PROBE AND SYSTEM FOR OPTOACOUSTIC IMAGING AND METHOD FOR CONTROLLING SUCH A PROBE

Abstract

The present invention relates to a probe and a system for optoacoustic imaging of an object as well as a method for controlling such a probe. An irradiation unit of the probe is configured to emit electromagnetic radiation and to irradiate the object with the electromagnetic radiation, and a detection unit of the probe is configured to detect primary acoustic waves emitted by the object in response to irradiating the object with the electromagnetic radiation. The probe further comprises a couplant compartment enclosing an acoustic coupling medium between the detection unit and the irradiation unit, on the one hand, and the object, on the other hand, the couplant compartment comprising a shielding element arranged between the object and the detection unit and being configured to at least partially transmit acoustic waves and to at least partially reflect and/or absorb electromagnetic radiation, the shielding element separating the couplant compartment into a first sub-compartment and a second sub-compartment such that electromagnetic radiation emitted by the irradiation unit can pass the first sub-compartment to impinge on the object but is at least partially hindered by the shielding element to enter the second sub-compartment, and primary acoustic waves emitted by the object can pass the shielding element and the second sub-compartment to impinge on the detection unit.

Claims

1. A probe for optoacoustic imaging of an object, the probe comprising: an irradiation unit configured to emit electromagnetic radiation and to irradiate the object with the electromagnetic radiation; a detection unit configured to detect primary acoustic waves emitted by the object in response to irradiating the object with the electromagnetic radiation; and a couplant compartment enclosing an acoustic coupling medium between the detection unit and the irradiation unit, on the one hand, and the object, on the other hand, the couplant compartment comprising a shielding element arranged between the object and the detection unit and being configured to at least partially transmit acoustic waves and to at least partially reflect and/or absorb electromagnetic radiation, the shielding element separating the couplant compartment into a first sub-compartment and a second sub-compartment such that electromagnetic radiation emitted by the irradiation unit can pass the first sub-compartment to impinge on the object but is at least partially hindered by the shielding element to enter the second sub-compartment, and primary acoustic waves emitted by the object can pass the shielding element and the second sub-compartment to impinge on the detection unit.

2. The probe according to claim 1, wherein the shielding element is arranged and/or configured to at least partially deflect and/or direct secondary acoustic waves emitted by the shielding element and/or any other element located outside of the object in response to electromagnetic radiation impinging thereon and/or which are scattered and/or reflected by any other element located outside of the object, away from the detection unit to reduce or avoid secondary acoustic waves to impinge on the detection unit.

3. The probe according to claim 1, wherein the shielding element (has a planar shape and/or is slanted with respect to a surface of the object and/or an axis perpendicular to a surface of the object and/or a lateral wall of the couplant compartment.

4. The probe according to claim 1, further comprising one or more acoustic trap elements arranged and/or configured to at least partially absorb secondary acoustic waves, which are emitted by the shielding element and/or any other element located outside of the object in response to electromagnetic radiation impinging thereon and/or which are scattered and/or reflected by any other element located outside of the object, to reduce or avoid secondary acoustic waves to impinge on the detection unit.

5. The probe according to claim 4, wherein the one or more acoustic trap elements is provided at an inner surface of the couplant compartment.

6. The probe according to claim 1, further comprising one or more optoacoustic trap elements arranged and/or configured to emit secondary acoustic waves in response to electromagnetic radiation impinging thereon such that a predominant part of the emitted secondary acoustic waves does not propagate towards and/or impinge on the detection unit.

7. The probe according to claim 6, wherein the one or more optoacoustic trap elements is provided at an inner surface of the couplant compartment, in particular on top of the one or more acoustic trap elements being provided at the inner surface of the couplant compartment.

8. The probe according to claim 1, wherein the shielding element comprises or is designed as a semi-transparent optical element being arranged and/or configured to at least partially transmit electromagnetic radiation emitted by the irradiation unit to impinge on the object, and to reflect and/or absorb electromagnetic radiation which has been reflected and/or scattered by the object and/or any other element located outside of the object.

