Sensor assembly for monitoring a bladder of a subject

Abstract

There is provided a sensor assembly (200) for monitoring a bladder (15) of a subject (10). The sensor assembly (200) comprises a carrier structure (242) and a plurality of ultrasound transducers (231-234) for emitting and detecting ultrasound signals, wherein the ultrasound transducers (231-234) are coupled to the carrier structure (242), and face in at least two different directions (U1-U4). The sensor assembly (200) further comprises a plurality of electrical connectors (238) for transmitting electrical signals between a data logger (120) and the ultrasound transducers (231-234) and a flexible circuit (240) electrically connecting the ultrasound transducers (231-234) to the electrical connectors (238).

Description

[0001] SENSOR ASSEMBLY FOR MONITORING A BLADDER OF A SUBJECT

[0002] FIELD OF INVENTION

[0003] The present disclosure relates to a sensor assembly, a medical device, a method, and a flexible circuit for monitoring a bladder of a subject.

[0004] BACKGROUND

[0005] The urinary bladder is part of the urinary system and performs a critical clinical function in humans and other mammals. It collects and stores urine, a waste product of the human or animal body, before that urine is expelled by urination.

[0006] Urination may change, and such changes may be a sign of a urinary condition or a wider urological condition. Changes in urination may include increases or decreases in frequency of urination, increases or decreases in volume expelled during urination, uncontrolled or involuntary urination, referred to as urinary incontinence, or by changes in how the urge to urinate is felt. These changes may be clinically significant, indicating, for example, a voiding dysfunction, infection, or, in males, an enlarged prostate. In humans, at least, such changes can be a source of embarrassment and discomfort.

[0007] Conventional ways of investigating urinary bladder function and urination are unsuitable for long-term monitoring and are either uncomfortable and highly invasive or require careful management. For example, in urodynamic testing, a patient may be required to keep a constant diary of urinary events and may be required to use an in-toilet device for measuring expelled volumes of urine. Such solutions are cumbersome, difficult to manage, and subject to error in how the diary is kept or how the device is used.

[0008] For voiding dysfunction, some specific solutions exist for children. These solutions use external ultrasound sensors fixed to the subject’s skin to determine when a volume of urine in the bladder exceeds a particular threshold and to alert the subj ect that it is time to urinate. Such solutions cannot be used in adults, due to significant differences in body and bladder shape. Such solutions are also highly dependent on posture of the subject.

[0009] SUMMARY

[0010] According to a first aspect, there is provided a sensor assembly for in vivo monitoring of a bladder of a subject. The sensor assembly comprises a carrier structure; a plurality of ultrasound transducers for emitting and detecting ultrasound signals and wherein the ultrasound transducers are coupled to the carrier structure and face in at least two different directions; a plurality of electrical connectors for transmitting electrical signals between a data logger and the ultrasound transducers; and a flexible circuit electrically connecting the ultrasound transducers to the electrical connectors.

[0011] Such a sensor assembly can be used to monitor urine flow in a different way to other techniques, such as those described above. Specifically, such a sensor assembly may enable dimensions of the bladder, which may be referred to as the urinary bladder, of the subject to be determined in vivo and relatively non-invasively. Enabling such measurements can provide improved insight into urination of the subject in a less cumbersome manner, which in turn can improve diagnosis by a physician.

[0012] The sensor assembly utilizes a single flexible circuit to connect multiple ultrasound transducers to corresponding electrical connectors. Thus, there is a single structure or body that provides the electrical connection between the ultrasound transducers and electrical connectors along which electrical signals relating to transmitted or received ultrasound signals can be communicated. The construction of the sensor assembly enables its use in in vivo settings. Particularly, the use of a flexible circuit to connect ultrasound transducers to electrical connectors allows for ease of manufacturing of the sensor assembly. This is because the ultrasound transducers and connectors can be attached to the flexible circuit, and the combined assembly can be mounted to the carrier structure. This ensures that the assembly is correctly manufactured, and also enables a repeatable and straightforward manufacturing process.

[0013] Because the flexible circuit is able to flex, it can adopt a particular shape, allowing the ultrasound transducers to be positioned in the at least two different directions. The flexible circuit, when being flexed to provide a particular shape or positioning of the ultrasound transducers, may become more rigid due to the shaping. Such rigidity may be useful in ensuring that the positioning of the ultrasound transducers is maintained on the carrier structure. In contrast, if the ultrasound transducers were directly connected to connectors, the flexibility of the connectors may dislodge the ultrasound transducers or cause disconnection.

[0014] Due to its thin profile, using a flexible circuit to connect to the ultrasound transducers may be particularly useful for where space is at a premium, such as in a sensor assembly for use in vivo, such as to measure dimensions of a bladder. For example, a flexible circuit may have a thickness of between 10 and 40 micrometres, making it particularly useful within small, minimally-invasive sensing assemblies.

[0015] A short length of flexible circuit may be used. The flexible circuit may be substantially shorter than the connectors to which it connects. For example, the flexible circuit may have a length dimension that is at least 5 times, 10 times, 20 times, or 50 times shorter than a length of the electrical connectors. The flexible circuit may have a length dimension that is less than 10 mm, less than 100 mm, or less than 500 mm. The electrical connectors may be referred to as elongate. The flexible circuit, transducers, and carrier structure may form a tip of the sensor assembly, with a casing and the electrical connectors being provided along a substantial length of the remainder of the sensor assembly.

[0016] The electrical connectors may comprise a plurality of wires or electrical filaments. The electrical connectors may be provided as part of one or more cables, which may be one or more coaxial cables. The cables may have single cores, or may be multi-core cables, and may include one or more screens.

[0017] An ultrasound transducer, which may be referred to as an ultrasonic transducer, may act as both an emitter and a detector, which may be referred to as transmitters and receivers. The ultrasound transducer may be configured to emit an ultrasound signal and to detect a reflection of the ultrasound signal from a surface. The signal may reflect off a wall of the bladder. The ultrasound signal may be emitted by exciting a piezoelectric element or a capacitive diaphragm using one or more electrical signals. The reflected ultrasound signal may be detected because a piezoelectric element or capacitive diaphragm is excited by the reflected ultrasound signal, resulting in an electrical signal. The electrical signals may be transmitted to and from the ultrasound transducer to the data logger. One or more modules within the data logger may be configured to determine a time between emission and detection, and may therefore be able to determine a distance between the ultrasound transducer and a surface from which the signal is reflected. Such distances may be used to determine dimensions of the bladder. A plurality of reflected signals may be received at the ultrasound transducer, and the modules within the data logger may be configured to determine which reflection is a direct reflection from a surface of interest.

[0018] An ultrasound transducer may be formed by providing at least two electrodes on a piezoelectric element, with one electrode representing a ground plane. Accordingly, a piezoelectric element comprising more than two electrodes may form a plurality of ultrasound transducers. Alternatively, each ultrasound transducer may be formed from a separate piezoelectric element.

[0019] Additionally, or alternatively, the ultrasound transducer may be a microscale ultrasound transducer or a nanoscale ultrasound transducer. The ultrasound transducer may be manufactured using micro-machining. The ultrasound transducer may be a MEMS transducer, such as a capacitive micromachined ultrasonic transducer (CMUT) or a piezoelectric micromachined ultrasonic transducer (PMUT). MEMS transducers may have contacts on at least one surface for electrical connection to an electrical connector. The flexible circuit may connect to these contacts.

[0020] The sensor assembly, or at least a portion of the sensor assembly, may be for implanting within the subject outside the urinary bladder of the subject, within a wall of the urinary bladder, or within the urinary bladder. When implanted outside the urinary bladder, the sensor assembly may be adhered or otherwise attached, such as by using a suture, to the urinary bladder. When implanted inside the urinary bladder, the sensor assembly may be attached to the urinary bladder, such as by suturing the assembly to a wall of the bladder, or alternatively may be left unattached within the internal volume of the bladder.

