what is disclosed is a system and method for estimating minute ventilation by analyzing distortions in reflections of structured illumination patterns captured in a video of a thoracic region of a subject of interest being monitored for respiratory function . a “ subject of interest ” refers to a subject being monitored for respiratory function such that a respiratory minute volume can be determined in accordance with the teachings hereof . fig1 shows an anterior ( frontal ) view 101 of an adult human as well as a posterior ( rear ) view 102 . target region 103 outlines the subject &# 39 ; s anterior thoracic region . target region 104 outlines the subject &# 39 ; s posterior thoracic region . a target region , as used herein , also refers to any view of a region of the subject &# 39 ; s body which performs a respiratory function from which respiratory minute volume can be derived . it should be appreciated that the use of the terms “ human ”, “ person ”, or “ patient ” herein is not to be viewed as limiting the scope of the appended claims solely to human subjects of interest . the teachings hereof apply equally to other subjects of interest which also have a respiratory function . such additional subjects include , for example , mammals , birds , fish , reptiles , and even certain insects . a “ respiratory function ” is a multi - stage process involving inhaling air into the lungs ( inspiration ), gas exchange , and exhaling air out of the lungs ( expiration ) followed by a post - expiratory pause . inhalation causes the lungs contained within the chest cavity to fill with air thereby expanding chest volume . inhalation is initiated by a diaphragm muscle and supported intercostal muscles . under normal conditions , the diaphragm is the primary driver of inhalation . when the diaphragm contracts , the rib cage expands and the contents of the abdomen are moved downward . this results in a larger thoracic volume and negative pressure ( with respect to atmospheric pressure ) inside the thorax . gas exchange is a primary function of the respiratory system . molecules of gases are exchanged between the external environment and a blood system . this exchange facilitates oxygenation of the blood and removal of carbon dioxide and other metabolic wastes from the body . gas exchange also helps maintain the acid - base balance of the body . the cellular mechanism of gas exchange is carried out by the simple phenomenon of pressure difference . when the atmospheric pressure is low outside , air from the lungs flow out into the environment . when the air pressure is low inside the lungs , the opposite occurs . exhalation is generally a passive process due to the natural elasticity of lung tissue which causes them to recoil from the stretch of inhalation thus forcing air out until the pressures in the chest and the pressure of the outside atmosphere reach equilibrium . during forced exhalation , as when blowing out a candle , expiratory muscles including abdominal muscles and internal intercostal muscles , generate abdominal and thoracic pressure which helps force air out of the lungs . during forced inhalation , as when taking a deep breath , external intercostal muscles and accessory muscles aid in expanding the thoracic cavity and bringing more air into the lungs . during vigorous inhalation ( at rates exceeding 35 breaths per minute ), or in an approaching respiratory failure , accessory muscles such as the sternocleidomastoid , platysma , the scalene muscles of the neck as well as the pectoral muscles and latissimus dorsi of respiration are recruited for support . a post - expiratory pause occurs when there is an equalization of pressure between the lungs and the atmosphere . the duration of the post - expiratory pause reduces with increased physical activity and may even fall to zero at high rates of exertion . when the subject is at rest , the duration of the post - expiratory pause is relatively long . the subject &# 39 ; s respiration cycle is the time interval between the beginning of inhalation and the end of the post - expiratory pause . immediately following the post - expiratory pause is the start of the next cycle . the subject &# 39 ; s respiration rate is the number of breaths a subject takes within a certain amount of time ( typically in breaths / minute ). respiration rate is often measured when a subject is at rest and simply involves counting the number of breaths taken in a minute . a resting adult human takes about 12 - 20 breaths per minute depending on the overall condition of the cardio - vascular and respiratory systems . restrictive pulmonary diseases such as pulmonary fibrosis , pneumothorax , infant respiratory distress syndrome , and the like , decrease lung volume , whereas obstructive pulmonary diseases such as asthma , bronchitis , and emphysema , obstruct airflow . fig2 shows the output from a spirometer of a normal person taking seven tidal breaths , followed by maximal inspiration and expiration . expiratory reserve volume ( erv ) is the maximal volume of air that can be exhaled from the end - expiratory position . residual volume ( rv ) is the volume of air remaining in the lungs after maximal exhalation ( residual air remains in the lungs no matter how hard one tries to expel all their air ). inspiratory reserve volume ( irv ) is the maximal volume of air that can be inhaled at the end - inspiratory level . vital capacity ( vc ) is the maximum amount of air a person can expel from the lungs after maximum inhalation . inspiratory capacity ( ic ) is the volume of air that can be inhaled after normal inspiration . functional residual capacity ( frc ) is the volume in the lungs at the end - expiratory position . total lung capacity ( tlc ) is the total volume of air in the lungs at maximal inflation . “ respiratory minute volume ” or “ minute ventilation ” is the amount of air exchanged by the lungs in one minute . it can also refer to the amount of air inhaled in one minute ( inhaled minute volume ) or the amount of air exhaled in one minute ( exhaled minute volume ). although the name implies a volume , minute ventilation is actually a flow because it represents a volume change over time . minute ventilation is an important parameter in respiratory medicine due to its relationship with blood carbon dioxide levels ( paco 2 ) which varies inversely with minute ventilation . for example , a person with increased minute volume due , for instance , to hyperventilation , should demonstrate a lower blood carbon dioxide level . the healthy human body alters respiratory minute volume in an attempt to maintain physiologic homeostasis . a normal minute volume while resting is about 5 - 8 liters per minute in adult humans . minute volume generally decreases at rest , and increases with exercise as waste gases will build up more quickly in the blood stream and must be more rapidly expelled through increased exhalation . a “ video ”, as is generally understood , is a time - varying sequence of image frames captured over time using a video camera . a fully populated 2d image captured using , for example , a 3 - channel color video camera is a 2d array of pixels with each pixel in the array having color values collected for pixels from each of those channels . a fully populated 2d image captured using , for example , a single channel video camera is a 2d array of pixels with each pixel in the array having an intensity value measured for that pixel location at a desired wavelength band of interest . the video may also contain other components such as , audio , time reference signals , and the like . the size of the video data may get large for longer video sequences . the video may also be processed or pre - processed to compensate for non - uniform illumination due to a curvature of a surface of the skin , for motion induced blur due to body or surface motion , imaging blur , and slow illuminant variation . motion in the video may be compensated for using , for example , a video - based 2d image or 3d surface stabilization techniques . “ receiving a video ” is intended to be widely construed and means to retrieve , receive , capture with a video camera , or otherwise obtain a video for processing for minute ventilation estimation in accordance with the present method . the video can be received from a memory or internal storage of the video camera system , or obtained from a remote device over a network . the video may also be retrieved from a media such as a cdrom or dvd . the video may be received by being downloaded from a website which makes such videos available for pre - processing or post - processing . one such web - based system is disclosed in the above - incorporated us patent application entitled : “ web - based system and method for video analysis ” by piratla et al . the video can also be retrieved using an application such as those which are widely available for handheld cellular devices and processed on the user &# 39 ; s cellphone or other handheld computing device such as an ipad . a “ video system ” refers to a video camera for capturing a video and a structured illumination source which projects light through a patterned grid or window . the pattern may be a pseudo - random pattern with known spatial characteristics . accurate 3d surface profiles of objects in a scene can be computed using structured - light principles and triangulation - based image reconstruction techniques . fig3 shows a single 2d image frame 300 being captured of a target region 303 of the subject of interest of fig1 . video camera 310 captures reflected energy off the target region emitted by structured illumination source 311 . video camera 310 is shown having a communication element 313 to effectuate a bi - directional communication with a remote device , such as a computer workstation , wherein the video is received for processing . a video imaging system may further comprise a video analysis module . controllers 314 and 315 are shown to effectuate a manipulation of structured illumination source 311 and 312 , respectively , to reduce artifacts . one method for reducing such artifacts is disclosed in the above - incorporated reference : “ enabling hybrid video capture of a scene illuminated with unstructured and structured illumination sources ”, by xu et al . a “ video analysis module ”, in one embodiment , comprises a hardware device such as an asic with at least one processor capable of executing machine readable program instructions for analyzing video images on a frame - by - frame basis for minute ventilation estimation . such a module may also comprise , in whole or in part , a software application working alone or in conjunction with one or more hardware resources . software applications may be executed by processors on different hardware platforms or emulated in a virtual environment . aspects of the video analysis module may leverage off - the - shelf software . a “ remote sensing environment ” refers to a non - contact , unobtrusive non - invasive means of acquiring data from a subject , i . e ., the sensing device does not physically contact the subject being sensed . the sensing device can be any distance away from the subject , for example , as close as less than an inch to as far as miles in the case of telemedicine . the teachings hereof find their intended uses in such a remote sensing environment such that the resting cardiac patient remains undisturbed . a “ depth map ” is a map containing depth values based upon an analysis of the amount of distortion of a structured light pattern reflected from surfaces in that region of the image . once the depth map has been generated , a volume can be calculated . in fig4 , structured illumination source 403 projects sinusoidal gratings 404 onto an object 405 and the reflection of the impinging sinusoidal gratings is captured by the camera system 402 as they bounce off the object . the sinusoidal gratings have known spatial characteristics of undistorted projected patterns . camera system 402 is shown having a communication element 406 for bi - directional communication with a remote device , such as a workstation ( not shown ) wherein the captured video is communicated for processing . if the scene is a planar surface without any 3d surface variation and oriented approximately parallel to the camera sensor , the pattern shown in the acquired image will be similar to that of the projected structured - light pattern . however , when the surface is non - planar and contains a 3d object 405 , the shape of the object distorts the projected structured light pattern . such light distortions can be detected by camera 402 . the geometric relationship between camera 402 , a structured illumination source 403 , and a point p on the surface of 3d object 405 can be expressed in terms of a triangulation as follows : accurate 3d image reconstruction can be based on a phase - shifting or phase modulation technique which measures phases at different locations on the object &# 39 ; s surface and computes depth information from these phases . fig5 shows the phase shift with three projection patterns , collectively at 501 , projected onto the object surface , and an example fringe image 502 . phase shift is a well - known method wherein intensities for each pixel ( x , y ) of the three projected fringe patterns are described by the following relationships : i 1 ( x , y )= i 0 ( x , y )+ i mod ( x , y ) cos ( φ ( x , y )− θ ), ( 2 ) i 2 ( x , y )= i 0 ( x , y )+ i mod ( x , y ) cos ( φ ( x , y )), ( 3 ) i 3 ( x , y )= i 0 ( x , y )+ i mod ( x , y ) cos ( φ ( x , y )+ θ ), ( 4 ) where i 1 ( x , y ), i 2 ( x , y ) and i 3 ( x , y ) are the intensities of three fringe patterns , i 0 ( x , y ) is the dc component ( background ), i mod ( x , y ) is the modulation signal amplitude , φ ( x , y ) is the phase , and θ is the constant phase - shift angle . phase unwrapping is the process that converts the wrapped phase to the absolute phase . the phase information φ ( x , y ) can be retrieved ( i . e ., unwrapped ) from the intensities in the three fringe patterns : the discontinuity of the arc tangent function at 2π can be removed by adding or subtracting multiples of 2π on the φ ′( x , y ) value ( of fig6 ): where k is an integer representing projection period . note that unwrapping methods only provide a relative unwrapping and do not solve for the absolute phase . the 3d ( x , y , z ) coordinates can be calculated based on the difference between measured phase φ ( x , y ) and the phase value from a reference plane . reference is now being made to the system of fig8 which utilizes a video camera 802 to sense reflected light emitted ( at 804 ) by patterned illumination source projector 805 being reflected off point p of object 806 , i . e ., a location in the subject &# 39 ; s thoracic region . detector 808 generates pixel intensity values for pixel locations in the image . pixel intensity values and wavelength data are provided to storage media 809 . in fig8 , depth z is calculated by geometries given by : the camera and the illuminator form a stereo pair with a baseline distance b = 7 . 5 cm . the projector sends out a fixed pattern of light and dark speckles . since the spatial characteristics of the pattern are known and the pattern warps as the depth of the target surface changes , distances to the target can be estimated by determining the shape of the warping locally . local correlation operations are performed between the captured and the stored pattern . the best match gives an offset from the known depth in pixels called disparity , d . the relationship between disparity and depth is given by : where z is the estimated depth in meters , f is the focal length of the camera in pixels , and b is the baseline distance . stripe indexing can also be used to achieve robust 3d surface reconstruction because the order in which the stripes are observed is not necessarily the same as the order in which the stripes are projected due to the inherent parallax existing in triangulation - based 3d surface imaging systems and the possibility to have stripes missing from the acquired image due to occlusion of 3d surface features . fig7 shows an example stripe projection system wherein structured source light 701 is projected through stripped projector 702 with stripe 703 being illustrated for explanatory purposes . the pattern is projected onto object 704 whereon light stripe 705 illuminates the object at pixel location 706 . pixel element 708 of camera matrix 707 detects the reflected source light at this pixel location . the collection of pixels forms the image . use of color for stripe indexing in the projection patterns helps alleviate the ambiguity problem faced by phase - shift or multiple - stripe techniques using monochromatic patterns . this type of system enables encoding of multiple patterns into a single color projection image with each pattern possessing a unique color value . in order to reduce the decoding error rate , one can select a color set in which each color has a maximum distance from any other color in the set . the maximum number of colors is limited to a distance between colors that generates a minimal crosstalk in the acquired images . it should be appreciated that if the target 3d object is static and the application does not impose stringent constraints on the acquisition time , multiple - shot ( sequential ) techniques can be used and may often result in more reliable and accurate results . on the other hand , if the target is moving , single - shot techniques are used to acquire a snapshot 3d surface image of the 3d object at a particular time instance . single - shot techniques can be classified into techniques using continuously varying structured - light patterns , those using 1d encoding schemes ( strip indexing ), and those using 2d encoding schemes ( grid indexing ). each technique has its own advantages and disadvantages , depending on the specific applications . some techniques can be combined . for further information on 3d imaging techniques , the reader is respectfully directed to the above - incorporated reference entitled : “ structured - light 3 d surface imaging : a tutorial ”, by jason geng . in order to convert the device - dependent depth readouts ( in bytes ) to device - independent quantities ( in inches or meters ), a calibration needs to be performed . the calibration of the spatial coordinates of the device ( from pixels to meters or inches ) can be performed in a manner which is substantially similar to the way a traditional rgb camera is calibrated . for example , the reference : “ a flexible new technique for camera calibration ”, z . zhang , ieee trans . on pattern analysis and machine intelligence , vol . 22 ( 11 ), 1330 - 1334 , ( 2000 ), teaches a method to estimate a spatial calibration model with 11 unknown parameters . calibration of the depth output requires knowledge of the geometric configuration of the stereo pair ( illumination and imaging modules ). as discussed , both the spatial coordinates and the depth readouts from the 3d imaging sensor can be translated into device independent units of length ( such as meters or inches ). this , however , does not guarantee that the estimated volumes correspond to the volume being measured , given the fact that the changes in chest cage volume may not be identical to the changes in lung volume due to differences in elasticity between the two . thus , additional calibration may be desirable . assuming a linear relation between estimated and actual volume , a proportionality constant can be estimated via laboratory tests conducted for different breathing levels over a range required for the measurements . the actual volume can be measured using a spirometer . the slope of the linear regression line between the measurements of the spirometer and those obtained with the 3d imaging system would provide the calibration constant . before minute ventilation is estimated , the region of the depth map corresponding to the subject &# 39 ; s body is preferably segmented in the images . this can be achieved in a plurality of ways . for example , since the distance from the camera to the bed &# 39 ; s surface is known , the location of the subject &# 39 ; s body can be extracted by detecting pixels surrounded by the bed &# 39 ; s surface and located closer to the camera than the bed itself . another method is to perform localization and then region - grow the target area to include pixels with similar depth information . this produces a resulting binary mask . chest cage localization can be performed by judicious application of morphological operations on the binary mask that results from the body segmentation stage . for example , morphological opening of the mask with an appropriate size structuring element will remove pixels corresponding to the extremities and head given their relative size with respect to the chest area . another way is to apply morphological skeletonization to the mask and determine the branch points of the resulting skeleton . these branch points will be approximately located at the neck and shoulders , thus providing indication of the location of the subject &# 39 ; s thoracic region . reference is now being made to the flow diagram of fig9 which illustrates one example embodiment of the present method for estimating respiratory minute volume from video captured of a subject of interest being monitored for respiratory function in a remote sensing environment . flow processing begins at step 900 and immediately proceeds to step 902 . at step 902 , receive a video of a target region of a chest area of a subject of interest being monitored for respiratory function . the video has been captured using a video camera and an illuminator configured to project a pattern of structured illumination . example target regions of a subject of interest are shown and discussed with respect to the subject of interest of fig1 . at step 904 , process the video to obtain a depth map at inspiration and expiration within the same breathing cycle over a plurality of contiguous breathing cycles over time . in one embodiment , the depth maps are determined by comparing the captured images of the video to known spatial characteristics of