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.