Abstract:
A tissue acquisition system includes radio frequency (RF) cutter loops which are extendable out a cannula to cut cylindrical tissue samples from a tissue of interest in a patient. The cannula includes inner and outer cannulae which are mutually rotatable and include cutouts through which the cutting loop can be rotated and longitudinally extended to perform the cuts. The tissue samples are then aspirated proximally through the cannula for collection.

Description:
[0001]    This application is a Continuation-in-Part of U.S. application Ser. No. 09/057,303, filed on Apr. 3, 1998, entitled “Breast Biopsy System and Method” to Burbank et al. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to a tissue sampling or removal system, and methods of sampling or removing tissue from a patient, and more particularly to a system and methods for sampling or removing tissue from a patient which maintains the integrity of the tissue sample.  
           [0004]    2. Brief Description of the Related Art  
           [0005]    It is often desirable and frequently necessary to sample or remove a portion of tissue from humans and other animals, particularly in the diagnosis and treatment of patients with cancerous tumors, pre-malignant conditions, and other diseases or disorders. Typically, in the case of cancer, particularly cancer of the breast, there is a great emphasis on early detection and diagnosis through the use of screening modalities, including physical examination, and particularly mammography, which is capable of detecting very small abnormalities, which are often not palpable during physical examination. When a physician establishes by mammography or other screening modality, e.g., ultrasound, that suspicious circumstances exist, a biopsy must be performed to capture tissue for a definitive diagnosis as to whether the suspicious tissue cells in the lesion are cancerous. Biopsy may be done by an open or percutaneous technique. Open biopsy, which is an invasive surgical procedure involving cutting into the suspicious tissue and directly visualizing the target area, removes the entire mass (excisional biopsy) or a part of the mass (incisional biopsy). Percutaneous biopsy, on the other hand, is usually done with a needle-like instrument through a relatively small incision, performed either blindly or with the aid of an imaging device such as ultrasound, MRI, or the like, and may be either a fine needle aspiration (FNA) or a core biopsy. In FNA biopsy, individual cells or clusters of cells are obtained for cytologic examination and may be prepared such as in a Papanicolaou smear. In core biopsy, as the term suggests, a core or fragment of tissue is obtained for histologic examination which may be done via a frozen section or paraffin section.  
           [0006]    The type of biopsy utilized depends in large part on circumstances present with respect to the patient, including the location of the lesion(s) within the body, and no single procedure is ideal for all cases. However, core biopsy is extremely useful in a number of conditions and is being used more frequently by the medical profession.  
           [0007]    To arrive at a definitive tissue diagnosis, intact tissue is needed from an organ or lesion within the body. In most instances, only part of the organ or lesion need be sampled. However, the portions of tissue obtained must be representative of the organ or lesion as a whole. In the past, to obtain tissue from organs or lesions within the body, surgery had to be performed to locate, identify and remove the tissue. With the advent of medical imaging equipment (x-rays and fluoroscopy, computed tomography, ultrasound, nuclear medicine, and magnetic resonance imaging) it became possible to identify small abnormalities even deep within the body. However, definitive tissue characterization still requires obtaining adequate tissue samples to characterize the histology of the organ or lesion.  
           [0008]    For example, mammography can identify non-palpable (not perceptible by touch) breast abnormalities earlier than they can be diagnosed by physical examination. Most non-palpable breast abnormalities are benign; some of them are malignant. When breast cancer is diagnosed before it becomes palpable, breast cancer mortality can be reduced. However, it is often difficult to determine if pre-palpable breast abnormalities are malignant, as some benign lesions have mammographic features which mimic malignant lesions and some malignant lesions have mammographic features which mimic benign lesions. Thus, mammography has its limitations. To reach a definitive diagnosis, tissue from within the breast must be removed and examined under a microscope. Prior to the late 1980&#39;s, reaching a definitive tissue diagnosis for non-palpable breast disease required a mammographically guided localization, either with a wire device, visible dye, or carbon particles, followed by an open, surgical biopsy utilizing one of these guidance methods to lead the surgeon to the non-palpable lesion within the breast.  
           [0009]    A very successful type of image guided percutaneous core breast biopsy instrument currently available is vacuum-assisted automatic core biopsy device. One such successful biopsy device is shown and disclosed in U.S. Pat. No. 5,526,822 to Burbank et al, which is expressly incorporated by reference herein. This device, known commercially as the MAMMOTOME™ Biopsy System, which is available from Ethicon Endo-Surgery, Inc., a division of Johnson &amp; Johnson, has the capability to actively capture tissue prior to cutting the tissue. Active capture allows for sampling through non-homogeneous tissues. The device is comprised of a disposable probe, a motorized drive unit, and an integrated vacuum source. The probe is made of stainless steel and molded plastic and is designed for collection of multiple tissue samples with a single insertion of the probe into the breast. The tip of the probe is configured with a laterally-disposed sampling notch for capturing tissue samples. Orientation of the sample notch is directed by the physician, who uses a thumbwheel to direct tissue sampling in any direction about the circumference of the probe. A hollow cylindrical cutter severs and transports the tissue samples to a tissue collection chamber for later testing. FIG. 5 c  illustrates a cutting loop  182  very similar to cutting loop  176 , except that the portion  184  of the cutting loop immediately adjacent actuating portion  140  (not illustrated) bends away from the rest of the cutting loop. Portion  184  is bent away in this manner in order to extend cutting loop  182  even farther out of cannula  102  when the cutting wire is rotated out of the inner cannula  116  and the outer cannula  152 .  
           [0010]    [0010]Figure 5 d  illustrates a cutting loop  186  in accordance with yet another embodiment. Cutting loop  186  includes an end  188 , two radial legs  190 ,  192 , and a middle portion  194  between the radial legs. Middle portion  194 , as illustrated in FIG. 5 d,  curves along a radius R c , although middle portion can alternatively extend linearly between radial legs  190 ,  192 . Radial legs  190 ,  192  extend generally linearly, so that when cannula  102  is used to gather a plurality of tissue samples around the cannula, the unsampled space around the cannula is minimized.  
           [0011]    Cutting loops herein are formed of a material so that the cutting loops can be used as a RF energy cutting loop. Preferably, the cutting loops are formed of stainless steel, tungsten, platinum, or nickel-titanium alloy wire. FIGS. 6 a  and  6   b  illustrate two embodiments of an end plug. In FIG. 6 a , an end plug  194  includes a mushroom-shaped body  196  having a dome-shaped head  198  and a cylindrical base  200 . End plug  194  is formed of a medical grade polymer, preferably high density polyethylene (HDPE). A cutting wire  202  is attached to head  198  on radially opposite sides of the head, and is embedded in the head at a free end  204  and a connecting portion  206 . Connecting portion  206  extends through base  200 , and terminates at a connector  208 . Connector  208  is positioned on base  200  so that it lines up with and is in physical and electrical contact with conductor  150  in inner cannula  116  when end plug  194  is assembled with inner cannula  116  and outer cannula  152 . Cutting wire  202  is formed of a material which allows the cutting wire to act as a RF cutting element when assembled with inner cannula  116  and when RF generator  106  is connected to the proximal end of conductor  150 .  
