Abstract:
Imaging apparatus, including an imaging unit, which consists of an image sensor, configured to capture images of a region and to output image signals in response to the captured images and an illumination source, configured to illuminate the region. The unit further includes a driver circuit, which is coupled to receive a digital value indicative of a target luminous flux of the illumination source and to generate a pulse-width-modulated (PWM) signal to drive the illumination source with a duty cycle of the signal determined by the value. The apparatus includes a camera control unit, which is configured to process the image signals so as to generate images of the region and to output the digital value indicative of the target luminous flux based on the images. A single cable connects the imaging unit to the camera control unit so as to convey the image signals and the digital value.

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to operation of an endoscope, and specifically to an illumination system used for the endoscope. 
     BACKGROUND OF THE INVENTION 
     An endoscope typically images a body cavity, and in order to image the cavity the cavity must be illuminated. 
     U. S. Patent Application 2009/0076329 to Su et al., whose disclosure is incorporated herein by reference, describes a disposable stereoscopic endoscope which has two imaging sensors and a solid state illumination source arranged inside the endoscope. 
     U. S. Patent Application 2011/0174861 to Shelton et al., whose disclosure is incorporated herein by reference, describes a surgical instrument with wireless communication between a control unit and a remote sensor. The disclosure states that the instrument may include a display powered by a battery and controlled by the control unit. 
     U.S. Pat. No. 7,410,462 to Navok et al., whose disclosure is incorporated herein by reference, describes a hermetic endoscope assemblage having compound optical widows. The disclosure states that the compound optical windows may have separate panes for an imaging system and an illumination system. 
     A “DUR-D” ureteroscope, produced by Olympus Corporation, of Tokyo, Japan, uses an endoscope protection system which exploits the ability of a CMOS sensor incorporated into the ureteroscope to detect colors. Information transmitted from the CMOS sensor to a control unit of the ureteroscope is used to quickly shut down a laser of the ureteroscope. 
     Documents incorporated by reference in the present patent application are to be considered an integral part of the application except that to the extent any terms are defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in the present specification, only the definitions in the present specification should be considered. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention provides imaging apparatus, including: 
     an imaging unit, which consists of: 
     an image sensor, configured to capture images of a region and to output image signals in response to the captured images; 
     an illumination source, configured to illuminate the region; and 
     a driver circuit, which is coupled to receive a digital value indicative of a target luminous flux of the illumination source and to generate a pulse-width-modulated (PWM) signal to drive the illumination source with a duty cycle of the signal determined by the value; 
     a camera control unit, which is configured to process the image signals so as to generate images of the region and to output the digital value indicative of the target luminous flux based on the images; and 
     a single cable connecting the imaging unit to the camera control unit so as to convey the image signals and the digital value. 
     Typically, the illumination source includes a light emitting diode (LED). A current provided by the driver circuit in an on-state of the duty cycle may be a minimum operating current of the LED. 
     A disclosed embodiment further includes a direct (DC) current source configured to drive the illumination source, wherein below a bounding value of the target luminous flux the driver circuit generates the PWM signal, and above the bounding value the DC source generates a DC current according to the target luminous flux. Typically, the driver circuit is located within a handle of an endoscope, and the DC source is located within the camera control unit. The driver circuit may be implemented as a variable current load. 
     In a further disclosed embodiment the single cable is configured to convey direct (DC) current from the camera control unit to the driver circuit so as to power the driver circuit. 
     In a yet further disclosed embodiment the imaging unit is included within an endoscope, and the illumination source and the driver circuit are located within a handle of the endoscope, and the handle is configured to be held by an operator of the endoscope for manipulation thereof. 
     There is further provided, according to an embodiment of the present invention, apparatus, including: 
     an endoscope, including: 
     a tube having a proximal end and a distal end configured for insertion into a body cavity; 
     an image sensor, mounted at the distal end and configured to generate image signals of a region of the body cavity in response to illumination received therefrom; 
     a handle, configured to fixedly connect to the proximal end of the tube and configured to be held by an operator of the endoscope for manipulation thereof; 
     a driver circuit mounted within the handle, configured to generate pulse-width-modulated (PWM) current; and 
     an illumination source, mounted within the handle, configured to receive the PWM current and in response to illuminate the body cavity so as to provide the illumination received therefrom; and 
