Patent Application
20100061596
The present application relates to medical methods and systems, and more particularly, to methods and systems for monitoring activity of a patient, such as a breathing activity of an infant.
A serious concern for parents of a newborn is the possibility of death by Sudden Infant Death Syndrome (SIDS). SIDS is commonly known as the sudden death of an infant under one year of age which remains unexplained after a thorough case investigation, including performance of a complete autopsy, examination of the death scene, and review of the clinical history. A SIDS death occurs quickly and is often associated with sleep, with no signs of suffering.
Although exact causes of SIDS are still unknown, mounting evidence suggests that some SIDS babies are born with brain abnormalities that make them vulnerable to sudden death during infancy. Studies of SIDS victims reveal that some SIDS infants have abnormalities in the “arcuate nucleus,” a portion of the brain that is likely to be involved in controlling breathing during sleep. However, scientists believe that the abnormalities that are present at birth may not be sufficient to cause death. Other factors, such as lack of oxygen and excessive carbon dioxide intake, may also contribute to the occurrence of SIDS. During sleep, a baby can experience a lack of oxygen and excessive carbon dioxide levels when they re-inhale the exhaled air. Normally, an infant can sense such inadequate air intake, and his breathing movement can change accordingly to compensate for the insufficient oxygen and excess carbon dioxide. As such, certain types of irregularity in an infant's breathing activity can be an indicator of SIDS or the likelihood of SIDS.
Therefore, monitoring of an infant's breathing activity for breathing irregularities could help prevent or detect the possibility of SIDS. One approach to monitor the breathing activity is to attach to the body of the infant a battery-powered electronic device that can mechanically detect the breathing movement. Although such device can monitor the infant's breathing directly, the battery can render the device large and heavy, which encumbers the tiny infant. Additionally, difficulty of attachment can be expected under this approach.
Another approach to monitor an infant's breathing activity is to install a pressure sensitive pad underneath the mattress where the infant is sleeping. The pad monitors the baby's breathing activity by measuring body movement. However, because the pad is unable to directly monitor the breathing movement, accuracy of the generated breathing data can be affected.
In another approach, a marker block with a plurality of markers is coupled to the infant's chest. By continuously tracking the positions of the markers, an infant's breathing movement can then be monitored during sleep.
In accordance with some embodiments, a method of determining a similarity with a portion of a physiological motion, includes obtaining a first image of an object, obtaining a second image of the object, determining a level of similarity between the first and second images, and correlating the determined level of similarity between the first and second images with a portion of the physiological motion.
In accordance with other embodiments, a computer product having a set of instructions, an execution of which causes a method of determining a similarity with a portion of a physiological motion to be performed, the method includes obtaining a first image of an object, obtaining a second image of the object, determining a level of similarity between the first and second images, and correlating the determined level of similarity between the first and second images with a portion of the physiological motion.
In accordance with other embodiments, a system for determining a similarity with a portion of a physiological motion includes means for obtaining a first image of an object and a second image of the object, means for determining a level of similarity between the first and second images, and means for correlating the determined level of similarity between the first and second images with a portion of the physiological motion.
Other and further aspects and features will be evident from reading the following detailed description of the embodiments, which are intended to illustrate, not limit, the invention.
The drawings illustrate the design and utility of embodiments, in which similar elements are referred to by common reference numerals. These drawings are not necessarily drawn to scale. In order to better appreciate how the above-recited and other advantages and objects are obtained, a more particular description of the embodiments will be rendered, which are illustrated in the accompanying drawings. These drawings depict only typical embodiments and are not therefore to be considered limiting of its scope.
Various embodiments are described hereinafter with reference to the figures. It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are represented by like reference numerals throughout the figures. It should also be noted that the figures are only intended to facilitate the description of the embodiments. They are not intended as an exhaustive description of the invention or as a limitation on the scope of the invention. In addition, an illustrated embodiment needs not have all the aspects or advantages shown. An aspect or an advantage described in conjunction with a particular embodiment is not necessarily limited to that embodiment and can be practiced in any other embodiments even if not so illustrated.
