Patent Publication Number: US-9883811-B2

Title: Apparatus and method for detecting biometric information

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority from Korean Patent Application No. 10-2014-0139069, filed on Oct. 15, 2014 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference. 
     BACKGROUND 
     1. Field 
     Apparatuses and methods consistent with exemplary embodiments relate to detecting biometric information. 
     2. Description of the Related Art 
     With the increasing interest in health, various types of biometric information detection apparatuses have been developed. In particular, with the spread of a variety of wearable devices, wearable devices specialized for health care have been developed. 
     Methods of detecting biometric information such as pulse waves may be roughly divided into invasive methods and noninvasive methods, among which the noninvasive methods are widely used because of simply detecting pulse waves without causing pain to a subject. 
     For accurate pulse wave analysis (PWA), information based on an optical signal or a pressure signal on a specific body surface of a subject needs to be obtained. Based on such information, biometric information of the subject may be obtained, and to reduce measuring errors, various methods are used. 
     SUMMARY 
     One or more exemplary embodiments provide an apparatus and method for detecting biometric information. 
     According to an aspect of an exemplary embodiment, there is provided an apparatus for detecting biometric information of an object including: a biometric signal measurer including a light-receiving element and a plurality of light-emitting elements; and a processor comprising a tracking unit configured to sequentially drive the plurality of light-emitting elements, receive a signal detected by the light-receiving element, and determine a tracking line that connects at least two positions of a radial artery of the object from the received signal, and an analyzing unit configured to detect a pulse wave signal at the at least two points on the tracking line and analyze biometric information from the detected pulse wave signal. 
     The plurality of light-emitting elements are arranged to surround the light-receiving elements. 
     The plurality of light-emitting elements are arranged isotropically with respect to the light-receiving element. 
     The biometric signal measurer may further include a plurality of light-receiving elements including the light-receiving element, the plurality of light-emitting elements may surround each of the plurality of light-receiving elements. 
     The light-receiving element and the plurality of light-emitting elements surrounding the light-receiving element form a first sub unit, and a plurality of sub units including the first sub unit are repetitively arranged in the form of a hive. 
     The analyzing unit may be further configured to measure a time delay between the at least two points and calculate a pulse transit time (PTT) from the time delay. 
     The analyzing unit may be further configured to analyze vessel elasticity, blood flow rate, arterial stiffness, and systolic blood pressure or diastolic blood pressure of a vessel, from the PTT. 
     The light-emitting element may include a light-emitting diode (LED) or a laser diode, and the light-receiving element may include a photodiode, a photo transistor (PTr), or a charge-coupled device (CCD). 
     The apparatus may further include a user interface configured to output a result regarding the analyzed biometric information. 
     The apparatus may include a communicator transmitting a result regarding the analyzed biometric information to an external device. 
     The biometric signal measurer may be wearable by the object. 
     The apparatus may be wearable by the object. 
     According to an aspect of another exemplary embodiment, there is provided a radial artery tracking method including: sequentially driving a plurality of light-emitting elements and radiating light from the plurality of light-emitting elements to an object, detecting optical signals through a light-receiving element according to the sequential driving of the plurality of light-emitting elements, determining, by a processor, at least two highest level signals among the detected optical signals, and determining, by the processor, a line connecting positions of at least two light-emitting elements corresponding to the determined at least two highest level signals as a tracking line. 
     According to an aspect of another exemplary embodiment, there is provided a method of detecting biometric information of an object including: sequentially driving a plurality of light-emitting elements and radiating light from the plurality of light-emitting elements to the object, detecting optical signals through a light-receiving element according to the sequential driving of the plurality of light-emitting elements, measuring a time delay between two or more highest level signals among the detected signals; and analyzing biometric information based on the measured time delay. 
     The biometric information may include vessel elasticity, blood flow rate, arterial stiffness, and systolic blood pressure or diastolic blood pressure of a vessel. 
     According to an aspect of another exemplary embodiment, there is provided a biometric signal measurer including: a plurality of light emitting elements configured to sequentially turn on and off and radiate light to a target area on a skin of a subject to deflect the radiated light from the target area; and at least one optical sensor configured to detect the deflected light and disposed at a center position of a perimeter formed by connecting the plurality of light emitting elements; wherein while one of the plurality of light emitting elements is turned on, remaining ones of the plurality of light stay turned off. 
     Wherein the plurality of light emitting elements are classified into as belonging to a least one of a first unit, a second unit, and a third unit, the at least one optical sensor includes a first optical sensor belonging to the first unit, a second optical sensor belonging to the second unit, and a third optical sensor belonging to the third unit, and the first, second, and third units are arranged in a form of a hive. 
     The first, second, and third units are sequentially controlled to turn on and off the plurality of light emitting elements sequentially. 
     At least one of the plurality of light emitting elements belongs to the first unit and the second unit and at least another one of the plurality of light belongs to the first unit and the third unit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and/or other aspects will be more apparent by certain exemplary embodiments, with reference to the accompanying drawings, in which: 
         FIG. 1  is a block diagram illustrating a schematic structure of an apparatus for detecting biometric information according to an exemplary embodiment; 
         FIG. 2  is a planar view illustrating arrangement of light-emitting elements and a light-receiving element of a multi-channel biometric signal measurer used in an apparatus for detecting biometric information according to an exemplary embodiment; 
         FIGS. 3A through 3C  illustrate selective activation of some light-emitting elements of a multi-channel biometric signal measurer based on different radial arteries for different persons according to an exemplary embodiment; 
         FIG. 4  is a flowchart illustrating a radial artery tracking method executed by an apparatus for detecting biometric information according to an exemplary embodiment; 
         FIGS. 5A through 5E  illustrate activation of some light-emitting elements of a multi-channel biometric signal measurer when radial artery tracking is performed by an apparatus for detecting biometric information according to an exemplary embodiment; 
         FIG. 6  illustrates an example of tracking a radial artery from a detection signal in driving illustrated in  FIGS. 5A through 5E ; 
         FIG. 7  is a flowchart illustrating a process of analyzing biometric information after tracking a radial artery in an apparatus for detecting biometric information according to an exemplary embodiment; 
         FIG. 8  illustrates a signal pattern detected at a plurality of points on a tracked radial artery; 
         FIG. 9  illustrates arrangement of light-emitting elements and a light-receiving element of a multi-channel biometric signal measurer used in an apparatus for detecting biometric information according to another exemplary embodiment; 
         FIG. 10  is a flowchart illustrating a radial artery tracking method executed in an apparatus for detecting biometric information including a multi-channel biometric signal measurer of  FIG. 9 ; 
         FIG. 11  illustrates activation of some light-emitting elements according to a radial artery pattern tracked using the flowchart illustrated in  FIG. 10 ; 
         FIG. 12  is a flowchart illustrating a process of analyzing biometric information after tracking a radial artery in an apparatus for detecting biometric information according to another exemplary embodiment; 
         FIG. 13  illustrates a signal pattern detected at a plurality of points on a tracked radial artery; and 
         FIG. 14  illustrates arrangement of light-emitting elements and a light-receiving element of a multi-channel biometric signal measurer used in an apparatus for detecting biometric information according to another exemplary embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Exemplary embodiments are described in greater detail below with reference to the accompanying drawings. 
     The matters defined in the description, such as detailed construction and elements, are provided to assist in a comprehensive understanding of the exemplary embodiments. However, it is apparent that the exemplary embodiments can be practiced without those specifically defined matters. Also, well-known functions or constructions are not described in detail since they would obscure the description with unnecessary detail. 
     As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. Expressions such as “at least one of,” when preceding a list of elements, modify the entire list of elements and do not modify the individual elements of the list. 
     Throughout the drawings, like reference numerals refer to like elements, and the size of each element may be exaggerated for clarity and convenience. 
     In the following description, when a layer, region, or component is referred to as being “above” or “on” another layer, region, or component, it can be directly or indirectly on the other layer, region, or component. 
     In the following embodiments, terms such as “first”, “second”, and so forth are used only for distinguishing one component from another component, rather than for restrictive meanings. 
     In the following embodiments, the terms “comprises” and/or “has” when used in this specification, specify the presence of stated feature, number, step, operation, component, element, or a combination thereof but do not preclude the presence or addition of one or more other features, numbers, steps, operations, components, elements, or combinations thereof. 
     Terms used herein, such as “unit” and “module” refer to a unit for processing at least one functions or operations, and may be implemented with hardware (e.g., a processor or circuit), software, or a combination thereof. 
