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Home | Alpha Telephone | Domain Names | Web Hosting | Get Traffic | xrEvidence | xrSoccer United States Patent
MR-compatible devices A catheter is used for medical treatments within an organism. The catheter comprises at least one lumen. Within the at least one lumen are at least two microcatheters, with at least one of the at least two microcatheters being connected to a source of liquid material to be delivered to the organism and another of the at least two microcatheters being connected to a system capable of effecting a medical treatment other than delivery of the liquid.
Primary Examiner: Sirmons; Kevin C. Assistant Examiner: Han; Mark K Attorney, Agent or Firm: RELATED APPLICATIONS This application is a continuation-in-part of U.S. patent application Ser. No. 09/131,031, filed Aug. 7, 1998, now U.S. Pat. No. 6,272,370, and is also a continuation-in-part of U.S. patent application Ser. No. 08/857,043, filed May 15, 1997, now U.S. Pat. No. 6,026,316. We claim: 1. A catheter for use within cerebral blood vessels of an organism, the catheter comprising at least one lumen, and within the at least one lumen at least two microcatheters, with at least one of the at least two microcatheters being connected to a source of liquid material to be delivered to the organism and another of the at least two microcatheters being connected to a system capable of effecting a medical treatment other than delivery of the liquid. 2. The catheter of claim 1 wherein the medical treatment other then delivery of the liquid comprises stimulation of natural activities. 3. The catheter of claim 2 wherein at least one opposed pair of microcoils is present on the catheter. 4. The catheter of claim 1 wherein the medical treatment other then delivery of the liquid comprises stimulation of natural activities of chemical producing systems. 5. The catheter of claim 4 wherein at least one opposed pair of microcoils is present on the catheter. 6. The catheter of claim 4 wherein electronic circuitry is located within the catheter. 7. The catheter of claim 4 wherein at least one opposed pair of microcoils is present on the catheter. 8. The catheter of claim 1 wherein the medical treatment other then delivery of the liquid comprises removal of deposits of materials. 9. The catheter of claim 8 wherein the at least two microcatheters pass within the lumen, and exit holes are provided in the catheter for the at least two microcatheters. 10. The catheter of claim 9 wherein deflectors are present within the lumen for directing the at least two microcatheters through the holes. 11. The catheter of claim 1 wherein at least one opposed pair of microcoils is present on the catheter. 12. The catheter of claim 11 wherein electronic circuitry is located within the catheter. 13. The catheter of claim 1 wherein electronic circuitry is located within the catheter. 14. The catheter of claim 1 wherein the at least two microcatheters pass within the lumen, and exit holes are provided in the catheter for the at least two microcatheters. 15. The catheter of claim 14 wherein deflectors are present within the lumen for directing the at least two microcatheters through the holes. 16. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises an endovascularly therapeutic application. 17. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises a pressure or flow measurement system. 18. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises a physiology monitoring system. 19. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises electrical stimulation. 20. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises dispersing of deposits. 21. The catheter of claim 1 also containing at least one optical fiber. 22. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises a balloon catheter. 23. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises an ablation system. 24. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises a cytotoxic irradiation system. 25. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises an electrophysiological monitoring system. 26. The catheter of claim 1 wherein electronic circuitry is located external to the catheter. 27. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises a diagnostic treatment. 28. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises microwave heating and the catheter comprises a microwave coil. 29. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises a liquid removal system. 30. The catheter of claim 1 wherein the medical treatment other than liquid delivery comprises a heating system. 31. A catheter for use within cerebral blood vessels of an organism, the catheter comprising at least one lumen, and within the at least one lumen at least two microcatheters, and a deflector within the lumen for deflecting microcatheters towards exit ports within the catheter. 32. A catheter for use within cerebral blood vessels of an organism, the catheter comprising at least one lumen, and within the at least one lumen at least two microcatheters, with at least one of the at least two microcatheters being connected to a source of liquid material to be delivered to the organism and another of the at least two microcatheters being connected to a system capable of effecting a medical treatment other than delivery of the liquid comprising stimulation of natural activities, wherein at least one opposed pair of microcoils is present on the catheter, and electronic circuitry is located within the catheter. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of delivery of medical devices to patients, especially a method where (e.g., neurological) devices are delivered using nonlinear magnetic stereotaxis in conjunction with non-invasive MR imaging observation techniques such as magnetic resonance imaging, and most especially where drug delivery by said devices is accomplished under real time, non-invasive observation techniques such as magnetic resonance imaging which can indicate metabolic responses to the delivered drug and/or changes in soluble/dispersed concentrations of materials within liquids and/or tissue of a patient in real time or near real time. The present invention also generally relates to medical devices which are compatible with those and other procedures performed during magnetic resonance imaging (MRI), and particularly to medical devices which can deliver drugs during procedures viewed with magnetic resonance (MR) imaging techniques. 2. Background of the Prior Art The concept of administering minimally invasive therapy and especially minimally invasive drug delivered therapy follows recent trends in medical and surgical practice towards increasing simplicity, safety, and therapeutic effectiveness. Image-guided, minimally invasive therapies have already superseded conventional surgical methods in several procedures. For example, transvascular coronary angioplasty is often now an alternative to open-heart surgery for coronary artery bypass, and laparascopic cholecystectomy is often an alternative to major abdominal surgery for gall bladder removal. The use of the less invasive techniques has typically reduced hospital stays by 1 2 weeks and the convalescence periods from 1 2 months to 1 2 weeks. While endoscopic, arthroscopic, and endovascular therapies have already produced significant advances in health care, these techniques ultimately suffer from the same limitation. This limitation is that the accuracy of the procedure is "surface limited" by what the surgeon can either see through the device itself or otherwise visualize (as by optical fibers) during the course of the procedure. That is, the visually observable field of operation is quite small and limited to those surfaces (especially external surfaces of biological masses such as organs and other tissue) observable by visible radiation, due to the optical limitations of the viewing mechanism. MR imaging, by comparison, overcomes this limitation by enabling the physician or surgeon to non-invasively visualize tissue planes and structures (either in these planes or passing through them) beyond the surface of the tissue under direct evaluation. Moreover, MR imaging enables differentiation of normal from abnormal tissues, and it can display critical structures such as blood vessels in three dimensions. Prototype high-speed MR imagers which permit continuous real-time visualization of tissues during surgical and endovascular procedures have already been developed. MR-guided minimally invasive therapy is expected to substantially lower patient morbidity because of reduced post-procedure complications and pain. The use of this type of procedure will translate into shorter hospital stays, a reduced convalescence period before return to normal activities, and a generally higher quality of life for patients. The medical benefits and health care cost savings are likely to be very substantial. A specific area where research is moving forward on advances of this type is in the treatment of neurological disorders. Specifically, the advent of new diagnostic and therapeutic technologies promises to extend the utility of intracerebral drug delivery procedures and thus possibly advance the efficacy of existing and/or planned treatments for various focal neurological disorders, neurovascular diseases and neurodegenerative processes. Currently, when the standard procedure requires neurosurgeons or interventional neuroradiologists to deliver drug therapy into the brain, the drug delivery device, such as a catheter, must either be passed directly through the intraparenchymal tissues to the targeted region of the brain, or guided through the vasculature until positioned properly. An important issue in either approach is the accuracy of the navigational process used to direct the movement of the drug delivery device. In many cases, the physical positioning of either part or all of the catheter's lumen within the brain is also important as, for example, in situations where a drug or some other therapeutic agent will be either infused or retroperfused into the brain through the wall or from the tip of the catheter or other drug delivery device. New technologies like intra-operative magnetic resonance imaging and nonlinear magnetic stereotaxis, the latter discussed by G. T. Gillies, R. C. Ritter, W. C. Broaddus, M. S. Grady, M. A. Howard III, and R. G. McNeil, "Magnetic Manipulation Instrumentation for Medical Physics Research," Review of Scientific Instruments, Vol. 65, No. 3, pp. 533 562 (March 1994), as two examples, will likely play increasingly important roles here. In the former case, one type of MR unit is arranged in a "double-donut" configuration, in which the