During use, the optical device 12 is placed or mounted onto a structure, such as a table, a ceiling, or a patient support, and the optical device 12 is used to view a patient 20. The processor 14 receives images from the optical device 12, processes the images, and determine information regarding the patient 20. If the system 10 includes the monitor 16, images generated by the optical device 12 and information determined by the processor 14 may be displayed in the monitor 16.
To begin method 200, an image template is obtained (step 202). In the illustrated embodiments, the optical device 12 is aimed at the object that moves with breathing to view at least a portion of such object, and an image frame is generated by the optical device 12. The object may be a part of the patient, or any object that is coupled with the patient, such as clothes (or portion thereof, blanket (or portion thereof, marker, etc. A portion of the image frame is then selected as the image template. In the illustrated embodiments, an area within the image frame over which there is some object movement is selected as the template.
Next, the optical device 12 is continued to view the object moving with breathing, and provides another image frame (input image) that contains an image of at least a portion of the patient 20 (step 204).
Next, a level of similarity between the image template 308 and a portion of the input image 400 is measured (step 206). In particular, the portion 450 of the input image 400 that is at the same relative position 310 (at which the image template 308 is obtained from the image frame 300) is used to compare with the image template 308. In other words, the measure of similarity is calculated between the template and a fixed sub-area of the input image 400 (i.e., the fixed sub-area of the image frame that is used to define the template). Various techniques may be used to measure the level of similarity between the image template 308 and the portion of the input image 400. In some embodiments, the processor 14 may perform a normalized cross correlation between the image template 308 and the portion of the input image 400.
Because the image template is obtained from an image frame that is generated when the patient 20 is at a certain position (e.g., a position that may correspond with a certain phase of a respiratory cycle), if the input image (e.g., input image 400a) is generated when the object moving with respiration is in the same position as that associated with the image template, the resulting level of correlation would be high. On the other hand, if the input image (e.g., input image 400b) is generated when the portion of the patient 20 is in a different position from that associated with the image template, the resulting level of correlation would be relatively low. It should be noted that the correlation determined by the processor may or may not be normalized. If normalized correlation is used, the value of the normalized correlation (correlation coefficient) is used to represent a level of similarity between the two images. In other embodiments, instead of cross-correlation, other similarity measures may be used, such as, mutual information, absolute difference, etc.
Returning to
As illustrated in the figure, the peak values (e.g., points 522, 526) in the time series 500 correlate with certain parts of a physiological motion (e.g., the parts of the breathing motion having amplitude that corresponds with line 504). Thus, the time series 500 may be used to correlate with the physiological motion of the patient 20. Also, in the illustrated example, the processor 14 may determine the period T of the patient's breathing cycle by calculating the time spacing between every other peak (e.g., between peak 522 and peak 528).
In accordance with some embodiments, the time series of similarity values may be used to determine physiological information about the patient 20. For example, in some embodiments, the time series of the measured level of similarities is analyzed by the processor 14 in real time to determine if there is a lack of motion by the patient 20. The no-motion condition can result from the patient 20 having stopped breathing, or because of a position shift that has left no moving object inside the camera field of view. Lack of motion can be detected by detecting a plurality of correlation points in the time series that form a “flat-line” configuration. In some embodiments, this is achieved by calculating the variation of the signal over a sliding time window that trails the current image frame. The length of the window can be a fixed number of seconds, or it can be an adaptive window, for example, set to two breathing cycles and updated periodically according to the latest estimate of the breathing period. The threshold value of signal variation resulting in a no-motion alert is a multiplier of the noise level in the signal. The noise level is estimated automatically by a real-time signal smoothing method. For example, if the signal 99 percentile amplitude variation over the sliding time window does not exceed a multiplier of six standard deviations of the noise, then the no-motion output alert is generated.
In some cases, the noise level used in automatic threshold setting for flat-line detection can be estimated by subtracting a smoothed portion of the signal from the original signal. The smoothed signal can be obtained by an Nth order polynomial fit to the signal over a sliding window that trails the current signal sample. For example, the fitting parameters can be N=3 and a window length of 1 second. Alternatively, an adaptive window length equal to 20% of the breathing period (which is estimated in real time) can be used. The polynomial value at the current sample time represents the smoothed version of the signal. The difference between this and the original signal is observed over the same time window as the one used for flat-line detection. The RMS value of the difference can be used as the noise platform for adaptive threshold setting in flat-line detection.