       FIG. 1  is a block diagram illustrating a schematic structure of an apparatus for detecting biometric information (or a biometric information detection apparatus)  500  according to an exemplary embodiment, and  FIG. 2  is a planar view illustrating arrangement of light-emitting elements and a light-receiving element of a multi-channel biometric signal measurer  100  used in the biometric information detection apparatus  500  according to an exemplary embodiment. 
     The biometric information detection apparatus  500  detects biometric information of an object OBJ. The biometric information detection apparatus  500  includes the multi-channel biometric signal measurer  100  and a processor  200  that controls the multi-channel biometric signal measurer  100  and performs biometric information analysis based on a measurement result. The biometric information detection apparatus  500  may further include a memory  300  and a user interface  400 . 
     The multi-channel biometric signal measurer  100  may include a light emitter  120  and a light receiver (also referred to as “optical sensor”)  130 . The light emitter  120  radiates light to the object OBJ, and the light receiver  130  detects light scattered or reflected from the object OBJ. The detected optical signal is used variously for biometric information analysis, as will be described in detail. 
     The object OBJ is a target for biometric information detection, and may be a biologic part that may contact or may be adjacent to the multi-channel biometric signal measurer  100  of the biometric information detection apparatus  500 , or may be a body part for which pulse wave measurement is easy to perform through photoplethysmography (PPG). PPG is an optical technique to detect blood volume changes of a vessel by illuminating the skin above the vessel and measuring changes in light of absorption. The object OBJ may be a part that is adjacent to a radial artery in a wrist. When a pulse wave is measured on the surface of the skin of the wrist through which a radial artery passes, an influence of external factors causing an error of measurement of, for example, the thickness of a skin tissue inside the wrist may be small. The radial artery is known as a blood vessel for which the more accurate blood pressure may be measured than other types of blood vessels in the wrist. However, the object OBJ is not limited to these examples, and may be a terminal part of a human body, such as a finger, a toe, or an earlobe, in which vessel density is high. 
     As shown in  FIG. 2 , the light emitter  120  of the multi-channel biometric signal measurer  100  may include a plurality of light-emitting elements  121  through  126 , and the light receiver  130  may include a light-receiving element  131 . The plurality of light-emitting elements  121  through  126  may be arranged to surround the light-receiving element  131 . Although six light-emitting elements, that is, first through sixth light-emitting elements  121 - 126  are arranged isotropically around the light-receiving element  131  in  FIG. 2 , the present disclosure is not limited to that example. 
     Light-emitting diodes (LEDs) or laser diodes may be used as the first through sixth light-emitting elements  121  through  126 . The first through sixth light-emitting elements  121  through  126  are sequentially driven one by one and may radiate light to the object OBJ. 
     The light receiver  130  may be a photodiode, a photo transistor (PTr), or a charge-coupled device (CCD). The light-receiving element  131  senses an optical signal scattered or reflected from the object OBJ. For example, a laser speckle generated by scattering of laser light radiated to the object OBJ may be detected. The laser speckle means an irregular pattern generated by interference or scattering when a laser having coherency is radiated to a scattering object. The light-receiving unit  130  detects an optical signal corresponding to the laser speckle. 
     The processor  200  may include a tracking unit  220 , a pulse wave analyzing unit  240 , and a biometric information analyzing unit  260 . 
     The tracking unit  220  sequentially drives the plurality of light-emitting elements  121  through  126  included in the multi-channel biometric signal measurer  100 , senses a signal detected by the light-receiving unit  130 , and tracks a position of a radial artery of the object OBJ from the sensed signal. More specifically, when the multi-channel biometric signal measurer  100  radiates light and detects an optical signal in contact with or in adjacent to the object OBJ, a signal-to-noise ratio of the detected optical signal varies with a relative position of the plurality of light-emitting elements  121  through  126  with respect to a radial artery of the object OBJ. For example, when among the plurality of light-emitting elements  121  through  126 , a light-emitting element that is close to a radial artery radiates light, an optical signal detected by the light receiver  130  has a high signal-to-noise ratio, and when a light-emitting element that is far from the radial artery radiates light, an optical signal detected by the light receiver  130  has much noise and thus a low signal-to-noise ratio. As such, by analyzing a signal-to-noise ratio of a detected optical signal, at least two light-emitting elements may be selected, and a line connecting positions of the light-emitting elements may be determined as a radial artery tracking line. 
