Tool for implanting a fiducial marker

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BACKGROUND OF THE INVENTION

The present invention relates to a method and apparatus for implanting a fiducial marker. More specifically, the invention relates to an apparatus and method that provide for the creation of a hole that does not penetrate the entire thickness of a segment of bone, and which is sized to accommodate a fiducial marker. The invention also provides for the insertion of an imaging marker or marker base into the hole so created.

Recent years have seen the development of diagnostic techniques that allow the practicing clinician to obtain high fidelity views of the anatomical structure of the human body. Imaging systems such as computed tomographic (CT) x-ray imagers, positron emission tomographic (PET) scanners, single photon emission computed tomography (SPECT) scanners and nuclear magnetic resonance imaging (MRI) machines have provided clinicians with the ability to improve visualization of the anatomical structure of the human body without surgery or other invasive techniques. In lieu of exploratory surgery, the patient can be scanned by such imaging systems, and the patient's anatomical structure can be reproduced in a form for evaluation by a trained doctor. A problem associated with such scanning techniques concerns the accurate selection and comparison of views of identical areas in images that have been obtained by imagers at different times or by images obtained essentially at the same time using different image modalities, e.g., CT, MRI, SPECT, and PET. This problem has two aspects. First, in order to relate the information in an image of the anatomy to the anatomy itself, it is necessary to establish a one-to-one mapping between points in the image and points of anatomy. This is referred to as registering image space to physical space.

The second aspect concerns the registration of one image space onto another image space. The goal of registering two arbitrarily oriented three dimensional images is to align the coordinate systems of the two images such that any given point in the scanned anatomy is assigned identical addresses in both images. The calculation of the rigid body transformation necessary to register the two coordinate systems requires knowledge of the coordinate vectors of at least three points in the two systems. Such points are called "fiducial points" or "fiducials," and the fiducials used are the geometric centers of markers, which are called "fiducial markers". These fiducials are used to correlate image space to physical space and to correlate one image space to another image space. The fiducial markers provide a constant frame of reference visible in a given imaging mode to make registration possible.

The general technique for using fiducial markers to obtain registration of image data is set forth in U.S. Pat. No. 4,991,579 and U.S. Pat. No. 5,142,930, the contents of both of which are incorporated herein by reference. Briefly, these patents teach implanting within a patient a series of at least three fiducial markers whose location can be determined in the image space of an imager.

Broadly speaking, image markers can be either temporary or permanent with respect to the duration of their placement within the human body. Permanent markers are unitary in construction, and are placed entirely beneath the epidermis of the skin for extended periods of time. Temporary markers have two parts: a base that is implanted into bone, and a temporary image marker portion that is attached to the base for brief intervals of time. In the temporary marker, the image marker portion protrudes from the skin.

In both the temporary and the permanent markers, the marker portion may take the form of a hollow container that is charged with aqueous imaging agents to provide imaging capability in the desired imaging modality or modalities. Patent application Ser. No. 08/017,167 (the contents of which are incorporated herein by reference) more fully discusses the structure of each type of marker and the imaging agents which can be used therewith.

Whichever type of marker is employed, it is necessary for the clinician to implant the marker into some solid, dimensionally stable portion of the anatomy. The preferred location for the placement of fiducial markers is bone, as it is generally dimensionally stable, and can provide a secure anchor site for a fiducial marker. The placement of a fiducial marker into bone requires that a hole be drilled for the fiducial marker.

Permanent fiducial markers typically are implanted in their entirety in bone tissue beneath the skin; temporary markers (as noted above) have distinct base and marker portions, with respect to which only a portion of the base need be implanted into bone. One method for implanting a fiducial marker is described in U.S. Pat. No. 5,178,164, which is incorporated herein by reference. According to this method, a marker is screwed into bone tissue under force. A hex-key like wrench engages a socket on the upper surface of the marker to provide the necessary drive connection between the two elements.

Numerous surgical tools have been developed to facilitate the insertion of foreign objects into the human body. Recent years, in particular, have seen the development of very specialized tools for many surgical procedures so as to minimize the invasiveness of the procedure in question. One such specialized tool is an apparatus for the insertion of a catheter into the ventricular portion of the brain, and is set forth in U.S. Pat. No. 4,931,056, which is incorporated herein by reference. The patent discloses a catheter guide apparatus comprising a hand operated twist drill device, configured for insertion in a first tubular guide. A second guide, of reduced diameter relative to the first tubular guide, is insertable into the first guide upon completion of a through-hole in the skull and subsequent removal of the twist drill, to facilitate entry of a catheter into the ventricle portion of the brain.

There remains a need for a tool specialized to facilitate the creation of a hole that is configured to accommodate a fiducial marker. There further remains a need for a tool that can quickly be reconfigured to facilitate the secure insertion of a fiducial marker into the hole so created. There further remains a need for a tool especially adapted for the insertion of a fiducial marker into bone tissue that is simple to use, minimally invasive, and which includes safety features to prevent the formation of an unwanted through-hole in bone tissue.

SUMMARY OF THE INVENTION

The present invention provides a tool for first creating a hole of predetermined depth into bone tissue, and then inserting a fiducial marker into the hole in the bone. The tool uses a guide assembly and means that cooperate with the guide assembly for perforating the skin, securely siting the guide assembly, forming the bore hole, and inserting the marker.

Before using the tool, the physician first determines the site at which the fiducial marker is to be inserted and marks that site with an incision. The insertion tool is then placed over the incision. The tool provides a guide assembly that includes a housing that is shaped to provide a secure abutment with respect to a desired portion of the anatomy of a patient. The housing contains a bore which accommodates both a cylindrical metal cannula and a spring that is entrained between a ring on the cannula and a shoulder within the housing; the cannula is shiftable within the housing against a force supplied by this spring. One end of the cannula terminates in a row of sharp teeth for establishing a firm connection between the housing and the patient's tissue. The other end of the cannula is inserted within a handle having an opening that leads to the hollow cannula. The cannula is sized to accommodate a number of implements useful in establishing a hole of proper size and inserting a marker, including an obturator, a hand drill, and a specialized insertion tool. After the incision has been made, an obturator having a sharp tip at its proximal end is inserted into the cannula. The length of the obturator is sufficient for a length of it to protrude beyond the proximal end of the cannula so that its pointed tip can be brought into contact with the incision site. The initial positioning of the guide assembly is accomplished simply by a downward shifting of the housing and the guide assembly along the length of the obturator until the teeth of the cannula contact tissue. The housing is then axially shifted along the cannula against the spring entrained between the cannula and the housing, until the housing abuts the patient's skin.

Once the tool housing is properly sited, the obturator is removed from the cannula and a hand drill inserted in its place. The hand drill is used to make a hole of predetermined diameter and depth (the depth of the hole drilled is limited by the manner in which the geometry of the housing, drill bit and drill bit length cooperate with one another). The hand drill is then removed from the cannula.

The tool can be used to insert either the marker base of a temporary fiducial marker or a permanent, fully implantable fiducial marker. Where a temporary marker is to be installed, its base, which may have a polygonal socket, is attached to the end of an insertion tool that terminates in a drive element. The insertion tool and marker base are then inserted into the cannula. By pressing the fiducial marker base into the hole and then rotating the handle of the insertion tool, the marker base (which has a self-tapping thread) can be screwed into the hole formed by the hand drill. The insertion tool is then pulled away from the fiducial marker base and is removed from the cannula. The procedure for inserting a permanent fiducial marker is similar, differing chiefly in that instead of screwing in the marker, it is press-fitted into the hole. At this point the procedure is complete, and the guide assembly is removed from the patient.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the accompanying figures, in which:

FIG. 1 is a cross-sectional view of the guide assembly;

