(19)
(11)EP 3 212 065 B1

(12)EUROPEAN PATENT SPECIFICATION

(45)Mention of the grant of the patent:
30.03.2022 Bulletin 2022/13

(21)Application number: 15855342.0

(22)Date of filing:  30.10.2015
(51)International Patent Classification (IPC): 
A61B 5/00(2006.01)
A61B 8/15(2006.01)
G01S 15/89(2006.01)
A61B 8/08(2006.01)
A61B 5/06(2006.01)
G01S 15/06(2006.01)
(52)Cooperative Patent Classification (CPC):
A61B 5/064; A61B 8/15; A61B 5/0095; A61B 8/0841
(86)International application number:
PCT/US2015/058444
(87)International publication number:
WO 2016/070115 (06.05.2016 Gazette  2016/18)

(54)

OPTO-ACOUSTIC IMAGING SYSTEM WITH DETECTION OF RELATIVE ORIENTATION OF LIGHT SOURCE AND ACOUSTIC RECEIVER USING ACOUSTIC WAVES

SYSTEM ZUR OPTOAKUSTISCHEN BILDGEBUNG MIT DETEKTION DER RELATIVEN AUSRICHTUNG EINER LICHTQUELLE UND EINES AKUSTISCHEN EMPFÄNGERS UNTER VERWENDUNG VON AKUSTISCHEN WELLEN

SYSTÈME D'IMAGERIE OPTO-ACOUSTIQUE AVEC DÉTECTION DE L'ORIENTATION RELATIVE DE SOURCE DE LUMIÈRE ET DE RÉCEPTEUR ACOUSTIQUE AU MOYEN D'ONDES ACOUSTIQUES


(84)Designated Contracting States:
AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC MK MT NL NO PL PT RO RS SE SI SK SM TR

(30)Priority: 30.10.2014 US 201462072997 P

(43)Date of publication of application:
06.09.2017 Bulletin 2017/36

(73)Proprietor: Seno Medical Instruments, Inc.
San Antonio, TX 78230 (US)

(72)Inventor:
  • ZALEV, Jason
    Thornhill, Ontario L4J 5C1 (CA)

(74)Representative: Leach, Sean Adam et al
Mathys & Squire The Shard 32 London Bridge Street
London SE1 9SG
London SE1 9SG (GB)


(56)References cited: : 
EP-A2- 1 953 564
WO-A1-2014/050020
JP-A- 2012 040 038
JP-A- 2014 144 109
US-A1- 2009 247 903
US-A1- 2012 232 364
US-A1- 2013 184 571
WO-A1-2008/131557
WO-A2-2013/056089
JP-A- 2014 061 124
US-A- 5 394 875
US-A1- 2011 306 857
US-A1- 2013 041 267
  
      
    Note: Within nine months from the publication of the mention of the grant of the European patent, any person may give notice to the European Patent Office of opposition to the European patent granted. Notice of opposition shall be filed in a written reasoned statement. It shall not be deemed to have been filed until the opposition fee has been paid. (Art. 99(1) European Patent Convention).


    Description


    [0001] This application is a non-provisional of and claims priority to U.S. Patent Application No. 62/072,997 filed October 30, 2014.

    [0002] This provisional application relates to opto-acoustic imaging systems such as those described in U.S. Patent Application No. 13/793,808 filed 11 March 2013.

    FIELD



    [0003] The present invention relates in general to the field of medical imaging, and in particular to opto-acoustic imaging systems.

    BRIEF DESCRIPTION OF THE DRAWINGS



    [0004] Objects, features, and advantages of the invention will be apparent from the following detailed description of preferred embodiments as illustrated in the accompanying drawings, in which reference characters refer to the same parts throughout the various views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating principles of the invention.

    Figures 1A and 1B are diagrams showing acoustic waves traveling through a tissue volume from an acoustic source to a proximate object.

    Figure 2 is a diagram showing a pattern of fiducial markers located on an outer surface of a proximate object.

    Figure 3 is a perspective view showing an optical delivery unit with an optical energy exit port positioned to optically illuminate tissue of a subject, and an acoustic receiving unit positioned to receive opto-acoustic return signal from the illuminated tissue and acoustic signal from a fiducial marker site of the optical delivery unit.

    Figure 4 is a perspective view showing optical energy being delivered to tissue at a position in a coordinate reference frame relative to a second position where acoustic signal is received from the tissue.

    Figure 5 is a perspective view showing a primary contact unit comprising a plurality of acoustic receivers at data collection positions in contact with a volume, and a secondary contact unit comprising an optically absorbing fiducial marking forming a pattern which emits an acoustic response that propagates through the volume.

    Figure 6 is a diagram showing an optically absorbing radially symmetric emitter.

    Figures 7A and 7B are diagrams showing an optically absorbing fiducial marker pattern with concentric rings.


    DETAILED DESCRIPTION



    [0005] Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The following description and drawings are illustrative and are not to be construed as limiting. Numerous specific details are described to provide a thorough understanding. However, in certain instances, well-known or conventional details are not described in order to avoid obscuring the description. References to one or an embodiment in the present disclosure are not necessarily references to the same embodiment; and, such references mean at least one.

    [0006] Reference in this specification to "an embodiment" or "the embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least an embodiment of the disclosure. The appearances of the phrase "in an embodiment" in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Moreover, various features are described which may be exhibited by some embodiments and not by others. Similarly, various requirements are described which may be requirements for some embodiments but not other embodiments.

    [0007] The present invention is described below with reference to block diagrams and operational illustrations of methods and devices for performing opto-acoustic imaging. It is understood that each block of the block diagrams or operational illustrations, and combinations of blocks in the block diagrams or operational illustrations, may be implemented by means of analog or digital hardware and computer program instructions. These computer program instructions may be stored on computer-readable media and provided to a processor of a general purpose computer, special purpose computer, ASIC, or other programmable data processing apparatus, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, implements the functions/acts specified in the block diagrams or operational block or blocks. In some alternate implementations, the functions/acts noted in the blocks may occur out of the order noted in the operational illustrations. For example, two blocks shown in succession may in fact be executed substantially concurrently or the blocks may sometimes be executed in the reverse order, depending upon the functionality/acts involved.

    [0008] When a handheld acoustic receiver and handheld light source are manually positioned proximate to tissue, the relative orientation and relative position of the light source is unknown. For opto-acoustic image formation using signals from the acoustic receiver, this presents a challenge, as knowing light source position and orientation are important for this process. Furthermore, the surface of the volume of tissue is subject to unknown deformation, and loss of or partial contact with the source or receiver.

    [0009] A solution is to track the relative orientation and/or position of the light source with respect to the probe. In an ideal situation, locating inertial positioning devices on both the acoustic receiver and on the light source would track the position and orientation of each device, and thus the relative positions and orientations could be computed from this information coupled with known initial reference positions. However, inertial positioning devices are subject to reliability issues. A reliable method, that might or might not be coupled with an inertial positioning implementation, involves using acoustic waves.

    [0010] Figures 1A and 1B are diagrams showing acoustic waves traveling through a tissue volume 170 from an acoustic source 160 to one or more proximate objects 164. Acoustic waves travel through the tissue volume 170 from one point on the tissue surface to another point on the surface. Acoustic waves may travel from an acoustic source 160 proximate to the surface of the tissue to reach a proximate object 164, proximate to the surface of the tissue. In such a manner, the propagation time, and/or directional information from the wave may be used to compute the position and orientation of the acoustic source relative to the proximate object (see Figure 1). In an embodiment not according to the invention, an acoustic transmitter, such as a transducer array, may transmit one or multiple directed acoustic wavefronts 162, each wavefront directed towards a particular direction. In an embodiment not according to the invention, the acoustic transmitter may transmit a non-directional wavefront. In an embodiment not according to the invention, the transmitter is located on the acoustic receiver. In an embodiment not according to the invention, the transmitter is located on the light source. In an embodiment, the transmitted wavefront may be received by a detector on an object 164 proximate to the tissue, such as in an embodiment not according to the invention on the light source, or in an embodiment on the acoustic receiver. In an embodiment, the detector may be the receiving elements of the acoustic receiver. In an embodiment not according to the invention, the detector may be located on the light source. In an embodiment, the transmitted acoustic wavefront is directly received by the acoustic detector on the proximate object. In an embodiment, the transmitted acoustic wavefront backscatters off of the proximate object 164. In an embodiment, the transmitted acoustic wavefront is transmitted by the same receiving elements as used by the acoustic receiver.

    [0011] In an embodiment, if the proximate object 164 does not house an acoustic detector, it may house fiducial markers. Figure 2 is a diagram showing a pattern of fiducial markers 208 located on an outer surface 200 of a proximate object 164. In an embodiment, the fiducial markers 208 are located on an outer surface 200 of the proximate object 164. In an embodiment, the proximate object 164 has fiducial markers 208 for backscattering the transmitted acoustic wave; the backscattered wavefronts from the fiducial markers 208 received by the acoustic receiver and are used to determine the position of the object. The fiducial markers 208 may create a strong acoustic backscatter, such as air-pockets of a known configuration.

    [0012] In an embodiment, an outer surface 200 (e.g. of the proximate object 164) has fiducial markers 208 for absorbing light from the light source to produce an opto-acoustic wavefront; the acoustic wavefront 152 received by the acoustic receiver and are used to determine the position of the object. The fiducial markers 208 may create a strong opto-acoustic return signal. In an embodiment, the fiducial markers comprise carbon-black which is an optical absorber that produces strong signal upon illumination. In an embodiment, the fiducial markers 208 have an asymmetric pattern so that the orientation of the markers cannot be confused by an axis of symmetry.

    [0013] In an embodiment, when a directed acoustic wave 162 is directed immediately towards a proximate object 164, this immediate direction will yield the highest intensity of the acoustic wave that reaches the proximate object 164; thus, upon receiving the highest intensity acoustic wave, the directional orientation becomes known. Furthermore, the propagation time, from when the wavefront originates until it is received, can also be clocked; combined with presumed or known the speed of sound in tissue, the distance between two proximate objects can be computed.

    [0014] In an embodiment, the receiving elements of the acoustic receiver are in a linear array configuration; typically, would such elements be multiplexed as transmitting elements, the wavefront can be directed only in-plane, and not substantially out-of plane, thus it may be difficult to locate a proximate object 164 that is not directly in the imaging plane with such a configuration.

    [0015] In an embodiment, fiducial markers are positioned in the direct path of the light source; thus, upon illumination by the light source, the fiducial markers become an acoustic source. In an embodiment, fiducial markers located on an optical window serving as an optical exit port to deliver optical energy to a volume. In an embodiment, due to the asymmetry of the marker pattern, the orientation and thus the identity of each marker is not confused. In a construction, the proximate object 164 is the acoustic receiver. The propagation time of each marker 208 in the marker pattern of the acoustic source can be measured by the acoustic receiver. By presuming or knowing the speed of sound in the tissue, the distance of each marker 208 to the acoustic receiver can be solved. Further, had a single marker been used, the position of the single marker 208 might be undetermined in 3D when using a linear array acoustic receiver which images a 2D imaging plane; when multiple markers are used, the orientation and position of the markers of known configuration can be fixed to a unique 3D position. Accordingly, in an embodiment, the position and orientation of the maker pattern in 3D is also solved. In an embodiment, this may be done by solving a least squares fit of the position and orientation against the received acoustic signals or against the computed distances. In an embodiment, a similar technique could be used in backscatter mode.

    [0016] In an embodiment, the volume of tissue can be illuminated for opto-acoustic imaging while simultaneously producing the acoustic source for fiducial markers (this is a "passive mode"); in the event that the acoustic source signal interferes with an image in the imaging plane, any interfering signal from the fiducial marker's acoustic source can be subtracted or mitigated from the image. In an embodiment, the fiducial markers are powered by a light source separate from the main opto-acoustic imaging optical source, such as by single or multiple optical fibers illuminating the fiducials, which may operate separately (this is an "active mode"). In an embodiment, the fiducial acoustic source may be produced directly by acoustic transducers rather than by opto-acoustic waves generated by optical absorption. In an embodiment, an omni-directional acoustic wave may be produced from a coating the end of an illuminated optical fiber.

    [0017] In an embodiment, opto-acoustic images may be enhanced by positioning an opto-acoustic light source at a first location to collect acoustic response and then at a second location to collect acoustic response; comparing the acoustic responses from first and second light source light; and then using at least a portion of information from first acoustic response location and second acoustic response location to produce an enhanced image. In an embodiment, the enhanced image mitigates the effects of optical fluence or optical penetration. In an embodiment, the image reveals contrast by displaying an image based on the difference between illumination at each location. In an embodiment, the fluence profile is solved, and mitigated from an absorption image.

