Patent Publication Number: US-2021187248-A1

Title: Methods for determining a position of a first medical device with respect to a second medical device, and related systems and medical devices

Description:
FIELD 
     This document relates to medical devices. More specifically, this document relates to methods for determining a position of a first medical device with respect to a second medical device, and related systems and medical devices. 
     SUMMARY 
     The following summary is intended to introduce the reader to various aspects of the detailed description, but not to define or delimit any invention. 
     Systems of medical devices are disclosed. According to some aspects, a system of medical devices includes a first medical device including an elongate member. The elongate member has a proximal portion defining a proximal end, a distal portion defining a distal end, and a lumen extending longitudinally therethrough from the proximal end to the distal end. The system further includes a second medical device including a needle advanceable through the lumen from the proximal end towards the distal end. The system further includes at least a first RLC circuit including an excitation voltage source, a resistor, a capacitor, an inductor, and an output voltage sensor. The inductor includes a coil that is supported by the first medical device and wound around the lumen. As the needle is advanced through the lumen, an output voltage of the RLC circuit is an indicator of a longitudinal position of the needle with respect to the elongate member. The voltage sensor is configured to sense the output voltage of the RLC circuit and generate a sensor signal based on the output voltage. A processor is in communication with the voltage sensor and is configured to receive and process the sensor signal from the voltage sensor, and generate a processor signal based on the sensor signal. An output device is in communication with the processor and is configured to receive the processor signal and generate an output based on the processor signal. The output is an indicator of the longitudinal position of the needle with respect to the elongate member. 
     In some examples, the elongate member includes a sidewall extending longitudinally between the proximal end and the distal end, and radially between an inner surface and an outer surface, and the coil is embedded in the sidewall. 
     In some examples, the inductor further includes a magnetic core positioned radially inwardly of the coil and supported by the first medical device. The magnetic core can be embedded in the sidewall. 
     In some examples, the inductor further includes a magnetic core, and the magnetic core is provided by a magnetic coating on the needle. In some examples, the needle is fabricated from a magnetic material to provide a magnetic core of the inductor. 
     In some examples, the coil extends continuously from the proximal portion to the distal portion. In some examples, the coil is positioned within the distal portion, proximate the distal end. 
     In some examples, the system further includes a second RLC circuit including a second excitation voltage source, a second resistor, a second capacitor, a second inductor comprising a second coil, and a second output voltage sensor. The second coil can be supported by the first medical device, wound around the lumen, and spaced proximally from the coil of the first RLC circuit. As the needle is advanced through the lumen, an output voltage of the second RLC circuit can be an additional indicator of the longitudinal position of the needle with respect to the elongate member. 
     In some examples, the output device includes at least one of a light and a screen. The output can include illumination of the light when the needle is at a predetermined longitudinal position with respect to the elongate member. The output can include a GUI showing an image of the longitudinal position of the needle with respect to the elongate member. 
     Methods for determining a position of a first medical device with respect to a second medical device are also disclosed. According to some aspects, a method for determining a position of a first medical device with respect to a second medical device includes: a. advancing the second medical device into a lumen of the first medical device, from a proximal end of the first medical device towards a distal end of the first medical device; b. during step a., applying an excitation voltage to an RLC circuit associated with the first medical device, and sensing an output voltage of the RLC circuit, whereby the output voltage is an indicator of a longitudinal position of the second medical device with respect to the first medical device; and c. generating an output based on the output voltage, wherein the output is an indicator of the longitudinal position of the second medical device with respect to the first medical device. 
     In some examples, step a. includes passing the second medical device through a coil of an inductor of the RLC circuit. 
     In some examples, step c. includes generating an image of the longitudinal position of the second medical device with respect to the first medical device, and updating the image as the output voltage changes. 
     In some examples, the method further includes adjusting a position of the second medical device with respect to the first medical device based on the output. 
