Patent Publication Number: US-2023134815-A1

Title: Guidance system for interventional devices with curved shape

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. Provisional Patent Application No. 62/989,926, filed Mar. 16, 2020. 
    
    
     FIELD 
     The invention relates to a system and method for guidance of a curved interventional device and more specifically a curved needle. 
     BACKGROUND 
     Tracking systems are widely used in medical practice to assist in the insertion of various devices (e.g., biopsy needles, ablation probes, catheters, endoscopes) into the target organ or location. The devices can be largely classified into rigid devices with a straight insertion path (e.g. biopsy and ablation devices) and flexible devices with insertion paths that can follow various trajectories (e.g. catheters and endoscopes). The former devices are typically inserted transcutaneously (i.e. through the skin and underneath tissues) to the target, sometimes with image guidance (e.g. ultrasound, X-ray, CT, MRI) and sometimes by manual palpation (e.g. in breast biopsy). 
     The current disclosure is intended for the transcutaneous insertion of devices under imaging guidance. Currently, most of the devices that are inserted this way are straight—biopsy needles, RF ablation probes, cryo-ablation probes. The device may slightly bend during the insertion, and this may result in inaccurate placement of the device into the target. Some solutions to this problem are being developed, for example the use of fiberoptic sensors to measure the needle bending (Patent application 20150190123). Another approach is to provide a steerable front end of the device, as used in many surgical tools for laparoscopic procedures (e.g. LaproFlex, Deam, The Netherlands). A few rigid devices use a curved needle that is initially inserted towards the target in a straightened configuration within a needle guide, and then deployed into the target while returning to its curved shape (e.g. Pakter curved needle (Cook Medical, USA); Avaflex for vertebroplasty (Stryker, USA); Star bone tumor ablation device (Merit Medical, USA); U.S. Pat. Nos. 6,592,559; 7,713,273; 10,123,809). 
     PCT patent application publication number WO2020100038A3, incorporated by reference herein in its entirety, discloses the use of curved needles with fixed geometry for biopsies. 
     However, guidance of curved needles using a tracking system such as is used for a straight device remains a challenge. There is thus a need for a guidance system and method that enables planning of the insertion position of a device with a curved component such as a curved biopsy needle, and for guidance of the device into the target. 
     SUMMARY 
     The following specification describes a guidance system for a guidance of a curved device to a target in a body and methods of use thereof. The system and method may include tracking and imaging for calculation and optimization of reaching the target. 
     There is provided, in accordance with embodiments of the invention, a system for guidance of a curved needle to a target tissue in a body. The system includes a curved needle having a curved section, the curved section configured to curve in a flexion plane and having known curvature parameters. The curved needle is enclosed within a straight needle guide, such that when enclosed within the straight needle guide, the curved section of the curved needle is straight, and upon distal deployment of the curved needle from the straight needle guide, the curved section that is deployed from the straight needle guide is curved with the known curvature parameters within the flexion plane. The system further includes a tracking system configured for tracking a position of the curved needle and the straight needle guide in the body, wherein the tracking system further includes an imaging component. The system further includes a processor configured to calculate a needle trajectory, the needle trajectory including a needle guide insertion length and a needle deployment length such that the curved needle is configured to reach the target tissue when said needle guide insertion length and said needle deployment length are used. The calculating is done based on the known curvature parameters, a chosen entry point, and a location of the target tissue. The system further includes a graphic user interface for displaying the calculated needle trajectory. In some embodiments, the known curvature parameters includes a known radius of curvature wherein the radius of curvature is constant. 
     In accordance with further features in embodiments of the invention, the system may include a sensor positioned on the curved needle or on the device. In accordance with further features in embodiments of the invention, the tracking system may be a tracking system with a three-dimensional scanning capability and is configured to track the position of the curved needle based on data from the sensor. The imaging component is configured to provide a scanning plane which includes the target tissue and an intersection line of the flexion plane with the scanning plane so that a rotated position of the curved needle may be determined for the chosen entry point such that when in the determined rotated position, the flexion plane of the curved needle includes the target tissue, thus providing the curved needle with capability of reaching the target tissue when deployed from the straight needle guide. 
     In accordance with further features in additional embodiments of the invention, the tracking system may be capable of providing two dimensional images, and the imaging component includes a probe with a two-dimensional scanning plane. The curved needle may be attached to the probe of the imaging component such that the flexion plane of the curved needle is in alignment with the two-dimensional scanning plane. 
     In accordance with further features in additional embodiments of the invention, the chosen entry point is offset from the target tissue. In some embodiments, the curved needle is a curved biopsy needle. 
     In accordance with further features in additional embodiments of the invention, the graphic user interface may display an image from the imaging component and may further display annotations on the image for guiding the device based on the calculated needle trajectory. 
     In accordance with further features in additional embodiments of the invention, the system may further include an automated controller, wherein the processor provides the calculated needle trajectory to the automated controller and the automated controller is configured to advance the curved needle to the target based on the calculated needle trajectory. 
     There is provided, in accordance with embodiments of the invention, a method for guidance of a curved needle to a target tissue. The method includes providing a curved needle having a curved section, the curved section configured to curve in a flexion plane and having known curvature parameters, the curved needle enclosed within a straight needle guide, such that upon distal deployment of the curved needle from the straight needle guide, the curved section that is deployed from the straight needle guide is curved with the known curvature parameters within the flexion plane, providing an imaging component for providing images of the target tissue and of the curved needle with respect to the target tissue, choosing an entry point into a body for the curved needle enclosed within the straight needle guide, positioning the straight needle guide with the curved needle therein at the entry point, calculating a needle guide insertion length, advancing the straight needle guide with the curved needle therein into the body by the calculated needle guide insertion length, calculating a needle deployment length, and advancing the curved needle distally past a distal end of the straight needle guide by the calculated needle deployment length until the target tissue is accessed. 
     In accordance with further features in embodiments of the invention, the method may include rotating the straight needle guide with the curved needle therein to align a flexion plane of the curved needle such that the target tissue can be accessed upon deployment of the curved needle or maintaining a position of the straight needle guide and rotating the curved needle within the straight needle guide to align a flexion plane of the curved needle such that the target tissue can be accessed upon deployment of the curved needle. The method may further include accessing a second target tissue by calculating a second needle guide insertion length and a second needle deployment length, retracting the curved needle back into the needle guide, repositioning the needle guide at the second needle guide insertion length, and advancing the curved needle distally past a distal end of the straight needle guide by the second needle deployment length. 
     In accordance with further features in embodiments of the invention, the method may include taking a tissue sample once the target tissue is accessed. The method may further include calculating a needle trajectory based on the calculated needle guide insertion length and on the calculated needle deployment length. Calculating the needle trajectory may be done by providing a starting orientation vector from a distal end of the straight needle guide to a point which is transversely adjacent the target tissue, providing a target vector from a distal end of the straight needle guide to the target tissue, calculating an angle between the orientation vector and the target vector, and based on the known curvature parameters calculating the projected needle trajectory. 
     In accordance with further features in embodiments of the invention, the method may include displaying the target tissue and the calculated needle trajectory. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the invention, suitable methods and materials are described below. In case of conflict, the patent specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and further aspects of the invention may be better understood by referring to the following description in conjunction with the accompanying drawings in which: 
         FIG.  1    is a photographic illustration of three orthogonal images with tracking annotation superimposed thereon for a straight needle configuration; 
         FIG.  2    is schematic illustration of a guidance system for guidance of a device having a curved needle, in accordance with embodiments of the invention; 
         FIGS.  3 A and  3 B  are illustrative examples of a device having a curved needle positioned within a needle guide, wherein the device is a core biopsy device, and the curved needle is a core biopsy needle positioned within a straight coaxial needle guide, in accordance with embodiments of the invention; 
         FIGS.  4 A- 4 D  are illustrations of the curved core biopsy needle of  FIGS.  3 A and  3 B , showing the different tip positions that can be obtained through the combined use of rotation and forward motion ( FIGS.  4 A- 4 B ), or through the use of needles with different radius of curvature ( 4 C), taken together with the curved configurations of the curved core biopsy needle, and further showing a cylindrical volume around a needle guide for a needle having a given radius R 1 , R 2  . . . Rn ( FIG.  4 D ), in accordance with embodiments of the invention; 
         FIG.  5    is a schematic illustration of a processor of the guidance system of  FIG.  2   , showing various components of the processor in accordance with embodiments of the invention; 
         FIGS.  6 A- 6 D  are cross-sectional and schematic illustrations of the curved needle and needle guide, and their positions with respect to a body tissue; 
         FIG.  7    is a geometric representation showing the parameters needed for calculating a needle guide deployment length and a needle deployment length in accordance with embodiments of the invention; 
         FIG.  8    is a flowchart illustration of a method of guidance of a curved needle to a target tissue, in accordance with embodiments of the invention; 
         FIGS.  9 A- 9 C  are illustrations of a display showing annotations overlaid over images from the imaging component of the system of  FIG.  2   , when tracking system has a three-dimensional scanning capability, in accordance with embodiments of the invention; 
         FIGS.  10 A- 10 C  are illustrations of a display as in  FIGS.  9 A- 9 C , showing three different target locations, wherein differences in needle guide deployment length and in needle deployment length both result in reaching different locations; 
         FIG.  11    is a schematic illustration of an experimental setup for testing calculation of parameters used in a guidance system for curved devices in accordance with embodiments of the invention; 
         FIGS.  12 A- 12 C  are graphical illustrations showing a process of calculating values for guidance of a curved needle to a target location, in accordance with embodiments of the invention; 
         FIGS.  13 A and  13 B  are illustrations of an imaging component having a probe with a scanning element depicting a needle attached to the probe in an angled orientation and in an aligned orientation, respectively, in accordance with embodiments of the invention; and 
         FIGS.  14 A and  14 B  are photographic illustrations of a display showing annotations when using a tracking system with a two-dimensional scanning capability, in accordance with embodiments of the invention. 
     
    
    
     It will be appreciated that for simplicity and clarity of illustration, elements shown in the drawings have not necessarily been drawn accurately or to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity or several physical components may be included in one functional block or element. Further, where considered appropriate, reference numerals may be repeated among the drawings to indicate corresponding or analogous elements. Moreover, some of the blocks depicted in the drawings may be combined into a single function. 
     DETAILED DESCRIPTION 
     In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. It will be understood by those of ordinary skill in the art that the invention may be practiced without these specific details. In other instances, well-known methods, procedures, components and structures may not have been described in detail so as not to obscure the invention. 
     Embodiments of the invention are directed to systems and methods for guiding a device within a body, and more particularly to guiding a curved device within a body. The systems and methods of the invention are designed to provide guidance for an interventional device having a curved shape to enable samples to be obtained from one or multiple locations within a target, which can later be used for both microscopic histopathology analysis and biomarker analysis of the tissue properties in these different locations. Alternatively, the interventional device can be configured for other uses, examples of which include but are not limited to treatment of multiple locations by heat deposition, or by injection of therapeutic agents, or by freezing. The principles and operation of systems and methods according to the invention may be better understood with reference to the drawings and accompanying descriptions. 
     Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein are for the purpose of description and should not be regarded as limiting. 
     It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination. Although the description herein is directed specifically to a biopsy device including a biopsy needle, it should be readily apparent that other curved devices may be guided using similar systems and methods and fall within the scope of the invention. 
     Guidance of a device with a straight needle can be done by tracking the position (location and orientation) of the device and superimposing a display of the needle tip location and needle orientation on scans that are acquired by imaging systems such as, but not limited to, X-ray, ultrasound, CT or MRI. An example of this type of guidance system is the EndoScout™ tracking system for MRI (disclosed in U.S. Pat. Nos. 6,516,213 and 9,037,213, incorporated by reference herein in their entireties). The graphic user interface (GUI) of the EndoScout™ adds tracking annotation to images from MRI scanners to help a user guide the device. An example of images from such a system is shown in  FIG.  1   , which is an illustration showing the use of three orthogonal images with tracking annotation superimposed thereon. The images shown in  FIG.  1    are for a straight needle configuration. For this type of needle, two or three views are shown (three in the example shown in  FIG.  1   ), which enables alignment of the device to the target. In the case of a straight device, even a single view that shows the target and the needle position (location and orientation) in reference to the scan plane can suffice to enable guidance of the needle to the target. However, when a curved needle is used, guidance is more complex. The invention, in embodiments thereof, is directed to guidance of a device with a curved needle. 
     Reference is now made to  FIG.  2   , which is a schematic illustration of a guidance system  10  for guidance of a device  12  having a curved needle  14 , in accordance with embodiments of the invention. System  10  includes a device  12  having a needle with a curved configuration, wherein in the present embodiment device  12  is a core biopsy device with a curved needle  14  positioned within a needle guide  20 . Examples of a curved needle  14  and a needle guide  20  for positioning of the curved needle  14  therein are described in PCT publication WO2020100038A3, incorporated herein by reference in its entirety. It should be readily apparent that the description herein with respect to a curved needle and a core biopsy device should be taken as illustrative, and that other curved interventional devices are included within the scope of the invention. 
     Reference is now made to  FIGS.  3 A and  3 B , which are illustrative examples of a device  12  having a curved needle  14  positioned within a needle guide  20 , wherein device  12  is a core biopsy device  50 , and curved needle  14  is a core biopsy needle  52  positioned within a straight coaxial needle guide  20  (in this case, a core biopsy straight coaxial needle guide  53 ). Core biopsy needle  52  includes a stylet  18  and a cutting cannula  16 . As shown in  FIG.  3 A , when core biopsy needle  52  is fully contained within coaxial needle guide  53 , core biopsy needle  52  has a straight configuration. In this straight configuration depicted in  FIG.  3 A , core biopsy needle  52  can be inserted into the body and directed to the target, moved distally and proximally (i.e. forward and backward), and rotated either together with coaxial needle guide  53  or rotated with respect to coaxial needle guide  53  (with the needle guide not rotated). In the embodiment shown in  FIG.  3 A , coaxial needle guide  53  can be inserted into the body towards the target using image guidance, as is commonly done in current clinical practice of image-guided intervention. Once coaxial needle guide  53  is in place in the body, core biopsy needle  52  is advanced through coaxial needle guide  53  until core biopsy needle  52  is in the desired position. In some embodiments, coaxial needle guide  53  is attached to the core biopsy needle device via a connector, such as a Luer lock, for example. In either case, the ability to rotate core biopsy needle  52 —either together with coaxial needle guide  53  or with respect thereto—is a key feature that enables the tip of the needle to reach different locations in a volume of interest. 
     Core biopsy needle  52  has a pre-curved configuration which is straightened when within coaxial needle guide  53 . As shown in  FIG.  3 B , when core biopsy needle  52  is deployed distally out of the needle guide  53 , a tip  23  of core biopsy needle  52  bends back to its unloaded curved configuration, and as it is further deployed distally out of coaxial needle guide  53 , tip  23  moves farther away from the center of coaxial needle guide  53 . It should be readily apparent that device  12  of the invention is not limited to core biopsy device  50  depicted in  FIGS.  3 A and  3 B , and that any device for insertion into a body which may assume a curved configuration is within the scope of the invention. Examples of other curved devices include, but are not limited to, heat ablation probes (where heat is generated by radiofrequency, microwave or laser); cryoablation probes (where tissue death is achieved by freezing); injection probes that can be used to inject drugs or lethal agents (e.g. ethanol injection) or to inject carrier agents (e.g. genetic material carriers like viruses, mRNA). 
     Reference is now made to  FIGS.  4 A- 4 D , which are illustrations of curved core biopsy needle  14 ,  52 , showing the different orientations that can be obtained through the combined use of rotation and forward motion, taken together with the curved configurations of curved core biopsy needle  14 ,  52 . As shown in  FIG.  4 A , when curved core biopsy needle  14 ,  52  including both a distal end of stylet  18  and a distal end of cutting cannula  16  are deployed out of coaxial needle guide  20 ,  53  and positioned distal to coaxial needle guide  20 ,  53 , core biopsy needle  14 ,  52  assumes a curved configuration, and rotation of core biopsy needle  14 ,  52  (before being deployed from coaxial needle guide  20 ,  53 ) provides access to multiple locations at a range of 360 degrees. Curved core biopsy needle  14 ,  52  is shown in multiple positions rotationally in  FIG.  4 A . Curved core biopsy needle  14 ,  52  is in some embodiments only curved at a curved section  15  of curved core biopsy needle  14 ,  52 . Rotation may be accomplished by rotating core biopsy needle  52  with respect to coaxial needle guide  20 ,  53 . Alternatively, an entire device  12  such as core biopsy needle device  50  may be rotated from outside of the body; in this embodiment coaxial needle guide  20  and curved needle  14  are rotated together. As shown in  FIG.  4 B , stylet  18  may be deployed distally out of coaxial needle guide  20 ,  53  by different amounts, leading to different locations away from coaxial needle guide  20 ,  53 . Stylet  18  is shown in  FIG.  4 B  in two different positions as a schematic depiction of the many different possible distally deployed positions of core biopsy needle  52  with respect to coaxial needle guide  20 ,  53 . It should be readily apparent that in embodiments of the invention, a distal end of cutting cannula  16  accompanies stylet  18  in its forward deployment. By combining the rotation of core biopsy needle  14 ,  52  within the needle guide  20 ,  53  (as shown in  FIG.  4 A ), different positions (i.e. depth within the tissue) of coaxial needle guide  20 ,  53 , and different amount of deployment of core biopsy needle  14 ,  52  from coaxial needle guide  20 ,  53  (as shown in  FIG.  4 B ), the tip of the stylet  18  (shown with a notch  25 , where the tissue sample is acquired) can be directed to any position around coaxial needle guide  20 ,  53 , and a tissue sample can be acquired at many different locations within the target (e.g. tumor). This feature of combined rotation, translation and distal needle deployment provides complete coverage of tissue volume around core biopsy needle  14 ,  52 . Also shown in  FIG.  4 B , a flexion plane  92  is defined as the plane within which curved needle  14  is configured to assume its curved shape. As shown in  FIG.  4 C , curved needle  14  may have various curvature parameters including, for example, various radii (R 1 , R 2 , . . . Rn), wherein the curvature parameters are important features in calculation of guidance parameters for guidance of device  12  to a target location. As shown in  FIG.  4 C , a core biopsy needle  14 ,  52  having a first radius of curvature R 1  will advance farther away radially from coaxial needle guide  20 ,  53  than a core biopsy needle  14 ,  52  having a second radius of curvature R 2  which is smaller than the first radius of curvature R 1 . Thus, the needle radius of curvature is a key geometric parameter used in calculation of guidance of device  12 , as will be explained further hereinbelow. Needles of varying radii of curvature allows for penetration through different paths to the target. 
     It should be noted that such variations in design can be used to enable biopsy sampling “around a corner” in cases where direct line of penetration to the target cannot be achieved due to anatomic constraints. In some embodiments of the invention, the radius of curvature of curved needle  14  (R 1  or R 2  or any Rn) is constant. That is, the shape of curved needle  14  is a circular arc. This minimizes damage to the surrounding tissue. 
     Reference is now made to  FIG.  4 D , which is a schematic illustration showing a cylindrical volume around needle guide  20  for a needle having a given radius R 1 , R 2  . . . Rn. As shown schematically in  FIG.  4 D , an unlimited number of locations for obtaining tissue samples in a cylindrical volume around a longitudinal axis  90  of the needle guide  20  is available using a curved device as in the invention. The radius of such cylindrical volume equals the radius of the curved needle (R 1  or R 2  or any Rn). While this feature provides a significant advantage over straight devices, position and advancement guidelines for such a device is complex. 
     Returning now to  FIG.  2   , guidance system  10  further includes a position tracking system  100 , a processor  30  and a display  114 . 
     Position Tracking System  100   
     In embodiments of the invention, position tracking system  100  is provided to allow a user to accurately direct curved needle  14  to targets in radial positions away from a needle insertion path and to register tissue acquisition sites on images of the targeted organ. Position tracking system  100  includes an imaging component  102  for imaging of the body tissue, and a sensing component  104  for sensing a position of curved needle  14  within the body tissue. 
     Imaging component  102  may be, for example, MRI, CT, ultrasound, or any other suitable imaging system. A system for tracking a device  12  such as a biopsy device using MRI gradient fields is the EndoScout™ Tracking System (Robin Medical Inc., Baltimore, Md.). The EndoScout™ Tracking System uses gradient fields of an MRI scanner to determine positioning of a device such as a biopsy needle in reference to MR images. In some embodiments that are based on non-MRI imaging (e.g. ultrasound, CT, X-ray), a tracking system such as the Aurora electromagnetic tracking system by Northern Digital Inc. (Waterloo, Ontario, Canada) can be used similarly to the use of the EndoScout™ in MRI-guided interventions. 
     In one embodiment, tracking system  100  has three-dimensional scanning capability, and imaging component  102  is configured to display either orthogonal images of the three-dimensional scan, or a three-dimensional display of the three-dimensional scan. In another embodiment, tracking system  100  has a two-dimensional scanning capability, and imaging component  102  has a probe with a two-dimensional scanning plane. 
     In the embodiment wherein the three-dimensional scanning capability is used, sensing component  104  may include one or more tracking sensors  105  attached to curved needle  14 . Tracking sensor  105  provides the position and orientation of curved needle  14 . Tracking sensor  105  can be positioned in various locations. In some embodiments, tracking sensor  105  may be positioned inside a body of the device  12 , as depicted in  FIG.  2   . The body of device  12  may include an enclosure that has within it a proximal end of needle  14  and a deployment mechanism, for example. In additional embodiments, tracking sensor  105  may be positioned around a proximal end of the coaxial needle guide  20 ,  53  or around a proximal end of the needle  14 . In yet additional embodiments, tracking sensor  105  may be positioned at the tip  23  of needle  14  (for example, at a tip of stylet  18  and/or cannula  16 ). In the following description, tracking sensor  105  is positioned inside the body of device  12 , but it should be readily apparent that similar results should be obtainable when tracking sensor  105  is placed at another location. Data from imaging component  102  and sensing component  104  are integrated by position tracking system  100 . These data may be sent to processor  30  for use in further calculations as will be described hereinbelow. 
     In the embodiment wherein two-dimensional scanning capability is used, a sensor may not be necessary. Reference is now made to  FIGS.  13 A and  13 B , which are illustrations of imaging component  102  having a probe  103  with a scanning element  107  for providing a two-dimensional scanning plane. In the embodiment shown herein, imaging component  102  is an ultrasound imaging system, and probe  103  is an ultrasound probe. Needle  14  may be attached to probe  103 , for example, using a probe connector  105 . A scanning plane of imaging component  102  is determined by the position of scanning element  107 . In one embodiment, as shown in  FIG.  13 A , needle  14  is oriented at an angle  109  to scanning element  107  and thus is at an angle  109  to a center line of the two-dimensional scanning plane produced by scanning element  107 . In another embodiment, as shown in  FIG.  13 B , needle  14  is aligned along a scanning plane of imaging component  102  as produced by scanning element  107 . Since the needle  14  is oriented with respect to probe  103  at a known angle  109 , the flexion plane with respect to imaging component  102  is known. This known parameter can be used in the calculations for guidance, as will be described further hereinbelow. 
     Processor  30  is configured to collect tracking data from position tracking system  100  and to further collect user data from a user input  32 , which may be collected before and/or during operation of guidance system  10 . Processor  30  is configured to process the collected data and to provide output to display  114  so that the user can use the processed data for guidance. In some embodiments, an automated system may include a configuration wherein processor  30  is configured to provide output directly to an automated controller for curved needle  14  so that a position of curved needle  14  can automatically be adjusted based on data from processor  30 . 
     Reference is now made to  FIG.  5   , which is a schematic illustration of processor  30  showing various components of processor  30  in accordance with embodiments of the invention. Processor  30  includes an input module  36  which is configured to receive user input  32  and tracking input  31  from position tracking system  100 . User input  32  may be received by input module  36  via a keyboard, mouse, or other input means. Tracking input  31  may be received by input module  36  via wired or wireless electronic communication between tracking system  100  and input module  36  of processor  30 . Processor  30  further includes a coaxial needle guide insertion length calculator  42 , a needle deployment length calculator  44  and an output  46 . 
     Reference is now made to  FIGS.  6 A- 6 D , which are schematic illustrations of curved needle  14  and needle guide  20 , and their various positions within a body.  FIG.  6 A  is a cross-sectional illustration of curved needle  14  fully enclosed within needle guide  20 . Needle guide  20  has a needle guide distal end  22  configured to enter the body tissue, a needle guide proximal end  24 , which is accessible to a user (e.g. by attachment to a body of the biopsy device) and can be manipulated in a translational and rotational direction, and a needle guide body  26  extending from needle guide proximal end  24  to needle guide distal end  22 . Curved needle  14  includes a needle distal end  27  having a needle tip  23  (which, in the embodiment shown herein, comprises both a tip of stylet  18  and a tip of cannula  16 ), a needle proximal end  28  (which, in the embodiment shown herein, comprises both a proximal end of stylet  18  and a proximal end of cannula  16 ) which is accessible to a user and can be manipulated in a translational and rotational direction, and a needle body  17  (which, in the embodiment shown herein, comprises both a body of stylet  18  and a body of cannula  16 ) extending from needle proximal end  28  to needle distal end  17 . Needle  14  is shown having two components: stylet  18  and cutting cannula  16 . For simplification and for purposes of calculation, the description of advancement of needle  14  from needle guide  20  refers to both stylet  18  and cutting cannula  16  advancing together. Although in some embodiments, stylet  18  and cutting cannula  16  are independently movable with respect to one another, this feature is not described since it does not relate to the navigation of the needle to the target. In some embodiments, for example when needle  14  is used for ablation or injection, needle  14  is a single unit. In either case, in the following description, needle  14  is considered to be one unit that moves independently of needle guide  20  during deployment and insertion of needle  14  until a target tissue is reached. Needle guide proximal end  24  and needle proximal end  28  which are manipulatable, may be manipulated manually or may be manipulated via an automated system. 
       FIGS.  6 B- 6 D  are schematic depictions of device  12  including needle  14  and needle guide  20  at various positions with respect to a target tissue. In  FIG.  6 B , device  12  is shown positioned at an entry point  60  of a body tissue  62 . Entry point  60  is a given parameter which may be decided by the user, for example, and which is a variable which can result in changes in calculations of other parameters as will be explained further hereinbelow. A target tissue  64  is shown at a location within a body tissue  62 . Needle guide distal end  22  is shown exactly at entry point  60 , prior to insertion of device  12  into body tissue  62 . For a given entry point  60 , the system  10  of the invention is configured to provide the following parameters to the user or to the automated system in order for the user to know how to manipulate device  12  so that curved needle  14  reaches target tissue location  64  in an accurate manner: a needle guide insertion length  70 , a needle guide stopping point  66  within body tissue  62 , and a needle deployment length  72 . Needle guide deployment length  70  is defined as the length of needle guide which needs to be inserted into body tissue  62  such that needle guide distal end  22  is positioned at needle guide stopping point  66 . This is shown schematically in  FIG.  6 C , wherein needle guide distal end  22  is at needle guide stopping point  66 , thus defining an external needle guide position point  25 . External needle guide position point  25  is the point along needle guide body  26  which is just external to entry point  60  of body tissue  62  when needle guide distal end  22  is at needle guide stopping point  66 . Needle guide stopping point  66  is a location within body tissue  62  at which needle guide  20  stops being inserted into body tissue  62 . Needle guide deployment length calculator  42  of processor  30  calculates needle guide deployment length  70  based on entry point  60  and needle guide stopping point  66 . 
     Needle deployment length  72  is defined as the straight length of needle  14  which needs to be advanced from needle guide stopping point  66  such that needle tip  23  can reach target tissue  64 . Since needle  14  is curved, needle deployment length  72  is not equal to the straight distance from needle guide stopping point  66  to target tissue  64 , but rather is calculated based on curved needle radius R (R is a parameter which is intrinsic to needle  14 . Different radii for needle  14  are designated by R 1 , R 2  . . . Rn). However, for the purposes of the user, the straight length of curved needle  14  which corresponds to this distance is the parameter which must be used so that the user can know how far to push the needle until it reaches its target. Needle deployment length calculator  44  of processor  30  is configured to calculate needle deployment length  72 . As shown in  FIGS.  6 C and  6 D , in order to calculate needle deployment length  72 , a needle starting position  142  on needle guide body  26  can be chosen. This needle starting position  142  is a point on needle guide body  26  which is aligned with a chosen point  143  of needle  14  prior to advancement of needle  14  with respect to needle guide  20 . As shown in  FIG.  6 D , once needle  14  is advanced into the tissue, the chosen point  143  of needle  14  has advanced, and is now aligned with an ending position  144 , which is the new point on needle guide body  26  associated with chosen point  143  of needle  14 . The distance between starting position  142  and ending position  144  is defined as needle deployment length  72 . Needle deployment length  72  thus represents the length of needle  14  which must be pushed proximally into the tissue once needle guide is held in place at needle stopping point in order for needle tip  23  to reach target tissue  64 . 
     Reference is now made to  FIG.  7   , which is a geometric representation showing the parameters needed for calculating needle guide deployment length  70  and needle deployment length  72 . For the purposes of calculation, device  12  including needle guide  20  and needle  14  is assumed to be oriented horizontally from point O to point P.
         Point O is entry point  60 ;   Point D is needle guide stopping point  66 ;   Point T is the location of target tissue  64 ;   Point P is the cross point of a transverse line that connects the target point T and the needle orientation line; and   Point C is the center of curvature of a circular curved needle  14 .   Vector OP is the starting orientation of the needle guide;   Vector OT is the direction from the needle tip to the target.   L is the distance from the tip of the needle guide to the target (segment OT);   A (segment OD) is the needle guide deployment length  70 ;   X (segment TP) is the transverse distance between target tissue location  64  and point P (i.e. the needle orientation line);   Z is the distance between points D and T;   Y is the distance between points P and D, which represents a straight line projection of needle deployment length  72  on the vector OP;   R is the radius of curvature of the curved needle (in this embodiment, the curved portion of the curved needle has a circular arc shape with constant radius of curvature R);
 
