The present invention is related to a method and system using acoustic information obtained from a joint as an indicator of a joint state.
Along with the advancement of aging, patients complaining joint pain is increasing. For example, in the report in the 2008 52nd Annual General Assembly and Scientific Meeting of the Japan College of Rheumatology, according to a wide range of epidemiological investigation, the prevalence rate of knee osteoarthritis from findings of deformation on X-rays is 44.6% for men at the age of 65 or higher and 66.0% for women at the age of 65 or higher, which are high prevalence rates. Since recovery from knee osteoarthritis is very difficult, it is one of the symptoms of which early discovery is especially desirable among joint conditions. Detection of an abnormal sound in a knee joint is examined as a potential method for early discovery.
Upon joint movement, sliding resistance due to degeneration, abrasion, or the like of a cartilage of a joint surface is caused, making a joint sound. This joint sound can be obtained by a bio-acoustic sensor and be utilized as an acoustic signal in diagnosis of arthrosis. Patent Literature 1 discloses an arthrosis diagnosis system using a bio-acoustic sensor, an angle sensor and a weighing meter. In this diagnosis system, the bio-acoustic sensor is attached on a skin near a joint and detects an abnormal sound caused upon bending/stretching of the joint, the angle sensor is attached near the joint and detects a bending/stretching angle of the joint, and the weighing meter detects a load working on the joint as the joint is bent/stretched. In addition, appropriate diagnosis of arthrosis is enabled by distinguishing the abnormal sound obtained by the bio-acoustic sensor from other noises while referring to detection results of the angle sensor and the weighing meter.
[PTL 1] Patent Literature 1: Japanese Patent No. 5754689 specification
There is a need for a new method and system of appropriately detecting a joint state from an acoustic of a joint using a system with a simple configuration.
In one aspect, the present invention provides a method of using acoustic information obtained from a joint as an indicator of a joint state. The method comprises: the step of, using a bio-acoustic sensor, obtaining an acoustic signal emitted by the joint during a time period at least including a first motion period in which the joint changes from a first form to a second form, a pause period of the joint and a second motion period in which the joint changes from the second form to the first form; the step of converting the acoustic signal that was obtained to time trend data at least showing a relationship between an acoustic signal intensity and time; and the step of setting a basic threshold value regarding the acoustic signal intensity from the time trend data and calculating first acoustic information based on the basic threshold value, characterized in that the first acoustic information is used as an indicator of the joint state.
In one embodiment of the method of the present invention, setting a basic threshold value regarding the acoustic signal intensity from the time trend data further comprises identifying an initial time and a terminal time of at least one non-signal time period from the time trend data and calculating the basic threshold value from time trend data in the non-signal time period. At least one of the initial time and the terminal time of the non-signal time period is identified under the condition of an absolute value of an average change rate of the acoustic signal intensity in a predetermined time period being a predetermined value or lower. The basic threshold value is calculated based on an average value and a standard deviation of an acoustic signal intensity in the non-signal time period in the time trend data and a first coefficient.
In one embodiment of the method of the present invention, calculating the first acoustic information based on the basic threshold value comprise calculating the first acoustic information by extracting an acoustic signal intensity exceeding the basic threshold value in the time trend data.
In one embodiment of the method of the present invention, converting the acoustic signal that was obtained to the time trend data at least showing a relationship between the acoustic signal intensity and time comprises digitally converting the acoustic signal that was obtained on a predetermined sampling frequency. The predetermined sampling frequency is about 25 Hz to about 2000 Hz. The first acoustic information is a count and/or intensity of the digitally converted acoustic signal exceeding the basic threshold value.
In one embodiment of the method of the present invention, the first acoustic information is calculated from an acoustic intensity corresponding to the first motion period in the time trend data.
In one embodiment of the method of the present invention, comparison between the first acoustic information and a pre-set discrimination threshold value is used as an indicator of the joint state.
In one embodiment of the method of the present invention, the step of calculating the acoustic information further comprises setting an additional threshold value of an acoustic signal intensity that is higher than the basic threshold value and calculating second acoustic information, wherein a combination of the first acoustic signal and the second acoustic signal is used as an indicator of the joint state.
In one embodiment of the method of the present invention, comparison between a combination of the first acoustic information and the second acoustic information and a pre-set discrimination value is used as an indicator of the joint state.
The joint to which the method of the present invention is applied may be a knee joint or an elbow joint.
In another aspect, the present invention also provides a system of detecting a joint state in accordance with the present invention. The system comprises: a bio-acoustic sensor obtaining acoustic information from a joint; and a detection apparatus detecting a joint state from a result of the acoustic information obtained by the bio-acoustic sensor.
In one embodiment of the system of the present invention, the system comprises: a data conversion part converting the acoustic signal obtained with the bio-acoustic sensor to time trend data at least showing a relationship between an acoustic signal intensity and time; a threshold setting part setting a basic threshold value regarding the acoustic signal intensity from the time trend data; an acoustic information calculation part calculating first acoustic information based on the basic threshold value; and an indicator calculation part calculating an indicator of a joint state based on the first acoustic information that was calculated.
In one embodiment of the system of the present invention, the system does not comprise an angle sensor.
The present invention provides a new method of estimating a joint state from an acoustic obtained with a bio-acoustic sensor and a system therefor. Since this enables a subject to easily measure the joint state, it is expected that this would contribute to monitoring of the joint state of the subject or early discovery of an abnormality.
The present example is described below. Unless specifically referred to, the terms used herein should be understood as being used in the meanings that are generally employed in the subject field. Therefore, unless defined otherwise, all of the technical terms and scientific terms used herein have the same meaning as those generally understood by those skilled in the art in the field to which the present invention belongs. In a case of contradiction, the present specification (including definitions) will be prioritized.
Herein, “about” refers to the concept of being within the range of ±10% of the number thereafter.
The present invention is related to a new method and system using acoustic information obtained from a joint as an indicator of a joint state. Embodiments of the present invention are described below in detail using the drawings. First, a method using acoustic information obtained from a joint as an indicator of a joint state by using a basic threshold value is described as a first embodiment.
The method in the present invention may be applied to detection of a joint state in various joints. For example, joints that may be targeted by the present invention include, but not limited to, a knee joint, an elbow joint, a finger joint, a shoulder joint, a wrist joint, an ankle joint, a hip joint, a jaw joint and so on. In a preferable embodiment, the present invention may be used in a knee joint, an elbow joint and a jaw joint, which generally repeatedly move mainly between a first form and a second form. More preferably, the present invention may be used in a knee joint and an elbow joint with more tendency to show joint state abnormality as acoustic information compared to other joints. Especially preferably, the present invention may be used in a knee joint.
In addition, the bio-acoustic sensor in the present invention may be invasive, or may be non-invasive. Preferably, the bio-acoustic sensor in the present invention is a non-invasive sensor that can easily be worn near a joint that is to be a measuring object. The means for wearing a non-invasive sensor near a joint may be any means. For example, the non-invasive sensor may be attached on a skin with an adhesive tape, or may be fixed on a skin near a joint of a subject with an appropriate band tool.
The bio-acoustic sensor is at least one or more for a joint of which joint state is sought to be detected, wherein any number of bio-acoustic sensors may be worn. For example, when a more accurate state of a joint is sought to be detected or the like, bio-acoustic sensors may be, for example, provided at a plurality of sites at the upper part, the inside and the outside of the joint to detect a difference or the like in the joint state between the inside portion and the outside portion.
While the location near a joint to which a bio-acoustic sensor is attached may be any location as long as it is possible to sense a joint noise in the joint, it is preferable that a bio-acoustic sensor is at a position that is as close as possible to the location where a joint sound is generated.
Therefore, in one embodiment, when a bio-acoustic sensor is provided near a knee joint, it is desirable that the bio-acoustic sensor is attached near a lower part of the patella 208 where the joint surface exists. In a preferable embodiment, the present invention can, for example, detect a joint sound of the joint surface where the femur 202 and the tibia 204 face each other with one acoustic sensor and use the joint sound as an indicator of a joint state. In another embodiment, in addition to an acoustic of the joint surface where the femur 202 and the tibia 204 face each other that is detected by one acoustic sensor, it is also possible to detect an acoustic inside and/or outside a joint with another one or two acoustic sensor and combine these to collectively estimate a joint state with good precision using more information.
In step 104, in a state in which a bio-acoustic sensor is worn, the subject moves the joint from a first form to a second form. In the repeating motion between the first form and the second form, this time period for moving the joint from the first form to the second form is called a “first motion period” herein. For example, in a knee joint, the first form may be a bent form in which the knee joint is closed and the second form may be an extended form in which the knee joint is open, or the first form may be an extended form in which the knee joint is open and the second form may be a bent form in which the knee joint is closed. In addition, after maintaining the second form for a predetermined time period (herein, this time period is called a “pause period” of the joint), the joint is moved so as to return from the second form to the first form. This time period for moving the joint from the second form to the first form is called a “second motion period” herein. A bio-acoustic sensor obtains an acoustic signal emitted by the joint during the time from the start of this first motion period, through the pause period, to the end of the second motion period (herein, this is called a “joint motion time period for one reciprocation”). It is possible to cover all forms and motions of the joint that are necessary for the present invention to estimate the joint state by obtaining an acoustic signal (joint sound) in a joint motion during a joint motion time period of one reciprocation with a bio-acoustic sensor. A joint sound in a joint motion time period of a plurality of reciprocations may be obtained in order to increase detection precision.
In addition, the magnitude of the load applied to a knee joint affects the magnitude of a joint sound. Thus, a bending/stretching motion may carry out both an active bending/stretching which is carried out while remaining in a sitting position without the foot touching the floor and a loaded bending/stretching which is a shift from a sitting position to a standing position to obtain an acoustic signal in each bending/stretching motion. Both the active bending/stretching and the loaded bending/stretching do not necessarily need to be performed. Only one may be performed. Compared to the active bending/stretching, the loaded bending/stretching has a great load applied to the knee joint, thereby generating a large joint sound. In this regard, it is better to carry out the loaded bending/stretching, in which a stronger acoustic signal can be obtained, for easier detection of the joint state.
In step 106, acoustic signals obtained by a bio-acoustic sensor are converted to time trend data by the detection apparatus discussed below. The time trend data is data in which the obtained acoustic signals are aligned in chronological order, at least showing the relationship between acoustic signal intensity and time.
In step 108, the detection apparatus sets a basic threshold value from the time trend data to calculate the first acoustic information. The basic threshold value is the acoustic signal intensity that is used as a criterion upon calculating the acoustic information that is used as an indicator of the joint state from an acoustic signal. The basic threshold value may be set to a predetermined acoustic signal intensity, or may be set to a value calculated from an acoustic signal obtained from each subject. Since the acoustic signal intensity upon moving a joint that is obtained by a bio-acoustic sensor differs among individuals, it is preferable to calculate a basic threshold value from an acoustic signal obtained from each subject. This enables suppression of variation in the difference in measured values among individuals and enables increase of precision of detection of a joint state.
In one embodiment, when a predetermined acoustic signal intensity is used as a basic threshold value, the acoustic signal intensity is set based on the measurement results obtained from various subjects.
When calculating a basic threshold value for each subject, the basic threshold value, for example, may be set to an average value of acoustic signal intensity obtained throughout the entire time period of measurement, or may be set to a value calculated from the acoustic signal intensity in a time period in which signals with low acoustic signal intensity are in succession. Herein, the time period in which signals with an acoustic signal intensity lower than a predetermined condition are in succession is called a “non-signal time period”. Since it can be considered that an acoustic signal with high acoustic intensity locally existing in time trend data expresses a joint sound due to sliding of bones with respect to one another upon joint motion, it is preferable for acoustic information to be calculated from the acoustic signal intensity excluding a signal during a non-signal time period in order to detect a joint state with good precision. For example, when bending/stretching motion of a joint is not carried out or the like, the acoustic signal intensity should originally be at zero value from a bio-acoustic sensor, but a signal including various noises and with low acoustic signal intensity is actually generated.
In one embodiment, the acoustic signal intensity of a non-signal is first identified in order to calculate the basic threshold value 454. The acoustic signal intensity of a non-signal may be calculated using the acoustic signal intensity in the non-signal time period 420 as a criterion. The non-signal time period 420, for example, may be determined by identifying an initial time 422 and a terminal time 424 thereof, or may be identified as a time period below a value of a signal intensity that was predetermined. Since the variation in acoustic signal intensity in the non-signal time period 420 differs among individuals, it is preferable to identify the initial time 422 and the terminal time 424 of the non-signal time period 426 for each subject.
In a representative embodiment, the initial time 422 and the terminal time 424 of the non-signal time period 420 may be identified under the condition of the absolute value of an average change rate of the acoustic signal intensity for each micro time being a predetermined value or lower successively throughout a predetermined time period 426. A micro time is a time that is sufficiently short compared to the non-signal time period 420 and the acoustic signal emission time periods 410 and 410′, which is preferably about 0.04 seconds or shorter. When an acoustic signal is digitally converted, a micro time may be a sampling cycle, and when a sampling frequency is 100 Hz, a micro time may be 0.01 second. In addition, the predetermined time period 426 may be any time period that can distinguish the non-signal time period 420 from the acoustic signal emission time periods 410 and 410′, and includes a plurality of the aforementioned micro times. For example, when a micro time is about 0.01 second, the predetermined time period 426 may be about 0.2 seconds.
When the absolute value of the average change rate of the acoustic signal intensity of a micro time is at or below a predetermined value successively throughout the predetermined time period 426, the initial time of the predetermined time period 426 may be identified as the initial time of the non-signal time period 420. In addition, when the absolute value of the average change rate of the acoustic signal intensity of a micro time is over the predetermined value in the predetermined time period 426, the terminal time of the predetermined time period 426 may be identified as the terminal time of the non-signal time period 420. The predetermined value may be appropriately adjusted in accordance with the length and acoustic signal intensity (unit) of the micro time.
As shown in
A basic threshold value 454 is set based on the acoustic signal intensity of an acoustic signal within the non-signal time period identified by the initial time 422 and the terminal time 424. The basic threshold value 454 may be, for example, the average value of acoustic signal intensity within the non-signal time period 420, a value resulted by adding a constant value to the average value of acoustic signal intensity within the non-signal time period 420, a value calculated from the average value of acoustic signal intensity within the non-signal time period 420 and the variation in signal intensity within the non-signal time period 420, or may be calculated as the maximum intensity within the non-signal time period 420. There is variation in acoustic signal intensity within the non-signal time period 420, and in order to appropriately evaluate this variation and set a basic threshold value 454, it is desirable that the basic threshold value 454 be set to a value calculated from the average value of acoustic signal intensity within the non-signal time period 420 and the variation in acoustic signal intensity within the non-signal time period 420. In this case, the average value of acoustic signal intensity within the identified non-signal time period 420 (average value of non-signal intensity 452 (Ave.)) is calculated, and, additionally, a standard deviation (SD) of acoustic signal intensity within the non-signal time period 420 is calculated as the variation in acoustic signal intensity within the non-signal time period 420. In a typical embodiment, a basic threshold value is calculated with TH=Ave.+αSD (formula 1) and the coefficient α of the standard deviation (SD) can be arbitrarily set. The coefficient α may be set so as to include, 80% or more, more preferably 90% or more, and typically all, of the acoustic signals within the non-signal time period 420. It is preferable that the coefficient α be set so as to not include an acoustic signal of time periods other than the non-signal time period 420 (an acoustic signal that originally should belong to the acoustic signal emission time period 410 or 410′) to the extent possible and not leak an acoustic signal of the non-signal time period 420. For example, a coefficient α is set to a value that is 3 or higher. Empirically, in order to extract as much signals having the intensity that exceeds a signal within the non-signal time period 420 as possible as acoustic information while excluding almost all signals within the non-signal time period 420 from the acoustic information with a basic threshold value, it is more preferable that the coefficient α be set to 3.
The first acoustic information may be calculated from the set basic threshold value 454. The first acoustic information may be in any form as long as calculation from the basic threshold value 454 is possible, which, for example, may be extracted as the acoustic signal intensity that exceeds the basic threshold value 454, may be a ratio of the time in which the acoustic signal intensity exceeds the basic threshold value 454 to the entire measurement time, may be the average value of signal intensity exceeding the basic threshold value 454, or, when the acoustic signal is a digital signal, may be a count of signals having an intensity that exceeds the basic threshold value and/or said intensity.
In the time trend data 402, the first acoustic information may be calculated from i) only a time period corresponding to a first motion period in which a joint changes from a first form to a second form, ii) only a time period corresponding to a second motion period in which a joint changes from a second form to a first form, iii) a time period corresponding to a joint motion period of one reciprocation, iv) a time period corresponding to a joint motion period of a plurality of reciprocations, or the like. Which time period to be selected depends on the desired information. For example, the motion period of changing from a bent form to an extended form and the motion period of changing from an extended form to a bent form actually differ in terms of the sliding joint surface and also differ in terms of the generated acoustic signal. Therefore, in a joint motion, it is preferable to calculate the first acoustic information based on the motion period in which the acoustic signal intensity is expressed significantly. For example, when a subject feels pain in a joint only upon the motion period of changing from an extended form to a bent form, the count of signals of only the motion period of changing from an extended state to a bent state may be calculated to use the count as an indicator for detection of a joint state. In addition, a joint state can be understood with more detail by calculating all of the counts of the signals of each time period of i) to iv).
In step 110, an indicator of a joint state is obtained from the obtained first acoustic information. Since the first acoustic information is a numerical value expressing the signal intensity, count of signals or the like that is calculated with the above-described method, it is possible to detect the joint state with this numerical value. For example, the first acoustic information may be an indicator of knee osteoarthritis, knee osteochondritis dissecans, meniscal damage, or the like. In addition, the first acoustic information may be an indicator showing not only a disease but also a daily joint state. When the first acoustic information is an indicator showing a daily joint state, it is possible to detect whether the joint state on the day of measurement is good or bad by comparison with the first acoustic information of himself/herself calculated in the past or comparison with a standard value of himself/herself. Meanwhile, when detecting a state of a disease such as knee osteoarthritis, it is preferable to compare information calculated as the first acoustic information with objective information.
When detecting a state of a disease with the first acoustic information, an indicator showing a joint state may be a comparison between the acoustic information and a pre-set discrimination threshold value.
This detection may also be, for example, two steps of “normal” and “abnormal”, or three stages of “healthy”, “pre-knee arthrosis” and “knee arthrosis”. The discrimination threshold value may be set using accumulated data of many subjects or the like as a criterion.
The present invention can calculate the first acoustic information that is used as an indicator of a joint state using only an acoustic signal obtained from a bio-acoustic sensor as discussed above. Therefore, the present invention is especially useful in terms of not needing to detect the progression/timing of a joint motion of a subject using other sensors such as a conventional angle sensor or a weighing meter to cross-reference with time trend data of an acoustic signal and being able to achieve low cost with a simple apparatus configuration. In addition, a weighing meter is an apparatus in any form that can measure motion acceleration. For example, the acceleration sensor may include a vibration system, an optical system and a semiconductor system. Preferably, the acceleration sensor is a semiconductor system (e.g., piezo-resistance type or electrostatic capacitance type) that can be miniaturized. In addition, the angle sensor is an apparatus in any form that can measure an angle and an angular speed. For example, the angle sensor may be a rotary sensor, inclination sensor, or may be a gyro sensor. Furthermore, while an angle sensor and a weighing meter are basically unnecessary, those apparatuses may be combined and used as needed in the present invention.
A conventional system of diagnosing a joint state from a joint sound not only uses a bio-acoustic sensor but also uses an angle meter and a weighing meter. This conventional system needed to use an angle sensor and a weighing meter to accurately detect the timing of a subject's motion of standing up from a chair for a joint motion and refer to this detection result to remove a noise involved in the motion of the detection data of a bio-acoustic sensor. As such, a conventional diagnosis system needs many sensors, becoming a high-cost apparatus with complicated apparatus configuration, thereby only being able to be practiced in a medical institution or the like. Meanwhile, since early discovery is important in joint diseases such as knee osteoarthritis as discussed above, easy detection of a joint state on a daily basis at home or the like is desired to be able to be carried out.
According to the present invention, it is possible to obtain a method and system for appropriately detecting a joint state from an acoustic of a joint, which can be easily practiced at home or the like using only a bio-acoustic sensor. The method and system of the present invention can naturally be used in medical institutions or the like as well, wherein, for example, a joint state can also be diagnosed in combination with X-ray imaging and examination by a physician.
Next, a second embodiment is described.
In the present embodiment, in step 708, a basic threshold value and an additional threshold value are set based on the time trend data to calculate the first and second acoustic information.
An additional threshold value 856 may be arbitrarily set as long as the value has the acoustic signal intensity that is different from the basic threshold value 854, which may be a value higher than or a value lower than the basic threshold value 854. Since extraction of an acoustic signal with higher acoustic signal intensity extracted using the additional threshold value as the second acoustic information while using the first acoustic information extracted using the basic threshold value 854 as a basis is effective for generating an indicator of a joint state with higher certainty, it is preferable that the additional threshold value 856 is set to a value higher than the basic threshold value 854.
The set value of the additional threshold value 856 may be any value. For example, the value may be set to a pre-set acoustic signal intensity, or may be set to a value calculated from an acoustic signal obtained from each subject.
The additional threshold value 856 can be calculated in any way. In one embodiment, said value can be calculated with (formula 1) in the same manner as the basic threshold value. The additional threshold value 856 can be calculated by differentiating a value of a coefficient a of a standard deviation (SD) of (formula 1) from a value used to calculate the basic threshold value 854. For example, when set to a signal intensity higher than the basic threshold value 854, an additional threshold value 856 may be a value calculated while replacing a first coefficient in a similar formula with a second coefficient with a higher value. This further eliminates some of the acoustic signals with comparatively high acoustic signal intensity in the signal emission time periods 810 and 810′ in addition to the non-signal time period 820. The first acoustic information may be calculated from the basic threshold value 854 and the second acoustic information may be calculated from the additional threshold value 856. Since an acoustic signal having an intensity exceeding the additional threshold value 856 may present information that is different from the first acoustic signal derived from the basic threshold value, combination of the first and second acoustic information enables detection of a joint state with higher precision. An embodiment using such an additional threshold value 856, for example, regardless of having a small count of signals having the acoustic signal intensity exceeding the basic threshold value 854, can appropriately detect an abnormality in a joint state of a subject with a characteristic of the signals having an extremely great intensity. For example, when a joint has an abnormality such as having a joint surface portion with extremely serious damage in the joint, a sound with a very high acoustic signal intensity is caused, thus enabling detection of the presence/absence of the existence of a joint surface portion with extremely serious damage with the second acoustic information showing the presence/absence, count and the like of the acoustic signals exceeding the additional threshold value 856.
In step 710, a joint state is detected using the combination of the first acoustic information and the second acoustic information as an indicator. The present embodiment may also carry out detection of a joint state using the discrimination threshold value described in
Next, a third embodiment is described.
In step 908, a basic threshold value and three additional threshold values are set based on the time trend data to calculate the first to fourth acoustic information.
In step 910, a joint state is detected using a combination of the first to fourth acoustic information as an indicator. In one embodiment, when a measurement result is within the range of the first signal intensity band 1070, a joint state is detected as G1, when a measurement result is within the range of the second signal intensity band 1072, a joint state is detected as G2, when a measurement result is within the range of the third signal intensity band 1074, a joint state is detected as G3, and when a measurement result is within the range of the fourth signal intensity band 1076, a joint state is detected as G4. This enables detection of a joint state (e.g., progression phase of knee osteoarthritis) from the first to fourth acoustic information.
In addition, detection of a joint state with higher precision may be carried out by weighting each count of signals of the first to fourth acoustic information (e.g., weighting the count of signals of the first acoustic information to about 1-fold, weighting the count of signals of the second acoustic information to about 2-fold, weighting the count of signals of the third acoustic information to about 3-fold, weighting the count of signals of the fourth acoustic information to about 5-fold). In addition, for example, symptom classification with a discrimination threshold value may be performed using a value resulted by adding up the count of signals of each signal intensity band that was weighted as an indicator.
The present application further provides a system of detecting a joint state in accordance with the method of the above-described first, second, or third embodiment.
The data conversion part 1122 converts an acoustic signal obtained with a bio-acoustic sensor 1110 to time trend data at least showing the relationship between acoustic signal intensity and time. The data conversion is carried out with the method described above. The data conversion part 1122 sends the converted time trend data to the threshold value setting part 1124.
The threshold value setting part 1124 sets a basic threshold value regarding the acoustic signal intensity from the time trend data received from the data conversion part 1124. The threshold value is set with the method in the first, second, or third embodiment. The threshold value setting part 1124 sends the time trend data and the set threshold value to the acoustic information calculation part 1126.
The acoustic information calculation part 1126 calculates acoustic information based on the threshold value. A method of calculating acoustic information is set with the method in the first, second, or third embodiment. The acoustic information calculation part 1126 sends the calculated acoustic information to the indicator calculation part 1128.
The indicator calculation part 1128 calculates the indicator of a joint state based on the calculated acoustic information. The method for calculating the indicator is calculated with the method in the first, second, or third embodiment. The calculated indicator may be displayed on any display device, transmitted by audio with any speaker device, or stored in any database or the like, as an indicator showing the joint state of a subject.
Although the present embodiment described a method and system using acoustic information obtained from a knee joint as an indicator of a joint state, the present method may be applied not only to a knee joint but also to other joints such as an elbow joint, a finger joint, a shoulder joint, a wrist joint, an ankle joint, a hip joint and a jaw joint. For example,
A test of detecting a joint state of a plurality of subjects was carried out based on the method of the present invention.
A subject carried out a plurality of repeating motion of a sitting position and a standing position using a chair, wherein a joint sound made by a knee joint during this motion was obtained by a bio-acoustic sensor. One bio-acoustic sensor was attached to the patella of the subject, wherein an angle sensor, weighing sensor, and other sensors were not used.
Regarding the acoustic signal obtained by a bio-acoustic sensor as an analog electric signal, the sampling frequency of digital conversion was set to 100 Hz, and the obtained digital signal was converted to time trend data using short-time Fourier transform.
Next, a non-signal time period in the time trend data was identified. The initial time and the terminal time of the non-signal time period were identified under the condition of the absolute value of the average change rate of acoustic signal intensity during 0.01 second being at or below a predetermined value successively for 0.2 seconds. Next, a basic threshold value for excluding a non-signal from the time trend data was identified. The basic threshold value was set to a value resulted by adding 3-fold (first coefficient) of the standard deviation of the intensity of the non-signal to the average value of intensity of the non-signal in the non-signal time period. In addition, a count of acoustic signals with an intensity exceeding the basic threshold value was calculated as acoustic information.
The progression phase of knee osteoarthritis was able to be estimated with the count of acoustic signals.
A test of detecting a joint state of a plurality of subjects was carried out based on the method of the present invention setting a basic threshold value and an additional threshold value and using acoustic information obtained from a joint as an indicator of a joint state.
An acoustic signal was obtained from a subject with a method similar to Example 1 and converted to time trend data of a digital signal.
A non-signal time period was identified and a basic threshold value was set using a method similar to Example 1. Herein, an additional threshold value was further set in addition to the basic threshold value. The additional threshold value was set by multiplying the standard deviation of a non-signal in the non-signal time period by a value that is 6-fold or 9-fold (second coefficient) with a method similar to the method for the basic threshold value. In addition, a count of acoustic signals with an intensity exceeding the threshold value and a count of acoustic signals with an intensity exceeding the additional threshold value were calculated as acoustic information.
The progression phase of knee osteoarthritis was estimated by combining two acoustic information. In addition to the estimation in Example 1, the estimation method herein can identify a subject that possibly has a particularly severe symptom and a subject having the initial symptom of knee arthrosis.
As discussed above, the use of a method using acoustic information obtained from a joint as an indicator of a joint state enabled good detection of a joint state of a subject only with the acoustic information obtained from a bio-acoustic sensor without using a complicated apparatus such as an angle sensor and a weighing meter.
Although the present invention has been exemplified using a preferable embodiment of the present invention as described above, the interpretation of the present invention should not be limited to this embodiment. It is understood that the scope of the present invention should be interpreted by the Claims alone. It is understood that those skilled in the art can practice an equivalent scope based on the description of the present invention and common general knowledge from the description of the specific and preferable embodiment of the present invention. It is also understood that any reference cited herein should be incorporated herein by reference in the same manner as the contents are specifically described herein.
The present invention is useful as an invention that can provide a method and system of appropriately detecting a joint state from an acoustic signal of a joint which can be easily practiced at a home or the like using only a bio-acoustic sensor.
Filing Document | Filing Date | Country | Kind |
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PCT/JP2020/040863 | 10/30/2020 | WO |