Abstract:
A method for determining a volume of ablated tissue includes the steps of supplying energy to tissue, indicating an axis within the tissue, and simulating slicing of the tissue substantially perpendicular to the axis to obtain a plurality of simulated slices. Each of the plurality of simulated slices has a thickness, a cross-sectional perimeter, and a trajectory point defined by the axis within the tissue. The method further includes the steps of determining a volume of each of the plurality of simulated slices based on the trajectory point, the cross-sectional perimeter, and the thickness of each simulated slice, and summing the volumes from each of the plurality of simulated slices to obtain the volume of the ablated tissue.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of priority to U.S. Provisional Application Ser. No. 60/984,605 filed on Nov. 1, 2007, which is incorporated by reference herein. 
    
    
     BACKGROUND 
     Technical Field 
     The present disclosure relates to electrosurgical apparatuses, systems and methods. More particularly, the present disclosure is directed to a system and method for determining the volume of an ablation lesion during and/or after a tissue ablation procedure utilizing electrosurgical electrodes and imaging means. 
     Background of Related Art 
     Energy-based tissue treatment is well known in the art. Various types of energy (e.g., electrical, ultrasonic, microwave, cryo, heat, laser, etc.) are applied to tissue to achieve a desired result. Electrosurgery involves application of high radio frequency electrical current to a surgical site to cut, ablate, coagulate or seal tissue. In monopolar electrosurgery, a source or active electrode delivers radio frequency energy from the electrosurgical generator to the tissue and a return electrode carries the current back to the generator. In monopolar electrosurgery, the source electrode is typically part of the surgical instrument held by the surgeon and applied to the tissue to be treated. A patient return electrode is placed remotely from the active electrode to carry the current back to the generator. 
     In the case of tissue ablation, high radio frequency electrical current is applied to a targeted tissue site to create an ablation volume. The resulting ablation volume may then be observed and various ablation metrics may be measured and recorded. Conventional methods of obtaining ablation metrics include recording the small diameter, large diameter, and height of the ablated tissue to calculate the volume. Typically, these three parameters are input for the equation for ellipsoidal volume to calculate an approximate ablation volume. Conventional methods such as this often provide inexact measurements, inconsistent recordings, as well as inaccurate reporting of achieved volumes. Further, conventional methods of volumetric calculation lack evaluative tools such as determining the effect of adjacent structures on the ablation volume, qualifying the completeness of the ablation volume, predicting specific volumes and/or shapes based on a given energy applicator configuration. 
     SUMMARY 
     The present disclosure relates to a method for determining a volume of ablated tissue. In a first step, energy is supplied to tissue. In a second step, an axis within the tissue is indicated. In a third step, a simulated slicing of the tissue substantially perpendicular to the axis is performed to obtain a plurality of simulated slices. Each of the plurality of simulated slices has a thickness, a cross-sectional perimeter, and a trajectory point that is defined by the axis. In a fourth step, a volume of each of the plurality of simulated slices is determined based on the trajectory point, the cross-sectional perimeter, and the thickness of each simulated slice. In a fifth step, the volumes from each of the plurality of simulated slices are summed to obtain the volume of the ablated tissue. 
     According to another embodiment of the present disclosure, an electrosurgical system includes an electrosurgical generator coupled to one or more electrodes configured to be inserted into a portion of tissue. The electrode(s) is further configured to supply electrosurgical energy to the portion of tissue to create an ablation volume. The system further includes a feedback unit coupled to an imager for imaging the portion of tissue to obtain a graphical scan of the ablation volume and the electrode(s). A controller marks an axis of the electrodes within the graphical scan. The controller is further configured to simulate slicing the graphical scan substantially perpendicular to the axis to obtain a plurality of simulated slices. Each of the plurality of simulated slices has a thickness, a cross-sectional perimeter, and a trajectory point defined by the axis of the electrode(s). The controller is further configured to determine a volume of each of the plurality of simulated slices based on the trajectory point, the cross-sectional perimeter, and the thickness of each simulated slice and further, to sum the volumes from each of the plurality of simulated slices to determine the ablation volume. 