9. The probe according to claim 1, wherein the irradiation unit is configured to emit polarized electromagnetic radiation, and the shielding element comprises or is designed as a polarizing filter being arranged and/or configured to at least partially transmit the polarized electromagnetic radiation emitted by the irradiation unit to impinge on the object, and to reflect and/or absorb electromagnetic radiation which has been reflected and/or scattered by the object and/or by any other element located outside of the object.

10. The probe according to claim 8, wherein the irradiation unit and the detection unit are provided at a proximal end of the couplant compartment, and the shielding element are at least partially provided at a distal end of the couplant compartment, which is opposite to the proximal end of the couplant compartment.

11. A system for optoacoustic imaging of an object comprising: a probe comprising: an irradiation unit configured to emit electromagnetic radiation and to irradiate the object with the electromagnetic radiation; a detection unit configured to detect primary acoustic waves emitted by the object in response to irradiating the object with the electromagnetic radiation; and a couplant compartment enclosing an acoustic coupling medium between the detection unit and the irradiation unit, on the one hand, and the object, on the other hand, the couplant compartment comprising a shielding element arranged between the object and the detection unit and being configured to at least partially transmit acoustic waves and to at least partially reflect and/or absorb electromagnetic radiation, the shielding element separating the couplant compartment into a first sub-compartment and a second sub-compartment such that electromagnetic radiation emitted by the irradiation unit can pass the first sub-compartment to impinge on the object but is at least partially hindered by the shielding element to enter the second sub-compartment, and primary acoustic waves emitted by the object can pass the shielding element and the second sub-compartment to impinge on the detection unit; and a processing unit configured to derive image data regarding at least one property the object based on the detected primary acoustic waves.

12. A method of controlling a probe for optoacoustic imaging of an object, the probe comprising a couplant compartment enclosing an acoustic coupling medium between a detection unit and an irradiation unit, on the one hand, and the object, on the other hand, the couplant compartment comprising a shielding element arranged between the object and the detection unit and being configured to at least partially reflect and/or absorb electromagnetic radiation, the shielding element separating the couplant compartment into a first sub-compartment and a second sub-compartment, the method comprising the following steps: controlling the irradiation unit to emit electromagnetic radiation passing the first sub-compartment to impinge on the object to cause the object to emit primary acoustic waves, wherein the emitted electromagnetic radiation is at least partially hindered by the shielding element to enter the second sub-compartment; and controlling the detection unit to detect primary acoustic waves having passed the shielding element and the second sub-compartment to impinge on the detection unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Further advantages, features and examples of the present invention will be apparent from the following description of following figures:

[0039] FIG. 1 shows an example of a system for optoacoustic imaging of an object;

[0040] FIG. 2 shows an example of a probe for optoacoustic imaging of an object; and

[0041] FIG. 3 shows another example of a probe for optoacoustic imaging of an object.

DETAILED DESCRIPTION

[0042] FIG. 1 shows an example of a system 100 for optoacoustic imaging of an object 2 comprising a probe 1 and a processing unit 50. The probe 1 has an irradiation unit 3 for irradiating the object 2 with electromagnetic radiation, a detection unit 4 for detecting primary acoustic waves P generated in the object 2 in response to irradiating the object with the electromagnetic radiation, a couplant compartment 5 containing a coupling medium for acoustically coupling the object 2 and the detection unit 4 and a shielding element 6 separating the couplant compartment 5 into a first sub-compartment 5a and a second sub-compartment 5b. The processing unit 50 is configured to generate image data regarding properties of the object 2 based on the primary acoustic waves P detected by the detection unit 4.

[0043] The detection unit 2, which is given for example by one or more, in particular an array of, ultrasonic transducers, comprises a detection surface 4a sensitive to primary acoustic waves P impinging on the detection unit 2. The detection unit 2 is configured to generate detection signals in response to the primary acoustic waves P impinging thereon. The detection signals can be transmitted to the processing unit 50, which is preferably configured to process the detection signals such that an optoacoustic image of the object 2 is reconstructed from the detection signals.

[0044] The probe 1 preferably comprises a housing 10, in particular for handheld operation, which may enclose the irradiation unit 3 and the detection unit 4 and forms and/or includes the couplant compartment 5. The coupling medium contained in the couplant compartment 5 is separated from the object 2 by a coupling element 7, e.g. a, preferably flexible, membrane, which is configured to contact the object 2 during image acquisition. In other words, the contact element 7 forms an interface between the couplant compartment 5 and the object 2.

