Note: Descriptions are shown in the official language in which they were submitted.
<br/>CA 02455439 2011-07-19<br/>Device Viewable Under an Imaging Beam<br/>Field of the invention <br/>[0002] The present invention relates generally to surgery under image <br/>guided<br/>navigation and more particularly relates to a method, device and system for <br/>surgical<br/>implantation of a medical device or the like, and/or postoperative evaluation <br/>of an <br/>implanted medical device or the like under image guidance.<br/>Backaround of the Jnvention <br/>[0003] Stroke and cardiac disease remain a major cause of morbidity and <br/>result<br/>in profound suffering and expense. Increased awareness and improvements in <br/>diagnostic procedures have significantly increased the diagnosis of cervical <br/>and <br/>intracranial and cardiac vascular stenosis. A vascular stenosis is now being <br/>treated <br/>endovascularly at a significantly increased frequency. However, follow-up has<br/>is predominantly been by angiography which evaluates the vascular contour <br/>but not the<br/>vascular wall. It is invasive, time consuming and expensive. Preliminary <br/>studies suggest <br/>that stent evaluation and restenosis pathophysiology can also be evaluated <br/>with Multi-<br/>detector Computed Tomography Angiography ("MDCTA") which would be a <br/>significant <br/>advantage of this technique over conventional angiography,<br/>[0004] More specifically, endovascular therapy has ushered in a new <br/>age of<br/>minimally invasive vascular treatment. Endovascular devices have been rapidly <br/>developed and refined. Present technologies have enabled precise deployment of <br/>stents in much smaller arteries and have become more flexible and compliant 30 <br/>they<br/>can be navigated through tortuosities. At the same time there has been a <br/>growing pool<br/>of physicians trained in modern endovascular therapies so services are more <br/>widely <br/>available. However, the monitoring of these patients has become suboptimal <br/>because it <br/>relies on conventional angiography which is invasive and expensive. It also <br/>requires the <br/>patient to spend a full day removed from their daily activities. It also <br/>requires that some<br/>patients on anticoagulation briefly discontinue their therapy or be admitted <br/>to the<br/>hospital for an extended period of time. New MDCTA technology has not been <br/>widely <br/>used or validated for follow up. However, preliminary case studies seem to <br/>indicate that<br/>1<br/><br/>CA 02455439 2011-07-19<br/>this technology is likely to provide additional beneficial information about <br/>the vascular <br/>wall and stent not obtainable from conventional angiograms. MDCTA is also non-<br/>invasive, requires a minimal amount of time and is less costly. MDCTA now has <br/>an axial <br/>resolution less than 0.5 mm and with the proposed development of new protocols <br/>and<br/>algorithms for image processing, this will be a superior tool to evaluate <br/>stenting and the<br/>etiology of any restenosis or stent failures. In particular, it will likely be <br/>able to separate <br/>negative remodeling from neointimal growth. It will also be able to evaluate <br/>for stent <br/>deformity and wall apposition as well as remodeling. MDCTA should also be <br/>applicable <br/>to other endovascular procedures such as follow up for aneurysm coilings.<br/>[0005] Indeed MDCTA reflects a number of advances in medical imaging <br/>that<br/>allow real time and/or three-dimensional image gathering under Computed <br/>Tomography <br/>(CT"), Magnetic Resonance Imaging ("MRI") or the like. For example, CT <br/>scanners <br/>such as the Toshiba Ac,quillionTm multi detector are capable of generating <br/>images in<br/>three different areas at frame rates of 13 frames a second, to thereby <br/>generate a three-<br/>dimensional rendering of the target area. Indeed, this and other advances in <br/>CT have <br/>led to the development of new CT applications including CT Angiography <br/>("CTA"), and <br/>CT Perfusion ("CTP"). These imaging modalities are rapidly developing into <br/>powerful <br/>tools in the diagnosis and treatment of both ischemic and hemorrhagic stroke <br/>and bilary<br/> occlusion. See, for example, the following prior art references:<br/>Kopp AF, Ohnesorge B, Flohr T, Georg C, Schroder S, Kuttner A, Martensen J, <br/>Claussen CD. [Cardiac muitidetector-row CT: first clinical results of<br/>retrospectively ECG-gated spiral with optimized temporal and spatial<br/> resolution]Rofo Fortschr Geb Rontgenstr Neuen Bildgeb Verfahr. 