Abstract:
A system for at least partially filling and marking a cavity at a site within a patient&#39;s body includes a marker delivery device having a chamber configured to contain a marking substance and having a mechanism configured to expel the marking substance. A quantity of the marking substance is contained within the chamber of the marker delivery device. The marking substance is configured to at least partially fill the cavity and form therein a porous bioabsorbable body. A delivery tube is coupled in fluid communication with the chamber of the marker delivery device. The delivery tube has a distal end with a discharge port through which the marking substance is expelled. A marker is configured to be delivered to the cavity from the distal end of the delivery tube and is configured to remain with the porous bioabsorbable body within the cavity upon the formation thereof.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a continuation of U.S. patent application Ser. No. 12/967,639, filed Dec. 14, 2010, which is a continuation of U.S. patent application Ser. No. 10/444,428, entitled “MARKER OR FILLER FORMING FLUID”, filed May 23, 2003, now U.S. Pat. No. 7,877,133, which is incorporated herein by reference. 
    
    
     FIELD OF INVENTION 
     This invention relates generally to the introduction of filler or marker material into a patient&#39;s body, and particularly to the filling a biopsy site within a patient&#39;s body from which a biopsy specimen has been taken with a mass of marker material. 
     BACKGROUND OF THE INVENTION 
     In diagnosing and treating certain medical conditions, it is often desirable to perform a biopsy, in which a specimen or sample of tissue is removed for pathological examination, tests and analysis. As is known, obtaining a tissue sample by biopsy and the subsequent examination are typically employed in the diagnosis of cancers and other malignant tumors, or to confirm that a suspected lesion or tumor is not malignant. The information obtained from these diagnostic tests and/or examinations is frequently used to devise a plan for the appropriate surgical procedure or other course of treatment. For example, breast biopsies may be taken where a suspicious lump or swelling is noticed in a breast. Examination of tissue samples taken by biopsy is of particular significance in the diagnosis and treatment of breast cancer. In the ensuing discussion, the biopsy and treatment site described will generally be the human breast, although the invention is suitable for marking biopsy sites in other parts of the human and other mammalian body as well. 
     After the biopsy sample is taken, it may take several days or weeks before the results of the examination of the sample are obtained, and still longer before an appropriate treatment decision is reached. If the decision involves surgery it is clearly important for the surgeon to find the location in the breast from where the tumor tissue has been taken in the biopsy procedure, so that the entire tumor and possibly surrounding healthy tissue can be removed. 
     However, radiographically visible tissue features, originally observed in a mammogram, may be removed, altered or obscured by the biopsy procedure. In order for the surgeon or radiation oncologist to direct surgical or radiation treatment to the precise location of the breast lesion several days or weeks after the biopsy procedure was performed, it is desirable that a biopsy site marker be placed in or on the patient&#39;s body to serve as a landmark for subsequent location of the lesion. 
     Various types of biopsy site markers have been described, including visible markers applied externally to the patient&#39;s skin, radiographically (X-ray)-detectable tissue markers such as clips and staples, and ultrasound-detectable markers, have also been described. X-ray-detectable marker wires may be inserted through a biopsy needle, leading from the surface of the patient&#39;s body to the biopsy site. Some markers may be biodegradable. 
     However, due to the consistency of breast tissue and the fact that these biopsy site markers are typically introduced while the breast is still compressed between the mammography plates, prior art biopsy markers may not remain at the specific biopsy location after the breast has been decompressed and removed from the mammography apparatus, and may suffer from additional disadvantages as well. In order to locate an X-ray-detectable marker left at a biopsy site, an additional mammography is generally required at the time of follow up treatment or surgery. In addition, once it is located using mammography, the biopsy site must usually be marked again with a location wire that is visible by eye to provide guidance to the clinician performing the treatment or surgery. However, as the patient is removed from the mammography apparatus, or otherwise transported, the position of the location wire can change or shift before the treatment or surgery is performed, which may result in treatments being misdirected to undesired locations. Furthermore, at least some prior art biopsy site markers can remain present at the site of implantation for an indefinite period of time and, if not surgically removed, may obscure or otherwise interfere with any subsequent mammography or imaging studies. 
     However, due to the large amount of fibrous tissue normally present in a human breast, and due to the presence of ligaments running through the breast, a marker that simply has a bright signal alone will not provide a useful signal that is readily discernable from the many anatomic features normally present within a human breast. Such markers are typically small, being sized to fit within a syringe or other delivery tube, and so are often not readily distinguishable from natural features of the breast, which include occasional small ultrasound-bright spots. 
     As an alternative or adjunct to radiographic imaging, ultrasonic imaging and visualization techniques (abbreviated as “USI”) can be used to image the tissue of interest at the site of interest during a surgical or biopsy procedure or follow-up procedure. USI is capable of providing precise location and imaging of suspicious tissue, surrounding tissue and biopsy instruments within the patient&#39;s body during a procedure. Such imaging facilitates accurate and controllable removal or sampling of the suspicious tissue so as to minimize trauma to surrounding healthy tissue. 
     For example, during a breast biopsy procedure, the biopsy device is often imaged with USI while the device is being inserted into the patient&#39;s breast and activated to remove a sample of suspicious breast tissue. As USI is often used to image tissue during follow-up treatment, it may be desirable to have a marker, similar to the radiographic markers discussed above, which can be placed in a patient&#39;s body at the site of a surgical procedure and which are visible using USI. However, radiopaque markers may not be visible with USI. A marker visible with USI enables a follow-up procedure to be performed without the need for traditional radiographic mammography imaging which, as discussed above, can be subject to inaccuracies as a result of shifting of the location wire as well as being tedious and uncomfortable for the patient. 
     Thus, there is need in the art for biopsy site markers that are deliverable into the cavity created by removal of the biopsy specimen and not into tissue that is located outside of that biopsy cavity, and which will not migrate from the biopsy cavity even when the breast tissue is moved, manipulated or decompressed. Moreover, such desired markers should remain detectable at the biopsy site (i.e., within the biopsy cavity for a desired time period); should not interfere with imaging of the biopsy site and adjacent tissues at a later time; and should be readily distinguishable in the various imaging procedures from lines of calcifications which frequently are signs for a developing malignancy. 
     SUMMARY OF THE INVENTION 
     The invention is directed to the deployment of a marker or filler forming material at intracorporeal locations such as biopsy sites, sites for cosmetic treatments and other sites which may need additional bulk. 
     The invention, in one form thereof, is directed to a system for at least partially filling and marking a cavity at a site within a patient&#39;s breast from which tissue has been removed. The system includes a syringe having an elongated body, an inner bore, and a plunger slidably disposed within the inner bore. A delivery tube has a distal end with a discharge port and a delivery tube bore in fluid communication with the inner bore of the syringe and the discharge port. A quantity of marker forming fluid is within the inner bore of the syringe and is configured to at least partially fill the cavity at the biopsy site and form therein a porous bioabsorbable body. A releasable remotely detectable distal tip at the distal end of the delivery tube includes a radiopaque metal and is configured to remain within the porous bioabsorbable body within the cavity upon the formation thereof. The releasable remotely detectable radiopaque distal tip at the distal end of the delivery tube defines the discharge port. 
     The invention, in another form thereof, is directed to a system for at least partially filling and marking a cavity at a site within a patient&#39;s body from which tissue has been removed. The system includes a delivery device having a chamber configured to contain a marking substance. The marker delivery device has a mechanism configured to expel the marking substance. A quantity of the marking substance is contained within the chamber of the marker delivery device. The marking substance is configured to at least partially fill the cavity at the biopsy site and form therein a porous bioabsorbable body. A delivery tube is coupled in fluid communication with the chamber of the marker delivery device. The delivery tube has a distal end with a discharge port through which the marking substance is expelled. A releasable remotely detectable distal tip is coupled to the distal end of the delivery tube and is configured to be released to remain within the porous bioabsorbable body within the cavity upon the formation thereof. 
     The marker or filler material is formed intracorporeally from a biocompatible solution having as a solute bioabsorbable polymeric material which is relatively insoluble in body fluid or other water based fluids and a water soluble, non-aqueous polar solvent such as dimethyl sulfoxide (DMSO). Suitable bioaborbable polymers include polylactic acid, polyglycolic acid, polycaprolactones and copolymers and blends thereof. When the marker or filler forming fluid contacts body fluid or other water based fluids present at intracorporeal locations, the non-aqueous solvent is quickly absorbed by the body fluid or water based fluid present at the site, precipitating a mass of the water insoluble bioabsorbable polymeric material at the site. The polymeric material forming the marker or filler mass is preferably inherently ultrasonically detectable or the marker fluid may be treated to have a plurality of gas bubbles or otherwise aerated, so that upon formation of the polymeric mass at the site, gas is incorporated in the solid mass forming to provide ultrasonically detectable porosity. 
     The following description of embodiments of the invention is primarily directed to deployment of mass at a biopsy site for purposes of remote detection of the biopsy site. However, it should be recognized that the invention may be employed to form filling or bulking masses at an intracorporeal locations for cosmetic and other uses, as previously alluded to. 
     After a biopsy specimen is removed from the patient, a guiding member such as a cannula or other tubular member is preferably left within the patient with the distal end thereof within or close to the biopsy site in order to provide subsequent access to the biopsy site. The tubular guiding member may be part of the biopsy system such as a SenoCor 360™ or a Mammotome® system which was used to separate the tissue specimen and remove it from the site but which remains in place after the specimen has been removed. The marker forming fluid embodying features of the invention, may be suitably delivered by a syringe with an elongated delivery tube which at least in part fits within a tubular guiding member leading to the biopsy site. 
     Generally, the amount of polymeric solute ranges from about 1 to about 50%, preferably about 10 to about 35% by weight of the marker or filler forming fluid. The ratio of the polymer solute to the solvent can be varied to adjust the delivery characteristics and the in-vivo lifetime (i.e. the time period in which the polymeric mass is at the biopsy site). For example a lower percentage of polymeric material in the mix will provide a softer or more friable marker mass within the cavity, whereas a higher percentage will provide a firmer marker mass. Lower percentages of solvent will provide thicker marker fluids which will not be readily displaced from the biopsy site, whereas higher percentages will provide a less viscous solution which is easier to deliver. High molecular weight polylactic acid provides a longer in-vivo life time, e.g. up to a year or more. A lower molecular weight polymeric material such as a copolymer of lactic acid (90%) and glycolic acid (10%) provides an in-vivo life time of about two to three weeks. A copolymer of lactic acid (65%) and glycolic acid (35%) with a molecular weight of about 60 kD has an in-vivo lifetime of about 12 to 14 weeks. 
     An ultrasound-detectable marker typically must remain in place and be remotely detectable within a patient for at least 2 weeks to have any practical clinical value. Thus, an ultrasound-detectable marker material embodying features of the invention is detectable at a biopsy site within a patient for a time period of at least 2 weeks, preferably at least about 6 weeks, and may remain detectable for a time period of up to about 20 weeks or more. An ultrasound-detectable marker mass embodying features of the invention is preferably not detectable after about one year, and usually not more than about 6 months after placement at a biopsy site. More preferably, the ultrasound-detectable marker mass should not be detectable with ultrasound after about 12 weeks from placement at a biopsy site. A preferable in-vivo lifetime for an ultrasound-detectable biopsy marker mass having features of the invention is about 6 weeks to about 12 weeks. 
     The detectable marker mass which forms in the biopsy cavity should be large enough to fill a substantial portion, preferably all of the cavity. This allows the detection and definition of the boundaries of the biopsy cavity. The accessing passageway leading to the biopsy cavity may also at least in part be filled with the marker fluid as well if desired, which allows the physician to follow to locate the marker mass. The marker mass which forms in the cavity is ultrasonically detectable, but the marker fluid may also include ultrasonically or radiographically detectable powders or other particulate to augment the detection of the polymeric mass or the biopsy cavity. Other therapeutic and diagnostic agents may be incorporated into the marker fluid such as pharmaceutical agents, chemotherapeutic agents, anesthetic agents, hemostatic agents, pigments, dyes, radiopaque agents, materials detectable by magnetic resonance imaging (MRI), inert materials, and other compounds. 
     In one embodiment of the invention, the delivery system is employed to incorporate a radiopaque or other type of long term or permanent marker element within the polymeric mass which forms in the biopsy cavity. For example, the distal end of the syringe assembly or the tubular guide member leading to the biopsy site may be provided with a distal tip which is formed of radiopaque or other suitable material and which is releasably secured to the distal portion of the syringe or guide member so that upon formation of the marker mass from the marker fluid, the distal tip of the syringe or guide member can be released within the formed polymer marker mass and the syringe or guide member then removed from the mass. 
     The biopsy site markers formed by the present invention provide ultrasonically bright images which can be readily distinguished from the ultrasound signals arising naturally from within a breast or other tissue and which readily contrasts with the dark ultrasound shadow region immediately behind the bright ultrasound echo region. The strength of the reflected signal, and the contrast with the shadow region, make the marked site readily detectable even to relatively inexperienced surgeons. The in-vivo lifetime of the marker at the biopsy site can be preselected by adjusting the amount of polymeric material in the marker fluid and the molecular weight thereof. The employment of the filler forming functions of the solution may be advantageously utilized in cosmetic treatments similar to the uses of collagen, e.g. wrinkle removal or minimization, or in situations in which additional bulk is needed within a patient&#39;s body, e.g., treating for urinary incontinence. 
     These and other advantages will be evident from the following detailed description when taken in conjunction with the accompanying exemplary drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is an elevational view, partially in section, of a marker fluid delivery system embodying features of the invention. 
         FIG. 1B  is a transverse cross-sectional view taken along line  1 B- 1 B shown in  FIG. 1A . 
         FIG. 1C  is a transverse cross-sectional view taken along line  1 C- 1 C shown in  FIG. 1A . 
         FIG. 1D  is a transverse cross-sectional view taken along line  1 D- 1 D shown in  FIG. 1A . 
         FIG. 2  is a partially cut-away, perspective view of a system as illustrated in  FIG. 1  shown depositing a marker fluid embodying features of the invention at a biopsy site within a breast of a female patient. 
         FIG. 3  is a perspective view, partially in section, of the distal portion of a delivery system having a releasable marker element on the distal tip of the delivery tube which acts as a long term or permanent marker. 
         FIG. 4  is a longitudinal, centerline cross-section of a delivery system having a releasable radiopaque distal tip. 
         FIG. 5  is a longitudinal, centerline cross-section of a delivery system having a releasable radiopaque distal tip which is threadably connected to the distal end of the delivery cannula and which has a grooved exterior to facilitate release of the distal tip. 
         FIG. 6  is a transverse cross-sectional view of the releasable distal tip shown in  FIG. 5  taken along the lines  6 - 6 . 
         FIG. 7  is an elevational view of a delivery cannula suitable for use to deliver the marker or filler forming fluid embodying features of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1A-1D  illustrate a system  10  for delivery of biopsy marker fluid  11  embodying features of the invention to a biopsy site within a patient&#39;s body. The system  10  includes a syringe  12  having a bore  13  containing a quantity of biopsy marker fluid  11 . A plunger  14  with a sealable distal end  15  is slidably disposed within the bore  13  of syringe  12 . Application of pressure to the head  16  of plunger  14  applies pressure to the fluid  11  and causes the discharge of fluid  11  from the bore  13  into the inner lumen  17  of delivery tube  18  secured to the discharge end of syringe  12 . The marker fluid  11  passes through the inner lumen or bore  17  of the delivery tube  18  and out the discharge port  19  in the distal end of delivery tube  18 . 
     As schematically illustrated in  FIG. 1A , delivery tube  18  is secured to the syringe  12  by a friction fit. However, those skilled in the art will recognize that a variety of connections may be made between the syringe  12  and the delivery tube  18  such as a conventional luer-lock. The delivery tube  18  may have markings, such as lines or dots spaced at regular intervals along the length of the tube to indicate its position within the patient. 
       FIG. 2  illustrates the marker fluid delivery system  10  shown in  FIGS. 1A-1D  with the distal portion of the delivery tube  18  operatively disposed within a patient&#39;s breast  20  with the distal tip  21  of the delivery tube  18  disposed within biopsy cavity  22  at the biopsy site  23  ready to deliver marker fluid  11 . An incision  24  in the breast  20  allows access to the cavity  22 . Biopsy tubular guide member  25  extends through incision  24  in the patient&#39;s breast  20  into cavity  22  at biopsy site  23 . The distal end  26  of syringe  12 , containing marker fluid  11 , is tightly engaged with delivery tube  18 , which extends within guide member  25  so as to locate delivery tube outlet port  19  within biopsy cavity  22 . The outer diameter of the delivery tube  18  is configured to allow the delivery tube to slidably fit inside the inner lumen  27  of biopsy guide member  25 . Markings  28  spaced at regular intervals along the outer surface of delivery tube  18  indicate the depth of insertion of the tube within the guide member  25  and aid in the proper placement of discharge port  19  into position within cavity  22 . Depression of plunger  14  of the syringe  12  forces marker fluid  11  out of syringe  12  through the inner lumen  17  of the delivery tube  18  and out port  19  into the cavity  22 . 
     Fluid  11  mixes with body fluid or other water based fluid which may be present in the cavity  22 . The solvent in fluid  11  is quickly dissolved in the body fluid or other water based fluid. The polymer solute which precipitates is relatively insoluble in the body fluid or other water based fluid which may be present in the cavity and forms a porous, ultrasonically detectable and bioabsorbable polymer mass  37  within the cavity  22 . The mass  37  preferably essentially fills the biopsy cavity  22  so as to define the periphery of the biopsy cavity and to ensure that the mass remains within the biopsy cavity and will not migrate. The mass is subsequently absorbed by tissue and fluids near the biopsy site, so that at the end of the in-vivo life time of the bioabsorbable mass  37 , the marker mass is no longer readily detectable at the site by ultrasonic means. Tissue ingrowth usually replaces the absorbed mass. 
     The preferred solvent for the fluid  11  is a pharmaceutical grade (USP) of DSMO. Other biocompatible water soluble, polar solvents are suitable. The preferred relatively water-insoluble bioabsorbable polymers are polylactic acid, poly glycolic acid, copolymers of lactic acid and glycolic acid, polycaprolactone. However, other suitable bioabsorbable, essentially water insoluble polymers include poly(esters), poly(hydroxy acids), poly(lactones), poly(amides), poly(ester-amides), poly(amino acids), poly(anhydrides), poly(ortho-esters), poly(carbonates), poly(phosphazines), poly(thioesters), poly(urethanes), poly(ester urethanes), polysaccharides, polylactic acid, polyglycolic acid, polycaproic acid, polybutyric acid, polyvaleric acid, and copolymers, polymer alloys, polymer mixtures, and combinations thereof. 
     The marker mass preferably essentially fills the biopsy cavity so as to define the periphery of the biopsy site cavity and to ensure that the marker mass remains within the biopsy cavity and will not migrate. The marker materials are resorbed by tissue and fluids near the biopsy site, so that, after their in-vivo life times, the marker materials are no longer USI-detectable at the biopsy site. 
     The marker fluid may also include radiopaque materials or radiopaque markers, so that the biopsy site may be detected both with ultrasound and with X-ray or other radiographic imaging techniques. Radiopaque materials and markers may include metal objects such as clips, bands, strips, coils, and other objects made from radiopaque metals and metal alloys, and may also include powders or particulate masses of radiopaque materials. Radiopaque markers may include liquid contrast agents such as Ethiodol or other non-water based contrast agents. Radiopaque markers may be of any suitable shape or size, and are typically formed in a recognizable shape not naturally found within a patient&#39;s body. Suitable radiopaque materials include stainless steel, platinum, gold, iridium, tantalum, tungsten, silver, rhodium, nickel, bismuth, other radiopaque metals, alloys and oxides of these metals, barium salts, iodine salts, iodinated materials, and combinations of these. The marker fluid may also include MRI-detectable materials or markers, so that the biopsy site may be detected with MRI techniques. MRI contrast agents such as gadolinium and gadolinium compounds, for example, are suitable for use with ultrasound-detectable biopsy marker materials embodying features of the invention. Colorants, such as dyes (e.g., methylene blue and carbon black) and pigments (e.g., barium sulfate), may also be included in the marker fluid of the invention. The colorant such as carbon black usually remains in the track or passageway leading to the marker or filler mass and this can be followed by the surgeon to the desired location. 
     Therapeutic agents to reduce bleeding, enhance clotting, to cause vasoconstriction, to prevent infections and other diseases, to reduce pain, chemotherapeutic agents to treat remnant cancer cells at the site may be incorporated into the marker fluid. Suitable therapeutic agents are provided in application Ser. No. 10/124,757, filed on Apr. 16, 2002, (now U.S. Pat. No. 6,862,470). 
       FIGS. 3 and 4  depict the distal portion of an alternative delivery tube  30  which is disposed within tubular guide  31  and which has a releasable radiopaque element  32  on the distal tip of the delivery tube. A cannula  33  is slidably disposed about the delivery tube  30 . Relative longitudinal movement between the cannula  33  and delivery tube  30 , as depicted by arrows  34  and  35 , pushes the radiopaque element  32  off the end of the tube into the cavity  36  as shown in  FIG. 4 . When the marker fluid  37  containing a non-aqueous, water soluble solvent and a relatively water insoluble polymeric solute is injected into the biopsy cavity  36  and the polymer mass is formed, the radiopaque element  32  is released from the delivery tube  30  and left within the polymer mass. The radiopaque element  32  is released within the polymer mass at a point in the formation of the mass which ensures that the position of the radiopaque element  32  is maintained after the distal end of the delivery tube  30  is removed from the cavity  36 . Preferably, the radiopaque element  32  is centrally located within the biopsy cavity  36 . 
       FIGS. 5 and 6  illustrate an alternative embodiment in which a releasable radiopaque element  40  is the distal tip of delivery tube  41 . As shown, the element  40  is threadably connected to the distal portion of the delivery tube  41  and has a grooved exterior  42  which helps to fix the tip in the polymeric mass. This allows the delivery tube  41  to be unscrewed from the tip element  40  and to be withdrawn from the patient, leaving the radiopaque tip  40  within the polymeric mass. 
     The releasable radiopaque element may have a variety of other shapes which are recognizable as not being naturally found within a patient&#39;s body to facilitate remote detection radiographically or ultrasonically. For example, the radiopaque may have an exterior transverse shape such as a star or a square. The radiographically detectable distal tip may be formed of a suitable radiopaque material such as stainless steel, platinum, gold, iridium, tantalum, tungsten, silver, rhodium, nickel, bismuth, other radiopaque metals, alloys and oxides of these metals. Radiopaque salts such as barium salts, iodine salts, iodinated materials, and combinations of these may be incorporated into polymeric or ceramic materials which form the releasable tip. 
     As shown in  FIG. 7 , the deployment system may have a delivery tube  50  with a needle-like distal tip  51  to facilitate advancement of the delivery tube through tissue to the target site. This embodiment is particularly suitable in those situations in which there is no guide tube or other cannula in place to provide access to the target site. 
     Markers embodying features of the present invention remain detectable at an intracorporeal site for a desired time period, and degrade or dissolve so as to not interfere with imaging of the biopsy site and adjacent tissues at a later time. Suitable marker materials typically do not migrate from the biopsy site before being dissolved or otherwise absorbed, and so provide reliable temporary marking of the location of a biopsy site and the margins thereof. The marker materials having features of the invention are readily distinguishable from natural body features including signs of a developing or an actual malignancy. The present invention also includes apparatus and method for delivering markers to a biopsy site. 
     The purpose of markers embodying features of the invention is to facilitate the location and performance of a surgical procedure that is performed while the marker is still detectable. The in-vivo lifetime of the marker mass remaining in the biopsy cavity is relatively short, e.g. less than one year, preferably less than about six months. Typically, the marker mass should have an in-vivo life time of about 6 to about 20 weeks, preferably 6 to 12 weeks. The disappearance of a marker after a longer period of time is required to avoid obscuring or interfering with follow-up imaging or further mammography. 
     Typically, the marker fluid embodying features of the present invention containing ultrasound-detectable solute of bioabsorbable polymeric material of the present invention is deposited at a biopsy site within a patient&#39;s body to form a biopsy marker mass at the site to allow for the subsequent location of the site by medical personnel. Thus, for example, a quantity of fluid formed of a non-aqueous water soluble solvent such as DSMO with a bioabsorbable polymeric material which is essentially insoluble in body fluids or other water based fluids is delivered into a cavity at a biopsy site. When the solution comes into contact with body fluid or other water based fluid at the biopsy site, the solvent is quickly dissolved in the body fluid and the relatively water insoluble polymeric solute forms a marker mass within the biopsy cavity. 
     The in-vivo lifetime of the polymeric material, i.e. the time period in which the polymeric mass is ultrasonically detectable, is related to the molecular weight of the polymer. For example, copolymers of lactic and glycolic acids having an initial molecular weight of about 45,000 Daltons (45 kD) before processing, are suitable for use in making an ultrasound-detectable marker material having an in-vivo lifetime of about 12 weeks. As is known to those of ordinary skill in the art, other materials, including other polymeric materials, may require a different starting molecular weight in order to obtain the same in-vivo lifetime. For example, polyglycolic acid typically degrades faster than other materials and as such requires a substantially higher initial molecular weight than polylactic acid or polycaprolactone to obtain a similar in-vivo lifetime. 
     Many properties of a material affects the intensity of its ultrasound reflection, including density, physical structure, molecular material, and shape. For example, sharp edges, or multiple reflecting surfaces on or within an object differing in density from its surroundings enhances its ability to be detected by ultrasound. Interfaces separating materials of different densities, such as between a solid and a gas, produce strong ultrasound signals. 
     The methods of the present invention provide materials having a porosity effective to produce strong ultrasound signals when located within the patient&#39;s biopsy cavity. The polymeric material may naturally form a porous mass or porosity can be formed by introducing a gas into the material during processing of a material, by release of gas from within the material, or by directing a gas into a material or by incorporating a blowing agent. 
     A typical human breast has a substantial number of features that are visualized with ultrasound. These features all have characteristic signals. Fibrous tissue or ligaments tend to show up as bright streaks, fat seems to appear as a dark gray area, the glandular tissue appears as a mottled medium gray mass. Cancerous lesions typically appear as a darker area with a rough outer edge which has reduced through transmission of the ultrasound energy. One advantage of the ultrasound-detectable biopsy marker materials of the present invention is that the materials provide an ultrasound signal which can be readily differentiated from anatomic structures within the breast, so that the identification and marking of a biopsy cavity does not require extensive training and experience. 
     The delivery syringe and the delivery tube attached to the syringe may be sized to accept any volume of marker or filler forming fluid desired to be injected into the desired intracorporeal site. The average Mammotome® biopsy removes about 0.5 to about 2, typically about 1 ml of tissue. The volume of marker fluid introduced into the biopsy cavity which remains after the removal of the tissue specimen is about the same as the tissue volume removed. Use of more marker fluid typically leads to some filling of the accessing passageway as well as of the cavity at the biopsy site. Smaller volumes of marker fluid may be used for smaller cavities at a biopsy site, such as are created with a single SenoCor 360™ biopsy or an automated Tru-Cut™ biopsy. 
     The solution embodying features of the invention may also be employed as a filler or bulking agent. For example, the filler forming fluid may be used in a manner similar to collagen for cosmetic purposes to minimize wrinkles, to fill pockmarks and other surface pits. The solution may also be used to bulk up an area of tissue for a variety of reasons. For example, if a radiation source for treating a tumor or a tumor site after removal of the tumor is located too close to the patient&#39;s skin, e.g. less than about 5 mm, the skin may be damaged or ultimately scarred by the irradiation. By deploying the filler forming fluid embodying features of the invention between the irradiation source and the skin, the damage or scarring to the skin can be reduced or eliminated. Depending upon the source of the radiation, either a single bolus or multiple bolus may be employed to bulk up the region and to displace the skin sufficiently to avoid damage. 
     The filler forming fluid embodying features of the invention may also be employed to provide a bulking mass about a urethra in the treatment of urinary incontinence, for a bulking mass about an anal sphincter for fecal incontinence and a bulking mass about an esophageal sphincter for gastroesophageal reflux disease. Other uses will become apparent to those skilled in the art. 
     While particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Accordingly, it is not intended that the invention be limited to the specific embodiments illustrated and shall be defined by the scope of the appended claims as broadly as the prior art will permit. Moreover, those skilled in the art will recognize that features shown in one embodiment may be utilized in other embodiments. Terms such a “element”, “member”, “device”, “sections”, “portion”, “section”, “steps” and words of similar import when used herein shall not be construed as invoking the provisions of 35 U.S.C. §112(6) unless the following claims expressly use the terms “means” or “step” followed by a particular function without specific structure or action.