Patent Publication Number: US-2007106111-A1

Title: Apparatus and method for frame acquisition rate control in an in-vivo imaging device

Description:
BACKGROUND OF THE INVENTION  
      Devices and methods for performing in-vivo imaging of passages or cavities within a body are well known in the art. Such devices may include, inter alia, various endoscopic imaging systems and devices, for example, an in-vivo capsule, for performing imaging in various internal body cavities.  
      While traveling inside the body, the imaging device may capture images of, for example, surfaces of the intestine and may transfer the captured images at a fixed frame rate, continuously, to an image recorder outside the body to be analyzed by a physician. The device may move unevenly inside the passages or cavities of the body. For example, an in-vivo capsule passing through a gastrointestinal (GI) tract may be moving “slowly” in some part of the GI tract, and at some point of time and/or position may start to move is “rapidly”. If the in-vivo device is capturing images at a fixed time interval, a physician performing diagnosis of the patient may experience receiving undesirably less images for that part of the GI tract as a result of this sudden change in the movement of capsule.  
      Various methods may be used to control the rate of images being captured by the imaging device and/or transferred to a receiver or recorder. Such methods may include for example manually sending a control signal to the imaging device to increase or decrease the rate of image capturing and the corresponding rate of frames being sent by the device.  
      However, an in-vivo imaging device performing image capturing of, for example, the GI tract may not always be monitored real time by a person, such as, for example a physician. The entire process of image capturing may be automatically recorded in an image recorder before image processing and/or image enhancement may be conducted on the recorded images. In addition, even if the process is real time monitored, it may often be too late for any human intervention to adjust the rate of image capturing when the device has already started changing its movement.  
     SUMMARY OF THE INVENTION  
      Embodiments of the present invention may provide an apparatus and method for adjusting the rate of image capturing and frame transmission in real time and for example automatically, in an in-vivo imaging device wherein the movement of the device may be at variable rate or the movement pattern of the device may be altered. For example, movement may be affected from time to time by factors such as internal pressure and the structure of passages and/or cavities, of the body.  
      Embodiments of the invention provide an in-vivo imaging device having a controller, wherein the controller is configured to, for example, during a cycle of image capturing, operate a light source and an imager to capture at least two images, process the two images, and adjust the cycle of image capturing in such a manner that, for example, the image frames captured and/or the stream of image frames captured may image the substantially entire area of interest, for example, substantially the entire GI tract or designated areas of the GI tract without human intervention, regardless of changes in the moving speed of the imaging device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be understood and appreciated more fully from the following detailed description of various embodiments of the invention, taken in conjunction with the accompanying drawings of which:  
       FIG. 1  is a conceptual illustration of an in-vivo imaging system according to one embodiment of the invention;  
       FIG. 2  is a simplified block diagram illustration of an in-vivo imaging device according to one embodiment of the invention;  
       FIG. 3  is a schematic diagram illustration of an in-vivo imaging device making a brief movement along a GI tract of a human body according to one embodiment of the invention;  
       FIG. 4  is a schematic illustration of the timing of an illumination and image acquisition process in an in-vivo imaging device having implemented a frame rate control mechanism according to one embodiment of the invention;  
       FIG. 5  is a schematic illustration of the timing of an illumination and image acquisition process in an in-vivo imaging device having implemented a frame rate control mechanism according to another embodiment of the invention;  
       FIG. 6  is a schematic illustration of the timing of an illumination and image acquisition process in an in-vivo imaging device having implemented a frame rate control mechanism according to yet another embodiment of the invention;  
       FIGS. 7A and 7B  are schematic views of a group of pixels of an imaging unit having implemented a frame rate control mechanism according to one embodiment of the invention;  
       FIG. 8  is a simplified flowchart illustration of a method of performing frame rate control by an in-vivo imaging device with pre-flash illumination according to one embodiment of the invention;  
       FIG. 9  is a simplified flowchart illustration of a method of performing frame rate control by an in-vivo imaging device with post-flash illumination according to another embodiment of the invention; and  
       FIG. 10  is a simplified flowchart illustration of a method of performing frame rate control by an in-vivo imaging device according to yet another embodiment of the invention. 
    
    
      It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity.  
