BLADDER MONITORING

Abstract

The present application discloses a bladder monitoring system comprising a wearable bladder monitoring device (1) including securing means (27, 29) for securing the device to a subject's (40) body; a phased array (11) of ultrasound transducers (10); and a phased array controller (13) adapted to control the phased array to direct a plurality of ultrasound beams (30, 30, 30) into the subject's body under a range of beam angles, as well as a signal processor (23) adapted to receive data pertaining to echo signals (31, 31, 31) of said ultrasound beams from the phased array. The signal processor is adapted to process said data in order to identify an edge of the subject's pelvic bone (43) proximal to the subject's bladder (41) from data pertaining to at least one of said echo signals; determine an orientation of the wearable bladder monitoring device relative to the pelvic bone based on beam angle information associated with the at least one of said echo signals; and derive bladder information from the data based on the determined orientation. A method of obtaining bladder (volume) information with such a system is also disclosed.

Claims

1. A bladder monitoring system comprising a signal processor adapted to: receive data from a wearable bladder monitoring device, said device including: securing means for securing the device to a subject's body; a phased array of ultrasound transducers; and a phased array controller adapted to control the phased array to direct a plurality of ultrasound beams into the subject's body under a range of beam angles, wherein said data pertains to echo signals of said ultrasound beams; and wherein the signal processor is adapted to receive said data from the phased array and to process said data in order to; identify an edge of the subject's pelvic bone proximal to the subject's bladder from data pertaining to at least one of said echo signals; determine an orientation of the wearable bladder monitoring device relative to the pelvic bone based on beam angle information associated with the at least one of said echo signals; and derive bladder information from the data based on the trajectories of the ultrasound beams passing through the bladder as a function of the determined orientation of the wearable bladder monitoring device relative to the pelvic bone.

2. The bladder monitoring system of claim 1, further comprising the wearable bladder monitoring device.

3. The bladder monitoring system of claim 2, wherein the wearable bladder monitoring device further comprises the signal processor.

4. The bladder monitoring system of claim 2, wherein the wearable bladder monitoring device further comprises an orientation sensor for determining an orientation of the subject, and wherein the signal processor is adapted to determine an orientation of the wearable bladder monitoring device relative to the pelvic bone based on beam angle information associated with the at least one of said echo signals and an orientation signal from the orientation sensor.

5. The bladder monitoring system of claim 4, further comprising a data storage device storing a plurality of bladder models, each associated with a particular orientation of the subject, wherein the signal processor is adapted to retrieve the defined bladder model from the data storage device based on said orientation signal.

6. The bladder monitoring system of claim 1, wherein the signal processor is adapted to estimate a diameter of the subject's bladder for each echo signal from the data pertaining to a subset of said echo signals.

7. The bladder monitoring system of claim 6, wherein the signal processor is further adapted to, for each echo signal in said subset: calculate a first optimal frequency of its associated ultrasound beam for imaging an anterior boundary of the bladder at which a slope of an intensity change of said associated ultrasound beam when passing through said anterior boundary is maximized; calculate a second optimal frequency of its associated ultrasound beam for imaging a posterior boundary of the bladder at which a slope of an intensity change of said associated ultrasound beam when passing through said posterior boundary is maximized; instruct the phased array controller to generate at least one further ultrasound beam under the beam angle of the associated ultrasound beam with the phased array, said at least at least one further ultrasound beam having a frequency corresponding to at least one of the first optimal frequency and the second optimal frequency or an average of the first optimal frequency and the second optimal frequency; and estimate the diameter of the subject's bladder for said beam angle from the at least one further echo signal of the at least one further ultrasound beam.

8. The bladder monitoring system of claim 7, wherein the at least one further ultrasound beam comprises: a first further ultrasound beam having the first optimal frequency and a second further ultrasound beam having the second optimal frequency.

9. The bladder monitoring system of claim 6, wherein the signal processor is adapted to estimate a bladder volume by fitting the estimated diameters of the subject's bladder to a defined bladder model and estimating the bladder volume from the fitting result.

10. The bladder monitoring system of claim 1, wherein the phased array controller is adapted to periodically generate said plurality of ultrasound beams.

11. The bladder monitoring system of claim 10, wherein the signal processor is adapted to derive a bladder function from the data pertaining to the respective echo signals of the periodically generated pluralities of ultrasound beams.

12. The bladder monitoring system of claim 10, wherein a frequency of said periodic generation is based on a previously determined bladder function by the signal processor.

13. The bladder monitoring system of claim 1, wherein the securing means include a strap attached to the wearable bladder monitoring device or an adhesive layer on a subject-facing surface of the wearable bladder monitoring device.

14. The bladder monitoring system of claim 1, wherein the wearable bladder monitoring device further comprises a wireless communication module for communicating with a remote device.

15. A method of monitoring a bladder with the bladder monitoring system of claim 1, the method comprising: securing the wearable bladder monitoring device to a subject's body; generating a plurality of ultrasound beams under a range of beam angles with the phased array; receiving echo signals of said ultrasound beams from the phased array; and processing data pertaining to said echo signals in order to: identify an edge of the subject's pelvic bone proximal to the subject's bladder from data pertaining to at least one of said echo signals; determine an orientation of the wearable bladder monitoring device relative to the pelvic bone based on beam angle information associated with the at least one of said echo signals; and derive bladder information from the data based on the trajectories of the ultrasound beams passing through the bladder as a function of the determined orientation of the wearable bladder monitoring device relative to the pelvic bone.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Embodiments of the invention are described in more detail and by way of non-limiting examples with reference to the accompanying drawings, wherein:

[0022] FIG. 1 schematically depicts a bladder monitoring system according to an embodiment;

[0023] FIG. 2 schematically depicts an operating principle of a bladder monitoring system according to an embodiment;

[0024] FIG. 3 schematically depicts an aspect of a bladder monitoring system according to an embodiment;

[0025] FIG. 4 schematically depicts an aspect of a bladder monitoring system according to another embodiment;

[0026] FIG. 5 schematically depicts a bladder monitoring system according to an embodiment in use on a subject;

[0027] FIG. 6 schematically depicts an aspect of typical echo signals received by a bladder monitoring system according to an embodiment;

[0028] FIG. 7 schematically depicts an angular dependence of ultrasound signals passing through a subject's bladder resulting from orientations of the bladder monitoring system according to an embodiment relative to the subject;

[0029] FIG. 8 is a flowchart of an example embodiment of a method of monitoring a bladder with a bladder monitoring system according to an embodiment;

[0030] FIG. 9 schematically depicts a bladder monitoring system according to another embodiment; and

[0031] FIG. 10 is a flowchart of an aspect of another example embodiment of a method of monitoring a bladder with a bladder monitoring system according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0032] It should be understood that the Figures are merely schematic and are not drawn to scale. It should also be understood that the same reference numerals are used throughout the Figures to indicate the same or similar parts.

[0033] FIG. 1 schematically depicts a bladder monitoring system according to an example embodiment. The bladder monitoring system comprises a wearable bladder monitoring device 1 that may be secured to an individual (subject) using suitable securing means, such as a strap or belt, or an adhesive layer as will be explained in more detail later. The wearable bladder monitoring device 1 comprises a phased array 10 of ultrasound transducer elements 11 under control of a phased array controller 13. Any suitable type of ultrasound transducer elements 11 may be used for this purpose, e.g. PZT elements, CMUT elements, PMUT elements, and so on, although CMUT elements are particularly preferred, in particular over PZT elements due to their superior (adjustable) resonance frequency range, which make CMUT elements particularly suitable for bladder monitoring purposes. As such transducer elements are well-known per se, they will not be explained in further detail for the sake of brevity only.

[0034] The phased array 10 may take any suitable shape, e.g. a one-dimensional array or two-dimensional array of ultrasound transducer elements 11 of any suitable size, such as a 44 mm array 10 having 16 ultrasound transducer elements 11 with a pitch in a range of 200-300 microns, by way of non-limiting example. Other dimensions are of course equally feasible. In an embodiment, the ultrasound transducer elements 11 are operable in a frequency range of 2-12 MHz, although other frequency ranges may be contemplated. As will be explained in more detail below, preferably the operation frequency of the ultrasound transducer elements 11 may be altered, although in alternative embodiment the ultrasound transducer elements 11 are arranged to be operated at a fixed resonance frequency, e.g. about 3-4 MHz.

[0035] The phased array controller 13 typically is arranged to steer ultrasound beams generated with the ultrasound transducer elements 11 of the phased array 10 under a range of angles, as schematically depicted in FIG. 2, in which by varying the delay times between the firing of the individual (lines of) ultrasound transducer elements 11 as is well-known per se, beam angles may be generated under a number of beam angles, e.g. 45 (a), 30 (b), 15 (c) and 0 (d), wherein the beam angle is defined relative to the transmission surface of the phased array 10. In an embodiment, the beam angle range ranges from 0 to 45, in which beam angles are altered in 15 increments, although a larger or smaller beam angle range utilizing larger or smaller beam angle increments of course may also be contemplated.

[0036] Now, upon returning to FIG. 1, the phased array 10 typically is operable in a transmit mode in which the ultrasound beams are generated under control of the phased array controller 13 and a receive mode in which the phased array is operable to receive echo signals induced by the generated ultrasound beams within the body of the individual wearing the wearable bladder monitoring device 1. As will be readily understood by the skilled person, the wearable bladder monitoring device 1 may be operated such that a transmit mode of an ultrasound beam under a particular beam angle is followed by the receive mode of its induced echo signals, before the next transmit mode of an ultrasound beam under a further particular beam angle is initiated, such as to ensure that for each ultrasound beam its echoes do not suffer interference from echoes of ultrasound beams under different beam angles.

[0037] The echo signals may be pre-processed by a down conversion stage 17, which may form part of the phased array controller 13 or may be a separate entity. The down conversion stage 17 may apply noise filtering and frequency down conversion of the echo signals, e.g. from the MHz domain to the KHz domain, and employ a signal envelope to the down converted echo signals to reduce the amount of data that needs to be provided to a signal processor for deriving the desired bladder information from the acquired echo signals. Other suitable data reduction techniques will be immediately apparent to the skilled person.

[0038] In FIG. 1, the signal processor 23 forms part of a remote device 5, e.g. a wearable smart device such as a smart watch, a portable smart device such as a mobile phone or tablet computer, a laptop computer, a personal computer, or the like in order to reduce the computational effort required from the wearable bladder monitoring device 1 such that the lifetime of the battery 15 of the wearable bladder monitoring device 1 may be extended. The remote device 5 may be configured to obtain the desired functionality for the signal processor 23 in any suitable manner, e.g. by means of a software program installed onto the remote device 5, such as an app or the like.

[0039] To this end, the down conversion stage 17 may be communicatively coupled to a data storage device 19, e.g. a memory or the like, on-board the wearable bladder monitoring device 1, with a wireless communication module 21 communicatively coupled to the data storage device 19 such that the data pertaining to the acquired echo signals as stored in the data storage device 19 may be periodically communicated to the remote device 5, e.g. in response to a communication request from the remote device. Any suitable wireless communication protocol, e.g. Bluetooth, Wi-Fi, a mobile communication protocol such as 3G, 4G, 5G or the like, a near field communication protocol (NFC), and so on, may be deployed for the communication between the wearable bladder monitoring device 1 and the remote device 5. As mentioned previously, the data pertaining to the acquired echo signals communicated from the wearable bladder monitoring device 1 to the remote device 5 preferably is reduced in size to minimize the amount of data that needs to be communicated in this manner in order to extend the lifetime of the battery 15. However, it should be understood that in alternative embodiments the signal processor 23 may be contained within the wearable bladder monitoring device 1. In such embodiments, the wireless communication module 21 may be used to communicate a processing result of the signal processor 23 to the remote device 5, e.g. for visualization of the processing result on a display 7 of the remote device 5.

