Abstract:
An insertion guide device guides an instrument toward a target location in a subject. The insertion guide device includes a base portion securable to the subject and an insertion guide portion defining an insertion axis. The insertion guide portion guides the instrument along the insertion axis, and the insertion guide portion is moveably supported by the base portion for movement of the insertion axis about at least two axes. Moreover, the insertion guide device includes a locking device that selectively fixes the insertion guide portion relative to the base portion. The locking device selectively fixes the insertion axis relative to the at least two axes substantially concurrently.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 10/325,615, filed on Dec. 20, 2002, issued as U.S. Pat. No. 7,636,596. The entire disclosure of the above application is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The present disclosure relates to an organ access device and method. Specifically, the invention relates to trajectory guidance of medical devices for procedures such as catheter or lead insertion. 
     BACKGROUND 
     This section provides background information related to the present disclosure which is not necessarily prior art. 
     A desire to reduce the disturbance of tissue during surgical procedures drives methods and devices for surgical insertion such as catheter insertion. The term “catheter” as used in this document is a broad term that generally describes an elongated tube for insertion into a region of a subject. Catheters include, but are not limited to, drug delivery catheters, optical catheters, micro-catheters, host catheters, etc. A small diameter catheter can be inserted into a subject along an insertion trajectory towards a target location within the subject with a minimal disturbance to surrounding tissue. 
     A drawback to catheter insertion procedures is that the target location is hidden within the subject. Only a small opening in the subject allows insertion of the catheter. Imaging techniques such as computed tomography (CT), magnetic resonance imaging (MRI) ultrasonic imaging, etc. are helpful in guiding a surgeon or other operator to insert the catheter towards the target location within the subject. Insertion guide devices are also useful in guiding the surgeon. 
     Local mounted insertion guide devices are desirable, in contrast to other guide devices such as head frames as used in neurosurgery. Local mounted insertion guide devices are not as cumbersome as head frames due to their light weight and smaller size. The subject does not need to be immobilized after imaging as is the case with head frame technology. Local mounted insertion guide devices are also less expensive to manufacture. In many instances they are fabricated from plastic materials, and may be disposable. Further, in contrast to head frame technology, local mounted insertion guide devices allow a subject to break up a surgical procedure into at least two different visits to the hospital. 
     One visit may include imaging, where a number of reference points called fiducial markers are attached to a subject. A target location tissue is imaged along with the fiducial markers, thus giving the surgeon a reference location of the target location in relation to the fiducial markers. If the fiducial markers are left secured to the subject, the subject may now return home and complete a surgical procedure at a second visit because the fiducial markers preserve a reference frame for the surgeon to target and work with. This was not possible using head frame technology, where a subject needed to remain secured inside a head frame until after completion of the surgical procedure. 
     Using a local mounting technique, an insertion guide device is also attached to the subject. The function of the insertion guide device is to guide a catheter along an axis into the subject to the target location where a selected operation such as drug delivery, tissue removal, etc. is performed. 
     A difficulty with this procedure arises in location tolerance when the insertion guide device is attached to the subject. In neurosurgery, the insertion guide device is frequently attached to the subject&#39;s skull using bone screws. The screws may not center in their ideal location, making precise alignment of the insertion guide device difficult. Further, in neurosurgery, a cranial drill is used to open a burr hole in the subject&#39;s skull. Variations in skull material, as well as limitations of the drilling operation can cause the burr hole location to deviate from it&#39;s ideal location, and the burr hole is not always perfectly round. 
     What is needed is a method and device that can be adjusted to compensate for location errors of an insertion guide device. What is also needed is a method and device that can be adjusted to compensate for location errors in forming an opening in a subject. What is also needed is a method and device that in other ways, improves accuracy and ease of use of an insertion guide device. 
     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. 
     The above mentioned problems of adjustability are addressed by the present disclosure and will be understood by reading and studying the following specification. Devices and methods are provided for adjusting an insertion guide device. The devices and methods discussed herein further offer improved accuracy and ease of use. 
     An insertion guide device is disclosed that guides an instrument toward a target location in a subject. The insertion guide device includes a base portion securable to the subject and an insertion guide portion defining an insertion axis. The insertion guide portion guides the instrument along the insertion axis, and the insertion guide portion is moveably supported by the base portion for movement of the insertion axis about at least two axes. Moreover, the insertion guide device includes a locking device that selectively fixes the insertion guide portion relative to the base portion to selectively fix the insertion axis relative to the at least two axes substantially concurrently. 