imaging coil is split axially into two components. Imaging studies of the patient are performed with this system while the surgeon is present in the axial gap and carrying out procedures on the patient. A second type of high-speed MR imaging system combines high-resolution MR imaging with conventional X-ray fluoroscopy and digital subtraction angiography (DSA) capability in a single hybrid unit. These new generations of MR scanners are able to provide the clinician with frequently updated images of the anatomical structures of interest, therefore making it possible to tailor a given interventional procedure to sudden or acute changes in either the anatomical or physiological properties of, e.g., a part of the brain into which a drug agent is being infused. Nonlinear magnetic stereotaxis is the image-based magnetically guided movement of a small object directly through the bulk brain tissues or along tracts within the neurovasculature or elsewhere within the body. Electromagnets are used to magnetically steer the implant, giving (for example) the neurosurgeon or interventional neuroradiologist the ability to guide the object along a particular path of interest. (The implant might be either magnetically and/or mechanically advanced towards its target, but is magnetically steered, in either case. That is, magnetic fields and gradients are used to provide torques and linear forces to orient or shift the position of the implant or device, with a mechanical pushing force subsequently providing none, some, or all of the force that actually propels the implant or device. Additional force may be provided magnetically.) The implant's position is monitored by bi-planar fluoroscopy, and its location is indicated on a computerized atlas of brain images derived from a pre-operative MR scan. Among other applications, the implant might be used to tow a pliable catheter or other drug delivery device to a selected intracranial location through the brain parenchyma or via the neurovasculature. Magnetic manipulation of catheters and other probes is well documented in research literature. For example, Cares et al. (J. Neurosurg, 38:145, 1973) have described a magnetically guided microballoon released by RF induction heating, which was used to occlude experimental intracranial aneurysms. More recently, Kusunoki et al. (Neuroradiol 24: 127, 1982) described a magnetically controlled catheter with cranial balloon useful in treating experimental canine aneurysms. Ram and Meyer (Cathet. Cardiovas. Diag. 22:317, 1991) have described a permanent magnet-tipped polyurethane angiography catheter useful in cardiac interventions, in particular intraventricular catheterization in neonates. U.S. Pat. No. 4,869,247 teaches the general method of intra parenchymal and other types of magnetic manipulation, and U.S. Pat. Nos. 5,125,888; 5,707,335; and 5,779,694 describe the use of nonlinear magnetic stereotaxis to maneuver a drug or other therapy delivery catheter system within the brain. U.S. Pat. No. 5,654,864 teaches a general method of controlling the operation of the multiple coils of a magnetic stereotaxis system for the purpose of maneuvering an implant to precisely specified locations within the body. Both of these technologies offer a capability for performing image-guided placement of a catheter or other drug delivery device, thus allowing drug delivery directly into the brain via infusion through the walls of the catheter or out flow of the tip off the catheter. In the case of drug delivery directly into the brain tissues, the screening of large molecular weight substances by the endothelial blood-brain barrier can be overcome. In the case of infusions into specific parts of the cerebrovasculature, highly selective catheterizations can be enabled by these techniques. In either case, however, detailed visual images denoting the actual position of the drug delivery device within the brain would be extremely useful to the clinician in maximizing the safety and efficacy of the procedure. The availability of an MR-visible drug delivery device combined with MR-visible drug agents would make it possible to obtain near real-time information on drug delivery during interventional procedures guided by non-linear magnetic stereotaxis. Drug delivery devices, such as catheters, that are both MR-visible and radio-opaque could be monitored by two modalities of imaging, thus making intra-operative verification of catheter location possible during nonlinear magnetic stereotaxis procedures. (Intra-operative MR assessment might require the temporary removal of the magnetic tip of the drug delivery catheter and interruption of the magnetic stereotaxis procedure to image the patient.). The geometry and magnetic strength of the magnetic tip will depend upon the particular type of catheter or medical device with which the tip is being used. In a preferred embodiment, the tip would have as small a maximum dimension as would be consistent with maintaining sufficient magnetic dipole moment to couple satisfactorily to the external magnetic fields and gradients used to apply torques and forces to the tip for the purpose of steering or moving the catheter or other medical device. It is preferred that the magnetic element (e.g., a distinct magnetic bead or seed or wire) or the magnetic tip have a maximum dimension of at least 0.5 mm, preferably from 0.5 to 8 mm, more preferably from about 1.0 to 6 mm, and most preferably from about 2 to 5 or 6 mm. To that end, the tip might be made of a permanently magnetic or magnetically permeable material, with compounds of Nd--B--Fe being exemplary, as well as various iron alloys (ferrites and steel alloys). The magnetic tip may be fixed to the distal end of the catheter in any number of ways, depending in part upon the method of use of the catheter, the specific type of catheter, the procedures and the use of the catheter. In one design, the magnetic tip might simply be a small spherical or oblate spheroid of magnetic material (e.g., having a geometry where the semi-major axis is from 1.1 to 3 times longer, preferably from 1.5 to 2.0 or 2.5 time longer than the semi-minor axis). The magnetic tip may be originally fixed to the distal end of the catheter or medical device or passed through the length of the catheter so that it abuts against the interal distal end of the catheter (as a foot would abut the end of a sock). As noted, the magnetic tip may be fixed in place either on the inside, outside or embedded within the composition of the distal end of the catheter or medical device. In a preferred embodiment, the magnetic tip may be thermally, solubly, mechanically, electronically or otherwise removably attached to and separable from the distal end of the catheter or medical device. A heat soluble link is taught in U.S. Pat. No. 5,125,888. In still another embodiment, the magnetic tip would constitute a plug in the end of an otherwise open-ended catheter, and the tip might either have an open bore along its axis, a plurality of open bores along its axis, or a single or plural configuration of holes along the side of the magnetic tip, any of which openings would be used to facilitate drug delivery from the catheter or to serve as an exit port for the delivery of some other therapy or device into a body part, such as the parenchymal tissues and/or the cerebrobasculature of the brain. Alternatively, the magnetic tip might simply constitute a solid plug that seals the end of the catheter. The distal end of the catheter at which the magnetic tip is placed must be configured such that axial forces and torques applied by either magnetic fields and gradients or by a guide wire internal to the catheter allow said distal end and magnetic tip to be propelled towards a target site with the body, and to do so without said distal end and magnetic tip separating from each other in an inappropriate way and/or at an undesired time or under undesired circumstances. If the magnetic tip must be removed, or detached and removed, prior to MR imaging of the patient, such a procedure could be accomplished by the method taught in U.S. Pat. Nos. 5,125,888; 5,707,335; and 5,779,694, which call for dissolving a heat separable link between the tip and the catheter by a pulse of radio-frequency energy. An alternative means of removing the magnetic tip is discussed by M. A. Howard et al. in their article, "Magnetically Guided Stereotaxis," in Advanced Neurosurgical Navigation, edited by E. Alexander III and R. J. Maciunas (Thieme Medical Publisher, New York, 1998), which calls for withdrawing the magnetic tip from along the inside of the catheter that it has just steered into place within the body. Without removal of the magnetic tip from the catheter, whole body magnetic forces might be produced on it by the field of the MR imaging system, and these could cause undesired movement of the catheter that it has just steered into place within the body. In the treatment of neurological diseases and disorders, targeted drug delivery can significantly improve therapeutic efficacy, while minimizing systemic side-effects of the drug therapy. Image-guided placement of the tip of a drug delivery catheter directly into specific regions of the brain can initially produce maximal drug concentration close to some targeted loci of tissue receptors following delivery of the drug. At the same time, the limited distribution of drug injected from a single catheter tip presents other problems. For example, the volume flow rate of drug delivery must be very low to avoid indiscriminate hydrodynamic damage or other damage to brain cells and nerve fibers. Delivery of a drug from a single point source may also limit the distribution of the drug by decreasing the effective radius of penetration of the drug agent into the surrounding tissue receptor population. Positive pressure infusion, i.e., convection-enhanced delivery of drugs into the brain, as taught by U.S. Pat. No. 5,720,720 may overcome the problem of effective radius of penetration. Also, U.S. patent application Ser. No. 08/857,043, filed on May 15, 1997 and titled "Method and Apparatus for Use with MR Imaging" describes a technology invented in-part by one of the present inventors comprising a method for observing the delivery of material to tissue in a living patient comprising the steps of a) observing by magnetic resonance imaging a visible image within an area or volume comprising tissue of said living patient, the area or volume including a material delivery device, b) delivering at least some material by the material delivery device into the area or volume comprising tissue of a living patient, and c) observing a change in property of said visible image of the area or volume comprising tissue of a living patient while said material delivery device is still present within the area or volume. This process, including the MRI visualization, is performed in approximately or actually real time, with the clinical procedure being guided by the MRI visualization. Research on magnetic catheterization of cerebral blood vessels generally has focused on design of transvascular devices to thrombose aneurysms, to deliver cytotaxic drugs to tumors, and to deliver other therapies without the risks of major invasive surgery. Examples of such studies include Hilal et al (J. Appl. Phys. 40:1046, 1969), Molcho et al (IEEE Trans. Biomed. Eng. BME-17, 134, 1970), Penn et al (J. Neurosurg. 38:239, 1973), and Hilal et al (Radiology 113:529,1974). U.S. Pat. Nos. 4,869,247, 5,654,864, 5,125,888, 5,707,335 and 5,779,694 describe processes and apparatus for the use of magnetic stereotaxis for the manipulation of an object or implant which is moved into position within a patient, particularly within the cranial region and specifically within the brain but in principle elsewhere in the body also. These patents do no not involve any contemplation of real time visualization of drug distribution within the brain, especially by MRI. It should be noted that the potential exists for interactive interference between the two systems, magnetic resonance imaging and magnetic stereotaxis, particularly where fine images are being provided by a system based on magnetic coils, especially as described in U.S. patent application Ser. No. 08/916,596, filed on Aug. 22, 1997, which is incorporated herein by reference for its disclosure of the design, construction, structure and operation of coils and catheters in MR-guided procedures. That application describes medical devices which are compatible with procedures performed during magnetic resonance imaging (MRI), and particularly to medical devices which can deliver drugs during procedures viewed with magnetic resonance (MR) imaging techniques. Medical procedures may now be performed on areas of the patient which are relatively small. Procedures may be performed on small clusters of cells, within veins and arteries, and in remote sections of the body with minimally invasive techniques, such as without surgical opening of the body. As these procedures, such as balloon angioplasty, microsurgery, electrotherapy, and drug delivery are performed within the patient with minimally invasive techniques without major surgical opening of the patient, techniques have had to be developed which allow for viewing of the procedure concurrent with the procedure. X-ray imaging, such as X-ray fluoroscopy, is a possible method of providing a view of the procedural area, but X-ray exposure for any extended period of time is itself harmful to the patient. Fiber optic viewing of the area does not provide any harmful radiation to the patient, but the fiber optics may take up too large a space to provide both the light necessary for viewing and a path for return of the light, and does not permit beyond the surface imaging (that is, only the surfaces of internal objects may be viewed from the position where the fiber optic device is located). Fiber optics or direct light viewing is more acceptable for larger area medical procedures such as gastroenterological procedures than for more microscopic procedures such as intraparenchymal drug delivery or endovascular drug delivery or procedures. Techniques have been developed for relatively larger area viewing of MR-compatible devices within a patient by the use of MR-receiver coils in the devices which are tracked by MR imaging systems. Little by way of specific design considerations have been given to devices which have MR viewing capability and specific treatment functions, and especially where the relationship of specific types of treatment and the MR receiver coils must be optimized both for a treatment process and for MR viewing ability. U.S. Pat. No. 5,211,165 describes a tracking system to follow the position and orientation of an invasive device, and especially a medical device such as a catheter, using radio frequency field gradients. Detection of radio frequency signals is accomplished with coils having sensitivity profiles which vary approximately linearly with position. The invasive device has a transmit coil attached near its end and is driven by a low power RF source to produce a dipole electromagnetic field that can be detected by an array of receive coils distributed around an area of interest of the subject. This system places the transmit coils within the subject and surrounds the subject with receive coils. U.S. Pat. No. 5,271,400 describes a tracking system to monitor the position and orientation of an invasive device within a subject. The device has an MR active sample and a receiver coil which is sensitive to magnetic resonance signals generated by the MR active sample. These signals are detected in the presence of magnetic field gradients and thus have frequencies which are substantially proportional to the location of the coil along the direction of the applied gradient. Signals are detected responsive to sequentially applied mutually orthogonal magnetic gradients to determine the device's position in several dimensions. The invasive devices shown in FIGS. 2a and 2b and rf coil and an MR active sample incorporated into a medical device and an MR active sample incorporated into a medical device, respectively. U.S. Pat. No. 5,375,596 describes a method and apparatus for determining the position of devices such as catheters, tubes, placement guidewires and implantable ports within biological tissue. The devices may contain a transmitter/detector unit having an alternating current radio-frequency transmitter with antenna and a radio signal transmitter situated long the full length of the device. The antennae are connected by a removable clip to a wide band radio frequency (RF) detection circuit, situated within the transmitter/detector unit. U.S. Pat. No. 4,572,198 describes a catheter for use with NMR imaging systems, the catheter including a coil winding for exciting a weak magnetic field at the tip of the catheter. A loop connecting two conductors supports a dipole magnetic field which locally distorts the NMR image, providing an image cursor on the magnetic resonance imaging display. U.S. Pat. No. 4,767,973 describes systems and methods for sensing and movement of an object in multiple degrees of freedom. The sensor system comprises at least one field-effect transistor having a geometric configuration selected to provide desired sensitivity. Published PCT Applications WO 93/15872, WO 93/15874, WO 93/15785, and WO 94/27697 show methods of forming tubing, including kink resistant tubing and catheters in which the catheters may contain reinforcing coils. Layer(s) of reinforcing materials may be deposited on and over the reinforcing coils. U.S. Pat. Nos. 5,451,774 and 5,270,485 describes a three-dimensional circuit structure including a plurality of elongate substrates positioned in parallel and in contact with each other. Electrical components are formed on the surfaces of the substrates, along with electrical conductors coupled to those components. The conductors are selectively positioned on each substrate so as to contact conductors on adjacent substrates. The conductor patterns on the substrates may be helical, circumferential, or longitudinal. Radio frequency signaling between substrates would be effected with a transmitting antenna and a receiving antenna, with radio frequency signal transmitting and receiving circuitry present in the substrates (e.g., column 7, lines 32 43). Circulation of cooling fluid within the device is shown. U.S. Pat. No. 5,273,622 describes a system for the fabrication of microstructures (including electronic microcircuitry) and thin-film semiconductors on substrates, especially continuous processes for use on elongate substrates such as fibers or filaments. U.S. Pat. Nos. 5,106,455 and 5,269,882 describes a method and apparatus for fabrication of thin film semiconductor devices using non-planar exposure beam lithography. Circuitry formed on cylindrical objects is shown. U.S. Pat. No. 5,167,625 describes a multiple vesicle implantable drug delivery system which may contain an electrical circuit which is responsive to signals (including radio signals) which can be used to effect drug delivery. PCT Application WO 96/33761 (filed 15 Apr. 1996) describes an intraparenchymal infusion catheter system for delivering drugs or other agents comprising a pump coupled to the catheter. A porous tip is disposed at a distal end of the catheter, the tip being porous to discharge an agent or dug at a selected site. The catheter may be customized during use by an expandable portion of the catheter system. Martin, A. J., Plewes, D. B. and Henkelman, R. M. in "MR Imaging of Blood Vessels with an Intravascular Coil," J. Mag. Res. Imag., 1992, 2, No. 4, pp. 421 429 describes a method for producing high-resolution magnetic resonance (MR) images of blood vessel walls using a theoretic receiver-coil design based on two coaxial solenoids separated by a gap region and with the current driven in opposite directions. The coils had diameters ranging from 3 to 9 mm. FIG. 3b appears to indicate that sensitivity decreases as the coils diameter moved from 9 to 7 to 5 to 3 mm. Investigation of the Q value of opposed loop and opposed solenoid coils indicated that opposed loop coils displayed low W values and that there was a general trend of lower Q values at smaller Q diameters among the opposed solenoid designs. Within the range investigated, it was stated that a compromise exists between the use of thicker wire for improved performance and thinner wire to limit the overall coil dimensions. Decoupling circuitry is also shown to be useful in performing the imaging functions with this catheter based system in MR imaging. Hurst, G. C., Hua, J., Duerk, J. I. and Choen, A. M., "Intravascular (Catheter) NMR Receiver Probe: Preliminary Design Analysis and Application in Canine Iliofemoral Imaging," Magn. Res. In Imaging, 24, 343 357 (1992) explores the feasibility of a catheter-based receiver probe for NMR study of arterial walls. Various potential designs, including opposed solenoids (e.g., FIG. 2b and FIG. 3 a and b) are examined. The catheter probe shown in FIG. 3 was constructed with five turns of 28 gauge wire per solenoid, with 7.5 mm between solenoids and nominal solenoid diameters of 2.8 mm, with the probe resonating at 64 MHz with a 110-pf capacitor. A device is described for use within an organism, said device may comprise an element having at least one pair of opposed RF receiver microcoils having a space between each microcoil of said pair of microcoils, the coils of said microcoils having diameters of less than 2.4 mm. The device may comprise a catheter having at least one lumen, where the at least one pair of microcoils is radially located about the at least one lumen and the coils have diameters of greater than 0.1 mm and less than 2.4 mm. The device may have no ports or at least one drug delivery port present within said device. The least one drug delivery port may be located so that at least some drug which is delivered through said port is delivered away from said device within said space between said microcoils. The delivery ports may comprise microcatheters present within said device which extend outside of said device to deliver at least some liquid material within a volume bordered by planes extending radially from the catheter at ends of the at least one pair of microcoils which define the space between each microcoil within said at least one pair of microcoils. The device, in response to radio frequency transmission, may generate a field which has an average strength within said volume than in comparable size volumes surrounding said catheter which are radially located directly over each of said microcoils. The at least one pair of microcoils preferably is embedded within a binder material which surrounds said lumen. The at least one pair of microcoils is electrically connected to a preamplifier within a portion of said device which may be inserted into an organism. Where electrical connections are present within said device, it is preferred that at least some of said electrical connections have been formed in situ within said device. This invention provides a method and object for selective intraparenchymal and/or neuroendovascular drug delivery and other concurrent medical treatment of abnormalities of the human central nervous system concurrent with nonlinear magnetic stereotaxis combined with magnetic resonance (MR) imaging and/or x-ray guidance. Magnetic Resonance Imaging (MRI) is used in combination with 1) an MR observable delivery device or 2) an MR observable medical device which can alter a water based molecular environment by performed medical operations, the delivery device or medical device being used in the presence of MR observable (in water, body fluid or tissue) compound(s) or composition(s). MRI images are viewed with respect to a molecular environment to determine the position of the delivery device or medical device (hereinafter collectively referred to as the "delivery device" unless otherwise specifically identified) and changes in the environment where the delivery device is present as an indication of changes in the molecular environment. As the delivery of material from the delivery device is the most MR visible event within the molecular environment in the vicinity of the delivery area, the changes in the molecular environment are attributable to the delivery of the MR observable compounds or compositions. Changes in signal properties, such as changes in the signal intensity within the MR images reflect the changes in the molecular environment and therefore track the location of delivered materials, and are indicative of delivery rates and delivery volumes in viewable locations. With the medical device, chemical composition within the molecular environment may also be altered as by the removal of deposits of certain materials into the liquid (water) environment or stimulated activity of tissue to release materials, where those materials can alter the MR response. Some materials that may be removed by medical procedures will not affect the MR response, such as calcium, but fatty materials may affect the response. Additionally, medical treatments which stimulate natural activities of chemical producing systems (e.g., the glands, organs and cells of the body which generate chemicals such as enzymes and other chemicals with specific biological activity [e.g., dopamine, insulin, etc.]) can be viewed under direct MR observation and any changes in chemical synthetic activity and/or delivery can be observed because of molecular environment changes which occur upon increased synthetic activity. One recently established method of reading the data obtained from the MR imaging is technically founded upon existing knowledge of Apparent Diffusion Coefficients (ADC) in particular regions of the body. There is significant published literature with respect to ADC values for specific tissues in various parts of animals, including various tissues of humans (e.g., Joseph V. Hajnal, Mark Doran, et al., "MR Imaging of Anisotropically Restricted Diffusion of Water in the Nervous System: Technical, Anatomic, and Pathological Considerations," Journal of Computer Assisted Tomography, 15(I): 1 18, January/February, 1991, pp. 1 18). It is also well established in the literature that loss of tissue structure through disease results in a decrease of the ADC, as the tissue becomes more like a homogeneous suspension. Clinical observations of changes in diffusion behavior have been made in various tissue cancers, multiple sclerosis, in strokes (where the reduction in diffusion precedes the increase in T2), and in epilepsy. (e.g., Y. Hasegawa, L. Latour, et al. "Temperature Dependent Change of Apparent Diffusion Coefficient of Water in Normal Ischemic Brain", Journal of Cerebral Blood Flow and Metabolism 14:389 390, 1994). Thus, ADC values are specific for specific types of tissues. Accordingly, as different drugs/chemicals are introduced into a tissue volume under MR observation, the change in ADC resulting from each drug/chemical interaction with the ambient water proton environment can be observed. While the ADC is the preferred means within the present invention of mapping the delivery of drug in tissue, other embodiments of the invention allow for additional tissue contrast parameters to track the delivery of a drug into tissue. In other words, the delivery of a drug into tissue will cause other MRI-observable changes which can be mapped (as is done for ADC) and which can be used to map the spatial distribution characteristics of the drug within and around the targeted tissue. While some of these observations may be larger in magnitude than others, any of the MRI contrast mechanisms' effects can be used as a tracking mechanism to longitudinally evaluate the spatial kinetics of drug movement within the imaging volume. The tissue contrast changes apparent on an MR image can arise from ADC, from alterations in the BO magnetic field (often referred to as magnetic susceptibility or ABO produced by the presence of a substance in said tissue), from alterations in local tissue T1 relaxation times, from local T2 relaxation times, from T2* relaxation times (which can be created by susceptibility differences), from the magnetization transfer coefficients (MTC is an effect produced by local communication between free water protons and those of nearby macromolecular structures), from the ADC anisotropy observed in oriented matter, and also from local differences in temperature which will affect in varying degrees all of the included tissue contrast parameters. In addition, the delivery of drug can also be tracked from magnetic field frequency shifts caused by the drug or arising from agents (e.g., MR taggants) added with unique frequency shifts from those of the local protons (such as that created from F-19 or fluorine-19 agents found in or added to the drug). MR imaging of the alterations in the BO magnetic field (also known as imaging of the local magnetic susceptibility) can reveal the spatial distribution of a drug from the interaction of the drug with the otherwise homogeneous magnetic field found in MRI. To enhance the alterations in the magnetic field BO caused by the drug, small amounts of a BO-altering added agent or agents can be added to the drug during delivery. This can include iron oxide particles, or other materials, such as those comprising lanthanide-, manganese-, and iron-chelates. In addition, vehicles containing differing gases (N.sub.2, O.sub.2, CO.sub.2) will also alter the local magnetic field and thus produce a magnetic susceptibility effect which can be imaged. The invention includes a device for use in conjunction with magnetic stereotaxis guidance and device delivery and a method for MR-guided targeted drug delivery into a patient, such as intracranial drug delivery, intraspinal drug delivery, intrarenal drug delivery, intracardial drug delivery, etc. The MR-visible drug delivery device is guided by magnetic stereotaxis to the target tissue and/or advanced within entrance points to the patient such as periventricular, intracerebroventricular, subarachnoid, intraparenchymal tissues or the cerebrovasculature under magnetic resonance imaging or real time X-ray fluoroscopy, and all of this is possibly also done in conjunction with conventional methods of neurosurgical or neuroradiologic catheter manipulation. The drug delivery device preferably has a linearly arranged array of radiopaque and MR-visible markers disposed at its distal end to provide easily identifiable reference points for trackability and localization under susceptibility MR imaging and X-ray fluoroscopy guidance. Additionally, active MR visualization of the drug delivery device is achieved or enhanced by means of RF microcoils positioned along the distal axis of the device. MR visibility can be variably adjustable based on requirements related to degree of signal intensity change for device localization and positioning, enhancement along the shaft of the device, enhancement around the body of the device, visibility of the proximal and distal ends of the device, degree of increased background noise associated with device movement, and other factors which either increase or suppress background noise associated with the device. Since the tip of the drug delivery device can be seen on MR and X-ray images and thus localized within the brain, the multiple point source locations of drug delivery are therefore known and can be seen relative to the tip or the shaft of the device. Targeted delivery of drug agents may be performed by any therapeutically effective drug delivery device or system, including, for example, those utilizing MR-compatible pumps connected to variable-length concentric MR-visible dialysis probes each with a variable molecular weight cut-off membrane, or by another MR-compatible infusion device which injects or infuses a diagnostic or therapeutic drug solution. Imaging of the injected or infused drug agent is performed by MR diffusion mapping using the RF microcoils attached to the distal shaft of the injection device, or by imaging an MR-visible contrast agent that is injected or infused through the walls of the dialysis fiber into the brain. The delivery and distribution kinetics of injections or infusions of drug agents at rates, for example, of between 1 .mu.l/min (or less) to 1000 .mu.l/min (or more) are monitored quantitatively and non-invasively using real-time contrast-enhanced magnetic susceptibility MR imaging combined with water proton directional diffusion MR imaging. One aspect of the present invention is to provide a non-invasive, radiation-free imaging system for tracking a drug delivery or other medical device to a target intracranial location in conjunction with or following magnetic stereotaxis manipulation and placement of the drug delivery device in the procedure. Another aspect of the present invention is to provide an imaging system for visualizing the distal tip of the drug delivery or other medical device at the target intracranial location in conjunction with or following magnetic stereotaxis delivery of the drug delivery device in the procedure. A third aspect of this invention is to provide for an MR-compatible and visible device that significantly improves the efficacy and safety of intracranial drug delivery using MR guidance in conjunction with or following magnetic stereotaxis delivery of the drug delivery device in the procedure. A fourth aspect of the present invention is to provide for interactive MR imaging of injected or infused MR-visible drug agents superimposed upon diagnostic MR images of the local intracranial anatomy in conjunction with or following magnetic stereotaxis delivery of the drug delivery device and manipulation and placement of the device in the procedure. A fifth aspect of the present invention is provide an MR imaging method for quantitative monitoring of the spatial distribution kinetics of a drug agent injected or infused from a drug delivery device into the central nervous system or cerebrovascular system to determine the efficacy of drug delivery at various sites, such as at intracranial target sites. A sixth aspect of the present invention is to provide for magnetically responsive catheters and other drug delivery devices which can be steered by an applied magnetic field using nonlinear magnetic stereotaxis to provide directional control of the tip of the device to guide the device to targeted intracranial locations. A seventh aspect of this invention is to provide for a magnetically responsive catheter device which can be steered or navigated through bulk tissues in the brain using nonlinear magnetic stereotaxis with minimal frictional drag and minimal tissue injury. An eighth aspect of this invention is to provide for a magnetically responsive catheter device which can be guided by nonlinear magnetic stereotaxis to sites of cerebrovascular lesions, including aneurysms, stroke sites, tumors, arteriovenous malformations and fistulae. A ninth aspect of the present invention is to provide an MR imaging method to evaluate how the spatial distribution kinetics of a drug agent injected or infused from a drug delivery device into the central nervous system is influenced by infusion pressure, flow rate, tissue swelling and other material properties of the brain, and by the physicochemical and pharmaco kinetics nature of the drug or therapeutic agent infused. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side elevational view, partially in cross-section, of a retroperfusion microcatheter or other drug delivery device which might be used for infusion, retroperfusion or other purposes according to one embodiment of the present invention, that is designed to be maneuvered intracranially via nonlinear magnetic stereotaxis. The view shows the disposition of radio-opaque and MR markers, and the relationship of the osmotic pump and microdialysis probe. FIG. 2 is a view of another embodiment of the device according to the present invention, and it shows a flow diagram for practice of the process of the present invention wherein the drug delivery device is positioned by nonlinear stereotaxis under MR guidance and then delivery of a drug is monitored by visualization of delivery. FIG. 3 is a view of another embodiment of the device according to the present invention. The view shows the disposition of microcoil elements at the distal tip of the drug delivery device. FIGS. 4a and 4b show the positioning of magnetic tips at the distal end of a delivery device in two of many embodiments of the present invention. FIG. 1 shows a drug delivery catheter according to a practice of the present invention. FIG. 2 shows a sectional view of a catheter emphasizing microcatheter exits on the catheter and wiring on the catheter. FIGS. 3a and 3b show schematic representations of circuitry for the catheter of the present invention. FIGS. 4a, b, and c shows graphic respresentations of Field Strength versus distance from the center of the gap between two opposed pairs of microcoils for three microcoil structures. FIG. 5 is a flow sheet representing aspects of the invention. DETAILED DESCRIPTION OF THE INVENTION In the following detailed description of the preferred embodiments, references made to the accompanying drawings which form a part hereof, and in which is shown by way of illustration specific preferred embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, and it is to be understood that other embodiments may be utilized and that structural, logical, physical, architectural, and electrical changes may be made without departing from the spirit and scope of the present invention. The following detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims and their equivalents. The practice of certain aspects of the present invention are applicable to all medical devices which might be used with magnetic resonance imaging viewing procedures occurring concurrently with the primary medical procedure. Features of the present invention which may individually have this general applicability within the medical device field include the types of RF-responsive coils provided to medical devices to assure their MR-compatibility, circuitry associated with the devices, and means for directing microelements/microcatheter components and the like within a catheter device. The preferred construction uses an opposed solenoid orientation of microcoils with the microcoil design based on two coaxial solenoids separated by a gap region and with the current driven in opposite directions across the two coils. One individual aspect of the present invention is the use of an opposed pair(s) of microcoils to accurately define a field around the device carrying the pair(s) of coils. By an opposed pair of coils is meant coils in which the angle of their coiling or winding about an axis is different (in a positive or negative sense, either with positive degree rotation away from a line perpendicular to the surface or negative degree rotation away from the line) between two sets of coils (e.g., receiver coils), usually with the angles differing from a plane perpendicular to the axis of the object about which the coils are wound or formed by +degrees for one coil and -degrees for the other coil as measured from the plane. Other individual advances in the potential areas of practice of the present invention include the circuitry which is connected to the coils, its shielding within the device, and decoupling circuitry associated with the wires to the coils. Little specificity has heretofore been provided within the actual design and engineering details of radio frequency detectable invasive medical devices which addresses a wide range of functional needs within the device. This invention provides a substantive advance in the design of such devices. Another area of import to the present invention is the option of providing drug delivery microcatheters within the radio frequency detectable device, with the receiver coils being usable in a process for detecting the actual delivery and movement of drugs according to the invention described in copending U.S. patent application Ser. No. 08/916,596 filed on Jun. 22, 1997 in the names of John Kucharczyk and Michael Moseley. FIG. 1 shows a preferred drug delivery catheter 2 according to the present invention. The catheter 2 comprises a central lumen 4 which exits through a port 6 in a tapered end 8 of the catheter 2. A first microcoil 10 is wrapped about the lumen 4 so that the individual coils 12 generally angle away from the tapered end 8. A lead wire 14 is connected to the first microcoil 12. A second microcoil 16 is wrapped about the lumen 4 and the individual coils 18 are generally angled towards the tapered end 8. This pair of first microcoil 10 (and 32, collectively referred to as 10) and second microcoil 16 (and 18, collectively referred to as 16) form an opposed pair of microcoils. The individual coils of 10 and 32 for the relatively proximal set of microcoils 10 and the individual coils 16 and 18 for the second microcoil 16 have opposite (positive versus negative) angles with respect to a plane A-B which would be perpendicular to the lumen 4, which effectively defines an axis for the catheter 2. Note that the pair of coils may have different spacing between adjacent coils, e.g., between 13 and 15, as compared top between 15 and 17). This difference in spacing will be discussed later. A lead wire 20 passes from the second microcoil 16 to electronic circuitry 22, as does the lead wire 14 from the first microcoil 10. There is a definite separation of space between the first microcoil 10 and the second microcoil 16 within which the RF responsive field (not shown) from the coils 10 16 is the largest. It is within the space B outside of the catheter 2 in a zone defined by the opposed ends 32 34 of the two microcoils 10 16 (respectively) where delivery of drug from microcatheters 24, 26, 28 and 30 would be most effectively observed. The microcoils 10 and 16 are embedded in a support material 34 which may be a polymeric material, composite material, inorganic material (e.g., inorganic oxide) or the like. The composition of this material should be biocompatable, preferably a polymeric material such as a polyamide, polyester, poly(meth)acrylate, polyvinyl acetate, cellulose acetate, or other classes of organic polymers which are biocompatable. This support material 34 may also comprise the composition of the tapered end 8. Lead wires 36 and 38 leave the circuitry 22 for connections to outside controls and/or power sources. The ends 24a, 26a, 28a, and 30a of the microcatheters 24, 26, 28 and 30 are shown, without their connection to a delivery system or pump for provision of agents or drugs being shown. The intermicrocoil spacing B (as opposed to the intramicrocoil spacing between the opposed sets of microcoils) will usually be optimized for each type of drug delivery or other type of procedure to be practiced by the MR-compatible device 2, whether a catheter or other device. The parameters which would be considered for optimization, particularly with respect to the location of the microcoils would include at least the diameter of the field from the coils which is desired, the strength of the field, the width of the field, the number of field locations (e.g., the number of pairs of opposed microcoils), the location of the pairs of microcoils with respect to the distal end of the catheter, the location of the microcoils with respect to the point of delivery of the agents or drugs, etc. These considerations would be in addition to such engineering and other design considerations such as the thickness and size of the coils, the composition of the coils, the location of the circuitry (within the catheter or connected to an external circuitry through leads), and the composition of the other materials within the catheter construction. Within said catheter construction at the more proximal end (away from the tip) may be a plastic layer 35 (which here is shown as a continuation of layer 8), a second insulating (e.g., plastic, ceramic, or biocompatible material as with the previous description of the support material for in layer 34) layer 37 which covers and electrically insulates the leads (wires) 36 and 38, and any preamplifier which may be present associated with the microcoils, from the shielding 39 which may form a layer around (radially away from) the leads 36 and 38 and/or preamplifier. Intracoil spacing and intramicrocoil considerations (which overlaps intercoil and intermicrocoil considerations, as with respect to coil diameters) should also be considered in optimizing the design of the systems of the present invention. Coils, particularly coils such as intra-vascular RF coil in MRI, can be very useful for MR imaging of vascular lumen morphology at a reduced field of view (FOV) with a high signal to noise ratio and spatial resolution. The most promising fundamental coil design for this type of purpose is a previously published (Martin, supra) opposed solenoid coil. The reported coils are two uniformly wound solenoids of an identical geometry and uniform coil diameter placed along a common axis with a reversed polarity. That particular coil design leaves a lot of room for improvement, based upon considerations not disclosed in the reference. One basis for improvement of the functional characteristics of the signaling is that a better intra-vascular coil can be obtained with a proper optimization for the current distribution within the coils. To optimize the current distribution on the surface of the cylinder (e.g., assuming a cylindrical shape for the underlying device, such as the catheter) with respect to a set of required field constraints, an analytical formulation for the magnetic field external to a cylindrical coil has been developed and is to be preferably used for our new coil design. Such an optimized coil yields an improved field strength and field uniformity. The uniform field strength is particularly important as certain methods of use of the devices of the invention use density readings and differentiations to generate the images or provide specific types pf information within the image (e.g., the rate of delivery of a drug or the degree of effect of a treatment represented by differences in signal density). The geometry of the RF coil is, for the present analysis, based upon a small cylinder of a finite length. The current density is confined on the surface of the cylinder in the coils. Solving an appropriate static magnetic field problem for the geometry, for a cylindrical shaped coil of radius a, the radial components of the magnetic field outside of the RF coil (>a) is given as .function..rho..PHI..times..mu..times..times..pi..times..infin..infin..tim- es..intg..infin..infin..times..PHI..function..times.'.function..times.'.ti- mes..times..times..rho..times.eI.function..times..times..PHI..times.d ##EQU00001## where J.sub..phi.(m,k) denotes the azimuthal component of the surface current density in the expression above defined as .PHI..function..times..pi..times..intg..times..pi..times.d.PHI.eI.times..t- imes..times..times..PHI..times..intg..infin..infin..times.d.PHI..function.- .PHI..times.eI.times..times. ##EQU00002## and I.sub.m(t) and K.sub.m(t) denote two kinds of modified Bessel functions, of m.sup.th order, wherein m denotes an integer (e.g., 1, 2, 3 . . . ), and I'.sub.m(t) and K'.sub.m(t) represent a first derivative of I.sub.m(t) and K.sub.m(t) with respect to t. The stored magnetic energy associated with the coil is found and given analytically in a form of series expansion as .mu..times..times..infin..infin..times..intg..infin..infin..times..PHI..fu- nction..times.'.function..times.'.function..times.d ##EQU00003## Specifically for a solenoid coil or a z-coil in which the surface current density has no z-component, these expressions for both energy and field are simplified as: .mu..times..times..intg..infin..infin..times..PHI..function..times.'.funct- ion..times.'.function..times.d.times..function..rho..PHI..times..mu..times- ..times..pi..times..intg..infin..infin..times..PHI..function..times.'.func- tion..times..times..rho..times.'.function..times.eI.times..times..times.d ##EQU00004## To seek an optimal (or energy minimum) solution for current density distribution on the surface of the cylinder satisfying a set of the field constraints at some spatial locations, an energy functional construction is defined as follows, .times..times..lamda..function..rho..function..times..mu..times..times..in- tg..infin..infin..times..PHI..function..times.'.function..times.'.function- ..times.d.times..times..lamda..function..times..mu..times..times..pi..time- s..intg..infin..infin..times..PHI..function..times.'.function..times..time- s..rho..times.'.function..times.eI.times..times..times.d ##EQU00005## where represents a set of L multipliers. The field constraints specify a set of desired field values at a few points over an imaging volume of interest. Minimizing the energy functional with respect to the current density functional, the variation to respect to the current density functional is performed: .delta..times..times..delta..times..times..delta..times..times..delta..del- ta..times..times..times..lamda..times..delta..times..times..rho..function.- .delta..times..times..mu..times..times..times..PHI..function..times.'.func- tion..times.'.function..times..lamda..times..times..mu..times..times..pi..- times.'.function..times..times..rho..times.'.function..times.eI.times..tim- es. ##EQU00006## Then, the optimized current density is expressed in terms of the L multipliers as, .PHI..function..times..times..lamda..times..times..pi..times..times..times- .'.function..times..times..rho.'.function..times.eI.times..times. ##EQU00007## Since J.sub..phi.(z) will be antisymmetric in z for the desired field distribution, then its Fourier component can be expressed as .PHI..function..times..intg..infin..infin..times.d.times..times..PHI..func- tion..times..function. ##EQU00008## Inserting the expression for current density into the field constraint equations, a set of linear equation for the multipliers .lamda. can be obtained: .rho..times..times..mu..times..pi..times..times..lamda..times..intg..infin- ..infin..times..function..times..function..times.'.function..times..times.- .rho.'.function..times.'.function..times..times..rho..times.'.function..ti- mes.d ##EQU00009## Solving the linear field constraint equations for the Langrange multipliers, then the current density can be determined from the expression involving these Langrange multipliers. For an RF coil of finite length (L), the surface current density can be expanded in terms of a sine series to a desired order, .PHI..function..times..times..function..times..times..times..pi..times..ti- mes..times..times..function..times. ##EQU00010## .PHI..function..times..intg..infin..infin..times.d.times..times..PHI..fun- ction..times..function. ##EQU00010.2## .times..times..times..times..times..times..times..times..times..times. ##EQU00010.3## .times..pi..times..times. ##EQU00010.4## wherein n is an integer (e.g., n=1, 2, 3, 4 . . . ) and J.sub.n denotes a set of expansion coefficients for the current density. Then the general expression in k-space for the surface current density for the finite length coil can be written as: .PHI..function..intg..infin..infin..times.d.times..times..times..function.- .times..times..times..pi..times..times..times.eI.times..times..times..time- s..times..PSI..function. ##EQU00011## where .PSI..sub.n(k) is an odd function in k, which is defined as .PSI..function..function..times..times..function..times..times. ##EQU00012## Using the new function expansion, the corresponding expressions for stored magnetic energy and field can be written as .times..mu..times..times..intg..infin..infin..times..times..times..times..- PSI..function..times.'.function..times.'.function..times.d.times..mu..time- s..times..times..times..times..times..intg..infin..infin..times..PSI..func- tion..times..PSI..function..times.'.function..times.'.function..times.d ##EQU00013## .function..rho..PHI..mu..times..times..pi..times..times..times..times..in- tg..infin..infin..times..PSI..function..times.'.function..times..times..rh- o..times.'.function..times..function..times.d ##EQU00013.2## The desired reception field distribution external to a coil can be translated into a few field constraint points at some selected locations. For each particular design, these field constraint points are defined as: z=0.000 .rho.=r B.sub..rho.=1.0 z=0.005 .rho.=r B.sub..rho.=0.8 The constraints specify a required field homogeneity of the coil at the gap as well as the relative field strength. The field constraint equations for radial component at various points of interests can be represented as follows .function..rho..times..times..mu..times..times..pi..times..times..times..t- imes..intg..infin..infin..times..PSI..function..times.'.function..times..t- imes..rho..times.'.function..times..function..times.d ##EQU00014## For convenience, both field and energy expressions are expressed in matrix form. Among the two, the matrix elements for b are given as .mu..times..times..pi..times..times..intg..infin..infin..times..PSI..funct- ion..times.'.function..times..times..rho..times.'.function..times..functio- n..times.d ##EQU00015## The magnetic stored energy in the coil is .times..mu..times..function..times..times..times..times..intg..infin..infi- n..times..PSI..function..times..PSI..function..times.'.function..times.'.f- unction..times.d.times..times..times..times. ##EQU00016## .times..times..times..times..times..times..times..times..times..times..ti- mes..times..times..times. ##EQU00016.2## .mu..times..function..times..intg..infin..infin..times..PSI..function..ti- mes..PSI..function..times.'.function..times.'.function..times.d ##EQU00016.3## The energy functional involving the field constraints equation is defined as .lamda..function..times..times..times..lamda..function..times. ##EQU00017## To seek the minimum condition of the energy functional, the F functional is minimized with respect to the current column vector J, i.e., .differential..differential..times..times..times..lamda..times. ##EQU00018## then we arrive the following minimum condition equation involving the current density, WJ=b.lamda.J=W.sup.1b.lamda. Using the field constraint equation as another independent equation: b.sup.TJ=B.sup.0 First, the Lagrange multipliers can be solved in the following linear equation, which combines both minimum condition and field constraint equations above. b.sup.TW.sup.1b.lamda.=B.sup.0 Using these values for these Lagrange multipliers, the surface current density for the coil can be uniquely determined as J=W.sup.1b.lamda. and then the current density is .PHI..function..times..times..function..times. ##EQU00019## The total current for one half of the coil is given by .intg..times..PHI..function..times.d.times..times. ##EQU00020## If the number of turns is set to N.sub.turn, the individual current can be determined as ##EQU00021## The inductance of the coil with N turns on one half of the coil is, .times. ##EQU00022## To determine the position for each current loop, the following integration of the current density is computed from the center of the coil, .function..intg..times..PHI..function.'.times.d'.times..times..times..func- tion..times. ##EQU00023## This integration allow the finding of all the spatial intervals for a total of N different discrete current wire loops. The exact location of each wire along the z-axis can be determined as the center of mass over the corresponding interval. .intg..times..PHI..function.'.times..times.d'.intg..times..PHI..function.'- .times..times.d' ##EQU00024## In conclusion, a means for optimization of the intracoil distribution of coils within each microcoil in an opposed pair of microcoils may be based on these or alternative mathematic modeling of the effects of current, coil properties, and individual coil or winding positioning and design. This particular scheme has been developed for a cylindrical shaped RF coil, the technique allowing a straight forward procedure in performing a design optimization for the current loop positions of an intravascular, intracavitary, intraparenchymal, or intraluminary MR imaging coil. Reference to FIG. 4 (a, b and c) will help to explain the way in which modification of intracoil design can benefit performance of the catheters of the present invention. FIG. 4a shows the Field Strength (y axis) as a function of distance away from a central point in the gap (e.g., midway between nearest ends of opposed microcoils separated by a distance of 2 d, as represented by space 19 in FIG. 1). FIG. 4a shows the Field Strength relationship in a cylindrical device having an opposed pair of microcoils with equal size of the individual windings and equal spacing between each of the windings. As can be noted fro FIG. 4a, the maximum field strength Fmax is a relatively sharp peak, and the filed strength diminishes as the distance from the center of the gap (x=0) changes. At a point halfway between the middle of the gap (with a dimension of d from ends of the opposed microcoils closest to each other) and the ends of the opposed microcoils, the field strength will drop off significantly, typically between 25 and 50% of Fmax. This rapid and significant change in the field strength can reduce the capability of the device in providing the type and quality of image in certain procedures. FIG. 4b shows an idealized version of a field strength distribution which can be provided with design considerations of the location, shape, thickness and distribution of the microcoils according to the modeling considerations discussed above. The effects of each individual winding contribution can be calculated mathematically as shown above, and then the individual contributions added together to determine the effective field strength. Some interactive effects may be considered in the mathematic summation of individual winding effects, to match the more realistic field effects from the combination of coils. A more attainable field strength distribution is shown in FIG. 4c, where a less idealized, but significantly improved field strength distribution is shown. FIG. 4c shows the relationship of field strength and position along the cylindrical device where the device has an opposed pair of microcoils with a spacing of 2 d between the near ends of the opposed pairs of coils (as shown as 19 in FIG. 1) which has the sections of windings of the coils (in FIG. 1, e.g., 13, 15 and 17) differentially spaced (e.g., different spacing between windings 13 and 15 as compared to the spacing between 15 and 17 on the same microcoil). The field strength is more uniform near the center of the gap (where x=0) as compared to the opposed microcoil structure whose field strength is shown in FIG. 4a. The field strength does diminish as the distance from the center of the gap increases, but the diminution rate is less than that for the uniform coil windings of FIG. 4a, although less than that for the idealized results of 4b. The field strength can be expected to drop less than 20% between the center of the gap and a position d/2 which is one half the distance from the center of the gap to the near end of a microcoil. It is preferred that the field strength diminish less than 17%, more preferably less than 15%, still more preferably less than 12%, and most preferably less than 10 or less than 8% between the Fmax and the field strength at the d/2 point, midway between the center of the gap and a near end of the microcoil. A device according to the present invention may also be described as a medical device for use within an organism, said medical device comprising an element having at least one pair of opposed RF receiver microcoils having a space between each microcoil of said pair of microcoils, said RF receiver microcoils each comprising at least three individual coils, said at least three individual coils of said microcoils having spacing between adjacent microcoils so that spacing between at least two pairs of individual coils within said microcoils differ by at least 10%. The spacing between pairs of the individual coils (or windings) as measured along a line within the plane within which the microcoils reside and parallel to the axis of the cylinder (or other shape) on which the surface lies may be at least 12%, at least 15% or at least 20% or more, as compared to other spacings between adjacent windings to effect improved results in the field strength distribution within the gap. Another design configuration which is allowable in the structures useful in the practice of the present invention is to have two layers of microcoils within the region defining one half of a pair of microcoils. That is, a first set of microcoils angled towards the gap may be located within one layer of the MR observable device, and a second set of microcoils (e.g., a set of windings) also may be angled towards the gap, but be located within an insulated layer overlaying or underlying the first set of microcoils. The spacing between coils in the sets of similarly angled microcoils may be of the same or different thickness, the same or different spacing between coils, and/or the same or different angles (although they both must be angled towards or both be angled away from the gap). The device may have at least one set of microcoils wherein a half of said at least one pair of microcoils comprises at least four windings having at least three spaces between adjacent windings of dimensions space 1, space 2 and space 3, wherein at least one of said at least three spaces does not equal the dimensions of at least one other of said spaces. Many available technologies and structural considerations known in the art may be included within the practice of the present invention, even if some of these considerations are used within the novel structural designs of the present invention. For example, the composition of the lumen 4, support material 34, and catheter casing 40 may be selected from amongst known biocompatable materials which have been developed for medical uses. The microcoils and circuitry forming a part of the catheter system may be provided by known techniques, even if those techniques have not heretofore been used within the medical device field. For example, the microcoils could be provided by wrapping filament of conductive material (especially copper, copper coated materials, and other RF antenna materials known in the art) or by forming the filaments on or over the lumen. Such forming processes would include deposition processes, growth deposition processes, deposition and etching processes, microlithography, masked deposition, and the like. The deposition processes may include such varied technologies such as plating, electroless plating, sputtering, seeded growth, (e.g., U.S. Pat. Nos. 4,775,556 and 4,710,403), high energy deposition or etching processes (e.g., U.S. Pat. Nos. 5,389,195 and 5,332,625), chemical deposition and etching processes, etc. The techniques for providing circuitry and wiring shown in U.S. Pat. Nos. 5,106,455; 6,167,625; and 5,269,882 are examples of other technologies generally useful in the deposition of circuitry on filamentary articles and surfaces. FIG. 2 shows a sectional view of a mid-range portion of a catheter 100 according to one configuration which may be used in the present invention. A microcatheter 102 is shown to have been deflected against an internal guiding element or deflector 106 so that and end 105 of the microcatheter 102 extends out of the catheter 100 through a hole 108 in the walls of the catheter 100. The microcatheter 102 has been deflected by the deflector 104 and rests against the deflector 104 beginning at a contact point 103. The hole 108 passes through what is shown in this FIG. 2 as three layers 110, 112 and 114 of material making up the substantive walls of the catheter 100. The deflector 104 helps to guide the microcatheter 100 into and through the hole 108. There would be a hole and deflector for each microcatheter which exits from the catheter (and these microcatheters may be provided with their own intrinsic microcoils) and these microcatheters (not shown) exits from the catheter 100, unless two or more microcatheters were to exit from a single hole, which is not a preferred construction simply for the reason that this would cause a major portion of the effects of the microcatheter (e.g., drug delivery) to occur in a limited area with respect to the surface of the catheter 100. The device may have at least three deflectors for directing each of at least three microcatheters through at least three distinct ports. Also shown in FIG. 2 are a pair of microcoils 116 and 118. These microcoils 116 and 118 have been shown to be embedded within layer 112 of the catheter 100. It is highly desirable for optimal performance of the imaging and location function of the catheter 100 that signal produced by the microcoils 116 and 118 be as precise and clear as possible. The presence of other circuitry and wires within the catheter can interfere with this type of performance, and so special considerations should be taken to avoid any interference problems with the electrical and electronic functions of the various parts of the catheter and its subcomponents. For example, the wires 120 and 122 which are connected to ends 124 and 126 of the microcoils 116 and 118, respectively, must not contact the microcoils 116 and 118 except where they are intended to be electrically connected thereto (e.g., at ends 124 and 126). This can be accomplishes in a number of different ways according to the practice of the present invention. There is less structural potential for problems of this type with the proximal microcoil 116, because its end 124 may be connected to a wire 122 and not pass over the coil circuitry. The wire 122 may therefore be located within the same layer 112 as the coil 116. With the distal microcoil 118, the wire 120 must pass back over both coils 116 and 118 and could contact or otherwise readily interfere with any signal coming from the microcoils 16 and 118. To prevent this, the microcoils 116 and 118 are shown within a single layer 112, but the wire 120 from the distal microcoil 118 is shown within layer 124 to reduce or eliminate any electrical or electronic interference or interaction with the coils 16 and 118 or other circuitry (not shown) in the catheter 100. The separation of these respective elements into separate layers can be accomplished according to numerous techniques available within the general manufacturing art once the need has been recognized for the appropriate location of the elements. For example, once microcoils have been laid down (by wrapping, deposition or etching, for example), a polymer or other insulating material may enclose the microcoils in a distinct layer (e.g., layer 112). Once this protective or enclosing layer has been established (with appropriate electrical connection points maintained for other electrical or electronic connections), the other wiring or circuitry may be then constructed on that covering enclosing layer (e.g., 112). This additional wiring or circuitry may be constructed by processes similar to those processes used to make the coils or other processes known to those skilled in the art, including wrapping, gross application of premade circuitry, deposition of circuit or wire elements, etching of circuits or wire elements, and other construction or microconstruction techniques known in the art. A main objective of this optional structure within the practice of certain constructions of the present invention is to provide circuitry and/or wiring within distinct layers (even if of the same polymer binder composition) of the catheter. The location of the wiring or additional circuitry is done with an intent to minimize crosstalk, interference, interaction or other related effects which could be detrimental to the performance of the microcoils and circuitry. Specific interactive wave effects or field effects could be considered in the design of the location of the respective elements in performing these considerations. A composite catheter for MR image monitored drug delivery according to certain aspects of the present invention may concern a composite device (needle or catheter) or other with a built in micro-imaging coil for MR imaging (spectroscopy) monitoring or other physiological monitoring during a therapeutic procedure. The micro coil can be interfaced to a conventional MR scanner to image the pathological change of the region at immediate proximity to the coil as well as the therapeutic site with a very high signal to noise ratio without interrupting the drug delivering process. These types of devices will become highly desirable in the near future for many neurological transparenchymal or endovascularly therapeutic applications. One of the composite devices is shown schematically in FIG. 1. As illustrated in FIG. 1, the catheter has a number of micro size tubes 24, 26, 28 and 30 in the lumen 4 for performing various functions such as physiologic measurements, drug delivery, material withdrawal, sampling, temperature moderation or alteration, electrical stimulation, and the like. At the tip of the catheter, there exists a micro coil 10 along with a micro sized pre-amplification unit 22 for MR imaging and spectroscopy. In general, such a composite device (or catheter) includes at least a micro-imaging coil which can be broken down into four modular parts as shown in FIG. 2: 1). Optimized imaging coil or electrode 2). Pre-amplification and decoupling integrated circuit 3). Signal transmission and shielding 4). Remote matching circuit. Although these four parts are not necessarily separated from each other for a specific composite device design, the separation of modules are only meant for the ease of the following description. In most cases, some of these modules are often integrated into one composite unit. The micro coil for MR imaging can be one of the following: a single loop, twisted wires, two opposed solenoids. All of these coil designs are extremely sensitive to the immediate region close to them. The detailed spatial sensitivity profile of a specific coil depends on its conductor pattern. For the opposed solenoids, the primary magnetic field flux for reception is squeezed out at the gap between the two coils (in a direction generally perpendicular to the windings and/or the axis of the cylindrical device around which the coils are wound or formed), the number of winding required is about at least about three, more preferably between three and twenty, still more preferably between 4 and 16 for each coil, and most preferably with 5 to 12 coils with a diameter of each coil on the order of 0.1 to 2.4 mm possible, more preferably diameters of 0.3 to 2.0 mm are used, and most preferably 0.5 2.0 mm diameters are used. By depositing the coils onto the surface, wider widths of the coils may be used with less volume being taken up by the coils, with thin layers of materials being deposited as the coils (e.g., with thicknesses of a few microns being possible, up to thicknesses equal to the width of the coils) depending on the size of the catheter. Although the coil is wound or deposited on a cylindrical surface of a small diameter, there exist some degrees of freedom for optimization. For the solenoid coil design, one of the degree of freedom is the spacing between the windings. To a certain extent, the design of the micro size coil can be numerically optimized for producing a desirable reception field pattern (uniformity) in space under the geometric shape constraint imposed by a given clinical device. Using a target field method, the conductor pattern can be numerically optimized to closely match any targeted reception field pattern. The coils within the microcoils may be formed or wound with spacing of from 2.0 coil diameters between centers of adjacent coils (so that the spacing between outer sides of adjacent coils is equal to the diameters of the individual coils) up to 10 coil diameters between centers of adjacent coils (so that the spacing between outer sides of adjacent coils is equal to nine diameters of the individual coils). Preferably the spacing is between 2.5 and 8 diameters, more preferably between 3 and 6 diameters. Furthermore, the material for the wire of coil can be any non-magnetic metal or metal alloys with a similar magnetic susceptibility as that of the human tissue. For example, the preferred materials can be simply copper, silver, Al and copper-Al composite. Both copper and silver are diamagnetic, and Al is paramagnetic. For minimizing the field disturbance, the coil conductor wire can be made to have multiple concentric layers of different metallic materials (Cu .chi.=-9.7.times.10.sup.-6 and Al .chi.=+20.7.times.10.sup.-6). The exact layer thickness or radius for different metal components can be numerically optimized for different size of the wires. For a zero susceptibility cylindrical shaped wire, the ratio of the radii is given by .chi..times..times..chi..times..times..chi..times..times. ##EQU00025## To minimize the mutual coupling between the microcoil and the volume coil used for image excitation, a decoupling circuit is preferably incorporated on the micro coil. During the excitation, such decoupling circuit element makes the micro coil invisible to the volume coil by detuning the resonant frequency of the imaging coil away from the transmitting RF frequency. One of the designs accomplishing the coil decoupling requirement is shown in FIG. 3. Where the unit includes a PIN diode denoted by D in series with the two capacitors (C1 and C2), the image coil is shown symbolically and denoted by L. The PIN diode D can be actively switched on and off by an external control voltage Vd across the diode. When the diode D is switched on, the coil L and two capacitors C1 C2 form a resonant circuit tuned to the frequency. This is an improved version of he circuitry including a pre-amplification unit. The unit also may include a PIN diode denoted in series with only one capacitor, the diode can be actively switched on and off by an external control voltage. An FET (denoting a field effect transistor) may be provided for signal amplification at RF frequency. To protect the FET component or any other type of pre-amplification module during the RF excitation, a crossed diode can be placed in front of the FET, bypassing excess induced current during RF transmission. The entire coil can be a composite. In another words, the entire imaging coil can be made of multiple coil elements connected in series or in a phased array fashion for simultaneously imaging at multiple locations along a catheter. All of these multiple coils can be similar or different in their geometrical shape. The |