2000 May;<br/>172(S):429-35.<br/>2<br/><br/>CA 02455439 2004-01-20<br/>Ohnesorge B, Flohr T, Becker C, Knez A, Kopp AF, Fukuda K, Reiser MF. <br/>[Cardiac imaging with rapid, retrospective ECG synchronized multilevel spiral <br/>CT]Radiologe. 2000 Feb;40(2):111-7<br/>Achenbach S, Moshage W, Ropers D, Nossen J, Bachmann K. Non-invasive<br/> coronary angiography with electron beam tomography: methods and clinical<br/>evaluation in post-PTCA follow-up Z Kardiol. 1997 Feb;86(2):121-30.<br/>Becker CR, Schoepf UJ, Reiser MF.Methods for quantification of coronary <br/>artery calcifications with electron beam and conventional CT and pushing the <br/>spiral CT envelope: new cardiac applications.Int J Cardiovasc Imaging. 2001<br/> Jun;17(3):203-11.<br/>Kopp AF, Schroeder S, Kuettner A, Baumbach A, Georg C, Kuzo R, <br/>Heuschmid M, Ohnesorge B, Karsch KR, Claussen CD. Non-invasive <br/>coronary angiography with high resolution multidetector-row computed <br/>tomography. Results in 102 patients.Eur Heart J. 2002 Nov;23(21):1714-25.<br/> Achenbach S, Ulzheimer S, Baum U, Kachelriess M, Ropers D, Giesler T,<br/>Bautz W, Daniel WG, Kalender WA, Moshage W. Non-invasive coronary <br/>angiography by retrospectively ECG-gated multislice spiral CT.Circulation. <br/>2000 Dec 5;102(23):2823-8.<br/>Knez A, Becker A, Becker C, Leber A, Boekstegers P. Reiser M, Steinbeck G.<br/> [Detection of coronary calcinosis with multislice spiral computerized<br/>tomography: an alternative to electron beam tomographyZ Kardiol. 2002 <br/>Aug;91(8):642-9.<br/>Mahnken All, Sinha AM, Wildberger JE, Krombach GA, Schmitz-Rode T, <br/>Gunther RW. [The influence of motion artifacts conditioned by reconstruction,<br/> on the coronary calcium score in multislice spiral CT]Rofo Fortschr Geb<br/>Rontgenstr Neuen Bildgeb Verfahr. 2001 Oct;173(10):888-92.<br/>[0006] However, despite these advances in medical device technology, <br/>and in<br/>particular stent technology and imaging technology, prior art stent <br/>technologies have certain<br/>limitations when viewed under such CT machines, particularly due to beam <br/>hardening<br/>- 3 -<br/><br/>CA 02455439 2004-01-20<br/>artefacts that are typically present, which thereby obscure the image and <br/>obviate or reduce the <br/>effectiveness of the CT machine as a post-operative diagnostic tool<br/>[0007] <br/> Due to these present limitations using MDCTA, it is common to rely on<br/>classical angiography for postoperative evaluation of endovascular procedures, <br/>yet such<br/>angiographic methods are invasive and expensive. In the USA, an angiogram can <br/>cost up to<br/>$8000.00, yet a corresponding MDCTA could be offered for as little as $400.00. <br/>Additionally, endovascular ultrasound has significant associated risks and is <br/>not suitable for <br/>the small intracranial vessels. In the end, it is believed that MDCTA has the <br/>potential to <br/>provide good visualization of the lumen as well as the arterial wall and <br/>stent. MDCTA<br/>actually visualizes the stent better than fluoroscopy and will likely prove to <br/>be the preferred<br/>technique when background subtraction is used to increase vascular <br/>conspicuity. It is also <br/>believed that MDCTA would also enable more precise outcome evaluation and <br/>allow for <br/>investigation of the underlying pathophysiology as well as evaluation of the <br/>stents and <br/>devices used.<br/>[0008] Polymer or lipid based drug delivery systems that can deliver drugs <br/>at a<br/>defined rate for up to five years from a single treatment have revolutionized <br/>medical therapy. <br/>Drug coated coronary stents have been shown to decrease restenosis rates in <br/>large clinical <br/>trials. See for example, the following references:<br/>"Sirilimus eluting stents versus standard stents in patients with stenosis of <br/>the<br/> coronary artery", Moses et al. New England Journal of Medicine, page 1315-<br/>1323 October 2, 2003 Vol. 349, No. 14.<br/>"Paclitaxel stent coating inhibits meointimal hyperplasia at 4 weeks in a <br/>porcine model of restenosis", Heldman et al. circulation 2001, 103-2289-95.