     Also, a method for guiding an instrument toward a target location in a subject is disclosed. The method includes securing a base portion to the subject and operatively supporting an insertion guide portion with the base portion. The insertion guide portion defines an insertion axis. Additionally, the method includes moving the insertion guide portion relative to the base portion and moving the insertion axis defined by the insertion guide portion about at least two axes. Moreover, the method includes concurrently fixing the insertion axis about the at least two axes and guiding the instrument along the insertion axis. 
     Still further, an insertion guide device for guiding an instrument through a hole in a subject toward a target location in the subject is disclosed. The hole includes an axis. The insertion guide device includes a base portion securable to the subject. The base portion includes an annular lip that extends inward. The device further includes an insertion guide portion defining a through hole that defines an insertion axis. The instrument is receivable in the through hole to be guided along the insertion axis. Moreover, the device includes a first portion fixed to the insertion guide portion. The first portion defines a slot that curves about a first axis of rotation that is positionable to be perpendicular to the axis of the hole in the subject. Also, the device includes a second portion disposed between the first portion and the base portion, and the second portion is rotatably supported by the base portion for rotation about a second axis of rotation that is positionable to be parallel to the axis of the hole in the subject. Furthermore, the device includes a locking device that includes a gripping device, a threaded member, and a base contacting portion. The base contacting portion includes a top portion that threadably receives the threaded member and a bottom portion having a lip. The lip extends radially inward. The threaded member is moveably received in the slot of the first portion to limit rotation of the first portion and the insertion guide portion about the first axis of rotation. Upon rotating the gripping device, the threaded member is selectively and threadably advanced relative to the base contacting portion such that the lip of the base contacting portion selectively abuts the annular lip of the base portion and such that the threaded member and the base contacting portion cooperate to pull the base portion, the first portion, and the second portion together to concurrently fix the insertion axis relative to the first and second axes of rotation. 
     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  shows a coordinate system in one embodiment of a neurosurgical procedure. 
         FIG. 2  shows an isometric view of an exemplary embodiment of an insertion guide device. 
         FIG. 3A  shows a side view of a portion of an exemplary embodiment of an insertion guide device. 
         FIG. 3B  shows a cross section view of a portion of an exemplary embodiment of an insertion guide device. 
         FIG. 3C  shows an isometric view of a part of an exemplary embodiment of an insertion guide device. 
         FIG. 4  shows a side view of an exemplary embodiment of a centering guide. 
         FIG. 5A  shows an isometric view of a portion of an exemplary embodiment of an insertion guide device. 
         FIG. 5B  shows a top view of a portion of an exemplary embodiment of an insertion guide device. 
         FIG. 5C  shows a cross section view taken along line  5 C- 5 C of  FIG. 5B . 
         FIG. 5D  shows a top view of a portion of an exemplary embodiment of an insertion guide device. 
         FIG. 5E  shows a cross section view taken along line  5 E- 5 E of  FIG. 5D . 
         FIG. 5F  shows a cross section view taken along line  5 F- 5 F of  FIG. 5D . 
         FIG. 6A  shows a cross section view of a portion of an exemplary embodiment of a fiducial marker. 
         FIG. 6B  shows a cross section view of a portion of an exemplary embodiment of a fiducial marker. 
         FIG. 6C  shows a portion of an exemplary embodiment of a fiducial marker. 
         FIG. 6D  shows a portion of an exemplary embodiment of a fiducial marker. 
         FIG. 7  shows an isometric view of an exemplary embodiment of an insertion guide device. 
         FIG. 8  shows an isometric view of an exemplary embodiment of an insertion guide device. 
         FIG. 9  shows a flow diagram of an exemplary embodiment of a method according to various teachings of the present disclosure. 
     
    
    
     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. 
       FIG. 1  shows a subject surface  100  along with one possible coordinate system for defining locations and orientations with respect to the subject. In one embodiment, the subject surface  100  includes a skull of a subject. An opening  102  in the subject surface is shown, along with a target location  104  within the subject. In one embodiment, the opening  102  includes a burr hole. An insertion axis  110  is shown that begins outside the subject surface  100  and ends at the target location  104 . The insertion axis  110  further passes through an insertion point  112  on its way to the target location  104 . The insertion point  112  is shown substantially within the center of the opening  102 . 
     In three dimensional space, using the chosen coordinate system shown in  FIG. 1 , the insertion axis  110  can be rotated about the insertion point  112  and further about any of three orthogonal axes that pass through the insertion point  112 . In this way, any orientation of the insertion axis  110  can be selected, while still passing through the insertion point  112 . In one embodiment, rotation about at least two of the three orthogonal axes is used to select an orientation of the insertion axis  110 . Although orthogonal axes are shown, non-orthogonal axes passing through the insertion point are also possible without departing from the scope of the present disclosure. 
     In one embodiment, a first rotational degree of freedom shown by arrow  122  is included. The first rotational degree of freedom is used for orienting the insertion axis  110 . As shown, the first rotational degree of freedom rotates about a first rotational axis  120  that passes through the insertion point  112 . In the embodiment shown, the first rotational axis  120  is normal to the subject surface  100  at the insertion point  112 . 
     In one embodiment, a second rotational degree of freedom shown by arrow  132  is included. The second rotational degree of freedom is used for orienting the insertion axis  110 . As shown, the second rotational degree of freedom rotates about a second rotational axis  130  that passes through the insertion point  112 . In the embodiment shown, the second rotational axis  130  is tangent to the subject surface  100  at the insertion point  112 . 
     In one embodiment, a third rotational degree of freedom shown by arrow  142  is included. The third rotational degree of freedom is used for orienting the insertion axis  110 . As shown, the third rotational degree of freedom rotates about a third rotational axis  140  that passes through the insertion point  112 . In the embodiment shown, the third rotational axis  140  is tangent to the subject surface  100  at the insertion point  112 . 
     The first degree of rotational freedom, the second degree of rotational freedom, and the third degree of rotational freedom all leave the location of the insertion point  112  fixed. The degrees of rotational freedom rotate about the insertion point  112  because the location of the opening in the subject  102  remains fixed during a surgical procedure. In one embodiment, a first degree of translational freedom is also included. In one embodiment, a first degree of translational freedom is defined by the adjustability of the location of the insertion point  112  along direction  114 . In one embodiment, a second degree of translational freedom is also included where the location of the insertion point  112  is adjustable along direction  116 . 
       FIG. 2  shows one embodiment of an insertion guide device  200 . The insertion guide device  200  includes a base unit  210 , and an insertion guide portion  220  coupled to the base unit  210 . The insertion guide portion  220  determines an insertion axis  222 . A number of attachment devices  230  are also shown coupled to the base unit  210 . In one embodiment, the attachment devices include a bone screw  232 . The attachment devices  230  are coupled to the base unit  210  through a number of insertion point adjustment devices  240 . In one embodiment, the insertion point adjustment devices  240  include a split clamping portion  241  and a screw  242 . The insertion point adjustment devices  240  allow the base unit to be adjusted with respect to the attachment devices  230  substantially along direction  244 . In one embodiment an insertion point adjustment device  240  is included for each attachment device  230 . In one embodiment, the insertion guide device  200  includes three attachment devices  230  and three insertion point adjustment devices  240 . 
     By adjusting at least one insertion point adjustment devices  240 , an insertion point (not shown) of the insertion axis  222  is translated through at least one degree of translational freedom to a selected location within the subject surface. Three attachment devices are convenient because they provide the most stable platform with a minimum number of contact points on the subject. 
       FIG. 2  also shows a first angular adjustment device  250  for adjusting a first rotational degree of freedom. The first angular adjustment device  250  permits rotation of a component of the insertion axis  222  about a first rotational axis that is substantially normal to the subject surface at the insertion point. The rotation of the insertion axis  222  in the first rotational degree of freedom is shown by arrows  254 . A locking device  252  is shown to secure an orientation of the insertion axis  222  in the first rotational degree of freedom as selected. In one embodiment, the locking device includes a threaded lock ring. 
     Also shown in  FIG. 2  is a second angular adjustment device  260  for adjusting a second rotational degree of freedom. The second angular adjustment device  260  permits rotation of the insertion axis  222  about the insertion point and further about a second rotational axis. In one embodiment, the second rotational axis is substantially tangent to the subject surface at the insertion point. In one embodiment, the second angular adjustment device  260  includes a rail  262  that guides the adjustment of the second angular adjustment device  260 . In one embodiment, a pair of rails  262  are used. In one embodiment, a locking device  264  is used to secure an orientation of the insertion axis  222  in the second rotational degree of freedom as selected. In one embodiment, the locking device  264  includes one or more set screws. 
     A centering guide  270  is further shown in  FIG. 2 . In one embodiment, the centering guide is fixed within the insertion guide portion  220  using a locking device  224 . In one embodiment, the locking device  224  includes one or more set screws. Embodiments of the centering guide are discussed in more detail later in the specification. 
     In one embodiment, selected elements of an insertion guide device such as insertion guide device  200  are fabricated from a substantially transparent material. Examples of transparent materials include, but are not limited to, polycarbonate, crystalline polymers, glasses, etc. An advantage of at least some of the elements of an insertion guide device being transparent is that it allows a user or surgeon to better view the opening in the subject, and to view within the opening into the subject. In many procedures, it is important to be able to view the opening in the subject, and further to view locations within the opening. Embodiments of insertion guide devices as described in this document are mounted to the subject at locations that are spaced laterally apart from the opening, thus providing a user or surgeon a better view of the opening. By further designing elements of an insertion guide device with substantially transparent material, a surgeon&#39;s ability to see the opening and inside the opening is increased. 
       FIG. 3A  shows an embodiment of an attachment device  330  and an insertion point adjustment devices  340  attached to a subject surface  300 . In one embodiment, the attachment device  330  includes a truncated cone portion  334  and a securing device  332  such as a bone screw. In one embodiment, the insertion point adjustment devices  340  includes a threaded portion  341  coupled to a gripping portion  342 . In one embodiment, the gripping portion  342  includes a knurled knob portion. In one embodiment, the threaded portion  341  engages a portion of a base  310  to provide motion of the base  310  substantially along directional arrows  344  with respect to the attachment device  330 . 
       FIG. 3B  shows a cross section of the attachment device  330  and an insertion point adjustment devices  340  of  FIG. 3A . In one embodiment, the threaded portion  341  and the gripping portion  342  are separately fabricated from the attachment device  330 . In one embodiment, the threaded portion is rotatably coupled to the attachment device  330  by a retaining device  338 . In one embodiment, the retaining device  338  includes a barb. A rotatably coupled arrangement allows the attachment device  330  to remain substantially fixed while adjustments are made to the threaded portion  341 . 
       FIG. 3C  shows an embodiment of an attachment device  350  including a substantially linear contact surface  352 . In one embodiment, features such as the substantially linear contact surface  352  and the truncated cone portion  334  help to reduce tissue damage due to attachment of the insertion guide device to a subject. 
     During many surgical procedures utilizing attached devices such as an insertion guide device, tissue damage as a result of attachment is an issue. In one embodiment, tissue damage is reduced by utilizing a minimum number of attachment devices. In one embodiment, three attachment devices are used to maintain a stable platform for the insertion guide device while minimizing a number of attachment locations. In one embodiment, the attachment devices are located apart from the opening in the subject, such as a burr hole. The more remote location of attachment devices reduces tissue damage at the opening or burr hole location. In one embodiment, the attachment devices raise a substantial portion of the insertion guide device above the subject surface. By raising the insertion guide device above the subject surface, tissue damage due to pinching large amounts of tissue under the insertion guide device is avoided. 
     In one embodiment, the shape of the attachment device or devices further reduces tissue damage. In one embodiment the truncated cone shape reduces a subject contact surface to a minimum area where sufficient support for the securing device such as a bone screw is provided, while reducing the contact area. In one embodiment, a cone shape is desirable due to the use of a round cutting device to pierce tissue on a subject&#39;s scalp prior to attachment. In one embodiment, a modified hypodermic needle is used to pierce the scalp, thus making a round attachment device convenient. In one embodiment, a substantially linear contact surface is desirable due to the use of a linear cutting instrument to pierce tissue on a subject&#39;s scalp prior to attachment. In one embodiment, a scalpel is used to pierce the scalp, thus making a substantially linear contact surface of an attachment device convenient. 