     DETAILED DESCRIPTION OF THE INVENTION  
      Various embodiments of the present invention are described herein. For the purpose of explanation, specific configurations and details may be set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to person skilled in the art that the present invention may be practiced without the specific details presented herein. Furthermore, well known features may be omitted or simplified in order not to obscure the present invention.  
      Certain basic aspects and operational procedures used in embodiments of the present invention may be described in co-pending U.S. patent application Ser. No. 10/202,608, filed Jul. 25, 2002 and published Jun. 26, 2003 under publication number US-2003-0117491-A1, in co-pending U.S. patent application Ser. No. 09/800,470, filed Mar. 8, 2001 and published Nov. 1, 2001 under publication number US-2001-0035902-A1, and/or in U.S. Pat. No. 5,604,531 to Iddan et al. The disclosures of the above applications and patent are incorporated herein by reference in their entirety.  
      It is noted that while embodiments of the invention described herein are adapted for imaging of the gastrointestinal (GI) tract, the devices and methods disclosed herein may-be adapted for imaging other body cavities or spaces.  
       FIG. 1  is a conceptual illustration of an in-vivo imaging system adapted to adjust an image acquisition and frame transmission rate according to one exemplary embodiment of the invention. System  2 , as shown in  FIG. 1 , may include an in-vivo imaging device  4  and an external receiver/transmitter module or unit  6 . System  2  may also include a separate computing unit such as a personal computer or workstation  8  and a display panel  18 .  
      According to one embodiment of the invention, device  4  may typically be or may include an autonomous, swallowable, oblong, oval, or spherical capsule, but device  4  may have other shapes and need not be swallowable or autonomous.  
      Embodiments of device  4  are typically autonomous, and are typically self-contained. For example, device  4  may be a capsule or other unit where all the components, for example, an imager, illumination units, power units, control units, and transmitting/receiving units, may be substantially contained or sealed within the device body in a container or shell  5 , wherein the container or shell  5  may include more than one piece. Device  4  may not require any wires or cables to, for example, receive power or transmit data. Device  4  may communicate with an external receiving/transmitting module, for example, receiver/transmitter  6 , to provide data, control, or other functions. Power may be provided to device  4  by, for example, one or more internal batteries or through a wireless receiving system. Other embodiments may have other configurations and capabilities. For example, components may be distributed over multiple sites or units. Control information may be received from an external source.  
      As illustrated in the following description, imaging device  4 , contained in container or shell  5 , may be able to gather information, such as, for example, a stream of images of inner walls of body lumens while passing through inside of a body. The stream of images may be transmitted to a receiver/transmitter  6  outside the body via a wireless or hard-wired medium  10 . Receiver/transmitter  6  may include a memory  12 , and may be able to record information received from device  4  on memory  12 . In addition, receiver/transmitter module  6  may include, for example, a processor  19  to process data received from device  4  and/or to generate control signals to be transmitted to device  4 . Other suitable data or signals may be processed by processor  19 . Optionally, receiver/transmitter  6  may include display panel  18  which may include an LCD, TFT, CRT, OLED or other suitable panels. In other words, display panel  18  may be integrated into receiver/transmitter  6 . Receiver/transmitter  6  may be able to transfer received or recorded information to display  18  or to workstation  8  via, for example, a wireless or hard-wired medium  14 , and may be able to do so while receiving/recording information from device  4 .  
      Workstation  8  may include a processor  17  to process and/or present information received from receiver/transmitter  6  to an operator while device  4  is still inside the patient&#39;s body, and while receiver/transmitter  6  is still recording information gathered by device  4 . For example, workstation  8  may include a display unit  16 , and may be able to display the stream of images recorded in memory  12  on display unit  16 . Display unit  16  may include an LCD, TFT, CRT, OLED or other suitable medium.  
