Abstract:
In vivo hyperthermia treatment of a target tissue can include imaging the target tissue with a magnetic resonance imaging (MRI) system, positioning a hyperthermia treatment probe in or proximate to the target tissue based on the imaging, and heating the target tissue by the probe. During the heating, changes in temperature of a volume of tissue that includes the target tissue can be monitored with the MRI system to determine an amount of the heating applied to the target tissue, and the heating can be terminated when the amount of the heating reaches a predetermined amount.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of and claims the benefit of priority under 35 U.S.C. §120 from U.S. application Ser. No. 13/601,134, filed Aug. 31, 2012, which is a continuation of U.S. application Ser. No. 11/957,876, filed Dec. 17, 2007, now U.S. Pat. No. 8,256,430, which is a divisional of U.S. application Ser. No. 10/701,834, filed Nov. 5, 2003, now U.S. Pat. No. 7,344,529, which is a continuation-in-part of U.S. application Ser. No. 10/014,846, filed Dec. 14, 2001, now U.S. Pat. No. 7,167,741, the entire contents of each of which is incorporated herein by reference, and which is a continuation-in-part of International Application No. PCT/CA01/00905, filed Jun. 15, 2001, which claims priority to U.S. application Ser. No. 09/593,699, filed Jun. 15, 2000, now U.S. Pat. No. 6,418,337. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The treatment of tumors by hyperthermia is known. In one known process, tumors and other lesions to be treated can be heated above a predetermined temperature of the order of 55 C so as to coagulate the portion of tissue heated. The temperature range is preferably of the order of 55 to 65 C and does not reach temperatures that can cause carbonization or ablation of the tissue. 
         [0003]    One technique for effecting the heating is to insert into the lesion concerned an optical fiber, which has at its inserted end an element that redirects laser light from an exterior source in a direction generally at right angles to the length of the fiber. The energy from the laser thus extends into the tissue surrounding the end or tip and effects heating. The energy is directed in a beam confined to a relatively shallow angle so that, as the fiber is rotated, the beam also rotates around the axis of the fiber to effect heating of different parts of the lesion at positions around the fiber. The fiber can thus be moved longitudinally and rotated to effect heating of the lesion over the full volume of the lesion with the intention of heating the lesion to the required temperature without significantly affecting tissue surrounding the lesion. We define the term “lesion” as used herein to mean any pathologic change in the tissue or organs of a mammalian subject including, but not limited to, tumors, aortic or other aneurysms, artery and vein malformations such as thrombosis, hemorrhages, and embolisms. 
         [0004]    At this time the fiber is controlled and manipulated by a surgeon with little or no guidance apart from the knowledge of the surgeon of the anatomy of the patient and the location of the lesion. It is difficult therefore for the surgeon to effect a controlled heating which heats the entire lesion while minimizing damage to surrounding tissue. 
         [0005]    It is of course well known that the location of tumors and other lesions to be excised can be determined by imaging using a magnetic resonance imaging system. The imaging system thus generates for the surgeon a location of the lesion to be excised but there is no system available which allows the surgeon to use the imaging system to control the heating effect. In most cases it is necessary to remove the patient from the imaging system before the treatment commences and that movement together with the partial excision or coagulation of some of the tissue can significantly change the location of the lesion to be excised thus eliminating any possibility for controlled accuracy. 
         [0006]    It is also known that magnetic resonance imaging systems can be used by modification of the imaging sequences to determine the temperature of tissue within the image and to determine changes in that temperature over time. 
         [0007]    U.S. Pat. No. 4,914,608 (LeBiahan) assigned to U.S. Department of Health and Human Services issued Apr. 3, 1990 discloses a method for determining temperature in tissue. 
         [0008]    U.S. Pat. No. 5,284,144 (Delannoy) also assigned to U.S. Department of Health and Human Services and issued Feb. 8, 1994 discloses an apparatus for hyperthermia treatment of cancer in which an external non-invasive heating system is mounted within the coil of a magnetic resonance imaging system. The disclosure is speculative and relates to initial experimentation concerning the viability of MRI measurement of temperature in conjunction with an external heating system. The disclosure of the patent has not led to a commercially viable hyperthermic treatment system. 
         [0009]    U.S. Pat. Nos. 5,368,031 and 5,291,890 assigned to General Electric relate to an MRI controlled heating system in which a point source of heat generates a predetermined heat distribution which is then monitored to ensure that the actual heat distribution follows the predicted heat distribution to obtain an overall heating of the area to be heated. Again this patented arrangement has not led to a commercially viable hyperthermia surgical system. 
         [0010]    An earlier U.S. Pat. No. 4,671,254 (Fair) assigned to Memorial Hospital for Cancer and Allied Diseases and issued Jun. 9, 1987 discloses a method for a non surgical treatment of tumors in which the tumor is subjected to shock waves. This does not use a monitoring system to monitor and control the effect. 
         [0011]    U.S. Pat. No. 5,823,941 (Shaunnessey) not assigned issued Oct. 20, 1998 discloses a specially modified endoscope which designed to support an optical fiber which emits light energy and is moved longitudinally and rotates angularly about its axis to direct the energy. The device is used for excising tumors and the energy is arranged to be sufficient to effect vaporization of the tissue to be excised with the gas thus formed being removed by suction through the endoscope. An image of the tumor is obtained by MRI and this is used to program a path of movement of the fiber to be taken during the operation. There is no feedback during the procedure to control the movement and the operation is wholly dependent upon the initial analysis. This arrangement has not achieved commercial or medical success. 
         [0012]    U.S. Pat. No. 5,454,807 (Lennox) assigned to Boston Scientific Corporation issued Oct. 3, 1995 discloses a device for use in irradiating a tumor with light energy from an optical fiber in which in conjunction with a cooling fluid which is supplied through a conduit with the fiber to apply surface cooling and prevent surface damage while allowing increased levels of energy to be applied to deeper tissues. This arrangement however provides no feedback control of the heating effect. 
         [0013]    U.S. Pat. No. 5,785,704 (Bille) assigned to MRC Systems GmbH issued Jul. 28, 1996 discloses a particular arrangement of laser beam and lens for use in irradiation of brain tumors but does not disclose methods of feedback control of the energy. This arrangement uses high speed pulsed laser energy for a photo-disruption effect. 
         [0014]    Kahn, et al. in Journal of Computer Assisted Tomography 18 (4):519-532, July/August 1994; Kahn, et al. in Journal of Magnetic Resonance Imaging 8: 160-164, 1998; and Vogl, et al. in Radiology 209: 381-385, 1998 all disclose a method of application of heat energy from a laser through a fiber to a tumor where the temperature at the periphery of the tumor is monitored during the application of the energy by MRI. However none of these papers describes an arrangement in which the energy is controlled by feedback from the monitoring arrangement. The paper of Vogl also discloses a cooling system supplied commercially by Somatex of Berlin Germany for cooling the tissues at the probe end. The system is formed by an inner tube through which the fiber passes mounted within an outer tube arrangement in which cooling fluid is passed between the two tubes and inside the inner tube in a continuous stream. 
       BRIEF SUMMARY OF THE INVENTION 
       [0015]    It is one object of the present invention, therefore, to provide an improved method and apparatus for effecting treatment of a patient by hyperthermia. 