<br/>"A Paclitaxel eluting stent for the prevention of coronary restenosis", Park <br/>et<br/>al. New England Journal of Medicine 2003, Vol. 348, page 1537-45.<br/>[0009] <br/> With respect to the drug delivery systems there are several types available <br/>at<br/>this time. These are principally those that are biodegradeable or those that <br/>are non <br/>biodegradeable. Biodegradable polymers release their loaded agents as they <br/>break down, <br/>while the matrix of non- biodegradable polymers remain intact even after all <br/>of the<br/>therapeutic agent has been released. These polymers release their loaded <br/>material by a<br/>- 4 -<br/><br/>CA 02455439 2004-01-20<br/>process of either bulk erosion or surface erosion and diffusion or <br/>degradation. The polymers <br/>and co-polymers that are available at the present time include ethylene vinyl <br/>acetate <br/>("EVAc"), a hydrophilic non biodegradable polymer, and biodegradeable polymers <br/>such as <br/>hydrophobic polymers such as poly[BIS(p-carboxyphenoxy)]propane-sebacic acid<br/>("PCPP:SA"), hydrophilic polymers and fatty acid dimer-sebacic acid ("FAD:SA") <br/>polymers<br/>that deliver drugs including hydrophilic drugs and compounds<br/>[0010] A process such as lyophilization can be used to load the <br/>polymer with the<br/>desired compound or drug or compounds or drugs. In this was PCPP:SA, a desired <br/>compound such as iodinated contrast material, and methyl chloride may undergo <br/>the<br/>lyophilization process to load the PCPP:SA with a material with the ability to <br/>attenuate x-ray<br/>radiation and be visible on a radiographic image.<br/>SUMMARY OF THE INVENTION<br/>[0011] In a first aspect of the invention there is provided a medical <br/>device made from<br/>a material operable to perform a therapeutic function of the device and <br/>wherein the material<br/>allows three-dimensional visualization of a surrounding tissue when the <br/>medical device is<br/>inserted into the tissue and viewed under an imaging beam.<br/>[0012] It is therefore an object of the invention to provide a <br/>medical device that is<br/>viewable under certain imaging beams that obviates or mitigates at least one <br/>of the above-<br/>identified disadvantages of the prior art.<br/>[0013] The medical device can be a stent and the surrounding tissue can be <br/>a lumen<br/>of a blood vessel. The stent can have a coating of a radioopaque material <br/>prior to insertion <br/>such that the stent that can be viewed during a conventional angiographic x-<br/>ray DA/DSA <br/>insertion and wherein the coating diminishes after insertion such that the <br/>stent can be viewed <br/>under CT post insertion. The stent can be coated with at least one of an <br/>antibiotic and a<br/>chemotherapy drug. The stent can be coated with at least one drug selected <br/>from the group<br/>consisting of a drug that is therapeutically effective to decrease attachment <br/>of platelets to the <br/>stent and a drug that is therapeutically effective to decrease restenosis. The <br/>drug can be <br/>selected from the group consisting of aspirin, plavix or paclitaxel.<br/>- 5 -<br/><br/>CA 02455439 2004-01-20<br/>[0014] In a particular implementation of the first aspect, the device <br/>can be selected<br/>from the group of devices for the treatment of obstruction due to clot, <br/>plaque, atheroma, <br/>tumours, and treatments involving intimal hyperplasia and recurrent stenosis.<br/>[0015] The material used to manufacture the medical device can be <br/>selected from the<br/>group consisting of plastic, composite carbon fiber and Inconel, nitinol, <br/>stainless steel, or a<br/>radio lucent material.<br/>[0016] The imaging system can be a substantially real-time CT <br/>machine, such as the<br/>Toshiba Acquillon.<br/>[0017] The medical device can have an image density of less than <br/>about 1200<br/>Hounsfield Units. The image density can be less than about 900 Hounsfield <br/>Units. The<br/>image density can be less than about 700 Hounsfield Units. The image density <br/>can be less <br/>than about 400 Hounsfield Units.<br/>[0018] The medical device can be a microcoil and the surrounding <br/>tissue is an<br/>aneurysm repaired with the microcoil.