WO2021019441A1

WO2021019441A1 - System for analysing the state of a bone or of a bone portion

Info

Publication number: WO2021019441A1
Application number: PCT/IB2020/057110
Authority: WO
Inventors: Enrico BENASSI; Giovanni TREGNAGHI; Ciro BOIANO; Roberto PUGLIESE; Artem Vladimirovich ELKIN
Original assignee: 3D.I.V.E. S.R.L.
Priority date: 2019-07-29
Filing date: 2020-07-28
Publication date: 2021-02-04
Also published as: IT201900013194A1

Abstract

It is disclosed a system for analysing the state of a bone or of a bone portion. The system comprises a first acoustic-mechanical exciter (2-1), a second acoustic-mechanical exciter (2-2), an electromechanical transducer (3-1) and a processing unit (4). The processing unit is configured to generate an analysis signal representative of an estimation of the presence or absence of an alteration of the bone or of the bone portion, as a function of the acoustic-mechanical signals generated by the first and second exciters and detected by the transducer.

Description

“System for analysing the state of a bone or of a bone portion”

DESCRIPTION

Technical field of the invention

The present invention relates to the analysis of a bone or of a bone portion to determine, for example, the presence of a fracture in the bone.

Prior art

It is known the use of three main types of apparatus for performing bone analyses, and in particular for determining potential lesions, such as, for example, fractures or degenerations.

These three main methods refer to the use of X-rays, magnetic fields and mechanical waves.

In the first case, the use of radiographic and tomographic apparatus is considered the gold standard, in particular for the identification of bone fractures.

Nuclear magnetic resonance (NMR) uses intense external magnetic fields and also enables the identification of non-mineral tissues (such as muscles, tendons, cartilage, etc.).

As regards the use of mechanical waves, the pairing of a tuning fork and a stethoscope has been proposed in the military field to detect a fracture of a long bone: the tuning fork and the stethoscope are rested on the epiphysis. The tuning fork generates vibrations at a well-defined, non-modulable frequency (440 Hz) with a spectrally monochromatic wave profile (sine wave without harmonic components above the fundamental); said vibrations are transmitted through the bone and detected by the stethoscope. The tuning fork is brought near the stethoscope along the diaphysis: the presence of a fracture is detected if a drastic decrease in the detected sound intensity is recorded.

In all three of the above-described methods, the presence of well-trained medical and technical personnel is required.

The use of X-ray and NMR apparatus is possible only in equipped medical facilities, such as a hospital or a clinic.

In many cases, however, it is necessary to be able to detect the presence of a bone lesion (for example a bone fracture) also in contexts where no hospitals or medical facilities are present, as for example in the case of emergency transport vehicles (for example ambulances and rescue helicopters), extreme sports, on boats and submarines, in aerospace stations, in war zones, in areas hit by natural catastrophes such as earthquakes or floods, in rural areas and in Third World areas.

In these cases the use of portable measuring instruments becomes necessary; furthermore, the possible presence of environmental noise during the examination is common, for example noise caused by explosions in a war zone, the noise of the siren in the case of transport in an ambulance, or noise caused by automobile traffic in the case of rescue for a road accident.

In the above-described cases, radiographic, tomographic and NMR apparatus are unusable due to the lack of portability.

Furthermore, the use of X-ray instruments in the veterinary field implies further problems, since the animal needs to be immobilised by personnel or sedated during the analysis; in the former case, personnel are exposed to radiation, whereas sedation is an operation that is risky for the animal itself.

The use of a tuning fork and stethoscope to detect the presence of a bone fracture is scarcely reliable, because the investigation is disturbed by the presence of environmental noises; furthermore, this approach is limiting, since it uses only one vibration frequency, in particular it is purely a sine/cosine wave.

US 2016/0331237 A1 represents an attempt to improve the tuning fork- stethoscope system.

US 2016/0331237 A1 describes a system that uses a smartphone to detect the presence of a possible bone fracture through the application of a vibration at a given frequency in a selected anatomic position and the detection of the resulting vibration transmitted by the bone by means of the microphone of a smartphone located in another anatomic position.

In particular, said analysis is performed by comparing the data detected by the sensors with the expected results stored into a database.

Brief summary of the invention

The present invention relates to a system for analysing the state of a bone tissue or of a bone portion as defined in the enclosed claim 1 and by its preferred embodiments described in dependent claims 2 to 1 1.

The Applicant has perceived that the analysis system in accordance with the present invention has the following advantages:

• The invention does not use harmful radiation such as, for example, X-rays. The invention can thus be employed when the use of X-rays is not advisable, as in the case of pregnant women, or in cases where frequent monitoring of the progression of a disease or healing is required.

• Compared with the use of a tuning fork and stethoscope, the mechanical wave profile is modulable.

• The system of the invention is lightweight and portable and it can thus also be transported in environments outside hospitals or it can be worn, as in cases of military medicine on the battlefield; the system of the invention can further be used in cases of home care.

• Compared with the prior art, the invention has a low sensitivity to acoustic disturbance and to vibrations coming from an external environment (typical of many emergency situations) and a greater sensitivity to the mechanical wave transmitted in the bone; by virtue of these features, the invention has greater precision and reliability in the identification of a possible alteration of the bone or of the bone portion (for example, a bone fracture);

• The identification of a possible lesion by means of the system of the invention is rapid; for this reason the use of the invention can improve the possibility of recovery from a lesion thanks to an immediate intervention thereupon.

• The system of the invention is considerably more economical than an X-ray, tomography or NMR apparatus and, compared with the prior art, the operation thereof does not entail the use of consumables or high energy consumption.

• Compared with the prior art, the operation of the system of the invention is simple and does not require specific training; the system of the invention can also be used by personnel who are not specialised in medicine. Furthermore, in some particular cases, as in the case of use in a war zone, the system enables a self-analysis of the possible alteration.

• Compared with the prior art, the invention can provide a display with three- dimensional components of the anatomic part analysed floating in air.

• The invention enables a reduction in the costs of the health system thanks to an early analysis of the suspected lesion, with a consequent reduction in recovery times, a lower cost of the apparatus used and of the maintenance thereof and the possibility of use by non-specialised personnel.

• The invention would enable the design of improved diagnostic protocols in the case of veterinary medicine. • By virtue of the features specified above, the invention can be provided as a first- aid device usable in a work environment, ships and submarines, aerospace vehicles, etc. and in the case of extreme sports, natural catastrophes, etc.

The present invention also relates to an open light field volumetric device for the display of floating stereoscopic 3D images or streams of images as defined in the appended claim 12.

The present invention also relates to a method for analysing the state of a bone or of a bone portion, wherein the method of analysis is defined in the appended claim 14 and in the preferred embodiment described in the dependent claim 15.