     a camera control unit (CCU), configured to control the image sensor and to generate an image of the body cavity in response to receipt of the image signals. 
     In an alternative embodiment the driver circuit is powered by a direct (DC) current, the apparatus further including a single cable connected between the CCU and the handle and configured to transfer the DC current to the driver circuit and to transfer the image signals to the CCU. 
     Typically, the PWM current is supplied by the driver circuit to the LED at a duty cycle, and a current provided by the driver circuit in an on-state of the duty cycle is a minimum operating current of the LED. 
     The CCU may be configured to process the image signals so as to output a digital value indicative of a target luminous flux of the illumination source, and the driver circuit may be coupled to receive the digital value and to generate the PWM current with a duty cycle determined by the value. 
     The apparatus may include a direct (DC) current source configured to drive the illumination source, so that below a bounding value of the target luminous flux the driver circuit generates the PWM signal, and above the bounding value the DC source generates a DC current according to the target luminous flux. 
     The apparatus may include a single cable, connecting the endoscope to the CCU, that is configured to convey the image signals from the image sensor to the CCU, and to convey direct (DC) current from the CCU to the driver circuit so as to power the driver circuit. 
     There is further provided, according to an embodiment of the present invention, a method for imaging, including: 
     configuring an image sensor within an imaging unit to capture images of a region and to output image signals in response to the captured images; 
     configuring an illumination source within the imaging unit to illuminate the region; 
     configuring a driver circuit within the imaging unit to receive a digital value indicative of a target luminous flux of the illumination source and to generate a pulse-width-modulated (PWM) signal to drive the illumination source with a duty cycle of the signal determined by the value; 
     processing the image signals in a camera control unit so as to generate images of the region and to output the digital value indicative of the target luminous flux based on the images; and 
     connecting the imaging unit to the camera control unit with a single cable so as to convey the image signals and the digital value. 
     There is further provided, according to an embodiment of the present invention, a method including: 
     inserting a tube of an endoscope into a body cavity, the tube having a proximal end and a distal end; 
     mounting an image sensor of the endoscope at the distal end and generating with the image sensor image signals of a region of the body cavity in response to illumination received therefrom; 
     fixedly connecting a handle of the endoscope to the proximal end of the tube, the handle being configured to be held by an operator of the endoscope for manipulation thereof; 
     mounting a driver circuit within the handle, and generating pulse-width-modulated (PWM) current with the driver circuit; 
     mounting an illumination source within the handle, and configuring the source to receive the PWM current and in response to illuminate the body cavity so as to provide the illumination received therefrom; and 
     configuring a camera control unit (CCU) to control the image sensor and to generate an image of the body cavity in response to receipt of the image signals. 
     The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken together with the drawings in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic illustration of an endoscope illumination system, according to an embodiment of the present invention; 
         FIG. 2  is a schematic diagram illustrating elements of an endoscope, a handle, and a camera control unit module, according to an embodiment of the present invention; 
         FIG. 3  is a schematic graph of luminous flux emitted by a light emitting diode (LED) vs. current driving the LED, according to an embodiment of the present invention; and 
         FIG. 4  is a schematic graph of mean DC current drawn by a LED vs. mean target flux of the LED, according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     An embodiment of the present invention comprises an endoscope which is connected by a single cable to a camera control unit (CCU), the CCU operating the endoscope. An image sensor in the endoscope generates image signals of an image captured by the endoscope, and the image signals are transferred via the single cable to the CCU, which processes the signals to display a corresponding image on a screen connected to the CCU. In a handle of the endoscope an illumination source, typically a light emitting diode (LED) is mounted, and the illumination source is driven by a driver circuit which is also mounted within the handle. Illumination provided by the source generates the image captured by the image sensor. 
     Continuous direct (DC) current or pulse-width-modulated (PWM) current may be supplied to the illumination source, which correspondingly generates continuous or pulsed luminous flux. Typically, a driver circuit is configured to supply the PWM current at different duty cycles when the illumination source is required to generate low average flux levels, the duty cycle being adjusted according to a required low flux level. In addition, a DC source, typically mounted in the CCU, may be configured to supply continuous DC current at a level that is adjusted according to a required high flux level. 
