Patent Publication Number: US-2021186305-A1

Title: Deflectable medical probe having improved resistance to forces applied in rotation

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to minimally invasive medical devices, and particularly to techniques for medical probes having improved maneuverability and durability. 
     BACKGROUND OF THE INVENTION 
     Various types of medical probes have mechanical designs intended to improve probe durability when maneuvered in a patient body. 
     For example, U.S. Patent Application Publication 2011/0152880 describes an instrument for performing minimally invasive surgical procedures. The instrument includes an elongate body and a support member disposed within or along the elongate body. The support member is configured to support steering, articulation, and angular rotational movement of the elongate body, provide torsion control, and support precise and accurate placement of the distal portion of the elongate body so that complex surgical procedure may be performed using the instrument. 
     U.S. Patent Application Publication 2017/0325841 describes an apparatus including a tube, shaped to define a tube lumen and a distal portion that has a plurality of articulated sections. The apparatus further includes a ribbon that passes longitudinally through the tube lumen and is connected to a distalmost one of the articulated sections, and a control handle disposed at a proximal end of the tube, the control handle being configured to flex the distal portion of the tube by pulling the ribbon. 
     SUMMARY OF THE INVENTION 
     An embodiment of the present invention that is described herein provides a medical probe, including a shaft, for insertion into a cavity of a patient body, and a distal-end assembly. The distal-end assembly is coupled to a distal end of the shaft and including a hollow tube, which is configured to deflect relative to a longitudinal axis of the hollow tube and to rotate about the longitudinal axis. The hollow tube having (i) an intrusion, having at least a first surface, and (ii) a protrusion, which is facing the intrusion and having a second surface. When the hollow tube is deflected, at least part of the protrusion protrudes into the intrusion so that a first section of the first surface and a second section of the second surface are facing one another, and when the hollow tube is deflected and rotated, the first and second sections of the first and second surfaces apply force to one another and thus resist rotation of the hollow tube. 
     In some embodiments, the distal-end assembly includes (i) a first slot, located at a first section along the longitudinal axis of the hollow tube, and having a first size that limits bending of the first section by a first local radius of curvature (LROC), and (ii) a second slot, located at a second different section along the longitudinal axis of the hollow tube, and having a second different size that limits bending of the second section by a second different LROC. In other embodiments, at least the first slot includes (i) a plurality of the intrusions having respective one or more first surfaces, and (ii) a plurality of the protrusions having respective one or more second surfaces, and the intrusions and protrusions are arranged along at least the first slot. In yet other embodiments, at least the first slot includes at least a given intrusion having a first given surface, and a given protrusion, which is facing the given intrusion and having a second given surface, when the hollow tube is not deflected, the first and second given surfaces do not apply force to one another. 
     In an embodiment, the medical probe includes a control handle, fitted at a proximal end of the shaft and configured to bend the first section by up to the first LROC and the second section by up to the second LROC. In another embodiment, the distal-end assembly includes an alloy of nickel and titanium. In yet another embodiment, the intrusion is shaped to fit over the protrusion, such that, when the hollow tube is deflected and rotated, the first and second sections do not slide relative to one another. 
     In some embodiments, the first and second sections of the first and second surfaces press against one another. In other embodiments, the protrusion has a shape selected from a list of shapes consisting of: rectangular, parallelogram, trapezoid, dome, and pyramid. In yet other embodiments, the cavity includes an ear-nose-throat (ENT) sinus. 
     There is additionally provided, in accordance with an embodiment of the present invention, a method for producing a medical probe, the method including providing a shaft for insertion into a cavity of a patient body. A distal-end assembly that includes a hollow tube that deflects relative to a longitudinal axis of the hollow tube and rotates about the longitudinal axis is coupled to a distal end of the shaft. The hollow tube has (i) an intrusion, having at least a first surface, and (ii) a protrusion, which is facing the intrusion and having a second surface. When the hollow tube is deflected, at least part of the protrusion protrudes into the intrusion so that a first section of the first surface and a second section of the second surface are facing one another, and when the hollow tube is deflected and rotated, the first and second sections of the first and second surfaces apply force to one another and thus resist rotation of the hollow tube. 
