Patent Publication Number: US-2010121188-A1

Title: Reducing contrast agent-induced toxicity

Description:
CROSS REFERENCE RELATED APPLICATIONS 
     This document claims priority to U.S. Provisional Application Ser. No. 60/850,836, filed on Oct. 10, 2006, the contents of which are herein incorporated by reference in their entirety. 
    
    
     BACKGROUND 
     1. Technical Field 
     This document provides methods and materials related to reducing or preventing a contrast agent-induced toxicity (e.g., a contrast agent-induced nephropathy). 
     2. Background Information 
     Nephropathy induced by contrast agents is a complication of diagnostic and therapeutic procedures that require administering a contrast agent to patients. In fact, contrast agent-induced nephropathy is the third leading cause of hospital-acquired acute renal failure. Contrast agent-induced toxicity can result in the need for dialysis, prolonged hospitalization, and an increased risk of death. 
     SUMMARY 
     This document provides methods and materials that can be used to reduce or prevent contrast agent-induced toxicity. For example, this document provides methods that can include administering a contrast agent that contains a material capable of being attracted to a magnetic field. Such a contrast agent can be administered to an organ to be imaged, a body part to be imaged, or the blood supply upstream of the organ or body parts to be imaged. In some cases, a capture element capable of supplying a magnetic field can be positioned in the blood stream downstream of the organ or body parts to be imaged such that a percentage of the administered contrast agent containing a material capable of being attracted to a magnetic field is captured before proceeding to other locations of the body. This document also provides contrast agents, capture elements, kits including contrast agents and capture elements, and methods for using such contrast agents and capture elements to reduce or prevent contrast agent-induced toxicity. The methods and materials provided herein can be used in a minimally invasive manner to reduce a patient&#39;s risk of experiencing contrast agent-induced toxicity such as contrast agent-induced nephropathy. 
     In general, one aspect of this documents features a device comprising, or consisting essentially of: (a) a catheter configured to be inserted into a blood vessel of a mammal; and (b) a capture element comprising: (i) an elongate member, and (ii) a magnetic field source, wherein the capture element is configured to be at least partially housed within the guide catheter, and wherein the magnetic field source is movable, relative to the guide catheter. The elongate member can comprise a proximal end portion and a distal end portion, and wherein the magnetic field source can be located at or near the distal end portion. The magnetic field source can be movable, relative to the guide catheter, in a direction away from a distal end of the guide catheter when the distal end of the guide catheter is located within the circulatory system of the mammal. The mammal can be a human. The guide catheter can be between 10 cm and 125 cm in length. The guide catheter can be between 0.1 mm and 0.4 cm in diameter (e.g., between 0.1 and 2.5 cm). The elongate member can comprise a wire. The magnetic field source can comprise an electromagnet. The capture element can comprise a coating located at least partially around the magnetic field source. The coating can comprise an inner surface and an outer surface, wherein the outer surface is configured to contact a contrast agent containing a material capable of being attracted to a magnetic field when a distal end of the guide catheter is located within the circulatory system of the mammal and the mammal received the contrast agent. The coating can comprise projections that extend away from the magnetic field source, thereby increasing the surface area of the coating for contact with the contrast agent. The coating can be a pleated coating. The capture element can comprise a fiber network located at or near a distal end portion of the elongate member, wherein the fiber network comprises the magnetic field source. The fiber network can define spaces having a diameter capable of allowing blood flow through the fiber network. The capture element can comprise a mesh located at or near a distal end portion of the elongate member, wherein the mesh comprises the magnetic field source. The mesh can define spaces having a diameter capable of allowing blood flow through the mesh. The mesh can be an expandable mesh. The capture element can comprise an expandable balloon attached to an expandable mesh. 