      While moving along the GI tract of a body, imaging device  4  may acquire images at a predetermined or initial acquisition rate. For example, device  4  may acquire images at a rate of two frames per second (2 Hz). Other base rates may be used. According to an exemplary embodiment of the invention, device  4  may also acquire certain “special” images and the special images may be processed, or partially processed, by device  4  to produce for example a control signal or a control parameter such as a frame rate control signal. Alternately, the special images may be sent to receiver/transmitter  6  and subsequently processed and/or analyzed by processor  19 . The special images may be “control images” used to analyze the imaging process, and not used for display to a user. A control or adjustment signal such as a frame rate control signal may be sent to device  4  by receiver/transmitter module  6  to adjust the functioning of device  4  or may be generated within device  4  as described above. Alternately, the image acquisition rate may be adjusted automatically or manually by an expert or physician examining the image at workstation  8 .  
       FIG. 2  is a simplified block diagram illustration of an in-vivo imaging device having a frame rate control system of image acquisition and transmission according to exemplary embodiment of the invention. Device  30 , which may be device  4  in  FIG. 1 , may include an imaging unit  34 , for example, a CMOS imager adapted for capturing images of the GI tract through an optical unit  32 . The images captured may include various images, for example “regular images” and “control images”. A “regular image” may be for example an images captured and transmitted to the outside of a body to be displayed on, for example, display panel  18  and/or display unit  16  of workstation  8  ( FIG. 1 ), for example, for diagnosis by a physician. A “control image” may be for example a special image captured for frame rate control purpose, and may not be recorded or displayed to a user. The control image may be captured by a subset or sub-group of pixels, as shown in  FIG. 7  below, of imager or imaging unit  34  ( FIG. 2 ) and may have different resolution from the regular image, and may not be displayed and/or suitably captured for display. Processor unit  36  and/or imaging unit  34  may process or analyze a set of control images to produce a control signal. Processor unit  36  may also be a controller to adjust parameters of the image acquisition process, such as the image acquisition and frame transmission rate based on the control signal. According to one embodiment of the invention, processor unit  36  may control the operation of imaging unit  34  and a transmitting/receiving unit  46  operatively connected to imaging unit  34  to transmit the captured control images to outside to be processed by processor  17  of workstation  8  or by receiver/transmitter  6  ( FIG. 1 ). Receiver/transmitter  6 , for example, may produce a control signal or otherwise alter the operating parameters of device  4 . The control signal or parameter adjustment may include the rate of image acquisition, and/or framing and transmission of the acquired images. According to one embodiment of the invention, processor unit  36  may transmit the control images and regular images to an external receiver, on a same frame to save transmission power, or may transmit the images separately. According to an exemplary embodiment of the invention, processor  36  may save all or part of the control images in a memory  38  during the acquisition, processing, and/or transmission of the control images.  
      Device  30  may also include one or more light sources  44  that are suitably connected to an illumination control unit  40 . Illumination control unit  40  may control the intensity, duration, and/or the number of illumination sources  44  used. Device  30  may further include one or more power sources  48 .  
       FIG. 3  is a schematic diagram illustration of an in-vivo imaging device making a brief movement along a GI tract of a human body according to one embodiment of the invention. Device  300  may briefly move from a position  321  to a position  322  along a GI tract  309 . Images of GI tract  309 , for example, at points  301 ,  302 , and  303 , may be captured in a pixel area  311  of an imaging sensor  310  when imaging device  300  is at position  321 . Images of the same may be captured in a slightly different pixel area  312  of the same imaging sensor  310  at position  322  after device  300  make the brief movement. While in  FIG. 3  device  300  is shown some distance from the lumen walls, in practice, the device in some applications may be pressed up against or surrounded by lumen walls or other tissue.  
      An averaged moving speed of imaging device  300 , over a predetermined time interval during which the brief movement is made, may be estimated or calculated by determining the amount of offset between pixel areas  311  and  312 , for example, through image pattern recognition based on techniques, such as for example, comparison of pixel level signal strength. However, the invention is not limited in this respect and an averaged or other moving speed may be estimated or calculated by other means. The estimated moving speed may be compared with a reference speed. A difference between the calculated speed and the reference speed may be used to determine the amount of adjustment of frame transmission rate that imaging device  300  may need to make.  
