Abstract:
Methods and apparatus are provided for measuring movement of an elongated instrument. The apparatus including a guide adapted to receive the elongated instrument and a sensor module that includes an optical image sensor or an optical rotary encoder to sense the received elongated instrument moving within the guide.

Description:
RELATED APPLICATION(S)  
       [0001]     This application claims the benefit of U.S. Provisional Application No. 60/784,705, filed on Mar. 22, 2006. The entire teachings of the above application are incorporated herein by reference. 
     
    
     FIELD OF INVENTION  
       [0002]     The present invention relates generally to methods and apparatus for measuring the axial or rotational movement of an elongate instrument for use during a medical procedure.  
       BACKGROUND  
       [0003]     Catheters, esophageal probes, endoscopes, laparoscopes and other medical instruments are frequently introduced into body lumens for a variety of purposes, including imaging and interventional therapy. For many such procedures, it is necessary to accurately monitor the position of the instrument, particularly the distal end of the instrument which is remote from the entry point. For example, it is frequently necessary to know the precise location of the distal tip of an instrument in order to perform a subsequent interventional procedure, to facilitate interchange of instruments, and to track the precise location of an instrument during the course of a single procedure.  
         [0004]     The penetration depth of elongate medical instruments has usually been monitored visually by the physician observing scale markings which have been placed on the side of the instrument. That is, the physician simply looks at the instrument at the point of entry and reads the approximate penetration depth from the scale. While this approach has the advantage of simplicity, it can suffer from limitations that restrict its effectiveness in modern medical procedures.  
         [0005]     For example, the accuracy of penetration which can be determined is limited by the lack of a fixed location against which to read the scale. The accuracy is further limited by the relatively broad spacing between scale markings which are required to permit visual reading. The visual reading of the scale further requires that the physician turn away from other areas where attention should be directed. Each reading which is obtained requires additional time to be recorded and becomes obsolete as soon as the device is moved in any fashion.  
       SUMMARY  
       [0006]     According to one aspect of the invention, an apparatus is featured for measuring movement of an elongated instrument.  
         [0007]     According to a first embodiment, the apparatus includes a guide adapted to receive the elongated instrument; a rotatable element positioned to cooperate with the guide and configured to rotate in response to axial movement of the elongated instrument within the guide; and a sensor module that includes an optical image sensor arranged in relation to the guide. The optical image sensor (a) captures images of the rotatable element as the rotatable element rotates in response to movement of the elongated instrument within the guide, (b) tracks microscopic surface features of the rotatable element across a set of the captured images, and (c) generates an indication of movement of the instrument based on the tracked microscopic surface features.  
         [0008]     The apparatus can further include a counter that determines displacement of the instrument based on the indication of movement generated by the sensor module and a scaler that converts the displacement to an indication of movement in standard units. The apparatus can further include a housing comprising a disposable component and a fixed component. The disposable component includes the guide and the rotatable element, and the fixed component including the sensor module. The guide of the apparatus can further include an adjustable guide ceiling adapted to urge the elongated instrument against the rotatable element as the instrument moves within the guide. The adjustable guide ceiling can be adapted to rise or fall to accommodate instruments of varying dimensions.  
         [0009]     According to a second embodiment, the apparatus for measuring movement of an elongated instrument, includes a guide adapted to receive the elongated instrument and a sensor module that includes an optical image sensor arranged in relation to the guide. The optical image sensor (a) captures images of the elongated instrument within the guide, (b) tracks microscopic surface features of the instrument across a set of the captured images, and (c) generates an indication of movement of the instrument based on the tracked microscopic surface features.  
         [0010]     The apparatus can further include a counter that determines displacement of the instrument based on the indication of movement generated by the sensor module and a scaler that converts the displacement to an indication of movement in standard units. The apparatus can further include a housing comprising a disposable component and a fixed component. The disposable component includes the guide, and the fixed component includes the sensor module. The apparatus can further include an adjustable guide ceiling adapted to urge against the elongated instrument as the instrument moves within the guide. The adjustable guide ceiling can be adapted to rise or fall to accommodate instruments of varying dimensions.  
         [0011]     According to a third embodiment, the apparatus for measuring movement of an elongated instrument includes a guide adapted to receive an elongated instrument; a rotatable element positioned to cooperate with the guide and configured to rotate in response to a received elongated instrument moving within the guide; and a sensor module that includes an optical rotary encoder arranged to be rotatably connected to the rotatable element. The optical rotary encoder generates an indication of movement of the instrument based on sensed rotation of the rotatable element in response to the movement of the elongated instrument within the guide.  
         [0012]     The apparatus can further include a counter that determines displacement of the instrument based on the indication of movement generated by the sensor module and a scaler that converts the displacement to an indication of movement in standard units. The apparatus can further include a housing comprising a disposable component and a fixed component. The disposable component includes the guide and the rotatable element, and the fixed component includes the sensor module. The guide of the apparatus can further include an adjustable guide ceiling adapted to urge the elongated instrument against the rotatable element as the instrument moves within the guide. The adjustable guide ceiling can be adapted to rise or fall to accommodate instruments of varying dimensions.  
         [0013]     According to another embodiment, the apparatus for measuring movement of an elongated instrument, includes a housing with a disposable component and a fixed component. The disposable component includes a guide adapted to receive an elongated instrument, and the fixed component includes a sensor module adapted to sense the received elongated instrument moving within the guide and to generate an indication of movement of the instrument.  
         [0014]     According to another aspect of the invention, a method is featured for measuring movement of an elongated instrument within a guide.  
         [0015]     According to a first embodiment, the method for measuring movement of an elongated instrument within a guide involves a rotable element being positioned to cooperate with the guide such that it rotates in response to the axial movement of the elongated instrument within the guide. The method includes the steps of capturing images of the rotatable element as the rotatable element rotates in response to movement of the elongated instrument within the guide; tracking microscopic surface features of the rotatable element across a set of the captured images; and generating an indication of movement of the instrument based on the tracked microscopic surface features.  
         [0016]     According to a second embodiment, the method for measuring movement of an elongated instrument within a guide includes the steps of capturing images of the elongated instrument within the guide; tracking microscopic surface features of the elongated instrument across a set of the captured images; and generating an indication of movement of the instrument based on the tracked microscopic surface features.  
         [0017]     According to a third embodiment, the method for measuring movement of an elongated instrument within a guide involves a rotatable element being positioned to cooperate with the guide, such that the rotatable element rotates in response to the axial movement of the elongated instrument within the guide. The method includes the steps of generating an indication of movement based on sensed rotation of the rotatable element in response to movement of the elongated instrument within the guide.  
         [0018]     According to another aspect, the invention features an apparatus for measuring movement of an elongated instrument. The apparatus includes a first component including a sensor module and a second component being removably attached to the first component. The second component includes a guide adapted to receive the elongated instrument. The sensor module of the first component is arranged in relation to the guide in the second component so that the sensor module is capable of detecting movement of the elongated instrument within the guide. The second component of apparatus can be disposable, such that it can be replaced with a third component that is capable of being removably attached to the first component and includes another guide adapted to receive the elongated instrument. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0019]      FIG. 1A  is a diagram illustrating an example of a measuring device for use during medical procedures.  
         [0020]      FIG. 1B  is a diagram of an endoscope to which embodiments of the measuring device can be applied.  
         [0021]      FIG. 2  is a diagram illustrating functional components of a measuring device.  
         [0022]      FIG. 3  is an exploded view of a first embodiment of the measuring device.  
         [0023]      FIGS. 4A through 4E  are diagrams illustrating a channel base according to the first embodiment of the measuring device.  
         [0024]      FIGS. 5A and 5B  are diagrams illustrating the sensor module according to the first embodiment of the measuring device.  
         [0025]      FIG. 6  is a diagram illustrating the channel base according to a second embodiment of the measuring device.  
         [0026]      FIG. 7  is a diagram illustrating a third embodiment of the measuring device that includes an optical rotary encoder.  
         [0027]      FIG. 8  is a timing diagram illustrating the output of a particular optical rotary encoder according to the third embodiment of the measuring device.  
         [0028]      FIG. 9  is a diagram illustrating an optional adjustable guide ceiling for use in any embodiment of the measuring device.  
         [0029]      FIG. 10  is a diagram illustrating an optional disposable component for use in any embodiment of the measuring device. 
     
    
     DETAILED DESCRIPTION  
       [0030]      FIG. 1A  is a diagram illustrating an example of a measuring device for use during medical procedures. The measuring device  10  includes a housing  12 , display  14 , function switches  16   a ,  16   b , and  16   c  (collectively  16 ). A channel inlet  18   a  and channel outlet  18   b  are positioned on opposing sides of the housing  12 . In operation, an elongated instrument (not shown) enters the housing through the channel inlet  18   a  and exits the housing  12  through the channel outlet  18   b . The device  10  can be used to measure axial movements of an instrument as it is advanced or withdrawn; rotational movement of an instrument as the instrument is rotated clockwise or counter clockwise; or combinations of both axial and rotational movement of an elongated instrument.  
         [0031]     The measuring device can include function switches  16  corresponding to the functions of unit conversion  16   a , hold  16   b , and reset  16   c . With the unit conversion function switch  16   a , an operator can change the units of the displayed measurements. For example, the measuring device  10  can convert between centimeters (cm) and millimeters (mm). Similarly, the device  10  can convert between degrees and radians. Other unit conversions are also possible. The hold function switch  16   b  enables an operator of the device to temporarily stabilize the displayed measurement, enabling the operator to properly record the measurement, for example. The reset function switch  16   c  enables the operator to zero the displayed measurement and thus reset the set point from which the measurements are made.  
         [0032]      FIG. 1B  is a diagram of an endoscope to which embodiments of the measuring device can be applied. Although the measuring device can be utilized with an endoscope, the measuring device can be utilized in other applications in which measurements of axial or rotational movement of an elongated instrument within any type of duct are desired. Likewise, the structural configuration of the measuring device can be modified to accommodate various applications. For example, the measuring device can be integrated or otherwise embedded into an endoscope itself or other similar scope. The measuring device can be fixed to a stationary platform such as a table. Other arrangements of the measuring device in relation to the lumen or other duct being measured can also be employed.  
         [0033]     As illustrated in  FIG. 1B , the endoscope  20  includes an opening  22  into a working channel through which an elongated instrument  30  can pass. The measuring device  10  can be detachably coupled to the endoscope by inserting and locking the channel outlet  18   b  of the device to the opening  22  of the working channel. For example, the channel outlet  18   b  can include a separate locking component (not shown) to lock the channel outlet into the working channel of an endoscope. Other locking mechanisms known to those skilled in the art for detachably coupling a device or instrument to the opening of a working channel can be implemented for detachably coupling the measuring device to the endoscope. The elongated instrument  30  enters into the channel inlet  1   8   a , through the device  10 , and out the channel outlet  18   b  into the working channel of the endoscope. As the instrument  30  is advanced, withdrawn, or rotated a corresponding axial or rotational measurement can be presented on the display  14 .  
         [0034]     In practice, the measuring device  10  is capable of determining penetration depth of an instrument or the dimensions of any tissue sample. For example, the measuring device  10  can be used to measure the distance between the distal end of the endoscope  20  to a targeted tissue sample (not shown). This can be performed by advancing the endoscopic instrument  30  through the device  10  into the working channel of the endoscope. Once the instrument  30  reaches the distal end of the endoscope  20 , the operator can zero the displayed measurement by depressing the Reset switch  16   c . From this reconfigured set point, the operator can continue advancing the instrument  30  until it reaches the targeted sample. The displayed measurement is the distance from the distal end of the endoscope  20  to the targeted sample.  
         [0035]     An operator of the measuring device  10  can also determine the dimensions of a targeted tissue sample, such as a polyp or stone for example. This sizing function can be performed by advancing the endoscopic instrument  30  until the targeted sample is reached, resetting the displayed measurement of the measuring device  10  by depressing the Reset switch  16   c , and advancing or withdrawing the instrument along the body of the tissue sample to obtain its length for display.  
         [0036]     In addition to displaying the real-time measurements through display  14  of the measuring device  10 , signals indicative of the real-time measurements can be coupled to a video monitor  40  for display. Such real-time measurement can overlay a corresponding video display of the distal end of the instrument  30  being operated within a field of interest.  