<br/>[0019] The configuration and structure of the medical device can be chosen <br/>to<br/>combine with the properties of the chosen material to provide a reduced beam <br/>hardened <br/>artifact. For example, where the device is a stent and the struts of the stent <br/>can be aligned or <br/>otherwise configured to reduce the beam hardened artifact.<br/>[0020] In another aspect of the invention there is provided an <br/>imaging processing unit<br/> for a CT machine comprising:<br/>a means for receiving mutli-plane images of mammalian tissue; <br/>a database of known medical devices and associated properties of the devices;<br/>a means for determining whether an object detected in the received images <br/>matches with a known medical device in the database, the means for<br/>determining based on the associated properties;<br/>means for applying a filter to the received images to enhance an image of the <br/>tissue that surrounds the implanted medical device based on the known <br/>associated properties; and,<br/>- 6 -<br/><br/>CA 02455439 2004-01-20<br/>means for presenting the image on an output device.<br/>[0021] The database of known medical devices can include at least one <br/>of a stent and<br/>a microcoil. The associated properties in the database can include a <br/>Hounsfield unit <br/>measurement of the device.<br/> Brief Description of the Drawings <br/>[0022] Embodiments of the invention will now be discussed, by way of <br/>example only,<br/>with reference to the attached Figures, in which:<br/>Figure 1 is a representation of an imaging system; <br/>Figure 2 is a side view of a prior art stent;<br/>Figure 3 is a representation of a beam hardened artifact caused by the prior <br/>art<br/>stent of Figure 2 when viewed under the imaging system of Figure 1;<br/>Figure 4 shows the beam hardened artifact of Figure 3 at a different angle; <br/>Figure 5 shows the beam hardened artifact of Figure 4 at a different angle;<br/>Figure 6 a side view of a stent in accordance with an embodiment of the<br/> invention;<br/>Figure 7 is a representation of the stent of Figure 6 when viewed under the <br/>imaging system of Figure 1;<br/>Figure 8 shows a microcoil in accordance with another embodiment of the <br/>invention;<br/> Figure 9 is a partial view of the microcoil of Figure 8;<br/>Figure 10 is a representation of a beam hardened artifact caused by a prior <br/>art <br/>microcoil when viewed under the imaging system of Figure 1;<br/>Figure 11 is a representation of the microcoil of Figure 9 after insertion <br/>into a <br/>patient and when viewed under the imaging system of Figure 1;<br/>- 7 -<br/><br/>CA 02455439 2004-01-20<br/>Figure 12 is a representation of a beam hardened artifact caused by a prior <br/>art <br/>carotid stent when viewed under the imaging system of Figure 1; and,<br/>Figure 13 is a representation of a carotid stent in accordance with another <br/>embodiment of the invention after the carotid stent has been inserted into a<br/> patient and when viewed under the imaging system of Figure 1.<br/>Detailed Description of the Invention <br/>[0023] Referring now to Figure 1, an imaging system is indicated <br/>generally at 30.<br/>Imaging system 30 comprises a patient chamber 34, an image processing unit 38 <br/>and a <br/>display 42. Imaging system 30 can be based on any known or established imaging<br/>technology, but in a present embodiment is based on computed tomography (CT) <br/>having<br/>substantially the same functionality as a machine like the Toshiba Acquillon. <br/>Thus, patient <br/>chamber 34 is operable to capture images of a patient P in at least three <br/>planes, and <br/>processing unit 38 is operable to assemble those captured images to present a <br/>three-<br/>dimensional rendering of a target area within patient P on display 42. Images <br/>on display 42<br/>can be navigated and/or viewed using the mouse and keyboard attached to <br/>processing unit 38,<br/>allowing the user to view a target area within patient P from any number of <br/>views. While not <br/>shown in Figure 1, image processing unit 38 can also be attached to other <br/>output devices in <br/>addition to display 42, such as a printer. Further, image processing unit 38 <br/>also typically <br/>includes a fixed storage device (such as a hard drive), a removable storage <br/>device (such as<br/>CD-Rewriter, or a tape drive) and a network interface card or other network <br/>interface means<br/>for connecting processing unit 38 to a network such as an intranet and/or the <br/>internet over <br/>which captured images can be delivered.<br/>[0024] Referring now to Figure 2, a prior art conventional coronary <br/>stent is indicated<br/>at 50. Figure 2 shows stent 50 in isolation, however, for purposes of <br/>explaining the prior art,<br/>it is to be assumed that stent 50 has been implanted in a coronary artery of <br/>patent P.<br/>[0025] Figure 3 shows an image 54 rendered on display 42 of system 30 <br/>of patient P.<br/>Image 54 shows a beam hardened artefact 52 as it is implanted inside a <br/>coronary artery 58 <br/>inside a heart 62 of patient P. The area identified as beam hardened artefact <br/>52 is an <br/>inaccurate reproduction of stent 50 as it is implanted inside artery 58. The <br/>beam hardening<br/>artefact 52 is created by the material of stent 50. Accordingly, system 30 is <br/>of limited value<br/>- 8 -<br/><br/>CA 02455439 2004-01-20<br/>in performing post-operative evaluations of stent 50 and for determining <br/>whether any <br/>restenosis has occurred of coronary artery 58.<br/>[0026] Figures 4 and 5 show additional images 54a and 54b, <br/>respectively, of different<br/>orientations of heart 62, which are readily produced on display 42 due to the <br/>imaging<br/>capability of system 30. In each image 54a and image 54b, stent 50 and the <br/>surrounding<br/>artery 58 are inaccurately reproduced due to beam hardening artefact 52 of <br/>stent 50. Thus, <br/>notwithstanding the great flexibility of system 30 in being able to provide a <br/>multiplicity of <br/>views of heart 62, in its current form stent 50 and system 30 do not provide <br/>meaningful <br/>images for post-operative evaluation of artery 58 and the progress of any <br/>restenosis that may<br/> be occurring in the lumen of artery 58 surrounding stent 50.<br/>[0027] Figure 6, shows a medical device in accordance with an <br/>embodiment of the<br/>invention as a stent 150. Stent 150 from outward appearances is substantially <br/>the same as <br/>prior art stent 50, and indeed, in the present embodiment is designed to <br/>provide substantially <br/>the same mechanical and therapeutic functionality as prior art stent 50. <br/>However, in contrast<br/>to prior art stent 50, stent 150 is made from a material that has a selected <br/>radiopacity such<br/>that the appearance of stent 150 is preserved when stent 150 is exposed to the <br/>imaging beam <br/>of system 30 and presented on display 42. Thus, when stent 150 is implanted in <br/>heart 62, <br/>then in an image 154 of heart 62 generated by system 30, the appearance of <br/>stent 150 will be <br/>maintained when heart 62 and stent 150 are shown in display 42, as shown in <br/>Figure 7. Since<br/>image 154 has no beam hardened artefacts, it is now possible to examine the <br/>lumen of artery<br/>58 surrounding stent 150, and thereby allow for an examination thereof for <br/>restenosis.<br/>[0028] As will be appreciated by those of skill in the art, presence <br/>or absence of a<br/>beam hardening artefact can be measured according to the properties of the <br/>imaging system <br/>being used and in relation to the Hounsfield units associated with the <br/>particular material or<br/>tissue being exposed to the imaging beam. A relation between the linear <br/>attenuation<br/>coefficient ( ) and the corresponding Hounsfield unit (H) can be expressed as:<br/>H = pMaterial ¨,uW ater <br/>x1000<br/>,uWater<br/>[0029] The value of the Hounsfield unit varies from -1000 (for air) <br/>to 1000 (for bone)<br/>to 3000, as more particularly shown in Table I.<br/>- 9 -<br/><br/>CA 02455439 2011-07-19<br/>Tissue Range of Hounsfield units<br/>Table It<br/>Material Hounsfield Unit <br/>Air -1000 <br/>Lung ___________________________ -500 to -200 <br/>Fat ____________________________ -200 to -50 <br/>Water 0 <br/>Blood 25 <br/>Muscle 25 to 40 <br/>Bone 200 to 1000 <br/>about 1000 can be prone to creating beam hardening artefacts. Thus, presently <br/>preferred <br/>materials from which stem 150 can be manufactured to have reduced beam <br/>hardening <br/>artefacts include certain plastic, composite carbon fiber and Inconel metals <br/>that have similar <br/>mechanical properties to prior art stent 50 such that substantially the same <br/>therapeutic effect<br/>in stent 150 is achieved as was available in prior art stern 50. In any event, <br/>the chosen<br/>material for stout 150 has a level of , Hounsfield density that diminish beam <br/>hardening <br/>artefacts to substantially preserve the appearance of the device under CT or <br/>other <br/>corresponding imaging beam.