           [0012]    Cutting wire  202  is provided distal of the distal end  210  of end plug  194  so that cannula  102  can be easily inserted into tissue, the RF energy from RF generator  106  passing through conductor  150  and to cutting wire  202 . Cutting wire  202  creates a slit in the tissue into which it is pressed, which allows cannula  102  to advance into tissue and to a site at which a tissue sample is desired, with a minimum of trauma to the patient. The use of cutting wire  202  also is advantageous because the RF cutting which is provided therewith allows entry of cannula  102  into target tissue to be made with much less pushing force than prior devices, and in particular than prior devices which rely on a sharpened or pointed cannula for entry into a target tissue. Similarly advantageous is that the use of RF energy cutting wires, including cutting wire  202  and cutting loops  138 ,  176 ,  182 , and  186 , may lead to significant reductions in bleeding.  
           [0013]    [0013]FIG. 6 b  illustrates an end plug  212  in accordance with yet another exemplary embodiment. End plug  212  is substantially similar to end plug  194 , and therefore only the differences between end plug  194  and end plug  212  will be described. Instead of connector  208 , end plug  212  includes a connector loop  214  which extends out of and then returns back into base  200 . Connector loop  214  is shaped and sized to make physical and electrical contact with a cutting loop as described above, so that the cutting loop can act as a RF energy conductor for cutting wire  202  in the place of a conductor  150  extending through inner cannula  116 . In FIG. 6 b , cutting loop  138  is illustrated, although any of the cutting loops described herein can alternatively be used; connector loop  214  is shaped and sized to make electrical contact with the cutting loop with which it is intended to be used. To utilize the advantages of end plug  212 , cutout  124  in inner cannula  116  should extend to the distal end of the inner cannula, so that the cutting loop can extend to the end plug.  
           [0014]    According to yet another embodiment (not illustrated), connector loop  214  can be replaced by an electrically conductive plate positioned on the proximal end surface of end plug  212 , and electrically connected to connecting portion  206 . A plate is advantageously used so that a single design of end plug can be used with any cutting loop, because such a plate makes physical and electrical contact with cutting loops having any point which will contact the plate.  
           [0015]    [0015]FIG. 7 illustrates a schematic perspective view of portions of inner cannula  116 , outer cannula  152 , and an end plug  194  or  212 , assembled together as cannula  102 . Outer cannula  152  preferably includes a mesh, screen, or array  216  including a plurality of openings  218  through sidewall  160  of the outer cannula. Screen  216  is provided along outer cannula  152  proximal of cutout  162 , for aspirating any vapors  220 , including smoke and odors, which may be evolved during the use of the RF cutting elements of cannula  102 . Vapors  220  which travel proximally along cannula  102  and which exit an opening in the tissue  222  being sampled can be aspirated through openings  218  and into main lumen  122  of inner cannula  116 . Inner cannula  116  is also provided with a mesh, screen, or array through its sidewall  126 , as described in greater detail below with reference to FIG. 8.  
           [0016]    [0016]FIG. 8 illustrates a perspective view of proximal portions of inner cannula  116 , proximal of the portions illustrated in FIG. 2. Inner cannula  116  includes a mesh, screen, or array  224  through sidewall  126 . Sidewall  126  is preferably provided with a longitudinally extending recess  226  which extends partially through sidewall  126 , and in which screen  224  is formed. Similar to screen  216  described above, screen  224  communicates main lumen  122  of inner cannula  116  with the exterior of the inner cannula. When inner cannula  116  is positioned in main lumen  172  of outer cannula  152 , screen  224  lies under screen  216 , so that vacuum that is applied to main lumen  122  of the inner cannula is effective to aspirate vapors through both screens can be widened by rotating inner cannula  116 , outer cannula  152 , or both to widen slot  236 .  
           [0017]    Step 5 is then initiated, whereby RF energy is again allowed to flow to cutting loop  138 , and cutting wire  136  is pushed in lumen  146 , which pushes the cutting loop through the tissue distal of the loop and toward the distal end of the tissue channel. At the end of this cutting stroke, illustrated in FIG. 12, cutting loop  138  has formed a second, cylindrical cut in the tissue to be sampled. RF generator  106  is then deactivated, and cutting loop  138  ceases to cut. The distal end of the cylinder of tissue cut in step 5 remains attached to the tissue mass in which cannula  102  has been inserted.  
           [0018]    Step 6 is then performed, by which outer cannula  152  is again rotated relative to inner cannula  116  to open the tissue channel to its maximum size. Alternatively, outer cannula  152  and inner cannula  116  can be counter-rotated away from each other, either serially or simultaneously, to open the tissue channel. Rotating both cannulae has the advantage of automatically centering the cylindrical tissue sample over the tissue channel, which aids in drawing it into the main channel  122 . During counter-rotation of the cannulae, cutting wire  136  can be slightly rotated, so as not to cut the tissue sample (yet), or can be held in position, which will result in some planar cutting of the tissue sample.  
           [0019]    As the tissue channel is widened, vacuum is applied to main lumen  122 , which draws the cylindrical tissue sample, beginning with the proximal end thereof, into the main lumen of inner cannula  116 . The tissue sample is still connected to the tissue mass, as discussed above. Once outer cannula has been rotated to maximize the size of the tissue channel, step 7 is commenced. RF energy is again allowed to flow to cutting loop  138 , and the cutting loop is rotated about axis  148  back into main lumen  122 . As cutting loop  138  is rotated, it performs a third, planar cut in the tissue to be sampled, at the distal end of the cylinder of tissue formed by the first two cuts. This step is illustrated in FIG. 13. Vacuum is applied to main lumen  122 , which draws the distal end of the tissue sample, just cut by cutting loop  138  &#39;s rotation back into the main lumen.  