         [0037]      FIG. 2  is a diagram illustrating functional components of a measuring device. The functional components include a sensor module  11 , a counter and scaling module  13 , a display driver  15 , and a display  17 . The sensor module  11  detects movement of an instrument and provides one or more signals indicative of the amount and direction of the detected movement to the counter and scaling module  13 . The counter and scaling module  13  receives the one or more signals and generates an accumulated value, or count, representing the net displacement of the instrument. The counter and scaling module  13  scales this count to a measurement value in desired units based on predetermined ratios of counts to desired units. This measurement value is then transmitted to the display driver  15 , which causes the display  17  to present the measurement value, preferably in real time. The measurement values can also be output to an external peripheral, such as a monitor (not shown).  
         [0038]     The sensor module can be implemented in a number of different ways to measure, or otherwise determine, the axial or rotational movement of an instrument. According to a first embodiment, the sensor module includes an optical image sensor that detects movement of the instrument indirectly by analyzing a sequence of captured images of a rotatable element that is in contact with the elongated instrument. According to a second embodiment, the sensor module includes an optical image sensor that detects movement of an instrument directly by analyzing a sequence of captured images of the instrument itself as it passes in view of the image sensor. According to a third embodiment, the sensor module includes an optical rotary encoder that detects movement of the instrument indirectly by coupling the encoder to a rotatable element in contact with the instrument. A number of optional features can be applied to each of these embodiments for further enhancement as described more fully below.  
         [0039]      FIG. 3  is an exploded view of a first embodiment of the measuring device. In the illustrated embodiment, the housing of the measuring device  100  includes a sensor front cover  110  and a sensor back cover  115 . The front cover  110  further includes a set of membrane switches  116  that can be depressed to trigger predefined functionality, such as unit conversion, hold and reset. Both the front and back covers each define notches in the sidewalls  112   a ,  112   b  and  117   a ,  117   b , respectively, into which the channel inlet  120   a  and channel outlet  120   b  are fixed. The channel outlet  120   b  can further include a channel lock  122  that locks the channel outlet  120   b  into the working channel of an endoscope. For example, as the channel outlet  120   b  is inserted into the working channel, the channel lock  122  extends over and engages the opening of the working channel. Other locking mechanisms known to those skilled in the art for detachably coupling a device or instrument to the opening of a working channel can be implemented for detachably coupling the measuring device to the endoscope.  
         [0040]     As the elongated instrument is inserted into the housing via the channel inlet  120   a , a channel base  130  guides the instrument toward the channel outlet  120   b .  FIGS. 4A through 4E  are diagrams illustrating a channel base according to the first embodiment of the measuring device. In  FIGS. 4A and 4B , a guide  132  is formed on an outer surface of the channel base  130   a  including a pair of sidewalls  132   a ,  132   b  extending from the base. The surface of the base  130  within the guide  132  can also be contoured to provide for self-centering of the instrument as it passes through the guide. A depression  134  is formed in the channel base  130  extending at least between the sidewalls of the guide  132 .  
         [0041]     Referring to  FIG. 4C , a roller  140  is positioned within the depression  134  of the channel base. As shown, the roller  140  projects through at least one of the sidewalls  132   a ,  132   b  external to the guide. As an instrument enters the guide, the instrument is urged against the roller  140  by an adjustable guide ceiling  200 . Optionally, the instrument can be urged against the roller using a fixed ceiling, another rotatable element or other opposing element. As the instrument continues to be advanced or withdrawn, the roller  140  rotates in a clockwise or counter-clockwise direction depending on the movement of the instrument. The roller  140  can be replaced with a ball bearing, cylinder, or other rotatable element known to those skilled in the art, for example.  
         [0042]     Referring to  FIGS. 4D and 4E , a through hole  136  is defined in the channel base  130  such that the roller  140  is exposed to a processing module positioned adjacent the opposing side of the base  130   b.    
         [0043]     Referring back to  FIG. 3 , the processing module  150  includes a sensor module  160 , a counter and scaling module  170  and an LCD display  180 . The sensor module  160  is aligned adjacent to the surface  130   b  of the channel base. The sensor module  160  captures and processes images of the exposed surface of the roller  140  to determine the corresponding axial movement of the elongated instrument within the guide.  
         [0044]      FIGS. 5A and 5B  are diagrams illustrating the sensor module according to the first embodiment of the measuring device. The sensor module  160  includes an optical image sensor  162 , a light source  164 , a lens  166 , and a clip  168 . The sensor  162  is mounted on a printed circuit board (PCB)  152  above a through hole  154  defined in the board. The light source  164 , such as a Light Emitting Diode (LED), is also mounted on the board  152  and interlocked to the sensor  162  with the clip  168 . The lens  166  is aligned below the sensor  162  through the hole defined in the board  154 . The clip  168  also holds the LED  164  in relation to the lens  166 .  
         [0045]     As shown in  FIG. 5B , the sensor module  160  is aligned to the channel base  130  directly above the exposed surface of the roller. An alignment projection  138  extending from a surface of the base plate, as shown in  FIG. 4B , can assist in alignment of the channel base  130  through hole  154  to the sensor module  160 . Light from the LED  164  is reflected through the lens  166  via the openings in the board  152  and the channel base  130  to illuminate the exposed surface of the roller  140  below.  
         [0046]     The sensor  162  focused through the lens  166  detects movement of the roller  140  by capturing images of the roller  140  as it turns. From these captured images, the optical sensor  162  detects microscopic features on the surface of the roller  140  in the images and tracks their movement across a set of frames. The amount and direction of the tracked movement corresponds to movement of the instrument passing through the channel guide  132 . The sensor  162  encodes the amount and direction of the tracked movement and transmits the encoded data to the counter and scaling module.  
         [0047]     For improved detection of surface feature detection, the roller  140  is manufactured such that its outer surface or portion thereof is optically irregular. For example, the roller can be manufactured out of a material that is capable of providing an inherently optically irregular surface (e.g., ceramics). The roller can also be manufactured such that the material is processed so that its outer surface is textured or otherwise roughened to provide an optically irregular surface. The roller can also be manufactured such that the roller or portion thereof is covered with another textured or roughened materials to provide such an irregular surface (e.g., rubber made coarse through the application of sandpaper). Other ways of manufacturing a roller or other rotatable element with an irregular optical surface can be applied that are known to those skilled in the relevant arts.  
         [0048]     Examples of suitable components for this embodiment include the Agilent ADNS-2030 Low Power Optical Mouse Sensor for the optical sensor  162 ; the HDNS-2100 for the lens  166 ; the HDNS-220 for the clip  168 , and the HLMP-ED80-xx000 LED for the light source  164 ; all from Avago Technologies having co-headquarters in San Jose, Calif. and Singapore. For more information regarding these components of the sensor module, refer to data sheet entitled “Agilent ADNS-2030 Low Power Optical Mouse Sensor,” the entire contents of which are incorporated herein by reference.  
         [0049]     Referring back to  FIG. 3 , the sensor  162  interfaces to the counter and scaling module  170 . The sensor  162  transmits the amount and direction of the tracked movement to the counter and scaling module  170  through one or more pulsed signals. For example, the Agilent ADNS-2030 Low Power Optical Mouse Sensor encodes the amount and direction of movement in a form of quadrature output. The quadrature output includes two pulsed signals that, in combination, represent both the amount and direction of tracked movement. As the instrument is moved in a first direction, the pulsed signals cycle through a predetermined sequence of states (e.g., 00, 01, 11, 10). Each change in state corresponds to a count, and a number of counts can be defined per measurement (e.g., centimeters, millimeters, radians, degrees, inch, etc). Conversely, as the instrument is moved in the opposing direction, the sequence of states continue in reverse, thus enabling the counter and scaling module  170  to detect a change in direction and increment/decrement the accumulated number of pulse counts accordingly. The counter and scaling module  170  accumulates the pulse counts and converts them into a measurement using a predetermined ratio of counts to desired units. The resulting measurement is then transmitted for presentation through the LCD display  180 . The counter and scaling module  170  can be implemented, for example, using a suitably programmed or dedicated processor (e.g., a microprocessor or microcontroller), hardwired logic, Application Specific Integrated Circuit (ASIC), and a Programmable Logic Device (PLD) (e.g, Field Programmable Gate Array (FPGA)).  
         [0050]     According to a second embodiment of the measuring device, movement of the instrument is sensed directly by analyzing a sequence of captured images of the instrument itself as it passes in view of an optical image sensor. This second embodiment of the measuring device can be implemented using the same sensor module as the first embodiment by modifying the channel base of the first embodiment such that the surface of the instrument itself passes within the view of the sensor module.  
         [0051]      FIG. 6  is a diagram illustrating the channel base according to the second embodiment of the measuring device. In particular, the channel base  130 ′ is modified to omit the roller and defines a through hole  136 ′ in a space between the sidewalls  132   a ′,  132   b ′ of the guide, such that the surface of the instrument is exposed to the opposing side of the base. Thus, as the elongated instrument traverses through or rotates within the guide  132 ′, light emitted from the LED  164  is reflected through the lens  166  through openings  154 ,  136 ′ in the board and channel base, respectively, to illuminate the surface of the instrument.  
         [0052]     The sensor  162 , which is aligned to the channel base  130 ′, captures images focused through the lens  166  of the exposed portion of the instrument as it moves within the channel guide  132 ′. From these captured images, the optical sensor  162  detects microscopic features on the surface of instrument in the images and tracks their movement across a set of frames along one or more axes (e.g., X-axis, Y-axis). The amount and direction of the tracked movement along X-axis corresponds to axial movement of the instrument being advanced or withdrawn. The amount and direction of the tracked movement along the Y-axis corresponds to rotation movement of the instrument within the guide. The sensor  162  encodes the amount and direction of the tracked movement along each axis and transmits the encoded data to the counter and scaling module  170  as described above in connection with the first embodiment. Subsequent processing and display is also similar to the first embodiment.  
         [0053]     According to a third embodiment of the measuring device, movement of the instrument is sensed indirectly by coupling an optical rotary encoder to a rotatable element that is in contact with the instrument. This third embodiment of the measuring device can be implemented using a different type of sensor module that includes an optical rotary encoder by modifying the processing module  150  and the channel base  130  of the first embodiment.  
         [0054]     For example,  FIG. 7  is a diagram illustrating a third embodiment of the measuring device that includes an optical rotary encoder. The processor module  400  includes a sensor module comprised of an optical rotary encoder  410 , a counter and scaling module  450  and a display  460 . The channel base  500  is similar to the base of the first embodiment, including a roller  510  or other rotatable element being rotatably connected to the optical rotary encoder  410 . As an instrument enters the guide  520 , the instrument is urged against the roller  510  by an adjustable or fixed ceiling or other opposing element causing the roller to rotate in a clockwise or counter-clockwise direction, depending on the direction of the axial movement of the instrument. In turn, the roller  510  rotatably engages the rotary encoder  410 , which converts the rotary motion of the roller into a linear measurement of predefined units, referred to herein as “counts”.  
         [0055]     According to particular embodiments, the optical rotary encoder  410  is implemented using Quick Assembly Two and Three Channel Optical Encoders HEDM-5500/5600, HEDS-5500/5540, and HEDS-5600/5640; all from Avago Technologies, Inc. with co-headquarters in Palo Alto, Calif. and Singapore. The outputs of the HEDS-5500/5600 and HEDM-5500/5600 are two square waves in quadrature (CH.A and CH.B). The HEDS-5540 and 5640 can also have a third channel index output (CH.I) which is generated once for each full rotation of the codewheel in addition to the two channel quadrature (CH.A and CH.B). Standard resolutions between 96 and 1024 counts per revolution are presently available for these encoders. For more information regarding these components, refer to their technical data sheet entitled “Quick Assembly Two and Three Channel Optical Encoders,” the entire contents of which are incorporated herein by reference.  
         [0056]      FIG. 8  is a timing diagram illustrating the output of a particular optical rotary encoder according to the third embodiment of the measuring device. Specifically, exemplary waveforms are shown for the output signals on channels CH.A, CH.B and CH.I of the identified Avago optical encoders. Each pulse corresponds to a count. The resolution of the encoder depends on the number of counts per revolution. When the roller  510  engages the rotary encoder in the counterclockwise direction channel CH.A leads channel CH.B. Conversely, if the roller  510  engages the rotary encoder in the clockwise direction channel CH.B leads channel CH.A. Thus, the phase difference between channels CH.A and CH.B can be used to detect whether the direction of instrument movement within the guide. The total count in a particular direction can be translated or scaled to the axial or rotational movement in a corresponding direction.  
         [0057]     The signal outputs of channels CH.A and CH.B are transmitted to the counter and scaling module  450 , which maintains an accumulated total number of counts and increments/decrements the accumulated count depending on the direction of the rotary motion. Assuming a particular number of counts per unit measurement (e.g, centimeters, millimeters, inches, etc.), the counter and scaling module  450  can convert the accumulate value into desired units of measurement for presentation through the display  460 . The resulting measurement represents movement of the instrument passing through the guide.  
         [0058]     Advantages of above-described embodiments include the ability to detect the amount and direction of instrument movement regardless of whether the elongated instrument includes optical marks and high accuracy and resolution.  
         [0059]     Optionally, any of the above-described embodiments can be further enhanced with an adjustable guide ceiling that enables instruments of different dimensions to pass through the guide of the channel base. For example, as shown in  FIG. 3  of the first embodiment of the measuring device, an adjustable guide ceiling  200  is provided including a channel finger  210 , a channel sprint  220 , and a back support  230 . This adjustable ceiling is capable of rising and falling to accommodate different sized instruments.  
         [0060]      FIG. 9  is a diagram illustrating an optional adjustable guide ceiling for use in any embodiment of the measuring device. In this illustrated embodiment, the channel finger  210  is loosely positioned within the sidewalls of the guide  132 . The channel spring  220  is formed as an arch having ends fixedly attached to the back support  230  that is located within the sensor back cover  115 . The channel spring  220  exerts a force on the channel finger such that it is urged into the guide  132 . According to one embodiment, the channel finger is constructed such that when the spring is in its maximally extended position, there is a minimal clearance between a lower surface of the channel finger  21  Oa and the roller  140 .  
         [0061]     In operation, as an elongated instrument is inserted into the channel guide  132 , an opposing force of the instrument causes the channel finger  210  to rise and push back on the channel spring  220 . As a result, the inserted instrument is urged against roller  140  causing it to turn. Preferably, the spring constant of the channel spring should be selected to minimize the resistance felt by the operator of the device as the instrument is inserted. Springs having different spring constants can be implemented to accommodate alternate ranges of instrument sizes.  
         [0062]     Optionally, a disposable component may be incorporated into any of the above-described embodiments. For example,  FIG. 10  is a diagram illustrating an optional disposable component for use in any embodiment of the measuring device. In this embodiment, the measuring device  300  includes a fixed component  310  and a disposable component  320 . The fixed component  310  includes at least a sensor module. The disposable component, which is removably attached to the fixed component, includes at least a guide adapted to receive the elongated instrument. The sensor module of the fixed component is arranged in relation to the guide in the disposable component so that the sensor module is capable of detecting movement of the elongated instrument within the guide, for example, as described above in connection with any of the foregoing embodiments.  
         [0063]     The disposable component can be removably attached to the fixed component using any suitable means known to one skilled in the relevant arts. For example, the disposable component can “snap” in and out of the fixed component; the disposable component can slide into and out a receptor of the fixed component; the disposable component can be attached to the fixed component using a fixing mechanism such as a screw or bolt, for example; the fixed component can include a locking mechanism to receive the disposable component in connection with the fixed component and a release mechanism to unlock or otherwise release the disposable component from the fixed component.  
         [0064]     The disposable component  320  contains at least those constituent components which are likely to become contaminated due to the advancement and withdrawal of an elongated instrument into a body lumen. For example, with respect to the first embodiment of the measuring device, such constituent components can include the channel base  130 , channel finger  210 , channel spring  220 , back support  230 , roller  140 , lens  166 , channel inlet  120   a , channel outlet  120   b  and channel lock  122  as described in  FIG. 3 . The fixed housing component  310  contains the remaining portions of the device including the battery  190 , the battery cover  195 , the processing module  150  and its constituent components excluding the lens  166 , as shown and described with respect to  FIG. 3 . The actual positioning and dimensions of the constituent components within the fixed and disposable components can be modified such that the disposable component  320  can be readily detached from the fixed component  310 . In this way, the disposable component can be replaced with another disposable component containing the same or a different set of device components depending on the application or instruments to be measured.  
         [0065]     While this invention has been particularly shown and described with references to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the scope of the invention encompassed by the appended claims.