      Various processes of control image acquisition, e.g., image capturing, may be schematically illustrated in the following exemplary embodiments of the invention. However, processes and approaches other than those listed below are also covered by the scope of the spirit of this application. In this application, the terms “acquisition” and “capturing” may be used interchangeably, and the terms “flash” and “illumination” may also be used interchangeably. The rate of image acquisition may be preferably the same as the rate of frame transmission but the invention is not limited in this respect. According to an exemplary embodiment of the invention, an imaging device may not necessary transmit all the images captured and may send, for example, every other images captured to control frame transmission rate. Therefore, the rate of frame transmission may be less than the rate of image acquisition.  
       FIG. 4  is a schematic illustration of the timing of an illumination and image acquisition process in an in-vivo imaging device having implemented a frame rate control mechanism according to one embodiment of the invention. The imaging device may use a pre-flash light pulse, which may be for example a light pulse  402  before for example a regular light flash  412 , to capture a first control image. The imaging device may subsequently capture a regular image using a regular flash and may apply at least part of the regular image as a second control image. The imaging device may then produce a control signal, which may be for example related to a change in scenery, illumination, changes in the average moving speed of the imaging device or other changes, by processing and analyzing the first and second control images. Furthermore, the imaging device may proceed to apply the control signal to adjust the rate or cycle of image acquisition or imaging and frame transmission or framing. Typically, the control images are not viewed by a user or displayed for a user, where regular images are.  
      According to one embodiment of the invention, the illumination and image acquisition process may include a series of cycles. For example, a first cycle  411  of duration ΔT 10  may start at time T 1  and end at time T 2 . A second cycle  421  of duration ΔT 20  may start at time T 2  and end at time T 3 . A third cycle  431  of duration ΔT 30  may start at time T 3  and end at time T 4 .  
      A cycle of illumination and image acquisition may have, for example, four periods. Other number of periods may be used. For example, first cycle  411  may include, for example, a pre-flash illumination period  402  and a following dark period  404  with a combined duration ΔT 0 , a regular flash period  412  of duration ΔT 11 , and a regular dark period  414  of duration ΔT 12 . Pre-flash illumination period  402  and regular flash period  412  are illustrated in  FIG. 4  by hatched bars. Duration ΔT 0  may be preferably fixed but the invention is not limited in this respect. The dark periods after regular flashes, e.g., dark period  414  of duration ΔT 12 , may be adjusted for frame rate control, as is described below in detail, according to one embodiment of the invention.  
      The second and third cycles  421  and  431  may have similar pre-flash illumination period  402  and dark period  404  as the first cycle  411 . In addition, second cycle  421  may have a regular flash period  422  of duration ΔT 21  and a regular dark period  424  of duration ΔT 22 , both of which may be the same or different from those of first cycle  411 . Similarly, third cycle  431  may have a regular flash period  432  of duration ΔT 31  and a regular dark period  434  of duration ΔT 32 , both of which may be the same or different from those of first cycle  411  as well.  
      During flash periods, for example, pre-flash illumination  402  and/or regular flash  412 , light source  44  ( FIG. 2 ) may be turned on to illuminate the GI tract, and one or more control images may be captured. During dark periods (e.g., periods when the light is not operated), for example, dark periods  404  and/or  414 , certain pixels of imaging unit  34  ( FIG. 2 ) may be scanned and image signals from the control images captured may be obtained. The image signals may be temporarily stored in a memory or transmitted to the outside of the human body.  
      During dark period  414 , or during any other period, the control image signals may be analyzed, for example, may be compared with each other or with a regular image, to obtain a control signal related to, for example, possible changes in image scenery, the orientation of the imaging device, and/or the average moving speed of the imaging device, although analysis of other factors may also be conducted. The analysis may be performed by an internal processor, for example, processor  36  ( FIG. 2 ) and/or by an external processor, for example, processor  19  of receiver/transmitter  6  ( FIG. 1 ) or processor  17  ( FIG. 1 ). The control image signals may be transmitted to an external processor along with the regular image signals, or may be sent as a separate frame. A control signal produced internally and/or received from an external processor may be applied to adjust imaging times or cycles, or imaging and/or lighting periods, for example, the rate or cycles of image acquisition or imaging and frame transmission or framing, so that for example more images may be captured when the rate of image changes increases, or the imaging device moves faster. Framing may include, for example, transmitting an image. The cycles may be adjusted through, for example, controlling the starting time of a subsequent cycle, for example starting time T 2  of second cycle  421 . For example, dark period  414  may be adjusted to control the rate or cycles of imaging and framing.  
