Abstract:
An in-vivo imaging device including a camera may include a frame storage device. Systems and methods which vary the frame capture rate of the camera and/or frame display rate of the display unit of in-vivo camera systems are discussed. The capture rate is varied based on for example, a physical quantity experienced by the camera system, or physical measurements related to the motion of the camera. Alternatively, the frame capture rate is varied based on comparative image processing of a plurality of frames. The frame display rate of the system may be varied based on comparative image processing of a multiplicity of frames. Both the frame capture and the frame display rates of such systems can be varied concurrently.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. Ser. No. 13/758,067, filed on Feb. 4, 2013, which is a continuation application of U.S. Ser. No. 13/424,684, filed on Mar. 20, 2012, which is a continuation application of U.S. Ser. No. 11/025,111, filed on Dec. 30, 2004, which is a continuation application of U.S. Ser. No. 10/705,982, filed on Nov. 13, 2003, which in turn is a continuation application of U.S. Ser. No. 09/571,326, filed on May 15, 2000, each of which being incorporated in its entirety by reference herein. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to an in-vivo camera system and, in particular, to a system and method for controlling the frame capture rate and frame display rate of images produced by such a camera system. 
     BACKGROUND OF THE INVENTION 
     Several in-vivo measurement systems are known in the art. They include swallowable electronic capsules which collect data and which transmit the data to a receiver system. These intestinal capsules, which are moved through the digestive system by the action of peristalsis, are used to measure pH (“Heidelberg” capsules), temperature (“CoreTemp” capsules) and pressure throughout the gastro-intestinal (GI) tract. They have also been used to measure gastric residence time, which is the time it takes for food to pass through the stomach and intestines. These intestinal capsules typically include a measuring system and a transmission system, where a transmitter transmits the measured data at radio frequencies to a receiver system. 
     Endoscopes are other types of devices that obtain images from the gastro-intestinal tract. There are currently two types of endoscopes. Fiber-optic endoscopes are pushed through the GI tract and use a fiber optic waveguide to transmit a light signal from the area of interest to electronics located outside the patient&#39;s body. Video endoscopes place an electronic camera at the area of interest and transfer the video data through a flexible cable to electronics located externally. 
     U.S. Pat. No. 5,604,531, assigned to the common assignee of the present application and incorporated herein by reference, teaches an in-vivo measurement system, in particular an in-vivo camera system, which is carried by a swallowable capsule. In addition to the camera system there is an optical system for imaging an area of the GI tract onto the imager and a transmitter for transmitting the video output of the camera system. The overall system, including a capsule that can pass through the entire digestive tract, operates as an autonomous video endoscope. It images even the difficult to reach areas of the small intestine. 
     Reference is now made to  FIG. 1  which shows a block diagram of the in-vivo video camera system described in U.S. Pat. No. 5,604,531. The system captures and transmits images of the GI tract while passing through the gastro-intestinal lumen. The system contains a storage unit  19 , a data processor  14 , a camera  10 , an image transmitter  8 , an image receiver  12  (often an antenna array), which usually includes an antenna array, and an image monitor  18 . Storage unit  19 , data processor  14 , image monitor  18 , and image receiver  12  are located outside the patient&#39;s body. Camera  10 , as it transits the GI tract, is in communication with image transmitter  8  located in capsule  6  and image receiver  12  located outside the body. Data processor  14  transfers frame data to and from storage unit  19  while the former analyzes the data. Processor  14  also transmits the analyzed data to image monitor  18  where a physician views it. The data can be viewed in real time or at some later date. 
     The number of pictures that need to be taken and which must be analyzed by the attending physician is great. Assuming a minimum of two images per second and a four to five hour dwell time in the GI tract, 30,000 images would be required during the transit of the GI tract by the capsule. If 20 frames per second (fps) are displayed as is standard, the physician would need about 30 minutes to examine the images of the entire GI lumen. 
     PCT Application PCT/IL98/00608, published as WO 99/30610 and Israeli Application 122602 assigned to the common assignee of the present application and incorporated herein by reference, recite a method for reducing the number of frames captured by an in-vivo camera, thereby extending its life. The method discussed in the aforesaid applications requires disconnecting the camera  10  from the power source when motion (velocity) is below a certain threshold value. 