In other embodiments, the time series of the measured level of similarities is analyzed by the processor 14 in real time to determine if there is irregularity (or lack of periodicity) in the breathing pattern of the patient 20.
In other embodiments, the time series of the measured level of similarities is analyzed by the processor 14 in real time to determine if the patient 20 has shifted in position.
It should be noted that the time series of measured level of similarities may be used to obtain other information regarding the patient 20 in other embodiments. Also, in other embodiments, the processor 14 may be configured to determine a combination or all of the above information (e.g., lack of motion, lack of periodicity in breathing, and/or position shift) about the patient 20.
The processor 14 next analyzes the time series to determine if there is a lack of periodicity in the patient's breathing (step 910)—e.g., using any of the techniques described herein. If the processor 14 determines that there is a lack of periodicity in the patient's breathing, the processor 14 then generates an alarm signal to report lack of periodicity (step 912). Alternatively, in stead of generating an alarm the processor 14 may use the detected lack of periodicity to guard against producing a false negative result for the detection of other conditions related to breathing.
Next, the processor 14 analyzes the time series to determine if the patient 20 has shifted position (step 914)—e.g., using any of the techniques described herein. If the processor 14 determines that the patient 20 has shifted position, then the processor 14 requires a new image template—e.g., using any of the techniques described herein (step 916). Alternatively, or additionally, the processor 14 may also generate an alarm signal to report position shift by the patient 20 (step 916). In any of the embodiments described herein, different sound pitch and different colors and shapes of warning signals may be used to distinguish the type of alerts (e.g., lack of motion alert, lack of periodicity alert, patient shift alert) and the severity of the alerts (e.g., the longer the duration of lack of motion, the more severe the alert).
In some embodiments, in order to maintain sensitivity, a new image template is acquired whenever one of the above conditions (no-motion, lack of periodicity, position shift) is detected. After this updating of the image template, the newly observed signal forms the basis for position-shift detection threshold also, the detection of flat-line and periodicity start anew by resetting the adaptive algorithm parameters and signal buffers.
As illustrated by the embodiments described herein, the system 10 is advantageous in that it does not require any attachment of markers that are specially designed for image detection. It also does not require the patient 20 to wear special clothing or cover, and will work as long as the optical device 12 field of view contains sufficient objects that move with the patient's breathing, such as a blanket, sheet, etc. Also, the above described techniques for determining lack of motion, lack of periodicity, and patient's position shift are advantageous because they involve simple image processing without the need to perform complex calculation to determine actual position of the patient 20 or patient's portion. The above described techniques are also advantageous in that they do not require use of complex object discrimination algorithms to identify object(s) in an image. This is because the same region of interest in each input image is compared with the template, regardless of what object is captured within the region of interest in each input frame. The embodiments of the technique described herein is also advantageous in that it is sensitive and allows pickup of smaller motion levels, such that analysis for lack of motion, periodicity, and patient shift can be performed for much smaller motion amplitudes. Because of the template re-acquisition feature, the technique is more robust because it can keep monitoring the breathing even when the patient 20 position shifts by large amounts, as long as some portion of the patient 20 that moves with breathing remains in the optical device's 12 field of view.
It should be noted that the method 900 should not be limited to the order of steps described above, and that the steps may have different orders. For example, in other embodiments, the processor 14 may perform step 910 and/or step 914 before step 904. Also, in other embodiments, two or more steps in method 900 may be performed in parallel. For example, in other embodiments, steps 904, 910, 914 may be performed in parallel by the processor 14.
In some embodiments, the processor 14 is configured to determine physiological information about the patient 20 using the time series of similarity values in real time (e.g., at substantially the same time or shortly after the current input image is obtained). Alternatively, the processor 14 may be configured to use the time series of similarity values retrospectively.
As discussed, in some embodiments, the image template in step 202 is obtained from an image within an area of an image frame in which there is patient's movement.
In the above embodiments, the image template is obtained when the patient 20 is at an arbitrary phase of a respiratory cycle. In other embodiments, the image template may be obtained when the patient 20 is at an end of an inhale or exhale phase. This merges the two peaks of
As illustrated in the figure, the peak values (e.g., points 1222,1226) in the time series 500 correlate with certain parts of a physiological motion (e.g., the end of the inhale phase). Thus, the time series 500 may be used to correlate with the physiological motion of the patient 20. Also, in the illustrated example, the processor 14 may determine the period T of the patient's breathing cycle by calculating the time spacing between adjacent peak (e.g., between peak 1222 and peak 1226). Also, as illustrated in the figure, obtaining the image template when the patient 20 is at the end of the exhale phase is advantageous in that the peaks in the time series of similarity values correspond with the respective peaks (end of inhale phase) in the breathing pattern.
In other embodiments, instead of obtaining the image template when the patient 20 is at the end of the inhale phase, the image template may be obtained when the patient 20 is at the end of the exhale phase. In such cases, the peaks in the time series of similarity values will correspond with the respective valleys (end of exhale phase) in the breathing pattern.
In the above embodiments, the peak values in the time series of similarity values correspond to certain positional value(s) associated with the patient's breathing. In other embodiments, the peak values in the time series of similarity values may correspond to other aspects associated with the patient's breathing. For example, in other embodiments, the peak values in the time series of similarity values may correspond to certain phase(s) of the patient's respiratory cycle.
It should be noted that the determined time series of similarity values should not be limited to the use described previously, and that the time series may also be used in other applications. In other embodiments, the determined time series may be used to gate a medical process, such as a diagnostic process in which a part of a patient is being imaged by an imaging machine, or a treatment process in which a part of the patient is being treated by a treatment device. For example, the peaks in the time series may be used to correspond to certain phase(s) of a respiratory cycle of a patient who is undergoing an imaging process (e.g., a CT imaging process, a PET process, a CT-PET process, a SPECT process, MRI procedure, etc.). Based on the detected peaks in the time series, the device that is used to obtain the image may be gated on or off so that images of the patient may be obtained at a desired phase of a respiratory cycle.
In other embodiments, instead of gating a generation of images, the time series of similarity values may be used to gate a collection of images retrospectively. In such cases, the time series is generated and recorded as the patient undergoes an imaging process. After a set of images are collected, the processor then analyzes the time series to bin the images such that images that are collected at a same phase of a respiratory cycle are grouped together. For example, the processor may associate all images that are generated at times at which the time series has similarity values of “0.9.” In other embodiments, the processor may be configured to bin images based on phases of a physiological cycle. For example, the processor may be configured to associate images that are generated at a same phase (e.g., 180°), or within a same phase range (e.g., 170°-190°) of a physiological cycle. [0061] Similarly, for treatment, the detected peaks of the time series of similarity values may be used to gate a beam on or off, and/or to gate an operation of a collimator (that is used to change a shape of the beam). In such cases, the beam has an energy that is sufficient for treating the patient, and may be a x-ray beam, a proton beam, or other types of particle beam. In some embodiments, after the processor detects a peak in the time series, the processor may be configured to activate or deactivate the beam, and/or to generate leaf sequencing signals to operate the leafs of the collimator, after a prescribed time that has lapsed since the detected peak.
In any of the embodiments described herein, the time series of similarity values may be analyzed in the frequency domain. For example, in any of the embodiments described herein, the processor 54 may be configured to perform spectral analysis using Fourier Transform to analyze the time series of similarity values. In some cases, the processor 54 may be configured to perform spectral analysis using the time series of similarity values to detect any of the conditions described herein, such as, object motion, lack of motion, periodicity, lack of periodicity, position shift, etc.
Computer System Architecture
The computer system 1500 may be coupled via the bus 1502 to a display 1512, such as a cathode ray tube (CRT), for displaying information to a user. An input device 1514, including alphanumeric and other keys, is coupled to the bus 1502 for communicating information and command selections to processor 1504. Another type of user input device is cursor control 1516, such as a mouse, a trackball, or cursor direction keys for communicating direction information and command selections to processor 1504 and for controlling cursor movement on display 1512. This input device typically has two degrees of freedom in two axes, a first axis (e.g., x) and a second axis (e.g., y), that allows the device to specify positions in a plane.