     The pulse wave analyzing unit  240  analyzes a pulse wave signal at at least two points on a tracking line determined by the tracking unit  220 . More specifically, the pulse wave analyzing unit  240  analyzes a time-specific strength change of an optical signal detected by the light receiver  130 . The pulse wave analyzing unit  240  may obtain a biometric signal by analyzing fluctuation of a laser speckle corresponding to a volume change of a vessel (for example, a radial artery) of the object OBJ. Herein, the obtained biometric signal may be a PPG signal converted based on a correlation between the analyzed fluctuation of the laser speckle and the volume change. The pulse wave analyzing unit  240  analyzes various parameters included in the PPG signal by analyzing waveform characteristics of the PPG signal. For example, the pulse wave analyzing unit  240  may calculate a delay time between pulse wave signals and calculate a pulse transit time (PTT). In this process, the pulse wave analyzing unit  240  may use various digital signal processing algorithms such as a noise cancellation algorithm, a differential signal extraction algorithm, and so forth. 
     The biometric information analyzing unit  260  analyzes various biometric information by using a pulse wave signal analysis result as an index. The biometric information analyzing unit  260  may analyze biometric information by using a predetermined algorithm for calculating various biometric information from the PTT calculated by the pulse wave analyzing unit  240 . For example, vessel elasticity, blood flow rate, arterial stiffness, systolic blood pressure of a vessel, diastolic blood pressure, or the like may be estimated. 
     The memory  300  stores a program for processing and controlling the processor  200  and stores input/output data. For example, a program for the tracking, the pulse wave analysis, and the biometric information analysis performed in the processor  200  may be stored as a code in the memory  300 . Measurement results of the multi-channel biometric signal measurer  100 , which are necessary for processing in the processor  200 , may be stored in the memory  300 . 
     The memory  300  may include storage media of at least one type of a flash memory type, a hard disk type, a multimedia card micro type, a card type (for example, a secure digital (SD) or extreme digital (XD)), a random access memory (RAM) type, a static random access memory (SRAM) type, a read-only memory (ROM) type, an electrically erasable programmable read-only memory (EEPROM) type, a programmable read-only memory (PROM) type, a magnetic memory type, a magnetic disk type, an optical disk type, and so forth. 
     The user interface  400  is an interface with a user and/or an external device, and may include an input unit and an output unit. Herein, the user may be a target for measurement of biometric information, that is, the object OBJ, but may also be a person who may use the biometric information detection apparatus  500 , such as a medical expert, so that the user may be a broader concept than the object OBJ. Through the user interface  400 , information necessary for operating the biometric information detection apparatus  500  may be input, and an analysis result may be output. The user interface may include, for example, a button, a connector, a keypad, a display unit, and the like, and may further include an audio output unit, a vibration motor, and so forth. 
     The biometric information detection apparatus  500  may further include a communicator  450  for transmitting an analysis result to an external device. The external device may be medical equipment using analyzed biometric information, a printer for printing a result, or a display device for displaying an analysis result. The external device may also be, but not limited to, a smart phone, a cellular phone, a personal digital assistant (PDA), a laptop, a personal computer (PC), or other mobile or non-mobile computing devices. 
     The communicator  450  may include a transmitter, a receiver, or a transceiver. The communicator  450  may be connected with the external device in a wired or wireless manner. For example, the communicator  450  may communicate with the external device by using, but not limited to, Bluetooth communication, Bluetooth low energy (BLE) communication, near field communication (NFC), wireless local area network (WLAN) communication, ZigBee communication, infrared data association (IrDA) communication, wireless fidelity direct (WFD) communication, ultra wideband (UWB) communication, Ant+ communication, Wi-Fi communication, or the like. 
     The biometric information detection apparatus  500  may be implemented in a wearable device that may be worn on the object OBJ. For example, the biometric information detection apparatus  500  may be implemented in the form of, but not limited to, a wrist watch, a bracelet, a wrist band, a ring, glasses, a hairband, or the like. 
     Alternatively, only a portion of the biometric information detection apparatus  500 , for example, the multi-channel biometric signal measurer  100  may be implemented in a form that is wearable on the object OBJ as illustrated. 
       FIGS. 3A through 3C  illustrate selective activation of some light-emitting elements of the multi-channel biometric signal measurer  100  according to a radial artery pattern that differs from person to person. 
       FIG. 3A  shows that a third light-emitting element  123  and a sixth light-emitting element  126 , which are closest onto a radial artery RA, are activated.  FIG. 3B  shows that the third light-emitting element  123  and the sixth light-emitting element  126 , which are closest onto the radial artery RA, are activated. Referring to  FIG. 3C , a first light-emitting element  121  and a fourth light-emitting element  124 , which are closest onto the radial artery RA, are activated. 
