Abstract:
An MRI guided surgical apparatus includes a heat source formed by a laser and an optical fiber carrying the heat energy into a part to be coagulated by hyperthermia with an end reflector to direct the energy in a beam to one side of the fiber end. The fiber includes a reinforcing sleeve along its length to prevent bending and twisting. The sleeve is mounted in a shielded, Piezo-electric motor which causes movement of the fiber longitudinally of its axis to move the end within the part and rotation of the fiber about its axis to cause the beam to rotate about the axis. A rigid elongate cannula is arranged for insertion to a position at the part of the patient having a bore for receiving a portion of the fiber adjacent the outlet end in sliding engagement therein such that the end can pass through the cannula into engagement with the part of the patient. A part of the sleeve projecting beyond the cannula is rigid and a further part connecting to the motor is stiff but less rigid. A magnetic resonance imaging system is arranged to generate a series of output signals over a period of time representative of temperature in the part as the temperature of the part changes during that time. The heat source is controlled in heat energy applied and location and orientation of the beam to continue the heating at a respective area in the part until the temperature at a selected location in the part normally at the boundary of a tumor reaches the required hyperthermic temperature as monitored whereupon the heating in the area is halted.

Description:
This invention relates to an apparatus for hyperthermia surgery in a patient using a magnetic resonance imaging system to effect guiding and control of the heating source. 
     BACKGROUND OF THE INVENTION 
     The excision of tumours by hyperthermia is known. Thus tumours and other masses to be excised 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 which can cause ablation of the tissue. 
     One technique for effecting the heating is to insert into the mass concerned an optical fiber which has at its inserted end an element which 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 mass at positions around the fiber. The fiber can thus be moved longitudinally and rotated to effect heating of the mass over the full volume of the mass with the intention of heating the mass to the required temperature without significantly affecting tissue surrounding the mass. 
     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 mass. It is difficult therefore for the surgeon to effect a controlled heating which heats all of the tumour while minimizing damage to surrounding tissue. 
     It is of course well known that the location of tumours and other masses 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 mass 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 surgery commences and that movement together with the partial excision or coagulation of some of the tissue can significantly change the location of the mass to be excised thus eliminating any possibility for controlled accuracy. 
     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. 
     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. 
     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 surgery system. 
     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. 
     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 tumours in which the tumour is subjected to shock waves. This does not use a monitoring system to monitor and control the effect. 
     SUMMARY OF THE INVENTION 
     It is one object of the present invention, therefore, to provide an improved method and apparatus for effecting controlled surgery by hyperthermia. 
     According to a first aspect of the invention there is provided a method for effecting surgery by hyperthermia comprising: 
     providing a heat source arranged to apply heat to a part of a patient on whom the surgery is to be effected; 
     operating a non-invasive detection system to generate a series of output signals over a period of time representative of temperature in the part as the temperature of the part changes during that time; 
     identifying a plurality of locations in the part to be heated to a required hyperthermic temperature; 
     using the output signals to monitor the temperature at the locations as the temperature changes over the period of time; 
     for each location, controlling the heat source to effect heating of an area of the part adjacent the location; 
     and, for each location, continuing the heating at the respective area until the temperature at the location reaches the required hyperthermic temperature as monitored whereupon the heating in the area is halted. 
     Preferably the heat source is controlled by controlling an amount of heat generated thereby and by controlling a selected area of the part to which the heat is applied. 
     Preferably the monitored locations are arranged at an outer periphery of a volume to be heated to the required hyperthermic temperature. 
     Preferably the method includes identifying the locations at the outer periphery of the volume, generally a tumor, to be heated from a preliminary series of signals from the non-invasive detection system. 
     Preferably the heat source is provided on an invasive probe inserted into the part and wherein the control of the heat source is effected by moving the probe. However other non-invasive but directional heating techniques can be used such as ultra-sound and other radiations. 
     Preferably the heat source is provided on an invasive probe and is arranged to cause heating in a predetermined direction relative to the probe and wherein the control of the heat source is effected by moving the probe to alter the direction. 