[0021] By facing in two different directions, it is meant that the ultrasound transducers are positioned such that ultrasound signals by the ultrasound transducers are emitted in at least the two different directions and are also received in those two different directions, albeit by opposite ultrasound transducers. For example, the plurality of ultrasound transducers may comprise a first ultrasound transducer facing in a first direction and a second ultrasound transducer facing in a second, different direction. The first direction and second direction may be along a common axis, which may be a radial axis of the sensor assembly, which results in the first direction being opposite to the first direction. The first direction and second direction may be along different axes. In examples, at least four ultrasound transducers may be provided, with each ultrasound transducer facing in a different direction. The four ultrasound transducers may be positioned along two different axes, which may be perpendicular. The ultrasound transducers of the plurality of ultrasound transducers, or at least some of the ultrasound transducers, may be longitudinally aligned.

[0022] The flexible circuit may be curved around at least part of the carrier structure. Curving the flexible circuit may provide some rigidity and stability. Curving the flexible circuit may also enable the single flexible circuit to connect to multiple ultrasound transducers and for those ultrasound transducers to be precisely positioned.

[0023] The flexible circuit may be said to be flexed, shaped, or bent around the carrier structure. For example, the flexible circuit may be shaped to have a cross-section in the shape of part or all of a circle or ellipse, thereby forming part or all of a tube along some or all of its length. The flexible circuit may be curved into the shape it adopts within the sensor assembly prior or during positioning of the ultrasound transducers.

[0024] A main portion or section of the flexible circuit may be curved. The main portion may be a portion to which the connectors connect. The main portion may be rectangular, when laid flat. The main portion may have a width dimension forming a circumference or perimeter of the flexible circuit when forming a tube or curved structure, and the width dimension may be greater than a length dimension. In other words, the flexible circuit or at least the main, rectangular portion that forms the tube or curved structure, may be wider than it is long when laid flat, ensuring that only a short region of the sensor assembly is covered by the rigid structure formed by the flexible circuit when rolled.

[0025] The flexible circuit may connect to the ultrasound transducers and other sensors at the main portion, and / or the flexible circuit may have a plurality of fingers or projections extending from the main portion for connecting to individual ultrasound transducers or to a collection of ultrasound transducers, and, optionally, to other sensors within the sensor assembly such as pressure sensors. The fingers may be curved to a lesser extent or may remain substantially flat in the sensor assembly. Each finger may correspond to a transducer or sensor provided within the sensor assembly or alternatively each finger may correspond to a plurality of related transducers or sensors, such as those within an array.

[0026] The flexible circuit may form a tube. Rolling a single flexible circuit into a tube may provide stability and rigidity within the sensor assembly.

[0027] The main portion of the flexible circuit may form the tube. Two ends of the main portion of the flexible circuit more generally may be connected to form the tube. The connection may be formed using an adhesive and / or a flexible substrate of the flexible circuit may be fused at the ends to form the tube.

[0028] As a tube, the flexible circuit surrounds a volume, and may have any cross-sectional shape that encompasses the volume. The tube may have a circular cross-section, an elliptical cross-section, or may have a cross-section of another shape. Having an elliptical crosssection may be useful as elliptical cross-sections can aid in preventing encrustation of urine crystals on the surface of the flexible circuit.

[0029] The flexible circuit may have a plurality of conductive traces that connect to electrodes of respective ultrasound transducers of the plurality of ultrasound transducers.

[0030] In some examples, the ultrasound transducers may be formed from piezoelectric elements, and in these examples, the ultrasound transducers may comprise an electrode on an outward-facing surface of a piezoelectric element. The ultrasound transducers may also comprise a ground plane on an inward-facing surface of the piezoelectric element. The outward-facing surface may be considered to be the surface pointing in the direction in which the ultrasound transducer faces. The outward-facing surface may be a surface facing radially outwardly, away from the carrier structure. The inward-facing surface may face the carrier structure. The ultrasound transducer may be coupled to the carrier structure at the inwardly-facing surface of the piezoelectric element. In examples, each ultrasound transducer may comprise an electrode on an outward-facing surface of a respective piezoelectric element. In other examples, some ultrasound transducers comprise respective electrodes on the same outward-facing surface of a piezoelectric element. In other words, multiple ultrasound transducers may be provided on the same outward-facing surface of a piezoelectric element. The ground plane may be specific to each ultrasound transducer or may be shared between two or more ultrasound transducers in such a configuration.

[0031] Where MEMS ultrasound transducers are used, a port for receiving or transmitting ultrasound signals may be provided on an outwardly-facing surface and the transducer may be coupled to the carrier structure at an inwardly-facing surface. The MEMS ultrasound transducer may be a bottom-port transducer, such that the port and electrical contacts are provided on the same surface, or a top-port transducer, where the port and electrical contacts are provided on opposing surfaces. In either case, the port may be provided on the outwardly-facing surface of the transducer when provided within the sensor assembly.

[0032] In either case, each ultrasound transducer may comprise a contact or electrode to which the flexible circuit connects. The electrodes may be for transmitting or receiving electrical signals corresponding to ultrasound signals. The ultrasound signals may be ultrasound signals received at the ultrasound transducer or those to be emitted by the ultrasound transducer. The flexible circuit may connect to the electrode or contact of each ultrasound transducer. Each conductive trace of the plurality of conductive traces may correspond to a particular ultrasound transducer. The conductive traces may extend along the flexible circuit to connect the electrode to an electrical connector. This may facilitate transmission of electrical signals to or from the ultrasound transducers.

[0033] Each ultrasound transducer may also comprise an electrode or contact forming a ground or ground plane. A connection to the ground plane may be formed, which may be referred to as the ground connection. The flexible circuit may form the ground connection by connecting directly or indirectly to the electrode or contact forming the ground plane of each ultrasound transducer, or the ground connection may be formed by other means, such as via the carrier structure or a conductive path provided on the carrier structure connecting to an electrical connector.

[0034] At least a portion of the carrier structure may be electrically conductive, such as a metallized surface, a metallic insert, a conductive tape, or the carrier structure may be at least partially formed from a conductive material. In some examples, the carrier structure may be substantially or entirely formed from a conductive material, or at least a main body of the carrier structure, that provides the surface to which the ultrasound transducers attach, may be formed from the conductive material. The ultrasound transducers and the carrier structure may be coupled together using a conductive adhesive to facilitate the ground connection.

[0035] The flexible circuit may comprise at least one further conductive trace that is connected to the at least the portion of the carrier structure that is electrically conductive. The at least one further conductive trace thereby forms part of the electrically conductive path between the ground planes and the electrical connector. The at least one further conductive trace may be a single conductive trace that connects the carrier structure and an electrical connector. A further conductive trace may electrically connect to the ground planes of all or a subset of the ultrasound transducers. This may enable the flexible circuit to also connect to ground electrical connections such as screens of coaxial cables.

[0036] Alternatively, the ground connection may be formed by other means, such as by the electrically conductive carrier structure or portion thereof forming an electrical connection with an electrical connector directly rather than via the flexible circuit. In other words, the at least the portion of the carrier structure that is electrically conductive may be directly connected to the electrical connector. Each of the conductive traces may connect to respective components or elements at an inner surface of the flexible circuit, when the flexible circuit is curved around the carrier structure.

[0037] Conductive traces may comprise conductive tape applied to a flexible substrate or conductive ink printed on a flexible substrate. The conductive traces may be provided on a single surface of the flexible circuit, across different surfaces of the flexible circuit, or within different layers of the flexible circuit. Conductive traces may connect to the ultrasound transducers via first contacts or pads, and to the electrical connectors via second contacts or pads. The contacts may be positioned at respective ends of the conductive traces. The conductive traces that connect to electrodes may extend from the main body of the flexible circuit, where they connect to the electrical connectors, along the fingers of the flexible circuit, where the connect to the ultrasound transducers.

[0038] The sensor assembly may further comprise a pressure sensor, wherein the flexible circuit electrically connects the pressure sensor to a corresponding electrical connector. Including a pressure sensor in addition to the ultrasound transducers allows for more comprehensive monitoring of the bladder, providing both dimensional and pressure data using a single sensor assembly. By utilizing the same flexible circuit, the manufacture of the sensor assembly is further improved, as the same flexible circuit is therefore used to connect the pressure sensors and the ultrasound transducers to electrical cabling.

[0039] The pressure sensor may be attached to the carrier structure. The pressure sensor may be attached to or close to a distal end of the carrier structure. The ultrasound transducers may be provided longitudinally between the pressure sensor and the electrical connectors. In such an arrangement, the use of the flexible circuit to connect to the pressure sensor avoids having to run an additional connector past the ultrasound transducers to the pressure sensor.

[0040] The flexible circuit may comprise a projection or finger for electrically connecting to the pressure sensor. The projection for connecting to the pressure sensor may be longer than the fingers for connecting to ultrasound transducers. The projection may pass between two ultrasound transducers along the carrier structure, or may otherwise bypass or circumvent at least one of the ultrasound transducers. The projection may bypass an ultrasound transducer by having an aperture that extends around the ultrasound transducer or a portion of the carrier structure to which the ultrasound transducer is mounted. In some examples, the pressure sensor may face in a different direction to the ultrasound transducers. This may facilitate using a linear projection for connecting to the pressure sensor, rather than incorporating a curve to avoid one or more of the ultrasound sensors.

[0041] The pressure sensor may comprise a MEMS sensor. The pressure sensor may be a first pressure sensor, and additional pressure sensors may be provided. For example, a second pressure sensor may be provided comprising a reference pressure sensor. The first pressure sensor may be configured for insertion into the urinary bladder and the second pressure sensor may be configured for insertion into an abdominal region of the subject. The pressure sensor may be covered by a biocompatible film, layer, or coating. The biocompatible coating may be a conformable coating.

[0042] One or more conductive traces and corresponding contacts may be provided on the projection for connecting to the pressure sensor. In some examples, a plurality of conductive traces and corresponding contacts may be provided for connecting to the pressure sensor. For example, four conductive traces may be provided, with contacts at respective ends of each conductive trace for connecting to the pressure sensor and the electrical connectors respectively. The conductive traces may extend along a length of the flexible circuit, such that the contacts are also provided at opposing ends of the flexible circuit.

[0043] The plurality of ultrasound transducers may comprise at least a first ultrasound transducer along a first radial axis of the sensor assembly, at least a second ultrasound transducer along a second radial axis of the sensor assembly that is perpendicular to the first radial axis, and a third ultrasound transducer along a longitudinal axis of the sensor assembly. This arrangement of ultrasound transducers enables measurement of the bladder in three dimensions, providing a more accurate assessment of bladder volume and shape.

[0044] Two first ultrasound transducers may be provided, facing in opposing directions along the first radial axis. Two second ultrasound transducers may be provided, facing in opposing directions along the second radial axis. Accordingly, a total of five ultrasound transducers may be provided, with two along each radial axis and one along the longitudinal axis. This may enable measurements of the bladder to be performed in three dimensions.

[0045] In such arrangements, the flexible circuit may connect to the first and second ultrasound transducers as described above, and may include a projection for connecting to the third ultrasound transducer. The projection may pass between or otherwise bypass or circumvent the first and second ultrasound transducers, as described above in relation to the pressure sensor. In some examples, such a third ultrasound transducer may be included as well as a pressure sensor. The same projection may be used to extend to both the third ultrasound transducer and the pressure sensor, or the flexible circuit may have two projections, with one extending to the third ultrasound transducer and another to the pressure sensor.

[0046] The plurality of ultrasound transducers may form at least two arrays that point in the at least two different directions. Arrays of ultrasound transducers may allow for improved resolution and more detailed imaging of the bladder in multiple directions. Arrays of ultrasound transducers may also enable beamforming to be performed, providing greater flexibility in how the sensor assembly may be used, especially in an environment where the surfaces from which the ultrasound signals are to be reflected may change orientation or position relative to the sensor assembly and / or where the sensor assembly may move relative to the surfaces.

[0047] Each array may be formed on a single piezoelectric element or may be formed across a plurality of longitudinally aligned piezoelectric elements.

[0048] Where ultrasound arrays are formed, each finger of the flexible circuit may correspond to a respective array and the fingers may extend between the arrays. The fingers may extend between piezoelectric elements. The fingers may electrically connect to the ultrasound transducers of a corresponding array.

[0049] The sensor assembly may comprise a casing that houses the plurality of ultrasound transducers, wherein the casing is formed of an acoustically transmissive material. An acoustically transmissive casing protects the ultrasound transducers while allowing efficient transmission of ultrasound signals, improving the overall performance and durability of the sensor assembly.

[0050] The casing may surround the ultrasound transducers. The casing may have a wall, and the wall may define an internal volume of the casing. The wall may separate an external environment and an internal volume of the casing. The ultrasound transducers may be provided within the internal volume of the casing. The ultrasound transducers may be housed within a sealed part of the casing or within an unsealed part of the casing. The casing may alternatively be referred to as a housing. The casing may comprise a catheter having a wall defining a lumen. The lumen may be closed at a distal end or close to the distal end by a seal. The ultrasound transducers may be provided within the lumen, either within a sealed part of the lumen or beyond the sealed part of the lumen. Where the ultrasound transducers are sealed within the casing, the casing may be filled with a liquid material for reducing losses in ultrasound transmission. In other words, the material may provide a suitable acoustic impedance to ensure efficient ultrasound transmission between the ultrasound transducers and the casing or acoustic windows. The casing may be sized so that the gap between the tube and window(s) is relatively small.

[0051] In some examples, the casing may comprise a plurality of acoustic windows that are aligned with the ultrasound transducers for transmitting ultrasound signals from the ultrasound transducers into and out of the casing. The acoustic windows may therefore face in the at least two different directions. There may be provided an acoustic window for each ultrasound transducer or an acoustic window may correspond to a plurality of ultrasound transducers. The acoustic windows may enable transmission of ultrasound into and out of the casing. Where acoustic windows are provided, the casing may be configured to prevent transmission of ultrasound signals.

[0052] To improve how the ultrasound signals are transmitted, the acoustic windows may be configured to direct or collimate ultrasound signals. The acoustic windows may be shaped as acoustic lenses.

[0053] The ultrasound transducers may be covered with a biocompatible coating. The biocompatible coating may be a conformable coating. A biocompatible coating may ensure the safety and compatibility of the sensor assembly for in vivo use. The biocompatible coating, which may be referred to as a biocompatible layer or a biocompatible film, may comprise one selected from: parylene; silicon oxide; titanium oxide; and diamond-like- carbon. The coating may be a thin film, having a microscale or nanoscale thickness. The biocompatible coating may be for preventing or resisting corrosion of the transducer by tissue or body fluid. The biocompatible coating may be for resisting or preventing fouling of a surface of the transducer by tissue or body fluid. The biocompatible coating may be for preventing materials forming the ultrasound transducers from coming into contact with tissue or body fluid. The ultrasound transducers may be covered with the biocompatible coating when they are not sealed within a casing. For example, the ultrasound transducers may be mounted on an outside of or externally to a casing. The casing may form the carrier structure. The flexible circuit may pass through the casing. The flexible circuit may also be covered by the biocompatible coating.

[0054] The ultrasound transducer may have an anti -reflective coating. The anti -reflective coating may improve transducer efficiency and may reduce reflections from the ultrasound transducer being received and interpreted as reflections from the bladder. A coating may be anti -reflective and biocompatible.

[0055] The carrier structure may comprise an insert for attenuating ultrasound signals, wherein the insert is provided between the ultrasound transducers. The ultrasound transducers may radiate ultrasound signals both inwardly and outwardly. The outwardly radiated signals are those that will reflect from a surface and whose reflections will be detected by the ultrasound transducers. The insert may attenuate inwardly radiating ultrasound signals. This may reduce unwanted excitations of the ultrasound transducers, which may otherwise cause anomalous readings. In turn, this reduction in interference, unwanted reflections, and / or cross-talk may improve the accuracy of measurements made using the ultrasound transducers.

[0056] The insert may be formed from a non-conductive material. The insert may be formed from a material that absorbs ultrasound signals and / or a material that is configured to scatter at least some incident ultrasound signals.

[0057] According to a second aspect, there is provided a medical device comprising a sensor assembly as described above and a data logger connected to the electrical connectors.

[0058] The data logger may be positioned outside of the subject. The data logger may be worn by the subject, by being attached to the skin of the subject or by being incorporated into a garment worn by the subject. The data logger may therefore be referred to as a wearable data logger. The data logger may be implantable. The sensor assembly may be implantable. A catheter may extend between the sensor assembly and the data logger.

