a biopsy marker , preferably a breast biopsy marker , has radio - opaque properties that are derived in situ , preferably based on a natural a biological response , such as calcification or accumulation or tissue - concentration of a chemical agent that acts as an imaging contrast . in an embodiment , a biodegradable foam such as collagen foam or gelatin foam is embedded with a biological tissue that is susceptible to the calcification . the biopsy marker is implanted to mark the biopsy site . the foam material provides ultrasonic visibility to access the implantation site . the biological tissue undergoes calcification in 30 days to 5 years depending on the chemistry of biological tissue used . the calcification generated in the biological tissue provides visibility in magnetic resonance imaging ( mri ) and x - ray imaging . as a result , the marker may be located using radiation - based imaging or ultrasonic imaging . many types of implantable tissues can be used to prepare a biopsy marker described in this invention . the implantable tissues used include but not limited to : bovine pericardium tissue , porcine dermal tissue , bovine or porcine arterial tissue , porcine aortic wall tissue and the like . a tissue that is rich in elastin such as porcine aortic wall tissue is even more preferred . it is believed that elastin rich tissue is highly susceptible to calcification . biomaterials that are derived from elastin protein may also be used . the biological tissue is preferred to be crosslinked or stabilized using glutaraldehyde . the tissue crosslinked using 0 . 2 to 2 % glutaraldehyde is even more preferred . in addition , biological ingredients that promote calcification may also be added in the tissue . these additives include bioactive and non - bioactive substances like bone growth factor , phospholipids , polyethylene glycol and the like . in another embodiment , an elastic protein - based biomaterial is processed to cause the material to have a 60 to 90 % porosity . the material is further processed to cause crosslinking using glutaraldehyde , 1 - ethyl - 3 -[ 3 - dimethylaminopropyl ] carbodiimide hydrochloride ( edc ) or other suitable crosslinker the elastin foam is then implanted as a biopsy marker where it undergoes rapid calcification . the calcification is then detected using standard x - ray or mri imaging techniques . the shape of the marker can depend on the clinical application . in general cylindrical , spherical , disk like shapes are preferred . irregular shapes may also be used . referring now to fig1 - 3 , a tissue marker 100 has an external layer of biodegradable foam 110 with a core of biological tissue 150 . the biodegradable foam has biocompatible gas within its voids . the biocompatible gas provides a low density structure within the marker body which provides high contrast when viewed using ultrasonic imaging equipment . this makes the marker visible under ultrasonic imaging modalities . the biological tissue 150 within is a material chosen for its tendency to calcify when placed in a human host . when the marker is placed within the body of a host , the biodegradable foam is broken down while the biological material 150 calcifies and eventually becomes visible under radiation imaging modalities . the period during which ultrasound can be used may last between weeks and many months , for example six months . in many therapeutic situations , this is more than sufficient time . the time during which the calcified remainder can be imaged may last for many years or it may be permanent . the calcification may take a year or two to occur . again , in many therapeutic situations , the radiation - imaging provided in the later stages is all that is required . therefore the loss of the ability to image under ultrasound is inconsequential . the benefits of the above device should be apparent . the calcified biological tissue is highly compatible with the host . some of the bulk of the marker which may be desirable for ultrasound imaging can be lost which may be desirable as well . in a preferred embodiment , which is by no means limiting of the invention , the marker may be generally cylindrical with a diameter of about 4 mm and a length of about 6 mm . the core of biological tissue may be about 1 mm in diameter and about 3 mm long . one example of a method for making and using the marker is illustrated in fig4 . in step 51 , a collagen solution is poured into a mold to partly fill the mold . just enough solution to create a spacer for the biological tissue is all that is required . then , in step s 2 , the collagen solution frozen in the mold . the biological material is inserted in the mold and collagen solution is poured into the space around it in step s 4 . then the whole mold is frozen and the frozen collagen solution lyophilized in step s 5 to remove the ice while leaving the collagen matrix behind . to use the marker , in step s 6 , the marker is implanted in a host . this step may be done as part of a biopsy procedure , for example . then , in step s 7 , the marker is imaged . step s 7 may occur repeatedly over a range of time , perhaps a year , after implantation . in step s 8 , perhaps over a year after implantation , the marker is imaged using radiation imaging modalities . steps s 7 and s 8 may overlap and are not necessarily chronologically - sequential in all instances . other steps are not necessarily sequential either . for example , steps s 3 and s 4 could be done simultaneously — the flow chart presents merely one example of the manufacturing and use processes . instead of using collagen foam to form voids , it is possible to form voids in a biodegradable material using other means . for example , voids could be molded in or machined into a piece of material implantation of a biological material can be done in a similar way , but forming a hole in a pre - made body of biodegradable material , inserting the biological material into the hole and subsequently sealing the hole . also , instead of molding the foam , it is possible to form the marker by dipping the biological material body 150 into a collagen or other suitable solution and freezing it in repeated steps until a coating of suitable thickness is obtained before lyophilizing the resulting structure . as discussed above , the biological tissue 150 may include bovine pericardium tissue , porcine dermal tissue , bovine or porcine arterial tissue , porcine aortic wall tissue and the like . as mentioned , a tissue that is rich in elastin such as porcine aortic wall tissue is even more preferred . it is believed that elastin rich tissue is highly susceptible to calcification . biomaterials that derived from elastin protein may also be used . the biological tissue is preferred to be crosslinked or stabilized using glutaraldehyde . the tissue crosslinked using 0 . 2 to 2 % glutaraldehyde is even more preferred . in addition , biological ingredients that promote calcification may also be added in the tissue . these additives include bioactive and non - bioactive substances like bone growth factor , phospholipids , polyethylene glycol and the like . while the above marker example of a cylindrical body is a preferred configuration , other shapes and combinations can be used . for example , more than one body of biological tissue could be integrated in the porous biodegradable body . also , the biological tissue need not be entirely encased within the body of the biodegradable portion . for example , an alternative method of manufacture may be to co - extrude under pressure such that the casing solution and the biological material are plastic but freeze quickly after exiting the extruder . the sublimation of the solute can then be done to the co - extruded billet before or after dividing it into pieces of appropriate length . markers having the above - described structures , or any similar structure , may be used according to the following method which may include steps 1 and 2 , steps 1 through 3 , or steps 1 through 4 , according to different embodiments . step 1 . insert a marker at a location . the location can be marked at a time and location of biopsy or otherwise positioned in a tissue mass . step 2 . identify a location of the marker using a first imaging modality . the modality may be ultrasound - based imaging . this step may include passing a corresponding form of energy through a soft tissue mass of a living host . step 3 . wait a period of time for calcification to occur . step 4 . identify a location of the marker using a second imaging modality that is different from the first imaging modality in step 2 . the second imaging modality may be x - ray - based imaging or mri . this step may also include passing a corresponding form of energy through a soft tissue mass of a living host . note that in the above method , not all steps are essential or necessarily separate . for example , the waiting step may be inherent in step 2 or step 4 . this specification should not be interpreted as implying that any particular element , step or function is an essential element of any of the claims . the scope of the patented subject matter is defined only by the claims and their equivalents . the calcification process is not the only kind of biological activity that could be exploited by a marker to cause the marker , or a portion thereof , to become imageable . a marker may incorporate any substance capable of concentrating an imageable substance . for example , the marker could incorporate a substance for which antibodies can be produced . in one exemplary approach , a marker may contain a biological tissue such as bovine pericardium tissue . a bovine tissue specific antibody could be made , labeled with a imaging tag and used . such antibodies may be grown , radioactively labeled , and injected in the host . the marker would then cause the antibody to concentrate in and about the included substance . this in turn would cause the concentration of the radioactive label to be high in the vicinity of the marker . the process is due to the combined action the antibody and the host . the result may cause the marker to be imageable using a radiation detector . using isotopes with a conspicuously - high cross - section for externally applied radiation could also be used to make a marker imageable by the same type of process . that is , the marker may incorporate a substance for which an antibody can be grown . the antibody could be grown using the selected isotope . due to the combined action the antibody and the host , the antibody concentrates at the marker site . then , the externally applied radiation may be used to image the concentrated isotope . antibodies could also serve as carriers of certain molecules or radicals that can be imaged using lower energy radiation due either to their absorption or stimulated - emission signatures . other labeling methods such as fluorescent labeling useful in fluorescent imaging , paramagnetic labeling useful in mri imaging and the like may also be used . while the present invention has been disclosed with reference to certain embodiments , numerous modifications , alterations , and changes to the described embodiments are possible without departing from the sphere and scope of the present invention , as defined in the appended claims . accordingly , it is intended that the present invention not be limited to the described embodiments , but that it has the full scope defined by the language of the following claims , and equivalents thereof .
an intracorporeal marker , for marking a site within living tissue of a host , includes an outer body portion of biodegradable material . an inner body portion is located in the outer body portion . the inner body portion includes biological material that becomes calcified in the living tissue of the host over time . an agent interacts with the biological material to promote calcification of the biological material of the inner body portion in the living tissue of the host .