Brief description of the drawings

Further characteristics and advantages of the invention will emerge from the following description of a preferred embodiment and variants thereof, said description being provided by way of example with reference to the attached drawings, wherein:

Figure 1 shows a block diagram of a system for analysing the state of a bone according to one embodiment of the invention;

Figure 2 schematically shows a possible pattern of the control signals of a pair of acoustic-mechanical exciters;

Figure 3 schematically shows a possible pattern of the signals detected by a pair of electroacoustic transducers;

Figures 4, 5, 6 and 7 show an open light field volumetric device comprising the system for analysing the state of a bone of Figures 1 to 3.

Detailed description of the invention

It should be noted that in the description below, identical or similar blocks, components or modules, even if they appear in different embodiments of the invention, are indicated by the same numerical references in the figures.

With reference to Figure 1 , it shows a system 50 for analysing in particular the state of a bone 9-1 and for detecting the presence of a possible alteration of the bone 9- 1 , for example the presence of a fracture of the bone 9-1 or other degenerative alterations, such as, for example, but not only, osteoporosis or a bone tumour.

The bone analysis system 50 comprises:

a first acoustic-mechanical exciter 2-1 ;

a second acoustic-mechanical exciter 2-2;

a first electromechanical transducer 3-1 ;

a second electromechanical transducer 3-2; a processing unit 4;

a first amplifier 5-1 ;

a second amplifier 5-2;

a first pre-amplifier 6-1 ;

a second pre-amplifier 6-2;

a first low-pass filter 7-1 ;

a second low-pass filter 7-2;

a short-range wireless signal transceiver 8.

For the purpose of explaining the invention, two acoustic-mechanical exciters, two electromechanical transducers, two amplifiers, two pre-amplifiers and two low-pass filters will be considered, but more in general the analysis system 50 can include more than two acoustic-mechanical exciters, more than two electromechanical transducers, more than two amplifiers, more than two pre-amplifiers, or more than two low-pass filters.

Furthermore, for the purpose of explaining the invention, an anatomic portion 9 of a limb (for example, the femur) in which an alteration 23 (for example, a fracture) is present will be considered, said portion comprising an internal bone 9-1 and a muscle tissue and other connected tissues 9-2 external thereto.

It should be observed that the invention is not limited to an anatomic portion of a limb, but more in general it is also applicable to other anatomic portions, such as, for example, an anatomic portion of the skull.

The anatomic portion to be analysed (for example the limb 9) can be in an environment in which strong acoustic disturbances and also vibrations are present, such as, for example, an industrial environment, a war setting, an area hit by natural disasters, etc.

The anatomic portion (in particular the limb 9) defines a direction X in which the bone 9-1 has a main longitudinal extension and a direction Y perpendicular to X in which the bone 9-1 has a lower transversal extension.

The term“acoustic-mechanical exciter” means a device capable of generating a mechanical wave, in particular of an acoustic type, i.e. with a frequency in the audio band (comprised between 20 Hz and 20 KFIz) which can also be perceived by humans, and/or infrasound (less than 20 Hz) and/or ultrasound (greater than 20 KFIz). In particular, the first and second acoustic-mechanical exciters 2-1 , 2-2 are devices capable of converting an electrical signal into an acoustic-mechanical vibration, such as, for example, magneto-dynamic exciters.

The first acoustic-mechanical exciter 2-1 is mechanically coupled to the limb 9 (externally thereto) and it has the function of generating a first acoustic-mechanical wave and injecting it into the limb 9, thereby generating a first vibration in the limb 9.

Preferably, the intensity of the generated first acoustic-mechanical wave is controlled as a function of the value of a first control signal S1_c (for example, an electric voltage), thus the first acoustic-mechanical exciter 2-1 is of an electromagnetic type.

Similarly, the second acoustic-mechanical exciter 2-2 is mechanically coupled to the limb 9 (externally thereto) and has the function of generating a second acoustic- mechanical wave and injecting it into the limb 9, thereby generating a second vibration in the limb 9.

Preferably, the intensity of the generated second acoustic-mechanical wave is controlled as a function of the value of a second control signal S2_c (for example, an electric voltage); therefore, the second acoustic-mechanical exciter 2-2 is of an electromagnetic type.

The first and second acoustic-mechanical waves propagate first inside the muscle tissue and other tissues 9-2 in the transversal direction of the limb 9 from the periphery towards the centre, then the first and second acoustic-mechanical waves propagate mainly inside the bone 9-1 in the direction of longitudinal extension of the limb 9.

The first and second exciters 2-1 , 2-2 are for example of an electromagnetic type and each can be made with the component E-12041808 sold by Soberton Inc. (USA).

In particular, the first and second exciters 2-1 , 2-2 are mechanically coupled to the limb 9, in particular on opposite sides with respect to a secondary transversal extent of the limb 9 (and thus on opposite sides with respect to a secondary transversal extension of the bone 9-1 ), as shown in Figure 1.

It should be observed that it is also possible to position the first and second exciters 2-1 , 2-2 in positions other than on opposite sides, for example in the event that it is not possible to apply them to the opposite sides in the direction of transversal extension of the limb 9. The first and second exciters 2-1 , 2-2 are supplied with harmonic signals having a same frequency and a phase difference comprised between 0 degrees (excluded) and 360 degrees (excluded), i.e. the first and second control signals S1_c, S2_c have a substantially sinusoidal or cosinusoidal pattern with an equal frequency and are phase shifted from each other by an angle comprised between 0 degrees (excluded) and 360 degrees (excluded); consequently, the first and second exciters 2-1 , 2-2 are such to generate the first and second acoustic-mechanical waves with a pattern whereby they are phase shifted from each other by an angle comprised between 0 degrees (excluded) and 360 degrees (included).

Preferably, the phase difference between the first and second control signals S1_c, S2_c is a value selected in the range comprised between 170 degrees and 180 degrees, i.e. selected from 170, 171 , 172, 173, 174, 175, 176, 177, 178, 179 and 180.

Preferably, the phase difference between the first and second control signals S1_c, S2_c is a value selected in the range comprised between 90 degrees (excluded) and 180; consequently, the first and second exciters 2-1 , 2-2 are such to generate the first and second acoustic-mechanical waves with a pattern whereby they are phase shifted from each other by an angle comprised between 90 (excluded) and 180 degrees.

Advantageously, the first and second exciters 2-1 , 2-2 are supplied in counter phase, i.e. the first and second control signals S1_c, S2_c are sinusoidal signals having the same frequency and, moreover, the first control signal S1_c has a counter-phase pattern with respect to the pattern of the second control signal S2_c (i.e. the first and second control signals S1_c, S2_c are phase shifted from each other by 180 degrees), as shown in Figure 2, in which:

at the instants when the first control signal S1_c has a maximum value, the second control signal S2_c has a minimum value;

at the instants when the second control signal S2_c has a maximum value, the first control signal S1_c has a minimum value.