     SUMMARY OF THE PRESENT INVENTION 
     It is an object of the present invention to provide a system and method for minimizing the time for reviewing images taken by an in-vivo camera system or by endoscopes. This is accomplished by either varying the rate of data display and/or varying the rate of data acquisition. 
     In one embodiment of the present invention, an in-vivo camera system includes an imager which can have its frame capture rate varied. It also includes at least one sensor for measuring a physical property relatable to the motion of the camera system, a data processor for determining a frame capture rate after receiving data from the sensor, and a controller for supplying the determined frame capture rate to the imager. The sensor can be, among other things, an accelerometer, an accelerometer connected to an integrator, a pressure sensor, an induction coil, or an ultrasonic transducer. 
     In another embodiment, an in-vivo camera system includes an imager which can have its frame capture rate varied, a storage device for storing frames captured by the imager, an image processor for calculating the required frame capture rate from at least two frames, and a controller for supplying the calculated frame capture rate to the imager. 
     In yet another embodiment of the present invention, a display system for displaying the output of an in-vivo camera system is described. The system includes a frame storage unit for storing frames of the camera system, and an image processor for correlating frames to determine the extent of their similarity. The processor generates a frame display rate which is slower when the frames are generally different and faster when the frames are generally similar. The embodiment also includes a display unit for displaying the frames received from the frame storage unit at the frame display rate. The display system described can also include a controller connected to a frame storage unit and the imager processor. The controller then varies the display rate of the aforementioned display unit. In the above embodiment the at least two frames can be consecutive or non-consecutive frames. 
     In still another embodiment a video camera system also includes a display system having a frame storage unit for storing at least two frames and an image processor for determining the similarity of at least two frames. The processor generates a frame display rate based on the similarity of the frame. The frame display rate is slower when the frames are generally different and faster when the frames are generally similar. The embodiment also includes a display unit for displaying the frames received from the frame storage at the required frame display rate. 
     In yet another embodiment an in-vivo camera system also includes a display system having a frame storage unit for storing at least two frames. The display system further includes an image processor for correlating at least two frames thereby determining the extent of their similarity and for generating a frame display rate based on that similarity. Finally, the display system includes a display unit for displaying the frames received from the frame storage at the frame display rate. 
     In one embodiment of the present invention, a method is taught for varying the frame capture rate of a series of frames generated by an in-vivo camera system. The method includes the steps of storing the frames in a storage device, correlating changes in the details of at least two frames, changing the frame capture rate to a predetermined frame capture rate according to the degree of change between the at least two frames and transmitting the capture rate to the imager. 
     In another embodiment, a method is taught for varying the frame capture rate of a series of frames generated by an in-vivo camera system. The method includes the steps of measuring a physical quantity experienced by the camera system, converting the physical quantity to a velocity of the camera, correlating the velocity with a predetermined frame capture rate, and transmitting the predetermined capture rate to the imager. The step of measuring includes the step of measuring acceleration, pressure, induced current or motion, the latter with an ultrasonic transducer. 
     In yet another embodiment of the present invention, a method is taught for varying the frame display rate of a series of frames generated by an in-vivo camera system, the method including the steps of storing the frames in a storage device, correlating changes in the details of at least two frames, and transmitting the required frame display rate to a storage device and a display unit. 
     Yet a further embodiment of the present invention teaches a method for varying the frame display rate of a series of frames generated by an in-vivo camera system which includes the step of repeating the display of a frame a predetermined number of times. 
     A similar further embodiment teaches a method for varying the frame display rate of a series of frames generated by an in-vivo camera system which includes the step of eliminating the display of at least one frame. 