       FIGS. 3A through 3C  illustrate an example in which a radial artery pattern varying from person to person is tracked according to a tracking result obtained from the multi-channel biometric signal measurer  100 . In pulse wave signal detection, the plurality of light-emitting elements indicated as being activated are driven one by one and an optical signal is detected. However, the present embodiment is not limited thereto, such that the plurality of light-emitting elements indicated as being activated may also be driven at the same time and an optical signal may be detected. 
       FIG. 4  is a flowchart illustrating a radial artery tracking method executed by the biometric information detection apparatus  500  according to an exemplary embodiment.  FIGS. 5A through 5E  illustrate activation of some light-emitting elements of the multi-channel biometric signal measurer  100  when radial artery tracking is performed by the biometric information detection apparatus  500  according to an exemplary embodiment.  FIG. 6  illustrates an example of tracking a radial artery from a detection signal in driving illustrated in  FIGS. 5A through 5E . 
     As shown in  FIG. 4 , light radiation, optical signal detection in a light-receiving element, and identification and storage of a signal level of a pulse wave (operations S 201  through S 204 ) are repeated as many times as the number of channels, that is, the number of light-emitting elements. 
     First, as illustrated in  FIG. 5A , when the first light-emitting element  121  is driven and the other light-emitting elements  122  through  126  are turned off, the light-receiving element  131  detects an optical signal in operation S 202 . 
     The detected optical signal may include a strength change over time in connection with a volume change of a radial artery, as descried before. A pulse wave is analyzed from the detected signal, and a signal level of the pulse wave is identified and stored as an index for use in radial artery tracking in operation S 203 . The signal level of the pulse wave may include information such as a signal-to-noise ratio. 
     Next, as illustrated in  FIGS. 5B through 5E , when second light-emitting elements  122  through sixth light-emitting elements  126  are driven and the other light-emitting elements are turned off, the light-receiving element  131  detects an optical signal in operation S 202 , and identifies and stores a signal level of a pulse wave in operation S 203 . 
     The stored results are compared to select two optimal points, and a tracking line is determined in operation S 204 . The two optimal points may be selected in a descending order of a signal-to-noise ratio. For example, a light-emitting element corresponding to the highest signal-to-noise ratio and a light-emitting element corresponding to the next highest signal-to-noise ratio may be selected, and a line connecting two positions may be determined as a tracking line. 
     Since the first light-emitting element  121  and the fourth light-emitting element  124  are located on the surface of the skin above the radial artery AR, the optical signal detected by the light-receiving element  131  has a higher signal-to-noise ratio when the first light-emitting element  121  or the fourth light-emitting element  124  is turned on as shown in  FIGS. 5A and 5B  than when one of the second, third, and sixth light-emitting elements  122 ,  123 , and  126  is turned on as shown in  FIGS. 5B, 5C, and 5E . That is, as illustrated in  FIG. 6 , a line connecting the positions of the first light-emitting element  121  and the fourth light-emitting element  124  may be determined as a radial artery tracking line. 
     Although it has been described that two light-emitting elements are disposed at positions facing a radial artery, the present embodiment is not limited thereto and various cases may exist. For example, one light-emitting element may face the radial artery and the other light-emitting element may be disposed in adjacent to the light-emitting element. In this case, the highest signal-to-noise ratio is clearly seen, but the second and third highest signal-to-noise ratios may be slightly different. In this case, a position of a light-emitting element corresponding to the highest signal-to-noise ratio is determined as a first optimal point, and an intermediate point between light-emitting elements corresponding to the second and third highest signal-to-noise ratios may be determined as a second optimal point. 
       FIG. 7  is a flowchart illustrating a process of analyzing biometric information after tracking a radial artery in the biometric information detection apparatus  500  according to an exemplary embodiment.  FIG. 8  illustrates a signal pattern detected at a plurality of points on a tracked radial artery. 
     Once a radial artery tracking line is determined, a PPG pulse wave signal at two points on the tracking line is obtained in operation S 206 . These two points may be the two optimal points determined in  FIGS. 4 and 5A through 5E . Thus, light may be radiated to corresponding positions and optical signal detection and pulse wave analysis may be performed. The results stored in operation S 203  of  FIG. 4  may also be used. 
     Next, a PTT is analyzed from two pulse wave signals in operation S 207 . 
     As illustrated in  FIG. 8 , by comparing waveforms of two obtained pulse wave signals P 1  and P 2 , a time delay Δt is analyzed. The time delay Δt is a parameter related to PTT information, from which the PTT may be analyzed. 
     Next, by using the pulse wave signal waveform information and the PTT information, biometric information may be analyzed in operation S 208 . The biometric information may include vessel elasticity, blood flow rate, arterial stiffness, systolic blood pressure, diastolic blood pressure, or information indicating whether a current blood pressure state is a normal state or an abnormal state. 
       FIG. 9  illustrates arrangement of light-emitting elements and a light-receiving element of a multi-channel biometric signal measurer  100 ′ used in an apparatus for detecting biometric information according to another exemplary embodiment. 
     The multi-channel biometric signal measurer  100 ′ may include a plurality of light-receiving elements and a plurality of light-emitting elements disposed to surround each of the plurality of light-receiving elements. 
     More specifically, a first light-receiving element  130 _ 1  and a plurality of light-emitting elements  11  through  16  surrounding the first light-receiving element  130 _ 1  form a first sub unit SU 1 . A second light-receiving element  130 _ 2  and a plurality of light-emitting elements  21  through  24 ,  15 , and  16  surrounding the second light-receiving element  130 _ 2  form a second sub unit SU 2 . A third light-receiving element  130 _ 3  and a plurality of light-emitting elements  31  through  33 ,  25 ,  15 , and  14  surrounding the third light-receiving element  130 _ 3  form a third sub unit SU 3 . 
       FIG. 10  is a flowchart illustrating a radial artery tracking method executed in an apparatus for detecting biometric information including the multi-channel biometric signal measurer  100 ′ of  FIG. 9 . 
     For one sub unit, when a plurality of light-emitting elements included in one sub unit are sequentially selected and driven one by one and the other light-emitting elements are turned off in operation S 211 , a light-receiving element detects an optical signal in operation S 212  and a signal level of a pulse wave is identified and stored in operation S 213 . After the foregoing processes are also done with respect to all the light-emitting elements included in the sub unit, stored pulse wave signal levels are compared to select an optimal point in operation S 215 . At this time, the selected optimal point may be one or more points, or zero (0) point. In the current embodiment, the foregoing measurement is repeated with respect to the plurality of sub units, such that two or more optimal points are selected eventually and for some sub units, an optimal point may not be selected. For example, for some sub units, a signal-to-noise ratio in every channel is very low and thus a signal-to-noise ratio difference is not meaningful, and in this case, an optimal point may not be selected. 
     Operations S 210  through S 215  are repeated with respect to a plurality of sub units, that is, first through third sub units SU 1 , SU 2 , and SU 3  and results are stored in operation S 216 . A tracking line is determined from an optimal point determined in measurement with respect to each sub unit in operation S 217 . The tracking line may be determined by two or more optimal points, and in this case, for example, some of the optimal points selected in operation S 215  may not be reflected in a finally determined tracking line. For the determination, a connection relationship between the optimal points selected in measurement with respect to each of the plurality of sub units or a total signal-to-noise ratio level of a channel may be considered. 
     When operations S 210  through S 215  are repeated with respect to the first, second, and third sub units SU 1 , SU 2 , and SU 3 , the light-emitting elements  14 ,  15 ,  16 , and  24  which belong to two or three of the sub units SU 1 , SU 2 , and SU 3  may be set to be turned on once and optical signals of the light-emitting elements  14 ,  15 ,  16 , and  24  may be measured once. For example, if the first unit SU 1  performs operations S 210 -S 214  prior to the second unit SU 2  and the third unit SU 3 , the first unit SU 1  may perform operations S 211 -S 213  for all of its light-emitting elements  12 - 16  but the second unit SU 2  may perform operations S 211 -S 213  only for the light-emitting elements  21 - 24  and skip operations S 211 -S 213  with respect to the light-emitting elements  15  and  16 . Further, the third unit SU 3  may perform operations S 211 -S 213  only for the light-emitting elements  31 - 33  and skip operations S 211 -S 213  with respect to the light-emitting elements  14 ,  15 , and  24 . In that case, two or more optimal points may be selected from the light emitting elements  11 - 16 ,  21 - 24 , and  31 - 33  regardless of the sub units SU 1 , SU 2 , and SU 3  which the light emitting elements  11 - 16 ,  21 - 24 , and  31 - 33  belong to. For example, if four optimal points are set to be selected and pulse wave signal levels measured from the light emitting elements  11 ,  15 ,  24 , and  33  are higher than the other light emitting elements  12 - 14 ,  21 - 23 , and  31 - 32 , a line connecting the light emitting elements  11 ,  15 ,  24 , and  33  may be determined as a tracking line in operation S 217 . 
       FIG. 11  illustrates activation of some light-emitting elements according to a radial artery pattern tracked using the flowchart illustrated in  FIG. 10 . 
       FIG. 11  shows determining a track line based on positions of the light-emitting elements  11 ,  14 , and  32 . 
       FIG. 12  is a flowchart illustrating a process of analyzing biometric information after tracking a radial artery by using the multi-channel biometric signal measurer  100 ′ of  FIG. 9  in an apparatus for detecting biometric information according to another exemplary embodiment, and  FIG. 13  illustrates a signal pattern detected by a plurality of points on a tracked radial artery. 
     Once the radial artery tracking line is determined, a PPG pulse wave signal at a plurality of points on the tracking line is obtained in operation S 218 . The two points may be two or more optimal points determined in  FIG. 10 . For example, as illustrated in  FIG. 11 , three points may be used. Light is radiated to corresponding positions, and a PPG pulse wave signal may be obtained by performing optical signal detection and pulse wave analysis. The result stored in operation S 213  of  FIG. 10  may be used. 
     Next, a PTT is analyzed from a plurality of pulse wave signals in operation S 219 . 
     As illustrated in  FIG. 13 , waveforms of three obtained pulse wave signals P 1 , P 2 , and P 3  are compared to analyze time delays Δt 1  and Δt 1 . The time delays Δt 1  and Δt 1  are parameters related to PTT information, from which the PTT may be analyzed. 
     Next, biometric information is analyzed by using pulse wave signal waveform information, PTT information, and so forth in operation S 220 . The biometric information may include vessel elasticity, blood flow rate, arterial stiffness, systolic blood pressure, diastolic blood pressure, or information indicating whether a current blood pressure state is a normal state or an abnormal state. 
     In the foregoing description, the multi-channel biometric signal measurer  100  of  FIG. 9  includes three sub units, but the multi-channel biometric signal measurer  100  may three or more sub units. 
       FIG. 14  illustrates arrangement of light-emitting elements and a light-receiving element of a multi-channel biometric signal measurer  100 ″ used in an apparatus for detecting biometric information according to another exemplary embodiment. 
     In the current embodiment, the multi-channel biometric signal measurer  100 ″ is configured such that a plurality of sub units SUk, each of which includes a light-receiving element  130 _k and a plurality of light-emitting elements k 1  through k 6  surrounding the light-receiving element  130 _k, are arranged in the form of a hive. Driving of the biometric information detection apparatus including the multi-channel biometric signal measurer  100 ″ is substantially the same as the foregoing description. 
     As the number of sub units SUk increases, the accuracy of radial artery tracking line analysis and the accuracy of pulse wave analysis and biometric information analysis based thereon may increase. 
     As described above, using the apparatus and method for detecting biometric information according to the one or more of the above exemplary embodiments, radial artery tracking is possible according to a radial artery pattern varying from person to person. 
     In addition, by using a pulse wave signal at a plurality of tracked points, various biometric information may be analyzed. 
     The computer readable code can be recorded/transferred on a medium in a variety of ways, with examples of the medium including recording media, such as magnetic storage media (e.g., ROM, floppy disks, hard disks, etc.) and optical recording media (e.g., CD-ROMs, or DVDs), and transmission media such as Internet transmission media. Thus, the medium may be such a defined and measurable structure including or carrying a signal or information, such as a device carrying a bitstream according to one or more exemplary embodiments. The media may also be a distributed network, so that the computer readable code is stored/transferred and executed in a distributed fashion. Furthermore, the processing element could include a processor or a computer processor, and processing elements may be distributed and/or included in a single device. 
     The foregoing exemplary embodiments and advantages are merely exemplary and are not to be construed as limiting. The present teaching can be readily applied to other types of apparatuses. Also, the description of the exemplary embodiments is intended to be illustrative, and not to limit the scope of the claims, and many alternatives, modifications, and variations will be apparent to those skilled in the art.