Site marker

A site marker and method of using a site marker are described and disclosed. The site marker comprises a bio-compatible and a plurality of elements, wherein the biocompatible material and at least one of the plurality of elements are imageable under different modalities.

TECHNICAL FIELD

The present disclosure relates to site markers used to identify biopsy locations in a patient's anatomy, and more specifically, to radiopaque site markers that are suitable for use in magnetic resonance imaging and/or magnetic resonance spectroscopy procedures.

BACKGROUND

In the diagnosis and treatment of breast cancer, it is often necessary to perform a biopsy to remove tissue samples from a suspicious mass. The suspicious mass is typically discovered during a preliminary examination involving visual examination, palpation, x-ray, magnetic resonance imaging (MRI), ultrasound imaging or other detection means.

When a suspicious mass is detected, a sample is taken by biopsy, and then tested to determine whether the mass is malignant or benign. This biopsy procedure can be performed by an open surgical technique, or through the use of a specialized biopsy instrument. To minimize surgical intrusion, a small specialized instrument such as a biopsy needle is inserted in the breast while the position of the needle is monitored using an imaging technique such as fluoroscopy, ultrasonic imaging, x-rays, or MRI. In addition, techniques such as magnetic resonance spectroscopy (MRS) imaging may be used to assess the likelihood or extent of cancerous cell growth by determining the level of certain compounds which are indicative of cancer cells.

In a relatively new procedure, referred to as stereotactic needle biopsy, the patient lies on a special biopsy table with her breast compressed between the plates of a mammography apparatus and two separate x-rays are taken from two different points of reference. A computer then calculates the exact position of the mass or lesion within the breast. The coordinates of the lesion are then programmed into a mechanical stereotactic apparatus which advances the biopsy needle into the lesion with precision. At least five biopsy samples are usually taken from locations around the lesion and one from the center of the lesion.

Regardless of the method or instrument used to perform the biopsy, subsequent examination of the surgical site may be necessary, either in a follow up examination or for treatment of a cancerous lesion. Treatment often includes a mastectomy, lumpectomy, radiation therapy, or chemotherapy procedure that requires the surgeon or radiologist to direct surgical or radiation treatment to the precise location of the lesion. Because this treatment might extend over days or weeks after the biopsy procedure, by which time the original features of the tissue may have been removed or altered by the biopsy, it is desirable to insert a site marker into the surgical cavity to serve as a landmark for future identification of the location of the lesion.

Known biopsy site markers have been found to have disadvantages in that the site markers are not visible under all available modalities or those that are useful for diagnosing and treating the patient. Moreover, because of this problem, when cancer is found at a biopsy site that has been previously marked with a site marker, due to the poor visibility of the biopsy site marker under ultrasound or other visualization modalities, the patient must undergo an additional procedure that places an additional device at the biopsy site to enable the surgeon to find the biopsy site in subsequent procedures Accordingly, a need has arisen for a site marker which addresses the foregoing issues.

DETAILED DESCRIPTION

Referring now to the discussion that follows and also to the drawings, illustrative approaches to the disclosed systems and methods are shown in detail. Although the drawings represent some possible approaches, the drawings are not necessarily to scale and certain features may be exaggerated, removed, or partially sectioned to better illustrate and explain the present invention. Further, the descriptions set forth herein are not intended to be exhaustive or otherwise limit or restrict the claims to the precise forms and configurations shown in the drawings and disclosed in the following detailed description.

Described herein are site markers which comprise a bio-compatible material and a plurality of elements, wherein the bio-compatible material and at least one of the plurality of elements are imageable with different modalities. In one embodiment, the bio-compatible material comprises a radiopaque material that is not itself MRI-imageable, and the plurality of elements are MRI-imageable. The radiopaque material allows the site marker to be radiographically imaged using techniques such as x-ray, computed tomography (CT) scanning, fluoroscopy, etc. The MRI-imageable elements have magnetic properties that allow the site marker to be visualized under MRI. As discussed further below, in exemplary configurations the bio-compatible radiopaque site marker defines a closed solid with a hollow interior in which the MRI-imageable elements are disposed or the MRI-imageable elements are suspended in the biocompatible radiopaque material itself.

FIG. 1illustrates a perspective view of a human breast10being implanted with a site marker12. Biopsy site14includes lesion16from which a tissue sample has been removed, resulting in a biopsy cavity18. One or more site markers12are implanted in the biopsy cavity18using a marker delivery system20, as shown inFIG. 1. In one embodiment, the marker delivery system20is slidably advanced through an inner lumen22of a biopsy device (not shown), which avoids the need to withdraw the biopsy device and thereafter insert the marker delivery system20. Delivering the site marker12in the biopsy cavity18without withdrawing the biopsy device reduces the amount of tissue damage and enables more accurate placement of the site marker12. The marker delivery system20illustrated inFIG. 1is exemplary only and it is understood that the site marker embodiments disclosed herein are suitable for use with other marker delivery systems.

Referring toFIG. 2, site marker12is illustrated in greater detail. Site marker12comprises a radiopaque element30formed from a radiopaque material into a desired shape, which is a pellet in the figure. Radiopaque element30is also preferably biocompatible so that it does not injure or cause a toxic or immunologic reaction in the patient's tissue. In preferred embodiments, the material comprising radiopaque element30is non-magnetic and non-MRI imageable. In an especially preferred embodiment, radiopaque element30is formed from a glass material. Any known biocompatible glass may be used, including but not limited to soda-lime, lead-alkali, borosilicate, aluminosilicate, silica and fused silica.

Radiopaque element30may be solid throughout or may comprise one or more internal hollow spaces. In the embodiment ofFIGS. 2 and 3A, radiopaque element30defines a fully, enclosed hollow internal volume32. Radiopaque element30may be formed into a variety of shapes; however, those shapes that will be more readily identified and distinguished from surrounding tissue structures when imaged are preferred. In the embodiment ofFIGS. 2 and 3A, radiopaque material30is provided in the shape of an elongated pellet. However, spherical shapes, elliptical shapes, cylindrical shapes, polyhedral shapes, and oval shapes may be used. In addition, site marker12may be symmetrical, asymmetrical, or have an irregular shape. Radiopaque element30is preferably dimensioned to be implanted using marker delivery system20and to be distinguishable from surrounding tissue.

Site marker12also preferably comprises an MRI-imageable material. In the embodiment ofFIGS. 2-3A, the MRI-imageable material comprises a plurality of MRI-imageable elements34which are disposed in hollow space32of radiopaque element30. Alternatively, MRI-imageable elements34may be disposed in a plurality of hollow spaces that are separated from one another within radiopaque element30. MRI-imageable elements34are preferably provided in an amount that allows site marker12to be viewed under MRI. MRI-imageable elements34may be loosely or tightly packed in hollow space32. The MRI-imageable elements34may have uniform or non-uniform, sizes, shapes, and/or compositions. In certain preferred embodiments, MRI-imageable elements34are selected from the group consisting of metals, ceramics, and mixtures thereof. Preferred metals include, titanium, tantalum, steel, platinum, gold, palladium, and combinations thereof. Preferred ceramics include metal oxides, such as alumina (Al2O3), zirconia (ZrO2), and magnetite (Fe3O4). In addition, individual MRI-imageable elements34may each comprise a plurality of different materials, such as an alloy. The use of a plurality of MRI-imageable elements34allows site marker12to be customized to particular imaging procedures and devices by adjusting the composition, amount, size, shape, and/or spatial distribution of MRI-imageable elements34. For example, for an MRI device with a relatively strong magnetic field, the number of MRI-imageable elements34may be reduced so that the magnetic field does not displace site marker24within the patient's anatomy, whereas for an MRI device with a relatively weaker magnetic field, the number of MRI-imageable elements34may be increased to ensure that site marker12is sufficiently visible on an MR image.