     The system may include an imager for producing frames and a storage device for storing frames. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be understood and appreciated more fully from the following detailed description taken in conjunction with the drawings in which: 
         FIG. 1  is a block diagram illustration of a prior art in-vivo video camera system; 
         FIG. 2  is a block diagram illustration of a system for varying the frame capture rate of the camera system of  FIG. 1  using a sensor to determine changes in video capsule velocity; 
         FIG. 3A  is a block diagram illustration of a further embodiment of  FIG. 2  using an accelerometer as a sensor; 
         FIG. 3B  is a block diagram illustration of a still further embodiment of  FIG. 2  using an accelerometer as a sensor with the control loop and sensor all inside the capsule; 
         FIG. 4  is a block diagram illustration of an alternative embodiment of the system of  FIG. 1  in which image data from two consecutive frames is compared; 
         FIG. 5  is a block diagram illustration for varying the frame display rate of the in-vivo video camera system of  FIG. 1  by comparing image data from two consecutive frames; 
         FIG. 6  is a block diagram illustration of a method for determining if the capsule has moved and a change in frame display rate is required; 
         FIG. 7  are histogram illustrations of a difference function useful in understanding the method of  FIG. 6 ; 
         FIG. 8A  is a block diagram illustration of a method for varying both the frame display rate and the frame capture rate as described in  FIGS. 4 and 5 ; and 
         FIG. 8B  is a block diagram illustration of a system as in  FIG. 8A  but also including a command processor. 
     
    
    
     Similar elements in different figures are given identical numbers throughout. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     The large volume of data collected by an in-vivo camera system, such as the one described above, is a result of the long period of time, usually several hours, that it takes the camera to traverse the gastro-intestinal tract. The camera transits the GI tract in fits and starts. Because of the intermittent motion of the capsule and its long residence time at some positions, the number of sequential images that are similar is very large. It would be preferable if such duplicative frames were eliminated entirely or at least reduced in number. Alternatively, the display time of individual frames can be shortened, thereby reducing the time required to view the image data stream. The present invention describes a number of ways to shorten viewing time: reducing the frame capture rate ( FIGS. 2-4 ) and/or reducing the frame display rate ( FIG. 5 ). 
     It should be understood that in all discussions both above and below, when the terms camera and imager are used they are equivalent. It should also be understood that the camera or imager being discussed in this application is one capable of having its frame capture rate and/or frame display rate varied. 
     One method to control the frame capture rate is to monitor the velocity of the capsule in the GI tract. Reference is now made to  FIG. 2 , which illustrates, in block diagram format, a system for controlling the frame capture rate of the camera  10 . The system comprises a sensor  11 , a data processor  14 , a frame capture rate controller  17 , a frame capture rate transmitter  16 , a capture rate receiver  9 , camera  10  and optionally, a database or look-up table  15 . Camera  10  and capture rate receiver  9  are both located within the capsule. 
     Sensor  11 , which measures motion directly or indirectly, is attached to, or placed within, the capsule  6  and relays the value of a measured motion-related physical property to data processor  14 . Data processor  14 , together with database (or a look-up table)  15  to which processor  14  is linked, determines the required frame capture rate based on current and past values of the measured property. When the camera is moving slowly, fewer frames need to be captured; when it moves quickly, the number of frames captured or displayed needs to be increased. Data processor  14  then provides the calculated capture rate to frame capture rate controller  17 , which, in turn, transmits the rate to camera  10 . For clarity,  FIG. 2  (as well as all later Figures) does not show the image transmitter  8  and image receiver  12  described above which is the actual link between sensor  11  and data processor  14 . 
     In the above embodiment, a database or look-up table is used. In other embodiments, database or look-up table  15  is not needed and processor  14  calculates the required frame capture rate directly using a suitable function. 
       FIG. 2  illustrates how the capture rate is transmitted to camera  10 . Frame capture controller  17  transfers the desired frame capture rate to frame capture rate transmitter  16 . Both controller  17  and transmitter  16  are outside the patient&#39;s body. Transmitter  16  transmits information about the required capture rate to capture rate receiver  9  located within capsule  6 . Capture rate receiver  9  then adjusts the frame capture rate of camera  10 . 