           [0020]    When cutting loop  138  has been rotated completely back into main lumen  122 , illustrated in FIG. 14, step  8  can start, in which vacuum continues to be applied to the main lumen, and outer cannula  152  is again rotated to close the tissue channel completely. RF energy is then cut off from cutting loop  138 . Because cutting wire  136  is fully within outer cannula  152 , the outer cannula can be rotated to completely close the tissue channel, i.e., there is no overlap of cutouts  124 ,  162 . Step 9 is then performed, whereby vacuum is applied to main lumen  122  to draw the cylindrical tissue sample proximally through the main lumen and into tissue collector  114 . Cutting wire  136  is then retracted to the proximal end of cutout  124 , which completes one cycle. Cannula  102  is then rotated in place about axis  118  so that cutting wire  136  will be adjacent an unsampled volume of tissue, and the cycle is repeated beginning with step 1. These cycles are repeated until cannula  102  has been rotated completely around axis  118 , at which time sampling is complete, and cannula  102  can be withdrawn from the patient.  
           [0021]    In accordance with yet another embodiment, system  100  can be used to perform a somewhat different process of obtaining a tissue sample. Table 2 below describes the steps of this latter embodiment, which can be described as a “one-stroke” version of the above-described process, which first process can be described as a “two-stroke” process. By “two-stroke” it is meant that cutting loop makes two trips along its path across the tissue channel: one distally to cut, one proximally to reset at the end of the cycle. In this latter, “one-stroke” embodiment of a process, the proximal return stroke of the cutting loop is utilized as a cutting stroke for a different, adjacent cylinder of tissue.  
                                                                                       TABLE 2                                       MODE OF   RF ENERGY   VACUUM   TISSUE            STEP   OPERATION   TIP   LOOP   SOURCE   CHANNEL                    1   Initial entry into   ON   OFF   OFF   CLOSED           tissue until located       2   Opening of Tissue   OFF   OFF   OFF   OPENING           Channel       3   Deployment of   OFF   ON   OFF   OPEN           Cutting Wire       4   Closing of Tissue   OFF   OFF   OFF   CLOSING           Channel       5   Distal Cutting of   OFF   ON   ON   CLOSED           Tissue       6   Opening of Tissue   OFF   OFF   ON   OPENING           Channel       7   Detachment of   OFF   ON   ON   OPEN           Tissue       8   Closing of Tissue   OFF   OFF   OFF   CLOSING           Channel       9   Retrieval of Tissue   OFF   OFF   ON   CLOSED           Sample       10   Rotate Cannula to   OFF   OFF   OFF   CLOSED           Next Site       11   Opening tissue   OFF   OFF   OFF   OPENING           channel       12   Deployment of   OFF   ON   OFF   OPEN           Cutting Wire       13   Closing of Tissue   OFF   ON   OFF   CLOSING           Channel       14   Proximal Cuffing of   OFF   ON   ON   CLOSED           Tissue       15   Opening of Tissue   OFF   OFF   ON   OPENING           Channel       16   Detachment of   OFF   ON   ON   OPEN           Tissue                  
 
           [0022]    Steps 1-9 of the process described in Table 2 are identical to steps 1-9 of the “two-stroke” process. At step 10, cannula  102  is rotated around axis  118  so that the (closed) tissue channel is under an unsampled tissue site. The tissue channel is then opened at step 11, followed by redeploying cutting loop  138  from within cannula  102 . Different from the “two-stroke” process described above, the cutting loop has not been repositioned at the opposite end of the tissue channel; instead, the cutting loop remains in the position after the third cut of the previous tissue sample, and essentially “back-tracks” through another tissue site on the subsequent stroke.  118  less, which overlaps the cutting cylinders more in each cutting stroke, thus reducing the volume of unsampled tissue.  
           [0023]    Yet another embodiment of a cutting wire is illustrated in FIGS. 20 and 21. FIG. 20 illustrates a bipolar cutting wire  300  which includes a simple cutting loop  302  and an actuating portion  304  which extends proximally from cutting loop  302 . Cutting wire  300  is a bipolar cutting wire and includes two conductors therein of approximately equal surface area. Cutting loop  302  includes a first, inner loop  306 , an insulating layer  308 , and an outer loop  310 . Inner and outer cutting loops  306 ,  310  are formed of materials similar to those of the cutting loops previously described, while insulating layer  308  is formed of a material which electrically insulates cutting loops  306 ,  310  from each other when energized. As illustrated in FIG. 21, which illustrates a cross-sectional view of cutting loop  302  taken at line  21 - 21  in FIG. 20, each of inner and outer cutting loops  306 ,  310  are connected physically and electrically to conductors  312 ,  314 , respectively, which are part of or comprise actuating portion  304 . An insulating and/or reinforcing layer  316  may be provided between conductors  312 ,  314 , to electrically insulate the conductors from each other, and to add mechanical strength to actuating portion  304 .  
           [0024]    According to yet another embodiment, illustrated schematically in FIG. 1 with dotted line  320  and in greater detail in FIG. 22, patient return pad  110  is replaced in system  100  with a return electrode  322  that is formed into cannula  152 , thus making cannula  102  a pseudo-bipolar RF cutting device. Cannula  102  is not a true bipolar cutting device in this embodiment, because a true bipolar device includes electrodes with substantially the same surface area, while return electrode  322  has a surface area significantly greater than the cutting loop. A large portion of the distal end of outer cannula  152  is the return electrode for the RF circuit, except for small portions at sidewalls  164 ,  166  and endwalls  168  and  170 . Sidewalls  164 ,  166  and endwalls  168  and  170  are preferably formed to be electrically insulating, so that incidental contact between the cutting loop and the sidewall will not short the RF energy circuit. Sidewalls  164 ,  166  and endwalls  168  and  170  can be coated with an electrically insulating material, formed of a different material and integrated into outer cannula  152 , or may comprise any other suitable structure which electrically insulates the cutting loop from the outer cannula. Outer cannula  152  includes an electrical conductor  324  connected between return electrode  322  and RF generator  106 .  
           [0025]    According to yet another embodiment (not illustrated), the device or mechanism by which the tissue samples are retrieved is not limited to only a source of vacuum. Instead of or in addition to vacuum source  108 , a tissue sampling mechanism can further include a grasper that is extendable through main lumen  122  to grasp a tissue sample therein and allow the practitioner to pull the sample proximally out of the cannulae. Alternatively, a tissue sampling mechanism can further include a piston-like element in the distal portions of main lumen  122 , which can be caused to move proximally in main lumen  122  to push a tissue sample therein proximally out of the cannulae. Other embodiments of tissue sampling mechanisms will be readily apparent to one of ordinary skill in the art and within the spirit and scope of the invention.  
           [0026]    While the invention has been described in detail with reference to preferred embodiments thereof, it will be apparent to one skilled in the art that various changes can be made, and equivalents employed, without departing from the scope of the invention.  
