Patent Application
20090259284
The invention relates to stents, stent elements, and/or stent-grafts and more particularly to stents or stent elements that have one or more electromagnetic coils integrally formed therein.
Tubular prostheses such as stents, grafts, and stent-grafts (e.g., stents having an inner and/or outer covering comprising graft material and which may be referred to as covered stents) have been widely used in treating abnormalities in passageways in the human body. In vascular applications, these devices often are used to replace or bypass occluded, diseased or damaged blood vessels such as stenotic or aneurysmal vessels. For example, it is well known to use stent-grafts, which comprise biocompatible graft material (e.g., Dacron® or expanded polytetrafluoroethylene (ePTFE) materials) supported by a framework (e.g., one or more stent or stent-like structures), to treat or isolate aneurysms. The framework provides mechanical support and the graft material or liner provides a blood barrier.
Aneurysms generally involve abnormal widening of a duct or canal such as a blood vessel and generally appear in the form of a sac formed by the abnormal dilation of the duct or vessel wall. The abnormally dilated wall typically is weakened and susceptible to rupture. Aneurysms can occur in blood vessels such as in the abdominal aorta where the aneurysm generally extends below the renal arteries distally to or toward the iliac arteries.
In treating an aneurysm with a stent-graft, the stent-graft typically is placed so that one end of the stent-graft is situated proximally or upstream of the diseased portion of the vessel and the other end of the stent-graft is situated distally or downstream of the diseased portion of the vessel. In this manner, the stent-graft spans across and extends through the aneurysmal sac and beyond the proximal and distal ends thereof to replace or bypass the weakened portion. The graft material typically forms a blood impervious lumen to facilitate endovascular exclusion of the aneurysm.
Such prostheses can be implanted in an open surgical procedure or with a minimally invasive endovascular approach. When the prosthesis is a stent-graft, a minimally invasive endovascular approach is preferred by many physicians over traditional open surgery techniques where the diseased vessel is surgically opened, and a graft is sutured into position such that it bypasses an aneurysm. The endovascular approach, which has been used to deliver stents and stent grafts, generally involves cutting through the skin to access a lumen of the vasculature. Alternatively, lumenar or vascular access may be achieved percutaneously via successive dilation at a less traumatic entry point. Once access is achieved, the prosthesis (e.g., a stent-graft) can be routed through the vasculature to the target site. For example, a stent-graft delivery catheter loaded with a stent-graft can be percutaneously introduced into the vasculature (e.g., into a femoral artery) and the stent-graft delivered endovascularly across the aneurysm where it is deployed.
When using a balloon expandable stent-graft, balloon catheters generally are used to expand the stent-graft after it is positioned at the target site. When, however, a self-expanding stent-graft is used, the stent-graft generally is radially compressed or folded and placed at the distal end of a sheath or delivery catheter. Upon retraction or removal of the sheath or catheter at the target site, the stent-graft self-expands.
More specifically, a delivery catheter having coaxial inner and outer tubes arranged for relative axial movement therebetween can be used and loaded with a compressed self-expanding stent-graft. The stent-graft is positioned within the distal end of the outer tube (sheath) and in front of a stop fixed to distal end of the inner tube. Once the catheter is positioned for deployment of the stent-graft at the target site, the inner tube is held stationary and the outer tube (sheath) withdrawn so that the stent-graft is gradually exposed and allowed to expand. The inner tube or plunger prevents the stent-graft from moving back as the outer tube or sheath is withdrawn. An exemplary stent-graft delivery system is described in U.S. Patent Application Publication No. 2004/0093063, which published on May 13, 2004 to Wright et al. and is entitled Controlled Deployment Delivery System, the disclosure of which is hereby incorporated herein in its entirety by reference.
Although the endovascular approach is much less invasive, and usually requires less recovery time and involves less risk of complication as compared to open surgery, among the challenges with the approach is positioning the prosthesis and/or locating the prosthesis position.
Generally speaking, physicians often use fluoroscopic imaging techniques to confirm prosthesis position before and during deployment. This approach requires one to administer a radiopaque substance, which generally is referred to as a contrast medium, agent or dye, into the patient so that it reaches the area to be visualized (e.g., the renal arteries). A catheter can be introduced through the femoral artery in the groin of the patient and endovascularly advanced to the vicinity of the renals. The fluoroscopic images of the transient contrast agent in the blood, which can be still images or real-time motion images, allow two-dimensional visualization of the location of the renals. The extensive use of X-rays and cytotoxic contrast that provide known risks from a procedure be carefully balanced with the benefits of the procedure to the patient. While physicians always try to use low dose rates during fluoroscopy, the duration of a procedure may be such that it results in a relatively high absorbed dose to the patient and physician. Patients who cannot tolerate contrast enhanced imaging or physicians who must or wish to reduce radiation exposure need an alternative approach.
Accordingly, there remains a need to develop and/or improve prosthesis positioning and locating apparatus and methods for endoluminal or endovascular applications.
Embodiments according to the present invention involve improvements in prosthesis construction to facilitate prosthesis localization (e.g., finding the position of the prosthesis in three-dimensional space), position tracking and/or monitoring.
In one embodiment according to the invention, a tubular member adapted for endovascular delivery in a human patient comprises a tubular wire framework, a coil and a capacitor, a portion of the tubular wire framework forms a core and the coil surrounds the core to form an inductor, the capacitor is coupled to the inductor to form an inductor capacitor circuit. In one example configuration, the inductor capacitor circuit can be an inductor capacitor series circuit.
In another embodiment according to the invention, an endovascular resonating marker assembly comprises a wire stent, a coil, and a capacitor, the coil being wound about a portion of the wire stent to form an inductor and the capacitor being coupled to the portion to form an inductor capacitor circuit.
In another embodiment according to the invention, an endovascular resonating marker assembly comprising a tubular wire stent element, a coil, and a capacitor, the coil being wound about a portion of the wire stent to form an inductor and the capacitor being coupled to the portion to form an inductor capacitor circuit.
In another embodiment according to the invention, a method of endovascularly navigating a device to a prosthesis comprises positioning in a vessel of a patient a prosthesis comprising a tubular wire framework, a coil and a capacitor, where a portion of the tubular wire framework forms a core, the coil surrounds the core to form an inductor and the capacitor is coupled to the inductor to form an inductor capacitor circuit signal element; generating an electromagnetic field in the region of the patient where the prosthesis is positioned; endovascularly advancing a device having an electromagnetic coil secured thereto toward the prosthesis; and monitoring the relative positions of the signal element and the electromagnetic coil based on signals emitted therefrom and indicative of their positions.
In another embodiment according to the invention, a method of evaluating prosthesis deployment comprises endovascularly positioning a prosthesis comprising a tubular wire framework having two resonating markers in a predetermined position; deploying the prosthesis; generating an electromagnetic field in the vicinity of the deployed prosthesis to activate the resonating markers so that they emit signals; determining the position of the markers based on their emitted signals; and evaluating the determined resonating marker positions as compared to the predetermined marker positions.
In another embodiment according to the invention, a method of evaluating prosthesis deployment comprises endovascularly positioning a prosthesis comprising a tubular wire framework having two resonating markers in a predetermined orientation; deploying the prosthesis; generating an electromagnetic field in the vicinity of the deployed prosthesis to activate the resonating markers so that they emit signals; determining the orientation of the markers based on their emitted signals; and evaluating the determined resonating marker orientations as compared to the predetermined marker orientations.
Other features, advantages, and embodiments according to the invention will be apparent to those skilled in the art from the following description and accompanying drawings.
The following description will be made with reference to the drawings where when referring to the various figures, it should be understood that like numerals or characters indicate like elements.
Regarding proximal and distal positions, the proximal end of the prosthesis (e.g., stent-graft) is the end closest to the heart (by way of blood flow) whereas the distal end is the end farthest away from the heart during deployment. In contrast, the distal end of the catheter is usually identified as the end that is farthest from the operator, while the proximal end of the catheter is the end nearest the operator. Therefore, the prosthesis (e.g., stent-graft) and delivery system proximal and distal descriptions may be consistent or opposite to one another depending on prosthesis (e.g., stent-graft) location in relation to the catheter delivery path.
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Endovascular resonating marker assembly 200 further includes resonating markers 204 and 206 integrally formed in the stent framework and positioned in a known or predetermined orientation relative to one another. In the illustrative example, resonating markers 204 and 206 are positioned in a central region of the stent to provide data indicative of where the central region of the state is positioned. More specifically, when acquired navigational data indicative of the position and/or orientation of the markers is sent to a computer or processor for display, the computer can process that information to display a representation of the markers and their relative positions on a display. Alternatively, the relative positions of the markers and the stent and the stent dimensions can be input in the computer so that the computer can process that information to display a representation of the stent.
Although two markers are shown in each of the foregoing illustrative embodiments, each assembly can have only one marker. A single marker coil provides position and orientation of the marker coil, which can be used to determine the position and/or orientation of the marker or marker assembly based on the relative positions of the marker, marker coil and stent framework and dimensions of the marker, marker coil and stent framework. Therefore, the single marker coil configuration can provide the vector orientation of the stent framework. However, two or more markers or marker coils can be used. In one example, a two coil configuration can be used to confirm and add reliability to the orientation and position measurements. One can subtract between the marker coils to verify the orientation and use the location of one marker coil as a check on the location of the other marker coil. More specifically, a navigation system such as navigation system 10 as shown in
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In the illustrative embodiment, the resonating marker 104 also can include a protective encapsulation or casing 104d to protect the signal element when tracked or implanted in a patient's body. Encapsulation or casing 104d seals and/or encapsulates the signal element and can be made of plastic, glass, or other suitable inert material. The signal element can be potted with a silicone type plastic or covered with a thin heat shrink. A PTFE heat shrink is desirable for providing insulation and blood compatibility. The markers can have an axial dimension or length of approximately 2-14 mm and a diameter of approximately 0.5-5 mm.
The core 104a can be the same material as the remainder of stent framework 101 or it can be different material. In the former case, stent framework 101, including core portion 104a, is made from any suitable material that provides the desired magnetic properties. Examples include 400 series stainless steel, a cobalt chrome alloy such as L605, tantalum, a nickel based alloy such as Inconel, shape memory alloys such as nitinol, a platinum-iridium alloy such as MP35N, and a niobium-based alloy C-103. When the core portion and the remainder of stent-framework 101 are made from different materials, the core portion can be a ferromagnetic material. For example, core portion 104a can be ferromagnetic material and the remainder of stent framework 101 can be nitinol. In this case, a portion of stent framework is cut away with two ends exposed. One end of the ferromagnetic core portion is then riveted to one of the stent wire exposed ends and the other end of the ferromagnetic core portion is riveted to the other stent wire exposed end in a manner similar to riveting a fluoroscopic marker to a stent. Further, the core can be provided with diametrically enlarged ferromagnetic end portions, which are not surrounded by coil wire, as described in U.S. Pat. No. 7,135,978 to Gisselberg et al. The end portions or end caps can have an outer diameter approximately the same as the outer diameter of coil 104b.
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Although particular capacitor constructions have been shown in
Use of the resonating marker assemblies illustrated in
According to another navigation system embodiment, the navigation system provides, without the use of patient-specific medical images, the position of one or more tracked elements with iconic representations to indicate the positions and/or orientations of the tracked elements, the relative positions and/or orientations of the tracked elements, or the positions and/or orientations of the marker assemblies of which they form a part. In other embodiments, such iconic representations can be displayed with or superimposed on patient-specific medical images.
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Tracking system 14, which measures positions and/or orientations, and which can for example incorporate known leadless tracking system 800, which is diagramatically shown in
The tracking system typically comprises a tracker 20 and one or more tracked or trackable elements such as 22a, 22b, 22c, 22d, 22e . . . n, which correspond to the markers that form part of resonating marker assembly 100 or 200 and these assemblies can have one or more markers as described above. The tracker provides navigation/tracking information provided to computer 18 so that the position and/or orientation of the marker coils in three-dimensional space can be displayed on display 16 with other marker coils or with a pre-acquired image or superimposed over a pre-acquired image.
When superimposing a tracking system data set over a pre-acquired data set, the data sets are registered. In one example, the preoperative image can be registered via two-dimensional or three-dimensional fluoroscopy. For example, after the preoperative data is acquired, a two-dimensional image is taken intraoperatively and is registered with the preoperative image as is known in the art. Regarding registering two-dimensional and three-dimensional images, see, for example, U.S. Patent Publication No. 2004/021571 to Frank et al. and entitled Method and Apparatus for Performing 2D and 3D Registration, the disclosure of which is hereby incorporated herein by reference in its entirety. In another example, an O-arm™ imaging system manufactured by Breakaway Imaging Inc. (Littleton, Mass.) can be used intraoperatively to take a picture/image of the navigation site to be navigated (see., e.g., U.S. Pat. No. 6,940,941, U.S. to Gregerson et al. and entitled Breakable Gantry Apparatus for Multidimensional X-Ray Based Imaging, U.S. Pat. No. 7,001,045 to Gregerson et al. and entitled Cantilevered Gantry Apparatus for X-Ray Imaging, U.S. Patent Publication No. 2004/0013225 to Gregerson et al. and entitled Systems and Methods for Imaging Large Field-of-View Objects, U.S. Patent Publication No. 2004/0013239 to Gregerson et al. and entitled Systems and Methods for Quasi-Simultaneous Multi-Planar X-Ray Imaging, U.S. Patent Publication No. 2004/0170254 to Gregerson et al. and entitled Gantry Positioning Apparatus for X-Ray Imaging, and U.S. Patent Publication No. 2004/0179643 to Gregerson et al. and entitled Apparatus and Method for Reconstruction of Volumetric Images in a Divergent Scanning Computed Tomography System, the disclosures of which are hereby incorporated by reference in their entirety). Another commercially available system for three-dimensional reconstruction of a volume space is the Innova® 3100 system built on GE's Revolution™ detector technology. A further representative system that performs image registration is described in U.S. Pat. No. 6,470,207 to Simon et al. and entitled Navigational Guidance Via Computer-Assisted Fluoroscopic Imaging, the disclosure of which is hereby incorporated herein by reference in its entirety.
A preoperative or intraoperative scan is taken of the target anatomical region where the tracked elements (e.g., resonating markers 104 and 106 or 204 and 206) are to be tracked to obtain a three-dimensional data set of the target anatomical region. The scan can be made using fluoroscopic x-ray techniques, CT, MRI or other known imaging modalities. That information is input into a computer 18, which is programmed to register the acquired data set from the tracker system with the preoperative or intraoperative three-dimensional data set so that one can track the XYZ coordinates of the tracked elements (e.g., resonating markers 104 and 106 or 204 and 206) in the coordinate system of the scanned anatomical structure. Methods for registering such data sets are well known in the art. The tracking system is set to generate electromagnetic energy in a volume of space in which the stent assembly is positioned so that the navigation system can provide the positional data of the markers in an XYZ coordinate system to computer 18, which processes that information to display the position of the stent assembly on the display. The physician or interventionalist introduces a resonating stent assembly (e.g., resonating marker assembly 100 or 200) and delivers it endovascualarly to the target area where a vascular treatment is to be provided, while observing the position of the stent assembly markers superimposed on the three-dimensional image of the anatomical structure on display 16. An optional step of updating the preoperative or intraoperative scan can be included. A commercially available scanner, which acquires an updated three-dimensional data set representative of the target region and simultaneously associates that with a marker, in this example, marker coils 104 and 106 or 204 and 206, can be used. One example is the O-arm™ Imaging System manufactured by Breakaway Imaging Inc. (Littleton, Mass.), which includes navigation software that registers the coordinate systems of the updated three-dimensional data set and the marker. Also see U.S. Pat. No. 6,470,207 to Simon, et al. Another option would be take an ultrasound or fluoroscopic scan to obtain a two-dimensional data set and registering that data set with tracked element data set using established technology such as the FluoroMerge TM™ or FluroNav systems marketed by Medtronic, Inc. (Minneapolis, Minn.).
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Source generator 818 is configured to generate the excitation signal 820 so that one or more marker assemblies 814 are sufficiently energized to generate the marker signals 822. The source generator 818 can be switched off after the marker assemblies are energized. Once the source generator 818 is switched off, the excitation signal 820 terminates and is not measurable. Accordingly, sensors 826 in sensor array 816 will receive only marker signals 822 without any interference or magnetic field distortion induced by the excitation signal 820. Termination of the excitation signal 820 occurs before a measurement phase in which marker signals 822 are measured. Such termination of the excitation signal before the measurement phase when the energized marker assemblies 814 are generating the marker signals 822 allows for a sensor array 816 of increased sensitivity that can provide data of a high signal-to-noise ratio to the signal processor 828 for extremely accurate determination of the three-dimensional location of the marker assemblies 814 relative to the sensor array or other frame of reference.
The miniature marker assemblies 814 in the system 800 are inert, activatable assemblies that can be excited to generate a signal at a resonant frequency measurable by the sensor array 816 remote from the target on which they are placed. The miniature marker assemblies 814 have, as one example, a diameter of approximately 2 mm and a length of approximately 5 mm, although other marker assemblies can have different dimensions. An example of such a marker detection systems are described in detail in U.S. Patent Publication No. 2002/0193685 to Mate et al. and entitled Guided Radiation Therapy System, filed Jun. 8, 2001 and published on Dec. 19, 2002, and U.S. Pat. No. 6,822,570 to Dimmer et al., entitled System For Spacially Adjustable Excitation Of Leadless Miniature Marker, all of the disclosures of which are incorporated herein in their entirety by reference thereto.
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The marker assembly 814 is energized, and thus activated, by the magnetic excitation field or excitation signal 820 generated by the source generator 818 such that the marker's signal element 836 generates the measurable marker signal 822. The strength of the measurable marker signal 822 is high relative to environmental background noise at the marker resonant frequency, thereby allowing the marker assembly 614 to be precisely located in three-dimensional space relative to sensor array 816.
The source generator 818 can be adjustable to generate a magnetic field 820 having a waveform that contains energy at selected frequencies that substantially match the resonant frequency of the specifically tuned marker assembly 814. When the marker assembly 814 is excited by the magnetic field 820, the signal element 836 generates the response marker signal 822 containing frequency components centered at the marker's resonant frequency. After the marker assembly 814 is energized for a selected time period, the source generator 818 is switched to the “off” position so the pulsed excitation signal 820 is terminated and provided no measurable interference with the marker signal 822 as received by the sensor array 816.
The marker assembly 814 is constructed to provide an appropriately strong and distinct signal by optimizing marker characteristics and by accurately tuning the marker assembly to a predetermined frequency. Accordingly, multiple uniquely tuned, energized marker assemblies 814 may be reliably and uniquely measured by the sensor array 816. The unique marker assemblies 814 at unique resonant frequencies may be excited and measured simultaneously or during unique time periods. The signal from the tuned miniature marker assembly 814 is significantly above environmental signal noise and sufficiently strong to allow the signal processor 828 (
A system corresponding to system 800 is described in U.S. Pat. No. 6,822,570 to Dimmer et al., entitled System For Spacially Adjustable Excitation Of Leadless Miniature Marker, the entire disclosure of which is hereby incorporated herein in its entirety by reference thereto. According to U.S. Pat. No. 6,822,570, the system can be used in many different applications in which the miniature marker's precise three-dimensional location within an accuracy of approximately 1 mm can be uniquely identified within a relatively large navigational or excitation volume, such as a volume of 12 cm×12 cm×12 cm or greater. One such application is the use of the system to accurately track the position of targets (e.g., tissue) within the human body. In this application, the leadless marker assemblies are implanted at or near the target so the marker assemblies move with the target as a unit and provide positional references of the target relative to a reference frame outside of the body. U.S. Pat. No. 6,822,570 further notes that such a system could also track relative positions of therapeutic devices (i.e., surgical tools, tissue, ablation devices, radiation delivery devices, or other medical devices) relative to the same fixed reference frame by positioning additional leadless marker assemblies on these devices at known locations or by positioning these devices relative to the reference frame. The size of the leadless markers used on therapeutic devices may be increased to allow for greater marker signal levels and a corresponding increase in navigational volume for these devices.
Other examples of leadless markers and/or devices for generating magnetic excitation fields and sensing the target signal are disclosed in U.S. Patent Publication No. 2003/0052785 to Gisselberg et al. and entitled Miniature Resonating Marker Assembly, U.S. Pat. No. 7,135,978 to Gisselberg et al. and entitled Miniature Resonating Marker Assembly, U.S. Pat. No. 6,889,833 to Seiler et al. and entitled Packaged Systems For Implanting Markers In A Patient And Methods For Manufacturing And Using Such Systems, U.S. Pat. No. 6,812,842 to Dimmer and entitled System For Excitation Of Leadless Miniature Marker, U.S. Pat. No. 6,838,990 to Dimmer and entitled System For Excitation Of Leadless Miniature Marker, U.S. Pat. No. 6,977,504 to Wright et al. and entitled Receiver Used In Marker Localization Sensing System Using Coherent Detection, U.S. Pat. No. 7,026,927 to Wright et al. and entitled Receiver Used In Marker Localization Sensing System And Having Dithering In Excitation Pulses all the disclosures of which are hereby incorporated herein in their entirety by reference thereto.
Another example of a suitable leadless marker construction and system is the Calypso® 4D Localization System, which is a target localization platform based on detection of AC electromagnetic markers, called Beacon® transponders, which are implantable devices. These localization systems and markers have been developed by Calypso® Medical Technologies (Seattle, Wash.).
Any feature described in any one embodiment described herein can be combined with any other feature of any of the other embodiments whether preferred or not.
Variations and modifications of the devices and methods disclosed herein will be readily apparent to persons skilled in the art.
