MEDICAL CATHETERS FOR ABLATION AND DETECTION

Abstract: Apparatus and methods for removal of obstructive material from a stent by modified electrosurgical ablation; penetrating and steering a catheter through an obstructed lumen, and detecting objects within a body via electromagnetic detection. An electrosurgical device (10) having at least one electrode (14) is positioned within the stent (20), and current is supplied to the electrode (14) to ablate material within or around the stent (20). The device may be properly positioned within the stent by using ultrasound transducers, fiber optics, impedance sensing or otherwise. In another aspect, by ablating material asymmetrically and advancing a catheter into (1010) the resulting void, the catheter (1010) can be steered through occlusive material (1060). Further, a device (2010) may be inserted within the body of a patient to determine the presence and location of an electromagnetically detectable object within the body.

Description: MEDICAL CATHETERS FOR ABLATION AND DETECTION FIELD OF THE INVENTION The present invention relates to the field of catheters that are used within a body to ablate material and find and manipulate objects within the body. BACKGROUND OF THE INVENTION The present invention has several aspects. The background of the invention is provided for the several aspects in sequence. Implantation of Stents Various methods have been used to remove obstructions from a tubular passageway (lumen) in the body of a patient. Such obstructions may occur in virtually all of the lumens in a body, and may be composed of many different substances. One example of such an obstruction is atherosclerotic plaque that may form within a coronary artery and may, if left untreated, prove fatal to the patient. However, obstructions may occur in any vein or artery such as a coronary, carotid, neurological, peripheral, or renal vein or artery. Other potentially obstructed lumens include bile ducts, all lumens of the genital-urinary tract such as fallopian tubes, and lumens of the gastrointestinal tract such as the intestines or colon. Examples of obstructive material are all forms of plaque such as fatty plaque, fibrous plaque, and calcific plaque; fibrotic material; mucous; thrombus; blood clots; and adhesions. These lumens and obstructive materials are given as examples only—many types of obstructions may occur within all of the lumens within the body. Any of these obstructions interfere with material transport and fluid flow within the lumen. In the case of the coronary arteries, such an obstruction may cause heart failure, such as a heart attack, which may prove fatal. Obstructions within other lumens cause a variety of medical problems that may vary depending upon the specific lumen and obstruction. It may be medically desirable to treat any of these obstructed lumens. A variety of methods and devices have been developed to remove these obstructions, or to at least alleviate their obstructing effect. For example, balloon angioplasty techniques include introducing a catheter having a deflated balloon into the obstructed lumen to the obstruction site, and inflating the balloon. The inflated balloon presses into the obstruction, or the wall of the lumen if no obstruction is present. Frequently, the balloon will press against both obstruction material and the wall of the lumen, as the obstruction material is not symmetrically located around the circumference of a lumen. The balloon stretches the lumen, so that the lumen is widened and the fluid flow through the lumen may be improved. However, balloon angioplasty does not remove the obstruction; instead, the balloon normally fractures plaque and stretches the elastic artery beyond its ability to recoil. A major shortcoming of balloon angioplasty is that the same elastic qualities of tissue lumens that allow them to be stretched also often cause the lumens to contract after the balloon is deflated and withdrawn from the lumen. The contracted lumen causes a restricted blood flow, so that the patient is no better off than before the angioplasty was performed, and may in fact be worse. While the angioplasty may be repeated, the operation is not without risks. Besides the risks involved in any surgical procedure, the balloon (or other mechanical) angioplasty involves a risk of rupturing the lumen. If this is a major blood vessel, as is often the case, death may result. Other complications, for example, dissections, flaps, tears, and restenosis, are also common, and may also result in severe injury and death. A solution to the problem of lumen contraction has been to insert an at least semi-rigid structure, such as a tube, into the lumen. This prevents the lumen from retracting to a smaller diameter than the tube. Such tubes are known as stents. Experimentation with stents has occurred since at least the 1960's. However, they have not come into widespread use until the 1990's. While the theory behind stents is quite simple and they have proven effective in preventing lumen restriction, complications often may arise in their use. In particular, obstructions may build up in or through the stent in much the same manner as they would if the stent was not in place, such as by, for example, tissue growth. Stents are commonly made so that they may be compressed as they are inserted through the lumen to the obstruction site, and then expanded, such as by, for example, inflating a balloon at the appropriate site. Stents are commonly made of wire mesh, although they are made of other materials and in other mechanical configurations. Other stent designs are designed to self expand and may be introduced under tension, or by other means. This mesh (or other) design gives the stents a mechanical strength that helps to prevent the lumen from constricting the expanded stent. Also, a stent is commonly designed to have a reduced surface area. The stent irritates the tissue at least to some extent and allows for thrombin, plaque, or other substances to accumulate within the interior surface or on the boundary of the stent. Such accumulation may again restrict fluid -4 - flow through the lumen, so that efficacy of the stent is reduced or, in severe cases, eliminated. Flow through a stent may also be restricted because of incomplete or otherwise improper deployment of the stent, or for other reasons. Various devices other than balloon angioplasty have been developed to remove obstructions from tissue lumens. Catheters equipped with cutting blades may be used to slice the obstruction from the lumen. Means for removing the severed obstruction must be completely effective, or the loosened obstruction may lodge in the lumen and completely restrict fluid flow therethrough. Various devices use heat to resolve obstruction material, such as are described in U.S. Patent Nos. 4,654,024 of Crittendon et al. and 4,748,979 and 4,672,962 of Hershenson. Laser angioplasty devices generally supply energy to the tip of a catheter to cauterize or burn away obstructions. See, for example, U.S. Patent Nos. 4,784,133 of Mackin; 4,685,458 of Lechrone; 4,770,653 of Shturman; 4,662,368 and 4,773,413 of Hussein; and 4,732,448 and 4,641,912 of Goldenberg. Radio frequency (RF) ablation is also known in the prior art to ablate obstruction material. In catheters, RF current is directed from an RF power source to an ablating electrode, from which the RF current travels through the obstruction material. In a monopolar device, the current return is generally through a relatively large conductive plate (patient plate) attached to the body of a patient back to the power supply. In a bipolar device, more than one electrode is present at the distal end of the catheter, and the current flows through the obstruction site between at least two of these electrodes. An RF catheter is described in U.S. Patent No. 5,454,809 of Janssen. The catheter described therein could be used in a lumen containing a stent. However, the presence of a stent causes some complications for RF ablation. The stent is, in general, formed of conductive material, such as wire mesh. If an ablating electrode came into contact with the stent, a short circuit could occur, which may damage the ablation catheter, the stent, or the lumen. However, the stent may also in some ways allow for improved ablation. One difficulty in all forms of angioplasty is determining the precise location of an angioplasty catheter within the lumen. The present invention allows for the stent to be used to determine the position of an ablating catheter, and for the subsequent ablation of the obstructive material. Another difficultly in ablation is controlling the current. The present invention overcomes these and other difficulties by providing a catheter and a method of use particularly suited to be used within a stent. Prior art has shown that the application of light may prevent restenosis and may otherwise be useful in internal surgery. Such energy application is described in, for example, U.S. Pat. Nos. 5,053,033 and 5,370,608. However, the application of such energy in connection with a stent, and particularly in the ablation of obstructive material, is unknown in the art. Steering Catheter Within Obstruction Angioplasty devices are used to treat lumens within the body that have been obstructed by an occlusive deposit, a prime example being an artery that has been partially or fully obstructed by plaque. Plaque obstructed arteries will be used to exemplify the background and representative embodiments of the present invention, it being understood that the application of the present invention is not so limited. The present invention has application to all lumens within the body any may be used to steer through, for example, fat, calcium, fiber, mucous, thrombus, adhesions, and all other obstructive material. Typically, a catheter is introduced into the body through an artery in the leg or arm and threaded to the occlusive site. The most common angioplasty technique in use today is balloon angioplasty, wherein a balloon is inflated at an occlusion site to dilate and expand the plaque into an arterial wall. Plaque is not removed by balloon angioplasty. Balloon angioplasty has several well known shortcomings. In particular, balloon angioplasty cannot be used to clear a totally obstructed lumen, because the balloon cannot in that case be passed to within the occluded vessel and then dilated. Other techniques have been developed for removing plaque from within an arterial wall. Heat can be used to resolve plaque. See for example U.S. Pat. Nos. 4,654,024 of Crittendon et al. and 4,748,979, 4,672,962 of Hershenson, and 5,009,655 of Daignault. Crittendon et al. describes a process to penetrate a completely blocked artery, by advancing a catheter having a heated tip through an artery to a completely obstructed site, and advancing the heater to soften the plaque until the obstruction is breached. Laser devices are also used to breach obstructions. See for example U.S. Pat. No. 5,484,433 of Taylor et al., which describes a laser ablating device having a selectively deflecting distal end so at least a portion of the ablation area extends beyond the cross sectional area of the catheter. RF energy may also be used to ablate an obstruction. See in particular U.S. Pat. No. 5,454,809 of Janssen which describes an RF electrosurgical catheter capable of asymmetrically resolving plaque by selectively activating at least one of a series of electrodes spaced about an electrode. The catheter may have an electrode arrangement that allows for ablation in a direction both axially to the catheter and radially away from the catheter. Before treating an occlusive deposit by ablation or otherwise, the distal end of the catheter (i.e., the end having the treating apparatus) must be placed within the lumen in contact or in close proximity to the occlusion. To this end, considerable effort has been expended in the fields of guidewires and steerable catheters. For example, U.S. Pat. No. 5,055,109 of Gould et al. and U.S. Pat. No. 4,998,917 of Gaiser et al. disclose catheters having a deflecting steerable tip. U.S. Pat. No. 5,108,368 of Hammerstag et al. discloses a catheter having what is described as a floppy tip, which may be steered by steering wires attached to a steering post at a distal end. Such steerable catheters that rely upon deflected wires or the like may or may not provide the degree of steerability that is necessary for a given surgical procedure. It is apparent that, in any event, such steering mechanisms increase the complexity, cost, and possibility of operative error. Also, it is apparent that such catheters are not particularly adapted to be steered within or through an occlusion; instead, they are generally used to steer a catheter to the site of an occlusion. Steering is generally only required for a catheter when the catheter is advancing through a curved lumen; otherwise, the catheter may simply be advanced straight ahead. Present catheters are of course capable of being inserted through tortuous lumens of the body to an 7/45157 1 -8- obstructed site. However, the steering capability does not extend to steering while a catheter is penetrating an obstruction. Occlusive deposits may occur in any portion of a lumen, and in particular in a curved portion. Advancing a catheter straight ahead in such a lumen may damage, or even penetrate, a lumen wall. That is always undesirable, and may in many cases be fatal to the patient, such as when a coronary artery is penetrated. It would therefore be desirable to provide a catheter that is steerable through an occlusive deposit. Further, it would be desirable for such a catheter to enable a user to visualize the position of the catheter with respect to the lumen, so that the catheter can be steered through a curved lumen without rupturing the lumen. Electromagnetic Detection of Objects Within a Body Recent surgical methods allow for minimally invasive surgery to be performed within the body of a patient. The word "surgery" as used herein should be understood to encompass any intervention of a foreign object into a body whatsoever, such as for exploratory, diagnostic, therapeutic, or other purposes. Typically, a catheter is inserted into the body of a patient, and surgery is performed through the catheter. This replaces so-called "open surgery", where relatively large incisions are made, allowing a surgeon direct access to the surgical site. Minimally invasive surgery causes less trauma and allows for a more rapid recovery than does open surgery. However, minimally invasive surgery adds complexity in that the surgeon cannot make direct visual contact with the surgical site. Therefore, some other means must be used to determine the position of the surgical equipment with respect to the surgical site. Several visualization methods are commonly used with minimally invasive surgery, including the use of endoscopy and similar techniques, fluoroscopy, and ultrasound transducers. However, none of these methods take advantage of the specific methods of detecting metal and other electromagnetically detectable objects that are known in other fields. Metal and other objects have electrical and magnetic properties that allow them to be sensed by suitable electronic circuity. Such circuity may take several forms, and generally operates by producing an electrical current and an associated electromagnetic field. The electromagnetic circuit parameters will be altered depending on the proximity of the detectable object. Such detectors are used, for example, for security to alert when metal objects are taken into secured areas such as airports, and in salvaging hidden metal objects, and in other applications for metal and non-metal objects. As used herein, the word metal is not restricted to any specific elements or compounds, but is meant to describe all materials that exhibit metallic properties such as conductivity and, depending on the metal, characteristic magnetic behavior. Capacitance and inductance are also parameters associated with metals and other compounds and may be used for detecting, locating, and probing objects. Further, as may be used herein "metal detection" includes all methods to detect an object by its influence upon electromagnetic probing signals, and may include classical metallic substances, magnetic substances, dielectric substances, and all other substances that may be detected by any electromagnetic means. Such substances may also be referred to as "electromagnetically detectable". As an example, a non¬ conductor such as the majority of plastic compounds act as dielectrics and therefore may be detected by measuring capacitance according to the present invention; such non- conductors are specifically included as being electromagnetically detectable as used herein. Metallic objects do not naturally occur in humans or animals; however, they may be introduced into a body for a variety of reasons. They may be introduced unintentionally (at least from the point of view of the recipient) as bullets or shrapnel. Or, they may be introduced in separate medical procedures. Many devices may be introduced into a body for therapeutic effects; examples are stents implanted within a lumen, or a pacemaker implanted to influence the beating of the heart. Metal objects may also be introduced temporarily during a surgical procedure, for the purpose of performing the surgery. In each of the above cases, it is useful for a surgeon to be able to determine the position of the metal or electromagnetically detectable object. Objects of a non-metallic nature may also be desired to be detected within the human body. Such objects may be composed of plastic, ceramic, rubber, or other materials. As one example, non-metallic stents, generally made of plastic, may be used within a lumen similarly as are metallic stents, and may need to be located within the body. Such objects' magnetic, conductive, capacitive, inductive, and other electromagnetic properties (or lack thereof) may also be detected, and their influence upon capacitive or inductive circuits may allow for their detection. Several surgical operations or procedures may be performed on or near electromagnetically detectable objects. Depending on the nature of the object, it may be desirable to, for example, insert it, install it, remove it, reposition it, or remove occluding materials from it. In each of these processes, as well as others, the position of the object must be determined. The present invention provides a device and method for the determination of the position of an electromagnetically detectable object within a body. The use of electromagnetic forces in therapeutic applications has received some attention in the past. U.S. Patent No. 5,424,641 of Ekwall discloses a magnetic field detector that, it is suggested, may be used within an implanted device such as a pacemaker. However, there is no suggestion to use the magnetic field detector to generally locate or sense metal objects that are located within a body. U.S. Patent No. 5,494,035 of Leuthold et al. discloses a device to locate a ferromagnetic object that has been implanted within a body. A magnetometer external to the body of the patient applies a magnetic field, which is affected by the presence of a metal object located within the body. There is no suggestion to apply a magnetic field through a device located within the body of the patient. Similarly, U.S. Patent No. 5,408,178 of Wikswo, Jr. et al. discloses a device that uses an externally applied magnetic field to probe an object. U.S. Patent No. 5,353,807 of DeMarco discloses a magnetically guidable medical instrument. Again, an externally generated magnetic field is used. U.S. Patent No. 5,140,265 of Sakiyama et al. discloses a device that is insertable within a body through an endoscope. The device includes eddy current detecting circuitry to probe a surface for flaws. While such a device may be useful to detect surface flaws, it is not generally useful for locating and positioning metal objects. Indeed, the Sakiyama device anticipates that an imaging device will be used in conjunction with the eddy current sensing circuitry. It can thus be appreciated that a need exists for a device that is insertable within the body of patient and may be used to locate and sense any electromagnetically detectable objects that may be found therein. The contents of all patents and other documents referred to herein are hereby incorporated by reference. SUMMARY OF THE INVENTION The present invention allows for the removal of obstructed material that has formed within a stent or other implanted device. The invention also allows for steering and guiding a catheter through obstructive material within a lumen of the body. The invention further provides for the detection and manipulation of electromagnetically detectable objects within a body. Removal of Obstructions from Stents The present invention provides a device and a method for removing obstructive material that has formed on or within a stent that has been implanted within a lumen of a subject. The device is a catheter of the type that may be inserted within any of the above discussed lumens. The device may be inserted using a guide wire of any known type, or by other guidance means. The distal end of the catheter includes means for applying ablative energy to the obstructive material. Such energy may be any electromagnetic energy delivered in any wave form or modulation, mechanical energy such as a direct mechanical force or acoustical or vibrational energy. A particularly effective form of energy is electrical current, such as radio frequency current. A device that uses current as the ablative energy has at least one electrode situated on or proximate to its distal end. The electrode is recessed from the catheter surface, or the catheter surface has spacers extending therefrom, so that the electrode is prevented from making direct physical contact with the stent. When the device is properly positioned within the stent, current is supplied from the electrode and flows through the obstructive material, thereby ablating and removing the material. Depending on the embodiment of the device, the current may also flow through the stent. This may be done by exploiting the conductive nature of a stent, or by directly grounding the stent with a stylet or probe. Alternatively, the current may be directed so as to be contained substantially within the surface or body of the stent. A plurality of electrodes may be used. The electrodes may be divided both along the longitudinal and circumferential directions of the catheter. The longitudinal divisions allow for selective, controlled ablation over the length of the stent. The circumferential divisions allow for selectively ablating nonsymmetrical obstructions that have formed around the surface of the stent. The catheter may include means to visualize the interior of the lumen in which it is inserted. Such means may include ultrasound transducers, fiber optics, or other means. The catheter may be precisely positioned based on the visualization, and, after ablation is partially performed, the catheter may be repositioned for further ablation. Such visualization techniques may also be used to determine the location of the catheter within the lumen within the framework of the stent, the location of the stent, and the composition and configuration of the obstructive material. Positioning of the catheter may be further aided by sensing the impedance between multiple electrodes on the catheter. The impedance will vary depending on whether the electrodes are within or not within the stent, because the stent is (in general) conductive and provides a change in electrical properties and propagation. For example, a stent may provide a good current path between two electrodes within the stent. By successively sensing impedance between electrodes and moving the catheter, the electrodes may be positioned within the stent before ablating energy is supplied. The catheter may be designed so that the electrode area is longer than the stent, or may be positioned so that part of the electrode area protrudes beyond the stent. The positioning of the catheter within the stent framework may be determined by selectively applying sensing signals to different electrical sensors. Once catheter positioning is detected, ablation of the obstructive material may be directed. The same electrodes may be used for sensing and ablating, or separate sensing and ablating electrodes may be provided. The device may also deliver fluid or solution through the catheter, and deliver fluid or solution through or near the distal end. Such fluid may be useful to help ablate the obstructive material, prevent or reduce restenosis, or for other therapeutic or diagnostic purposes. Further, energy may be supplied by the device to increase the efficacy of the fluid. This energy may be electrical energy supplied through the ablating or sensing electrode(s) . Or, the energy may be separately supplied, such as optical, mechanical, or acoustical energy. The energy may be continuous, intermittent, pulsed, modulated, or otherwise controlled so as to produce the maximum desired effect. The fluid or solution may contain suspended materials, chemical, or other therapeutic or diagnostic agents. If electricity is used to enhance the fluid or solution effect, the electricity may be applied to provide electroporation, iontophoresis, electro-osmosis, iontherapy, or other method of using energy to either force, assist, or increase the efficacy of the fluid or solution, or otherwise increase bioabsorption or bioavailability. The device may also include means such as electrodes to ablate obstructive material that is not within a stent. Electrodes used within a stent will normally be situated so that they do not contact the stent, else a short circuit may result. Conversely, electrodes may be intentionally designed to contact the stent so as to direct current flows, apply therapeutic energy, or otherwise produce a desired effect such as removing obstructive material or reducing or discouraging regrowth or deposition of the same. In either event, the electrodes to ablate obstructive material out of a stent should be positionable against or very close to the obstructive material. Therefore, one embodiment of the invention includes two sets of electrodes. The first set is recessed and is used to ablate within the stent; the second set is extended and used to ablate at either end of the stent. Steering Catheter The present invention provides a catheter that may be used to ablate an obstruction within a lumen, and in particular an obstruction that spans the entire cross section of a lumen. It may also be used to provide 1 4 6 -16- access through a lumen that cannot be easily passed with convention guidewires or other technologies, even if such a lumen is not totally occluded. The catheter can be steered through the obstructive material. Thus, the catheter can be used to penetrate an occlusive deposit located within a curved lumen, without penetrating the lumen wall. The catheter preferably includes and is used in conjunction with visualization means. This enables the catheter device to visualize the lumen structure, and to steer the device when the lumen curves so that the catheter remains generally centered within the lumen. The catheter has a distal end that is inserted into a lumen of the body to reach an occlusive site within the lumen and a proximal end that remains outside of the body of the patient. The catheter has ablating elements at its extreme distal end, such as radio frequency (RF) electrodes. Other elements could be used instead of or in addition to RF electrodes, such as other types or frequencies of electromagnetic energy such as lasers. It is critical that the electrodes can be focused to direct energy to specified locations within the lumen. This may be accomplished by an array of electrodes spaced around the circumference of the catheter, each of the electrodes being selectively activated. Material, such as plaque, that is in the area proximate to an activated electrode will be ablated, while material a further distance away from the electrode will not be affected. The dimensions of the zone of ablation are determined primarily by the type and amount of energy supplied to the electrode, and may be affected by other factors such as the material being ablated. Most preferably, the electrodes are configured so that they may ablate in the direction along the axis of the catheter as well as radially away from the catheter axis; stated another way, the electrodes should be both "forward firing" and "side firing". A number of electrode configurations may accomplish this result. Alternatively, electrodes with only a forward firing component or only a side firing component could be used. The catheter steering device and method of the present invention exploits the density of an obstruction site to enable steering therethrough. To move the catheter directly through an obstruction, that is, for rectilinear motion, the material directly ahead of the catheter is ablated. Depending upon the specific electrode configuration used, some material around the sides of the catheter may also be ablated. Forward ablation is accomplished by activating one or more ablating electrodes so that the RF energy is primarily focused in the axial direction. Once this void is created, the catheter is advanced into this void. It can be appreciated that this ablation and subsequent motion has the effect of moving the catheter rectilinearly, so long as the void is created primarily directly ahead of the catheter. To steer the catheter, a void is created that is offset from the catheter axis. This is accomplished by activating one or more ablating electrodes in such a manner so that material is non-symmetrically ablated with respect to the catheter direction. Pressure is then applied to the catheter. The pressure would in a uniform environment again cause the catheter to proceed directly ahead. However, the environment is no longer uniform, in that a void has been created offset to the catheter axis. The distal end of the catheter is suitably flexible so that the catheter head advances into the void instead of directly forward. This will occur so long as the force required to bend the catheter end is less than that required to force the catheter through the relatively dense obstructive material. It should be understood that the term void as used herein does not refer to a vacuum; it merely refers to an area within an obstructive site wherein the obstructive material has been ablated. Such voids could contain blood or other body fluids, or gas, or could be a partial vacuum. In any case, the ablated area will in general offer much less mechanical resistance than will the surrounding obstructive material. The above process may be repeated to continue steering the catheter. After a void is created and the catheter is advanced, another void may be created so that the catheter motion may continue. This second void could be in the same direction as the first void with respect to the catheter axis; this would further steer the catheter in that direction. Or, the second void could be directly in front of the catheter (such as by firing all electrodes or otherwise as discussed in more detail below) to resume rectilinear motion. Or, the second void could be created in yet another direction, to change the direction of catheter steering. The steering and movement of the catheter can be continuous, in that it is unnecessary to halt the movement of the catheter between electrode activations. Pressure may be continuously exerted on the catheter to advance the catheter, with voids being continuously created in front of the catheter. The location of the voids will determine the direction of catheter travel. The present invention preferably includes visualization means so that the catheter can be meaningfully steered. While the catheter may be steered for any desired reason, it is anticipated that primary application will be steering to maintain the position of the catheter within a tortuous lumen. Thus, the user of the catheter must be apprised of the curvature of the lumen. Ultrasound transducers are a preferred visualization means. A number of transducers may be used to form a transducer array, and different transducer array configurations may be used with good results. For example, the transducers may be beneath the ablating electrodes and "look through" the transducers, or the transducers may be offset from the transducers, such as by being placed further proximal on the catheter body than the electrodes. Different transducer arrays will provide different images. One useful array is a side looking array, which may be implemented by an array that forms a ring around the body of the catheter. Such an array provides a slice of a cross sectional area in the plane of the array, which is perpendicular to the catheter axis and thus perpendicular to the direction of catheter travel. The side looking array, coupled with a display such as a CRT (cathode ray tube) monitor, provides the user with a cross sectional view of the lumen, and the position of the catheter within the lumen. With this information, the user may appropriately steer the catheter. If the catheter is generally within the center of the lumen, the user can continue forward motion of the catheter. If the catheter is not in center of the lumen, the user can steer the catheter in the appropriate direction to center the catheter. The steering performed with a side looking array will not maintain the catheter within the precise center of the lumen, because