    [0018] Figure 3 is a perspective view of a system according to the invention showing an optical delivery unit 304 with an optical energy exit port 302 positioned to optically illuminate tissue 305 of a subject, and an acoustic receiving unit 306 positioned to receive opto-acoustic return signal from an optically absorbing physiological structure 308 of the illuminated tissue 305 and acoustic signals from fiducial marker sites 301, 303 of the optical delivery unit 304. A coordinate reference frame is shown at 307.

    [0019] In an embodiment, the invention can provide a method for determining position and orientation of an optical delivery unit 304 relative to an acoustic receiving unit 306, for applications in the field of opto-acoustic imaging. According to the invention, the optical delivery unit 304 comprises a first fiducial marker site 301 configured to emit acoustic responses. In preferred embodiments, it comprises a second fiducial marker site 303 configured to emit acoustic responses. In an embodiment, the method comprises sampling and recording a plurality of acoustic signals from a volume of a subject. Each of the plurality of acoustic signals may be collected at a different data collection position relative to a coordinate reference frame 307. In an embodiment, the method comprises identifying in each of the plurality of acoustic signals a response of a first fiducial marker and, in an embodiment, a response of a second fiducial marker. Each identified response indicates a separation (e.g. a separation in time between clocked events or a separation in distance) between a fiducial marker site and a data collection position, where an acoustic signal is collected. In an embodiment, the separation is determined by determining the amount of time that has elapsed between a triggering event when an acoustic wave is initially emitted (e.g. by the fiducial marker site) until it is received by the acoustic receiver, and can be converted to distance by using a presumed speed of sound. The identified signal permits determining position and orientation of the optical delivery unit in the coordinate reference frame by using each of the identified responses of the first fiducial marker (and each of the identified responses of the second fiducial marker).

    [0020] In accordance with the invention, it is possible to determine position but not orientation using a single fiducial marker. In certain circumstances, using two or more fiducial markers permits determining relative position as well as relative orientation.

    [0021] In an embodiment, the first fiducial marker and the second fiducial marker produce acoustic responses due to an absorption of optical energy that is delivered by the optical delivery unit. In an embodiment, a produced response of the first optically absorbing fiducial marker is stronger at a first predominant optical energy wavelength delivered by the optical delivery unit compared to that of a second predominant optical energy wavelength delivered by the optical delivery unit. In an embodiment, a produced response of the second fiducial marker is stronger at the second predominant optical energy wavelength compared to that of the first predominant optical energy wavelength. In an embodiment, the step of identifying for the responses comprises: locating a first target with a high intensity in a reconstructed sinogram for the first predominant optical energy wavelength and with a low intensity in a reconstructed sinogram for the second predominant optical energy wavelength; locating a second target with a low intensity in the reconstructed sinogram for the first predominant optical energy wavelength and with a high intensity in the reconstructed sinogram for the second predominant optical energy wavelength; identifying the response of the first fiducial marker as from the located first target; and, identifying the response of the second fiducial marker as from the located second target. Thus, in an embodiment, fiducial markers can be identified by having wavelength specific optical absorption.

    [0022] In exemplary configurations, determining the position and orientation of the optical delivery unit comprises: determining values for a rotation matrix and a translation vector to rotate and translate vectors values that describe fiducial marker positions to a configuration (e.g. position and orientation) that fits to explain separations that are measured upon identifying the responses of the first fiducial marker and/or the identified responses of the second fiducial marker. In an embodiment, the separations are time separations measured in units of samples and are converted to distance separations by multiplying with a constant speed of sound for the volume and dividing with a constant sampling rate of an analog to digital converter. In exemplary configurations, the response of the first fiducial marker comprises a distinguishable acoustic response that can be distinguished from the response of the second fiducial marker. In an embodiment, each of the plurality of acoustic signals is processed. In an embodiment, an image of the volume using the processed acoustic signals is outputted to a display. In an embodiment, each identified response of the first fiducial marker comprises a distinguishable acoustic response, and the step of processing comprises separating distinguishable acoustic responses from each of the plurality of acoustic signals.

    [0023] Methods for determining values for a rotation matrix and a translation vector to solve position and orientation in the context of wireless radio sensor networks is described by Equation 4b of Chepuri, Sundeep Prabhakar, et al. "Rigid Body Localization Using Sensor Networks." Signal Processing, IEEE Transactions on 62.18 (2014): 4911-4924.

    [0024] In an embodiment, a system includes an optical energy delivery unit comprising optical energy exit port adapted to deliver optical energy to a volume of a subject; an acoustic receiving unit comprising acoustic receiver(s) adapted to receive acoustic signal from the volume; a fiducial marker site configured to emit acoustic response to be received by the acoustic receiving unit; a processing unit configured to perform processing of signals received by said acoustic receiving unit, which processing comprises determining a relative position of the optical energy delivery unit respective to the acoustic receiving unit using a received acoustic response emitted from the fiducial marker; and a display unit adapted to display an opto-acoustic image representing the volume. The opto-acoustic image may produced by using information about the determined relative position, because such information may help to enhance the resulting opto-acoustic image (e.g. fluence compensation, light source correction, etc.). In an embodiment, an additional fiducial marker site is configured to emit acoustic responses to be received by said acoustic receiver. In an embodiment, the processing unit determines a relative orientation and/or the relative position of the optical energy delivery unit respective to the acoustic receiving unit using a received acoustic response emitted by the fiducial marker site and/or a received acoustic response emitted by additional fiducial marker site. In an embodiment, the fiducial marker site and the additional fiducial marker site are located on a distal surface of the optical energy delivery unit. In an embodiment, the optical energy exit port is located on the distal surface of the optical energy delivery unit. In an embodiment, the processing performed by the processing unit further comprises the steps of: i) retrieving a list of position values respective to a first coordinate reference frame (typically the list would comprise a position for the fiducial marker site and a position for the additional fiducial marker site); ii) determining values for a rotation matrix and a translation vector to rotate and translate the list of position values to a configuration respective to a second coordinate reference frame (typically, the determined values would comprise a solution that accounts for propagation delays of fiducial response component of the signals received by the acoustic receiving unit); and, iii) producing the relative orientation and the relative position per the rotation matrix and translation vector, which can then be used.

    [0025] In an embodiment, the processing unit is further configured to perform steps comprising: i) separating a distinguishable acoustic response component emitted by the fiducial marker from remaining components of the signals received by the acoustic receiving unit; and, ii) generating an opto-acoustic image of the volume using those remaining components. The generation of opto-acoustic images using separated components is further described in U.S. Patent Application No. 14/512,896 entitled "Systems And Methods For Component Separation In Medical Imaging".