[0059] According to a third aspect, there is provided a method for assembling a sensor assembly as described above. The method comprises: providing a carrier structure, a flexible circuit, a plurality of ultrasound transducers, and a plurality of electrical connectors; while the flexible circuit is laid flat, electrically connecting the electrical connectors to the flexible circuit and the ultrasound transducers to the flexible circuit; and mounting the ultrasound transducers on the carrier structure.

[0060] This method allows for efficient and accurate assembly of the sensor assembly, ensuring proper electrical connections before final mounting of the components.

[0061] Mounting the ultrasound transducers may comprise positioning the ultrasound transducers to face in the at least two different directions, such as mounting a first ultrasound transducer to face in a first direction and mounting a second ultrasound transducer to face in a second direction. Mounting the ultrasound transducers may comprise adhering or otherwise fixing the ultrasound transducers to the carrier structure. The ultrasound transducers may be fixed using a conductive adhesive.

[0062] The method may comprise, prior to mounting the ultrasound transducers on the carrier structure, flexing the flexible circuit to curve around the carrier structure. Flexing the flexible circuit before mounting the ultrasound transducers allows for improved positioning and ensures a secure fit around the carrier structure.

[0063] The method may comprise, prior to mounting the ultrasound transducers on the carrier structure, rolling the flexible circuit to form a tube. Rolling the flexible circuit into a tube before mounting the ultrasound transducers provides additional structural support and allows for a more compact sensor assembly design.

[0064] According to a fourth aspect, there is provided flexible circuit for use in a sensor assembly as described above. The flexible circuit may be specifically designed to accommodate the specific arrangement of ultrasound transducers and electrical connections for the bladder monitoring sensor assembly, enabling efficient manufacturing and assembly. The flexible circuit may have any features as described above. The flexible circuit may comprise a first conductive layer and a second conductive layer, wherein the first conductive layer comprises a plurality of conductive traces, and wherein part of the conductive traces branch from a main body of the flexible circuit.

[0065] The techniques described herein may be used within a subject for monitoring of other organs or for other uses where ultrasound measurement is desirable. While the above examples described herein are described for circumstances where the subject is human, the subject may alternatively be an animal having a urinary bladder. Specifically, the subject may be a mammal having a urinary bladder, such as a dog or a horse. BRIEF DESCRIPTION OF FIGURES

[0066] Aspects of the disclosure will be described, by way of example, with reference to the following drawings, in which:

[0067] Fig. 1 is a schematic diagram of a system for monitoring a bladder of a subject.

[0068] Fig. 2 is a longitudinal section of a first sensor assembly.

[0069] Fig. 3 is a cross section of the first sensor assembly.

[0070] Fig. 4A is a plan view of an upper surface of a piezoelectric element of the first sensor assembly and Fig. 4B is a plan view of a lower surface of a piezoelectric element of the first sensor assembly.

[0071] Fig. 5 shows an arrangement of conductive traces of a flexible circuit of the first sensor assembly.

[0072] Fig. 6 is a broken longitudinal section of a second sensor assembly.

[0073] Fig. 7 is a cross section of the second sensor assembly.

[0074] Fig. 8 shows an arrangement of conductive traces of a flexible circuit of the second sensor assembly.

[0075] Fig. 9 is a longitudinal section of a third sensor assembly.

[0076] Fig. 10 is a cross section of the third sensor assembly.

[0077] Fig. 11 shows an arrangement of conductive traces of a flexible circuit of the third sensor assembly.

[0078] Fig. 12 is a longitudinal section of a fourth sensor assembly.

[0079] Fig. 13 is a longitudinal section of a fifth sensor assembly.

[0080] Fig. 14 is a flow chart illustrating a method for assembling a sensor assembly.

[0081] Common reference numerals are used throughout the figures to indicate similar features. DETAILED DESCRIPTION

[0082] The present disclosure describes a sensor assembly designed for in vivo monitoring of a bladder of a subject. The sensor assembly includes a carrier structure and a plurality of ultrasound transducers. These ultrasound transducers are coupled to the carrier structure and are oriented to emit and detect ultrasound signals in at least two different directions. The sensor assembly also includes a plurality of electrical connectors that transmit electrical signals between a data logger and the ultrasound transducers. A flexible circuit is incorporated in the sensor assembly to electrically connect the ultrasound transducers to the electrical connectors. This configuration allows for efficient manufacturing of the sensor assembly and ensures accurate positioning of the ultrasound transducers. The flexible circuit, due to its ability to flex and adopt a particular shape, enables the ultrasound transducers to be positioned in the desired directions. The sensor assembly may also include a pressure sensor, which is electrically connected to a corresponding electrical connector via the flexible circuit. This sensor assembly can be used to monitor the bladder in a non-invasive manner, providing valuable insights into urination patterns of the subject.

[0083] To provide context to the techniques described herein, Fig. 1 provides an overview of a system 100 for monitoring a urinary bladder 15 of a subject 10. The subject 10 is a human subject in this example. A urinary system 12 of the subject 10 is schematically depicted in Fig. 1, including a pair of kidneys 13, ureters 14, the urinary bladder 15 and a urethra 16.

[0084] A physician 20 may desire to monitor the urinary bladder 15 to understand how urine flows into and / or out of the urinary bladder 15. The system 100 is used for such monitoring. The system 100 includes a plurality of sensors 110. The plurality of sensors 110 form part of a single sensor assembly 111. The sensor assembly 111 has been implanted into the subject 10, and is positioned within an internal volume of the urinary bladder 15.

[0085] The arrangement of sensors of the sensor assembly 111 are not visible in Fig. 1, but example sensor assemblies are described below in more detail. The sensor assembly 111 includes at least a plurality of ultrasound sensors facing in two different directions, and may also include a pressure sensor configured to detect a pressure in the bladder. In examples, the ultrasound sensors may face in three different directions and / or may be arranged to enable measurement of two or three dimensions of a urinary bladder. The sensor assembly 111 is in communication with one or more data modules 120 via a wired connection 125. The one or more data modules 120 depicted in Fig. 1 include a data collection module 121 and a data analysis module 122. The data collection module 121 receives bladder data 115 from the sensor assembly 111. The bladder data 115 may include a combination of measurements which may comprise some or all of a first dimension 116, a second dimension 117, and a third dimension 118 of the urinary bladder 15, and a pressure 119 of the urinary bladder 15.

[0086] The data collection module 121 may receive and collate the bladder data 115 from the one or more sensors 110. The bladder data 115 is then provided to the data analysis module 122 for analysis. The data analysis module 122 may determine parameters associated with the urinary bladder 15 based on the bladder data 115. Fig. 1 shows four such parameters: a volume, V, of the urinary bladder, a urine flow rate, Q, a postvoid residual volume, PVR, and a pressure parameter, p, such as average pressure, maximum or minimum pressure, or instantaneous pressure.

[0087] The system 100 includes a data output module 140 in communication with the one or more data modules 120. The data output module 140 receives data from the data analysis module 122, and outputs it to one or more locations. In the example of Fig. 1, the data output module 140 outputs the data to a remote computing system 150. The remote computing system 150 includes a display device 160 and the data received by the remote computing system 150 can be displayed on the display device 160 to allow the physician 20 to view it.

[0088] The system 100 may include data storage 170. The data analysis module 122 may store the parameters it has determined in the data storage 170. The data analysis module 122 may store the bladder data 115 in the data storage 170. The data storage 170 may be local to the data analysis module 122, and so may be stored directly. Alternatively, the data storage 170 may be remote from the data analysis module 122 and so the parameters and / or bladder data 115 may be stored in the data storage 170 by outputting the data via the data output module 140. Alternatively, or additionally, the data collection module 121 may store the bladder data 115 in the data storage 170.

[0089] Figs. 2 to 12 describe different example sensor assemblies that may be used as the sensor assembly 111 in Fig. 1. Turning initially to Figs. 2 and 3, a first sensor assembly 200 is shown. Fig. 2 shows a longitudinal section of the first sensor assembly 200, while Fig. 3 shows a cross-section of the first sensor assembly 200 along the line A-A shown in Fig. 2. The first sensor assembly 200 includes a plurality of ultrasound transducers 231-234, arranged to face in four different directions U1-U4 along two radial axes RAI, RA2 of the assembly 200. This may enable measurement of at least two dimensions of a bladder of a subject, when the sensor assembly is implanted within the subject.

[0090] The first sensor assembly 200 includes a casing 210, formed of an acoustically transmissive material, thereby allowing ultrasound signals to be transmitted between an internal volume 222 of the casing 210 and an external environment 224. The casing 210 has a wall 216 that defines the internal volume 222, separating it from the external environment 224. The casing 210 is closed at a distal end 218 by a distal end seal 220, to prevent urine entering the internal volume 222. The internal volume 222 is filled with a liquid to improve transmission of ultrasound signals by providing a suitable acoustic impedance between the ultrasound transducers 231-234 and the casing 210 to ensure efficient transmission between the two. The liquid may be or may comprise, for example, one of diethylene glycol, propylene glycol, and butanol.

[0091] Within the internal volume 222, the assembly 200 includes four ultrasound transducers 231-234. The ultrasound transducers 231-234 are formed on individual piezoelectric elements, indicated generally as 230. Each ultrasound transducer 231-234 is formed by providing an electrode on an upper surface 235 of the corresponding piezoelectric element 230 and a ground plane on a lower surface 236 of the piezoelectric element. The upper surface faces outwardly, in use, while the lower surface faces inwardly. Although the ultrasound transducers are described as being formed from piezoelectric elements in relation to these figures, other types of ultrasound transducers may be used, such as capacitive ultrasound transducers.

[0092] This arrangement of electrodes and ground plane on the piezoelectric element 230 to form an ultrasound transducer is shown in the plan views shown in Figs. 4A and 4B.

[0093] Fig. 4A shows the upper surface 235 of the piezoelectric element 230, while Fig. 4B shows the lower surface 236. As can be seen in Fig. 4A, an electrode 260 is provided on the upper surface 235 of the piezoelectric element 230. The electrode 260 comprises an electrically conductive layer deposited, printed or otherwise provided on the upper surface 235. The electrode 260 has a circular shape covering part of the upper surface 235, and an electrode tab 261 extends from the circular electrode 260, providing a connection point for an electrical connection. In Fig. 4B, it can be seen that the lower surface 236 is entirely covered by a ground plane 262, comprising an electrically conductive layer printed or otherwise provided on the lower surface 236. In other examples the electrodes and ground planes may be provided in different shapes or configurations to those shown in Figs. 4A and 4B. By providing an electrode and ground plane on the piezoelectric element, an ultrasound transducer is formed. This configuration allows for the generation of ultrasound signals when an electrical potential is applied between the electrode and the ground plane, and a detection of ultrasound signals when an acoustic wave is incident on the transducer. Multiple ultrasound transducers may be formed on a piezoelectric element in other examples, by providing separate electrodes on the upper surface 235.

[0094] Although Fig. 4A shows the electrode being provided only on an upper surface 235 of the electrode, in some examples the electrode may be provided over multiple surfaces, and may, for example, partially overlap onto a side surface of the piezoelectric element.

[0095] Returning to Figs. 2 and 3, two of the four ultrasound transducers are shown in Fig. 2, which are a first ultrasound transducer 231 and a second ultrasound transducer 232. All four ultrasound transducers, including the first and second ultrasound transducers 231, 232 as well as a third ultrasound transducer 233 and a fourth ultrasound transducer 234, can be seen in Fig. 3.

[0096] The ultrasound transducers 231 -234 are mounted on a carrier structure 242 and are oriented to emit and receive ultrasound signals in different directions. The ultrasound transducers are oriented to emit and receive ultrasound signals along two different radial axes RAI, RA2 and in four different directions U1-U4. A first direction U1 and a second direction U2 are aligned along a first radial axis RAI, while a third direction U3 and a fourth direction U4 are aligned along a second radial axis RA2. The first radial axis RAI and second radial axis RA2 are perpendicular to each other.

[0097] The first ultrasound transducer 231 is arranged to emit ultrasound signals in the first direction U1 and to receive ultrasound signals in the second direction U2. The first ultrasound transducer 231 can be therefore said to face in the first direction U 1. The second ultrasound transducer 232 is aligned with the first ultrasound transducer 231 along the first radial axis RAI and emits ultrasound signals in the second direction U2 and receives ultrasound signals in the first direction U 1. The second ultrasound transducer 232 therefore faces in the second direction U2, in an opposite direction to the first ultrasound transducer 231. The third ultrasound transducer 233 emits ultrasound signals in the third direction U3 and receives ultrasound signals in the fourth direction U4. The third ultrasound transducer 233 can be said to face in the third direction U3. The fourth ultrasound transducer 234 is aligned with the third ultrasound transducer 233 along the second radial axis RA2 and emits ultrasound signals in the fourth direction U4 and receives ultrasound signals in the third direction U3. The fourth ultrasound transducer 234 therefore faces in the fourth direction U4, in an opposite direction to the third ultrasound transducer 233.

[0098] While particular directions of emission and detection are described here, it will be appreciated that ultrasound signals propagating in different directions to the first to fourth directions U 1 -U4 in these figures may be emitted or received by the ultrasound transducers. The directions described here are the main directions in which the ultrasound transducers are arranged to emit and receive in, and are therefore the directions along which the dimensions of the bladder are to be determined.

[0099] The carrier structure 242, to which the ultrasound transducers are mounted, has a crossshaped cross-section. The carrier structure 242 is arranged to lie along a longitudinal axis LA of the sensor assembly, and the cross-shaped cross-section is aligned to be symmetrically arranged about the first and second radial axes RAI, RA2. An ultrasound transducer 231-234 is provided on a respective one of each of four arms of the carrier structure 242, so that the ultrasound transducers are arranged to face in the four directions U1-U4.

[0100] The carrier structure 242 comprises an insert 244, which may be referred to as a filling, for attenuating ultrasound signals. The insert 244 is positioned part of the way along the carrier structure 242 between the ultrasound transducers 231-234. The insert 244 is non- conductive and is configured to absorb and / or scatter at least some ultrasound signals that may interfere with the operation of the ultrasound transducers, such as inwardly radiated ultrasound signals. The insert 244 may be formed by drilling through the carrier structure along the axes on which the ultrasound transducers will sit. The holes may then be filled with the material for attenuation to form the insert. The material may be an epoxy material, for example.

[0101] The carrier structure 242 is coupled to the casing so that its position within the internal volume is maintained, although this is not shown in these Figures to preserve clarity. Electrical signals for exciting the piezoelectric elements, so that ultrasound signals are emitted, and electrical signals from the piezoelectric elements being excited by received ultrasound signals are carried by electrical connections to and from a data logger, such as data logger 120 in Fig. 1. The electrical connections in this case comprise coaxial cables 238.

[0102] The coaxial cables 238 connect to the ultrasound transducers via a flexible circuit 240. The flexible circuit 240 is curved around the carrier structure 242, facilitating the positioning of the ultrasound transducers and the electrical connections within the sensor assembly 200. The curvature of the flexible circuit 240 may be determined based on the shape and size of the carrier structure 242, as well as the desired positioning of the ultrasound transducers and the electrical connections.

[0103] The flexible circuit 240 forms a tube within the sensor assembly 200. The tubular shape of the flexible circuit 240 provides a compact and efficient arrangement for the electrical connections within the sensor assembly 200. The tubular shape of the flexible circuit 240 also provides structural support to the ultrasound transducers, helping to maintain their positioning within the sensor assembly 200.

[0104] The flexible circuit 240 aids manufacture, by enabling electrical connections to be formed prior to insertion of the transducers into the sensor assembly. The flexible circuit 240 can be laid flat, and all connections made through it, before being curved, to surround the carrier structure. The flexible circuit 240 is curved and connected at the ends to form the tube, ready for insertion into the casing 210. The ultrasound transducers 231-234 can then be mounted on the carrier structure, and the sensor assembly can be fully assembled.

[0105] The flexible circuit 240, in forming a tube, has an inner surface 250, which faces radially inwardly towards the carrier structure 242, and an outer surface 248, which faces radially outwardly away from the carrier structure 242. A plurality of conductive traces are provided on the inner surface 250 of the flexible circuit 240 that provide electrical connections to the electrodes and the ground planes of the ultrasound transducers 231-234. The connections to the electrodes are direct connections, while the connection to the ground planes is made indirectly, via the carrier structure. The carrier structure 242, which is, in this example, formed from an electrically conductive material, and forms an electrical connection to the lower surfaces 236 of the piezoelectric elements 230, and therefore the ground planes on them. The ultrasound transducers 231-234 are mounted with a conductive adhesive to facilitate such electrical connection. The flexible circuit 240 is connected to the carrier structure further along the sensor assembly at a contact of the flexible circuit, enabling an electrically conductive path to be formed between the ground planes of the ultrasound transducers and the electrical connectors, via the carrier structure 242 and the flexible circuit 240.

[0106] To illustrate the arrangement of conductive traces on the flexible circuit 240, Fig. 5 is provided, showing a schematic plan view of the inner surface 250 of the flexible circuit 240.

[0107] The flexible circuit 240 has a main portion 243 and a plurality of fingers 241. The main portion 243 has a rectangular shape, with a width dimension W that is greater than a length dimension L. Accordingly the main portion 243 has two longer sides, along a width of the main portion, and two shorter sides, along a length of the main portion. The fingers 241 extend linearly from one of the longer sides, such that they are perpendicular to the width dimension and parallel to the length dimension of the main portion 243. The flexible circuit 240 is rolled to form a tube along its width dimension, such that the width dimension forms the perimeter of the tube formed by the flexible circuit 240. Accordingly, by rolling in this dimension, and having the fingers 241 extend from one of the longer sides, the fingers 241 become distributed around the tube when rolled, allowing them to connect to the ultrasound transducers.

[0108] The inner surface 250 comprises a plurality of conductive traces 276A, 276B that extend across the flexible circuit 240. There are provided four conductive traces 276A for connecting a respective electrode 260 of an ultrasound transducer to an electrical connector, and one further conductive trace 276B for connecting the carrier structure to an electrical connector, thereby forming the electrically conductive path from the ground planes to the electrical connector. The four conductive traces 276A extend from the main portion 243 along respective ones of the fingers 21. The further conductive trace 276B extends lengthways along the main portion 243 only.

[0109] At one end of each of the four conductive traces 276A is a contact 272A for connecting to the electrode 260 of the ultrasound transducer. These contacts 272A are provided on the fingers 241. At the opposite end of each of the four conductive traces 276A is a contact 274 A for connecting to the cores of the coaxial cables 238. These contacts 274 A are provided on the main portion 243. The further conductive trace 276B for connecting to the carrier structure 242, similarly has a contact 272B at one end for connecting to the carrier structure 242 and another contact 274B at the other end for connecting to the electrical connector. The contacts may be adhered to the electrodes and / or cables, or may be otherwise connected, such as by soldering.

[0110] In this example, the conductive traces are provided on the surface of the flexible circuit, and more specifically on surface of a flexible substrate of the flexible circuit but in other examples they may be provided as traces embedded between layers of flexible substrate.

[0111] When rolled, such a flexible circuit 240 as shown in Fig. 5 forms a tube and each of the fingers 241 , traces 276A, and various contacts 272 A, 274A associated with the ultrasound transducers are distributed evenly around the tube, thereby allowing for regular placement of and connection to the ultrasound transducers.

[0112] A second sensor assembly 300 is shown in the broken longitudinal section of Fig. 6 and the cross-section of Fig. 7. The section of Fig. 7 is taken along the line B-B in Fig. 6, and the section of Fig. 6 is taken along the line C-C shown in Fig. 7. The second sensor assembly 300 is similar to the first sensor assembly 200, with the addition of a pressure sensor 354 and corresponding adaptations of the flexible circuit to connect to the pressure sensor and the arrangement of the ultrasound transducers within the sensor assembly to accommodate the adapted flexible circuit.

[0113] Accordingly, the second sensor assembly 300 has a casing 310 comprising a wall 316 and a seal 320 at a distal end 318, four ultrasound transducers, with a first ultrasound transducer 331 being visible in Fig. 6 and the first ultrasound transducer 331, second ultrasound transducer 332, third ultrasound transducer 333, and fourth ultrasound transducer 334 being visible in Fig. 7 .

[0114] The ultrasound transducers 331-334 are arranged like the ultrasound transducers 231-234 shown in Fig. 3 except that in this example they are rotated by 45 degrees. This rotation allows a flexible circuit 340 to extend linearly between two of the ultrasound transducers, in this case the second ultrasound transducer 332 and the fourth ultrasound transducer 334, and to connect to the pressure sensor 354. In other examples, part of the flexible circuit 340 may bend around and pass between two ultrasound transducers, and the transducers may remain arranged as shown in Fig. 3. The ultrasound transducers 331-334 are provided on a carrier structure 342 that includes an insert 344. The flexible circuit 340 is provided to connect electrical connectors, in the form of coaxial cables 338, to the ultrasound transducers 331-334 and the pressure sensor 354.

[0115] The pressure sensor 354 is mounted on the carrier structure 342, and particularly to a platform 355 that extends through the casing 310 at its seal 320, and beyond the distal end 318. The platform 355 provides a surface on which the pressure sensor 354 sits and to which it is fixed. By this arrangement, the ultrasound transducers 331-334 are provided longitudinally between the pressure sensor 354 and the coaxial cables 338. The pressure sensor 354 is covered in a biocompatible film or coating, but this is not shown here to preserve clarity. The pressure sensor 354 is provided outside of the casing 310 to enable it to perform pressure measurements within the bladder environment, when implanted within the subject.

[0116] The pressure sensor 354 is also electrically connected to a corresponding electrical connector, i.e. a corresponding coaxial cable 338, via the flexible circuit 340. In other words, the same flexible circuit 340 is used to connect each of the different sensors present in the sensor assembly 300 to corresponding electrical connectors. This allows the pressure sensor 354 to be positioned at a desired location within the sensor assembly 300, while still being electrically connected to the data logger via the flexible circuit 340 and the electrical connectors. In other arrangements, the pressure sensor 354 may be provided at an alternative location, but may still remain exposed to the environment external to the casing 310.

[0117] An inner surface 350 of the flexible circuit 340 of the second sensor assembly 300 is shown in a plan view in Fig. 8. The flexible circuit 340 includes an inner surface 350. As in Fig. 5, reference to inner and outer refer to the relative positions of the surfaces when the flexible circuit 340 is curved to form a tubular structure. The inner surface 350 comprises a plurality of conductive traces 376A.These traces 376A connect to the electrodes of the ultrasound transducers at one contact 372 A and to cores of the coaxial cables at another contact 374A. The conductive traces extend from a main portion 343 of the flexible circuit 340, which is similar to the main portion 243 of the flexible circuit 240, along respective fingers 341, which are similar to the fingers 241 of the flexible circuit 240. The flexible circuit 340, in addition to the plurality of fingers 341 corresponding to the ultrasound transducers and the main portion 343, includes a projection 345 that extends from the main portion 343 of the flexible circuit 340 between two fingers 341. The projection 345 extends in parallel with the fingers 341, and forms an extended finger, being longer than the fingers 341 so that it can extend past the ultrasound transducers to form an electrical connection with the pressure sensor 354. On the inner surface 350, the flexible circuit 340 therefore includes four further conductive traces 375, with corresponding contacts 377 at an end of the projection 345 for connecting to the pressure sensor 354, and corresponding contacts 379 at an opposing end for connecting to a coaxial cable 338. Although four traces and corresponding pairs of contacts are shown here, fewer or more than four may be provided in other embodiments.

[0118] When the flexible circuit 340 is rolled to form a tube around the carrier structure, the arrangement of the projection 345 between the fingers 371 enables the projection 345 to pass between two ultrasound transducers, as best seen in Fig. 7.

[0119] In the example of Figs. 6 to 8, it is not shown how a ground connection may be formed to preserve clarity of the figures. The ground connection to both the ultrasound transducers and the pressure sensor may be provided via the carrier structure, having a conductive portion or being formed from an electrically conductive material, as described in relation to Figs. 2 to 5. In such examples, the flexible circuit has a conductive trace and contacts for connecting the carrier structure to a coaxial cable screen or other electrical connector. Alternatively, an electrically conductive or partially electrically conductive carrier structure may be connected directly to an electrical connector to form the ground connection.

[0120] Figs. 9 and 10 show a third sensor assembly 400. Fig. 9 shows a longitudinal section of the third sensor assembly 400 while Fig. 10 shows a cross-section of the third sensor assembly 400 along the line D-D. The third sensor assembly 400 is similar to the first sensor assembly 200 as it has four piezoelectric elements 430 distributed around a carrier structure and a flexible circuit connecting to the piezoelectric elements, but instead of individual ultrasound transducers, the third sensor assembly 400 includes a plurality of ultrasound transducers formed on each of the piezoelectric elements, thereby forming a plurality of ultrasound arrays. Only two of the arrays, a first array 431 A formed from a plurality of ultrasound transducers 432A on a first piezoelectric element 430A and a second array 43 IB formed from a plurality of ultrasound transducers 432B on a second piezoelectric element 430B are visible in Fig. 9. The four piezoelectric elements 430A-430D forming four arrays 431 A-D are shown in Fig. 10, but the ultrasound transducers are not visible in this view.

[0121] Providing arrays of transducers may enable steering of the ultrasound signals during emission, and enhanced steering in relation to received ultrasound signals also. This may enable greater detail to be obtained relating to dimensions or shapes of the bladder, and may even enable a form of three-dimensional mapping to be performed.

[0122] Each array is formed on a single piezoelectric element 430, but in other examples arrays may be formed across a plurality of longitudinally aligned piezoelectric elements.

[0123] A further difference in this example is that the carrier structure 442 has an annular crosssection and comprises an insert 444 extending within the internal bore of the carrier structure 442.

[0124] As in earlier aspects, the third sensor assembly 400 includes a casing 410 that defines an internal volume 422, filled with a liquid for improving acoustic transmission between the ultrasound transducers and the casing. The ultrasound transducers are provided within the internal volume 422 and are mounted on the carrier structure 442. A plurality of electrical connectors in the form of coaxial cables 438 extend along the casing 410 to connect to the ultrasound transducers via a flexible circuit 440. The ultrasound transducers are formed as electrodes 460 on the upper surface of the piezoelectric element 430. A single ground plane is provided on the lower surface of each piezoelectric element. The ground planes electrically connect to the electrically conductive carrier structure 442, which allows for a ground connection to be made, either via the flexible circuit 440 or via a separate electrical connector (the ground connection is not shown to preserve clarity).

[0125] An inner surface of the flexible circuit is shown in Fig. 11, which is arranged to enable connections to the electrodes of each array. Referring to Fig. 11, the flexible circuit 440 includes a plurality of fingers 441 that extend from a main portion 443 of the flexible circuit 440. These fingers 441 are arranged to run alongside the piezoelectric elements 430, as can be best seen in Fig. 9. Each finger 441 corresponds to a particular array and therefore to a piezoelectric element. The fingers 441 connect to electrodes of the ultrasound transducers via contacts 472 on tabs 477 on the fingers 441, with one tab and contact being provided for each ultrasound transducer. The electrodes connect to contacts 474 via conductive traces 476 for connecting the electrodes to corresponding electrical connectors. Similarly, one contact 474 and conductive trace 476 is provided for each ultrasound transducer.

[0126] Fig. 12 shows a fourth sensor assembly 500 in a longitudinal sectional view. The fourth sensor assembly 500 is similar to the first sensor assembly 200, but rather than the ultrasound transducers 531, 532 being within the casing 510, they are provided outside of it. The carrier structure 542 and part of the flexible circuit 540 are also provided outside of the casing 510. The carrier structure 542 is integrated with the casing 510. The ultrasound transducers 531, 532, carrier structure 542, and part of the flexible circuit 540 that is provided outside of the casing 510 is covered by a biocompatible film 520. The biocompatible film 520 is a protective layer that shields the ultrasound transducers and the flexible circuit from the surrounding environment. The biocompatible film 520 prevents direct contact between the ultrasound transducers and the body tissues, reducing the risk of tissue irritation or damage. The biocompatible film 520 is acoustically transparent, allowing ultrasound signals to pass through it without significant attenuation. The biocompatible film 520 is represented here by a rectangular shape, although in reality it may be a conformable coating, such that it conforms to the components that it is coating.

[0127] To enable this arrangement, the flexible circuit 540 is shown to extend through a distal end of the casing 510, with the coaxial cables 538 being provided within the casing 510. In other examples, the coaxial cables 538 may extend through the distal end, being partially disposed within the casing 510 and partially extending out from it.

[0128] Although shown with an arrangement of transducers similar to the first sensor assembly in Fig. 2, the biocompatible film may be used with any of the arrangements described herein. In some examples, the wall of the casing may extend over the transducers but the casing may not be sealed at its distal end, so that urine can enter part of the casing. The casing may be sealed elsewhere along its length. In this case, the ultrasound transducers may also be coated with the biocompatible film. Such an arrangement may provide for protection of the ultrasound transducers.

[0129] As in other examples, the carrier structure 542 is electrically conductive, at least in part, and so a ground connection is formed via the carrier structure 542. This may be via the flexible circuit 540 or via a direct connection to an electrical connector. Fig. 13 shows a fifth sensor assembly 600. The fifth sensor assembly 600 is arranged like the second sensor assembly 300 shown in Figs. 6 to 8, although with a fifth ultrasound transducer 635 along a longitudinal axis LA of the sensor assembly 600 within the casing 610, rather than a pressure sensor as in Figs. 6 to 8. The fifth ultrasound transducer 635 is in addition to four other ultrasound transducers, arranged as described and shown in the second sensor assembly 300. A first ultrasound transducer 631 is visible in Fig. 13 in addition to the fifth ultrasound transducer 635, while the second, third, and fourth ultrasound transducers are not visible in this view. In some examples, the fifth ultrasound transducer may be referred to as a third ultrasound transducer, with ultrasound transducers along the same axes being referred to together, i.e. ultrasound transducers along the first radial axis may be 'first' ultrasound transducers, while ultrasound transducers along the second radial axis may be 'second' ultrasound transducers.

[0130] The fifth ultrasound transducer 635 faces in a fifth direction U5, and is oriented to emit ultrasound signals in the fifth direction U5 and to receive ultrasound signals in a sixth direction U6 that is opposite to the fifth direction U5. The fifth and sixth directions U5, U6 are directions parallel to the longitudinal axis LA. Accordingly, the fifth sensor assembly 600 includes ultrasound transducers along a first radial axis of the sensor assembly, a second radial axis of the sensor assembly that is perpendicular to the first radial axis, and the longitudinal axis LA of the sensor assembly that is perpendicular to both radial axes. This allows for determination of three different dimensions along said axes.

[0131] Like the other ultrasound transducers, the fifth ultrasound transducer 635 is mounted on the carrier structure 642, on an end of the carrier structure rather than around its sides as with the other transducers 631, 632. The carrier structure 642 also includes an insert 644 between the ultrasound transducers in this example.

[0132] The fifth sensor assembly 600 also includes a flexible circuit 640 that electrically connects the ultrasound transducers, including the fifth ultrasound sensor 635, to a plurality of electrical connectors, such as coaxial cables 638. The flexible circuit 640 includes a projection 656 that extends from the main body of the flexible circuit to connect with the fifth ultrasound transducer 635. The projection 656 may be a projection such as that described in Figs. 6 to 8 for use with the pressure sensor. The projection 656 has a conductive trace on an inner surface that connects to an electrode on an outwardly-facing surface of the fifth ultrasound transducer 635. As in earlier examples, the ground planes of the ultrasound transducers of the fifth sensor assembly 600 are connected to an electrical connector via the carrier structure 642, which is at least partially electrically conductive and forms an electrically conductive path from the ground planes. Although not shown, the carrier structure may connect directly to an electrical connector such as a coaxial cable 638 or via the flexible circuit 640.

[0133] The fifth sensor assembly 600 of Fig. 13 provides a way to perform measurements in three dimensions using ultrasound transducers. Such a fifth ultrasound transducer may be introduced into the other examples described herein, to permit such measurements to be performed. Alternatively, to enable measurements to be performed of three or more dimensions, multiple sensor assemblies may be provided, or multiple arrangements of ultrasound transducers within the same casing may be provided. For example, two separate sets of ultrasound transducers may be provided connected by individual flexible circuits to their respective electrical connections.

[0134] The flexible circuits of the examples described above improve assembly and manufacture of said sensor assemblies. Fig. 14 shows a method 700 for assembling the sensor assembly 200. The method 700 comprises three sequential steps 710, 720, 730. The first step 710 involves providing a carrier structure, a flexible circuit, a plurality of ultrasound transducers, and a plurality of electrical connectors. The carrier structure may be a rigid or semi-rigid structure designed to support the ultrasound transducers. The flexible circuit is a thin, flexible substrate with conductive traces that provide electrical connections between the ultrasound transducers and the electrical connectors. The ultrasound transducers are piezoelectric elements that are capable of emitting and detecting ultrasound signals. The electrical connectors are devices that facilitate the transmission of electrical signals between the ultrasound transducers and a data logger.

[0135] In the second step 720, while the flexible circuit is laid flat, the electrical connectors are electrically connected to the flexible circuit and the ultrasound transducers are also electrically connected to the flexible circuit. This step involves attaching the electrical connectors and the ultrasound transducers to the conductive traces on the flexible circuit. The electrical connectors and the ultrasound transducers may be attached to the flexible circuit using soldering, conductive adhesive, or other suitable attachment methods. The flexible circuit may be laid flat during this step to facilitate the attachment of the electrical connectors and the ultrasound transducers. In the third step 730, the ultrasound transducers are mounted on the carrier structure. This step involves positioning the ultrasound transducers on the carrier structure and securing them in place. The ultrasound transducers may be mounted on the carrier structure using adhesive, mechanical fasteners, or other suitable attachment methods. The ultrasound transducers are oriented to face in at least two different directions, allowing the sensor assembly to emit and detect ultrasound signals in multiple directions. This configuration enables the sensor assembly to measure at least two dimensions of a bladder of a subject.

[0136] In some aspects, the method 700 may further comprise flexing the flexible circuit to curve around the carrier structure prior to mounting the ultrasound transducers on the carrier structure. This step involves bending or curving the flexible circuit so that it conforms to the shape of the carrier structure. The flexible circuit may be flexed to form a tube or other shape that accommodates the ultrasound transducers and the electrical connectors. Flexing the flexible circuit allows it to adopt a particular shape, enabling the ultrasound transducers to be positioned in the desired directions.

[0137] In some cases, the method 700 may further comprise rolling the flexible circuit to form a tube prior to mounting the ultrasound transducers on the carrier structure. This step involves rolling the flexible circuit into a tubular shape, providing a compact and efficient arrangement for the electrical connections within the sensor assembly. The tubular shape of the flexible circuit also provides structural support to the ultrasound transducers, helping to maintain their positioning within the sensor assembly.

[0138] The method 700 provides a structured approach for assembling the sensor assembly, with each step contributing to the overall assembly process. This method allows for efficient manufacturing of the sensor assembly and ensures accurate positioning of the ultrasound transducers.

[0139] The order of the steps of the methods described herein is exemplary, but the steps may be carried out in any suitable order, or simultaneously where appropriate. Additionally, steps may be added or substituted in, or individual steps may be deleted from any of the methods without departing from the scope of the subject matter described herein.

[0140] Although in the examples above, at least four ultrasound transducers are provided, in other embodiments the sensor assembly may comprise two, three, or more than five ultrasound transducers. The transducers may be arranged along any axes. Similarly, in each of the example assemblies, the carrier structure comprises an insert. In other examples, the carrier structure may lack the insert.

[0141] In some examples, rather than the casing being acoustically transmissive, the casing may comprise a plurality of acoustic windows that are aligned with the ultrasound transducers for transmitting ultrasound signals from the ultrasound transducers into and out of the casing. The acoustic windows may be configured to direct or collimate ultrasound signals. For example, the acoustic windows may be shaped as acoustic lenses. This configuration may enhance the accuracy and precision of the measurements obtained by the sensor assembly.

[0142] In some aspects, the ultrasound transducers may be attached to or provided on an exterior of the casing.

[0143] The flexible circuit may be shaped to have a cross-section in the shape of part or all of a circle or ellipse, thereby forming part or all of a tube along its length.

[0144] Aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples without losing the effect sought. For example, in examples, the sensor assemblies of Figs. 6 and 13 may be combined, such that an assembly including ultrasound transducers oriented along three different axes and a pressure sensor is formed.

[0145] The aspects shown in the figures and described above are provided as diagrammatic representations only.

Claims

CLAIMS1. A sensor assembly (200) for in vivo monitoring of a bladder (15) of a subject (10), the sensor assembly (200) comprising:- a carrier structure (242);- a plurality of ultrasound transducers (231-234) for emitting and detecting ultrasound signals wherein the ultrasound transducers (231-234) are coupled to the carrier structure (242) and face in at least two different directions (U1-U4);- a plurality of electrical connectors (238) for transmitting electrical signals between a data logger (120) and the ultrasound transducers (231-234); and- a flexible circuit (240) electrically connecting the ultrasound transducers (231-234) to the electrical connectors (238).

2. The sensor assembly (200) of claim 1, wherein the flexible circuit (240) is curved around at least part of the carrier structure (242).

3. The sensor assembly (200) of claim 1 or claim 2, wherein the flexible circuit (240) forms a tube.

4. The sensor assembly (200) of any preceding claim, wherein the flexible circuit (240) has a plurality of conductive traces that connect to electrodes of respective ultrasound transducers of the plurality of ultrasound transducers.

5. The sensor assembly (200) of claim 4, wherein at least a portion of the carrier structure is electrically conductive, and wherein the at least the portion of the carrier structure forms an electrically conductive path between ground planes of the plurality of ultrasound transducers and an electrical connector.

6. The sensor assembly (200) of claim 5, wherein the flexible circuit comprises at least one further conductive trace that is connected to the at least the portion of the carrier structure that is electrically conductive, the at least one further conductive trace thereby forming part of the electrically conductive path between the ground planes and the electrical connector.

7. The sensor assembly (200) of claim 5, wherein the at least the portion of the carrier structure that is electrically conductive is directly connected to the electrical connector.

8. The sensor assembly (200) of any preceding claim, further comprising a pressure sensor (354), wherein the flexible circuit (240) electrically connects the pressure sensor (354) to a corresponding electrical connector.

9. The sensor assembly (200) of any preceding claim, wherein the plurality of ultrasound transducers comprises at least a first ultrasound transducer along a first radial axis of the sensor assembly, at least a second ultrasound transducer along a second radial axis of the sensor assembly that is perpendicular to the first radial axis, and a third ultrasound transducer along a longitudinal axis of the sensor assembly.

10. The sensor assembly (200) of any preceding claim, wherein the plurality of ultrasound transducers form at least two arrays (431, 432) that point in the at least two different directions.

11. The sensor assembly (200) of any preceding claim, comprising a casing that houses the plurality of ultrasound transducers, wherein the casing is formed of an acoustically transmissive material.

12. The sensor assembly (200) of any preceding claim, wherein the ultrasound transducers are covered with a biocompatible coating (520).

13. The sensor assembly (200) of any preceding claim, wherein the carrier structure comprises an insert (244) for attenuating ultrasound signals, wherein the insert (244) is provided between the ultrasound transducers (231-234).

14. A medical device comprising the sensor assembly (200) of any preceding claim and a data logger (120) connected to the electrical connectors.

15. A method (700) for assembling the sensor assembly (200) of any of claims 1 to 13, the method (700) comprising:- providing (710) a carrier structure, a flexible circuit, a plurality of ultrasound transducers, and a plurality of electrical connectors;- while the flexible circuit is laid flat, electrically connecting (720) the electrical connectors to the flexible circuit and the ultrasound transducers to the flexible circuit; and- mounting (730) the ultrasound transducers on the carrier structure.

16. The method (700) of claim 15, comprising, prior to mounting the ultrasound transducers on the carrier structure, flexing the flexible circuit to curve around the carrier structure.

17. The method (700) of claim 15 or claim 16, comprising, prior to mounting the ultrasound transducers on the carrier structure, rolling the flexible circuit to form a tube.

18. A flexible circuit (240) for use in the sensor assembly of any of claims 1 to

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