Patent Publication Number: US-6210337-B1

Title: Ultrasonic endoscopic probe

Description:
This is a division of U.S. patent application Ser. No. 09/060,408, filed Apr. 14, 1998, which is a division of U.S. patent application Ser. No. 08/655,393, filed May 30, 1996, now U.S. Pat. No. 5,762,067. 
    
    
     This invention relates to ultrasonic endoscopic probes by which an ultrasonic transducer located at the distal tip of an endoscope is manipulated while located within the body from an external control unit. 
     U.S. Pat. 5,479,930 describes an ultrasonic endoscopic probe with an ultrasonic transducer at the distal tip of the probe. The distal tip includes an articulation section which is capable of being articulated in up-down and left-right directions so that the transducer may be remotely moved and aimed at a region of the body which the user desires to image. Once the user has articulated the distal tip with its transducer in the desired manner the articulation section may be locked in its articulated position while the user views ultrasonic images produced from echoes received by the transducer. 
     In accordance with the principles of the present invention, an improved ultrasonic endoscopic probe is provided which includes a variable force locking mechanism. The articulating section of the distal tip may be locked in a desired position with variable locking forces. The variable locking forces permit the articulating section to yield in response to movement of the body so as to prevent injury when a patient moves, or the probe is accidentally withdrawn from a body cavity of a patient when locked in an articulated position. The locking force is applied by means of a braking surface of one material which engages a different material of an articulation mechanism to prevent binding or seizing of the articulation mechanism. The articulating section is articulated by a control cable which includes a tension adjustment device. The tension adjustment device also serves as a range limiter to limit the range of articulation of the articulating section. The control cable passes through a cable conduit, which is seated in a spring loaded mechanism which absorbs forces which are suddenly applied to the articulating section. The articulating section is formed of a plurality of pivot rings and pivot beads. The rings and beads are made of metallic and polymeric material, respectively, and include apertures which seat the beads in the rings, and through which the control cable passes. The ultrasonic transducer at the distal tip of the probe is rotatable and includes a sliding membrane between the transducer and acoustic window to allow the transducer to rotate smoothly without sticking or binding. 
    
    
     In the drawings: 
     FIG. 1 is a plan view of an endoscopic probe of the present invention; 
     FIG. 2 is a cross-sectional view of the articulation control system of the probe of FIG. 1; 
     FIG. 3 illustrates the principle of the articulation locking mechanism of an articulating probe; 
     FIG. 4 is a plan view of the variable force articulation locking mechanism of the present invention; 
     FIG. 5 a  is a plan view of the handle of an endoscopic probe of the present invention; 
     FIG. 5 b  is partial cutaway side view of the handle of FIG. 5 a,  showing the cable guide strain relief and cable limit stop arrangements; 
     FIG. 6 is a cross sectional view of the sleeve for the cable guide strain relief arrangement of FIG. 5; 
     FIGS. 7 a  and  7   b  are side and front views of one of the pivot rings of the articulating section of the probe of FIG. 1; 
     FIG. 8 illustrates the articulating link assembly of the probe of FIG. 1; 
     FIG. 9 is an enlarged view of the articulating link assembly of FIG. 8; and 
     FIG. 10 illustrates the distal tip of the probe in which the ultrasonic transducer is rotatably located. 
    
    
     Referring first to FIG. 1, a plan view of an ultrasonic endoscopic probe is shown. The probe includes a handle  10  where the major controls of the probe are located. Extending from one end of the handle  10  is an endoscope tube  12 . The endoscope tube is suitable for insertion into a body cavity such as the esophagus, rectum, or through a surgical incision and can range up to a length of 100 cm. At the end of the endoscope tube  12  is the distal tip  14  of the probe where an ultrasonic transducer is located. 
     Extending from the other end of the handle  10  is an electrical cable  16  which terminates at a connector  18 . The connector  18  is suitable for connecting the probe to an ultrasound system which energizes the probe and displays images formed from the acoustic signals transmitted and received by the transducer at the tip of the probe. 