     Preferably the heat source comprises a laser, an optical fiber for communicating light from the laser, a mounting for the optical fiber allowing invasive insertion of an end of the fiber into the part of the patient, a light directing element at an end of the fiber for directing the light from the laser to a predetermined direction relative to the fiber and a position control system for moving the end of the fiber. 
     Preferably there is provided a cannula through which the fiber is inserted, the cannula having an end which is moved to a position immediately adjacent but outside the part to be heated and the fiber having a rigid end portion projecting from the end of the cannula into the part. 
     According to a second aspect of the invention there is provided an apparatus for effecting surgery by hyperthermia comprising: 
     a heat source arranged to apply heat to a part of a patient on whom the surgery is to be effected; 
     a non-invasive detection system arranged to generate a series of output signals over a period of time representative of temperature in the part as the temperature of the part changes during that time; 
     and a control system comprising: 
     a first means arranged to identify a plurality of locations in the part to be heated to a required hyperthermic temperature; 
     a second means arranged to use the output signals to monitor the temperature at the locations as the temperature changes over the period of time; 
     and a third means arranged to control the heat source to effect heating of an area of the part adjacent each location; 
     the control system being arranged in response to said temperatures at the locations to operate the third means to control the selection of the area to which heat is applied and to control the amount of heat applied to the area. 
     Preferably the control system includes a first control for controlling an amount of heat generated by the heat source and a second control for moving the heat source to effect heating at a selected area of the part to which the heat is applied. 
     Preferably the heat source comprises: an optical fiber having an inlet end and an outlet end; a laser source for supplying light energy into the fiber at the inlet end; a light deflector at the outlet end for directing the light in a beam at an angle to a longitudinal axis of the fiber at the outlet end such that rotation of the fiber about the axis causes the beam to rotate about the axis; and a rigid elongate cannula arranged for insertion to a position at the part of the patient; the cannula having a bore arranged for receiving a portion of the fiber adjacent the outlet end in sliding engagement therein such that the end can pass through the cannula into engagement with the part of the patient. 
     Preferably the third means of the control system comprises a drive assembly for causing a first longitudinal movement of the fiber relative to the cannula along its length and for causing a second rotational movement of the fiber about its axis. 
     Preferably there is provided a mounting for the drive assembly for supporting the drive assembly exteriorly of the cannula and wherein the fiber has a reinforcing sleeve member surrounding and attached to a portion of the fiber so as to extend from the drive assembly to the outlet end, the sleeve member holding the fiber against lateral bending during said longitudinal movement and against torsional twisting during said rotational movement and the sleeve member being arranged to extend through the cannula. 
     Preferably the sleeve includes at least a portion which is integrally molded from a fiber reinforced polymer. 
     Preferably the sleeve includes a first portion at the outlet end which is formed of a first material, such as glass which is substantially rigid to rigidly support that portion of the fiber projecting in cantilever manner beyond the end of the cannula and a second portion connected to and extending from the first portion to the drive assembly, the second portion being formed of a second material such as liquid crystal polymer which is stiff but less rigid than the first portion to allow some flexing when the fiber is inserted into the cannula. In another arrangement, the sleeve can be wholly formed from a material which allows the necessary stiffness but does not have the brittleness of for example glass. 
     Preferably the reinforcing sleeve includes an engagement portion attached thereto for engaging the drive assembly including a portion of polygonal cross-section for engaging into a drive collar of corresponding cross-section of the drive assembly for driving rotational movement of the fiber and including a shoulder section for engaging against a drive member of the drive assembly for driving longitudinal movement of the fiber. 
     Preferably the non-invasive detection system comprises a magnetic resonance imaging system including a magnet to generate a magnetic field for the imaging system and an antenna for detecting radio frequency signals from the part of the patient; and wherein the third means of the control system includes a member located within and arranged to be moved within the magnetic field and a motor for driving movement of the member, the motor including no ferro-magnetic components such that it is usable in the magnetic field and the motor and a drive coupling thereto being shielded by a surrounding conductor to prevent interference with the radio frequency signals. 
     Preferably the third means of the control system includes a driven member rotatable about an axis and a reciprocating drive element arranged to cause a ratcheting movement of the driven member. 
     Preferably the reciprocating drive element comprises a piezo-electric motor. 
     Preferably one driven member includes a sleeve arranged to receive the fiber therethrough and the fiber and sleeve are non circular or polygonal in shape such that rotation of the member causes rotation of the fiber about the axis while allowing longitudinal sliding movement of the fiber relative to the sleeve. 
     Preferably one driven member has a female threaded bore therein and wherein the fiber has attached thereto a screw engaging the bore such that rotation of the driven member about the axis causes the screw to effect movement of the fiber longitudinally along the axis. 
     According to a third aspect of the invention there is provided an apparatus comprising: 
     a magnetic resonance imaging system arranged to generate an image from a sample and including a magnet to generate a magnetic field and an antenna for detecting radio frequency signals from the sample; 
     a member located within and arranged to be moved within the magnetic field; 
     and a motor having a drive coupling thereto for driving movement of the member, the motor including a reciprocating element for generating a motive force for the motor; 
     the motor including no ferro-magnetic components such that it is usable in the magnetic field and the motor and the drive coupling being shielded by a surrounding conductor to prevent interference with the radio frequency signals. 
     According to a fourth aspect of the invention there is provided an apparatus for laser surgery on a part of a patient comprising: 
     an optical fiber having an inlet end and an outlet end; 
     a laser source for supplying light energy into the fiber at the inlet end; 
     a light deflector at the outlet end for directing the light in a beam at an angle to a longitudinal axis of the fiber at the outlet end such that rotation of the fiber about the axis causes the beam to rotate about the axis; 
     a rigid elongate cannula arranged for insertion into the part of the patient; 
     the cannula having a bore arranged for receiving a portion of the fiber adjacent the outlet end in sliding engagement therein such that the end can pass through the cannula into engagement with the part of the patient; 
     a drive assembly for causing a first longitudinal movement of the fiber relative to the cannula along its length and for causing a second rotational movement of the fiber about its axis; 
     the fiber having a reinforcing sleeve member surrounding and attached to a portion of the fiber adjacent the outlet end, the sleeve member holding the fiber against lateral bending during said longitudinal movement and against torsional twisting during said rotational movement. 
     According to a fifth aspect of the invention there is provided a method for effecting surgery comprising: 
     providing a radiation source arranged to apply radiation to a part of a patient on whom the surgery is to be effected, the radiation being arranged to cause ablation of the part; 
     operating a non-invasive detection system to generate a series of output signals over a period of time representative of the effect of the radiation in the part as the radiation affects the part during that time; 
     identifying a plurality of locations in the part to ablated; 
     using the output signals to monitor the effect of the radiation at the locations as the radiation affects the part over the period of time; 
     for each location, controlling the radiation source to effect ablation of an area of the part adjacent the location; 
     and, for each location, continuing the radiation at the respective area until the effect of the radiation at the location reaches the required ablation as monitored whereupon the radiation in the area is halted. 
     It will be noted therefore that the ablation of the part can be effected by other forms of controlled directional radiation other than heat. The radiation is directed to the tip of the probe and controlled in direction and location while the effect of the radiation is monitored. Various forms of radiation can be used provided they are directional and controllable and effect ablation of the part. 
     Preferably the monitored locations define an outer periphery of a volume such as a tumour to be ablated. 
     Preferably the method includes identifying the outer periphery of the volume to be ablated from a preliminary series of signals from the non-invasive detection system and monitoring the effect of the radiation over the full area defined by the outer periphery. 
     Preferably the radiation source is provided on an invasive probe inserted into the part and wherein the control of the radiation source is effected by moving the probe. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     One embodiment of the invention will now be described in conjunction with the accompanying drawings in which: 
     FIG. 1 is a schematic illustration of an apparatus for effecting MRI guided laser surgery according to the present invention. 
     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. 
     FIG. 3 is a side elevational view of the laser probe of the apparatus of FIG.  1 . 
     FIG. 4 is an end elevational view of the laser probe of the apparatus of FIG.  1 . 
     FIG. 5 is a cross sectional view of the laser probe and drive motor therefor of the apparatus of FIG.  1 . 
     FIG. 6 is an exploded view of the drive motor of the apparatus of FIG.  1 . 
     FIG. 7 is a schematic illustration of the shielding of the apparatus of FIG.  1 . 
     FIG. 8 is a schematic illustration of the effect of the apparatus on a tumour or other mass to be ablated. 
    
    
     DETAILED DESCRIPTION 
     In FIG. 1 is shown schematically an apparatus for carrying out MRI controlled laser surgery. 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 . 
     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. 
     The apparatus further includes a laser surgery system including an optical fiber  20  which transmits heat energy in the form of light from a laser  21  mounted outside the room  11 . The fiber extends into the room to a tip  21  (FIG. 2) at which the energy escapes into the relevant part of the patient as discussed hereinafter. The position of the fiber  20  within the patient and the orientation of the fiber is 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 receives information from the MRI console and from position detectors of the motor  22  so as to operate movement of the motor  22  and to operate a power output from the laser  21  so as to control the position and amount of heat energy applied to the part within the body of the patient. 
     In FIG. 2 is shown on a larger scale the patient table  14  to which is attached the stereotaxic frame  23  so that the frame is fixed relative to the table and extends over the head  26  of the patient. The frame 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 by a bracket  27  of the motor. The position of the motor on the frame 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 about a point  30  within the frame so that the direction of the fiber projecting forwardly from the motor can be changed relative to the frame. 
     The apparatus further includes a rigid cannula  31  which surrounds the fiber  20  and which is arranged to allow sliding movement of the fiber longitudinally in the cannula and rotational movement within the cannula while generally holding the fiber in a direction axial of the cannula. The cannula is formed of a suitable rigid ceramic material so that it is stiff and resistant to bending and has sufficient strength to allow the surgeon to insert the cannula into the required location within the body part of the patient. 
     In the arrangement as shown, the apparatus is arranged for operating upon a tumour  32  within the brain  33  of the patient. The surgeon therefore creates an opening  34  in the skull of the patient and directs the cannula  31 , in the absence of the fiber  20 , through the opening  34  to the front edge of the tumour  32 . 
     The position of the tumour 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 which constitutes the extremities of the tumour. The surgical analysis by which the surgeon determines exactly which portions of the material of the patient 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. 
     The angle of insertion of the cannula is arranged so that, of course, it avoids as far as possible areas of the patient which should not be penetrated such as major blood vessels and also so that the cannula is directed so that, when it reaches the outside surface, it points toward a center of the tumour. 
     The optical fiber structure generally indicated at  20  in FIG. 3 includes an actual glass fiber element  35  which has an inlet end (not shown) at the laser and a remote end  36 . At the remote end is provided a reflector or prism which directs the laser energy in a beam  37  to one side of the end  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. 
     The fiber element itself as indicated at  35  is however encased in an enclosure to allow the fiber to be manipulated in the motor  22 . Around the fiber is formed a sleeve  38  including a first end portion  39  and a second longer portion  40 . The end portion  39  encloses the end  36  which is spaced from a tip  41  of the end portion. The end portion extends over the length of the order of 7 to 11 cms. The longer second portion  38  is of the order of 48 to 77 cms in length and extends from a forward end  41  through to a rear end  42 . The front portion  39  is formed of a rigid material such as glass. The longer rear portion  40  is formed of a stiff material which is less brittle than glass and yet maintains bending and tortional stiffness of the fiber so that forces can be applied to the sleeve portion  40  to move the tip  36  of the fiber to a required position within the tumour. The second portion  40  is formed of a material such as fiber reinforced plastics. 
     The two portions are bonded together to form an integral structure of common or constant diameter selected as a sliding fit through the cannula. The rigid front portion has a length so that it can extend from the end of the cannula at the forward or closest edge of the tumour through to the rear edge of the tumour. An average tumour might have a diameter of the order of 0.5 to 5.0 cms so that the above length of the forward portion is sufficient to extend through the full diameter of the tumour while leaving a portion of the order of 1.25 cms within the end of the cannula. In this way the substantially rigid forward portion maintains the forward portion of the fiber lying substantially directly along the axis of the cannula without any bending or twisting of the forward portion within the cannula. The longer second portion is not formed from glass since this would provide a complete structure which is too brittle to allow the surgeon to insert the structure into the cannula without the danger of cracking or fracturing the structure under any bending loads. A less brittle material is therefore selected which can accommodate some bending loads caused by manual insertion of the structure into the cannula and yet can communicate the forces from longitudinal and rotational movement as described herein after. 
     The sleeve portion  40  has attached to it a first polygonal or non-circular section  44  and a second end stop section  45 . Both of the drive sections  44  and  45  are connected to the second portion so as to communicate driving action to the second portion. Thus the polygonal section  44  is arranged to co-operate with a drive member which acts to rotate the second portion and therefore the fiber along its full length about an axis longitudinal of the fiber. The second end stop section  45  is arranged to co-operate with a longitudinally movable drive element which moves the second portion and therefore the fiber longitudinally. In this way the tip  36  can be moved from an initial position in which it projects just beyond the outer end of the cannula outwardly into the body of the tumour until the tip reaches the far end of the tumour. In addition the tip can be rotated around the axis of the fiber so that the heat energy can be applied at selected angles around the axis. By selectively controlling the longitudinal movement and rotation of the tip, therefore, the heat energy can be applied throughout a cylindrical volume extending from the end of the cannula along the axis of the cannula away from the end of the cannula. 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 so as to effect heating of the body part of the patient over a selected volume with the intention of matching the volume of the tumour out to the predetermined closed surface area defining the boundary of the tumour. 
     As shown in FIG. 4, the non-circular cross section of the drive portion  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 drive portion and provided that the drive portion can co-operate with a surrounding drive member to receive rotational driving force therefrom. The end stop member  45  is generally cylindrical with a top segment  45 A removed to assist the operator in insertion of the fiber into the drive motor. 
     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 drive members  44  and  45  into the sleeve  38  for driving longitudinal and rotational movement of the tip  36 . 
     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 portions engaged together to surround the drive elements with the fiber extending axially along a center of the housing. At the front  53  of the housing 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. 
     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 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. 
     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 frusto-conical lead in section  65  converging to a drive surface  66  surrounding the drive member  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 drive member  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 drive portion  44  has a constant cross section, it can slide through the drive surface  66  forwardly and rearwardly. 
     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 . However rotation of the disk  61  acts to drive the lead screw longitudinally of the axis of the housing and therefore of the axis of 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. 
     The disks  59  and  61  are driven in a ratchetting action by drive motors  77  and  78  respectively. In the preferred embodiment the drive motors are provided by piezo-electric drive elements in which a piezo-electric crystal is caused to oscillate thus actuating a reciprocating action which is used to drive by a ratchet process angular rotation of the respective disk. 
     The reciprocating action of the piezo-electric 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 which 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. 
     In other alternative arrangements (not shown), the ratchetting 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 ratchetting 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. 
     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 elements which allows the encoder to detect accurately 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 of course obtained by moving the lead screw longitudinally which carries the end stop  45  longitudinally. The movements are independent so that the fiber can be rotated while held longitudinally stationary. 
     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 which 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 which must be detected for the MRI analysis to be effective. 
     As shown in FIG. 7, therefore, the room  11  is surrounded by a conductor which prevents penetration of radio frequency interference into the area within the room at the magnet. In addition the cable  24  and the motor  22  are surrounded by a conductor  80  which extends through an opening  81  in the conductor at the wall  11  through a cable port  82  within the wall  83  of the enclosure so that the whole of the motor and the cable are encased within the conductor  80  which is connected to the conductor within the wall. Thus the conductor  80  acts as a “worm hole” in the shielding thus retaining the motor  22  and the cable  24  effectively external to the shielding at the periphery of the room. The use of a Piezo-electric 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. 