Consequently, the first and second exciters 2-1 , 2-2 are such to generate the first and second acoustic-mechanical waves with a pattern whereby they are counter- phased to each other, i.e.:

at the instants when the first acoustic-mechanical wave has a maximum value, the second acoustic-mechanical wave has a minimum value; at the instants when the second acoustic-mechanical wave has a maximum value, the first acoustic-mechanical wave has a minimum value.

By virtue of the position on opposite sides of the first and second exciters 2-1 , 2- 2 and by virtue of the phase shifted (in particular counter-phase) supply of the first and second exciters 2-1 , 2-2, one obtains that in the point substantially halfway along the transversal extension of the bone 9-1 (and thus well within the bone 9-1 ) the stimulation of a mechanical type is maximised, thus allowing an effective propagation of the mechanical wave (i.e. of the vibrations) inside the bone to be analysed; furthermore, in this manner the vibrations transmitted in the part of the other tissues are reduced.

In contrast, the propagation of the acoustic component is minimised inside the other tissues because of the phase shifted (in particular counter-phase) harmonic pattern of the first and second acoustic-mechanical waves: in this manner the bone analysis system 50 is more immune to the acoustic signal that is propagated in the tissues that are not of interest and in the air of the environment surrounding the limb 9, so a greater sensitivity only to the vibration transmitted into the bone 9-1 is obtained.

It should be observed that the invention is also applicable to the case where the first and second control signals S1_c, S2_c are not of a sinusoidal type (i.e. monochromatic signals at a single equal frequency), but they are signals that occupy a narrow frequency band, such as, for example, a complex spectral signal composed by the overlapping of two (or more) sinusoidal signals with respective frequencies f1 , f2, ... fn that are different from one another and have values close to one another, typically comprised in the audio band between 20 Hz and 20 KHz, such as, for example, but not only f1 = 1 KHz, f2=1.1 KHz (and f3= 1.2 KHz), and/or infrasounds and/or ultrasounds.

The first and second electromechanical transducers 3-1 , 3-2 are devices capable of converting an acoustic-mechanical vibration into an analog or digital electrical signal, such as, for example, microphones and accelerometers (for example, of the MEMS type).

The first electromechanical transducer 3-1 is mechanically coupled to the limb 9 (externally thereto) at a given distance from the first and second acoustic-mechanical exciters 2-1 , 2-2 along the main longitudinal extension of the limb 9, wherein said distance is chosen so as to comprise inside the position of the possible fracture 23 it is intended to detect.

For example, for a femur the distance between the first exciter 2-1 and the first electromechanical transducer 3-1 is equal to about 20 cm. The first electromechanical transducer 3-1 has the function of detecting a first mechanical wave (i.e. a vibration) that has propagated in the bone to be analysed 9-1 along the direction of longitudinal extension from the first and second exciters 2-1 , 2-2 towards the first electromechanical transducer 3-1 , thus generating a first detection signal S1_d which is a function of the intensity of the first mechanical wave detected.

Similarly, the second electromechanical transducer 3-2 is mechanically coupled to the limb 9 (externally thereto) at a given distance from the first and second acoustic- mechanical exciters 2-1 , 2-2 along the main longitudinal extension of the limb 9, wherein said distance is chosen so as to comprise inside the position of the possible fracture 23 it is intended to detect.

For example, for a femur the distance between the second exciter 2-2 and the second electromechanical transducer 3-2 is equal to about 20 cm.

The second electromechanical transducer 3-2 has the function of detecting a second mechanical wave (i.e. a vibration) that has propagated in the bone to be analysed 9-1 along the direction of longitudinal extension from the first and second exciters 2-1 , 2-2 towards the second electromechanical transducer 3-2, thus generating a second detection signal S2_d, which is a function of the intensity of the second mechanical wave detected.

The first and second electromechanical transducers 3-1 , 3-2 are for example of an electromagnetic type and each can be made with the component E-12041808 sold by Soberton Inc. (USA).

In particular, the first and second electromechanical transducers 3-1 , 3-2 are mechanically coupled to the limb 9, in particular on opposite sides with respect to a secondary transversal extension of the limb 9, as shown in Figure 1 : in this manner, the bone to be analysed 9-1 will be in a position that is halfway between the first and second transducers 3-1 , 3-2.

Consequently, the vibrations that are propagated in the transversal direction produce the first and second detection signals S1_d, S2_d with a sinusoidal pattern with an equal frequency and which are phase shifted from each other by an angle comprised between 0 degrees (excluded) and 360 degrees (excluded), in particular comprised between 90 degrees and 180 degrees, even more in particular equal to 180 degrees (counter-phased) as shown in Figure 3.

It should be observed that it is also possible to position the first and second electromechanical transducers 3-1 , 3-2 in positions other than on opposite sides, for example in the event that it is not possible to apply them on opposite sides in the direction of transversal extension of the limb 9.

Advantageously, if the first and second control signals S1_c, S2_c are sinusoidal signals with the same frequency and a relative counter-phased pattern, the vibrations that are propagated in the transversal direction produce the first and second detection signals S1_d, S2_d with a sinusoidal pattern whereby they are counter-phased to each other (i.e. they are phase shifted by 180 degrees), i.e.:

at the instants when the first detection signal S1_d has a maximum value, the second detection signal S2_d has a minimum value;

at the instants when the second detection signal S2_d has a maximum value, the first detection signal S2_d has a minimum value.

By virtue of the position on opposite sides of the first and second electromechanical transducers 3-1 , 3-2, one obtains greater efficiency in the reception of the vibrations transmitted in the bone of interest 9-1 , a lower sensitivity to vibrations not transmitted by the bone of interest 9-1 and a lower sensitivity to the acoustic waves transmitted through the air of the environment surrounding the limb 9.

Preferably, the acoustic-mechanical exciters 2-1 and 2-2 are housed in suitable containers (for example made of fabric or plastic material) adapted to transmit the vibration.

These containers are inserted, through openings, into fabric bands which are wrapped around the anatomic portion to be examined; for example, in the case of a limb 9, the bands have a circular shape and form a respective ring around the anatomic portion.

This has the advantage of enabling the acoustic-mechanical exciters 2-1 and 2-2 to be slid easily along the band, so that they can be correctly positioned.

Advantageously, the acoustic-mechanical exciters 2-1 and 2-2 are rotated about an axis defined by the main direction of extension of the anatomic portion to be analysed.

The previous considerations regarding the acoustic-mechanical exciters 2-1 , 2-2 are similarly applicable to the electromechanical transducers 3-1 and 3-2, i.e. they can also slide and rotate.

The band defined by the acoustic-mechanical exciters 2-1 , 2-2 is placed at a certain distance from the band defined by the electromechanical transducers 3-1 , 3-2, so that the anatomic portion to be analysed is comprised within said distance. With reference to Figure 3, it shows a possible pattern of the first detection signal S1_d generated by the first electromechanical transducer 3-1 and of the second detection signal S2_d generated by the second electromechanical transducer 3-2.