[0040] In yet a further embodiment, the wearable bladder monitoring device 1 is configured to upload the data pertaining to the acquired echo signals with a wireless communication module 21 into a remote data repository acting as an intermediary data storage device from which the remote device 5 may download the stored data. This has the advantage that the remote device 5 does not have to be within communication range of the wearable bladder monitoring device 1 but instead may download the data at any suitable point in time to evaluate this data. For example, the remote data repository may be a cloud storage solution or the like, which may be accessed by both the wearable bladder monitoring device 1 and the remote device 5 over a network connection such as the Internet, in which case the wearable bladder monitoring device 1 may establish a wireless connection with an Internet hub such as a router or the like within communication range of the wireless communication module 21 through which the data pertaining to the acquired echo signals may be uploaded into the remote data repository.

[0041] Any suitable type of battery 15 may be used within the wearable bladder monitoring device 1. The battery 15 may be non-rechargeable, which for example may be acceptable where the wearable bladder monitoring device 1 is a disposable device. Alternatively, the battery 15 may be a rechargeable battery in which case the wearable bladder monitoring device 1 may comprise a recharging port (not shown) through which the battery 15 may be recharged in any suitable manner. In the absence of such a recharging port, the battery 15 may be recharged using wireless recharging, e.g. NFC recharging as is well-known per se.

[0042] FIG. 3 schematically depicts a cross-section of a wearable bladder monitoring device 1 in which a subject-facing surface of the wearable bladder monitoring device 1 is covered with an adhesive layer 27, e.g. an adhesive polymer layer or the like, for adhering the wearable bladder monitoring device 1 to an abdominal skin region of the subject, such that ultrasound beams 30 originating from the ultrasound transducer elements 11 can be steered into the subject's body under control of the phased array controller 13 as previously explained. The use of an adhesive layer 27 has the advantage of achieving a particularly secure fit between the abdominal skin region of the subject and the wearable bladder monitoring device 1, in particular if no hair is present in this skin region.

[0043] FIG. 4 schematically depicts a cross-section of a wearable bladder monitoring device 1 in which the wearable bladder monitoring device 1 comprises a strap 29 for securing the bladder monitoring device 1 against the abdominal skin region of the subject. Such a strap 29 may be secured against the subject in any suitable manner, e.g. using a fastening member arrangement such as a belt buckle at one end of the strap 29 and holes for receiving the belt buckle at another end of the strap 29, a fastening clip through which the strap 29 can be adjusted in an non-engaged configuration of the clip and in which the strap 29 can be affixed in an engaged configuration of the clip, a Velcro arrangement, and so on. It should furthermore be understood that the strap 29 does not necessarily include a fastening member arrangement; alternatively, the strap 29 may be a closed loop, e.g. a closed belt or the like, which is elastic such that the strap 29 can be stretched to position the wearable bladder monitoring device 1 over the desired abdominal skin region of the subject, such that the elastic force of the stretched elastic strap 29 retains the wearable bladder monitoring device 1 in the desired position and preferably in a preferred orientation. In further embodiments, the wearable bladder monitoring device 1 may have a fastening arrangement in which the adhesive layer 27 is combined with a strap 29 according to any of the aforementioned embodiments.

[0044] FIG. 5 schematically depicts the positioning of the wearable bladder monitoring device 1 on the abdominal region of the subject 40. The wearable bladder monitoring device 1 preferably is positioned in an abdominal region in between the pelvic bone 43 and the bellybutton (not shown) of the subject 40, e.g. a few centimetres below the belly button in order to facilitate a good viewing angle of the bladder 41 of the subject 40, i.e. to minimize the area of the bladder 41 that is obscured from direct view of a phased array 10 of ultrasound transducer elements 11. In the context of the present application, such a direct view is a transmission path of an ultrasound beam 30 towards the bladder 41 that does not first have to pass through a skeletal structure such as a bone.