Θ is the angle between the OP and OT vectors; and
 
α is the angle of the curved needle arc.
 
The two key parameters that are calculated by processor  30  are A (needle guide deployment length  70 ) and ARC TD  (curved needle deployment length  72 ). It should be readily apparent that these two parameters are related to one another and thus, if one changes, the other may change as well. Entry point  60  (point O) is a given, and when this value is changed, the other parameters will change accordingly.
 
Triangle OPT is a right-angle triangle, so X is given by the distance L and the angle Θ:
       

         X=L *sin(Θ)  (1)
 
     and the distance of the segment OP (Y+A) is given by: 
         Y+A=L *cos(Θ)→ A=L *cos(η)− Y   (2)
 
     Triangle DCT is an isosceles triangle, so: 
         Z= 2 R *sin(α/2)  (3)
 
     The Sine Law in triangle TDO gives: 
         Z /sin(Θ)= L /sin(180−α/2)= L /sin(α/2)  (4)
 
     Equations (3) and (4) can be combined to determine the angle α: 
       2 R *sin(α/2)/sin(Θ)= L /sin(α/2)→sin(α/2)=SQRT( L *sin(Θ)/2/ R )  (5)
 
     The Pythagorean theorem in triangle DTP gives Y from X and Z: 
         Y =SQRT( Z   2   −X   2 )  (6)
 
     The different geometric variables are calculated as follows:
         The distance L is calculated as the distance from point O (available from the tracking system) to point T (the target position determined by the user on the coordinate system of the tracking system).   The angle Θ is calculated as the angle between the vector OP (available from the tracking system) and the vector OT (the vector pointing from the point O to the target position).   The distance X is calculated from L and Θ by equation (1).   The angle α is determined from L, R and Θ by equation (5).   The distance Z is determined from R and α by equation (3).   The distance Y is calculated from Z and X by equation (6).   The distance A is calculated from Y, L and Θ by equation (2).       

     These parameters enable the advancement of the needle guide to point D (needle guide stopping point  66 ) where the deployment of the curved needle should be done. The length of deployment of the curved needle (needle deployment length  72 ) is determined by the length of the arc DT: 
       ARC TD   =R*α   (7)
 
     With the angle α in radians. Thus, as is clear from equation 7, needle deployment length  72  is dependent on radius R of curved needle  14 . 
     Reference is now made to  FIG.  8   , which is a flowchart illustration of a method  200  of guidance of a curved needle to a target tissue, in accordance with embodiments of the invention. First, a curved needle within a straight needle guide is provided (step  202 ). Either before, after or simultaneously to providing the curved needle within the straight needle guide, imaging component  102  of position tracking system  100  provides (step  204 ) an image of a body tissue. The provided image may be a three-dimensional image, may be orthogonal views of a three-dimensional image, or may be a two-dimensional image. An entry point for the needle guide is determined (step  206 ) based on the provided image. The provided image includes the target or targets and critical anatomic structures that may obstruct access to a target (e.g. large blood vessel, nerves bundle, the gastrointestinal tract, bone). The user then positions (step  208 ) needle guide  20  with needle  14  positioned therein at the determined entry point  60 . Positioning of the needle guide includes placement of the needle guide at the entry point  60 , placing the needle guide  20  at a chosen orientation. Positioning of the needle guide may also include rotation of the needle guide  20  or keeping the needle guide steady while rotating the needle  14  within the needle guide  20 . In some embodiments, needle  14  is not initially positioned within needle guide  20  and is only advanced therethrough once needle guide  20  is in its position in the tissue. In those instances, needle guide  20  may be inserted with an internal obturator that provides a sharp tip for the insertion of the needle guide  20  through the tissue). Processor  30  calculates (step  210 ) needle guide insertion length  70 , and needle guide is advanced (step  212 ) into the body by the calculated needle guide insertion length  70  until needle guide stopping point  66 . Processor  30  also calculates (step  214 ) a needle deployment length  72  and the needle is advanced (step  216 ) from the needle guide by the calculated needle deployment length  72 . It should be readily apparent that the steps of calculating may be done before or interspersed with the steps of advancing, such that in some embodiments processor  30  does all of the calculating, after which device  12  is positioned and advanced, but in other embodiments, calculating is done during advancement, and may be based on imaging or sensing of device  12  during the procedure. If the target location has been reached, then the body tissue is accessed (step  218 ) and the relevant procedure (such as biopsy, for example) can be performed. If the target location has not been reached, then a new entry point may be determined, and new calculations may be made. In some embodiments, this process may be repeated until the target tissue is reached. Tracking system and/or imaging system continues to track the deployment of the curved needle and to calculate adjustments so that the curved needle reaches the target. 
     Optionally, for example when the procedure is biopsy, the curved needle  14  is retracted (step  220 ) back into the needle guide  20  and a tissue sample obtained in the procedure is unloaded for further analysis, as described in PCT patent publication WO2020100038A3. 
     In some embodiments, multiple target locations may be desired, and since needle  14  is curved, it is possible to access various locations without moving needle guide  20 , or to reach various locations with re-positioning of needle guide  20 . If an additional target location is desired, the curved needle  14  is retracted back into the needle guide  20 , a new needle guide stopping point  66  may need to be calculated for the new target location and the needle guide  20  may need to be translated (i.e. moved forward or backward) to the new stopping point  66  (step  222 ). After needle  14  is retracted back into the needle guide  20 , it may need to be rotated so the flexion plane of the curved needle is aligned such that the new target location is accessible. A new needle deployment length  72  is calculated (step  214 ) and needle  14  is advanced by the calculated new needle deployment length  72  to the new target. 
     Graphic User Interface 
     A particular feature of the invention, in embodiments thereof, is display  114 , designed to present real-time position and orientation of curved needle  14  and needle guide  20  (as provided by position tracking system  100 ) overlaid on an image of target tissue  64 . 
     Reference is now made to  FIGS.  9 A- 9 C , which are photographic illustrations of display  114  showing annotations  110 , when using a tracking system  100  with a three-dimensional scanning capability. Annotations may include an overlay of calculated values with images from imaging component  102 , and may further show a calculated needle trajectory, for example.  FIG.  9 A  shows an image from the imaging component  102  of tracking system  100 , having target tissue  64  therein, and annotation of the intersection line  93  between the flexion plane  92  of the needle and the image plane (which may be the scanning plane in 2D imaging, or generated from 3D imaging data). The flexion plane  92  may not include the target tissue initially, but as device  12  and/or needle  14  is rotated, the annotation of intersection line  93  is rotated over the image (white arrow) until it reaches the target tissue  64 , which indicates that flexion plane  92  includes the target tissue therein, thus providing the curved needle  14  with capability of reaching the target tissue when deployed from the straight needle guide. 
       FIG.  9 B  shows different projected positions of needle  14  based on advancement of needle guide  20  to various locations (i.e. various needle guide stopping points). It is clear from  FIG.  9 B  that one of the parameters which determines whether needle  14  will reach target tissue  64  is the needle guide insertion length  70 . The needle guide is advanced (white arrow) until the projected curved needle trajectory reaches the target  64 .  FIG.  9 C  is an illustration of deployment of the curved needle  14  by calculated needle deployment length  72  (depicted in  FIG.  9 C  as “Arc Length”), such that curved needle tip  23  reaches target tissue  64 . It should be readily apparent that an arc length of needle  14  corresponds to needle deployment length  72  as calculated by processor  30  and described above with reference to  FIGS.  6 A- 6 D  and  FIG.  8   . 
     In some embodiments, multiple target locations are desired. Reference is now made to  FIGS.  10 A- 10 C , which are photographic illustrations showing three different target locations, wherein differences in needle guide insertion length  70  and in needle deployment length  72  both result in reaching different locations. As shown in  FIG.  10 A , a first needle guide insertion length and a first needle deployment length are used to reach a first location (arrow head). As shown in  FIG.  10 B , a second needle guide insertion length and a second needle deployment length are used to reach a second location (arrow head). As shown in  FIG.  10 C , the second needle guide insertion length is maintained (white arrow in  FIGS.  10 B- 10 C ), but a third needle deployment length is used to reach a third location (arrow head). These two parameters may be varied in order to reach multiple locations. While changing these two parameters enable access to different targets in a single plane, rotation of the straightened curved needle within the straight needle guide (or rotation of the whole device, including the needle guide and the straightened curved needle in it) enables access to targets in different planes, and thus provides device  12  the possibility to reach any point in a cylindrical volume around the needle guide insertion line, as described with reference to  FIG.  4 D  above. It is thus a feature of the invention, in embodiments thereof, that by using the various calculations, multiple target locations may be reached. This can be done manually or automatically based on processor  30 . 
     Reference is now made to  FIGS.  14 A and  14 B , which are photographic illustrations of display  114  showing annotations  110 , when using a tracking system  100  with a two-dimensional scanning capability. As described above with reference to  FIGS.  13 A and  13 B , when imaging component  102  with a two-dimensional scanning capability is used, such as an ultrasound probe, needle  14  may be attached to the probe such that orientation of flexion plane  92  with respect to target tissue  64  is known. As an example, a clinical grade ultrasound scanner used to guide needle insertion can provide automatic detection of the needle artifact in the scan, and graphic annotation of the detected needle is added over the ultrasound real-time scan (for example Needle Viz™, Butterfly Networks, Inc., Guilford, Conn., USA). Since the ultrasound scan is planar, if the device  12  and/or needle  14  is positioned in the scanning plane, the device artifact in the scan images represents the device location and orientation in reference to the ultrasound probe and in reference to the organs that are scanned and seen in the scan images. An example of a probe connector  105  is a needle holder such as standard ultrasound needle guides (for example, Civco https://www.civco.com/products/ultrasound-needle-guides/). Thus, if the curved needle is attached to the ultrasound probe through a needle holder, and the flexion plane of the curved needle is aligned with the scan plane of the scanner, then the curved needle can be guided based on the tracking of the needle artifact in the scan images. 
     As shown in  FIG.  14 A , the tip (distal end)  1102  of the graphic annotation of the needle guide artifact in the scan images represents the tip of the needle guide. An arc  1104  having a radius equal to the radius of the curved portion of the needle, and length equal to the length of the curved portion of the needle, is generated and attached to the tip of the graphic annotation of the needle guide, that is overlaid in the ultrasound scan images. This arc represents the trajectory of the curved needle portion if the needle guide is stopped at the current position and the curved needle is deployed out of the needle guide. When the target is identified in the scan images, that is an indication that the scanning plane cuts through the target, and thus the flexion plane is also aligned such that the curved needle can reach the target. 
     As shown in  FIG.  14 B , once it is clear that the target is in alignment, the user can advance the needle guide deeper. As in the previous embodiment, the needle guide  20  is advanced by the calculated needle guide insertion length  70 . The graphic annotations  110  of the needle guide and the arc at its tip is overlaid on the scan images. If the user advances the needle guide by the calculated needle guide insertion length  70 , then the arc  1104  in the graphic annotation should cross the target, as shown in  FIG.  14 B . This is the stopping point of the needle guide  20 . Alternatively, the user can advance the needle guide with continuous scan and monitor the advancement of the tracking annotation until the arc  1104  of the annotation reaches the target. The user can now deploy the curved needle by needle deployment length  72 , and can monitor its progress until it reaches the desired point in the target. 
     Experimental Example 
     An experimental example of guidance of a device  12  with a circular curve with a known radius R using the system and methods of the invention is provided. In the present example, device  12  was a Pakter curved needle (Cook Medical) that has a proximal straight portion and a distal curved portion that can be deformed into a straight configuration within a straight needle guide. A commercial electromagnetic tracking system  100  (Aurora, Northern Digital Inc., Waterloo, ON) with a tracking sensor  105  for real-time tracking of the position (location and orientation) of device  12  was used. This was a simplified setup to provide guidance in a two-dimensional (2D) plane, similar to the embodiment wherein device  12  is attached to probe  103 . 
     A guidance algorithm for the curved needle was programmed in Matlab. In the present example, the real-time position data of the needle was obtained from the tracking system  100 . The target position was input by the user. The algorithm calculated the geometry of the system and presented a real-time guidance display enabling the operator to guide the curved device  12  to the target. In the experiment, the operator was able to input into the system different entry points and different needle guide orientations. 
     Reference is now made to  FIG.  11   , which shows the experimental setup. As shown in  FIG.  11   , a thick foam  80  of approximately 10 cm in height was placed on the tracking field generator  100 , simulating a body lying over the generator. A thin foam  82  of approximately 5 mm thickness was placed over thick foam  80 . Thin foam  82  functioned as a device holder, in order to simulate a user operating device  12  or to simulate probe connector  105 . Device  12  was placed on top of thick foam  80  and under thin foam  82  to simulate device  12  being held by the operator or by probe connector  105 , and inserted into the body. The Aurora tracking sensor  105  was attached to the proximal end of the curved needle and provided the position of the needle tip and orientation of the needle guide (taking into account the distance between the sensor position at the proximal end of the needle and the needle tip). The sensor  105  was attached to the needle such that its axial direction was parallel to the direction of the straight part of the needle direction, and one of the transverse directions coincides with the direction of the curved needle flexion when it is deployed out of the needle guide (these two directions define the flexion plane of the curved needle that is used as the 2D guidance plane in this simplified experimental setup). 
     As shown in  FIGS.  12 A- 12 C , a laptop computer provides real-time 2D display of the needle position (location and orientation) that is registered to the flexion plane of the needle. A target position  84  was marked on thick foam  80  and target position  84  was tracked via a second tracking sensor that was temporarily placed over the position of the marked target (not shown). 
     During the planning phase (before insertion of needle guide  20  into the body) the operator chooses the entry point  60  to the body and rotates the needle to bring the flexion plane of the needle to include the target. 
       FIG.  12 A  depicts a screen view showing determination of the entry point  60  as follows: the needle guide encloses the curved needle in a straight configuration; the tip of the needle guide is placed at the entry point  60 ; the system verifies that a target  164  can be reached by the tip of the curved needle and displays a line to the target. At this point the operator presses a “set” button to set the entry point  60 . 
       FIG.  12 B  depicts a screen view showing needle guide insertion: The operator pushes forward the needle guide to reach needle guide stopping point  166 . At needle guide stopping point  166 , the curved trajectory line (shown as a dashed line) reaches the target  164 . At this point the needle guide should not be moved further and the curved needle should be deployed and advanced to the target. Now the operator pushes the “Start Curve” button and moves to the deployment phase. 
       FIG.  12 C  depicts a screen view showing needle deployment. Once the “Start Curve” button is pressed, the system assumes that the curved needle is deployed and provides a real-time virtual display of the needle trajectory to the target (curved line) as it is advanced through the needle guide. In the final configuration, real-time imaging with ultrasound or MRI may be used and the needle may be viewed in the scan. 
     While certain features of the invention have been illustrated and described herein, many modifications, substitutions, changes, and equivalents may occur to those of ordinary skill in the art. 
     It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the invention.