     According to yet another embodiment of the present disclosure, a method of storing a library of ablation data related to the use of a treatment device includes a first step of providing a treatment device having a particular configuration. In a second step, electrosurgical energy is supplied to the treatment device for application to tissue to generate a plurality of feedback parameters based on the particular configuration of the treatment device. In a third step, an imaging device is provided for imaging tissue to create one or more images corresponding to the plurality of feedback parameters based on the particular configuration of the treatment device. The imaging device is configured to communicate with a feedback unit for storing the library of ablation data. In a fourth step, the image(s) and the plurality of feedback parameters are stored in the library of ablation data for subsequent retrieval. The image(s) and the plurality of feedback parameters correspond to the particular configuration of the treatment device applied to tissue. In a fifth step, a completeness factor is determined based on deviations between the image(s) corresponding to feedback parameters based on the particular configuration of the treatment device and ablation data stored in the library corresponding to feedback parameters generated by application to tissue of a treatment device having substantially the same configuration. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the present disclosure are described herein with reference to the drawings wherein: 
         FIG. 1A  shows an electrosurgical system for tissue ablation, measuring ablation volume, and displaying image scan data according to one embodiment of the present disclosure; 
         FIG. 1B  shows an electrode defining a path through tissue for heating ablation according to one embodiment of the present disclosure; 
         FIG. 1C  shows a sliced segment of the tissue of  FIG. 1B ; 
         FIG. 2  illustrates a method for determining an ablation volume according to embodiments of the present disclosure; and 
         FIG. 3  shows an electrosurgical system for tissue ablation, measuring ablation volume, and displaying image scan data according to another embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Particular embodiments of the present disclosure are described hereinbelow with reference to the accompanying drawings. In the following description, well-known functions or constructions are not described in detail to avoid obscuring the present disclosure in unnecessary detail. 
     The present disclosure provides for a system and method for determining a volume of an ablation lesion and providing a geometric reconstruction of the ablation volume. The ablation lesion may be created by applying any suitable energy, such as radiofrequency (“RF”), microwave, electrical, ultrasound, heat, cryogenic, and laser. For the purposes of illustration, the following description assumes the application of RF energy to create ablation lesions in accordance with embodiments of the present disclosure. 
     Referring to  FIG. 1A , an ablation electrode  100  is shown having an insulated shaft  102  and an electrically exposed tip  103 . Electrode  100  may be, for example, a high frequency or RI thermo-ablation electrode configured to be placed in the body of a patient (not explicitly shown) so that the tip  103  is near a target volume, such as a cancerous tumor or other tissue structure within the body. A hub or junction connector element illustrated schematically by  106  may be any type of connection device such as jacks, hoses, ports, etc. that connect the RF electrode to a power source, such as a radiofrequency (RF) generator  107 . The generator  107  according to an embodiment of the present disclosure can perform monopolar and bipolar electrosurgical procedures, including tissue ablation procedures. The generator may include a plurality of outputs for interfacing with various electrosurgical instruments (e.g., a monopolar active electrode, return electrode, bipolar electrosurgical forceps, footswitch, etc.). Further, the generator includes suitable electronic circuitry configured for generating radio frequency power specifically suited for various electrosurgical modes (e.g., cutting, blending, division, etc.) and procedures (e.g., monopolar, bipolar, vessel sealing, tissue ablation). 
     Also shown is a control system  109  coupled to generator  107 , which may be a computer, a microprocessor, or an electromechanical device configured to receive RF energy input parameters from RF generator  107 , such as power, current, voltage, energy, time, impedance, etc. In some embodiments, a coolant supply system (not explicitly shown) may also be included, for example, in operative cooperation with RF generator  107  and/or incorporated within RF generator  107 . The coolant supply system is configured to output various feedback parameters such as temperature, multiple temperatures at different points, and the like into the control system  109 . The coolant supply system parameters can then be used as feedback control input parameters. Based on one or more of these parameters, the control system  109  modulates, moderates, or otherwise monitors output response at the generator  107 . 
     Also shown in  FIG. 1  is a computer system  111 , which may be, for example, a PC or computer graphic workstation. The computer system  111  is coupled to the control system  109 . Computer system  111  processes the parameters of the RF generator  107  and coolant supply system (not explicitly shown) plus other geometric parameters regarding the electrode as well as image scan data taken before, during or after thermo-surgery. Computer system  111  assimilates all of these parameters and displays them in various representations, digital representations, and analog meter type representations, as an interface to the operator or controller of the processor during the preplan process or during the process of ablation heating itself. In one embodiment, image data  120  might represent image scan data from such image scanners such as from CT, MRI, PET, or other tomographic or X-ray, plain film, or digitized image scan data. That data may be stored in the computer system  111  and be represented as an array of raw data, slices, reconstructed slices, three-dimensional renderings, “slice and dice” three-dimensional or two-dimensional renderings, contoured or segmented anatomical structures, color rendered, differentiated structures, both pathological and normal so that the surgeon may substantially visualize the anatomy and pathology of the patient prior to, during, or after the procedure. Data from CT or MRI may be taken days or even months prior, and could be put into stereotactic or non-stereotactic space, for example, by utilizing any suitable imaging software and/or image processing software in conjunction with one or more graphic references or other suitable marking systems or software. 
     Image data  121  may represent ultrasound scan data or sonic monitoring data such as from a sonic detector system that can visualize before, during, and after the thermo-surgery procedure the course of the electrode in the body, electrode position with respect to anatomy, and even the process of the heating mechanism and result thereof. This data could also be fed into computer system  111  and represented in various ways alternatively on a graphics display screen. Image data  121  may be stored in computer system  111  to correspond with particular configurations of electrode  100 , such as, for example, geometric parameters of the electrode tip  103 . In this manner, a library of feedback data may be stored in computer system  111  and indexed according to particular configurations of the electrode, thereby assisting the surgeon in predicting future ablation results for a given electrode configuration. Further, there may be calculation algorithms, look-up tables, heuristic algorithms, historical clinical data, etc. that can be used in a preplan setting and displayed, implemented, overlaid, and used to control the image data, course of RF generator output, as well as the control system to tailor or preplan the results of the ablation that can be visualized again on the computer system  111  and further computed and stored therein. 
     Computer system  111  includes a display  115  for outputting image data  120  and  121 , such as the real-time or preplanned trajectory of a probe path  126  and electrode tip as the tip  126  is inserted into the body and/or a tumor structure represented by a cloud of dots  125 . This might also be, for example, the display from an ultrasonic, CT, or MRI scanner that actually visualizes the probe  126  and a tumor  125  or a profused volume corresponding to the destructive ablation volume, perhaps represented or visualizable as volume  125 . Use of CT contrast agents or dyes can be used to mark the ablation volume following ablation, and this can give a direct view of the results immediately following the heating process. 
     Display  115  may also be configured to show a preplanned path of an electrode in a particular slice or reconstructed slice plane of volumetric rendering in a three-dimensional aspect (not explicitly shown), and also configured to show isotherm surfaces or intersected surfaces or isotherm lines (not explicitly shown), which might represent a preplan or a calculation of the ablation volume around the tip of the electrode. Display  115  may also be configured to show a view, slice, or reconstructed slice, and within it a preplanned or actual plan or post-thermosurgery path representing the approach of a thermosurgical probe  100  into the patient&#39;s anatomy to achieve a target volume that might be seen on that image slice such as for example a tumor as seen on image data  120  and  121 . 
     Volumetric calculations for ablation volumes may be determined from cross-sectional perimeters of slices of a target tissue site and/or block of tissue and subsequently reconstructed and graphically represented in a 2-D and/or 3-D manner on display  115 , as will be discussed in further detail below. 
     Turning now to  FIG. 1B , a trajectory or path  131  of electrode  100  through ablation volume  125  is shown. Path  131  may also be defined as an axis of electrode  100  through ablation volume  125 . Electrode  100  is used to create an ablation lesion at a targeted site such as volume  125  by heating tissue via application of RF energy from the generator  107  to the tissue. Path  131  of electrode  100  through volume  125  provides a trajectory reference or point  135  from which volumetric calculations may be made for volume  125 , as will be discussed in further detail below. Volume  125  may be deconstructed into a plurality of slices, depicted here as  125   a ,  125   b ,  125   c , and  125   d , for enabling volumetric determination of volume  125  and, further, graphical representation in display  115 ,  FIG. 1C  shows a cross-sectional view of any slice  125   n  of the plurality of slices  125   a - d  indicated by line  1 C- 1 C in  FIG. 1B . Each of the plurality of slices  125   n  defines a cross-sectional perimeter  140   n  generally concentric about trajectory point  135   n.    
     In one embodiment of the present disclosure, the reconstructed graphical representation is fitted to a specific geometry (e.g., ellipsoidal, spherical, etc.) for viewing on display  115 . For example, Euclidean distances between perimeter  140  of volume  125  and the perimeter of a pre-specified geometry may be minimized to fit volume  125  to the pre-specified geometry. In this manner, valuable feedback may be provided to a surgeon on the consistency and/or the predictability of the ablation volume achieved based on given energy applicator configurations (e.g., electrode size, electrode tip geometry, etc.). The graphical representation of the reconstructed ablation also allows the surgeon to qualify the completeness or a completeness factor of the ablation lesion achieved based on geometrical similarity between the lesion and any one or more of a particular preplanned geometry provided, for example, by the control system  109 . The graphical representation of the reconstructed ablation may also be used to determine the impact from adjacent structures such as, for example, other electrodes, lungs, bones, vessels, tissue extraneous to the present procedure, etc. on a given ablation, as will be discussed in further detail below. 
     A method for volumetric determination of an ablation volume for subsequent geometric reconstruction and graphical representation according to embodiments of the present disclosure will now be described with reference to  FIG. 2  in conjunction with  FIGS. 1B and 1C . 
     In step  300 , electrosurgical energy is supplied from the RF generator  107  to the electrode  100 . As illustrated in  FIG. 1B , electrode  100  is used to create an ablation lesion by heating volume  125  via application of RF energy from the generator  107  to volume  125 . 
     In step  310 , path or trajectory  131  of electrode  100  through a target site such as, for example, volume  125  ( FIG. 1B ) is indicated. Path  131  of electrode  100  through volume  125  defines trajectory point  135  therethrough relative to perimeter  140  of tissue block  125 . Trajectory point  135  may be substantially defined through the center of mass of tissue block  125 . Trajectory  131  and/or trajectory point  135  may be marked with CT contrast agents or dyes following ablation, giving a direct view of the results immediately following the heating process. 
     In step  320 , volume  125  is cut or “sliced” substantially perpendicular to trajectory point  135  into a plurality of slices  125   a - d . Slices  125   a - d  may be obtained via an image scanner such as, for example, CT, MRI, PET, or other tomographic or X-ray, plain film, or digitized image scan data for subsequent 2D or 3D graphical representation. In this manner; various dimensions and/or measurements of each of the plurality slices  125   a - d  may be indicated such as, for example, thicknesses, volume, cross-sectional perimeter, etc. for each of the plurality of slices. 
     In step  330 , a thickness, indicated in  FIG. 1B  as A, and a cross-sectional perimeter  140   a - d  for each of the plurality of slices  125   a - d  is determined. Cross-sectional perimeters  140   a - d  for each of the plurality of slices  125   a - d  may be derived, for example, from scan data  121  in the computer system  111  such as post-ablation MR images that may or may not include CT contrast agent. Other embodiments of the present disclosure may include deriving from a measurement taken using conventional means such as, for example, dial calipers, slide calipers, digital calipers, electronic calipers, or the like. 
     In step  340 , the volume of each of the plurality of slices  125   a - d  is determined. Any suitable method for determining volume may be used such as, for example, the contour or perimeter method. This method utilizes each slice of volumetric data individually and models the shape of the volume as defined on each slice. For example, cross sectional perimeter  140   a - d  for each slice  125   a - d  may be used to determine the volume using such method. Alternatively, for each slice  125   n , thickness A may be multiplied by the perimeter area of that particular slice to determine the slice volume. This determination is carried out for each of the plurality of slices  125   a - d.    
     In step  350 , the volume determinations derived in step  340  for each of the plurality of slices  125   a - d  are summed to yield an ablation volume. In this manner, an accurate volumetric determination is made rather than approximated calculations yielded by conventional and/or presently competing volumetric calculation methods. 
     Referring now to  FIG. 3  in conjunction with  FIGS. 1B, 1C, and 2 , a patient&#39;s body is represented schematically by element P, and there is a target volume represented by the dashed line  301 . A thermosurgery probe  302  is inserted into the patient&#39;s body such that the tip of the probe  303  is placed within the target volume  301 . Attached to or in conjunction with or cooperatively coupled with the probe (or probes)  302  is an imaging device  311  which, when placed against the surface of the patient&#39;s skin or an organ within the patient&#39;s body, images a portion of the patient&#39;s body P, including the probe  302  and the target volume  301  or the environment around these elements. 
     The radiofrequency, laser, high frequency, or other power generator is represented by  304 , and in the case of a high frequency generator, a reference electrode  305  is attached to the patient&#39;s body around the shoulder region is shown in  FIG. 3 . The reference electrode  305  might be a gel pad, large area, conductive pad or other type of standard reference electrode that is used in electrosurgery. The imaging device  311  is connected to a monitoring circuit or controller system  360  that can be used to image, analyze, filter, and monitor the image scan data or the like which is received from the imaging device  311 . This system  360  may also involve a power source and processor for the imaging device  311 . The system  360  includes a feedback unit  309  configured to control monitoring, preplanning, and/or imaging of an ablation area. Feedback unit  309  includes at least one display  315  and/or  325  configured to graphically display 2D or 3D image data. For example, in display  315  there may be represented in 2D or 3D slice or volume representations, image scan data taken from an image scanner such as CT, MR, PET, or ultrasound prior to, during, or after the thermal ablation. In this instance, a patient&#39;s skin  317  is defined, a target volume (e.g., tumor  316 ) is shown, and in the dashed line is a preplanned probe path  318  for a thermal ablation high frequency electrode (e.g., probe  326 ). By means of such visualization, the probe path  318  can be manipulated within the image or image stack of CT or MR slices, and an optimal path for placement can be achieved. This path could be achieved by criterion from the surgeon such as bringing the probe path along a principal axis of the tumor  316  or from a direction that avoids some critical structures such as arteries, lung, optic nerve, neural structures, etc. Thus, based on image scan data taken from the imaging device  311  prior to the thermal ablation, the surgeon can do a preplanned study and decide on the optimal positioning of the probe  326 . 
     On the display  325  is shown a real-time representation of the probe  326  as it is inserted into the patient&#39;s body. The margin  327  may be a reconstruction, either theoretical or actual, of the result of the RF heat ablation. For example, if the window represents an ultrasonic reconstruction, this could be a theoretically generated graphic representation within a preplanned ultrasonic slice direction and probe direction to show what the ecogenic or ultrasonic image would look like when particular cooled tip RF, generator parameters are invoked or used. This window may alternatively represent real-time image data from the CT or MR or other type of scanning means, if the patient is within such a scanner during the RF heating process. The window may also represent the changes or modifications or digitally subtracted differential changes of the tissue volume as a result, directly or indirectly, of the ablation isotherms. Thus, one may visualize directly the effect of heating on the patients tissue, and this may be displayed in such a window. There may be a superposition of a preplanned or prescanned tumor volume, as compared to the actual volume of the tumor at the time of surgery or the ablation volume as one detects it during surgery. 
     Direct detection of changes in the physiology as a result of the heating to gauge the extent of the ablation volume can be done by ultrasound, CT, MRI, PET, and other imaging modalities, and can be displayed on the display  325  of the feedback unit  309  or, indeed, on the graphics display of the ultrasound or CT, MR, or other scanning machine as supplied by standard manufacturers. Each of these scanning devices has a graphics display on a CRT, liquid crystal, or other means which can display the results of the tomographic or volumetric scanning. These can be used in conjugation with the thermosurgery to evaluate the effect of the thermosurgery itself. Use of ultrasound and standard sonic detection and scanning may be used in conjugation with the thermosurgery to evaluate the effect of the lesion or ablation process. 
     The entire process of the heating could be preplanned by the operator hours or days before based on the imaging and preplanned calculations of ablation volume with the tip geometry and ablation parameters described with respect to  FIG. 1 . Thus, system  360  could basically mediate the entire process of supply of RF power from generator  304 . Indwelling controllers, electronics, microprocessors, or software may be programmed to govern the entire process or allow preplan parameters by the operator based on his selection of a tip geometry and overall ablation volume as selected according to a tumor or pathological volume to be destroyed. Many variants or interconnections of the block diagram shown in  FIG. 3  or additions of said diagram could be devised by those skilled in the art of regulation systems. 
     While several embodiments of the disclosure have been shown in the drawings and/or discussed herein, it is not intended that the disclosure be limited thereto, as it is intended that the disclosure be as broad in scope as the art will allow and that the specification be read likewise. Therefore, the above description should not be construed as limiting, but merely as exemplifications of particular embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.