FIG. 2 shows the cannula guide tube subassembly, partially in section;

FIG. 3 shows the obturator and its engagement with the guide assembly;

FIG. 4 shows the position of the guide assembly-and obturator when the obturator is sited over the insertion site;

FIG. 5A is a plan view of the hand drill;

FIGS. 5B and 5C are side and end views, respectively, of a drill bit employed with the hand drill;

FIGS. 5D and 5E are side and end views, respectively, of the handle portion of the hand drill;

FIG. 6 is a side view, partially in section, of the hand drill inserted in the guide assembly;

FIG. 7A shows a temporary marker base that can be used with the present invention;

FIG. 7B shows a permanent marker that can be used with the present invention;

FIG. 8 is a side view, partially in section, of the cooperation between the insertion tool, clip, and temporary marker base;

FIG. 9A is a perspective view of the clip shown in FIG. 8, which helps secure the temporary marker base to the insertion tool;

FIG. 9B is a side-sectional view of a clip which is configured to secure a permanent marker to the insertion tool;

FIG. 9C is an end view of the clip shown in FIG. 9B;

FIG. 10 is a sectional view showing the insertion tool, the temporary marker base and guide housing, in which the cannula guide tube is shown shifted with respect to the guide housing;

FIG. 11 is a magnified view of the proximal end of FIG. 10, and highlights the tip of the proximal end of the cannula and the threaded portion of the temporary marker base;

FIGS. 12A-12C provide perspective views of the principal elements of the tool kit, including the guide assembly (FIG. 12A), insertion tool (FIG. 12B) and obturator (FIG. 12C);

FIGS. 13A and 13B are partial side sectional and end views, respectively, of a tool for removing the base of a temporary fiducial marker after it has been inserted; and

FIGS. 14A and 14B illustrate the use of an additional embodiment that employs a trocar instead of an obturator in a two-stage process. FIG. 14A is a sectional view of the embodiment at a first stage of its use and FIG. 14B is an elevational view of the embodiment at a second stage of its use.

DETAILED DESCRIPTION

Turning initially to FIG. 1, there is illustrated a guide assembly 10 of the present invention. The guide assembly 10 serves to provide a means for establishing and maintaining a geometrically constrained passageway with respect to the patient for the introduction of a drill for forming a hole. The guide assembly is subsequently used in a similar manner to receive a specialized tool for inserting a fiducial marker or marker base into the hole. The guide assembly is made up of two principal components which shall be discussed in turn: a guide housing 12, and a cannula guide tube subassembly 20.

The generally tubular guide housing 12, which may be made of plastic, has an inner bore 18 running along the longitudinal axis of the guide housing. The bore begins at the distal annular surface 13 of the guide housing 12 and continues a distance before increasing in diameter at shoulder 19. At the proximal end of the guide housing 12, the walls of the housing flare outward in a perpendicular direction away from the axis of the cylinder to form a base 14. The base 14 is scalloped in shape, forming a concave depression 16.

Fitted into the guide assembly 10 is a cannula guide tube subassembly 20 (see FIG. 2). This subassembly consists of a stainless steel metal cannula guide tube 22 that fits within the bore 18 of the housing 12. The cannula guide tube 22 is hollow, and terminates at its proximal end in a row of sharp teeth 26. The function of these teeth is to help provide a secure connection between the guide assembly and the tissue of the patient so as to prevent shifting of the housing and guide assembly during drilling and insertion of the marker. At its distal end, the cannula guide tube 22 is fitted to the bore of a plastic cap 28. The diameter of the bore at the proximal end of the cap is such that the bore securely accommodates the distal end of the cannula guide tube 22. The bore increases in diameter in the distal direction to form a bore of greater diameter at 30a. The bore then widens along a conical segment 30b before reassuming a cylindrical shape at 30c, which defines the distal entrance 29 to the bore (and hence to the guide tube) at the distal face 27. An annular ring 24 is affixed to the cannula guide tube 22 inte