# Patent

## Title
Activity analysis, fall detection and risk assessment systems and methods

## Abstract

Aspects of the present disclosure include methods and corresponding systems for performing health risk assessments for a patient in the home environment. In various aspects, depth image data for a person may be obtained and subsequently processed to generate one or more parameters, such as temporal and spatial gait parameters. Subsequently, the generated parameters may be processed with other medical information related to the patient, such as electronic health records, to perform various health risk assessments.

## Background
CROSS REFERENCE TO RELATED APPLICATION
The present non-provisional utility application claims priority under 35 U.S.C. §119(e) to co-pending provisional applications, including Application No. 61/687,608 entitled “Activity Analysis, Fall Detection, and Risk Assessment Using Depth Camera for Eldercare and Other Monitoring Applications” filed on Apr. 27, 2012, and which is hereby incorporated by reference here; Application No. 61/649,770 entitled “Activity Analysis, Fall Detection And Risk Assessment Systems And Methods” filed on May 21, 2012, and which is hereby incorporated by reference herein; and Application No. 61/788,748 entitled “Activity Analysis, Fall Detection And Risk Assessment Systems And Methods” filed on Mar. 13, 2013, and which is hereby incorporated by reference herein.


FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
This invention was made with government support under grant number 0931607awarded by the National Science Foundation. The government has certain rights in the invention.


TECHNICAL FIELD
The present invention relates to methods and systems for activity monitoring of a patient, and more specifically, to methods and systems for obtaining measurements of temporal and spatial gait parameters of the patient for use in health risk assessment.
BACKGROUND
Human activity analysis from video is an open problem that has been studied within the areas of video surveillance, homeland security, and eldercare. For example, the monitoring of human activity is often employed in the medical industry to detect any abnormal or dangerous events, such as falls and/or the risk of falls for a patient. Various parameters, such as gait parameters and/or other locomotive measurements corresponding to a medical patient, are often monitored and considered indispensable in the diagnosis of frailty and fall risk, and in particular, when providing medical care for the elderly.
Falls are a significant issue among the elderly. For example, it is estimated that between 25-35% of people 65 years and older fall each year, and many of such falls result in serious injuries, such as hip fractures, head traumas, and the like. Moreover, the medical costs associated with such falls are astronomical. In the year 2000, it is estimated that over $19 billion dollars were spent treating fall-related injuries for the elderly. Such costs do not account for the decreased quality of life and other long term effects often experienced by many elderly patients after suffering a fall.
Thus, a low-cost monitoring system that would allow for continuous, standardized assessment of fall risk may help address falls and the risk of falls among older adults. Moreover, to enable older adults to continue living longer, in particular, in an independent setting, and thus reduce the need for expensive care facilities, low-cost systems are needed that detect both adverse events such as falls, and the risk of such events.
It is with these concepts in mind, among others, that various aspects of the present disclosure were conceived.



BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features, and advantages of the present disclosure set forth herein will be apparent from the following description of exemplary embodiments of those inventive concepts, as illustrated in the accompanying drawings. It should be noted that the drawings are not necessarily to scale; however, the emphasis instead is being placed on illustrating the principles of the inventive concepts. Also in the drawings, the like reference characters refer to the same parts throughout the different views. The drawings depict only exemplary embodiments of the present disclosure and, therefore, are not to be considered limiting in scope.
FIG. 1 is a block diagram illustrating a computing environment for obtaining one or more parameters to perform health risk assessments, according to aspects of the present disclosure.
FIG. 2 is a block diagram illustrating an example living unit, according to aspects of the present disclosure.
FIG. 3 is a block diagram illustrating a remote device, according to aspects of the present disclosure.
FIG. 4 is a flowchart illustrating an example for obtaining temporal and spatial gait parameters for performing health risk assessments, according to aspects of the present disclosure.
FIG. 5 is a flowchart illustrating walk sequences, according to aspects of the present disclosure.