Referring toFIG. 3B, an alternative embodiment of a site marker is depicted. In accordance with the embodiment, site marker12includes radiopaque element30with MRI-imageable elements34suspended within the material comprising radiopaque element30to define a solid mixture. InFIG. 3B, site marker12is in the shape of an annulus with a hollow interior38. The cross-sectional thickness of the annulus has been exaggerated to better depict MRI-imageable elements34. Site marker12may also comprise a solid body with no hollow interior or void spaces. MRI-imageable elements34may be uniformly or non-uniformly distributed throughout any or all of the dimensions (e.g., length, width, height, radius) of the radiopaque material comprising radiopaque element30. In addition, MRI-imageable elements34may have the same or different, sizes, shapes, and/or compositions. In one implementation, the MRI-imageable elements34are combined with the radiopaque material while the radiopaque material is in a molten state to form site marker12. If the radiopaque material is provided as a granular material and heated to create a molten state, the MRI-imageable elements34may also be combined with the granular material prior to heating. The mixture of radiopaque material and MRI-imageable elements34is then heated to a molten state and solidified, such as by cooling.

In the embodiment ofFIG. 3B, MRI-imageable elements34may be tightly packed within the radiopaque material so as to abut adjacent elements34or they may be spaced apart from one another along any or all of the dimensions of site marker12. In addition, MRI-imageable elements34may define certain regions in which they are tightly packed and others in which they are spaced apart from one another, thereby defining a non-uniform spatial distribution. As with the previous embodiment, the compositions, sizes, shapes, distribution, and/or number of MRI-imageable elements34are preferably selected to provide the required degree of magnetic sensitivity in the MRI device and procedure that are being used.

As is known to those skilled in the art, magnetic resonance spectroscopy (“MRS”) is a procedure that can be used to obtain information about the chemical content of tissue regions of interest, such as breast lesions. In MRI, the absorbed RF signal is used to create an image. However, in MRS, the absorbed RF signals are used to create a spectrum that is indicative of the presence of different groups of atoms surrounding a specific nucleus (e.g.,31P,1H,13C,23Na). Proton MRS (i.e., the nucleus is1H) is preferred. As is known to those skilled in the art, metabolites have one or more defined chemical shift values (ppm) on a magnetic resonance spectrum. For example, alanine has a shift of 1.47 ppm, N-acetylaspartate has shifts of 2.0 and 2.6 ppm, creatine has a shift of 3.0 and 3.9 ppm, water has a shift of 5.0 ppm, and choline has shifts of 3.2 ppm. It has been found that choline levels may be used to distinguish malignant from benign lesions. Bolan, et al., “Imaging in Breast Cancer: Magnetic Resonance Spectroscopy,”Breast Cancer Research2005, 7:149-152 and Nofray, U.S. Pat. No. 7,289,840. However, certain metallic site markers may interfere with the choline spike in an MRS spectrum. Thus, for applications in which MRS is contemplated, site marker12is preferably selected to be visible under MRI and MRS compatible.

In certain illustrative embodiments, MRI-imageable elements34comprise one or more metals having a composition, size, shape, distribution, and/or number that allows site marker12to be both MRI-imageable and MRS-compatible. In other illustrative embodiments, MRI-imageable elements34comprise ceramic materials, such as one or more of the metal oxides described above, having a composition, size, shape, distribution, and/or number that provides MRS-compatibility. As used herein, the term “MRS compatible” means that the materials do not distort the MRS spectrum. In those embodiments wherein MRS is performed to determine whether a lesion is benign or malignant, the MRI-imageable elements preferably do not distort at least the choline peak of the MRS spectrum.