       FIG. 4  shows one embodiment of a centering device  470  similar to the embodiment illustrated in  FIG. 2 . The device configuration and use of a centering device is not, however, limited to the embodiment illustrated in  FIG. 2 . The centering device  470  includes an insertion axis  472 , a first diameter portion  474  and a second diameter portion  476 . In one embodiment, the first diameter portion  474  forms a close tolerance fit within an insertion guide portion so that the insertion axis  472  can be adjusted using adjustable features of the insertion guide device embodiments as described above. In one embodiment, the second diameter portion  476  forms a close tolerance fit within an opening in a subject such as a burr hole. In one embodiment, the second diameter portion  476  fits inside an irregular opening in a subject such as a burr hole to effectively find an approximate center of an irregular opening. 
     In a surgical procedure, such as neurosurgery, after installation of an insertion guide device, an insertion point may not be aligned over the center of a round burr hole, or the effective center of an irregular burr hole. In one embodiment, the translational location of the insertion point can be adjusted using insertion point adjustment devices as described above. In one embodiment, a centering guide can be further utilized to indicate to a user when the insertion point is aligned with the center of the opening in the subject. In one embodiment, when the insertion point has been moved such that the second diameter portion  476  fits at least partially within the opening in the subject, the insertion point is aligned with the opening in the subject. 
     In one embodiment, a centering device is used to center an insertion point of an insertion guide device over an opening in a subject prior to attachment of the insertion guide device on the subject. The centering device allows a fast and efficient location of attachment points for the insertion guide device in embodiments where the location of attachment points has not already been determined. 
       FIG. 5A  shows a portion of an insertion guide device  500 . In one embodiment, attachment devices and insertion point adjustment devices as described above are used in conjunction with embodiments described in  FIGS. 5A-5C . An insertion guide portion  520  is shown coupled to a first portion  522 . The insertion guide portion  520  is further coupled to a second portion  530 . The insertion guide portion  520  is further coupled to a base portion  510 . A first angular adjustment device is shown in  FIG. 5A  that permits rotation adjustment of an insertion axis  502  along direction  524 . A second angular adjustment device is shown in  FIG. 5B  that permits rotation adjustment of an insertion axis  502  along direction  526 . 
     In one embodiment, the portion of an insertion guide device  500  includes a locking device  540  that fixes both the first angular adjustment device and the second angular adjustment device concurrently when actuated. In one embodiment, the locking device  540  includes a gripping device  542  such as a knob. In one embodiment, the locking device  540  includes a threaded member  544  coupled to the gripping device  542 . In one embodiment, the threaded member  544  passes through a slot  548  in the first portion  522 , allowing the first portion to move along direction  524  with respect to the body portion  510 . In one embodiment, the locking device  540  includes a base contacting portion  546 . The base contacting portion  546  can include a contacting lip  547  that extends radially inward ( FIG. 5C ). Also, the base portion  510  can include a base lip  549  that extends radially outward ( FIG. 5C ) to abut with the contacting lip  547 . 
     In operation, the embodiment shown in  FIGS. 5A-5C  fixes an orientation of the insertion axis  502  in multiple degrees of freedom concurrently by tightening the threaded member  544  with the gripping portion  542 . The threaded member in turn tightens the base contacting portion  546  against the base  510 . This tightening motion pulls the base  510 ; the first portion  522 , and the second portion  530  together, substantially fixing their respective locations. 
     Using one locking device  540  to fix multiple adjustment devices is desirable in one embodiment because it allows a surgeon to quickly and easily secure all movement of an insertion axis  502  in a single locking operation once a desired orientation is found. A tradeoff is also present, in that during some operations, precise adjustment requires that each degree of freedom, or angular adjustment is focused on independently. When independent focus on each degree of freedom is necessary, individual angular adjustment and individual locking devices are desirable. 
     An additional embodiment is shown in  FIGS. 5D-F .  FIG. 5D  shows a portion of an insertion guide device  550 . In one embodiment, attachment devices and insertion point adjustment devices as described above are used in conjunction with embodiments described in  FIGS. 5D-5F . An insertion guide portion  551  is shown coupled to a first portion  552 . The insertion guide portion  551  is further coupled to a second portion  560 . The insertion guide portion  551  is further coupled to a base portion  570 . A first angular adjustment device is shown in  FIG. 5D  that permits rotation adjustment of an insertion axis  503  along direction  554 . A second angular adjustment device is shown in  FIG. 5D  that permits rotation adjustment of an insertion axis  503  along direction  556 . 