the user is only alerted to the necessity of steering after the catheter is no longer in the center of the lumen. However, this is not a deficiency, because the primary purpose of steering is simply to guide the catheter through a tortuous lumen without penetrating the lumen sidewall y and it is not in general necessary to keep the catheter exactly centered. Depending upon the application, other ultrasound visualization arrays may be useful, and are included within the scope of the present invention. Control means are also included as an aspect of the present invention to allow the user to precisely guide the catheter. In connection with the steering method described above, steering control is essentially performed by selectively ablating portions of material to create a void, and advancing the catheter into the void. One steering mechanism is a joy stick, wherein moving the joy stick to different coordinates causes the electrodes corresponding to the same coordinates to fire. A button or the like can be activated to forward fire the electrode or electrodes for rectilinear motion. Other steering mechanism are described below. A second control means may be provided to assist a user in accurately determining the contours of a lumen wall. Modern ultrasound imaging may not provide a level of resolution to display a lumen wall with a high degree of clarity. Instead, a somewhat amorphous boundary is generally displayed. The boundary may appear sharper at some circumferential areas than at others. A user may select certain points that appear to correspond to the boundary of the lumen, and computer software may then select a curve of best fit to include these points and display a boundary. Alternatively, or in addition to software, the user may generate the boundary of the lumen. The present invention may thus be used to bore through an obstructed tortuous lumen without puncturing the lumen sidewall. In general, this is only the first stage of a multistage treatment for the obstruction. One therapeutic approach included as an aspect of the present invention is to first use a catheter as described above to form a passageway through an obstruction. Afterwards a second treating catheter, such as a catheter according to U.S. Pat. No. 5,454,809, may be inserted through the passageway, and additional obstructive material may be ablated. Such a regime may include further, successively larger treating catheters, and may be repeated until the obstructive material is substantially removed. The present invention has application to any lumen and obstruction within the human body. Exemplary lumens are all blood vessels, fallopian tube, intestine and all portions of the alimentary canal, bile ducts, and brain vessels. Electromagnetic Detection Within a Body The present invention is a medical device for detecting metal and other objects within a body, and a method for using such a device. Such a device has an elongate tube with a distal end and a proximal end. The distal end is insertable and manipulable within a lumen of a body, such as, for example, a coronary or peripheral artery. Detecting sensors located on or about the distal end of the catheter sense the location of an electromagnetically detectable object, and transmits this information through the catheter to a display located outside the body. The display may convey the sensed information in differing levels of detail, such as informing the user of the distance between the sensor and the object, or providing the user with a graphic of the object. Depending upon the configuration used, one or more sensors may be used to obtain more complete sensing data by comparing the received signals of the sensors. A particularly useful application of the present invention is for the detection of stents; one or.more sensors may be used to inform a user when a device enters and exits a stent, and when the device is centered within the stent. The present invention may be more generally used for any medical procedure involving metal or other compounds, to locate, position, and monitor such objects. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross section of the distal end of an embodiment of the invention, showing an electrode disposed within an elongate tube. FIG. IA is radial cross section taken along the line IA - IA of FIG. 1. FIG. IB is a longitudinal cross section of the embodiment of FIG. 1 within a stent. FIGs. IC and ID are radial cross sections similar to one FIG. IA, depicting segmented electrodes. FIG. 2 is a longitudinal cross section of the distal end of an alternate embodiment of the invention, including an electrode recessed within a ridge. FIG. 2A is a radial cross section taken along the line 2A - 2A of FIG. 2. FIG. 2B is the radial cross section of FIG. 2, showing the distal end of the device within a stent. FIG. 3 is a longitudinal cross section of the distal end of another embodiment of the invention, showing a plurality of axially spaced electrodes. FIG. 4 is a view similar to FIG. IB, showing the device in another position with respect to the stent. FIG. 5 is a longitudinal cross section similar to FIG. 2, showing the device within a stent. FIG. 6 is a longitudinal cross section similar to FIG. 3, showing the device within a stent. FIG. 7 shows an embodiment of the invention similar to FIG. 6, with the stent being grounded. FIG. 8 is a longitudinal cross section of an embodiment of the invention similar to that depicted in FIG. 3, without a longitudinally active electrode, and including therapeutic enhancers. FIG. 8A is radial cross section of FIG. 8. FIG. 9 is a longitudinal cross section of an embodiment of the invention with active electrodes of two different radial extensions. FIGs. 10A and 10B show separate embodiments of the distal end of a catheter with separate ablating and sensing electrodes. FIGs. IIA, IIB, and lie show perspective views of separate embodiments of the distal end of a catheter with a mechanical insulator to prevent contact between the electrode and stent. FIGs. 12 and 12A show an electrode arrangement and schematic respectively of embodiment of the invention using an array of interleaved active and return electrodes. FIG. 13 is a cross sectional view of the distal end of a catheter according to an aspect of the present invention. FIG. 13A is an end view taken along the line IA - IA of FIG. 1, showing an exemplary electrode configuration. FIGS. 14, 14A, 14B, 14C, and 14D are sequential cross sectional views of a catheter according to the present invention penetrating an obstruction within a non-curved lumen. FIGS. 15, 15A, 15B, and 15C are sequential cross sectional views of a catheter according to the present invention penetrating an obstruction within a curved lumen. FIGS. 16, 16A, and 16B are views of a display of the catheter position within a lumen. FIG. 17 is a view of a display and associated controls for locating a catheter position with respect to a lumen. FIGS. 18, 18A, and 18B are end-on views of electrode arrangements according to embodiments of the present invention. FIGS. 19 and 19A are side views of the distal ends of catheters according to the present invention, showing alternative shapes. FIG. 20 is a perspective view of an alternative ultrasound array positioned within a catheter, with the distal tip of the catheter cut away. FIG. 20A is a perspective view of another alternative ultrasound array positioned within a catheter, with the distal tip of the catheter cut away. FIG. 20B is a cross sectional view taken along the line 20B - 20B of FIG. 20A. FIG. 21 is a side view of a catheter according to the present invention having steering electrodes and an additional ablating electrode. FIG. 22 is a perspective view of a device according to the present invention in the proximity of an electromagnetically detectable metal object. FIG. 23 is display screen that may be included with the present invention to provide a graphic of a sensed electromagnetically detectable object. FIG. 24 is a perspective view of an embodiment of the present invention including a plurality of electromagnetic sensing elements. FIG. 24A is a perspective view of an embodiment of the present invention having a coaxial probing array with a central transmit coil and a plurality of spaced receive coils. FIG. 24B is a perspective view of an embodiment of the present inventions with the sensing portion of a catheter having a transmit coil and a single receive coil with multiple sensor taps. FIGS. 24C is a top view of an embodiment of the present invention having multiple sensing coils whose axes are orthogonal to the catheter axis. FIG. 25 is a perspective view of an embodiment of the present invention being used in conjunction with the positioning of a metal object. FIG. 26 is a perspective view of an embodiment of the present invention that includes material ablating means, along with accumulated material on a metal object. FIG. 27 is a perspective view of an embodiment of the present invention including a "GSA" catheter positioned within a stent, with the stent broken away for illustration. FIG. 28 is a cross sectional view of an embodiment of the present invention positioned within a stent at a radial offset. FIG. 28A is a side elevation view of a sensor on a catheter according to an embodiment of the present invention situated within a stent. FIGS. 29 and 29A are perspective views of an embodiment of the invention useful for retrieving or manipulating a stent. FIGS. 30, 30A, 30B, and 30C are cross sectional views of stents improperly deployed within a lumen, that may be corrected with an embodiment of the present invention. FIGS. 30C and 30D are elevation cut-away views showing improperly deployed stents similar to FIG. 30. DETAILED DESCRIPTION OF THE INVENTION The present invention allows for the removal of obstructed material that has formed within a stent or other implanted device. The invention also allows for steering and guiding a catheter through obstructive material within a lumen of the body. The invention further provides for the detection and manipulation of electromagnetically detectable objects within a body. Removal of Obstructions from Stents FIG. 1 shows a longitudinal cross section of the distal end 10 of a catheter to remove an obstruction from the lumen of a patient, where the obstruction is surrounded by a stent. The catheter is constructed of an appropriate size and of appropriate materials so that it may be inserted within and along a lumen, as is known in the art. A common method of catheter insertion is to use a guide wire. Such a guide wire may pass at least partially through the catheter, and may be passed through a lumen by itself or through a guiding catheter. The guide wire may be first extended to a desired position in front of the catheter, and the catheter may then be advanced over the guide wire. The guide wire may pass through the entire body of the catheter, or may only pass through a section of the catheter, such as a port located near the distal end. Alternatively, the guide wire may simply be an extension from the end of the catheter, and the guide wire and the catheter may be advanced in unison. The present invention has application with any guide wire system which mechanically guides the catheter to its desired destination. It may also have an active guidance system on the same catheter, or may be used with no guidance system. The body of the catheter is formed primarily by a catheter wall 11, that is tubular and defines a bore within the catheter. The distal end 10 of the catheter may be positioned, for example, by the use of a guide wire, where the guide wire is threaded through the lumen to the obstructed site. The catheter may then be passed over the guide wire to the site. Additional means for positioning the catheter are discussed below. An electrode 14 is disposed within the bore of the catheter proximate the distal end 10. The electrode 14 may be annular and may surround the interior bore of the catheter, as shown in the radial cross section view of FIG. IA. The electrode 14 is recessed within the bore of the catheter, so that a lip 12 of the catheter wall 11 extends radially, but not distally, beyond the electrode 14. In an electrically ablating embodiment, the catheter wall is made of an insulating material, such as any of a number of plastics. The electrode 14 is in electrical communication with a power source, such as an RF or other power source. The RF power source generates and supplies current of a suitable wave form to the electrode 14 to ablate obstructive material. The wave form may also, or in addition, be applied to enhance the bioabsorption or otherwise increase the utility of medicine or other fluids delivered through the catheter, as discussed previously and below. FIG. 4 shows the distal end 10 of the catheter after it has been positioned within a lumen that has been implanted with a stent 20. The stent 20 has a tubular body that is positioned against the bore of a lumen. Stents are most commonly made of metal wire, although other materials and configurations are used, and may be used with the present invention. Obstructive material 24 7/451 4 -28- is shown disposed between the stent 20 and the distal end of the catheter 10. As an example, this obstructive material may be clotted blood that has formed from the lumen wall through the openings of the stent. However, this obstruction could be any obstructive material found within any lumen, as has been described above. The obstructive material restricts the effective diameter of the lumen implanted with the stent 20 and therefore interferes with flow of fluid (or other substance) therethrough. It is thus desirable to remove these deposits 24. This may be done by inserting the distal end 10 of the catheter through the stent 20, until the distal end has substantially passed through the stent 20. From this point, the catheter is withdrawn from the stent 20, so that its path is retraced. Visualization means 16 may be included within the distal end 10 of the catheter, so that an operator of the device may be apprised of the exact location of the distal end 10 of the catheter in relation to the stent 20. The visualization means 16 may be ultrasound transducers that are coupled to suitable ultrasound processors, although other visualization techniques such as, for example, fiber optics, or electrical impedance sensing, may also be used. The visualization means 16 may provide information as to the amount of obstructive material, its physical configuration and location, and type of material that may be within, or outside of, the stent. The visualization means may include sensing of any other parameters of the stent, obstructive material, or lumen. The catheter operator may then precisely guide the obstruction removal process. The visualization means 16 may be used in conjunction with ablation, so that after material is ablated, visualization is again performed, the catheter is positioned to a new location, and ablation is again performed. The process may be successively repeated. The visualization means may be used, where practical, to determine the progress of the obstructive material removal, and the approaching of the outside of the lumen. For example, within a coronary artery, the thickness and composition of the plaque and approaching the intima, media, or adventitia. The stent may also be marked with radiopaque markers and be seen using fluoroscopy techniques. Such markings, if present, may be used in conjunction with, or instead of, the visualization means 16 to determine the position of the stent 20 within the body of a patient. Conversely, the stent may be made of material which renders it highly radiopaque and makes it impossible to quantify flow or luminal opening within the framework of the stent by conventional dye injection. The imaging/visualization technique within the catheter will allow visualization in that event. As the catheter is withdrawn, the electrode 14 will pass beneath all of the obstruction material 24 within the stent 20. When it is detected that the electrode 14 is beneath an obstructive site 24, current is applied to the electrode 14. As the electrode 14 is proximate the distal end 10 of the catheter, a path exists between the electrode 14 and the obstructive material 24 around the lip 12 of the catheter. The current travels this minimum path to the obstructive material 24, and thereby ablates the material 24. FIG. IB shows the catheter in a retracted position through the stent 20. As can be seen, the obstructive material distal to the distal end 10 of the catheter has been ablated. The obstructive material 24 proximal to the electrodes 14 will be ablated as the catheter is further withdrawn. When the catheter is completely 1 46 -30- withdrawn from the stent 20, virtually all of the obstructive material will have been ablated. It can be appreciated that the configuration of the electrode 14 prevents contact between the electrode 14 and the stent 20. Contact is blocked by the lip 12 of the catheter wall 11. This prevents a possible short circuit that may occur if the electrode was to contact the stent 20. The return current from the electrode 14 to the power supply may be accomplished in several ways. A patient plate may be located on the body of the patient, and in electrical communication with the power supply. Alternatively, a bipolar embodiment could be used, as discussed below in connection with other embodiments. It should be appreciated that while selective activation of the electrode 14 has been described as the catheter is withdrawn, any other activation method could be used. For instance, the electrode 14 could be activated as the catheter is advanced. Or, the electrode 14 could be activated when the catheter is motionless, or in any other manner, or a combination of such methods may be used. Particularly if the stent 20 is made of metal or another electrical conductor, the stent 20 may act as a virtual ground, thereby protecting the lumen in which the stent is implanted. The above embodiment has been described as having a single electrode 14. However, multiple electrodes could be used instead. One configuration is to arrange electrodes around the circumference of the catheter, as shown in FIGs. IC and ID. In FIG. IC, two electrodes 14a and 14b, each having a circumferential arc of approximately half the circumference of the catheter are used. Each electrode 14a and 14b could be activated individually, to selectively ablate obstructive material proximate the electrodes. FIG. ID shows a catheter with three electrodes 14c, 14d, and 14e arranged around the circumference of the catheter. This allows for greater resolution of ablation for non-symmetric obstructions. Of course, more than three divisions may be used, allowing for still greater resolution. The use of multiple electrodes is discussed in greater detail in the context of alternative embodiments of the invention, below. While the above embodiment has been described as using electrosurgical ablation, it should be appreciated that other forms of ablation may be similarly used. For instance, the ablation may occur as the result of standard electrosurgical wave forms of cutting or coagulation, customized wave forms, dc current, pulsed current, modulated current using any combination of modulating and carrier wave forms, laser energy of any frequency and modulation, direct mechanical energy, acoustical or ultrasonic energy, direct application of thermal energy, or corrosive chemicals. Referring to FIG. 2, an alternate embodiment of a distal end 30 of a catheter is shown in longitudinal cross section. The distal end 30 is formed by a catheter wall 31. The distal end 30 is preferably tapered, so that the catheter may be smoothly advanced through a lumen. A recessed annular ridge 33 defines a groove in which electrodes 34a, 34b, 34c, and 34d are seated. As shown in the radial cross section of FIG. 2B, the electrodes 34 substantially surround the surface of the distal end 30, but are separated by thin strips of the catheter wall 35, so that they are electrically isolated from one another. The electrodes 34 are sized so that they are recessed within the annular ridge 33. A return electrode 36 is located on the catheter proximal to the electrodes 34. The electrode 36 may surround the catheter wall 31, or may have any other shape. The electrode 36 has a relatively large surface area compared to the surface area of each of the electrodes 34, so that the current density through the electrode 36 is low enough to prevent damage to tissue adjacent to the electrode 36. FIG. 5 shows the catheter of FIG. 2 within a stent 20 implanted within a lumen. The catheter may be positioned in the stent by the use of the visualization means 37. As discussed above, these visualization means may include ultrasound transducers, fiber optics, or any other visualization means. Referring to FIG. 6, the catheter may be withdrawn or advanced through the stent, and any of the electrodes 34 may be activated when the electrode passes obstructive material 24. The circumferential division of electrodes 34a, 34b, 34c, and 34d allows for greater selectivity of obstruction ablation. Obstructions may or may not be located symmetrically around the circumference of a lumen or a stent. Therefore, it may be desirable to apply ablation selectively around the circumference of the catheter. Referring to FIG. 2B, the catheter of FIG. 2 is shown within a stent 20 with electrodes 34a and 34b adjacent obstructive material 24, and electrodes 34c and 34d not adjacent obstructive material. In that case, electrodes 34a and 34b may be activated, and electrodes 34c and electrodes 34d may be made inactive. Of course, suitable electric switching apparatus must be included in the circuit linking electrodes 34 and the power supply generator, as is well known in the art of electronics. In this example, current will flow from the electrodes 34a and 34b, through the obstructive material 24, and to the return electrode 36. The obstructive material 24 will be ablated in this process. It should be appreciated that the current flow may be directed in a number of variations. The current flow may be from an active electrode, through the stent, and to the return electrode or electrode(s) . The current flow may also be directed so as to keep more or less of the current flow within the framework of the stent. While the above embodiment has been described with a return electrode, ablation could be performed without a specific return electrode, so that the current returns to the power supply through capacitive coupling, or through an electrode attached to the patient's skin. The return electrode 36 may be sized so that it will contact the stent 20, thereby grounding the stent. This will lower the impedance between the return electrode 36 and the electrodes 34, and allow for precise ablating of obstructing material between the electrodes 34 and the stent 20. However, it may be inconvenient to have the electrode 36 sized to contact the stent 20, because the electrode may then interfere with the longitudinal motion of the catheter through the stent 20. One solution to this problem is to use an inflatable balloon located beneath the electrode 36 to selectively increase the diameter of the catheter at the position of the electrode 36. The balloon may be deflated when the catheter is moved through the lumen, and may be inflated when the movement of the catheter is halted and current is applied through the electrodes 34. Good results may be also be obtained without placing the electrode 35 in direct electrical communication with the stent 20. Further, if a metallic stent 20 is used, electricity will flow through the stent 20, instead of the surrounding tissue, because of the superior conductance of metal, thus causing the stent to act as a virtual ground. The division of the electrodes 34 into four units is shown as an example only, it being understood that either more or fewer divisions could be used. A non-segmented, unitary electrode could be used as described in the embodiment shown in FIG. 1, although this would not allow for circumferentially selective ablating. More than four segments would allow for more circumferential selectivity, although, after a point, such selectivity may be unnecessary. The precise number of divisions is a matter of design choice and may depend on the specific application. Another embodiment of the distal end 50 of a catheter according to the present invention is shown in longitudinal cross section in FIG. 3. A catheter wall 51 defines the body of the catheter. A series of five electrode rings 60, 62, 64, 66, and 68 are disposed around the distal end 50. Five rings are shown and described only as an example; any number or rings may be used with good results depending on the specific application. Each ring may be either a solid ring and thus form a unitary electrode, or may be segmented into separate electrodes as described above. The use of segments allows for circumferentially selective ablation. Each ring (and ring segment, if a segmented ring is used) may be individually activated by being placed in electrical communication with the power supply. The catheter wall 51 includes spacers 61, 63, 65, and 67 that project axially away from the catheter axis. The spacers are situated between electrode rings, and have a diameter greater than the rings, so that the electrodes are prevented from contacting rigid objects external to the catheter. In one embodiment of the invention, each of the rings 60, 62, 64, 66, or 68 may be used as either an active or a return electrode. Thus, any combination of the electrodes may be selected as active electrodes, and any combination of electrodes may be selected as return electrodes. FIG. 6 shows the distal end 50 of the catheter situated in a stent 20, including obstructive material 24. Preferably, the section of the distal end 50 including electrodes 60, 62, 64, 66, and 68 is longer than the stent 20. Good results may be obtained if the active electrode area is approximately the same length as the stent 20, or a considerably longer distal end 50 may be used, such as one with a length in the range of, for example, about two to ten times the length of the stent 20. The catheter preferably includes means to sense the impedance, including the resistance, capacitance, and inductance, between a selected active electrode and a selected return electrode. Such impedance detectors are well known in the art of electronics and may take a variety of forms, generally sensing the amount of power required to produce a given current flow between two electrodes, as well as other parameters. Impedance sensing allows for the determination of the position of the distal end 50 with respect to a metallic stent 20. To position the catheter, an electrical signal may be sent to one of the electrodes, such as the middle electrode 64. This signal is preferably of a significantly lower magnitude, and may have other electrical parameters, than the ablating current that may be transmitted through an electrode when ablation is desired. The other electrodes 60, 62, 66, and 68 will be sequentially selected as the return electrodes. The impedance sensed between the electrode 64 and the 1 466 -36- selected return electrode will vary depending on the position of the distal end 50; if both, the electrode 64 and the selected return electrode are enclosed within the stent 20, the impedance between the electrodes will be much lower than if either both of the electrodes are not within the stent or if only one electrode is within the stent. This is because a metallic stent 20 is a better conductor than the ordinary fluids and tissue found within the body of a patient, so that impedance will be lower when the signal travels through the stent 20 rather than simply through the body. In the context of FIG. 6, a relatively high impedance will be found between electrode 64 and electrode 60, because electrode 60 is not within the stent. A relatively low impedance will be found between electrode 64 and electrode 62, because electrodes 62 and 64 are within the stent. Likewise, the impedance will be relatively low between electrodes 64 and 66, and will be relatively high between electrodes 64 and 68. The values of what impedance values are relatively low and what are relatively high will depend to some extent on the specific catheter design and the stent configuration. The catheter may be calibrated through routine experimentation so representative values of the impedance between a specific set of electrodes for a given position in relation to a stent may be obtained. After performing the above impedance sensing, it will be known that electrodes 64, 66, and 62 are within the stent and that electrodes 60 and 68 are not within the stent. Ablation may then be performed, directing the current between electrodes 62, 64, and 66. Electrodes 60 and 68 will remain electrically inactive and will not take part in the ablation. It may happen that none of the electrodes are within the stent 20. In that event, a relatively high impedance will be found between all of the electrodes. The distal end 50 of the catheter may then be repositioned, and impedance sensing being again performed. Successive iterations of impedance selection and distal end 50 movement may be performed until the distal end is within the stent 20. The desired position is that the stent 20 be completely filled by the distal end 50, so that there is no section of the stent 20 that does not contain an electrode. In the above described embodiment, the stent 20 is not grounded. However, as explained above in connection with the impedance sensing, the stent may conduct current and therefore act as a virtual ground, shielding all tissue located exterior to the stent. Therefore, higher currents may be used while reducing the risk of damaging the lumen wall in which the stent is located. These currents will ablate the obstructive material 24 located within the stent. However, the current may be contained within the stent by use of appropriate energy, if desired. It should be appreciated that the distal end 50 used within the catheter is exemplary only, and that many modifications could be made, such as in the number and configuration of electrodes. For instance, the catheter of FIG. 3. is shown with the most distal ring 60 being tapered along with the extreme distal end 50 of the catheter. This allows for "forward" ablation, i.e., ablation longitudinal to the axis of the catheter. However, a modified distal end 80 as depicted in FIG. 8 shows a series of electrode rings 82 without a forward facing distal electrode ring. Instead, the most distal of the rings 82 surrounds the catheter and does not have a distally projecting component. Spacers 81 insure that the electrode rings 80 are separated from the stent. Also, the impedance sensing may be performed otherwise than explicitly explained above. For instance, it is not necessary to use the middle electrode in impedance sensing—any set of electrodes may be used. As another example, one electrode could be selected as active electrode and the remainder of electrodes could be simultaneously selected as a return electrode, allowing for simultaneous impedance sensing and location determination. It may be desirable to modify the above embodiment to directly ground the stent. While the stent acts as a virtual ground in the above example, a direct electrical connection will improve the shielding effect of the stent. One method of grounding the stent is through the use of conducting connecting stylets or probes 70 and 72, as shown in FIG. 7. The stylets or probes 70 and 72 are at their proximal ends placed in electrical communication with the power supply. The distal ends of the stylet or probes protrude from the body of the catheter until electrical contact is made with the stent 20, as shown in FIG. 7, thereby grounding the stent 20. The positioning of the stylets or probes 70 and 72 may be performed by any means to position wires within a lumen, such being routinely performed in, for example, the insertion of guide wires into a lumen. The stylets or probes 70 and 72 may be maintained within the catheter until the distal end 50 is correctly positioned, so that they will not interfere with the motion of the catheter through the lumen. After the catheter is positioned and the stylets or probes 70 and 72 are attached and ablation is performed, the stylets or probes may be retracted into the catheter and the catheter may be removed from the lumen. Non-retractable stylets or probes may also be used. In the above embodiment, sensing the electrical parameters as modified by the presence of the stent has been described using the same electrodes that may also be used to perform ablation. However, different electrodes could be used to perform sensing than perform ablation. FIG. 10A shows a section of a catheter distal end with a series of ablating electrodes 100 and a separate series of sensing electrodes 110. The sensing electrodes may, but need not be, smaller than the ablating electrodes, as in general the sensing electrodes will supply less energy than the ablating electrodes. FIG. 10B depicts an alternate embodiment of a catheter with separate ablating electrodes 120 and sensing electrodes 130. The sensing electrodes need not be annular; they may be window-like recessions or have any other form. The ablating electrodes may also have any configuration as discussed above. Any of the above described catheters or variations thereof may be further modified by the addition of electrodes that may be effectively used to ablate obstructive material in a lumen that is not contained within a stent. An example of such a catheter is shown in FIG. 9, depicting the distal end 90 of the catheter. The distal end includes two electrode rings 94 that are radially spaced away from the body of the catheter, and two electrode rings 92 that do not radially extend as far as the electrode rings 94. The electrode rings 92 will thus be shielded from a stent in which the distal end 90 of the catheter is placed, by the protrusion of the electrode rings 94. While in a stent, the electrode rings 94 act as spacers similar to the spacers 61, 63, 65, and 67 shown in the embodiment depicted in FIG. 3. When the distal end 90 is positioned within the stent, the electrodes 92 may be activated to ablate any obstructive material within the stent. When the distal end is not positioned within a stent, the electrodes 94 may be positioned directly against obstructive material and activated so as to ablate the material. When a stent is not involved, it is generally desirable to maintain actual contact or near contact between an ablating electrode and obstructive material. The electrodes may be activated as the catheter is projected through a lumen, or withdrawn, or when the catheter is held steady. The electrode rings shown in FIG. 9 may be solid rings or may be segmented in any manner, as discussed above. Further, it should be understood that the number and configuration of electrodes in FIG. 9 is only to illustrate the concept of using separate electrodes within and without a stent. Any number of rings could be used, in any configuration. Separate spacers instead of electrodes could be used. Or, recessed electrodes could be used instead of spacers, as described in an above embodiment. The electrodes to be used within a stent may be positioned on a separate section of the catheter instead of being commingled with the electrodes to be used out of the stent. Other catheter configurations may be used to separate the electrode(s) from physically contacting the stent. FIGs. IIA, IIB, and 11C show perspective views of three different insulation patterns where insulation covers an electrode. In FIG. IIA, approximately spherical holes in an insulation sheath 140 prevent physical contact between an electrode 142 and a stent. In FIG. IIB, cross hatching in the insulation sheath 150 shields and electrode 152. In FIG. 11C approximately rectangular holes in an insulation sheath 160 shield an electrode 162. The number and dimensions of the holes or cross hatches is determined by the minimum exposed area necessary for ablation, and the maximum insulated area required to insure non-contact with the stent frame. The mechanical insulator may be of any design or shape, or suitable material; the patterns of FIGs. IIA, IIB, and 11C are merely representative patterns. The substrate used in the fabrication of the insulation may be the same as the catheter tubing. However, any substrate having suitable mechanical and electrical properties may be used. The insulation may be used with any number of electrodes, of any shape and configuration. With reference to FIGs. 12 and 12A, a further electrode arrangement is provided that allows for another method of varying the electric field and current density supplied by the electrodes. The arrangement further provides for increased flexibility of the portion of the catheter that supports the electrodes. As shown in FIG. 12, the distal end of a catheter may include perforated insulation 170 similar to that described in connection with FIG. 11. The insulation depicted in FIG. 12 is similar to that of FIG. IIA as an example only—other insulation could be used with good results. The insulation 170 perforations expose an electrode array having interspaced positive (or signal) electrodes 180 and negative (or return) electrodes 190. The positive electrodes 180 are arranged in parallel, as are the negative electrodes 190. The electrodes are arranged so that the positive electrodes 180 are spaced about the catheter in a plurality of rings. The negative electrodes 190 are similarly spaced about the catheter. Each positive ring may be substantially coincident with each negative ring. However, the actual position of the positive and negative electrodes are tangentially offset so that no surface area of the catheter has both positive and negative electrodes. The physical interrelationship of the positive and return electrodes allows for increased control of the electric field, compared to an arrangement that does not have interleaved positive and negative electrodes. The use of a plurality of smaller electrodes allows for greater flexibility of the catheter head, because the catheter body is in general more flexible than the electrodes. The use of numerous, separated electrodes allows the catheter body to flex in between the electrodes. A solid electrode that surrounds the catheter body, or a major portion of the catheter body, in contrast, prevents the catheter from flexing. A less flexible catheter may interfere with the physical insertion of the catheter through a lumen or stent. The parallel electrical circuity is depicted in FIG. 12A. FIG. 12A depicts a representative portion of positive electrodes 180 and negative electrodes 190, not the entirety of the electrodes. As can be seen, the positive electrodes 180, separate positive electrode "rings" 180 are connected in parallel with one another, as are separate negative electrode 190 "rings", with the positive and negative electrodes intermeshed with each other. Another aspect of the invention is the ability to supply fluids through the catheter and introduce these fluids into the lumen in which the catheter has been inserted. With reference to FIG. 8, the catheter includes fluid ducts 86 and 88 which extend to the distal end of the catheter. Fluid ports 87 and 89 allow fluid to be introduced into the lumen from the fluid ducts 86, 88 respectively. Such fluid is typically medicine to enhance the ablating, therapeutic, or diagnostic process in conjunction with the electrode ablation. The fluid may be deposited, or even forced, from the ducts 87 and 89 into the surrounding tissue. Along with the fluid deposition, the catheter may include means to enhance the effect of the fluid on the surrounding tissue. Such means may include, but are not limited to, the application of electrical energy, such as by the electrodes 82; any other electromagnetic energy such as light; mechanical energy such as direct stimulation; ultrasound or acoustic or other vibrational energy. Such means may be applied prior, during, or subsequent to the application of fluid, or in any combination of these time periods. Such means, in addition to the electrodes 82, may be conveyed through the body of the lumen, as shown in cross section in FIG. 8A. A guide wire 100 may be used to position the catheter to the desired site, along with any desired visualization means as described above. The fluid is delivered through ducts 86 and 88. Ducts 110 and 120 may deliver therapeutic energy, as discussed above, to be used in conjunction with the fluid. The fluid delivery system with therapeutic energy may be used in conjunction with any of the described embodiments, or any variations thereof. Also, the fluid system is not limited to two ducts—one duct or any number of ducts may be used to deliver as many types of fluid as is desired. The fluid need not be liquid; it may be gaseous or in any other form. In addition, a suction duct 130 may be used to remove substances from the lumen, such as therapeutic fluid, obstructive material, or any other substance. Also, while two fluid ports have been described, any number of fluid ports, including one or more, could be used. PC / 96/18466 -44- Steering Catheter The distal end 1010 of a catheter, according to one embodiment of the present invention is shown in cross section in FIG. 13. The distal end 1010 as used herein refers to the end of an elongate catheter tube that is insertable within a lumen of the body of a patient; the opposite end of the catheter is termed the proximal end and remains exterior to the body. The extreme distal end is further referred to as the tip 1012. One embodiment of the tip 1012 tapers conically in cross section as depicted in FIG. 13; other embodiments having different shapes are discussed hereinbelow. The tip 1012 supports a plurality of circumferentially spaced electrodes 1020, denoted as 1020a, 1020b, 1020c, and 1020d (as seen in FIG. 13A) . The electrodes are capable of supplying RF ablating current, and are selectively activatable so that any one or more of the electrodes may conduct current at any time, as controlled by a user. Details as to the structure of a cathode including selectively activatable ablating electrodes may be found in U.S. Pat. No. 5,454,809. As with the tip shape, other numbers of electrodes besides the four depicted can be used. The electrodes 1020 extend over portion of the tip 1012 that is tapered in cross section, as well as a portion of the tip that is untapered. The tapered portion of the electrodes 1020 may be termed "front-firing" in that a significant component of RF current flow is in the direction of the catheter axis. The untapered portion of the electrodes may be termed "side-firing" in that the primary direction of current flow is radially away from the catheter axis. Each electrode 1020 thus has a front- firing and side-firing component. The catheter tip 1012 preferably includes means for a user to visualize the area surrounding the catheter, such an ultrasound array 1030. The ultrasound array 1030 may be a side looking array, in which case the array will be a band of ultrasound elements annularly spaced about the tip 1012 circumference. While the array 1030 is depicted as being substantially on the surface of the catheter, it should be appreciated that the array 1030 could be located somewhat beneath the catheter surface. The flexibility of the catheter tip 1012 may be different than the flexibility of the catheter section 1014 proximal to the tip. A differently flexing catheter tip 1012 relative to the catheter section 1014 may allow the catheter to be inserted from the exterior of the body through a lumen (or series of lumens) to an obstruction site. The relative flexibility of the catheter tip 1012 allows for steering the catheter through an obstruction site. With reference to the sequential series of FIG. 14 to FIG. 14D, the catheter distal end 1010 is shown in cross section penetrating an occlusive deposit 1040 that is within a lumen 1050. In FIG. 14, the catheter has been inserted through the lumen until the distal end is approximately at the surface of an obstruction. This point may be determined by, for example, the use of a guidewire that has been inserted to the obstruction site. The guidewire cannot be inserted further, because it cannot penetrate the obstruction. This lack of motion allows the user to determine that an obstruction has been reached. Angiography or other techniques may also be used to determine the location of an obstruction. The electrodes 1020 are fired to create a void 1042, as shown in FIG. 14B. The electrodes 1020 are fired to create the void 1042 directly in line with the catheter axis. This may be done by firing all electrodes 1020a - 1020d simultaneously. The forward firing component of the electrodes will create a component of the void in line with the catheter. The side firing component of the electrodes 1014 will create a component of the void radially away form the catheter; stated another way, the void 1042 will have a somewhat greater cross section than that of the catheter tip 1012. Since all the electrodes are fired simultaneously, the void 1042 is essentially symmetrical with respect to the catheter axis. As shown in FIG. 14B, the catheter tip is inserted into the void 1042, until the catheter is again approximately at the surface of the obstruction. The catheter has thus been advance partially through the occlusion. The electrodes are again fired, to create another void 1044, as shown in FIG. 14C. The void 1044 is created in exactly the same manner as the void 1042, so that the void 1044 is in-line with the catheter end 1012, and of a somewhat greater diameter than the catheter. The above process is successively performed until the catheter distal end 1012 has completely breached the occlusive deposit 1044, as shown in FIG. 14D. It should be understood that what have been described as voids 1042 and 1044 are for the purposes of illustration, and do not necessarily correspond to non-overlapping, physically distinct areas. The ablation process could be formed continuously, so that the electrodes are firing and the cathode is moving simultaneously, and the void is being progressively made through the occlusive deposit. In the sequential views of FIG. 15 to FIG. 15D, the catheter tip 1012 is shown penetrating an occlusive deposit 1060 within a curved lumen 1070. The curved lumen 1070 may represent any lumen within the human (or even non-human) body. All lumens do in fact have at least some radius of curvature; lumen 1070 represents a lumen that has an obstruction that extends a significant distance in respect to a the curvature. In this context, "significant curvature" includes the occurrence where a straight line segment beginning at approximately the center of one end of an obstruction would penetrate the sidewall of the lumen before clearing the other end of the obstruction. In such a situation, a catheter incapable of turning is incapable of clearing such an obstruction, as it would penetrate the lumen sidewall (and thus seriously injure or kill the patient) before boring through the obstruction. In FIG. 15, the catheter tip 1012 is shown partially penetrating the obstruction 1060. At this point, the catheter tip 1012 has been introduced identically as in FIG. 14 above. That is, the electrode 1020 has been activated to create a void in the obstructive material 1060 directly in line with the catheter, and the catheter tip 1012 has been advanced. The lumen can be seen to curve substantially at line A-A. Thus at this point it is desirable to steer the catheter so that it tracks the curvature of the lumen 1070. In FIG. 15A, the void 1072 has been created in the obstructive material by activating the electrodes 1020 of the catheter. However, the electrodes are activated selectively so that the void 1072 is not in line with the catheter; instead, the void is created primarily in the direction of the lumen 1070 curvature. This is done by selectively firing one (or more) of the electrodes 1020a - 1020d. To create the void 1072, the electrode 1020c is activated. (Electrode 1020c is merely used as an example; any of the electrodes 1020 may be activated depending upon the specific orientation of the catheter) . This creates forward ablation area, because of the forward firing component of the electrode 1020c. The side firing component creates what is shown to be a downward area of the ablation void 1072. As shown in FIG. 15B, the catheter tip 1012 is next advanced into the void 1072. The flexibility of the tip 1012 and the density of the obstructive material 1060 cause the tip 1012 to enter the void 1072 instead of continuing rectilinear motion. It can be appreciated that the catheter has now been steered, and has been redirected to follow the path of the lumen. As shown in FIG. 15C, another void 1074 is created ahead of the catheter tip 1012. The void 1074 is shown to be directly axially in line the catheter tip 1012. The void 1074 is created identically to the voids 1042 and 1044 previously described, such as by firing the four electrodes 1020a - 1020d simultaneously. The catheter tip may then be advanced into the void 1074. The void 1074 is selected to be directly in line with the tip to correspond to the curvature of the lumen 1070. The asymmetrical ablation 1072 substantially tracks the curvature of the lumen 1070 at line A-A, and the lumen 1070 is straight thereafter. If the lumen 1070 were further curved, another asymmetric ablation zone would be created to further steer the catheter tip 1012 to correspond to the curvature of the lumen 1070. As described above, a catheter according to the present invention cai penetrate an obstructed, curved lumen. Thereafter, a second treating catheter can be steered through the path created, and further ablate (or otherwise treat) the occlusion site. As one aspect of the invention, the second catheter is substantially identical to the first catheter except that it has a larger diameter, so that the size of the penetrative path is increased. Multiple iterations of inserting progressively larger catheters may be performed as described above. Alternatively, or in addition to using iterations of catheters, other debulking techniques may be used to further clear an obstruction. A catheter according to the present invention including such debulking means in described below in connection with FIG. 21. The steering technique described in connection with FIG. 15 is primarily useful along with visualization so that the catheter may be steered to correspond to the curvature of the lumen. FIGS. 16, 16A, and 16B show sequential views provided by the ultrasound array 1030. In FIG. 16, the side looking ultrasound array 1030 samples are depicted on a display monitor 1080. The monitor 1080 may be a CRT screen, or any other display means such as LCD screen or the like. The catheter tip 1010 appears as a vacant circle (assuming a catheter of circular cross section is used) . This is because the ultrasound array looks away from the surface of the catheter tip 1010, and receives no input from within the catheter body. Obstructive material 1060 may appear in various shades of gray (shown as cross-hatch) . (Of course, the monitor 80 could display any other desired representations.) The material 1060 may be used to determine the location of the lumen 1070 sidewall, because the actual sidewall of the lumen may or may not in general appear on the ultrasound visualization monitor 1080. If it does not, the user must determine the approximate location of the lumen 1070 sidewall. This may be done by visually determining the most exterior -50- gray scale, and constructing the position of the lumen 1070 therefrom. FIG. 17 shows an aspect of the invention that assists a user in determining the lumen 1070 sidewall position. It should be understood that the device and method of FIG. 17 is only one technique that may be used, and is not essential to practice the invention. A pointing device such as a mouse 1102 is engaged with the monitor 1080. Both the mouse 1102 and the monitor 1080 may be engaged with a control device such as a computer 1100. The user clicks the mouse 1102 when the cursor 1062 is located at the gray scale area of the obstructive material 1060 that appears to correspond to the lumen 1070 sidewall. The computer 1100 can generate a projection circle (or other shape) of best fit to approximate the lumen 1070 sidewall. The computer 1100 may then query the user to determine if the user agrees with the generated circle (or other shape) ; that is, to see if the generated circle appears to correspond to the lumen 1070 sidewall as displayed on the monitor. A targeting circle 1090 (or other desired shape or indicator) is generated by the computer 1100 at the center of lumen 1070. The position of the catheter tip 1010 is compared to the position of the targeting circle 1090 to determine the proper direction of steering. In FIG. 16, the tip 1010 is approximately coincident with the targeting circle 1090. This indicates that the catheter tip 1010 is centered within the lumen 1070. In this case, rectilinear motion of the catheter is desirable to maintain the centered position of the catheter. FIG. 16A depicts the imaging of the lumen 1070 when the catheter is no longer centered. Such imaging may correspond to the catheter position depicted in FIG. 15. The lumen 1070 has curved, so that the catheter O 97/4 5 -51- tip 1010 appears non-centered with respect to the targeting circle 1090. To re-center the catheter, the user ablates obstructive material 1070 non-symmetrically, in the direction from the catheter tip 1010 towards the targeting circle 1090. In the catheter location illustrated in FIG. 16A, the catheter must be steered in the "downward" direction. This corresponds to the ablation void created by the electrode 1020c. The user may then activate electrode 1020c, and thereafter advance the catheter into the resultant void. The computer 1100 can display on the monitor 1080 the electrode configuration in relation to the ablation direction, to assist the user in determining the proper steering direction. In FIG. 16B, the catheter tip 1010 is shown being centered with respect to the targeting circle 1090; this would correspond to the position of, for example, FIG. 15B. The user may then forwardly ablate and move the catheter, as described above. It should be appreciated that "downward" does not necessarily correspond to a specific external direction, but is merely describes a reference direction. The electrodes 1020 remain in fixed relation to the ultrasound array 1030, so that any offset between the catheter tip 1010 and the targeting circle 90 can be reduced by ablating the obstructive material in the apparent direction between the tip 10 and the targeting circle 1090. An embodiment of the present invention preferably includes a joy stick 1104 engaged with the computer 1100 that allows the user to selectively activate any one of the electrodes 1020. In the embodiment using the four spaced electrodes 1020a - 1020d above described, the joy stick 1104 can be manipulated in the four compass /18466 -52- directions, each direction corresponding to an activation of one of the electrodes 1020a - 1020d ^ Thus, the user will move the joy stick in the direction most closely matching the direction of offset between the catheter tip 1010 and the targeting circle 1090. The joy stick 1104 preferably includes an activator such as a button that simultaneously activates all of the electrodes 1020. This button will be activated to create a void directly in front of the catheter, and should be used when the catheter tip 1010 is essentially centered within the targeting circle, as in FIG. 16B. Other steering means may be included besides (or in addition to) the joy stick 1104. The computer 1100 may include voice recognition hardware and software so that a user can control ablation by speaking. For instance, the computer 1100 could may recognize the command "ablate forward" to activate all electrodes 1020a - 1020d simultaneously. The computer could recognize other commands to active individual electrodes. Voice recognition may be particularly beneficial because the operator may also be advancing the catheter with using hand-operated controls and may therefore not have his or her hands free to manipulate a second set of controls. Another control that may be useful is a touch sensitive monitor 1080, which may be the simplest control for a user to operate. Other control means may also be used, such as, for example, a track ball, keyboard, touch pad, laser pointer, or any other device. The computer 1100 may automatically select an ablation direction, select an electrode 1020 to effect the desired steering to move the catheter in that direction, and query the user whether to perform the ablation. The computer 1100 may select the direction by comparing the targeting circle 1090 position and the lumen 1070 position, and attempting to center the targeting circle. Such an automated control allows for ease of operation, and still allows for the user to directly monitor the steering process. The above embodiment have been described as having four ablating electrodes 1020a - 1020d. However, it should be appreciated that other number of ablating electrodes may be used. FIG. 18 shows an embodiment of a catheter having two ablating electrodes 1110a and 1110b angularly spaced about the catheter tip. Such a device would not have as great a steering resolution has the embodiment having four electrodes, but may be sufficiently steerable for some applications. FIG. 18A shows an embodiment of a catheter having three electrodes 1112a, 1112b, and 1112c angularly spaced about the catheter tip. Such a device would have intermediate resolution between an the embodiment of FIG. 18 and the embodiment having four ablating electrodes. Another catheter arrangement is shown in FIG. 18B. Here, five electrodes are arranged about the catheter tip. Electrodes 1114a, 1114b, 1114c, and 1114d are angularly spaced about the catheter tip, similarly to the electrodes 1020a - 1020d described above. Electrode 1114e is located in the center of the catheter tip. Activating electrode 1114e will ablate an area directly in front of the catheter, and is used when the catheter is to be advanced directly ahead without steering. Electrode 1114e corresponds to simultaneously activating electrodes 1020a - 1020d described above, in that it is used for forward ablation. However, electrode 1114 could be used while also activating one or more of electrodes 1114a - 1114d, to adjust the degree of forward and side ablation to a desired amount. It should be appreciated that the catheter could have more than five electrodes, either with or without a center firing electrode, to obtain a desired amount .of resolution. With reference to FIG. 19, the catheter tip may have shapes other than the conical shape described in connection with FIG. 13. FIG. 19 shows what may described as a rounded catheter tip 1120. The cross sectional view of the tip generally terminates at a circular arc. This profile may, in some applications, advance more smoothly through a lumen than the catheter tip of FIG. 13. FIG. 19A shows what may be described as a "bullet tip" 1130. The cross sectional view of FIG. 19A follows a curve that is somewhat more tapered than the rounded tip of FIG. 19. The precise amount of curvature can be varied as desired. The tip of FIG. 19A may more smoothly slide through a lumen than does the catheter tip of FIG. 13, depending upon the lumen and obstructive material contained therein. The electrode arrangement of the tips of both FIG. 19 and 19A may be in any configuration described hereinabove. With reference to FIG. 20, an alternative ultrasound array 1140 is disclosed. The array 1140 is "forward looking", in that the array members are substantially perpendicular to the catheter 1142 axis. The array thus generates waves in the direction of the catheter axis, so that the resulting image is a view of the area in front of the catheter 1140. The array may be located within the body of the catheter 1142, and looks through the extreme distal tip 1144 of the catheter 1142. This may be done by signal processing, wherein the known acoustical effects the catheter tip 1144 (and other constants) may be filtered. Alternatively, the forward looking array 1140 may be positioned on the catheter tip 1144 itself. The forward looking array 1140 may provide somewhat simpler steering options for the catheter user, because the image corresponds to the direction of catheter travel. Another alternative ultrasound array 1150 is depicted within a catheter 1152 in FIGS. 20A and 2OB. The array 1150 is shaped as a segment of a cone, with the axis of the cone being the catheter axis. The cone may have any angle, 45 degrees being a representative value. The conical array 1150 shape will give information in both the forward and side directions of the catheter. In a sense, the ultrasound array 1150 is a combination of the side looking and forward looking arrays discussed above. A shallow cone segment has a higher forward looking component, and a steep cone segment has a higher side looking component. The conical array provides a user with information about a lumen directly in front of the catheter and to the side of a catheter. Useful information may exist both in front of and to the side of the catheter. For example, it may be easier to sense information about the location of obstructive material in front of the catheter, and to sense information about the lumen curvature from the side of the catheter. It should be understood that shapes other than a cone could be used to generate a forward and side looking component, and they are included within the scope of the invention. For instance, the array could be a segment of another sold such as a paraboloid or a pyramid. Another ultrasound embodiment is described with reference to FIG. 20C. In FIG. 20C, the ultrasound array includes four planar segments 1154a, 1154b, 1154c, and 1154d disposed within a catheter 1155, the catheter 1155 incorporating any of the other embodiments disclosed herein. Each segment 1154 includes a plurality of array elements. The segments 1154 are sloped from the catheter axis towards the more proximal area of the catheter 155. Each segment has a front edge relatively closer to the axis and a back edge relatively further form the axis, and the segments are circumferentially spaced about the catheter. Any of the above described arrays may incorporate variable phasing. That is, the individual array elements can be activated in different timing relationships, which can effectively shape the ultrasound signals to provide a variably focused array, and to sense in more than one direction. This may be particularly effective in connection with the embodiment of FIG. 20C, as shifting the phase can adjust the look between the longitudinal and radial directions with respect to the cathether. With reference to FIG. 21, another embodiment of the invention is a catheter 160 having a proximal ablating electrode 1164 in addition to steering electrodes 1170. The steering electrodes 1170 may be of any type described above or any variation thereof, that may be selectively activated to steer the catheter 1160 through a lumen. The steering electrodes 1170 are positioned on a tip 1166 that is of smaller diameter than the catheter 1160 section proximal to the tip 1166. The ablating electrode 1164 is located just proximal the tip 1166, and may be activated to ablate material within a lumen. An advantage of using the wider ablating electrode 1164 in conjunction with the steering electrodes 1170 is that the steering electrodes 1170 may allow for more precise steering through a lumen, while the ablating electrode 1164 may ablate a greater amount of material. The electrode 1164 could be replaced with segmented electrodes. Further, it may possible to use an ablating electrode that does not have a larger diameter than the steering electrodes. W 7 1 -57- As yet another aspect of the present invention, the ablation and steering of a catheter as.described above may be performed using other forms of energy besides RF to create the voids used for steering. These other forms of energy include, without limitation, laser energy, ultrasound or other acoustical energy, non RF electrical energy, thermal energy, and direct mechanical energy such as cutting blades. These other forms of energy have been used to bore through an obstruction. However, these forms of energy may be used to create a non-symmetrical void with respect to a catheter axis. The catheter than may be moved into the void. The process may be repeated to steer the catheter in a desired direction, substantially as described above. A catheter using a non-RF ablative energy may be constructed using appropriate modifications to any of the embodiments described above, as may be understood by one skilled in the art. Electromagnetic Detection Within a Body The use of catheters and similar insertable devices within the body of a patient allows for minimally invasive surgical procedures to be performed; these procedures may be less traumatic and more effective than traditional open surgical procedures. As useful as such surgical devices are, their use presents a number of difficulties. One of these difficulties is accurately determining the position of the device within the body of the patient. Since the devices are used within the opaque body of a patient, direct visual observation is not possible. Even in more traditional open surgery, the precise location of medical instruments or other objects within a body in not always readily observable. W /4515 -58- Metal objects do not naturally occur within the bodies of human beings or similar animals. However, such objects may enter and remain lodged within a body, either intentionally or unintentionally. For example, bullets or shrapnel may enter and remain within the body of a patient. Other objects, both metals and non-metals, such as metal tools, may also enter the body. Proper medical attention may call for the removal of such objects. Electromagnetically detectable objects may enter the body during the course of medical treatment, and may remain within the body for various lengths of time. Some objects may only be intended to remain within the body during the performance of a specific surgical procedure. Other objects may be implanted on a more permanent basis. For instance, a stent may be inserted within a lumen of a body to improve or maintain fluid (or other material) flow through the lumen. Such a stent may be intended to be permanently implanted within the body. However, the stent may be improperly inserted, and require subsequent removal or adjustment. Or, the stent may eventually become obstructed with any of a variety of obstructive materials. In all of the aforementioned situations, it is desirable to know the position of a metal or other electromagnetically detectable object within the body of the patient. Methods currently exist that allow the determination of objects within a body: fiber optics, fluoroscopy, ultrasound, and other methods are used with varying degrees of success. However, none of these previous methods capitalize on electromagnetic detection techniques. A device with electromagnetic detection circuitry can determine the location of metal and other objects within the body of a patient using electromagnetic detection principles, and avoid some of the hazards, complications, and expenses associated with previously known visualization means. An embodiment of the invention is displayed in FIG. 22. A catheter 2010 may be inserted into the body of a patient, such as through a lumen to reach a stent 2008. Depending on the procedure used, the catheter 2010 operator may or may not be able to directly observe the device. Visualization techniques such as IVUS, angioscopy, ultrasound, fluoroscopy, and others may, but need not, be used with the present invention. The catheter 2010 includes a sensor 2020 that provides a signal responsive to the location of the stent 2008 (or any other electromagnetically detectable object) with respect to the sensor 2020. The sensor outputs a signal proportionate to its distance from the stent 2008. The sensor 2020 may be wound induction coils of the type that generate a magnetic field, and detect the variance of the field in response to an electromagnetically detectable object. The sensor 2020 may also include electrodes, in a plate or any other configuration, of the type that generate an electric field, and detect the variance the field in response to the proximity of metallic, magnetic, dielectric, or other materials. Such detectors are well known and are used for purposes such as locating concealed metal objects secreted on persons entering secured areas, finding coins or other metal and non-metal objects buried under sediment, and for other purposes. Other detecting circuity schemes, such as those incorporating piezoelectric circuit elements, are also known and included within the scope of this invention. Specific embodiments of the present invention may detect an object through the measurement of capacitance or inductance as well as through eddy current detection. The sensor may be in communication with a display 2030 that provides the user with an indication of the location of the sensor 2020 with respect to the object such as the stent 2008 (see FIG. 23) . The location information may include several parameters, depending upon the application. With reference to FIG. 28A (which also illustrates aspects of an embodiment discussed below) , the axial location may be monitored. The axial location refers to the location of the sensor 2090 (and catheter) along the longitudinal axis of the stent 2080. The display 2030, of various types described below, begins to indicate as the sensor approaches the stent, maximizes when the sensor is centered within the stent, and minimizes again as the sensor exits the stent. With reference to FIG. 28, the radial location of the sensor may also be determined. The radial location refers to the location of the sensor 2090 in relation to the sidewall of the stent 2080. The display indicates the position of the sensor in what are labeled as both the x and y coordinates of the stent 2080. The display 2030 may provide more or less detailed information depending on the specific application. For example, the display 2030 may provide audible information through a speaker 2032 that varies as the sensor 2020 is positioned within or around the stent 2008. The audible information could vary in pitch, tone, modulation, volume, etc. For example, the pitch could increase as the sensor 2020 is positioned within the stent 2008 and would be at a maximum pitch (or other parameter) when the sensor was centered within the stent. In that event, as the catheter is manipulated within the lumen, the operator will be continuously informed of the location of the sensor 2020 with respect to the stent 2008 and of any changes thereof. Another effective display 2030 is a visual display that indicates the location of the sensor 2020 with respect to the stent 2008. The visual display may have a linear progression of lights, wherein, for example, a greater segment of lights are illuminated as the sensor is centered within the stent. The lights may be of any type, such as an LED (light emitting diode) , LCD (liquid crystal display) , or CRT (cathode ray tube) . Other indicators may also be used, such as various types of scopes (for example, an oscilloscope) , or meters (for example, a d'arsonval meter) . In these cases the output signal would be at a maximum (or minimum) when the sensor is centered within the stent. The display may be calibrated so that the display displays a given indication depending on a predefined location of the sensor 2020 with respect to the stent 2008. Alternatively, the display could display the actual location of the sensor 2020 with respect to stent 2008, such as by using any of the above described display elements to display a numerical quantity representing distance or another parameter. More complex displays may also be included in the present invention. For example a display 2036 may generate a graphic of the stent 2008 (see FIG. 23) . The display 2036 may be a computer controlled LCD or CRT screen or any other display capable of displaying two dimensional (or more) graphical data. The graphic may be formed as the catheter approaches and is oriented around the stent 2008. In this way, an image of the stent 2008 may be formed by combining the data sensed by the sensor 2020 when the sensor 2020 is oriented at different positions. More complex graphics may be generated, among other ways, by including a plurality of sensors 2022 on the catheter (see FIG. 24) . Each of the plurality of sensors 2022 will individually sense the proximity of the stent 2008. By combining the data from each of the plurality of sensors 2022, a more complete graphic of the stent may be formed than when only one sensor 2020 is used. Moving the sensors 2022 with respect to the stent allows for a still more accurate graphic to be generated. With reference to FIG. 24A, another arrangement useful for stent detection (among other applications) is provided. A catheter has a central transmit coil 2024, and a plurality of receive sensors 2025a, 2025b, 2025c, 2025d, 2025e, and 2025f spaced on either side of the transmit coil 2024. The distance between the receive sensors 2025a and 2025f should be greater than the length of a stent to be detected by the catheter. This allows for precise detection of the stent. While only one transmit coil 2024 is shown, more than one transmit coil may be provided. Also, six receive sensors are only provided as an illustrative example, and more or fewer may be used. With reference to FIG. 24B, an alternative sensor arrangement is shown that is also useful for stent detection. Here, the catheter has a central transmit coil 2028 and a single receive coil 2029, the receive coil 2029 being preferably longer than the stent detected by the catheter. The transmit coil 2028 is preferably centered within the receive coil 2029; more than one transmit coil 2028 may also be used, in which case the transmit coils would be spaced so that the midpoint of the aggregated transmit coils is approximately centered within the receive coil 2029. The receive coil 2029 has a number of sensor taps 2029a, 2029b, 2029c, 2029d, 2029e, and 2029f, preferably arranged symmetrically about the midpoint of the coil 2029. The center most taps 2029c and 2029d are most preferably spaced so that the length between them is marginally shorter than the length of the stent. The exterior sensor tap groups (2029a and 2029b; and 2029e and 2029f) may be spaced more closely together than are taps 2029c and 2029d. This arrangement allows for precise determination of when the sensing portion of the catheter enters the stent, from either direction, and also for a precise determination of when the sensors are centered within the stent. The taps 2029c and 2029d allow for centering detection, and the exterior tap groups allow for accurate determination of when the catheter is entering or exiting the stent. Another embodiment of the invention is illustrated with reference to FIG. 24C. A probing array 2110 is provided that has an axis orthogonal to the axis of a catheter 2108. The probing array 2110 may consist of one or more transmit coils 2112 co-planar with one or more receive coils 2114. The embodiment of FIG. 24C, two transmit coils 2112 are wound within one receive coil 2114. However, it should be appreciated that the probing array could comprise other numbers of transmit and/or receive coils. The receive coils could be within the transmit coils. The coils may be wound around either a ferromagnetic or non-ferromagnetic core. The probing array 2110 generates a field primarily orthogonal to the catheter axis. This field will be normal to a stent (or other object) that is generally parallel to the catheter axis. The field may thus generate more eddy currents than coaxial probing array, which may improve sensitivity. With reference to FIG. 25, the catheter 2010 may be used in the positioning of an object as well as the location and detection of an object. This would be performed similarly to the locating of the object (such as the stent 2008) described above. However, the location of the stent 2008 would be sensed repeatedly while the stent is being positioned. For instance, the catheter 2010 may be held fixed, while a separate positioning tool 2006 is used to move the stent 2008. As the stent 2008 is moved, the movement is monitored by the sensors 2022, and displayed to the operator. Either a linear display could be used to display parameters such as the distance from the stent to the sensors 2022, or a graphical display means as described above could be used. The operator may adjust the positioning of the stent 2008 depending on its sensed location, to interactively achieve the desired position. With reference to FIG. 26, the catheter is also useful for treating or otherwise working with deposits or other materials located on or around electromagnetically detectable objects found within the body of a patient. For example, an implanted electromagnetically detectable object 2040 may accumulate plaque 2042 after it has been in the body for a period of time (see FIG. 26) . Besides plaque; mucous, fat, fiber, or other natural or unnatural undesirable material may form around or on a metal or other electromagnetically detectable structure. There are a number of ways to treat such material, such as, for example only and without limitation: balloon angioplasty, laser ablation, electrical ablation such as RF (radio frequency) , mechanical cutters, and other methods. In all of these methods, it is generally desirable for the operator of the treatment device to be aware of the ablating means of the device with respect to the unwanted material. Frequently this is critical, because the device may remove desirable instead of undesirable tissue if the device is activated improperly. FIG. 26 shows the an ablating device 2050 in the proximity of an electromagnetically detectable metal implant within a body. As the device is positioned with respect to the implant, sensors 2060 detect the location of the implant. The operator of the device may reposition the device until the ablating means 2070 are in the desired range of operation with respect to the implant. The position will vary somewhat depending on the type of ablating device 2050 that is used. For example, a mechanical cutter will be positioned so that the cutting element contacts the obstructive material. An RF or a laser ablation device may be operated somewhat further from the implant. Regardless of the specific device, the spatial relationship between the ablating means 2070 and the implant can be correctly maintained by manipulating the device in response to its location as sensed by the metal detecting sensors. Once properly positioned, the ablating means 2070 may be deployed to remove the plaque 2042. Another useful embodiment of the invention is in connection with a "GSA" catheter (guided selective atherectomy, a trademark procedure of Advanced Coronary Intervention, described generally in U.S. Pat. No. 5,454,809), as may be understood with reference to FIG. 27. A "GSA" catheter 2090 is positioned within a stent 2080. The "GSA" catheter 2090 has four active electrodes, 2100, 2102, 2104, and 2106, spaced around its circumference. Each of the four electrodes has a matched sensor: sensor 2101 with electrode 2100, sensor 2103 with electrode 2102, sensor 2105 with electrode 2104, and sensor 2107 with electrode 2106. In "GSA" operations, the electrodes may be operated independently of one another, so that an electrode may be activated only when needed, thereby reducing trauma to surrounding tissue. In the example shown, each sensor may provide information for determining when to activate an electrode. An electrode may be activated when it is within a predefined distance form the stent 2080. This avoids problems associated with activating an electrode when it is too close to the stent 2080 (possible short circuit) or too far from the stent (ineffective ablating) . The sensor allows an operator to determine when the stent is within the predefined operating range. It can be appreciated that the sensor allows for positioning in both the axial direction of the stent (and catheter) , and the radial direction. FIG. 28 shows the catheter at a radial offset within a stent; by comparing signal strengths at the sensors, the radial offset of the catheter may be determined. It should be understood that the catheter 2090 is illustrative only, and that many changes could be made while still embodying the concept of a sensor or sensors in use with a "GSA" catheter. For example, as few or many electrodes as desired may be used. Further, the number of electrodes need not correspond to the number of sensors. Also, "GSA" is only one illustrative surgical technique that may benefit from the present invention. Another application of an embodiment of the present invention is described in connection with FIG. 2008. A catheter 2120 may include a sensing probe(s) 2130 according to any above described embodiment of the invention and a hook 2140 to assist in the proper placement of a permanent or temporary implantable device. Such a device, for example, a stent 2008, may not be radiopaque and thus cannot be located by the use of x-ray of similar techniques. The catheter 2120 may be include means to deploy a stent, such as inflatable balloon (not shown) , and the location of the stent 2008 may be confirmed during the implant procedure. The same deployment device 2120 could be used to confirm the stent 2008 location after deployment. The device 2120 could be used in retrieval (see FIG. 8A) or repositioning of the stent 2008 if it is not correctly positioned. Such a deployment and/or retrieval device may be used to monitor and correct any deficiency in the stent deployment process. The stent 2008 may be not fully deployed within a lumen 2140 as in FIG. 30 (cross- section) , not roundly deployed as in FIG. 30A (cross- section) , irregularly deployed as in FIG. 30B (cross- section) , having mis-deployed struts as in 30C (side view) , collapsed as in FIG. 30D (side view) , or inadvertently deployed within an interior arterial wall as in FIG. 30D (cross section) . Aside from the above described embodiments and applications, the present invention may be used either as described or with modifications in conjunction with other therapeutic and diagnostic catheters, probes, scopes, and devices. The devices may work with any occlusion, such as plaque, mucous, fat, fiber, adhesions, or other natural or unnatural occlusive deposits. The device may be useful in the treatment, diagnosis, and removal of any of the above described types of material. Additionally, the device may be useful for accessing arteries, veins, capillaries, fallopian tubes, urethra, the alimentary canal, or other lumens or conduits within any body cavity, tissue, organ or structure. This accessing may be done in conjunction with other procedures, such as cut down, surgery, or needle puncture. While the device has been discussed in the context of minimally invasive surgery, it should be understood that is only an exemplary use, and that the present invention may be useful in a wide range of medical applications. It should be further understood that the invention is not limited to the specific applications described. For example, the device could be used for animal as well as human subjects. The subject may also be non-living. For example, the device may be useful to locate and aid in the extraction of electromagnetically detectable objects from a cadaver. It should be understood that any aspect of the invention disclosed herein could be combined with any other aspect to effect a desired result.

Claims: CLAIMS The invention claimed is: 1. A device for ablation of obstructive material within a stent, the device comprising: an elongate flexible tube having a distal end and a proximal end and an interior surface therebetween; a first electrode proximate the distal end; a power supply in electrical communication with said electrode; and wherein said first electrode is shielded from physical contact with the stent when the first electrode is positioned within the stent. 2. The device of claim 1, wherein said first electrode is located on the interior surface of said elongate flexible tube, and said elongate tube has a lip extending distal to said first electrode. 3. The device of claim 2, further comprising a first plurality of electrodes on the interior of said elongate flexible tube proximate the distal end, said electrodes being circumferentially spaced about the interior of the tube; and the power supply allowing current to be selectively supplied to any of the plurality of electrodes. 4. The device of claim 3, further comprising a return electrode in electrical communication with the current supply, the return electrode being attachable to a patient. 5. The device of claim 3, further comprising means for visualizing the location of said distal end of said elongate tube and determining the composition and amount of the obstructive material. 6. The device of claim 5, wherein the means for visualizing include an ultrasound transducer. 7. The device of claim 5, wherein the means for visualizing include fiber optics. 8. The device of claim 5, wherein the means for visualizing include fluoroscopy. 9. The device of claim 1, wherein said tube has a groove proximate said distal end; said first electrode being situated within said groove; and said first electrode being sized so that it does not fill the groove. 10. The device of claim 1, further comprising a plurality of grooves within said tube and a plurality of electrodes, wherein at least one of said plurality of electrodes is situated in each of said plurality of grooves. 11. The device of claim 9, further comprising a return electrode located on said tube. 12. The device of claim 11, wherein said return electrode may be positioned so as to physically contact said stent. 13. The device of claim 1, further comprising a plurality of electrodes located on said tube, at least some of the plurality of electrodes being located further distal on the catheter than other of the plurality of electrodes; and the current supply allowing each of the plurality of electrodes to independently receive current. 14. The device of claim 13, wherein at least one of the plurality of electrodes may be alternately made a supply or return electrode by the current source. 15. The device of claim 13, further comprising means for sensing the impedance between at least two of said electrodes. 16. The device of claim 15, further comprising spacers disposed about said tube proximate said electrodes, said spacers projecting radially further from the tube than said electrodes. 17. The device of claim 16, wherein said plurality of electrodes are arranged in a series of rings located around said tube. 18. The device of claim l wherein the electrode directs current distal to the distal end of the device. 19. The device of claim 1, further comprising a second electrode, the second electrode projecting radially further from the axis of tube than the first electrode. 20. The device of claim 19, further comprising a first plurality of electrodes and a second plurality of electrodes; each of the first plurality of electrodes being shielded from contact with the stent when each of the first plurality of electrodes are positioned within the stent; and each of the second plurality of electrodes extending further from the tube axis than each of the first plurality of electrodes. 21. The device of claim 1, further comprising means for delivering bioactive fluid exterior to the tube. 22. The device of claim 21, further comprising means for delivering energy to increase the bioactivity of the fluid. 23. The device of claim 22, wherein the energy to increase the bioactivity of the fluid consists of electrical energy, optical energy, mechanical energy, or acoustical energy. 24. The device of claim 1, further comprising at least two sensing electrodes proximate the distal end, and means to sense the impedance between the sensing electrodes. 25. The device of claim 1, further comprising insulating material that partially covers the electrode. 26.. The device of claim 25, wherein the insulating material is perforated. 27. The device of claim 25, wherein the insulating material is cross hatched. 28. The device of claim 1, further comprising: a first plurality of electrodes including the first electrode, the first plurality of electrodes being disposed about the distal end of the catheter; a second plurality of electrodes, each of the second plurality of electrodes being disposed about the distal end of the catheter; the first plurality of electrodes being interspaced with the second plurality so that members of the first plurality alternate with members of the second plurality across a portion of the distal end of the catheter; and wherein the first plurality are electrically interconnected in parallel to a first polarity and the second plurality are electrically interconnected in parallel to an opposite polarity. 29. The device of 28, wherein the first plurality of electrodes and the second plurality of electrodes are arranged in a series of spaced rings. 30. A method of removing obstructive material from the interior of a stent implanted in a subject, comprising: engaging said subject with an elongate electrosurgical device including a proximal end and a distal end an electrode proximate said distal end; positioning said device so that the electrode is at least partially within the stent; supplying current from a current source to said electrode to ablate said obstructive material. 31. The method of claim 30, wherein the positioning step includes using visualization means to visualize the position of the distal end in relation to said stent. 32. The method of claim 30, wherein the visualization means include ultrasound transducers. 33. The method of claim 30, wherein the visualization means include fiber optics. 34. The method of claim 30, wherein said device contains at least two electrodes proximate said distal end, and the positioning step includes determining the position of the distal end in relation to the stent by establishing current flow between at least two of said electrodes and determining the impedance therebetween. 35. The method of claim 34, further comprising the step of establishing direct electrical communication between said stent and said current source. 36. The method of claim 30, further comprising the step of supplying bioactive fluid through the device to medicate said subject. 37. The method of claim 36, further comprising supplying energy to increase the bioactivity of the fluid. 38. The method of claim 37, wherein the energy to increase the bioactivity of the fluid consists of electrical energy, optical energy, mechanical energy, or acoustical energy. 39. The method of claim 30 further comprising the step of ablating material exterior to said stent, the step of ablating material exterior to said stent being performed by a second electrode. 40. The method of claim 30, wherein the positioning step includes measuring the impedance between at least two sensing electrodes located on said device. 6 -74- 41. A therapeutic method to increase flow through an at least partially obstructed lumen, comprising the steps of: deploying a stent within the obstructed lumen; inserting a catheter within the stent, during or after the stent deployment step; and using the catheter to ablate obstructions from the stent. 42. The method of claim 41, wherein the step of using the catheter to ablate obstructions includes performing RF ablation. 43. A device for penetrating occlusive material within a lumen of a body, the device comprising: a catheter body insertable within the lumen, the body defining an axis therethrough, the catheter body terminating at a distal tip; ablating means on the catheter for ablating a portion of the occlusive material distal to the distal tip to create a void; whereby the catheter is insertable within the void to penetrate the occlusive material. 44. The device of claim 43, wherein the ablating means includes at least one RF electrode. 45. The device of claim 43, wherein the ablation means comprises a plurality of RF electrodes spaced about the catheter body, the electrodes being individually actuatable to non-symmetrically ablate material with respect to the catheter axis so that the void is created non-symmetrically with respect to the catheter axis, whereby the catheter can be steered by creating the void in a desired direction and advancing the catheter into the void. 46. The device of claim 45, wherein all of the electrodes are activatable simultaneously to create a void distal to the distal tip of the catheter so that the catheter can be advanced straight ahead. 47. The device of claim 45, further comprising a center electrode, the center electrode located substantially in line with the catheter axis, whereby activating the center electrode creates a void distal the distal tip of the catheter. 48. The device of claim 45, further comprising means for visualizing the lumen. 49. The device of claim 48, wherein the visualization means includes an ultrasound array. 50. The device of claim 49, wherein the ultrasound array provides visualization information radially away from the catheter axis. 51. The device of claim 50 wherein the ultrasound array is an annular band about the catheter axis. 52. The device of claim 49, wherein the ultrasound array provides visualization information distal to the distal end of the catheter in the direction of the catheter axis. 53. The device of claim 49, wherein the ultrasound array provides visualization information distal to the distal end of the catheter and information radially away from the catheter axis. 54. The device of claim 53, wherein the ultrasound array is generally shaped as a truncated cone segment. 55. The device of claim 49, wherein the ultrasound array comprises a plurality of array segments, each segment being generally planar and occupying a plane at an angle to the catheter axis. 56. The device of claim 55, wherein the segments are comprise elements that may be activated with variable phase. 57. The device of claim 49, further comprising a computer and a monitor for generating a view of the lumen. 58. The device of claim 57, further comprising a control for selectively activating one or more of the electrodes. 59. The device of claim 58, wherein the control comprises a joy stick, mouse, track ball, keyboard, or touch sensitive screen. 60. The device of claim 58, wherein the control is voice activated. 61. The device of claim 58, wherein the computer is capable of selecting an electrode and querying a user whether to activate the selected electrode. 62. The device of claim 61, further comprising an additional ablation electrode proximal to the tip electrode, the additional ablation electrode for ablating material radially away from the catheter. 63. The device of claim 62, wherein the additional electrode is radially further from the catheter axis than are the prior-mentioned electrodes. 64. The device of claim 43, wherein the ablating means comprise at least one of electrical energy, laser energy, acoustical energy, or direct mechanical energy. 65. A method of penetrating occlusive material within a lumen of a body, comprising the steps of: (a) activating ablating means positioned on a catheter to ablate obstructive material in front of the catheter, thereby creating a void; (b) advancing the catheter into the void; and (c) repeating steps (a) and (b) until the occlusive material is penetrated. 66. The method of claim 65, further comprising the step of steering the catheter through the occlusive material by non-symmetrically ablating the material in step (a) with respect to the catheter. 67. The method of claim 65, further comprising the steps of visualizing the lumen on a monitor, and steering the catheter so that the catheter remains generally centered there-within. 68. The method of claim 67, further comprising the steps of ablating additional obstructive material around the catheter. 69. A device for the detection an electromagnetically detectable object within the body of a patient, comprising: an elongate tube having a distal end and a proximal end, the distal end being insertable and manipulatable within the body of the patient; a sensor to detect the electromagnetically detectable object, the sensor located proximate the distal end of the tube, the sensor being insertable within the body of the patient, the sensor generating a signal in response to the objects; and signal processing electronics to process the signal; and an indicator responsive to the signal processing electronics to indicate the position of the sensor with respect to the object. 70. The device of claim 69, wherein the sensor is responsive to metallic objects. 71. The device of claim 69, wherein the sensor is responsive to non-metallic objects. 72. The device of claim 69, wherein the body of the patient has a lumen, and the device is a catheter manipulatable within said lumen. 73. The device of claim 72, wherein the device is sized to fit through the lumen, and wherein the lumen is selected from the class consisting of an artery, vein, capillary, fallopian tube, urethra, and alimentary canal. 74. The device of claim 69, wherein the indicator includes an audio speaker that emits sounds of varying characteristics depending upon the position of the sensor with respect to the object. 75. The device of claim 73, wherein the indicator includes a visual display. 76. The device of claim 75, wherein the visual display is a gauge of the distance between the sensor and the object. 77. The device of claim 75, wherein the visual display displays a graphical image of the object. 78. The device of claim 69, further comprising an operative surgical component that is located proximate the distal end of the tube or on the distal end of the tube. 79. The device of claim 78, wherein the operative surgical component is an inflatable balloon. 80. The device of claim 78, wherein the operative surgical component is a mechanical cutter. 81. The device of claim 78, wherein the operative surgical component is a laser ablating device. 82. The device of claim 82, wherein the operative surgical component is an electrical ablating device. 83. The device of claim 82, wherein the electrical ablating device is an RF device. 84. The device of claim 78, wherein the operative surgical component is a positioning component. 85. The device of claim 84, wherein the positioning component is a hook dimensioned to place and retrieve a stent. 86. The device of claim 69, wherein the sensor comprises a plurality of discrete sensors. 87. The device of claim 86, wherein the sensors are arranged in a coaxial array, the array, comprising one or more central transmit sensors, and a plurality of receive sensors are spaced symmetrically about the one or more central transmit sensors. 88. The device of claim 86, wherein the sensors comprise a center transmit sensor having a length and a receive sensor having a length greater than the center sensor, and the receive sensor has a plurality of taps. 89. The device of claim 88, wherein the plurality of taps includes interior taps spaced a distance from each other, the interior taps being spaced about the transmit sensor, and two groups of exterior sensor taps, each group of exterior sensor taps being located on opposite sides of the transmit sensor, each group of exterior sensor taps including two sensors located a distance from one another that is less than the distance separating the interior taps. 90. The device of claim 86, wherein the sensor includes a coil having an axis orthogonal to the axis of the elongate tube. 91. The device of claim 90, wherein the sensor includes a transmit coil and a co-planar receive coil. 92. The device of claim 91, wherein the sensor includes a receive coil and more than one transmit coil, the transmit coils being circumscribed by the receive coil. 93. The device of claim 69, wherein the circuitry utilizes electric field sensitive techniques. 94. The device of claim 93, wherein the electric field sensitive techniques are selected from the group consisting of capacitance sensing and impedance sensing. 95. A method of performing surgery comprising: inserting a surgical device within the body of a patient, the device including electromagnetic detection sensor; and determining the presence and location of an object within the body by activating the sensor. 96. The method of claim 95, wherein the object is metal. 97. The method of claim 95, wherein the object is non-metal. 98. The method of claim 95, further comprising the step of: positioning the surgical device after determining the location of said metal object. 99. The method of claim 98, further comprising the step of: performing a surgical procedure in conjunction with said determining and positioning steps. 100. The method of claim 99, wherein the surgical procedure includes balloon angioplasty. 101. The method of claim 99, wherein the surgical procedure includes laser ablating. 102. The method of claim 99, wherein the surgical procedure includes mechanical cutting. 103. The method of claim 98, wherein the surgical procedure includes deploying a stent, monitoring the deployment with the sensor to determine if the stent is deployed to a desired criteria, redeploying the stent if it is not deployed to the desired criteria, and repeating the above steps until the desired deployment is achieved. 104. The method of claim 99, wherein the surgical procedure includes RF ablation.

Inventors: JANSSEN W MICHAEL, MANGANARO WILLIAM M, JANSSEN, W., MICHAEL, MANGANARO, WILLIAM, M.
Applicants: ADVANCED CORONARY INTERVENTION, JANSSEN W MICHAEL, MANGANARO WILLIAM M, JANSSEN, W., MICHAEL, MANGANARO, WILLIAM, M.
Application year: 1996
Main classification: A61N1
IPC codes: A61B5, A61B17, A61B18, A61F2, A61N1