referring now to the drawings wherein the showings are for the purposes of illustrating the preferred embodiments of the invention only and not for purposes of limiting same , with reference first to fig1 the subject invention is shown in use with an open “ c ” magnetic resonance ( mr ) imaging device 10 of the type well known in the art . since the imaging device 10 forms no part of the present invention , it will be described with a minimum of detail . as shown in the figure , the “ c ” type mr imaging device 10 includes a magneto motive force means 12 in the form of a pair of resistive magnet drivers 14 , 15 disposed adjacent pole pieces 16 , 17 on opposite ends of a c - shaped ferromagnetic flux path 18 . the magneto motive force means 12 together with a magnetic flux stabilizing means 20 creates and stabilizes a magnetic field across an air gap 22 between the pole faces and along the ferromagnetic flux path 18 . a retractable patient support 24 selectively supports a patient or subject to be examined in the air gap 22 defined between the pole faces . an energizing and calibration system 26 is used to set up the magnetic field across the air gap 22 . magnetic resonance electronics 28 selectively induce magnetic resonance of dipoles in the image region and process resultant received magnetic resonance signals to create an image or other diagnostic information . the ferromagnetic flux path 18 includes a c - shaped ferromagnetic member 30 having a first end 31 , a second end 32 , and a middle portion 33 . the first pole piece 16 on the first end 31 of the flux path together with the second pole piece 17 on the second end 32 define the air gap 22 therebetween . the c - shaped member 30 is configured to minimize the length of the ferromagnetic flux path while spacing the ferromagnetic flux path sufficiently from the gap to minimize distortion to the magnetic field in the air gap . the magnetic flux stabilizing means 20 includes a superconducting cryodriver 34 which encircles a segment of the middle portion 33 of the c - shaped ferromagnetic member 30 . as is well known by those skilled in the art , the cryodriver 34 includes a cryostat 36 which houses an annular superconductor magnet that encircles the flux path . alternatively , the magnetic flux can be generated by coils made of aluminum or copper conductors , for example , and energized by a precision current supply . the patient support 24 includes a patient supporting surface 40 in a substantially horizontal plane . the supporting surface has a longitudinal axis lengthwise therealong and a perpendicular transverse axis there across , both in the horizontal plane . an elevation adjusting means 41 selectively adjusts the relative height of the supporting surface . the supporting surface is slidably mounted on a support frame 42 to provide a means for moving the supporting surface in the horizontal plane . preferably , a motor drive 43 is mounted to the frame to drive the patient supporting surface therealong . a surgical instrument guidance and localizer device 50 is adapted to selectively carry a minimally invasive surgical instrument 52 . the localizer device 50 is positionable relative to the patient by an interventionist during pre - surgical planning and while carrying out surgical procedures in accordance with the present invention . the surgical instrument in the illustrated embodiment includes a manually guided biopsy needle 54 adapted to engage the guidance device 50 and slide therealong to enter the patient &# 39 ; s body along a precise trajectory and extract a piece of tissue from a precise location for analysis . it is to be appreciated , however , that numerous other instruments and guidance devices are contemplated . it is to be noted that the position and orientation of the localizer device 50 and the minimally invasive surgical instrument 52 mechanism carried thereon are monitoring by the imaging device 10 . preferably , passive optical tracking , such as available from northern digital inc . under their tradename polaris ™ is used . passive optical tracking of the localizer device 50 removes the need for cable connections and / or power supplies at the localizer device . alternatively , active or hybrid optical or other tracking systems can be used as well . a plurality of passive reflective targets , such as retro - reflective spheres or disks 60 are mounted on the localizer device 50 in a fixed , known relationship to the minimally invasive surgical tool 52 . a corresponding array of transmitters and receivers 62 is mounted in a fixed relationship to the imaging apparatus 10 , preferably affixed to the ceiling of the room . each time the transmitters are actuated and the emitted signal is reflected from the passive reflective targets 60 and then received by the receivers 62 , the position and orientation of the localization device 50 and therefore of the surgical instrument 52 carried thereon are accurately and quickly calculated substantially in real time using geometric triangulation techniques . by positioning the localization device on a plurality of markers 44 disposed in a known , fixed relationship to the coordinate system of the imaging apparatus 10 , the coordinate systems of the surgical instrument 52 and the imaging apparatus 10 can be readily correlated . analogously , by positioning the localization device 50 on a calibration and verification area 46 formed on the patient table 24 , the coordinate system of the surgical instrument 52 and the patient table 24 can be readily coordinated . to verify the orientation and position of the guidance device 50 relative to the patient support , a tip of the guidance device or a pointer carried thereon is touched to the calibration and verification area 46 and an assessment is made whether the electronic signals indicative of patient support location and surgical instrument location , in fact , place both at the same point in space . similarly , one or more markers 44 on the imaging apparatus in a fixed , known location relative to a plane of the magnetic resonance signals is touched by the tip of the guidance device or pointer and the electronic position signals are compared to be sure that the coordinate systems of the volumetric scanner 10 and the guidance device 50 are accurately correlated . with reference to fig2 an instrument coordinate circuit 100 determines the position and trajectory of the surgical instrument 52 carried on the guidance device 50 in instrument space , particularly a coordinate system of the instrument . the instrument coordinate circuit is connected with the receivers 62 to receive signals indicative of changes of position and orientation of the instrument in instrument space . an instrument - planning scanner correlating processor 102 determines the correlation or transform between the minimally invasive surgical instrument 52 and the volumetric scanner 10 coordinate systems . the correlation or transform is normally described in terms of offset ( particularly offset along the axis of the patient support ), angular offset or rotation , and scaling . in one embodiment , the instrument 52 is touched to three or more markers 44 which are in a known relationship to the volumetric scanner coordinate system . by measuring the coordinates of the instrument in the instrument coordinate system while touching each marker , three or more common points in the two coordinate systems are determined . by determining a barrycenter , centroid , or other characteristic point of the common points , the offset between the two coordinate systems is determined . by determining the angular difference between the rays from the characteristic point to each point in each coordinate system , the angular offset is determined . by determining a difference in physical displacement between the characteristic point and the corresponding points in each coordinate system , the scaling factor is determined . of course , in a system such as the illustrated embodiment in which the instrument and the volumetric scanner are electronically linked by arrays of emitters and receivers , the transform or relationship between the volumetric scanner and the instrument coordinate systems are determined during a calibration of the electronic system during installation . the touching of the markers can be eliminated or used merely to confirm that the instrument and the mr scanner coordinates have not become misaligned . an instrument - to - patient table correlating processor 104 performs a similar calculation or uses similar known physical relationships to determine the correlation or transform between the patient table and the surgical instrument . preferably , a phantom having a multiplicity of marks is disposed in a known position on the table to provide a larger number of corresponding points in both coordinate systems for the correlating process . images of the phantom can be used to derive transforms between the patient table space and planning or real time image coordinate systems . table resolvers 110 located in the patient table 24 contribute vertical and longitudinal offsets to the correlation between the instrument and the patient table when the table is raised or lowered and when the patient supporting surface 40 is moved axially . an instrument - to - patient correlation processor 112 determines the correlation between the instrument coordinate system and a patient coordinate system . again , this is preferably done by placing the instrument on three or more known reference points on the patient . such points may include readily identifiable anatomical structures such as the tip of the nose , distinctive points on bones , fiducial markers that are imaged during the volumetric imaging process , or the like . an instrument - to - volumetric image coordinate system transform processor 120 receives the correlation or transform from the instrument - to - planning scanner correlating processor 102 . the instrument - to - volumetric image processor operates on input position and orientation coordinates in image space to transform them into volumetric image data space or vice - versa . knowing the position of the surgical instrument in volumetric or planning data space enables the position of the instrument and orientation of same to be superimposed on the volumetric planning image data . during a medical procedure , the patient is positioned in the imaging apparatus and a volumetric image data set is generated . the volumetric image data set is stored in a volumetric or planning data memory 122 . the position of the patient during the generation of the planning data , particularly as the table moves to generate spiral or slice data , is stored in conjunction with the volumetric planning data such that the data is correlated with the patient table coordinate system . the operator control 38 controls the volume planning image data memory or a video processor 124 such that selected slices , projection images , surface renderings , or other conventional displays of the data are generated for display on a planning image display 126 . preferably , the planning image display includes corresponding sagittal , coronal , and transverse axial slices through one or more selected common points of intersection . with reference to fig3 in accordance with the present invention , during the planning stage before implementation of an interventional surgical procedure , a patient planning image 130 is presented on the planning image display 126 . the at least one patient planning image 130 is preferably a single image slice drawn from a first image volume data set generated by scanning the patient in the imaging device . preferably , in accordance with the invention , at least five ( 5 ) image slices are contained in each image volume data set generated in a single patient scan . movement of a virtual surgical instrument 132 within the patient planning image 130 is preferably controlled at the interventionist &# 39 ; s control console 38 . however , the localizer device 50 can also selectively be used as well . in addition , movement of a set of virtual cross - hairs 134 is also preferably controlled at the interventionist &# 39 ; s control console 38 . however , the localizer device 50 can also selectively be used as well . preferably , the control console includes at least one operator interface device 39 ( fig2 ) to enable the operator to point to a plurality of selected virtual locations on one or more sectional planning images 130 of the patient shown on the planning image display 126 . in the embodiment illustrated , the interface device 39 is a standard mouse , but other “ pointing ” type devices can be used as well including a trackball , a joystick or the like . in accordance with a first preferred embodiment of the present invention , the form of presentation of the patient planning image 130 to be shown on the planning image display 126 is planned by placing a plurality of graphical point symbols 136 in the first sectional image 130 of the patient using the virtual cross - hairs 134 and the interface device 39 or , alternatively , using the localizer device 50 . the plurality of graphical point symbols 136 selectively placed in the first sectional image 130 define a boundary in the image volume data set to be displayed in a subsequent sectional image of the patient to be displayed . in a first form , the second sectional image of the patient to be displayed is derived by the present invention using exclusively the set of image slices contained in the data stored in the volumetric planning data memory 122 without further processing . the data is merely scaled or otherwise manipulated ( but without interpolation ) so that the boundary in the image volume data set is displayed to fill the planning image display 126 . in a second form , the second sectional image of the patient to be displayed is derived using the set of image slices contained in the data stored in the volumetric planning data memory 122 after additional further processing . the data comprising the first image volume data set is preferably interpolated and then scaled so that the boundary in the interpolated image volume data set is displayed to fill the planning image display 126 . in a third form , the second sectional image of the patient to be displayed is derived by re - scanning the patient in the imaging device 10 to acquire a second image volume data set and to generate a new set of image slices for storage in the volumetric planning data memory 122 . preferably , the second area of the patient to be re - scanned is defined by and bounded by the plurality of graphical point symbols 136 that were selectively placed in the first sectional image 130 . the collected data from the patient re - scan is scaled so that the boundary in the new image volume data set is displayed to fill the planning image display 126 . each of the above forms of deriving the second image volume data set is selectively available to an interventionist using suitable controls at the operator control console 38 . the first form provides the quickest update in the displayed image . the second form provides a somewhat slower image display update , but presents a more comprehensive overall view of the virtual anatomy . as indicated above , however , interpolation typically degrades the image quality and affects image appearance . the third form provides the slowest image update but presents the most detailed view of the portion of the patient &# 39 ; s anatomy selected from the first image slice . with continued reference to fig3 a virtual surgical instrument 132 is shown superimposed on the patient planning image 130 . the position and orientation of the virtual surgical instrument 132 is selected and controlled at the operator console 38 using the interface device 39 or , alternatively , by using a physical localizer 50 . the virtual surgical instrument 132 defines a virtual tool trajectory 140 extending through the patient planning image 130 . it is an advantage of the present invention that the virtual tool trajectory 140 is represented in a first graphical form 142 for a first portion thereof extending on a first side of the image slice shown on the display as the patient planning image 130 . also , it is a further advantage of the present invention that the virtual tool trajectory 140 is represented in a second graphical form 144 for a second portion thereof extending on a second side of the image slice shown on the display as the patient planning image 130 . the presentation of the virtual tool trajectory 140 in two distinct graphical forms enables easy , quick and accurate visualization of the trajectory in a 3 - d conceptual form even though the patient planning image is in reality essentially a two - dimensional image . in that way , an interventionist can recognize first portions 142 of the virtual tool trajectory 140 that lie “ between ” the interventionist and the plane of the image slice defining the patient planning image . in addition , the interventionist can recognize second portions 144 of the virtual tool trajectory 140 that lie “ beyond ” the plane of the image slice defining the patient planning image . in addition , each of the plurality of graphical symbols 136 including a virtual entry point 150 , a virtual target point 152 , a pivot point 153 , cross - hairs 134 , etc . are similarly represented to enable a “ 3 - dimensional ” planning visualization in a 2 - dimensional image 130 . with continued reference to fig3 the interventionist can , as an alternative to the above , define the virtual tool trajectory 140 by selecting a virtual entry point 150 and a virtual target point 152 on the image of the patient by placing the virtual cross - hairs 134 at a selected positions on the patient planning image 130 and actuating one or more suitable control switches ( not shown ). target and entry points that lie “ between ” the interventionist and the plane of the image slice defining the patient planning image are displayed in a first unique graphical form such as , for example , as differently colored highlighted points . similarly , target and entry points that lie “ beyond ” the plane of the image slice defining the patient planning image are displayed in a second unique graphical form such as , for example , as differently colored flashing or strobed points . after the virtual target point 152 is selected in accordance with the above , the present invention provides means for interactive guidance of physical surgical tools into the body of the patient along the planning trajectory as represented by the virtual tool trajectory 140 . preferably , with reference now to fig4 a - 4 c , a virtual bulls - eye 160 and a virtual proximity scale 170 are displayed on the operator console 38 to assist interventionists while introducing surgical tools into the patient . the virtual bulls - eye 160 and scale 170 are responsive to the position and orientation of the localizer device 50 as tracked by the optical tracking system to provide a visual real time indication of the correctness of the tool path defined by the position of the localizer . more particularly , the size of the virtual bulls - eye 160 displayed becomes slightly larger , from the size shown in fig4 a to the size shown in fig4 b , when the physical localizer device 50 is aligned with the virtual tool trajectory 140 . also , the position of the proximity scale 170 changes from the indicator position 172 to the indicator position 174 . in addition , the size of the virtual bulls - eye 160 grows slightly from the size shown in fig4 b to the size shown in fig4 c when the physical localizer device 50 is advanced along a path defined in a virtual planning space by the virtual tool trajectory 140 towards the target point within the patient . further , the position of the proximity scale 170 changes from the position 174 to the indicator position 176 . preferably , the virtual bulls - eye 160 is increased in size to completely fill the outer scope scale 162 when the surgical tool 52 reaches the target point . in that way , the interventionist is provided with a real time visualization of the progress of the introduction of the surgical tool into the patient &# 39 ; s body . further , the color of the virtual bulls - eye 160 changes such as , for example , from red to blue , when the surgical tool is advanced beyond the selected target point . in addition , preferably , the size of the vertical bulls - eye 160 is decreased and the portion shown on the virtual scale 170 is changed in proportion to the distance that the surgical tool is moved beyond the selected target point . the interventionist is thereby provided with further real time visualization of the progress of the correctness of the introduction of the surgical tool into the patient &# 39 ; s body . the invention has been described with reference to the preferred embodiments . obviously , modifications and alterations will occur to others upon reading and understanding the preceding description . it is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof .