Abstract:
Improved imaging and monitoring systems for use with a closed loop cryosurgical system. As described herein, various systems can be used alone or in conjunction with one another to plan and/or monitor cryosurgical procedures in order to improve cryosurgical outcomes. These systems can include computer assisted planning systems, non-ultrasound based imaging systems and temperature monitoring systems utilized individually or in combination. Through the use of these systems, the precision by which cryosurgical procedures are performed are enhanced.

Description:
PRIORITY CLAIM 
       [0001]    The present application claims priority to U.S. Provisional Application No. 60/820,288, filed Jul. 25, 2006 and entitled, “CRYOSURGICAL IMAGING AND MONITORING SYSTEMS, which is herein incorporated by reference in its entirety. 
     
     FIELD OF THE INVENTION 
       [0002]    The present disclosure relates to cryosurgical systems for use in the treatment of cancerous tumors or lesions, and more particularly to imaging and monitoring systems for use in cryosurgical systems. 
       BACKGROUND OF THE INVENTION 
       [0003]    Cryosurgical probes are used to treat a variety of diseases. Cryosurgical probes quickly freeze diseased body tissue, causing the tissue to die after which it will be absorbed by the body, expelled by the body, sloughed off or replaced by scar tissue. Cryothermal treatment can be used to treat prostate cancer and benign prostate disease. Cryosurgery also has gynecological applications. In addition, cryosurgery may be used for the treatment of a number of other diseases and conditions including breast cancer, liver cancer, glaucoma and other eye diseases. 
         [0004]    A variety of cryosurgical instruments variously referred to as cryoprobes, cryosurgical probes, cryosurgical ablation devices, cryostats and cryocoolers have been used for cryosurgery. These devices typically use the principle of Joule-Thomson expansion to generate cooling. They take advantage of the fact that most fluids, when rapidly expanded, become extremely cold. In these devices, a high pressure gas mixture is expanded through a nozzle inside a small cylindrical shaft or sheath typically made of steel. The Joule-Thomson expansion cools the steel sheath to a cold temperature very rapidly. The cryosurgical probes then form ice balls which freeze diseased tissue. A properly performed cryosurgical procedure allows cryoablation of the diseased tissue without undue destruction of surrounding healthy tissue. 
         [0005]    Cryosurgery is typically carried out under ultrasound guidance to monitor the size and positioning of ice balls with respect to targeted tissue. Ultrasound can be used to visualize the process of freezing during cryosurgery as the interface between frozen tissue and non-frozen tissue is associated with a change in acoustic impedance that reflects ultrasound waves, allowing the interface to be depicted. However, ultrasound can be difficult to use and currently is regulated for use only by radiologists who have received specialized training with it. In addition, ultrasound can create a “shadow region” that obscures vision behind the ice ball. Thus if growth of the ice ball is non-uniform, the lack of vision within the shadow region can lead to vital organs being accidentally frozen. 
       SUMMARY OF THE INVENTION 
       [0006]    The present disclosure is directed to improved imaging and monitoring systems for use with a closed loop cryosurgical system. As described herein, various systems can be used alone or in conjunction with one another to plan and/or monitor cryosurgical procedures in order to improve cryosurgical outcomes. These systems can include computer assisted planning systems, non-ultrasound based imaging systems and temperature monitoring systems utilized individually or in combination. Through the use of these systems, the precision by which cryosurgical procedures are performed is enhanced. 
         [0007]    In one aspect of the present disclosure, a cryosurgical system can utilize a computer assisted planning system and the related methods of implementing the computer assisted planning system to promote cryosurgical treatment uniformity within captured, targeted tissue. The computer assisting planning system can use finite element simulation to tessellate the surface of a captured image of a region to be cryosurgically treated with uniformly sized hexagons. Once these hexagons have been simulated, the center of each hexagon can be used as a placement recommendation or target for a cryoprobe. A guide or template can be used to align the cryoprobes with the hexagons so as to guide them to the placement recommendations. 
         [0008]    In another aspect of the present disclosure, a cryosurgical system can use a non-ultrasound based imaging system to visualize a cryosurgical treatment region in real-time. Representative non-ultrasound based imaging systems can utilize either electrical impedance tomography (“EIT”) or near-infrared imaging (“N-IR”). EIT measures electrical resistance across gaps between electrodes placed on the body or needles placed in the body. N-IR measures near infrared absorbance between light fibers placed inside or outside the body. Using the measurements obtained with either EIT or N-IR imaging, a computer program can be used with either system to calculate and depict ice ball location and size at any point in time based on these measurements. 
         [0009]    In yet another aspect of the present disclosure, a cryosurgical system can be monitored and controlled utilizing a temperature monitoring system and associated algorithms. The temperature monitoring system can use cryoprobes having servo-actuated valves to control the temperature at the cryoprobe tips as well as thermocouples inserted into desired areas within the prostate. The temperature monitoring system can use a proportional-integral-derivative control to monitor the behavior of the system. The servo-actuated valves can then be rapidly adjusted in order to maintain the desired temperature. 
         [0010]    The above summary of the various representative embodiments of the invention is not intended to describe each illustrated embodiment or every implementation of the invention. Rather, the embodiments are chosen and described so that others skilled in the art may appreciate and understand the principles and practices of the invention. The figures in the detailed description that follows more particularly exemplify these embodiments. 
     
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0011]    These as well as other objects and advantages of this invention, will be more completely understood and appreciated by referring to the following more detailed description of the presently preferred exemplary embodiments of the invention in conjunction with the accompanying drawings of which: 
           [0012]      FIG. 1  is a side view of an embodiment of a cryosurgical system according to the present disclosure. 
           [0013]      FIG. 2  is a flow chart illustrating a representative computer aided planning procedure for use with a cryosurgical system according to the present disclosure. 
           [0014]      FIG. 3  is a flow chart illustrating a representative cryosurgical treatment procedure according to the present disclosure. 
           [0015]      FIG. 4  is a flow chart illustrating a representative temperature monitoring algorithm according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0016]    A closed loop cryosurgical system  100  according to the present disclosure is illustrated in  FIG. 1 . Cryosurgical system  100  can include a refrigeration and control console  102  with an attached display  104 . Control console  102  can contain a primary compressor to provide a primary pressurized, mixed gas refrigerant to the system and a secondary compressor to provide a secondary pressurized, mixed gas refrigerant to the system. The use of mixed gas refrigerants is generally known in the art to provide a dramatic increase in cooling performance over the use of a single gas refrigerant. Control console  102  can also include controls that allow for the activation, deactivation, and modification of various system parameters, such as, for example, gas flow rates, pressures, and temperatures of the mixed gas refrigerants. Display  104  can provide the operator the ability to monitor, and in some embodiments, adjust the system to ensure it is performing properly and can provide real-time display as well as recording and historical displays of system parameters. One exemplary console that can be used with an embodiment of the present invention is used as part of the Her Option® Office Cryoablation Therapy available from American Medical Systems of Minnetonka, Minn. 
         [0017]    With reference to  FIG. 1 , the high pressure primary refrigerant is transferred from control console  102  to a cryostat heat exchanger module  110  through a flexible line  108 . The cryostat heat exchanger module  110  can include a manifold portion  112  that transfers the refrigerant into and receives refrigerant out of one or more cryoprobes  114 . The cryostat heat exchanger module  110  and cryoprobes  114  can also be connected to the control console  102  by way of an articulating arm  106 , which may be manually or automatically used to position the cryostat heat exchanger module  110  and cryoprobes  114 . Although depicted as having the flexible line  108  as a separate component from the articulating arm  106 , cryosurgical system  100  may incorporate the flexible line  108  within the articulating arm  106 . A positioning grid  116  can be used to properly align and position the cryoprobes  114  for patient insertion. 
         [0018]    A cryosurgical system according to the present disclosure can utilize a computer-assisted planning procedure  200  illustrated graphically in  FIG. 2 . The computer-assisted planning procedure  200  can be used to plan and predict a cryosurgical procedure prior to treatment. A cross-sectional image of a region to be treated such as, for example, the cross-section of the prostate or other target tissue is first captured at an imaging step  201  using an imaging technique such as, for example, trans-rectal ultrasound (TRUS), computed tomography (CT), or magnetic resonance imaging (MRI), or other suitable imaging technique. At a point selection step  202 , the user can select a number of points, for example eight, from the captured image which a software portion of the computer-assisted planning system uses at boundary definition step  204  to interpolate a freeze boundary around the cross-section image. In a prostate application, a circle must also be placed over the urethra at a freeze safety step  206  to ensure it is not in the freeze zone defined by the freeze boundary. The software portion can include a finite element simulation algorithm to tessellate the surface of the generated prostate shape with uniformly sized hexagons at a grid definition step  208 . The size of the hexagons should have the same chord diameter as an iceball generated by a cryoprobe would have after a set period of time. This period of time can be specified by the user or can be preset in the software program. Once the hexagons are generated, the center of each hexagon is recommended as a location for placement of a cryoprobe tip, which is the portion of the cryoprobe used for freezing and forming the ice ball, at cryoablation treatment step  210 . 
         [0019]    The software portion of the computer-assisted planning procedure  200  can also mathematically simulate the freezing process at a cryosurgical simulation step  212  so that the user can “watch” the procedure before performing it. System parameters that will lead to a desired outcome can therefore be confirmed before performing the operation. A guide or template, similar to the type used in brachytherapy, can be used to align cryoprobes with the hexagons at a probe alignment step  214  and guide them into the prostate. Through the use of software including a finite element analysis algorithm, the computer-assisted planning system provides for more accurate cryoprobe placement and more complete cryoablation as the software portion can account for the irregular size and shape of the prostate or other targeted tissue so as to provide for uniform cryoprobe distribution. 
         [0020]    A representative cryosurgical treatment procedure  300  for utilizing cryosurgical system  100  in the cryoablation of the prostate is illustrated in  FIG. 3 . In performing the cryosurgical treatment procedure  300 , a first step generally involves an imaging step  301  in which tumors are identified and located within the prostate. Imaging step  301  can be accomplished with any of a variety of suitable imaging systems including, for example, Magnetic Resonance Imaging (MRI), Computed Tomography Imaging (CT), Near-Infrared Imaging (N-IR), Electrical Impedance Tomography (EIT) and the like, used either individually or in combination. 
         [0021]    Once a tumor has been identified and located, a treatment planning step  302  can make use of the computer assisted planning procedure  200  discussed previously can be used to plan and map the prostate. Treatment planning step  302  can include mathematical simulation of the cryosurgical treatment procedure to determine freezing and heating boundary conditions, temperature conditions through the cryoablation process and to recommend locations for insertion of the cryoablation probes. 
         [0022]    Following treatment planning step  302 , a treatment preparation step  304  can involve prepping the patient and equipment for treatment. Generally, treatment preparation step  304  can include activating the cryosurgical system  100  and positioning the cryosurgical system  100  and related components with respect to the patient. Treatment preparation step  304  can include positioning a needle insertion grid such as, for example, a brachytherapy style grid, with respect to the patient such that insertion of the cryoprobes can be accomplished in accordance with treatment planning step  302 . 
         [0023]    Once the cryosurgical system  100  is positioned and ready for treatment, a treatment step  306  involving freezing and heating cycles of the inserted cryoprobes is initiated. During the freezing step, iceballs are formed at the tip of the cryoprobes for freezing and consequently killing the targeted tissue of the tumor. During treatment step  306 , the size and formation of the iceball must be carefully monitored such that the iceball is freezing only targeted tissue and does not accidentally freeze vital organs or other non-targeted, healthy tissue. Treatment step  306  can further include the use of heating probes to protect certain areas such as nerve bundles or the rectum from freezing. 
         [0024]    So as to avoid the previously discussed disadvantages associated with ultrasound imaging, a cryosurgical system according to the present disclosure can also include a non-ultrasound imaging system to track ice ball growth throughout treatment step  306 . The non-ultrasound imaging system is advantageous in that shadow regions commonly associated with ultrasound imaging are avoided so as to reduce the potential for damage to healthy tissue or vital organs during treatment step  306 . 
         [0025]    One representative non-ultrasound imaging system that can be used during treatment step  306  comprises an electrical impedance tomography (EIT) system. With an EIT system, electrodes can be placed on the body or needles positioned within the body. The EIT system then measures the electrical resistance across gaps between the electrodes placed on the body and/or needles placed in the body. Based on the measured electrical resistance, a computer running EIT software can visualize the size and position of the ice ball in real time and without the limitation of shadow regions in proximity to the ice ball. 
         [0026]    Another representative imaging system that can be used to monitor iceball growth during treatment step  306  can comprise a near-infrared imaging (N-IR) system. With a N-IR system, light fibers can be placed inside or outside the body and near-infrared absorbance measurements are taken. Based on the absorbance measurements, a computer running N-IR software can be used to visualize the size and position of the ice ball in real time and without the limitation of shadow regions in proximity to the ice ball. 
         [0027]    Utilizing either the EIT or N-IR imaging systems, an operator can continually monitor the cryosurgical treatment to ensure that the ice ball is freezing all of the targeted tissue while not contacting the surrounding, healthy tissue during treatment step  306 . By using non-ultrasound based imaging systems, physicians other than radiologists can image and perform cryosurgical treatment. Through the use of EIT or N-IR imaging systems including careful positioning of the electrodes and light fibers, a 360 degree view of the ice ball can be generated in real-time as cryosurgical treatment is being performed and the view of the tissue behind the ice ball is not obscured as is commonly encountered with ultrasound based imaging systems. 
         [0028]    Cryosurgery according to the present disclosure can further be aided through the use of a temperature monitoring system and associated temperature monitoring algorithm  400  that is illustrated in  FIG. 4 . Through the use of temperature monitoring algorithm  400 , temperatures are more evenly controlled within the prostate throughout the cryoablation process and less experience and expertise on the part of the use is necessary to achieve a desired treatment outcome. 
         [0029]    Generally, a first step of temperature monitoring algorithm  400  involves a cryoprobe positioning step  402  wherein a plurality of cryoprobes are positioned within identified locations in the prostate. The cryoprobe locations can be identified prior to insertion using the previously discussed computer-assisted planning procedure  200 . Preferably, the temperature monitoring system can utilize cryoprobes having servo-actuated valves to selectively control the flow rate of refrigerant gas to the cryoprobes. Next, a thermocouple positioning step  404  involves placing thermocouples into areas where precise temperature control is desired. These areas can include, for example, the urethra, neurovascular bundles, the rectum and the like. Throughout the cryosurgical procedure, the individual thermocouples continually read and transmit temperature data (T actual ) to the temperature monitoring system. 
         [0030]    Once the cryoprobes and thermocouples are positioned, a user can specify the desired temperature of operation (T user ) in a temperature selection step  406 . Once the user specifies T user , a computer running a temperature monitoring software program can begin a temperature controlling step  408  that incorporates the T user  value as well as the T actual  values in a feed back loop that drives the process output proportional to the sum of: 1) a proportionality constant multiplied by the difference between the last read T actual  value and the T user  value (the proportional control); 2) a second proportionality constant multiplied by the difference between the last read T actual  value and the integral of the error from the T user  value (the integral control) and; 3) a third proportionality constant multiplied by the difference between the error between T actual  and T user  at the current time step and at the previous time step (the derivative control). Based on these calculations in the temperature controlling step  408 , the temperature monitoring system can continually adjust the servo-actuated valves for each cryoprobe based on the process output after each time step in order to obtain a closer approximation between T actual  and T user . In some instances, the user may manually adjust the proportionality constants within the temperature monitoring software program in order to obtain a more stable operation. 
         [0031]    The above temperature control algorithm  400  gives a higher likelihood of a stable operating temperature. Use of a derivative control alone can yield a process that is sensitive to perturbations or external thermal “noise.” The proportional and integral controls can be used with or without the derivative part of the control. The proportional control is a relatively standard control and the integral control allows correction for bias. The derivative control can allow for even faster response, but may do so at the expense of stability. 
         [0032]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiments, it will be apparent to those of ordinary skill in the art that the invention is not to be limited to the disclosed embodiments. It will be readily apparent to those of ordinary skill in the art that many modifications and equivalent arrangements can be made thereof without departing from the spirit and scope of the present disclosure, such scope to be accorded the broadest interpretation of the appended claims so as to encompass all equivalent structures and products.