     Five of the probe controls are shown in FIG.  1 . Two buttons  20  and  22  control selection of the image plane to be scanned by the transducer within the probe tip. The probe tip is connected to the endoscope tube by an articulating section  30  by which the tip can be articulated in any of four directions from the handle by the left-right articulation control knob  24  and the up-down articulation control knob  26 . Reciprocating brake buttons  28 ,  28 ′ are used to lock and unlock the articulating section in any articulated position. 
     Referring to FIG. 2, a cross-sectional view of the articulation control system of the probe of FIG. 1 is shown. The left-right control knob  24  is attached to one end of a shaft  32 . A pulley  34  is connected to the other end of the shaft  32  and is rotated by rotation of the control knob  24 . As the pulley is rotated, the cables  76 , 76 ′ (not shown in this drawing) which are wrapped around and attached to the two grooves of the pulley and extend to the articulating section of the probe are reciprocated. The reciprocation of the cable causes the distal tip  14  of the probe to articulate to the left or the right, depending upon the direction in which the knob  24  is turned. 
     The up-down control knob  26  is connected by screws  36  to an upper pulley  38 . Both the knob  26  and the pulley  38  surround the shaft  32  of the control knob  24  and operate independently therefrom. As the pulley  38  is rotated, the cables  74 , 74 ′ (not shown in this drawing) which are wrapped around and attached to the two grooves of the pulley and extend to the articulating section of the probe are reciprocated. The reciprocation of this cable causes the distal tip  14  of the probe to articulate up or down, depending upon the direction in which the knob  26  is turned. 
     The handle  10  also contains a locking mechanism by which the articulating section  30  can be locked in a particular articulated or unarticulated position. The principle of the locking mechanism is illustrated in FIG. 3, in which an articulating mechanism pulley  128  and articulation control cable  129  are locked in position by a brake pad  146   a.  The brake pad  146   a  is seen to have a concave end surface which engages the circumference of the pulley  128 . The brake pad  146   a  is urged against the pulley  128  by movement of the brake cam  140   a,  which moves in a reciprocating manner as indicated by arrow  152 . As the brake cam is moved to the upper left, a cam follower  142   a  is depressed by surface  141  of the brake cam  140   a.  The cam follower in turn compresses a spring  148   a  inside the body of the brake pad  146   a,  causing the brake pad to bear more forcefully against the circumference of the pulley  128 , thereby impeding its rotation and articulation of the distal end of the probe. 
     Referring back to FIG. 2, the upper and lower pulleys  38  and  34  are engaged by brake pads  146   a  and  146   b,  respectively. To avoid binding or seizing of the lock mechanism due to a metal on metal contact, the concave surfaces of the brake pads are lined with a layer of a polymeric material. This enables the pulleys to be turned smoothly when engaged lightly by the brake pads. Apertures are located in the sides of the brake pads opposite the concave surfaces. Each aperture is engaged by a push rod  40   a,    40   b.  Each push rod has a flange surface  41   a,    41   b  which compresses a spring  48   a,    48   b  against the brake pad. 
     The push rods are urged against the brake pads and springs by a pair of pivoting rockers. A long rocker  50   a  is pivotally connected at a pivot point  52   a  to push rod  40   a.  A short rocker  50   b  is pivotally connected at a pivot point  52   b  to push rod  40   b.  The long rocker  50   a  has a rocker arm  54   a  which rides on the cam surface of a step cam  56   a.  The short rocker  50   b  has a rocker arm  54   b  which rides on the cam surface of a step cam  56   b.  Both rockers pivot about a common pivot point  51 , chosen in accordance with the positions of the push rods, step cams, and the length of the rocker arms of the rockers. 
     The step cams have a number of discrete steps in diameter along their length, represented by the concentric circles in FIG.  2  and clearly shown in the plan view of FIG. 4 for step cam  56   b.  The step cams are moved transversely across the body of the handle  10  as indicated by the directional arrow  58 . At either end of each step cam is a button, one of which,  60   b,  is shown in FIG.  4 . As the button  60   b  is depressed and the step cam  56   b  moves upward in the drawing, the rocker arm  54   b  clicks smoothly to ride on a decreased diameter of the step cam surface. If discrete detent settings are not desired the step cam surface could be made to smoothly vary without steps using, for instance, a threaded mechanism with a thumbwheel for adjustment. As the rocker arm moves to a smaller diameter cam surface the rocker  50   b  pivots to pull the push rod  40   b  away from the brake pad  146   b.  The force on spring  48   b  is decreased, decreasing the locking force of the brake pad  146   b  against the lower pulley  34 . As the locking force is decreased the upper knob  24  will turn more easily to articulate the articulating section of the probe in the left-right direction. 
     As the button on the other end of the step cam  56   b  (not shown in this drawing) is depressed the braking force against the pulley  34  increases. At the highest cam surface (greatest diameter) the pulley  34  is firmly restrained from moving. As discussed in U.S. Pat. No. 5,402,793, this force can be chosen to firmly retain the articulating section in an articulated position, but also to be of a low enough force to be overcome by a forced straightening of the articulating section without injury if the probe is inadvertently withdrawn from the body in an articulated position. 
     In a preferred embodiment, the force required by the user to engage the articulation brake increases as each successive step of the step cam is attained. Correspondingly, as the brake is released the rocker arm cascades continuously and easily to the full brake release setting. This affords a quick and easy release of the brake in the event of an emergency. 
     Each push rod  40   a,    40   b  opposes the arm of a microswitch  62   a,    62   b.  When the rocker arm of a rocker is riding on the smallest diameter of the step cam the microswitch for that brake is not actuated. But when the step cam is moved to begin applying a braking force to a pulley, the arm of the associated microswitch is moved by the push rod sufficient to close the microswitch, thereby sending a signal through the cable  16  to the ultrasound system. A warning is then displayed on the ultrasound system display, alerting the user that the “ARTICULATION LOCK IS ENGAGED” so that the user will not inadvertently withdraw the probe from the body of the patient with the articulating section locked in a curved position. This further aids in avoiding patient discomfort or injury. 
     It will be appreciated that other sensors may be employed in place of the microswitch, such as optical, pressure, or magnetic sensors which will sense when a braking force is being applied to the articulating mechanism. 
     It is seen that a sequence of “a” suffix brake elements extend to the right of the upper pulley  38 , ending with the lower step cam  56   a.  Correspondingly, the sequence of “b” suffix brake elements extend from the lower pulley  34  and end at the upper positioned step cam  56   b.  As a result, the upper and lower step cams lock the upper and lower articulation control knobs, respectively. This positional correspondence of the lock buttons and knobs gives the probe handle an intuitive sense of operation, which is significant because the user is generally focusing his attention on the patient or ultrasonic image display while operating the handle controls by touch. 
     While the previously described arrangement is seen to be a fully mechanical implementation it will be appreciated that other implementations such as electromechanical arrangements are also possible. In place of the step cams, rockers and push rods one could substitute an electrically controlled solenoid arrangement, for instance. Other variations will also be apparent to those skilled in the art. 
     As previously mentioned, each pulley has two grooves. The articulation control cable is fastened at one end to ride in one groove. The cable then extends through the endoscope tube  12  to a point where it is affixed to or wrapped around a point in the articulating section  30 . The cable continues back through the endoscope tube where it is fastened at the other end to ride in the other groove of the pulley. 
     In order to facilitate adjustment of the cable tension a cable adjuster is inserted in line with the cable just ahead of the pulley. An adjuster  70  is located in line on each side of the cable. One of the adjusters  70   a  for the up-down control cable  74  is shown in FIG. 5 b,  as is one of the adjusters  72   b  for the lower, left-right control cable  76 . The other two adjusters ( 70   a′,    72   b′ ) are on the other side of the handle and are not visible in this drawing. Each adjuster is comprised of male and female threaded parts  71  and  73 , which screw together to increase the cable tension and apart to relax the cable tension. The cable length extending to the articulating section of the probe is connected to the distal threaded part  71 , and the short remaining cable length  74 ′ which leads to the pulley is connected to the proximal threaded part  73 . Just before engaging the pulley groove the short cable length  74 ′ passes through a cable guide  80 , which guides the cable into the pulley groove. 
     The cable adjusters serve a dual purpose. In addition to cable tension adjustment, the adjusters  70  serve as articulation control end stops. The proximal end of the proximal adjuster part  73  is covered with a polymeric sleeve  78  which serves as a bumper. As control knob  26  is turned to articulate the probe by winding cable section  74 ′ onto the pulley  38 , the adjuster  70   a  and bumper sleeve  78  approach the cable guide  80 . The end of this range of adjustment is reached when the bumper sleeve  78  contacts the cable guide  80 . Thus, an end stop within the handle  10  prevents the imposition of excessive force on the cable  74  and the articulating section of the probe. 
     When the control knob is turned in the other direction, the adjuster  70   a′  on the other side of the handle approaches and contacts a cable guide  80 ′ on the other side of the handle as the short cable section  74 ′ at the opposite end of the cable is wound onto its pulley groove. The range of control permitted by the end stops is fixed by the lengths of the terminating cable sections  74 ′. 
     The major lengths  74 ,  76  of the articulation control cables extend through the endoscope tube in cable conduits  84 ,  86 , which are preferably spiral wound conduits formed of wire which is generally square or rectangular in cross section and may also be squarely wound so that the interior cross sectional area of the conduit is square or rectangular, which minimizes friction between the cable and the inner surface of the conduit. Such conduits are more fully described in U.S. Pat. No. 5,450,851. 
     In an articulating probe of the present invention it is possible for a sudden excessive force to be placed upon the articulation control cables from a variety of causes. One such cause would be dropping the probe so that it lands on its distal tip, with the force of the fall causing the articulation section to bend. To guard against the shock of such a sudden force it is desirable to provide a means for alleviating this sudden force on the cables. In FIG. 5 b  the end of each cable conduit is seated in a sleeve  90 , with the terminus of the cable conduit seated against a narrowing  96  of the internal diameter of the sleeve. The cable  74 ,  76  passes through the end of the cable conduit and through the proximal smaller diameter portion  98  of the sleeve. The proximal portion of the sleeve is fitted into an aperture of a handle member  11  and held in place by a nut  92  on the threaded proximal end of the sleeve  90 . The body of the sleeve  90  is surrounded by a spring  94  which is retained between the flanged distal end of the sleeve and the handle member  11 . 
     When a sudden excessive force is applied to the articulating section of the probe, the force is transmitted to the control cables and their cable conduits. The force is transmitted through the conduit to the terminus of the cable conduit, where it is applied to the sleeve  90  at the narrowing  96  of the sleeve. The force will cause the sleeve to be urged in the proximal direction. As the sleeve  90  moves in this direction the sudden force is damped by compression of the spring  94 , which alleviates the sudden buildup of force on the articulation mechanism of the probe. 
     A preferred implementation of the articulation section  30  is shown in FIGS. 7-10. The preferred embodiment is constructed of a series of pivot rings  120 , one of which is shown in FIGS. 7 a  and  7   b.  The rings are hollow to permit passage of cables and other connections to the transducer at the tip of the probe. Around the periphery of each ring are four apertures  100 . Each aperture is formed of a conical hole  102  and a semi spherical depression  104  as shown in FIG. 7 a.  Apertures which oppose each other across the ring are paired so that two have the conical hole facing one direction and the other two are reversed. In FIG. 7 b  apertures  100  are paired, as are apertures  100 ′. 