     In another aspect, this documents features a method for reducing the amount of circulating contrast agent within a mammal, wherein the mammal received a contrast agent containing a material capable of being attracted to a magnetic field. The method comprises, or consists essentially of: (a) obtaining a device comprising: (i) a catheter configured to be inserted into a blood vessel of a mammal; and (ii) a capture element comprising: (1) an elongate member, and (2) a magnetic field source, wherein the capture element is configured to be at least partially housed within the guide catheter, and wherein the magnetic field source is movable, relative to the guide catheter, (b) inserting the magnetic field source into the circulatory system, and (c) exposing blood of the mammal to a magnetic field from the magnetic field source under conditions wherein the contrast agent is attracted to the magnetic field and contacts the device, thereby reducing the amount of circulating contrast agent within the mammal. 
     In another aspect, this documents features a method for performing a contrast agent imaging procedure having reduced risk of contrast agent-induced toxicity. The method comprises, or consists essentially of: (a) administering a contrast agent into a mammal, wherein the contrast agent comprises a material capable of being attracted to a magnetic field, (b) obtaining a device comprising: (i) a catheter configured to be inserted into a blood vessel of a mammal; and (ii) a capture element comprising: (1) an elongate member, and (2) a magnetic field source, wherein the capture element is configured to be at least partially housed within the guide catheter, and wherein the magnetic field source is movable, relative to the guide catheter, (c) obtaining an image from the mammal, (d) inserting the magnetic field source into the circulatory system, and (e) exposing blood of the mammal to a magnetic field from the magnetic field source under conditions wherein the contrast agent is attracted to the magnetic field and contacts the device, thereby reducing the amount of circulating contrast agent within the mammal. 
     In another aspect, this documents features a device comprising, or consisting essentially of: (a) a guide catheter defining a lumen and having a proximal end and a distal end, wherein the guide catheter is configured to be inserted into a blood vessel of a mammal; and (b) a capture element comprising: (i) an elongate member having a proximal end portion and a distal end portion, and (ii) a magnetic field source located at or near the distal end portion, wherein the capture element is configured to be at least partially housed within the guide catheter, and wherein the magnetic field source is movable, relative to the guide catheter, in a direction away from the distal end of the guide catheter when the distal end of the guide catheter is located within the circulatory system of the mammal. The mammal can be a human. The guide catheter can be between 10 cm and 125 cm in length. The guide catheter can be between 100 cm and 110 cm in length. The guide catheter can be between 0.1 mm and 0.4 cm in diameter (e.g., between 0.1 and 2.5 cm in diameter). The guide catheter can be between 0.2 cm and 0.3 cm in diameter. The elongate member can comprise a wire. The magnetic field source can comprise a permanent magnet. The magnetic field source can comprise an electromagnet. The capture element can comprise a coating located at least partially around the magnetic field source. The coating can comprise an inner surface and an outer surface, wherein the outer surface is configured to contact a contrast agent containing a material capable of being attracted to a magnetic field when the distal end of the guide catheter is located within the circulatory system of the mammal and the mammal received the contrast agent. The coating can comprise projections that extend away from the magnetic field source, thereby increasing the surface area of the coating for contact with the contrast agent. The coating can be a pleated coating. The capture element can comprise a coating surrounding the magnetic field source. The capture element can comprise a fiber network located at or near the distal end portion, wherein the fiber network comprises the magnetic field source. The fiber network can define spaces having a diameter capable of allowing blood flow through the fiber network. The fiber network can define spaces having a diameter between about 5 nm and 1 cm. The capture element can comprise a mesh located at or near the distal end portion, wherein the mesh comprises the magnetic field source. The mesh can define spaces having a diameter capable of allowing blood flow through the mesh. The mesh can define spaces having a diameter between about 5 nm and 1 cm. The mesh can be an expandable mesh. The mesh can comprise nitinol. The capture element can comprise an expandable balloon attached to an expandable mesh. 
     In another aspect, this documents features a method for reducing the amount of circulating agent within a mammal, wherein the mammal received an agent containing a material capable of being attracted to a magnetic field. The method comprises, or consists essentially of: (a) inserting a device comprising a magnetic field source into a blood vessel of the mammal, and (b) exposing blood of the mammal to a magnetic field from the magnetic field source under conditions wherein the agent is attracted to the magnetic field and contacts the device, thereby reducing the amount of circulating agent within said mammal. The mammal can be a human. The magnetic field source can be inserted into a right atrium, superior vena cava, inferior vena cava, coronary sinus, or pulmonary artery. The magnetic field can have a Gaussian strength of between 0.1 and 10,000 Gauss. The agent can be a contrast agent. 
     In another aspect, this documents features a method for reducing the amount of circulating contrast agent within a mammal, wherein the mammal received a contrast agent containing a material capable of being attracted to a magnetic field. The method comprises, or consists essentially of: (a) obtaining a device comprising: (i) a guide catheter defining a lumen and having a proximal end and a distal end, wherein the guide catheter is configured to be inserted into a blood vessel of a mammal; and (ii) a capture element comprising: (1) an elongate member having a proximal end portion and a distal end portion, and (2) a magnetic field source located at or near the distal end portion, wherein the capture element is configured to be at least partially housed within the guide catheter, and wherein the magnetic field source is movable, relative to the guide catheter, in a direction away from the distal end of the guide catheter when the distal end of the guide catheter is located within the circulatory system of the mammal, (b) inserting the magnetic field source into the circulatory system, and (c) exposing blood of the mammal to a magnetic field from the magnetic field source under conditions wherein the contrast agent is attracted to the magnetic field and contacts the device, thereby reducing the amount of circulating contrast agent within the mammal. The mammal can be a human. The magnetic field source can be inserted into a right atrium, superior vena cava, inferior vena cava, coronary sinus, or pulmonary artery. The magnetic field can have a Gaussian strength of between 0.1 and 10,000 Gauss. 
     In another aspect, this documents features a method for performing a contrast agent imaging procedure having reduced risk of contrast agent-induced toxicity. The method comprises, or consists essentially of: (a) administering a contrast agent into a mammal, wherein the contrast agent comprises a material capable of being attracted to a magnetic field, (b) obtaining a device comprising: (i) a guide catheter defining a lumen and having a proximal end and a distal end, wherein the guide catheter is configured to be inserted into a blood vessel of the mammal; and (ii) a capture element comprising: (1) an elongate member having a proximal end portion and a distal end portion, and (2) a magnetic field source located at or near the distal end portion, wherein the capture element is configured to be at least partially housed within the guide catheter, and wherein the magnetic field source is movable, relative to the guide catheter, in a direction away from the distal end of the guide catheter when the distal end of the guide catheter is located within the circulatory system of the mammal, (c) obtaining an image from the mammal, (d) inserting the magnetic field source into the circulatory system, and (e) exposing blood of the mammal to a magnetic field from the magnetic field source under conditions wherein the contrast agent is attracted to the magnetic field and contacts the device, thereby reducing the amount of circulating contrast agent within the mammal. The mammal can be a human. The contrast agent can comprise iodine. The contrast agent can be injected into a coronary artery, systemic circulation, organ specific blood vessel, or a body cavity containing space. The image can be an X-ray image, MRI image, radioactive scan image, fluorescent image, PET image, or CT image. The magnetic field source can be inserted into a right atrium, superior vena cava, inferior vena cava, coronary sinus, or pulmonary artery. The magnetic field can have a Gaussian strength of between 0.1 and 10,000 Gauss. The inserting step can be performed before obtaining the image from the mammal. The inserting step can be performed after obtaining the image from the mammal. The inserting step can be performed before the administering step. The inserting step can be performed after the administering step. 
     Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although methods and materials similar or equivalent to those described herein can be used to practice the invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In case of conflict, the present specification, including definitions, will control. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. 
     The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims. 
    
    
     
       DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view of a device having a guide catheter with a capture element located within the guide catheter. 
         FIG. 2  is a view of the device depicted in  FIG. 1  with the capture element extending outside the guide catheter. 
         FIG. 3  is a view of a device having a guide catheter with a capture element located within the guide catheter. 
         FIG. 4  is a view of the device depicted in  FIG. 3  with the capture element extending outside the guide catheter. 
         FIG. 5  is a view of the device depicted in  FIG. 3  with the capture element located within a tightly fitting guide catheter. 
         FIG. 6  is a view of the device depicted in  FIG. 5  with an expanded view of the capture element extending outside a tightly fitting guide catheter. 
         FIG. 7  is a view of a device having a guide catheter with a capture element located within the guide catheter. 
         FIG. 8  is a view of the device depicted in  FIG. 7  with the capture element extending outside the guide catheter. 
         FIG. 9  is a view of the device depicted in  FIG. 7  located within a blood vessel with the capture element extending outside the guide catheter. 
         FIG. 10  is a view of a device having a guide catheter with a capture element located within the guide catheter. 
         FIG. 11  is a view of the device depicted in  FIG. 10  with the capture element extending outside the guide catheter. 
         FIG. 12  is a view of the device depicted in  FIG. 10  with an expanded view of the capture element located within a tightly fitting guide catheter. 
     
    
    
     DETAILED DESCRIPTION 
     This document provides methods and materials that can be used to reduce or prevent contrast agent-induced toxicity. In general, the methods provided herein can include administering a contrast agent to a mammal and magnetically capturing at least some of the administered contrast agent so as to reduce the amount of contrast agent circulating within said mammal. For example, this document provides methods that can include administering a contrast agent containing a material capable of being attracted to a magnetic field. In some cases, a contrast agent can be an MRI contrast agent such as Gd-labeled albumin, Gd-labeled dextran, chromium-labeled red blood cells, gadolinium oxide, superparamagnetic iron oxide, ultrasmall superparamagnetic iron oxide (USPIO) particles, and hepatobiliary contrast agents, or an X-ray contrast agent. An X-ray contrast agent can contain iodine (e.g., iohexol, iodixanol, or ioversol) or barium. In some cases, hafnium, tantalum, tungsten, and oxides can be used as X-ray contrast agents. Examples of commercially available contrast agents include, without limitation, Myoview™ (technetium Tc-99m tetrofosmin), Omnipaque™ (iohexol), Optison™ (Perflutren Protein-Type A Microspheres for Injection, USP), Visipaque™ (iodixanol), Omniscan™ (gadodiamide), Visipaque™ (iodixanol), Omnipaque™ (iohexol), Omniscan™ (gadodiamide), and Visipaque™ (iodixanol). In some cases, the devices and methods provided herein can be adapted to capture agents other than or in addition to MRI or X-ray contrast agents. Such other agents include, without limitation, agents designed for use in Positron Emission Tomography (PET), radioactive imaging, fluorescent imaging, or other imaging techniques. 
     As described herein, a contrast agent can contain a material capable of being attracted to a magnetic field. For example, a contrast agent can be attached to a paramagnetic (e.g., magnesium, molybdenum, lithium, and tantalum), ferromagnetic (e.g., iron, nickel, and cobalt), or superparamagnetic material (e.g., a particle or nanoparticle). Any type of attachment can be used to attach a contrast agent and a material capable of being attracted to a magnetic field. For example, a contrast agent and paramagnetic, ferromagnetic, or superparamagnetic material can be chelated. Examples of contrast agents, contrast agents containing material capable of being attracted to a magnetic field, and methods for making such contrast agents are provided elsewhere (see, e.g., U.S. Pat. No. 5,324,503; U.S. Pat. No. 5,660,814; and U.S. Patent Application Publication No. 2005/0113675). 
     A contrast agent provided herein can be administered to any part of a mammal&#39;s body. For example, a contrast agent can be administered to a body cavity to be imaged, an organ to be imaged, a body part to be imaged, or the blood supply upstream of an organ or body part to be imaged. In some cases, a contrast agent can be administered intravenously, intraarterially, intrathecally, or intraabdominally. When imaging heart tissue or the cardiac region of a mammal, a contrast agent can be administered to a coronary artery via an intra-arterial injection. When imaging a specific organ or tissue in a mammal, a contrast agent can be administered to the target organ via a tissue or organ selective blood vessel. 
     After administering a contrast agent to a mammal, an image of the desired location can be obtained. For example, an MRI or X-ray image can be obtained after an MRI or X-ray contrast agent is administered to a human patient. 
     The devices provided herein can be used to remove a percentage (e.g., up to 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or 100 percent) of the contrast agent administered to a mammal. In some cases, the devices provided herein can be used to remove between 5 and 75 percent of the contrast agent administered to a mammal. Such a removal can help reduce the mammal&#39;s risk of developing contrast agent-induced toxicity (e.g., contrast agent-induced nephropathy). Contrast agent-induced nephropathy as used herein with respect to a human refers to a condition where a human has either a greater than 25% increase of serum creatinine or an absolute increase in serum creatinine of 0.5 mg/dL. 
     In general, a device provided herein can contain a guide catheter and a capture element. A guide catheter can be configured to house a capture element and can be configured to be inserted into a blood vessel within a mammal (e.g., a mammal&#39;s femoral vein or artery). A capture element can be capable of supplying a magnetic field that can be positioned in the blood stream of a mammal. For example, a device provided herein can be configured to have the ability to position a magnetic field source of a capture element downstream of an organ or body part to be imaged such that a percentage of the administered contrast agent containing a material capable of being attracted to a magnetic field is captured before proceeding to other locations of the body (e.g., the mammal&#39;s kidneys). In some cases, a capture element can contain an elongate member and a magnetic field source. An elongate member can be a wire or catheter that is configured to fit within a guide catheter in a movable manner. In some cases, an elongate element can extend through the length of the guide catheter, and the magnetic field source can be positioned at a distal end of the elongate element. A user can manipulate a proximal end of a capture element to alter the location or position of a magnetic field source attached to a distal end portion of a capture element. 
     A guide catheter can be made of soft, pliable material (e.g., polytetrafluoroethylene (PTFE), polyethylene, polypropylene, or any other suitable material). An elongate member of a capture element can be made of a rigid or semi-rigid material (e.g., wire) or any other suitable material that can provide the elongate member with at least temporary rigidity so as to allow deployment or positioning of a magnetic field source. Examples of such materials include, without limitation, non-magnetized metals that can develop a magnetic field by induced magnetism via a strong magnetic field applied outside the body (e.g., MRI or Stereotaxis). 
     A magnetic field source can be a permanent magnet or an electromagnet. For example, a capture element can include an electromagnetic coil. A magnetic field source can provide a Gaussian strength of about 0.1 to about 10,000 Gauss (e.g., about 100 to about 10,000 Gauss). In some cases, a magnetic field source can be configured into a fiber network or a mesh. A fiber network can be a disordered array of magnetic fibers capable of supplying a magnetic field. Such a fiber network can define openings such that blood can flow through the fiber network. A mesh can be configured to define openings (e.g., an orderly array of openings) that allow blood can flow through the mesh. For example, a mesh can have a honeycomb-like structure. In some cases, a mesh containing a magnetic field source can be made of a shape memory material (e.g., nitinol). In such cases, the mesh can be configured to assume an expanded shape when the mesh exits the distal end of the guide catheter. 
     Any portion of a capture element (e.g., an elongate member, a magnetic field source, or both) can be covered on its exterior surface with a coating (e.g., PTFE, DACRON®, or other suitable material) to, for example, prevent tissue trauma. Examples of suitable coatings are described elsewhere (e.g., U.S. Patent Application Publication No. 2005/0277959). In some cases, a capture element can include an electromagnetic coil that contains a coating. Such a coating can form any shape. For example, a coating can be shaped to form pleats or fingers. In such cases, an increased surface area for contrast agent attachment can be provided. 
     In some cases, a capture element can include an expandable balloon structure that includes a magnetic field source. For example, a device provided herein can contain an expandable balloon at least partially surrounded with an expandable mesh capable of supplying a magnetic field. The balloon and mesh can be configured to assume an expanded shape when the balloon and mesh exit the distal end of the guide catheter and the balloon is inflated. 
     A device provided herein can include one or more additional elements to assist with positioning of a guide catheter or a capture element. These additional elements can be contained within the guide catheter or within an outer sheath that also contains the guide catheter. Positioning elements can be deflecting and/or steerable to, for example, facilitate their positioning within a device. Appendage positioning elements include, for example, suction catheters, forceps, and cryogenic-tipped catheters, which can be used to, for example, position a capture element. See, e.g., U.S. Patent Application Publication Nos. 2005/0154404 and 2004/0030335, and U.S. Pat. No. 6,488,689. In some cases, a device provided herein can be positioned by an externally applied magnetic field. 
     A device provided herein can include a removal element configured to remove captured items from the mammal in an intermittent or continuous manner. For example, a device provided herein can include a removal element that provides suction to a portion of a capture element that captures items (e.g., contrast agent). The suction can draw any captured items from the distal end of the device to a location outside a mammal&#39;s body. For example, a tube or lumen can be engineered into a shaft of a capture element such that agents captured by the magnetic field source can be removed intermittently or constantly without having to remove the device from a mammal&#39;s body. In such cases, a suction device can be attached to the end of the tube or lumen that is positioned outside a mammal&#39;s body during use. 
     The devices provided herein can have any suitable length and width (e.g., diameter). For example, a device can have a length between about 30.5 cm and about 183 cm (e.g., between about 61 cm and 153 cm, between about 76 cm and about 137 cm, or between about 91 cm and about 122 cm), such that its distal end can be placed within the cardiac region of a human and its proximal end can be positioned outside the human&#39;s body. Further, a device can have any suitable diameter. For example, a device can have an overall diameter (e.g., diameter of the outer sheath, or diameter of the guide catheter if there is no outer sheath) suitable for passage through the circulatory system and into a coronary sinus. In some cases, a device can have a diameter between about 0.05 cm and about 1.5 cm, between about 0.1 cm and about 1.0 cm, between about 0.15 cm and about 0.5 cm, between about 0.2 cm and about 0.4 cm, or about 0.2 cm, about 0.3 cm, or about 0.4 cm. In some cases, a device can have an unexpanded diameter between about 0.1 mm and about 1.5 cm, between about 0.5 mm and about 1.0 cm, or between about 1.0 mm and about 0.5 cm. Such an unexpanded diameter can be configured to expand to a maximum expanded diameter between 0.15 mm and 15 cm (e.g., between 0.15 mm and 5 mm). 
     A device can include any suitable mechanism to facilitating advancing an elongate element so that a magnetic field source extends away from the distal end of a guide catheter. For example, an elongate member (e.g., wire) of a capture element can be “cocked” with a spring mechanism. A clinician can actuate the spring mechanism, and the resulting forward pressure applied on the capture element can cause an elongate member to advance a pre-set distance. For example, the length of an elongate member that exits the guide catheter can be limited to between about 0.1 mm and about 15 cm. 
     The devices provided herein can be readily deployed in a percutaneous manner. In addition, the devices can be adapted to minimize trauma to the tissue they contact such that there is little or no erosion through the tissue, reducing the likelihood of bleeding and cardiac tamponade. Further, the devices can be reversible and/or repositionable, such that a clinician can position the capture element as desired. 
     In some cases, the devices and methods provided herein can be adapted to capture items other than or in addition to contrast agents. Such other items can include, without limitation, chemicals, drugs, toxins, immune complexes, pathogens, normal cells, malignant cells, and nano-devices. For example, a device provided herein can be designed to capture contrast agents and pathogens. In some cases, the devices and methods provided herein can be designed to use a magnetic field source, a binding force, an electrostatic force, or a combination thereof. For example, a device provided herein can be adapted to have a capture element having ligands or antibodies with the ability to bind a particular item (e.g., a toxin, immune complex, pathogen, normal cell, or malignant cell). In some cases, the devices and methods provided herein can be configured such that a drug attached to biotin can be administered to a mammal and then captured using a capture element coated with streptavidin. In some cases, the devices and methods provided herein can be configured such that a drug attached to streptavidin can be administered to a mammal and then captured using a capture element coated with biotin. 
     In reference to  FIGS. 1 and 2 , device  100  can contain guide catheter  102  having a proximal end  104  and a distal end  106 . Guide catheter  102  can house at least a portion of capture element  108 . Capture element  108  can have proximal end portion  110  and distal end portion  112 . Proximal end portion  110  can be configure to form an elongate member. A part of distal end portion  112  can be configured to form a magnetic field source. For example,  FIGS. 1 and 2  depict the magnetic field source as an electromagnetic coil, which can be powered via a battery or external power source. A magnetic field source can be surrounded by a coating  114  of any shape. In  FIGS. 1 and 2 , coating  114  is shaped to provide pleats, which can increase the surface area available to capture contrast agent.  FIG. 1  depicts device  100  in a configuration where distal end portion  112  is located within guide catheter  102 , while  FIG. 2  depicts device  100  in a configuration where distal end portion  112  is located outside guide catheter  102 . The configuration depicted in  FIG. 1  can be used while inserting device  100  into a mammal or withdrawing device  100  from a mammal. The configuration depicted in  FIG. 2  can be used to capture contrast agent from blood within a mammal. 
     In reference to  FIGS. 3 and 4 , device  200  can contain guide catheter  202  having a proximal end  204  and a distal end  206 . Guide catheter  202  can house at least a portion of capture element  208 . Capture element  208  can have proximal end portion  210  and distal end portion  212 . Proximal end portion  210  can be configured to form an elongate member. A part of distal end portion  212  can be configured to form a magnetic field source  214 . For example,  FIGS. 3 and 4  depict magnetic field source  214  as a expandable mesh. As indicated herein, a magnetic field source can be a permanent magnet or an electromagnet such as an electromagnet powered via a battery or external power source.  FIG. 3  depicts device  200  in a configuration where distal end portion  212  is located within guide catheter  202 , while  FIG. 4  depicts device  200  in a configuration where distal end portion  212  is located outside guide catheter  202 . The configuration depicted in  FIG. 3  can be used while inserting device  200  into a mammal or withdrawing device  200  from a mammal. The configuration depicted in  FIG. 4  can be used to capture contrast agent from blood within a mammal. The mesh can be shaped and configured in any three dimensional structure. For example, a mesh can have a plurality of layers, uniform or variable mesh sizes, multiple magnetic components, or one or more protective layers. 
     In some embodiments, the elongated portion of a capture element can fit closely within a guide catheter. For example, a capture element can be located within a tightly fitting guide catheter as depicted in  FIGS. 5 ,  6 , and  12 . With reference to  FIG. 5 , magnetic field source  214  is in the form of a mesh that can be deformed to fit within guide catheter  202  when capture element  208  is completely retracted into guide catheter  202 . As explained above, magnetic field source  214  can expand when the distal end portion  212  of capture element  208  is extended outside guide catheter  202 . See, e.g., 
       FIG. 4 . 