     Typically, the CCU is configured to calculate a digital value according to a target luminous flux required from the illumination source. The digital value may set if PWM or continuous DC current is to be generated, and may also set the duty cycle (for the PWM). 
     By locating the driver circuit in the handle of the endoscope, embodiments of the present invention only generate PWM current within the handle. Thus, in the single cable connecting the CCU to the endoscope, there is no transfer of PWM current. (In prior art systems this type of transfer causes interference in the image signals transferred in the cable.) Rather, in embodiments of the present invention, even when PWM current is required from the driver circuit, only the DC current needed to power the driver circuit is transferred via the single cable, so that there is no interference with the image signals in the cable. 
     DETAILED DESCRIPTION 
     Reference is now made to  FIG. 1 , which is a schematic illustration of an endoscope illumination system  10 , according to an embodiment of the present invention. System  10  may be used in an invasive medical procedure, typically a minimally invasive procedure, on a body cavity  12  of a patient in order to image a region of the body cavity. By way of example, in the present description the body cavity is assumed to be the abdomen of a patient, and body cavity  12  is also referred to herein as abdomen  12 . However, it will be understood that system  10  may be used to image a region in substantially any body cavity, such as the bladder or the chest, or in another entity. 
     System  10  is operated by a camera control unit (CCU) module  14 , located in an endoscope module  16  which operates an endoscope  18 . Endoscope module  16  comprises a processor  20  communicating with a memory  22 , and the processor and memory may be used by the endoscope module in order to control CCU module  14 , as well as to perform at least some of the functions of the CCU module, described below. 
     Endoscope module  16  may also comprise other modules, such as an image processing module and a zoom/pan module, which may be used by processor  20 , but which for simplicity are not shown in the diagram. The processor uses software stored in memory  22 , in the form of the modules referred to above as well as in other forms, to operate system  10 . Results of the operations performed by processor  20  may be presented on a screen  26  to an operator  24 , assumed by way of example to be a medical physician, of system  10 . Screen  26  typically displays an image, acquired by endoscope  18 , of a region of body cavity undergoing the procedure. Alternatively or additionally, screen  26  may be used to display a graphic user interface to operator  24 . The software may be downloaded to processor  20  in electronic form, over a network, for example, or it may, alternatively or additionally, be provided and/or stored on non-transitory tangible media, such as magnetic, optical, or electronic memory. 
     To perform a procedure, the physician inserts a trocar  40  into abdomen  12 , and then inserts endoscope  18  into the abdomen via the trocar. So that the physician can manipulate the endoscope, the endoscope is attached to a handle  44  which is configured to be gripped by the physician. Typically, handle  44  and endoscope  18  are produced as a single unitary system wherein the handle and the endoscope are fixedly attached. 
     Elements of endoscope  18  are controlled by CCU module  14 , and in order to provide this control handle  44  is connected by a single cable  50  to the CCU module. The elements of endoscope  18  that are controlled by the CCU module are described in more detail with reference to  FIG. 2  below. 
       FIG. 2  is a schematic diagram illustrating elements of endoscope  18 , handle  44 , and CCU module  14 , according to an embodiment of the present invention. Endoscope  18  comprises a tube  52  which may be rigid or flexible. The tube is connected at its proximal end to handle  44 . An image sensor  56 , located at the distal end of tube  52 , is arranged to capture images of a region of cavity  12 . For its operation, the image sensor receives driving signals, generated by sensor circuitry  60  which acts as a sensor driver. Circuitry  60  is located within handle  44 , is typically implemented as a printed circuit board, and is also referred to herein as handle board  60 . In operation, sensor  56  generates image signals corresponding to the captured images, and transfers the image signals to handle board  60  wherein the image signals are pre-processed. The driving signals and the image signals are typically transferred between handle board  60  and sensor  56  using a cable  62 , which traverses tube  52 . 
     The pre-processing performed by board  60  converts the image signals into conditioned signals, which are in a form suitable for transmission to CCU module  14  via a conductor  64  in cable  50 . Cable  50  comprises other conductors, the functions of which are described below, and the conductors within the cable are typically shielded by a cable shield  68  which may be configured to act as a return. Typically, the pre-processing performed by board  60  to generate conditioned signals comprises amplification, filtration, and impedance conversion of the image signals. 
     The region of cavity  12  that is imaged by sensor  56  is illuminated from an illumination source  72 , which comprises a light emitting diode (LED), so that source  72  is also referred to herein as LED  72 . Typically LED  72  is mounted in handle  44 , and the illumination generated by the LED may be transferred from the LED, so that it exits from the distal end of tube  52 , by a fiber optic  76 . LED  72  may be driven by a LED driver circuit  80 , which is incorporated within handle  44 , typically by being configured as part of handle board  60 . Driver circuit  80  provides pulse width modulated (PWM) driving current to LED  72  according to a digital value V CON  received, typically as a communication signal, by the circuit, and the manner of operation of the driver circuit is described below. Alternatively, LED  72  may be driven with DC current by a DC current source block  92  in CCU module  14 . DC current source  92  is also described below. 
       FIG. 3  is a schematic graph of luminous flux emitted by LED  72  vs. current driving the LED, according to an embodiment of the present invention. The flux φ is measured in lumens, and the current I is continuous direct (DC) current measured in mA. The graph illustrates that as the current increases, the flux emitted by LED  72  also increases. Since the DC current is continuous, the flux emitted by the LED is also continuous. The graph also illustrates that there is a minimum DC current I MIN , at which the flux emitted by the LED is a minimum flux φ MIN . Typically, a specification for the LED does not include operating currents below I MIN , since for such currents the quality of the flux emitted by the LED is uncertain. Consequently, for stable operation within its specification, the LED is not operated at currents below I MIN , so that the graph has a first termination at this current. The graph has a second termination at a maximum current I MAX  at which the LED is able to operate. At the maximum current, LED  72  emits a maximum flux φ MAX . 
     In order for LED  72  to emit an average luminous flux less than φ MIN , embodiments of the present invention pulse the LED intermittently between an on-state and an off-state, using pulse-width-modulation (PWM). In the on-state the LED is driven with a DC current I MIN  or higher; in the off-state there is no driving current for the LED. 
     For LED  72  to emit flux at levels above and below the minimum flux level φ MIN  the LED is configured to operate in one of two states: 
     In a continuous operating state the LED receives a continuous DC current, with a value greater than or equal to I MIN . 
     In a PWM operating state the LED receives a pulsed DC current, with a duty cycle that may be varied, but so that in the on-state of the LED the current supplied to the LED is greater than or equal to I MIN . 
     The two different operating states of LED  72  are described in more detail below. 
     In the continuous operating state of the LED, the flux emitted by LED  72  is according to the continuous DC current driving the LED. In this state the current driving the LED is greater than or equal to I MIN , and in response the flux emitted by the LED is continuous and is greater than or equal to φ MIN . 
     In the PWM operating state of the LED, the flux emitted by LED  72  depends on the duty cycle of the pulsed DC current driving the LED, and is also dependent on the level of the pulsed DC current in the duty cycle on-state. (As stated above, the level of the DC current in the on-state is greater than or equal to I MIN .) For example, if the current in the on-state is equal to I MIN , then the flux emitted from the LED can be varied between 0 lumens, for a duty cycle of 0, and φ MIN  lumens, for a duty cycle of 100%. 
     Returning to  FIG. 2 , CCU module  14  comprises a local controller  84 , CCU circuitry  88 , and a DC current source block  92 . Circuitry  88  includes an image processing section which receives the pre-processed image signals from board  60 , and in response generates final image signals of an image to be displayed on screen  26 . Typically, CCU  14  receives image data from an image pre-processing section of board  60 , and uses the data, in an automatic light control (ALC) system, to drive LED so that images presented on screen  26  are within an acceptable dynamic range of brightness, i.e., have neither completely saturated nor completely unsaturated portions. Circuitry  88 , under control of local controller  84 , implements the ALC system to adjust the received pre-processed signals, whose effective brightness is a function of the illumination flux transmitted by the LED into cavity  12 , and to achieve final image signals having the brightness set by operator  24 . Typically, circuitry  88  is implemented as a field programmable gate array (FPGA). 
     The effective brightness of the pre-processed signals is a function of the flux emitted by the LED, and in turn the flux is a function of the mean DC current supplied to the LED. Controller  84  is coupled to circuitry  88 , and uses the coupling to decide on a mean target luminous flux, φ T , to be emitted by the LED. From the mean target luminous flux the controller calculates a desired mean DC current to be supplied to the LED. If the desired mean DC current is below I MIN , the controller transmits a digital control signal V CON , corresponding to the desired mean target luminous flux and the desired mean DC current, to driver  80  via a conductor  82  in cable  50 . In the description herein, control signal V CON  is assumed, by way of example and for simplicity, to be positive. 
       FIG. 4  is a schematic graph of mean DC current, I MEAN , drawn by LED  72  vs. mean target flux φ T  of the LED, according to an embodiment of the present invention. The graph illustrates two regions of operation of LED  72 : 
     A PWM region, defined by the range of values of the mean target flux φ T  given by expression (1):
 
0≦φ T &lt;φ MIN   (1)
 
     In the PWM region LED  72  operates in a pulsed flux transmitting state, by driver  80  operating in the PWM operating state referred to above. In this state the driver supplies pulsed DC, also termed PWM, current to the LED. The duty cycle of the pulses supplied in the PWM state typically varies between 0 and 100%. The DC current in the on-state of the duty cycle is typically I MIN , although the DC current in the on-state may be higher than I MIN . For simplicity, in the following description the DC current drawn by the LED in its on-state is assumed to be I MIN . (Those having ordinary skill in the art will be able to adapt the description, mutatis mutandis, for cases where the DC current in the on-state of the PWM duty cycle is higher than I MIN , in which case the maximum duty cycle value may be less than 100%.) The mean DC current of the LED in the PWM operating state of its driver is in the range given by expression (2):
 
0≦I&lt;I MIN   (2)
 
     It will be understood from the above that in the PWM region, corresponding to the operating state of driver  80 , the flux is pulsed, and the value of the mean flux φ T  is dependent on the duty cycle of the pulses supplied by the driver. 
     A continuous region of operation of LED  72  is defined by the range of values of the mean target flux φ T  given by expression (3):
 
φ MIN ≦φ T ≦φ MAX   (3)
 
     In the continuous region LED  72  operates in a continuous transmitting state, where current source  92  supplies a constant DC current to the LED. The supplied DC current is given by expression (4):
 
I MIN ≦I≦I MAX   (4)
 
     From consideration of the above expressions and of the description associated with the expressions, it will be understood that the minimum flux level φ MIN  acts as a bounding value: for a mean target flux φ T  below φ MIN  LED  72  operates in a PWM state; above φ MIN  the LED operates in a continuous state. 
     Returning to  FIG. 2 , controller  84  uses circuitry  88  to assess a current demand for LED  72 . If the demand is within the range given by equation (4), then circuitry  88  outputs a signal V ADJ , having a value dependent on the current demand, to DC current source  92 . On receipt of V ADJ , source  92  generates an appropriate current, I DC , which is supplied directly to LED  72 . 
     If the current demand for LED  72  is within the range given by equation (2), then instead of LED  72  being driven by source  92 , the LED is driven, in a PWM mode, by driver  80 . In this case, controller  84  outputs a signal V CON , having a value dependent on the mean current demand of the LED, to driver  80 , and the driver supplies an appropriate PWM current to the LED. 
     In an alternative embodiment, driver  80  is implemented as a variable current load. While the current demand for LED  72  is in the range given by equation (4), then driver  80  is configured as a zero load, and I DC  is supplied to the LED. If the current demand for the LED is in the range given by equation (2), then driver  80  is configured to vary its load characteristics in a switching manner, so as to generate the appropriate PWM current and to supply this PWM current to the LED. 
     In all cases no PWM current is conveyed through cable  50 . Rather, for the purpose of driving LED driver  80 , only DC current is conveyed through the cable. 
     As is described above, cable  50  comprises conductors  64 ,  96 , and  82  which respectively transfer digital image signals, DC current, and a digital control value. The pulse-width-modulated current used by LED  72  is produced by LED driver  80 . By locating driver  80  in handle  44  there is no need for any pulse-width-modulated current to be transferred via cable  50 . Thus, unlike prior art systems wherein pulse-width-modulated current for powering an LED is transferred in the same cable as digital image signals, causing interference with the image signals, in embodiments of the present invention no pulse-width-modulated current is transferred in cable  50 . Rather, the power needed for the pulse-width-modulation of LED  72  is transferred within cable  50  as DC current, completely eliminating any interference that would be caused if pulse-width-modulated current were transferred in cable  50 . 
     Furthermore, by placing only driver  80  in handle  44 , and generating the DC current, used when the LED is not in a PWM state, in CCU  14 , embodiments of the present invention reduce the size of the handle compared to endoscope systems that have the DC source and driver  80  in the handle. 
     It will be appreciated that the embodiments described above are cited by way of example, and that the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described hereinabove, as well as variations and modifications thereof which would occur to persons skilled in the art upon reading the foregoing description and which are not disclosed in the prior art.