In particular, Figure 3 shows a first time interval DT1 (comprised between 0 ms and about 20 ms) in which it is supposed that the bone 9-1 is healthy (i.e. no fracture 23 is present), whereas it is supposed that a fracture 23 is present in the second time interval DT2 (following DT1 , comprised between 20 ms and 60 ms).

It is possible to observe the following behaviour in Figure 3:

the first detection signal S1_d and the second detection signal S2_d have a sinusoidal pattern and are counter-phased to each other (i.e. they are phase shifted by 180 degrees), both during the first time interval DT1 and during the second time interval DT2;

the amplitude of the first and second detection signals S1_d, S2_d is much smaller in the time interval DT2 in which the fracture 23 is present, compared to the amplitude of the first and second detection signals S1_d, S2_d in the time interval DT1 in which the bone 9-1 is intact.

The processing unit 4 comprises:

a first input terminal adapted to receive the first filtered detection signal S1_d_f; a second input terminal adapted to receive the second filtered detection signal S2_d_f;

an analog-to-digital converter configured to sample the first and second filtered detection signals S1_d_f, S2_d_f, and perform an analog to digital conversion of the first and second filtered detection signals S1_d_f, S2_d_f;

a first output terminal adapted to generate the first activation signal S1_a;

a second output terminal adapted to generate the second activation signal S2_a; a third output terminal adapted to generate an analysis signal S_an;

an input/output terminal adapted to transmit/receive an input/output data signal S_rx_tx.

The processing unit 4 has the function of generating the analysis signal S_an representative of an estimation of the presence or absence of an alteration inside the bone 9-1 , such as, for example, a fracture 23 in the bone 9-1 or the presence of osteoporosis or of a bone tumour in the bone 9-1.

The processing unit 4 is for example a microprocessor running an appropriate software program. Alternatively, the processing unit 4 consists in a microcontroller or a programmable electronic device (FPGA).

In particular, the processing unit 4 is configured to generate a first activation signal S1_a and a second activation signal S2_a, which have a sinusoidal pattern with the same frequency and are phase shifted from each other by an angle comprised between 0 degrees and 360 degrees, preferably comprised between 90 degrees and 180 degrees, even more preferably equal to 180 degrees (i.e. counter-phased), similarly to what was illustrated previously for the first and second control signals S1_c, S2_c, in order to maximise the mechanical stimulation in the bone 9-1 in the central point of the transversal extension as illustrated above

Preferably, the processing unit 4 is configured to vary the value of the sinusoidal signal frequency of the first and second activation signals S1_a, S2_a, which can be a value comprised between 20 Hz and 20 KHz and/or in the infrasound and/or ultrasound region.

In general, the analysis system 50 allows different bones to be analysed, by appropriately modifying the characteristics of the used acoustic-mechanical waves.

Preferably, the processing unit 4 is configured to vary the value of the phase shift between the first and second activation signals S1_a, S2_a, which can be a value comprised between 0 degrees (excluded) and 360 degrees (excluded), preferably comprised between 90 degrees (excluded) and 180 degrees, even more preferably equal to 180 degrees (i.e. the first and second activation signals S1_a, S2_a are counter-phased to each other).

Furthermore, the processing unit 4 is configured to receive a first filtered signal S1_d_f and a second filtered signal S2_d_f, and it is configured to sample and process the first and the second filtered signals S1_d_f, S2_d_f, thus the processing unit 4 is such to generate the analysis signal S_an representative of the estimation of the presence or absence of an alteration in the bone 9-1 , such as, for example, a fracture 23 in the bone 9-1 or the presence of osteoporosis or of a bone tumour.

Advantageously, the processing unit 4 is configured to vary the relative phase between the first and second activation signals S1_a, S2_a and/or to vary the relative amplitude between the first and second activation signals S1_a, S2_a, in order to take into consideration the position of the first and second exciters 2-1 , 2-2, in particular in the event that it is not possible to position them symmetrically (i.e. on opposite sides with respect to the direction of transversal extension of the limb 9): this allows to appropriately control the intensity of the vibration transmitted in the bone 9-1 and then detected by the first and/or second exciter 2-1 , 2-2.

Preferably, the analysis system 50 is such to have two operating modes:

a calibration mode, in which a dynamic variation of the relative phase and/or amplitude between the first and second activation signals S1_a, S2_a is performed, as illustrated above, in order to find the best value of the relative phase difference and/or amplitude which allows to obtain an optimal propagation of the vibration in the bone 9-1 and a better detection at the first and/or second transducer 3-1 , 3-2 of the vibration that has propagated in the bone 9-1 ;

a subsequent normal operating mode, in which an estimation of the alteration of the bone 9-1 is performed, as illustrated above.

Preferably, the processing unit 4 performs a digital filtering of the first and second sampled filtered signals S1_d_f, S2_d_f, which maximises the signals in phase opposition detected by the first and second transducers 3-1 , 3-2 and minimises the detected common-mode signals from the environment surrounding the analysis system 50.

In particular, the processing unit 4 is configured to calculate a difference between the first filtered signal S1_d_f and the second filtered signal S2_d_f, thus generating a difference signal; thus, the processing unit 4 is such to generate, as a function of the difference signal, the analysis signal S_an representative of the estimation of the presence or absence of an alteration in the bone 9-1.

Advantageously, the difference signal is sampled (by means of an analog-to- digital converter inside the processing unit 4) with a sampling frequency that is synchronous with the excitation frequency of the first and second exciters 2-1 , 2-2, thus generating a sampled difference signal.

Preferably, the processing unit is configured to calculate the root mean square of the sampled difference signal: this allows to obtain maximum sensitivity to the signals that are in phase with the excitation signal and minimum sensitivity to all the signals that are out of phase with respect to the excitation signal, such as acoustic disturbances and external mechanical vibrations.

Preferably, the processing unit 4 is configured to convert the analysis signal S_an into a digitised image IMAGE_S_an representative of the estimation of the presence or absence of the alteration 23 in the anatomic portion 9, as will be described in greater detail below. The use of an electromagnetic transducer maximises the mechanically transmitted vibration compared to acoustic generation in the air, both during transmission and during reception, and the use of an exciter (in place of a microphone) avoids direct coupling between the transmitter and receiver through the propagation of sound waves in the air.

Therefore the system is less sensitive to disturbances of an acoustic type coming from the external environment.

A differential technique is used for transmission, i.e. two and/or more exciters which (when they are supplied in phase opposition) will create a maximum mechanical stimulation of the middle point relative to the position of the exciters on the anatomic portion 9: this will create a maximum vibrational stress of the bone 9-1.

Conversely, the acoustic component that will be transmitted by the medium that is not is of interest will tend to become null because of the phase opposition of the excitation signal: this allows to obtain greater efficiency in the mechanical stimulation of the bone of interest, fewer vibrations transmitted in the part not of interest and less acoustic generation in the air by the exciters.

The use of a differential technique for reception by means of two electromechanical transducers positioned so that the bone or the bone portion of interest is in a median position relative to the two receivers allows greater efficiency in the reception of vibrations transmitted by the bone or bone portion of interest, lower sensitivity to the vibrational components not transmitted by the part of interest and a lower sensitivity to the acoustic component transmitted through the air.

The two signals coming from the two receivers will be processed so as to obtain the difference thereof; in this manner one obtains a rejection of the signals having the same phase, whereas the signals in phase opposition will be maximised; therefore, the signal transmitted by the bone or bone portion of interest will be maximised, the signals transmitted through the medium that is not of interest will be cancelled out and the acoustic signals coming from the outside will tend to become null since the two receivers will detect the remote acoustic signals as being in phase agreement and therefore those signals will be eliminated.

The difference signal of the two receivers is sampled with a sampling frequency that is synchronous with the excitation frequency of the exciters.

The root square mean is calculated for the data thus sampled and this results in the maximum sensitivity to the signals in phase correlation with the excitation signal and the minimum sensitivity to all the signals that are not in a phase relation with the excitation signal, such as acoustic disturbances and external mechanical vibrations.

The transceiver 8 comprises an input/output terminal connected to the output/input terminal of the processing unit.

The transceiver 8 has the function of transmitting a short-range wireless signal S_r, as a function of the data signal S_rx_tx transmitted by the processing unit 4.

The transceiver 8 further has the function of receiving the short-range wireless signal S_r and of forwarding it on the data signal S_rx_tx towards the processing unit 4.

The short-range wireless signal S_r can be for example of the Bluetooth or WiFi type.

Alternatively, the transceiver 8 is of the USB type and thus it generates a signal S_r of a wired type.

The first amplifier 5-1 comprises an input terminal adapted to receive the first activation signal S1_a and comprises an output terminal adapted to generate the first control signal S1_c.

The first amplifier 5-1 has the function of amplifying the first activation signal S1_a and generating therefrom the first control signal S1_c.

The second amplifier 5-2 comprises an input terminal adapted to receive the second activation signal S2_a and comprises an output terminal adapted to generate the second control signal S2_c.

The second amplifier 5-2 has the function of amplifying the second activation signal S2_a and generating therefrom the second control signal S2_c.

The first and second amplifiers 5-1 , 5-2 are for example amplifiers in class AB.

The first pre-amplifier 6-1 comprises an input terminal adapted to receive the first detection signal S1_d and comprises an output terminal adapted to generate a first amplified detection signal S1_d_a, obtained by means of an amplification of the first detection signal S1_d.

The second pre-amplifier 6-2 comprises an input terminal adapted to receive the second detection signal S2_d and comprises an output terminal adapted to generate a second amplified detection signal S2_d_a, obtained by means of an amplification of the second detection signal S2_d.

Preferably, the first and second pre-amplifiers 6-1 , 6-2 have a gain that varies among at least 4 values.

The first low-pass filter 7-1 comprises an input terminal adapted to receive the first amplified detection signal S1_d_a and comprises an output terminal adapted to generate a first filtered detection signal S1_d_f, obtained by means of a filtering of a low-pass type (in the band comprised between 20 Hz and 20 KHz and/or infrasound and/or ultrasound) of the first amplified detection signal S1_d_a, in order to eliminate the disturbances detected by the system 50.

The second low-pass filter 7-2 comprises an input terminal adapted to receive the second amplified detection signal S1_d_a and comprises an output terminal adapted to generate a second filtered detection signal S2_d_f, obtained by means of a filtering of a low-pass type (in the band comprised between 20 Hz and 20 KHz and/or infrasound and/or ultrasound) of the second amplified detection signal S2_d_a, in order to eliminate the disturbances detected by the system 50.

Preferably, the analysis system 50 is connected to an electronic device 10 by means of the transceiver 8 configured to transmit and receive the short-range wireless signal S_r (for example, of the Bluetooth or WiFi type).

By means of the electronic device 10 it is possible to control and display the analysis of the bone 9-1 or of the bone portion.

The electronic device 10 can be of a mobile type (for example a smartphone, a tablet, a portable personal computer) or of a fixed type (for example, a desktop personal computer).

Preferably, the analysis system 50 further comprises a three-axis accelerometer and/or gyroscope connected to the processing unit for the purpose of detecting the movement and position of the anatomic portion, such as, for example, a limb 9.

It is also an object of the present invention a method for analysing the state of a bone or of a bone portion.

The method of analysis comprises the steps of:

a) mechanically applying a first acoustic-mechanical exciter to an anatomic portion 9 comprising a bone or a bone portion;

b) mechanically applying a second acoustic-mechanical exciter to said anatomic portion 9, wherein the first and second exciters are applied on opposite sides with respect to a secondary transversal extension of the anatomic portion 9;

c) applying a first electromechanical transducer to the anatomic portion 9 at a distance that comprises a suspected position of an alteration of the bone or of the bone portion;

d) applying a second electromechanical transducer to the anatomic portion 9 at a distance that comprises the suspected position of an alteration of the bone or of the bone portion, wherein the first and second transducers are applied on opposite sides with respect to a secondary transversal extension of the anatomic portion 9;

e) generating a first acoustic-mechanical wave at the first exciter as a function of a first control signal having a sinusoidal pattern and injecting it into the bone or bone portion of the anatomic portion 9;

f) generating a second acoustic-mechanical wave at the second exciter as a function of a second control signal having a sinusoidal pattern and injecting it into the bone or bone portion of the anatomic portion 9, wherein the first and second control signals have a same frequency and are phase shifted from each other by an angle comprised between 0 degrees, excluded, and 360 degrees, excluded;

g) detecting, at the first electromechanical transducer, a mechanical wave propagated through the bone or bone portion and generating therefrom a first detection signal S1_d;

h) detecting, at the second electromechanical transducer, a mechanical wave propagated through the bone or bone portion and generating therefrom a second detection signal S2_d;

i) processing the first and second detection signals S1_d, S2_d;

j) detecting, as a function of said processing, an estimation of the presence or absence of an alteration 23 inside the bone or bone portion.

Preferably, in step f) the first and second control signals are phase shifted from each other by an angle comprised between 90 degrees and 180 degrees.

Preferably, in step f) the first and second control signals are counter-phased to each other, i.e. they are phase shifted by an angle equal to 180 degrees.

Preferably, in step i) said processing comprises calculating a difference between the first and second detection signals.

The analysis system 50 enables a mapping of the entire volume of space occupied by the anatomic portion 9 of interest.

The anatomic portion that it is desired to analyse occupies a region of the physical space and can be modelled using a different coordinate system according to the type of symmetry that best approximates that of the anatomic portion itself.

For example, a limb will be described by a system with a cylindrical symmetry, in which one can identify a main axis of extension of the limb and the directions perpendicular thereto; a skull by a system of coordinates with a spherical or spheroidal symmetry having its centre in the centre of gravity.