DETAILED DESCRIPTION
Aspects of the present disclosure include methods and corresponding systems for performing health risk assessments for a patient in the home environment. In various aspects, depth image data for a medical patient is obtained and subsequently used to generate one or more parameters, such as temporal and spatial gait parameters. Subsequently, the generated parameters may be used with other medical information related to the patient, such as electronic health records, to perform various health risk assessments, such as for example, alerting health care professionals of alarming trends or other health risks associated with the patient.
Falls represent a substantial health risk among the elderly, as the risk of falls generally increases with age. It is estimated that one out of every three older adults (age 65 and over) falls each year, many of which suffer serious injuries, such as hip fractures, head traumas, etc. Typically, the result of such falls is a reduction in a person's gait ability, such as a reduction in mobility and independence, all of which may ultimately increase the risk of early death. The causes of such falls are known as “risk” factors. Although, generally, no single risk factor can be considered the single cause of a given fall, the greater the number of risk factors to which an individual is exposed, the greater the probability of a fall and the more likely the results of the fall will threaten the person's independence.
Research has shown that gait parameters, which describe the pattern of movement in animals and humans, are indispensable in assessing risk factors, making fall risk assessments, the diagnosis of fall risk, or the like. For example, studies have indicated that gait parameters may be predictive of future falls and adverse events in older adults and, further, that scores on certain mobility tests are good indicators of fall risk. Despite these findings, gait parameters and mobility tests are generally assessed infrequently, if at all, and are typically monitored through observation by a clinician with a stop watch or a clinician using equipment in a physical performance lab, both of which are expensive and labor-intensive. Such sparse, infrequent evaluations may not be representative of a person's true functional ability. Aspects of the present disclosure involve methods and systems for monitoring patient gait parameters continuously, during everyday activity, in a cost-effective, efficient manner. Monitoring such parameters and/or activities may offer significant benefits for fall risk and mobility assessment.
FIG. 1 illustrates an example system 100 for obtaining depth image data and subsequently processing the depth image data to generate gait parameters (both temporal and spatial) for use in health risk assessment, in accordance with aspects of the present disclosure. The system 100 is an example platform in which one or more embodiments of the methods may be used. However, it is contemplated that such methods and/or processes may also be performed on other conventional computing platforms, as are generally known in the art.
Referring now to FIG. 1, a user, such as an administrator, clinician, researcher, family member, etc., may use a remote device 102 to receive and/or otherwise obtain depth image data from one or more depth camera(s) 108. Depth image data may include any type of data captured from a camera capable of being processed to generate a representation of an object, and in particular, a patient in a given location, such as a three-dimensional point cloud representation, of that person or patient. In one embodiment, the depth image data may include audio and may be captured in an audio format, such as by one or more microphones associated with the depth cameras 108, or other type of recording device. The remote device 102 may be located in a living unit, outside a living unit but in a living community, or in a location outside the living community, and may include various hardware and accompanying software computing components that may be configured to receive and/or otherwise capture the depth image data. For example, as illustrated, the remote device 102 may execute an image analysis application 109 that receives depth image data associated with a particular patient. Subsequently, the image analysis application 109 may process the depth image data to extract, generate and/or otherwise compute temporal and/or spatial gait parameters of a patient for use in various health risk assessments. The image analysis application 109 may provide the temporal and/or spatial gait parameters and corresponding risk assessments for display, such as for example, as part of a graphical user interface.
A user may use the remote device 102 as a stand-alone device to compute temporal and spatial gait parameters for use in health risk assessment, or may use the remote device 102 in combination with a central computing device 106 available over a network 104. In some embodiments, the central computing device 106 may also be under the control of the same user but at a remote location, such as a location outside of the living community. For example, according to various aspects, the remote device 102 may be in a client-server relationship with the central computing device 106, a peer-to-peer relationship with the central computing device 106, or in a different type of relationship with the central computing device 106. In one embodiment, the client-server relationship may include a thin client on the remote device 102. In another embodiment, the client-server relationship may include a thick client on the remote device 102.
The remote device 102 may communicate with the central processing device 106 over a network 104, which may be the Internet, an intranet, a local area network, a wireless local network, a wide area network, or another communication network, as well as combinations of networks. For example, the network 104 may be a Mobile Communications (GSM) network, a code division multiple access (CDMA) network, an Internet Protocol (IP) network, a Wireless Application Protocol (WAP) network, a WiFi network, or an IEEE 802.11 standards network, as well as various combinations thereof. Other conventional and/or later-developed wired and wireless networks may also be used.
The central computing device 106 may include various hardware and accompanying software computing components to operate in substantially the same manner as the remote device 102 to receive depth image data. In one embodiment, the central computing device 106 may be a single device. Alternatively, in another embodiment, the central computing device 106 may include multiple computer systems. For example, the multiple computer systems may be in a cloud computing configuration.
One or more depth cameras 108 and/or sets of depth cameras 108 may be included in the system 100 to generate video signals of the objects (e.g., persons) residing in the living unit. The depth cameras 108 and/or sets of depth cameras 108 may include various computing and camera/lense components such as an RGB camera, infrared sensitive camera, from which a depth image and/or depth image data may be obtained. Other computing and/or camera components may also be included, as are generally known in the art. An example configuration of one or more depth cameras 108 in various living areas is described in greater detail below.
