Patent Publication Number: US-2022233089-A1

Title: Techniques for determining tissue types

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application is a continuation-in-part of the U.S. patent application titled, “IMPEDANCE-CALIBRATED DIAGNOSTIC MEDICAL DEVICES,” filed on Aug. 9, 2021, and having Ser. No. 17/397,896, which claims the benefit of U.S. Provisional Patent Application No. 63/142,242, filed Jan. 27, 2021; U.S. Provisional Patent Application No. 63/142,247, filed Jan. 27, 2021; U.S. Provisional Patent Application No. 63/142,254, filed Jan. 27, 2021; and U.S. Provisional Patent Application No. 63/142,260, filed Jan. 27, 2021. The present application is also a continuation-in-part of the U.S. patent application titled, “TECHNIQUES FOR CONTROLLING MEDICAL DEVICE TOOLS,” filed on Aug. 26, 2021, and having Ser. No. 17/412,973, which claims the benefit of U.S. Provisional Patent Application No. 63/142,242, filed Jan. 27, 2021; U.S. Provisional Patent Application No. 63/142,247, filed Jan. 27, 2021; U.S. Provisional Patent Application No. 63/142,254, filed Jan. 27, 2021; and U.S. Provisional Patent Application No. 63/142,260, filed Jan. 27, 2021. The subject matter of these related applications is hereby incorporated herein by reference. 
    
    
     BACKGROUND 
     Field of the Various Embodiments 
     Embodiments of the present disclosure relate generally to electronics and medical diagnostic technology and, more specifically, to techniques for determining tissue types. 
     Description of the Related Art 
     In minimally invasive medical procedures, a healthcare professional typically inserts a medical device, such as an endoscope or a bronchoscope, into the patient&#39;s body and positions the instrument head of the medical device at a target location, such as the location of a tumor. The instrument head usually includes some form of tool, such as and without limitation, a camera, a fiber optic light source, a pair of forceps, and/or a tissue sample extraction tool that can be used to extract tissue samples from the target location for further evaluation. 
     One drawback that exists with many conventional medical devices is the difficulty of determining a tissue type at a location where the instrument head of a medical device tool is positioned. For example, a healthcare professional can visually inspect an image of tissue captured by a camera while the tissue is illuminated by a light source. However, tissue types can vary in appearance, and different tissue types can have similar appearances. As another example, the tissue type on one side of the instrument head, such as on a left side of the instrument head, can differ from the tissue type on the other side of the instrument head, such as on a right side of the instrument head. As yet another example, a medical device can be used to extract a tissue sample from a given location, and a healthcare professional can determine how to treat the tissue at the given location by visually inspecting or performing a biopsy on the tissue sample. However, if the instrument head moves between sampling the tissue and treating the tissue, then the healthcare professional could end up treating tissue that is different than the extracted tissue. 
     In view of the above drawbacks, medical devices oftentimes include components that are configured to determine the tissue type contacting the instrument head. However, many techniques for determining tissue type are inaccurate and, accordingly, are insufficient for confirming that a given tool is positioned correctly at a given target location. For example, triangulation and ultrasound imaging typically require calibrating the relevant positioning system relative to both the medical device tool and a mapping of the patient&#39;s body via a medical scan. Errors introduced in the calibration process can produce errors when determining whether the medical device tool is positioned correctly at the target location. Also, any physiological changes within the patient, such as the size, shape, or location of a tumor, between the time when a medical scan is conducted and the time when the medical procedure begins can change the target location. Thus, positioning a medical device tool based on a medical scan can sometimes result in applying the medical device tool to healthy tissue instead of at the target location. 
     As the foregoing illustrates, what is needed in the art are more effective techniques for determining tissue types at locations where the instrument heads of medical devices are positioned. 
     SUMMARY 
     Embodiments are disclosed for medical devices. In various embodiments, a medical device includes an instrument head that includes two or more electrodes and a medical device tool; an impedance bridge selectively coupled to the two or more electrodes; and a processor coupled to the impedance bridge. 
     Embodiments are disclosed for controlling a medical device. In various embodiments, a method includes controlling a medical device includes recording, at one or more frequencies, two or more impedance measurements, each impedance measurement being associated with two or more electrodes included in an instrument head of the medical device, and determining, based on the two or more impedance measurements, a map of tissue types at a location associated with the instrument head. 
     At least one technical advantage of the disclosed medical device relative to the prior art is that the disclosed medical device is able to determine a map of tissue types at a location where the instrument head of a medical device is positioned prior to when a medical device tool is activated or during activation. For example, the disclosed medical device can determine whether the tissue types of portions of tissue located where the instrument head of a medical device is positioned match the expected tissue types at a given target location prior to activating the relevant medical device tool. In this manner, the disclosed medical device can ensure that medical device tools are applied to a selected tissue type, such as a tumor, rather than some other tissue type, such as healthy tissue. Also, the disclosed medical instrument can apply medical device tools at target locations more accurately than is possible with conventional medical devices. Consequently, the disclosed medical device can be used to perform various procedures, such as and without limitation, delivering therapeutic drugs or energy or extracting tissue samples, at specific locations more accurately and reliably than what can be achieved using conventional medical devices. These technical advantages provide one or more technological advancements over prior art approaches. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a medical device, according to various embodiments; 
         FIG. 2  is a more detailed illustration of the instrument head of  FIG. 1 , according to various embodiments; 
         FIG. 3  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIG. 4A  is an illustration of an electrode configuration associated with the instrument head of  FIG. 3 , according to various embodiments; 
         FIG. 4B  is an illustration of an electrode configuration associated with the instrument head of  FIG. 3 , according to other various embodiments; 
         FIG. 5  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIG. 6  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIG. 7  is more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIGS. 8A-8B  are more detailed illustrations of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIG. 9  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIG. 10  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIG. 11  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIG. 12  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIG. 13  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIG. 14  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIGS. 15A-15B  are more detailed illustrations of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIGS. 16A-16B  are more detailed illustrations of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIGS. 17A-17B  are more detailed illustrations of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIG. 18A  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments; 
         FIG. 18B  is an illustration of a grid pattern associated with the instrument head of  FIG. 18A , according to various embodiments; 
         FIG. 19  is a more detailed illustration of the external electrical components of  FIG. 1 , according to various embodiments; 
         FIG. 20  is a more detailed illustration of the medical device of  FIG. 1 , according to various embodiments; and 
         FIG. 21  is a flow diagram of method steps for controlling a medical device tool, according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth to provide a more thorough understanding of the various embodiments. However, in the range of embodiments of the concepts includes some embodiments omitting one or more of these specific details. 
       FIG. 1  illustrates a medical device  100 , according to various embodiments. As shown, the medical device  100  includes, without limitation, an instrument head  108 , wires  104 , and external electrical components  106 . The instrument head  108  is positioned at a location  102  (e.g., a location of a tumor). While not shown, the instrument head  108  includes, without limitation, two or more electrodes, a conduit, and a medical device tool, such as and without limitation, a camera, a fiber optic light source, a therapeutic drug delivery tool that delivers a therapeutic drug to the location  102 , an energy delivery tool that delivers energy to the location  102 , or a tissue sample extraction tool that extracts a tissue sample from the location  102  for further evaluation. The external electrical components  106  generate current at various frequencies. The wires  104  conduct the current between the external electrical components  106  and the instrument head  108 . The external electrical components  106  include a processor that selectively couples to the two or more electrodes in the instrument head  108 . The processor of the external electrical components  106  measures the impedance of current conducted through tissue between the selected electrodes. As described in greater detail below, the medical device  100  generates, based on the impedance measurements, a tissue type map of tissue at the location  102 . For example and without limitation, based on the impedance measurements, the tissue type map can indicate whether portions of tissue at the location  102  of the instrument head  108  are a tumor tissue type or a non-tumor tissue type. 
       FIG. 2  is a more detailed illustration of the instrument head  108  of  FIG. 1 , according to various embodiments. As shown, the instrument head  108  includes, without limitation, two or more electrodes  202 , a sheath  204  including an aperture  302 , a camera  206 , and a light source  208 . 
     The sheath  204  encloses wires  104  that couple the two or more electrodes  202  to the external electrical components  106 . The wires  104  selectively couple two or more of the electrodes  202  to the external electrical components  106 . The selected electrodes  202  conduct current, at various frequencies, through tissue between the selected electrodes  202 . Although not shown in  FIG. 2 , the external electrical components  106  measure an impedance of the current conducted by the selected electrodes  202 . The external electrical components  106  can record a set of impedance measurements for different combinations of selected electrodes  202 . As an example (without limitation), the external electrical components  106  can record a first impedance measurement of the tissue between two or more electrodes  202  on a left side of the instrument head  108  and a second impedance measurement of the tissue between two or more electrodes  202  on a right side of the instrument head  108 . As another example (without limitation), the external electrical components  106  can record a first impedance measurement between two or more electrodes  202  when the instrument head  108  is positioned at a first location and a second impedance measurement between the two or more electrodes  202  when the instrument head  108  is positioned at a second location. For each impedance measurement, the external electrical components  106  determine a tissue type of the tissue between the selected two or more electrodes  202 . The external electrical components  106  generate a tissue type map based on the impedance measurements. 
     The sheath  204  also encloses wires that couple the camera  206  and the light source  208  to the external electrical components  106  (e.g., a power source, a processor, a display, or the like). The sheath  204  physically protects the enclosed wires from contact with an interior surface of a catheter. The sheath  204  also electrically insulates the enclosed wires while conducting current, which preserves the integrity of an electrical signal carried by the current and prevents the current from being conducted through other parts of the catheter or tissue contacting the sheath  204 . 
     In some embodiments, the external electrical components  106  can perform one or more operations, based on the tissue type map, to control one or both of the camera  206  or the light source  208 . For example (without limitation), if the tissue type map indicates that tissue at a location associated with the instrument head  108  is of a tumor tissue type, the external electrical components  106  can activate the camera  206  to capture an image of the tissue. In various embodiments, the external electrical components  106  can store the captured image and/or display the captured image on a display for viewing by a healthcare professional. If the tissue type map indicates that tissue at a location associated with the instrument head  108  is of a non-tumor tissue type, the external electrical components  106  can refrain from activating the camera. Selectively activating the camera  206  based on the tissue type map can cause the medical device to limit captured images to tissue of the tumor tissue type. As another example (without limitation), if the tissue type map indicates that tissue at a location associated with the instrument head  108  is of a tumor tissue type, the external electrical components  106  can deliver power to the light source  208  to illuminate the tissue between the electrodes. If the tissue type map indicates that tissue at a location associated with the instrument head  108  is of a non-tumor tissue type, the external electrical components  106  can refrain from delivering power to the light source  208 . Selectively powering the light source  208  based on the tissue type map can identify, for a healthcare professional, the tissue of the tumor tissue type. 
     As shown, the electrodes  202  of the instrument head  108  have a curved shape. In some embodiments, each of the two or more electrodes  202  includes a flexible material, such as aluminum. For example (without limitation), in some embodiments, each of the two or more electrodes  202  bends or curves when extended from the aperture  302  and straightens when retracted into the aperture  302 . In some embodiments, each of the two or more electrodes includes a shape memory material, such as Nitinol, which causes the electrodes to form a particular shape (e.g., a curved shape) when the electrode is in an unconstrained state (e.g., when the electrode is extended from the aperture  302 ). 
     Although not shown in  FIG. 2 , in various embodiments, the instrument head  108  includes other types of medical device tools. For example (without limitation), the instrument head  108  can include a conduit that delivers therapeutic drugs or energy and/or a tissue extractor that extracts a tissue sample of the tissue at the location associated with the instrument head  108 . The external electrical components  106  can perform one or more operations, based on the tissue type map, to control these and other types of medical device tools included in the instrument head  108 . Using the tissue type map to perform the one or more operations can operations can allow a healthcare professional to deliver therapeutic drugs or energy selectively to tissue of a particular tissue type and/or to extract a tissue sample of a particular tissue type for further evaluation. 
       FIG. 3  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, two electrode pairs  202 - 1 ,  202 - 2 , an aperture  302 , a sheath  204 , a camera  206 , and a light source  208 . As previously discussed, the wires  104  selectively couple two or more of the electrodes  202  to the external electrical components  106 . For example (without limitation), when the external electrical components  106  are coupled to only a first electrode pair  202 - 1  that is positioned on a left side of the instrument head  108 , the external electrical components  106  record impedance measurements that indicate a tissue type located on a left side of the instrument head  108 . When the external electrical components  106  are coupled to only a second electrode pair  202 - 2  that is positioned on a right side of the instrument head  108 , the external electrical components  106  record impedance measurements that indicate a tissue type located on a right side of the instrument head  108 . When the external electrical components  106  are coupled to both electrode pairs  202 - 1 ,  202 - 2 , the external electrical components  106  record impedance measurements that indicate a tissue type located ahead of (e.g., distal to) the instrument head  108 . 
     As shown, each electrode of the electrode pairs  202 - 1 ,  202 - 2  is shaped to curve outward relative to a longitudinal axis (e.g., a lengthwise axis) of the instrument head  108 . In various embodiments, each electrode of the electrode pairs  202 - 1 ,  202 - 2  extends to an adjustable extension length relative to the aperture  302  of the instrument head  108 . For example (without limitation), in various embodiments, the external electrical components  106  includes an electrical or mechanical actuator that, when operated, extends one or more of the electrodes from the aperture  302  and/or retracts one or more electrodes toward the aperture  302 . 
       FIG. 4A  is an illustration of an electrode configuration associated with the instrument head  108  of  FIG. 3 , according to various embodiments. As previously discussed, the electrodes of the instrument head can extend from the aperture  302  of the sheath  204  to an adjustable extension length relative to the aperture  302 . In  FIG. 4A , the electrodes extend from the aperture  302  to an extension length  404 - 1  that is long. Due to a curvature  406  of the electrodes, a distance  402 - 1  between each pair of electrodes  202  is large. Due to the large distance  402 - 1 , the impedance measurements by the external electrical components  106  indicate a tissue type of a large portion of tissue at the location  102  of the instrument head  108 . The small area results in a coarse, low-resolution determination of the tissue type of a large area of tissue. 
       FIG. 4B  is an illustration of an electrode configuration associated with the instrument head  108  of  FIG. 3 , according to other various embodiments. As previously discussed, the electrodes of the instrument head can extend from an aperture  302  to a selected length. In  FIG. 4B , the electrodes extend, relative to the aperture  302 , to an extension length  404 - 2  that is shorter than the extension length  404 - 1  shown in  FIG. 4A . Due to a curvature  406  of the electrodes, a distance  402 - 2  between each pair of electrodes  202  is smaller than the distance  402 - 1  shown in  FIG. 4A . Due to the small distance  402 - 2 , the impedance measurements by the external electrical components  106  indicate a tissue type of a small portion of tissue at the location  102  of the instrument head  108 . The small area results in a precise, high-resolution determination of the tissue type of a small area of tissue. 
     In various embodiments, a medical device can adjust the extension lengths  404  of the two or more electrodes  202 , relative to the aperture  302 , to adjust the impedance measurements during a medical procedure. For example (without limitation), the medical device can initially record impedance measurements while the extension length  404  of the electrodes relative to the aperture  302  is long, and the external electrical components  106  can generate a coarse tissue type map. When the coarse tissue type map indicates that the tissue contacting the instrument head  108  is of a selected tissue type (e.g., a tumor tissue type), the electrodes can retract toward the aperture  302  to a shorter extension length  404  relative to the aperture  302 , and the external electrical components  106  can generate a fine tissue type map over a smaller area. By adjusting the extension lengths  404  of the electrodes  202  relative to the aperture  302 , the medical device can quickly determine a general area of a selected tissue type based on a low-resolution tissue type map, and then precisely locate the selected tissue type within the general area based on high-resolution tissue type map. 
       FIG. 5  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a clamp  502 , two or more electrodes  202 , and a sheath  204 . As previously discussed, the sheath  204  encloses wires that selectively couple the two or more electrodes  202  to external electrical components  106  (not shown). In various embodiments, the electrodes  202  are located at different positions along a length of the clamp. As shown, the clamp  502  includes a pair of jaws, each jaw including two or more teeth arranged along a longitudinal axis (e.g., a length axis) of the clamp  502 . In various embodiments (without limitation), each electrode  202  can be coupled to one of the teeth of the clamp  502 . The electrodes  202  are therefore located at different positions along the longitudinal axis. The jaws of the clamp  502  can be engaged (e.g., without limitation, by an electrical and/or mechanical actuator) to clamp a portion of tissue. The external electrical components  106  can selectively couple to respective pairs of electrodes (e.g., without limitation, a first electrode on an upper jaw at a selected position, and a second electrode on a lower jaw at the selected position). The external electrical components  106  can generate one or more impedance measurements of the tissue between the selected electrodes at the selected position of the clamp. Based on the impedance measurements for respective pairs of electrodes, the external electrical components  106  can generate a tissue type map of tissue types along the length of the clamp. 
       FIG. 6  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a guidewire  602 , an extension  606 , two or more electrodes  202 , a sheath  204 , a camera  206 , and two light sources  208 . As previously discussed, the sheath  204  encloses wires that selectively couple the two or more electrodes  202  to external electrical components  106  (not shown). 
     As shown, the guidewire  602  extends in a forward direction from an extension  606  of the instrument head. The electrodes  202  are located at different positions along a length of the guidewire  602 . As shown in the magnified view  604  of  FIG. 6 , each electrode  202  can enclose a circumference of the guidewire  602 . As shown, some electrodes  202  are also located along a length of the extension  606 . The extension  606  includes sections of electrically insulating material  608  that electrically insulate respective pairs of electrodes  202  located on the sheath  204 . The external electrical components  106  can selectively couple to the electrodes  202  along the length of the extension  606  to record impedances and generate a first tissue type map. For example, (without limitation), the external electrical components  106  can generate a first tissue type map. Based on the first tissue type map, the external electrical components  106  can confirm that the instrument head  108  is correctly positioned at a targeted location  102 , such as the location of a tumor. Then, the external electrical components  106  can record impedance measurements of the electrodes  202  located along the guidewire  602  to generate a second tissue type map of the tissue contacting the guidewire  602 . The second tissue type map can confirm that the guidewire  602  is contacting tumor tissue type before or during operations associated with the guidewire  602  (e.g., without limitation, delivering a therapeutic agent or energy). In some embodiments, the external electrical components  106  perform operations associated with the guidewire based on the second tissue type map. For example (without limitation), the external electrical components  106  can activate the camera  206  or the light sources  208  when the second tissue type map indicates that the guidewire  602  is contacting a tumor tissue type. 
       FIG. 7  is more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204  including an aperture  302 , a guidewire  602  including two or more electrodes  202 , a sheath  204 , a camera  206 , and two light sources  208 . As previously discussed, the sheath  204  encloses wires that selectively couple the two or more electrodes  202  to external electrical components  106  (not shown). 
     As shown, the guidewire  602  selectively retracts into the sheath  204 . For example (without limitation), the guidewire  602  can fully retract into the sheath  204  while the instrument head  108  is being moved toward a targeted location  102 . When the instrument head  108  is located at the targeted location  102 , the guidewire  602  can extend through the aperture  302  of the sheath  204  to contact the tissue at the location  102 . The external electrical components  106  can record impedance measurements of the electrodes  202  located along the extended guidewire  602  to generate a second tissue type map of the tissue contacting the guidewire  602 . The second tissue type map can confirm that the guidewire  602  is contacting tumor tissue type before or during operations associated with the guidewire  602  (e.g., without limitation, delivering a therapeutic agent or energy). Also, after the medical procedure, the guidewire  602  can retract into the sheath  204  while the instrument head  108  is being removed from the location  102 . The selective retraction and extension can protect the guidewire  602  from physical forces during movement of the instrument head  108 . 
       FIGS. 8A-8B  are more detailed illustrations of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204  including an aperture  302 , a guidewire  602 , and an extension  606  including two or more electrodes  202 . As previously discussed, the sheath  204  encloses wires that selectively couple the two or more electrodes  202  to external electrical components  106  (not shown). 
     As shown in  FIG. 8A , the extension  606  extends from the aperture  302  of the sheath  204 . The extension  606  bends at a bending location  802  along the length of the extension  606 . In some embodiments, the extension  606  includes a shape memory material, such as Nitinol, which causes the extension  606  to bend at the bending location  802  when the extension  606  extends from the sheath  204 . Alternatively or additionally, in some embodiments (not shown), the extension  606  includes a channel, and wires within the channel attach to one or more locations of an interior surface of the channel. Electrical and/or mechanical actuators can apply tension to one or more of the wires, causing the extension  606  to bend at the bending location  802 . The bending of the extension  606  can position the guidewire  602  at a location of tissue that is difficult to reach with a straight extension  606 . 
     As further shown in  FIG. 8B , the extension  606  forms a curved shape  804  along a length of the extension  606 . In some embodiments, the extension  606  includes a shape memory material, such as Nitinol, which causes the extension  606  to form the curved shape  804  when the extension  606  extends from the sheath  204 . Alternatively or additionally, in some embodiments (not shown), the extension  606  includes a channel, and wires within the channel attach to one or more locations of an interior surface of the channel. Electrical and/or mechanical actuation of one or more of the wires can cause the extension  606  to form the curved shape  804 . The curved shape  804  of the extension  606  can position the guidewire  602  at a location of tissue that is difficult to reach with a straight extension  606 . In some embodiments, the extension  606  can selectively bend at a bending location  802  as shown in  FIG. 8A  (e.g., in response to actuation of one wire) and/or selectively form a curved shape  804  as shown in  FIG. 8B  (e.g., in response to actuation of two or more wires). Further, the external electrical components  106  can record impedance measurements of the one or more electrodes  202 , or selected subsets thereof, to determine impedance measurements of tissue types at various locations near the instrument head  108 . The external electrical components  106  can generate a tissue type map based on the impedance measurements. 
       FIG. 9  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204  including an aperture  302  and an extension  606  including two or more electrodes  202 . As previously discussed, the sheath  204  encloses wires that selectively couple the two or more electrodes  202  to external electrical components  106  (not shown). 
     As further shown in  FIG. 9 , the extension  606  selectively forms a first curved shape, a second curved shape, or a straight shape. For example (without limitation), when retracted into the sheath  204 , the extension  606  can form a straight shape. When extended through the aperture  302  of the sheath  204 , the extension  606  can form a straight shape, wherein a tip  902  of the extension  606  is oriented in a forward direction. The extension  606  can also selectively form a first curved shape  904  along a length of the extension  606  by curving in a first direction. The extension  606  can also selectively form a second curved shape  904  along a length of the extension  606  by curving in a second direction that is opposite the first direction. In some embodiments (not shown), the extension  606  includes a channel, and a set of wires within the channel attach to respective locations of an interior surface of the channel. Electrical and/or mechanical actuation of a first subset of the wires can cause the extension  606  to form the first curved shape  904 . Electrical and/or mechanical actuation of a second subset of the wires can cause the extension  606  to form the second curved shape  906 . Electrical and/or mechanical actuation of a third subset of the wires can cause the extension  606  to form the second curved shape  906 . The selective shaping of the extension  606  between of the straight shape, the first curved shape  904 , or the second curved shape  906  can position the tip  902  of the extension  606  at various locations of tissue that are difficult to reach with a straight extension  606 . Further, the external electrical components  106  can record impedance measurements of the one or more electrodes  202 , or selected subsets thereof, to determine impedance measurements of tissue types at various locations near the instrument head  108 . The external electrical components  106  can generate a tissue type map based on the impedance measurements. 
       FIG. 10  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204  including an aperture  302  and an extension  606  including two or more electrodes  202 . As previously discussed, the sheath  204  encloses wires that selectively couple the two or more electrodes  202  to external electrical components  106  (not shown). 
     As further shown in  FIG. 10 , the extension  606  selectively forms a circular shape  1002  that encircles a longitudinal axis (e.g., a length axis) of the instrument head. For example (without limitation), when retracted into the sheath  204 , the extension  606  can form a straight shape. When extended through the aperture  302  of the sheath  204 , a first portion  1004  of the extension  606  can extend in a straight or forward direction. Another portion of the extension  606  that is distal to the first portion  1004  can form a circular shape  1002 . For example (without limitation), the extension  606  can include a shape memory material, such as Nitinol, which forms the circular shape  1002  in an unconstrained state. Alternatively or additionally, in some embodiments, the extension  606  includes a channel (not shown), and a set of wires within the channel attach to respective locations of an interior surface of the channel. Electrical and/or mechanical actuation of a first subset of the wires can selectively cause the extension  606  to form the circular shape  1002 . The external electrical components  106  can record impedance measurements of the one or more electrodes  202 , or selected subsets thereof, to determine impedance measurements of tissue types at various locations along the circular shape  1002 . The external electrical components  106  can generate a circularly shaped tissue type map based on the impedance measurements. 
       FIG. 11  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204  including an aperture  302  and an extension  606  including two or more electrodes  202 . As previously discussed, the sheath  204  encloses wires that selectively couple the two or more electrodes  202  to external electrical components  106  (not shown). 
     As further shown in  FIG. 11 , the extension  606  selectively forms a wave shape  1102  relative to a longitudinal axis (e.g., a length axis) of the instrument head. For example (without limitation), when retracted into the sheath  204 , the extension  606  can form a straight shape. When extended through the aperture  302  of the sheath  204 , a first portion  1004  of the extension  606  can extend in a straight direction. Another portion of the extension  606  that is distal to the first portion  1004  can form a wave shape  1102 . For example (without limitation), the extension  606  can include a shape memory material, such as Nitinol, which forms the wave shape  1102  in an unconstrained state. Alternatively or additionally, in some embodiments, the extension  606  includes a channel (not shown), and a set of wires within the channel attach to respective locations of an interior surface of the channel. Electrical and/or mechanical actuation of the wires can selectively cause the extension  606  to form the wave shape  1102 . The external electrical components  106  can record impedance measurements of the one or more electrodes  202 , or selected subsets thereof, to determine impedance measurements of tissue types at various locations along the wave shape  1102 . The external electrical components  106  can generate a wave-shaped tissue type map based on the impedance measurements. 
       FIG. 12  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204  including an aperture  302  and an extension  606  including two or more electrodes  202 . As previously discussed, the sheath  204  encloses wires that selectively couple the two or more electrodes  202  to external electrical components  106  (not shown). 
     As further shown in  FIG. 12 , the extension  606  selectively forms a spiral shape  1202 . For example (without limitation), when retracted into the sheath  204 , the extension  606  can form a straight shape. When extended through the aperture  302  of the sheath  204 , a first portion  1004  of the extension  606  can extend in a straight direction. Another portion of the extension  606  that is distal to the first portion  1004  can form a spiral shape  1202 . For example (without limitation), the extension  606  can include a shape memory material, such as Nitinol, which forms the spiral shape  1202  in an unconstrained state. Alternatively or additionally, in some embodiments, the extension  606  includes a channel (not shown), and a set of wires within the channel attach to respective locations of an interior surface of the channel. Electrical and/or mechanical actuation of the wires can selectively cause the extension  606  to form the spiral shape  1202 . The external electrical components  106  can record impedance measurements of the one or more electrodes  202 , or selected subsets thereof, to determine impedance measurements of tissue types at various locations along the spiral shape  1202 . The external electrical components  106  can generate a spiral-shaped tissue type map based on the impedance measurements. In various embodiments, a plane of the spiral shape  1202  can be oriented in a parallel orientation, a perpendicular orientation, and/or an oblique orientation relative to a longitudinal axis (e.g., a length axis) of the instrument head  108 . 
       FIG. 13  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204 , an extension  606  including an aperture  302 , and at least two guidewires that respectively include an electrode  202 . As previously discussed, the sheath  204  encloses wires that selectively couple the electrodes  202  to external electrical components  106  (not shown). 
     As shown, the at least two guidewires  602  extend from the extension  606  in a rake configuration. As shown, each of the at least two guidewires  602  extends from the instrument head  108  in a different direction. More particularly, each of the two or more guidewire  602  extends from the aperture  302  of the extension  606  in a different direction. Each of the two or more electrodes  202  is located at a tip of one of the guidewires  602 . The rake configuration of the guidewires  602  spreads the electrodes  202  in a lateral direction relative to a longitudinal axis (e.g., a length axis) of the instrument head  108 . of the extension  606  that is distal to the first portion  1004  can form a spiral shape  1202 . For example (without limitation), each guidewire  602  can include a shape memory material, such as Nitinol. Each guidewire can include a bending location that bends the guidewire  602  in a particular direction. When retracted into the extension  606 , each guidewire  602  can form a straight shape. When extended through the aperture  302  of the extension  606 , each guidewire  602  can form a bent shape in which the guidewire  602  bends in a direction relative to the longitudinal axis of the instrument head  108 . The external electrical components  106  can record impedance measurements of the two or more electrodes  202 , including selected subsets thereof, to determine impedance measurements of tissue types between various pairs of guidewires  602  of the rake. The external electrical components  106  can generate a linear tissue type map based on the impedance measurements, wherein the linear tissue type map extends in a lateral direction relative to the longitudinal axis of the instrument head  108 . In various embodiments, the lateral direction can be oriented perpendicular to the longitudinal axis of the instrument head  108  (as shown), parallel to the longitudinal axis of the instrument head, or in an oblique direction relative to the longitudinal axis of the instrument head. 
       FIG. 14  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204  including an aperture  302 , an extension  606  terminating in an extension tip  1402 , and two or more guidewires  602 , each extending between the sheath and the extension tip  1402 , wherein each guidewire  602  includes one or more electrodes  202  respectively located at a lateral position along the guidewire  602 . As previously discussed, the sheath  204  encloses wires that selectively couple the electrodes  202  to external electrical components  106  (not shown). 
     As shown, the guidewires  602  extend laterally from the sheath  204  to the extension tip  1402 . Each guidewire  602  protrudes in an outward direction relative to a longitudinal axis of the extension  606 . Further, each guidewire  602  protrudes in different outward direction relative to the longitudinal axis of the extension  606  than the other guidewires  602 . For example (without limitation), each guidewire  602  can include a shape memory material, such as Nitinol. When retracted into the sheath  204 , each guidewire  602  can form a straight shape. In an unconstrained state, each guidewire can form a protruding shape that protrudes the guidewire  602  in a particular direction. When extended through the aperture  302  of the sheath  204 , each guidewire  602  can form a protruding shape in which the guidewire  602  protrudes in an outward direction relative to the longitudinal axis of the extension  606 . The external electrical components  106  can record impedance measurements of two or more electrodes  202 , including selected subsets thereof, to determine impedance measurements and tissue types of the tissue near the instrument head  108 . For example (without limitation), the external electrical components  106  can record a first set of impedance measurements between two or more electrodes  202  at a first position along the lengths of the respective guidewires  602  and a second set of impedance measurements between two or more electrodes  202  at a second position along the lengths of the respective guidewires  602 . As another example (without limitation), the external electrical components  106  can record a first set of impedance measurements between two or more electrodes  202  of a first guidewires  602  and a second set of impedance measurements between two or more electrodes  202  of a second guidewire  602 . The external electrical components  106  can generate a volumetric tissue type map based on the impedance measurements, wherein the volumetric tissue type map includes layers of tissue types in various directions, distances, and lateral positions relative to the extension  606 . 
       FIGS. 15A-B  are more detailed illustrations of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204  including an aperture  302 , an extension  606  terminating in an extension tip  1402 , a wire  1502  that extends along the extension  606  through the extension tip  1402 , and two or more guidewires  602 , each extending between the sheath and the extension tip  1402 , wherein each guidewire  602  includes one or more electrodes  202  respectively located at a lateral position along the guidewire  602 . As previously discussed, the sheath  204  encloses wires that selectively couple the electrodes  202  to external electrical components  106  (not shown). 
     As shown in  FIG. 15A , the extension tip  1402  is positioned at a first position along the wire  1502 . As a result, the guidewires  602 , which extend laterally from the sheath  204  to the extension tip  1402 , are flush and/or parallel with the extension  606 . The external electrical components  106  can record a first set impedance measurements of two or more electrodes  202  in the flush and/or parallel orientation, including selected subsets thereof, to determine impedance measurements and tissue types of tissue near the instrument head  108 . For example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  at a first position along the lengths of the respective guidewires  602  and a second subset of impedance measurements between two or more electrodes  202  at a second position along the lengths of the respective guidewires  602 . As another example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  of a first guidewires  602  and a second subset of impedance measurements between two or more electrodes  202  of a second guidewire  602 . 
     As shown in  FIG. 15B , the extension tip  1402  retracts (e.g., moves in a retraction direction  1504 ) relative to the extension  606 . As a result, the extension tip  1402  in a retraction direction  1504  compresses each guidewire  602 , causing each guidewire  602  to protrude in an outward direction  1506  relative to a longitudinal axis (e.g., a length axis) of the extension  606 . In some embodiments (not shown), a wire connected to the extension tip  1402  can be electrically and/or mechanically actuated to create tension that pulls the extension tip  1402  in the retraction direction  1504 . Due to the coupling of the guidewires  602  and the extension tip  1402 , retracting the extension tip  1402  changes a shape of the guidewires  602  from the flush or parallel configuration shown in  FIG. 15A  to the protruding configuration shown in  FIG. 15B . Further, due to the arrangement of the guidewires  602  around the extension  606 , each guidewire  602  protrudes in different outward direction relative to the longitudinal axis of the extension  606  than the other guidewires  602 . The external electrical components  106  can record a second set of impedance measurements of two or more electrodes  202 , including selected subsets thereof, to determine impedance measurements of tissue types between various pairs of guidewires  602  of the protruding shapes. For example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  at a first position along the lengths of the respective guidewires  602  and a second subset of impedance measurements between two or more electrodes  202  at a second position along the lengths of the respective guidewires  602 . As another example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  of a first guidewires  602  and a second subset of impedance measurements between two or more electrodes  202  of a second guidewire  602 . Based on the first set of impedance measurements and the second set of impedance measurements, the external electrical components  106  can generate a volumetric tissue type map, wherein the volumetric tissue type map includes layers of tissue types in various directions, distances, and lateral positions relative to the extension  606 . 
       FIGS. 16A-B  are more detailed illustrations of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204  including an aperture  302 , an extension tip  1402 , a wire  1502  that extends along the extension  606  to the extension tip  1402 , and two or more bands  1602 , each band  1602  extending between the sheath and the extension tip  1402 , wherein each band  1602  includes one or more electrodes  202  respectively located at a lateral position along the band  1602 . As previously discussed, the sheath  204  encloses wires that selectively couple the electrodes  202  to external electrical components  106  (not shown). 
     As shown in  FIG. 16A , the extension tip  1402  is positioned at a first position along the wire  1502 . As a result, the bands  1602 , which extend laterally from the sheath  204  to the extension tip  1402 , are parallel with the wire  1502 . The external electrical components  106  can record a first set impedance measurements of two or more electrodes  202  in the parallel orientation, including selected subsets thereof, to determine impedance measurements and tissue types of tissue near the instrument head  108 . For example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  at a first position along the lengths of the respective bands  1602  and a second subset of impedance measurements between two or more electrodes  202  at a second position along the lengths of the respective bands  1602 . As another example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  of a first band  1602  and a second subset of impedance measurements between two or more electrodes  202  of a second band  1602 . 
     As shown in  FIG. 16B , the extension tip  1402  retracts (e.g., moves in a retraction direction  1504 ). As a result, the extension tip  1402  compresses each band  1602 , causing each band  1602  to protrude in an outward direction  1506  relative to a longitudinal axis (e.g., a length axis) of the wire  1502 . In some embodiments, the wire  1502  can be electrically and/or mechanically actuated to create tension that pulls the extension tip  1402  in the retraction direction  1504 . Due to the coupling of the bands  1602  and the extension tip  1402 , retracting the extension tip  1402  changes a shape of the bands  1602  from the parallel configuration shown in  FIG. 16A  to the protruding configuration shown in  FIG. 16B . Further, due to the arrangement of the bands  1602  around the wire  1502 , each band  1602  protrudes in different outward direction relative to the longitudinal axis of the wire  1502  than the other bands  1602 . The external electrical components  106  can record a second set of impedance measurements of two or more electrodes  202 , including selected subsets thereof, to determine impedance measurements of tissue types between various pairs of bands  1602 . For example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  at a first position along the lengths of the respective bands  1602  and a second subset of impedance measurements between two or more electrodes  202  at a second position along the lengths of the respective bands  1602 . As another example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  of a first band  1602  and a second subset of impedance measurements between two or more electrodes  202  of a second band  1602 . Based on the first set of impedance measurements and the second set of impedance measurements, the external electrical components  106  can generate a volumetric tissue type map, wherein the volumetric tissue type map includes layers of tissue types in various directions, distances, and lateral positions relative to the wire  1502 . 
       FIGS. 17A-B  are more detailed illustrations of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204 , an extension tip  1402 , and a balloon  1702  including two or more bands  1602 , each band  1602  extending from the extension tip  1402  along a surface of the balloon  1702 , wherein each band  1602  includes one or more electrodes  202  respectively located at a lateral position along the band  1602 . As previously discussed, the sheath  204  encloses wires that selectively couple the electrodes  202  to external electrical components  106  (not shown). 
     As shown in  FIG. 17A , the balloon  1702  is in a collapsed configuration. As a result, the bands  1602 , each extending laterally from the extension tip  1402  along the surface of the balloon  1702  in a different direction, are parallel with a longitudinal axis (e.g., a length axis) of the instrument head  108 . The external electrical components  106  can record a first set impedance measurements of two or more electrodes  202  in the parallel orientation, including selected subsets thereof, to determine impedance measurements and tissue types of tissue near the instrument head  108 . For example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  at a first position along the lengths of the respective bands  1602  and a second subset of impedance measurements between two or more electrodes  202  at a second position along the lengths of the respective bands  1602 . As another example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  of a first band  1602  and a second subset of impedance measurements between two or more electrodes  202  of a second band  1602 . 
     As shown in  FIG. 17B , the balloon  1702  is in an expanded configuration in which the surface of the balloon  1702  expands in an outward direction  1704  relative to the longitudinal axis of the instrument head  108 . As a result, each band  1602  located on the surface of the balloon  1702  protrudes in an outward direction  1506  relative to the longitudinal axis of the instrument head  108 . In some embodiments, the balloon  1702  can be electrically and/or mechanically inflated with air or any other medium. Due to the location of the bands  1602  on the surface of the balloon  1702 , inflating the balloon  1702  changes a shape of the bands  1602  from the parallel configuration shown in  FIG. 17A  to the protruding configuration shown in  FIG. 17B . Further, due to the arrangement of the bands  1602  around the longitudinal axis of the instrument head  108 , each band  1602  protrudes in different outward directions  1704  relative to the longitudinal axis of the instrument head  108  than the other bands  1602 . The external electrical components  106  can record a second set of impedance measurements of two or more electrodes  202 , including selected subsets thereof, to determine impedance measurements of tissue types between various pairs of bands  1602 . For example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  at a first position along the lengths of the respective bands  1602  and a second subset of impedance measurements between two or more electrodes  202  at a second position along the lengths of the respective bands  1602 . As another example (without limitation), the external electrical components  106  can record a first subset of impedance measurements between two or more electrodes  202  of a first band  1602  and a second subset of impedance measurements between two or more electrodes  202  of a second band  1602 . Based on the first set of impedance measurements and the second set of impedance measurements, the external electrical components  106  can generate a volumetric tissue type map, wherein the volumetric tissue type map includes layers of tissue types in various directions, distances, and lateral positions relative to the longitudinal axis of the instrument head  108 . 
       FIG. 18A  is a more detailed illustration of the instrument head of  FIG. 1 , according to other various embodiments. As shown, the instrument head  108  includes, without limitation, a sheath  204 , an extension  606  including an aperture  302  and an extension tip  1402 , a wire  1502  that extends along the extension  606  through the extension tip  1402 , and two or more guidewires  602 , each guidewire  602  extending between the extension and the extension tip  1402 , wherein each guidewire  602  includes one or more electrodes  202  respectively located at a lateral position along the guidewire  602 . As previously discussed, the sheath  204  encloses wires that selectively couple the electrodes  202  to external electrical components  106  (not shown). 
     As shown in  FIG. 18A , each guidewires  602  extend laterally from the sheath  204  to the extension tip  1402 . Also, each guidewire  602  protrudes in an outward direction  1506  relative to a longitudinal axis (e.g., a length axis) of the extension  606 . For example (without limitation), the guidewires  602  can retract into the sheath  204  and can be in a parallel configuration when retracted into the sheath  204 . When extended from the sheath  204 , each guidewire  602  can extend in a different direction relative to the other guidewires  602 . Due to the arrangement of the guidewires  602  around the extension  606 , each guidewire  602  protrudes in different outward direction relative to the longitudinal axis of the extension  606  than the other guidewires  602 . The external electrical components  106  can record impedance measurements of two or more electrodes  202 , including selected subsets thereof, to determine impedance measurements of tissue types between various pairs of guidewires  602  of the protruding shapes. For example (without limitation), the external electrical components  106  can record a first set of impedance measurements between two or more electrodes  202  at a first position along the lengths of the respective guidewires  602  and a second set of impedance measurements between two or more electrodes  202  at a second position along the lengths of the respective guidewires  602 . As another example (without limitation), the external electrical components  106  can record a first set of impedance measurements between two or more electrodes  202  of a first guidewires  602  and a second set of impedance measurements between two or more electrodes  202  of a second guidewire  602 . 
       FIG. 18B  is an illustration of a grid pattern  1802  associated with the instrument head of  FIG. 18A . As shown, each electrode  202  is located at a node of the grid pattern  1802  at a particular position along a longitudinal axis (e.g., a length axis) of the extension  606  and/or a different lateral distance from the extension  606 . Based on impedance measurements recorded between various pairs of nodes of the graph pattern  180 , the external electrical components  106  can generate a grid tissue type map, wherein the grid tissue type map includes layers of tissue types in various directions, distances, and lateral positions relative to the extension  606 . 
       FIG. 19  is a more detailed illustration of the external electrical components of  FIG. 1 , according to various embodiments. As shown, the external electrical components  106  include wires  104 , an amplifier  1902 , an impedance bridge  1904 , and a processor  1906 . The wires  104  conduct current at various frequencies between a selected two or more electrodes  202  and the external electrical components  106 . In various embodiments, the amplifier  1902  is an analog interface amplifier that amplifies a supplied voltage and/or a return voltage while the wires  104  conduct current at various frequencies between the impedance bridge  1904  and the selected two or more electrodes  202 . In various embodiments, the impedance bridge  1904  is an impedance load that the processor  1906  measures to determine an impedance of a circuit including the impedance bridge  1904 , the amplifier  1902 , and the selected two or more electrodes  202 . The processor  1906  generates frequencies for a current that the wires  104  conduct between the impedance bridge  1904  and the selected two or more electrodes  202 . 
     While the wires  104  conduct current at various frequencies, the processor  1906  records one or more impedance measurements  1908  of the circuit including the at selected least two electrodes  202 . The processor  1906  determines, based on the impedance measurements  1908 , a tissue type  1910  of a portion of tissue between the selected two or more electrodes  202 . In various embodiments, the processor  1906  determines the tissue type  1910  by comparing the impedance measurements  1908  with one or more characteristic impedance measurements associated with one or more tissue types. For example and without limitation, based on the comparing, the processor  1906  can determine which tissue type is associated with characteristic impedance measurements that are closest to the impedance measurements of the portion of tissue between the selected two or more electrodes  202 . In various embodiments, the processor  1906  can determine a Cole relaxation frequency of the portion of tissue based on the impedance measurements  1908 , and can compare the Cole relaxation frequency to one or more characteristic Cole relaxation frequencies of one or more tissue types. The Cole relaxation frequency corresponds to a frequency associated with a greatest impedance measurement  1908  included in the one or more impedance measurements  1908 . In various embodiments, the Cole relaxation frequency is a frequency of a maximum normalized impedance measurement of the portion of tissue between the two or more electrodes  202 . For example and without limitation, based on a Cole relaxation frequency below a threshold frequency (e.g., 10 5  Hz), the processor  1906  can determine that the portion of tissue between the selected two or more electrodes  202  is a non-tumor tissue type. Similarly, for example and without limitation, based on a Cole relaxation frequency above the threshold frequency, the processor  1906  can determine that the portion of tissue between the two or more electrodes  202  is a tumor tissue type. 
     In various embodiments, the processor  1906  determines a tissue type map  1912  based on the determined tissue types  1910 . For example (without limitation), the processor  1906  selectively delivers current to a sequence of selected two or more electrodes  202  that are positioned at respective locations relative to the instrument head  108  (e.g., a first pair of electrodes on a left side of the instrument head  108  and a second pair of electrodes on a right side of the instrument head  108 ). Alternatively or additionally, as another example (without limitation), the processor  1906  selectively delivers current to the two or more electrodes  202  taken at a first point in time when the instrument head  108  is positioned at a first location within a patient&#39;s body and a second point in time when the instrument head  108  is positioned at a second location within the patient&#39;s body. Based on the determined tissue types  1910  of the sets of electrodes positioned at respective locations and/or at different points in time, the processor  1906  determines a tissue type map  1912  of tissue types  1910  near the instrument head  108 . For example (without limitation), based on the grid pattern  1802  of  FIG. 18B , the processor  1906  can determine the tissue types  1910  between respective pairs of electrodes  202  positioned at adjacent nodes of the grid pattern  1802 . The tissue type map  1912  indicates the determined tissue types  1910  of the tissue between each pair of adjacent nodes of the grid pattern  1802 . 
     In various embodiments, the processor  1906  performs one or more operations  1914  to control a medical device tool based on the determined tissue type  610 . For example and without limitation, in various embodiments in which the instrument head  108  includes a camera  206 , the processor  1906  can perform operations  1914  that include activating the camera  206  to capture an image of the tissue at the location  102  of the instrument head  108 . For example and without limitation, in various embodiments in which the instrument head  108  includes a light source  208 , the processor  1906  can perform operations  1914  that include activating the light source  208  to illuminate the tissue at the location  102  of the instrument head  108 . For example and without limitation, in various embodiments in which the instrument head  108  includes a therapeutic drug delivery tool, the processor  1906  can perform operations  1914  that include activating the therapeutic drug delivery tool to deliver one or more therapeutic drugs to the tissue at the location  102  of the instrument head  108 . For example and without limitation, in various embodiments in which the instrument head  108  includes an energy delivery tool, the processor  1806  can perform operations  1914  that include activating the energy delivery tool to deliver energy to the tissue at the location  102  of the instrument head  108 . For example and without limitation, in various embodiments in which the instrument head  108  includes a tissue sample extraction tool, the processor  1906  can perform operations  1914  that include activating the tissue sample extraction tool to extract a tissue sample from the tissue at the location  102  of the instrument head  108 . 
     In various embodiments, the processor  1906  presents the tissue type map  1912  indicating the determined tissue types  1910  at the location  102  of the instrument head  108 . For example and without limitation, the processor  1906  can display the tissue type map  1912  using a visual output (e.g., a light-emitting diode, a liquid crystal display, or the like). For example and without limitation, where the target location  102  is a tumor, the displayed tissue type map  1912  can indicate that a determined tumor tissue type at a particular position relative to the instrument head  108  (e.g., on a left side or a right side of the instrument head  108 ) matches an expected tissue type of the tissue at the location  102 . Presenting the indication can inform a user of the medical device  100  that the location  102  of the instrument head  108  matches a target location. Further, in various embodiments, the processor  1906  performs the one or more operations  1914  to control a medical device tool based on presenting the tissue type map  1912  and receiving a signal to activate the medical device tool. 
       FIG. 20  is a more detailed illustration of the medical device  100  of  FIG. 1 , according to various embodiments. As shown, the medical device  100  includes an instrument head  108  and external electrical components  106 . As shown, the instrument head  108  includes two or more electrodes  202  that are selectively coupled to the external electrical components  106  by wires  104 . In various embodiments, without limitation, each of the two or more electrodes  202  is coupled to the external electrical components  106  by one wire  104  or by respective wires of a plurality of wires  104 . As shown, the instrument head  108  also includes a medical device tool  2002 , such as and without limitation, a therapeutic drug delivery tool, an energy delivery tool, or a tissue sample extraction tool. In various embodiments, the instrument head  108  includes, without limitation, two or more medical device tools  2002 , which can be of one kind or of different kinds. 
     As shown, the external electrical components  106  include an amplifier  1902 , an impedance bridge  1904 , and a processor  1906 . The amplifier  1902  amplifies a supplied voltage and/or a return voltage while the wires  104  conduct current at various frequencies between the impedance bridge  1904  and a selected set of electrodes of the two or more electrodes  202 . The impedance bridge  1904  is an impedance load that the processor  1906  measures to determine an impedance of a circuit including the impedance bridge  1904 , the amplifier  1902 , the wires  104 , and the two or more electrodes  202 . The processor  1906  records, at various frequencies, one or more impedance measurements  1908 . The processor  1906  determines a tissue type map  1912  of tissue types at the location  102  of the instrument head  108  based on the impedance measurements  1908 . In various embodiments and without limitation, the processor  1906  determines the tissue types indicated by the respective impedance measurements  1908  based on a Cole relaxation frequency of the portion of tissue contacting the selected two or more electrodes  202 . In various embodiments and without limitation, the processor  1906  determines the tissue type map  1912  as areas of tumor tissue types and/or non-tumor tissue types. In various embodiments and without limitation, based on the tissue type map  1912 , the processor  1906  determines that tissue types  1910  at the location  102  of the instrument head  108  match the expected tissue types of tissue at a target location, which indicates or confirms that the instrument head  108  is positioned at the target location  102 . For example and without limitation, if the target location  102  is a tumor, the processor  1906  can determine whether the instrument head  108  is positioned at a target location  102  by determining that the tissue types  1918  indicated by the tissue type map  1912  are a tumor tissue type. 
     As shown, the processor  1906  is coupled to a conduit  2004  of the medical device tool  2002 . Based on the tissue type map  1912 , the processor  1906  performs one or more operations  1914  to control the medical device tool  2002 . In various embodiments and without limitation, the medical device tool  2002  includes a therapeutic drug delivery tool, and the processor  1906  performs an operation  1914  of causing the medical device tool  2002  to deliver one or more therapeutic drugs to tissue at the location  102  of the instrument head  108 . For example and without limitation, the processor  1906  can cause one or more therapeutic drugs through one or more drug delivery conduits to and through the therapeutic drug delivery tool. In various embodiments and without limitation, the medical device tool  2002  includes an energy delivery tool, and the processor  1906  performs an operation  1914  of causing the conduit  2004  and the medical device tool  2002  to deliver energy to tissue at the location  102  of the instrument head  108 . For example and without limitation, the processor  1906  can current to be conducted through wires in the conduit  2004  to and through the energy delivery tool. In various embodiments and without limitation, the medical device tool  2002  is a tissue sample extraction tool, and the processor  2006  performs an operation  1914  of causing the tissue sample extraction tool to extract a tissue sample from tissue at the location  102  of the instrument head  108 . For example and without limitation, the external electrical components  106  can include an actuator coupled to the tissue sample extraction tool by wires in the conduit  2004 , and the processor  1906  can activate the actuator to cause the tissue sample extraction tool to extract the tissue sample. 
     In various embodiments, the medical device  100  reports the tissue type map  1912  to a user of the medical device  100 . For example and without limitation, the medical device  100  can display the tissue type map  1912  using a visual output (e.g., a liquid crystal display (LCD), a light-emitting diode (LED) display to present a visual indication of determined tissue types  1910 , such as a light, symbol, text, graphic, or the like). In various embodiments and without limitation, the processor  1906  can include, in the displayed tissue type map  1912 , an indication that the determined tissue types  1910  match the expected tissue type of tissue at a target location (e.g., using a visual output, an audio output, or the like). 
       FIG. 21  is a flow diagram of method steps for controlling the medical device  100  of  FIG. 1 , according to various embodiments. Although the method steps are described in conjunction with the systems of  FIGS. 1-20 , persons skilled in the art will understand that any system configured to perform the method steps, in any order, falls within the scope of the present invention. 
     As shown, a method  2100  begins at step  2102 , where a processor  1906  records, at one or more frequencies, two or more impedance measurements  1908 , wherein each impedance measurement  1908  is associated with two or more electrodes  202  included in an instrument head  108  of the medical device  100 . In various embodiments and without limitation, the processor  1906  determines a Cole relaxation frequency of tissue between the selected two or more electrodes  202  in the instrument head  108 , e.g., as a frequency of a maximum normalized impedance measurement of the tissue between the selected two or more electrodes  202 . 
     At step  2104 , the processor  1906  determines, based on the two or more impedance measurements  1908 , a tissue type map  1912  at a location associated with the instrument head  108 . In various embodiments and without limitation, the processor  1906  determines the tissue type map  1912  that classifies different areas of the tissue as one of a tumor tissue type or a non-tumor tissue type. In various embodiments and without limitation, the processor  1906  determines whether the tissue types indicated in the tissue type map  1912  match expected tissue types at a target location  102 . In various embodiments, the processor  1906  determines the tissue type map  1912  by comparing the impedance measurements  1908  to one or more characteristic impedance measurements associated with one or more tissue types. In various embodiments and without limitation, the processor  1906  determines whether the tissue type map  1912  indicates determined tissue types  1910  that match expected tissue types at a target location  102  (e.g., in order to determine whether the instrument head  108  is positioned at the target location). The method can return to step  2102  to record additional impedance measurements  1908  and to determine a second or updated tissue type map  1912 . 
     In sum, the disclosed medical device measures the impedance of tissue in a location where an instrument head of a medical device is positioned. The medical device determines a tissue type map based on impedance measurements associated with two or more electrodes included in the instrument head. The disclosed approach advantageously results in the medical device determining a tissue type map of the tissue types at the location where the instrument head is located (e.g., without limitation, on various sides of the instrument head). 
     At least one technical advantage of the disclosed medical device relative to the prior art is that the disclosed medical device is able to determine a map of tissue types on one or more sides of the instrument head of a medical device prior to when a medical device tool is activated or during activation. For example, the disclosed medical device can determine whether the tissue types of portions of tissue located where the instrument head of a medical device is positioned match the expected tissue types at a given target location prior to activating the relevant medical device tool. In this manner, the disclosed medical device can ensure that medical device tools are applied to a selected tissue type, such as a tumor, rather than some other tissue types, such as healthy tissue. Also, the disclosed medical instrument can apply medical device tools at target locations more accurately than is possible with conventional medical devices. Consequently, the disclosed medical device can be used to perform various procedures, such as and without limitation, delivering therapeutic drugs or energy or extracting tissue samples, at specific locations more accurately and reliably than what can be achieved using conventional medical devices. These technical advantages provide one or more technological advancements over prior art approaches. 
     1. In some embodiments, a medical device comprises an instrument head that includes two or more electrodes and a medical device tool; an impedance bridge selectively coupled to the two or more electrodes; and a processor coupled to the impedance bridge. 
     2. The medical device of clause 1, wherein each of the two or more electrodes is shaped to curve outward relative to a longitudinal axis of the instrument head. 
     3. The medical device of clauses 1 or 2, wherein each of the two or more electrodes includes a flexible material. 
     4. The medical device of any of clauses 1-3, wherein each of the two or more electrodes comprises Nitinol. 
     5. The medical device of any of clauses 1-4, wherein the two or more electrodes extend to an adjustable extension length relative to an aperture of the instrument head. 
     6. The medical device of any of clauses 1-5, wherein the medical device tool includes a clamp, and the two or more electrodes are located at different positions along a length of the clamp. 
     7. The medical device of any of clauses 1-6, wherein the medical device tool includes a guidewire, and the two or more electrodes are located at different positions along a length of the guidewire. 
     8. The medical device of clause 7, wherein the instrument head includes a sheath, and the guidewire selectively retracts into the sheath. 
     9. The medical device of any of clauses 1-8, wherein the instrument head includes a sheath, the sheath includes an extension, and the guidewire selectively retracts into the extension. 
     10. The medical device of any of clauses 1-9, wherein the instrument head includes an extension, and the two or more electrodes are located at different positions along a length of the extension. 
     11. The medical device of clause 10, wherein the extension selectively bends at a bending location. 
     12. The medical device of clauses 10 or 11, wherein the extension selectively forms a curved shape. 
     13. The medical device of clause 12, wherein the extension selectively forms a first curved shape, a second curved shape, or a straight shape. 
     14. The medical device of any of clauses 10-13, wherein the extension selectively forms a circular shape that encircles a longitudinal axis of the instrument head. 
     15. The medical device of any of clauses 10-14, wherein the extension selectively forms a wave shape relative to a longitudinal axis of the instrument head. 
     16. The medical device of any of clauses 10-15, wherein the extension selectively forms a spiral shape. 
     17. The medical device of any of clauses 1-16, wherein the instrument head includes two or more guidewires, each guidewire extends from the instrument head in a different direction, and each of the two or more electrodes is located at a tip of a respective one of the two or more guidewires. 
     18. The medical device of any of clauses 1-17, wherein the instrument head includes two or more guidewires, each guidewire protrudes from the instrument head in a different outward direction, and each of the two or more electrodes is located at a lateral position along a respective one of the two or more guidewires. 
     19. The medical device of clause 18, wherein the two or more electrodes are arranged in a grid pattern. 
     20. The medical device of clauses 18 or 19, wherein the two or more guidewires are coupled to an extension tip of the instrument head, and retracting the extension tip changes a shape of each guidewire from a parallel configuration to a protruding configuration. 
     21. The medical device of any of clauses 1-20, wherein the instrument head includes two or more bands, each band protruding from the instrument head in different outward directions, each of the two or more electrodes is located at a lateral position along one of the two or more bands, the two or more bands are coupled to an extension tip of the instrument head, and retracting the extension tip changes a shape of each band from a parallel configuration to a protruding configuration. 
     22. The medical device of any of clauses 1-21, wherein the instrument head includes a balloon, a surface of the balloon includes two or more bands, each of the two or more electrodes is located at a lateral position along a respective one of the two or more bands, and inflating the balloon changes a shape of each band from a parallel configuration to a protruding configuration. 
     23. In some embodiments, a method for controlling medical device tools comprises recording, at one or more frequencies, two or more impedance measurements, wherein each impedance measurement is associated with two or more electrodes included in an instrument head of a medical device; and determining, based on the two or more impedance measurements, a tissue type map at a location associated with the instrument head. 
     24. The method of clause 23, wherein the two or more impedance measurements include a first impedance measurement associated with a first subset of the two or more electrodes and a second impedance measurement associated with a second subset of the two or more electrodes. 
     25. The method of clauses 23 or 24, wherein the two or more impedance measurements include a first impedance measurement associated with a first extension length of the two or more electrodes relative to an aperture of the instrument head and a second impedance measurement associated with a second extension length of the two or more electrodes relative to the aperture of the instrument head. 
     26. The method of any of clauses 23-25, wherein the two or more impedance measurements include a first impedance measurement taken at a first point in time and a second impedance measurement taken at a second point in time. 
     Any and all combinations of any of the claim elements recited in any of the claims and/or any elements described in this application, in any fashion, fall within the contemplated scope of the present invention and protection. 
     The descriptions of the various embodiments have been presented for purposes of illustration, but are not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. 
     Aspects of the present embodiments may be embodied as a system, method or computer program product. Accordingly, aspects of the present disclosure may take the form of an entirely hardware embodiment, an entirely software embodiment (including firmware, resident software, micro-code, etc.) or an embodiment combining software and hardware aspects that may all generally be referred to herein as a “module,” a “system,” or a “computer.” In addition, any hardware and/or software technique, process, function, component, engine, module, or system described in the present disclosure may be implemented as a circuit or set of circuits. Furthermore, aspects of the present disclosure may take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon. 
     Any combination of one or more computer readable medium(s) may be utilized. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable storage medium may be, for example, but not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples (a non-exhaustive list) of the computer readable storage medium would include the following: an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. In the context of this document, a computer readable storage medium may be any tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. 
     Aspects of the present disclosure are described above with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to embodiments of the disclosure. It will be understood that each block of the flowchart illustrations and/or block diagrams, and combinations of blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus to produce a machine. The instructions, when executed via the processor of the computer or other programmable data processing apparatus, enable the implementation of the functions/acts specified in the flowchart and/or block diagram block or blocks. Such processors may be, without limitation, general purpose processors, special-purpose processors, application-specific processors, or field-programmable gate arrays. 
     The flowchart and block diagrams in the figures illustrate the architecture, functionality, and operation of possible implementations of systems, methods and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagrams may represent a module, segment, or portion of code, which comprises one or more executable instructions for implementing the specified logical function(s). It should also be noted that, in some alternative implementations, the functions noted in the block may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. It will also be noted that each block of the block diagrams and/or flowchart illustration, and combinations of blocks in the block diagrams and/or flowchart illustration, can be implemented by special purpose hardware-based systems that perform the specified functions or acts, or combinations of special purpose hardware and computer instructions. 
     While the preceding is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.