undistorted patterns such that an amount of distortion of the captured patterns can be characterized at both inspiration and expiration over a plurality of breathing cycles . at step 906 , estimate chest volume at inspiration and at expiration from the respective depth maps . a chest volume is estimated after both inspiration and expiration for each breathing cycle over a predetermined amount of time such as one minute . in one embodiment , chest volume is estimated by tessellating surface points at various locations of the surface of the depth map and computing a reference point location which , in various embodiments , comprises either a centroid , a weighted arithmetic mean , or a rank - ordered statistic of surface point locations . tessellation is a technique for covering ( or tiling ) a surface with flat patterns ( or surfaces ) so that there are no overlaps and no gaps . tetrahedrons are created by connecting triangles in the tessellation with the reference point . a tetrahedron is a polygon having four vertices with each face being formed by connecting three of the vertices to form a triangle . three points of each triangle define a plane . there are four faces of a tetrahedron . a volume is computed for each tetrahedron . the total volume is the aggregate of all the tetrahedral volumes . at step 908 , estimate a minute ventilation for the subject based upon the estimated chest volumes . in one embodiment , the minute ventilation ∂ v e is given by : where v i and v m are estimated chest volumes at maximum inspiration and maximum expiration , respectively , in each breathing cycle . in another embodiment , the minute ventilation ∂ v e is given by : ∂ v e = f rr ×( v i − v m ), where v i and v m are estimated chest volumes at maximum inspiration and maximum expiration , respectively , in each breathing cycle , and f rr is the subject &# 39 ; s respiration rate ( preferably in cycles per minute ). at step 910 , communicate the minute ventilation to a memory . in this embodiment , further processing stops . the flow diagrams depicted herein are illustrative . one or more of the operations illustrated in the flow diagrams may be performed in a differing order . other operations may be added , modified , enhanced , or consolidated . variations thereof are intended to fall within the scope of the appended claims . reference is now being made to fig1 which illustrates a block diagram of one example video processing system 1000 for implementing various aspects of the present method as described with respect to the flow diagram of fig9 . in fig1 , workstation 1004 is placed in communication with communication element 1002 for receiving detected grid patterns from , for instance , video camera 303 of fig3 , and for otherwise effectuating communication between various devices and computer workstation 1004 via network 1001 . computer 1004 comprises monitor device 1003 and user interface 1005 for enabling a display of information for a user and for effectuating a user input or selection . an operator of the present system may use the graphical user interface 1003 to identify or otherwise select images of the captured video for processing or re - processing , and provide user input as may be required for the implementation hereof . pixels and / or regions identified or otherwise detected in the received video may be retrieved from a remote device over network 1001 . various portions of the video may be stored to a memory or storage device 1011 in communication with workstation 1004 or may be communicated to a remote device over network 1001 via a communications interface ( not shown ) for remote storage or further processing . workstation 1004 and communications interface 1002 are in communication with image processing unit 1006 for processing the video in accordance with the teachings hereof . video processing unit 1006 is shown comprising a buffer 1007 . such a buffer may be used for queuing information about the received image such as , for instance , one or more target regions within the image frames , size of the video , time / date information , and the like . the buffer may be configured to also store data , mathematical formulas and other representations to facilitate processing of the image in accordance with the teachings hereof . video pre - processor 1008 performs any pre - processing of the video as may be desired or required to compensate for non - uniform illumination due to a curvature of a surface of the skin , for motion induced blur due to body or surface motion , imaging blur , and slow illuminant variation . processor 1008 may further be programmed to reduce the dimensionality of the data and performing independent component analysis ( ica ) on the video signal . light distortion determinator 1009 determines an amount of distortion in the received pattern . the distortion is the determined amount of 3d surface variation . converter 1010 converts the determined amount of distortion to a depth value , on a pixel - by - pixel basis , for each image frame of the video and generates a depth map for each of the inspiration and expiration cycles of the subject . depth map generator 1012 retrieves the depth map values from storage device 1011 and generates a depth map at inspiration and expiration for each breathing cycle . 