The remote device 102, the central computing device 106, or both may communicate with a database 110. The database 110 may include depth image data 112 and parameters 114. The depth image data 112 may be stored based on the video signals generated by the depth cameras 108. In general, the depth image data 112 may include depth data, such as a pattern of projected light, from which a depth image may be produced. In some embodiments, the video signals generated by the depth cameras 108 prior to converting the images to depth images are not stored in the database 110 or elsewhere in the system 100. The processing performed on the depth image data 112 may be stored as the parameters 114 in the database 110. The depth image data 112 may be used to track the person's activity as described in greater detail below.
While aspects of the present disclosure have been described as being performed using multiple devices within a computing environment, such as computing environment 100 shown in FIG. 1, it is contemplated that such aspects may be performed locally, using only a single device, such as the central processing device 106, and in such cases the remote device 102 is integrated into or otherwise in direct connection with the central processing device 106. In such an arrangement, the central processing device 106 may be in direct communication with the depth cameras 108 and the database 110.
FIG. 2 illustrates an example living unit 200, according to an example embodiment. The living unit 200 is shown to have a person 202 (e.g., a medical patient being monitored) in an area 204 of the living unit 200. The depth cameras 108 of FIG. 1 are shown as two depth cameras 206, 208, although the system may be implemented using a single depth camera 208 or more than two depth cameras. These depth cameras 206, 208 may be deployed in the living unit 200 to generate video signals depicting the person 202 from different views in the area 204.
According to one embodiment, the depth cameras 206, 208 may be Microsoft KinectTM cameras that are placed at various locations within the area 204, capable of performing 3D motion tracking using a skeletal model, gesture recognition, facial recognition, and/or voice recognition. Each Microsoft KinectTM camera may include one or more sensors, an IR sensitive camera, or the like, that use a pattern of actively emitted infrared light in combination with a complementary metal-oxide-semiconductor (“CMOS”) image sensor and/or an IR-pass filter to obtain depth image data, such as a depth image, that is generally invariant to ambient lighting. Each Microsoft KinectTM camera may also include a standard RGB camera and/or other camera components as are generally known in the art.
For example, in one particular embodiment, the depth cameras 206, 208 may capture image depth data of the person 202, such as 3D motion tracking data at 30 frames per second, all of which may be invariant to changes in visible light. In some embodiments, the depth cameras 206, 208 are static in the area 204. As such, the depth cameras 206, 208 may not physically move locations within the living unit 200, change focus, or otherwise alter their view of the area 204. Alternatively, in other embodiments, the depth cameras 206, 208 may be deployed to generate additional video signals of the person 202. The depth cameras 206, 208 may then be appropriately deployed in the area 204 or elsewhere in the living unit 200 to generate video signals of the person 202. The video signals generated by the depth cameras 206, 208 may be provided to the remote device 102 shown in the form of a computing system 210. As shown, the computing system 210 is deployed in the living unit 200. However, the computing system 210 may be elsewhere. Any depth image data 112 captured from the depth cameras 206, 208 (e.g., a Microsoft KinectTM camera) may be used to extract or otherwise generate gait parameters of walking speed, right/left stride time and/or right/left stride length, stride to stride variability, trunk sway, gait asymmetry, entropy, and the like. Entropy is used as a measure of regularity in gait. A comprehensive explanation of Entropy is described in an Appendix entitled: “In-Home Measurement Of The Effect Of Strategically Weighted Vests On Ambulation,” which is incorporated by reference in its entirety herein.
FIG. 3 is an example block diagram illustrating the various hardware and/or software components of the remote device 102 according to one exemplary embodiment of the present disclosure. The remote device 102 may include a processing system 302 that may be used to execute the image analysis application 109 that receives depth image data (i.e. depth image data 112) and generates one or more temporal and/or spatial gait parameters for health risk assessment. The processing system 302 may include memory and/or be in communication with a memory 322, which may include volatile and/or non-volatile memory. The processing system 302 may also include various other computing components.
The remote device 102 may include a computer readable media (“CRM”) 304, which may include computer storage media, communication media, and/or another available computer readable media medium that can be accessed by the processing system 302. For example, CRM 304 may include non-transient computer storage media and communication media. By way of example and not limitation, computer storage media includes memory, volatile media, non-volatile media, removable media, and/or non-removable media implemented in a method or technology for storage of information, such as machine/computer readable/executable instructions, data structures, program modules, or other data. Communication media includes machine/computer readable/executable instructions, data structures, program modules, or other data. The CRM 304 is configured with the image analysis application 109. The image analysis application 109 includes program instructions and/or modules that are executable by the processing system 302. Generally, program modules include routines, programs, instructions, objects, components, data structures, etc., that perform particular tasks or implement particular abstract data types.
According to one aspect, the image analysis application 109 may include a receiving module 306 that receives depth image data 112 from one or more depth cameras 108. For example, the receiving module 306 may receive a pattern of projected infrared light from a Microsoft KinectTM camera. More particularly, the depth image data 112 received from the Microsoft KinectTM camera (at 30 frames per second) may be an 11-bit 640×480 image which is invariant to visible lighting. The precision of the distance measurement for each pixel is dependent on the distance from the KinectTM, with the precision decreasing from approximately one centimeter at two meters to approximately ten centimeters at six meters. The depth image data 112 may be stored in a database or other type of data store, where each data entry in the database corresponds to a walk and/or walk sequence identified in a particular space, such as an apartment corresponding to the patient.
Optionally, before the receiving module 306 receives any depth image data 112 from the depth cameras 108, a calibration module 308 may estimate calibration parameters for the depth cameras 108. For example, in the embodiment in which the depth cameras 108 are Microsoft KinectTM cameras, intrinsic, distortion, and stereo parameters for the IR and the RGB cameras of the KinectTM may be estimated according to a calibration pattern, such as a checkerboard calibration pattern and/or the like. Subsequently, calibration of any depth image data 112 returned from the Microsoft KinectTM may be performed, as the depth image data 112 returned from the KinectTM may require some form of transformation to obtain usable and accurate distances. For example, the following equations may be used to transform a raw KinectTM depth image data depth value, D, an integer value typically in the range [660, 1065], for a given pixel, (x, y), to a distance, d:




  
    
      
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where x′ and y′ are the normalized pixel coordinates computed using the intrinsic and distortion parameters of the IR camera. The parameters b, f, k1, k2, k3, and k4 are optimized over a large ( ̃3,000) set of training points and the equation attempts to adjust for distortion effects. The training points are obtained by placing a large checkerboard calibration pattern in the environment, while moving the KinectTM over a large range of distances and viewing angles with respect to the pattern. Using the known intrinsic parameters of the IR camera of the KinectTM the position of the calibration pattern with respect to the camera in each frame can be estimated. Simultaneously, the values associated with the pattern in the depth image data may be recorded. Following collection of the training data, a global optimization is performed using, for example, the CMA-ES algorithm although other optimization algorithms may be used. The CMA-ES algorithm is an optimization algorithm used to find a solution that minimizes an objective function. Example values for the parameters {b, f, k1, k2, k3, k4} used to transform the raw depth values to inches are {14145.6, 1100.1, 0.027, −0.014, 1.161, 3.719}.

After receiving, and optionally calibrating, depth image data, the receiving module 306 may automatically initiate a computation module 310 that analyzes, parses, and/or otherwise processes the depth image data to generate one or more parameters by executing one or more algorithms and/or equations. For example, the computation module 310 may extract gait parameters, such as walking speed, stride time, and stride length from the depth image data (e.g., a 3-dimensional representation of objects within a space, such as a room within a home or apartment).
A brief description of the various computations that may be performed by the computation module 310 will now be provided. Initially, foreground objects, represented as a set of 3D points, may be identified from depth image data using a dynamic background subtraction technique. Subsequently, a tracking algorithm may be used to track any extracted 3D objects and/or points. Walks may then be identified from the path histories of the tracked objects. More particularly, a set of criteria including path straightness, speed, duration, and distance may be used to identify suitable walks from the path histories.
Accordingly, initially, in one embodiment, the computation module 310 may initiate a background model module 312, which executes a background subtraction algorithm, optionally, in conjunction with a background model initialization algorithm and/or a background model updating algorithm, to generate a background model. Specifically, the background module 312 may generate the background model from the depth image data 112 captured by the depth cameras 108. In one embodiment, the background modeling algorithm may use a mixture of distributions approach typically run at 15 frames per second. The distributions are simple ranges defined by a minimum and maximum value. The background model consists of Kb background and Kf foreground distributions for each pixel in the disparity image. Each distribution, Dk(x,y), is defined by three floating point values, an upper bound, a lower bound, and a weight:

Dk(x,y)≡{[lk(x,y),uk(x,y)],Wk(x,y)}

The background modeling algorithm may be initialized over a set of training frames using the procedure defined in “Algorithm 1—Background Model Initialization” as described below:










Algorithm 1-Background Model Initialization

















CONSTANTS: Wmax, Winit, ΔW



INPUT: set of training disparity images, I



SET: Wj(x, y) = 0, j = 1:Kb + Kf , x = 1:width, y = 1:height










for each image i
I









for each pixel pi(x, y), x = 1:width, y = 1:height



if pi(x, y) = valid disparity value



for each distribution Dj(x, y), j = 1:Kb



if Wj(x, y) > 0 and pi(x, y) matches [Ij(x, y), uj(x, y)]



//Update the distribution and weight



Wj(x, y) = min(Wj(x, y) + ΔW, Wmax)



Ij(x, y) = min(pi(x, y) − 1, Ij(x, y))



uj(x, y) = max(pi(x, y) + 1, uj(x, y))



 if no distributions were matched



 //Replace least weight BACKGROUND distribution



    



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  Wj(x, y) = Winit



  Ij(x, y) = pi(x, y) − 1



  uj(x, y) = pi(x, y) + 1









where Wmax represents the maximum allowed weight a distribution can have; Winit represents the initial weight given to a new distribution; delta W is the increment added to a distribution's weight if the distribution is matched. Further, Dj(x,y) refers to distribution j for pixel x,y and contains and Wj(x,y) refers to the weight of distribution j for pixel x,y. The variable lj(x,y) refers to the lower bound of distribution j for pixel x,y and uj(x,y) refers to the lower bound of distribution j for pixel x,y. Finally, pi(x,y) refers to the value of pixel x,y in image i.

It should be noted that only background distributions are initialized over the training frames. The foreground distributions are left uninitialized with Wk(x,y)=0. Once initialized, the model is updated at each new frame using the procedure defined in “Algorithm 2—Background Model Updating” as described below:










Algorithm 2-Background Model Updating















CONSTANTS: Wmax, Winit, ΔW, Wadapt, ΔR


INPUT: new disparity image, i


for each pixel pi(x, y), x = 1:width, y = 1:height


 if pi(x, y) = valid disparity value


  for each distribution Dj(x, y), j = 1:Kb + Kf


   if Wj(x, y) > 0 and pi(x, y) matches [Ij(x, y), uj(x, y)]


    //Update the distribution range and weight


    Wj(x, y) = min(Wj(x, y) + ΔW, Wmax)


    Ij(x, y) = min(pi(x, y) − 1, Ij(x, y) + ΔR)


    uj(x, y) = max(pi(x, y) + 1, uj(x, y) − ΔR)


   else


    //Decay distribution weight


    Wj(x, y) = max(Wj(x, y) − ΔW, 0)


 if no distributions were matched


  //Replace least weight FOREGROUND distribution


    



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  Wj(x, y) = Winit


  Ij(x, y) = pi(x, y) − 1


  uj(x, y) = pi(x, y) + 1


 for each distribution Dj(x, y), j = Kb + 1:Kb + Kf


  //Adapt FOREGROUND to BACKGROUND


  if Wj(x, y) > Wadapt


      



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   Wk(x, y) = Wj(x, y)


   Ik(x, y) = Ij(x, y)


   uk(x, y) = uj(x, y)


   Wj(x, y) = 0









In Algorithm 2, Wmax and Wmin are the same as described for Algorithm 1. Delta W is a value that, in addition to being added to a distribution's weight if a distribution is matched, may be subtracted from a distribution's weight if the distribution is not matched given the pixel has a valid depth value. Wadapt represents the threshold at which a foreground distribution will be converted to a background distribution. Delta R represents a value that is used to keep the upper and lower bounds of a distribution from simply growing apart over time.

A foreground/segmentation module 314 may process any background models (i.e., the frames) generated by the background model module 312 to extract, segment, classify and/or otherwise identify a foreground and/or foreground pixels. Thus, the foreground/segmentation module 314 may classify a pixel as foreground and/or as background.
More particularly, given the background model, for each pixel, the first step of foreground segmentation is to compare the disparity value of each pixel from the current frame against its background model. If the disparity value of a pixel is found to match one of its active (Wk(x,y)>0) background distributions, then the pixel is classified as background; otherwise the pixel is classified as foreground. All pixels for which a valid disparity value is not returned are assumed to be background. A pixel is found to match a distribution if it lies within the range defined by the distribution, or its distance from the range is less than a threshold T (for this work T=0.25). Following such an initial classification, a block-based filtering algorithm may be applied to eliminate noise. Finally, morphological smoothing and hole-filling is used to further clean the image.
A 3D Segmentation module 316 may generate three-dimensional (“3D”) models for tracking from any extracted foreground. Specifically, given the extracted foreground for a frame, 3D objects are formed and evaluated for tracking. In one embodiment, the intrinsic and extrinsic calibration parameters generated by the calibration module 308 may be processed by the computation module 310 to convert the 3D foreground pixels into a set of 3D points.
Following conversion of the foreground pixels to a set of 3D points, object segmentation by the 3D segmentation module 316 is performed. More particularly, the set of the 3D points may be projected onto a discretized (1×1 inch) ground plane and single-linkage clustering is used to group the points into objects. The ground plane is discretized to limit the number of points considered by the clustering algorithm, and a distance of six inches is used for the single-linkage clustering threshold. In one embodiment, various parameters may be extracted from each 3D object (a cloud of 3D points), at each frame: avg x/y/z, max x/y/z, min x/y/z, covariance matrix, time stamp, ground plane projection of points below 22 inches and a correlation coefficient based on such a projection.
An estimate of volume may be obtained for each 3D object by summing the range of Z values for each location in the discretized ground plane that are part of the object. Any objects with a volume estimate greater than or equal to a threshold, V, are considered valid and retained for tracking, while any objects with volume estimates less than V are discarded. (For this work, V=725.) The 3D objects obtained from the current frame are compared against a set of currently tracked objects. All those new objects which match an existing object based on location and volume are used to update the existing tracked object, while all those that do not match an existing object are used to create new entries in the tracked object list. Each tracked object maintains a history of up to 30 seconds. Tracked objects are discarded if not updated for 20 seconds.
A sequence identification module 318 may be used to automatically identify walking sequences from the 3D objects (e.g. the tracked objects). Subsequently, the analyzed walking sequences may be processed by the computation module 310 to generate various gait parameters such as, in one embodiment, a walking speed, average speed, peek speed, stride time (e.g. individual stride time), and/or stride length (e.g. individual stride length), average stride length, height of the person walking, among others.
In one embodiment, as illustrated in FIG. 5, the identification of walk sequences may be determined using the histories of the tracked 3D objects. After each new frame, the history of each tracked object is evaluated to determine if a walk has just started, ended, or is currently in progress. For example, upon initialization of a 3D object in the tracked object set, the object is assumed to “not be in a walk” (operation 502). The object stays in the “not in walk” state until the speed of the object goes above a threshold, Ts. Thus, the state of the object changes from “not in walk” to “in walk” (operation 504). The object remains in such a state until one of two conditions is met: 1) the object's velocity drops below the threshold; or 2) the current walk does not meet a straightness requirement (operation 506). Upon one of these two conditions being met, the length and duration of the walk are assessed to determine if the walk should be analyzed for stride parameters and saved (operation 510). If the walk is saved, the state of the object returns to “not in walk” (operation 512). However, if the walk is not saved and the straightness requirement was the reason for termination, then the oldest points in the walk are iteratively discarded until the remaining points meet the straightness requirement. The state of the object is then returned to the in walk state (operation 514).
The straightness requirement consists of two measures: a global measure focused on the straightness of the entire path, and a local measure focused on abrupt changes. The first measure represents the average squared distance of each point in the sequence to a best fit line. The second measure represents the maximum deviation in walking direction computed over a small sliding window vs. that of the best fit line for the entire walk. Thresholds for both measures control the degree of straightness required for a walking sequence to be saved. In order to diminish the potential impact of capturing the beginning or the end of a walk on the computed average speed, only the middle 50 percent (based on time) of each walk is used to compute average speed.
The resulting output may be a dataset in which each entry corresponds to a walk identified in a given area. Each entry may be associated with the following features: height of the person, walking speeds, and, if possible, average stride time and average stride length, in addition to the time the walk occurred. Thus, each walk, xi, is initially associated with either two or four features:




  
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            ⁢
            no
            ⁢
            
              
            
            ⁢
            stride
            ⁢
            
              
            
            ⁢
            data
          
        
      
      
        
          
            {
            
              h
              ,
              s
              ,
              st
              ,
              sl
            
            }
          
        
        
          else
        
      
    
  




where h, s, st, and sl, are height, walking speed, stride time, and stride length, respectively. In order to include the information from walks without stride parameters in the computations, which due to furniture placement, etc., may make up the majority of walks in some areas (e.g. area 204), stride time and stride length values are estimated for the walks lacking them using the mean of the three nearest neighbors with stride information.

In one particular embodiment, the dataset may include walks from all the persons (e.g. person 202) of the area 204 (e.g. an apartment), as well as any visitors. As such, before any gait measurement estimates can be performed, a procedure for identifying walks from the specific person(s) is necessary.
One approach makes the assumption that each person will create a cluster, or mode, in the dataset, representing their typical, in-home, habitual gait. These clusters are modeled as Gaussian distributions in the 4D feature space. The basic procedure is to fit a Gaussian Mixture Model (GMM), λ={ρr, μr, Σr}, r=1, . . . , K, with the number of distributions, K, equal to the number of persons 202 in the area 204 to the dataset, X={x1, . . . , xN}:




  
    

  
  ⁢
  
    
      p
      ⁡
      
        (
        
          
            x
            i
          
          ❘
          λ
        
        )
      
    
    =
    
      
        ∑
        
          r
          =
          1
        
        K
      
      ⁢
      
        
      
      ⁢
      
        
          ρ
          r
        
        ⁢
        
          g
          ⁡
          
            (
            
              
                
                  x
                  i
                
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                  μ
                  r
                
              
              ,
              
                ∑
                r
                
                  
                
              
            
            )
          
        
      
    
  




where g(x|μr,Σr), r=1, . . . , K, are the multivariate Gaussian distributions, and ρr, r=1, . . . , K, are the mixture weights.