      According to one embodiment of the invention, adjustment of cycles may be implemented starting at a subsequent cycle, for example, third cycle  431 , instead of during the immediate cycle  421 .  
      According to another embodiment of the invention, the image frame acquisition and/or transmission rate may also be lowered, reduced, or shortened by selectively transmitting captured images and skipping transmission of certain other images without adjusting the cycle of imaging.  
      Pre-flash light pulse  402  may have duration of Δt 1 . A first control image may be captured during pre-flash illumination, and scanned into a first control image signal, for example, during dark period  404 . The image may be scanned from a group of pixels which maybe, for example, a subset of pixels of imager or imaging unit  34  ( FIG. 2 ). Pixels of the imager may be reset during dark period  404 . A regular image may be captured after regular flash period  412  and scanned into a regular image signal, for example, during dark period  414 . The first control image signal and the regular image signal may be transmitted to, for example, external receiver/transmitter  6 . Processor  19  of external receiver/transmitter  6  (or processor  17  of workstation  8 ) may extract a second control image signal (“redacted image signal”) from the regular image signal associated with, for example, the subset of pixels for the first control image signal. Alternatively, the second control image signal may be extracted by internal processor  36  of device  30  ( FIG. 2 ). The second control image signal may be compared with the first control image signal and a rate of change in image position or image scenery, corresponding to an averaged speed of the imaging device relative to, for example, the scenery change, may be estimated or calculated. According to one embodiment of the invention, control image signals may be normalized in power for proper signal processing.  
      It will be appreciated by person skilled in the art that the first and second control images may be captured from different cycles of image acquisition and frame transmission. For example, the first control image may be captured during pre-flash illumination  402  of cycle  411  and the second control image may be captured during regular flash  422  of cycle  421 .  
       FIG. 5  is a schematic illustration of the timing of an illumination and image acquisition process in an in-vivo imaging device having implemented a frame rate control mechanism according to another embodiment of the invention.  
      The imaging device may capture a regular image after a regular flash and at least part of the regular image may be applied as a first control image. The imaging device may apply a post-flash light pulse, which is for example a light pulse  502  after for example a regular flash  512 , to capture a second control image. The imaging device may scan the first and second control images to obtain a first and second image signals, and process the image signals to obtain a control signal. The control signal may reflect for example a change in the orientation or average moving speed of the imaging device, and may be used to adjust the imaging cycles, acquisition and imaging, and frame transmission or framing. Typically, the control images are not viewed by a user or displayed for a user, where regular images are.  
      According to one embodiment of the invention, the illumination and image acquisition process may include a series of cycles. For example, a first cycle  511  may start at time T 1  and end at time T 2  with a duration ΔT 10 . A second cycle  521  may start at time T 2  and end at time T 3  with a duration ΔT 20 . A third cycle  531  may start at time T 3  and end at time T 4  with a duration ΔT 30 .  
      A cycle of image acquisition and processing may have for example four periods; other numbers of periods may also be used. For example, first cycle  511  may include a regular flash period  512  of duration ΔT 11 , a regular dark period  514  of duration ΔT 0 , and a post-flash illumination period  502  and a following dark period  504 , having a combined duration ΔT 12 . Regular flash period  512  and post-flash illumination period  502  are illustrated in  FIG. 5  by hatched bars. Duration ΔT 0  may be preferably fixed but the invention is not limited in this respect. Post-flash illumination period  502  may start at a time t 1 . According to one embodiment of the invention, the dark periods after post-flash illumination, e.g., dark period  504  of duration ΔT 12 , may be adjusted for frame rate control, as described below in detail.  
      As similarly described above in  FIG. 4 , during regular flash  512  and post-flash illumination  502 , control images may be captured. During dark periods  514  and  504 , at least a subset of pixels of imaging unit  34  ( FIG. 2 ) may be scanned to obtain a set of control image signals from the control images captured. The pixels may be re-set during dark periods  514  and  504 . The set of image signals may be processed or analyzed, for example, by an internal processor  36  ( FIG. 2 ) and/or by an external receiver/transmitter  6  ( FIG. 1 ) and/or processor  17  ( FIG. 1 ), to produce for example a control signal or adjustment parameter. According to one embodiment of the invention, the image signals may be transmitted to an external processor along with the regular image signals, or may be sent as a separate frame. The control signal produced internally or received externally may be applied to adjust the period or cycle of imaging, for example, timing or cycles of image acquisition or imaging and frame transmission or framing. The periods or cycles may be adjusted through controlling, for example, the starting time T 2  of second cycle  521 . For example, dark period  504  of duration ΔT 12  may be adjusted to control the rate or cycles of imaging, lighting, and/or framing.  
      According to one embodiment of the invention, the cycles of framing may also be lowered by selectively transmitting some captured images and skipping some other images without adjusting the cycle of imaging. According to another embodiment of the invention, adjustment may be made by adjusting the starting time of other subsequent cycles, such as cycle  531 .  
      A regular image signal may be obtained by scanning an image captured after regular flash period  512 . According to one embodiment, the regular image signal may be transmitted to, for example, external receiver/transmitter  6  and processed by processor  19  (or processor  17  of workstation  8 ) to obtain a first control image signal (“redacted image signal”). According to another embodiment, the first control image signal may be obtained by internal processor  36  of device  30  ( FIG. 2 ). The first control image signal may be extracted from a subset of pixels of imager  34 . A second control image may be captured during post-flash illumination  502 , and scanned into a second control image signal, for example, during dark period  504 . Post-flash light pulse  502  may have duration of Δt 1 . The second control image signal may be compared with the first control image signal, and factors such as, for example, a rate of image scenery change, and/or change in image position corresponding to an averaged speed of the imaging device, may be estimated or calculated. According to one embodiment of the invention, the first and second control image signals may be normalized in power for proper signal processing and comparison to produce a control signal. The control signal may, for example, increase or decrease the rate of image acquisition or imaging or frame transmission or framing, or to lower frame transmission rate by skipping certain images captured while keeping the image acquisition rate constant relative to the rate of image changes. For example, more images may be captured when the rate of image changes increases, an indicator of some drastic condition change in the GI tract.  
      According to one embodiment of the invention, the first and second control images may be captured from different cycles of image acquisition and frame transmission. For example, the first control image may be captured during regular flash  512  of cycle  511  and the second control image may be captured from cycle  521  or any subsequent cycles. Two or more control images may be captured to produce one or more control signals to control the operational characteristics of the imaging device.  
       FIG. 6  is a schematic illustration of the timing of an illumination and image acquisition process in an in-vivo imaging device having implemented a frame rate control mechanism according to yet another embodiment of the invention. The imaging device may not require extra flashes other than the regular flashes, and may obtain a set of control images through, for example, multiple scanning of the imaging sensor during a regular flash period. Image signals scanned from control images captured may be processed and/or analyzed to adjust the rate or cycles of image acquisition or imaging and frame transmission or framing.  
      According to an exemplary embodiment of the invention, the illumination and image acquisition process may include a series of cycles or periods. For example, a first cycle  611  may start at time T 1  and end at time T 2  with a duration ΔT 10 . A second cycle  621  may start at time T 2  and end at time T 3  with a duration ΔT 20 . A third cycle  631  may start at time T 3  and end at time T 4  with a duration ΔT 30 .  
      A cycle of image acquisition and processing may have a regular flash period and a regular dark period. For example, first cycle  611  may have a flash period  612  of a duration ΔT 11 , and a dark period  614  (e.g., when no illumination is used) of a duration ΔT 12 . Flash period  612  is represented by the hatched bar in  FIG. 6 . Dark period  614  of duration ΔT 12  may be adjusted for frame rate control, as is described below in detail, according to an exemplary embodiment of the invention.  
      According to one embodiment of the invention, during flash period  612 , the imaging device, for example, device  30  ( FIG. 2 ), may scan and store, record, at time t 1 , a first group of image data, and scan and store, record, at time t 2 , a second group of image data. A difference in scanned signal strength, during a time interval Δt 1  between t 1  and t 2 , may be applied as a first control image signal. Subsequently, the imaging device may scan and store, record, at time t 3 , a third group of image data, and scan and store, record, at time t 4 , a fourth group of image data. A difference in scanned signal strength, during a time interval Δt 2  between t 3  and t 4 , may be applied as a second control image signal. It will be appreciated by a person skilled in the art that the imaging device may scan at three different times to obtain three groups of image data. Differences in signal strength between any two groups of image data may be used as the first and second control image signals.  
      The first and second image signals may also be stored in a memory to be processed and/or transmitted to an external processor for processing later, for example, during dark period  614 . According to one embodiment of the invention, the time difference between t 1  and t 3  of duration ΔT 0  may be predetermined but the invention is not limited in this respect. The time interval between t 1  and t 3  may be adjusted within flash period  612 .  
      During dark period  614 , or a part thereof, first and second image signals obtained from time intervals Δt 1  and Δt 2  may be processed by processor  36 , processor  19  ( FIG. 2 ), and/or transmitted to an external processor for processing. A possible change in the image data, or moving speed of the imaging device may be estimated or calculated, and used to determine the rate or cycle adjustment to image acquisition or imaging and frame transmission or framing. The rate or cycle adjustment may be made through controlling the starting time T 2  of second cycle  621 , or any subsequent cycles. The pixels of imaging unit  34  may be re-set during dark period  614 .  
      According to one embodiment of the invention, time durations of Δt 1  and Δt 2  may be adjusted based on a desired sharpness of images and intensity of illumination during image acquisition. In addition, signals scanned from control images captured during Δt 1  and Δt 2  may need normalization in power for proper signal processing.  
      In the embodiments of the invention shown in  FIGS. 4, 5 , and  6  above, and other embodiments, when a reduction in frame transmission rate is desired, instead of reducing the rate of image acquisition, the imaging device may keep the same rate of image acquisition or imaging. Instead, the imaging device may transmit frames of images at a lower transmission rate by selectively transmitting images and skipping certain other images captured according to exemplary embodiments of the invention.  
       FIGS. 7A and 7B  are schematic top views of a group of pixels of an imaging unit having implemented a frame rate control mechanism according to one embodiment of the invention. In  FIG. 7A , pixel group  700 , which may be for example part of imaging unit  34  in  FIG. 2 , is schematically illustrated by a 15×18 pixel array. However, it will be appreciated by person skilled in the art that the number of pixels may be larger or smaller depending on various factors, for example, the time interval between the two images sampled, and the expected average moving speed of the imaging device, etc.  
      According to one embodiment of the invention, pixels that are sampled or scanned for acquiring control images may be specially fabricated pixels and may be, for example, analog photodiodes with special readout such as parallel access or sampling circuitry. Such pixels may be advantageous because of shortened readout of scanning results, compared with the time required to sequentially scan the same number of pixels in an imaging sensor, for example, a CMOS imager, having uniform pixel construction.  
      A first set of image pixel outputs may be recorded which may include, for example, an image represented by pixels  711 - 716 . After a pre-determined time interval, a second set of pixel outputs may be recorded. By analyzing the second pixel outputs, the image represented by pixels  711 - 716  may be identified to have moved to a position represented by pixels  721 - 726 . For example, a distance moved by the imaging device may be represented by a pixel movement indicating a pixel “distance” of  4  vertical and  3  horizontal, or a linear distance of  5  pixels. Since the movement of the image happened during the pre-determined time interval, a rate of device movement may be computed and may be used to adjust the rate of imaging acquisition and frame transmission.  
      Since the intensity of flashing and the duration of illumination may be different for the two imaging operations, the intensity of signals or data produced by the pixel group may be different. To facilitate pattern recognition and processing, the signals may be amplified and/or attenuated to have comparable intensity or may be normalized during processing by software.  
       FIG. 8  is a simplified flowchart illustration of a method of performing frame rate control by an in-vivo imaging device with pre-flash control image sampling according to one exemplary embodiment of the invention.  
      At block  802 , the imaging device, for example, imaging device  30  ( FIG. 2 ), may perform a pre-flash illumination for acquisition of a first control image. Following the pre-flash illumination, at block  804 , the imaging device may scan a set of pre-selected pixels of an imaging sensor or unit  34  of the imaging device  30 , and obtain a first control image signal. The imaging device  30  may then reset the pixels and wait for a pre-determined time to lapse as indicated at block  806 . At block  808 , the imaging device  30  may proceed to perform a regular flash and, after the regular flash, scan the pixels to obtain a regular image. A second control image signal (also referred to herein as a redacted image signal) may be extracted or sampled from the regular image obtained, is possibly from the corresponding set of pre-selected pixels for the first control image, as indicated at block  810 . The extraction or sampling may be performed by an internal processor  36  of imaging device  30  and/or an external processor, for example, processor  19  and/or processor  17  ( FIG. 1 ). At block  812 , the first and second control image signals may be analyzed, and may be compared. In one example, an averaged moving speed, relative to the scenery change of the GI tract, may be computed. The analyzing and computing process may include normalizing power of captured control image signals and may include, as described above, transmitting the control image signals to external receiver/transmitter  6 , and subsequently receiving a control signal from the external receiver/transmitter  6 . The control images may also be analyzed internally by processor  36  ( FIG. 2 ) to produce the control signal. As indicated at block  814 , the rate of image acquisition and frame transmission of the imaging device may be adjusted by the rate control signal.  
       FIG. 9  is a simplified flowchart illustration of a method of performing frame rate control by an in-vivo imaging device with post-flash control image sampling, according to another exemplary embodiment of the invention.  
      The imaging device, e.g., imaging device  30  ( FIG. 2 ), may perform a regular flash for the acquisition of a regular image at block  902 . After the regular flash, the imaging device may scan the pixels to get the regular image signal. A first control image signal (also referred to herein as a redacted image signal) may be extracted or sampled from the regular image signal, from a set of pre-selected pixels of imaging unit or sensor  34  of imaging device  30 , as indicated at block  904 . At block  906 , the imaging device may reset the pixels and wait for a pre-determined time to lapse. The imaging device may proceed to perform a post-flash illumination at block  908 . Following the post-flash illumination and at block  910 , the imaging device may scan, for example, the corresponding set of pre-selected pixels to obtain a second control image signal. At block  912 , the first and second control image signals may be analyzed and factors such as, for example, an averaged moving speed, relative to image scenery change of the GI tract, may be computed. The process of analyzing and computing may include normalizing power of captured control image signals and may include, as described above, transmitting the control images to external receiver/transmitter  6  for analysis, and subsequently receiving a control signal from external receiver/transmitter  6 . The control image signals may also be analyzed internally by processor  36  ( FIG. 2 ) to produce the control signal. As indicated at block  914 , the rate of image acquisition and frame transmission of the imaging device may be adjusted by the control signal.  
       FIG. 10  is a simplified flowchart illustration of a method of performing frame rate control by an in-vivo imaging device, according to a further exemplary embodiment of the invention.  
      The imaging device may perform a regular flash for image acquisition at block  1002 . During the regular flash, the imaging device may scan, at time t 1 , a pre-selected set of pixels of an imaging sensor of the imaging device and save the results at block  1004 . The imaging device may scan, at time t 2 , the same set of pixels and save the results at block  1006 . The imaging device may wait for a pre-determined time to lapse at block  1008 . The imaging device may scan, at time t 3 , the same set of pixels and save the results at block  1010 . The imaging device may scan, at time t 4 , the same set of pixels and save the results at block  1012 . The regular flash may end at block  1014 . At block  1016 , a difference in results obtained at times t 1  and t 2  may be computed and saved as a first control image. Similarly, a difference in results obtained at times t 3  and t 4  may be computed and saved as a second control image. However, the above computation in difference of results may be performed before the regular flash ends. At block  1018 , the first and second control images may be processed. The processing may include normalizing power of captured control images, transmitting the control images to an external receiver for analysis, and receiving a rate control signal from the external receiver. However, the invention is not limited in this respect and the control images may be analyzed internally by processor  36  ( FIG. 2 ) to produce the rate control signal. At block  1020 , the rate of image acquisition and frame transmission of the imaging device may be adjusted by the rate control signal.  
      In further embodiments, other operations, and other series of operations, may be used.  
      It will be appreciated by those skilled in the art that while the invention has been described with respect to a limited number of embodiments, many variations, modifications and other applications of the invention may be made which are within the scope and spirit of the invention.