    [0026] Such techniques may be used to separate the signal of the fiducial marker from the remainder of the opto-acoustic signal to improve generated images when using fiducial markers.

    [0027] In an embodiment, the processing unit is further configured to perform steps comprising: i) generating a first opto-acoustic representation of the volume when the optical energy delivery unit is at a first relative placement respective to a placement of the acoustic receiving unit as determined by the processing unit; ii) generating a second opto-acoustic representation of the volume when the optical energy delivery unit is at a second relative placement respective to the placement of said acoustic receiving unit as determined by said processing unit; iii) computing a difference between the first opto-acoustic representation of the volume and the second opto-acoustic representation of the volume; and iv) generating an image to display based on the computed difference. In an embodiment, the generated image is an image spatially representing the computed difference. The differences that occur within the volume between two or more different optical illumination conditions may yield useful insight about the physical details of the volume.

    [0028] In an embodiment, the processing unit is configured to perform steps comprising: determining when the optical energy delivery unit and acoustic receiving unit are suitably located at relative position with respect to one another to form a proper opto-acoustic image. For example, in certain circumstances, if the optical energy delivery unit is too far away, the optical energy may be too weak and result in a poor image, so detecting when this does or does not occurs is of benefit. Furthermore, using systems and methods described herein, it is possible to determine when both of the optical energy unit and acoustic receiving unit are acoustically coupled to the volume, which could signify proper placement of the units. For example, if the optical delivery unit is not touching the volume, this may prevent an acoustic signal from a fiducial marker from reaching the acoustic receiver, and thus could be used to determine if the unit is in contact with the volume, which is useful if making contact with the volume is required for proper illumination, or in an embodiment, if loss of contact with the volume triggers a safety mechanism to prevent delivery of optical energy.

    [0029] In an embodiment, a system includes an acoustic receiver located on a distal surface of a primary contact unit. The primary contact unit makes contact with the volume. In an embodiment, the primary contact unit comprises a distal end that includes its distal surface. In an embodiment, the distal end of the primary contact unit is adapted to acoustically couple with a surface of a volume (e.g. of tissue). In an embodiment, the primary contact unit further comprises a proximal end, that is positioned away from the distal end. In exemplary constructions, a first optically absorbing fiducial is located on a distal surface of a secondary contact unit. The secondary contact unit also makes contact with the volume. In an embodiment, the secondary contact unit comprises a distal end that includes its distal surface. In an embodiment, the distal end of the secondary contact unit is adapted to acoustically couple with the volume. In an embodiment, the system comprises a processing subsystem configured to perform processing comprising: i) identifying responses of the first optically absorbing fiducial (and/or of the second optically absorbing fiducial) by analyzing signals received by the acoustic receiver; and, ii) determining the position and orientation of the secondary contact unit respective to the primary contact unit using the identified responses.

    [0030] Figure 4 is a perspective view showing optical energy being delivered by optical delivery unit 406 to an object of interest 404 within the tissue being imaged, the optical delivery unit being located at a first position in a coordinate reference frame 403 relative to a second position where acoustic signal is received from the tissue. Fiducial markers 408 are provided on the optical exit port / optical window 405 of the optical delivery unit 406.

    [0031] In exemplary constructions, the first optically absorbing fiducial comprises a first optically absorbing pattern which when activated by an optical energy produces an acoustic response that can be received by the acoustic receiver. Figure 5 is a perspective view showing a primary contact unit 502 comprising a plurality of acoustic receivers at first and second data collection positions 503, 504 in contact with a volume 501, and a secondary contact unit 508 comprising an optically absorbing fiducial marking 509 at a distal surface 506, the fiducial marking 509 forming a pattern 507 which emits an acoustic response 505 that propagates through the volume 501. In typical use, the primary contact unit 502 and the secondary contact unit 508 are both coupled to the volume 501. In Figure 5, the primary contact unit 502 is shown decoupled from the volume 501 for illustrative purposes only.

    [0032] In an embodiment, the fiducial comprises radially symmetric spherical layers. In an embodiment, the fiducial contains optically absorbing concentric rings. In an embodiment, a second optically absorbing fiducial is located on the distal surface of the secondary contact unit, and the second optically absorbing fiducial comprises a second optically absorbing pattern. In an embodiment, the first optically absorbing pattern comprises an optically absorbing material with a greater optical absorption coefficient at a predominant wavelength of the optical energy compared to an optical absorption coefficient of the distal surface for the same predominant wavelength. In an embodiment, the optically absorbing material is selected from the group consisting of: a toner, a dye, a colorant, a screen printing ink, a plastisol based ink, a PVC based ink, a chemical deposit, a masked screening deposit, an adhesive film, and a decal. In an embodiment, the produced acoustic response of the fiducial comprises a distinguishable acoustic response component, which is characterized by a unique frequency spectral characteristic corresponding to the first optically absorbing pattern. In an embodiment, an emitter comprising concentric spherical layers, or concentric rings on a flat surface, may be used to produce unique frequency spectral characteristic, which is adjustably by varying the geometry and intensity of the layers or rings.

    [0033] With reference to Figure 6, in an embodiment, an emitter to multi-directionally emit acoustic signals with approximately equal signal content towards all relevant directions is based on such a physical phenomenon which occurs in radially symmetric opto-acoustic sources. In an embodiment, a radially symmetric emitter 660 comprises a first concentric layer 661 comprising a carrier material and a first concentration of an electromagnetically absorbing material; and, a second concentric layer comprising the carrier material and a second concentration of the electromagnetically absorbing material; wherein the emitter is adapted to emit, following the absorption of electromagnetic energy, an acoustic signal toward a first heading and a similar signal toward a second heading, which acoustic signal emitted toward the first heading is essentially the same as the similar signal emitted toward the second heading, in a manner whereby an acoustic receiver configured to detect signal from the emitter will receive the same signal regardless of if it is positioned to receiving the signal by way of the first heading or positioned elsewhere to receive the signal by way of the second heading. In an embodiment, the emitter further comprises additional concentric layers, wherein each additional concentric layer comprises the carrier material and a concentration of the electromagnetically absorbing material. Such an emitter is shown in Figure 6. In an embodiment, the outermost diameter of the emitter is 1mm, thus the emitter may serve as a compact fiducial on the surface of a handheld unit in contact with a volume of tissue. In an embodiment, such an emitter may scale to larger (or smaller) sizes suitable for a variety of applications where emitting similar and/or identifiable acoustic signals to multiple positions is desired.

