Abstract:
A method and apparatus for performing minimally-invasive image-guided laser ablation of targeted region within a tissue or organ comprising the following: A guidance tool that can guide laser source to a predefined target region from a planning image; A controller that can control energy from laser source, duration of its application and dosage of energy from laser source; and a computer with software that can compute thermometry based on precise location and duration of application or dosage of the laser source. The computer receives signal from controller and can control or shut-off laser energy.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a non-provisional of U.S. Provisional Patent Application 61/700,273, filed Sep. 12, 2012, the entirety of which is expressly incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
     PRIOR ART 
       [0002]    U.S. Pat. No. 8,155,416, issued on Apr. 10, 2012 for invention titled “Methods and apparatuses for planning, performing, monitoring and assessing thermal ablation,” discloses a thermal ablation system using an x-ray system to measure temperature changes throughout a volume of interest in a patient. Image data sets captured by the x-ray system during a thermal ablation procedure provide temperature change information for the volume being subjected to the thermal ablation. However, the invention does not disclose a method of using a guidance tool or tracking method for thermal ablation. Also, there are no claims on performing the thermal ablation under ultrasound guidance with real time thermal monitoring or multi-modality image overlays with thermal maps. 
         [0003]    In their patent application Ser. No. 12/213,386 filed Jun. 18, 2008 titled “Methods and devices for image-guided manipulation or sensing or anatomic structures”, the inventors disclose devices and methods for identifying or observing a precise location in the body through and/or upon which medical procedures such as laser ablation may be efficiently and safely performed. The methods disclosed in the patent application use image guidance with ultrasound or optical coherence tomography imaging with no computation or display of thermal maps/thermal measurements or tracking methods. The method disclosed does not allow for any means to control the laser sources to localize the ablation. 
         [0004]    U.S. Pat. No. 6,669,693, issued on Dec. 30, 2003 for invention titled “Tissue ablation device and methods of using,” discloses a tissue ablating device and the method of using radiofrequency signal and monitoring with ultrasound or intra cardiac echo device for treating cardiac arrhythmias. The patent has no claims on providing thermal measurements, thermal maps or overlays with other imaging modalities. The method claimed does not provide for any control of ablation sources or use of a guidance tool or tracking method to localize the tissue ablation. 
         [0005]    U.S. Pat. No. 8,137,340, issued on Mar. 20, 2012 for invention titled “Apparatus and method for soft tissue ablation employing high power diode-pumped laser,” and U.S. Pat. No. 7,313,155, issued on Dec. 25, 2007 for invention titled “High power Q-switched laser for soft tissue ablation,” disclose laser ablation with a high power diode-pumped laser and high power Q-switched solid-state laser respectively for ablating soft tissue with laser. The inventions do not detail laser temperature control methods, guidance tools or tracking methods, or method of performing targeted tissue ablation. 
       BACKGROUND 
       [0006]    A large number of medical procedures involve local tissue ablation in order to treat a condition or ablate a malignancy. For example, tissue ablation can be used to treat a benign condition called benign prostate hyperplasia (BPH), as well as a malignant condition such as prostate cancer. Thermal ablation methods find widespread applications in such medical procedures where both, cooling and heating methods are involved. Cryotherapy ablates the tissue by cooling it down to a temperature where the cell necrosis occurs while laser therapy performs cell necrosis by raising temperature to unsafe limits for the tissue being ablated. When trying to localize the ablation, cryotherapy suffers from the disadvantage that the temperature gradient is very large from the body temperature to the ablation temperature. The tissue has to be locally cooled down to around −40 degrees Celcius to ablate, which results in temperature gradient of 77 degrees Celcius compared to body temperature. As a result, while the tissue is being locally cooled, the surrounding tissue also cool down to very unsafe temperatures. The ablation is thus hard to control and causes irreparable damage to healthy tissue. 
         [0007]    Tissue ablation through heating does not suffer from this drawback since the temperature only needs to be raised from 37 degree Celcius to about 60 degree Celcius. As a result, the ablation zone can be contained to small regions while limiting the damage to surrounding structure. Laser ablation provides one such method where localized heat can be provided to a target within an organ, gland or soft tissue such that the target area can be completely and reliably ablated while preserving important surrounding structures. Laser energy is typically applied to the internal tissues and structures using a hypodermic needle sleeve. The needle is inserted to the target and a fiber, through which laser energy is applied, is inserted through the needle to place it at the target. The laser source is then activated and the delivered thermal energy ablates tissue within the ablation zone. The traditional drawback to using laser ablation is that it cannot be performed under ultrasound guidance since traditional ultrasound does not provide thermometry information. One compromise has been to observe temperature of ablation using MR thermometry. However, this method is cumbersome, very expensive, and requires prolonged access to MR gantry, which makes it an unfeasible procedure for a vast majority of surgeons. In addition, the learning curve to perform a laser ablation in MR gantry can be very steep. 
         [0008]    We solve this problem by providing methods and apparatus for performing targeted laser ablation such that the laser energy can be delivered very precisely and the temperature measurement can be performed without requiring real-time analysis of MRI images. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  shows a conceptual diagram showing ablation using a grid template. 
           [0010]      FIG. 2  shows an overall diagram showing laser ablation using a grid template and thermometry feedback to controller and user. 
           [0011]      FIG. 3  shows an overall workflow for a laser ablation device using an external grid template and hypodermic needle based thermal sensors. 
           [0012]      FIG. 4  shows a method for performing laser ablation such that the safety zone is unharmed while the ablation zone is completely ablated. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0013]    This disclosure claims methods and apparatus for performing targeted laser ablation for a medical procedure. The target may include a malignancy or benign inflammation. Specifically, the apparatus includes three essential components: i) a guidance tool that guides laser source to target region, ii) a controller that controls laser energy and iii) a computer with software that computes and displays temperature measurements. 
         [0014]    The guidance tool used for placing laser to the target tissue may contain a tracking device such that after an initial calibration with real world, the tracking device can be manipulated to align a needle with the desired target within the tissue. The only requirement for the tracking tool is to provide a trajectory for aligning the needle. 
         [0015]    The controller provides the interface between the computer and the laser source. The computer monitors the temperature, and in case of a software based tracking system, the trajectory of the needle. The computer provides feedback to the controller to start or stop laser energy delivery. In addition, the computer is equipped with a display monitor that provides thermal and visual feedback to the user. 
         [0016]      FIGS. 1 and 2  show one particular embodiment in detail where a brachytherapy-like grid is used to guide needles. Note that the methodology does not change even if a tracking system is used for guiding various needles to their targets. As shown in  FIG. 1 , the apparatus includes a grid, which has pinholes at various grid locations. Each pinhole location may be individually identified. For example, if the rows are labeled as  1 , 2 , 3 , . . . , and the columns are labeled as a,b,c, . . . , then any pinhole can be represented by index (i,j), where i ε { 1 ,  2 , 3 , . . . } and j ε {a,b,c, . . . }. 
         [0017]    A planning image form a previous patient visit may be used for planning the laser ablation. The laser ablation plan that includes the location and trajectories of laser sources, ablation zone and the region to be spared, hereafter referred to as safety zone, is used as the input for the procedure. The plan may be defined such that it corresponds to the grid after the grid has been calibrated to correspond to the frame of reference of the planning image. For example, if a laser source k is to be inserted through a pinhole at location (i,j) to a depth D k , and activated for a duration of t k , then the ablation plan may be completely represented by the set {(i, j), D k , t k }. In addition, locations for insertion of thermal sensors may be planned in advance based on both ablation zones and safety zones. Note that an ablation zone may require application of more than one laser sources simultaneously. Let T safety   high  and T safety   low  represent the thresholds for the highest temperature allowed in safety zone beyond which the laser source must be shut down and the maximum temperature threshold before laser source can be activated, respectively. Let T ablation   low  represent the minimum temperature required in ablation zone. In general, T ablation   low &gt;T safety   high &gt;T safety   low  and nominal values in tissue for T ablation   low , T safety   high  and T safety   low  are 60° C., 55° C. and 50° C. respectively. Then, the entire laser ablation must be performed such that the temperature in ablation zone reaches higher than T ablation   low  while the temperature of the safety zone never reaches unsafe limits, i.e., more than T safety   high . 
         [0018]      FIG. 2  shows an overall scheme for a localized targeted laser ablation. The laser source(s) and temperature sensors are placed at the planned locations using a fixed grid, which may be attached to an ultrasound transducer or to a guidance tool. The needles may also be directly placed using a guidance tool under live ultrasound guidance. The laser placement is done in two stages: first, a hollow needle, which acts as a guide or sleeve for the laser fiber to be inserted through, is placed to desired location; and then, the laser fiber is inserted along the needle such that the laser source(s) reaches the tip of the needle sleeve. The sleeve may be removed after insertion of the laser fiber. In addition to the laser source(s), needles are also inserted to measure temperatures inside tissue, around the ablation zone and around the safety zone. 
         [0019]    The controller acts as an interface between the computer and the hardware through temperature measurements and control of laser delivery. Controller is connected to the output of the thermal sensors and provides the temperature measurements to the computer. In addition, controller takes inputs from computer to start or stop the activation of laser source(s). 
         [0020]    The computer has algorithms for computation and display of thermal maps in addition to the individual thermal sensor measurements as identified on a virtual grid displayed on a monitor. The user may interact with the computer to define the pinhole locations and laser plan onto the virtual grid. If live ultrasound image is available, the virtual grid is overlaid on the live ultrasound image and the individual needles are defined in at least two orthogonal views containing the needles. For a prostate procedure, the two orthogonal views would be transverse, which will correspond with the virtual grid and contain all the pinholes in its place and sagittal, which will contain the entire needle length in its plane. The two views for each needle define the complete placement of needles including locations of laser sources. The needles and their grid locations may be manually entered by the user or automatically computed by analyzing the ultrasound video capture after each needle is placed. After all needles and sources are placed, the laser ablation is performed. 
         [0021]    As shown in  FIG. 3 , when patient comes for thermal ablation, upon administration of local or general anesthesia, the surgeon positions the patient and attaches the grid such that the grid locations correspond to the planning image grid points. This may require some physical adjustments based on ultrasound image or some other body markers. For example, for prostate ablation, a transrectal ultrasound transducer may be introduced into the rectum of patient and the grid may be mounted using a rigid fixture on to the probe. The probe pressure and insertion depth then can be adjusted such that the alignment of attached grid template with the virtual template from the planning image is ensured. In another arrangement, external markers or fiducials may be attached on the patient&#39;s skin such that they can be used as reference while positioning the ablation equipment relative to a planning image that contains tissue image in addition to the geometry or image of the fiducials. Such a procedure is part of initial calibration before each procedure, which may also include software based co-registration from the planning images to a live imaging modality such as ultrasound. 
         [0022]    After positioning the patient and the grid or guidance tool as per the planned procedure, the user inserts the needles for laser sleeves into place as per the predefined plan. As mentioned earlier, this may be done using grid under live ultrasound guidance or ultrasound coupled with a tracking system. When the needles are placed, the user places the laser fibers by inserting it along the needle sleeves till the tip reaches end of the sleeve. At this point, the sleeve may be withdrawn. Next, the user inserts the needles containing thermal sensors around the ablation zone and safety zones. Let T safety  and T ablation . represent the maximum temperature in safety zone and minimum temperature in ablation zone, respectively. 
         [0023]      FIG. 4  provides a detailed procedure for performing laser ablation while maintaining control of temperatures experienced by ablation and safety zones. Upon placement of the laser source(s) and the thermal sensors, the user initializes the delivery of laser energy. The computer starts calculating the temperature based on a combination of ultrasound thermometry, heat equations and the measurements at each thermal sensor. The temperatures can be displayed as a color-coded overlay or isothermal contours such that the temperatures in ablation and safety zones can be computed and monitored in real-time. If the safety zone reaches high temperature threshold T safety   high  before ablation is completed, the computer automatically sends signal to controller for shutting off the laser. The system then waits for temperature to drop below T safety   low , following which it activates the laser again. The process is repeated till temperature reaches at least T ablation   low  inside the ablation zone. 
         [0024]    ablat /ow ion i