<br/>[0031] It is thus presently preferred that stent 150 (or other medical <br/>devices according<br/>to the present invention) be made from a material or materials to have an <br/>overall image<br/>density of less than about 1200 Hounsfield Units. Such medical devices can <br/>also have an <br/>overall image density of less than about 900 Hounsfield Units. Such medical <br/>devices can <br/>also have an overall image density of less than about 700 Hounsfield Units. <br/>Such medical <br/>devices can also have an overall image density of less than about 400 <br/>Hounsfield Units.<br/>present invention. The medical devices within the scope of the invention <br/>include devices for <br/>the treatment of obstruction due to clot, plaque, atheroma, tumours or the <br/>like, and/or <br/>treatments involving intimal hyperpla.sia and recurrent stenosis after stent <br/>placenaent. An <br/>appropriate device is delivered into the vascular or bilary system under image <br/>guidance. The<br/>- 10 -<br/><br/>CA 02455439 2011-07-19<br/>post placement follow up of the lumen is enabled by the diminished density and <br/>beam <br/>hardening artefact of the construct and coating of the stent.<br/>[0033] A specific example of another medical device within the scope <br/>of the<br/>invention is shown in Figures 8 and 9, which shows a microcoil 250 for <br/>treatment of an<br/>aneurysm and which is introduced via a guiding cathether 240 and a <br/>microcatheter 245. As <br/>best seen in Figure 8, guiding cathether 240 is inserted through an incision <br/>260 near the <br/>femoral artery or brachial artery or other suitable location and passed <br/>through the venous <br/>system of the patient until it reaches a blood vessel 264 proximal to an <br/>aneurysm 268 in<br/> the patient's head.<br/>[0034] Figure 10 shows an image 254 of the resulting beam hardened artefact <br/>252 when a <br/>prior art microcoil (not shown) is post-operatively examined using imaging <br/>system 30 has <br/>been previously inserted in the patient according to the method described in <br/>reference to <br/>Figure 8. The beam hardened artefact 252 thus renders it difficult, if not <br/>impossible, to<br/>accurately examine the prior art microcoil using imaging system 30.<br/>[0035] However, as seen in image 354 shown in Figure 11, when microcoil 250 is <br/>inserted <br/>according to the method described with reference to Figure 8, then microcoil <br/>250, the now-<br/>repaired aneurysm 268 and blood vessel 264 leading thereto are all visible on <br/>display 42<br/>and therefore capable of post-operative evaluation.<br/>[0036] Another medical device within the scope of the invention is a carotid <br/>stent, for <br/>placement in the carotid artery. Figure 12 shows an image 454 of a sagittal <br/>view of patient <br/>along a plane that includes the carotid artery 470 of the patient. Image 454 <br/>is characterized<br/>by a beam hardened artefact 452 through which the lumen of an implanted prior <br/>art stent<br/>can be Identified, but artefact 452 is severe enough to obscure the lumen of <br/>the carotid <br/>artery 470, therefore preventing a determination as to whether restenosis is <br/>occuring in the <br/>lumen of artery 470 surrounding the prior art stent. However, as shown in <br/>Figure 13, when a <br/>carotoid stent 550 in accordance with an embodiment of the present invention <br/>is used, stent<br/>550 and the lumen of artery 470 surrounding the stent 550 can be viewed and <br/>the<br/>occurence of restenonls determined.<br/>[0037] In other embodiments of the invention, the specific structure and/or <br/>configuration <br/>and/or shape of stent 150 (or other medical device) is chosen to further <br/>reduce the device's<br/>overall radiopacity. For example, the weave of the stents structure can be <br/>chosen to reduce<br/>11<br/>=<br/><br/>CA 02455439 2011-07-19<br/>the radiopacity, and therefore the measured level of Hounsfield units <br/>associated with the <br/>stent. Other aspects of the present invention provide a stent having a reduced <br/>number of <br/>passages of the stent or devices across the stenosis before dilating and <br/>deploying the stent <br/>in the stenos's. In certain prior art stents, it is necessary to cross the <br/>wire, pre-dilate, and<br/>deploy the stent posteriorly. As a further example, a stent in accordance with <br/>an<br/>embodiment of the present invention can Include a self-expanding yet balloon <br/>mounted and <br/>intelligently be restrained. For example, the stent can be mounted on a <br/>balloon that is <br/>deployed by inflation of the balloon. Such a stent is self-expanding but is <br/>delivered on a <br/>balloon. The inflation of the balloon breaks the restraining polymeric bands <br/>and results in<br/>the self-expansion of the stent once the initial stimulus has been given, This <br/>polymeric<br/>material is drug-coated and thrombosis resistant. This polymeric material <br/>helps restrain <br/>plaque and potential embolic material behind the stent. The overall <br/>configuration of the stent <br/>has reduced beam hardened artifacts post insertion when viewed under CT.<br/>is p038] The number of passages of hardware across the stent or devices <br/>across the stent is<br/>reduced from five (as found in prior art stents) to two (according to an <br/>embodiment of the <br/>present invention) and thus, restrain against the wall of the vessel deep to <br/>the stent the <br/>material that would otherwise become potentially an embolic source. This can <br/>be helpful in <br/>reducing the risks of stroke after carotid stenting and in some circumstances <br/>can help<br/>reduce the need for distal flow protection devices which themselves have <br/>stroke risk.<br/>[0039] In another variation of the present invention, stent 150 is coated <br/>(either in its entirety<br/>or in particular locations) with an opacifier to temporarily increase the <br/>Hounsfield units <br/>associated with stent 150 during its insertion, to allow stent 150 to be <br/>inserted using<br/>traditional means. Such a coating would be configured to gradually abate and <br/>dissolve into<br/>the patient's blood stream, such that the radiopacity and associated <br/>Hounsfield units of <br/>stent 150 would decrease over time, such that under a post-operative CT <br/>evaluation, the <br/>Hounsfield units associated with stent 150 are low enough to allow proper <br/>visualization of <br/>the 30 lumen of artery 58 surrounding stent 150. Suitable materials for <br/>coating stent 150<br/>include gold, iodine, ionic and non ionic iodinated compounds, ethiodol, and <br/>lipiodol,<br/>barium, tungsten, tantalum, gadolinium. Whatever coating is chosen, the amount <br/>and rate of<br/>12<br/><br/>CA 02455439 2004-01-20<br/>dissolving of the coating is chosen to reduce toxicity experience by the <br/>patient during <br/>dissolution.<br/>[0040] In a presently preferred embodiment, the aforementioned <br/>coating is a<br/>hydrophilic polymer containing a restenosis inhibiting drug and a density <br/>enhancing<br/>radiologic material such as lyophilizied iodinated contrast material, which is <br/>embedded into<br/>the polymer. This coating is then placed over a stent 150 that is made from a <br/>suitable <br/>material such as a plastic or metal, such as stainless steel, inconel or metal <br/>glass (materials <br/>already approved by The United States of America Food and Drug <br/>Administration), or an <br/>optimal arrangement of strands of another metal can be used. The result is <br/>that stent 150 is<br/>both drug eluting and density eluting (i.e. the level of Hounsfield units <br/>associated with the<br/>stent decreases over time.)<br/>[0041] In another embodiment of the invention, certain post <br/>processing software is<br/>provided in image processing unit 38 to maximize vascular conspicuity in <br/>conjunction with <br/>the known Hounsfield units and other imaging properties associated with stent <br/>150 or other<br/>medical device in accordance with the present invention. For example, where a <br/>level of<br/>Hounsfield units associated with stent 150 is known, then upon detection by <br/>system 30 of an <br/>item within the patient at that particular level of Hounsfield units, then <br/>that information can <br/>be used to identify the item as stent 150 and then to further enhance the <br/>image of the <br/>surrounding vascular region based on the known imaging properties (ie. <br/>radiopacity,<br/> structure, etc.) and using known signal processing an filtering techniques.