     In the method of operation, the patient is located on the patient table and so to be restrained so that the head of the patient is held fixed within the magnet to prevent motion artefacts. The MRI system is then operated in conventional manner to generate an image of the portion, generally a tumour, to be excised. The surgeon alone or in conjunction with suitable software available to one skilled in the art then analyses the images developed to locate the closed area surrounding the volume of the tumour and defining the external perimeter of the tumour as indicated at FIG. 8 at  90 . The surgeon also determines the best route for directing the cannula to the tumour to avoid damaging intervening tissue and to provide a best course to the centre of the tumour which may be irregular in shape. 
     Having determined the course and direction of the cannula, the opening  34  is formed and the cannula inserted as previously described. 
     With the cannula in place, the motor is mounted on the frame and the frame adjusted to locate the motor so that the fiber can be inserted directly along the length of the cannula. With the motor properly aligned along the axis of the cannula, the fiber is inserted through the bore of the motor and into the cannula so as to extend through the cannula until the tip emerges just out of the outer end of the cannula. The distance of the motor from the cannula can be adjusted so that the tip just reaches the end of the cannula when the lead screw is fully retracted and the end stop is located in place in the clamp  72 . 
     With the motor and fiber thus assembled, the MRI system is arranged to carry out experiments which generate temperature measurements 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 experiments to detect the temperature are continued, the fiber is moved longitudinally to commence operation at a first position just inside the volume of the tumour. At a selected angular orientation of the beam, pulses of radiation are emitted by the laser and transmitted into the tumour 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 tumour, the tumour is heated locally basically in the volume defined by the beam but also heat is conducted out of the volume of the beam into the remainder of the tumour at a rate dependent upon the characteristics of the tumour itself. Heating at a localised area defined by the beam is therefore continued until the heat at the boundary layer  90  is raised to the predetermined coagulation temperature of the order of 55 to 65° C. Once the boundary layer reaches this temperature, heating at that zone is discontinued and the fiber is moved either longitudinally or angularly or both to move to the next zone of the tumour 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. 
     It is of course desirable to effect heating as quickly as possible so as to minimize the operation duration. For this purpose the number of pulses per second may also be varied based upon the above predication depending upon the characteristics of the tumour as detected in the initial analysis. However the energy application rate cannot be so high that the temperature rises too quickly so that over shooting of the desired temperature at the boundary occurs with the possibility of damage to tissue outside the boundary. The rate of energy application is therefore selected depending upon the size and consistency of the tumour to effect heating at a controlled rate in order to achieve the required temperature at the boundary without the possibility of over shoot. 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 tumour and increases to a second larger distance  93  toward the center of the tumour. 
     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. 
     After a first disk shaped portion of the tumour is thus heated, the fiber is moved longitudinally through a distance dependant upon the diameter of the tumour at that location and dependant upon the beam angle so as to ensure the next disk shaped volume of tumour heated contains all of the tumour structure without intervening localised portions of the tumour which are not heated to the required temperature. Thus the fiber is moved longitudinally in steps which may vary in distance depending upon the diameter and structure of the tumour as determined by the initial analysis. However the total heating of the tumour is preferably determined by the temperature at the boundary without the necessity for analysis of the temperatures of the tumour inside the boundary or any calculations of temperature gradients within the tumour. 
     When the complete boundary of the tumour has been heated to the predetermined coagulation temperature, the surgery is complete and the apparatus is disassembled for removal of the fiber and the cannula from the patient. 
     The system allows direct and accurate control of the heating by controlling the temperature at the surface area defined by the boundary of the tumour so that the whole of the volume of the tumour is properly heated to the required temperature without the danger of heating areas external to the tumour beyond the coagulation temperature. 
     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.