The Gaussian distribution representing each person (e.g. person 202 such as a person) is used to identify walks from that particular person. Any walk whose likelihood given a distribution is greater than a threshold is assumed to be from the person that the distribution represents, and is used in computing gait parameter estimates for that person. The classification may be performed independently for each distribution. Thus, a walk could be included in the estimates of more than one person, if the distributions overlap. The steps of model initialization and updating are described below and illustrated in FIG. 2.
An output module 320 processes the depth image data 112 and/or the one or more generated parameters 114 to perform one or more health risk assessments. For example, the parameters 114 and depth image data 112 may be used to assess a patient's risk of falling and/or the onset of illness.
In one embodiment, the actual assessment of fall/health risk may be based on mapping the various gait parameters to standard clinical measures such as a Timed-up-and-Go (TUG) test, and the Habitual Gait Speed (HGS) test. For example, in one embodiment, a simple neural network model that can “predict” TUG time based on an individual person's average gait speed. It is contemplated that any gait parameter may be mapped to standard measures. For example, a TUG time above 16 or 20 seconds indicates a high risk of falling in the next year. Accordingly, the gait parameter data and/or gait parameter estimates may be used to predict a score that a person, such as a patient, would receive on various clinical measures, tests, and the like, such as the TUG, HGS, Berg Balance-Short Form, Short Physical Performance Battery, and Multi-Directional Reach Test data, etc.
FIG. 4 depicts an example method and/or process 400 for obtaining depth image data and subsequently processing the depth image data to generate temporal and spatial gait parameters for use in health risk assessment. Process 400 may be executed by at least one processor encoded with, or executing instructions of, an image analysis application 109. Initially, at 402, process 400 includes receiving depth image data for a particular patient from one or more depth cameras 108. For example, depth image data may be received from a Microsoft KinectTM camera device located in the home of an elderly gentleman. At 404, the depth image data may be analyzed to generate at least one three-dimensional object. For example, a three-dimensional representation of the elderly gentlemen patient may be generated. At 406, a walking sequence may be identified based on the at least one three-dimensional object. For example, a walking sequence corresponding to the elderly gentleman patient may be identified. At 408, one or more parameters may be generated from the walking sequence. For example, one or more temporal and spatial gait parameters may be generated corresponding to the elderly gentleman. At 410, the generated parameters are used to perform various health risk assessments for a particular patient (e.g. the elderly gentlemen) and results of the health risk assessments may be provided for display at 412.
The description above includes example systems, methods, techniques, instruction sequences, and/or computer program products that embody techniques of the present disclosure. However, it is understood that the described disclosure may be practiced without these specific details. In the present disclosure, the methods disclosed may be implemented as sets of instructions or software readable by a device. Further, it is understood that the specific order or hierarchy of steps in the methods disclosed are instances of example approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the method can be rearranged while remaining within the disclosed subject matter. The accompanying method claims present elements of the various steps in a sample order, and are not necessarily meant to be limited to the specific order or hierarchy presented.
The described disclosure may be provided as a computer program product, or software, that may include a machine-readable medium having stored thereon instructions which may be used to program a computer system (or other electronic devices) to perform a process according to the present disclosure. A machine-readable medium includes any mechanism for storing information in a form (e.g., software, processing application) readable by a machine (e.g., a computer). The machine-readable medium may include, but is not limited to, magnetic storage medium (e.g., floppy diskette); optical storage medium (e.g., CD-ROM); magneto-optical storage medium; read only memory (ROM); random access memory (RAM); erasable programmable memory (e.g., EPROM and EEPROM); flash memory; or other types of medium suitable for storing electronic instructions.
It is believed that the present disclosure and many of its attendant advantages will be understood by the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the components without departing from the disclosed subject matter or without sacrificing all of its material advantages. The form described is merely explanatory, and it is the intention of the following claims to encompass and include such changes.
While the present disclosure has been described with reference to various exemplary embodiments, it will be understood that these embodiments are illustrative and that the scope of the disclosure is not limited to them. Many variations, modifications, additions, and improvements are possible. More generally, embodiments in accordance with the present disclosure have been described in the context of exemplary implementations. Functionality may be separated or combined in blocks differently in various embodiments of the disclosure or described with different terminology. These and other variations, modifications, additions, and improvements may fall within the scope of the disclosure as defined in the claims that follow.

## Claims

1. A method comprising:
receiving, by at least one processor, depth image data from at least one depth camera, wherein the depth image data comprises a plurality of frames that depict a person walking through a home environment over time, the frames comprising a plurality of pixels;
performing, by the at least one processor, segmentation on the pixels of the frames;
in response to the segmentation, (1) generating, by the at least one processor, a three-dimensional (3D) data object based on the depth image data, and (2) tracking, by the at least one processor, the 3D data object over a plurality of frames of the depth image data, wherein the tracked 3D data object comprises time-indexed spatial data that represents the person walking through the home environment over time;
identifying, by the at least one processor, a walking sequence from the tracked 3D data object, wherein the identifying step comprises:
the at least one processor determining a speed for the tracked 3D data object over a time frame;
the at least one processor comparing the determined speed with a speed threshold;
in response to the comparison indicating that the determined speed is greater than the speed threshold, the at least one processor assigning a state indicative of walking to the tracked 3D data object;
while the tracked 3D data object is in the assigned walking state:
the at least one processor determining a walk straightness for the tracked 3D data object;
the at least one processor determining a walk length for the tracked 3D data object;
the at least one processor determining a walk duration for the tracked 3D data object;
the at least one processor saving the tracked 3D data object in memory as the identified walking sequence when (i) the determined walk straightness exceeds a straightness threshold, (ii) the determined walk length exceeds a walk length threshold, and (iii) the determined walk duration exceed a walk duration threshold;
the at least one processor excluding from the identified walking sequence in the memory the time-indexed spatial data from the tracked 3D data object corresponding to a time period where the determined walk straightness is less than the walk straightness threshold;
the at least one processor repeating the speed determining step and the comparing step for the tracked 3D data object while the tracked 3D data object is in the assigned walking state; and
the at least one processor assigning a state indicative of not walking to the tracked 3D data object in response to a determination that the speed of the tracked 3D data object in the walking state has fallen below the speed threshold;


analyzing, by the at least one processor, the time-indexed spatial data from the identified walking sequence to generate one or more gait parameters; and
performing, by the at least one processor, at least one health risk assessment based on the one or more gait parameters to determine a health risk assessment score for the person.

