Abstract:
A tracking system for stone treatment by extracorporeal shock wave lithotripsy includes a data processing unit, a motion controller, a servo-moving platform, a stone image-processing module, a stone localization module, and a moving-mechanism control module. With the use of the stone-tracking system, the performance of an extracorporeal shock wave lithotriptor can be greatly improved, resulting in less side effect such as tissue damage.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an automatic stone-tracking system for stone treatment. In particular, the present invention relates to an automatic stone-tracking system that may locate the instant position of the stones, allowing subsequent accurate fragmentation of the stones without the risk of inadvertent injury to the tissues of the patient. 
   2. Description of the Related Art 
   In the recent twenty years, the extracorporeal shock wave lithotripsy (ESWL) has provided a new technique for the treatment of stones by a non-invasive fashion of surgery rather than a traditional invasive fashion. Although the ESWL has been widely used by urologists, the efficiency for stone fragmentation, estimated from the stone-free rate, is approximately 60-70% under urologist&#39;s monitoring during treatment. This is due to the calculus movement caused by patient&#39;s respiration during treatment, resulting in inaccurate targeting of shock waves. Up to date, there is no lithotriptor with highly accurate stone targeting in the international market of lithtriptors. 
   SUMMARY OF THE INVENTION 
   An objective of the present invention is to provide a real-time, automatic tracking system for stones so that the instant stone position of a patient can be localized and controlled by a lithotriptor. 
   A stone-tracking system in accordance with the present invention comprises a servo-motion unit, an ultrasound scanner, a motion controller, and a data processing unit. The servo-motion unit comprises a motion platform including an arc track, and a shock-wave reflector is mounted on the arc track. The ultrasound system comprises an ultrasound scanning probe mounted on the motion platform for localizing a position of a stone of a patient at any instant and sending information of the stone position. The motion controller is connected to the servo-motion unit for controlling the servo-motion unit. The data processing unit is connected to the ultrasound system and the motion controller. The data processing unit receives the information of the stone position from the ultrasound system and sends a signal to the motion controller in response to the information of the stone position to cause relative movement between the motion platform and a bed on which the patient lies until focus of the shock-wave reflector is coincident with the stone position. 
   The performance of the stone-tracking system was found to be very efficient on stone fragmentation. 
   Other objectives, advantages, and novel features of the invention will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a block diagram of a stone-tracking system in accordance with the present invention. 
       FIG. 2  is a schematic view of a servo-control system of the stone-tracking system used for stone treatment. 
       FIG. 3  is a schematic view illustrating stone displacement on the plane of an ultrasound stone image. 
       FIG. 4  is a schematic view illustrating the stone position, an ultrasound scanning probe, a shock-wave reflector, and a moving platform. 
       FIG. 5  is a schematic flow chart illustrating stone tracking for lithortripsy. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , an automatic stone-tracking system in accordance with the present invention comprises a data processing unit  1 , an ultrasound system  2 , a motion controller  3 , and a servo motion unit  4 . The term “stone” referred to herein means kidney calculi, ureteral calculi, bladder calculi, or any other calculi formed in a human body. 
   In this embodiment, the data processing unit  1  is a computer that is installed with a program  11  (module) of stone image processing, a program  12  (module) of stone localization, and a program  13  (module) for controlling a motion platform  41 . The computer  1  is connected with the ultrasound scanner  2  and the motion platform  41 . 
   The ultrasound system  2  includes an ultrasound scanning probe  21  for localizing the stone position at any instant. The stone images are transmitted to the computer at a rate of about 10 images per second. Consequently, the stone displacements from the second focus of the shock-wave reflector  42 , (U, V), due to patient&#39;s respiration are computed, as shown in FIG.  3 . The first focus means the geometrical position of the shock wave reflector where the shock waves are produced. The second focus is the location where shock waves are focused to produce a high pressure enough for stone fragmentation. The term “focus” is referred herein as the geometrical position of the second focus of the ellipsoidal shock-wave reflector  42 . The symbol θ denotes an inclination angle between the image plane and the YZ plane (X=0). The displacements of the motion platform  41  are related with the stone displacements by the following equation:
 
(Δ X,ΔY,ΔZ )=( U  sin θ, V,U  cos θ)
 
The displacements (ΔX,ΔY,ΔZ) will be transmitted to the motion controller  3 . With the computed displacements (ΔX,ΔY,ΔZ) the motion controller  3  commands three drivers  47  to activate three servomotors  43  which subsequently move the motion platform  41 . Thus a moving stone can be continuously localized to be within an effective pressure region for stone fragmentation.
 
