BIMODAL PROBE COMPLIMENTING WITH AN ULTRASONIC TRANSDUCER AND OPTODES AND A METHOD FOR THEM MANUFACTURING

Description

TECHNICAL FIELD

[0001] The invention relates to a probe combining an optical and ultrasound modality for the in-vivo diagnosis of biological tissues, as well as the application of such a probe to detect and analyze cancerous tumors. EARLIER ART

[0002] One of the goals of medical diagnosis is to improve sensitivity and specificity to reduce the number of false positives, while ensuring that no true positives are missed. This can be achieved by combining different measurement techniques. For example, combining PET (Positron Emission Tomography) and MRI (Magnetic Resonance Imaging) scans can enhance the characterization of biological tissue. Ultrasound, combined with optical measurements, also improves tissue characterization. These modalities can be integrated into simple and inexpensive devices for point-of-care diagnostic applications.

[0003] Regarding optical measurements, the use of optical fibers in a probe has already been described in the prior art, with the fibers extending from a central unit comprising light sources and / or optical detectors. For example, US patent application US20140187958A1 describes a diagnostic probe for intracavity use, comprising an ultrasound transducer and a series of optical fibers for characterizing fluorescence. The use of optical fibers has the following drawbacks: small collection area, and limited digital aperture; signal attenuation and distortion; reduced flexibility, and robustness affected by the cable connecting the probe to the central unit.

[0004] US 2017 / 049417 A1 discloses a portable bimodal probe for prostate cancer detection; it includes an ultrasound transducer (22) and optodes (14, 16) arranged on either side.

[0005] Photoacoustic detection is not a bimodal approach. This method is based on emitting a light pulse into a tissue, which then converts it into ultrasound waves. In most cases, devices combine photoacoustic and conventional ultrasound imaging techniques. Tomowave Labs (Houston, Texas, USA), for example, has developed a breast cancer measurement device based on photoacoustic imaging. See also US20130190595A1. In this device, a patient's breast is placed in a receptacle. An ultrasound transducer and optical components scan around the receptacle. The main drawback is that such a device is not portable and is not designed for point-of-care diagnostic applications.

[0006] There figure 1This diagram illustrates a prior art diffuse optical tomography (DOT) measurement device. It comprises a light emitter 31 and an optical detector 32, directed towards a region of interest on the body 40 of a patient, and positioned in contact with the patient's skin 41.

[0007] The light emitter 31 generates photons, which are absorbed or scattered depending on the composition of the tissue being examined. The optical properties of a tumor 43 are generally slightly different from those of the surrounding tissue 42, allowing it to be localized. Some of the scattered photons are collected by the optical detector. This detector is preferably a single-photon counting detector (or single-photon counting detector) with high sensitivity over a large detection area. The dashed lines 44 represent the average path length of scattered photons through the tissue 40 and the tumor 43, these photons being detected by the optical detector 32.

[0008] When analyzing the composition of tumor 43, an optimal configuration is obtained when the emitter 31 and the detector 32 are placed symmetrically with respect to the tumor 43. The penetration depth z of the mean path of the photons can be adjusted by reducing the distance between the emitter 31 and the detector 32, and / or by tilting them with respect to a direction normal to the plane formed by the surface of the skin 41. Emitter / detector pairs, positioned in other locations, allow for tomographic reconstruction of the examined tissue.

[0009] The use of single-photon counting optical detectors allows for measurements in the time domain. This enables the detection of photons that have propagated through the tissue based on their time of flight (TOF). This provides two important advantages: information regarding the average depth of the detected photons in the tissue and improved discrimination between the absorption and scattering of light within the tissue. Knowing the relative positions of the emitter and detector, as well as the wavelength, allows for the determination of biological properties of the measured tissue, such as oxygenation, structure, lipid concentration, etc. Determining these biological properties, combined with the tumor geometry (obtained with ultrasound imaging), increases the specificity and selectivity of malignant tumor screening. DESCRIPTION OF THE INVENTION

[0010] One object of the invention is a portable probe according to claim 1.

[0011] The optical modality of the invention is based, or may be based, on diffuse optical tomography. The optical measurements performed for diffuse optical tomography, combined with the ultrasound modality, provide improved indicators of the physiological or pathological state of the tissue examined. Thus, the invention improves diagnosis, with greater specificity and sensitivity. This is particularly relevant for cancer screening and characterization.

[0012] The combination of ultrasound and optical modalities requires the superposition of their respective fields of observation. To this end, an object of the invention is a method for fixing the position of each component of a portable bimodal probe. A particular aspect of the invention is that the ultrasound probe is arranged between at least one light emitter and an optical detector. Another particular aspect concerns the use of optical measurements according to a time-domain approach. Based on this type of measurement, a reconstruction of the examined tissue is performed based on a temporal distribution of detection times of photons that have propagated through the tissue. This allows for a quantitative analysis of absorption and diffusion coefficients reduced in the tissue. The result is a better definition of the volume of a tumor present in the tissue.

[0013] Another object of the invention is a method for manufacturing a bimodal probe, according to the attached method claims.

[0014] The invention will be better understood by reading the description of the examples of embodiment presented, in the continuation of the description, in connection with the figures listed below, the latter not limiting the scope of the claims. FIGURES

[0015] There figure 1 is a schematic description of a diffuse optical tomography (DOT) system. figure 2 is a functional diagram of an example system combining ultrasound (US) and diffuse optical tomography (DOT) modalities. figure 3 is a perspective view of a portable bimodal probe embodiment. figure 3 allows us to define the main directional axes. figure 4 is a perspective view similar to the figure 3 , according to a shaded representation. The figure 5is a perspective view of an example optode featuring a single-photon counting detector with a large detection area. figure 6 is a perspective view of another embodiment, comprising two optodes combined in the same housing. figure 7A is a diagram representing a side view section of an embodiment relating to the retention of an ultrasonic transducer and optodes in a molded part, so as to constitute a protective distal end comprising an ultrasonic acoustic lens. figure 7B is a diagram representing a side view section of another embodiment relating to the retention of ultrasonic transducers and optodes in a molded part. According to this embodiment, the mold forms an opening allowing the insertion of an ultrasonic transducer confined within its own protective casing. The figure 7Cis a diagram representing a side-view section of another embodiment in which the optodes are inclined with respect to a longitudinal direction of the probe. figure 8 This is a perspective view of an example of a mounting bracket, allowing the retention of an optode. figure 9 describes the main steps of a process for assembling components that form a bimodal ultrasonic / optical probe. PRESENTATION OF SPECIFIC IMPLEMENTATION METHODS

[0016] The present invention relates to a bimodal probe, combining ultrasound (US) imaging and optical measurements to obtain biological parameters for cancer tumor screening. More specifically, the optical modality is based on diffuse optical tomography (DOT).

[0017] There figure 2shows an example of a device comprising a bimodal probe 30 electrically connected to a main unit 10 via a plurality of electrical wires assembled in a single cable 20.

[0018] The weight and size of the probe 30 are such that it can be handheld and manipulated to be positioned in contact with a patient's body 40, oriented towards a region of interest, and more specifically a tumor 43 to be examined. A coupling gel is generally applied to the interface between the probe and the body being analyzed, so as to facilitate the propagation of ultrasound waves across the interface. The gel may also have optical properties, for example absorption, to prevent crosstalk between the optical components. With regard to the optical modality, the probe comprises optodes, each optode having a light emitter 31 and / or optical detector 32. The components 31 and 32 of the same optode are electrically connected to a driver circuit 33.The latter is configured to provide power supply or synchronization signals and to convert the detected signal into digital data. A bidirectional link connects the optical driver circuit 33 to an optical processing unit 12 via a cable 20. The probe 30 also includes an ultrasonic transducer 34, composed of elementary ultrasonic transducers, which converts electrical signals from an ultrasonic processing unit 13 into ultrasonic acoustic waves. These waves are emitted towards the body 40. The ultrasonic transducer 34 also converts ultrasonic waves reflected by the body 40 into electrical signals for processing by the ultrasonic processing unit 13. In the ultrasonic transducer, the elementary ultrasonic transducers are preferably aligned along a transverse axis parallel to an X-axis described in relation to the [missing information]. figure 3 .

[0019] The main unit 10 includes a user interface 11, which allows control of the optical processing unit 12 and the ultrasonic processing unit 13. The optical processing unit 12 and the ultrasonic processing unit 13 produce an electrical signal to control the probe components. They also process the signals measured by the probe to provide usable information for the user.

[0020] On the figure 3 We have represented a coordinate system 1, in order to clarify the description. The coordinate system 1 defines a longitudinal direction Z (along the depth), which points towards the body 40, an elevation direction Y and an azimuthal direction X.

[0021] As depicted on the figures 3 And 4In a preferred embodiment, the probe 30 has a distal end 35, intended to be applied in contact with the patient's skin 41. The distal end is confined within a front cover 36, which forms the nose of the probe 30. The front cover 36 extends from a central cover 37. The latter is extended by a hollow connector 38, into which the cable 20 is inserted. The distal end 35 has input / output interfaces for the ultrasound transducer 34, the light emitter 31, and the optical detector 32. In the preferred embodiment, the probe 30 has a plurality of light emitters 31a...31h and a plurality of optical detectors 32a...32h. Preferably, at least one light emitter 31a and at least one optical detector 32a are arranged in an optode, as described in connection with the figure 3Optical detectors 32a...32h have a large detection area. The detection area of ​​a detector corresponds to the area of ​​a sensitive component of said detector. Thus, each optical detector 32a...32h has a detection area, each side of which preferably extends to a width greater than 0.5 mm, or even 5 mm. The detection area is typically larger than 5 x 5 mm², and can be, for example, 10 x 10 mm². Each light emitter can comprise a plurality of elementary light emitters, which can, for example, emit light at different wavelengths. Each elementary light emitter can be a laser diode or a light-emitting diode. The detection area of ​​at least one detector, or even of each detector, is larger than the emission area of ​​each emitter.

[0022] Each light emitter is preferably configured to emit a light pulse. In the case of a time-resolved optical measurement, the pulse duration is less than a few tens of picoseconds (ps), for example, less than 50 ps or 10 ps (FWHM: full width at half maximum). A light emitter could, for example, be a pulsed laser diode.

[0023] The emitters and detectors define, in pairs, emitter / detector pairs. The emitter / detector pairs 31a / 32a, 31b / 32b...31h / 32h are placed on either side of the acoustic transducer 34. The distance between the emitter and detector 31a / 32a, 31b / 32b... of the same optode is preferably between 1 mm and 20 mm, and for example, on the order of 7 mm. This makes it possible to obtain a measurement of the optical properties of a tumor located near the skin, i.e., at a depth of less than 5 cm, for example, between 0 cm and 5 cm. Depending on the elevation direction Y, the distal end 35 comprises successively: a row of 4 optical detectors 32a....32d; a row of 4 light emitters 31a...31d; the ultrasonic transducer 34; a row of 4 light emitters 31e....31h; a row of 4 optical detectors 32e....32h.

[0024] The emitters and detectors are aligned parallel to the X-axis, along which the ultrasonic transducer extends, positioned on either side of it. As a result, the field of view of the ultrasonic imaging modality overlaps with the field of view of the diffuse optical imaging modality. The ultrasonic transducer 34 is delimited by a perimeter. The distance between each optical detector and the perimeter can range from 0.5 mm to 20 mm.

[0025] A protective material fills the remainder of the distal end. The protective material may be silicone rubber, or any other polymerizable or curable biocompatible material, as described in connection with the figures 7A to 7CWhen the ultrasonic transducer extends 34 mm along the Y-axis by a height of 5 mm, the space between the transducer and the nearest rows of optical components (detectors or light emitters) extends approximately 1 mm along the Y-axis. This configuration allows for an overlap of the respective observation fields of the optical modality and the acoustic transducer. Each field of view corresponds to an image formed in a plane parallel to the X and Z axes. Furthermore, such a configuration allows the use of an emitter / detector pair comprising an optical emitter 31a of one optode and an optical detector 32b, 32c, 32d, 32e, 32f, 32g, and 32h of a different optode, offset along the X and / or Y axis. Thus, the probe allows the definition of emitter / detector pairs in which the axis connecting the emitter to the detector is inclined with respect to the elevation axis Y, or the azimuthal axis X, in the XY plane.This allows the distance between the emitter and the detector to be varied from a minimum value, as previously described (between 1 mm and 20 mm, for example, 7 mm), to a maximum value, the latter being on the order of 30 to 80 mm, for example, 40 mm, or 60 mm, for the most distant emitter / detector pairs. The placement of the ultrasonic sensor between the emitter and the detector also allows for an overlap of the respective observation fields of the optical modality and the optical transducer. Combining different emitter / detector distances makes it possible to combine measurements to perform a tomographic reconstruction.

[0026] It can be understood from the above that several optical detectors can be used to measure the scattered photons emitted by the same light emitter. Component retention on the probe

[0027] There figure 5represents an optode comprising an optical detector 32, the latter comprising a sensitive component 53, that is to say, a light-sensitive component. The optical detector 32 is a single-photon counting detector.

[0028] The sensitive component 53 is connected to a printed circuit board 54 of the PCB type (Printed Circuit Board), the latter providing mechanical support for the sensitive component 53, as well as an electrical connection with the sensitive component 53. The electrical connections of the PCB 54 can be extended to the optical driver circuit 33 (cf. figure 2 ), using a flexible printed circuit board or electrical wires.

[0029] The sensitive component 53 is recessed relative to the front face of a housing 52. The housing 52 is preferably made of a metallic material to provide electrical shielding for the components, as well as rigid mechanical attachment. The front face of the housing 52 is intended to be positioned between the sensitive component 53 and the tissue being examined. The front face of the housing 52 defines an opening to allow the passage of light. To prevent direct contact between the sensitive component 53 and the skin, which would lead to a risk of contamination, the opening is closed by an optically transparent plate 51. The plate 51 may be made of glass, polymer, or any other material transparent to the optical wavelengths used in diffuse optics measurements.The transparent plate 51 is connected to the housing 52 and may protrude from its front face. The dimensions of the transparent plate 51, in the azimuthal and elevation directions, are smaller than the dimensions of the housing. The thickness of the transparent plate 51 can vary between 0.4 mm and a few millimeters. Another opening, not shown in the figure... figure 5 , is made in another face of the housing 52 to allow electrical connections.

[0030] The housing 52 and the various components it contains, described in the preceding paragraph, are referred to as the "optode." The optode comprises one or more optical emitters 31. These may, for example, be one or more light-emitting diodes or one or more laser sources. An optode may have optical emitters emitting at different wavelengths. An optode includes an electronic acquisition circuit to measure variations in the light backscattered by the tissue being examined, that is, light that has propagated through the tissue. The acquisition circuit allows for time-resolved measurements of photons backscattered by the tissue being examined and detected by the optode's optical detector 32. This involves, for example, establishing a temporal distribution of the photons detected by the optical detector 32, or the parameters of such a distribution.Thus, an optode is a single-piece component, comprising an optical detector 32 and a light emitter 31 and an acquisition circuit connected to the optical detector 32.

[0031] There figure 6 This shows another example of an optode embodiment in which two sensitive components 63a and 63b are grouped in a single housing 61. The housing 61 has an internal metal partition, positioned around each optical component to prevent crosstalk. The optical component comprises transparent plates 64a and 64b separated from each other by a gap 62. The gap between the two transparent plates provides optical isolation between them. The gap between the two transparent plates extends over a distance of between 1 mm and 3 mm, or between 0.5 mm and 20 mm.

[0032] The method of implementation described in connection with the figure 6includes, but is not limited to, two optical detectors. The invention extends to optodes comprising housings, as previously described, comprising a combination of at least one optical detector and optical emitters, arranged in the same housing.

[0033] THE figures 7A , 7B and 7Cshow side view sections of an embodiment for rigidly fixing an ultrasonic transducer 63 and optodes 62a and 62b, as previously described, and for applying a protective material 65 at the distal end. The protective material 65 may be a polymer, for example, silicone rubber, or another biocompatible material. The protective material may be prepared in liquid form and then poured into a mold 61. After solidification of the material 65 by polymerization, the mold 61 is removed. The ultrasonic transducer 63 and the optodes 62a and 62b are arranged in their final position and securely held by two flanges 64 on two of their lateral sides. On the figure 7AOnly one flange 64 is visible. Components 62a, 62b, and 63 can be held onto each flange by screwing, gluing, or other assembly methods. During the molding operation, the flanges are temporarily screwed onto the mold 61 to maintain the external surfaces of the transparent plates of the optodes 62a and 62b in contact with the bottom of the mold 61.

[0034] On the figure 7AAn ultrasonic transducer 63 is shown recessed relative to the ends of the optodes 62a and 62b. The bottom surface of the mold 61 has a semi-cylindrical cavity 66 extending around an axis parallel to a transverse axis of the transducer, in this case, the X-axis. The length of the cylindrical cavity 66 corresponds to the entire length of the ultrasonic transducer (i.e., the assembly of elementary ultrasonic transducers) along the transverse X-direction. The semi-cylindrical cavity 66 is filled with silicone rubber or any other material exhibiting the same acoustic characteristics. The semi-cylindrical cavity 66 thus forms an acoustic lens. The distance between the external surface of the transducer 63 and the apex of the cavity 66 is typically between 1 mm and 2 mm. The resulting acoustic lens forms a protrusion, extending from its distal end by a distance generally less than 1 mm.When the material 65 is solidified, the assembly comprising the ultrasonic transducer 63, the optodes 62a and 62b, the flange 64, and the cylindrical material 66 extends around an axis parallel to a transverse axis of the transducer, in this case, the X-axis. The length of the cylindrical cavity 66 corresponds to the entire length of the ultrasonic transducer (i.e., the assembly of elementary ultrasonic transducers) along the transverse X-direction. The semi-cylindrical cavity 66 is filled with silicone rubber or any other material exhibiting the same acoustic characteristics. The semi-cylindrical cavity 66 then forms an acoustic lens. The distance between the external surface of the transducer 63 and the apex of the cavity 66 is typically between 1 mm and 2 mm. The resulting acoustic lens forms a protrusion, extending from its distal end by a distance generally less than 1 mm.When the material 65 has solidified, the assembly comprising the ultrasonic transducer 63, the optodes 62a and 62b, the flange 64 and the molded material 65, is removed from the mold and placed in a cavity formed in the front cover 36 of the probe, the front cover forming a nose. The flange is then attached to the front cover 36.

[0035] There figure 7BThis represents another embodiment of an assembly method. According to this embodiment, the mold has a recess 67. The recess 67 defines a surface inside the mold corresponding to the surface of an acoustic transducer that has been previously covered by its own protective casing. After the material 65 has solidified, the assembly comprising the optodes 62a, 62b, the flange 64, and the molded material 65 is removed from the mold. The recess 67 allows a hollow cavity to be formed in the molded material between the optodes 62a and 62b. The method includes an additional step of introducing the transducer 65 into the hollow cavity previously formed in the polymerized material. After the ultrasonic transducer has been inserted into the hollow cavity, it can be mechanically attached to the flange 64, which holds the optodes 62a and 62b.This embodiment is preferred because it allows the transducer to be integrated after it has been previously tested.

[0036] There figure 7C represents a similar embodiment to the embodiment shown on the figure 7A Optodes 62a and 62b are inclined relative to the longitudinal Z axis, which corresponds to the longitudinal axis of the ultrasound transducer. The inclination angle can, for example, reach 20°. Such a configuration is particularly suitable when a cancerous tumor, or any other area of ​​interest, is located in a rounded part of the body, such as a breast or the neck.

[0037] There figure 8This is a perspective view of a preferred embodiment in which a flange 70 is connected to an optode 71. A groove 72 extends along a lateral face of the optode 71, parallel to the longitudinal axis Z, i.e., perpendicular to the front face. The cross-section of the groove can describe various shapes, for example, a square, a rhombus, or a rounded cross-section. The flange 70 has an extension portion, extending parallel to the longitudinal axis Z, parallel to the groove 72. The flange 70 also has a protrusion for providing a mechanical connection with the optode. The shape of the protrusion can vary, depending on the cross-section of the groove 72, such that the flange can slide along the groove, along the longitudinal axis Z, with the protrusion engaged in the groove. The flange is held fixed along the elevation direction Y. The flange 70 is fixed to the optode by means of a screw 74.An oblong through-hole 73 is provided in the flange to allow adjustment of the optode's position in the longitudinal direction. A second flange is similarly fixed to an opposite lateral face of the optode 71. Thus, all degrees of freedom are constrained, except for a slight adjustment of the optode's translation along the longitudinal Z direction. This adjustment in the longitudinal direction allows for precise positioning of the optode front faces, and of any ultrasonic transducer, in the desired position. When the optode front faces are slightly recessed from the mold bottom, a thin layer of protective material can be placed between the front faces and the mold bottom. This layer should preferably be removed at the end of the molding process.When all the components, held by the flange, are positioned as desired, screw 74 (or other means of fastening) is tightened.

[0038] There figure 9 illustrates the main steps in a manufacturing process for the distal end of a probe, as previously described, bearing in mind that obtaining a complete probe involves further manufacturing steps. Probe manufacturing includes certain steps 81 to 89 listed below. Step 82 relates only to the embodiment described in connection with the figures 7A And 7C . Assembly step 88 only concerns the embodiment described in connection with the figure 7B . Step 81: Assembly of the optodes with the flanges; Step 82: Assembly of the ultrasonic transducer with the flanges; Step 83: Positioning of the optodes and the ultrasonic transducer, then tightening of the screws; Step 84: Placement of the assembled optodes in the mold, and temporary attachment of the mold to the flanges; Step 85: Filling of the mold with a biocompatible protective material, for example, a polymer, and polymerization; Step 86: Removal of the mold; Step 87: Insertion of the assembly, coated with the polymer protection, into the probe cover; Step 88: Insertion of the ultrasonic transducer into the hollow cavity in the polymer; Step 89: Securing the assembly in the front cover of the probe.

Claims

1. Portable bimodal probe, intended to be applied against a biological tissue to be examined, the probe comprising: - an ultrasonic transducer (34, 63), configured to emit ultrasonic waves into the tissue and to receive ultrasonic waves reflected by the tissue, the transducer extending along a transverse axis; - at least two optodes (32, 60, 62a, 62b), disposed on either side of the transverse axis, such that the transducer extends between the two optodes; - each optode comprising a housing (52, 61), the housing comprising: • a light emitter (31) configured to emit at least one light wave toward the tissue; • and an optical detector (32) configured to detect a light wave scattered by the tissue, the optical detector having a detection surface (53, 63a, 63b) formed of a semiconductor material; the bimodal probe being such that: • the optical detector of each optode is a single photon detector; • the housing of each optode includes an electronic acquisition circuit (54), connected to the optical detector, and configured to count a quantity of detected photons as a function of time; - the optodes are arranged such that at least one light emitter and at least one optical detector are disposed on opposite sides of the transducer.

2. Bimodal probe according to claim 1, wherein at least one light emitter is a laser source or a light-emitting diode.

3. A bimodal probe according to any of the preceding claims, wherein an optode comprises a plurality of light emitters, each light emitter being configured to emit light at a wavelength different from that of another light emitter of the optode.

4. A bimodal probe according to claim 1, wherein at least one optode is housed in a housing, the housing having a front face defining an aperture, the detection surface being set back with respect to the front face, the aperture allowing light to be transmitted to or from the optode.

5. A bimodal probe according to claim 4, wherein at least one optode comprises a transparent plate (51, 64a, 64b) extending across the aperture, such that when the bimodal probe is applied against tissue, the transparent plate is placed in contact with the tissue.

6. Bimodal probe according to claim 5, wherein at least one optode comprises a plurality of optical detectors, emerging set back from a single front face, the front face defining an aperture, the optode comprising as many transparent plates as there are optical detectors, each transparent plate being spaced apart from another transparent plate.

7. Bimodal probe according to claim 1, comprising several light emitters and several optical detectors, such that: - the light emitters are aligned parallel to the transverse axis (X); - the optical detectors are aligned parallel to the transverse axis.

8. Bimodal probe according to claim 7, wherein the light emitters and / or optical detectors are distributed in a matrix array.

9. Bimodal probe according to claim 1, comprising several light emitters and several optical detectors, the bimodal probe being such that the distances between an optical detector and light emitters vary between 1 mm and 80 mm.

10. Bimodal probe according to claim 1, wherein the ultrasonic transducer is delimited by an outer perimeter, the distance between the outer perimeter of the ultrasonic transducer and each optical detector being between 0.5 mm and 20 mm.

11. A bimodal probe according to claim 1, wherein at least one optode is housed in a housing (52, 61), the housing having a front face defining an aperture, the aperture allowing light to be transmitted to or from the optode, and wherein the housing has a side face perpendicular to the front face, the side face having a groove (72) extending perpendicular to the front face.

12. Bimodal probe according to claim 11, wherein each optode is kept securely fastened with the acoustic transducer by a flange (64, 70), the flange being fixed to at least two optodes ( ), arranged on either side of the transducer, by a fixing means (74) engaged in the groove (72) of each of them.

13. Bimodal probe according to claim 12, wherein the fixing means allows the position of each optode to be adjusted by translating the flange in each groove by a distance of between 1 mm and 2 mm.

14. Method of manufacturing a bimodal probe according to any of claims 11 to 13, using optodes having a transparent plate extending at the front face, the method comprising the following steps: - assembling optodes (62a, 62b) by means of a flange (64), the flange connecting two opposite optodes of the assembly, the flange being configured to be translated in grooves made in the housings of said opposite optodes; - placing the assembly in a mold (61), the mold having a surface forming a bottom, such that the transparent plate of each optode is applied against the bottom of the mold; - filling the mold with a polymerisable biocompatible material (65) such that the material extends around the assembly; - polymerising the biocompatible material; - removing the assembly from the mold, such that the biocompatible material forms a shell around the assembly, the removed assembly forming a distal end (35) of the probe; - attaching the distal end of the probe to a probe cover (36, 37).

15. Method of manufacturing according to claim 14, wherein the bottom of the mold has a recess (67), the recess being formed such that: - when the transparent plate of each optode is applied against the bottom of the mold, the recess lies between at least two optodes; - upon removal of the assembly from the mold, the recess in the mold releases a hollow cavity in the biocompatible material; the method being such that after removal of the assembly, the method includes inserting an ultrasonic transducer (63) into the hollow cavity, the ultrasonic transducer having been previously covered with a protective envelope.

16. Method of according to claim 15, in which an ultrasonic transducer (63) is connected to the flanges prior to filling the mold, the transducer forming part of the assembly.