     A special case of the system in  FIG. 2  is illustrated in  FIG. 3A  where the sensor is an accelerometer  111  whose output is processed by an integrator  13 . The processor is a motion processor  114 . The remaining elements are as shown in  FIG. 2 . Accelerometer  111  is in communication with integrator  13 . Accelerometer  111 , which is typically placed in the interior of capsule  6 , determines the instantaneous acceleration of capsule  6  as it moves through the GI tract. Integrator  13  converts the acceleration data to velocity. Integrator  13  can be a stand-alone element connected to motion processor  114  (as in  FIG. 3A ) or it can be an integral part of motion processor  114 . In either case, integrator  13  transfers information regarding the velocity of the capsule to motion processor  114 . Motion processor  114 , together with database (or look-up table)  15 , determines the required frame capture rate. Processor  114  relays the calculated capture rate to frame capture rate controller  17 . As described above ( FIG. 2 ), frame capture controller  17  relays the required frame capture rate via frame capture rate transmitter  16  to capture rate receiver  9  within capsule  6 . 
     In lieu of database (or look-up table)  15  in  FIG. 3A , motion processor  114  can utilize a function that relates velocity to frame capture rate. The function can then be used to calculate the required rate. The function, capture rate vs. capsule velocity, will usually be monotonically increasing. 
     The small accelerometer  111  used in  FIG. 3A  can be purchased from numerous suppliers. A suitable integrator  13  can also be obtained from many different vendors. Alternatively, an integrator can be built using an operational amplifier or implemented numerically using an A/D converter and a microprocessor. 
     In another embodiment, the integrator can be omitted from  FIG. 3A . In that case, data from the accelerometer  111  can be processed directly to determine the required frame capture rate. 
     The system in  FIG. 1  has been shown and described with processing and storage units outside the body, but they do not have to be. Through miniaturization of the components, most, if not all, electronic elements in  FIGS. 2 and 3A  above and  FIGS. 4 ,  5  and  8  below, can be attached to or placed within capsule  6  and in direct communication with camera  10 . 
     In fact, for the embodiments illustrated in  FIGS. 2 and 3A , a similar but alternate placement of components is possible. Referring to  FIG. 3B , the previous embodiments would have sensor  11  (or accelerometer  111 ), integrator  13 , data processor  14 , and frame rate controller  17  positioned inside capsule  6  and in direct communication with camera  10 . Frame rate transmitter  16  and capture rate receiver  9  would then be superfluous. 
     Other sensors can be used which can determine velocity. A pressure sensor attached to the capsule is one such sensor. When the rate of peristalsis increases, velocity of the capsule through the small intestine increases. A pressure sensor can detect peristaltic induced pressure (and/or changes in pressure) exerted by the walls of the small intestine. The relation between pressure (and/or changes in pressure) and velocity can be determined empirically, and then utilized to determine the frame capture rate. 
     If the patient is placed in a magnetic field, capsule  6  can contain an induction coil which functions as a velocity sensor. The magnetic field induces a current in the coil whose magnitude is a function of the velocity of the coil through the field. Data on the induced current is transmitted to motion processor  114  and processed as in  FIG. 3A . 
     While the sensors  11  discussed with  FIGS. 2 and 3  above are in-vivo sensors and are attached directly to capsule  6 , external sensors can also be used. A Doppler ultrasound unit continuously tracking the capsule can serve as an external sensor. Such a unit would be in communication with motion processor  114  which would process velocity data and convert it to a frame capture rate as discussed hereinabove. The conversion of ultrasonic Doppler data to velocity data is well-known in the art. Once the velocities have been calculated, a function, database or look-up table can be used to define the desired capture rate. 
     In yet another embodiment, several physical properties are measured concurrently and used to determine an optimum frame capture rate. This embodiment requires multiple sensors  11 , each attached to the capsule  6 , or possibly, as with an ultrasound sensor, outside the body. Each sensor would measure a different property. A data processor  14  or  114  as in  FIGS. 2 and 3 , or even a set of processors  14 , one for each property being measured, interprets the data and determines a suitable frame capture rate. The analyses performed by the several processors are relayed to a central command processor (not shown) where their results are combined to obtain an optimum overall frame capture rate. The overall optimal rate is then relayed from the central command processor to frame capture rate controller  17 , which transmits it to camera  10  in a manner identical to that described in  FIG. 2 . 
     In all of the above embodiments where the velocity of the capsule is determined, the conversion of velocity data to frame capture rate does not necessarily require the use of digital data. Analog data provided by the sensor may be used directly to determine the required frame capture rate if proper ancillary analog circuitry is employed. 
     Reference is now made to  FIG. 4  which illustrates another method for varying the frame capture rate.  FIG. 4  shows camera  10 , storage unit  19 , an image processor  214 , frame capture controller  17  and optionally, database or look-up table  15 . Camera  10  captures a frame that is transmitted as described in  FIG. 1  to external storage unit  19 . Images are stored sequentially in unit  19 . The stored data is comprised of one or more pixel properties. Color and intensity are among the properties that can be stored. 
     Image processor  214  receives images for comparison from storage unit  19 . Processor  214  compares each image I n  in the data stream to its predecessor I n-1 . If the stream of images is too lengthy or rapid, non-adjacent images can be compared, e.g. image I n  with the image I n-k , where k&gt;1. For this latter embodiment, the capture rate can be calculated for each k th  image, where k&gt;0. As described below with respect to  FIG. 6 , the comparison can be made on a pixel-by-pixel basis or, alternatively, on a pixel cluster basis. Based on the comparison of the two images, processor  214  calculates the required frame capture rate. 
     Frame capture rate controller  17  receives information about the required frame capture rate from image processor  214 . As shown in  FIG. 2  and described above, controller  17  transfers the required frame capture rate to camera  10 . For clarity, the requisite elements for this transfer have not been included in  FIG. 4  but can be seen in  FIG. 2 . 
     All of the methods discussed above relate to the frame capture rate. An alternative approach for reducing overall presentation time of the datastream of the system is to use a variable frame display rate. In such situations, the frame capture rate can, but need not, be held constant. When the analysis of the pixels in consecutive frames indicates that the capsule is at rest or moving slowly, the images are displayed at a fast display rate. If the analysis indicates that the capsule is moving rapidly through the GI tract, the images are displayed more slowly. 
     Reference is now made to  FIG. 5 , where a block diagram illustrates such a system. The diagram shows camera  10 , storage unit  119 , an image processor  314 , frame display rate controller  21 , image monitor  18  and, optionally, database or look-up table  15 . Camera  10  transmits frames to storage unit  119 . After the acquisition of a given number of frames and their storage in the buffer of storage unit  119 , two consecutive frames P n  and P n-1 , are sent to image processor  314 . The frames, either on a pixel-by-pixel or pixel cluster basis, are compared using a suitable function or set of functions. The function will usually be monotonically increasing. Image processor  314 , based on its analysis of the compared frames, relays the required frame display rate to frame display controller  21 . Frame display controller  21  provides the required frame display rate to storage unit  119 . The latter releases an image P m  or images P m  through P m+p  to image monitor  18 . P m  may, but need not be, frames P n  or P n-1 . As discussed above, it should be remembered that the frame comparison need not be performed between adjacent images P n  and P n-1  but between P n  and P n-k , where k&gt;1. 
     The functions used by image processors  214  and  314  in  FIGS. 4 and 5  to make their determinations can be based on: 
     Calculating the simple difference in a given property between corresponding pixels of two, not necessarily consecutive, frames; 
     Calculating the cross-correlation function between two, not necessarily consecutive, frames; and 
     Calculating the changes of local statistical distributions β and between corresponding local statistical distributions β in two, not necessarily consecutive, frames. 
     Local statistical distributions can include the mean, the variance or the standard deviation of given pixel clusters. The pixel cluster, for example, can be the pixels in the upper left quadrant (64×64 pixels) of a 256×256 image. The above approaches are illustrative only; other approaches may also be used. 
     When the image display rate is calculated for non consecutive images, P j  and P j+k , where k&gt;1, the images P j+1  and P j+k−1 , between the non-consecutive images are speeded up or slowed done as determined by the display rate calculation for frames P j  and P j+x . 
     Reference is now made to  FIG. 6  where a block diagram of a function which can be used to determine the required display rate is illustrated.  FIG. 6  shows the operations needed for comparing image P i  and P i+x , where x is usually, but not necessarily, 1. Initially, each image P i  is divided (step  50 ) into a multiplicity of cells A i (m,n), where 1&lt;m&lt;M and 1&lt;n&lt;N. 
     The average intensity, I Ai(m,n)  of each cell A i (m,n) of image P i  is then calculated (step  52 ) from data provided by image receiver  12  of  FIG. 1 . The absolute value of the difference D i (k,l) of the average intensities I of A i (k,l) and A i+x (k,l) of corresponding cells A(k,l) in frames P i  and P i+x  is determined (step  54 ). D i (k,l) is defined as:
 
 D   i ( k,l )=| I   A     i     (k,l)   −I   A     i+x     (k,l) |
 
It is readily apparent that where D i (k,l) is small, the capsule is moving slowly.
 
     The D i (k,l) values are then organized into a histogram (step  56 ). The y-axis of the histogram is D i (k,l) and the x-axis is the number of corresponding pairs of cells, A i (k,l) and A i+x (k,l), which have a difference of magnitude D i (k,l). Referring to  FIG. 7 , curve (a) represents a histogram of essentially similar cells in consecutive (or non-consecutive) frames, while curve (b) shows a histogram of cells in significantly different frames. It should readily be apparent that if two images are similar, the histogram of the differences in the cells of these images are concentrated at low values of D i (k,l). If the images are different, the histogram contains higher values of D i (k,l). It should also be readily apparent that the center of mass CM a  of curve (a) is further to the right than the CM b  of curve (b) and represents a slower moving capsule. 
     Returning to  FIG. 6 , the center of mass CM of the histogram is determined in step  58 . The CM of the histogram can be correlated (step  60 ) with the velocity of the capsule by using an empirically determined correlation supplied (step  66 ) by a database or look-up table. On the basis of the CM of the histogram, a difference between images is determined and a velocity calculated (step  62 ). The capture or display rate as a function of the difference or similarity in the compared images can be provided (step  68 ) from another empirically developed database, look-up table or mathematical function. The capture or display rate is then varied (step  64 ) accordingly. 
     Reference is now made to  FIGS. 8A and 8B , which illustrate yet another embodiment of the invention.  FIG. 8A  shows a combined system where both the frame capture rate and the frame display rate are varied concurrently to minimize total data stream display time.  FIG. 8A  is a fusion of the systems shown in  FIGS. 4 and 5 . There could equally well have been a combined system of the embodiments described in  FIG. 2  or  3  and  5 . 
     In  FIG. 8A , two storage units  19  and  119  and two image processors  214  and  314  are shown. The system also includes frame capture rate controller  17 , frame display rate controller  21 , image monitor  18  and camera  10 . One storage unit  19  stores data for the frame capture rate analysis while the other unit  119  stores data for the frame display rate calculation. Each image processor  214  and  314  processes a different rate calculation. Image processors  214  and  314  could use the same or different algorithms to calculate the required capture and display rates. 
       FIG. 8B  is similar to  FIG. 8A  but contains a command processor  414  which coordinates and optimizes the capture and display rate calculations, while minimizing total presentation time. The command processor  414  receives results calculated by processors  214  and  314  and transfers the optimized overall rates to capture and display controllers  17  and  21  respectively. 
     Currently, data is collected by the video camera at a rate of 2 frames per second (fps) and screened at a normal video rate of 30 fps. This screening rate is too fast for the eye to discern changes and the display rate must be slowed. An alternative to slowing down the display rate is to repeat the same frame several times, displaying the repeated frames at the standard rate. Repeating a frame is a way of changing the display rate in cases where it is impossible to change the display rate of individual frames directly. Methods such as those discussed above, which measure the difference between corresponding pixels in two frames, can be used to determine if repetitive screening of the same frame is required. Repetition of frames, however, increases the total length of the data stream. Therefore, the processor must determine when the trade-off between repeating frames and a longer, more time-consuming, data stream is advantageous. 
     It should be readily apparent, that if the capsule is moving too slowly, an inordinate number of frames may be identical. If that is the case, the frame rate controller, based on the pixel comparisons of the image processor, can speed up the display rate by eliminating one or more identical frames. 
     It should also be readily apparent that the above-described methods for varying frame capture and display rates can be applied to video endoscopes with little or no modification. 
     It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described herein above. Rather the scope of the invention is defined by the claims that follow: