodiment, however, goes further than that byidentifying the signals that reliably pass through the body part (in this examplebreast 100) and to discount the signals associated with all of the transducers thatdo not satisfy this criteria. In the example depicted in Figure 13, a number of thetransducers within the perimeter of the body part (breast 100 in this example) arediscounted on the basis that they provide a poor quality signal. This is achievedby analysing the pulse-echo return of the signal emitted by the individualtransceivers and it is determined from the pulse-echo whether the transducers arein a zone of good return, such that all transducers disposed that exhibit a poorreturn will have their signals discounted during the subsequent assessment of thedata. In the case of an embodiment in which an array of receivers is used,receivers in a location of poor return can be identified by determining whether thesignals they receive have been subjected to no or minimal attenuation, inparticular an attenuation that is not consistent with passage of the ultrasonic beamthrough body tissue.In the example shown at Figure 13, the reason why some of the transducerelements falling within the perimeter of the body part (breast 100 in this example)are deemed to provide a poor return will generally result from poor direct contactof the body to the apparatus at those locations. This will typically be as aconsequence of an air gap between the transducer element or contact plate and apart of the body.While the embodiments described above include transducer plates facingone another, in which could be described as a vertical orientation such as onetransducer plates lies above the other, it is to be understood that this is just oneexample implementation and that in other implementations the transducer platescould be disposed in other orientations including facing one another in a horizontaldirection. What is relevant is that the transducer plates 30, 32, 200-210 arepreferably disposed so as to face one another, in particular to have the samespacing between the array of transducers and the receiver (or in the alternative anarray of receivers and one transmitter or an array of transmitters). Having thetransducer plates parallel to one another simplifies the subsequent signalprocessing because in normal conditions the attenuation will be the same acrossthe array. It is not excluded, however, that in other embodiments the transducerplates may not be parallel, with the processing unit of the system being configuredto take into account the different spacings across the transducer plates and thedirectional response of the receiver.Similarly, while in the preferred embodiment the transducer plates arepreferably flat plates, in other embodiments they may be curved, for example toconform better to the shape of a body part. Again, in the case of curvedtransducer plates, the processor unit will be configured to take into accountdifferences in the spacings between the transducer plates across the area of thetransducer elements and the directional response of the receiver.As a consequence, the person skilled in the art will appreciate that apractical implementation of the teachings above can take a variety of differentforms. Having described the principal elements of the apparatus, the disclosureproceeds to describe the signals obtained by the apparatus and how these areprocessed. In brief terms, the apparatus produces a series of ultrasound bursts whichtravel through tissue under investigation and which are then transduced into avoltage by an ultrasound sensor. The following describes how the apparatusproduces the ultrasound bursts and how the received sensor voltages can be usedfor tissue characterisation.Referring to Figure 14, this shows in schematic form the transmission stage300 of the system. The circuit is Figure 14 is just one example as to how thetransmission electronics could be configured. It is intended that for commercialembodiments the electronic circuitry would be simplified to have a simpletransmission electronics format rather than the multi-stage form shown in Figure14. The skilled person will be able to derive an appropriate circuit configuration ofthis type from the teachings herein, and will also appreciate that the circuitryshown in Figure 14 could be used to carry out other functionalities.The purpose of the transmission stage 300 is to generate timed drivesignals to send to the one or more ultrasound transducers 320 (labelled "Tx" inFigure 14) to generate the desired ultrasound pulses used to "interrogate" thetissue 100 under investigation.The transmission stage 300 comprises a signal generator 302 whichgenerates drive voltages. A computer or control unit 304 drives the signalgenerator 302, in particular the: (i) voltage amplitude; (ii) sine wave frequency; (iii)tone burst duration; (iv) tone burst spacing of the signals outputted by the signalgenerator 302.An amplifier and multiplexer module 306 is connected to the output of thesignal generator 302 and includes a first amplifier stage 308 which amplifies thedive signals from the signal generator 302 to the voltages required by the plane-piston ultrasound transducers to produce sufficient ultrasound power that will bemeasurable by the sensor after attenuation from the tissue under investigation.The transmission stage 300 amplifies the drive signals from the signal generator302 and sends the drive signals to each of the ultrasound transducers such thatmeasurable signal level is detected by the sensor. The speed of the switching andthe electrical power the switch is required to handle determines the type ofswitching network and the amplifier configuration around it.The transmission stage 300 in this embodiment comprises a multistageamplification configuration to a plurality of transmitters. More specifically, theamplifier and multiplexer stage includes a switch network 310 connected to andcontrolled by the computer or processor unit 304, for switching the transmissionsignal to one of a series of second stage amplifiers 312, each associated with arespective ultrasonic transmitter 320. The switch network 310 typically sends thedrive signal to the plurality of ultrasound transducers 320 in quick succession,preferably at a switching rate in the order of 10s of milliseconds.In the case of the use of a switch network 310 designed for fast switchingand which is unable to handle high electrical power, and as shown in theembodiment of Figures 14 and 15, the circuit amplifies the drive signal to an"intermediate" drive level with a high-quality class A first stage amplifier 308,switches through the switching network 310 the "intermediately" amplified drivesignals to each of the channels, and then amplifies these to the "full" drive signalpower with cheaper, lower quality class A / B second stage amplifiers 312. Anenlarged view of this section of the circuitry is shown in Figure 15.For a tomography implementation of the system and method describedherein a typical scan would involve 10,000 individual measurements. For thetissue constitution or composition assessments disclosed herein, fast switching isnot necessary so it is possible to use a more simple and less expensiveconfiguration of a type as shown in Figure 16, comprising for example a singleclass A amplifier 308 and a high power, slower switching network 310. Thesecond stage amplifiers 312 would not be necessary.The purpose of the ultrasound transmission array 320 is to produceultrasound beams from one or more positions in the array to interact with a volumeof tissue 100 under investigation and produce a signal that can be registered bythe sensor 352. The characteristics of the ultrasound tone bursts (frequency,amplitude, duration, timing and so on) are determined by transmission electronicsand are chosen to register sufficient signal in the sensor 352 (after attenuation bythe tissue 100 under investigation) but without exceeding diagnostic ultrasoundoutput power limits set by regulation. This is the ALARA principle (as low asreasonably achievable), and the limits are tissue dependent.The type of ultrasound transducers 320 used for this purpose can beplane-piston transducers. This type of transducer produces highly directional, highintensity beams with a directionality that depends on its size compared to thewavelength. The detection stage 350 includes a sensor unit 352 which comprises areference signal receiver 354 and a signal receiver 356 configured and disposedto receive the ultrasound beams from the transmitter array 320. The referencereceiver 354 is designed to obtain a reference signal for use in normalising thesignals received by the signal receiver 356, in a manner disclosed below. Thereference receiver and signal receiver 354, 356 are coupled to a signal amplifier358, which amplifies the receiver signals to the required level for an oscilloscopeunit 360. The oscilloscope unit 360 is fed with the signal from the receiver 356,the signal from the reference receiver 354 and a difference signal, being thedifference between the signal