Photoacoustic imaging device and transducer attachment method

Abstract

The photoacoustic imaging device uses a number of acoustoelectronic transducers. The transducers have a sound receiving surface that forms part of the surface of the basin of the breast cup. The transducers each have a foil adhesively connected to its sound receiving surface and a reflective coating provided on the basin side of the foil. The reflective (e.g. gold) coating is used to minimize photoacoustic sound generation at the surface of the transducer, which can lead to image artifacts when this sound is reflected from within the basin. By providing a coating on a smooth foil of copper foil or polymer foil adhered to the transducer surface, a reduction in photoacoustic sound generation at the surface sufficient for a significant reduction in photoacoustic image artifacts can be achieved. The foil can be attached to the transducer in the form of a patch after the transducer is attached on the basin, and the patch can extend from the transducer to the periphery of the basin to reduce photoacoustic sound generation in the gap between the transducer and the surface of the basin.

Description

[Technical field]

[0001] The present invention relates to an optoacoustic imaging device and a method for mounting an acoustoelectronic transducer within the optoacoustic imaging device, for example when the optoacoustic imaging device is assembled. [Background technology]

[0002] Photoacoustic imaging involves sending light pulses into tissue and forming a sound-generated image (usually a 3D image) due to absorption of the light in the tissue (as used herein, "sound" covers "ultrasound"). The tissue is presented in a basin that also contains an acoustic contact liquid, such as water.

[0003] The pulses are preferably very short (nanosecond), intense (near) infrared pulses provided by a light source having an output or distributed light output on the walls of the basin.

[0004] In the tissue, the light pulse causes optical absorption, which causes an increase in temperature that causes thermal expansion, which in turn leads to pressure transients that cause low intensity sound waves (especially from the blood). An array of ultra-sensitive broadband acoustic through the walls of the basin to electronic transducers in the aperture detects these waves.

[0005] The detection results can be used to reconstruct images with high spatial resolution, for example the complete 3D vasculature.

[0006] In particular, the acoustic intensity detected from photoacoustic transduction in deeper tissue further away from the superficial location (skin) where the light is delivered is very small.

[0007] This should make it possible to distinguish between the subtle photoacoustic responses from (more) deeply lying tissues, such as blood vessels, and the noise and artifacts in the 3D image reconstruction of these vessels. This calls for the suppression of artifacts that interfere with small ultrasound signals. It has been shown that the disturbing artifacts can be due to light reaching the receiving surface of the acousto-electronic transducer and causing an optoacoustic conversion at that surface.

[0008] The direct (ultrasonic) signal from such photoacoustic conversion can be easily cancelled by time windowing, as this direct signal precedes the arrival of acoustic waves from the tissue which must travel from the location of photoacoustic conversion within the tissue.

[0009] However, sound generated at the receiving surface of the acoustoelectronic transducer can also travel into the tissue and be reflected from there back to the acoustoelectronic transducer. Artifacts resulting from such reflections have proven to be quite difficult to eliminate by signal processing. Instead, the inventors have attempted to reduce the photoacoustic automatic response of the surface of the acoustoelectronic transducer. A possible approach to reduce the photoacoustic response from this surface is to coat the surface with a light-reflecting layer that reflects near-infrared light, minimizing the light that reaches the surface of the coating and underneath the coating where photoacoustics can occur, without significantly reducing the acoustic transmission from the tissue to the surface of the acoustoelectronic transducer.

[0010] For example, a gold coating may be used. Gold has the additional beneficial property of being inert, particularly to oxygen, thereby protecting the reflective surface. Gold is known to be a very effective reflector for (near) infrared light. References [1] See Paquin, RE, "Properties of Metals", in BASS.M(eic.) Handbook of Optics, Volume II Devices, Measurements, and Properties, Chapter 35, pages 35.1-35.74, McGraw-Hill Professional, New York, second edition (1995); ISBN 0-07-047974-7, TABLE 3 Reflectance of Selected Metals at Normal Incidence (pages 35.33-34). [2] See also Lynch, DW, "Mirror and Reflector Materials", in Weber, MJ (ed.), CRC Handbook of Laser Science and Technology, IV, Optical Materials, Part 2:Properties, CRC Press, Boca Raton, Florida (2003); ISBN 0-8493-3512-4, Section 1.3, Fig. 4.2.8.

[0011] In principle, a very thin (sub-micrometer (e.g., hundreds of nanometers)) reflective gold coating may be sufficient to prevent significant light transmission to the surface underlying the acoustoelectronic transducer. This is advantageous because it can be used to ensure that the gold layer is thin enough to avoid losses in transmitted ultrasound intensity, e.g., due to reflection.

[0012] However, it has been found that although the gold layer has a minimum thickness to be sufficiently reflective, similar artifacts due to the underlying surface of the acoustoelectronic transducer still occur. Without a gold coating significantly thicker than necessary for reflection, a gold coating on the surface of the acoustoelectronic transducer has been found to only slightly reduce artifacts similar to those of photoacoustic transduction at the surface of the acoustoelectronic transducer.

[0013] A sufficient thickness of this coating is required to obtain a coating that overcomes the roughness of the transducer's sound receiving surface and to cover the entire area with a sufficiently thick layer of gold. When evaporation or sputtering is used to deposit such a gold layer, the layer will suffer from shadows, and when the treated surface is not completely smooth, the result is a phenomenon in which gaps and indentations in the surface do not have a (sufficient) thickness of gold everywhere, which results in a situation in which light can still be absorbed on the surface in areas that are not (sufficiently) covered. As a result, undesired photoacoustic signals can still be generated, which will have a negative impact on the signal-to-noise ratio (SNR) of the system.

[0014] To overcome this, the receiving surface can either be pre-treated to obtain a sufficiently smooth surface and thus a uniform reflecting layer, or a relatively thick layer of reflecting material must be applied, which layer, on the other hand, must be thin enough to allow complete transmission of ultrasound.

[0015] US2019 / 275562 discloses an ultrasonic transducer with a ground electrode on a membrane above the receiving surface of the transducer, the ground electrode being connected to the metal housing of the transducer. This is used, for example, to prevent electromagnetic interference from RF fields used to create an acoustic signal from the sample by heating the sample. It has been found that metal rubber sheets can function as conductive membranes. In principle, membranes with conductive layers can also be used for ultrasonic transducers in photoacoustic imaging systems, where the ground electrode on the membrane can reflect a portion of the light that can reach the surface of the acoustoelectronic transducer. However, such a membrane structure does not guarantee the combination of high transmission of a weak photoacoustic signal from the sample and high reflectivity of the light from the light pulse. Summary of the Invention

[0016] The objective is to reduce artifacts resulting from photoacoustic conversion in transducers used in photoacoustic imaging devices (eg, for mammography applications).

[0017] According to one aspect, reduction of artifacts due to the photoacoustic response of a transducer is achieved by an optoacoustic imaging device comprising: A basin for receiving the tissue to be imaged A light source configured to provide light to the interior of the basin. A plurality of acousto-electronic transducers, each transducer of the plurality having a receiving surface forming a portion of the surface of the basin at a respective different location within the surface of the basin, each with a foil adhesively connected to the receiving surface and a reflective coating provided on the basin side of the foil. The use of a foil such as a metal foil, or more specifically a copper foil with a reflective coating such as a gold coating, and an adhesive facilitates installation and repair of the photoacoustic imaging system in a manner that achieves the high demands of artifact suppression in the context of photoacoustic imaging devices. Such a foil can be installed even after the transducers are mounted in the basin during initial assembly or repair.

[0018] Preferably, a robust highly reflective material such as gold is used for the reflective coating.

[0019] It has been found that when a reflective coating, such as a gold coating, that is reflective to light from a light source (e.g., in the near infrared), is used on the basin side surface of a smooth flexible metal foil, such as a copper foil, the reflective coating is sufficient to reduce artifacts in a manner that allows for better sensitive photoacoustic imaging than when the reflective surface is used directly on the surface of an acoustoelectronic transducer. This is because the metal foil allows the smoothness of the reflective coating to be improved compared to when the coating is applied directly on the transducer surface, which is then assumed to reduce the photoacoustic conversion due to light absorption by the reflective coating as a result of multiple reflections by the reflective coating. Preferably, the patch is used where the coating surface is smooth such that its RMS slope value is less than 0.42, more preferably at most 0.1. Preferably, the foil surface underlying the coating also has an RMS slope value less than 0.42, more preferably at most 0.1. The smoothness of a metal foil, for example manufactured using cold rolling, may be sufficient to improve the smoothness of the reflective coating. Alternatively, a polymer foil with comparable smoothness may be used.

[0020] Preferably, a gold coating is used over the copper layer. Gold is a good infrared and near infrared light reflector. Furthermore, the gold and copper layers provide little reduction in ultrasonic transmission to the ultrasonic transducer, and these layers can be made thin to minimize reduction in sound transmission. Additionally, gold is resistant to degradation of light reflection, and copper provides more robust smoothness.

[0021] In one embodiment, the smooth foil may be attached to the sound receiving surface of the transducer using an adhesive layer that may be provided on the transducer side surface of the foil before the foil is applied to the sound receiving surface of the transducer. The adhesive is selected for ease of application and to allow easy removal of the coated foil from the transducer when replacement of either the foil or the transducer is required. The smooth foil may be provided in the form of an adhesive tape.

[0022] The acousto-electronic transducers each have a conductive housing around an axis perpendicular to the receiving surface. In one embodiment, the conductive housing is electrically connected to a metal foil. The metal foil can thus perform two functions: reducing the generation of photoacoustic signals and shielding the electromagnetic fields at the transducer.

[0023] In addition to the functional benefits, the cost of applying the reflective material is also significantly reduced, since applying the reflective material onto a foil is less expensive than applying it onto a transducer. Positioning the foil within a deposition chamber is much easier and more effective than the complete transducer element.

[0024] In an embodiment in which the transducers extend through an opening in the base structure of the basin, a copper foil is provided in a patch on each of the multiple acoustoelectronic transducers, extending from the receiving surface of the acoustoelectronic transducer to the surface of the base structure around the opening through which the acoustoelectronic transducer extends. The gap between the transducer and the base structure may include an O-ring to prevent water leakage from the basin or other material. However, it has been found that the gap or material in the gap may contribute to photoacoustic noise generation. The use of a gold-coated copper patch extending from the receiving surface of the transducer through the gap to the surface of the base structure around the transducer may prevent or at least reduce photogeneration of acoustic noise generation in the gap.

[0025] The edges of the patch may also give rise to some photoacoustic noise generation, but the intensity of these sounds is found to be smaller than that from the gaps.

[0026] Preferably, the different transducers of the plurality of acoustoelectronic transducers each have their own foil with a reflective coating in the form of a mutually separate patch, such that when the surface of the transducer is shallowly damaged or worn from such cleaning, for example after disinfecting the wall of the measuring basin in which the transducer is mounted, the patch can be easily removed and replaced by another patch, without the need to remove and replace the complete transducer element, which is significantly more expensive and requires a significant amount of labor time than replacing a patch.

[0027] These and other objects and advantages will become apparent from the following detailed description of illustrative embodiments which proceeds with reference to the drawings. [Brief description of the drawings]

[0028] [Figure 1] FIG. 2 illustrates the basin of an optoacoustic imaging device. [Diagram 2] FIG. 2 shows a schematic diagram of a portion of a basin of an optoacoustic imaging device. [Diagram 3] FIG. 2 is a schematic top view of an acoustoelectronic transducer; [Figure 4] FIG. 2 is a diagram showing a cross section of a patch. [Diagram 5] FIG. 1 is an exemplary diagram illustrating normalized RMS ultrasonic signal amplitude. [Figure 6] 1 illustrates an embodiment of a conductive layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0029] 1 shows a basin of an optoacoustic imaging device in the form of a hemispherical bowl 1 having an interior for receiving a breast (not shown) in vivo. The surface of the bowl 1 is defined by a basic structure 10 with an opening for one or more outputs 12 of a light source and an acousto-electronic transducer 14 for providing light into the bowl 1. By way of example, a hemispherical bowl 1 for receiving a breast is shown, but it should be understood that other types of tissue may be imaged and that basins of different shapes may be used.

[0030] FIG. 2 shows diagrammatically a portion of the basin of an optoacoustic imaging device, including a basic structure 10 (shown flat to simplify the drawing) with an acoustoelectronic transducer extending through an aperture.

[0031] 3 shows a schematic top view of the acoustoelectronic transducer 14. A patch 16 of gold coated copper foil is provided at least above the acoustoelectronic transducer 14. The patch 16 covers the sound receiving surface of the acoustoelectronic transducer 14. Preferably, the patch 16 extends on the base structure 10 around the opening containing the acoustoelectronic transducer 14, as shown in the figure.

[0032] A cross section of the patch 16 is shown (not to scale) with a copper foil 40, a gold coating 42 on the basin side surface of the copper foil 40, and an adhesive layer 44 on the transducer side surface of the patch 16. In the illustrated embodiment, an 18 micrometer thick copper foil was used with a 0.5 micrometer thick gold coating. Preferably, a nickel diffusion barrier layer between the copper and gold layers, or a NiCr, Cr layer instead of the nickel diffusion barrier, can be used. Other examples include cobalt, palladium, copper tin alloys, and alloys of such materials. The bottom of the copper foil was attached to the surface of the acoustoelectronic transducer 14 by a 32 micrometer thick acrylic adhesive. However, copper foil thicknesses between 1 and 100 micrometers and gold coating thicknesses between 0.1 and 2 micrometers, more preferably between 0.2 and 2 micrometers, can be used. The coating layer can be applied by electroplating or other deposition methods such as sputtering or evaporation. Instead of a metal foil, a polymer foil with similar smoothness can be used. In one example, a 25 micrometer thick polyimide foil was used with a 0.4 micrometer thick gold coating. Optionally, a thin Ti layer can be used as an adhesion promoter between the polyimide and gold on top of the polyimide foil, and the surface of the acoustoelectronic transducer 14 is attached to the bottom of the foil by a 45 micrometer thick silicone adhesive.

[0033] The thickness of the adhesive layer is not critical and can vary slightly between different locations, but the adhesive layer can be optimized for ultrasonic matching, for example, by mating it with a layer on the transducer surface (see Callens et al., "Matching ultrasonic transducer using two matching layers where one of them is glue," NDT&E International 37 (2004) 591-597).

[0034] The thickness of the combination of coating, metal layer, and adhesive layer is preferably kept low so that ultrasonic absorption and reflection by the combination does not significantly reduce the ultrasonic signal strength at the transducer. For example, the thickness of the combination may be less than 100 micrometers, such as about 1 micrometer gold, 2 micrometer nickel, 18 micrometer copper, and 32 micrometer acrylic adhesive in a layer of about 50 micrometers.

[0035] Although an embodiment is described in which each acousto-electronic transducer 14 has its own isolation patch, it should be understood that alternative patches may be used that cover more than one acousto-electronic transducer 14 within a basin wall, or even all of these acousto-electronic transducers 14.

[0036] However, with respect to the gap, the surface of the base structure 10 of the bowl and the top surface of the acoustoelectronic transducer 14 form a quasi-continuous surface with almost no step between the base structure 10 and the top surface of the acoustoelectronic transducer 14 (e.g., with a step less than 0.1 mm high). At most, a small gap (e.g., less than 0.1 mm wide) exists between the acoustoelectronic transducer 14 and the base structure 10. An O-ring or other means may be provided in the gap to prevent water leakage from the basin. The top surface of the acoustoelectronic transducer 14 serves as the sound receiving surface.

[0037] The acoustoelectronic transducers may be installed in the photoacoustic imaging device by mounting each acoustoelectronic transducer in a position where it extends through an aperture, so that the receiving surface of the acoustoelectronic transducer forms part of the surface of the basin. A foil may then be attached to the receiving surface. This may be done for all of the acoustoelectronic transducers. A (patch of) foil may be provided with an adhesive layer on the surface opposite the surface with the gold coating in order to attach the foil to the acoustoelectronic transducer.

[0038] A transducer with an acoustic matching layer on the receiving layer may be used. Although efficient gold deposition on some acoustic matching layers is not possible, this can be overcome by applying a gold coating to a foil. When applying a foil to the receiving surface with an acoustic matching layer, this avoids the need to treat the entire transducer, or at least its active elements as a whole, by applying a reflective material directly to the entire receiving surface of the transducer.

[0039] If necessary, the foil with the gold coating over the one or more acoustoelectronic transducers can be later removed and replaced with new foil. When the foil is attached to the sound receiving surface (either initially or as a replacement), the foil is preferably attached so that it extends from the receiving surface of the one or more acoustoelectronic transducers to a surface of the base structure around the opening through which the one or more acoustoelectronic transducers 14 extend.

[0040] In operation, the light source transmits a light pulse through its output 12 into the bowl 1 and the acoustoelectronic transducer 14 receives the generated sound inside the bowl 1. The generated sound includes the sound generated due to the absorption of the light pulse. The acoustoelectronic transducer 14 receives the sound through its receiving surface and converts the received sound into an electronic signal. The acoustoelectronic transducer 14 may use a piezoelectric material for this purpose. The photoacoustic imaging device comprises a data processing system (not shown, for example a computer) coupled to the electronic output of the acoustoelectronic transducer 14 and configured (for example programmed) to calculate the amplitude of the generated sound as a function of the position inside the bowl 1. Methods for carrying out such calculations are known per se. The resulting amplitude of the generated sound as a function of the position can be represented in the form of a 3D or 2D image.

[0041] Figure 5 shows the results of an experiment on the surface of a transducer with different exemplary surface configurations. The ultrasound signal levels resulting from photoacoustic transduction at the surface of the transducer are shown. The transducer was mounted in a holder similar to a basin. Light pulses of varying near-infrared wavelengths were delivered to the transducer in the holder. A 3D photoacoustic imager was used to measure the ultrasound signal induced by illuminating the transducer.

[0042] Signal levels were determined within the 3D photoacoustic reconstruction images by calculating the root mean square (RMS) of the reconstructed initial pressure levels across a thin (2.4 mm) cylindrical deposition centered at the center of the transducer surface and extending radially (7.2 mm) across a radius of the patch larger than the 5 mm radius of the transducer surface (e.g., 6 mm) to capture all of the signal generated from the patch. Signal levels were normalized to the average signal level of the directly deposited surface (b) for each wavelength.

[0043] Different curves are obtained using an acoustoelectronic transducer 14(c) covered by a patch of copper foil with a gold coating, an acoustoelectronic transducer 14(b) with a gold coating directly on the surface of the acoustoelectronic transducer 14, and an acoustoelectronic transducer 14(a) without a gold coating.

[0044] As can be seen, the gold-coated copper foil patch 16(c) results in a significant photoacoustic amplitude reduction. The transducer without a reflective layer (i.e., the receiving layer is directly exposed to the irradiating light) produces a signal level that is 2.6 times greater than the transducer with a surface on which a 1 micrometer gold layer is directly deposited via sputter deposition. The transducer with the gold-coated copper patch applied produces a signal level that is further reduced by an average of 2.8 times.

[0045] Although a theoretical explanation is not necessarily required to effect such a reduction, it may be tentatively assumed that the reduction in photoacoustic amplitude is due to a reduction in multiple reflections (and their associated absorption) from the gold coating as a result of the improved smoothness of the gold coating when the gold coating is provided on the copper foil rather than directly on the acoustoelectronic transducer 14. The improved smoothness of the gold coating is in turn due to the fact that the copper foil facilitates providing a smoother substrate for the gold coating than the acoustoelectronic transducer 14.

[0046] Bergstrom, Journal of Applied Physics 103, 103515 (2008): "The absorption of light by rough metal surfaces_a three-dimensional ray-tracing analysis", presents simulation results of the relationship between reflectance and surface smoothness, expressed in terms of surface roughness. To express this relationship, surface roughness can be characterized in terms of the root-mean-square (RMS) slope of the surface (the square root of the spatial average of the sum of the squares of dh / dx and dh / dy, where h is the height of the surface, and dh / dx and dh / dy are the derivatives of the height along different directions on the surface). Assuming a Gaussian height distribution, the RMS slope is equal to Sqrt(2) * sigma / L

[0047] where sigma is the root mean square of the height h and L is the correlation length of the height (see Bergstrom). The RMS slope can be determined by a profilometer, e.g., an optical profilometer observation through a microscope. For example, the RMS slope can be determined via RΔq measured using a profilometer according to the definition and method in [ISO 3287:1997]. Note that the RΔq value is a square root multiple that is twice as large as the RMS slope definition used in Bergstrom.

[0048] In the cases described below, simulations with normal or near-normal (less than 30 degrees off normal) incident light show that multiple reflections associated with causing photoacoustic signal generation at a surface are largely prevented, or at least greatly reduced. RMS gradient < 0.42 (approximately 0.3 * sqrt(2))

[0049] Optical absorption beyond this value due to multiple reflections increases significantly. An RMS slope of 0.42 can be estimated to yield a normalized RMS photoacoustic signal of about 0.35 in a configuration where a gold coating is used. As can be seen in Figure 5, a gold layer deposited on a transducer without a copper foil results in a significantly higher photoacoustic signal due to optical absorption.

[0050] More preferably, this RMS slope is at most 0.1. For a thin coating layer on an underlying foil, this maximum formally applies to the surface of the coating layer. However, if the underlying foil has at most this maximum RMS slope value, this will usually ensure that the RMS slope of the coating is also less than this maximum. The RMS slope of the thin coating layer is substantially the same as or slightly lower than the RMS slope of the underlying foil, becoming less as the coating thickness increases. The RMS slope of cold rolled copper foil (and other metal foils) meets this requirement. Copper foils available for use on printed circuit boards are available to achieve RMS slope values ​​below 0.42 and 0.1. The smoother copper foils are available for use in GHz range printed circuit boards.

[0051] Based on experiments, it was found that the RMS slope with gold deposited directly on the transducer surface was 2.1, which is significantly higher than required to prevent or at least significantly reduce multiple reflections, whereas a gold coating on a copper foil produced a sufficiently low RMS slope, at most 0.1, to prevent or at least significantly reduce multiple reflections.

[0052] In one experiment, the photoacoustic amplitude as a function of position on and around the acoustoelectronic transducer was measured by suspending a piece of wall structure in a bowl 1 with the acoustoelectronic transducer in an opening through the wall structure piece. The photoacoustic amplitude as a function of position was reconstructed using measurements with the acoustoelectronic transducer 14 in the base structure of the bowl. The resulting image shows a ring of photoacoustic amplitude around the acoustoelectronic transducer in an opening through the wall structure piece. The root mean square (rms) amplitude of this ring was reduced by about a factor of two when a patch of gold-coated copper foil extended through the gap between the acoustoelectronic transducer in the opening and the wall structure piece. This reduction can be attributed to preventing light from reaching the gap between the acoustoelectronic transducer and the wall structure. The remaining lower rms amplitude ring of photoacoustic amplitude appears to be associated with the edge of the patch. This rms amplitude can be reduced by rounding the edges of the patch.

[0053] 6 shows an embodiment in which a conductive layer 50 is provided between the adhesive of the patch 16 and the surface of the acoustoelectronic transducer 14. Alternatively, the conductive layer 50 can be the copper layer of the patch, where the adhesive layer of the patch 16 is conductive. The conductive layer 50 or the adhesive layer of the patch 16 is electrically connected to the base structure 10 of the bowl, which is also conductive. This makes it possible to use the conductive layer 50 and / or the copper foil to shield the transducer 14 from external electromagnetic interference.

[0054] The acoustoelectronic transducer 14 may have a conductive housing 54 about the normal axis of the receiving surface. Conductive Housing 54. In an embodiment, the housing 54 is electrically connected to the conductive layer 50.

Claims

1. a basin for receiving the tissue to be imaged; a light source configured to provide light to an interior of the basin; a plurality of acousto-electronic transducers, each transducer of the plurality having a receiving surface forming part of the surface of the basin at a respective different position within the surface of the basin, each with a foil adhesively connected to the receiving surface and a reflective coating provided on the basin side of the foil; A photoacoustic imaging device comprising:

2. The foil is a metal foil, The optoacoustic imaging device of claim 1 , wherein the reflective coating is a material that is more reflective to the light from the light source than a material of the metal foil.

3. the surface of the basin is formed by a base structure having an opening; the acoustoelectronic transducer extends through the opening in the base structure; An optoacoustic imaging device as described in claim 1 or 2, wherein the device comprises respective patches of the foil, each via a respective one of the plurality of acousto-electronic transducers.

4. The optoacoustic imaging device of claim 3 , wherein each of the patches extends from the receiving surface of the acoustoelectronic transducer to the surface of the base structure around the opening through which the acoustoelectronic transducer extends.

5. The optoacoustic imaging device of claim 1 , wherein the reflective coating is a gold coating.

6. The photoacoustic imaging device of claim 3 , wherein the gold coating has a thickness between 0.1 and 2 micrometers.

7. The photoacoustic imaging device of claim 1 , wherein the foil is a copper foil.

8. a nickel layer between the gold coating and the copper foil; The photoacoustic imaging device of claim 7 , wherein the nickel layer preferably has a thickness of at least 2 micrometers.

9. The photoacoustic imaging device of claim 7 or 8, wherein the copper foil has a thickness between 1 and 200 micrometers.

10. The optoacoustic imaging device of claim 1 , wherein the foil is adhesively connected to the receiving surface by an acrylic or silicone-based glue.

11. the acoustoelectronic transducer has a conductive housing about a normal axis of the receiving surface; The foil is a metal foil, The optoacoustic imaging device of claim 1 , wherein the conductive housing is electrically connected to the metal foil.

12. 13. A method of mounting an acousto-electronic transducer in an optoacoustic imaging device, the optoacoustic imaging device comprising a base structure defining a surface of a basin for receiving tissue to be imaged, the base structure defining an opening in the base surface, the method comprising: mounting the acoustoelectronic transducer in a position such that the transducer extends through the opening such that a receiving surface of the acoustoelectronic transducer forms part of the surface of the basin; and subsequently adhesively attaching a foil to the sound receiving surface, the foil having a reflective coating on a side of the foil facing the interior of the basin; A method comprising:

13. 13. The method of claim 12, wherein the foil is a patch of foil extending from the receiving surface of the acousto-electronic transducer to the surface of the base structure around the opening through which a first of the acousto-electronic transducers extends.

14. 14. A method according to claim 12 or 13, wherein the metal foil has a pre-applied layer of adhesive on a further side facing the sound receiving surface.

15. a respective foil patch attached to the sound receiving surface of a respective acoustoelectronic transducer extending through all of the apertures; 15. The method of claim 12, 13 or 14, wherein each of the respective metal foil patches has a reflective coating on a side of the foil facing the interior of the basin.

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