The type of analysis described above is applied to the points in space following the approximated symmetry of the portion 9; for example in the case of a limb, the exciters and the detectors are moved by translating them along the direction of the main axis and completing a rotation of 360 degrees for every portion of the limb. The result is an analysis of the entire limb.

Assuming this, it is possible to consider a healthy anatomic portion as consisting of a composite material with elastic properties.

The device is applied to the anatomic portion so as to measure the various physical properties as a function of the space.

Every property will thus have a different value in the coordinate system considered. The recorded signals are therefore re-processed by the processing unit 4. In particular, the signal is processed by means of a Fourier spectral analysis (transform and inverse transform of the signal, following the application of an appropriately calibrated cutoff).

In every point of this mapping, the device, because of how it was configured, will provide different values for every property in every point in space and for every frequency used.

The properties of interest are the mechanical properties of the anatomic portion, such as Young’s modulus, the bulk modulus, the impedance and so on.

Such properties will vary in space from point to point and we will thus develop every property in a Taylor series, in particular the development will take place as a function of the components of the force field generated by the device at the various frequencies.

From the various coefficients of the development in Taylor series we will have information about the elastic properties of the system in response to the stimuli generated by the device as a function of the frequencies used in the various points in space.

It is logical to assume that each of these properties is a function which, despite being unknown in its analytic form, will behave normally from an analytic viewpoint if the bone or bone portion does not have alterations: it is continuous, has a continuous derivative, etc. When an alteration of the composite material is present in one or more of the aforesaid properties, it will show a discontinuity in the region affected by the lesion.

In general it is always possible to attribute a grey scale that describes the values of the properties in the range of assumed values.

From these values we can extract a point-to-point colorimetric map of the space. It will thus be possible to obtain a representation with three-dimensional components of the anatomic portion analysed.

Since the space not is isotropic, we will also have to consider the gradient and the upper derivatives.

A discontinuity will be displayed as a distinct colour variation in the region of the space involving the region itself.

This type of analysis will enable a mapping of the areas affected by a lesion. Different types of lesions give rise to different types of lesions.

For example, the imaginary impedance will be tied to the energy dissipation in the region. Quantifying the real and complex components of phonic impedance as a function of the frequency of the mechanical wave evaluated in the physical space analysed (in particular the anatomic portion 9) makes it possible to quantify the energy conservation and dissipation of the transmitted wave.

The presence of a lesion or alteration in the bones analysed compared to a condition of normality is evidenced by a variation in the aforesaid physical quantities in the points of space affected by the lesion. Based on an evaluation of the transmission times (and elastic response times and delay times of the propagation medium, i.e. of the bones analysed) and the recorded differential impedance values it will be possible to assign to the vectorial numerical value a grey or colour scale that will enable the conversion of an oscillating signal (such as those in Figures 2 and 3) into an image with three-dimensional components.

Properties varying as a function of the different frequencies used will enable the mapping of the different types of lesions in different types of bones.

Once the maps of the different properties have been obtained as a function of the space and of the frequencies used, each of which takes concrete form as a graphic representation of the anatomic portion analysed 9, one proceeds to the representation thereof in a three-dimensional form floating in space.

The device allows to obtain a map of the mechanical properties of the different bones making up the anatomic portion in the space occupied by the portion itself, preferably as a function of the different frequencies of the mechanical waves used. The data are re processed by the processing unit 4 so as to reveal possible discontinuities or anomalous values in particular regions of the aforesaid physical space. The numerical data are thus converted into a grey or colour scale, consequently forming images of the anatomic portion under analysis, one for each physical property of interest.

In particular, with reference to Figure 1 , the processing unit 4 is configured to convert the analysis signal S_an into a digitised image IMAGE_S_an representative of the estimation of the presence or absence of the alteration 23 in the anatomic portion 9.

The processing unit 4 is configured to perform the conversion as a function of the physical-mechanical properties Pi of the different bones comprised in the anatomic portion 9.

The physical-mechanical properties Pi of the different bones comprised in the anatomic portion 9, as already mentioned, comprise one or more among, at least, Young’s modulus, the bulk modulus and the impedance.

The invention provides an open light field volumetric device for the display of floating stereoscopic 3D images or streams of images wherein the floating images are generated from the analysis signal S_an converted into a digitised image IMAGE_S_an representative of an estimation of the presence or absence of an alteration 23 in an anatomic portion 9.

The space inside the anatomic portion 9 is physically tessellated in the three dimensions of the space to determine the digitised image IMAGE_S_an.

In other words, the space is divided into an ordered collection of small parallelepipeds, each of known dimensions, for example (Dc, Ay, Az).

At the centre of each of these small parallelepipeds, the different physical properties are sampled; in practical terms, a numerical value is attributed to each of the aforesaid small parallelepipeds.

From a computing viewpoint, these values are gathered into an ordered array so that each number included therein corresponds in a biunique manner to a point of the physical space. The number of parallelepipeds will be determined by the overall dimensions of the anatomic portion to be analysed, with the addition of surrounding empty margins.

Three integer indexes (i, j, k) allow to identify within the array the value of the property Pi sampled in a given point of space by the device. Once the sampling of the property Pi has been obtained as a function of the space and for the different frequencies selected for the analysis of the bone/bones of interest, it will be possible to operate on that array by calculating the spatial gradients, the Hessian and possibly the upper derivatives.

The numerical values obtained are then analysed: the minimal value of the property Pi_min (and of the derivatives thereof) and the maximum value Pi_max are determined; the extreme values of the defined colour scale are attributed to these extreme values; for example (but not only) black to Pi_min and white to Pi_max.

Every other value is normalised within this interval of values, thus having a corresponding colour (or shade of grey). From a graphic viewpoint, the initial tessellation is now considered and the parallelepiped is coloured with the corresponding colour identified. In this manner, a digitised image of the anatomic portion is formed for each property and at the different frequencies used for the analysis.

It will optionally be possible to carry out graphic processing operations (e.g. smoothing) in order to obtain a graphically better image.

