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EP-3949840-B1 - PULSE RATE DETECTION DEVICE AND PULSE RATE DETECTION PROGRAM

EP3949840B1EP 3949840 B1EP3949840 B1EP 3949840B1EP-3949840-B1

Inventors

  • JONES, MICHAEL

Dates

Publication Date
20260506
Application Date
20200327

Claims (5)

  1. A pulse rate detection device (1) comprising: a moving image obtaining means (8) configured to obtain a moving image captured by photographing a body surface of a subject; a pulse rate obtaining means (2) configured to obtain a pulse rate of the subject on the basis of change of a pixel value of the body surface in the moving image; and a reliability obtaining means (2) configured to obtain reliability of the obtained pulse rate, wherein the pulse rate obtaining means (2) is configured: to obtain the pulse rate from a pulse rate peak in a frequency domain of the obtained moving image, and to obtain the disturbance peak in a frequency domain of a disturbance factor; wherein the reliability obtaining means (2) is configured to obtain the reliability on the basis of a signal-to-noise ratio of the obtained pulse rate; and wherein the device further comprises: a reducing means (2) configured to reduce the reliability if the disturbance peak in the frequency domain of a disturbance factor that reduces accuracy of the obtained pulse rate is equal to or closer than a predetermined amount to the obtained pulse rate peak, and an output means (5) configured to output the obtained pulse rate, if the reliability is equal to or greater than a predetermined first reliable criteria (S 450); otherwise, if the reliability is less than said first reliable criteria but is equal to or greater than a predetermined second reliability criteria (S 465) and a change of the obtained pulse rate is within a predetermined appropriate range (S 465).
  2. The pulse rate detection device (1) according to claim 1, wherein the change of the pulse rate is a difference between the obtained pulse rate and an immediate past pulse rate, and the output means (5) is configured to output the obtained pulse rate as being within the appropriate range if the difference there between is equal to or less than predetermined criteria.
  3. The pulse rate detection device according to claim 1, wherein the disturbance factor is due to a movement of the body surface, and the reducing means (2) is configured to reduce the reliability if a movement peak in the frequency domain of the movement of the body surface is equal to or closer than the predetermined amount to the obtained pulse rate peak.
  4. The pulse rate detection device according to claim 1 or 3, wherein the disturbance factor is due to variation of light illuminating the body surface, and the reducing means (2) is configured to reduce the reliability if a light peak in the frequency domain of the variation of light is equal to or closer than the predetermined amount to the obtained pulse rate peak.
  5. A pulse rate detection program for causing a computer to realize: a moving image obtaining function for obtaining a moving image captured by photographing a body surface of a subject; a pulse rate obtaining function for obtaining a pulse rate of the subject on the basis of change of a pixel value of the body surface in the moving image; and a reliability obtaining function for obtaining reliability of the obtained pulse rate, wherein the pulse rate obtaining function obtains: the pulse rate from a pulse rate peak in a frequency domain of the obtained moving image, and the disturbance peak in a frequency domain of a disturbance factor; wherein the reliability obtaining function obtains the reliability on the basis of a signal-to-noise ratio of the obtained pulse rate; and wherein the pulse rate detection program is further configured to cause a computer to realize: a reducing function for reducing the reliability if the disturbance peak in the frequency domain of a disturbance factor that reduces accuracy of the obtained pulse rate is equal to or closer than a predetermined amount to the obtained pulse rate peak, and an output function for outputting the obtained pulse rate, if the reliability is equal to or greater than a predetermined first reliable criteria (S 450); otherwise, if the reliability is less than said first reliable criteria but is equal to or greater than a predetermined second reliability criteria (S 465) and a change of the obtained pulse rate is within a predetermined appropriate range (S 465).

Description

TECHNICAL FIELD The present invention relates to a pulse rate detection device and a pulse rate detection program, and relates to, for example, detection of a pulse rate by image processing. BACKGROUND ART It is important to detect a pulse rate in order to grasp a health condition and a physiological state of a subject. Usually, the pulse rate is detected by attaching an instrument to the subject, but there has been a high demand for easily detecting the pulse rate, and therefore technologies for detecting the pulse rate of the subject in a noncontact manner have been actively researched. This can monitor, for example, a pulse rate of a driver of a vehicle and thereby further promoting traffic safety. The article entitled "Non-contact monitoring techniques - Principles and applications" by D. Teichmann, C. Bruser, B. Eilebrecht, A. Abbas, N. Blanik, and S. Leonhardt (Con. Proc. IEEE Eng., Med. Biol. Soc. 34th Ann. Int. Conf., San Diego, CA, USA, 2012, pp. 1302-1305) discloses such a technology of detecting the pulse rate of the subject in such a noncontact manner. This technology photographs an arm of the subject with a camera, and obtains changes of skin color, brightness, or the like from a camera image to detect the pulse rate. Since the brightness and the color of a body surface change due to blood flow, the pulse rate can be detected by executing image processing of video. However, when the pulse rate is detected under an environment where there is a disturbance such as the subject moving or environmental light changing, there is a problem that degree of reliability (reliable accuracy) of the detected pulse rate is uncertain. For example, when a pulse rate is detected for a certain period, 86% of the detections are reliable and rest of the detections are not reliable due to a disturbance, it is uncertain which portion of the detections are reliable. Moreover, there is also another problem that even if the reliability of the detected value can be evaluated, a period during which the pulse rate can be detected becomes shorter as the evaluation is made more stringent. The article entitled "Developing a novel noise artifact detection algorithm for smartphone PPG signals: Preliminary results" by Basher Syed Khairul et al. (Proceedings of 2018 IEEE EMBS INTERNATIONAL CONFERENCE ON BIOMEDICAL & HEALTH INFORMATICS (BHI), pages 79 - 82, XP033345131) discloses an approach using an algorithm based on variable frequency complex demodulation (VFCDM) to detect noise artefacts in a smartphone's pulsatile signal recorded from a fingertip video in order to increase the accuracy of atrial fibrillation (AF) detection. Further related art is known from the document US 2017/238805 A1, the document US 2015/302158 A1 and the document JP 2013 013644 A1. SUMMARY OF INVENTION The object of the present invention is to output a pulse rate that is highly reliable. According to the present invention, in order to achieve the above object, there are provided a pulse rate detection device and a pulse rate detection program, as defined by the claims. The present disclosure can be summarized as follows. (1) A first aspect of the present disclosure provides a pulse rate detection device comprising: a moving image obtaining means configured to obtain a moving image captured by photographing a body surface of a subject; a pulse rate obtaining means configured to obtain a pulse rate of the subject on the basis of change of a pixel value of the body surface in the moving image; a reliability obtaining means configured to obtain reliability of the obtained pulse rate; and an output means configured to output the obtained pulse rate, if the obtained reliability is equal to or greater than predetermined reliable criteria and, if the obtained reliability is less than reliable criteria and change of the obtained pulse rate is within a predetermined appropriate range.(2) A second aspect of the present disclosure provides the pulse rate detection device according to the first aspect, wherein the change of the pulse rate is a difference between the obtained pulse rate and an immediate past pulse rate, and the output means outputs the obtained pulse rate as being within the appropriate range if the difference therebetween is equal to or less than predetermined criteria.(3) A third aspect of the present disclosure provides the pulse rate detection device according to the first or second aspect, wherein the pulse rate obtaining means obtains the pulse rate from a pulse rate peak in a frequency domain of the obtained moving image, and the reliability obtaining means obtains the reliability on the basis of an SN ratio of the obtained pulse rate.(4) A fourth aspect of the present disclosure provides the pulse rate detection device according to the third aspect, further comprising a reducing means configured to reduce the reliability if a disturbance peak in the frequency domain of a disturbance factor that reduces accuracy of the obtained pulse rate is eq