     In some embodiments, the method includes forming at least one of the first and second slot using a laser cutting technique. 
     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, pictorial illustration of an ear-nose-throat (ENT) procedure using an ENT system, in accordance with an embodiment of the present invention; and 
         FIGS. 2A and 2B  are schematic, pictorial illustrations of a medical probe having a deflectable and rotatable distal-end assembly, in accordance with embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Overview 
     Some medical procedures require insertion of a medical probe into a branched organ of a patient, such as a sinus of a patient ear-nose-throat (ENT) system. Maneuvering of the probe within the sinus to a desired location, may result in a breakage of the probe due external forces applied to the probe, e.g., by a bone of the ENT system. 
     Embodiments of the present invention that are described hereinbelow provide a medical probe having improved resistance to probe breakage when maneuvering the medical probe within branched organs in a patient body. 
     In some embodiments, the medical probe comprises a shaft for insertion into a cavity of a patient body, such as a sinus of a patient ENT system, and the distal-end assembly is coupled to the distal end of the shaft. The distal-end assembly comprises a hollow tube, which is configured to deflect relative to a longitudinal axis of the hollow tube and to rotate about the longitudinal axis. 
     In some embodiments, the hollow tube has at least an intrusion having at least one surface, referred to herein as a first surface. The hollow tube also has at least a protrusion, which is facing the intrusion and having at least another surface, referred to herein as a second surface. 
     In some embodiments, when the tube is deflected, at least part of the protrusion protrudes into the intrusion so that a first section of the first surface and a second section of the second surface are facing one another. When the hollow tube is deflected and rotated, the first and second surfaces that are facing one another, are applying force to one another, and thus, resist rotation and breakage of the hollow tube. In some embodiments, the hollow tube may comprise multiple protrusions and respective intrusions patterned along the circumference of the hollow tube, so as to improve the resistance to rotation and breakage of the hollow tube. 
     In some embodiments, the plurality of protrusions and intrusions may improve the deflecting ability, and therefore the flexibility, of the hollow tube. The maximal deflecting ability at a given location along the hollow tube is specified by a local radius of curvature (LROC) at that location. 
     In some embodiments, a first set of one or more protrusions and respective intrusions, which is located at a first, distalmost, section of the hollow tube, has a given size that limits the bending ability of the distalmost section by a predefined LROC. In some embodiments, a second set of one or more protrusions and respective intrusions, which is located along the hollow tube at a second section, proximal to the first section, has a size smaller than the given size, resulting in a LROC larger than the predefined LROC of the distalmost section. 
     In some embodiments, the hollow tube may comprise multiple sets of one or more protrusions and respective intrusions that are formed along the longitudinal axis of the tube, wherein the size of the protrusions and respective intrusions increases with the proximity to the distal end of the tube. Thus, the LROC corresponding to the protrusions and respective intrusions decreases with their proximity to the distal end of the tube. 
     In some embodiments, the distal-end assembly comprises a control handle fitted at the proximal end of the shaft. The distal-end assembly further comprises one or more pulling wires, which run through a longitudinal lumen of the tube, and are coupled to the distalmost section of the hollow tube and to the control handle. In some embodiments, a user of the medical probe may apply the pulling wires for deflecting one or more sections of the distal-end assembly up to the desired respective LROCs. Moreover, when the hollow tube is deflected the user may rotate the medical probe about the longitudinal axis without a concern of breaking within the patient ENT system. 
     The disclosed techniques improve the flexibility and durability of a narrow medical probe, so as to improve the maneuverability of the medical probe in rigid branched organs. 
     System Description 
       FIG. 1  is a schematic, pictorial illustration of an ear-nose-throat (ENT) procedure using an ENT system  20 , in accordance with an embodiment of the present invention. In some embodiments, ENT system  20  comprises a medical probe, referred to herein as an ENT tool  28 , which is configured to carry out the ENT procedure, such as but not limited to treating infection from one or more sinuses  48  of a patient  22 . 
     In some embodiments, ENT tool  28  comprises a shaft  38 , coupled to the distal end, which a physician  24  inserts into a nose  26  of patient  22 . ENT tool  28  further comprises a handheld apparatus  30 , coupled to a proximal end of shaft  38  and configured to assist physician  24  in maneuvering the distal end of shaft  38  in a head  41  of patient  22 . Shaft  38  is shown in detail in  FIGS. 2A and 2B  below. 