     In one embodiment, the portion of an insertion guide device  551  includes a locking device  580  that fixes both the first angular adjustment device and the second angular adjustment device concurrently when actuated. In one embodiment, the locking device  580  includes a gripping device  582  such as a knob. In one embodiment, the locking device  580  includes a threaded member  584  coupled to the gripping device  582 . In one embodiment, the threaded member  584  passes through a slot  588  in the first portion  552 , allowing the first portion  552  to move along direction  554  with respect to the body portion  570 . In one embodiment, the locking device  580  includes a base contacting portion  586 . 
     In operation, the embodiment shown in  FIGS. 5D-5F  fixes an orientation of the insertion axis  503  in multiple degrees of freedom concurrently by tightening the threaded member  584  with the gripping portion  582 . The threaded member in turn tightens the base contacting portion  586  against the base  570 . This tightening motion pulls the base  570 ; the first portion  552 , and the second portion  560  together, substantially fixing their respective locations. 
     In one embodiment, the portion of an insertion guide device  551  includes a second locking device  590  that fixes both the first angular adjustment device and the second angular adjustment device concurrently when actuated. In one embodiment, the locking device  590  includes a gripping device  592  such as a knob. In one embodiment, the locking device  590  includes a threaded member  594  coupled to the gripping device  592 . In one embodiment, the threaded member  594  passes through a slot  598  in the first portion  552 , allowing the first portion  552  to move along direction  554  with respect to the body portion  570 . In one embodiment, the locking device  590  includes a base contacting portion  596 . 
     One advantage of designs shown in  FIGS. 5D-F  includes the ability to quickly and easily secure all movement of an insertion axis  503  in a single locking operation once a desired orientation is found. An additional locking device, such as locking device  590  provides extra security that the degrees of freedom of the insertion guide device  551  will not accidentally move out of the selected alignment. 
       FIGS. 6A-6D  show a number of embodiments of fiducial markers and portions of fiducial markers according to embodiments of the invention. In  FIG. 6A , a securing device  610  is shown with a subject securing portion  612 , a transition portion  614 , and an upper securing portion  616 . In one embodiment, the subject securing portion includes a bone screw portion. In one embodiment, the upper securing portion includes a threaded portion. 
     An interchange portion  620  is also shown in  FIG. 6A . In one embodiment, the interchange portion  620  includes a mating portion  622  that engages the upper securing portion  616  of the securing device  610 . In one embodiment, the mating portion  622  includes a mating threaded portion. Also shown is a holding region  624  such as a groove. 
       FIG. 6B  shows an embodiment of a portion of a fiducial marker  650 . A subject securing device  652 , such as a more conventional bone screw, is shown attaching an interchange portion  654  to a subject surface. Similar to  FIG. 6A , a holding region  656  such as a groove is shown coupled to the interchange portion  654 . In one embodiment, the use of a more conventional bone screw is more cost effective in manufacturing of the portion of the fiducial marker  650 . 
       FIG. 6C  shows an interchangeable indicator  630 . The interchangeable indicator  630  includes an upper portion  634  that functions to indicate a point location in a medical imaging device such as a CT or MRI device, etc. In one embodiment, the upper portion reflects a selected wavelength of light that in turn indicates a position of a portion of a subject, using a detection device. A mating portion  632  is further shown attached to the upper portion  634 . The mating portion  632  is adapted to be removably positioned within a holding region such as the holding regions  624  and  656  described above. 
       FIG. 6D  shows an adaptor device  640  for use with embodiments of the insertion guide device as described above. In one embodiment, the interchangeable indicator  630  is adapted to be removed after initial subject imaging is complete. The adaptor device  640  may then be inserted into an embodiment of the fiducial markers or portions of fiducial markers as described above. In one embodiment, the insertion guide device is then directly mountable to the fiducial markers or portions of fiducial markers without additional attachments needed. Tissue damage, as discussed above, is reduced using this configuration, as well as increased targeting accuracy due to the use of the exact fiducial locations to mount the insertion guide device. 