The computer system 1500 may be used for performing various functions (e.g., calculation) in accordance with the embodiments described herein. According to one embodiment, such use is provided by computer system 1500 in response to processor 1504 executing one or more sequences of one or more instructions contained in the main memory 1506. Such instructions may be read into the main memory 1506 from another computer-readable medium, such as storage device 1510. Execution of the sequences of instructions contained in the main memory 1506 causes the processor 1504 to perform the process steps described herein. One or more processors in a multi-processing arrangement may also be employed to execute the sequences of instructions contained in the main memory 1506. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the invention. Thus, embodiments of the invention are not limited to any specific combination of hardware circuitry and software.
The term “computer-readable medium” as used herein refers to any medium that participates in providing instructions to the processor 1504 for execution. Such a medium may take many forms, including but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media includes, for example, optical or magnetic disks, such as the storage device 1510. Volatile media includes dynamic memory, such as the main memory 1506. Transmission media includes coaxial cables, copper wire and fiber optics, including the wires that comprise the bus 1502. Transmission media can also take the form of acoustic or light waves, such as those generated during radio wave and infrared data communications.
Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, or any other magnetic medium, a CD-ROM, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, and EPROM, a FLASH-EPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read.
Various forms of computer-readable media may be involved in carrying one or more sequences of one or more instructions to the processor 1504 for execution. For example, the instructions may initially be carried on a magnetic disk of a remote computer. The remote computer can load the instructions into its dynamic memory and send the instructions over a telephone line using a modem. A modem local to the computer system 1500 can receive the data on the telephone line and use an infrared transmitter to convert the data to an infrared signal. An infrared detector coupled to the bus 1502 can receive the data carried in the infrared signal and place the data on the bus 1502. The bus 1502 carries the data to the main memory 1506, from which the processor 1504 retrieves and executes the instructions. The instructions received by the main memory 1506 may optionally be stored on the storage device 1510 either before or after execution by the processor 1504.
The computer system 1500 also includes a communication interface 1518 coupled to the bus 1502. The communication interface 1518 provides a two-way data communication coupling to a network link 1520 that is connected to a local network 1522. For example, the communication interface 1518 may be an integrated services digital network (ISDN) card or a modem to provide a data communication connection to a corresponding type of telephone line. As another example, the communication interface 1518 may be a local area network (LAN) card to provide a data communication connection to a compatible LAN. Wireless links may also be implemented. In any such implementation, the communication interface 1518 sends and receives electrical, electromagnetic or optical signals that carry data streams representing various types of information.
The network link 1520 typically provides data communication through one or more networks to other devices. For example, the network link 1520 may provide a connection through local network 1522 to a host computer 1524 or to equipment 1526 such as a radiation beam source or a switch operatively coupled to a radiation beam source. The data streams transported over the network link 1520 can comprise electrical, electromagnetic or optical signals. The signals through the various networks and the signals on the network link 1520 and through the communication interface 1518, which carry data to and from the computer system 1500, are exemplary forms of carrier waves transporting the information. The computer system 1500 can send messages and receive data, including program code, through the network(s), the network link 1520, and the communication interface 1518.
Although particular embodiments of the present inventions have been shown and described, it will be understood that it is not intended to limit the present inventions to the preferred embodiments, and it will be obvious to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the present inventions. For example, the term “processor” should not be limited to a device having only one processing unit, and may include a device or system that has more than one processing units/processors. Thus, the term “processor” may refer to a single processor or a plurality of processors. Also, the term “image” should not be limited to image that is actually displayed, and may refer to image data or undisplayed image that is capable of being presented in an image form. Further, the term “patient” should not be limited to a person or animal that has a medical condition, and may refer to a healthy person or animal. In addition, any discussion herein with reference to an image of the patient or patient portion may refer an image of the patient (or patient portion) itself, the clothing that the patient is wearing, and/or the blanket that is covering the patient. Thus, an image of the patient or patient portion should not be limited to an image of the patient or patient portion itself. The specification and drawings are, accordingly, to be regarded in an illustrative rather than restrictive sense. The present inventions are intended to cover alternatives, modifications, and equivalents, which may be included within the spirit and scope of the present inventions as defined by the claims.
This application is related to U.S. patent application Ser. No. ______, entitled “Systems and methods for determining a state of a patient,” having Attorney Docket No. VM 08-030US, filed concurrently herewith.