     In an embodiment, system  20  further comprises a magnetic position tracking system, which is configured to track the position of one or more position sensors in head  41 . The magnetic position tracking system comprises magnetic field-generators  44  and multiple position sensors (not shown). The position sensors generate position signals in response to sensing external magnetic fields generated by field-generators  44 , thereby enabling a processor  34  (described in detail below) to estimate the position of each sensor within head  41  of patient  22 . 
     This method of position sensing is implemented in various medical applications, for example, in the CARTO™ system, produced by Biosense Webster Inc. (Irvine, Calif.) and is described in detail in U.S. Pat. Nos. 5,391,199, 6,690,963, 6,484,118, 6,239,724, 6,618,612 and 6,332,089, in PCT Patent Publication WO 96/05768, and in U.S. Patent Application Publications 2002/0065455 A1, 2003/0120150 A1 and 2004/0068178 A1, whose disclosures are all incorporated herein by reference. 
     System  20  further comprises a location pad  40 , which comprises field-generators  44  fixed on a frame  46 . In the exemplary configuration shown in  FIG. 1 , pad  40  comprises five field-generators  44 , but may alternatively comprise any other suitable number of field-generators  44 . Pad  40  further comprises a pillow (not shown) placed under head  41  of patient  22 , such that field-generators  44  are located at fixed and known positions external to head  41 . 
     In some embodiments, system  20  comprises a console  33 , which comprises a memory  49 , and a driver circuit  42  configured to drive, via a cable  37 , field-generators  44  with suitable signals so as to generate magnetic fields in a predefined working volume in space around head  41 . 
     In some embodiments, console  33  comprises processor  34 , typically a general-purpose computer, with suitable front end and interface circuits for receiving signals from ENT tool  28  having multiple magnetic sensors (not shown) coupled thereto, via a cable  32 , and for controlling other components of system  20  described herein. 
     In some embodiments, processor  34  is configured to estimate the position of each position sensor. Based on the estimated positions of the respective sensors, in the coordinate system of the magnetic position tracking system, processor  34  is configured to derive the position, orientation and radius of curvature of a deflected distal end of ENT tool  28  that is shown in  FIGS. 2A and 2B  below. 
     In the context of the present invention and in the claims, the terms “bending” “deflecting” are used interchangeably and refer to deflection or bending of one or more sections of ENT tool  28  as will be described in detail in  FIGS. 2A and 2B  below. 
     In some embodiments, processor  34  is configured to receive via an interface (not shown), one or more anatomical images, such as computerized tomography (CT) images depicting respective segmented two-dimensional (2D) slices of head  41 , obtained using an external CT system (not shown). The term “segmented” refers to displaying various types of tissues identified in each slice by measuring respective attenuation of the tissues in the CT system. 
     Console  33  further comprises input devices  39  for controlling the operation of system  20 , and a user display  36 , which is configured to display the data (e.g., images) received from processor  34  and/or to display inputs inserted by physician  24  or another user of input devices  39 . 
     In some embodiments, processor  34  is configured to select one or mode slices from among the CT images, such as an anatomical image  35 , and to display the selected slice on user display  36 . In the example of  FIG. 1 , anatomical image  35  depicts a sectional front-view of one or more sinuses  48  of patient  22 . 
     In some embodiments, processor  34  is configured to register between the coordinate systems of the CT system and the magnetic position tracking system, and to overlay the position of the distal end of ENT tool  28 , on anatomical image  35 . 
       FIG. 1  shows only elements related to the disclosed techniques, for the sake of simplicity and clarity. System  20  typically comprises additional modules and elements that are not directly related to the disclosed techniques, and therefore, are intentionally omitted from  FIG. 1  and from the description of system  20 . 
     Processor  34  may be programmed in software to carry out the functions that are used by the system, and to store data in memory  49  to be processed or otherwise used by the software. The software may be downloaded to the processor in electronic form, over a network, for example, or it may be provided on non-transitory tangible media, such as optical, magnetic or electronic memory media. Alternatively, some or all of the functions of processor  34  may be carried out by dedicated or programmable digital hardware components. 
     Deflectable and Rotatable Distal-End Assembly Having Intrusions and Protrusions Patterned in a Single Tube 
       FIG. 2A  is a schematic, pictorial illustration of ENT tool  28  having a deflectable and rotatable distal-end assembly  134  in a straight position, in accordance with an embodiment of the present invention. In some embodiments, shaft  38  and distal-end assembly  134  are configured to rotate about a longitudinal axis  50  of ENT tool  28 . The rotation capability is represented by an arrow  43 . Note that the rotation may be carried out clockwise and/or counterclockwise so as to improve the maneuverability of distal-end assembly  134 . In such embodiments, physician  24  may rotate both shaft  38  and distal-end assembly  134  together, by rotating a control handle  128  described in detail below. In alternative embodiments, physician  24  may rotate shaft  38  and distal-end assembly  134  separately. 
     Reference is now made to an inset  80 . In some embodiments, distal-end assembly  134  comprises a hollow tube  66 , which is coupled to the distal end of shaft  38  and is typically made from a single piece of any suitable material, such as but not limited to a suitable alloy of nickel and titanium, e.g., Nitinol™ or super-elastic Nitinol™, having high repeatability. 
     In some embodiments, tube  66  is sized and shaped for being comfortably inserted through nose  26  into sinuses  48  or any other organ in head  41  of patient  22 . Tube  66  is also sized and shaped for allowing a medical instrument, such as a sinuplasty balloon, a surgical tool, a suction or irrigation tool, or any other suitable tool, to be subsequently inserted through a lumen  140  of tube  66 , which is described in detail below. 
     In some embodiments, tube  66  of distal-end assembly  134  has multiple slots, such as slots  77 A,  77 B,  77 C and  77 D, each of which formed at a respective section, also referred to herein as a rib, of distal-end assembly  134 . 
     In the example of  FIG. 2A , slot  77 A is the distal-most patterned section of distal-end assembly  134  and has the largest size from among slots  77 A- 77 D patterned in tube  66 . Similarly, slot  77 D is the proximal-most patterned section of distal-end assembly  134  and has the smallest size from among slots  77 A- 77 D of tube  66 . As will be depicted in  FIG. 2B  below, the slot size determines the bending limit of the respective section of distal-end assembly  134 . 
     In some embodiments, each of slots  77 A- 77 D has one or more protrusions and intrusions, which may be formed, by laser cutting or using any other suitable technique, on a section of the circumference of tube  66 . 
     Reference is now made to an inset  92 , showing slot  77 A of tube  66 . In some embodiments, slot  77 A comprises multiple intrusions  99 A,  99 B,  99 C,  99 D and  99 E, which are sized and shaped to fit snugly over respective protrusions  88 A,  88 B,  88 C,  88 D and  88 E of tube  66 . For example, intrusion  99 A is adapted to fit over protrusion  88 A, and intrusion  99 D is adapted to fit over protrusion  88 D. 
     Reference is now made back to inset  80 . In some embodiments, when distal-end assembly  134  is in a straight position, also referred to herein as unflexed state (as shown in inset  80 ), protrusion  88 A and intrusion  99 A are may be disengaged from one another, whereas protrusion  88 D and intrusion  99 D are partially engaged with one another. In the straight position, slot  77 A has the maximal size, e.g., along longitudinal axis  50 . In other embodiments, distal-end assembly  134  may have any other suitable configuration. For example, in the straight position protrusion  88 A and intrusion  99 A may be at least partially engaged with one another. Moreover, in the straight position at least one protrusion may be partially or fully inserted into the respective intrusion. 
     Reference is now made back to inset  92 . In some embodiments, protrusion  88 A has surfaces  55 A and  55 B, and intrusion  99 A has surfaces  56 A and  56 B. Note that when tube  66  is not deflected (e.g., in the unflexed state), surfaces  55 A and  56 A are not facing one another. Similarly, when tube  66  is not deflected, surfaces  55 B and  56 B are not facing one another. 
     In some embodiments, tube  66  has a non-patterned surface, referred to herein as a spine  78 . In some embodiments, slots  77 A- 77 D are patterned along the circumference of tube  66  and are therefore circular. The circular slots may be formed on any suitable portion of the circumference of tube  66 . For example, at least one of the circular slots may cover between about 20% and about 95% of the circumference of tube  66 . 