of the receiver 356 and that of the reference receiver354. The output of the oscilloscope unit 356, is connected to the computer orcontrol unit 354 for analysis of the receiver signals and determination of a measureof tissue composition of the body part 100, in the preferred embodiments of anaverage tissue composition across an area identified for analysis (such as theentire body part being analysed or a part thereof).The person skilled in the art will be familiar with specific circuit componentscan be used with the circuit, these being part of the skilled person’s commongeneral knowledge.The sensor response is used to determine insertion loss and subsequentlyacoustic attenuation. The acoustic attenuation can be measured against athreshold value, typically indicative of a value expected of a particular tissue typeor condition, such that when the measured acoustic attenuation is above thethreshold a determination can be reached that the person needs further medicalevaluation. In the preferred embodiments, acoustic attenuation can be correlatedin a continuous manner to tissue composition, for example percentage offibroglandular tissue, fat fraction or breast density category, as explained aboveIn some embodiments, a smaller beam can be generated, so as to obtain ameasure through a part of an organ or other body part, useful in determiningvariations in tissue composition across a body part and therefrom whether anyparticular region produces a higher acoustic attenuation indicative of a tissueanomaly requiring specific investigation (such as a region of suspected cancercells). The system and method could, in some embodiments, produce a variety ofacoustic attenuation measures, for example an overall measure and one or moremeasures targeted to a specific area of the organ or body part disposed in theapparatus. It will be appreciated that a threshold may be dependent on the particularorgan being examined, the medical condition being looked for, the separation ofthe emitter(s) from the receiver(s), the amount of any non-patient acousticattenuation reducing material within the zone of the opposing emitter / receiverassembly (such as the adjustable bladder) and so on.The selection of emitters and / or receivers which could obtain ameasurement of a particular patient could be determined in a pre-scan procedure.This could be performed utilising the distinctive difference in response from a Tx-Tissue-Rx path vs a Tx-Air-Rx path with methods for example including:(i) Pulse-echo ultrasound emitter response,(ii) Electrical impedance response,(ii) Low sensor output response.Figure 17 illustrates a case where there are multiple ultrasound emitters,and which emitters contribute to the assessment of tissue composition given thecontact area.Referring now to Figures 18 to 21, these show three flow charts showingthe steps of the preferred embodiments performed by the system and methodtaught herein. The flow chart of Figure 18 is an overall description of themeasurement sequence. The flow charts of Figures 19 to 21 show further detailsof the two steps delimited by the dotted boundary lines in Figure 18. Figures 19and 20 show two versions of sequential ultrasound emission events where themeasurements are temporally separated. The flow chart of Figure 21 is a versionwhere ultrasound emission is performed simultaneously.Referring first to Figure 18, this shows the overall scan procedure of apreferred embodiment. The procedure 500 starts at step 502, at which therelevant organ or organ parts to be tested with a person is positioned such that theorgan is between the emitter and receiver assemblies, in the manner describedabove. Simultaneously, the procedure 500 obtains calibration data for thesubsequent measurements, at step 504, typically from a register or database ofthe system. The calibration data, as explained above, may include measurementsmade through reference materials, data relevant to the particular organ beingexamined, the nature or characteristics of the patient undergoing examination, thespacing of the emitter and receiver assemblies from one another, the amount ofattenuation material other than body part between the emitter and receiverassemblies (for example the adjustment bladder previously described) and so on.At step 506 the system and method carry out a pre-scan to determine thearea of the body part in the apparatus that is considered to be adequately coupledto the emitter and receiver assemblies. As described above, where there isinadequate coupling or where emitters fall outside the area of the body part, thesewill produce results that are inconsistent with proper scan results and the systemcan then determine either to switch off the relevant emitters or to ignore the outputof those emitters as the apparatus and method sequence through themeasurement steps.At step 508 an ultrasound scan is taken utilising only the emitters that havebeen determined in step 506 to be sufficiently well coupled to the organ or bodypart under examination.At step 510 the system and method use the ultrasound data, that is thereceiver response to ultrasound exposure, to obtain a measure of the bulkacoustic attenuation experienced through the body part under examination. Asdescribed above, in the preferred embodiment the measure is obtained from all ofthe emitted power from the emitters selected to be operated during the scan.Referring now to Figure 19, this shows one embodiment of the proceduresteps 508 and 510 of Figure 18, in which a sequential multi-element measurementis carried out in respect of only those emitters that have been determined to beadequately coupled to the body part under examination at step 506. In thismethod sequence, at step 512 one of the ultrasound emitters is fired to generate abeam through the body part. It is to be understood, as explained above, that thesensor (or array of sensors) is preferably of a size and dimensions sufficient toreceive the whole of or substantially the whole of the beam from the emitter,without needing to move one relative to the other, and that the receiver is largeenough in size and dimensions to be able to receive the signals from all of theemitters in the array without any movement between them during the emitting andreceiving stages. This may typically be achieved by ensuring that the area of thereceiver is at least as large as the area of the beams generated by all of theemitters in the array when the ultrasonic energy of those beams is not scattered byany object lying between the emitters and receiver.More specifically, the optimum receiver size to capture the total acousticpower generated by an ultrasound emitter will vary as a function of emitter type,emitter frequency, emitter size, emitter-receiver separation, the transmissionmedium, sound speed and transmission medium inhomogeneities. For acousticfields generated by a plane-piston emitter, a model can be used to determine theminimum receiver size, of which Figure 39 shows an example (Figure 39 beingderived from Beissner, K., Minimum target size in radiation force measurements,J. Acoust. Soc. Am. 76, pp. 1505-1510 (1984)). Referring to Figure 39, this showsthe receiver radius required to capture 98% of the acoustic power generated by aplane-piston emitter as a function of the emitter-receiver separation for threeemitter frequencies. These calculations are provided for:(i) a single emitter-receiver pair,(ii) an emitter radius of 5 mm,(iii) in a homogeneous material with a speed of sound of 1520 ms-1, whichcan be taken to be average sound speed of breast tissue.For example, Figure 39 suggests that for a 2 MHz device with a maximumemitter-receiver separation of 100 mm, the receiver radius is required to be 52mm. For measurements of inhomogeneous materials, such as biological softtissues, the receiver radius requirement to capture 98% of the acoustic powertransmitted through the tissue will increase to account for disruptions in theacoustic pressure distribution by the acoustic and physical properties of tissue(density, speed of sound, attenuation & backscatter). For example, a margin of50% in the receiver radius requirement could be employed. Following the aboveexample, for a 2MHz device with a maximum emitter-receiver separation of 100mm, the receiver radius is 78 mm (the receiver could be larger than this if desired).For systems with an array of emitters and a single receiver, the receiverradius requirement, previously discussed, represents the distance the receivermust extend beyond the centre of any of the outer set of emitters.At step 514, the method obtains the response of the receiver to ultrasoundexposure and stores that in a memory of the system. At step 516 the systemdetermines whether all of the emitters that have been deemed to be satisfactorycoupled to the body part have been utilised and if not, the process proceeds tostep 518, at which the next emitter in the array is selected and then at step 512 isfired, also repeating step 514. The measurement obtained by the receiver at step514 is also saved in memory, maintaining in memory the previousmeasurement(s). At step 516 when it is determined that all of the emitters in theselection have been fired, the process proceeds to step 518. With use ofcalibration data (step 520) the system and method calculate the acoustic insertionloss for each emitter. Next, at step 522 the system and method calculate anacoustic attenuation coefficient for each emitter, making use of data on theemitter-sensor separation (step 524). It will be appreciated that the emitter-sensorseparation may not be the same for all of the emitters in the array, depending onthe orientation between the emitter array and receiver, which may vary when theseare adjustable or when these are not parallel to one another. The acousticattenuation coefficient obtained at step 522 provides a measure of attenuation of abeam from each emitter through the space between the emitter and the receiverand typically through the bulk of the body part under examination.At step 526 the system and method determine the average measurementsof bulk acoustic attenuation through the body part that has been examined. Thiswill, of course, be dependent upon the number of emitters of the array that havebeen fired.Referring now to Figure 20, this shows another embodiment of thesequence for steps 508 and 510 of Figure 18. In this embodiment, at step 542one of the emitters of the set of emitters deemed to be satisfactorily coupled to thebody part is fired and at step 544 the system and method obtain the receiverresponse to ultrasound exposure. At step 546 the system and method calculatethe acoustic insertion loss on the basis of calibration data obtained at step 548,while at step 550 the system and method calculate an acoustic attenuationcoefficient in connection with that emitter, utilising also data relating to theseparation of that emitter to the sensor. At step 554 the system and methoddetermine whether all of the emitters in the selection have been fired and if this isnot the case, the process moves to step 556, at which the next emitter is selectedand then subsequently fired at step 542, repeating steps 544 to 550. Once it hasbeen determined at step 554 that all of the emitters of the selection have beenfired, the process moves to step 560 at which the average measurements of thebulk acoustic attenuation is calculated, as described previously.Figure 21 shows a different embodiment of process for steps 508 / 510 ofFigure 18. In this embodiment, all of the ultrasound emitters identified as beingsatisfactorily coupled to the body part under examination are fired at step 570 andat step 572 the system and method obtain and store the receiver response tomultiple simultaneous ultrasound exposures. At step 574 the system and methodcalculate the acoustic insertion loss on the basis of multi-element calibration dataobtained at step 576, as explained above. At step 580 the system and methodcalculate the bulk acoustic attenuation, on the basis also of the emitter-sensordistance determined at step 578. In cases where the emitters are at differentspacings relative to the receiver, for example because they are not parallel to oneanother, at step 578 calibration data as a function of emitter-sensor separation willbe used to obtain the measure of bulk attenuation at step 580.In the flow charts of Figures 18 to 21, the bulk acoustic measurement ispreferably determined in relation to a tissue composition parameter, such as thepercentage of Fibroglandular tissue or breast density category, using calibrationdata. The skilled person will appreciate that the determined acoustic parameter isfrequency dependent. That is, changes in tissue composition will produce greaterchanges in measured acoustic attenuation coefficient for higher frequencies.In relation to the relative sizes of the emitter(s) and receiver(s), these arelikely to differ in dependence on different applications.In general, it is preferred that the area of tissue exposed is sufficiently largethat the derived acoustic attenuation coefficient from the measurement isrepresentative of the bulk or averaged properties of the tissue. As explainedabove, this could be from a single emitter, or a combination of emitters drivensimultaneously or sequentially.For single emitter systems, the emitter may be translated or re-positionedacross the tissue under test to increase the area of tissue evaluated and thereforeincrease statistical confidence in the measurement.For breast tissue composition assessment, the expected considerationsare: (i) tissue thickness (therefore approx. emitter-receiver separation): 40 –100 mm(ii) tissue homogeneity (approx. area of tissue to expose to berepresentative of the bulk): >1 cm2(iii) emitter centre frequency selection: 2 – 4 MHz(iv) preferable emitter type: flat piston transducers(v) emitter active diameter selection: 5 – 20 mmIt is to be understood that the system and method taught herein may utilisemultiple single-frequency emitters (that is emitters that can only efficiently operateat one frequency) or multiple multi-frequency emitters or both multiple single-frequency emitters as well as multiple multi-frequency emitters. In the case ofmulti-frequency emitters, the system and method can operate these at differentfrequencies, and thereby optimally tune the acoustic beam to the tissue or otherorgan part under examination. In the case of single-frequency emitters, the arraycould comprise a proportion that operate at a first frequency and anotherproportion at a second different frequency. For example 50% could be 2MHzemitters and 50% 4MHz emitters.Figure 22 shows an example of the preferred structure for the sensor 352.The structure of the ultrasound receiver (transducer) is as disclosed in andcovered by the applicant’s earlier EP-3,588,023, for example, and is able toprovide phase insensitive ultrasound detection for use in a variety of ultrasoundapparatus and fields, including the medical field. The receiver structure could bedescribed as being a tri-laminar array formed of first and second pyroelectriclayers separated by a spacer. The skilled person will appreciate that the structureincludes a number of other layers that provide ancillary functions to the three layercore structure.Referring to Figure 22, this shows a preferred embodiment of receiver array or transducer 410, which includes first and second pyroelectric electrodes 414, 412 preferably formed of poled polyvinylidene difluoride (PVDF). The pyroelectric layers 414, 412 in this embodiment have a thickness of 28 micrometres, although may in other embodiments have a thickness anywhere in the range from 1 to 60 micrometres. The thickness of the pyroelectric layers 414, 412 is typically dependent upon the nature of the material used for these layers and upon the pyroelectric characteristics desired for the detector. Thinner layers 412 and 414 can provide greater gains in peak amplitude and reduced time to peak due to more rapid heat diffusion through the material of the layer. PVDF layers that are too thick can lead to higher reflections and reduced sensitivity. The first and second pyroelectric electrode layers 414, 412 are in thepreferred embodiments identical in constitution (material) and size (thickness andvolume). This ensures that the signals from the first and second pyroelectricelements are directly comparable. The skilled person will appreciate, however,that in other embodiments the first and second pyroelectric layers 412, 414 maybe different, for example to be of different size (e.g. thickness) or material, in whichcase it is preferred that the detection apparatus is configured to calibrate thesignals from the first and second pyroelectric elements so as to produce a reliableand usable differential signal therefrom.In the case where the two electrodes are precisely the same, it is envisaged that one could reverse the polarity of the two signals (by flipping one of the membranes around) and sum their outputs directly to derive a difference signal. In practice, it is advantageous to be able to monitor the signals separately (as well as the differential or summation) as this can provide diagnostic information about how good any particular measurement is during the scan to reduce artefacts. Disposed between the first and second pyroelectric electrode layers 414,412 is a spacer layer 16 that acts:1) to separate electrically the pyroelectric layers 412, 414; and2) to keep the two pyroelectric layers 412, 414 close enough such that theysee effectively the same vibration or background acoustic excitation; while3) maintaining sufficient distance to ensure that the pyroelectric layers 412,414 generate significant differences in their pyroelectric responses.The first or lower (as viewed in Figure 22) pyroelectric electrode layer 414 isdisposed adjacent the absorbing highly backing layer 418, which acts as the heatsource. This structure provides two distinct signals (at separate timestamps), the difference between which provides a more accurate signal. The spacer layer 416of the embodiment of transducer 410 shown in Figure 22 has a thickness of 9micrometres, which has been found particularly effective in tests, although could have a thickness from 1 to 100 micrometres. The spacer 416 may be made of polyethylene terephthalate, another polyester such as Mylar®, polymethyl methacrylate, or any other suitable polymer in the case of electrodes formed, for example, of PVDF. For electrode layers made of other materials, the spacer layer could likewise be made of a different material, as explained above. The spacer 416 provides electrical separation between the first and second pyroelectric layers 414, 412 but is preferably heat conductive (most preferably being substantially transparent to heat). In some embodiments the spacer layer 416 may be made of polyvinylidene fluoride (PVDF). This configuration provides the best acoustic impedance match as is same as the material either side. The spacer layer has been formed as an unpoled layer so as not to be piezo or pyroelectrically active. Poling is the process which essentially lines up the molecules so that the material responds to changes in pressure and temperature. There is an optimum thickness for the spacer layer 416. Specifically, theinventor has discovered that too thick a spacer layer has a deleterious effect onthe directional response of the sensor, that is the way the output of the deviceresponds to ultrasound striking the surface of the device at an angle (rather thanperpendicularly). The preferred device should be omnidirectional, such that atwhatever angle the ultrasound is incident, the output of the device should be thesame. Spacers of up to 100 micrometres in thickness can greatly enhance theresponse to non-perpendicular incidence and as a consequence tissue imaging,while significant departures from this thickness will adversely affect tissuereconstructions. Too thin a spacer layer 416 can result in the pyroelectricresponse of the two layers 412, 414 being very similar to one another, such thatdifferential operation will reduce the output voltage waveform and therefore thesensitivity of the device. Tests to date have shown that the optimum thickness ofthe spacer layer is in the region of 9 micrometres.The sensor structure 410 preferably also includes a high energyabsorbency base or backing layer 418 for boosting sensor sensitivity. A suitablematerial for the backing absorber is based on a di-functional polytetramethyleneglycol. In order to achieve significantly increased absorption above that of thebase material, small micro-balloons of the material Expancel® may be used.Additionally, in order to modify the acoustic impedance of the backing material sothat it is better matched to water, a high-density filler may be added to increase thematerial density to a value of 1,910 kg m-3. The absorption coefficient of thematerial at 3 MHz is preferably greater than 950 dB cm-1.The absorbing layer 418, with which the first pyroelectric layer 414 ispreferably in direct, or intimate, contact, is very absorbing of ultrasound energy atthe generated frequency. In practice, following transmission through the firstpyroelectric layer 414, the majority of the acoustic power is absorbed within amillimetre or so of the pyroelectric layer, leading to heat being generated whichdissipates across the various sensor layers.There is preferably also provided a protective layer 420 disposed so as to overlie the top of the array 410, which is transparent to ultrasound and made of electrically insulating and preferably water impermeable material. This may be of the same material as the spacer layer, although in the preferred embodiment the outside is metallised (for example with a thin spray coating) and grounded for electrical shielding from stray radiofrequency sources. The protective layer 420 may be of any suitable thickness, 9 micrometresfor example. The protective layer is provided for physical protection and optimallyshould have no or minimal effect on the performance of the first and secondpyroelectric elements 414, 412.In practice, the layers 412-420 may be bonded to one another by a suitablebonding or adhesive, preferably having non-matched characteristics. In thepreferred embodiments, the glue has properties (acoustic etc.) that aresubstantially identical to the properties of the material layers on either side, as theyare deposited from the material applied in solvent form. The glue layers can alsobe made conducting by doping with metallic flakes. The preferred glue layer onlyhas an adhesive function, with the matching of the properties meaning that thesensitivity of the device can be maximised. In practical embodiments, thestructure disclosed herein can be bonded together with a non-property matchedglue. This is advantageously made as thin as possible to reduce losses,preferably just a few micrometres thick. In practice, an off-the shelf glue can beused that is adapted to bond together layers of PVDF and non-matched means interms of acoustic impedance (Z) in relation to the (PVDF) layers. An example is anitrile-rubber-based adhesive such as BOSTIK® 1755 (diluted to 5 wt% withBOSTIK 6322 thinner).In preferred embodiments, further thin layers may be disposed in intimatecontact with the pyroelectric layers 412, 414 to dissipate the signal away morerapidly (essentially increasing thermal conductivity), thereby ensuring that thesignal from the sensor 410 decays to background as quickly as possible (a factorwhich affects scanning speed as it dictates when the next firing of the transducercan be executed.In summary, the preferred structure of ultrasonic sensor includes first andsecond overlaying pyroelectric layers and an electrically insulating spacer layerdisposed between the first and second pyroelectric layers so as to separate thefirst and second pyroelectric layers are respectively a measurement electrode anda reference electrode.Further details of this ultrasonic sensor can be found in the applicant’spatent publication EP-3,588,023.Figure 23 shows a simulation of the intensity of an ultrasound fieldproduced by an ideal plane-piston transducer operating at 2 MHz. The informationderived from tissue 100 under investigation comes from only the tissueencountered by the whole beam. This fact can be used in the following ways:i) narrow beams can investigate narrow portions of tissue 100, and multiplemeasurements (either one transducer 356 scanned or an array of transducers)can build up a projection image to understand the spatial distribution of acousticproperties. Narrow beams can be made narrower (focused) using acoustic lensesand other methods known in the art;ii) broad beams (weakly focused) can investigate larger portions of tissue ina single measurement, therefore reducing the need for multiple narrowmeasurements. This effectively uses the acoustic field to achieve spatialaveraging. Again, acoustic lenses and other methods known in the art can beused to achieve this effect.Piezo-ceramic transducers can be used to produce megahertz frequencyultrasound beams and have a resonant frequency at which they operate withmaximum efficiency. To generate at multiple frequencies from a single device, theconfiguration of the circuit could:(i) have multiple transducers with different resonant frequencies,(ii) drive individual transducers at harmonics of the resonant frequency,(iii) drive the transducer off-resonance (for sufficiently broadband devices),for instance driving a 2 MHz transducer at both 1.5 and 2.5 MHz.Frequencies for optimal transmission through different human tissues havebeen found to be as follows:(ii) 0.2 - 1 MHz -> bone(ii) 2 - 5 MHz -> soft tissueOperation of the circuit at multiple frequencies can be used to determine thefrequency dependent acoustic attenuation properties of tissue, which can provideadditional diagnostic information. Figure 24 is a graph from F. T. D’Astous and F.S. Foster, “Frequency dependence of ultrasound attenuation and backscatter inbreast tissue” (Ultrasound in Medicine and Biology, vol. 12, no. 10, pp. 795–808,1986.), which shows the differing frequency dependence of ultrasound attenuation(d / df) for various breast tissue components.Operating the apparatus at different frequencies can enable the detection ofdifferent tissue / organ types within a volume of interest, such as soft tissue, bone,and so on. Transmission frequency can therefore be used to filter or tune thesystem to a specific tissue type.The purpose of the detection stage 350 of the preferred embodiment is totransduce the attenuated ultrasound power into a voltage signal and record the fullsensor response for signal processing and to calculate an acoustic attenuationmeasurement. The purpose of the sensor 356 is to transduce the attenuated ultrasoundenergy into a voltage signal. In an embodiment, the system comprises a singletrilaminar pyroelectric sensor 356 of the type disclosed in the applicant’s earlierpatent publications identified above. The characteristics of this sensor type areadvantageous for the following reasons:(i) they can have a large-area, able to collect the whole transmitted beamenergy after refraction and diffraction from ultrasound interaction with aheterogeneous medium,(ii) they are phase-insensitive, which responds to power or time-averagedintensity and is immune to phase-related ultrasound measurement errors such asphase cancellation,(iii) they are omni-directional and are able to receive transmitted beamenergy from a large range of incident angles (flat to ±40º), which means thatissues of alignment (parallelism of the sensor relative to the transducer array) aremuch less important,(iv) they have a tri-laminar construction, able to measure low ultrasoundpowers (as a result of high attenuation by the medium or low initial transmissionpowers) in the presence of significant environmental noise that might be expectedin clinical environments,(v) they are broadband, and able efficiently to transduce incident ultrasoundfrom multifrequency sources using a single sensor.A trilaminar sensor of the type disclosed herein and in EP-3,588,023 and / orWO-2010 / 084319 generates two signals from a single ultrasound exposure, onefrom each membrane (labelled as "Sig Rx" and "Ref Rx" in the signal chaindiagram of Figure 14). The character of these signals is determined by: (1) thecharacteristics of the ultrasound exposure, and (2) the signal amplifier electronics.A further advantage can be gained with the use of multiple receivers. Twoadvantages of multiple receivers include:(i) faster measurement sequences by measuring different parts of the tissueunder investigation at the same time,(ii) more diagnostic information about the tissue from understanding howthe ultrasound beam has travelled through the tissue, that is of the sound speedproperties of the medium.The purpose of the signal amplifier 358 is:(i) to work in sympathy with the sensor electrical properties to produce avoltage whose amplitude (during ultrasound exposure) is proportional to thereceived acoustic power (if the sensor is sufficiently large to collect the wholebeam area),(ii) to amplify and condition the sensor response such that the pyroelectriccomponent is measurable above sources of noise.In addition to the amplified and conditioned "signal" and "reference" sensorresponses from the receivers 354, 356, the detection unit 350 also produces athird output, which is an electronic difference between the two sensor responses.This can be described as the "difference" sensor response and is labelled "Diff" inFigure 14. The difference signal provides an important signal on whichsubsequent processing is carried out. The details of the signal amplifier operationare outlined in the applicant’s earlier EP-3,588,023 and WO-2010 / 084319.The purpose of the oscilloscope unit 360 is to record the timeseries voltageresponses from the "signal", "reference" and "difference" output channels of thesignal amplifier 358. The oscilloscope unit 360 is preferably of a type that is ableto measure a wide range of voltage sizes (few volts to few milli volts) over theduration of a few milliseconds. Accurate and precise recordings of thesepyroelectric signals is advantageous for the subsequent analysis and conversionto an acoustic attenuation measurement.The computer or processing unit 304 preferably coordinates the followingcomponents of the signal chain:(i) drive signal generation settings (including frequency) and signaltriggering (turning the ultrasound exposure ON and OFF),(ii) switching the drive signal to the desired ultrasound transducerspositioned over different parts of the tissue under investigation,(iii) signal amplifier settings,(iv) oscilloscope settings and signal capture triggering.The computer or processing unit 304 preferably allows for both "static"measurement sequences (settings are set once in the measurement setup and donot change) and "dynamic" (closed loop) measurement sequences, used tooptimise data acquisition.Examples of "dynamic" algorithms include:(i) drive signal settings and sequencing can be adjusted on-the-fly torespond to the resultant sensor signals to adjust ultrasound power to safediagnostic levels following the ALARA principle;(ii) the switching network can be programmed to select transducers whichhave the desired sensor response or perhaps the expected transducer impedance.The utility of this sequence type can be demonstrated with a couple of examples,explained below.With reference first to the example of Figures 25 to 27, this shows how thecomputer system can select only transducers with only good coupling to the objectof interest, that is the body tissue to be analysed. The example refers to breasttissue, although the skilled person will appreciate from the teachings herein howthey would be implemented with other body tissues and tissue types. In the firststage, ultrasound is fired from all of the transducers. Once fired, the control unitmeasures and grades the response signal, for example to set categories as shownin these Figures, for instance, a good response (green) category, a poor response(brown) category, and no response (black) category. The grading could be bymeans of a threshold and look-up table, which may be predetermined or couldalso be adjusted by means of feedback through machine learning, or artificialintelligence. In the third stage (Figure 27) on those transmitters that have beendeemed to provide a good response for the measurement sequence are then fired,with the other transmitters being left idle. In the example of Figure 27, thetransmitters in green are those selected to be used, whereas the transmitters inblue are not.With reference now to Figures 28 to 30 these show another exampleimplementation, which enables a selection of transducers positioned over a regionof interest, for example to select bone-only measurement positions in a scan of apatient’s limb, for example a leg. In the first stage (Figure 28), ultrasound is firedfrom all of the transducers. In the second stage (Figure 29), the system measuresand grades the responses through the body part. As with the earlier embodiment,the grading could be based upon a threshold and look-up table associated with theexpected response for that particular body part (bone for example, soft tissue andso on) with in this embodiment there being three grade categories, onerepresentative of the expected response (green in Figure 29), one representativeof poor response or a response that is not associated with bone tissue (brown infor example Figure 29) and regions in which there has been no response (thoseindicated in black in Figure 29). The system then only makes use of thosetransmitters from which it has been determined that there is a good response. Inthe example of Figure 30 those transmitters that are identified in green, whereasthe transmitters identified in blue are not used. It will be apparent in particularfrom Figure 25 that while several other ultrasonic beams have passed throughbody tissue, the system has filtered the receiver signals to identify only body tissueof particular interest.As explained above, the filtering for particular body tissue types, basedupon frequency of the ultrasonic signal, which exhibits different rates of acousticattenuation through different body types, thereby enabling the apparatus andmethod to focus on particular body types for the assessment of that tissue type.Use of different frequencies can also be used for different assessment specificityIn order to achieve these practical implementations, the signal amplifiersettings can be adjusted by the computer or control unit 304, preferablydynamically, to minimise the effect of varying noise sources on the sensor signalduring a measurement sequence. Furthermore, the oscilloscope unit 360preferably comprises an auto-ranging algorithm to account for large variations andreceived sense of voltages with measurement through different types.The apparatus and method preferably use an algorithm which converts apyroelectric sensor response into a measurement of volume-averaged acousticattenuation of the tissue under investigation. The following parameters arepreferably determined for the calculation of acoustic attenuation:(i) pyroelectric voltage experienced by the sensor 352 with the tissue 100under investigation in the ultrasound path (this will be dependent on frequency, ifthe transducer is driven at various frequencies),(ii) pyroelectric voltage experienced by the sensor 352 with the calibrationmaterial(s) in the ultrasound path (system calibration is described below),(iii) temperature of the calibration material(s) during the referencemeasurement, (iv) ultrasound pathlength through the tissue under investigation.To calibrate the apparatus and method, measurements can be completedusing a block(s) of material of known attenuation which could simulate theapproximate attenuation of body tissue to be analysed. The loss expected at thefrequency or frequencies of interest should be known. In principle, suchcalibration could be carried out daily, and the voltages and uncertainties(repeatability) loaded in the software prior to measurements on a person oranimal. This can also be beneficial for quality assurance and understanding theuncertainty contributions to the measurement.Temperature of the device elements, calibration materials and tissue underinvestigation are all need measured, controlled and / or accounted for. Onepossible solution to avoiding large temperature variation across elements and overtime can be to heat consistently all elements (device and calibration materials)approximately to body temperature.Figure 31 is a graph of pyroelectric voltage measurement, being anexample of the three signals recorded by the oscilloscope (the graph “rear” =sig / signal and the graph “front” = ref / reference). Capturing all three signals canprovide information on the quality of the measurement and potential furtherdiagnostic information. This particular response is from a differential sensor of thetype shown in Figure 22, hence three outputs from the sensor electronics. Thepeak voltage is proportional to the acoustic power incident on the sensor.The change in voltage (V, or the peak signal), from the "rest" state to the"excited" state of the sensor during ultrasound exposure, is the importantmeasurement in the preferred embodiments. Measuring this voltage can bedifficult, particularly in conditions of poor signal to noise of a type as depicted inFigure 32, and / or when measurements are performed in quick succession and thesensor has not had time to return to the "rest" state, as depicted in Figure 33.Figure 34 is an example acoustic simulation through a computational breastphantom which has been compressed to a thickness of 40 mm. The coloursindicate the strength of acoustic intensity from a simulated 10 mm wide ultrasoundemitter (on the left-hand side) through the 40 mm of breast tissue. Thediminishing intensity is a function of the breast tissue composition. The sensor issimulated from the acoustic intensity on the right-hand side of the simulation.Referring now to Figure 35, this shows the result of multiple acousticsimulations determining the acoustic attenuation coefficients of computationalbreast phantoms with varying tissue composition. This example shows two sets ofmeasurements where the computational phantom was compressed and measuredfrom two different directions.There are a few ways to measure the pyroelectric voltage which haveadvantages and disadvantages in these conditions. Two example ways include:(i) direct measurement, which is the simplest, most naive approach whichrequires least computation;(ii) maximum likelihood estimation, which has demonstrated the bestperformance for noise resistance although requires more computation and anextra measurement step.As detailed in the applicant’s earlier patent publications, the pyroelectricsensor response (V) is proportional to the received acoustic power (P), if a set ofspecial conditions are met. The calculation of insertion loss (IL) is as follows: where subscripts ref and t denote measurement made with the reference materialand tissue paths, respectively. This is a form of correction, cancelling the effect oftime-invariant differences in the sensitivities of the ultrasound transducers andvariations in the sensitivity of the sensor across its face. The sensor is largeenough to capture the whole ultrasound beam, and therefore, the insertion lossmeasured at a particular position is dependent on the acoustic properties of thematerial encountered by the whole beam.Next, the system and method convert from a "total loss encountered(relative to the reference) by the ultrasound beam" to a "loss per unit distanceencountered (relative to reference) by the ultrasound beam". To do this thesystem obtains a measure of the distance the loss was measured over and theconditions of the reference measurement, and therefrom calculates: where dt is the ultrasound pathlength through the tissue under investigation(assuming a simple straight-line path between source and receiver). dt can besimple to determine if there is no compliant coupling mechanism, and a little morecomplicated (but relatively simple with some trigonometry) if there is. Parameterssuch as the separation of the transmitter and receiver plates (ds) and the couplingpaddle angle (θ) are recorded by the device and used in the calculation of dt.Figures 36 and 37 are two examples of dt considerations with and without acompliant mechanism. In Figure 36 dt = ds, because the tissue thickness is equalto the plate separation. In Figure 37, dt ≠ ds, although the tissue thickness can becalculated with knowledge of the plate separation, coupling paddle angle,ultrasound transducer position, and other standoff distances.Any uncertainty in the measurements can be addressed in known way byrounding or thresholding, for instance with reference to the standard deviation inthe signals.The derived acoustic attenuation coefficient measurements can be used inthe following manner.In the case of breast density assessment, for example, the inventors havedemonstrated (through acoustic simulation and in-vivo testing) that acousticattenuation in breast tissue is related to the ratio of fat and fibro-glandular tissues,that is to breast density.The graph of Figure 38 shows the results of acoustic simulations throughsimulated breasts of varying breast density (% fat on the x axis) showing therelation to the measured parameter (IL on the y axis). For this example, thesimulated measurements where through the same 70mm pathlength of tissue soIL is directly proportional to acoustic attenuation in this case.It will have been appreciated by the skilled person from the teachings abovethat the system and apparatus disclosed herein can comprise an array of largetransducers (preferably receivers). Preferably, the apparatus and method use asingle large area detector (phase-insensitive) to measure the transmitted power.The system and method obtain a measure of bulk or volume averaged tissueproperties. While in prior art systems the aim is to use transducers having widthsless than the width of a selected portion of a patient’s body to be imaged, relatingto the ability to define organ boundaries which is required for the imaging(scanning) of internal structures, in the taught system and method, the transduceris large in extent for the purposes of deriving bulk volume averaged properties.The receive detector is sufficiently large to capture a broad transmitted beam.The above disclosure focuses on an example implementation of theapparatus. In practical implementations, the apparatus could take a variety offorms, of which some have been described above. One embodiment provides theapparatus as a tabletop or countertop device, having a frame supporting theemitter and sensor plates in facing relationship, possibly parallel to one anotherbut in other embodiments at an angle to one another such that the separationbetween them reduces into the volume of the frame. Such orientation can bemore suitable for the shape of a breast when facing towards the device. For thisembodiment, the system calibrates for the spacing between the emitters andreceiver across the array, in a manner described above. Advantageously, thespacing between the emitter and sensor plates is adjustable, as described above,and the apparatus may also be provided with a bladder as described, although inother embodiments there may be provided a conformable layer over at least oneof the plates of the types described above.In another embodiment, the apparatus is of a form that it is connected to arolling stand, to facilitate movement of the apparatus in a medical facility. Yetanother embodiment provides a wall-mountable version of the device.In all of the described and possible embodiments, it is envisaged that oneor both of the upper and lower transducer plates may be movable so as to adjustthe plate spacing relative to the organ part to be assessed. It will be appreciatedalso that these embodiments could also be implemented as devices to analyseother objects, not just for medical applications, as described herein.In principle, acoustic attenuation measurements, with the apparatus andmethodology described in this document, can be used as a biomarker for otheruseful parameters in other tissue of the human or animal body, including forexample: Muscle - varying fibrous content, which can be objectively and longitudinallyassessed with the disclosed apparatus and method, and can be a useful indicationof acute and chronic muscle conditions, such as sports injury assessment andmuscular dystrophy monitoring, respectively;Bone - varying bone density, which again can be objectively andlongitudinally assessed with the disclosed apparatus and method, and can be auseful indication of acute and chronic bone conditions, such as fractureassessment and osteoporosis monitoring, respectively.The skilled person will appreciate that the method and apparatus disclosedherein can be used in the analysis of other bodily tissues and organs, all within thecompetence of the skilled person.Then disclosures in British patent application numbers GB-2402708.8 andGB-2402709.6, from which this application claim priority, and in the abstractaccompanying this application are incorporated herein by reference.

Claims

CLAIMS1. An object composition or constitution assessment apparatus comprising:first and second panel elements disposable in spaced apart and facingrelationship, at least one of the first and second panel elements being adjustablerelative to the other in separation;at least one ultrasound emitter disposed at or on one of the first and secondpanel elements;at least one ultrasound receiver disposed at or on the other of the first andsecond panel elements, whereby the at least one ultrasound emitter and the atleast one ultrasound receiver face one another;a support structure to which the first and second panel elements areattached; anda processing unit coupled to the at least one ultrasound transmitter andreceiver and configured to determine the received ultrasound signal which isproportional to the acoustic power transmitted through the object representative ofthe total acoustic attenuation through the object assessed, and to determinetherefrom an object composition or constitution measure associated with the objectassessed.

2. Apparatus according to claim 1, wherein the processing unit is configured todetermine the insertion loss from each of a plurality of emitters and therefrom abulk or volume average acoustic attenuation across a determined area of theobject assessed.

3. Apparatus according to claim 1, wherein the apparatus is configured todetermine the composition or constitution of as body part of a human or animal.

4. Apparatus according to claim 3, wherein the body part comprises an organor tissue.5 Apparatus according to any preceding claim, wherein the support structureand panel elements permit a subject to undergo tissue composition assessment ofa body part of that subject while in a generally upright position, advantageouslystanding or seated.

6. Apparatus according to any preceding claim, wherein at least one of thefirst and second panel elements comprises an adjustment element with an objector patient facing plate orientable relative to the associated first or second panelelement and relative to a part of an object or patient’s body to be assessed.

7. Apparatus according to claim 6, wherein the adjustment element isconfigured to reduce or minimise air gaps between the transmitter and receiverelements and the object or part of a patient’s body to be assessed.

8. Apparatus according to claim 6 or 7, wherein the adjustment element iscoupled to at a respective one of the first and second panel elements by a hinge orpivot and configured to rotate thereabout.

9. Apparatus according to any one of claims 6 to 8, wherein the adjustmentelement comprises a compliant mechanism disposed at an object or patientremote side of the object or body part facing panel and configured to allowadjustment of an angle of tilt of the object or patient facing panel.

10. Apparatus according to claim 9, wherein the compliant mechanismcomprises a bladder selectively fillable with a fluid.

11. Apparatus according to claim 10, comprising a fluid source, a pump coupledto the source and a pressure or volume sensor, the fluid source being coupled tothe bladder for filling the bladder with fluid to a determined pressure or volume.

12. Apparatus according to any one of claims 9 to 11, wherein the compliantmechanism is made of an acoustically transmissible material, wherein the at leastone ultrasonic emitter or the at least one ultrasonic receiver is disposed behind thecompliant mechanism relative to the object or patient facing surface such that inuse ultrasonic beams pass through the material of the compliant mechanism.

13. Apparatus according to any preceding claim, wherein the at least oneultrasound receiver is shaped and sized to be at least as large as an areaexpected to be covered by an object or person’s body part to be assessed whenplaced between the lower and upper panel elements.

14. Apparatus according to any preceding claim, comprising an array ofultrasound emitters, the array advantageously being shaped and sized to be atleast as large as an area expected to be covered by an object or person’s bodypart to be assessed when placed between the lower and upper panel elements.

15. Apparatus according to any preceding claim, wherein the at least oneultrasound emitter is adjustable and / or movable relative to the at least one receiverso as to be able to emit an adjustable or movable ultrasonic beam towards the atleast one emitter.

16. Apparatus according to claim 15, wherein the at least one ultrasoundemitter has an adjustable ultrasonic beam angle.

17. Apparatus according to any preceding claim, wherein the processing unit isconfigured to determine on the basis of an ultrasonic signal sensed at the at leastone ultrasonic receiver and of the detected distance between the at least oneultrasonic emitter and the at least one ultrasonic receiver an attenuation of theacoustic power and to determine therefrom a measure of composition orconstitution of the object or organ.

18. Apparatus according to claim 17, wherein the processing unit is configuredto determine on the basis of a thickness of compliant and / or other materialbetween the at least one ultrasonic emitter and / or the at least one ultrasonicreceiver and the or an object or tissue contact panel of the apparatus a lostultrasonic attenuation from the compliant and other material and to adjust themeasured attenuation on the basis of the determined lost ultrasonic attenuation.

19. Apparatus according to claim 18, wherein the processing unit is configuredto calculate thickness of compliant and / or other material on the basis of ameasured angle of the object or tissue facing surface relative to the at least oneultrasonic emitter or receiver, or on the basis of volume of fluid in the or a fillablebladder.

20. Apparatus according to any preceding claim, wherein the processing unit isconfigured to apply a calibration value to the acoustic energy signals received atthe receiver to take into account factors including: sensor spacing, lost emitterenergy through intervening materials of the apparatus.

21. Apparatus according to claim 20, wherein the calibration value includes oneor more of: measurements made through reference materials, data relevant to a particularorgan or object to be examined, nature or characteristics of a patient or object undergoingexamination, spacing of the emitter and receiver assemblies from one another, theamount of attenuation material other than body part between the emitter and receiverassemblies.

22. Apparatus according to any preceding claim, wherein the processing unit isconfigured to determine acoustic attenuation across substantially the whole areaof an object or body part and to determine a bulk or volume averaged acousticattenuation through the object or body part.

23. Apparatus according to any preceding claim, wherein the processing unit isconfigured to determine acoustic attenuation across a plurality of select areas ofan object or organ and to determine an ultrasound attenuation map across theareas of the object or organ.

24. Apparatus according to any preceding claim, wherein the processing unit isconfigured to operate the at least one transmitter at different frequencies, for theanalysis of different tissue types and / or for different assessment specificity.

25. Apparatus according to claim 24, wherein the processing unit is configuredto determine a measure of tissue composition or constitution of a selected tissuetype within a body part being tested.

26. Apparatus according to any preceding claim, wherein one or both of the firstand second panel elements comprises a pivot or hinge configured to tilt at least apart of the panel element.

27. Apparatus according to any preceding claim, wherein the apparatus isconfigured to obtain a determination of object or tissue composition or constitutionin a plurality of planes by adjustment of the orientation and / or disposition of thetransmitter and receiver elements relative to an object or body part beinganalysed.

28. Apparatus according to claim 27, comprising a gimbal mechanism coupledto the panel elements and operable to adjust the orientation of the first and secondpanel elements.

29. Apparatus according to any preceding claim, wherein the apparatus isconfigured to assess breast tissue composition or constitution.

30. Apparatus according to any preceding claim, wherein the at least onereceiver has a size and area at least as large as a size and area of the ultrasonicbeam or beams emitted by the emitter or emitters during expected operation of theapparatus.

31. A method of assessing the composition or constitution of an objectcomprising:disposing first and second panel elements in spaced apart and facingrelationship, at least one ultrasound emitter being disposed at or on one of the firstand second panel elements and at least one ultrasound receiver disposed at or onthe other of the first and second panel elements, whereby the at least oneultrasound emitter and the at least one ultrasound receiver face one another;and determining from received ultrasound signal or signals which isproportional to the acoustic power transmitted through the object representative ofthe total acoustic attenuation through the object assessed, and to determinetherefrom an object composition or constitution measure associated with the objectassessed.

32. A method according to claim 31, wherein an overall object composition orconstitution measurement is determined across an area of the object assessed.

33. A method according to claim 31 or 32, wherein the method is carried out todetermine the composition or constitution of an organ or tissue of human or animalpatient.

34. A method according to claim 33, wherein the method is practiced on anorgan of a person while in a generally upright position, advantageously standing orseated.

35. A method according to any one of claims 31 to 34, wherein at least one ofthe first and second panel elements comprises an orientation adjustable object orpatient facing plate, wherein the method comprises adjusting the orientation of theplate relative to the associated first or second panel element and relative to anobject or part of a patient’s body to be assessed.

36. A method according to claim 35, comprising adjusting the orientation of theobject or patient facing plate to reduce or minimise air gaps between thetransmitter and receiver elements and the object or part of a patient’s body to beassessed.

37. A method according to claim 35 or 36, comprising operating a compliantmechanism disposed at a remote side of the object or patient facing panel to allowadjustment of an angle of tilt of the object or patient facing panel.

38. A method according to claim 37, comprising selectively filling with a fluid abladder of the compliant mechanism by operating a fluid source with a pumpcoupled to the source and a pressure or volume sensor, and selectively filling thebladder to a determined pressure or volume.

39. A method according to any one of claims 31 to 38, comprising receivingultrasonic signals across an area at least as large as an area covered by an objector person’s body part to be assessed.

40. A method according to any one of claims 31 to 39, comprising emittingultrasonic signals across an area at least as large as an area covered by an objector person’s body part to be assessed.

41. A method according to any one of claims 31 to 40, including adjustingand / or moving the at least one ultrasound emitter relative to the at least onereceiver so as to emit an adjustable or movable ultrasonic beam towards the atleast one emitter.

42. A method according to claim 41, including adjusting an ultrasonic beamangle of the at least one ultrasound emitter.

43. A method according to any one of claims 31 to 42, including determining onthe basis of an ultrasonic signal sensed at the at least one ultrasonic receiver andof the detected distance between the at least one ultrasonic emitter and the atleast one ultrasonic receiver an attenuation of the total acoustic power and todetermine therefrom a measure of object or organ composition or constitution.

44. A method according to claim 43, including determining on the basis of athickness of compliant and / or other material between the at least one ultrasonicemitter and / or the at least one ultrasonic receiver and the or an object or body partcontact panel of the apparatus a lost ultrasonic attenuation from the compliant andother material and to adjust the measured attenuation on the basis of thedetermined lost ultrasonic attenuation.

45. A method according to claim 44, including calculating a thickness ofcompliant and / or other material on the basis of a measured angle of the object orpatient facing surface relative to the at least one ultrasonic emitter or receiver, oron the basis of volume of fluid in the or a fillable bladder.

46. A method according to any one of claims 31 to 45, comprising applying acalibration value to the acoustic energy signals received at the receiver to take intoaccount factors including: sensor spacing, lost emitter energy through interveningmaterials of the apparatus.

47. A method according to claim 46, wherein the calibration value includes oneor more of: measurements made through reference materials, data relevant to a particularorgan or object to be examined, nature or characteristics of a patient or object undergoingexamination, spacing of the emitter and receiver assemblies from one another, theamount of attenuation material other than body part between the emitter and receiverassemblies.

48. A method according to any one of claims 31 to 47, including determining anattenuation across substantially the whole area of an object or organ anddetermining an average attenuation through the object or organ.

49. A method according to any one of claims 31 to 48, including determining anattenuation across a plurality of select areas of an object or body part and anattenuation map across the areas of the object or body part.

50. A method according to any one of claims 31 to 49, including operating theat least one transmitter at different frequencies, for the analysis of different objector tissue types.

51. A method according to claim 50, including determining a measure of tissuecomposition or constitution of a selected tissue type within a body part beingtested.

52. A method according to any one of claims 31 to 51, including obtaining adetermination of object or organ composition or constitution in a plurality of planesby adjustment of the orientation of the transmitter and receiver elements relative toan object or body part being analysed.

53. Apparatus or a method according to any preceding claim, for theassessment of at least one of:a) assessment of an appropriate screening modality;b) risk of developing cancer;c) the existence of a potential cancerous growth;d) an acute or chronic muscle condition;e) the existence or risk of muscular dystrophy;f) an acute or chronic bone condition;g) the existence or risk of osteoporosis.

54. A method of identifying a medical condition in a patient by use of apparatusor a method according to any preceding claim.

55. A method according to claim 54, in the assessment of at least one of:a) assessment of an appropriate screening modality;b) risk of developing cancer;c) the existence of a potential cancerous growth;d) an acute or chronic muscle condition;e) the existence or risk of muscular dystrophy;f) an acute or chronic bone condition;g) the existence or risk of osteoporosis.

56. A tissue composition or constitution assessment apparatus comprising:first and second panel elements disposable in spaced apart and facingrelationship, at least one of the first and second panel elements being adjustablerelative to the other in separation;at least one ultrasound emitter disposed at or on one of the first andsecond panel elements;at least one ultrasound receiver disposed at or on the other of the firstand second panel elements, whereby the at least one ultrasound emitter and theat least one ultrasound receiver face one another;a support structure to which the first and second panel elements areattached; anda processing unit coupled to the at least one ultrasound transmitter andreceiver and configured to determine from received ultrasound signals a tissuecomposition or constitution measure associated with the organ tissue assessed;wherein at least one of the first and second panel elements comprises anadjustment element with a tissue facing plate orientable relative to the associatedfirst or second panel element and relative to a part of a patient’s body to beassessed.

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