Patent Publication Number: US-2022211413-A1

Title: Needle-Tract Assistant Including Components and Methods Thereof

Description:
BACKGROUND 
     In a healthy person, blood flowing from the stomach, esophagus, or intestines first flows through the liver. In an unhealthy person having, for example, liver damage, there can be blood flow-restricting blockages in the liver such that blood cannot easily flow therethrough. Such a condition is known as portal hypertension. Common causes of portal hypertension include alcohol abuse, too much iron in the liver (e.g., hemochromatosis), hepatitis B, hepatitis C, or blood clots in a vein that flows from the liver to the heart. When portal hypertension occurs, the blood flow-restricting blockages can elevate pressure in the portal vein causing it to rupture and seriously bleed. A person with portal hypertension can also have bleeding from the veins of the stomach, esophagus, or intestines (e.g., variceal bleeding), a buildup of fluid in the belly (e.g., ascites), or a buildup of fluid in the chest (e.g., hydrothorax). 
     Portal hypertension is often treated by way of a percutaneous procedure involving placement of a transjugular intrahepatic portosystemic shunt (“TIPS”) between the hepatic vein and the portal vein as shown in  FIG. 13  to establish blood flow through the liver. Placement of a portosystemic shunt between the right hepatic vein and the right portal vein is generally preferred. A typical procedure for placing a portosystemic shunt in accordance with the foregoing includes placing an introducer sheath in a distal portion of the right hepatic vein followed by advancing a stiffening cannula, optionally as part of a cannula-in-catheter assembly, through the introducer sheath to the distal portion of the right hepatic vein. A needle-in-catheter assembly is subsequently inserted into the stiffening cannula, the stiffening cannula is wedged against the wall of the right hepatic vein, and the needle-in-catheter assembly is thrust through the liver parenchyma into the right portal vein with a single needle throw. However, such a needle throw is blindly performed. As such, there is a risk of overshooting the portal vein in such procedures, which can introduce complications, prolong the procedures, decrease success rates, and the like. 
     Disclosed herein is a needle-tract assistant including components and methods thereof that address at least the forgoing shortcomings. 
     SUMMARY 
     Disclosed herein is a needle-tract assistant for establishing a needle tract of a predetermined length. The needle-tract assistant includes, in some embodiments, a needle thruster and a needle-in-catheter assembly removably loaded in the needle thruster. The needle thruster includes a cradle, a carriage within the cradle, and a plunger coupled to the carriage. The carriage is configured to move between a proximal-end portion and a distal-end portion of the cradle. The plunger is configured to move the carriage within the cradle. The plunger is also configured to allow a user to set the predetermined length of the needle tract before establishing the needle tract. The needle-in-catheter assembly includes a hub, a catheter tube extending from a distal-end portion of the hub, and a needle disposed within the catheter tube. 
     In some embodiments, the cradle of the needle thruster includes a longitudinal opening between the proximal-end portion and the distal-end portion of the cradle. The longitudinal opening is configured to allow the needle-in-catheter assembly to be removed from the needle thruster through the opening. 
     In some embodiments, the cradle of the needle thruster includes a proximal-end opening at a proximal end of the cradle and a distal-end opening at a distal end of the cradle. The plunger extends through the proximal-end opening of the cradle. The catheter tube and needle extend through the distal-end opening of the cradle when the needle-in-catheter assembly is disposed in the needle thruster. 
     In some embodiments, the cradle of the needle thruster includes a longitudinal rail extending along an inner surface of the cradle. The longitudinal rail is configured to guide movement of the plunger, the carriage, or both the plunger and the carriage within the cradle. 
     In some embodiments, the plunger of the needle thruster includes a longitudinal channel extending along an outer surface of the plunger. The longitudinal channel is configured to receive the longitudinal rail of the cradle. 
     In some embodiments, the cradle of the needle thruster includes a spiral rail spiraling around an inner surface of the cradle. The spiral rail is configured to guide movement of the plunger, the carriage, or both the plunger and the carriage within the cradle. The spiral rail is also configured to govern a linear velocity of the plunger, the carriage, or both the plunger and the carriage within the cradle. 
     In some embodiments, the cradle of the needle thruster includes a spiral channel spiraling around an outer surface of the plunger. The spiral channel is configured to receive the spiral rail of the cradle. 
     In some embodiments, the carriage of the needle thruster includes an unloading mechanism for unloading the needle-in-catheter assembly from the carriage. 
     In some embodiments, the unloading mechanism includes a compression spring-loaded lever shaped to form a proximal-end portion of a receptacle in the carriage. The receptacle is configured to receive the hub of the needle-in-catheter assembly. The lever is configured to compress the spring of the unloading mechanism upon pressing the lever toward the cradle. By pressing the lever toward the cradle, lever assumes a spring force of the unloading-mechanism spring and increases a length of the receptacle, which allows the hub of the needle-in-catheter assembly to be removed from the receptacle. 
     In some embodiments, the hub of the needle-in-catheter assembly includes a loading mechanism for loading the needle-in-catheter assembly in the carriage. 
     In some embodiments, the loading mechanism includes a compression spring-loaded proximal-end cap of the hub of the needle-in-catheter assembly. The proximal-end cap is configured to move toward the distal-end portion of the hub and compress the spring of the loading mechanism upon loading the hub in the receptacle of the carriage. A spring force exerted by the loading-mechanism spring holds the hub in the receptacle of the carriage. 
     In some embodiments, the hub of the needle-in-catheter assembly includes an internal chamber in a proximal-end portion of the hub. A port of the hub and one or more microlumens longitudinally extending through the catheter tube are fluidly connected to the internal chamber. 
     In some embodiments, the needle of the needle-in-catheter assembly extends through the internal chamber of the hub without a fluid connection with the internal chamber of the hub. 
     In some embodiments, a distal end of the needle of the needle-in-catheter assembly distally extends beyond a distal end of the catheter tube of the of the needle-in-catheter assembly. A distal-end portion of the catheter tube including the distal end of the catheter tube has a tapered distal tip including one or more openings corresponding to the one or more microlumens of the catheter tube. 
     Also disclosed herein is a needle-in-catheter assembly for establishing a needle tract. The needle-in-catheter assembly includes a hub, a catheter tube extending from a distal-end portion of the hub, and a needle disposed within the catheter tube. The catheter tube is a double-walled catheter tube including an outer wall and an inner wall. The needle is fixed to a compression spring-loaded proximal-end cap of the hub. 
     In some embodiments, the needle is disposed within a needle lumen longitudinally extending through the catheter tube. The needle lumen is defined by an inner surface of the inner wall of the catheter tube. 
     In some embodiments, the catheter tube includes one or more microlumens longitudinally extending through the catheter tube. Each of the one or more microlumens defined by an inner surface of the outer wall of the catheter tube, an outer surface of the inner wall of the catheter tube, and one or more struts longitudinally extending through the catheter tube between the outer wall and the inner wall of the catheter tube. 
     In some embodiments, the hub includes an internal chamber in a proximal-end portion of the hub. A port of the hub and the one or more microlumens are fluidly connected to the internal chamber. 
     In some embodiments, the needle extends through the internal chamber of the hub without a fluid connection with the internal chamber. 
     In some embodiments, a distal end of the needle distally extends beyond a distal end of the catheter tube. A distal-end portion of the catheter tube including the distal end of the catheter tube has a tapered distal tip including one or more openings corresponding to the one or more microlumens of the catheter tube. 
     In some embodiments, the hub includes a loading mechanism including the proximal-end cap of the hub for loading the needle-in-catheter assembly in a carriage of a needle thruster. The proximal-end cap is configured to move toward the distal-end portion of the hub and compress the spring of the loading mechanism upon loading the hub in a receptacle of the carriage. A spring force exerted by the loading-mechanism spring holds the hub in the receptacle of the carriage. 
     In some embodiments, the hub includes a longitudinal handle extending from the hub between a proximal-end portion and the distal-end portion of the hub. 
     Also disclosed herein is a method of establishing a needle tract of a predetermined length with a needle-tract assistant. The method includes, in some embodiments, inserting a needle-in-catheter assembly into a stiffening cannula disposed in an introducer sheath positioned in a hepatic vein, the needle-in-catheter assembly including a needle having a distal end extending beyond that of a catheter surrounding the needle; moving a plunger of a needle thruster to set a carriage coupled to the plunger in position within a cradle of the needle thruster for establishing the needle tract of the predetermined length; loading a hub of the needle-in-catheter assembly in the carriage of the needle thruster; and thrusting the plunger of the needle thruster toward a distal end of the needle thruster to thrust the needle-in-catheter assembly through a liver parenchyma into a portal vein, thereby forming the needle tract of the predetermined length. 
     In some embodiments, the method further includes radiographically determining a length for the needle tract of the predetermined length before setting the carriage of the needle thruster in position within the cradle for establishing the needle tract of the predetermined length. 
     In some embodiments, the method further includes radiographically confirming a length of the needle tract after forming the needle tract of the predetermined length by counting a number of evenly spaced radiopaque rings on the catheter of the needle-in-catheter assembly. 
     These and other features of the concepts provided herein will become more apparent to those of skill in the art in view of the accompanying drawings and following description, which disclose particular embodiments of such concepts in greater detail. 
    
    
     
       DRAWINGS 
         FIG. 1  illustrates a first view of a first needle-tract assistant, in accordance with some embodiments. 
         FIG. 2  illustrates a second view of the first needle-tract assistant, in accordance with some embodiments. 
         FIG. 3  illustrates a third view of the first needle-tract assistant, in accordance with some embodiments. 
         FIG. 4  illustrates a first view of a second needle-tract assistant, in accordance with some embodiments. 
         FIG. 5  illustrates a second view of the second needle-tract assistant, in accordance with some embodiments. 
         FIG. 6  illustrates a third view of the second needle-tract assistant, in accordance with some embodiments. 
         FIG. 7  illustrates a transverse cross section of either the first needle-track assistant or the second needle-tract assistant, in accordance with some embodiments. 
         FIG. 8  illustrates a first view of a distal-end portion of a needle disposed in a catheter tube, in accordance with some embodiments. 
         FIG. 9  illustrates a second of a distal-end portion of a needle disposed in a catheter tube, in accordance with some embodiments. 
         FIG. 10  illustrates a first view of a longitudinal cross section of the first needle-tract assistant, in accordance with some embodiments. 
         FIG. 11  illustrates a second view of a longitudinal cross section of the first needle-tract assistant, in accordance with some embodiments. 
         FIG. 12  illustrates a catheter tube-advancing mechanism of a hub of a needle-in-catheter assembly, in accordance with some embodiments. 
         FIG. 13  illustrates a procedure involving placement of a TIPS between a hepatic vein and a portal vein, in accordance with some embodiments. 
     
    
    
     DESCRIPTION 
     Before some particular embodiments are disclosed in greater detail, it should be understood that the particular embodiments disclosed herein do not limit the scope of the concepts provided herein. It should also be understood that a particular embodiment disclosed herein can have features that can be readily separated from the particular embodiment and optionally combined with or substituted for features of any of a number of other embodiments disclosed herein. 
     Regarding terms used herein, it should also be understood the terms are for the purpose of describing some particular embodiments, and the terms do not limit the scope of the concepts provided herein. Ordinal numbers (e.g., first, second, third, etc.) are generally used to distinguish or identify different features or steps in a group of features or steps, and do not supply a serial or numerical limitation. For example, “first,” “second,” and “third” features or steps need not necessarily appear in that order, and the particular embodiments including such features or steps need not necessarily be limited to the three features or steps. Labels such as “left,” “right,” “top,” “bottom,” “front,” “back,” and the like are used for convenience and are not intended to imply, for example, any particular fixed location, orientation, or direction. Instead, such labels are used to reflect, for example, relative location, orientation, or directions. Singular forms of “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. 
     With respect to “proximal,” a “proximal portion” or a “proximal-end portion” of, for example, a catheter disclosed herein includes a portion of the catheter intended to be near a clinician when the catheter is used on a patient. Likewise, a “proximal length” of, for example, the catheter includes a length of the catheter intended to be near the clinician when the catheter is used on the patient. A “proximal end” of, for example, the catheter includes an end of the catheter intended to be near the clinician when the catheter is used on the patient. The proximal portion, the proximal-end portion, or the proximal length of the catheter can include the proximal end of the catheter; however, the proximal portion, the proximal-end portion, or the proximal length of the catheter need not include the proximal end of the catheter. That is, unless context suggests otherwise, the proximal portion, the proximal-end portion, or the proximal length of the catheter is not a terminal portion or terminal length of the catheter. 
     With respect to “distal,” a “distal portion” or a “distal-end portion” of, for example, a catheter disclosed herein includes a portion of the catheter intended to be near or in a patient when the catheter is used on the patient. Likewise, a “distal length” of, for example, the catheter includes a length of the catheter intended to be near or in the patient when the catheter is used on the patient. A “distal end” of, for example, the catheter includes an end of the catheter intended to be near or in the patient when the catheter is used on the patient. The distal portion, the distal-end portion, or the distal length of the catheter can include the distal end of the catheter; however, the distal portion, the distal-end portion, or the distal length of the catheter need not include the distal end of the catheter. That is, unless context suggests otherwise, the distal portion, the distal-end portion, or the distal length of the catheter is not a terminal portion or terminal length of the catheter. 
     Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the art. 
     As set forth above, portal hypertension is often treated by way of a percutaneous procedure involving placement of a TIPS between the hepatic vein and the portal vein as shown in  FIG. 13  to establish blood flow through the liver. Placement of a portosystemic shunt between the right hepatic vein and the right portal vein is generally preferred. A typical procedure for placing a portosystemic shunt in accordance with the foregoing includes placing an introducer sheath in a distal portion of the right hepatic vein followed by advancing a stiffening cannula, optionally as part of a cannula-in-catheter assembly, through the introducer sheath to the distal portion of the right hepatic vein. A needle-in-catheter assembly is subsequently inserted into the stiffening cannula, the stiffening cannula is wedged against the wall of the right hepatic vein, and the needle-in-catheter assembly is thrust through the liver parenchyma into the right portal vein with a single needle throw. However, such a needle throw is blindly performed. As such, there is a risk of overshooting the portal vein in such procedures, which can introduce complications, prolong the procedures, decrease success rates, and the like. 
     Disclosed herein is a needle-tract assistant including components and methods thereof that address at least the forgoing shortcomings. 
       FIGS. 1-3  illustrate different views of a first needle-tract assistant  100 , in accordance with some embodiments.  FIGS. 4-6  illustrate different views of a second needle-tract assistant  200 , in accordance with some embodiments.  FIG. 7  illustrates a transverse cross section of either the first needle-track assistant  100  or the second needle-tract assistant  200 , in accordance with some embodiments.  FIGS. 10 and 11  illustrate different views of a longitudinal cross section of the first needle-tract assistant  100 , in accordance with some embodiments.  FIG. 12  illustrates a catheter tube-advancing mechanism of a hub  132  of a needle-in-catheter assembly  130  or  230 , in accordance with some embodiments. 
     The needle-tract assistant  100  or  200  includes a needle thruster  110  or  210  and the needle-in-catheter assembly  130  or  230  removably loaded in the needle thruster  110  or  210 . 
     Beginning with the needle thruster  110  or  210 , the needle thruster  110  includes a cradle  112  or  212 , a carriage  114  or  214  movably disposed within the cradle  112  or  212 , and a plunger  116  or  216  coupled to the carriage  114  or  214 . Each of the cradle  112  or  212 , the carriage  114  or  214 , and the plunger  116  or  216  will now be described. 
     The cradle  112  or  212  of the needle thruster  110  or  210  includes a longitudinal opening between a proximal-end portion and a distal-end portion of the cradle  112  or  212 . The longitudinal opening is configured to allow the needle-in-catheter assembly  130  or  230  to be inserted or removed from the needle thruster  110  or  210  through the opening. 
     The cradle  112  or  212  of the needle thruster  110  or  210  includes a proximal-end opening at a proximal end of the cradle  112  or  212  and a distal-end opening at a distal end of the cradle  112  or  212 . The plunger  116  or  216  extends through the proximal-end opening of the cradle  112  or  212 . A catheter tube  134  or  234  and a needle  137  or  237  extend through the distal-end opening of the cradle  112  or  212  when the needle-in-catheter assembly  130  or  230  is disposed in the needle thruster  110  or  210 . While configured differently for each needle thruster of the needle thrusters  110  and  210 , the distal-end opening at the distal end of the cradle  112  or  212  has smaller dimensions (e.g., diameter, width, etc.) than a distal end of the needle-in-catheter assembly  130  or  230 , thereby providing a stop for the needle-in-catheter assembly  130  or  230 . 
     The cradle  112  of the needle thruster  110  includes a longitudinal rail  118  extending along an inner surface of the cradle  112 . The longitudinal rail  118  is configured to guide movement of the plunger  116 , the carriage  114 , or both the plunger  116  and the carriage  114  within the cradle  112 . Differently, the cradle  212  of the needle thruster  210  includes a spiral rail  218  spiraling around an inner surface of the cradle  212 . The spiral rail  218  is configured to guide movement of the plunger  216 , the carriage  214 , or both the plunger  216  and the carriage  214  within the cradle  212 . The spiral rail  218  is also configured to govern a linear velocity of the plunger  216 , the carriage  214 , or both the plunger  216  and the carriage  214  within the cradle  212 . 
     The carriage  114  or  214  of the needle thruster  110  or  210  is configured to move between the proximal-end portion and the distal-end portion of the cradle  112  or  212  such as on a same or different rail than the longitudinal rail  118  or spiral rail  218  along the inner surface of the cradle  112  or  212 . 
     The carriage  114  or  214  of the needle thruster  110  or  210  includes an unloading mechanism for unloading the needle-in-catheter assembly  130  or  230  from the carriage  114  or  214 . The unloading mechanism includes a compression spring-loaded lever  122  or  222  shaped to form a proximal-end portion of a receptacle  124  or  224  (not shown) in the carriage  114  or  214 . (For the receptacle  224 , see the receptacle  124  of  FIGS. 10 and 11 . The receptacle  224  is analogous to the receptacle  124 .) The receptacle  124  or  224  is configured to receive the hub  132  or  232  of the needle-in-catheter assembly  130  or  230 . The lever  122  or  222  is configured to compress the spring  126  or  226  (not shown) of the unloading mechanism upon pressing the lever  122  or  222  toward the cradle  112  or  212 . (For the spring  226 , see the spring  126  of  FIGS. 10 and 11 . The spring  226  is analogous to the spring  126 .) By pressing the lever  122  or  222  the toward the cradle  112  or  212 , the lever  122  or  222  assumes a spring force of the unloading-mechanism spring  126  or  226  and increases a length of the receptacle  124  or  224 , which allows the hub  132  or  232  of the needle-in-catheter assembly  130  or  230  to be removed from the receptacle  124  or  224 . 
     The plunger  116  or  216  of the needle thruster  110  or  210  is configured to move the carriage  114  or  214  within the cradle  112  or  212 . The plunger  116  of the needle thruster  110  includes a longitudinal channel  120  extending along an outer surface of the plunger  116 . The longitudinal channel  120  is configured to receive the longitudinal rail  118  of the cradle  112 . Differently, the cradle  212  of the needle thruster  210  includes a spiral channel  220  spiraling around an outer surface of the plunger  216 . The spiral channel  220  is configured to receive the spiral rail  218  of the cradle  212 . 
     The plunger  116  or  216  of the needle thruster  110  or  210  is also configured to allow a user to set the carriage  114  or  214  within the cradle  112  or  212  in accordance with the predetermined length of the needle tract before establishing the needle tract. The needle thruster  210  is different from the needle thruster  110  in that the needle thruster  210  is also configured to allow the user to lock the carriage  214  within the cradle  212  once set in accordance with the predetermined length of the needle tract before establishing the needle tract. As best shown in  FIG. 6 , the needle thruster  210  includes a compression spring-loaded lever  228  along a longitudinal side of the cradle  212 . The lever  228  includes a tooth configured to extend through the longitudinal side of the cradle  212  and engage a toothed rack incorporated into the carriage  214  when the spring between the lever  228  and the longitudinal side of the cradle  212  is in its most relaxed state, thereby locking the carriage  214  within the cradle  212 . When the lever  228  is pressed toward the longitudinal side of the cradle  212 , the tooth disengages the toothed rack of the carriage  214  so the plunger can freely move the carriage  214  to set the carriage  214  in accordance with the predetermined length of the needle tract before establishing the needle tract. 
     With the exception of the compression spring  126  or  226 , which can be made of, for example, stainless steel, the needle thruster  110  or  210  can be made by molding pieces of the needle thruster  110  or  210  and coupling the resulting molded pieces together to make the needle thruster  110  or  210 . The molded pieces can be molded by, for example, injection molding with polyethylene, polycarbonate, or some other medically acceptable thermoplastic. The molded pieces can be coupled together by pressing the molded pieces together if configured with snap-together connectors, adhering the molded pieces together with an adhesive, bonding the molded pieces together with solvent, or a combination thereof. 
     Adverting to the needle-in-catheter assembly  130  or  230 , the needle-in-catheter assembly  130  or  230  includes the hub  132  or  232 , the catheter tube  134  or  234  extending from a distal-end portion of the hub  132  or  232 , and the needle  137  or  237  disposed within the catheter tube  134  or  234 . (See  FIG. 8 .) Each of the hub  132  or  232 , the catheter tube  134  or  234 , and the needle  137  or  237  will now be described. 
     The hub  132  or  232  of the needle-in-catheter assembly  130  or  230  includes a longitudinal handle  133  or  233  extending from the hub  132  or  232  between a proximal-end portion and the distal-end portion of the hub  132  or  232 . The handle  133  or  233  is configured for handling the needle-in-catheter assembly  130  or  230 . For example, the handle  133  or  233  can be used to manipulate the needle-in-catheter assembly  130  or  230  when using the needle-in-catheter assembly  130  or  230  separately from the needle thruster  110  or  210 , loading the needle-in-catheter assembly  130  or  230  in the needle thruster  110  or  210 , or when unloading the needle-in-catheter assembly  130  or  230  from the needle thruster  110  or  210 . 
     The hub  132  or  232  of the needle-in-catheter assembly  130  or  230  includes a catheter tube-advancing mechanism for advancing the catheter tube  134  or  234  with respect to the needle  137  or  237 . The catheter tube-advancing mechanism includes a threaded distal-end plug  139  or  239  (not shown) of the hub  132  or  232  of the needle-in-catheter assembly  130  or  230 . (For the distal-end plug  239 , see the distal-end plug  139  of  FIG. 12 . The distal-end plug  239  is analogous to the distal-end plug  139 .) The distal-end plug  139  or  239  of the catheter tube-advancing mechanism is configured to advance from the distal-end portion of the hub  132  or  232  upon turning the distal-end plug  139  or  239  in a first direction. Upon turning the distal-end plug  139  or  239  in a second direction, the catheter tube-advancing mechanism is configured to withdraw the distal-end plug  139  or  239  into the distal-end portion of the hub  132  or  232 . Because the catheter tube  134  or  234  is fixedly attached to the distal-end plug  139  or  239 , the catheter tube  134  or  234  is also advanced from the distal-end portion of the hub  132  or  232  upon turning the distal-end plug  139  or  239  in the first direction and withdrawn into the distal-end portion of the hub  132  or  232  upon turning the distal-end plug  139  or  239  in the second direction. The catheter tube-advancing mechanism allows the catheter tube  134  or  234  to be advanced up to or beyond a distal tip of the needle  137  or  237  such as after establishing the needle tract of the predetermined length with the needle-in-catheter assembly  130  or  230 . The needle  137  or  237  can be subsequently removed from the needle-in-catheter assembly  130  or  230  by disconnecting a compression spring-loaded proximal-end cap  135  or  235  of the hub  132  or  232  of the needle-in-catheter assembly  130  or  230  and withdrawing the needle  137  or  237  from the needle-in-catheter assembly  130  or  230 . 
     The hub  132  or  232  of the needle-in-catheter assembly  130  or  230  includes a loading mechanism for loading the needle-in-catheter assembly  130  or  230  in the carriage  114  or  214 . The loading mechanism includes the compression spring-loaded proximal-end cap  135  or  235  of the hub  132  or  232  of the needle-in-catheter assembly  130  or  230 . The proximal-end cap  135  or  235  is configured to move toward the distal-end portion of the hub  132  or  232  and compress the spring  136  or  236  (not shown) of the loading mechanism upon loading the hub  132  or  232  in the receptacle  124  or  224  of the carriage  114  or  214 . (For the spring  236 , see the spring  136  of  FIGS. 10 and 11 . The spring  236  is analogous to the spring  136 .) A spring force exerted by the loading-mechanism spring  136  or  236  holds the hub  132  or  232  in the receptacle  124  or  224  of the carriage  114  or  214 . 
     The hub  132  or  232  of the needle-in-catheter assembly  130  or  230  optionally includes a needle-advancing mechanism for advancing the needle  137  or  237  with respect to the catheter tube  134  or  234  or both the needle  137  or  237  and the catheter tube  134  or  234  together with respect the hub  132  or  232 . Such a needle-advancing mechanism can include a threaded needle-advancing mechanism configured to advance the needle  137  or  237  or both the needle and the catheter tube  134  or  234  together upon turning a threaded element (e.g., the proximal-end cap  135  or  235 ) of the threaded needle-advancing mechanism in a first direction. Upon turning the threaded element in a second direction, the threaded needle-advancing mechanism is configured to retract the needle  137  or  237  or both the needle and the catheter tube  134  or  234  together. Such a needle-advancing mechanism can alternatively include a slide-based needle-advancing mechanism configured to advance the needle  137  or  237  or both the needle and the catheter tube  134  or  234  together upon sliding a slideable element (e.g., a tab disposed in a longitudinal slot of the handle  133  or  233 ) of the slideable needle-advancing mechanism in a first direction. Upon sliding the slideable element in a second direction, the slideable needle-advancing mechanism is configured to retract the needle  137  or  237  or both the needle and the catheter tube  134  or  234  together. 
     The hub  132  or  232  of the needle-in-catheter assembly  130  or  230  includes an internal chamber  138  or  238  (not shown) in a proximal-end portion of the hub  132  or  232 . (For the internal chamber  238 , see the internal chamber  138  of  FIGS. 10 and 11 . The internal chamber  238  is analogous to the internal chamber  138 .) A port  140  or  240  of the hub  132  or  232  and one or more microlumens  141  or  241  longitudinally extending through the catheter tube  134  or  234  are fluidly connected to the internal chamber  138  or  238 . The needle  137  or  237  of the needle-in-catheter assembly  130  or  230  extends through the internal chamber  138  or  238  of the hub  132  or  232  without a fluid connection with the internal chamber  138  or  238  of the hub  132  or  232 . The needle  137  or  237  is fixed to the proximal-end cap  135  or  235  of the hub  132  or  232 . 
       FIGS. 8 and 9  illustrate different views of a distal-end portion of the needle  137  or  237  disposed in the catheter tube  134  or  234 , in accordance with some embodiments. 
     The catheter tube  134  or  234  of the needle-in-catheter assembly  130  or  230  is a double-walled catheter tube including an outer wall  142  or  242  and an inner wall  144  or  244 . A distal-end portion of the catheter tube  134  or  234  including a distal end of the catheter tube  134  or  234  has a tapered distal tip including one or more openings corresponding to one or more microlumens  141  or  241  of the catheter tube  134  or  234 . Each of the one or more microlumens  141  or  241  is defined by an inner surface of the outer wall  142  or  242  of the catheter tube  134  or  234 , an outer surface of the inner wall  144  or  244  of the catheter tube  134  or  234 , and one or more struts  146  or  246  longitudinally extending through the catheter tube  134  or  234  between the outer wall  142  or  242  and the inner wall  144  or  244  of the catheter tube  134  or  234 . The one or more microlumens  141  or  241  are configured to allow a bodily fluid such as blood to flash back into the internal chamber  138  or  238  for drawing the bodily fluid from the port  140  or  240  without withdrawing the needle  137  or  237 . 
     The catheter tube  134  or  234  of the needle-in-catheter assembly  130  or  230  can include a number of evenly spaced radiopaque rings  148  or  248  on the catheter tube  134  or  234  for radiographically confirming a length of the needle tract after forming the needle tract of the predetermined length by counting of the needle-in-catheter assembly  130  or  230 . 
     The needle  137  or  237  of the needle-in-catheter assembly  130  or  230  can be a hollow needle or a solid needle as shown. A distal end of the needle  137  or  237  distally extends beyond the distal end of the catheter tube  134  or  234  of the of the needle-in-catheter assembly  130  or  230 . The needle  137  or  237  is disposed within a needle lumen longitudinally extending through the catheter tube  134  or  234 . The needle lumen is defined by an inner surface of the inner wall  144  or  244  of the catheter tube  134  or  234 . 
     With the exception of the cannula tube  134  or  234 , the needle  137  or  237 , and the compression spring  136  or  236 , which can respectively be made of polyurethane, stainless steel, and stainless steel, the needle-in-catheter assembly  130  or  230  such as the hub  132  or  232  can be made by molding pieces of the needle-in-catheter assembly  130  or  230  and coupling the resulting molded pieces together to make the needle-in-catheter assembly  130  or  230 . The molded pieces can be molded by, for example, injection molding with polyethylene, polycarbonate, or some other medically acceptable thermoplastic. The molded pieces can be coupled together by pressing the molded pieces together if configured with snap-together connectors, adhering the molded pieces together with an adhesive, bonding the molded pieces together with solvent, or a combination thereof. 
     Methods 
     Each needle-tract assistant of the needle-tract assistants  100  and  200  is configured for establishing a needle tract of a predetermined length during at least a procedure involving placing a portosystemic shunt between the hepatic vein and the portal vein, which reduces the risk of overshooting the portal vein. As such, the needle-tract assistants  100  and  200  can reduce complications, shorten procedure times, increase success rates, and the like for procedures such as the foregoing procedure. 
     A method of establishing a needle tract of a predetermined length with the needle-tract assistant  100  or  200  includes inserting the needle-in-catheter assembly  130  or  230  into a stiffening cannula disposed in an introducer sheath positioned in a hepatic vein, the needle-in-catheter  130  or  230  assembly including the needle  137  or  237  having the distal end extending beyond that of the catheter tube  134  or  234  surrounding the needle  137  or  237 ; moving the plunger  116  or  216  of the needle thruster  110  or  210  to set the carriage  114  or  214  coupled to the plunger  116  or  216  in position within the cradle  112  or  212  of the needle thruster  110  or  210  for establishing the needle tract of the predetermined length; loading the hub  132  or  232  of the needle-in-catheter assembly  130  or  230  in the carriage  114  or  214  of the needle thruster  110  or  210 ; and thrusting the plunger  116  or  216  of the needle thruster  110  or  210  toward a distal end of the needle thruster  110  or  210  to thrust the needle  137  or  237  and catheter tube  134  or  234  of the needle-in-catheter assembly  130  or  230  through a liver parenchyma into a portal vein, thereby forming the needle tract of the predetermined length. 
     The method further includes advancing the catheter tube  134  or  234  up to or beyond the distal tip of the needle  137  or  237  after establishing the needle tract of the predetermined length by turning the distal-end plug  139  or  239  in the first direction; and removing the needle  137  or  237  from the needle-in-catheter assembly  130  or  230  by disconnecting the proximal-end cap  135  or  235  of the hub  132  or  232  of the needle-in-catheter assembly  130  or  230  and withdrawing the needle  137  or  237  from the needle-in-catheter assembly  130  or  230 . 
     The method further includes radiographically determining a length for the needle tract of the predetermined length before setting the carriage  114  or  214  of the needle thruster  110  or  210  in position within the cradle  114  or  214  for establishing the needle tract of the predetermined length. 
     The method further includes radiographically confirming the length of the needle tract after forming the needle tract of the predetermined length by counting a number of the evenly spaced radiopaque rings  148  or  248  on the catheter tube  134  or  234  of the needle-in-catheter assembly  130  or  230 . 
     While some particular embodiments have been disclosed herein, and while the particular embodiments have been disclosed in some detail, it is not the intention for the particular embodiments to limit the scope of the concepts provided herein. Additional adaptations and/or modifications can appear to those of ordinary skill in the art, and, in broader aspects, these adaptations and/or modifications are encompassed as well. Accordingly, departures may be made from the particular embodiments disclosed herein without departing from the scope of the concepts provided herein.