In particular, with reference to figures 4 to 7, the open light field volumetric device for displaying floating stereoscopic 3D images or streams of images comprises:

- emitter means 1 configured to transmit a main beam MB of light rays R1 i representative of a stream of two-dimensional images BJMAGES, in first main directions d1 iM;

- the system for analysing the state of a bone 9-1 or of a bone portion according to what was previously described, configured to convert the analysis signal S_an into the digitised image IMAGE_S_an representative of an estimation of the presence or absence of an alteration 23 in the anatomic portion 9;

wherein the stream of two-dimensional images BJMAGES comprises a sequence of the digitised images IMAGE_S_an representative of an estimation of the presence or absence of an alteration 23 in the anatomic portion 9;

- a reflection system 50 provided with a single system aperture AP, wherein the reflection system 50 is coupled to the emitter means 1 and comprises in turn:

- first concave reflection means (10), structured as continuous hole-free surfaces, arranged to receive at least said main beam MB of light rays R1 i and to reflect at least the main beam MB of light rays R1 i in second main directions d2iM obtained as a function of the first main directions d1 iM and of a first conformation Confl of the first concave reflection means 10; - second concave reflection means 20, structured as continuous hole-free surfaces, arranged to receive at least the main beam of light rays R1 i along the second directions d2i1 M and reflect at least said beam in third main directions d3i1 M obtained as a function of said second main directions d2i1 M and of a second conformation Conf2 of the second concave reflection means 20;

- wherein the first concave reflection means 10 are mounted relative to said second concave reflection means 20 with the concavities C_10; C_20; facing each other and coaxial;

- wherein foci F1 ; F2 of the first concave reflection means 10 and of the second concave reflection means 20 lie on a straight line defining the azimuth axis A-A of the reflection system 50;

- wherein the first concave reflection means 10 and the second concave reflection means 20 intersect each other along an open intersection curve C_int_AP lying in a reference plane P perpendicular to the azimuth axis A-A of the reflection system 50;

- wherein the first concave reflection means 10 and the second concave reflection means 20, by intersecting each other along the open intersection curve C_int_AP, determine a conformation of said single system aperture of system AP;

- wherein the first concave reflection means 10 and the second concave reflection means 20 are structured so that:

at least the main beam of light rays R1 i reflected by the concave reflection means 20 comes out from the reflection system 50 along the third directions d3i1 M through the single system aperture AP;

- wherein an image IMM generated as a function of the main beam of light rays R1 i is perceived by an observer located at a variable viewing distance Ah relative to the second concave reflection means 20, when the observer looks towards the second concave reflection means 20 along two visual cones CL, CR having respective directrix DIR_L, DIR_R;

- wherein the variable viewing distance Ah is variable between a first distance hi and a second distance h2 along a reference direction dir_M,

- wherein vertices VL, VR of the two cones CL, CR coincide with the observation points QL, QR of the observer,

- wherein the cones CL, CR intersect the second concave reflection means 20 along respective distinct curves KL, KR having respective areas AL, AR;

- wherein the device further comprises:

an adjuster 30 adapted to set the reference direction dir_M, defined as a function of the directrix DIR_L, DIR_R and of the third main directions d3iM, so as to determine a measure of overlap OVL of the areas AL, AR, thereby creating an effect of viewing the image IMM as a stereoscopic floating image with three-dimensional components in a neighbourhood of a floating point F for the observer positioned at the variable viewing distance Ah.

The emitter means 1 are preferably configured to transmit the main beam MB of light rays R1 i in the first main transmission directions d1 iM, wherein:

the first main transmission directions d1 iM are defined as a function of:

- a luminous point Po in the Cartesian space situated on the emitter means 1 inside the reflection system (50) from which the main beam (MB) is emitted

- a main angle w of the main beam MB coming out from the emitter means 1 , wherein the main angle w is defined relative to a reference plane P in which the open intersection curve (C_INT_AP) lies and

the first and second conformations Confl ; Conf2 are defined as a function of:

- a focal distance f of the concave reflection means 10,20;

- a distance c between the first concave reflection means 10 and the second concave reflection means 20.

The advantages of the invention are summarised below:

a) The analysis system 50 illustrated above allows to have a very low sensitivity to all the acoustic and vibrational disturbances coming from an outside environment.

b) The analysis system 50 allows different bones of human or animal anatomic portions and the possible lesions thereof to be selectively analysed.

c) The analysis system 50 allows to obtain a greater sensitivity to the signals transmitted by the bone or bone portion of interest and thus an easier and more precise identification of a possible discontinuity in the propagation of the signal indicative of the presence of a possible tissue lesion.

d) The analysis system 50 allows to display the anatomic portion of interest by means of a real-time reconstruction with floating three-dimensional components.

Claims

1. System (50) for analysing the state of a bone (9-1 ) or of a bone portion, the system comprising:

a first acoustic-mechanical exciter (2-1 ) configured to:

• generate a first acoustic-mechanical wave, as a function of a first control signal (S1_c);

• inject the first acoustic-mechanical wave into the bone or bone portion; a second acoustic-mechanical exciter (2-2) configured to:

• generate a second acoustic-mechanical wave as a function of a second control signal (S2_c);

• inject the second acoustic-mechanical wave into the bone or bone portion; an electromechanical transducer (3-1 ) configured to detect a mechanical wave propagated through the bone or bone portion and generate therefrom a first detection signal (S1_d);

a processing unit (4) configured to:

• generate the first and second signals (S1_c, S2_c) for controlling the operation of the first and second acoustic-mechanical exciters, wherein the first and second control signals are sinusoidal signals having a same frequency and are phase shifted from each other by an angle comprised between 0 degrees and 360 degrees, 0 and 360 excluded;

• receive and process the first detection signal (S1_d) and generate therefrom an analysis signal (S_an) representative of an estimation of the presence or absence of an alteration (23) inside the bone or bone portion.

2. Analysis system according to claim 1 , wherein the processing unit is configured to generate the first control signal and the second control signal having a counter-phase pattern with respect to each other.

3. Analysis system according to claim 1 or 2, comprising a further electromechanical transducer (3-2) configured to detect said propagated mechanical wave and generate therefrom a further detection signal (S2_d),

wherein the processing unit (4) is further configured to:

• receive and process the detection signal (S1_d) and the further detection signal (S2_d) having a sinusoidal pattern with the same frequency and phase shifted from each other by an angle comprised between 0 degrees and 360 degrees, 0 and 360 excluded; • calculate the difference between the detection signal and the further detection signal;

• generate, as a function of said difference, said analysis signal (S_an) representative of the estimation of the presence or absence of an alteration (23) inside the bone or bone portion.

4. Analysis system according to claim 4, wherein the detection signal of the electromechanical transducer has a counter-phase pattern with respect to the further detection signal of the further electromechanical transducer.

5. Analysis system according to any one of the preceding claims, further comprising:

a first amplifier (5-1 ) interposed between the processing unit and the first acoustic-mechanical exciter, the first amplifier being configured to amplify the first control signal of the first acoustic-mechanical exciter;

a second amplifier (5-2) interposed between the processing unit and the second acoustic-mechanical exciter, the second amplifier being configured to amplify the second control signal of the second acoustic-mechanical exciter.

6. Analysis system according to any one of claims 3 to 5, further comprising:

a first cascade connection of a first pre-amplifier and of a first low-pass filter, said first connection being interposed between the first transducer and the processing unit; a second cascade connection of a second pre-amplifier and of a second low- pass filter, said second connection being interposed between the second transducer and the processing unit.

7. Analysis system according to any one of the preceding claims, further comprising:

a transceiver connected to the processing unit and configured to transmit/receive a wireless signal;

a mobile electronic device (10) connected to the transceiver by means of the wireless signal.

8. Analysis system according to any one of the preceding claims, further comprising a three-axis gyroscope and/or accelerometer connected to the processing unit.

9. System according to any one of the preceding claims, wherein said processing unit (4) is configured to convert said analysis signal (S_an) into a digitised image (IMAGE_S_an) representative of said estimation of the presence or absence of said alteration (23) in an anatomic portion (9) comprising the bone or bone portion.

10. System according to claim 9, wherein said processing unit (4) is configured to perform said conversion as a function of the physical-mechanical properties (Pi) of different bones comprised in said anatomic portion (9).

11. System according to claim 10, wherein said physical-mechanical properties (Pi) of the different bones comprised in said anatomic portion (9) comprise one or more among, at least, Young’s modulus, the bulk modulus and the impedance.

12. Open light field volumetric device for display of floating stereoscopic 3D images or streams of images comprising:

- emitter means (1 ) configured to transmit a main beam (MB) of light rays (R1 i) representative of a stream of two-dimensional images (BJMAGES), in first main directions (d1 iM);

- a system for analysing the state of a bone (9-1 ) or of a bone portion according to any one of claims 1 to 1 1 , the system being configured to convert an analysis signal (S_an) into a digitised image (IMAGE_S_an) representative of an estimation of the presence or absence of an alteration (23) in an anatomic portion (9) comprising the bone or bone portion;

wherein said stream of two-dimensional images (BJMAGES) comprises a sequence of said digitised images (IMAGE_S_an), according to claim 9, representative of an estimation of the presence or absence of an alteration (23) in said anatomic portion (9);

- a reflection system (50) provided with a single system aperture (AP), wherein said reflection system (50) is coupled to said emitter means (1 ) and comprises in turn:

- first concave reflection means (10), structured as continuous hole-free surfaces, arranged to receive at least said main beam (MB) of light rays (R1 i) and reflect at least said main beam (MB) of light rays (R1 i) in second main directions (d2iM) obtained as a function of said first main directions (d1 iM) and of a first conformation (Confl ) of the first concave reflection means (10);

- second concave reflection means (20), structured as continuous hole-free surfaces, arranged to receive at least said main beam of light rays (R1 i) along said second directions (d2i1 M) and reflect at least said beam in third main directions (d3i1 M) obtained as a function of said second main directions (d2i1 M) and of a second conformation (Conf2) of the second concave reflection means (20);

- wherein said first concave reflection means (10) are mounted relative to said second concave reflection means (20) with the concavities (C 0; C_20;) facing each other and coaxial; - wherein foci (F1 ; F2) of said first concave reflection means (10) and of said second concave reflection means (20) lie on a straight line defining the azimuth axis (A-A) of the reflection system (50);

- wherein said first concave reflection means (10) and said second concave reflection means (20) intersect each other along an open intersection curve (C_int_AP) lying in a reference plane (P) perpendicular to said azimuth axis (A-A) of the reflection system (50),

- wherein said first concave reflection means (10) and said second concave reflection means (20), by intersecting each other along said open intersection curve (C_int_AP), determine a conformation of said single system aperture (AP);

- wherein said first concave reflection means (10) and said second concave reflection means (20) are structured so that:

- at least said main beam of light rays (R1 i) reflected by the second concave reflection means (20) comes out from said reflection system (50) along said third directions (d3i1 M) through said single system aperture (AP);

- wherein an image (IMM) generated as a function of the main beam of light rays (R1 i) is perceived by an observer located at a variable viewing distance (Ah) relative to said second concave reflection means (20), when the observer looks towards said second concave reflection means (20) along two visual cones (CL, CR) having respective directrix (DIR_L, DIR_R);

- wherein said variable viewing distance (Ah) is variable between a first distance (hi ) and a second distance (h2) along a reference direction (dir_M),

- wherein vertices (VL, VR) of the two cones (CL, CR) coincide with the observation points (QL, QR) of the observer,

- wherein said cones (CL, CR) intersect said second concave reflection means (20) along respective distinct curves (KL, KR) having respective areas (AL, AR);

- wherein the device further comprises:

an adjuster (30) adapted to set said reference direction (dir_M), defined as a function of said directrix (DIR_L,DIR_R) and of said third main directions (d3iM), so as to determine a measure of overlap (OVL) of said areas (AL,AR), thereby creating an effect of viewing said image (IMM) as a stereoscopic floating image with three-dimensional components in a neighbourhood of a floating point (F) for said observer positioned at said variable viewing distance (Ah).

13. Open volumetric device according to claim 12, wherein said emitter means (1 ) are configured to transmit said main beam (MB) of light rays (R1 i) in said first main transmission directions (d1 iM), wherein:

said first main transmission directions (d1 iM) are defined as a function of:

- a luminous point (Po) in the Cartesian space situated on said emitter means (1 ) inside said reflection system (50) from which said main beam (MB) is emitted

- a main angle (w) of said main beam (MB) coming out from said emitter means (1 ), wherein the main angle (w) is defined relative to a reference plane (P) in which said open intersection curve (C_INT_AP) lies

said first and second conformations (Confl ; Conf2) are defined as a function of:

- a focal distance (f) of said concave reflection means (10,20)

- a distance (c) between said first concave reflection means (10) and said second concave reflection means (20).

14. Method for analysing the state of a bone (9-1 ) or of a bone portion, comprising the steps of:

a) mechanically applying a first acoustic-mechanical exciter to an anatomic portion (9) comprising the bone or bone portion;

b) mechanically applying a second acoustic-mechanical exciter to said anatomic portion, wherein the first and second exciters are applied on opposite sides with respect to a secondary transversal extension of the anatomic portion;

c) applying a first electromechanical transducer to the anatomic portion at a distance which comprises a position of a suspected alteration of the bone or of the bone portion;

d) applying a second electromechanical transducer to the anatomic portion at a distance which comprises the suspected position of an alteration of the bone or of the bone portion, wherein the first and second transducers are applied on opposite sides with respect to a secondary transversal extension of the anatomic portion;

e) generating a first acoustic-mechanical wave at the first exciter as a function of a first control signal having a sinusoidal pattern and injecting it into the bone or bone portion;

f) generating a second acoustic-mechanical wave at the second exciter as a function of a second control signal having a sinusoidal pattern and injecting it into the bone or bone portion of the anatomic portion, wherein the first and second control signals have a same frequency and are phase shifted from each other by an angle comprised between 0 degrees and 360 degrees, 0 and 360 excluded; g) detecting, at the first electromechanical transducer, a mechanical wave propagated through the bone or bone portion and generating therefrom a first detection signal (S1_d);

h) detecting, at the second electromechanical transducer, a mechanical wave propagated through the bone or bone portion and generating therefrom a second detection signal (S2_d);

i) processing the first and second detection signals (S1_d, S2_d);

j) detecting, as a function of said processing, an estimation of the presence or absence of an alteration (23) inside the bone or bone portion.

15. Analysis method according to claim 14, wherein in step f) the first and second control signals are counter-phased with respect to each other.