Abstract:
When a mechanical frame or gantry is used to move one or more electromagnets about a subject, the pulsed magnetic fields of the magnets need to be triggered, but only when the coil is in an appropriate physical position. Trigger points are established along the movement pathway (e.g., along the support frame) for the electromagnets that trigger the pulsation of the current being supplied to the given electromagnet. Use of the present invention allows firing of a magnetic coil to coordinate with the position of that coil, without need for expensive robotics or computerized motion control.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Patent Application Ser. No. 60/954,018, filed on Aug. 13, 2007, titled “GANTRY AND SWITCHES FOR POSITION-BASED TRIGGERING OF TMS PULSES IN MOVING COILS.” 
     
    
     INCORPORATION BY REFERENCE 
       [0002]    All publications and patent applications mentioned in this specification are herein incorporated by reference in their entirety to the same extent as if each individual publication or patent application was specifically and individually indicated incorporated by reference. 
       FIELD OF THE INVENTION 
       [0003]    The devices and methods described herein relate generally to the triggering of electromagnets used for Transcranial Magnetic Stimulation. 
       BACKGROUND OF THE INVENTION 
       [0004]    Magnetic stimulation of the body, for example repetitive transcranial magnetic stimulation (rTMS), is most efficiently accomplished if magnetic pulses are discharged from the coil while the coil is in the proper position. While it is possible to simply deliver a constant stream of pulses throughout a stereotyped movement of the coil(s), such an approach is likely to fall short on therapeutic effects and measure high on adverse effects. Properly positioned TMS coils ensure that maximal therapeutic effect is delivered, while minimal adverse effects are elicited. Treatments that make use of properly positioned TMS coils include those methods previously described and disclosed by the inventors in U.S. patent application Ser. No. 10/821,807 “Robotic Apparatus of Stereotactic Transcranial Magnetic Stimulation”. 
         [0005]    One means for delivering pulses with a coil in the proper position is to simply deliver a constant stream of pulses, with the assumption that at least some of the time, the coil(s) will be appropriately positioned to induce the desired effects. A disadvantage of this approach is that pulses will likely be also delivered at inappropriate locations, producing unwanted side effects. Consequently, means have been developed by which it can be assured that the coil is pulsed while in the proper physical position. One means for delivering TMS pulses while the coil is in a pre-designated position is a robotic node-based approach, in which a computer instructs a robot regarding the precise position into which an electromagnetic coil is to be moved. Once that position has been achieved, the robot signals the computer that it is now in that position. Only at this point, the computer executes a software function, instructing the TMS device to fire one or more pulses. This method is used by Fox et al. in U.S. Pat. No. 7,087,008. 
         [0006]    Using robotics and computerized motion control is both slow and expensive. It would be desirable to have synchronizing means that did not depend on expensive and/or slow computerized robotic control. It would be desirable to adapt a low-cost, reliable, and high-speed gantry system to enable firing of a magnetic coil when at specific physical positions. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention involves an approach to synchronizing pulse firing at optimized positions that does not depend upon the use of a computer. This method involves moving the coil(s) in a stereotyped pattern, for example on a motorized gantry, and tripping firing signal switches as the coil moves into a series of firing positions. 
         [0008]    In an alternative approach, a mechanical proxy for the coil, for example a timing chain, coordinates timing of firing relative to coil positioning. 
         [0009]    In yet another alternative embodiment, timing between firing and coil positioning is coordinated by the timecode encoding of both the movement of the coil, for example on a gantry, and the triggering of the pulses. With the timing of pulses synchronized to the time code of the gantry, firing will occur only when the coil is in the proper position, provided that all system components operate in a manner that is true to their time base. This approach may be accomplished by electronic means, using a common clock that is attached to both gantry and pulse generation units (or by using multiple synchronized clocks). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  shows an embodiment in which one or more coils orbiting a circular gantry are triggered to fire by a post located at each predetermined station. 
           [0011]      FIG. 2  illustrates the use of optical switches at two stations on a gantry. 
           [0012]      FIG. 3A  shows a coil array that moves back and forth along a semicircular arc, while position of the array is indicated at a point on the gantry remote from the actual coil location. 
           [0013]      FIG. 3B  shows further details of the embodiment outlined in  FIG. 3A   
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]      FIG. 1  illustrates an embodiment involving a circular frame gantry  100 . Positioned around the perimeter of frame  100  are trigger points  110 . These trigger points need not be uniformly distributed around the frame perimeter. Embodiments of trigger the devices  120  to be triggered when trigger points  110  are in proximity as shown in  FIG. 1  may include an electromechanical switch (such as a standard normally-open push-button switch (Jameco Electronics, Belmont, Calif.)) or switches held on a support  130  tripped by physical or non-physical contact with trigger points. Alternative embodiments for the switches may include Hall effect sensors, reed switches, interruption of light beams, interruption of audio beams, microphones where the trigger points emit audio, or radio-frequency devices such as RFID tags, or similar devices. For locations that should not be stimulated (when it is desired to protect underlying tissue), the trigger is not installed or otherwise not enabled such that no magnetic pulse firing at that trajectory will occur. The operator may place the trigger positions manually. The locations may be determined by finding the appropriate positions on a map related to target locations or be calculated using a computer during a pre-procedure treatment planning process. For example, triggers may be positioned or set based on calculated beam trajectories produced by radiosurgery treatment planning software such as MultiPlan® Treatment Planning System (Accuray Inc., Sunnyvale, Calif.). In some variations the triggers are positioned based on treatment plans derived or created as part of a pre-treatment step for the patient. This treatment plan may include one or more maps of the patient&#39;s anatomical (e.g., brain) structures, e.g., using one or more imaging modalities. Configuration of trigger points so as to make them active or inactive when the coil passes by may be conducted during the pre-procedure process by loading the treatment plan into a configuration utility. For example, trigger points that are required to be active in order to deliver energy to a target in accordance with the treatment plan, and which are not to be avoided as per the treatment plan, are configured in the “active” position. In the example shown in  FIG. 1 , coils  140  and  150  travel on circular frame gantry  100 . Any appropriate track or gantry may be used. 
         [0015]    Treatment plans for medical energy delivery systems, including stereotactic radiosurgery, radiotherapy and ultrasound are well known in the art. In general these systems include means for calculated the predicted dose to be delivered to a specified target, while avoiding, or limiting dose to specified structures. Examples include the MultiPlan software by Accuray, Inc., Santa Clara, Calif. 
         [0016]      FIG. 2  illustrates the use of optical switches at two stations on a gantry. Moving Coil Position Unit  210  is composed principally of TMS coil  215  and light-emitting diode (LED)  214 , and is moved along a stereotyped path  260  along a gantry (not shown). LED  214  draws power from voltage supply  211 , as limited by resister  212 , and grounded by ground  213 . Trajectory line  260  shows a portion of the stereotyped path that the coil moves with respect to the gantry (represented by the area below trajectory line  260 ). Within the gantry below trajectory line  260 , two stations—Station A  220  and Station B  230  are located at different physical locations on the gantry. Both Station A  220  and Station B  230  are optical detection switches. For example, in Station A  220 , photodiode  224  receives power from voltage supply  221 , as limited by resister  222 . When Moving Coil Position Unit  210  moves into place on the gantry next to Station A  220 , light from LED  214  strikes photodiode  224 , dropping its resistance and allowing current to flow through to trigger  223 , which transmits a trigger signal via line  224  in order to signal the TMS pulse generator unit  240  to discharge its capacitors  245 . The electrical pulse released from capacitors  245  is sent down cable  247  to TMS coil  215 . As the automated movement of the Moving Coil Position Unit  120  moves away from Station A  220 , light will no longer reach photodetector  223 . Until an appropriate station with the requisite detector is reached, no further triggers will be sent to TMS Pulse Generator  240 . Subsequently, When Moving Coil Position Unit  210  moves into place on the gantry next to Station B  230 , light from LED  214  strikes photodiode  234 , dropping its resistance and allowing current to flow through to trigger  233 , which transmits a trigger signal via line  234  in order to signal the TMS pulse generator unit  240  to discharge its capacitors  245 . The electrical pulse released from capacitors  245  is sent down cable  247  to TMS coil  215 . During the pre-procedure time, automated configuration by the treatment planning system may be accomplished. During this process, specific optical switch positions are designated as “on” or “off” depending the specific target and structures to be avoided in the present treatment plan. An alternative embodiment is to have a single receiver (e.g., light sensor) and multiple transmitters (e.g., light emitters). 
         [0017]      FIG. 3A  shows coil array  300 , which includes coil  301 , coil  302  and coil  303 . In this particular example, each component coil is a double air-core coil. Coil array  300  is able to move as an integral whole, back and forth along a path described by arc  315  and angle of travel  310 , the lateral bounds of which are described by lines  311  and  312 . This semicircular path is designed to accommodate the curvature of the human skull while moving from a dorsal anterior position to a dorsal posterior position. The coil array is arranged in a semicircular arc, while the position of the array is indicated at a point on the gantry that is remote from the actual coil location. Coil array  300  is rigidly affixed to a gantry (not shown in  3 A, but represented as gantry struts  357  and gantry tiller  355  in  FIG. 3B ), which lies substantially along the plane of line  311  and  312 . This gantry is moved back and forth by gantry tiller  305 , which is endowed firing switch markers  306 ,  307  and  308 . These may be, for example, physical features such as protuberances or recesses, or may be optical markers such as line patterns, or optically readable symbols for an optical encoder. 
         [0018]    An alternative embodiment is to move the coil back and forth, rotating in a horizontal pane with the axis of rotation in the center of the skull. 
         [0019]      FIG. 3B  shows further details of the embodiment outlined in  FIG. 3A . A patient  360  is placed between gantry structures including a gantry bar  357 , gantry bar  358  and gantry bar  359  (the companion gantry bar to  359  (equivalent to gantry bar  358  relative to gantry bar  357 ) is not shown), resting his or her chin on chin rest  365 . A coil array including coil  351 , coil  352  and coil  352  are held in a configuration and stabilized by means including connector bar  354 . The array is affixed to gantry bars  357  and  358 , and gantry tiller  355 , preferably using moveable connections, for individualized size and targeting adjustments. Gantry tiller includes firing switch markers  356 . These may be physical features such as protuberances or recesses, or may be optical markers such as line patterns. Gantry tiller  355  is turned back and forth along arc  361  by motor unit  370 , which may be, for example, a servo or step motor. In this manner, coils  351 ,  352  and  353  are moved in an arc over the head of patient  360 . coil array and gantry may be partially or completely covered by enclosure  375 , for enhancement of safety and aesthetic appeal. Enclosure  375  can be air cooled to dissipate heat generated by the coil array. 
         [0020]    As with previous embodiments discussed, prior to use with a specific patient, the operator may place the trigger positions manually. The locations can be determined by finding the appropriate positions on a map related to target locations or be calculated using a computer. For example, a method o treatment may include a pretreatment phase in which a map of the patient&#39;s anatomy is used to help place one or more triggers. The treatment map may include the calculation of the energy to be applied to one or more regions. Further, pre-treatment may include the step of determining the position of one or more triggers to activate stimulation. Finally, the timing or speed of the motion of the treatment device (e.g., the magnet(s) along the gantry) may be determined. The pre-treatment steps may include setting up the device and preparing the patient based on the pre-treatment determinations (the treatment map). After pre-treatment is completed, the patient may be positioned in the device (if they have not already been positioned) and the treatment step may begin, moving the magnet(s) on the gantry, and triggering the application of energy based on the pre-positioned triggers. 
         [0021]    In an alternative embodiment, a given trigger position may be automatically enabled by during an electronic configuration process involving input of a completed treatment plan. Because the treatment plan calls for specific pulse trajectories, the closest matching coil positions may be automatically enabled. This may be accomplished by any appropriate method, including using a computer system to differentially register or ignore specific switch output positions in accordance with the configuration settings. 
         [0022]    As noted previously, a variety of types of trigger device may be used and the invention is not limited by the particular variations specifically discussed herein. 
       REFERENCES 
       [0023]    Traad, Monique. “A Quantitative Positioning Device For Transcranial Magnetic Stimulation”. Engineering In Medicine and biology Society, 1990. Proceedings of the Twelfth Annual International Conference of the IEEE. Philadelphia, Pa., Nov. 1-4, 1990. p. 2246. 
         [0024]    Fox et al., Apparatus and methods for delivery of transcranial magnetic stimulation, U.S. Pat. No. 7,087,008. 
         [0025]    Walsh V, and A. Pascual-Leone, “Transcranial Magnetic Stimulation: A Neurochronometrics of Mind,” MIT Press, Cambridge, Mass. 2003. 
         [0026]    U.S. patent application Ser. No. 10/821,807 “Robotic Apparatus of Stereotactic Transcranial Magnetic Stimulation”. Schneider M B and Mishelevich D J.