2. The method of claim 1, wherein generating the 3D data object comprises:
for each frame within the plurality of frames, the at least one processor (1) segmenting pixels within that frame into background pixels and foreground pixels according to at least one background model, (2) converting the
foreground pixels into a set of three-dimensional 3D points, (3) segmenting the set of 3D points to generate
at least one 3D object for tracking, the generated 3D data object being representative of an object within the space and comprising a plurality of 3D points that define a spatial position of the represented object, (4) maintaining a list that identifies each 3D data object for tracking, (5) comparing each generated 3D data object with each tracked 3D data object on the list, (6) for each generated 3D data object that matches a tracked 3D data object on the list, updating the matching tracked 3D data object based on the matching generated 3D data object, wherein the updated tracked 3D data object comprises a plurality of 3) points that define the spatial position of the represented object over time, and (7) for each generated 3D data object that does not match any tracked 3D data object on the list, adding the non-matching 3D data object to the list as a new 3D data object for tracking.

3. The method of claim 1, wherein the depth image data comprises three-dimensional motion tracking data captured at thirty frames per second.

4. The method of claim 1, wherein performing the health risk assessment comprises mapping the one or more parameters to a standard clinical measure to generate the health risk assessment score.

5. The method of claim 1, wherein the at least one depth image camera comprises a Microsoft Kinect.

6. The method of claim 1, wherein the one or more gait parameters comprises at least one of walking speed, stride time, and stride length.

7. A system comprising:
a memory configured to (1) store a model of walk characteristics data for a person of interest and (2) store a plurality of walk sequence data sets in association with the person of interest; and
at least one processor for cooperation with the memory, the at least one processor configured to receive and process the depth image data to populate the memory with the walk sequence data sets associated with the person of interest;
wherein the at least one processor is further configured to:
receive depth image data from at least one depth camera, wherein the depth image data comprises a plurality of frames that depict a space over time, the frames comprising a plurality of pixels;
process the pixels within the frames to generate and track a plurality of three-dimensional (3D) data objects that represent a plurality of objects that are moving within the space over time, each tracked 3D data object comprising a plurality of 3D points that define a spatial position of its represented object over time;
process the 3D points of each tracked 3D data object to make a plurality of determinations as whether any tracked 3D data object is indicative of a person walking;
identify a plurality of walking sequences in response to the walking determinations, each identified walking sequence corresponding to a tracked 3D data object;
analyze the 3D points of the tracked 3D data objects corresponding to the identified walking sequences to generate data indicative of a plurality of walk characteristics for the identified walking sequences;
save a walking sequence data set for each identified walking sequence, each walking sequence data set comprising the walk characteristics data for its corresponding walking sequence;
cluster each saved walk sequence data set and compare the clustered walk sequence data sets with the stored model;
based on the comparison, determine whether any of the clustered walk sequence data sets are attributable to the person of interest;
in response to a determination that a clustered walk sequence data set is attributable to the person of interest, store that walk sequence data set in the memory in association with the person of interest;
perform at least one health risk assessment based on at least one of the stored walk sequence data sets associated with the person of interest; and
communicate a result of the health risk assessment for display.

8. The system of claim of claim 7, wherein, as part of the pixel processing operation, the at least one processor is further configured to:
for each frame within the plurality of frames, (1) segment pixels within that frame into background pixels and foreground pixels according to at least one background model, (2) convert the
foreground pixels into a set of three-dimensional (3D) points, (3) segment the set of 3D points to generate
at least one 3D data object for tracking, the generated 3D data object being representative of an object within the space and comprising a plurality of 3D points that define a spatial position of the represented object, (4) maintain a list that identifies each 3D data object for tracking, (5) compare each generated 3D data object with each tracked 3D data object on the list, (6) for each generated 3D data object that matches a tracked 3D data object on the list, update the matching tracked 3D data object based on the matching generated 3D data object, wherein the updated tracked 3D data object comprises a plurality of 3D points that define the spatial position of the represented object over time, and (7) for each generated 3D data object that does not match any tracked 3D data object on the list, add the non-matching 3D data object to the list as a new 3D data object for tracking.

9. The system of claim 8, wherein the depth image data comprises three-dimensional motion tracking data captured at thirty frames per second.

10. The system of claim 8, wherein the at least one processor, as part of the health risk assessment, is configured to map the walk characteristics data for at least one of the stored walking sequence data sets associated with the person of interest to a standard clinical measure to generate a health risk assessment score.

11. The system of claim 8, wherein the at least one depth image camera comprises a Microsoft Kinect.

12. The system of claim 8, wherein the walk characteristics data comprises at least one of walking speed, stride time, and stride length.

13. A system comprising:
at least one depth camera configured to capture depth image data of an area within a field of view of the at least one depth camera;
a memory configured to (1) store a model of walk characteristics data for a person of interest and (2) store a plurality of walk sequence data sets in association with the person of interest;
at least one processor for cooperation with the at least one depth camera and the memory, the at least one processor configured to receive and process the depth image data to populate the memory with the walk sequence data sets associated with the person of interest;
wherein the at least one processor is further configured to:
receive depth image data from at least one depth camera, wherein the received depth image data comprises a plurality of frames that depict the space over time, the frames comprising a plurality of pixels;
process the pixels within the frames to generate and track a plurality of three-dimensional (3D) data objects that represent a plurality of objects that are moving within the space over time, each tracked 3D data object comprising a plurality of 3D points that define a spatial position of its represented object over time;
process the 3D points of each tracked 3D data object to make a plurality of determinations as whether any tracked 3D data object is indicative of a person walking;
identify a plurality of walking sequences in response to the walking determinations, each identified walking sequence corresponding to a tracked 3D data object;
analyze the 3D points of the tracked 3D data objects corresponding to the identified walking sequences to generate data indicative of a plurality of walk characteristics for the identified walking sequences;

save a walking sequence data set for each identified walking sequence, each walking sequence data set comprising the walk characteristics data for its corresponding walking sequence;
cluster each saved walk sequence data set and compare the clustered walk sequence data sets with the stored model;
based on the comparison, determine whether any of the clustered walk sequence data sets are attributable to the person of interest;
in response to a determination that a clustered walk sequence data set is attributable to the person of interest, store that walk sequence data set in the memory in association with the person of interest;
map at least one of the stored walk sequence data sets associated with the person of interest to a clinical measure indicative of a fall risk to thereby compute a fall risk score for the person of interest;

compare the compound fall risk score with a threshold; and
in response to the fall risk score comparison resulting in a determination that the computed fall risk score exceeds the threshold, generate an alert for display that is indicative of a high fall risk for the person of interest.

14. The system of claim of claim 13, wherein, as part of the pixel processing operation, the at least one processor is further configured to:
for each frame within the plurality of frames, (1) segment pixels within that frame into background pixels and foreground pixels according to at least one background model, (2) convert the
foreground pixels into a set of three-dimensional (3D) points, (3) segment the set of 3D points to generate
at least one 3D data object for tracking, the generated 3D data object being representative of an object within the space and comprising a plurality of 3D points that define a spatial position of the represented object, (4) maintain a list that identifies each 3D data object for tracking, (5) compare each generated 3D data object with each tracked 3D data object on the list, (6) for each generated 3D data object that matches a tracked 3D data object on the list, update the matching tracked 3D data object based on the matching generated 3D data object, wherein the updated tracked 3D data object comprises a plurality of 3D points that define the spatial position of the represented object over time, and (7) for each generated 3D data object that does not match any tracked 3D data object on the list, add the non-matching 3D data object to the list as a new 3D data object for tracking.

15. The system of claim 13, wherein the depth image data comprises three-dimensional motion tracking data captured at thirty frames per second.

16. The system of claim 13, wherein the clinical measure comprises a Timed-up-and-Go (TUG) test such that the computed fall risk score comprises a TUG time for the person of interest.

17. The system of claim 13, wherein the at least one depth image camera comprises a Microsoft Kinect.

18. The system of claim 13, wherein the walk characteristics data comprises at least one of walking speed, stride time, and stride length.

19. The system of claim 13, wherein the at least one processor, as part of the 3D points processing operation and the walking sequences identification operation, is further configured to, for each of a plurality of the tracked 3D data objects:
determine a speed for the tracked 3D object over a time frame;
compare the determined speed with a speed threshold;
in response to the speed comparison indicating that the determined speed is greater than the speed threshold, assign a state indicative of walking to the tracked 3D data object
while the tracked 3D data object is in the assigned walking state:
determine a walk straightness for the tracked 3D data object;
determine a walk length for the tracked 3D data object;
determine a walk duration for the tracked 3D data object;
save the tracked 3D data object in the memory as an identified walking sequence when (i) the determined walk straightness exceeds a straightness threshold, (ii) the determined walk length exceeds a walk length threshold, and (iii) the determined walk duration exceeds a walk duration threshold;
exclude from the identified walking sequence in the memory the 3D points from the tracked 3D object corresponding to a time period where the determined walk straightness is less than the walk straightness threshold;
repeat the speed determination operation and the speed comparison operation for the tracked 3D data object while the tracked 3D data object is in the assigned walking state; and
assign a state indicative of not walking to the tracked 3D data object in response to a determination that the speed of the tracked 3D data object in the walking state has fallen below the speed threshold.

20. The system of claim 7, wherein the at least one processor, as part of the 3D points processing operation and the walking sequences identification operation, is further configured to, for each of a plurality of the tracked 3D data objects:
determine a speed for the tracked 3D object over a time frame;
compare the determined speed with a speed threshold;
in response to the speed comparison indicating that the determined speed is greater than the speed threshold, assign a state indicative of walking to the tracked 3D data object
while the tracked 3D data object is in the assigned walking state:
determine a walk straightness for the tracked 3D data object;
determine a walk length for the tracked 3D data object;
determine a walk duration for the tracked 3D data object;
save the tracked 3D data object in the memory as an identified walking sequence when (i) the determined walk straightness exceeds a straightness threshold, (ii) the determined walk length exceeds a walk length threshold, and (iii) the determined walk duration exceeds a walk duration threshold;
exclude from the identified walking sequence in the memory the 3D points from the tracked 3D object corresponding to a time period where the determined walk straightness is less than the walk straightness threshold;
repeat the speed determination operation and the speed comparison operation for the tracked 3D data object while the tracked 3D data object is in the assigned walking state; and
assign a state indicative of not walking to the tracked 3D data object in response to a determination that the speed of the tracked 3D data object in the walking state has fallen below the speed threshold.