[0045] Preferably, the housing 10 comprises lateral walls 10a as well as a proximal wall 10b of the couplant compartment 5, wherein the proximal wall 10b may be at least partially constituted by the irradiation unit 3 and/or the detection unit 4, in particular by the detection surface 4a. In other words, in present example the detection unit 4 and the irradiation unit 3 are disposed at a proximal end of the couplant compartment 5, and the couplant compartment 5 is sealed by the contact element 7 which is provided at a distal end of the couplant compartment 5.

[0046] The shielding element 6, for example a thin metal or metallized foil or membrane, which separates the coupling compartment 5 into the first and second sub-compartments 5a, 5b is configured to at least partially transmit acoustic waves and at least partially reflect electromagnetic radiation. The shielding element 6 hinders electromagnetic radiation emitted by the irradiation unit 3 into the first sub compartment 5a towards the object 2 and/or subsequently at least partially reflected at the object 2 to enter the second compartment 5b and to impinge on the detection unit 4, where it would generate an unwanted parasitic detection signal due to secondary acoustic waves generated at the detection surface 4a, thereby causing artifacts in the reconstructed optoacoustic image. At the same time, the primary acoustic waves P generated in the object 2 enter the couplant compartment 5 through the coupling element 7 and can pass the shielding element 6 and the second sub-compartment 5b to impinge on the detection unit 4 substantially unhindered.

[0047] FIG. 2 shows an example of a probe 1 for optoacoustic imaging of an object 2. In present example, the probe 1 comprises a shielding element 6a, 6b, wherein a first part 6a of the shielding element is provided at a distal end of couplant compartment 5, and a second part 6b of the shielding element separates the couplant compartment 5 into a first sub-compartment 5a and a second sub-compartment 5b (similarly to shielding element 6 shown in FIG. 1).

[0048] Further, an irradiation unit 3 for emitting electromagnetic radiation towards the object 2 is arranged at least partially in the first sub-compartment 5a at a proximal end of the couplant compartment 5, and a detection unit 4 for detecting primary acoustic waves generated in the object 2 in response to the irradiation with electromagnetic radiation is at least partially located in the second sub-compartment 5b at the proximal end of the couplant compartment 5.

[0049] The second part 6b of the shielding element is configured to at least partially transmit acoustic waves and to at least partially reflect and/or absorb electromagnetic radiation (like shielding element 6 shown in FIG. 1).

[0050] In distinction to this, the first part 6a of the shielding element is configured to at least partially transmit electromagnetic radiation emitted by the irradiation unit 3 to impinge on the object 2, and at the same time to reflect and/or absorb electromagnetic radiation which has been reflected and/or scattered by the object 2 and/or any other element located outside the object 2.

[0051] To this end, the first part 6a may comprise or be designed as a semi-transparent optical element at least partially separating the couplant compartment 5 from the object 2. For example, the first part 6a may comprise a coating, in particular a metal coating, disposed on coupling element 7 (cf. FIG. 1). Thus, electromagnetic radiation emitted by the irradiation unit 3 traverses the first sub-compartment 5a and passes through the first part 6a of the shielding element to impinge on the object 2. However, a part of this electromagnetic radiation reflected by the object 2, in particular at the surface of the object 2, cannot reenter the couplant compartment 5 due to the reflective and/or absorptive properties of the first part 6a. Thereby, generation of secondary acoustic waves, in particular within the couplant compartment 5, which would cause the detection 4 unit to generate a parasitic (detection) signal, can be suppressed or at least reduced.

[0052] Alternatively or additionally, for example, the first part 6a may be configured to act as a polarizing filter, letting electromagnetic radiation having a first polarization pass through and blocking off electromagnetic radiation having a second polarization perpendicular to the first polarization. The irradiation unit 3 may be configured to emit polarized electromagnetic radiation, in particular having the first polarization, e.g. by means of a polarizing element 3a. Thus, the electromagnetic radiation emitted by the irradiation unit 3 may pass the first part 6a, but upon being at least partially reflected and/or scattered by the object 2, which at least partially changes polarization of the electromagnetic radiation, the electromagnetic radiation is reliably blocked off by the first part 6a.