     Medical devices are also disclosed. According to some aspects, a medical device includes an elongate member having a proximal portion defining a proximal end, a distal portion defining a distal end, a sidewall extending longitudinally between the proximal end and the distal end and radially between an inner surface that and an outer surface, and a lumen defined by the inner surface and extending longitudinally through the elongate member from the proximal end to the distal end. The medical device further includes an inductor including a coil embedded in the sidewall and wound around the lumen. The coil is electrically connectable to an excitation voltage source, a resistor, a capacitor, and an output voltage sensor to form an RLC circuit. 
     In some examples, the inductor further includes a magnetic core positioned radially inwardly of the coil and supported by the elongate member. The magnetic core can be embedded in the sidewall. 
     In some examples, the coil extends continuously from the proximal portion to the distal portion. In some examples, the coil is positioned within the distal portion, proximate the distal end. 
     In some examples, the device includes a second inductor. The second inductor can include a second coil embedded in the sidewall and wound around the lumen. The second coil can be spaced proximally from the coil of the first RLC circuit. The second coil can be electrically connectable to a second excitation voltage source, a second resistor, and a second output voltage sensor to form a second RLC circuit. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings are for illustrating examples of articles, methods, and apparatuses of the present disclosure and are not intended to be limiting. In the drawings: 
         FIG. 1  is a perspective view of a first example system of medical devices, showing a first medical device, second medical device, and control unit, spaced apart and disconnected from each other; 
         FIG. 2  is a perspective view of the system of  FIG. 1 , showing the second medical device inserted into the first medical device, and the first medical device connected to the control unit; 
         FIG. 3  is a longitudinal cross section taken along line  3 - 3  in  FIG. 2 , schematically showing the control unit and related parts; 
         FIG. 4  is a simplified graph showing the change in output voltage as the second medical device of  FIGS. 1 to 3  is advanced through the first medical device of  FIGS. 1 to 3 ; 
         FIG. 5  is a cross-section similar to that of  FIG. 3 , showing a first medical device, second medical device, and control unit of a second example system; 
         FIG. 6  is a simplified graph showing the change in output voltage as the second medical device of  FIG. 5  is advanced through the first medical device of  FIG. 5 ; 
         FIG. 7  is a cross-section similar to that of  FIG. 3 , showing a first medical device, second medical device, and control unit of a third example system; 
         FIG. 8  is a cross-section similar to that of  FIG. 3 , showing a first medical device, second medical device, and control unit of a fourth example system; 
         FIG. 9  is a simplified graph showing the change in output voltage as the second medical device of  FIG. 8  is advanced through the first medical device of  FIG. 8 ; 
         FIG. 10  is a cross-section similar to that of  FIG. 3 , showing a first medical device, second medical device, and control unit of a fifth example system; 
         FIG. 11  is a simplified graph showing the change in output voltage as the second medical device of  FIG. 10  is advanced through the first medical device of  FIG. 10 ; and 
         FIG. 12  is a cross-section similar to that of  FIG. 3 , showing a first medical device, second medical device, and control unit of a sixth example system. 
     
    
    
     DETAILED DESCRIPTION 
     Various apparatuses or processes or compositions will be described below to provide an example of an embodiment of the claimed subject matter. No example described below limits any claim and any claim may cover processes or apparatuses or compositions that differ from those described below. The claims are not limited to apparatuses or processes or compositions having all of the features of any one apparatus or process or composition described below or to features common to multiple or all of the apparatuses or processes or compositions described below. It is possible that an apparatus or process or composition described below is not an embodiment of any exclusive right granted by issuance of this patent application. Any subject matter described below and for which an exclusive right is not granted by issuance of this patent application may be the subject matter of another protective instrument, for example, a continuing patent application, and the applicants, inventors or owners do not intend to abandon, disclaim or dedicate to the public any such subject matter by its disclosure in this document. 