         [0016]    According to a first aspect of the invention there is provided a method for effecting treatment in a patient comprising:
   Identifying a volume in the patient the whole of which volume is to be heated to a required temperature, the volume being defined by a peripheral surface of the volume;   providing a heat source and applying heat to the volume within the patient by;   providing the heat source on an invasive probe having a longitudinal axis and an end;   inserting the end of the probe into the volume;   arranging the probe to cause directing of heat from the end in a direction at an angle to the longitudinal axis such that a heating effect of the probe lies in a disk surrounding the axis;   arranging the direction of the heat so as to define a heating zone which forms a limited angular orientation of heating within the disk such that, as the probe is rotated, the probe causes heating of different angular segments of the volume within the disk;   with the probe at a fixed axial position, rotating the probe about the axis so that the heating zone lies in a selected segment;   wherein the application of heat by the probe to the selected segment causes heat to be transferred from the segment into parts of the volume outside the segment surrounding the end of the probe;   and applying cooling to the end of the probe so as to extract heat from the parts surrounding the probe by conduction of heat therefrom.   
 
         [0026]    Cooling of the probe may be optional. For example, when utilizing focused ultrasound and e-beam energy, cooling may not be as relevant or may not be required. With ultrasound energy, fluid may be used as the conduction medium as more specifically describe below. When cooling is used, preferably the amount of cooling to the probe is arranged relative to the heating such that the parts of the volume surrounding the end of the probe are cooled sufficiently to cause a net heating effect by which substantially only the segment of the heating zone is heated to the required temperature and the parts outside the segment are not heated to the required temperature. This is preferably arranged so that the cooling maintains the parts outside the segment below a temperature sufficient to cause coagulation of the tissues therein. Thus when the probe is rotated to take up a new angle within a new segment, the tissue in the new segment is not in a condition by pre-heating that would interfere with the transmission and diffusion of the heat to that segment. 
         [0027]    The arrangement of the present invention, that is the method defined above or the method or probe defined hereinafter, can be used on a rigid probe which is intended to be inserted in a straight line into a specific location in the body of the patient, or can be used on a flexible probe which can be guided in movement through a part of the body such as a vein or artery to a required location. 
         [0028]    While the most likely and currently most suitable energy source is that of laser light, the arrangements described and defined herein can also be used with other energy sources of the type which can be directed at an angle from the axis of the probe through which they are supplied such as electron beams or ultrasound generators. 
         [0029]    In one exemplary arrangement, the above method can be used with MRI real time control of the surgery by which a non-invasive detection system, such as MR1, is operated to generate a series of output signals over a period of time representative of temperature in the patient as the temperature of the patient changes during that time. The output signals are used to monitor at least one temperature of the volume as the temperature changes over the period of time. The application of heat to the probe is then controlled in response to the changes in temperature wherein the temperature at the peripheral surface of the volume is monitored and a measure of the temperature at a location on the peripheral surface of the volume is used as the determining factor as to when to halt heating by the probe to the location. However the cooling effect can be used without the MRI monitoring to provide an enhanced system in which the whole of the volume required can be heated to the required temperature. 
         [0030]    In the method in which temperature is monitored, the determination as to when to halt heating by the probe to the location is made based upon the temperature at the peripheral surface of the volume, with the exception that temperatures within the volume may be monitored to ensure that no serious or dangerous over-temperature occurs within the volume due to unexpected or unusual conditions. Thus any such over-temperature may be detected and used to halt further treatment or to trigger an alarm to the doctor for analysis of the conditions to be undertaken. 
         [0031]    When used as a rigid probe for treatment within a body part such as the brain or liver, the probe itself may be sufficiently rigid and strong to accommodate the forces involved and not require the use of a cannula or, alternatively, there may be provided a cannula through which the probe is inserted, the cannula having an end which is moved to a position immediately adjacent but outside the volume and the probe having a rigid end portion projecting from the end of the cannula into the volume. When used as a non-rigid probe for treatment within a body part such as the brain or liver, the probe itself may require the use of a cannula through which the probe is inserted as described herein. 
         [0032]    In one embodiment of the present invention, the heat source comprises a laser, an optical fiber for communicating light from the laser and a light-directing element at an end of the fiber for directing the light from the laser to the predetermined direction relative to the fiber forming the limited angular orientation within the disk. 
         [0033]    In accordance with one embodiment of the present invention which provides the necessary level of cooling in a readily controllable process, the end of the probe is cooled by liquid-to-liquid, liquid-to-gas and gas-to-gas cooling by:
   providing on the probe a supply duct for a cooling fluid extending from a supply to the end of the probe;   providing an expansion zone of reduced pressure at the end of the probe so as to cause the cooling fluid to expand as a gas thus generating a cooling effect;   and providing on the probe a return duct for return of the expanded gas from the end of the probe.   
 
         [0037]    In this arrangement, the return duct is preferably of larger cross-sectional area than the supply duct and the supply duct includes a restricting orifice at its end where the return duct is larger in cross-sectional area by a factor of the order of 200 times larger than the orifice of the supply duct. 
         [0038]    Preferably where the probe comprises a tube the supply duct is arranged inside the tube and the return duct is defined by an inside surface of the tube. 
         [0039]    In this arrangement, the supply duct is attached as tube to an inside surface of the tube and the fiber itself is attached also to the inside. 
         [0040]    In this arrangement, the orifice is provided by a restricting valve or neck in the supply duct immediately upstream of the expansion chamber at the end of the probe. 
         [0041]    Where the fiber has a chamfered end of the fiber it may include a reflecting coating thereon for directing the light energy to the side. The arrangement of the chamfered end can have the advantage or feature that the chamfered end is located in the gas rather than being wetted by cooling fluid which can, when there is no coating, interfere with the reflective properties of the coating and thus with the proper control and direction of the light. 
         [0042]    In this arrangement, the chamfered end can be arranged directly at 45 degrees to provide a light direction lying wholly in a radial plane at right angles to the axis of the fiber. The chamfered end may carry a coating arranged to reflect light at two different wavelengths. 
         [0043]    In order to accurately control the cooling effect to maintain the net heating required, there is preferably provided a temperature sensor at the end of the probe, which may be located inside the tube with the connection therefor passing through the probe to the control system outside the probe. 
         [0044]    Preferably the temperature at the end of the probe is controlled by varying the pressure in the fluid as supplied through the supply duct. This system can allow the temperature to be maintained between about zero and minus 20 degrees Celsius, which provides the required level of cooling to the probe for the net heating effect. 
         [0045]    According to a second aspect of the invention there is provided a method for effecting treatment in a patient comprising:
   identifying a volume in the patient to be heated to a required temperature;   providing a heat source for applying heat to the volume within the patient,   providing a probe mounting the heat source allowing invasive insertion of an end of the probe into the patient,   providing a position control system for moving the end of the probe to a required position within the patient;   inserting the end of the probe into the volume;   providing on the probe a supply duct for a cooling fluid extending from a supply to the end of the probe;   providing an expansion zone of reduced pressure at the end of the probe so as to cause the cooling fluid to expand as a gas thus generating a cooling effect;   and providing on the probe a return duct for return of the expanded gas from the end of the probe.   
 
         [0054]    According to a third aspect of the invention there is provided a probe for use in effecting treatment in a patient comprising:
   a heat source for applying heat to a volume within the patient,   a probe body mounting the heat source thereon for allowing invasive insertion of an end of the probe into the patient,   a supply duct on the probe body for a cooling fluid extending from a supply to the end of the probe;   the probe body being arranged to provide an expansion zone of reduced pressure at the end of the probe body so as to cause the cooling fluid to expand as a gas thus generating a cooling effect;   and a return duct on the probe body for return of the expanded gas from the end of the probe.   
 
         [0060]    According to a fourth embodiment of the present invention there is provided a method of applying heat to tissue in vivo comprising:
   identifying a quantity of tissue as a target;   inserting an elongate transmitting medium percutaneously and feeding said elongate transmitting medium toward said target until a distal end of said elongate transmitting medium is operationally proximate said target;   applying energy to said target by sending energy through said elongate transmitting medium, said energy exiting said distal end and heating said target;   monitoring said energy application to ensure surrounding non-targeted tissue is not damaged by heat;   determining whether the entire targeted area has been heated;   if necessary, translating said elongate transmitting medium to an unheated area of said target;   applying energy to said unheated area of said target.   
 
         [0068]    The step of identifying a quantity of tissue as a target may be accomplished by analyzing magnetic resonance images and mapping out the extents of a tumor imaged thereby; or by conducting a body contouring analysis to determine areas of fatty tissue to be removed; or by analyzing magnetic resonance images to locate a lesion imaged thereby. 
         [0069]    The step of inserting an elongate transmitting medium percutaneously and feeding said elongate transmitting medium toward said target until a distal end of said elongate transmitting medium is operationally proximate said target may be accomplished by:
   determining a safest straight path between the skull and the target;   forming a hole in the skull;   inserting said elongate transmitting medium through said hole toward said target until said distal end of said elongate transmitting medium is operationally proximate said target   
 
         [0073]    Alternatively, the step of inserting an elongate transmitting medium percutaneously may include the step of inserting a cannula into said hole until a distal end of said cannula is operably proximate said target;
   securing the cannula relative the skull;   and inserting said elongate transmitting medium through said cannula toward said target until said distal end of said elongate transmitting medium is operationally proximate said target;   or by:   inserting said elongate transmitting medium in an artery;   feeding said elongate transmitting medium through the artery until a distal end of the elongate transmitting medium is operationally proximate a lesion or other target;   or by percutaneously inserting the elongate transmitting medium proximate an area of fat targeted for heat treatment.   
 
         [0080]    The step of applying energy to the target through the elongate transmitting medium may be accomplished by sending light, laser, collimated, or non-collimated, through an optical fiber. More specifically, this step may be accomplished by:
   a) causing said energy to exit said distal end at an angle, greater than zero, to a longitudinal axis of the elongate transmitting medium;   b) rotating said elongate transmitting medium around said longitudinal axis, thereby creating a shaped area of treated tissue;   c) advancing said elongate transmitting medium;   d) repeating steps a)-c) until the entire target has been heated.   
 
         [0085]    Step a) may be accomplished by causing said energy to exit said distal end approximately perpendicularly to said longitudinal axis of the elongate transmitting medium such that performing step b) results in a shaped area of treated tissue that is disc-shaped; or by causing said energy to exit said distal end at an angle other than perpendicular to said longitudinal axis of the elongate transmitting medium such that performing step b) results in a shaped area of treated tissue that is cone-shaped. 
         [0086]    Alternatively, the step of applying energy to said target by sending energy through said elongate transmitting medium, said energy exiting said distal end and heating said target, may be accomplished by allowing said energy to exit said distal end along a longitudinal axis of the elongate transmitting medium. 
         [0087]    The step of monitoring said energy application to ensure surrounding non-targeted tissue is not damaged by heat may be accomplished by taking temperature readings on non-targeted tissue immediately adjacent said targeted tissue; or by cycling cooling fluid to and from the distal end of the elongate transmitting medium as necessary to prevent damaging said surrounding nontargeted tissue. 
         [0088]    A fifth embodiment of the present invention provides a method of destroying unwanted fat cells comprising:
   a) identifying fat cells to be destroyed thereby defining a target that is a volume of fat cells;   b) percutaneously inserting a probe having a distal end capable emitting energy;   c) positioning said probe such that said distal end is operationally proximate said target;   d) emitting energy from the distal end of the probe sufficient to destroy fat cells;   e) moving the distal end of the probe through the volume of fat cells and emitting energy from the distal end, either successively or simultaneously, until the targeted volume of fat cells has been destroyed.   
 
         [0094]    This method may also include cooling the distal end of the probe to prevent overheating cells that are not included in the volume of fat cells. 
         [0095]    A sixth embodiment of the present invention provides a method of coagulating blood in a vascular lesion that includes
   a) identifying a vascular lesion;   b) percutaneously inserting a probe having a distal end capable emitting energy;   c) positioning said probe such that said distal end is operationally proximate said lesion;   d) emitting energy from the distal end of the probe sufficient to coagulate said vascular lesion   wherein said coagulation results in cessation or reduction of flow to said vascular lesion.   
 
         [0101]    Step b) may include forming an entry hole in the skull of the patient, fastening a cannula to the entry hole that is constructed and arranged to create an insertion path for a rigid or nonrigid probe that is aimed directly at the lesion, and inserting the probe into the cannula. 
         [0102]    A seventh embodiment of the present invention provides a method of repairing, reconstruction or removing tissue comprising:
   a) identifying a target that comprises healthy tissue to be repaired, reconstructed or removed;   b) percutaneously inserting a probe having a distal end capable emitting energy;   c) positioning said probe such that said distal end is operationally proximate said target;   d) emitting energy from the distal end of the probe sufficient to repair, reconstruct or remove said target;   e) moving the distal end of the probe through the target tissue and emitting energy from the distal end, either successively or simultaneously, until the targeted volume has been repaired, reconstructed or removed.   
 
         [0108]    This method may also include cooling the distal end of the probe to prevent overheating cells that are not included in the targeted tissue. 
         [0109]    The method may also include targeting healthy tissue or targeting scar tissue. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0110]      FIG. 1  is a schematic illustration of an apparatus for effecting MRI guided laser treatment according to the present invention. 
           [0111]      FIG. 2  is a schematic illustration of the apparatus of  FIG. 1  on an enlarged scale and showing the emission of laser energy into the brain of a patient. 
           [0112]      FIG. 3  is a side elevation of the laser probe of the apparatus of  FIG. 1 . 
           [0113]      FIG. 4  is an end elevation of the laser probe of the apparatus of  FIG. 1 . 
           [0114]      FIG. 5  is a cross-sectional view of the laser probe and drive motor therefor of the apparatus of  FIG. 1 . 
           [0115]      FIG. 6  is an exploded view of the drive motor of the apparatus of  FIG. 1 . 
           [0116]      FIG. 7  is a schematic illustration of the shielding of the apparatus of  FIG. 1 . 
           [0117]      FIG. 8  is a schematic illustration of the effect of the apparatus on a tumor or other lesion to be coagulated. 
           [0118]      FIG. 9  is a longitudinal cross-sectional view through an alternative form of a probe that provides a flow of cooling fluid to the end of the probe for cooling the surrounding tissue. 
           [0119]      FIG. 10  is a cross-sectional view along the lines  10 - 10  of  FIG. 9 . 
           [0120]      FIG. 11  is a longitudinal cross-sectional view through a further alternative form of probe which provides a flow of cooling fluid to the end of the probe for cooling the surrounding tissue. 
           [0121]      FIG. 12  is a cross-sectional view along the lines  12 - 12  of  FIG. 11 . 
           [0122]      FIG. 13  is a photograph of a cross-section of a tissue sample that has been heated in three separate segments showing the absence of heating outside the segments. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0123]    In  FIG. 1  is shown schematically an apparatus for carrying out MRI controlled laser treatment. The apparatus comprises a magnetic resonance imaging system including a magnet  10  provided within a shielded room  11 . The magnet  10  can be of any suitable construction and many different magnet arrangements are available from different manufacturers. The magnet includes field coils for generating variations in the magnetic field which are not shown since these are well known to one skilled in the art together with a radio frequency antenna coil which receives signals from the sample in this case indicated as a human patient  13 . 
         [0124]    The patient  13  rests upon a patient support table  14  on which the patient is supported and constrained against movement for the operative procedure. The fields of the magnet are controlled on an input control line  15  and the output from the antenna coil is provided on an output line  16  both of which communicate through a surgeon interface  17  to the conventional MRI control console  18 . The MRI console and the magnet are shown only schematically since these are well known to one skilled in the art and available from a number of different manufacturers. 
         [0125]    The apparatus further includes a laser treatment system including an optical fiber assembly  20  that transmits heat energy in the form of light from a laser  21  mounted outside the room  11 . The fiber assembly  20  extends from the laser  21  to a terminus  36  ( FIG. 2 ), from which the energy escapes into the relevant part of the patient  13  as discussed hereinafter. The position of the fiber assembly  20  within the patient  13  and the orientation of the fiber are controlled by a drive motor  22  supported in fixed adjustable position on a stereotaxic frame  23 . The motor communicates through a control line  24  to a device controller  25 . In general the device controller  25  receives information from the MRI console  18  and from position detectors of the motor  22  and uses this information to control the motor  22  and to operate a power output from the laser  21 , thereby controlling the position and amount of heat energy applied to the part within the body of the patient  13 . 
         [0126]    In  FIG. 2  is shown on a larger scale the patient table  14 . The stereotaxic frame  23  is attached to the table  14  and extends over the head  26  of the patient  13 . The frame  23  is shown schematically and suitable details will be well known to one skilled in the art, but carries the motor  22  in a position on the frame  23  through the use of a motor bracket  27 . The position of the motor  22  on the frame  23  remains fixed during the procedure but can be adjusted in the arcuate direction  28  around the arch of the frame  23 . The frame  23  can also be adjusted forwardly and rearwardly on the table  14 . The bracket  27  also allows rotation of the motor  22  about a point  30  within the frame  23  so that the direction of the fiber assembly  20  projecting forwardly from the motor  22  can be changed relative to the frame.  23 . 
         [0127]    Referring now to  FIG. 3 , the basic components of the fiber assembly  20  of the apparatus are shown. The fiber assembly  20  includes a rigid cannula  31  surrounding a glass fiber element  35 , and arranged to allow sliding and rotational movement of the fiber element  35  within the cannula  31  while holding the fiber element  35  in a direction axial of the cannula.  31 . The cannula  31  is formed of a suitable rigid MRI compatible material such as ceramic so that it is stiff and resistant to bending and has sufficient strength to allow the surgeon to insert the cannula  31  into the required location within the body part of the patient.  13 . 
         [0128]    In the arrangement as shown, the apparatus is arranged for operating upon a tumor  32  ( FIG. 2 ) within the brain  33  of the patient.  13 . The surgeon therefore creates an opening  34  in the skull of the patient  13  and directs the cannula  31 , in the absence of the rest of the fiber assembly  20 , through the opening  34  to the front edge of the tumor  32 . The cannula  31 , once in place, will act as a guide for the remainder of the fiber assembly  20 . 
         [0129]    The position of the tumor  32  is determined in an initial set of MRI experiments using conventional surgical and an analytical techniques to define the boundaries, that is a closed surface within the volume of the brain  33  which constitutes the extremities of the tumor  32 . The surgical analysis by which the surgeon determines exactly which portions of the material of the patient  13  should be removed is not a part of this invention except to say that conventional surgical techniques are available to one skilled in the art to enable an analysis to be carried out to define the closed surface. 
         [0130]    The angle of insertion of the cannula  31  is selected to best avoid possible areas of the patient  13  that should not be penetrated, such as major blood vessels, and also so the cannula  31  is pointed toward a center of the tumor  32 . 
         [0131]    The fiber assembly  20  further includes an actual glass fiber element  35 , which has an inlet end (not shown) at the laser  21  and a terminus  36 . At the terminus  36  is provided a reflector or prism, which directs the laser energy in a beam  37  to one side of the terminus  36 . Thus the beam  37  is directed substantially at right angles to the length of the fiber and over a small angle around the axis of the fiber. The beam  37  forms a cone having a cone angle of the order of 12 to 15 degrees. Such fibers are commercially available including the reflector or prism for directing the light at right angles to the length of the fiber. 
         [0132]    The fiber element  35  is encased to allow the fiber element  35  to be manipulated in the motor  22 . Around the fiber element  35  is a sleeve  38  including a first end portion  39  and a longer second portion  40 . The end portion  39  encloses the terminus  36 , which is spaced from a tip  41  of the end portion  39 . The end portion  39  has a length on the order of 7 to 11 cm. The second portion  40  is on the order of 48 to 77 cm in length and extends from a forward end  141  through to a rear end  42 . The first end portion  39  is formed of a rigid material such as glass. The second portion  40  is formed of a stiff material which is less brittle than glass and yet maintains bending and torsional stiffness of the fiber element  35  so that forces can be applied to the second portion  40  to move the terminus  36  of the fiber element  35  to a required position within the tumor  32 . The second portion  40  is formed of a material such as fiber-reinforced plastics. 
         [0133]    The two portions  39  and  40  are bonded together to form an integral structure of common or constant diameter selected as a sliding fit through the cannula  31 . The first end portion  39  and the cannula  31  are sized so that it the first end portion  39  can extend from the distal end of the cannula  31  and reach a distal end of the tumor  32 . An average tumor might have a diameter of the order of 0.5 to 5.0 cm so that the above length of the forward portion is sufficient to extend through the full diameter of the tumor  32  while leaving a portion of the order of 1.25 cm within the end of the cannula  31 . In this way, the substantially rigid first end portion  39  remains relatively coaxial with the cannula  31 . 
         [0134]    The second portion  40  has attached to it a polygonal or non-circular section  44  and a stop section  45 , both of which act as attachment points for rotational and longitudinal sections, respectively. Thus the polygonal section  44  is arranged to co-operate with a drive member that acts to rotate the second portion  40  and therefore the fiber element  35 . The stop section  45  is arranged to co-operate with a longitudinally movable drive element that moves the second portion  40 , and therefore the fiber element  35 , longitudinally. In this way the terminus  36  can be moved from an initial position, just beyond the outer end of the cannula  31 , outwardly into the body of the tumor  32  until the tip reaches the far end of the tumor  32 . In addition the terminus  36  can be rotated around the axis of the fiber element  35  so that heat energy can be applied at selected angles around the axis. By selectively controlling the longitudinal movement and rotation of the terminus  36 , therefore, heat energy can be applied throughout a cylindrical volume extending from the end of the cannula  31  along the axis of the cannula  31  away from the end of the cannula.  31 . In addition by controlling the amount of heat energy applied at any longitudinal position and angular orientation, the heat energy can be caused to extend to required depths away from the axis of the cannula  31  so as to effect heating of the body part of the patient  13  over a selected volume with the intention of matching the volume of the tumor  32  out to the predetermined closed surface area defining the boundary of the tumor  32 . 
         [0135]    As shown in  FIG. 4 , the non-circular cross-section of section  44  is rectangular with a height greater than the width. However of course other non-circular shapes can be used provided that the cross-section is constant along the length of the non-circular section  44  and provided that the non-circular section  44  can co-operate with a surrounding drive member to receive rotational driving force therefrom. The stop section  45  is generally cylindrical with a top segment  45 A removed to assist the operator in insertion of the fiber into the drive motor. 
         [0136]    Turning now to  FIGS. 5 and 6 , the drive motor  22  is shown in more detail for effecting a driving action on the fiber through the sections  44  and  45  into the sleeve  38  for driving longitudinal and rotational movement of the terminus  36 . 
         [0137]    The drive motor comprises a housing  50  formed by an upper half  51  and a lower half  52  both of semi-cylindrical shape with the two halves engaged together to surround the sections  44  and  45  with the sleeve  38  extending axially along a center of the housing.  50 . At the front  53  of the housing  50  is provided a boss defining a bore  54  within which the sleeve  38  forms a sliding fit. This acts to guide the movement of the sleeve at the forward end of the housing. 
         [0138]    Within the housing is provided a first annular mount  55  and a second annular mount  56  spaced rearwardly from the first. Between the first annular mount  55  and the front boss is provided a first encoder  57  and behind the second annular mount  56  is provided a second encoder  58 . The first annular mount  55  mounts a first rotatable drive disk  59  on bearings  60 . The second annular mount carries a second drive disk  61  on bearings  62 . Each of the drive disks is of the same shape including a generally flat disk portion with a cylindrical portion  63  on the rear of the disk and lying on a common axis with the disk portion. The bearings are mounted between a cylindrical inner face of the annular portion  55 ,  56  and an outside surface of the cylindrical portions  63 . Each of the disks is therefore mounted for rotation about the axis of the fiber along the axis of the housing. 
         [0139]    The disk  59  includes a central plug portion  64 , which closes the center hole of the disk portion and projects into the cylindrical portion  63 . The plug portion has a chamfered or frustoconical lead in section  65  converging to a drive surface  66  surrounding the section  44  and having a common cross-sectional shape therewith. Thus the tip portion  41  of the sleeve  38  can slide along the axis of the housing and engage into the conical lead in section  65  so as to pass through the drive surface or bore  66  until the section  44  engages into the surface  66 . In the position, rotation of the disk  59  drives rotation of the sleeve  38  and therefore of the fiber. As the noncircular section  44  has a constant cross-section, it can slide through the drive surface  66  forwardly and rearwardly. 
         [0140]    The disk  61  includes a plug member  67 , which engages into the central opening in the disk member  61 . The plug  67  has an inner surface  68 , which defines a female screw thread for co-operating with a lead screw  69 . The lead screw  69  has an inner bore  70  surrounding the sleeve  38  so that the sleeve  38  is free to rotate and move relative to the bore  70 . The lead screw  69  also passes through the cylindrical portion  63  of the disk  61 . Rotation of the disk  61  acts to drive the lead screw longitudinally along the axes of the housing and the sleeve  38 . A rear end  71  of the lead screw is attached to a clamping member  72 . The clamping member  72  includes a first fixed portion  73  attached to the rear end  71  of the lead screw and a second loose portion  74  which can be clamped into engaging the fixed portion so as to clamp the end stop members  45  in position within the clamping member. The loose portion  74  is clamped in place by screws  75 . The top segment  45 A of the end stop  45  engages into a receptacle  76  in the fixed portion  73  so as to orient the sleeve  38  relative to the lead screw. 
         [0141]    The disks  59  and  61  are driven in a ratcheting action by drive motors  77  and  78  respectively. In an exemplary embodiment the drive motors are provided by piezoelectric drive elements in which a piezoelectric crystal is caused to oscillate thus actuating a reciprocating action that is used to drive by a ratchet process angular rotation of the respective disk. 
         [0142]    The reciprocating action of the piezoelectric crystal  77  and  78  is provided by two such motors  77  co-operating with the disk  59  and two motors  78  co-operating with the disk  61 . Each motor is carried on a mounting bracket  77  A,  78 A that is suitably attached to the housing. The end clamp  72  is generally rectangular in cross-section and slides within a correspondingly rectangular cross-section duct  72 A within the housing. Thus the lead screw  69  is held against rotation and is driven axially by the rotation of the disk  61  while the fiber is free to rotate relative to the lead screw. The use of a piezoelectric crystal to drive disks is particularly suitable and provides particular compatibility with the MRI system but other drive systems can also be used as set forth previously. 
         [0143]    In other alternative arrangements (not shown), the ratcheting action can be effected by a longitudinally moveable cable driven from the device controller  25  outside the room  11 . In a further alternative arrangement, the motor may comprise a hydraulic or pneumatic motor which again effects a ratcheting action by reciprocating movement of a pneumatically or hydraulically driven prime mover. Thus selected rotation of a respective one of the disks can be effected by supplying suitable motive power to the respective motor. 
         [0144]    The respective encoder  57 ,  58  detects the instantaneous position of the disk and particularly the sleeve portion  63  of the disk, which projects into the interior of the encoder. The sleeve portion therefore carries a suitable element, which allows the encoder to accurately detect the angular orientation of the respective disk. In this way the position of the disks can be controlled by the device controller  25  accurately moving the disk  59  to control the angular orientation of the fiber and accurately moving the disk  61  to control the longitudinal position of the fiber. The longitudinal position is obtained by moving the lead screw, which carries the end stop  45 . The movements are independent so that the fiber can be rotated while held longitudinally stationary. 
         [0145]    As the motor driving movement of the fiber is used while the magnet and the MRI system is in operation, it is essential that the motor and the associated control elements that are located within the room  11  are compatible with the MRI system. For this purpose, the power supply or control cable  24  and the motor must both be free from ferromagnetic components that would be responsive to the magnetic field. In addition it is necessary that the motor  22  and the cable  24  are both properly shielded against interference with the small radio frequency signals that must be detected for the MRI analysis to be effective. 
         [0146]    Referring now to  FIG. 7 , the room  11  is shielded to prevent radio waves from penetrating the walls of the room  11  and interfering with the proper operation of the MRI machine  10 . Additionally, the cable  24  and the motor  22  are surrounded by a conductor  80 , which extends through an opening  81  in the wall of the room  11 . The conductor also passes through a cable port  82  within a wall  83  of the enclosure so that the whole of the motor and the cable are encased within the conductor  80 . 
         [0147]    In the method of operation, the patient  13  is located on the patient table and restrained so that the head of the patient  13  remains motionless to prevent motion artifacts. The MRI system is then operated in conventional manner to generate images of the targeted tumor  32 . The images are used to determine the size and shape of the tumor  32  and to define the external perimeter  90  of the tumor  32  ( FIG. 8 ). The surgeon also determines an optimal location to place the cannula  31  so that the cannula  31  is aimed at the targeted tumor  32  without causing damage to surrounding tissue. Next, the opening  34  is formed in the skull of the patient  13  and the cannula  31  inserted. 
         [0148]    With the cannula  31  in place, the motor  22  is mounted on the frame  23  and the frame  23  adjusted to locate the motor  22  so that the fiber assembly  20  can be inserted directly into the cannula.  31 . With the motor  22  properly aligned along the axis of the cannula,  31 , the fiber assembly  20  is inserted through the bore of the motor  22  and into the cannula  31  so as to extend through the cannula  31  until the terminus  36  emerges just out of the outer end of the cannula  31 . The distance of the motor from the cannula  31  can be adjusted so that the terminus  36  just reaches the end of the cannula  31  when the lead screw is fully retracted and the end stop is located in place in the clamp  72 . 
         [0149]    With the motor and fiber thus assembled, the MRI system measures temperatures in the boundary zone  90 . The temperature is detected over the full surface area of the boundary rather than simply at a number of discrete locations. While the measurements are taken, the fiber is moved longitudinally to commence operation at a first position just inside the volume of the tumor  32 . At a selected angular orientation of the beam, pulses of radiation are emitted by the laser and transmitted into the tumor  32  through the beam  37 . The pulses are continued while the temperature in the boundary layer  90  is detected. As the pulses supply heat energy into the volume of the tumor  32 , the tumor  32  is heated locally basically in the segment shaped zone defined by the beam but also heat is conducted out of the volume of the beam into the remainder of the tumor  32  at a rate dependant upon the characteristics of the tumor  32  itself. Heating at a localized area defined by the beam is therefore continued until the heat at the boundary layer  90  is raised to the predetermined coagulation temperature on the order of 55 to 65 C. Once the boundary layer reaches this temperature, heating at that segment shaped zone within the disk is discontinued and the fiber is moved either longitudinally to another disk or angularly to another segment or both to move to the next segment shaped zone of the tumor  32  to be heated. It is not necessary to predict the required number of pulses in advance since the detection of temperature at the boundary is done in real time and sufficiently quickly to prevent overshoot. However, predictions can be made in some circumstances in order to carry out the application of the heat energy as quickly as possible by applying high power initially and reducing the power after a period of time. 
         [0150]    It is desirable to effect heating as quickly as possible so as to minimize the operation duration. Heating rate may be varied by adjusting the number of pulses per second or the power of the heat source. Care is taken to vary these parameters to match the characteristics of the tumor  32 , as detected in the initial analysis. Thus the system may vary the energy pulse rate or power-time history of the heat source to modify the penetration depth of the heat induced lesion so that it can control the heating zone of an irregularly shaped lesion. The energy application rate should not be high enough to result in over heating the tissue outside of the perimeter of the tumor. The rate of heat application can also be varied in dependence upon the distance of the boundary from the axis of the fiber. Thus, the axis of the fiber is indicated at  91  in  FIG. 8  and a first distance  92  of the beam to the boundary is relatively short at the entry point of the fiber into the tumor  32  and increases to a second larger distance  93  toward the center of the tumor  32 . In addition to pulses per second, it is also possible to adjust the power-time history of the laser energy to maximize penetration into the lesion. That is to use high power first for a short period of time and then ramp the power down throughout the duration of the treatment at that particular location. 
         [0151]    In some cases it is desirable to maintain the fiber stationary at a first selected longitudinal position and at a first selected angular orientation until the temperature at the boundary reaches the required temperature. In this case the fiber is then rotated through an angle approximately equal to the beam angle to commence heating at a second angular orientation with the fiber being rotated to a next angular orientation only when heating at that second orientation is complete. In this way heating is effected at each position and then the fiber rotated to a next orientation position until all angular orientations are completed. 
         [0152]    After a first disk shaped portion of the tumor  32  is thus heated, the fiber is moved longitudinally through a distance dependant upon the diameter of the tumor  32  at that location and dependant upon the beam angle so as to ensure the next heated area does not leave unheated tumor tissue between the two successive disk shaped areas. Thus the fiber is moved longitudinally in steps, which may vary in distance depending upon the diameter and structure of the tumor  32  as determined by the initial analysis. However the total heating of the tumor  32  is preferably determined by the temperature at the boundary without the necessity for analysis of the temperatures of the tumor  32  inside the boundary or any calculations of temperature gradients within the tumor  32 . When the complete boundary of the tumor  32  has been heated to the predetermined coagulation temperature, the treatment is complete and the apparatus IS disassembled for removal of the fiber assembly  20  and the cannula  31  from the patient  13 . 
         [0153]    The system allows direct and accurate control of the heating by controlling the temperature at the surface area defined by the boundary of the tumor  32  so that the whole of the volume of the tumor  32  is properly heated to the required temperature without heating areas external to the tumor  32  beyond the coagulation temperature. In order to maximize the amount of heat energy which can be applied through the fiber and thereby to effect treatment of larger tumors, it is highly desirable to effect cooling of the tissue immediately surrounding the end of the fiber so as to avoid overheating that tissue. Overheating beyond the coagulation temperature is unacceptable, as it will cause carbonization, which will inhibit further transmission of the heat energy. Without cooling it is generally necessary to limit the amount of heat energy that is applied. As energy dissipates within the tissue, such a limitation in the rate of application of energy limits the size of the tumor to be treated since dissipation of energy prevents the outside portions of the tumor from being heated to the required coagulation temperature. 
         [0154]    In  FIGS. 9 and 10  is therefore shown a modified laser probe which can be used in replacement for the probe previously described, bearing in mind that it is of increased diameter and thus minor modifications to the dimensions of the structure are necessary to accommodate the modified probe. 
         [0155]    The modified probe  100  comprises a fiber  101  which extends from a tip portion  102  including the light dispersion arrangement previously described to a suitable light source at an opposed end of the fiber as previously described. The probe further comprises a support tube  103  in the form of a multi-lumen extruded plastics catheter for the fiber which extends along the fiber from an end  104  of the tube just short of the tip  102  through to a position beyond the fiber drive system previously described. The tube  103  thus includes a cylindrical duct  104  extending through the tube and there are also provided two further ducts  105  and  106  parallel to the first duct and arranged within a cylindrical outer surface  107  of the tube. 
         [0156]    The supporting tube  103  has at its end opposite the outer end  104  a coupling  108  which is molded onto the end  109  and connects individual supply tubes  110 ,  111  and  112  each connected to a respective one of the ducts  104 ,  105  and  106 . Multi-lumen catheters of this type are commercially available and can be extruded from suitable material to provide the required dimensions and physical characteristics. Thus the duct  104  is dimensioned to closely receive the outside diameter of the fiber so that the fiber can be fed through the duct tube  110  into the duct  104  and can slide through the support tube until the tip  102  is exposed at the end  104 . 
         [0157]    While tubing may be available which provides the required dimensions and rigidity, in many cases, the tubing is however flexible so that it bends side to side and also will torsionally twist. The support tube is therefore mounted within an optional stiffening tube or sleeve  114 , which extends from an end  115  remote from the tip  102  to a second end  106  adjacent to the tip  102 . The end  116  is however spaced rearwardly from the end  104  of the tubing  103 , which in turn is spaced from the tip  102 . The distance from the end  106  to the tip  102  is arranged to be less than a length of the order of 1 inch. The stiffening tube  114  is formed of a suitable stiff material that is non-ferro-magnetic so that it is MRI compatible. The support tube  103  is bonded within the stiffening tube  114  so that it cannot rotate within the stiffening tube and cannot move side to side within the stiffening tube. The stiffening tube is preferably manufactured from titanium, ceramic or other material that can accommodate the magnetic fields of MRI. Titanium generates an artifact within the MRI image. For this reason the end  116  is spaced as far as possible from the tip  102  so that the artifact is removed from the tip to allow proper imagining of the tissues. 
         [0158]    At the end  116  of the stiffening tube  114  is provided a capsule  120  in the form of a sleeve  121  and domed or pointed end  122 . The sleeve surrounds the end  116  of the stiffening tube and is bonded thereto so as to provide a sealed enclosure around the exposed part of the tube  103 . The capsule  120  is formed of quartz crystal so as to be transparent to allow the escape of the disbursed light energy from the tip  102 . The distance of the end of the stiffening tube from the tip is arranged such that the required length of the capsule does not exceed what can be reasonably manufactured in the transparent material required. 
         [0159]    The tube  111  is connected to a supply  125  of a cooling fluid and the tube  112  is connected to a return collection  126  for the cooling fluid. Thus, the cooling fluid is pumped through the duct  105  and escapes from the end  104  of the tube  103  into the capsule and then is returned through the duct  106 . The cooling fluid can simply be liquid nitrogen allowed to expand to nitrogen gas at cryogenic temperatures and then pumped through the duct  105  and returned through the duct  106  where it can be simply released to atmosphere at the return  126 . 
         [0160]    In an alternative arrangement the supply  125  and the return  126  form parts of a refrigeration cycle where a suitable coolant is compressed and condensed at the supply end and is evaporated at the cooling zone at the capsule  120  so as to transfer heat from the tissue surrounding the capsule  120  to the cooling section at the supply end. 
         [0161]    The arrangement set forth above allows the effective supply of the cooling fluid in gaseous or liquid form through the ducts  105  and  106  and also effectively supports the fiber  101  so that it is held against side to side or rotational movement relative to the stiffening tube  114 . The location of the tip  102  of the fiber is therefore closely controlled relative to the stiffening tube and the stiffening tube is driven by couplings  130  and  131  shown schematically in  FIG. 9  but of the type described above driven by reciprocating motor arrangements as set forth hereinbefore. 
         [0162]    In  FIGS. 11 and 12  is shown the tip section of an alternative probe in which cooling of the tip section is effected using expansion of a gas into an expansion zone. The tip only is shown as the remainder of the probe and its movements are substantially as previously described. 
         [0163]    Thus the probe comprises a rigid extruded tube  200  of a suitable material, for example titanium, that is compatible with MRI (non-ferromagnetic) and suitable for invasive medical treatment. A further smaller cooling fluid supply tube  202  is also separately formed by extrusion and is attached by adhesive to the inside surface of the outer tube. An optical fiber  204  is also attached by adhesive to the inside surface the outer tube so that the fiber is preferably diametrically opposed to the tube  202 . 
         [0164]    The tube  202  is swaged at its end as indicated at  205 , which projects beyond the end of the tube  201 , to form a neck section of reduced diameter at the immediate end of the tube  202 . Thus in manufacture the extruded tube  201  is cut to length so as to define a tip end  207  at which the outer tube terminates in a radial plane. At the tip end beyond the radial plane, the outer of the inner tube  202  is swaged by a suitable tool so as to form the neck section  205  having an internal diameter of the order of 0.003 to 0.005 inch. 
         [0165]    The fiber  204  is attached to the tube  201  so that a tip portion  208  of the fiber  204  projects beyond the end  207  to a chamfered end face  209  of the fiber which is cut at 45 degrees to define a reflective end plane of the fiber. 
         [0166]    The end  207  is covered and encased by a molded quartz end cap  210  that includes a sleeve portion  211  closely surrounding the last part of the tube  200  and extending beyond the end  207  to an end face  212 , which closes the capsule. The end face  212  is tapered to define a nose  213 , which allows the insertion of the probe to a required location as previously described. The end of the tube  201  may be reduced in diameter so that the capsule has an outer diameter matching that of the main portion of the tube. However in the arrangement shown the capsule is formed on the outer surface so that its outer diameter is larger than that of the tube and its inner diameter is equal to the outer diameter of the tube. 
         [0167]    A thermocouple  214  is attached to the inside surface of the outer tube  200  at the end  207  and includes connecting wires  215  which extend from the thermocouple to the control unit schematically indicated at  226 . Thus the thermocouple provides a sensor to generate an indication of the temperature at the end  207  within the quartz capsule. The quartz capsule is welded to or bonded to the outer surface of the tube as indicated at  215  so as to form a closed expansion chamber within the quartz capsule beyond the end  207 . The inner surface  216  of the quartz capsule is of the same diameter as the outer surface of the tube  200  so that the expansion chamber beyond the end of the tube  200  has the same exterior dimension as the tube  200 . 
         [0168]    The quartz capsule is transparent so as to allow the reflected beam of the laser light from the end face  209  of the fiber to escape through the transparent capsule in the limited angular direction substantially at right angles to the longitudinal axis of the fiber and within the axial plane defined by that longitudinal axis. 
         [0169]    The tube  202  is connected at its end opposite to the tip to a fluid supply  219 , which forms a pressurized supply of a suitable cooling fluid such as carbon dioxide or nitrous oxide. The fluid supply  219  is controlled by the control unit  216  to generate a predetermined pressure within the fluid supply to the tube  202  which can be varied so as to vary the flow rate of the fluid through the neck  205 . The fluid is supplied at normal or room temperature without cooling. The fluid is normally a gas at this pressure and temperature but fluids that are liquid can also be used provided that they form a gas at the pressures within the expansion chamber and thus go through an adiabatic gas expansion through the restricted orifice into the expansion chamber to provide the cooling effect. 
         [0170]    Thus the restricted orifice has a cross-sectional area very much less than that of the expansion chamber and the return duct provided by the inside of the tube  201 . The items that reduce the effective cross-sectional area of the return tube  201  are the optical fiber, the supply tube, two thermocouple wires, the shrink tube that fixes the thermocouple wires to the optical fiber and the adhesives used to bond the items into place (at the inlet of the discharge duct). Without the area of the adhesives included in the calculation, the exhaust duct area is about 300 times larger than a delivery orifice diameter of 0.004″ (the target size). When considering the area occupied by the adhesives, the exhaust duct inlet area would be approximately 200 to 250 times larger than the 0.004″ diameter orifice. Considering the manufacturing tolerance range of the supply tube orifice diameter alone, the exhaust duct area could be anywhere between 190 to 540 times larger than the orifice area (without considering the area occupied by adhesives). It is our estimation that a 200/1 gas expansion will be required to achieve appropriate cooling. 
         [0171]    This allows the gas as it passes into the expansion chamber beyond the end  205  to expand as a gas thus cooling the quartz capsule and the interior thereof at the expansion chamber to a temperature in the range −20 C to 0 C. This range has been found to be suitable to provide the required level of cooling to the surface of the quartz capsule so as to extract heat from the surrounding tissue at a required rate. Variations in the temperature in the above range can be achieved by varying the pressure from the supply  219  so that in one example the pressure would be of the order of 700 to 850 psi at a flow rate of the order of 5 liters per min. 
         [0172]    The tube  202  has an outside diameter of the order of 0.014 inch OD, while the tube  203  has a diameter of the order of 0.079 inch. Thus a discharge duct for the gas from the expansion chamber is defined by the inside surface of the tube  200  having a flow area which is defined by the area of the tube  200  minus the area taken up by the tube  202  and the fiber  207 . This allows discharge of the gas from the expansion chamber defined within the quartz capsule at a pressure of the order of 50 psi so that the gas can be simply discharged to atmosphere if inert or can be discharged to an extraction system or can be collected for cooling and returned to the fluid supply  219  if economically desirable. Tip cooling is necessary for optimum tissue penetration of the laser or heating energy, reduction of tissue charring and definition of the shape of the coagulated zone. The gas expansion used in the present invention provides an arrangement that is suitable for higher power densities required in this device to accommodate the energy supplied by the laser heating system. 
         [0173]    The tip  208  of the fiber  204  is accurately located within the expansion zone since it is maintained in fixed position within the quartz capsule by its attachment to the inside surface of the outer tube. The fiber is located forwardly of the end  207  sufficiently that the MRI artifact generated by the end  207  is sufficiently removed from the plane of the fiber end to avoid difficulties in monitoring the temperature within the plane of the fiber end. The outlet orifice of the tube  202  is also located forwardly of the end  207  so as to be located with the cooling effect generated thereby at the plane of the fiber end. 
         [0174]    The end face  209  is located within the expansion chamber  216  so that it is surrounded by the gas with no liquid within the expansion chamber. Thus, in practice there is no condensate on the end face  209  nor any other liquid materials within the expansion chamber that would otherwise interfere with the reflective characteristics of the end face  209 . 
         [0175]    The end face  209  is coated with a reflective coating such as a dual dielectric film. This provides a reflection at the two required wavelengths of the laser light used as a visible guide beam and as the heat energy source such as He—Ne and Nd:YAG respectively. An alternative coating is gold, which can alone provide the reflections at the two wavelengths. 
         [0176]    The arrangement of the present invention provides excellent MRI compatibility both for anatomic imaging as well as MR thermal profiling. Those skilled in the art will appreciate that the cooling system in accordance with the present invention may also be used with circumferential fibers having point-of-source energy. 
         [0177]    In operation, the temperature within the expansion zone is monitored by the sensor  214  so as to maintain that temperature at a predetermined temperature level in relation to the amount of heat energy supplied through the fiber  204 . Thus the pressure within the fluid supply is varied to maintain the temperature at that predetermined set level during the hyperthermic process. 
         [0178]    As described previously, the probe is moved to an axial location within the volume to be treated and the probe is rotated in steps so as to turn the heating zone generated by the beam B into each of a plurality of segments within the disk or radial plane surrounding the end face  209 . Within each segment of the radial plane, heat energy is supplied by the beam B that is transmitted through the quartz capsule into the tissue at that segment. The heat energy is dissipated from that segment both by reflection of the light energy into adjacent tissue and by conduction of heat from the heated tissue to surrounding tissue. As stated previously, those skilled in the art will appreciate that the probe used with the cooling system in accordance with the present invention may include circumferential fibers having point-of-source energy. 
         [0179]    The surface of the capsule is cooled to a temperature so that it acts to extract heat from the surrounding tissue at a rate approximately equal to the dissipation or transfer of heat from the segment into the surrounding tissue. Thus the net result of the heating effect is that the segment alone is heated and surrounding tissue not in the segment required to be heated is maintained without any effective heating thereon, that is no heating to a temperature which causes coagulation or which could otherwise interfere with the transmission of heat when it comes time to heat that tissue in another of the segments. In this way when a first segment is heated to the required hyperthermic temperature throughout its extent from the probe to the peripheral surface of the volume, the remaining tissues in the areas surrounding the probe are effectively unheated so that no charring or coagulation has occurred which would otherwise prevent dissipation of heat and in extreme cases completely prevent penetration of the beam B. 
         [0180]    Thus when each segment in turn has been heated, the probe can be rotated to the next segment or to another segment within the same radial plane and further heating can be effected of that segment only. 
         [0181]    In practice in one example, the laser energy can be of the order of 12 to 15 watts penetrating into a segment having an angle of the order of 60 to 80 degrees to a depth of the order of 1.5 cm. In order to achieve this penetration without causing heating to the remaining portions of the tissue not in the segment, cooling of the outside of the capsule to a temperature of the order of minus 5 degrees C. is required. 
         [0182]    In  FIG. 13  is shown an actual example of a cross-section of tissue that has been heated in three separate segments marked as sectors 1, 2 and 3. The central dark area is where the probe was located before it was removed to allow the cross-sectional slice to be taken. The darker area that forms approximately 100 degrees opposite sector 2 indicates no heating has been applied to that area. The lighter color in the sectors 1, 2 and 3 indicates coagulation of the tissue. Similarly it will be noted that the tissue is of the darker color (not heated) in the smaller areas between sectors 2 and 3 and between sectors 1 and 2. Thus the cooling effect of the present invention achieves the effect required of limiting or prevention heating to the areas outside the selected segments. 
         [0183]    The tube  200  is in the example shown above of a rigid structure for insertion in a straight line as previously described into a specific location. The use of a rigid material such as titanium for the outer tube avoids the necessity for the cannula  31  previously described and allows the alignment of the probe in its mounting and drive arrangement as previously described to the required location in the patient  13  without previously setting up a cannula  31 . However other arrangements can be provided in which the tube  200  is formed of a fully or partial flexible material allowing the tube  200  to bend so as to allow insertion along suitable passageways such as veins or arteries within the patient  13  by using guiding systems well known to one skilled in the art. 
         [0184]    Another exemplary embodiment of the invention provides a method of using a directed energy beam in conjunction with an MRI machine to heat targeted tissue in a patient. In accordance with the aforementioned teachings, the method can be used, not only to destroy tumors, but any tissue, healthy or otherwise, that has been identified as undesirable. While the apparatus of the present invention has been described as useable for the identification and destruction of lesions, in particular tumors, the following applications are also considered within the scope of the present invention. 
         [0185]    A first application pertains to treating patients having aneurysms and stokes. One object of the present invention is to treat aneurysms before the rupture that results in hemorrhagic stroke. Symptoms of aneurysms are found and diagnosis is made during the “pre-event” period prior to stroke. During this period, patients are typically treated with endovascular coils. Once the aneurysm “pops” and hemorrhagic stroke occurs, the current therapy involves clipping the ruptured vessel, usually within three days of the event. The goal is to prevent rebleeding. Both procedures are risky and treatment can be much more easily accomplished with the probe and cooling system in accordance with the present invention. 
         [0186]    Strokes occur when an aneurysm in a blood vessel in the brain ruptures, causing brain damage. Aneurysms and ruptured blood vessels have long been treated using open brain surgery, an extremely risky procedure. Recently, a procedure known as coil embolization has gained popularity because it obviates the need to open the skull and expose the brain. Coil embolization involves feeding a catheter into an artery in the groin and guiding the catheter through the arteries to the affected site in the brain. Platinum coils are then sent up through the catheter to the aneurysm, where the coils fill the ballooned area. The coils are detached and left in the artery permanently, blocking the flow. 
         [0187]    Coil embolization is not free of complications. For example, if the aneurysm opening is too wide, allowing the coils to slip out, a stent or flexible mesh tube must be inserted across the opening of the artery to hold them in place. Sometimes, surgery is still necessary if the aneurysm is not the appropriate shape for embolization. Even without complications, the procedure requires significant patience and skill to feed a catheter from the groin into a targeted area of the brain. 
         [0188]    The method of the present invention can be used to treat vascular lesions, such as aneurysms, and strokes and avoid many of the complications of coil embolization. Targeting the lesion or rupture is accomplished in the same manner as locating a tumor. The size and location of the targeted lesion or rupture is determined and an optimal placement for the cannula is chosen. Targeted vessels should be on the order of 1 mm to 5 mm and are more preferably on the order of 2 mm to 3 mm in diameter. A hole is drilled or otherwise formed in the skull and the cannula is carefully inserted so that the cannula assumes the intended placement. A fiber assembly is inserted through the cannula in the aforementioned manner until the target is reached. Notably, the execution of heating the targeted area may be effected using a straight beam rather than an angled beam if the targeted area is sufficiently small. Additionally, the energy source may include non-collimated light or other form of radiant energy. It may be true that the necessary temperature to effect the cauterization of the lesion will be lower than that needed to terminate tumor tissue. Alternatively, cauterization of an lesion could be effected, according to the present invention, by threading a more flexible, yet otherwise structurally similar, catheter through an artery in the groin to the targeted site. Obviously, the catheter, or fiber assembly, would be much longer than that used with the aforementioned cannula. 
         [0189]    A second alternative application of the present invention is useful in cosmetic surgery. The field of cosmetic surgery includes many procedures that remove excess healthy tissue such as skin, manipulate muscle tissue and remove fat cells, for example. 
         [0190]    Fat cells are removed using liposuction, a procedure that involves sucking the cells through a small vacuum tube. Liposuction is a relatively violent way of removing cells and often causes damage to the cells immediately surrounding those removed. Predictably, a significant amount of fluid is also sucked through the vacuum probed during the procedure. Fluid loss is a major concern when performing liposuction. 
         [0191]    The probe, cooling system and method of the present invention can be used to destroy targeted fat cells by heating the cells with radiant energy, such as collimated or non-collimated light. The fat cells are heated to a temperature just below the carbonization temperature and the remains are absorbed by the body. No fluid is removed from the body, thereby allowing a more extensive shaping procedure to be performed. Again, this procedure may be performed with a probe having an angled beam or an axial, point-of-source energy beam. 
         [0192]    The probe, cooling system and method in accordance with the present invention may also be used in cosmetic surgical procedures such as rhytidectomy, which involves the removal and redraping of excess skin and resupporting and tightening underlying muscles and tissues; blepharoplasty, which involves the removal of lax or excess kin on the upper and lower eyelids to minimize sagging; laser resurfacing to remove superficial scars, age lines and sometimes, precancerous skin lesions; rhinoplasty, which involves the reconstruction and sculpting of the bone and cartilage to reshape the nose; and trauma reconstruction, which involves the repair of facial injuries or deformities from previous injuries. Other cosmetic surgical procedures involving the removal, repair or reconstruction of tissue are also within the scope of the present invention and these procedures may be performed with a probe having an angled beam or an axial, point-of-source energy beam. 
         [0193]    Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without departing from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.