     The articulating section  30  is constructed by assembling the pivot rings in alternating fashion as shown in FIG.  8 . The two semi spherical depressions on one side of a ring oppose two semi spherical depressions on the opposing ring. A polymeric pivot bead  106  formed of a material such as nylon with a diametric hole  108  is seated in each set of opposing semi spherical depressions. The sequence of opposing pivot beads thus alternates 90° in orientation from one side of each ring to the other. The cable conduits of each cable are seated in the proximal end ring  110 . The cables exit the conduits and pass through the apertures  100  and pivot bead holes  108  and are terminated at the distal end ring  112 . 
     As the articulating section  30  bends each ring pivots with respect to its neighbor on a pair of pivot beads  106  as shown in FIG.  8 . One set of pivot beads accommodates bending in one direction (e.g., up-down) and the next pair of pivot beads accommodates bending in another direction (e.g., left-right.) In FIG. 8 the articulating section is bent down by the tensioning of the lower cable  74 . 
     The conical holes  102  and the pivot beads  106  advantageously accommodate the bending of the articulating section  30  without allowing the cables to rub against the pivot rings. This is more clearly shown in the enlarged view of FIG.  9 . There it is seen that the conical shape of the holes  102  provides an expanded opening through which the cables  74  will pass without contacting the pivot rings regardless of the bending of the articulating section. The cables extend from the hole  108  of one pivot bead to the next without any contact with the pivot rings. This permits the articulating section to bend smoothly and wear longer without fraying of the articulation control cables. 
     At the distal end of the articulating section is a housing  114  shown in FIG. 10 which contains the ultrasonic transducer  130 . In a preferred embodiment the transducer  130  is an array transducer which is affixed in a rotatable transducer mount  132 . The transducer mount rotates on a shaft  134  under control of a drive shaft  136  and gear train. As the user turns the drive shaft  136  from the control section of the probe, preferably through control of a motor which turns the drive shaft, the transducer rotates to change the image plane of the transducer to a new orientation. The transducer  130  is covered with an acoustic matching layer and an acoustic lens  160 . The acoustic lens may be made of a material such as a cured RTV compound and provides the transducer with focusing in the elevational direction. The space  166  around the rotating transducer is filled with an acoustic coupling fluid and is sealed with a cover  162  which is durable and exhibits the desired acoustic properties. The cover  162  forms the acoustic window through which ultrasonic energy is transmitted and received by the transducer. Preferably the cover  162  is acoustically transparent and thin so that it will not cause reverberation artifacts from the transmitted ultrasonic waves. A sheet of 1.0 mil Mylar® has been found to possess the desired properties. 
     As the transducer  130  rotates, it does so in contact with the cover  162 . Since the space  166  in which the transducer is located is filed with acoustic fluid, which is often an oil-based compound with lubricating properties, it would be expected that the transducer surface would rotate smoothly against the cover, lubricated as it is by the acoustic fluid. However, the preferred RTV lens material is a non-wetting material, and has been found to adhere to the Mylar cover even in the presence of the acoustic fluid. To overcome this problem the transducer and its acoustic lens are covered with a thin, acoustic membrane  164 . A preferred material for the membrane  164  a polymeric material such as 0.1 mil Mylar, shaped to the surface shape of the acoustic lens  160 . When the acoustic lens  160  is dome shaped as shown in the drawing, the membrane  164  is also dome shaped and its shape resembles that of a contact lens. When the membrane  164  is made of Mylar and the acoustic lens  160  is made of RTV material, the membrane  164  will stick to the RTV lens and rotate with it. The Mylar lens will not stick to the Mylar cover  162 , however, but rotates smoothly against it, aided by an intervening thin layer of the acoustic fluid. Thus, the transducer with its Mylar membrane  164  rotates smoothly against the cover  162  without binding or sticking.