Abstract:
A test system and method for determining thermal effects of tissue ablation on an ex vivo tissue includes a power generator, a grounding patch, and a material block configured to emulate an electrical property of a patient. The power generator electrically connects to an electrode to generate an electrical current in the electrode. The grounding patch electrically connects to the power generator, and the material block electrically connects to the grounding patch. Furthermore, the material block includes an ex vivo tissue patch configured to emulate an in vivo tissue of the patient. As such, selectively engaging the electrode to the ex vivo tissue patch electrically connects the electrode to the grounding patch through the material block for electrocauterizing the ex vivo tissue patch.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the priority of Application Ser. No. 61/804,881 filed Mar. 25, 2013 (pending), the disclosure of which is hereby incorporated by reference herein. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to a test system and method for determining thermal effects of tissue ablation on a tissue, and more particularly, to a test system and method for effectively testing and comparing the thermal effects of tissue ablation by a variety of models and/or devices. 
     BACKGROUND 
     One of the most common and dangerous electrosurgical procedures is monopolar electrosurgery for removing polyps, such as colorectal polyps, with an endoscope and hot biopsy forceps. While such biopsy forceps are widely used for removing polyps that may be associated with colorectal cancer, successfully removing polyps with minimal damage to a patient&#39;s tissue requires significant training to properly inspect an ablation region for thermal damage. For example, a practitioner, such as a doctor, nurse, or other trained medical professional, typically visually inspects the ablation region for growth of a white peripheral crest to indicate a depth of the thermal effects into the tissue caused by the ablation of the polyp. 
     On the one hand, visually overestimating the depth of the thermal effects of the ablation may lead the practitioner to incorrectly conclude that the polyp has been completely removed by the biopsy forceps and, in turn, may fail to fully remove the polyp. On the other hand, visually underestimating the depth of the thermal effects of the ablation may cause the practitioner to inadvertently damage the patient&#39;s tissue resulting in potentially life-threatening complications. Such underestimations are further complicated by the fact that these complications may include a delayed perforation of the patient&#39;s tissue after the patient as left the practitioner and is no longer surrounded by trained medical professionals for immediate treatment. 
     Due to the difficulty associated with estimating the thermal effects of ablation, particularly in vivo with the patient, a variety of theoretical models and devices have been developed to aid in measuring and/or predicting the depth of ablation. For example, one theoretical model attempts to correlate duration and output power of an electrosurgical device to the patient&#39;s tissue to the depth of ablation. Another theoretical model focuses on thermal management of the biopsy forceps for limiting the effective heat field in the patient&#39;s tissue via simulated computer models. However, further development of these models and devices are, to some extent, limited by an inability to accurately and precisely compare the effectiveness of these developments. 
     There is a need for a test system and method of determining the thermal effects of tissue ablation on an ex vivo tissue that addresses present challenges and characteristics such as those discussed above. 
     SUMMARY 
     An exemplary embodiment of a test system for determining thermal effects of tissue ablation on an ex vivo tissue patch includes a power generator, a grounding patch, and a material block configured for emulating an electrical property of a patient. The power generator is electrically connected to an electrode and configured to generate an electrical current in the electrode. The grounding patch is electrically connected to the power generator, and the material block is electrically connected to the grounding patch. The material block includes the ex vivo tissue patch configured to emulate an in vivo tissue of the patient. Accordingly, selectively engaging the electrode to said ex vivo tissue patch electrically connects the electrode to the grounding patch through the material block for electrocauterizing the ex vivo tissue patch. 
     An exemplary embodiment of a material block for emulating an electrical property of a patient includes a polyacrylamide gel base and an ex vivo tissue patch. The ex vivo tissue patch is directly connected to the polyacrylamide gel base and configured to emulate an in vivo tissue of the patient. As such, the polyacrylamide gel base and the ex vivo tissue patch are configured to collectively emulate an electrical property of the patient. 
     In use, an exemplary method for determining thermal effects of tissue ablation on an ex vivo tissue patch includes connecting an ex vivo tissue patch to a polyacrylamide gel base to form a material block configured to emulate an in vivo tissue of a patient and an electrical property of the patient. The method also includes electrocauterizing the ex vivo tissue patch with an electrode and burning a hole into a portion of the ex vivo tissue patch. Furthermore, the method includes measuring the electrical property of the material block. 
     Various additional objectives, advantages, and features of the invention will be appreciated from a review of the following detailed description of the illustrative embodiments taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below serve to explain the invention. 
         FIG. 1  is a schematic view of a colon of a patient. 
         FIG. 2  is a diagrammatic view of an exemplary method of determining thermal effects of tissue ablation on an ex vivo tissue patch. 
         FIG. 3  is a diagrammatic view of an exemplary test assembly for performing the method of  FIG. 2 . 
         FIG. 4A  is a cross-section view of the ex vivo tissue patch of  FIG. 2  after removing a portion of the ex vivo tissue patch with the test assembly of  FIG. 3 . 
         FIG. 4B  is a chart showing an exemplary grading scale for indicating a depth of ablation on the ex vivo tissue patch of  FIG. 4A . 
         FIG. 5  is a chart showing an electrical impedance value of an exemplary material block including a polyacrylamide gel. 
         FIG. 6  is a chart showing an electrical capacitance value of an exemplary material block including a polyacrylamide gel. 
     