In certain embodiments, MRI-imageable elements34may comprise multiple groups of elements, each of which differs in its ability to be visualized under different imaging modalities. For example, MRI-imageable elements34may comprise metal elements in one portion of radiopaque element30and ceramic elements in another portion of radiopaque element30. In another example, different metals may be used in different portions of radiopaque element30. In yet another example, multiple types of metals and/or ceramics may comprise MRI-imageable elements34. The use of multiple types (e.g., multiple compositions, sizes, shapes) of MRI-imageable elements provides variable imaging properties along the different dimensions (e.g., length and width or diameter) of radiopaque element30. In still another embodiment, the spatial distribution of MRI-imageable elements within radiopaque element30may be uniform or non-uniform. In one example of a non-uniform distribution, two groups of MRI-imageable elements34may be included in radiopaque element30and spaced apart from one another. The composition, size, number, shape, and spatial distribution of each group of MRI-imageable elements34may be selectively adjusted to achieve a desired degree of visualization under specific imaging modalities. Different MRI-imageable elements34may be used which differ in their ability to be visualized under certain modalities or in their compatibility with certain modalities. However, they also may differ in the degree to which they can be visualized in any one modality.

A method of using site marker12to identify the location of a biopsied tissue specimen will now be described. In accordance with the method, site marker12is provided as described in the foregoing embodiments. A suspected cancerous mass is located in the patient, and a tissue sample is removed from the identified location. The site marker12is then implanted at the location. The patient may then be x-rayed in the area of the body surrounding the location and the location of the site marker12may be identified on the x-ray image. In addition, the patient may be subjected to MRI, and the site marker12may be identified on the MRI image. Either or both of the x-ray and MRI images may then be examined to determine whether there is any tumor growth at the biopsy site. If necessary, the patient may be re-biopsied at the biopsy location or may undergo a lumpectomy by correlating locations on the patient's anatomy to the site marker location on either or both of the x-ray image and the MRI image. In certain preferred embodiments, the site marker12is implanted by inserting site marker delivery system20through the inner lumen of a biopsy device (not shown) to better ensure that the site marker12is implanted at the location from which the biopsy sample was taken.

It may be desirable to further obtain a MRS spectrum of the tissue in the area of the biopsy site to determine the levels of chemical entities indicative of cancer. In a preferred embodiment, MRI-imageable elements34are selected in the manner described above to provide an MRI-compatible site marker12, and an MRS spectrum is obtained following implantation of site marker12. The choline shift is then evaluated to determine whether cancerous cells may be developing or increasing in number. In certain embodiments, a baseline choline level is obtained from an MRS spectrum prior to applying a therapeutic treatment (e.g., chemotherapy or a lumpectomy) and a follow up spectrum is obtained to identify relative changes in the choline level proximate site marker12.

It will be appreciated that site markers and methods described herein have broad applications. The foregoing embodiments were chosen and described in order to illustrate principles of the methods and apparatuses as well as some practical applications. The preceding description enables others skilled in the art to utilize methods and apparatuses in various embodiments and with various modifications as are suited to the particular use contemplated. In accordance with the provisions of the patent statutes, the principles and modes of operation of this invention have been explained and illustrated in exemplary embodiments.

It is intended that the scope of the present methods and apparatuses be defined by the following claims. However, it must be understood that this invention may be practiced otherwise than is specifically explained and illustrated without departing from its spirit or scope. It should be understood by those skilled in the art that various alternatives to the embodiments described herein may be employed in practicing the claims without departing from the spirit and scope as defined in the following claims. The scope of the invention should be determined, not with reference to the above description, but should instead be determined with reference to the appended claims, along with the full scope of equivalents to which such claims are entitled. It is anticipated and intended that future developments will occur in the arts discussed herein, and that the disclosed systems and methods will be incorporated into such future examples. Furthermore, all terms used in the claims are intended to be given their broadest reasonable constructions and their ordinary meanings as understood by those skilled in the art unless an explicit indication to the contrary is made herein. In particular, use of the singular articles such as “a,” “the,” “said,” etc. should be read to recite one or more of the indicated elements unless a claim recites an explicit limitation to the contrary. It is intended that the following claims define the scope of the invention and that the method and apparatus within the scope of these claims and their equivalents be covered thereby. In sum, it should be understood that the invention is capable of modification and variation and is limited only by the following claims.