Abstract:
A trajectory guide assembly that guides an instrument relative to a patient includes a mounting seat configured to be supported by the patient. The assembly also includes a trajectory member moveably supported by the mounting seat. The trajectory member defines a trajectory passage. Also, the assembly includes a cap member moveably supported by the trajectory member. The cap member defines a cap opening, and the cap member is selectively moveable to a first position relative to the trajectory member to retain the instrument in both the cap opening and the trajectory passage. Additionally, the cap member is selectively moveable to a second position relative to the trajectory member to release the instrument.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional application of U.S. patent application Ser. No. 10/894,958 (issued as U.S. Pat. No. 7,637,915), filed Jul. 20, 2004, which is a divisional application of U.S. patent application Ser. No. 09/932,141 (issued as U.S. Pat. No. 6,902,569), filed Aug. 17, 2001, which claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 60/225,952, filed Aug. 17, 2000, the disclosures of which are incorporated herein by reference in their entirety. 
    
    
     FIELD 
     This document relates generally to surgical trajectory guides. More specifically, but not by way of limitation, it relates to apparatuses and methods that facilitate alignment of surgical and observational instruments into a body. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     In the treatment of some diseases or defects associated with a patient, it has been found necessary to access specific targets within a patient. In the treatment of some diseases of or defects of human beings, it has been found necessary to access specific portions of the brain. Currently there are several methods for inserting surgical and observational instruments into a patient&#39;s brain. 
     U.S. Pat. No. 3,055,370 issued to McKinney et al. shows one currently used method for placing a surgical instrument to access a specific portion of the brain. The surgical instrument of the &#39;370 patent includes a ball which has a bore. The direction of the bore can be changed. The instrument has an elongated tube of a specific length. A stylet is inserted within the tube to access the globus pallidus and perform a pallidotomy. An opening or burr hole is made in the skull at a specific landmark on the skull. Next, X-rays are taken in the fore-and-aft (AP) and lateral positions, and the line of the bar is projected downwardly by a ruler both in the fore-and-aft (AP) and lateral positions, so that the direction of the needle can be determined before it is inserted. When the direction of the longitudinal axis of the tubular member is determined to be satisfactory, a holder is threaded further into a tap to force a surface against a ball and lock a tubular member into place. Alignment of the trajectory is not measurable along a specific line occurring at the intersection of two planes. Alignment is dependent on placement of the burr hole at a specific location to determine one plane. X-rays are used to determine another plane-based use of common landmarks on the skull. The end result is that an educated guess is being used to position the stylet at the globus pallidus for the pallidotomy. One shortcoming with the method of using X-ray imaging to direct a surgical or observational instrument, is that many of the destinations within a patient are not viewable via X-ray. Another shortcoming relates to the slight shifting of intracranial contents, once a burr hole is placed and the dura and arachnoid are penetrated. Once cerebrospinal fluid is released via the burr hole, the intracranial contents (i.e. brain) may shift one or more millimeters. In such a case, the calculated trajectory is no longer accurate. Hence, there is an inherent inaccuracy with the described scheme. 
     Several other methods are also used to place instruments, catheters, or observational tools into patients. Currently, surgical procedures are performed through craniotomy flaps or craniotomy burr holes. A burr hole of about 14 mm is made in the skull. Needles or probes are typically passed through the burr hole into the brain using framed stereotaxy, frameless stereotaxy or freehand without stereotaxy. 
     The freehand method depends very heavily on the knowledge and judgment of the surgeon. In the freehand method, the surgeon determines the insertion point with a couple of measurements from a known landmark. The surgeon then looks at the measured point, makes adjustments, determines the angle of insertion and then inserts the surgical instrument or tool. 
     In framed stereotaxy, a ring frame is mounted to the patient&#39;s skull by multiple (typically three or four) pins or screws. This ring frame is used to determine a three dimensional data set. From this data set, Cartesian coordinates are calculated for both the lesion, the location of the pins or screws, and the fiducial marks on the frame. The ring frame fits into a large frame. A large frame is then attached to the patient in the operating suite. The large frame provides known positions and guides the surgical or observational instruments. The large frame is used to position the instrument to be introduced into the patient through a burr hole so that it intersects the target. In frameless stereotaxy, the ring frame is replaced with several markings on the patient&#39;s skull which can be used to determine several known positions. The large frame is replaced by a camera. The camera is usually infrared or some such device. Multiple sensors readable by the camera are placed on the instrument. For example, the surgical instrument or tool is provided with one or more light emitting diodes (“LEDs”) which are tracked by the camera. The position of the surgical instrument can be calculated from the information from the LEDs on the surgical instrument or observational tool. 
     U.S. Pat. No. 4,955,891 and U.S. Pat. No. 4,805,615, both issued to Carol, each discuss the use of stereotaxy surgery with computerized tomographic (“CT”) scanning. CT scanning is used to determine the exact position of a lesion or specific portion of the brain. After the exact position of the lesion or specific portion of the brain is determined, a phantom fixture is set up. The phantom fixture replicates the position of the ring frame on the patient. A phantom target is set up. The instrument can then be positioned on the phantom such that it intersects the target. The information from the phantom can then be used in actually positioning the instrument in the operating suite. 
     U.S. Pat. No. 4,998,938 issued to Ghajar et al. shows another surgical device for facilitating the insertion of an instrument into a patient&#39;s cranial cavity through a burr hole. The device includes a guide having an end configured to pass into the burr hole. There is a separate locking member. A body member includes alignment markings to help with insertion of a catheter or stylet. Unlike the &#39;370 patent, there is no movable member for adjusting the path of the guide. 
     The methods currently in use all have a number of shortcomings. Most of the techniques currently used to place a surgical instrument or observational tool within a patient employ a limited amount of accuracy. In particular, current framed, frameless, and freehand methods compute or predict trajectories on the basis of imaging data or anatomic landmarks that do not account for the slight, but real shifting of the brain upon opening the cranium and meninges to the level of the subarachnoid space. This inherent inaccuracy inherently limits the success of these various methodologies. In other words, these systems do not use any means of updating the data files to include data obtained following the placement of a surgical burr hole and opening of the meninges. In addition, all the methods require large amounts of judgment on the part of the surgeon placing the surgical instrument or tool, and in particular, offer no direct feedback on the success or failure of the trajectory to reach the target. Very few of the techniques use an imaging or scanning apparatus to aid in the placement of the surgical instrument or observational tool. The only one that does requires a phantom frame and target to be set up to simulate the real geometry. In short, none of the apparatuses appear to use an imaging or scanning apparatus as extensively as they could be used to minimize the time and effort needed to accurately place a surgical instrument into a patient, and to offer immediate data on the success or failure of the trajectory to reach the target. 
     The trajectory guide system taught in Published International Patent Application PCT/US98/10008 (International Publication number WO 98/51229) addresses these and other shortcomings of prior art surgical working platform systems as described above. The disclosed system provides a means for accurately determining the trajectory of a surgical instrument within a passage which in turn lies within a guide or positioning stem that extends from a movable member that is selectably lockable in position with respect to a base. Some embodiments of this system employ removable guide stems or positioning stems that can be removed from the movable member once an appropriate trajectory has been chosen and a surgical instrument inserted into the passage formed within the chosen stem and movable member. One disadvantage of this system is that there may be axial movement introduced to the instrument by the process of removing the stem; that is, the instrument may be disadvantageously introduced further into the body, or disadvantageously removed farther from the body, by the axial motion of the stem as it is removed. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     A trajectory guide assembly that guides an instrument relative to a patient is disclosed. The assembly includes a mounting seat configured to be supported by the patient. The assembly also includes a trajectory member moveably supported by the mounting seat. The trajectory member defines a trajectory passage. Also, the assembly includes a cap member moveably supported by the trajectory member. The cap member defines a cap opening, and the cap member is selectively moveable to a first position relative to the trajectory member to retain the instrument in both the cap opening and the trajectory passage. Additionally, the cap member is selectively moveable to a second position relative to the trajectory member to release the instrument. 
     Also, a trajectory guide assembly that guides an instrument relative to a patient is disclosed. The trajectory guide assembly includes a mounting seat configured to be supported by the patient, and the mounting seat includes a hemispherical seat portion defining a seat opening passing therethrough. The assembly also includes a ball member rotatably supported within the hemispherical seat portion. The ball member defines a trajectory passage, and the trajectory passage and the seat opening are configured to simultaneously receive the instrument. Moreover, the assembly includes a cap member that is moveably supported by the ball member. The cap member defines a cap opening. Also, the cap member is selectively moveable to a first position relative to the ball member to retain the instrument in each of the cap opening, the trajectory passage, and the seat opening, and the cap member is selectively moveable to a second position relative to the ball member to release the instrument. 
     Still further, a method for guiding an instrument relative to a patient is disclosed that includes supporting a mounting seat on the patient and supporting a trajectory member on the mounting seat. The method also includes rotating the trajectory member relative to the mounting seat to point an axis of a trajectory passage toward a target in the patient. Furthermore, the method includes moving a cap member relative to the trajectory member to expose the trajectory passage through an opening in the cap member. Also, the method includes introducing the instrument through the opening in the cap member, the trajectory passage, and into the patient toward the target. Additionally, the method includes moving the cap member relative to the trajectory member to retain the instrument in both the opening and the trajectory passage and between the cap member and the trajectory member. 
     Moreover, a trajectory guide assembly that guides an instrument relative to a patient is disclosed. The trajectory guide assembly includes a mounting seat configured to be supported by the patient. The mounting seat includes a flange defining a hole that receives a fastener for selectively securing the mounting seat to the patient. The mounting seat further includes a hemispherical seat portion that defines a seat opening. The assembly also includes a spherical ball member rotatably supported within the hemispherical seat portion, and the ball member defines a trajectory passage. The trajectory passage has a width that is less than a width of the seat opening of the mounting seat. Furthermore, the assembly includes a first set screw that extends through the mounting seat and selectively secures the spherical ball member in a fixed position relative to the mounting seat. Moreover, the assembly includes a cap member that is slidably supported by the ball member, and the cap member defines a cap opening and a slot. The cap opening has a width that is less than a width of the trajectory passage. Additionally, the assembly includes a second set screw that is moveably received in the slot and that selectively secures the cap member in a fixed position relative to the ball member. The slot limits movement of the cap member relative to the ball member. Furthermore, the cap member is selectively moveable to a first position relative to the ball member to retain the instrument in each of the seat opening, the trajectory passage, and the cap opening and between the cap member and the trajectory member. Also, the cap member is selectively moveable to a second position relative to the ball member to release the instrument. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a block diagram of a patient scanning system. 
         FIG. 2  is a side view of a patient on which the trajectory guide is being used. 
         FIG. 3  is an exploded isometric view of the trajectory guide with a removably attached guide member installed. 
         FIG. 4  is an exploded isometric schematic view of the trajectory guide with a removably attached positioning member installed inside the removably attached guide member. 
         FIG. 5   a  is an exploded isometric view of the movable member or ball and guide stem of the trajectory guide. 
         FIG. 5   b  is a cross-sectional view of the movable member or ball of the trajectory guide. 
         FIG. 5   c  is a cross-sectional view of the movable member or ball of the trajectory guide after insertion of the relaxable stabilizer and removably attached guide member. 
         FIG. 5   d  is a cross-sectional view of the assembly of  FIG. 5   c , after further insertion of a catheter or instrument. 
         FIG. 5   e  is a view of the assembly of  FIG. 5   d , after unscrewing and partial removal of the removably attached guide member. 
         FIG. 5   f  is a view of the assembly of  FIG. 5   e , after complete removal of the removably attached guide member. 
         FIG. 5   g  is a close up side view of a portion of  FIG. 5   f.    
         FIGS. 6   a  and  6   b  are isometric views of one example of a base of the trajectory guide. 
         FIGS. 6   c - 6   e  are bottom, side, and top views, respectively, of the base of  FIGS. 6   a  and  6   b.    
         FIG. 6   f  is a cross sectional view taken along the line  6   f - 6   f  of  FIG. 6   c.    
         FIG. 6   g  is a side view of the base of  FIG. 6   c.    
         FIGS. 7   a  and  7   b  are isometric views of one example of the locking member of the trajectory guide. 
         FIG. 7   c  is a top view of the example of the locking member of the trajectory guide. 
         FIG. 7   d  is a cross-sectional view of the example of the locking member of the trajectory guide, taken along the line  7   d - 7   d  of  FIG. 7   c.    
         FIGS. 8   a ,  8   b  and  8   c  are perspective views showing the use of a base with a flexible instrument that is tunneled under a skin flap. 
         FIG. 9   a  is a perspective view of one example of a cap member of a trajectory guide. 
         FIGS. 9   b  and  9   c  are side and bottom views, respectively, of the cap member of  FIG. 9   a.    
         FIG. 9   d  is a close up side view of a portion of  FIG. 9   b.    
         FIG. 10   a  is an isometric view of a preferred embodiment of a alignment or positioning member for the trajectory guide. 
         FIG. 10   b  is an exploded side view of the embodiment of  FIG. 10   a.    
         FIG. 10   c  is a side view of a portion of the embodiment of  FIG. 10   b.    
         FIG. 10   d  is a side cross sectional view of the embodiment of  FIG. 10   c.    
         FIG. 10   e  is an end view of the embodiment of  FIG. 10   d.    
         FIG. 10   f  is a detailed view of a portion of the embodiment of  FIG. 10   e.    
         FIG. 11   a  is a partial cutaway side view of an alternative embodiment of the base and alignment guide. 
         FIG. 11   b  is a side view illustrating the use of the alternative embodiment of  FIG. 11   a  with the alignment member from  FIG. 10 . 
         FIG. 12   a  is a partial cutaway isometric view of yet another alternative embodiment of the base and alignment guide. 
         FIG. 12   b  is an isometric view illustrating the use of the alternative embodiment of  FIG. 12   a.    
         FIG. 13   a  is a top perspective view of a movable member, a guide stem, and a two-piece base including a mounting seat and a collar. 
         FIG. 13   b  is a top exploded view of a cap and the mounting seat and the movable member of  FIG. 13   a.    
         FIG. 13   c  is a bottom exploded view of the mounting seat and cap of  FIG. 13   b.    
         FIG. 13   d  is a bottom perspective view of the mounting seat and cap of  FIG. 13   b.    
         FIG. 13   e  is a top perspective view of the cap and mounting seat of  FIG. 13   b.    
         FIG. 14   a  is a top perspective view of a two-piece base, including a mounting seat and collar, and a movable member. 
         FIG. 14   b  is an exploded side view of the two-piece base of  FIG. 14   a.    
         FIG. 15   a  is a top perspective view of a low-profile mounting seat, movable member and guide stem. 
         FIG. 15   b  is a side view of the apparatus illustrated in  FIG. 15   a.    
         FIG. 16   a  is a top view of a low-profile mounting seat, movable member, and collar. 
         FIG. 16   b  is a side view of the mounting seat and collar of  FIG. 16   a.    
         FIG. 16   c  is a top exploded view of the two-piece base provided by the mounting seat and collar of  FIGS. 16   a  and  16   b.    
         FIG. 17  is a top perspective view illustrating an example of an instrument that has been laterally bent into one of the grooves of the mounting seat of  FIGS. 16   a - 16   c.    
         FIG. 18   a  is a bottom perspective view of an example of a low-profile mounting seat and cap. 
         FIG. 18   b  is a top view of the cap and mounting seat of  FIG. 18   a.    
         FIG. 18   c  is a side perspective view of the cap and mounting seat of  FIGS. 18   a  and  18   b.    
         FIG. 19   a  is a side view of a mounting seat, ball, and stabilizing cap. 
         FIG. 19   b  is a top view of the ball and cap with aligned openings. 
         FIG. 19   c  is a top view of the ball and cap with offset openings to grasp and stabilize an instrument. 
     
    
    
     Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION 
     Example embodiments will now be described more fully with reference to the accompanying drawings. 
     This application incorporates International Patent Application PCT/US98/10008 (International Publication number WO 98/51229) by reference, together with the disclosure of its U.S. counterpart, issued U.S. Pat. No. 5,993,463, which is also incorporated herein by reference in its entirety. 
     Scanning System Example 
       FIG. 1  is a block diagram of a patient scanning system  100 . The specific scanning system shown is for a magnetic resonance imaging (“MRI”) system. An MRI scanning system  100  includes a computer  102 . The computer  102  includes a central processing unit (“CPU”)  104  and memory  106 . The CPU  104  and memory  106  has the capacity to perform multiple calculations used to determine images as well as positions of various organs, or portions or within an image field. The computer  102  controls an image data processing portion  110 , a system controller and waveform generator portion  120 , and an XYZ gradient producing portion  130 . The XYZ gradients are amplified and used to provide a gradient magnetic field in the X, Y, and Z directions as part of a magnet system  140 . The magnet system  140  includes a magnet which produces a magnetic field through which a patient can pass. The shape of the magnet varies among MRI systems. The shape of the magnet and its relation to the table upon which the patient lies, determines whether the patient can be accessed by a surgeon while an MRI is being performed. There are many styles of MRI devices that do not place the surgeon within a close enough proximity to allow access to the patient during an MRI scan operation. 
     The MRI system  100  also includes gradient amplifier  150 . Also included are a set of RF amplifiers  160  and RF coils  162  which are used in conjunction with the magnet system  140  to produce and transmit RF pulses in the magnetic field. Either the same RF coil or another RF coil is used to detect the MR signals from the interrogated tissues. This detected MR signal is then amplified by a preamplifier  164  and received by a receiver  166  for transmission to the data acquisition system  170  and then transmitted to the image data processing computer system  110 . The data acquisition system is input to the system controllers and waveform generator portion  120  of the computer  102  as part of a feedback loop. The data is interpreted and placed on a display  180  associated with the computer of the MRI system  100 . The computer  102  and the CPU  104  and memory  106  can use data acquired from the MRI system  100  to build up images of a portion of the patient which is being scanned. The images are typically referred to as slices. For example, a horizontal slice and a vertical slice can be made of the portion of the body or patient being imaged. The computer can also recalculate and build other slices for use by doctors and radiologists having any selected orientation needed to facilitate study of various items within a patient. For example, lesions can be found within the body as well as certain organs. Different slices can be requested to facilitate study of these targets. From the data acquired, the position of the lesions or organs can also be very accurately determined using a Cartesian or polar coordinate system. The above description of the MR scanner is simply for demonstrative purposes and multiple alternative MR scanning systems can be described herein. 
     Trajectory Guide Example 
     Within some parts of a patient, it is critical to very accurately place a surgical instrument. For example, in neurosurgery, it is very critical to have instruments, such as catheters or needles, placed very accurately within the cranium or head of a patient.  FIG. 2  shows a side view of a patient on which trajectory guide  200  is being used. The trajectory guide  200  includes a base unit  210 , a movable member  220 , a locking member  230  and a guide stem  240 . The base unit  210  is attached to the skull of the patient. In the particular embodiment shown, the attachment is made by way of bone screws. However, it is contemplated, that there may be any number of ways to attach the base  210  to the skull. For example, the base  210  could also be threaded to screw into a burr hole  250 . The flange could also be added to the base  210  to attach the base to the skull. 
     The movable member  220  has an axial opening  222  which is shown in  FIG. 2  as dotted lines. The guide stem  240  also has an elongated opening  242  therein. The opening  242  is also shown as dotted lines in  FIG. 2 . The passage  242  in the guide stem  240  and the axial opening  222  in the movable member or ball  220  form a line or a trajectory  260  which intersects with a target  270  within the patient. The guide stem  240  and movable member or ball  220  form the first part of the trajectory  260 . A surgical instrument or observational tool can be inserted into the opening  242  of the guide stem  240  and passed through the passage in the movable member  220  and then further inserted into the patient a selected distance to the target  270 . The opening  242  in the guide stem  240  and the passage  222  in the movable member  220  guide a surgical instrument along the trajectory  260  to the target  270 . Of course, the movable member  220  is locked into place by locking member  230  before a surgical instrument  280  is placed through the opening  242  in the guide member  240 . 
       FIG. 3  shows an exploded isometric view of the trajectory guide  200  with a guide member installed. As shown in  FIG. 3 , the trajectory guide  200  is comprised of a base  210 , a movable member  220 , a locking member  230 , and a guide member  240 . The base  210  includes a cylindrical portion  212  and a flange  214 . The flange  214  includes a plurality of countersunk screw openings  215 ,  216 , and  217 . The countersunk screw openings  215 ,  216 , and  217  receive bone screws which are screwed into the skull bone or the bone of a patient. The cylindrical portion  212  fits within the burr hole  250  in the patient. The base also includes a semi-spherical seat  218 . Although not shown in  FIG. 3 , there is an opening in the base  210  having a first end which terminates at the seat  218  and another end which terminates at the bottom of the base  210 . 
     As shown in  FIG. 3 , the movable member  220  is essentially a spherical member or a ball. The spherical member or ball fits within the seat  218 . The spherical member or ball moves freely within the seat  218 . The ball-shaped movable member  220  also has an opening. The opening passes through the ball shaped movable member. One end of the opening may have a set of internal threads therein, which can be used to receive mating threads which are placed onto the guide stem or member  240  or positioning stem (discussed with respect to  FIG. 4 ). 
     The locking member  230  also has an opening therethrough. The locking member  230  includes a cylindrical bottom portion  232  and a flange  234 . The opening through the locking member  230  has sufficient space to allow movement of movable member  220  when the locking member is in an unlocked or untightened position. Although not shown in  FIG. 3  or  4 , the bottom of the cylindrical portion  232  of the locking member  230  includes a set of external threads. The set of external threads engage a set of internal threads on the base unit  210  (shown in  FIGS. 6   a - 6   g ). As will be detailed later, when the external threads of the locking member  230  are engaged with the threads on the base  210 , a portion of the locking member engages the movable member  220  to fix the movable member and the axial opening  222  therethrough at a fixed position. 
     A guide stem or guide member  240  is also shown in  FIG. 3 . The guide stem has an elongated opening  242  therein. The elongated opening passes through the length of the guide stem  240 . One end of the guide stem includes a set of external threads which engage the internal threads of the spherical, movable member  220 . When the external threads of the guide stem  240  engage the internal threads of the movable member  220 , the opening  242  is substantially aligned with the axial opening  222  in the movable member. The opening  242  and axial opening  222  form the first part or guide for the trajectory  260  to the target  270  within the patient. It should be noted that the movable member  220  need not necessarily be a spherical element, although the spherical shape allows the ball to have a universal joint type swivel action which is preferred. It should also be noted that the locking member  230  can be formed in most any shape. A flange  234  is useful in that it allows additional leverage for tightening or loosening the locking member. Any shape capable of being turned or placed into a locking position with respect to the movable member  220  is acceptable. 
     Positioning Member Example 
       FIG. 4  is a schematic illustration that shows an exploded isometric schematic view of the trajectory guide  200  with a positioning member  400 .  FIG. 4  is a schematic illustration intended to illustrate the functionality of the positioning member. In  FIG. 4 , an end  410  of positioning stem  400  has been inserted into guide stem or guide member  240 . Positioning stem  400  may also include a first locator  420  and second locator  430 . First locator  420  includes a small opening  422  located at one end of the positioning stem  400 . The small opening  422 , which is shown in phantom in  FIG. 4 , is filled with a fluid or a substance that can be seen by a scanning device such as the MRI scanning device  100  described and shown in  FIG. 1 . After a fluid or substance is inserted into the opening  422  the end is sealed with a cap and adhesive. Similarly, the second locator  430  includes an opening  432  which contains a substance which is readable by a scanner such as an MRI scanner shown in  FIG. 1 . As shown in  FIG. 4 , the first locator  420  and the second locator  430  are coaxial with the axis of the cylinder formed by the positioning stem  400 . It is contemplated that a first locator  420  and a second locator  430  could also be formed in an offset position from the axis of the cylinder formed by the positioning stem  400 . 
       FIGS. 10   a - 10   f  show one example of a positioning stem. In  FIG. 10   b , positioning stem  1700  includes a main portion  1710  having a substantially hollow portion  1711  capable of accepting optional end cap  1712 . This two-piece construction may be used, for manufacturing reasons, but is not required if a one-piece construction performing the same functionality is desired. A fluid such as (but not necessarily) saline, which is readable by nuclear magnetic resonance (NMR) imaging system, is housed or kept in a chamber  1711  of positioning stem  1700 . In this example, the fluid is contained between a proximal portion  1750  of end cap  1712  and a distal portion  1760  of main portion  1710 . The fluid within chamber  1711  can be easily located under NMR and is used for alignment of the positioning stem, so that opening  222  within movable member  220  is on a straight line trajectory with a target within the patient. 
     Alternatively, positioning stem  1700  may include a region of solid material that appears on the MR image only by virtue of its absence of MR visibility. 
     A series of bump-like protrusions or other features  1740  are arranged around a circumference of a distal portion of tapered distal shaft end  1730 . Similarly, a series of box-like features  1770  are arranged around the central portion of the main portion  1710 , proximal of the tapered distal shaft end  1730  and distal of a stop  1780 . Features  1740  and  1770  are optional features that help hold positioning stem  1700  in place as it is inserted into guide stem  240  until it is stopped in place by stop  1780 . 
     Movable Member Example 
       FIGS. 5   a  and  5   b  show one example of a movable member  220  that includes two mating, substantially hemispherical portions  220   a  and  220   b  that, when assembled, provide a substantially spherically shaped movable member  220 . Movable member  220  has an axial opening  222  therein. Axial opening  222  includes a first opening  223  in upper hemispherical portion  220   a , and a second opening  224  in lower hemispherical portion  220   b . The inside surface of first opening  223  is threaded as indicated by reference numeral  225 . First opening  223  and threads  225  receive an external threaded portion  241  of guide stem  240 . Second opening  224  is of a sufficient diameter to allow an instrument, such as a needle, probe, catheter, endoscope, or electrode to pass through the axial opening  222 . Movable member  220  is made of a rigid or semi-rigid biocompatible polymer material. Suitable materials include polycarbonate or DELRIN®. 
     Lower hemispherical portion  220   b  further includes a recess  226  sized and shaped to accept a relaxable stabilizer  227 . Relaxable stabilizer  227  is sized and shaped to complement the size and shape of recess  226 , thus fitting closely inside recess  226  so as not to move out of proper position inadvertently. Also, relaxable stabilizer  227  has an axial opening  228  that generally is coaxial with axial opening  222  of the movable member  220 . 
     Because movable member  220  is preferably a relatively stiff material such as polycarbonate, and relaxable stabilizer  227  is relaxable and therefore made of a relatively more compliant material such as silicone, the two hemispherical portions  220   a  and  220   b  and the relaxable stabilizer  227  will generally be manufactured separately and assembled into the configuration shown in  FIG. 5   b . However, the scope of the invention includes an integrally constructed movable member having a material that is relaxable, and that otherwise performs the functions of the relaxable stabilizer as described below. Other suitable materials for relaxable stabilizer  227  include latex, C-flex, Viton, Buna-N, polyurethane, Kraton, and Santoprene. 
       FIGS. 5   c  through  5   g  illustrate one process of positioning a instrument  229  within the movable member  220  so as to restrict or prohibit axial motion of the instrument  229 . 
     Before attachment of guide stem  240  to movable member  220  as shown in  FIG. 5   c , a suitable tool (not shown) is used to stretch (or otherwise increase the inside diameter of) the relaxable stabilizer  227 , until the axial opening  228  of relaxable stabilizer  227  is large enough to accept the outer diameter of the guide stem  240 . This permits the stem to be fully inserted into the movable member  220 , through the stretched axial opening  228  in relaxable stabilizer  227 , and then screwed into place utilizing external threads  241  and internal threads  225 . The result of this operation is shown in  FIG. 5   c.    
     Relaxable stabilizer  227  is sized and shaped such that: (1) upon removal of the tool, the previously stretched inside diameter of its axial opening  228  will attempt to return to a size somewhat less than the outer diameter of guide stem  240 ; but (2) relaxable stabilizer  227  will not hold guide stem  240  so tightly that it cannot be removed by unscrewing it from the movable member  220 . 
     Before removal of guide stem  240 , an instrument  229  may be inserted into the passage through opening  242  of guide stem  240 , as shown in  FIG. 5   d . Then, as guide stem  240  is removed from the vicinity of relaxable stabilizer  227  as shown in  FIG. 5   e , relaxable stabilizer  227  will continue to return to a size that applies sufficient pressure or friction to the outer diameter of the instrument  229 . This prevents axial migration of instrument  229 , both while removing the guide stem  240  entirely over the proximal end of instrument  229 , and also during any subsequent movement of the proximal segment of the instrument  229  as instrument  229  is secured or tunneled as described herein.  FIGS. 5   f  and  5   g  are closeup views of relaxable stabilizer  227  after it is relaxed back into a position that will securely hold instrument  229  in place. 
     From this description it can be appreciated that the relaxable stabilizer  227  operates in a manner exactly opposite from known stabilization techniques, because the relaxable stabilizer  227  relies on self-relaxation to provide stabilizing force to instrument  229 , as opposed to techniques in which compression of a material provides stabilization. For example, the well-known Touhy-Borst valve uses a compressible “O-ring” to provide stabilization of objects such as guidewires, leads, catheters, and the like upon twisting by a clinician&#39;s hand, but the present relaxable stabilizer stabilizes instruments by relying on relaxation, not compression. 
     Base Example 
       FIGS. 6   a  to  6   g  show an example of base  210  of trajectory guide  200 . Base  210  includes a generally cylindrical portion  212  and a flange  214 . Flange  214  includes openings  215 ,  216 , and  217 . Flange  214  also a seat  218  that receives movable member  220 . Seat  218  is part of an opening  600  which includes an internally threaded portion  610 . Internally threaded portion  610  is dimensioned so as to receive the threads of cylindrical portion  232  of locking member  230 . Groove  219  lies in base  210  and is sized and shaped to accommodate a flexible instrument  229  or other instrument, as discussed further herein with respect to a stabilization or tunneling procedure. 
     In other embodiments, base  210  may separated into two or more pieces.  FIGS. 13   a - 13   e ,  14   a - 14   b ,  15   a - 15   b ,  16   a - 16   c ,  17 , and  18   a - 18   c  show several examples of structures and methods of using a multi-piece base  210 , such as a separate seat/mount and an internally threaded locking collar attachable thereto The internal threads of the locking collar receive the external threads of the cylindrical portion  232  of locking member  230 . By separating base  210  into more than one piece, its profile above the skull may advantageously be reduced. 
     Lockable Member Example 
       FIGS. 7   a - 7   d  illustrate an example locking member  230  of trajectory guide  200 . Locking member  230  includes cylindrical portion  232  and flange  234 . The external surface of the cylindrical portion  232  is threaded to form a threaded external surface  700 . The threads associated with the externally threaded surface  700  are dimensioned so as to engage the internally threaded surface  610  of opening  600  of base  210 . Locking member  230  also includes an opening  710  which passes through locking member  230 . Locking member  230  also has a locking surface  720 . In this particular example, locking surface  720  is shaped so that it smoothly engages the spherical face of movable member  220 . Flanges  234  are outwardly extended so that the threads of the threaded surface  700  can be easily engaged with internal threads  610  of opening  600  of base  210 . Other geometric shapes could be used for the locking member and other locking surfaces could be employed. 
     Instrument Placement Example 
     In operation, a patient undergoes a scan with an apparatus such as an MRI or magnetic resonance imaging system  100  as part of a normal diagnostic medical procedure. A scan can be used to locate a particular organ within a patient or to locate lesions or any other target  270  within the patient. It should be noted that targets are not necessarily limited to being within the head of a patient. There can also be other areas of a patient where it would be critical to accurately place a surgical or observational tool. In addition, it should also be noted that the patient need not necessarily be human. A patient may include any living animal. Once a target is found and located using an MRI or other scanning system, base  210  of trajectory guide  200  can be attached to the patient. The base is affixed to the patient in an area near the target  270 . The computer  102  of scanning device  100  is used to determine the exact location of the target  270 . The exact location can be found in any type of coordinate system, although normally a Cartesian coordinate system is used. Once base  210  is attached to the patient, the remaining portions of trajectory guide  200  are attached to base  210 . In other words, movable member  220 , guide stem  240 , locking member  230 , and positioning stem  400  are added to form a complete trajectory guide  200 . 
     Scanning system  100  reads first locator  420  and second locator  430  of positioning stem  400 . A line defined by first locator  420  and second locator  430  is calculated by computer  102 . The calculated line corresponds to the center line of axial opening  222  and opening  242  of guide stem  240 . If the line aligns with target  270 , locking member  230  is used to lock movable member  220  into position. If the line does not intersect target  270 , positioning stem  400  is moved until the line formed by first locator  420  and second locator  430  intersects target  270 . If the patient and positioning stem  400  can be easily reached by a surgeon during a scanning operation, positioning stem  400  can be moved or readjusted manually. If the patient is remote from the surgeon or cannot be reached by the surgeon, a hydraulic or other actuator may be used to move positioning stem  400 . Once such a trajectory line is formed, the locking member  230  is secured. 
     After fixing the position of movable member  220 , positioning stem  400  is removed from guide stem  240 . Opening  242  in guide stem  240 , and opening  224  in movable member  220  form the trajectory  260 . An instrument  229  may be placed through the guide opening to intersect target  270 . 
     Tunneling Procedure Example 
       FIGS. 8   a ,  8   b  and  8   c  illustrate one procedure for securing the distal portion of a flexible instrument  229  so that the proximal portion of flexible instrument  229  may be tunneled under a skin flap.  FIG. 8   a  shows base  210  positioned against a surface  304  of a body, e.g., a skull of a patient. 
     Base  210  is attached to the patient as described above. Flexible instrument  229  extends through movable member  220  to target location  270  and is secured in place by relaxable stabilizer  227  (not shown in  FIGS. 8   a    8   c ), again as described above. As shown, guide stem  240  has been removed over the proximal (as shown, the upper) portion of flexible instrument  229 . In this example, base  210  is a multi-piece base in which the locking collar has also been removed. 
     In  FIG. 8   b , the proximal portion of flexible instrument  229  has been laterally bent into groove  219  (shown in  FIG. 8   a  and covered by the instrument  229  in  FIG. 8   b ) so that it lies generally parallel to the surface  304  of the body and extends for approximately 5 cm. As noted before, this distance is a typical example, but depends on the clinical situation. The proximal end of instrument  229  is then turned generally upward, away from the surface  304  of the body, for a distance of approximately 2 cm (again, a typical example but dependent upon clinical conditions). A rigid or flexible cap  310  has been inserted into the opening  218  of the base  210 . In one example, outer ridges of cap  310  engage internal threads  610  of base  210  to hold cap  310  in place. In another example, snap feet on cap  310  engage mating features of base  210  to hold cap  310  in place. This covers the portion of moveable member  220  remaining in base  210 . 
     In  FIG. 8   c , skin flap  221  (which would be a scalp flap in neurosurgery) is placed over the surface  304  of the body to cover base  210 , cap  310 , and the proximal portion of instrument  229 . A suitable hole in the skin flap permits the upturned proximal portion of instrument  229  to be exposed outside the skin flap. 
     Cap Example 
       FIGS. 9   a - 9   d  illustrate one example of cap  310  in detail. In this example, cap  310  includes a relatively larger top  320  and a relatively smaller, generally cylindrical base  330 . The exterior of base  330  also has an opening  340  designed to permit the flexible catheter to bend and extend through opening  340  and groove  219  of base  210 . 
     Any means for attaching cap  310  to base  210  is within the scope of the invention. In one example, cap  310  includes a feature that snap-fits into base  210 . In another example, the exterior of the base  330  has several circumferential ridges  350  shaped and located to engage internal threads  610  of base  210 . In this particular example, the ridges are parallel and thus not external threads that would mate into the internal threads  610  of the base in a manner similar to that of the external threads of the locking ring. However, such a threaded cap is also within the scope of the invention. 
     Alternative Embodiments 
       FIG. 11   a  shows a modified guide stem  240   a , which includes a ball-shaped end  220   c  located within base  210 . Modified guide stem  240   a  also has an axial opening  222   a  that is similar in function to axial opening  222  previously described. Modified guide stem  240   a  may be shorter than previously described guide stem  240  but otherwise functions similarly. 
       FIG. 11   b  illustrates using alignment stem  1700  as described above. Locking ring  230  is used to secure the ball-shaped end  220   c  within base  210 , thereby aligning axial opening  222   a  as desired. After removal of alignment stem  1700 , a catheter is inserted directly into axial opening  222   a  so that it may be held in place by any convenient means for securing the catheter in place. For example, the diameter of axial opening  222   a  could be chosen so that, even though ball-shaped end  220   c  is constructed of a rigid material, friction alone would be adequate to grip the catheter in place yet allow sufficient movement to insert the catheter to the desired position. The catheter is tunneled under the skin as described above; the relatively shorter length of modified guide stem  240   a  permits the skin flap to cover the base without removal of a relatively longer guide stem  240 , as previously described. 
       FIGS. 12   a  and  12   b  illustrate schematically still another example within the scope of the invention.  FIG. 12   a  shows alignment stem  1700  and a separate one-piece ball  220   d  located within base  210 . Ball  220   d  is adapted to engage alignment stem  1700  according to the principles described above. Ball  220   d  has an axial opening  222   b  that is similar in function to axial opening  222  of the preferred embodiment. Base  210  also contains alignment material  290  as shown. 
     Alignment stem  1700  is employed as described above, and locking ring  230  is used to secure ball  220   d  within the base  210 , thereby aligning axial opening  222   b  as desired. After removal of alignment stem  1700 , catheter  229  is inserted directly into axial opening  222   a , emerging from the distal outlet and then puncturing through alignment material  290 , which secures catheter  229  in place. The catheter is then tunneled under the skin as described above for the preferred embodiment. 
     The catheters used in the preferred embodiment of neurosurgery typically range in size from 3 to 12 French (1-4 millimeters in diameter). This is small enough that a wide range of materials are suitable for alignment material  290 , notably many medical-grade silicones and urethanes. 
     Yet another variation on this embodiment combines two means for securing the catheter in place. For example, the first means could be either the embodiment of  FIGS. 11   a  and  11   b , or the previously described embodiment of a two-piece ball  220  and relaxable stabilizer  227 . The second means for securing catheter  229  in place could be the alignment material  290 . 
     Reduced Profile Examples 
       FIGS. 13   a - 13   e  are various views illustrating an alternate example of a two piece version of base  210 . Two-piece base  1300  includes a mounting seat  1302  and a collar  1304 . In this example, mounting seat  1302  includes a flange with bone screw holes. Mounting seat  1302  also includes a hemispherical recess for receiving a swiveling one or two piece ball-shaped movable member  220 . Movable member  220  includes an opening  223  into which a guide stem  240  is threaded. Cylindrical collar  1304  includes internal threads for receiving a locking member  230  for securing movable member  220 , after it has been positioned to provide the desired trajectory, while an instrument  280  is inserted through guide stem  240  toward target  270 . Collar  1304  includes a coupler, such as legs that detachably snap-fit into receptacles  1308  in base  1302 . After instrument  280  is guided to target  270 , guide stem  240  is then removed over instrument  280 . This allows relaxable stabilizer  227  to hold instrument  280  in place. Locking member  230  and collar  1304  are also then removed. Instrument  280  is bent laterally into a groove  1310  in base  1302 . Cap  1312 , which includes legs  1314  for snap-fitting into receptacles  1308 , is then snapped onto base  1302 . Cap  1312  also includes one or more grooves  1316 , which aligns with the one or more grooves  1310  in base  1302  for allowing instrument  280  to pass laterally therethrough. This example illustrates how, by separating base  210  into more than one piece (e.g.,  1302  and  1304 ), its profile above the skull may advantageously be reduced by removing one of the pieces (e.g.,  1304 ). 
       FIGS. 14   a - 14   b  are various views illustrating another alternate example of a two piece version of base  210 . Two-piece base  1400  includes a mounting seat  1402  and a collar  1404 . In this example, mounting seat  1402  includes a flange with bone screw holes. Mounting seat  1402  also includes a hemispherical recess for receiving a swiveling one or two piece ball-shaped movable member  220 . Movable member  220  includes an opening  223  into which a guide stem  240  is threaded. Cylindrical collar  1404  includes internal threads for receiving a locking member  230  for securing movable member  220 , after it has been positioned to provide the desired trajectory, while an instrument  280  is inserted through guide stem  240  toward target  270 . Collar  1404  includes a coupler, such as countersunk holes for receiving screws  1406  that detachably engage internally threaded receptacles  1408  in base  1402 . This example illustrates how, by separating base  210  into more than one piece (e.g.,  1402  and  1404 ), its profile above the skull may advantageously be reduced by removing one of the pieces (e.g.,  1404 ). 
       FIGS. 15   a  and  15   b  are various views illustrating another example of a low profile mounting seat  1502 , to which a removable internally threaded collar can be snap-fit, along with a movable member  220  and guide stem  240 . This example includes three grooves  1504  into which an instrument  280  can be laterally bent. A matching cap with an aligning groove is then snap-fitted into the receptacles. 
       FIGS. 16   a - 16   c  are various views illustrating another example of a two-piece base  1600  including a mounting seat  1602 , a removable internally-threaded collar  1604 , and a movable member  220 . This example of mounting seat  1602  includes three grooves  1604  into which an instrument  280  can be laterally bent after removing collar  1604 . In this example, collar  1604  includes a coupler, such as attachment feet  1606  that are pushed toward each other by the user in order to snap collar  1604  into and out of receptacles  1608  in mounting seat  1602 . This example also includes three grooves  1610  into which an instrument  280  can be laterally bent after removing collar  1604 , as illustrated in  FIG. 17 . A matching cap with an aligning groove is then snap-fitted into the receptacles  1608 . 
       FIGS. 18   a - 18   c  are various views illustrating an alternate example of a low-profile mounting seat  1802  portion of a two-piece base and a cap  1804 . In this example, mounting seat  1802  includes three grooves  1806  into which an instrument  280  can be laterally bent. Cap  1804  includes a single groove  1808  that is aligned, by rotating cap  1804  with respect to mounting seat  1802  before snap-fitting it thereto, to the groove in mounting seat  1802  into which instrument  280  has been laterally bent. Three feet in cap  1804  align with matching receptacles  1810  in mounting seat  1802  so that groove  1808  in cap  1804  is capable of being aligned with any of the grooves  1806  in mounting seat  1802 . 
     Stabilizer Sliding Cap Example 
       FIGS. 19   a - c  are various views illustrating an alternative example capable of using a cap or other slide component to stabilize a catheter or other medical instrument.  FIG. 19   a  is a side view of a mounting seat  1902  with laterally extending flanges  1904  that include bone screw openings  1906 . A hemispherical seat portion of mounting seat  1902  receives a one-piece ball  1908  with a trajectory passage  1910  extending therethrough. The hemispherical seat portion of mounting seat  1902  also includes an opening  1912  that aligns with passage  1910  as ball  1908  is swiveled within mounting seat  1902  by manipulating a guide stem that is threaded into passage  1910  as discussed above. In this example, a set screw locking member  1912  is inserted through an opening  1914  in mounting seat  1902  to secure ball  1908  in place after the desired position has been obtained. A hemispherically conformal cap  1916  is situated about the top of ball  1908 .  FIG. 19   b  is a top view illustrating opening  1918  being concentrically aligned to the top opening of passage  1910  through ball  1908 . As shown in  FIG. 19   b , the passage  1910  can have a width (e.g., diameter) that is greater than a width (e.g., diameter) of the opening  1918 . Cap  1916  also includes a slot  1920  through which set screw  1922  passes. Set screw  1922  engages an underlying threaded opening on the top surface of ball  1908 .  FIG. 19   c  is a top view illustrating how cap  1916  can be slid along ball  1908  in the direction of slot  1920  to offset opening  1918  in cap  1916  from the top opening of passage  1910  in ball  1908 . This reduces the effective area of passage  1910  through which a catheter or other instrument has been passed. By tightening set screw  1922 , cap  1916  is used to grasp and stabilize the catheter or other instrument through passage  1910 . Cap  1916  is any rigid, semi-rigid, relaxable, or flexible material (or combination thereof) suitable for grasping and stabilizing an instrument by narrowing the effective cross-sectional area of passage  1910 , e.g., by offsetting the opening  1918  of cap  1916 . 
     Other Aspects 
     The invention as described above can be used with various known aspects of remote actuation systems, perhaps with minor modifications to accommodate the features of the invention that would be within the ordinary skill of the art. Suitable examples are the mechanical and hydraulic remote actuation and control devices taught in the International Patent Application cited above. Similarly, mechanisms to laterally displace the apparatus without changing the trajectory of the catheter or instrument held by the relaxable stabilizer in the movable member may be employed. An example would be the stage mechanism taught in the same International Patent Application. Any suitable system for computerized monitoring and/or control of the invention may be employed. 
     Other Uses 
     The invention can be practiced in conjunction with trajectory guides adapted for various parts of the body, including uses related to biopsies or therapy provided to organs in or near the abdomen or pelvis. Among the uses are liver biopsies, renal biopsies, pancreatic biopsies, adrenal biopsies. In addition, some procedures require both a biopsy as well as a therapy. The biopsy needle is used first and then an instrument used in therapy is substituted for the biopsy needle. The instrument for applying therapy includes instruments for thermal ablation, and instruments for providing shunts to various organs such as TIPS (transjugular interhepatic portal systemic shunts). The inventive trajectory guide can also be used to conduct biliary drainages, and used to conduct other biopsies and treatments at or near the abdomen of the pelvis. The trajectory guide can also be used for procedures on the back and near the spine of a patient. Nerve blocks, epidural injections, facet injections, sacroiliac joint injections, and spinal cordotomy are just a few of the procedures possible with the trajectory guide. Non-brain treatments and biopsies in the head and neck can also be accomplished using the trajectory guide. Trigeminal neuralgia can be treated using the trajectory guide. Biopsies of the pleura, the lung, and the mediastinum and removal of emphysematous to reduce the volume of the lung can be done percutaneously using the trajectory guide. The trajectory guide can also be used for fetal surgery such as for diversion of fetal hydrocephalus, and for treatment of fetal hydronephrosis. These are just a sampling of the possible procedures that can be done using the body portal type trajectory guide. Numerous other procedures will be accomplished using this device. In addition, the device will give rise to other future surgical procedures. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.