     As indicated herein, a magnetic field source can be powered via a battery or external power source. For example, electrical leads can extend from a battery or external power source to a magnetic field source. With reference to  FIG. 6 , electrical leads  250  and  252  can extend from magnetic field source  214  to a battery or external power source. 
     In reference to  FIGS. 7 and 8 , device  300  can contain guide catheter  302  having a proximal end  304  and a distal end  306 . Guide catheter  302  can house at least a portion of capture element  308 . Capture element  308  can have proximal end portion  310  and distal end portion  312 . Proximal end portion  310  can be configure to form an elongate member. A part of distal end portion  312  can be attached to expandable balloon  314  having magnetic field source  316  in the form of an expandable mesh.  FIG. 7  depicts device  300  in a configuration where distal end portion  312  is located within guide catheter  302 , while  FIG. 8  depicts device  300  in a configuration where distal end portion  312  is located outside guide catheter  302 . The configuration depicted in  FIG. 7  can be used while inserting device  300  into a mammal or withdrawing device  300  from a mammal. The configuration depicted in  FIG. 8  can be used to capture contrast agent from blood within a mammal. 
     As described herein, a device provided herein can be placed into a blood vessel to capture agents from blood.  FIG. 9  depicts an example of the use of the devices provided herein. In this case, device  300  can extend from outside a mammal into blood vessel  350  of a mammal. The devices can extend into a blood vessel in either direction: upstream against blood flow as shown in  FIG. 9  or down stream with blood flow. As depicted in  FIG. 9 , guide catheter  302  can be placed within blood vessel  350 . Once in position, capture element  308  can be deployed such that capture element  308  extends beyond distal end  306 . In this example, expandable balloon  314  can be inflated, and agent  352  coupled to material  354 , which is capable of being attracted to a magnetic field, can be captured by magnetic field source  316 . During use of the devices provided herein, the concentration of agents upstream of the device can be higher than the concentration of agents downstream of the device. 
     In reference to  FIGS. 10 and 11 , device  400  can contain guide catheter  402  having a proximal end  404  and a distal end  406 . Guide catheter  402  can house at least a portion of capture element  408 . Capture element  408  can have proximal end portion  410  and distal end portion  412 . Proximal end portion  410  can be configure to form an elongate member. A part of distal end portion  412  can be configured to form a magnetic field source. For example, a part of distal end portion  412  can be configured to form funnel  414  having inlet opening  418  and outlet opening  416 . All or a portion of the inner surface of funnel  414  can form a magnetic field source. For example, the entire inner surface of funnel  414  can contain magnetic material, thereby forming a magnetic field source. In some cases, outlet opening  416  can contain a mesh that forms a magnetic field source. For example, outlet opening  416  can be covered with a mesh that forms a magnetic field source. In some cases, the inner surface of funnel  414  can be pleated to increase the surface area of the inner surface. 
       FIG. 10  depicts device  400  in a configuration where distal end portion  412  is located within guide catheter  402 , while  FIG. 11  depicts device  400  in a configuration where distal end portion  412  is located outside guide catheter  402 . The configuration depicted in  FIG. 10  can be used while inserting device  400  into a mammal or withdrawing device  400  from a mammal. The configuration depicted in  FIG. 11  can be used to capture contrast agent from blood within a mammal. 
     In some embodiments, the elongated portion of a capture element can fit closely within a guide catheter. For example, a capture element can be located within a tightly fitting guide catheter as depicted in  FIGS. 5 ,  6 , and  12 . With reference to  FIG. 5 , magnetic field source  214  is in the form of a mesh that can be deformed to fit within guide catheter  202  when capture element  208  is completely retracted into guide catheter  202 . As explained above, magnetic field source  214  can expand when the distal end portion  212  of capture element  208  is extended outside guide catheter  202 . See, e.g.,  FIG. 4 . 
     Other Embodiments 
     It is to be understood that while the invention has been described in conjunction with the detailed description thereof, the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.