     In some embodiments, slots  77 A- 77 D may be patterned symmetrically along the circumference of tube  66 . For example, two sets of circular slots, such as slots  77 A- 77 D, may be patterned symmetrically with the aforementioned protrusions and intrusions at both sides of spine  78 . 
     In some embodiments, tube  66  may have an additional pattern connecting between the circular slots. In the example of  FIG. 2A , the additional pattern is mechanically connecting between protrusions  88 A (and intrusions  99 A) of slots  77 A that are extended from both sides of spine  78 . 
     In the example configuration of  FIG. 2A , tube  66  has ten slots, but in other configurations tube  66  may have any suitable number of slots, e.g., between 3 and 20, 4 and 20, 5 and 20, 6 and 20, 7 and 20, 8 and 20, 9 and 20, 10 and 20, 11 and 20, 12 and 20, 13 and 20, 14 and 20, and 15 and 20 slots having any suitable size and shape. Note that the slots may have a similar shape and different size, or a different shape, or any suitable combination of the above. 
     In alternative embodiments, the size of the slots may gradually increase from the proximal end to the distal end. In other embodiments, the size of the slots may alter along longitudinal axis  50 . For example, slot  77 A may be larger than slot  77 B, but smaller than the size of slot  77 C. 
     In yet other embodiments, the size of the slots, protrusions and intrusions of tube  66  may have any other suitable distribution along longitudinal axis  50 . Additionally or alternatively, the size of the protrusions and intrusions of tube  66  may have any other suitable distribution across longitudinal axis  50 . 
     Reference is now made back to the general view of  FIG. 2A . In some embodiments, ENT tool  28  comprises control handle  128 , which is coupled to handheld apparatus  30  shown in  FIG. 1  above and is fitted at the proximal end of shaft  38 . Control handle  128  is configured to bend and straighten distal-end assembly  134  relative to longitudinal axis  50  of ENT tool  28 . 
     Reference is now made to an inset  70 , which is a traversing sectional view BB of shaft  38 . In some embodiments, shaft  38  is hollow and shaped to define a tube lumen  140 . ENT tool  28  comprises a pull wire  130 , made from or comprising a suitable alloy of nickel and titanium, such as Nitinol™ or other suitable materials, which passes proximally-distally through tube lumen  140 . 
     In some embodiments, pull wire  130  may be connected to a ring or any other element coupled to a selected section, such as the distalmost section, of hollow tube  66 , for example, distal to slot  77 A. As will be described in  FIG. 2B  below, pull wire  130  facilitates adjusting the configuration of the distal portion of tube  66 . In other embodiments, ENT tool  28  may comprise a ribbon (not shown), instead of, or in addition to pull wire  130 . The ribbon may comprise Nitinol™ or any other suitable material. A configuration of the aforementioned ribbon in an ENT tool is described in detail in U.S. Patents Application Publications 2017/0325841, which is incorporated herein by reference. 
     As shown in  FIG. 2A , in the unflexed state of tube  66 , each of the slots, and sections between the slots, is generally flush with its neighbors along longitudinal axis  50  at the circumference of tube  66 . 
     Reference is now made to an inset  60 , which is a sectional view AA of control handle  128  along longitudinal axis  50 . As described above, control handle  128  is fitted at the proximal end of shaft  38 . In some embodiments, control handle  128  is rotatable and is configured to control pulling wire  130 . 
     As will be described in  FIG. 2B  below, by turning control handle  128  in one direction, pull wire  130  is pulled, thus causing flexion of distal-end assembly  134 . Conversely, by turning control handle  128  in the opposite direction, pull wire  130  is pushed, thus causing tube  66  of distal-end assembly  134  to be unflexed and straight as shown in  FIG. 2A . 