     In one embodiment, the adaptor device  640  includes an upper portion  644  with a receiving portion  646 . The receiving portion is adapted to couple with attachment devices of insertion guide devices as described above. In one embodiment, the receiving portion includes a groove, although the present disclosure is not so limited. Although an adaptor device is shown in  FIG. 6D  for use in coupling an insertion guide device to a number of fiducial markers or portions of a number of fiducial markers, the present disclosure is not so limited. The insertion guide device may also be directly attached to a number of fiducial markers or portions of a number of fiducial markers directly without use of an adaptor device. 
       FIG. 7  shows an embodiment of an insertion guide device  700 . The insertion guide device  700  includes a base unit  710 , and an insertion guide portion  720  coupled to the base unit  710 . The insertion guide portion  720  determines an insertion axis similar to embodiments shown above. A number of attachment devices  730  are also shown coupled to the base unit  710 . The attachment devices  730  are coupled to the base unit  710  through a number of insertion point adjustment devices  740 . In one embodiment, the insertion point adjustment devices  740  include a split clamping portion  741  and a screw  742 . The insertion point adjustment devices  740  allow the base unit  710  to be adjusted with respect to the attachment devices  730  similar to embodiments discussed above. In one embodiment an insertion point adjustment device  740  is included for each attachment device  730 . In one embodiment, the insertion guide device  700  includes three attachment devices  730  and three insertion point adjustment devices  740 . By adjusting at least one insertion point adjustment devices  740 , an insertion point (not shown) is translated through at least one degree of translational freedom to a selected location within the subject surface. 
       FIG. 7  also shows a first angular adjustment device  750  for adjusting a first rotational degree of freedom. The first angular adjustment device  750  permits rotation of a component of the insertion axis about a first rotational axis. In one embodiment, the first rotational axis is substantially tangent to the subject surface at the insertion point. In one embodiment, at least one rail  752  guides the insertion guide portion  720  along the first rotational degree of freedom. A locking device  754  is shown to secure an orientation of the insertion axis in the first rotational degree of freedom as selected. In one embodiment, the locking device includes at least one set screw. 
       FIG. 7  also shows a second angular adjustment device  760  for adjusting a second rotational degree of freedom. The second angular adjustment device  760  permits rotation of a component of the insertion axis about a second rotational axis. In one embodiment, the second rotational axis is substantially tangent to the subject surface at the insertion point. In one embodiment, at least one rail  762  guides the insertion guide portion  720  along the second rotational degree of freedom. A locking device  764  is shown to secure an orientation of the insertion axis in the first rotational degree of freedom as selected. In one embodiment, the locking device includes at least one set screw. 
       FIG. 7  also shows a third angular adjustment device  716  for adjusting a third rotational degree of freedom. The third angular adjustment device  716  permits rotation of a component of the insertion axis about a third rotational axis. In one embodiment, the third rotational axis is substantially normal to the subject surface at the insertion point. In one embodiment, a rotating body portion  712  is allowed to rotate with respect to the body  710 . A locking device  714  is shown to secure an orientation of the insertion axis in the third rotational degree of freedom as selected. In one embodiment, the locking device includes at least one set screw. 
     In one embodiment, the insertion guide portion  720  includes a locking device  722 . In one embodiment the locking device  722  includes a knob attached to a threaded portion that bears down against a back plate  724 . In one embodiment at least two of the rotational degrees of freedom of the insertion guide device  700  can be concurrently fixed using the locking device  722 . In one embodiment, the first rotational degree of freedom and the second rotational degree of freedom can be concurrently fixed using the locking device  722 .  FIG. 7  shows an embodiment where the rails  752  and rails  762  are fixed between the locking device  722  and the back plate  724  upon actuation of the locking device  722 . 
       FIG. 8  shows one embodiment of an insertion guide device  800 . The insertion guide device  800  includes a base unit  810 , and an insertion guide portion  820  coupled to the base unit  810 . The insertion guide portion  820  determines an insertion axis  802  similar to embodiments shown above. A number of attachment devices  830  are also shown coupled to the base unit  810 . In one embodiment, the attachment devices  830  include a bone screw  832 . The attachment devices  830  are coupled to the base unit  810  through a number of insertion point adjustment devices  840 . In one embodiment, the insertion point adjustment devices  840  include a split clamping portion and a screw  842 . 
