Abstract:
The present invention is directed to a system and method for measuring the dilatation and effacement of the uterine cervix in a manner that is non-invasive to the cervix. The system having a probe and a monitoring unit serve to measure the cervix dimensions during routine clinical visits and is also suitable for personal checkup at home. The probe primarily includes a camera for imaging the cervix and a set of circles of different diameters imprinted on the imaging window of the probe. The probe is inserted into the vagina until its imaging window abuts the cervix. The system captures and displays images of the cervix opening superimposed with the set of concentric circles, which allows the user to perform a visual comparison and determine the diameter of the opening. The probe may also include an ultrasonic transducer operating in pulse-echo mode to measure the thickness of the cervix and determine its effacement.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/621,726, filed Oct. 25, 2004, entitled Cervix Monitor, the entire contents of which application are incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to a method and system for measuring the dimensions of the uterine cervix, in particular, the size of the opening of the cervix and the thickness of the cervix.  
       BACKGROUND OF THE INVENTION  
       [0003]     Measuring the cervix dimensions, in particular the diameter of the opening of the cervix and the thickness of the cervix is desirable during pregnancy, in particular the late stages of pregnancy, because the dimensions of cervix can be an indicator of the woman&#39;s susceptibility to preterm labor (or premature labor, used interchangeably herein). In current clinical practice, the diameter of the opening of the cervix (or cervical diameter, used interchangeably herein) and the thickness of the cervix (or cervical effacement, used interchangeably herein) is performed manually by inserting a gloved hand into the vagina and then using the fingers to probe the diameter and depth of the opening of the cervix. This method is known as digital probing and suffers several inherent limitations, including the following. First, the method is approximate as the accuracy of the measurement depends on the experience of the health care provider. Second, the method can cause discomfort to the patient during each session of digital probing which may be performed repeatedly. Third, hand examinations can increase the risk of infection to the to the mother and the fetus despite the use of gloves. Fourth, the method is known to induce labor and therefore should be avoided especially in women susceptible to preterm labor or suffering from an incompetent cervix.  
         [0004]     There have been many attempts to develop devices for accurate and user-independent measurement of the cervical diameter and effacement. However, previous techniques failed to gain wide clinical acceptance due to several limitations, including the complexity of use, inaccuracy of measurements, tissue trauma caused by the devices or their components, including the manner by which the components are attached to the cervix, costly sterilization between uses, and/or patient discomfort.  
         [0005]     Consequently, the manual method of digital probing continues to be a favored method of monitoring cervical diameter and effacement. Therefore, there exists a desire for a system and method to measure the cervical diameter and effacement in a manner that is noninvasive to the cervix and preferably that is minimally invasive to the patient.  
       SUMMARY OF THE INVENTION  
       [0006]     The present invention is directed to a system and method for measuring the dilatation and effacement of the uterine cervix in a manner that is non-invasive to the cervix.  
         [0007]     The system having a probe and a monitoring unit serve to measure the cervix dimensions during routine clinical visits and is also suitable for personal checkup at home. The probe primarily includes a camera for imaging the cervix, a lens to provide an optimal field of view for the camera at close range to the cervix, a light source to illuminate the cervix, and a set of circles corresponding to different diameters imprinted on the imaging window of the probe. Advantageously, the probe is configured to provide a predetermined distance from which the camera has an appropriate range to image the cervix opening. The probe is inserted into the vagina until the imaging window of the probe abuts the cervix. The system captures and displays images of the cervix opening superimposed with the set of concentric circles, which allows the user to perform a size comparison between the opening and the circles and determine the diameter of the opening. The probe may also include an ultrasonic transducer operating in pulse-echo mode to measure the thickness of the cervix and determine its effacement. The images provided by the camera facilitate the positioning of the ultrasound transducer on the lip of cervix in a minimally invasive manner.  