           [0027]    Accordingly, at step  12  cutting loop  138  is redeployed out of the tissue channel by rotating cutting wire  136 . Cutting wire  136  is energized during step  12 , causing cutting loop  138  to make a first planar cut in the new tissue site. The tissue channel is then closed in step  13 , and, in step  14 , a second, cylindrical, proximal cut is made in the second tissue sample with cutting loop  138 . The tissue channel is then opened in step  15 , and vacuum, preferably high vacuum, is applied to main lumen  122 , and the third, planar, proximal cut is made by rotating cutting wire  136  back into the proximal end of the open tissue channel in step  16 . These cycles are repeated until cannula  102  has been rotated completely around axis  118 , at which time sampling is complete, and cannula  102  can be withdrawn from the patient.  
           [0028]    Yet another exemplary embodiment of a process for sampling tissue is similar to the “one-stroke” process described above, and includes fewer steps. The “one-stroke” process is performed up to the point where all three cuts have been made with cutting loop  138 . Instead of closing the tissue channel, and thus enclosing cutting loop  138  in main lumen  122 , the cutting loop  138  is immediately rotated back out of the main lumen before closing the tissue channel. The tissue channel is then closed and the tissue sample is retrieved, as described above, with cutting loop  138  outside of cannula  102 . Cannula  102  is then rotated about axis  118 , with cutting loop  138  energized, which causes cutting loop  138  to perform a first, planar, distal cut for a tissue sample from tissue adjacent to where the prior tissue sample had been taken. Second and third cuts are then performed in a manner similar to “one-stroke” process described above, except that cutting loop  138  is immediately rotated out of main lumen  122  after making the third, planar, proximal cut. Thus, several steps are eliminated from the “one-stroke” process, including opening and closing the tissue channel, which can lead to greater efficiency in the process.  
           [0029]    [0029]FIG. 15 illustrates a flow diagram of the “two-stroke” process, described above with reference to Table 1. The logic contained in the process described in FIG. 15 can be implemented in controlling vacuum source  108 , motor driver  112 , and RF generator  106  by a programmable logic controller (not illustrated), a general purpose digital computer in communication with a memory element containing computer readable instructions which embody the control logic (not illustrated), application specific integrated circuit (ASIC) (not illustrated), or discrete digital signal processing (DDSP) (not illustrated).  
           [0030]    At step  240 , the process is initiated with patient preparation and equipment power-up sequences. At step  242 , corresponding to step 1 in Table 1, cannula  102  is inserted into the tissue to be sampled. A decision is made at step  244  whether or not cannula  102  is properly positioned: if it is not, the cannula is repositioned at step  246 , and step  244  is performed again. If cannula  102  is properly positioned, the “door” or tissue channel is opened, step 2 in Table 1, and cutting loop  138  is deployed, step 3 in Table 1. A decision is made whether cutting loop  138  is deployed: if not, step  248  is repeated. If cutting loop  138  is deployed, a longitudinal cut is performed at step  252 , corresponding to step 5 in Table 1. A decision is then made whether the cut was completed: if not, step  252  is repeated; if the cut was completed, step  256  is performed. Step  256  corresponds to steps 6-9 in Table 1. After the wire has been reset in step  256 , a decision is made at step  258  whether the sample has been received: if not, step  256  is repeated until the sample has been properly received. A decision is then made at step  260  whether sampling is complete: if not, the inner and outer cannulae are rotated relative to one another to close the “door” or tissue channel at step  264 , and the process returns to step  248 . If tissue sampling is complete, cannula  102  is removed from the patient in step  262 , and post-procedure bandaging and tissue retrieval from tissue collector  114  is performed.  
           [0031]    [0031]FIG. 16 illustrates a flow diagram of the “one-stroke” process, described above with reference to Table 2. Several of the steps of the process described in FIG. 16 are the same as those in the process described with reference to FIG. 15 and Table 1, and therefore will not be further described. The logic contained in the process described in FIG. 16 can be implemented in controlling vacuum source  108 , motor driver  112 , and RF generator  106  by a programmable logic controller (not illustrated), a general purpose digital computer in communication with a memory element containing computer readable instructions which embody the control logic (not illustrated), application specific integrated circuit (ASIC) (not illustrated), or discrete digital signal processing (DDSP) (not illustrated).  
           [0032]    In FIG. 16, after the decision in step  254  is made that a complete longitudinal cut has been made, the sample is retrieved, as described above with reference to Table 2. After performing steps  258 , and if the decision is made that sampling is not complete, step  264  is performed, and step  252  is repeated. As described above with reference to Table 2 , the cut performed in step  252  is a longitudinal cut after cannula  102  has been rotated into a new volume of tissue. If sampling is complete after step  260 , step  272  is performed, in which the status of the tissue channel or “door” is verified to be open, cutting loop  138  is rotated back into main lumen  122 , and cannula  102  is removed from the patient.  
           [0033]    [0033]FIG. 17 illustrates a cutting pattern achieved by a system  100 . In FIG. 17, a plurality of cylindrical cuts  280   a - h  are made by cannula  102  having a cutting loop  138  (not illustrated in FIG. 17). As illustrated in FIG. 17, while system  100  retrieves a plurality of samples, small areas  281  are left unsampled, because cutting loop  138  is generally circular. Cutting loops  176 ,  182 , and  186  are specifically configured to extend cylindrical cuts  280  into these areas. For example, FIG. 18 illustrates a distal end view of cannula  102  including cutting loop  176  or  182 , which includes portion  180  which closely conforms to the external diameter of cannula  102 . Thus, cutting loop  176  or  182  extends into areas  281  when longitudinal cuts are performed, which samples tissue closer to the center of the tissue mass of interest, as illustrated in FIG. 19. Alternatively, cannula  102  can merely be rotated around axis and into the inner cannula main lumen proximal of any tissue samples which may have been collected.  
           [0034]    Inner cannula is also optionally provided with aspiration regulator  228 , which is positioned in recess  226 . Recess  226  is provided to allow aspiration regulator  228  to slide between inner cannula  116  and outer cannula  152  to selectively cover or uncover portions of screens  216  and  224 . In yet another embodiment, neither recess  226  nor aspiration regulator  228  is provided, in which embodiment vapor aspiration is regulated by regulating only the vacuum applied to main lumen  122 . In the embodiment illustrated in FIGS. 7 and 8, aspiration regulator  228  includes a curved plate  230  and an actuation member  232  extending proximally from the curved plate. Curved plate  230  is curved to conform to the outer diameter of inner cannula  116  in recess  226 . By moving actuation member  232  proximally and distally, the number of openings  234  which can fluidly communicate with openings  218  is controlled, thereby regulating the strength of aspiration through screen  216  and screen  224  when vacuum is applied to main lumen  122 .  
           [0035]    A method of operating the above-described apparatus for collecting tissue samples will now be described with reference to FIGS.  9 - 14 , and with reference to Table 1 below. Table 1 describes the status of several of the elements of system  100  during use thereof.  
                                                                                       TABLE 1                                       MODE OF   RF ENERGY   VACUUM   TISSUE            STEP   OPERATION   TIP   LOOP   SOURCE   CHANNEL                    1   Initial entry into   ON   OFF   OFF   CLOSED           tissue until located       2   Opening of Tissue   OFF   OFF   OFF   OPENING           Channel       3   Deployment of   OFF   ON   OFF   OPEN           Cutting Wire       4   Closing of Tissue   OFF   OFF   OFF   CLOSING           Channel       5   Distal Cutting of   OFF   ON   ON   CLOSED           Tissue       6   Opening of Tissue   OFF   OFF   ON   OPENING           Channel       7   Detachment of   OFF   ON   ON   OPEN           Tissue       8   Closing of Tissue   OFF   OFF   ON   CLOSING           Channel       9   Retrieval of Tissue   OFF   OFF   ON   CLOSED           Sample and Re-           setting of Cutting           Wire Position                  
 
           [0036]    In Table 1, the column labeled “Tip” refers to whether RF generator  106  is activated to apply RF energy to cutting wire  202 , “Loop” refers to whether RF generator  106  is activated to apply RF energy to cutting loop  138 ,  176 ,  182 , and/or  186 , and the status of the “Tissue Channel” refers to the radial alignment of cutouts  124 ,  162 : when the cutouts are radially aligned, an open “tissue channel” is formed into cannula  102  through both cutouts, and when the cutouts are not radially aligned, the tissue channel is closed.  
           [0037]    [0037]FIG. 9 illustrates the distal end of cannula  102  in a condition to be inserted into tissue to be sampled. The tissue channel in the fully closed position; inner cannula  116  is visible through cutout  162 , but cutout  124  is not radially aligned with cutout  162 . End plug  194  (or  212 , if desired) has been mounted on the distal end of the inner cannula or the outer cannula. As stated in Table 1 above, step 1 proceeds with the advancement of cannula  102  into the tissue with RF energy being applied to cutting wire  202 , which allows cannula  102  to be easily advanced into the tissue to the target site. Once the target site has been accessed, as assessed by measuring the advancement of the cannula into the tissue and comparing with prior measurements, or by ultrasound, MRI, X-ray, or other imaging devices, outer cannula  152  is caused to rotate relative to inner cannula  116 . This relative rotation, step 2 above, is continued until the tissue channel is completely open, i.e., the maximum overlap between cutouts  124  and  162  (corresponding to the smaller of angles α and β). This orientation is illustrated in FIG. 10, wherein cutting loop  138  is also illustrated. Cutting loop  138  is in a retracted position, during insertion of cannula  102  into the tissue and the relative rotation of the inner and outer cannulae, which shields the patient from premature exposure to the cutting wire  136 .  
           [0038]    Step 3 above is then commenced, wherein cutting wire  136 , including cutting loop  138 , is rotated around longitudinal axis  148 , which causes the cutting loop to pass through both cutouts  124 ,  162  and into the tissue into which cannula  102  has been inserted. During rotation of cutting loop  138 , RF energy is allowed to flow to cutting loop  138 , so that the cutting loop cuts tissue as it rotates. Cutting loop  138  is rotated until it is entirely out of cannula  102 , thus forming a first, planar cut in the tissue to be sampled. Application of RF energy through cutting loop  138  is then ceased.  
           [0039]    In step 4, outer cannula  152  is rotated to close the tissue channel, except for a small slot  236  between a sidewall of cutout  124  and a sidewall of cutout  162  which is present because cutting wire  136  still extends through the cutouts, and prevents the outer cannula from rotating to completely close the tissue channel. This stage is illustrated in FIG. 11. The vacuum source is then preferably activated to begin drawing tissue close to cannula  102 , and in particular toward slot  236 . If it is necessary to draw the tissue closer to cannula  102 , vacuum source  108  can be adjusted to increase the negative pressure applied through lumen  122 . Alternatively, slot  236  element (not illustrated in FIG. 2; see FIGS. 6 a  and  6   b ) provided on a distal end of cannula  102 .  
           [0040]    [0040]FIGS. 3 a  and  3   b  illustrate cross-sectional views of inner cannula  116 , as taken at line  3 - 3 . In the embodiment illustrated in FIG. 3 a,  inner cannula  116  includes a sidewall  126  which has a thickness T, and has an outer radius R o . Actuating portion  140  of cutting wire  136  is not illustrated in FIG. 3 a  for purposes of clarity, but is located in lumen  146 . Inner cannula  116  can optionally further be provided with an additional lumen  147  in sidewall  126 , which extends from cutout  124  proximally to the proximal end of the inner cannula, for allowing a practitioner to inject an anesthetic, e..g., Lidocaine, into the tissue to be sampled. Alternatively, such an anesthetic can be injected distally through main lumen  122 , in which embodiment lumen  147  can be eliminated. In yet another embodiment (not illustrated), inner cannula  116  is formed slightly undersized relative to outer cannula  152  (see FIG. 4) to form an annular lumen therebetween, for injecting such an anesthetic. In yet another embodiment (not illustrated), a channel can be formed in the exterior surface of inner cannula  116 , which together with the inner surface of outer cannula  152  (see FIG. 4) forms a pathway for a practitioner to inject an anesthetic distally to anesthetize the tissue to be sampled.  
           [0041]    [0041]FIG. 3 b  illustrates an alternate embodiment, in which an inner cannula  116 ′ has a sidewall  126 ′ with thickness that varies continuously between a maximum T max  and a minimum T min . Inner cannula  116 ′ includes an outer radius R o  and an inner radius R i , which are taken from two separate longitudinal axes which are separated by a distance D. Lumen and conductor  150  are preferably located in the thickest part of sidewall  126 ′, so that the average thickness of the sidewall can be reduced while still providing lumen  146  and conductor  150 .  
           [0042]    Turning now to FIG. 4 a , a distal portion of an outer cannula  152  of cannula  102  is illustrated in perspective. Outer cannula  152  is generally tubular in construction, and includes a distal end  154 , a proximal end (not illustrated), and a longitudinal axis  156  extending between the proximal end and distal end  154 . Outer cannula  152  includes a main lumen  158  extending through the outer cannula which has an inner radius R i  selected to be slightly larger than outer radius R o  of inner cannula  116 ,  116 ′, so that the inner cannula can be slidingly received in the outer cannula main lumen.  
           [0043]    Outer cannula  152  includes a sidewall  160  which preferably has a constant thickness formed of a material which is similar to that of inner cannula  116 . In a manner similar to inner cannula  116 , outer cannula  152  includes a cutout, slot, window, or fenestration  162  formed in sidewall  160 . Cutout  162  is formed by sidewalls  164 ,  166 , a proximal endwall  168 , and a distal endwall  170 . The longitudinal length of cutout  162 , i.e., the length of sidewalls  164 ,  166 , is preferably selected to be substantially the same as the length of sidewalls  128 ,  130  of inner cannula  116 . In a less preferred embodiment, the length of sidewalls  164 ,  166  can be more or less than the length of sidewalls  128 ,  130 .  
           [0044]    Preferably, sidewalls  164 ,  166  are longitudinally extending, i.e., extend parallel to axis  156 , and endwalls  168 ,  170  extend perpendicular to sidewalls  164 ,  166 . The angular separation of sidewalls  164 ,  166 , that is, the angle β which is defined between sidewalls  164 ,  166 , is selected so that the cutout  162  is large enough to allow cutting loop  138  to be rotated through the outer cannula cutout, when inner cannula  116  is in lumen  158 . Angle β is typically about  180 °, although other values for angle βare within the spirit and scope of the invention as will be readily apparent to one of ordinary skill in the art. The inner surface  172  of lumen  158  is preferably coated with a lubricious material to facilitate rotation of inner cannula  116  relative to outer cannula  152 , as described in greater detail below.  
           [0045]    [0045]FIG. 4 b  illustrates another embodiment of outer cannula  152 , in which sidewall  160  is provided with the passageway for cutting wire  136 , as a small lumen  169 . Cutting wire  136  (illustrated in phantom in FIG. 4 b ) is located in lumen  169  in a manner similar to lumen  146  (see FIG. 2), such that cutting wire  136  is rotatable and longitudinally extendable therein. In the embodiment illustrated in FIG. 4 b , angle β is greater than angle α of inner cannula  116 , so that cutting loop  138  will not catch on sidewall  128  as cutting loop  138  is rotating into and out of main lumen  122 .  
           [0046]    [0046]FIGS. 5 a - 5   d  illustrate end views of several embodiments of cutting loops usable in the present invention. The cutting loops illustrated in FIGS. 5 a - 5   d  are preferably closed cutting loops. The term “closed” within the context of cutting loops as described in the present application refers to geometries of a cutting loop which, when projected onto a plane that is perpendicular to actuating portion  140 , form a continuous and closed shape. Thus, the term “closed” includes geometries of cutting loops with free ends that do not touch the rest of the loop, as well as those that do not have free ends. Closed cutting loops have the advantage of allowing a sample of tissue to be cut with a minimum number of cutting strokes.  
           [0047]    [0047]Figure 5 a  illustrates cutting loop  138  as illustrated in FIG. 2. Cutting loop  138  is generally circular, has an outer radius R o , and is closed. Cutting loop  138  includes an end  174  that meets with the rest of the cutting loop and is preferably welded or soldered thereto. FIG. 5 b  illustrates a cutting loop  176  in accordance with yet another embodiment. Cutting loop  176  includes a generally circular portion  178  describing an outer radius R o , and an end  180  which has been joined to the rest of the cutting loop. End  180  extends inwardly from the circular portion  178 , and preferably is curved on a radius R E  taken from a point outside of cutting loop  176 . End  180  is provided as an inwardly extending curved portion of loop  176  in order to reduce the amount of unsampled space when the cannula  102  is used to sample tissue, as described in greater detail below.  
           [0048]    While this type of system functions very well as a core biopsy device, there are occasions when it may be useful to have the capability of acquiring a relatively large intact tissue sample. One such core biopsy device is disclosed in U.S. Pat. No. 5,111,928, to Komberg et al, also expressly incorporated in its entirety by reference herein. In the device disclosed by Komberg et al., a tissue receiving port is disposed at the distal end of the device and is oriented longitudinally. A disadvantage of this type of device, however, is the inability to acquire a tissue sample having a cross-section larger than that of the cannula through which the sample will be removed. Additionally, it is difficult, using such a device, which obtains cylindrical shaped specimens, to determine whether an entire lesion of interest is being removed or whether a further procedure will be necessary. This is particularly true because most lesions of interest are typically spherical in shape, having a diameter of approximately 1 cm. The only way one can tell whether the entire lesion has been removed using the Komberg technique is to remove and examine the specimen, determine whether each of the margins of the specimen is “clean,” meaning that there is no evidence of lesion, or “dirty,” meaning that legion tissue is evident right to the edge of the specimen. Of course, if one or more specimen margins is “dirty,” it is almost a certainty that a portion of the lesion remains in the patient, and if the biopsy test results on the lesion are positive, a further surgical procedure will be indicated.  
           [0049]    U.S. patent application Ser. No. 09/057,303, priority to which is claimed herein, discloses apparatuses and methods for precisely isolating a target lesion, resulting in a high likelihood of“clean” margins about the lesion. This advantageously will often result in the ability to both diagnose and treat a malignant lesion with only a single percutaneous procedure, with no followup percutaneous or surgical procedure required, while minimizing the risk of migration of possibly cancerous cells from the lesion to surrounding tissue or the bloodstream. Various tissue acquisition instrument embodiments are disclosed for segmenting the target tissue, including embodiments wherein the instrument comprises a cutting element which is extendable radially outwardly and movable circumferentially to define a peripheral margin about a tissue sample, and other embodiments wherein the cutting element is extendable radially outwardly and movable axially to define peripheral margins about the tissue sample.  
         SUMMARY OF THE INVENTION  
         [0050]    According to a first exemplary embodiment of the present invention, a tissue acquisition device useful in retrieving tissue samples from a patient comprises an inner cannula having a proximal end, a distal end, and a longitudinal axis extending between said proximal and distal ends, said inner cannula including a tubular sidewall, a main lumen extending along said longitudinal axis from said proximal end toward said distal end, a small lumen extending longitudinally through said sidewall from said proximal end toward said distal end, and a cutout in said sidewall distal of said small lumen; an outer cannula having a proximal end, a distal end, and a longitudinal axis extending between said proximal and distal ends, said outer cannula including a tubular sidewall, a main lumen extending along said longitudinal axis from said proximal end toward said distal end, and a cutout in said sidewall; a cutting wire positioned in said small lumen, said cutting wire having a proximal end and a distal end and being rotatable and longitudinally extendable in said small lumen, said cutting wire including a cutting loop at a said distal end which extends out of said small lumen; wherein said inner cannula is positioned in said outer cannula main lumen with said inner cannula cutout positioned at the same longitudinal position as said outer cannula cutout.  
           [0051]    According to a second exemplary embodiment of the present invention, a system for sampling tissue from a patient comprises a radio frequency (RF) energy generator capable of generating RF energy, and a tissue acquisition device as described above, said cutting wire of said tissue acquisition device in electrical communication with said RF energy generator.  
           [0052]    According to a third exemplary embodiment of the present invention, a method of sampling tissue from a patient comprises the steps: inserting a cannula into tissue of a patient, said cannula including a pair of concentric cannulae each having a cutout therein, said cannula including a RF energy cutting loop in said cannula; cutting said tissue along a plane by moving said RF energy cutting loop from a position inside said cannula to a position outside said cannula while applying RF energy to said RF energy cutting loop; cutting said tissue by moving said RF energy cutting loop along a first path extending partially along the length of said cannula while applying RF energy to said RF energy cutting loop; and cutting said tissue along a plane perpendicular to said path by moving said RF energy cutting loop.  
           [0053]    According to a fourth exemplary embodiment of the present invention, a tissue acquisition device useful in retrieving tissue samples from a patient comprises a generally cylindrical cannula having a longitudinal axis and a cutout, an electrically energized cutting wire loop arranged generally in a plane substantially parallel to said cannula longitudinal axis, said loop being rotatable about a loop axis which extends generally parallel to said cannula longitudinal axis, said loop axis being offset from said cannula longitudinal axis, whereby, upon rotation of said loop about said loop axis, said loop moves from a location within said cannula to a location extending through said cutout.  
           [0054]    Still other objects, features, and attendant advantages of the present invention will become apparent to those skilled in the art from a reading of the following detailed description of embodiments constructed in accordance therewith, taken in conjunction with the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0055]    The invention of the present application will now be described in more detail with reference to preferred embodiments of the apparatus and method, given only by way of example, and with reference to the accompanying drawings, in which:  
         [0056]    [0056]FIG. 1 is an illustration of a first exemplary embodiment of a tissue acquisition system;  
         [0057]    [0057]FIG. 2 is a schematic illustration of a portion of an inner cannula of the tissue acquisition system illustrated in FIG. 1;  
         [0058]    [0058]FIG. 3 a  is a cross-sectional view of the inner cannula illustrated in FIG. 2, taken at line  3 - 3 ;  
         [0059]    [0059]FIG. 3 b  is a cross-sectional view of an alternate embodiment of the inner cannula illustrated in FIG. 2, taken at line  3 - 3 ;  
         [0060]    [0060]FIG. 3 c  is a cross-sectional view of another alternate embodiment of the inner cannula illustrated in FIG. 2, taken at line  3 - 3 ;  
         [0061]    [0061]FIG. 3 d  is a cross-sectional view of yet another alternate embodiment of the inner cannula illustrated in FIG. 2, taken at line  3 - 3 ;  
         [0062]    [0062]FIG. 3 e  is a cross-sectional view of another alternate embodiment of the inner cannula illustrated in FIG. 2, taken at line  3 - 3 ;  
         [0063]    [0063]FIG. 4 a  is a schematic illustration of a portion of an outer cannula of the tissue acquisition system illustrated in FIG. 1;  
         [0064]    [0064]FIG. 4 b  is a schematic illustration of a portion of an alternate embodiment of an outer cannula of the tissue acquisition system illustrated in FIG. 1;  
         [0065]    [0065]FIG. 5 a  is a schematic illustration of a portion of a cutting loop of the tissue acquisition system illustrated in FIG. 1;  
         [0066]    [0066]FIG. 5 b  is a schematic illustration of a portion of an alternate embodiment of a cutting loop of the tissue acquisition system illustrated in FIG. 1; FIG. 5 c  is a schematic illustration of a portion of another alternate embodiment of a cutting loop of the tissue acquisition system illustrated in FIG. 1;  
         [0067]    [0067]FIG. 5 d  is a schematic illustration of a portion of yet another alternate embodiment of a cutting loop of the tissue acquisition system illustrated in FIG. 1;  
         [0068]    [0068]FIG. 6 a  is a schematic illustration of a distal tip portion of the tissue acquisition system illustrated in FIG. 1;  
         [0069]    [0069]FIG. 6 b  is a schematic illustration of portions of an alternate embodiment of the tissue acquisition system illustrated in FIG. 1;  
         [0070]    [0070]FIG. 7 is a schematic illustration of proximal portions of a cannula;  
         [0071]    [0071]FIG. 8 is a schematic illustration of proximal portions of an inner cannula;  
         [0072]    FIGS.  9 - 14  are perspective illustrations of a cannula, illustrating an exemplary process of sampling tissue;  
         [0073]    [0073]FIG. 15 is an illustration of an exemplary process;  
         [0074]    [0074]FIG. 16 is an illustration of an alternate process;  
         [0075]    [0075]FIG. 17 is an illustration of cuts that can be made in tissue;  
         [0076]    [0076]FIG. 18 is an end view of yet another exemplary embodiment of a cannula;  
         [0077]    [0077]FIG. 19 is an illustration of cuts that can be made in tissue;  
         [0078]    [0078]FIG. 20 is an illustration of yet another embodiment of a cutting loop;  
         [0079]    [0079]FIG. 21 is a cross-sectional view taken along line  21 - 21  in FIG. 20; and  
         [0080]    [0080]FIG. 22 is an illustration of yet another embodiment of an outer cannula. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0081]    Referring to the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures.  
         [0082]    In FIG. 1, a system  100  for sampling or removing tissue from a patient (not illustrated), includes a cannula  102 , which is preferably constructed of materials so that it can economically be disposable. System  100  further includes an actuator  104  to which cannula  102  is removably attached. Actuator  104  is preferably non-disposable, i.e., is constructed of materials and includes components which are intended to be reused. Actuator  104  is the interface between cannula  102  and an RF generator  106  and vacuum source  108 , and also includes at least two motors (not illustrated): a first motor which rotates an outer cannula (not illustrated in FIG. 1; see FIG. 4) of the cannula  102 , as well as rotates a cutting wire (not illustrated in FIG. 1; see FIGS. 2 and 5 a - 5   d ); and a second motor which moves the cutting wire longitudinally. Additionally, actuator  104  includes switches and proximity sensors which provide control signals for controlling the first and second motors, RF generator  106 , and vacuum source  108 :  
         [0083]    Actuator  104  is connected to and in electrical communication with RF generator  106 , which is connected to and in electrical communication with a patient return pad  110  for the RF cutting system, described in greater detail below. The switches in actuator  104  (not illustrated) control the application of RF energy by the cannula  102 , as described in greater detail below. A motor driver  112  is also connected to actuator  104 , and provides power to the motors in actuator  104 . Motor driver  112  receives signals from the switches and proximity sensors in actuator  104 , which are used as feedback control signals to control the states of the motors. Vacuum source  108  preferably includes a vacuum pump or other suitable source of vacuum (not illustrated), and is preferably controllable to at least two vacuum pressure levels. The vacuum pump can also be controllable over a continuum of pressure levels. A tissue collector  114 , such as a vacuum jar or similar device, is positioned between vacuum source  108  and cannula  102 , and collects tissue sampled or removed from a patient which have been drawn from cannula  102  by the vacuum generated by vacuum source  108 . Tissue collector  114  can be reusable or, preferably, disposable.  
