FETAL MONITORING SYSTEM AND METHOD
20180368753 ยท 2018-12-27
Inventors
- Bin Yin (Shanghai, CN)
- Sheng Jin (Shanghai, CN)
- Mingdong LI (Shanghai, CN)
- Yuqiang Wu (Shanghai, CN)
- Lin LI (Shanghai, CN)
Cpc classification
A61B5/4343
HUMAN NECESSITIES
A61B2562/04
HUMAN NECESSITIES
International classification
Abstract
A system and method is provided for monitoring the fetal position and/or orientation of the fetus of an expectant mother. An acoustic sensor array is positioned over the belly. The pattern of acoustic sensor signals is processed to determine a fetal orientation and/or to determine movement over time of the fetus.
Claims
1. A system for monitoring the fetal movement of the fetus of an expectant mother, comprising: an acoustic sensor array for positioning over the belly, each acoustic sensor of the acoustic sensor array configured to receive an acoustic signal generated by fetal heartbeat; and a processor for processing the acoustic sensor signals received continuously over ft multiple predetermined time periods, wherein the processor is adapted to determine a geometric center of spatial distribution from the acoustic sensor signals received each time for one predetemined time period and to determine a fetal movement by detecting a change in the position of the geometric center of the spatial distributions.
2. A system as claimed in claim 1, wherein the sensor array comprises an array of passive sound sensors.
3. A system as claimed in claim 1, wherein the processor is adapted to determine a duration of a movement event by counting the number of successive predetermined time periods during which there is determined movement.
4. A system as claimed in claim 3, wherein the processor is adapted: to classify a determined movement as a movement event when a minimum number of successive predetermined time periods is reached; and/or to classify sequential movements as the same movement event if they are separated by a number of successive periods without detected movement, which number does not exceed a preset value.
5. A system as claimed in claim 1, wherein the processor is adapted to classify a determined movement as a fetal position change when the change in center of distribution position exceeds a threshold.
6. A system as claimed in claim 1, wherein the processor is adapted to classify a determined movement as fetal orientation change or fetal position change by pattern recognition based on a training database of acoustic signal distributions; wherein the fetal orientation refers to the angle of the fetal long axis to that of the expectant mother's abdomen; wherein the fetal position refers to the location of the fetus relative to the geometric center of the expectants mother's abdomen.
7. A system as claimed in claim 1, comprising: a memory; and a data transmission unit for transmitting the acoustic sensor data to the processor or to the memory, in a wired or wireless fashion.
8. A system as claimed in claim 1, further comprising a user interface device for presenting the results of the processing to the user.
9. A method for monitoring the fetal movement of the fetus of an expectant mother, comprising: receiving acoustic signals at the belly of the expectant mother sensed by an array of acoustic sensors; and processing the acoustic sensor signals received continuously over multiple predetermined time period, thereby to determine a geometric center of spatial distribution from the acoustic sensor signals received each time for one predetermined time period and to determine a fetal movement by detecting a change of the position of the geometric center of the spatial distributions.
10. A method as claimed in claim 9, comprising determining a duration of a movement event by counting the number of successive predetermined time periods during which there is determined movement.
11. A method as claimed in claim 10, comprising: classifying a determined movement as a movement event when a minimum number of successive predetermined time periods is reached and/or to classify sequential movements as the same movement event if they are separated by a number of successive periods without detected movement which number does not exceed a preset value.
12. A method as claimed in claim 9, comprisingclassifying a determined movement as a fetal position change when the change in center of distribution position exceeds a threshold.
13. A method as claimed in claim 9, comprising: classifying a determined movement as fetal orientation change or fetal position change by pattern recognition based on a training database of acoustic signal distributions: wherein the fetal orientation refers to the angle of the fetal long axis to that of the pregnant woman's abdomen; wherein the fetal position refers to the location of the fetus relative to the geometric center of pregnant woman's abdomen.
14. A computer program comprising code means which is adapted, when said program is run on a computer, to perform the method of claim 9.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] Examples of the invention will now be described in detail with reference to the accompanying drawings, in which:
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DETAILED DESCRIPTION OF THE EMBODIMENTS
[0063] The invention provides a system and method for monitoring the fetal position and/or orientation of the fetus of an expectant mother. By tracking position changes, movement can also be monitored. An acoustic sensor array is positioned over the belly. The pattern of acoustic sensor signals is processed to determine a fetal orientation and/or to determine a position and therefore movement over time of the fetus.
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[0065] A processor is provided for processing the detected acoustic sensor signals. In the example shown, the processor is provided in a remote device such as a smart phone 8 to which the sensor signals are transmitted from the sensor array 4 wirelessly. The processor may instead be part of the system, for example a watch-type device. The data communication also may be over a wired connection to the processor rather than wireless. The processing may also be carried out remotely at a central back-end processing location, with communication for example over the internet.
[0066] There is a memory for storing the sensor data, and for storing the results of the processing. In the example of
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[0068] The microphones essentially measure air pressure, and other pressure sensors may instead be used, for example contact pressure sensors such as piezoelectric sensors or MEMS sensors.
[0069] The microphones 10 may be built in to a textile patch 12 that can be worn on the abdomen of the expectant mother, with the help of any suitable fixation mechanism such as the elastic strap 6. Another option is to embed the sensor array into the abdominal portion of maternity clothes, so that the sensor array becomes an integral part of the clothing. In this case, the sensor array 4 needs to be made washable.
[0070] The size of the patch 12 is sufficient to cover the abdomen under which the uterus is located. The inter-sensor distance of the microphone array is typically in the range of a few centimeters, for example 1 to 5 cm, and a two dimensional sensor array is provided. The sensors may be evenly distributed over the patch area but this is not essential. They may for example be more densely packed at the locations where the heart signal is usually strongest.
[0071] There is a compromise between the spatial resolution required and the number of microphones (thus the cost and hardware complexity as well as the processing complexity).
[0072] The patch 12 is designed to fit the curvature of the abdomen, and therefore the substrate as well as the wiring among sensors must be, to some degree, stretchable and bendable.
[0073] There are preferably at least 5 sensors in the array, and preferably more, for example 10 or more, or even 20 or more.
[0074] The beating heart of the fetus acts as a sound source, creating a sound wave propagating from the fetal heart outwards. This sound wave arrives at the mother's belly, and is picked up by the sensor array.
[0075] As shown in
[0076] Due to the anisotropic nature of the sound propagating path, the wave front does not remain spherical upon arriving on the belly. The magnitude of the sound field intensity depends on the length of the path followed to reach the belly as well as the composition of the propagation path. A stronger heart sound may be captured by a microphone on the mother's belly that is placed closer to the fetal heart, but this is not necessarily the case. Thus, a single identification of a maximum intensity signal is not a reliable indicator of the position of the heart.
[0077]
[0078] A sound signal is captured by each sensor in the array, transmitted to the memory and/or processor and logged as a function over time. The intensity of the sound signal at each sensor may be locally calculated, for instance, by an analogue integrator. The rate of transmission and data logging needs to be sufficiently high in order to capture fetal movement and position changes, which can be in the range of a few to a few tens Hz.
[0079] The data processing may be carried out in real time, or it may be performed later based on stored sensor data. The data processing unit reads out the heart sound intensity data from the memory. The data are in the form of a 2-dimensional array, and also a function of time, meaning there is an array of data stored every T seconds, where T is the data logging period.
[0080] Thus, every signal in the array is a function of time s.sub.i, j(t), where (i,j) denotes the two-dimensional index of the sensor in the array, and all the signals at a same time moment t form a 2-dimensional frame S(t).
[0081] The sensor data are actually a collection of temporal and spatial changes of the fetal heart sound.
[0082] The data processing includes various signal processing steps, including signal conditioning, and then calculation of the center of distribution, and extraction of the fetal movement and position/orientation information.
[0083] The initial signal conditioning is responsible for filtering out noise, which applies to both the individual sensor s.sub.i, j(t) signals and the overall frame S(t) signal.
[0084] After signal conditioning, the center of distribution C(t): (i.sub.c(t), j.sub.c(t)), is calculated from each 2-dimensional frame S(t). The center is defined with reference to the sensor array, i.e. as a row and column index.
[0085] This calculation is known to skilled persons in the field and thus not explained in detail.
[0086] The center of distribution signal C(t) may be considered directly linked to the position of the fetal heart relative to the sensor array, even though not necessarily at a location on the belly closest to the heart (as a result of different propagation paths). Therefore, from the temporal variation of C(t), information about the fetal movement i.e. position change may be derived. For orientation information, pattern recognition is used since identification of a single point is not sufficient to determine orientation.
[0087] The following are some examples of how a fetal movement can be detected, based on tracking the center of distribution.
[0088] A threshold is applied to the amount of change in the signal C(t) for two successive sampling times kT and (k+1)T. Thus, when:
C(t.sub.(k+1)T)C(t.sub.kT)>.sub.m (Eq. 1)
a fetal movement is recorded of a duration of T, where .sub.m is a pre-set movement threshold value.
[0089] When the above threshold change is sustained for N consecutive pairs of position values a fetal movement of a duration of NT is recorded.
[0090] Additional rules may be added to avoid recording of ambiguous movement. For instance, a fetal movement may be identified and recorded only when Eq. 1 above holds consecutively for a certain number of sampling times. In this way, a determined movement is only classified as a movement event when a minimum number of successive predetermined time periods are reached.
[0091] A fetal movement event (by which is meant one continuous chain of movements) may also be determined to be finished only when Eq. 1 does not hold consecutively for a certain number of sampling times. In this way, sequential movements are classified as the same movement event if they are separated only by a short interval of no detected movement, i.e. a maximum number of successive periods without detected movement.
[0092] The end position can be the same as the starting portion by the end of a movement, according to the criteria defined above.
[0093] In order to determine the type of a movement change (which may either be caused by a shift in orientation or a change of the position), movement as represented by C(t) of more than a threshold is identified. Thus, when:
C(t.sub.(k+1)T)C(t.sub.kT)>.sub.p (Eq. 2)
and thereafter the position value stays around C(t.sub.(k+1)T) for a prolonged time T.sub.p, a fetal position change is recorded. .sub.p is a pre-set threshold value that is normally larger than .sub.m. The setting of T.sub.p depends on the gestational stage, typically ranging from a few minutes to hours. According to this definition, a position change is a movement of the fetus as a whole towards a certain direction that ends at a different position from that when it begins.
[0094] In this way, a determined movement is classified as a fetal position change when the change in center of distribution position exceeds a threshold.
[0095] In the third trimester, especially when approaching the final stage of pregnancy, the fetus grows into such a size that it becomes more restricted in the uterus. A position change is not easy at this stage, and is also slow, and most often only relates to a change of the presenting part of the fetus relative to the pelvis of the mother. This movement, with no global position change but with rotation of the fetus, is termed an orientation change.
[0096] In this case, the data sampling period T.sub.o takes a significantly larger value, i.e., T.sub.o>>T, up to a few tens of minutes and even hours.
[0097] An orientation change is recorded when:
C(t.sub.(k+1)T.sub.
and the position value stays around C(t.sub.(k+1)T.sub.
[0098] In
[0099] The functioning of the system has been simulated. According to the simulation results, the sound intensity distribution projected on the sensor array is asymmetrical.
[0100] Besides the method mentioned above, pattern recognition of the sound pressure distribution can also be used to determine both the orientation and the position of the fetus, with a training database of collections of sound pressure patterns. One specific example of distinguishing between head-up and head-down orientations of the fetus by the pattern recognition will now be presented, based on the simulation results.
[0101] A complex finite element method (FEM) was established for the simulation. The model includes the physiological parts shown in
[0102] The parameters used in this simulation were tissue density values and bulk modulus values, acquired from literature relating to a gestational age of 34 weeks. The values are shown in the table below.
TABLE-US-00001 TABLE 1 Density Bulk Modulus Organ (g/cm.sup.3) (GPa) Pregnancy skin 1.12 2.5 Pregnancy muscle 1.11 2.3 Pregnancy body fluid 1.01 2.2 Pregnancy heart 1.12 2.5 Pregnancy spine and rib 1.138 20 Uterus 1.12 2.18 Placenta 1.12 2.2 Amniotic fluid 1 2.18 Fetus 1.1 10 Fetus heart 1.12 2.5
[0103] A heart sound as shown in
[0104] Note that for the determination of fetal orientations of head-up or head-down, 12 microphones is enough. However, more may be used for other purposes.
[0105] The effective sound pressure of each point was recorded, which is the sound pressure that can be detected by the microphones, integrated over a time period t=0.05 s. This sound pressure is given by:
where p.sub.e,i is the effective sound pressure recorded by the i.sup.th microphone and t is time.
[0106] p.sub.i is the instantaneous sound pressure at the abdomen surface at the sensor location. The effective sound pressure is thus defined essentially as a root mean square value.
[0107] The effective sound pressure from the sensors on the 12 selected points for head-up and head-down orientations are plotted in
[0108] The head up results are shown as circles and the head down results are shown as dots.
[0109] From the results in
[0110] To demonstrate how the pattern recognition method functions, 100 sets of data points were been generated for each possible orientation by applying a random noise with Gaussian distribution with a standard deviation of 5.6%. This is used to estimate the maximal possible density and modulus change that could happen during gestation.
[0111] This analysis is based on the acoustic wave motion equation:
where is the medium density, v is the velocity, t is the time, p is the sound pressure, d is the distance to the sound source.
[0112] If the effect of other parameters is ignored, and the density of the medium changes by x%, the sound pressure on the abdominal surface can be roughly estimated by:
p.sub.2=p.sub.1(|p.sub.0||p.sub.1|)x% (Eq. 6)
where p.sub.1 is the original sound pressure before the density change and p.sub.0 is the sound pressure of the inner heart sound.
[0113] The density of the fetus changes during pregnancy, whereas the density of the expectant mother remains essentially constant. These changes can also be taken into account when interpreting the sound pressure signals. Thus, the data processing may evolve over time.
[0114] The dataset of 200 data points was used to create a binary classifier (to classify head-up and head-down orientations) and evaluate its performance. Following the same logic a classifier distinguishing more than 2 fetus positions may be generated if there is a need to do so in practice.
[0115] In the analysis, the correctly classified instances were 199 out of 200.
[0116] In
[0117] The plots of the head-up orientation are shown with diamonds and are generally in the region 90 whereas the plots for the head-down orientation are shown with crosses and are generally in the region 92. However, there is significant overlap so that sensors 3 and 5 do not easily enable the head-up and head-down orientations to be determined.
[0118] In
[0119] The plots of the head-up orientation are in the region 90 whereas the plots for the head-down orientation are in the region 92. There is no overlap so that sensors 7 and 8 enable the head-up and head-down orientations to be determined.
[0120] In
[0121] The plots of the head-up orientation are in the region 90 whereas the plots for the head-down orientation are in the region 92. There is no overlap so that sensors 11 and 12 enable the head-up and head-down orientations to be determined.
[0122] It is thus clear that for distinguishing the head-up from head-down orientation, the signals from the microphones at the bottom of the 34 sensor array as illustrated in
[0123] The example above shows that using pattern recognition to identify the fetal orientation can be very promising. Note that only 12 sensors were used for this example but more sensors may be used to lead to higher accuracy of detection. In this example, only readings from each sensor were used as features for classification; other features like the linear combinations of these sensors or the difference between sensors in certain areas can also be fed into the classifier when needed.
[0124] In real applications, a predictive model may be established with proper training. The training process could involve detecting and recording the sound pressure pattern of the fetal heart sound on pregnant women's abdomen. Features may then be selected or extracted from these patterns. In this way, a relationship may be formulated between the selected feature(s) and the actual fetal orientations detected by a sonograph.
[0125] After having established model from training, actual fetal orientation prediction can be implemented by recording the sound pressure pattern of the fetal heart sounds on the pregnant woman's abdomen. The features are then selected or extracted from the sensed signals, and the fetal orientation is predicted based on the model built up in the training process.
[0126] If the system is provided with the sonograph information obtained during regular antenatal check-ups at hospital, this information may be used for calibration purposes. The classifier model may in this way be tailor-made to suit more a specific person, which leads to an improved accuracy.
[0127] Determining the fetal orientation may also be used to derive a fetal position, instead of relying on the center of distribution as described above. A training database with collections of sound pressure patterns associated with different fetal positions can be established as the training process. A classifier algorithm giving the fetal position can be determined in a similar way as the fetal orientation described above.
[0128] Thus, orientation can be determined by a classifier applied to the sound pressure distribution, with or without also determining the center of distribution. The position (or position change) can be determined either based on the center of distribution alone or based on a classifier in the same way as the orientation.
[0129] As explained above, the data detected by the sensors may be transmitted to a memory in a wired or wireless fashion. The data transmitted can be analogue or converted to digital prior to the transmission. Transmission is carried out at the pre-defined data logging rate, typically a few Hz that is sufficient for capturing the wanted fetal activity information. If power savings are desired and/or minimizing radiation, wired transmission will be used preferred.
[0130] The data storage unit stores the data collected by the detection unit as well as the analysis results from the data processing unit. It can be a wearable storage medium wirelessly or in a wired fashion connected to the detection unit.
[0131] The display device unit uses the analysis results stored in the memory, and communicates with the user (mother-to-be and/or family members) by visualizing the fetal activity info on the display. The content of the visualization may include the amount of fetal movement, the trajectory of the fetal position/orientation change, and overall fetal activity level, as a function of time. Warnings can be provided if, for instance, the amount of fetal movement is below the limit, or the position of the fetal seems not optimal when approaching the expected delivery date. The communication to the user can be provided upon a request from the user, or instantly if an immediate warning is necessary.
[0132] The system described above makes use of a controller or processor for processing the sensed data and for performing the data analysis.
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[0134] The computer 130 includes, but is not limited to, PCs, workstations, laptops, PDAs, palm devices, servers, storages, and the like. Generally, in terms of hardware architecture, the computer 130 may include one or more processors 131, memory 132, and one or more I/O devices 133 that are communicatively coupled via a local interface (not shown). The local interface can be, for example but not limited to, one or more buses or other wired or wireless connections, as is known in the art. The local interface may have additional elements, such as controllers, buffers (caches), drivers, repeaters, and receivers, to enable communications. Further, the local interface may include address, control, and/or data connections to enable appropriate communications among the aforementioned components.
[0135] The processor 131 is a hardware device for executing software that can be stored in the memory 132. The processor 131 can be virtually any custom made or commercially available processor, a central processing unit (CPU), a digital signal processor (DSP), or an auxiliary processor among several processors associated with the computer 130, and the processor 131 may be a semiconductor based microprocessor (in the form of a microchip) or a microprocessor.
[0136] The memory 132 can include any one or combination of volatile memory elements (e.g., random access memory (RAM), such as dynamic random access memory (DRAM), static random access memory (SRAM), etc.) and non-volatile memory elements (e.g., ROM, erasable programmable read only memory (EPROM), electronically erasable programmable read only memory (EEPROM), programmable read only memory (PROM), tape, compact disc read only memory (CD-ROM), disk, diskette, cartridge, cassette or the like, etc.). Moreover, the memory 132 may incorporate electronic, magnetic, optical, and/or other types of storage media. Note that the memory 132 can have a distributed architecture, where various components are situated remote from one another, but can be accessed by the processor 131.
[0137] The software in the memory 132 may include one or more separate programs, each of which comprises an ordered listing of executable instructions for implementing logical functions. The software in the memory 132 includes a suitable operating system (O/S) 134, compiler 135, source code 136, and one or more applications 137 in accordance with exemplary embodiments.
[0138] The application 137 comprises numerous functional components such as computational units, logic, functional units, processes, operations, virtual entities, and/or modules.
[0139] The operating system 134 controls the execution of computer programs, and provides scheduling, input-output control, file and data management, memory management, and communication control and related services.
[0140] Application 137 may be a source program, executable program (object code), script, or any other entity comprising a set of instructions to be performed. When a source program, then the program is usually translated via a compiler (such as the compiler 135), assembler, interpreter, or the like, which may or may not be included within the memory 132, so as to operate properly in connection with the operating system 134. Furthermore, the application 137 can be written as an object oriented programming language, which has classes of data and methods, or a procedure programming language, which has routines, subroutines, and/or functions, for example but not limited to, C, C++, C#, Pascal, BASIC, API calls, HTML, XHTML, XML, ASP scripts, JavaScript, FORTRAN, COBOL, Perl, Java, ADA, .NET, and the like.
[0141] The I/O devices 133 may include input devices such as, for example but not limited to, a mouse, keyboard, scanner, microphone, camera, etc. Furthermore, the I/O devices 133 may also include output devices, for example but not limited to a printer, display, etc. Finally, the I/O devices 133 may further include devices that communicate with both inputs and outputs, for instance but not limited to, a network interface controller (NIC) or modulator/demodulator (for accessing remote devices, other files, devices, systems, or a network), a radio frequency (RF) or other transceiver, a telephonic interface, a bridge, a router, etc. The I/O devices 133 also include components for communicating over various networks, such as the Internet or intranet.
[0142] When the computer 130 is in operation, the processor 131 is configured to execute software stored within the memory 132, to communicate data to and from the memory 132, and to generally control operations of the computer 130 pursuant to the software. The application 137 and the operating system 134 are read, in whole or in part, by the processor 131, perhaps buffered within the processor 131, and then executed.
[0143] When the application 137 is implemented in software it should be noted that the application 137 can be stored on virtually any computer readable medium for use by or in connection with any computer related system or method. In the context of this document, a computer readable medium may be an electronic, magnetic, optical, or other physical device or means that can contain or store a computer program for use by or in connection with a computer related system or method.
[0144] The system and method described above may be used for fetal/pregnancy monitoring products.
[0145] Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. 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. Any reference signs in the claims should not be construed as limiting the scope.