     Generally disclosed herein are systems of medical devices, where the systems include an RLC circuit (i.e. at least one RLC circuit). The RLC circuit can be used to determine a position of a first medical device of the system with respect to a second medical device of the system. For example, a system of medical devices can include a first medical device (e.g. a catheter in the form of a sheath or dilator) that in use is advanced into a patient&#39;s body to a target location (e.g. advanced via a femoral vein to a patient&#39;s heart) and a second medical device (e.g. a perforation device including a needle) that in use is passed through the first medical device towards the target location. The inductor of the RLC circuit can include a coil that that is wound so that as the second medical device is passed through the first medical device, it passes through the coil. In use, an excitation voltage can be applied to the RLC circuit, and an output voltage of the RLC circuit can be sensed and monitored. Passage of the second medical device through the coil can change the inductance of the inductor and thus change the output voltage of the RLC circuit (e.g. the output voltage can become non-resonant). The output voltage can thus be used as an indicator of a position of the second medical device with respect to the first medical device. Accordingly, by sensing the output voltage, it can be determined, for example, whether a perforating tip of a needle is approaching a distal end of the catheter, or has passed beyond a distal end of the catheter. This can facilitate ease of use of the medical devices, and enhance patient safety. 
     Referring now to  FIGS. 1 and 2 , a first example system  100  of medical devices is shown. In the example shown, the system  100  includes a first medical device  102  in the form of a catheter, and a second medical device  104  in the form of a perforation device. The catheter can be, for example, a sheath, a dilator, or an alternative device that is intended for use by passing another medical device therethrough (e.g. coaxially therethrough). The perforation device can be, for example, a mechanical perforation device, or a radiofrequency (RF) perforation device. In alternative examples, the second medical device can be alternative type of medical device that is intended for use by being passed through another medical device. 
     Referring also to  FIG. 3 , in the example shown, the first medical device  102  includes a hub  106  and an elongate member  108  extending from the hub  106 . The elongate member  108  has a proximal portion  110  defining a proximal end  112  of the elongate member  108 , a distal portion  114  defining a distal end  116  of the elongate member  108 , and a lumen  118  (shown in  FIG. 3 ) extending longitudinally through the elongate member  108  from the proximal end  112  to the distal end  116 . The elongate member  108  includes a sidewall  120 , which extends longitudinally between the proximal end  112  and the distal end  116 , and radially between an inner surface  122  (shown in  FIG. 3 ) that defines the lumen  118 , and an outer surface  124 . The sidewall  120  can be made from an electrically insulating material, such as an electrically insulating polymer (e.g. polyurethane). 
     Referring still to  FIGS. 1 to 3 , in the example shown, the second medical device  104  includes a hub  126  and a needle  128  extending from the hub  126 . The needle  128  is electrically conductive (e.g. is metallic). The needle  128  has a proximal portion  130  defining a proximal end  132  of the needle  128 , and a distal portion  134  defining a distal end  136  of the needle  128 . The distal end  136  of the needle  128  includes a perforating tip  138 . As shown in  FIG. 2 , the needle  128  is advanceable through the hub  106  and through the lumen  118 , from the proximal end  112  of the elongate member  108  towards the distal portion  114  of the elongate member  108 , to position the perforating tip  138  of the needle  128  proud of the distal end  116  of the elongate member  108 . 
     Referring to  FIG. 3 , the system  100  further includes an inductor, which in the example shown includes a coil  140 , and a magnetic core  142 . The inductor is part of an RLC circuit. RLC circuits in general are known in the art, and are not described in detail herein. Briefly, in addition to the inductor, the RLC circuit further includes a resistor and a capacitor, as well as an excitation voltage source and an output voltage sensor. The parts of the RLC circuit, other than the inductor, are shown collectively at  144  in  FIG. 3 . 
     Referring still to  FIG. 3 , in the example shown, the coil  140  is supported by the first medical device  102 , and is wound around the lumen  118 . As used herein, the term “supported by” indicates that the coil is integral with, embedded in, connected to, mounted to, adhered to, affixed to, or otherwise secured to the first medical device  102 , so that the coil moves with the first medical device  102 . In the example shown, the coil is embedded in the sidewall  120 . The coil  140  can be, for example, a wire such as copper wire. 