   In this embodiment, the motion controller  3  is an electronic board that is connected with three sets of motors  43  (preferably servomotors) and drivers  47  equipped with encoders  48  and three reducers  46 . By using the control method of proportional integral and derivative, the motion controller  3  analyzes the motor locations and speeds from the encoders  48 , and motivates the motors  43  and the reducers  46 . 
   The servo motion unit  4  consists of a motion platform  41  with three-axis motion, three AC servomotors  43  with encoders  44 , three reducers  46 , and three insulators  45  (optionally). The servomotors  43 , reducers  44 , and insulators  46  are connected together. These three servomotors  43  are installed on the motion platform  41  and cause the motion platform  41  to do three-dimensional motion. The travel of each of the servomotors  43  is fed back to the motion controller  3 . Each reducer  44  is provided to reduce the speed of the associated servomotors  43 . Each insulator  45  is preferably Bakelite™ for isolating the associated servomotors  43  from the ground to thereby avoid interference and damage resulting from high voltage. 
   Lying on the motion platform  41  is the arc track  40  with a radius. The shock-wave reflector  42  and the ultrasound scanning probe  21  are mounted on the arc track  40 . Since the arc center is the second focus of the shock-wave reflector  42 , and always lies on the ultrasound image plane, a doctor (urologist) can judge whether the moving stone lies on the second focus by using the ultrasound images. 
   The stone localization module  12  is a computer program that computes the data of the instant stone location transmitted from the ultrasound system  2 . The stone localization module  12  (program) provides the instant stone displacements from the second focus of the shock-wave reflector  42  for the motion controller  3 . The stone localization module  12  consists of a transformation between the stone displacements on the image plane  41  and the displacements of the motion platform on a reference frame. 
   The stone image processing module  11  is a computer program that can determine the stone size and its center, and record the stone trajectory. The stone image processing module  11  (program) is developed by an automatic gray level threshold method that is based on the principle of gray level histogram entropy. The threshold is applied in a pre-selected region of interest that moves to follow the stone in real time. 
   The moving-mechanism control module  13  is a computer program that controls the motion of the motion platform  41  that moves in accordance to the stone displacements. The moving-mechanism control module  13  is used for the motion controller  3 . 
   In an embodiment of the invention, the focus of the shock-wave reflector is moved to the stone position by means of moving the motion platform  41  when the stone is displaced as a result of respiration of the patient. In an alternative embodiment, the stone is moved to the focus of the shock-wave reflector  42  by means of moving the bed when the stone is displaced as a result of respiration of the patient on the bed. 
   It was verified that the performance of the improved lithotriptor with the stone-tracking system based on the efficiency of stone fragmentation. An in vitro study was made to verify the designed stone tracking system. The result of stone fragmentation with and without tracking conditions is shown in Table 1. It was found that the efficiency of lithotriptor with the stone-tracking system in accordance with the present invention is increased to 86% from 45% which was obtained at the conditions of no stone tracking and no doctor&#39;s monitoring. 
   Since the designed stone-tracking system is of real time, the second focus of the shock-wave reflector  42  can be instantly adjusted to the stone position during stone treatment. Consequently the patient&#39;s calculus can be accurately struck and fragmented by shock waves, resulting in less number of shock waves, less damage of the tissues in the vicinity of the stone, and less treatment time. 
   The following Table 1 shows comparison of efficiency of stone fragmentation with and without stone tracking. 
   
     
       
             
             
             
           
             
             
             
           
         
             
                 
             
             
               Sample 
               Without tracking (%) 
               With tracking (%) 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               1 
               36.9 
               84.5 
             
             
               2 
               63.9 
               93.1 
             
             
               3 
               38.3 
               84.0 
             
             
               4 
               46.1 
               82.1 
             
             
               5 
               50.4 
               88.9 
             
             
               6 
               35.2 
               82.1 
             
             
               7 
               52.6 
               81.7 
             
             
               8 
               17.4 
               86.0 
             
             
               9 
               37.6 
               91.6 
             
             
               10 
               48.4 
               70.6 
             
             
               11 
               39.8 
               83.7 
             
             
               12 
               58.8 
               98.9 
             
             
               13 
               60.7 
               85.1 
             
             
               Average ± SD 
               45.1 ± 12.7 
               85.6 ± 6.8 
             
             
                 
             
           
        
       
     
   
   The efficiency of stone fragmentation is defined as the ratio of the number of shock waves needed for fragmenting a fixed stone to the number of shock waves for a moving stone at the condition of requiring fragment sizes being less than 2 mm. 
   Although the invention has been explained in relation to its preferred embodiment, it is to be understood that many other possible modifications and variations can be made without departing from the scope of the invention as hereinafter claimed.