    
    
     DETAILED DESCRIPTION 
     With reference to  FIGS. 1-3 , a test assembly  10  includes a material block  12  having an ex vivo tissue patch  13  for emulating an in vivo tissue  14  of a patient  16 . The test assembly  10  further includes a power generator  18 , such as the electrosurgical device  18 , electrically connected to an electrode  20  and a grounding patch  22 . With reference to the term “emulate” described herein, the material block  12  emulates the patient  16  by having physical and/or electrical properties that correlate to the physical and/or electrical properties of the patient  16 . According to an exemplary embodiment, the physical and/or electrical properties of the material block  12  may be similar or generally the same as the patient  16 . Alternatively, the physical and/or electrical properties of the material block  12  may be different from the patient  16 , so long as a user, such as a doctor, nurse, lab technician, or similarly trained professional, can correlate these properties to the patient  16 . As such, the material block  12  is electrically connected to the grounding patch  22 , and the electrode  20  is brought into selective engagement with the ex vivo tissue patch  13  to electrocauterize the ex vivo tissue patch  13  and ablate a portion of the ex vivo tissue patch  13 . Generally, the test assembly  10  and method described herein are described as an exemplary test to compare one or more devices for performing an ablation. Alternatively or in addition, the test may also be useful for teaching, training, and testing new or used equipment. 
     According to an exemplary embodiment, the material block  12  is configured to emulate a portion of a colon  26  of the patient  16 .  FIG. 1  shows a schematic view of the patient  16  and the colon  26 . The colon  26  generally extends from the anus  28  and rectum  30  to the descending colon  31  and upward to the transverse colon  32 . From the transverse colon  32 , the colon  26  extends downward toward the ascending colon  34  and cecum  36 . Typically, the colon  26  is inspected, such as during a colonoscopy, with an endoscope (not shown) having a hot biopsy forceps (not shown) configured for ablating a polyp via electrocauterization. While testing and training with an endoscope and biopsy forceps in vivo is often useful, the difficulties associated with estimating depth of tissue ablation in vivo require significant training. For this reason, the test assembly  10  and material block  12  having an ex vivo tissue patch  13  may be used to develop devices, including endoscopes and biopsy forceps, such as those discussed in U.S. patent application Ser. No. 14/203,990 filed on Mar. 11, 2014, the disclosure of which is hereby incorporated by reference in its entirety. 
     The colon  26  includes a wall having several layers between an interior of the colon  26  and an exterior of the colon  26 . The layers of the wall, from the interior to the exterior, include the mucosa, the submucosa, an inner layer of the muscularis propria, and an outer layer of the muscularis propria. Thus, in the event of an in vivo ablation via a biopsy forceps, the initial layer to be electrocauterized is the mucosa. Of course, deeper ablations may extend through the remaining layers and, in the event of perforation, effectively burn through the entire wall of the colon  26 . According to an exemplary embodiment, the material block  12  is configured to emulate the wall of the colon  26  during ablation. However, it will be appreciated that the material block  12  may be configured to replicate other tissues of the patient  16 . For this reason, the invention described herein is not intended to be limited to emulating colon tissue of the patient  16 . 
       FIG. 2  schematically shows a method, or test model, of generally forming the material block  12 , electrocauterizing the ex vivo tissue patch  13 , and preparing the electrocauterized ex vivo tissue patch  13 . The material block  12  includes the ex vivo tissue patch  13  and a gel base  38 . An exemplary ex vivo tissue patch  13  is formed from a porcine colon  40 ; however, it will be appreciated that any colon that emulates the patient colon  26  may be so used. The porcine colon  40  is rinsed with phosphate-buffered saline (PBS) and then fixed with 70% ethanol for storage at −20° C. within a freezer (not shown). Prior to testing, the porcine colon  40  is warmed to room temperature and rinsed with distilled water to remove the ethanol. Once the ethanol is removed, the porcine colon  40  is cut into one or more ex vivo tissue patches  13 , which, according to an exemplary embodiment, are each sized to be a 1 inch by 1 inch square. 
     The gel base  38  is formed from a polyacrylamide gel (PAG) having a 15% resolution gel formula with the reagents listed below in Table 1 and generally includes acyrlamide, bisacrylamide, tris(hydroxymethyl)amino methane (Tris-HCl Buffer), ammonium persulfate (APS), tetramethylethylenediamine (TEMED), and distilled degas water in the amounts shown for 60 ml of gel. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Gel Reagents List 
               
             
          
           
               
                   
                   
                 Quantity (60 ml of 
               
               
                 Reagent 
                 Description 
                 Gel) 
               
               
                   
               
               
                 Acrylaminde/ 
                 40% Solution 
                 22.5 ml 
               
               
                 Bisacrylaminde 
                   
                   
               
               
                 Tris—HCl Buffer 
                 1.5M, pH 8.8 
                   15 ml 
               
               
                 APS 
                 white to yellowish 
                 60 mg 
               
               
                   
                 crystals 
                   
               
               
                 TEMED 
                 solution 
                 50-60 μl 
               
               
                 Distilled degas water 
                   
                 22.5 ml 
               
               
                   
               
             
          
         
       
     
     The acyrlamide/bisacrylamide solution and Tris-HCl buffer are mixed together and pooled into a frame, such as a plastic mold. The APS is weighted and dissolved in distilled water and added into the frame with the other materials. To begin consolidating the gel, TEMED is added into the frame and, after about 20 minutes, the gel base  38  is formed. The gel base  38  may then be stored in cold distilled water until needed for testing with the ex vivo tissue patch  13 . Please note, however, that APS is not stable and should be prepared for each gel base  38 . By way of example, other volumes of gel bases  38  with relative quantities of these materials are shown in Table 2. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Detailed Gel Formula for 60 ml and 80 ml of gel 
               
             
          
           
               
                 Reagent 
                 Amount for 60 ml of Gel 
                 Amount for 80 ml of Gel 
               
               
                   
               
               
                 Acrylaminde/ 
                 22.5 ml 
                 30 ml 
               
               
                 Bisacrylaminde 
                   
                   
               
               
                 Tris—HCl Buffer 
                   15 ml 
                 20 ml 
               
               
                 APS 
                 60 mg 
                 80 mg 
               
               
                 TEMED 
                 50-60 μl 
                 80 μl 
               
               
                 Distilled degas water 
                 22.5 ml 
                 30 ml 
               
               
                   
               
             
          
         
       
     
     In order to quantify the emulation of the electrical property of the gel base  38 , which may also include the ex vivo tissue patch  13  attached thereto, an electrical impedance of the gel block was measured under radio-frequency and included the measurements shown in Table 3. Notably, the cauterization electrode  20  was also included in the following measurements for improved accuracy. 
     
       
         
               
             
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Electrical Impedance Measurement Parameters 
               
             
          
           
               
                 Parameter 
                 Value 
               
               
                   
               
               
                 Experiment Type 
                 Frequency Sweep, Control Voltage 
               
               
                 DC potential 
                   0 mV 
               
               
                 AC potential 
                 2000 mV 
               
               
                 Frequency (lower bound) 
                 50 Hz 
               
               
                 Frequency (upper bound) 
                 300 kHz 
               
               
                 Frequency Sweep Type 
                 Log 
               
               
                 Frequency Step 
                 Decade 
               
               
                 Frequency Interval 
                 50 
               
               
                   
               
             
          
         
       
     
     The ex vivo tissue patch  13  is connected to the gel base  38  to form the material block  12 . The material block  12  is then electrically connected to the grounding patch  22 , which may also be referred to herein as a returning electrode, of the test assembly  10  shown in  FIG. 2  and  FIG. 3 . The test assembly  10  generally includes a cauterizing portion A and an electrical measurement portion B, both of which are electrically connected to the electrode  20  via a switch  44  for isolating the cauterizing and electrical measurement portions A, B. 
     The cauterizing portion A includes the electrosurgical device  18  operatively connected to a CPU (not shown) and a power measurement circuit  46 . The electrosurgical device  18  provides power to the electrode  20  via the power measurement circuit  46  and is controlled by the CPU for precise cauterization control. The power measurement circuit  46  may be monitored during use to verify the power being delivered to the electrode  20 . Notably, the switch  44  isolates the electrical measurement portion B from the cauterizing portion A so that power and, more particularly electrical current, is delivered to a head  48 , or tip, of the electrode  20  rather than the measurement portion B. 
     The measurement portion B includes an electrical measurement circuit  50 , which according to an exemplary embodiment is a capacitance and impedance measurement circuit  50 . The electrical measurement circuit  50  is operatively connected to a CPU (not shown) for collecting electrical values detected before cauterization and after cauterization. For example, the electrical measurement circuit  50  and CPU will determine the capacitance values by counting the discharging/charging time with constant voltage/current. According to an exemplary embodiment, the electrode  20  and head  48  are in the form of a one-foot RF cable, rather than a biopsy forceps and endoscope. However, it will be appreciated that such a biopsy forceps, or other equivalent electrode, may be used as described herein. 
     During an exemplary test of the test assembly  10 , an electrical property of the material block  12  is collected via the electrical measurement circuit  50 , such as capacitance and/or impedance. Then, the head  48  selectively engages the ex vivo tissue patch  13  to form one or more holes  52  (see  FIG. 4A ) in the ex vivo tissue patch  13 . Once the hole  52  (see  FIG. 4A ) if formed, the electrical property of the material block  12  is again collected via the electrical measurement circuit  50 . An exemplary set of electrocauterization test parameters are shown below in Table 4. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Electrocauterization Test Parameters 
               
             
          
           
               
                   
                 Parameter 
                 Unit 
                 Values 
                 Count 
               
               
                   
                   
               
               
                   
                 Power 
                 watt 
                 30, 50, 80 
                 3 
               
               
                   
                 Duration 
                 second 
                 0.5, 1.5, 
                 3 
               
               
                   
                   
                   
                 3.0 
                   
               
               
                   
                 Contacting 
                   
                 low, high  
                 2 
               
               
                   
                 Area 
                   
                   
                   
               
               
                   
                   
               
             
          
         
       
     
     With respect to  FIG. 2  and  FIGS. 4A-4B , photographs are taken of the holes  52  after the electrocauterization. The ex vivo tissue patch  13  is removed from the gel base  38  for undergoing histological analysis for quantifying the size of each hole  52 . Generally, the analysis requires dehydration of the ex vivo tissue patch  13 , embedding the ex vivo tissue patch  13  in paraffin, slicing the paraffin to form cross-sectional slices of the ex vivo tissue patch  13 , staining the cross-sectional slices, and inspecting the cross-sectional slices with a microscope  62 . The following will provide additional details for this analysis. 
     With the ex vivo tissue patch  13  removed from the gel base  38 , the ex vivo tissue patch  13  is manipulated with ethanol and xylene for dehydration  54 . The following steps outline the dehydration process in Table 5. Once dehydrated, each ex vivo tissue patch  13  is submerged and embedded in melted paraffin until the paraffin hardens into paraffin blocks  56 . Each paraffin block  56  is sliced from 6 to 12 times to define 6 to 12 10 μm slides  58  of the ex vivo tissue patch  13 . 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 5 
               
             
             
               
                   
               
               
                 Sample Dehydration Procedure 
               
             
          
           
               
                   
                 Step 
                 Reagent 
                 Time 
               
               
                   
                   
               
               
                   
                 1 
                 70% Ethanol 
                 Overnight 
               
               
                   
                 2 
                 70% Ethanol  
                 2.0 hours 
               
               
                   
                 3 
                 70% Ethanol  
                 1.5-2.0 hours 
               
               
                   
                 4 
                 70% Ethanol  
                 30 min (repeat 3 times) 
               
               
                   
                 5 
                 Xylene 
                 20 min (repeat 3 times) 
               
               
                   
                 6 
                 Paraffin I 
                 1.0-2.0 hours 
               
               
                   
                 7 
                 Paraffin II  
                 Overnight 
               
               
                   
                 8 
                 Paraffin II  
                 30 min 
               
               
                   
                   
               
             
          
         
       
     
     Preferably, the slides  58  are stained for viewing details of the cross-sections of the ex vivo tissue patch  13 . According to an exemplary embodiment, each slide  58  is stained with haematoxylin and eosin (H&amp;E)  60 . Staining the slides  58  with H&amp;E  60  includes hydrating each slice of the ex vivo tissue patch  13 , applying the H&amp;E  60 , and dehydrating each slide  58  again for photographing and storage. The following Table 6 outlines the successive operations for staining each slide  58 . 
     
       
         
               
             
               
               
             
           
               
                 TABLE 6 
               
             
             
               
                   
               
               
                 H&amp;E Staining Procedure (including hydration and dehydraton) 
               
             
          
           
               
                 Operation 
                 Time 
               
               
                   
               
               
                 Submerge slides in Xylene I, II, and III 
                 5 minutes 
               
               
                   
                 (each) 
               
               
                 Submerge slides in 100% Ethanol I and II 
                 5 minutes 
               
               
                   
                 (each) 
               
               
                 Submerge slides in 95% Ethanol 
                 5 minutes 
               
               
                 Submerge slides in 70% Ethanol 
                 5 minutes 
               
               
                 Wash slides in distilled water 
                 3 minutes 
               
               
                 Submerge slides in Haematoxylin 
                 2 minutes 
               
               
                 Wash slides in circulating bath with tap 
                 20 minutes  
               
               
                 water 
                   
               
               
                 Wash slides in distilled water 
                 3 minutes 
               
               
                 Submerge slides in 70% Ethanol 
                 3 minutes 
               
               
                 Submerge slides in Eosin 
                 30 seconds 
               
               
                 Submerge slides in 95% Ethanol 
                 3 minutes 
               
               
                 Submerge slides in 100% Ethanol I, II, and 
                 3 minutes 
               
               
                 III 
                 (each) 
               
               
                 Submerge slides in Xylene I, II, and III 
                 3 minutes 
               
               
                   
                 (each) 
               
               
                   
               
             
          
         
       
     
       FIG. 4A  shows an exemplary photograph of a slide  58  defining the hole  52  within the ex vivo tissue patch  13 . Notably, the hole  52  has a diameter L1 and a depth L2. The diameter L1 and depth L2, taken in conjunction with the other slides  58 , may be used to calculate the volume of the hole  52  formed in the ex vivo tissue patch  13 . It will be appreciated that the volume may be calculated using known mathematical estimations, such as a volume of a spherical cap, or may be scanned for measurement. In any case, the depth L2 may then be correlated to an injury grade shown in  FIG. 4B . For example, a depth through the mucosa correlates to an injury grade 1, whereas, a depth through the inner layer of the muscularis propria correlates to an injury grade 4. 
     By understanding the measurements, such as the depth and the volume, of the hole  52 , the electrical values, such as the capacitance and impedance, can be compared to the resulting hole  52  and correlated for comparing other treatments ex vivo or predicting injury grades of a hot biopsy forceps in vivo. By way of example,  FIG. 5  shows impedance values and capacitance values taken during cauterization with the test assembly  10  of  FIG. 3 . With respect to  FIG. 5 , the material block  12  had an impedance value of 300Ω at a frequency range of 150 kHz to 300 kHz. Notably, at relatively low-frequency, the material block  12  has a relatively stable impedance value and, as such, emulates the similar electrical impedance values of in vivo tissue  14 . Furthermore,  FIG. 6  shows a capacitance value correlated to the volume of the hole  52  measured from the slides  58 . In this way, the capacitance values measured before and after ablating a portion of the ex vivo tissue  13  can be used to indicate to a user the size of the hole  52  formed during during cauterization. 
     While the present invention has been illustrated by the description of one or more embodiments thereof, and while the embodiments have been described in considerable detail, they are not intended to restrict or in any way limit the scope of the appended claims to such detail. For example, the references to the colonoscopy procedure and the polyp tissue are not intended to limit the invention. It will be appreciated that the invention may be used in relation to any electrosurgical procedure and on any patient tissue. The various features shown and described herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative device and method and illustrative examples shown and described. Accordingly, departures may be from such details without departing from the scope of the general inventive concept.