     Referring still to  FIG. 3 , in the example shown, the magnetic core  142  is positioned within the coil  140  and is also supported by the first medical device  102 . In the example shown, the magnetic core  142  is embedded in the sidewall  120 , radially inwardly of the coil  140 . The magnetic core  142  can be, for example, a magnetic tape that is wound around the lumen  118  and embedded in the sidewall  120 . 
     Referring still to  FIG. 3 , in the example shown, the coil  140  and magnetic core  142  extend continuously from the proximal portion  110  to the distal portion  114  of the elongate member  108 . In alternative examples, a coil and/or magnetic core can extend along less than the entire length of the elongate member, such as along a majority of the length of the elongate member, or along only a small section of the elongate member. For example, a coil and magnetic core can be relatively short in length, and can be positioned within the distal portion of the elongate member, proximate the distal end (e.g. right at the distal end, or slightly proximal of the distal end). 
     Referring still to  FIG. 3 , the system further includes a control unit  146 . The control unit  146  houses the components of the RLC circuit other than the inductor (i.e. the excitation voltage source, a resistor, a capacitor, and an output voltage sensor, shown at  144 ), which are electrically connected to the coil  140  to complete the RLC circuit. The coil  140  can optionally be removably electrically connected to the control unit  146 , for example with a male connector (shown in  FIG. 1 ) that can connect to a female connector of the control unit  146 . 
     The control unit further  146  houses a processor  148 , and an output device  150 , described in further detail below 
     In use, an excitation voltage can be applied to the RLC circuit from the excitation voltage source as the needle  128  approaches and is advanced through the lumen  118 . The excitation voltage can be tuned so that, in the absence of the needle  128  in the lumen  118 , the circuit is resonant. The output voltage of the RLC circuit can be sensed as the needle  128  approaches and is advanced through the lumen  118 . As the needle  128  enters and is advanced in the lumen  118 , the inductance of the RLC circuit will change due to the presence of the needle  128 . As shown in  FIG. 4 , the change in inductance will cause the output voltage of the RLC circuit to change—i.e. it can become non-resonant. The output voltage can thus be used as an indicator of the longitudinal position of the needle  128  with respect to the elongate member  108 . For example, the output voltage can be an indicator of when the perforating tip  138  is well shrouded within the elongate member  108  (and thus when a patient&#39;s anatomy is protected from being perforated by the needle  128 ), or when the perforating tip  138  is at the distal end  116  of the elongate member  108  (i.e. when the needle  128  is ‘primed’ for use), or when the perforating tip  138  has passed beyond the distal end  116  of the elongate member  108  and is exposed (and thus when a patient&#39;s anatomy is not protected from being perforated by the needle  128 ). 
     Referring back to  FIG. 3 , the voltage sensor of the RLC circuit is in communication with the processor  148 , and the processor  148  is in communication with the output device  150 . The output voltage sensor senses the output voltage of the RLC circuit, and can generate a signal (referred to herein as a “sensor signal”) based on the sensed output voltage. The processor  148  can include various components (e.g. an analog to digital converter, isolation circuitry, and a microcontroller), and is configured to receive and process the signal from the output voltage sensor, and to generate a signal (referred to herein as a “processor signal”) based on the sensor signal. The output device  150  can receive the processor signal, and can generate an output based on the processor signal. 
     In some examples, the output device  150  can include a light, and the processor signal can cause illumination of the light, or a change in color of the light. For example, when the sensor signal indicates that the output voltage has reached a predetermined value that corresponds to the perforating tip  138  being at a predetermined longitudinal position with respect to the elongate member  108  (e.g. the perforating tip being at the distal end  116  of the elongate member  108 ), the processor  148  can signal the output device  150  to change the color of the light from green to red. 
     In some examples, the output device  150  can include a screen that shows a graphical user interface (GUI). The processor signal can cause the output device  150  to generate an image showing the longitudinal position of the needle  128  within the elongate member  108 . For example, as the needle  128  is advanced through lumen  118  and the output voltage changes, the image can change based on the output voltage. 
     Referring now to  FIG. 5 , an alternative example system is shown. In the example of  FIG. 5 , features that are like those of  FIGS. 1 to 3  will be referred to with like reference numerals, incremented by 400. 
     The system  500  of  FIG. 5  is similar to the system  100  of  FIGS. 1 to 3 , and includes a first medical device  502  in the form of a catheter having an elongate member  508  with a lumen  518 , a second medical device  504  including a needle  528  that is advanceable through the lumen  518 , and a control unit  546 , which houses a processor  548  and an output device  550 . The system  500  further includes an inductor, which is part of an RLC circuit. The RLC circuit further includes an excitation voltage source, a resistor, a capacitor, and an output voltage sensor, which are shown collectively at  544  in  FIG. 5 . In the example of  FIG. 5 , the inductor includes a coil  540 , and a magnetic core  542 ; however the magnetic core  542  of the inductor is provided by the needle  528 , which includes a coating of a magnetic material (e.g. a coating of epoxy containing suspended ferrites or magnetic tape). 
     In use, an excitation voltage can be applied to the RLC circuit from the excitation voltage source as the needle  528  approaches and is advanced through the lumen  518 . The excitation voltage can be tuned so that, when the needle  528  is fully inserted into the elongate member  508 , the circuit is resonant. The output voltage of the RLC circuit can be sensed as the needle  528  approaches and is advanced through the lumen  518 . As the needle  528  enters and is advanced in the lumen  518 , the inductance of the RLC circuit will change due to the presence of the needle  528 . As shown in  FIG. 6 , the change in inductance will cause the output voltage of the RLC circuit to change—i.e. it will become resonant. Similarly to the example of  FIGS. 1 to 3 , the output voltage can thus be used as an indicator of the longitudinal position of the needle  528  with respect to the elongate member  508 . 
     Referring now to  FIG. 7 , another alternative example system is shown. In the example of  FIG. 7 , features that are like those of  FIGS. 1 to 3  will be referred to with like reference numerals, incremented by 600. 
     The system  700  of  FIG. 7  is similar to the system  500  of  FIG. 5 , and includes a first medical device  702  in the form of a catheter having an elongate member  708  with lumen  718 , a second medical device  704  including a needle  728  that is advanceable through the lumen  718 , and a control unit  746 , which houses a processor  748  and an output device  750 . The system  700  further includes an inductor, which is part of an RLC circuit. The RLC circuit further includes an excitation voltage source, a resistor, a capacitor, and an output voltage sensor, which are shown collectively at  744  in  FIG. 7 . Similarly to the example of  FIG. 5 , the inductor includes a coil  740 , and a magnetic core  742  that is provided by the needle  728 ; however, in the example of  FIG. 7 , the needle  728  is fabricated from a magnetic material, such as silicon steel, manganese-zinc ferrite, iron, etc., so that the needle  728  as a whole is magnetic. 
     The system of  FIG. 7  can be operated similarly to the system of  FIG. 5 —i.e. the excitation voltage can be tuned so that, when the needle  728  is fully inserted into the elongate member  708 , the circuit is resonant. The output voltage can thus be used as an indicator of the longitudinal position of the needle  728  with respect to the elongate member  708 . 
     Referring now to  FIG. 8 , another alternative example system is shown. In the example of  FIG. 8 , features that are like those of  FIGS. 1 to 3  will be referred to with like reference numerals, incremented by 700. 
     The system  800  of  FIG. 8  is similar to the system  100  of  FIGS. 1 to 3 , and includes a first medical device  802  in the form of a catheter having a lumen  818 , a second medical device  804  including a needle  828  that is advanceable through the lumen  818 , and a control unit  846 , which houses a processor  848  and an output device  850 . 
     The system  800  of  FIG. 8  includes a plurality of RLC circuits (three of which are shown). Each RLC circuit includes an inductor that includes a coil and a magnetic core (i.e. the first RLC circuit includes a first coil  840   a  and a first magnetic core  842   a ; the second RLC circuit includes a second coil  840   b  and a second magnetic core  842   b ; and the third RLC circuit includes a third coil  840   c  and a third magnetic core  842   c ). Each coil  840   a ,  840   b ,  840   c  is embedded in the sidewall  820 , and each magnetic core  842   a ,  842   b ,  842   c  is embedded in the sidewall  820  radially inwardly of the coils  840   a ,  840   b ,  840   c , respectively. The inductors are longitudinally spaced apart so that the second inductor is spaced proximally from the first inductor, and the third inductor is spaced proximally from the second inductor. The first RLC circuit further includes an excitation voltage source, a resistor, a capacitor, and an output voltage sensor, which are shown collectively at  844   a  in  FIG. 8 ; the second RLC circuit further includes an excitation voltage source, a resistor, a capacitor, and an output voltage sensor, which are shown collectively at  844   b  in  FIG. 8 ; and the third RLC circuit further includes an excitation voltage source, a resistor, a capacitor, and an output voltage sensor, which are shown collectively at  844   c  in  FIG. 8 . 
     In use, an excitation voltage can be applied to each RLC circuit from the respective excitation voltage source as the needle  828  approaches and is advanced through the lumen  818 . In use, each RLC circuit can be tuned so that a drop in signal amplitude occurs as the needle  828  passes the inductor of that circuit. The output voltage of each RLC circuit can be sensed as the needle  828  approaches and is advanced through the lumen  818 . As the needle  828  enters and is advanced into the lumen  818 , the inductance of each RLC circuit will change due to the presence of the needle  828 . As shown in  FIG. 9 , the change in inductance will cause the output voltage of each RLC circuit to change—i.e. it will become non-resonant as the needle  828  passes by that inductor. The output voltage of each RLC circuit can thus be used as an indicator of the longitudinal position of the needle  828  with respect to the elongate member  808 . 
     Referring now to  FIG. 10 , another alternative example system is shown. In the example of  FIG. 10 , features that are like those of  FIGS. 1 to 3  will be referred to with like reference numerals, incremented by 900. 
     The system  1000  of  FIG. 10  includes a first medical device  1002  in the form of a catheter having an elongate member  1008  with a lumen  1018 , a second medical  1004  device including a needle  1028  that is advanceable through the lumen  1018 , and a control unit  1046 , which houses a processor  1048  and an output device  1050 . The system  1000  of  FIG. 10  is similar to the system  800  of  FIG. 8 , in that the system  1000  of  FIG. 10  includes a plurality of RLC circuits (three of which are shown). Each RLC circuit includes an inductor that includes a coil that is embedded in the sidewall  1020  (i.e. the first RLC circuit includes a first coil  1040   a ; the second RLC circuit includes a second coil  1040   b ; and the third RLC circuit includes a third coil  1040   c ). The coils  1040   a ,  1040   b ,  1040   c  are longitudinally spaced apart so that the second coil  1040   b  is spaced proximally from the first coil  1040   a , and the third coil  1040   c  is spaced proximally from the second coil  1040   b.    
     The first RLC circuit further includes an excitation voltage source, a resistor, a capacitor, and an output voltage sensor, which are shown collectively at  1044   a  in  FIG. 10 ; the second RLC circuit further includes an excitation voltage source, a resistor, a capacitor, and an output voltage sensor, which are shown collectively at  1044   b  in  FIG. 10 ; and the third RLC circuit further includes an excitation voltage source, a resistor, a capacitor, and an output voltage sensor, which are shown collectively at  10044   c  in  FIG. 8 . 
     Similarly, to the system of  FIG. 5 , in the system of  FIG. 10 , the magnetic core  1042  of each inductor is provided by the needle  1028 , which includes a coating of a magnetic material (e.g. a coating of epoxy containing suspended ferrites or magnetic tape). 
     In use, an excitation voltage can be applied to each RLC circuit from the respective excitation voltage source as the needle  1028  approaches and is advanced through the lumen  1018 . Each RLC circuit can be tuned so that the circuit becomes resonant as the needle  1028  passes the inductor of that circuit. The output voltage of each RLC circuit can be sensed as the needle  1028  approaches and is advanced through the lumen  1018 . As the needle  1028  enters and is advanced into the lumen  1018 , the inductance of each RLC circuit will change due to the presence of the needle  1028 . As shown in  FIG. 11 , the change in inductance will cause the output voltage of each RLC circuit to change—i.e. it will become resonant as the needle  1028  passes by that inductor. The output voltage of each RLC circuit can thus be used as an indicator of the longitudinal position of the needle  1028  with respect to the elongate member  1008 . 
     Referring now to  FIG. 12 , another alternative example system is shown. In the example of  FIG. 12 , features that are like those of  FIGS. 1 to 3  will be referred to with like reference numerals, incremented by 1100. 
     The system  1200  of  FIG. 12  is similar to the system  1000  of  FIG. 10 , and includes a first medical  1202  device in the form of a catheter having an elongate member  1208  with a lumen  1218 , a second medical device  1204  including a needle  1228  that is advanceable through the lumen  1218 , and a control unit  1246 , which houses a processor  1248  and an output device  1250 . 
     Similarly to the system  1000  of  FIG. 10 , the system  1200  includes a plurality of RLC circuits (three of which are shown). Each RLC circuit includes an inductor that includes a coil that is embedded in the sidewall  1220  (i.e. the first RLC circuit includes a first coil  1240   a ; the second RLC circuit includes a second coil  1240   b ; and the third RLC circuit includes a third coil  1240   c ). The coils  1240   a ,  1240   b ,  1240   c  are longitudinally spaced apart so that the second coil  1240   b  is spaced proximally from the first coil  1240   a , and the third coil  1240   c  is spaced proximally from the second coil  1240   b.    
     Similarly to the system  1000  of  FIG. 10 , each inductor includes a magnetic core  1242  that is provided by the needle  1228 ; however, in the system  1200  of  FIG. 12 , the needle is fabricated from a magnetic material, such as silicon steel, manganese-zinc ferrite, iron, etc, so that the needle  1228  as a whole is magnetic. 
     The system  1200  of  FIG. 12  can be operated similarly to the system  1000  of  FIG. 10 —i.e. the excitation voltage can be tuned so that, when the needle  1228  is fully inserted into the elongate member  1208 , the circuit is resonant, and the output voltage can thus be used as an indicator of the longitudinal position of the needle  1228  with respect to the elongate member  1208 . 
     The devices and systems described above can be used in various medical procedures, but may be particularly useful in transseptal perforation procedures, in which a dilator (i.e. a first medical device) is advanced via the femoral vein towards the heart and positioned adjacent the fossa ovalis of the atrial septum, and then a transseptal perforation device (i.e. a second medical device) is advanced into and through the lumen of the dilator, from the proximal end of the dilator towards the distal end of the dilator. In such procedures, as the transseptal perforation device is advanced through the lumen of the dilator, an excitation voltage can be applied to the RLC circuit(s), and the output voltage of the RLC circuit(s) can be sensed and monitored, to provide an indicator of the longitudinal position of the transseptal perforation device with respect to the dilator. 
     As described above, an output can be generated based on the output voltage, to provide an indication of the longitudinal position of the transseptal perforation device with respect to the dilator. The output can be, for example, in the form of an image, or a light. This can help an operator to ensure that the perforating tip of the perforation device is shrouded within the dilator until it is ready for use by the operator. 
     Optionally, based on the output, the position of the transseptal perforation device can be adjusted with respect to the dilator. For example, if a red light illuminates before the user is ready to perforate the fossa ovalis, the user can withdraw the transseptal perforation device proximally, until a green light illuminates. 
     While the above description provides examples of one or more processes or apparatuses or compositions, it will be appreciated that other processes or apparatuses or compositions may be within the scope of the accompanying claims. 
     To the extent any amendments, characterizations, or other assertions previously made (in this or in any related patent applications or patents, including any parent, sibling, or child) with respect to any art, prior or otherwise, could be construed as a disclaimer of any subject matter supported by the present disclosure of this application, Applicant hereby rescinds and retracts such disclaimer. Applicant also respectfully submits that any prior art previously considered in any related patent applications or patents, including any parent, sibling, or child, may need to be re-visited.