[0053] FIG. 3 shows another example of a probe 1 for optoacoustic imaging of an object 2. Similarly to the example shown in FIG. 1, the probe 1 of the present example comprises a detection unit 4 configured to detect primary acoustic waves generated the object 2 in response to the electromagnetic radiation R emitted by an irradiation unit 3. The probe 1 also comprises a shielding element 6 configured to at least partially reflect and/or absorb electromagnetic radiation R and to at least partially transmit acoustic waves, in particular primary acoustic waves generated in the object 2. The shielding element 6 separates a couplant compartment 5 into a first sub-compartment 5a and a second sub-compartment 5b.

[0054] Preferably, the probe 1 further comprises one or more acoustic trap elements 8 for at least partially absorbing secondary acoustic waves, e.g. secondary acoustic waves S generated in and emitted by the shielding element 6.

[0055] Alternatively or additionally, the probe 1 comprises optoacoustic trap elements 9 for at least partially absorbing electromagnetic radiation R emitted by the irradiation unit 3 and reflected in the couplant compartment 5, in particular at an interface between the probe 1 and the object 2 and/or at the object 2 and/or at the shielding element 6.

[0056] As shown in the present example, the electromagnetic radiation R, e.g. in form of an irradiation cone, emitted by the irradiation unit 3 traverses the first sub-compartment 5a and impinges on the object 2, in particular a surface of the object 2 facing the probe 1. A first, major part of the radiation R penetrates the object 2 and generates primary acoustic waves beneath the surface of the object 2, wherein the primary acoustic waves contain information, in particular image information, relating to the object 2. A second, minor part of the radiation is reflected at the interface between the probe 1 and the object 2, in particular at the surface of the object 2 and/or within the object 2. Said second part of the radiation R at least partially impinges on the shielding element 6, which is arranged at least partially in between the irradiation unit 3 and the detection unit 4, in particular slanted with respect to the surface of the object 2 and/or a perpendicular axis on the surface of the object 2 and/or the lateral walls (see 10a, 10b in FIG. 1) of the couplant compartment 5.

[0057] The shielding element 6, being at least partially absorptive to the electromagnetic radiation R, absorbs at least some of the impinging second part of the electromagnetic radiation R and may thereby generate secondary acoustic waves S. In order to avoid at least a major part of the secondary acoustic waves S emitted by the shielding element 6 to impinge on the detection unit 4, the shielding element 6 is preferably arranged and/or configured to at least partially emit and/or direct said generated secondary acoustic waves S away from the detection unit 4, in particular towards the acoustic trap elements 8, in particular towards the acoustic trap elements 8 being preferably arranged at the (lower) lateral wall of second sub-compartment 5b and/or towards the acoustic and/or optoacoustic trap elements 8, 9 being preferably arranged at the (upper) lateral wall of first sub-compartment 5a.

[0058] To this end, the shielding element 6 may preferably have a planar shape, such that in combination with the slanted orientation of the shielding element 6, no or only a minor part of the shielding element 6 faces the detection unit 4. In particular, the planar shape in combination with the slanted orientation of the shielding element 6 allows that a section of the shielding element 6, in which the second part of the electromagnetic radiation R impinges on the shielding element 6, is not facing the detection unit 4 but preferably the acoustic and/or optoacoustic trap elements 8, 9.

[0059] The acoustic trap elements 8 are arranged on lateral walls of the couplant compartment 5. Preferably, the acoustic trap elements 8 are formed by a coating disposed on the lateral walls of the couplant compartment 5. For example, the lateral walls of the couplant compartment 5 may be at least partially coated by rock wool, glass fibers, textile, foam or a thin polystyrene film or a combination thereof. While strongly attenuating, in particular damping, impinging secondary acoustic waves S, these materials also have a very low conversion efficiency, i.e. they absorb most of impinging electromagnetic radiation R without converting it into acoustic waves.

[0060] Thus, the acoustic trap elements 8 are not only configured to at least partially absorb the secondary acoustic waves S emitted by the shielding element 6, but also secondary acoustic waves S emitted by any other element located outside object 2 in response to the electromagnetic radiation R impinging thereon and/or which are scattered and/or reflected by any other element located outside of the object 2. In particular, the acoustic trap elements disposed on the lateral walls of the couplant compartment 5 at least partially suppress the reflection of secondary acoustic waves S within the couplant compartment 5. In this arrangement, the acoustic trap elements 8 also hinder secondary acoustic surface waves propagating along the lateral walls of couplant compartment 5 from reaching the detection unit 4.

[0061] The shielding element 6, being at least partially reflective to the electromagnetic radiation R, reflects at least some of the impinging second part of the electromagnetic radiation R, in particular directs some of the impinging second part of the electromagnetic radiation R towards the optoacoustic trap elements 9. If not for the shielding element 6, the second part of the electromagnetic radiation R would, at least partially, impinge on the detection unit 4 and generate secondary acoustic waves S, in particular secondary surface acoustic waves, at a detection surface of the detection unit 4, which would in turn cause the detection unit 4 to generate parasitic (detection) signals. This is indicated by the dotted lines.

[0062] The optoacoustic trap elements 9, similarly to the acoustic trap elements 8, are arranged on the lateral walls of couplant compartment 5, in particular on top of the acoustic trap elements 8. This allows an immediate absorption of secondary acoustic waves S emitted by the optoacoustic trap elements 9 by the acoustic trap elements 8 upon impinging electromagnetic radiation R, in particular some of the second part of the electromagnetic radiation R reflected at the object 2 and subsequently at the shielding element 6.

[0063] The optoacoustic trap elements 9 may comprise the same or at least similar materials as utilized in the acoustic trap elements 8. Further, the optoacoustic trap elements 9 are preferably shaped such that the emitted secondary acoustic waves S are direct away from the detection unit 4, in particular towards the acoustic trap elements 8. For example, as indicated in FIG. 3, the optoacoustic trap elements 9 may have a triangular or semi-spherical shape, wherein the major part of the surface of the optoacoustic trap elements 9 faces the acoustic trap elements 8.

[0064] The probe 1, in particular the irradiation unit 3, is coupled to a radiation source 50, e.g. a laser, configured to generate the electromagnetic radiation, preferably in the near infrared range (NIR) of the electromagnetic spectrum, which is for example coupled to the irradiation unit 3 by means of a light guide, e.g. an optical fiber. The irradiation unit 3 can be formed by a distal end of said light guide. Additionally or alternatively, the irradiation unit 3 may comprise irradiation optics, e.g. for collimating, diffusing, focusing and/or directing the emitted electromagnetic radiation, in particular onto or towards the object 2, respectively. The irradiation optics are preferably configured to shape and/or direct the electromagnetic radiation in such a way that it does not, at least not directly, impinge on the detection unit 4. Alternatively or additionally, the irradiation optics are configured to shape and/or direct the electromagnetic radiation in such a way that the electromagnetic radiation does not impinge on the shielding element 6.

[0065] The probe 1 is further coupled to detection electronics 40 configured to process, or at least pre-process, detection signals generated by the detection unit 4 upon primary acoustic waves impinging thereon. For example, the detection signals may be amplified, filtered and/or converted to digital signals by means of the detection electronics 40. Alternatively or additionally, the detection electronics 40 may be configured to control the detection unit 4 in particular as a function of the radiation source 30, e.g. to only detect primary acoustic waves only during the predefined duration during which the irradiation unit 3 emits electromagnetic radiation.

[0066] In another embodiment (not shown), the radiation source 30 and/or the detection electronics 40 may be part of the probe 1.

[0067] Preferably, the shielding element 6 shown in FIGS. 1 and 3 and/or the second part 6b of the shielding element shown in FIG. 2 has or includes an inclination angle with respect to a surface normal to the surface of the object 2 and/or to a side wall or lateral wall (see, e.g., lateral walls 10a in FIG. 1) of the coupling compartment 5, wherein the inclination angle has a value between 10 and 60, preferably between 20 and 40, in particular approximately 30. In this way, primary acoustic waves P can efficiently pass the shielding element 6 or the second part 6b of the shielding element to impinge on the detection unit 4, while secondary waves S are efficiently deflected away from the detection unit 5, as exemplarily indicated by curved lines representing secondary waves S in FIG. 3.