         [0084]    [0084]FIG. 2 illustrates a distal portion of an inner cannula  116  which forms a part of cannula  102 . Inner cannula  116  is generally tubular, and has a longitudinal axis  118  which extends between a distal end  120  and a proximal end (not illustrated). Inner cannula  116  includes a main tissue lumen  122  which extends longitudinally from the proximal end to the distal end  120 . Inner cannula  116  is preferably formed of a relatively rigid, electrically non-conductive, and biocompatible material. The proximal portions of inner cannula  116 , not illustrated in FIG. 2, are generally tubular like the distal portions thereof illustrated in FIG. 2.  
         [0085]    Inner cannula  116  further includes a cutout, slot, window, or fenestration  124  through the sidewall  126  of inner cannula  116 , which exposes main lumen  122  to the exterior of the inner cannula. Cutout  124  is preferably formed by two sidewalls  128 ,  130 , a distal endwall  132 , and a proximal endwall  134 . More preferably, sidewalls  128 ,  130  are longitudinally extending, i.e., extend parallel to axis  118 , and endwalls  132 ,  134  extend perpendicular to sidewalls  128 ,  132 . The angular separation of sidewalls  128 ,  130 , that is, the angle a which is defined between sidewalls  128 ,  130 , is selected so that the cutout  124  is large enough to allow a cutting loop  138  of a cutting wire  136  to be rotated in and out of main lumen  122 , as described in greater detail below. Angle a is typically about 180°, although other values for angle a are within the spirit and scope of the invention as will be readily apparent to one of ordinary skill in the art.  
         [0086]    Inner cannula  116  is optionally provided with a lubricious coating  142  on the inner side of sidewall  126 , which allows a tissue sample to be more easily drawn along main lumen  122 . Inner cannula  116  is also optionally provided with a lubricious coating  144  on the outer side of sidewall  126 , which allows the inner cannula to be more easily rotated within an outer cannula (see FIG. 4) of cannula  102 .  
         [0087]    A cutting wire  136  is provided in inner cannula  116 . Cutting wire  136  includes a cutting loop  138  and a longitudinally extending actuating portion  140 . Actuating portion  140  is slidably received in a passageway which extends from the proximal end of cannula  102  to the region of cutout  124 . In the embodiment illustrated in FIG. 2, the passageway which receives actuating portion  140  is a small, second lumen  146  formed in sidewall  126  of inner cannula  116 . Alternatively, as illustrated in FIG. 3 c , the passageway can take the form of a channel  146 ′ formed in the external surface of inner cannula  116 , in which actuating portion  140  is slidably and rotatably received. Channel  146 ′ cooperates with the internal surface of an outer cannula  152  (see FIG. 4 a ) to retain actuating portion  140  in channel  146 ′. According to yet another embodiment, the passageway can be formed as a channel  146 ″ in the inner surface of outer cannula  152 , as illustrated in FIG. 3 d  (see also FIG. 4 a ). According to yet another embodiment, illustrated in FIG. 3 e , the passageway is formed as two shallower channels  149 ,  151 , one formed in each of the external surface of inner cannula  116  and the internal surface of outer cannula  152 . In the embodiment illustrated in FIG. 3 e , one of shallow channels  149 ,  151  (channel  151  in FIG. 3 e ) has a much larger circumferential length which describes an angle ∈, than the other shallow channel, to allow inner cannula  116  and outer cannula  152  to rotate relative to each other without being locked by actuating portion  140 , for reasons described in greater detail below. Preferably, angle ∈ is greater than or equal to angles α and β, described below with reference to FIG. 4 a  and  4   b.  Lumen  146  or channels  146 ′,  146 ″, or  149  and  151  are optionally also coated with a lubricious material to facilitate sliding cutting wire  136  therethrough.  
         [0088]    In the embodiment illustrated in FIG. 2, cutting loop  138  is a generally circular and closed loop, and preferably lies in a plane perpendicular to a longitudinal axis  148  of actuating portion  140  and lumen  146 . Cutting loop  138  can take forms other than a generally circular closed loop, as described in greater detail below. FIG. 2 illustrates lumen  146  continuing on the distal side of cutout  124 ; optionally, lumen  146  terminates at proximal endwall  134  and opens into cutout  124 .  
         [0089]    Cutting loop  138  is both longitudinally extendable in cutout  124 , and rotatable into and out of lumen  122 , because actuating portion  140  is slidably and rotatably received in the passageway. As discussed above with reference to angle a, the size of cutout  124  is selected so that cutting loop  138  is rotatable from a first position (illustrated in FIG. 2) in which the cutting loop is entirely contained within inner cannula  116 , and a second position in which the cutting loop has been rotated around axis  148  so that almost all of the cutting loop has passed through the cutout and is outside of the inner cannula. Because actuating portion  140  of cutting wire  136  remains in the passageway, e.g., lumen  146 , in both the first and second positions, those portions of cutting loop  138  immediately adjacent the actuating portion  140  will not extend beyond the outer wall of sidewall  126  in the second position.  
         [0090]    Lumen  146  is preferably located in sidewall  126  so that it intersects proximal endwall  134  at a location significantly closer to one of sidewalls  128 ,  130 , than the other of the sidewalls of cutout  124 . While lumen  146  can, in a less preferred embodiment, be centered between sidewalls  128 ,  130 , locating lumen  146  so that actuating portion  140  of cutting wire  136  is immediately adjacent one of sidewalls  128 ,  130  allows cutting loop  138  to be made much larger than if lumen  146  were closer to being centered. Thus, locating lumen  146  in sidewall  126  immediately adjacent sidewall  128 , as illustrated in FIG. 2, allows for a larger cutting loop  138 , because the distance between axis  148  and the opposite sidewall (  130 , as illustrated in FIG. 2) is larger, thus providing more space for the cutting loop to rotate out of lumen  122 . This allows cutting loop  138  to be relatively large. Inner cannula  116  further includes an electrical conductor  150  in sidewall  126 , which extends from the proximal end to the distal end  120  of the inner cannula. Electrical conductor  150  is provided to provide electrical communication between RF generator  106  and a cutting