COATINGS OF EMISSION OF MAGNETIC RESONANCE SIGNALSCROSS REFERENCE TO RELATED REQUESTS This application claims the benefit of the priority date according to 35 U.S.C. § 119 of the North American Provisional Application No. 60/086817, filed on May 26, 1998. DECLARATION REGARDING RESEARCH OR DEVELOPMENTSPONSORED BY THE FEDERAL GOVERNMENT This invention is made with the support of the Government through the contributions numbers NIH 1 ROÍ HL57983; NIH 1 R29HL57501 granted by the National Institute of Health(National Institute of Health), and NSF-DMR 9711226 and NSF-EEC8721845 (ERC) granted by the National Science Foundation(National Foundational for Science). The American government has certain rights over this invention. BACKGROUND OF THE INVENTION This invention relates, generally, to coatings that emit magnetic resonance signals, and particularly to coatings of this type that contain paramagnetic metal ions, and to a process for the application in medical devices of said coatings in such a way that the devices can be easily visualized in magnetic resonance images during diagnostic or therapeutic procedures performed in combination with magnetic resonance imaging (MRI).
Since its introduction, magnetic resonance (MR) has been used largely only for diagnostic applications. With the progress of magnetic resonance imaging, however, it is possible to replace many applications of diagnostic x-ray imaging with magnetic resonance imaging. For example, the accepted standard for classifying a vascular disease was, once, x-ray contrast angiography. Nowadays, angiographic magnetic resonance imaging techniques are increasingly being used to detect vascular abnormalities and, in some specific clinical cases, contrast-enhanced magnetic resonance angiograms are rapidly approaching the diagnostic standard established by x-ray angiography. More recently, advances in magnetic resonance imaging equipment and magnetic resonance imaging sequences began to allow the use of magnetic resonance in certain therapeutic procedures. That is, certain therapeutic procedures or therapies are performed on a patient while the patient and the instruments, devices or agents employed and / or implanted are being visualized. The use of magnetic resonance imaging in this form of image-guided therapy is often referred to as an interventional magnetic resonance imaging (MR intervention). These initial applications have included: the monitoring of laser and ultrasound ablations, the guidance of needle placement for biopsy, and the visualization of disease, such as tumors, interoperatively. 5 Endovascular therapy is of particular interest in interventional magnetic resonance imaging. Endovascular therapy refers to a general class of minimally invasive intervention techniques (or surgery) that are used to treat vascular abnormalities. Unlike the techniquesconventional surgical, endovascular therapies have access and treat the disease from within the vessels. Usually, the vascular system is accessed through the femoral artery. A small incision is made in the groin and the femoral artery is punctured. It is inserted aftera cover for vascular access. A catheter can then be manipulated with the addition of a guidewire under fluoroscopic guidance to the area of interest. The guide wire is then removed from the lumen of the catheter, and either a therapeutic device is injected (e.g., a balloon, stent,coil) with the appropriate delivery device, or an agent (eg, embolizing agent, anti-vasospasm agent) through the catheter. In any case, the catheter functions as a conduit and ensures the precise and localized administration of the therapeutic device or agent.
Once the device or agent is placed in its place, its administration system is removed, that is, the catheter is removed, the sheath is removed, and the incision is closed. The duration of an average endovascular procedure is approximately 3 hours, even when difficult cases may require more than 8 hours. Traditionally, such procedures were performed under fluoroscopic x-ray guidance. The realization of these procedures under magnetic resonance guidance offers numerous advantages. Safety issues are related to the relatively large dosages of ionizing radiation that is required in the case of fluoroscopy with x-rays. While the risk caused by radiation to the patient is a relatively minor concern (since it is more than compensated by the potential benefit of the procedure), the exposure of the personnel performing the intervention can be a main problem. In addition, the complication rate in relation to contrast agents for magnetic resonance is much lower than that observed in the case of iodinated contrast agents commonly used iodine. Other advantages of magnetic resonance-guided procedures include the ability of magnetic resonance to provide three-dimensional images. In contrast, most x-ray angiography systems can only acquire a series of projection images. Magnetic resonance has clear advantages when multiple projections or volume reformation are required in order to understand the treatment of complex three-dimensional vascular abnormalities such as arterial / venous malformations (AVMs) and aneurysms. In addition, MRI is sensitive to several "functional" parameters including temperature, blood flow, tissue perfusion, brain diffusion and activation. This additional diagnostic information, which, in principle, can be obtained before, during and immediately after therapy, can not be obtained in the case of x-ray fluoroscopy alone. It is likely that once adequate MRI-based endovascular procedures have been developed, the next challenge will be the integration of this functional information with conventional tracking and anatomical imaging devices. Nowadays, both "passive" and "active" approaches are being used to monitor the placement of interventional devices under the guidance of magnetic resonance imaging. With active tracking, visualization is achieved by incorporating one or several small radio frequency (RF) coils into the device, for example, a catheter. The position of the device is calculated from the magnetic resonance signals detected by the coil. Then, this information is superimposed on an anatomical image already acquired. The advantages of active tracking include excellent temporal resolution and excellent spatial accuracy, as well as the ease with which you can update at 20Hz, that is, 20 times per second, the position of the tip of a device, for example, a catheter However, active methods allow the visualization of only a discrete point or discrete points in the device. Typically, only the tip of the device is "active", that is, displayed. Although it is possible to incorporate several RF coils (4-6 in typical clinical magnetic resonance systems) into a device, it remains impossible to determine the position in more than a few discrete points throughout the device. While this may be acceptable for tracking rigid biopsy needles, this represents a significant limitation for tracking flexible devices such as, for example, in the case of endovascular therapy. In addition, intravascular heating due to RF-induced currents is a concern in the case of active methods. As indicated above, the fixation of the coils in flexible catheters presents numerous challenges. Likewise, the effect of the mechanical properties of catheters is a concern. Ladd et al. (Ladd et al., Proc. ISMRM (1997) 1937) have solved some of the deficiencies of an active catheter by designing an RF coil that is wrapped around the catheter. This allows the visualization of a considerable length of a catheter, but does not solve the problems of RF heating and mechanical catheter performance. Passive tracking technologies employ the fact that endovascular devices do not generally emit a detectable magnetic resonance signal, and therefore result in areas of signal loss or signal voids in magnetic resonance images. Said signal loss, for example, occurs with a polyethylene catheter. Following the vacuum, the movement of the catheter can be inferred. An advantage of passive tracking methods compared to active methods is that they allow the "visualization" of the entire length of a device. Signal voids, however, are certainly not optimal for tracking devices since they can be confused with other sources of signal loss. An additional source of passive contrast occurs if the device has a magnetic susceptibility very different from the tissue (eg, metal guide wires and stents). The differences in susceptibility cause local distortions in the magnetic field and result in regions of signal enhancement and signal loss surrounding the device. Numerous published reports describe passive catheter visualization schemes based on signal voids or susceptibility-induced artifacts. A major drawback of the currently available passive techniques is that the display depends on the orientation of the device relative to the main magnetic field. Despite the recognition and study of various aspects of visualization problems of medical devices in therapeutic procedures, especially endovascular ones, the prior art has not produced satisfactory and reliable techniques for visualization and tracking of the entire device in a procedure under resonance guidance magnetic BRIEF SUMMARY OF THE INVENTION The present invention offers a process for the coating of medical devices in such a way that the devices are easily visualized, especially in T-l weighted magnetic resonance images. Due to the high signal caused by the coating, all of the coated devices can be easily visualized for example during an endovascular procedure. The above advantages as well as other advantages of the present invention are obtained in a coating that emits magnetic resonance (MR) signals which includes a polymer complex containing paramagnetic metal ions and a method for visualizing medical devices in image formation of magnetic resonance, which includes the step of coating the devices with the polymer containing paramagnetic ions. Specifically, the present invention offers a coating for visualizing medical devices in magnetic resonance imaging, which ... comprises a complex of the formula(I): P - X - L - Mn + (I) Where P is a polymer, X is a surface functional group, L is chelate, M is a paramagnetic ion and n is an integer that is 2 or greater than 2. In Another aspect, the invention is a coating for visualizing medical devices in a magnetic resonance imaging system, comprising a complex of the formula (II): P-X-J-L-Mn + (II) Where P is a polymer, X is a surface functional group, L is chelate, M is a paramagnetic ion and n is an integer that is 2 or greater than 2 and J is the linker molecule or spacer. In a further aspect, the invention is a magnetic resonance imaging system that includes a magnetic resonance device for generating a magnetic resonance image of a white object (as defined below) in a formation region. of image (in accordance with what is defined below) and an instrument for use with the white object in the region of image formation. The instrument includes a body of a size suitable for use in the target object and a poly-paramagnetic complex coating wherein the complex is represented by the formula (I): P-X-L-Mn + (I) Where P is a polymer, X is a surface functional group, L is chelate, M is a paramagnetic ion and n is an integer that is 2 or greater than 2. In another aspect, the invention relates to a method for visualizing medical devices in magnetic resonance imaging which includes the steps of (a) coating the medical device with a polymer-paramagnetic complex of the formula (I): P -'X-L-Mn + (I) Where P is a polymer , X is a surface functional group, L is chelate, M is a paramagnetic ion and n is an integer that is 2 or greater than 2; (b) place the device inside a white object; and (c) forming images of the white object and the coated device. Other advantages of a more complete appreciation of the specific attributes of this invention will be obtained by examining the following drawings, detailed description of preferred embodiments, and appended claims. It is expressly understood that the drawings are for the purpose of illustration and description only, and are not intended to define the limitations of the invention. BRIEF DESCRIPTION OF THE DRAWINGS The preferred exemplary embodiment of the present invention will now be described in conjunction with the accompanying drawing in which like reference numerals refer to like elements in all the drawings and in which: Figure 1 is a schematic representation of a three stage coating method according to the present invention; Figure 2 is a schematic representation of a four step coating method employing a linker; 3 and 3A are a schematic representation of a plasma reactor for use in the method of the present invention; FIG. 3A is an enlarged view of the steam supply assembly of the plasma reactor of FIG. 3; Figure 4 represents several images > in magnetic resonance of coated devices in accordance with the present invention; Figure 5 represents temporary photographs by magnetic resonance of a catheter filled with Gd-DTPA; Figure 6 represents temporary photographs by magnetic resonance of a catheter filled with Gd-DTPA that travels in the common carotid of a dog; and Figure 7 depicts temporary magnetic resonance photographs of a catheter filled with Gd-DTPA in the aorta of a dog. DETAILED DESCRIPTION OF THE INVENTION The present invention relates in general terms to coating substances that are capable of emitting magnetic resonance signals. The present invention is more particularly adapted for use in the coating of medical devices in such a way that they can be easily visualized in magnetic resonance images. Accordingly, the present invention will be described below with details regarding these purposes; however, those skilled in the art will note that said description of the invention is only an example and should not be construed as limiting the full scope of the invention. The present invention offers coatings containing paramagnetic ions. The coatings of the present invention are characterized by their ability to emit magnetic resonance signals and to allow the visualization of the entirety of a device or instrument coated in this way in magnetic resonance procedures in interventions. The coatings are also valuable in providing improved visibility in interoperative magnetic resonance of surgical instruments after coating them with the signal increase coatings of the present invention. It is also anticipated that improved visualization of implanted devices coated in this way, for example stents, may find numerous magnetic resonance applications for diagnostic purposes. These attributes of the coating in accordance with the present invention are achieved through a novel combination of physical properties and chemical functionalities. In the following description of the method of the invention, processing steps are carried out at room temperature(RT) and under atmospheric pressure unless otherwise specified. Throughout the specification, the term "medical device" is used in a broad sense to refer to any tool, instrument or other object (eg, a catheter, biopsy needle, etc.) that is used to perform or which is useful for performing an operation on a target, or a device that is itself implanted in the body (of a human being or of an animal) for some therapeutic purpose, for example, a stent, a graft, etc., and a "white" or "white object" is the whole or a part of a human or animal patient placed in the "imaging region" of a magnetic resonance imaging system (the imaging region "being the space within a magnetic resonance imaging system in which the image of a target can be formed.) Endovascular procedures performed under magnetic resonance guidance are especially interesting. Endovascular procedures include the treatment of partial vascular occlusions with balloons, the treatment of arterial-venous malformations with embolic agents, the treatment of aneurysms with stents or coils, as well as the treatment of vasospasm induced by sub-arachnoid hemorrhage (SAH) with applications local paraverina. In these therapeutic procedures, the device or agent is administered through the lumen of a catheter, whose placement has traditionally been based on several measures; in the fluoroscopic X-ray guidance. In one aspect, the present invention provides a method for coating the surface of medical devices with a coating that is a polymeric material containing a paramagnetic ion, said coating is generally represented by formula (I); P - X - L - Mn + (I) Where P is a polymer, X is a surface functional group such as for example an amino group or a carboxyl group, L is chelate, M is a paramagnetic ion that binds to L, and n is an integer that is 2 or greater than 2. It is understood that a medical device can be constructed appropriately from a polymer whose surface is then functionalized with X, or a medical device that can be suitably coated with a polymer whose surface it is then functionalized appropriately. Such coating methods are generally known in the art. To increase the rotational mobility of M1"11", the coating optionally contains a linker J molecule or spacer, and is generally represented by formula (II); P - X - J - L - Mn + (II) Where P, X, L and M are in accordance with what is defined above and J is the linker molecule or spacer that binds the functional group of surface X and chelate L, is say, J is an intermediate between the surface functional group and the chelate. P is suitably any polymer, including, without limitation, polyethylene, polypropylene, polyesters, polycarbonates, polyamides such as nylon, polytetrafluoroethylene (Teflon®), and polyurethanes that can be functionalized on the surface with a group X. It will be noted that some polymer surfaces they may require an additional coating with hydrophilic layers. J is suitably a bifunctional molecule, for example, a lactam having an amino group and a carboxyl group available, an a, β-diamine having two available amino groups or a fatty acid anhydride having two carboxyl groups available. X is suitably an amino group or a carboxyl group. L is suitably any chelate having a stability constant, K, relatively high (eg,> 1020) for the chelate-paramagnetic complex. Such chelates include, but are not limited to, diethylenetriaminpentaacetic acid (DTPA), tetraazacyclododecanthetraacetic acid (DOTA), and tetraazacyclotetradecantracetic acid (TETA). The paramagnetic ion is suitably a multivalent paramagnetic metal that includes, not limited to, transition metals and lanthanides such as iron, manganese, chromium, cobalt and nickel. Preferably, M ^ is a lanthanide that is highly paramagnetic, more preferably the gadolinium ion (III) that has seven unpaired electrons in the 4f orbit. It will be noted that the gadolinium (III) ion (Gd (III)) is frequently used in contrast agents for magnetic resonance, that is, agents that ience or enhance signals, because it is highly paramagnetic having a large magnetic moment due to the seven unpaired electrons in the orbit 4f. In such contrast agents, gadolinium is generally combined with a chelating agent, as for example DTPA. The resulting 'complex (Gd-DTPA or Magnevist; Berlex Imaging, Wayne, New Jersey) is very stable in vivo, and has a constant training > 1023, making this product a safe element for human use. Similar agents have been developed by chelation of gadolinium ion with other complexes, for example, MS-325, Epix Medical, Cambridge, Massachusetts. Gadolinium (III) causes a localized reduction of T-l in the protons in its environment, providing increased visibility in magnetic resonance images weighted with T-l. The magnetic resonance emission emission coatings according to the present invention are synthesized in accordance with a three or four stage process. The three-stage method includes: (i) the plasma treatment of the surface of a polymeric material (a material coated with a polymer) to provide surface functional groups, for example, by using a nitrogen-containing gas or nitrogen-containing vapor as per example hydrazine (NH2NH2) to provide amino groups; (ii) the binding of a chelating agent, eg, DTPA, to the surface functional group; and (iii) coordination of a functional paramagnetic metal ion such as Gd (III) with the chelating agent. It will be noted that the bond between the surface functional groups and the chelates is frequently an amide bond. In addition to hydrazine, other plasma gases that can be used to provide surface amino functional groups including urea, ammonia, a combination of nitrogen-hydrogen or combinations of these gases. Plasma gases that provide surface functional carboxyl groups include carbon dioxide or oxygen. A schematic reaction process of a preferred embodiment of the present invention appears in Figure 1. As specifically shown in Figure 1, the polyethylene is treated with a hydrazine plasma to provide functionalized amino groups for surface. The amino groups react with DTPA in the presence of a coupling catalyst, for example, 1,1 '-carbonyldiimidazole, to effect an amide bond between the amino groups and the DTPA groups. The amino-DTPA surface groups are then treated with gadolinium (III) chloride by coordinating the gadolinium (III) ion with DTPA. To increase the rotational component of the interaction of the paramagnetic ion with the water of the environment, the coatings that emit magnetic resonance signals are adequately elaborated through a four-step process, which is similar to the three-step process except that before the step (ii), that is, prior to the reaction when the chelating agent, a linker or a spacer molecule, eg, a lactam, is bound to the surface functional groups, resulting in the coating of the formula (II). An illustrative schematic reaction process employing "a lactam is shown in Figure 2. As can be seen in Figure 2, a polyethylene with an amino-functionalized surface reacts with a lactam.The amino groups and the lactam molecules are connected through an amide bond It will be noted that "m * in the designation of the amino-lactam bond is suitably an integer greater than 1. The polyethylene-amino-lactam complex then reacts with DTPA which forms a second amide bond in the distal end of the lactam molecule. The last step in the process, the coordination of the gadolinium ion (III) with DTPA (not shown in Figure 2) is the same as the step illustrated in Figure 1. Specific reaction conditions to form a coating in accordance with the present invention, which employs functionalized amino groups for surface, includes plasma treatment of a polymeric surface, for example, a polyethylene surface, an energy input of 50 in a hydrazine atmosphere within a plasma chamber, represented schematically in the figure 3, for 5-6 minutes, at 13 Pa at 106 Pa (100 mT-800mT). As can be seen in Figure 3, an exemplary plasma chamber, designated generally by the reference numeral 20, includes a cylindrical stainless steel reaction chamber 22 suitably having a diameter of 20 cm, a lower electrode 24 connected to ground and an upper electrode 26, both suitably constructed of stainless steel. The electrodes 24 and 26 suitably have a thickness of 0.8 cm. The upper electrode 26 is connected to an RF energy source (not shown). Both electrodes can be removed, which facilitates post-plasma cleaning operations. The lower electrode 24 also forms part of a vacuum line 28 through a stainless steel pipe 30 having a conical, circularly perforated supporting shape, having a control valve 31. The evacuation of the chamber 22 is effected uniformly through a narrow space (3 mm) that exists between the lower electrode 24 and the bottom of the chamber 22. An upper electrode 26 is directly connected on a threaded end of a hermetic metal / ceramic feed 32 to the vacuum that ensures both the isolation of the RF energy line of the reactor and the dissipation of RF energy towards the electrodes. A space 34 between the upper electrode 26 and the upper wall of the chamber 22 is occupied by three glass discs 36 of the Pyrex® brand with a diameter of 20 cm and a thickness of 1 cm, removable. The disks 36 insulate the upper electrode 26 from the stainless steel upper part of the reactor 20 and allow adjustment of the electrode space. The reactor volume placed outside the perimeter of the electrodes is occupied by two glass cylinders 38 of Pirex® provided with four through holes 40 placed symmetrically for diagnostic purposes. This reactor configuration substantially eliminates the non-plasma areas of the gas environment and considerably reduces the radial diffusion of the plasma species, thereby causing a more uniform plasma exposure of the substrates (electrode). As a result, a surface treatment and uniform deposition processes (film thickness variation of 6 to 10%) can be provided. The removable upper part of the reactor 20 seals the chamber 22 in vacuum with the aid of a copper gasket and holding bolts 42. This part of the reactor also houses a narrow circular gas mixing chamber 44 equipped with an orifice system. a diameter of 0.5 mm of shower type, and a connection 46 of gas supply and monomer. This gas supply configuration ensures a uniform penetration and uniform flow of gases and steam through the reaction zone. The entire reactor 20 is controlled by thermostat by electric heaters mounted on the external surface of the chamber 22 and integrated in an aluminum foil 48 which protects a jacket of glass wool 50 to avoid external losses of thermal energy. For diagnostic purposes, four symmetrically placed stainless steel port hole pipes 51 are connected and welded through the insulation jacket 50 on the reactor wall. These port holes are equipped with interchangeable, optically smooth .quartz 52 windows. A steam supply assembly 54, as can be seen in Figure 3A, includes a plasma reservoir 56, valve 58, VCR connectors 60 and connecting stainless steel pipe 62. The assembly 54 is integrated into two blast jackets. 1 cm thick copper 64 equipped with controlled electric heaters to process low volatility chemicals. The assembly 54 is insulated using a glass wool jacket liner. The thermostatic capacities of reactor 20 are within the range of 25-250 ° C. Once the device has been coated it is functionalized on the surface, is then immersed in a solution of the chelating agent, for example DTPA, for example, in anhydrous pyridine, typically with a coupling catalyst, for example, 1,1 '-carbonyldiimidazole, for a sufficient time for the chelate to react with the amine groups, for example, 20 hours. The surface is washed sequentially with solvents, for example, pyridine, chloroform, methanol and water. The chelated surface is then soaked in a solution of a paramagnetic ion salt, GdCl3'6H20 in water, for a sufficient time for the paramagnetic ion to react with the chelate, for example 12 hours. The surface is then washed with water. In testing processes, each step has been verified to confirm that the union actually occurs. To verify the functionalization of the amino group, x-ray photoelectron spectroscopy (XPS) was used. An XPS spectrum of the polyethylene surface was taken before and after the plasma treatment. The XPS spectrum of polyethylene before the treatment showed no nitrogen peak. After treatment, the nitrogen peak was 5.2% in relation to carbon and oxygen peaks of 63.2% and 31.6%, respectively. To determine if the amino groups were accessible for chemical reactions, after step (i) the surface was reacted with p-fluorophenonepropionic acid and rinsed with solvent (tetrahydrofuran). This reagent, selected due to the good sensitivity of the fluorine atoms to XPS, produces many photoelectrons with x-ray excitation. The result of the XPS experiment showed a significant fluorine signal. The peaks for fluorine, nitrogen, carbon and oxygen were: 3.2%, 1.5%, 75.7% and 19.6%, respectively.
This showed that the amino groups were accessible and capable of chemical reaction. Since the coatings according to the present invention are preferably applied to catheters and since the surface of a catheter is cylindrical, it is observed that, in order to coat commercial catheters, the plasma reaction must be carried out by rotating the catheter shaft of the catheter. normal way to the propagation direction of plasma sheath. Such rotation devices are known and can be easily employed in the plasma reactor illustrated in Figure 3. To verify that surface amination occurs for these surfaces, atomic force spectroscopy (AFM) is used to study the morphology of the surface since XPS requires a well-defined planar surface in relation to the incident x-ray beam. Once coated, coating densities (eg, nmol Gd3 + / m2) are measured using NMR and optimum coating densities can be determined. It is also understood that metal surfaces can be treated with coatings in accordance with the present invention. Metal surfaces, for example guide wires, can be coated with polymers, for example, polyethylene, through various known surface coating techniques, for example, melt coating, a well known method for coating polymers on metal surfaces. Once the metal surfaces are coated with polymers, all other chemical steps described here apply. The present invention is further explained through the following examples which should not be considered as limiting the scope of the present invention. Example 1: Preparation of coated polyethylene sheets. Polyethylene sheets were coated in a three-stage process described here. Surface Amination A polythene sheet of 11.53 cm(4.5 inches) in diameter and 0.0254 mm (1 thousandth of an inch) in thickness was placed in a 50 kHz stainless steel plasma reactor, capacitively coupled(as illustrated schematically in Figures 3 and 3A) and a plasma treatment with hydrazine of the polyethylene film was carried out. The substrate film was placed on the lower electrode. First, the base pressure in the reactor was established. Then, the hydrazine pressure was raised slowly by opening the valve to the liquid hydrazine tank. The following plasma conditions were used: base pressure = 60 T; treatment hydrazine pressure = 350 mT; RF energy = 25 W; treatment time = 5 minutes; source temperature (hydrazine tank) = 60 ° C; substrate temperature = 40 ° C. The surface atomic composition of the plasma-treated and untreated surfaces was evaluated using XPS (Perkin-Elmer Phi-5400, power 300 W, Mg source, 15 kV, angle 45). Coating of DTPA. In a dry 25 mL flask, 21.5 mg of DTPA was added to 8 mL of anhydrous pyridine. In a small vessel, 8.9 mg of carbonyldiimidazole (CDI), as a coupling catalyst, was dissolved in 2 mL of anhydrous pyridine. The CDI solution was added slowly to the reaction flask with stirring, and the mixture was stirred at room temperature for 2 hours. The solution was then emptied into a dry Petri dish, and the polyethylene film treated with hydrazine-plasma was immersed in the solution. The Petri dish was sealed in a drying device after being purged with dry argon for 10 minutes. After the reaction for 20 hours, the polyethylene film was carefully washed in sequence with pyridine, chloroform, mechanol and water. The surface was checked with XPS, and the results showed the presence of carbonyl groups, which demonstrates the presence of DTPA. Coordination of Gadolinium (III). 0.70 g of GdCl3'6H20 was dissolved in 100 mL of water. The polyethylene film treated with DTPA was soaked in the solution for 12 hours. The film was washed with water. The surface was revised with XPS and presented two types in a link energy (BE) = 153.4 eV and BE = 148.0 eV, which corresponds to chelated Gd3 + and free Gd3 +, respectively. The film was washed repeatedly with water until the disappearance of the free Gd3 + peak at 148.0 eV of the XPS spectrum. The results of the treatment in terms of reactive surface atomic concentration appear in Table 1 below. Table 1 Relative surface atomic concentration of untreated and treated PE surfaces% Gd% N% 0 Untreated PE 0. 0 0. 0 2. 6 97. 4PE treated with 0. 0 15. 3 14. 5 70 2 hydrazine-plasma PE coated with 0.0 5.0 37.8 57.2DTPAPE coated with 1.1 3.7 35.0 60.3Gd. Example 2: Preparation of coated polyethylene sheets including linker. Coated polyethylene sheets are prepared according to the method of example 1, except that after surface amination, the polyethylene sheet reacts with a lactam and the sheet is washed before proceeding to the chelation step. The surface of the film is checked for amine groups using XPS. Example 3: Formation of images of coated polyethylene and polypropylene sheets The increase of the magnetic resonance signal was evaluated by polyethylene and polypropylene imaging coated sheets, prepared according to that described in example 1, with echo techniques. remembered by gradient (GRE) and echo of revolution (SE) in a clinical scanner 1.5 T. The leaves were kept in stationary form in a container filled with a tissue imitator, yogurt, and the increase in the contrast of the coating was calculated by the normalization of the signal near the leaf by the yogurt signal. Magnetic resonance images of SE and GRE weighted by TI showed an increase in the signal near the coated polymer sheet. The IT estimates near the coated surface and in the yogurt were 0.4 s and 1.1 s, respectively. No enhancement was observed near the control sheets. The magnetic resonance images acquired appear in Figure 4. Example 4: In-view catheter visualization test filled with Gd-DTPA. The following examples demonstrate the utility of Gd-DTPA for visualizing a catheter under magnetic resonance guidance. A single lumen catheter filled with Gd-DTPA 3-6 French (1-2 mm) was visualized in an acrylic ghost using a conventional magnetic resonance scanner (1.5 T Signa, General Electric Medical Systems), while being manually moved to discrete intervals at a predetermined distance either in the read direction or in the phase encoding direction. The ghost consisted of an acrylic block in which a series of channels had been perforated. The installation allowed the determination of the position of the tip of the catheter with the precision of ± 1 mm (quadratic mean). Catheter photographs are shown in Figure 5. Example 5: Gd-DTPA filled catheter visualization test for in vivo evaluation, commercially available single lumen catheters filled with Gd-DTPA (4-6% solution) , within a range of sizes between 3 and 6 French (1-2 mm) and catheter / guidewire combinations were visualized either in the aorta or in the carotid artery of four dogs. All the experiments in animals were carried out in combination with protocols approved by institutions and were carried out with the animals under general anesthesia. The lumen of the catheter was opened at one end and closed at the other end by a stopper. This keeps the Gd-DTPA solution in the catheter. The possibility of leakage of Gd-DTPA from the lumen of the catheter through the open end was small and was considered safe since the Gd-DTPA used in these experiments is commercially available and approved for use in magnetic resonance. The reconstructed images produced during catheter screening were superimposed on previously acquired angiographic images typically acquired using a 3D TRICKS image sequence (FR Korosec, R. Frayne, TM Grist, CA Mistretta, 36 Magn. Reson. Medicine. (1996) 345 -351, which is incorporated herein by reference) in combination with either an intravenous or intraarterial injection of Gd-DTPA (0.1 mmol / kg). On some occasions, subtraction techniques were used to eliminate the background signal from the catheter images before they were superimposed on a path image. Photographs of the carotids and aortas of dogs are shown in figures 6 and 7, respectively. Example 6: In vivo catheter visualization by magnetic resonance Using dogs, a catheter coated with a coating according to the combination of guidewire and present invention was initially placed in the femoral artery. Under the magnetic resonance guidance, the catheter is first moved to the aorta, then to the carotid artery, then to the illis circle, and to the middle cerebral artery. The movement of the catheter can be clearly seen in the vessels. The time to perform this procedure is recorded as well as the smallest vessel actually handled. Example 7: Paramagnetic ion safety test A gadolinium leaching test is performed to determine the stability of the Gd-DTPA complex. Polyethylene sheets coated with a coating in accordance with the present invention are subjected to stimulated blood plasma buffers and blood plasma itself. NMR scans are taken and distinguished between chelated Gd3 + and free Gd3 +. The results indicate that the Gd3 + complex is stable under simulated blood conditions. Example 8: Biocompatibility test A biocompatibility test was performed on polymeric surfaces coated in accordance with the present invention employing a method of adsorption of serum albumin labeled with fluorescent dyes. If the albumin is irreversibly adsorbed in accordance with that detected by coated catheter surface fluorescence, the coating is considered to be bioincompatible. Example 9: Determination of signal intensities ofCoating A clinical 1.5T scanner (Signa, General Electric Medical Systems) is used to determine the optimal range of coating densities (in mmol Gd3li? F2) to produce an appreciable increase in the signal in a series of silicon platelets coated with a polyethylene-Gd-containing coating according to the present invention. Platelets are placed in a water bath and are cross-scanned using a moderately high resolution gradient echo gradient echo sequence (FGRE) with TR = approximately 7.5 ms / TE = approximately 1.5 ms, 256 x 256 acquisition matrix and a field of view (FOV) of 16 cm x 16 cm. The inversion angle varies from 10 ° to 90 ° in 10 ° increments for each coating density. A region of interest (ROI) is placed in the water adjacent to the platelet and the absolute signal is calculated. For the calibration of signal measurements obtained in different imaging experiments, the image of a series of 10 calibration flasks is also formed. The bottles contain several concentrations of Gd-DTPA, within a range of 0 mmol mL "1 to 0.5 mmol mL" 1. This range of concentrations corresponds to a range of relaxation times TI (from <10 ms to 1000 ms) and a range of relaxation times T2. the signals in each vial are also measured and used to normalize the signals obtained near the platelets. Normalization corrections for effects due to different pre-scan settings between acquisitions and variable image scaling are applied through the browser. A range of concentrations in the jars facilitates the normalization in pieces. An optimum range of coating densities is determined. In summary, the present invention offers a method for visualizing medical devices under magnetic resonance guidance, employing a coating, which is a complex of paramagnetic polymer-ion substance, on medical devices. While the present invention has been described and exemplified with certain specificity, those skilled in the art will note that various modifications, including variations, additions and omissions, may also be made in what has been described. Accordingly, such modifications are also encompassed by the present invention and the scope of the present invention is limited only by the broadest interpretation that can legally be granted to the appended claims.