<br/>[0042] While only specific combinations of the various features and <br/>components of<br/>the present invention have been discussed herein, it will be apparent to those <br/>skilled in the art <br/>that desired subsets of the disclosed features and components and/or <br/>alternative combinations <br/>of these features and components can be utilized, as desired. For example, the <br/>stents, coils<br/>and other medical devices according to the present invention can be coated <br/>with a material to<br/>decrease the risk of infection and restenosis, using techniques and compounds <br/>described in <br/>EP0797988A2 and EP1155689A2 to Angiotech Pharmaceuticals Inc. of Canada, and <br/>the <br/>University of British Columbia.<br/>[0043] The present invention also provides certain novel methods for <br/>evaluating<br/>cervical and intracranial vascular stents using CT, including MDCTA, that is <br/>reliable and low<br/>cost and then to use these techniques for long term evaluation and outcome <br/>analysis of<br/>- 13 -<br/><br/>CA 02455439 2004-01-20<br/>stenting. Sensitivity and specificity can then be determined for MDCTA by <br/>comparison to <br/>conventional catheter angiogram results. The radiographic density of the <br/>stent, coil or other <br/>device can be altered to enhance CT, X Ray, Ultrasound and MRI visibility of <br/>the lumen. <br/>For the purpose of enhanced accuracy of CT diagnostic imaging beam hardening <br/>artefacts<br/>will be reduced and/or minimized. The devices in the present invention are in <br/>contrast to prior<br/>art devices that have been developed for conventional fluoroscopy guidance and <br/>thus are of a <br/>radiodensity or radiopacity that exceeds the needs of CT for clear <br/>visualization, this excess <br/>density creates unwanted beam hardening artefact.<br/>[0044] Furthermore, the present invention allows for a relatively non-<br/>invasive means<br/>to visualize the lumen of a blood vessel surrounding a previously installed <br/>stent (or other site<br/>of an implanted medical device). Due to the reduced beam hardening artefacts <br/>of the stent, <br/>obscuration of the lumen is reduced. This results in the ability to visualize <br/>the lumen non-<br/>invasively as compared follow-ups conducted by invasive repeat catheter <br/>angiography, with <br/>its resultant risk of stroke, death and/or injury to an important vessel or to <br/>otherwise obscure<br/>a critical finding. CTA and CTP are relatively less invasive imaging <br/>modalities that have<br/>been shown to aid in the diagnosis and treatment of acute ischemic stroke. <br/>Both utilize high-<br/>speed spiral CT scanning and three-dimensional volumetric reconstruction <br/>software to create <br/>various types of images following injection of IV contrast solution. CTA can <br/>provide three-<br/>dimensional vascular delineation similar to other non-invasive techniques as <br/>well as<br/>visualization of adjacent non-vascular soft-tissue. CTA can also offer rapid <br/>volume<br/>acquisition, limited reconstruction artifact and scan completion during the <br/>period of peak <br/>intravascular contrast enhancement. Using CTA, it is often possible to see <br/>filling defect in a <br/>vessel as a result of contrast displacement by clot or thrombus. The <br/>sensitivity for detecting <br/>flow abnormality in vessels in the circle of Willis by CTA can be at least 89% <br/>when<br/>compared to digital subtraction angiography ("DSA"), and CTA does not carry <br/>the up to 5%<br/>risk of complication, and the up to 0.5% risk of permanent stroke that DSA has <br/>been shown <br/>to carry.<br/>[0045] The above-described embodiments of the invention are intended <br/>to be<br/>examples of the present invention and alterations and modifications may be <br/>effected thereto,<br/>by those of skill in the art, without departing from the scope of the <br/>invention which is defined<br/>solely by the claims appended hereto.<br/>- 14 -<br/>