     For example, the proximal end of pull wire  130  may be coupled to a sliding element  142 , which is configured to slide between an extreme proximal position and an extreme distal position. By turning control handle  128 , sliding element  142  is slid proximally or distally, thus causing tube  66  to be flexed or unflexed. In some embodiments, the inner surface of control handle  128  may be shaped to form a female threading  144 , and control handle  128  may also comprise a complementary male threading  146 , which is engaged with female threading  144 . In an embodiment, when physician  24  (or any other operator of ENT tool  28 ) turns control handle  130 , male threading  146 , which is coupled to sliding element  142 , moves the sliding element proximally or distally along longitudinal axis  50 , and controls the state of tube  66  as described above. 
     In some embodiments, the protrusion and intrusions of distal-end assembly  134  (e.g., protrusions  88  and intrusions  99 ) may have any suitable shape, such as but not limited to, rectangular, parallelogram, trapezoid, dome shaped, pyramid shape, or any type of polygon. 
     This particular configuration of distal-end assembly  134  is shown by way of example, in order to illustrate certain problems that are addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such a medical probe (e.g., ENT tool  28 ). Embodiments of the present invention, however, are by no means limited to this specific sort of example configuration of ENT module, and the principles described herein may similarly be applied to other sorts of medical probes. 
       FIG. 2B  is a schematic, pictorial illustration of ENT tool  28  having distal-end assembly  134  in a deflected position, in accordance with an embodiment of the present invention. 
     Reference is now made to an inset  90  showing a longitudinal cross-section of control handle  128 . As described in  FIG. 2A  above, when physician  24  turns control handle  128 , pull wire  130  is pulled along longitudinal axis  50  towards the proximal end of ENT tool  28 , and tube  66  is deflected. In some embodiments, control handle  128  is further configured, subsequently to the aforementioned turning, to hold the ribbon in place, thus to maintain the position of tube  66 . For example, the engagement of threading  144  with threading  146 , as shown in  FIG. 2B , may prevent the sliding element from sliding. 
     In other embodiments, control handle  128  may comprise any other suitable mechanism for preventing undesired sliding of the aforementioned pull wire or ribbon or any other mechanism suitable for deflecting distal-end assembly  134  of ENT tool  28 . 
     Reference is now made to an inset  100  showing distal-end assembly  134  in a fully deflected position. In some embodiments, when pull wire  130  is pulled proximally along longitudinal axis  50 , tube  66  is deflecting and the protrusions of tube  66  are inserted into the respective intrusions thereof. 
     Reference is now made to an inset  150  showing the protrusions and intrusions of slot  77 A. In some embodiments, in the fully deflected position shown in  FIG. 2B , protrusions  88 A,  88 B,  88 C,  88 D and  88 E of slot  77 A, are inserted into intrusions  99 A,  99 B,  99 C,  99 D and  99 E, respectively. In such embodiments, surface  55 A of protrusion  88 A and surface  56 A of intrusion  99 A are facing one another and are typically in physical contact with one another. Similarly, surface  55 B of protrusion  88 A and surface  56 B of intrusion  99 A are facing one another and are typically in physical contact with one another. 
     In some embodiments, when tube  66  is deflected and rotated at the same time (as shown in the general view of  FIG. 2B ), surfaces  55 A and  56 A apply force to one another and thus resist the rotation of tube  66 . Similarly, when tube  66  is deflected and rotated at the same time, surfaces  55 B and  56 B apply force to one another. Note that the size and shape of the protrusions and intrusions of tube  66  allow complete insertion of the protrusions into the respective intrusions, and physical contact, without sliding, between the aforementioned surfaces. 
     In some embodiments, the size of the outer and inner diameters of tube  66  may be about 4.2 mm and 3.6 mm, respectively. Therefore, the wall thickness of tube  66  (i.e., between the outer and inner surfaces) may be about 0.2 mm, and the size tolerance of the aforementioned protrusions and intrusions may be about 0.01 mm. 
     In other embodiments, the inner and outer diameter, and the wall thickness may have any other size suitable for a respective medical procedure carried out in a respective organ of patient  22 . 
     In the context of the present disclosure and in the claims, the terms “about” or “approximately” for any numerical values or ranges indicate a suitable dimensional tolerance that allows the part or collection of components to function for its intended purpose as described herein. For example, “about” or “approximately” may refer to the range of values ±20% of the recited value, e.g. “about 90%” may refer to the range of values from 72% to 100%. 
     In such embodiments, when tube  66  is deflected and rotated at the same time, surfaces  55 A and  56 A, and surfaces  55 B and  56 B, may not slide relative to one another. Rather, surfaces  55 A and  56 A may press one another, or may apply any other force (e.g., a combination of pressing and shearing and/or friction) to one another. When tube  66  is deflected and, at the same time, is also rotated against a bone or another rigid tissue, the inter-surface force described above improves the resistance of tube  66  to rotation, and therefore improves the durability of tube  66  against breakage. The inventors found that, compared to a deflectable Nitinol™ tube having fewer pairs of protrusions and intrusions with a length of about 40 mm and a wall thickness of 0.2 mm, the breakage resistance of tube  66  having the same material, length and wall thickness, may increase about fourfold by having slots  77 , protrusions  88  and intrusions  99  with the tolerances described above. An example configuration of fewer pairs of protrusions and intrusions is shown, for example, in U.S. patent application Ser. No. 16/421,430 filed May 23, 2019, which is assigned to the assignee of the present patent application and whose disclosure is incorporated herein by reference. 
     As described in  FIG. 2A  above, each of slots  77 A- 77 D has a slit, formed on a section of the circumference of tube  66 . The size (e.g., width) of the slit determines the slot angle when physician  24  is bending tube  66 . In the example of  FIG. 2B , the slit of slot  77 A is larger than the slit of slot  77 C, and therefore, the slot angle of slot  77 A is larger than the slot angle of slot  77 C. Note that in the unflexed state shown in  FIG. 2A  above, physician  24  is not bending tube  66  and therefore the sections of tube  66  remain flush with one another. 
     In some embodiments, the slit size and/or the size of the protrusion and intrusion typically determine the maximal amount of deflection of the respective section. The maximal deflection ability at a given location along tube  66  may be specified by a local radius of curvature (LROC) at that location. 
     In such embodiments, a larger slot, protrusion and intrusion enable increased the amount of deflection, measured by a smaller LROC. As shown in inset  100 , R A , which is the LROC of slot  77 A is smaller than R C , which is the LROC of slot  77 C. Note that the term “local” refers to the arc formed by the bending of the outer surface of tube  66  at the position of the respective slot. 
     This configuration refers to the sizes of the remaining slots and respective LROCs of tube  66  are within the ranges defined above between slots  77 A and  77 D. For example, at maximal deflection, the LROC of slot  77 C is typically smaller than that of slot  77 D, and is larger than that of slot  77 A. Note that the dimensions described above are provided by way of example, and in other embodiments, the slots, intrusions, protrusions and LROCs may have any other suitable dimensions. 
     Note that the LROCs described above are indicative of the LROC at a maximal deflection or bending of tube  66  at each respective section. In some embodiments, physician  24  may apply less-than maximal bending to tube  66  by applying a smaller turning or rotation angle to control handle  128 . In such embodiments, only a portion of a given protrusion (e.g., protrusion  88 A) may be inserted into the respective intrusion (e.g., intrusion  99 A), and the LROC may be larger compared to the fully deflected LROC shown in inset  100 . 
     In some embodiments, when physician  24  moves ENT tool  28  in head  41  of patient  22 , at least one section of tube  66  may by fully deflected and another section may be partially deflected or not deflected at all. For example, physician  24  may position distal-end assembly  134  at the ostium of sinus  48  (as shown in  FIG. 1  above), and subsequently deflect only the third distalmost part of tube  66 . 
     In this example embodiment, the ostium of sinus  48  may fix the sections of slots  77 C and  77 D to be substantially flush with shaft  38  (as shown in  FIG. 2A  above), physician  24  may partially deflect the section comprising slot  77 B, whereas the section comprising slots  77 A may be fully deflected to obtain the R A  LROC shown in inset  100 . In other example embodiments, physician  24  may partially or fully deflect any other one or more sections of tube  66  so as to maneuver distal-end assembly  134  to a desired location in head  41 , e.g., based on the tracked position of distal-end assembly  134  in anatomical image  35  shown in  FIG. 1  above. 
     Although the embodiments described herein mainly address medical probes used minimally invasive procedures carried out in the ear-nose-throat (ENT) of a patient, the methods and systems described herein can also be used in other applications. 
     It will thus 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 sub-combinations 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. 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.