    [0034] In an embodiment, the concentric layers are spherical. In an embodiment, the emitter emits an omni-directional acoustic response corresponding to a radically symmetric energy absorption profile. In an embodiment, the concentration of the electromagnetically absorbing material is smoothly varied between successive concentric layers to achieve a continuous band-limited emitted acoustic signal profile. The time domain signal received at time t at a distance x away from a radially symmetric profile is p(t-t0, x) = (x-c(t-t0))/xH(x-c(t-t0)|), where H(|x|) is a function describing the radial profile, c is the speed of sound, and t0 is the time of the emission. In an embodiment, the radial profile of a physical object G(|x|) that will provide a heating profile H(|x|) is dependent on the fluence of the optical energy reaching portions of the physical object. This makes it possible to control and predict the received signal by constructing an appropriate radial source. The time domain shape is H(x-c(t-t0)|), thus in an embodiment, is possible to identify different fiducial markers by detecting different such time domain shapes. In an embodiment, the emitted acoustic signal comprises an identifiable acoustic signal due to unique concentration of electromagnetically absorbing material in each layer, wherein the identifiable acoustic signal can be identified by processing when the emitted acoustic signal is received by an acoustic receiver. In an embodiment, identifying the signal involves correlating a (processed) received signal with a known unique signature of a fiducial, and determining if and where the correlation is greatest (or greater than a threshold). In an embodiment, the correlation is cross-correlation performed in the frequency domain and converted back to the time domain to determine cross-correlation peaks. In an embodiment, the unique concentration of electromagnetically absorbing material in each layer generates a binary code representing the digits zero and one based on either a first or a second concentration of electromagnetically absorbing material. In an embodiment, this is used to create a unique signature. In an embodiment, the different unique signatures corresponding to different identifiable fiducial are orthogonal, so one fiducial would be less likely to be confused with another. In an embodiment, the unique concentration of electromagnetically absorbing material in each layer generates a unique time domain or frequency domain signature. In an embodiment, the electromagnetically absorbing material is optically absorbing material. In an embodiment, the carrier material is a polymer such as a plastisol and the optically absorbing material is a colorant. In an embodiment, the layers of the spherical emitter are manufactured by suspending a spherical core object by a wire and dipping in a series of material baths comprising carrier and varied concentration of absorber to form layer. In an embodiment, the layers are manufactured by vapor deposition process, where the optical absorption of each layer is controlled by varying the optical absorption of each layer. In an embodiment, a light source or optical fibre is at the center of the spherical core. In an embodiment the emitter is a bead. In an embodiment, the emitter is embedded in the outer surface of a handheld probe. In embodiment, the emitter is a buoy. In an embodiment, the emitter is a spherical tip affixed to the end of an optical fibre.

    [0035] With reference to Figures 7A and 7B, in an embodiment, a fiducial is a decal shaped like an archer's target that is printed on a surface 562 to be coupled to a volume. The geometry (i.e., sizes and spacing of rings) of the archer's target shape can be varied to influence the resulting opto-acoustic signal. In an embodiment, an optically absorbing fiducial marker adapted to emit an identifiable acoustic signal, comprising: a surface 562 (e.g. an outer surface of an optical delivery unit adapted to couple with a volume) comprising a first material and a second material, the first material having an optical absorption coefficient that is greater than that of the second material, wherein the first material is patterned on the surface 562 to form a plurality of optically absorbing concentric rings 560, which concentric rings 560 are concentric to a common point 565 on the surface 562, each concentric ring 560 having an inner radius 563 and an outer radius 564 dimension, and for each ring 560 the first material is distributed on the surface 562 spanning from a radial distance of its inner radius 563 to its outer radius 564 with respect to the common point 565. In an embodiment, each of the plurality of optically absorbing concentric rings 560 comprises a thin layer of the first material adhered to the second material. In an embodiment, the bulk of the surface is made from the second material. In an embodiment, the second material is a plastic, and the first material is an ink. In an embodiment, the surface 562 is adapted to emit an identifiable acoustic signal resulting from the absorption of optical energy by the concentric rings 560, the identifiable acoustic signal encoding the spatial distribution of the concentric rings 560 to permit identification of the fiducial marker by processing of signal received by an acoustic receiver. In an embodiment, the surface 562 further comprises a set of additional optically absorbing concentric rings, which additional concentric rings are concentric to a second point on the surface that is different from the common point. For example, the surface can have two identifiable markers on it.

    [0036] In an embodiment, a fiducial comprises optically reflective material which has weaker optical absorption (e.g. than a material it is adhered to), and a pattern which produces acoustic signal due to strong optical absorption is associated with a relief portion of the pattern that does not comprise the optically reflective material.

    [0037] Some aspects of the system and method disclosed above can be embodied, at least in part, in software. That is, the techniques may be carried out in a special purpose or general purpose computer system or other data processing system in response to its processor, such as a microprocessor, executing sequences of instructions contained in a memory, such as ROM, volatile RAM, non-volatile memory, cache or a remote storage device. Functions expressed in the claims may be performed by a processor in combination with memory storing code and should not be interpreted as means-plus-function limitations.

    [0038] Routines executed to implement the embodiments may be implemented as part of an operating system, firmware, ROM, middleware, service delivery platform, SDK (Software Development Kit) component, web services, or other specific application, component, program, object, module or sequence of instructions referred to as "computer programs." Invocation interfaces to these routines can be exposed to a software development community as an API (Application Programming Interface). The computer programs typically comprise one or more instructions set at various times in various memory and storage devices in a computer, and that, when read and executed by one or more processors in a computer, cause the computer to perform operations necessary to execute elements involving the various aspects.

    [0039] A machine-readable medium can be used to store software and data which when executed by a data processing system causes the system to perform various methods. The executable software and data may be stored in various places including for example ROM, volatile RAM, non-volatile memory and/or cache. Portions of this software and/or data may be stored in any one of these storage devices. Further, the data and instructions can be obtained from centralized servers or peer-to-peer networks. Different portions of the data and instructions can be obtained from different centralized servers and/or peer-to-peer networks at different times and in different communication sessions or in a same communication session. The data and instructions can be obtained in entirety prior to the execution of the applications. Alternatively, portions of the data and instructions can be obtained dynamically, just in time, when needed for execution. Thus, it is not required that the data and instructions be on a machine-readable medium in entirety at a particular instance of time.