3d volume processor 1013 receives the generated depth maps and generates a 3d volume for each respective depth map . minute ventilation calculator 1014 retrieves the 3d volumes generated for each inspiration and expiration cycle for a predetermined amount of respiratory cycles , and estimates the subject &# 39 ; s minute ventilation over those respiratory cycles . information as required to perform any of the functions of any of the modules may be retrieved from storage device 1011 or may be received via a user input using the user interface of workstation 1004 . processor 1014 is shown in communication with transmitter 1015 which is used to communicate the subject &# 39 ; s estimated minute ventilation to a third party such as , for example , the patient &# 39 ; s physician , nurse , or respiratory therapist . such a communication may take include some or all of the original video . transmitted images may , in turn , be displayed on a graphical display device , such as that of workstation 1004 , for visual review and further processing . the modules and processing units of fig1 are in communication with monitor 1003 to present thereon information for a user selection . any of the modules and / or processing units of fig1 are in communication with storage device 1011 via pathways shown and not shown and may store / retrieve data , parameter values , functions , pages , records , and machine readable / executable program instructions required to perform their various functions . each of the modules and processing units of the video processing system 1006 is also in communication with workstation 1004 via pathways not shown and may further be in communication with one or more remote devices over network 1001 . it should be appreciated that some or all of the functionality for any of the modules may be performed , in whole or in part , by components internal to the workstation . it should also be appreciated that the workstation has an operating system and other specialized software configured to display a variety of numeric values , text , scroll bars , pull - down menus with user selectable options , and the like , for entering , selecting , or modifying information displayed on display device 1003 . various modules of the embodiments hereof may designate one or more components which may , in turn , comprise software and / or hardware designed to perform the intended function . a plurality of modules may collectively perform a single function . each module may have a specialized processor capable of executing machine readable program instructions . a module may comprise a single piece of hardware such as an asic , electronic circuit , or special purpose processor . a plurality of modules may be executed by either a single special purpose computer system or a plurality of special purpose computer systems in parallel . connections between modules include both physical and logical connections . modules may further include one or more software / hardware modules which may further comprise an operating system , drivers , device controllers , and other apparatuses some or all of which may be connected via a network . it is also contemplated that one or more aspects of the present method may be implemented on a dedicated computer system and may also be practiced in distributed computing environments where tasks are performed by remote devices that are linked through a network . one or more aspects of the methods described herein are intended to be incorporated in an article of manufacture , including one or more computer program products , having computer usable or machine readable media . for purposes hereof , a computer usable or machine readable media is , for example , a floppy disk , a hard - drive , memory , cd - rom , dvd , tape , cassette , or other digital or analog media , or the like , which is capable of having embodied thereon a computer readable program , one or more logical instructions , or other machine executable codes or commands that implement and facilitate the function , capability , and methodologies described herein . furthermore , the article of manufacture may be included on at least one storage device readable by a machine architecture or image processing system embodying executable program instructions capable of performing the methodology described in the flow diagrams . various presently unforeseen or unanticipated alternatives , modifications , variations , or improvements therein may become apparent and / or subsequently made by those skilled in the art , which are also intended to be encompassed by the following claims . accordingly , the embodiments set forth above are considered to be illustrative and not limiting . various changes to the above - described embodiments may be made without departing from the spirit and scope of the invention . the teachings of any printed publications including patents and patent applications , are each separately hereby incorporated by reference in their entirety .
what is disclosed is a system and method for estimating minute ventilation by analyzing distortions in reflections of structured illumination patterns captured in a video of a thoracic region of a subject of interest being monitored for respiratory function . measurement readings can be acquired in a few seconds under a diverse set of lighting conditions and provide a non - contact approach to patient respiratory function that is particularly useful for infant care in an intensive care unit , sleep studies , and can aid in the early detection of sudden deterioration of physiological conditions due to detectable changes in patient chest volume . the systems and methods disclosed herein provide an effective tool for minute ventilation estimation and respiratory function study and analysis in a non - contact remote sensing environment .