[0045] As is schematically depicted in FIG. 5, the beam steering applied by the phased array controller 30 typically results in a plurality of ultrasound beams under a range of beam angles being created, wherein different (subsets of) ultrasound beams travel through different anatomical structures of the subject 40. For example, ultrasound beams 30 as indicated by the finely dashed arrows travel through tissue only, whereas ultrasound beams 30 as indicated by the solid arrows travel through a small layer of tissue before travelling through the bladder 41, whilst ultrasound beams 30 as indicated by the coarsely dashed arrow travelling towards the pelvic bone 43.

[0046] An important aspect of embodiments of the present invention is that such different paths of the ultrasound beams 30, 30, 30 lead to clearly distinguishable echo signals, as is schematically depicted in FIG. 6, in which echo signal intensities (y-axis) as a function of time (i.e. object distance from the phased array causing the signal reflection; x-axis) are depicted. Specifically, the ultrasound beams 30 travelling through tissue only typically yield an echo signal 31 having a continually decreasing signal intensity with increasing echo acquisition time delay, whereas the ultrasound beams 30 travelling through the bladder 41 cause echo signals 31 that are characterised by a sudden change 33 in the echo signal intensity, or by a pair of such signal intensity changes 33 and 33, which signal intensity changes are characteristic of the echo signals encountering the anterior wall of the bladder 41 at a first distance from the phased array 10 (signal intensity change 33) and the posterior wall of the bladder 41 at a second distance from the phased array 10 (signal intensity change 33), with the echo signal in between these respective signal intensity changes indicative of the medium, e.g. urine or tissue, in the bladder 41 in between the anterior and posterior wall portions imaged by the ultrasound beam from which the echo signal 31 has originated. Finally, the echo signal 31 resulting from ultrasound beams 30 incident on the pelvic bone 43 is characterised by a sharp intensity peak caused by the reflection of the ultrasound beams by the pelvic bone 43 at a relatively close distance from the phased array 10.

[0047] The distance between the intensity changes in an echo signal 31 indicative of the anterior and posterior wall portions imaged by an ultrasound beam 30 from which this echo signal originates may be used to estimate a diameter of a section of the bladder 41, as schematically depicted in FIG. 7, in which an ultrasound beam 30 enters the bladder 41 through anterior wall portion 41a. However, depending on the relative orientation of the wearable bladder monitoring device 1 to the abdominal region of the subject 40, as expressed by the angle in FIG. 5, the ultrasound beam 30 may exit the bladder through its posterior wall portion 41b if the wearable bladder monitoring device 1 is oriented relative to the abdominal region of the subject 40 under a first angle .sub.1, giving rise to an estimated diameter d1 as being the distance (time delay) between the midpoints of the edges 33 and 33 of the echo signal, which midpoints may be interpreted as the estimated locations of the anterior wall portion 41a and the posterior wall portion 41b.

[0048] However, the ultrasound beam 30 may exit the bladder through its posterior wall portion 41c if the wearable bladder monitoring device 1 is oriented relative to the abdominal region of the subject 40 under a second angle .sub.2, giving rise to an estimated bladder diameter d2, with typically d2d1. In this context, the angle may be defined as the angle between the subject-facing surface plane of the wearable bladder monitoring device 1 and the plane of the abdominal skin contact region onto which the wearable bladder monitoring device 1 is placed. This therefore shows that the relative orientation of the wearable bladder monitoring device 1 to the abdominal region of the subject 40 has an impact on the bladder monitoring data, in particular on the length of a path of an ultrasound beam 30 through a section of the bladder 41 as explained above.

[0049] The operation of the bladder monitoring system according to embodiments of the present invention is designed to factor in such orientational dependency of the wearable bladder monitoring device 1 on the bladder monitoring results, as will now be explained in more detail with the aid of FIG. 8, in which a flowchart of a method 100 of monitoring the bladder 41 of a subject 40 with such a bladder monitoring system is shown. The method 100 starts in operation 101 with the placement of the wearable bladder monitoring device 1 in a defined location on the abdomen of the subject 40, e.g. just under the subject's bellybutton as previously explained, after which in operation 103 the phased array controller 13 controls the phased array 10 to generate a plurality of ultrasound beams 30 into the subject's body under a range of beam angles, e.g. a range from 0-45 with defined beam angle increments, e.g. 5 or 15 increments. For each generated ultrasound beam 30, an echo signal 40 is received in operation 105 before the ultrasound beam 30 under the next beam angle is generated in a repeat of operation 103. Any suitable acquisition period for the echo signals 40 may be deployed in operation 105, e.g. an acquisition period of several milliseconds.

[0050] Each received echo signal may be pre-processed by the pre-processing state 17 in operation 107, which pre-processing may include one or more or noise filtering, signal down conversion, signal enveloping and signal digitization, and which may further include storing the pre-processed signal in data storage device 19 for subsequent processing by the signal processor 23, either on a remote device 5 or on the wearable bladder monitoring device 1 as previously explained. It is checked in operation 108 if all ultrasound signals 30 under the desired beam angles have been generated, the respective echo signals 40 have been collected and pre-processed. If this is not the case, the method 100 reverts back to operation 103 in which the next ultrasound beam 30 is generated, e.g. under an adjusted beam angle.

[0051] Otherwise, the method 100 proceeds to operation 109 in which the acquired (pre-processed) ultrasound echo signals 40 are passed on to the signal processor 23, which may involve a wireless communication between the wearable bladder monitoring device 1 and the remote device 5 as previously explained in case the signal processor 23 is located on the remote device 5, in which the signal processor 23 processes the received data in order to determine the orientation angle of the wearable bladder monitoring device 1 relative to the abdomen of the subject 40. Specifically, the signal processor 23 evaluates the respective echo signals 40 to identify the subset of echo signals 40 reflected by the pelvic bone 43, which echo signals may be identified as previously explained with the aid of FIG. 6, in order to identify the edge of the pelvic bone 43 proximal to the bladder 41 from this subset of echo signals 40. This echo signal for example may be identified by systematically evaluating the echo signals as a function of reducing beam angle of the ultrasound beams corresponding to these echo signals in order to find the ultrasound beam 30 with the lowest beam angle leading to an echo signal reflecting off the pelvic bone 43. Because the wearable bladder monitoring device 1 is positioned in an (approximately) fixed position relative to the pelvic bone 43, the relative orientation angle of the wearable bladder monitoring device 1 can be derived from this beam angle information by the signal processor 23 in operation 111 of the method 100.

[0052] In operation 113, the signal processor 23 fits the echo signals 31 of the ultrasound beams 30 passing through a section of the bladder 41 to a bladder model. In operation 115, the signal processor 23 may estimate a diameter or cross-sectional length of the bladder section from the distance or time delay between the respective edges 33 and 33 of each echo signal 31 indicative of the anterior and posterior wall sections of the bladder 41 delimiting this bladder section. The positioning of the trajectory of the ultrasound beams 30 onto this bladder model may be based on the determined orientation angle of the wearable bladder monitoring device 1, such that a distinction can be made between trajectories resulting from different orientation angles of the wearable bladder monitoring device 1, such as example orientation angles .sub.1 and .sub.2 as schematically depicted in FIG. 7.

[0053] Based on the trajectories fitted onto the bladder model and the respective diameters (cross-sectional lengths) of the bladder 41 along these respective trajectories, the signal processor 23 may in operation 117 estimate a bladder volume of the bladder 41. This for example may be based on the number of ultrasound beams 30 and the respective beam angles of these beams as well as on a defined orientation of the bladder model relative to the pelvic bone 43, such that a portion of the bladder model obscured from the ultrasound beams 30 by the pelvic bone 43 as a function of the orientation angle of the wearable bladder monitoring device 1 can be estimated from the determined orientation angle . Consequently, the volume of the portion of the bladder 41 visible to the ultrasound beams 30 may be extrapolated to a total bladder volume in this manner.

[0054] In an embodiment, the wearable bladder monitoring device 1 may be adapted to periodically repeat the monitoring of the bladder at a defined monitoring frequency such as to monitor changes in the bladder volume over the monitoring period. This for example may be used to determine a rate of change in the bladder volume, from which diagnostic observations may be derived, such as a rehydration or dehydration rate of the subject 40. Also, monitoring the bladder volume over a period of time may provide valuable insights into the retention volume of the bladder 41, which has previously explained is an indicator of prostate and urinary tract conditions, with the consequent bladder stretching being a key contributor to the occurrence of delirium in elderly subjects 40. In order to preserve the battery life of the battery 15, the defined monitoring frequency should be chosen as low as possible. In an embodiment, the signal processor 23 is adapted to define the monitoring frequency from an evaluation of a previous bladder monitoring event or set of bladder monitoring events, e.g. based on a previously determined filling or emptying rate of the bladder 41 or on a suspected pathology of the bladder 41.

[0055] The method 100 optionally may further comprise the generation of a warning signal in operation 119 with the signal processor 23, which warning signal for example may be generated as an audible or visible warning signal with the remote device 5 under control of the signal processor 23. The signal processor 23 may generate the warning signal in response to the estimation of a particular bladder volume or change in the bladder volume. Such a warning signal for example may be generated to wake a sleeping subject 40 in case of the bladder 41 of the subject 40 gets overly full, e.g. in order to prevent wetting of the subject's bed in case of incontinence. Alternatively, such a warning signal may be used to inform an athlete about his or her hydration levels, e.g. to ensure appropriate post-exercise rehydration. Alternatively, the warning signal may be generated by an alarming system connected to the remote data repository, which alarming system may be adapted to process the data uploaded into the remote data repository by the wearable bladder monitoring device 1 and to generate the warning signal based on said processing. The method 100 may subsequently terminate in operation 121.

[0056] In order to further refine the bladder volume estimation from the data pertaining to the echo signals generated with the wearable bladder monitoring device 1, this device may further comprise an orientation sensor 25 as schematically depicted in FIG. 9. Such an orientation sensor 25, e.g. an accelerometer or the like, is typically adapted to determine the orientation, e.g. posture or pose, of the subject 40, as different orientations of the subject 40 may lead to changes in the shape of the bladder 41. Therefore, by including the orientation data provided by the orientation sensor 25 in the data to be provided to the signal processor 23, the signal processor 23 may estimate the bladder volume of the bladder 41 of the subject 40 based on the combination of the data pertaining to the echo signals 31 of the ultrasound beams 30 and the orientation data provided by the orientation sensor 25.

[0057] In an embodiment, the signal processor 23 has access to a plurality of bladder models, e.g. stored in a data storage device (not shown), which may be contained by the device also containing the signal processor 23, e.g. the remote device 5 or the wearable bladder monitoring device 1, or may be a remote data storage device accessible over a network such as the Internet by the signal processor 23, e.g. through wireless communication module as will be readily understood by the skilled person. Each bladder model may be associated with a particular orientation (posture or pose) of the subject 40, such that the appropriate bladder model may be selected by the signal processor 23 based on the orientation data generated with the orientation sensor 25.

[0058] A further refinement of the accuracy of the bladder volume estimation may be obtained by optimizing the resonance frequencies of the ultrasound beams 30 passing through the bladder 41. This can be understood as follows. As previously explained, the echo signals 31 of the ultrasound beams 30 exhibit a pair of steep intensity changes 33 and 33 corresponding to the ultrasound beam 30 passing through an anterior wall section and a posterior wall section respectively of the bladder 41. In order to accurately locate the respective positions of these anterior and posterior wall sections, this intensity change preferably should be as steep as possible, such that the distance over which this intensity change is spread is minimized, thereby minimizing the uncertainty in the exact locations of these wall sections and consequently improving the accuracy of the estimated distance, i.e. bladder diameter or cross-sectional length, between these wall sections.

[0059] This may be achieved by tuning the frequency of the ultrasound beams 30 as a function of the actual depth and size of the bladder 41, as will be explained in further detail with the aid of FIG. 10, which depicts a flowchart of a refinement of the method 100 in which such frequency optimization is deployed. As is well-known per se, the ultrasound frequency is proportional to the image resolution and inversely proportional to the imaging depth. Hence, for a bladder 41 there exists an optimal ultrasound frequency f1 for the measurement of the anterior wall section of the bladder 41 as well as an optimal ultrasound frequency f2 for the measurement of the posterior wall section of the bladder 41, with typically f1f2 due to the different distances of the anterior and posterior wall sections from the abdominal surface of the subject 40.

[0060] Hence, in an embodiment the wearable bladder monitoring device 1 is adapted to tune the ultrasound frequency of the ultrasound beams 30, i.e. at least of the ultrasound beams passing through the bladder 41, in order to improve the accuracy of the anterior and posterior wall section localizations. To this end, in operation 103 the phased array controller 13 may control the phased array 10 to generate ultrasound beams at various beam angles at an initial frequency f.sub.i, which initial frequency typically is a relatively low frequency, e.g. a frequency of about 2 MHz, in order to generate a relatively wide angle ultrasound beam, with the echo signals induced by these ultrasound beams being acquired in operation 105 as previously explained. This enables the bladder monitoring system to roughly determine the position and size of the bladder 41 due to the wide angled nature of the low frequency ultrasound beam.

[0061] This rough estimation of the position and size of the bladder 41 is used in operation 201 to determine a first distance d.sub.a to the anterior wall of the bladder 41 and a second distance d.sub.b to the posterior wall of the bladder 41, which distances in combination with the attenuation rate of ultrasound waves in fat tissue, e.g. about 0.5 dB/MHz/cm, to determine an optimal ultrasound frequencies f1 and f2 for imaging the anterior and posterior walls of the bladder 41, e.g. using the formula f=M/(0.5*D), in which f is the optimal ultrasound frequency, M is the maximum attenuation threshold for the signal to noise ratio specific phased array 10 and D is the distance to the wall section to be imaged.

[0062] Subsequently, the bladder 41 may be imaged in operation 203 with ultrasound signals at the determined optimal ultrasound frequencies f1 and f2 with the respective echoes of these ultrasound signals being acquired in operation 205 such that the bladder volume estimation with the signal processor 23 may be based on the echo signals of the ultrasound beams at the optimal ultrasound frequencies f1 and f2 in order to improve the accuracy of the bladder volume estimation. This for example may be achieved by combining the ultrasound beams at the optimized frequencies under various beam angles as previously explained into a single evaluation, e.g. by mapping the echo signals of these ultrasound beams onto a bladder model as previously explained. Alternatively, rather than performing multiple ultrasound measurements at the respective optimal ultrasound frequencies f1 and f2, a single measurement (scan) may be performed at an ultrasound frequency that is an average of the optimal ultrasound frequencies f1 and f2, e.g. a weighted average at 110% of the optimal ultrasound frequency f2 for imaging the posterior wall sections, as f2 typically is lower than f1.

[0063] As previously explained, the acquired echo signals may be pre-processed in operation 107 and further processed as explained in more detail with the aid of the flowchart of FIG. 8. It is noted that where such frequency optimization of the ultrasound beams is to be included in the operation of the wearable bladder monitoring device 1, the ultrasound transducer elements 11 preferably are CMUT elements due to their superior bandwidth characteristics compared to e.g. PZT elements.

[0064] It should be noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word comprising does not exclude the presence of elements or steps other than those listed in a claim. The word a or an preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means of hardware comprising several distinct elements. In the device claim enumerating several means, several of these means can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.