         [0008]     A handle portion of the probe facilitates the insertion and removal of the probe from the vagina and protects electrical connections between the probe and the monitoring unit. The handle portion is generally rigid or preferably semi flexible but is adapted to have sufficient rigidity to facilitate the insertion of the probe into the vagina.  
     
    
     DETAILED DESCRIPTION  
       [0009]     Referring to  FIG. 1 , the present invention includes a system  100  for measuring the diameter of the opening  102  of the cervix  104  in a manner that is non-invasive to the cervix. The system includes a probe  106  that is inserted into a vagina  108  of the patient  110  to gather data relating to the cervix  104 , in particular, the diameter of the opening  102 , and a monitoring unit  112  that is in communication with the probe  106  and receives image data from the probe  106  which is displayed to a health care provider located proximately to the patient. Accordingly, the patient need not have her cervix digitally probed.  
         [0010]     Referring to  FIGS. 1 and 2 , a preferred embodiment of the cervix probe  106  includes generally a distal probe head  114  and a proximal probe handle  116  extending proximally from the probe head. The probe head  114  includes a housing  118  encapsulating a lens  120  and a camera  122  that is proximal of the lens and adapted to capture image data of objects within a predetermined field of view  124  of the lens. The housing  118  also contains at least one light source  126  positioned to illuminate the field of view  124  of the lens inside the vagina. The lens  120 , the camera  122  and the light source  126  are fixedly mounted within the housing  118 . 
     
    
       [0011]     The housing  118  may be generally cylindrical in shape along a longitudinal axis  138  with preferably a streamlined distal end  140  to facilitate insertion into the vagina  108 . The housing has a length in the range of about 4 cm to 7 cm, and more preferably about 5 cm. The housing has a diameter of about 3 cm. The housing  118  may preferably be made of an optically transparent plastic material such as, for example, polycarbonate or acrylic; however, other materials such as Pyrex may be used. The housing  118  may be hermetic to protect its internal components from contamination by the outside environment. The housing  118  may also be coated or made of a hydrophobic (i.e. water repellent) material to prevent fluids, if any, from adhering to its exposed surfaces.  
         [0012]     The camera  122  is of the miniature type with a size ranging between about 16×16×8 mm and 6×6×3 mm and more preferably 8×8×4 mm. The lens  120  may be a wide angle lens, its field of view (FOV)  124  ranging between about 120 to 190 degrees and more preferably about 170 to 180 degrees to enable imaging of the cervix  104  from a relatively close range. In that regard, the range is generally provided by a predetermined distance or separation  130  between the lens  120  and the distal end  140  of the housing  118  which is also generally the distance between the lens  120  and the cervix  104 , since the probe  106 , as described below in further detail, is inserted into the vagina with the distal end  140  generally abutting the cervix  104  or the cervix opening  102 . Accordingly, the camera  122  and the lens  120  are selectively and fixedly situated within the housing  118  at the distance  130  from the distal end  140  of the housing  118 . In particular, the distance  130  is selected to provide enough range to allow the field of view  124  of the lens  122  to capture a dilated cervix opening (at about 4 cm or so) when the distal end  140  is abutting, or is proximate to, the cervix  104  or the opening  102 . The distance  130  may range between about 1 cm to 2.5 cm, and more preferably about 2 cm. The camera  122  may be of any type, including color, grayscale, CCD, CMOS, analog, digital, multispectral, or thermal. Optical filters may also be used to remove certain wavelength bands to enhance the image and/or clarify features of interest such as the opening  102  of the cervix  104 .  
         [0013]     One or more light sources  126  are disposed around the camera  122  to provide the proper illumination necessary for imaging without saturating the camera  122  by, for example, internal reflection. The light sources  126  may be light emitting diodes (LEDs) of the miniature surface mount type (SMD), bulbs, or optical fibers. The optical fibers, if used, may have a tip that is polished at an angle to provide side emission. The light sources  126  may emit white or monochromatic light at certain wavelengths, including infrared, to provide better viewing of different tissues/materials, glare reduction and/or improved imaging. The light sources  126  may be aimed at different angles and may be illuminated simultaneously, individually and/or in groups to improve imaging and/or image quality and avoid saturation of the camera  122 .  
         [0014]     The probe handle  116  is rigid or preferably semi flexible to enable the insertion of the probe into the vagina  108 . The outer diameter of the handle  116  is no greater and preferably smaller than the diameter of the housing  118  as shown in  FIGS. 1 and 2 . The handle  116  is preferably long enough to allow it to exit the vagina  108  when the distal end  140  of the housing  118  is abutting the cervix  104 . A suitable length ranges about 14 cm to 25 cm and more preferably about 16 cm to 20 cm. The probe handle  116  may be continuous with the probe head  114  and made of the same material such as polycarbonate or acrylic plastic. Alternatively, the handle  116  may be made of a semi flexible material such as silicone, Tygon or any other semi flexible rubber. The probe handle  116  and may be hollow to accommodate a battery pack (not shown) and allow the passage of the cable  134  that includes the electrical wires to and from the camera  122 . The probe handle  116  may be configured with an aperture to enable the cable  134  to exit at or near the proximal end of the handle and extend to the monitoring unit  112 . It is understood by one of ordinary skill in the art that the electrical connection between the probe  106  and the monitoring unit  112  by which image data and/or control signals are sent and received need not be accomplished by wires but that it can be wireless as well, or a combination of the two.  
         [0015]     The distal end  140  of the housing  118  has a set of concentric circles  144  having different diameters imprinted on the transparent housing  118  as shown in  FIGS. 3A and 3B . Each circle is tagged with a number that indicates the diameter that it represents when imaged by the camera  122 . For example the diameter of the innermost circle may correspond to 1-cm, the next circle may correspond to 2-cm, and so forth. The camera  122  is configured to image the set of concentric circles  144  superimposed over the image of the cervix  104  that abuts the distal end  140  when the probe  106  is properly applied. The actual diameter of each circle may be adjusted to compensate for the variable radial magnification of the wide-angle lens  120  and/or the optical distortion caused by the curvature of the distal end  140 . Accordingly, the actual diameter of each circle may be different from the physical diameter that it represents. The circles may be continuous, dashed or dotted, and may be color-coded to facilitate their visual identification. The set of concentric circles  144  may be printed with a fluorescent or a semi-reflective material that would glow when illuminated by the light source  126  and appear to the camera  122  as haloes to improve their visibility.  
         [0016]     Alternatively, the set of concentric circles  146  may be off-centered from the longitudinal axis  138  of the probe head  114  as shown in  FIG. 3C  to accommodate for the angulation of the cervix  104  relative to the vagina  108 . This off-centricity may improve the overlap of the circles  146  with the opening  103  of the cervix and therefore simplify the visual comparison to identify the circle that best matches the size of the opening  102 .  
         [0017]     Alternatively, a graduated crosshairs  142  may be imprinted on the transparent housing  118  as shown in  FIG. 3D .  
         [0018]     Yet alternatively, the set of concentric circles may be electronically generated and superimposed on the image of the camera  122 . The user may select to turn off the electronically generated circles when positioning the probe next to the cervix and turn them on when ready to take the measurements.  
         [0019]     The monitoring unit  112  has a screen  113  that displays the image  115  of the opening  102  superimposed with images  117  of the circles  144  (or the off-centered circles  146 , or the graduated crosshairs  142 ). For this probe embodiment, the monitoring unit  112  may be a video monitor, a TV, or a computer.  
         [0020]     In a typical probe application procedure, the probe  106  is inserted into the vagina  108  until the distal end  140  of the housing  118  touches the cervix  104 . This may be done under live video guidance from the camera  122  or by determining that further insertion of the probe is blocked by the cervix  104 . The camera  122  images the cervix  104  with the superimposed set of concentric circles  144  (or the off-centered circles  146 , or the graduated crosshairs  142 ) and transmits the images to the monitoring unit  112 . The orientation of the probe  106  may be adjusted such that the circles  144  (or the off-centered circles  146 , or the graduated crosshairs  142 ) coincide with the cervix opening  102 . The diameter of the cervix opening  102  may be determined by identifying the circle that best matches the size of opening  102 .  
         [0021]     It is understood by one of ordinary skill in the art that the electrical connection between the probe  106  and the monitoring unit  112  by which image data and/or control signals are sent and received need not be accomplished by wires but that it can be wireless as well, or a combination of the two. The cervix probe  106  may include a wireless transmitter (not shown) that can transmit real-time images of the cervix directly to a local TV tuned to a predetermined channel, or to a dedicated video receiver that is connected to a TV or a video monitor.  
         [0022]     In an alternative embodiment, the probe may include a processor (not shown) to superimpose an electronically generated dynamic circle (not shown) over the images of the cervix  104  captured by the camera  120 . The diameter and the position of the dynamic circle may be varied using control buttons  119  located on the handle  116  to achieve a visual overlap and size match with the underlying image  115  of the opening  102 . A numerical indicator (not shown) on the screen  113  may be used to indicate the actual physical diameter corresponding to the dynamic circle. The effective diameter of the dynamic circle may vary depending on its location within the field of view  124  of the wide-angle lens  120  and proper calibration should be applied.  
         [0023]     Another embodiment of the system  100  shown in  FIG. 4  includes an ultrasound transducer  150  to measure the thickness  105  of the cervix  104 . Other than the addition of the ultrasound transducer  150 , the probe  206  is similar to the probe  106  in all components, functions and applications.  
         [0024]     The ultrasound transducer  150  is positioned in the probe head  114 , and preferably positioned in the distal end  140 , to contact the cervix  104  when the probe  206  is fully inserted into the vagina  108 . The transducer  150  lies within the field of view  124  of the lens  120  and appears as a small spot  158  on the image of the cervix  104  captured by the camera  122  and displayed on the screen  213  of the monitoring unit  212 . Live video images from the camera  122  may be used to orient the probe  206  and position the small spot  158  representing the transducer  150  on the rim (or lip) of the cervix  104 . The back of the ultrasound transducer  150  may be coated with a fluorescent or a semi-reflective material to enhance its visualization within the field of view  124 . The ultrasound transducer  150  may be a circular piezoelectric element with a diameter between 1 to 5 mm, and more preferably between 2 to 3 mm. The transducer is driven using a micro-coaxial cable (e.g. AWG-40) to maximize visibility around the transducer  150 .  
         [0025]     The ultrasound transducer  150  may be operated in A-mode (Amplitude mode) in a similar fashion to common corneal pachemetry. In a typical A-mode operation, the ultrasound transducer  150  transmits ultrasound pulses into the cervix  104  and receives echoes returned from the acoustical interfaces along the travel path  152 . A first major echo  160  may be received from the transducer/cervix interface  154  and a second major echo  162  may be received from the cervix/uterus acoustical interface  156 . The arrival time of the first echo  160  and the second echo  162  may be converted to a distance scale  164  using the known velocity of sound in the tissue (about 1500 m/s) and displayed on the screen  213  of the monitoring unit  212 . The distance difference between the first echo  160  and the second echo  162  represents the thickness  105  of the cervix  104  and may be read directly from the distance scale  164 .  
         [0026]     A block diagram showing the main components of the monitoring unit  212  controlling the probe  206  is shown in  FIG. 5 . The monitoring unit  212  includes a processor  260 , a display  213 , an ultrasonic pulser/receiver  262 , an analog to digital converter  264 , a video digitizer  266 , and an illumination driver  268 . In a typical operation, the processor  260  triggers the ultrasonic pulser/receiver  262  to pulse the transducer  150  within the probe head  114  to transmit an ultrasonic pulse into the cervix  104  as shown in  FIG. 4 . The ultrasound echoes returned from the cervix  104  are amplified by the ultrasonic pulser/receiver  262  and digitized by the analog to digital converter  264 . The processor  260  processes the digitized echoes to determine the time between the first echo  160  and the second echo  162  and convert the time scale to a distance scale  164  using the known velocity of sound in tissue (about 1500 m/s). The processor  260  determines the thickness  105  of the cervix  104  by calculating the distance difference between the first echo  160  and the second echo  162 . The echoes  160  and  162  may also be displayed along a distance scale  164  on the screen  213 .  
         [0027]     Simultaneously, the illumination driver  268  powers up the light sources  126  to illuminate the field of view  124  and enable imaging of the cervix  104  by the camera  122 . The images acquired by the camera  122  are digitized by the video digitizer  266  and processed by the processor  260  to correct for the spatial distortions caused by the wide-angle lens and/or the curvature of the distal end  140 .  
         [0028]     The captured image of the cervix may be preprocessed to correct for any spatial distortion caused by the wide-angle lens  120  of the camera  122 . The wide-angle lens  120  (i.e. fisheye) may be used to enable the imaging of the cervix  104  from a relatively close distance of approx. 2 cm. Wide-angle lenses can introduce an image distortion known as the barrel distortion, which is caused by the uneven magnification between the edges and the center of the lens. Barrel distortion is a type of radial distortion in which horizontal and vertical lines appear to be bent outwards toward the edges of the image. Algorithms to correct barrel distortion in images are readily available in the literature, e.g., Mundhenk, T. N., et al., “Techniques for fisheye lens calibration using a minimal number of measurements,” Proceedings of the SPIE, SPIE-Int. Soc. Opt. Eng., 4197, pp. 181-90, 2000, and e.g. James P. Helferty, et al., “Videoendoscopic Distortion Correction and Its Application to Virtual Guidance of Endoscopy,” IEEE Transactions on Medical Imaging, Vol. 20, No. 7, pp 605-617, 2001. These algorithms may be applied to the images captured by the video digitizer (not shown) to minimize or remove barrel distortion. In addition, algorithms for the correction of perspective distortion (e.g. Waltz, F. M., “Implementation of real-time perspective correction,” Proceedings of the SPIE—SPIE-Int. Soc. Opt. Eng. 849, pp. 179-83, 1988) may be also applied to correct for distortions caused by the non-perpendicular imaging of the cervix (i.e. when the probe is at a tilted viewing angle of the cervix). The distortion-corrected images may be color balanced and filtered using, for example, a median filter to improve image quality.  
         [0029]     As shown in  FIG. 4 , the screen  213  displays an image  115  of the cervix opening  102  superimposed with the images  117  of the set of concentric circles  144  for a size match to determine the diameter of the opening  102 . Simultaneously, the screen  213  displays the echoes  160  and  162  on the distance scale  164  to indicate the thickness  105  of the cervix  104 .  
         [0030]     Alternatively, The processor  260  may also generate a dynamic circle (not shown) that can be used to determine the diameter of the opening  102  of the cervix  104  as described in the above embodiments.  
         [0031]     Although the above detailed description describes and illustrates various preferred embodiments, the invention is not so limited. Many modifications and variations will now occur to persons skilled in the art. As such, the preceding description has been presented with reference to presently preferred embodiments of the invention. Workers skilled in the art and technology to which this invention pertains will appreciate that alterations and changes in the described structure may be practiced without meaningfully departing from the principal, spirit and scope of this invention.  
         [0032]     Accordingly, the foregoing description should not be read as pertaining only to the precise structures described and illustrated in the accompanying drawings, but rather should be read consistent with and as support to the following claims, which are to have their fullest and fair scope.