    [0040] Examples of computer-readable media include but are not limited to recordable and non-recordable type media such as volatile and non-volatile memory devices, read only memory (ROM), random access memory (RAM), flash memory devices, floppy and other removable disks, magnetic disk storage media, optical storage media (e.g., Compact Disk Read-Only Memory (CD ROMS), Digital Versatile Disks (DVDs), etc.), among others.

    [0041] In general, a machine readable medium includes any mechanism that provides (e.g., stores) information in a form accessible by a machine (e.g., a computer, network device, personal digital assistant, manufacturing tool, any device with a set of one or more processors, etc.).

    [0042] In various embodiments, hardwired circuitry may be used in combination with software instructions to implement the techniques. Thus, the techniques are neither limited to any specific combination of hardware circuitry and software nor to any particular source for the instructions executed by the data processing system.

    [0043] The above embodiments and preferences are illustrative of the present invention. It is neither necessary, nor intended for this patent to outline or define every possible combination or embodiment. The inventor has disclosed sufficient information to permit one skilled in the art to practice at least one embodiment of the invention. The above description and drawings are merely illustrative of the present invention and that changes in components, structure and procedure are possible without departing from the scope of the present disclosure. The invention is defined by the appended claims.

    [0044] For example, elements and/or steps described above and/or in the following claims in a particular order may be practiced in a different order without departing from the invention. Thus, while the invention has been particularly shown and described with reference to embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the disclosure.


    Claims

    1. A system comprising:

    an optical energy delivery unit (304) comprising an optical energy exit port (302) adapted to deliver optical energy to a volume of a subject, the optical energy delivery unit comprising a fiducial marker site (301, 303);

    an acoustic receiving unit (306) comprising one or more acoustic receivers adapted to receive acoustic signals from the volume;

    the fiducial marker site configured to emit an acoustic response to be received by said acoustic receiving unit;

    a processing unit configured for processing signals received by said acoustic receiving unit, which processing comprises determining a relative position of said optical energy delivery unit respective to said acoustic receiving unit using the acoustic response emitted by the fiducial marker site; and,

    a display unit adapted to display an opto-acoustic image representing the volume.


     
    2. The system of claim 1, wherein the opto-acoustic image is produced, at least in part, by using data describing the determined relative position.
     
    3. The system of claim 1, further comprising:

    an additional fiducial marker site configured to emit acoustic responses to be received by said acoustic receiving unit,

    wherein the processing further comprises determining a relative orientation and the relative position of said optical energy delivery unit respective to said acoustic receiving unit using a received acoustic response emitted by the fiducial marker site and the acoustic response emitted by the additional fiducial marker site.


     
    4. The system of claim 3, wherein the fiducial marker site and the additional fiducial marker site are located on a distal surface of said optical energy delivery unit.
     
    5. The system of claim 4, wherein the optical energy exit port is located on the distal surface of the optical energy delivery unit.
     
    6. The system of claim 3, wherein the processing unit is further configured such that the processing comprises:

    retrieving a list of position values relative to a first coordinate reference frame, the list comprising a position for the fiducial marker site and a position for the additional fiducial marker site;

    determining values for a rotation matrix and a translation vector to rotate and translate the list of position values to a configuration relative to a second coordinate reference frame, wherein the determined values comprise a solution that accounts for propagation delays of fiducial response component of said signals received by said acoustic receiving unit; and,

    producing the relative orientation and the relative position per the rotation matrix and translation vector.


     
    7. The system of claim 1, wherein the processing unit is further configured such that the processing comprises:

    separating a distinguishable acoustic response component emitted by said fiducial marker sitefrom remaining components of said signals received by said acoustic receiving unit; and,

    generating an opto-acoustic image of the volume using said remaining components.


     
    8. The system of claim 1, wherein the processing unit is further configured such that the processing comprises:

    generating a first opto-acoustic representation of the volume when said optical energy delivery unit is at a first relative placement respective to a placement of said acoustic receiving unit as determined by said processing unit;

    generating a second opto-acoustic representation of the volume when said optical energy delivery unit is at a second relative placement respective to the placement of said acoustic receiving unit as determined by said processing unit;

    computing a difference between the first opto-acoustic representation of the volume and the second opto-acoustic representation of the volume; and

    generating the opto-acoustic image based upon the computed difference.


     
    9. The system of claim 1, wherein the processing unit is further configured to determine when the optical energy delivery unit and acoustic receiving unit are within a proximity adequate to form an opto-acoustic image.
     
    10. The system of claim 1, wherein the fiducial marker site comprises:

    a first concentric layer comprising a carrier material and a first concentration of an electromagnetically absorbing material; and

    a second concentric layer comprising the carrier material and a second concentration of the electromagnetically absorbing material.


     
    11. The system of claim 10, wherein the fiducial marker site further comprises additional concentric layers, wherein each additional concentric layer comprises the carrier material and a concentration of the electromagnetically absorbing material.
     
    12. The system of claim 10, wherein the concentration of the electromagnetically absorbing material is smoothly varied between successive concentric layers to achieve a continuous band-limited emitted acoustic signal profile.
     
    13. The system of claim 10, wherein the acoustic response emitted by the fiducial marker site is identifiable due to a unique concentration of electromagnetically absorbing material in each layer processing by the acoustic receiving unit.
     
    14. The system of claim 13, wherein the unique concentration of electromagnetically absorbing material in each layer generates a binary code representing the digits zero and one based on either a first or a second concentration of electromagnetically absorbing material that is used, or wherein the unique concentration of electromagnetically absorbing material in each layer generates a unique time domain or frequency domain signature.
     
    15. The system of claim 10, wherein the carrier material is a plastisol and the electromagnetically absorbing material is an optically absorbing material, for example, a colorant.
     


    Ansprüche

    1. Ein System, das Folgendes beinhaltet:

    eine optische Energiezuführungseinheit (304), die einen Ausgangsanschluss für optische Energie (302) beinhaltet, der dazu eingerichtet ist, einem Volumen eines Individuums optische Energie zuzuführen, wobei die optische Energiezuführungseinheit eine Lokalisationsmarkerstelle (301, 303) beinhaltet;

    eine akustische Empfangseinheit (306), die einen oder mehrere akustische Empfänger beinhaltet, die dazu eingerichtet sind, akustische Signale von dem Volumen zu empfangen;

    wobei die Lokalisationsmarkerstelle dazu ausgelegt ist, eine akustische Antwort auszugeben, die von der akustischen Empfangseinheit empfangen werden soll;

    eine Verarbeitungseinheit, die zum Verarbeiten von Signalen, die von der akustischen Empfangseinheit empfangen werden, ausgelegt ist, wobei das Verarbeiten das Bestimmen einer relativen Position der optischen Energiezuführungseinheit im Verhältnis zu der akustischen Empfangseinheit unter Verwendung der von der Lokalisationsmarkerstelle ausgegebenen akustischen Antwort beinhaltet; und

    eine Anzeigeeinheit, die dazu eingerichtet ist, ein das Volumen darstellendes optoakustisches Bild anzuzeigen.


     
    2. System nach Anspruch 1, wobei das optoakustische Bild mindestens teilweise durch die Verwendung von Daten produziert wird, die die bestimmte relative Position beschreiben.
     
    3. System nach Anspruch 1, das ferner Folgendes beinhaltet:

    eine zusätzliche Lokalisationsmarkerstelle, die dazu ausgelegt ist, akustische Antworten auszugeben, die von der akustischen Empfangseinheit empfangen werden sollen,

    wobei das Verarbeiten ferner das Bestimmen einer relativen Orientierung und der relativen Position der optischen Energiezuführungseinheit im Verhältnis zu der akustischen Empfangseinheit unter Verwendung einer empfangenen akustischen Antwort, die von der Lokalisationsmarkerstelle ausgegeben wird, und der akustischen Antwort, die von der zusätzlichen Lokalisationsmarkerstelle ausgegeben wird, beinhaltet.


     
    4. System nach Anspruch 3, wobei sich die Lokalisationsmarkerstelle und die zusätzliche Lokalisationsmarkerstelle auf einer distalen Oberfläche der optischen Energiezuführungseinheit befinden.
     
    5. System nach Anspruch 4, wobei sich der Ausgangsanschluss für optische Energie auf der distalen Oberfläche der optischen Energiezuführungseinheit befindet.
     
    6. System nach Anspruch 3, wobei die Verarbeitungseinheit ferner so ausgelegt ist, dass das Verarbeiten Folgendes beinhaltet:

    Abrufen einer Liste von Positionswerten im Verhältnis zu einem ersten Koordinatenbezugsrahmen, wobei die Liste eine Position für die Lokalisationsmarkerstelle und eine Position für die zusätzliche Lokalisationsmarkerstelle beinhaltet;

    Bestimmen von Werten für eine Rotationsmatrix und einen Translationsvektor zum Rotieren und Verschieben der Liste von Positionswerten zu einer Konfiguration im Verhältnis zu einem zweiten Koordinatenbezugsrahmen, wobei die bestimmten Werte eine Lösung beinhalten, die die Ausbreitungsverzögerungen der Lokalisationsmarkerantwortkomponente der von der akustischen Empfangseinheit empfangenen Signale berücksichtigt; und

    Produzieren der relativen Orientierung und der relativen Position entsprechend der Rotationsmatrix und des Translationsvektors.


     
    7. System nach Anspruch 1, wobei die Verarbeitungseinheit ferner so ausgelegt ist, dass das Verarbeiten Folgendes beinhaltet:

    Trennen einer unterscheidbaren akustischen Antwortkomponente, die von der Lokalisationsmarkerstelle ausgegeben wird, von den übrigen Komponenten der von der akustischen Empfangseinheit empfangenen Signale; und

    Erzeugen eines optoakustischen Bilds des Volumens unter Verwendung der übrigen Komponenten.


     
    8. System nach Anspruch 1, wobei die Verarbeitungseinheit ferner so ausgelegt ist, dass das Verarbeiten Folgendes beinhaltet:

    Erzeugen einer ersten optoakustischen Darstellung des Volumens, wenn sich die optische Energiezuführungseinheit an einer ersten relativen Platzierung bezüglich einer Platzierung der akustischen Empfangseinheit, bestimmt durch die Verarbeitungseinheit, befindet;

    Erzeugen einer zweiten optoakustischen Darstellung des Volumens, wenn sich die optische Energiezuführungseinheit an einer zweiten relativen Platzierung bezüglich der Platzierung der akustischen Empfangseinheit, bestimmt durch die Verarbeitungseinheit, befindet;

    Berechnen einer Differenz zwischen der ersten optoakustischen Darstellung des Volumens und der zweiten optoakustischen Darstellung des Volumens; und

    Erzeugen des optoakustischen Bilds auf der Grundlage der berechneten Differenz.


     
    9. System nach Anspruch 1, wobei die Verarbeitungseinheit ferner dazu ausgelegt ist, zu bestimmen, wann sich die optische Energiezuführungseinheit und akustische Empfangseinheit in einer zum Bilden eines optoakustisches Bilds ausreichenden Nähe befinden.
     
    10. System nach Anspruch 1, wobei die Lokalisationsmarkerstelle Folgendes beinhaltet:

    eine erste konzentrische Schicht, die ein Trägermaterial und eine erste Konzentration eines elektromagnetisch absorbierenden Materials beinhaltet; und

    eine zweite konzentrische Schicht, die das Trägermaterial und eine zweite Konzentration des elektromagnetisch absorbierenden Materials beinhaltet.


     
    11. System nach Anspruch 10, wobei die Lokalisationsmarkerstelle ferner zusätzliche konzentrische Schichten beinhaltet, wobei jede zusätzliche konzentrische Schicht das Trägermaterial und eine Konzentration des elektromagnetisch absorbierenden Materials beinhaltet.
     
    12. System nach Anspruch 10, wobei die Konzentration des elektromagnetisch absorbierenden Materials zwischen aufeinanderfolgenden konzentrischen Schichten fließend ineinander übergeht, um ein kontinuierliches bandbegrenztes ausgegebenes akustisches Signalprofil zu erzielen.
     
    13. System nach Anspruch 10, wobei die akustische Antwort, die von der Lokalisationsmarkerstelle ausgegeben wird, aufgrund einer eindeutigen Konzentration von elektromagnetisch absorbierendem Material in der Verarbeitung jeder Schicht durch die akustische Empfangseinheit identifizierbar ist.
     
    14. System nach Anspruch 13, wobei die eindeutige Konzentration von elektromagnetisch absorbierendem Material in jeder Schicht einen binären Code erzeugt, der die Ziffern null und eins repräsentiert, basierend entweder auf einer ersten oder zweiten Konzentration des verwendeten elektromagnetisch absorbierenden Materials, oder wobei die eindeutige Konzentration von elektromagnetisch absorbierendem Material in jeder Schicht eine eindeutige Zeitdomänen- oder Frequenzdomänensignatur erzeugt.
     
    15. System nach Anspruch 10, wobei das Trägermaterial ein Plastisol ist und das elektromagnetisch absorbierende Material ein optisch absorbierendes Material, zum Beispiel ein Farbmittel, ist.
     


    Revendications

    1. Système comprenant :

    une unité d'apport d'énergie optique (304) comprenant un orifice de sortie d'énergie optique (302) conçu pour apporter de l'énergie optique à un volume d'un sujet, l'unité d'apport d'énergie optique comprenant un site de points repères (301, 303) ;

    une unité de réception acoustique (306) comprenant un ou plusieurs récepteurs acoustiques conçus pour recevoir des signaux acoustiques en provenance du volume ;

    le site de points repères étant configuré pour émettre une réponse acoustique à recevoir par ladite unité de réception acoustique ;

    une unité de traitement configurée pour le traitement de signaux reçus par ladite unité de réception acoustique, ledit traitement comprenant la détermination d'une position relative de ladite unité d'apport d'énergie optique par rapport à ladite unité de réception acoustique en utilisant la réponse acoustique émise par le site de points repères ; et

    une unité d'affichage conçue pour afficher une image opto-acoustique représentant le volume.


     
    2. Système selon la revendication 1, dans lequel l'image opto-acoustique est produite, au moins en partie, en utilisant des données décrivant la position relative déterminée.
     
    3. Système selon la revendication 1, comprenant en outre :

    un site de points repères supplémentaire configuré pour émettre des réponses acoustiques à recevoir par ladite unité de réception acoustique,

    dans lequel le traitement comprend en outre la détermination d'une orientation relative et de la position relative de ladite unité d'apport d'énergie optique par rapport à ladite unité de réception acoustique en utilisant une réponse acoustique reçue émise par le site de points repères et la réponse acoustique émise par le site de points repères supplémentaire.


     
    4. Système selon la revendication 3, dans lequel le site de points repères et le site de points repères supplémentaire sont situés sur une surface distale de ladite unité d'apport d'énergie optique.
     
    5. Système selon la revendication 4, dans lequel l'orifice de sortie d'énergie optique est situé sur la surface distale de l'unité d'apport d'énergie optique.
     
    6. Système selon la revendication 3, dans lequel l'unité de traitement est en outre configurée de telle sorte que le traitement comprenne :

    la récupération d'une liste de valeurs de position relative à une première fenêtre de coordonnées de référence, la liste comprenant une position pour le site de points repères et une position pour le site de points repères supplémentaire ;

    la détermination de valeurs pour une matrice de rotation et un vecteur de translation pour faire pivoter et déplacer en translation la liste de valeurs de position pour produire une configuration relative à une deuxième fenêtre de coordonnées de référence, les valeurs déterminées constituant une solution qui tient compte des retards de propagation de la composante de réponse des repères desdits signaux reçus par ladite unité de réception acoustique ; et

    la production de l'orientation relative et de la position relative selon la matrice de rotation et le vecteur de translation.


     
    7. Système selon la revendication 1, dans lequel l'unité de traitement est en outre configurée de telle sorte que le traitement comprenne :

    la séparation d'une composante de réponse acoustique distinguable émise par ledit site de points repères des composantes restantes desdits signaux reçus par ladite unité de réception acoustique ; et

    la génération d'une image opto-acoustique du volume en utilisant lesdites composantes restantes.


     
    8. Système selon la revendication 1, dans lequel l'unité de traitement est en outre configurée de telle sorte que le traitement comprenne :

    la génération d'une première représentation opto-acoustique du volume lorsque ladite unité d'apport d'énergie optique se trouve à un premier emplacement relatif par rapport à un emplacement de ladite unité de réception acoustique tel que déterminé par ladite unité de traitement ;

    la génération d'une deuxième représentation opto-acoustique du volume lorsque ladite unité d'apport d'énergie optique se trouve à un deuxième emplacement relatif par rapport à l'emplacement de ladite unité de réception acoustique tel que déterminé par ladite unité de traitement ;

    le calcul d'une différence entre la première représentation opto-acoustique du volume et la deuxième représentation opto-acoustique du volume ; et

    la génération de l'image opto-acoustique en fonction de la différence calculée.


     
    9. Système selon la revendication 1, dans lequel l'unité de traitement est en outre configurée pour déterminer quand l'unité d'apport d'énergie optique et l'unité de réception acoustique sont suffisamment proches pour former une image opto-acoustique.
     
    10. Système selon la revendication 1, dans lequel le site de points repères comprend :

    une première couche concentrique comprenant un matériau de support et une première concentration d'un matériau électromagnétiquement absorbant ; et

    une deuxième couche concentrique comprenant le matériau de support et une deuxième concentration du matériau électromagnétiquement absorbant.


     
    11. Système selon la revendication 10, dans lequel le site de points repères comprend en outre des couches concentriques supplémentaires, chaque couche concentrique supplémentaire comprenant le matériau de support et une concentration du matériau électromagnétiquement absorbant.
     
    12. Système selon la revendication 10, dans lequel on fait varier progressivement la concentration du matériau électromagnétiquement absorbant entre les couches concentriques successives pour obtenir un profil de signal acoustique émis continu et à bande limitée.
     
    13. Système selon la revendication 10, dans lequel la réponse acoustique émise par le site de points repères est identifiable en raison d'une concentration unique de matériau électromagnétiquement absorbant dans le traitement de chaque couche par l'unité de réception acoustique.
     
    14. Système selon la revendication 13, dans lequel la concentration unique de matériau électromagnétiquement absorbant dans chaque couche génère un code binaire représentant les chiffres zéro et un basés soit sur une première, soit sur une deuxième concentration de matériau électromagnétiquement absorbant qui est utilisée, ou dans lequel la concentration unique de matériau électromagnétiquement absorbant dans chaque couche génère une signature unique de domaine temporel ou de domaine fréquentiel.
     
    15. Système selon la revendication 10, dans lequel le matériau de support est un plastisol et le matériau électromagnétiquement absorbant est un matériau optiquement absorbant, par exemple un colorant.
     




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    Cited references

    REFERENCES CITED IN THE DESCRIPTION



    This list of references cited by the applicant is for the reader's convenience only. It does not form part of the European patent document. Even though great care has been taken in compiling the references, errors or omissions cannot be excluded and the EPO disclaims all liability in this regard.

    Patent documents cited in the description




    Non-patent literature cited in the description