     The insertion point adjustment devices  840  allow the base unit  810  to be adjusted with respect to the attachment devices  830  similar to embodiments discussed above. In one embodiment, the insertion point adjustment devices  840  allow the base unit  810  to be adjusted with respect to the attachment devices  830  substantially along direction  844 . In one embodiment an insertion point adjustment device  840  is included for each attachment device  830 . In one embodiment, the insertion guide device  800  includes three attachment devices  830  and three insertion point adjustment devices  840 . 
     By adjusting at least one insertion point adjustment device  840 , an insertion point  804  is translated through at least one degree of translational freedom to a selected location within the subject surface. In one embodiment, the insertion point  804  is adjustable in both an X-axis and a Y-axis as shown by coordinate axes  806 . 
     In one embodiment, the insertion guide device  800  does not include any adjustment about rotational degrees of freedom as described above. In one embodiment, an orientation of the insertion axis  802  is pre-determined upon fabrication of the body  810  and the insertion guide portion  820 . In one embodiment, the insertion guide device  800  is custom fabricated using stereolithography rapid prototyping or other suitable custom fabrication techniques. 
       FIG. 9  shows a flow diagram of one method of aligning an insertion guide using embodiments of the invention as described above. As shown in  FIG. 9 , fiducial markers are first installed on a subject, such as a surgical patient. The subject is then imaged using imaging techniques as described above, such as CT or MRI techniques, etc. An image is generated of the subject with tissue shown in relation to the fiducial markers, which are concurrently imaged using the selected imaging technique. The target location within the subject is determined, and a trajectory is computed between a location external to the subject, to the target location. 
     An embodiment of an insertion guide device is then adjusted using degrees of freedom as described in embodiments above, to substantially coincide with the computed trajectory in relation to the fiducial markers. In one embodiment, attachment devices and corresponding insertion point adjustment devices are asymmetrically spaced about a circumference of the base unit of the insertion guide device to provide easy orientation of the insertion guide on the fiducial markers. 
     The insertion guide device is then attached to the fiducial markers in a state of substantial alignment with the desired trajectory as determined by imaging. One advantage of a method as described above, is that substantial alignment of the insertion guide is possible without the subject being present. This allows time in the operating room to be reduced. Optionally, alignment of the insertion guide can be performed on the subject. Although substantial alignment of the insertion guide device can be accomplished without the subject being present, it is sometimes necessary to perform fine adjustment with the insertion guide device attached on the subject. As described previously, variations in mounting an insertion guide device or opening a burr hole can make fine adjustments necessary. 
     Although particular orders of operations in the method described above are discussed, one of ordinary skill in the art, with the benefit of the present specification will recognize that other orders of operation are possible without departing from the invention. 
     CONCLUSION 
     Thus, an insertion guide has been shown that includes at least one insertion point adjustment device. Using embodiments of an insertion guide device as described above, a user such as a surgeon is able to adjust a lateral position of an insertion point to more precisely center the insertion point within an opening in a subject, such as a burr hole. Selected embodiments described above further include a centering guide that easily indicates to a user when the insertion point is substantially centered within the opening in the subject. 
     Selected embodiments described above further include adjustments of rotational degrees of freedom of an insertion axis. These adjustments allow a user to align the insertion axis with a target location within a subject, without changing the lateral (translational) location of the insertion point. Selected embodiments described above permit a user to fix multiple degrees of rotational freedom using a single locking device. 
     Selected embodiments described above further include the ability to attach an insertion guide device to at least one existing fiducial marker. The ability to attach to a fiducial marker improves accuracy of the insertion guide device by aligning more precisely with imaged locations on a subject, and tissue damage or other attachment surface damage is reduced by eliminating a separate attachment procedure for the insertion guide device, apart from the attachment of the fiducial markers. 
     Selected embodiments described above further include attachment of a large percentage of an insertion guide device at a distance above a subject surface. Reducing a contact surface area reduces tissue damage or other attachment surface damage due to an attachment procedure. Embodiments utilizing substantially transparent materials increase viewability of an opening in a subject. 
     Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that any arrangement which is calculated to achieve the same purpose may be substituted for the specific embodiment shown. This application is intended to cover any adaptations or variations of the present disclosure. It is to be understood that the above description is intended to be illustrative, and not restrictive. Combinations of the above embodiments, and other embodiments will be apparent to those of skill in the art upon reviewing the above description. The scope of the present disclosure includes any other applications in which the above structures and fabrication methods are used. The scope of the present disclosure should be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled.