Patent Application: US-11541605-A

Abstract:
the present invention discloses a method for determining the position and / or orientation of a catheter or other interventional access device or surgical probe using phase patterns in a magnetic resonance signal . in the method of the invention , global two - dimensional correlations are used to identify the phase pattern and orientation of individual microcoils , which is unique for each microcoil &# 39 ; s position and orientation . in a preferred embodiment of the invention , tracking of interventional devices is performed by one integrated phase image projected onto the axial plane and a second image in an oblique plane through the center of the coil and normal to the coil plane . in another preferred embodiment , the position and orientation of a catheter tip can be reliably tracked using low resolution mr scans clinically useful for real - time interventional mri applications . in a further preferred embodiment , the invention provides real - time computer control to track the position of endovascular access devices and interventional treatment systems , including surgical tools and tissue manipulators , devices for in vivo delivery of drugs , angioplasty devices , biopsy and sampling devices , devices for delivery of rf , thermal , microwave or laser energy or ionizing radiation , and internal illumination and imaging devices , such as catheters , endoscopes , laparoscopes , and related instruments .

Description:
as used herein the phrase “ phase pattern ” refers to a spatial map of phase in the mr signal in a particular plane of interest . as used herein the phrase “ catheter tracking ” refers to the act of determining information about the position and / or orientation of a catheter tip . as used herein the phrase “ marker for perturbing the phase of the magnetic resonance signal ” means using a receive coil of arbitrary shape used to introduce phase into the mr signal through its receive sensitivity field or using a material of arbitrary shape and sufficient magnetic susceptibility to perturb the static magnetic field in the volume surrounding the material . as used herein the phrase “ microcoil ” refers to small tuned radiofrequency antenna used to receive mr signal or transmit an mr excitation field . as used herein the phrase “ field map ” refers to a spatial map of the static magnetic field in a plane of interest . active mri tracking of catheters and other interventional probes has been a subject of research for more than a decade , but most studies have focused on magnitude sensitivity methods for localizing such devices . the fundamental weakness with this approach is that it produces inaccurate localization when the peak of the magnitude projections does not correspond to the location of the center of the microcoil . the magnitude sensitivity profile of the coil also changes with different coil orientations . the magnitude projection method is also inheritably susceptible to noise , high - resolution projections are needed , and orientation information cannot be obtained from projections alone . the present invention addresses these various limitations of magnitude sensitivity methods by providing a novel method for determining the position and orientation of interventional access devices and surgical probes based on phase patterns in the mr signal around a marker positioned on the device or probe . more particularly , the present invention provides a method of determining the position and / or orientation of a medical device in a patient &# 39 ; s body which involves placing the medical device in a patient &# 39 ; s body and placing the patient in a magnetic resonance imaging ( mri ) scanner . the medical device includes at least one marker for perturbing the phase of the magnetic resonance signal which is measured by the mri scanner . based on the received magnetic resonance signals acquired from the patient &# 39 ; s body using the magnetic resonance imaging scanner , at least one map of the spatial distribution of the phase of the received signals is reconstructed , and using characteristics of the spatial distribution of the phase , the device position and / or orientation are determined . in a preferred embodiment of the invention the marker is a small circular microcoil positioned on the device or probe . in this embodiment , the microcoil is used to acquire the mr signal . however , it will be appreciated that the microcoil does not need to be circular , it may for example be elliptical or square , and in addition any other type of marker may be used so long as it perturbs the phase of the magnetic resonance signal , for instance through any type of susceptibility mechanism . in this latter case , the marker is selected so that the difference in magnetic susceptibility between the marker and adjacent water in the body yields unique phase patterns in the signal around the marker which can be mapped using the mr signal received by an external coil . another example includes the introduction of a small piece of ferromagnetic material onto the probe which disrupts the local magnetic field . in this embodiment , mr signals can be acquired using an mr reception coil located external to the body . a further example is the introduction of a small bubble of carbon dioxide in a balloon attached to the device . again , the difference in magnetic susceptibility between the gaseous carbon dioxide and adjacent water in the body yields unique phase patterns in the signal around the balloon which can be mapped using the mr signal received by an external coil . when using a small circular microcoil positioned on the device or probe the method of the present invention determines the position and orientation of interventional access devices and surgical probes based on phase patterns in the mr signal around the small circular microcoil positioned on the device or probe . the microcoil may be connected electrically to the mr system or signals from the coil may be coupled optically or inductively to a transducer which is electrically connected to the mr scanner . the latter embodiments provide some electrical isolation between the patient and the scanner . one can configure the system so that it is possible to separately receive signals from different coils at the same time . that said , when using microcoils , phase images are derived from the signal from each microcoil . in the method of the invention , accurate position and orientation information can be obtained over a circular area of at least 4 microcoil diameters . moreover , since only a sample of the information is needed to position and orient the catheter , highly redundant localization information is available and global correlations can be used to identify the phase patterns . the present invention will now be described further with particular reference to certain non - limiting embodiments and to the accompanying drawings in fig1 to 4 . in the method of the invention , the sensitivity field of a circular microcoil is evaluated . the theory of reciprocity states that the sensitivity field of an mr receive coil is equivalent to the magnetic field produced when current i is passed through the coil . the receive sensitivity of a circular receive coil can be described in cylindrical coordinates by the following equations : b z ′ = μ ⁢ ⁢ ik 4 ⁢ π ⁢ ar ⁡ [ k ⁡ ( k ) + a 2 - r 2 - z ′ 2 ( a - r ) 2 + z ′ 2 ⁢ e ⁡ ( k ) ] [ 1 ] b r = μ ⁢ ⁢ ikz ′ 4 ⁢ π ⁢ ⁢ r ⁢ ar ⁡ [ - k ⁡ ( k ) + a 2 + r 2 + z ′ 2 ( a - r ) 2 + z ′ 2 ⁢ e ⁡ ( k ) ] ⁢ ⁢ where [ 2 ] k = 4 ⁢ ar ( a - r ) 2 + z ′ 2 , [ 3 ] a is the coil &# 39 ; s radius , μ is the magnetic permeability of the medium surrounding the coil , r is radial distance from the centre of the coil and z ′ is distance in the perpendicular direction . k ( k ) and e ( k ) are elliptic integrals of the first and second kind respectively . the directional component of the sensitivity introduces spatially varying phase patterns into the mr signal that are dependent solely on the position and orientation of the coil within the magnetic field . assuming constant phase in the mr signal in the absence of the receive coil , the phase distribution introduced by the receive coil can be identified through a phase reconstruction of an image acquired from the receive coil . with reference to fig1 a , when the radius of the microcoil is smaller compared to the field of view ( fov ) ( field of view being the size , in linear dimensions , of the acquired phase pattern ), so that it satisfies the condition ( a & lt ; fov / 10 ), the simulated magnetic field receive phase pattern around the circular microcoil 1 in the axial plane ( perpendicular to the static field pointing along z ) through the center of the coil has lines of constant phase extending in the radial direction from its edges 2 . according to the invention , the phase pattern in the axial plane is independent of coil pitch about the x axis ( magnet coordinate system ) ( fig1 b ) and rotates by angle θ / 2 3 with coil rotation about the z axis by angle θ ( fig1 c ), wherein this phase pattern is also independent of axial slice , wherein the same phase pattern results if the signal is integrated over the z - direction ( magnet coordinate system ) ( fig1 d ). further in the method of the invention , the phase pattern in an oblique slice through the center of a micro coil lying in the z - x plane and normal to the coil plane ( fig2 a ) consists of two areas of constant phase , wherein the areas of constant phase have a value of π / 2 + θ above and below the coil and a value of − π / 2 + θ to the sides of the coil . the discontinuities 6 between the two areas extend in the radial direction from the coil edges . according to the invention , the phase pattern rotates by an angle φ / 2 7 with coil rotation by angle φ about the direction normal to the oblique plane ( fig2 b ). with reference to fig2 c , when the coil is rolled by angle θ about the z axis , the values of phase in the two constant areas increase by θ to form a value of π / 2 + θ above and below the coil 8 and − π / 2 + θ to the sides of the coil 9 . with reference to fig3 , according to a preferred embodiment of the invention , the phase patterns around a circular microcoil can be used to determine the position and orientation of the microcoil . in the method of the invention , an axial projection image ( no slice selection gradient ) of the microcoil &# 39 ; s sensitivity pattern is first created ( fig3 a ). in a preferred embodiment , the microcoil can be positioned on the x - y plane with reference to lines of constant phase which propagate radially from the edges of the microcoil . the amount θ by which the microcoil is rotated about the static field b o is determined by determining the amount by which the phase pattern is rolled . further in the method of the invention , an oblique slice is then prescribed ( drawn ) through the center of the microcoil and perpendicular to the plane in which the microcoil lies 10 ( fig3 b ). prescribing ” means selecting an imaging plane , often done by drawing a line on an mr image to define a plane perpendicular to the current image passing through that line . with reference to fig3 c , the microcoil can then be located on a third axis based on discontinuities in the oblique phase pattern 6 which extend radially from the microcoil &# 39 ; s edges . further in the method of the invention , the pitch angle φ by which the coil is rotated about a vector perpendicular to the oblique plane , can be determined by calculating the angle at which oblique phase pattern is rotated with respect to a reference phase pattern . the phase in the two regions can then be sampled to verify the calculation of θ . the angles θ and φ form two euler angles from which the microcoil &# 39 ; s normal can be determined . in order to evaluate the utility of the present invention , a small microcoil with diameter 4 - mm - outside diameter ( 30 gauge insulated magnet wire , 4 windings ) was placed on the distal tip of a 6f angiographic catheter and embedded in an agar phantom . phase patterns were obtained using a 1 . 5 t ge signa cv / i mr scanner with a spin echo pulse sequence ( fov = 8 cm , te = 17 ms , tr = 5000 ms , 256 × 256 ). the phase patterns obtained from the microcoil are shown in fig4 a and 4 c with reference to simulated phase patterns around microcoils in a similar orientation . in the axial phase pattern obtained without slice selection ( fig4 a ) radial lines of constant phase extending from the coil &# 39 ; s edges can clearly be seen , wherein the phase pattern resembles the simulations ( fig4 b ). the phase pattern in the oblique slice ( fig4 c ) consists of two regions of constant phase , wherein phase values in these regions are in agreement with the predicted values ( fig4 d ). in another embodiment of the invention , phase inhomogeneities can be corrected for by obtaining two separate phase images at different echo times and generating a field map to perform post - acquisition corrections of static magnetic field inhomogeneities . in another embodiment , the necessary phase images can be acquired rapidly using a fast acquisition technique . in this embodiment the methods for tracking the device are identical to previous embodiments with the exception that a rapid acquisition technique is used to collect the phase data in the planes described in fig3 a - 3 c . in this embodiment , phase image quality is sacrificed for acquisition speed to enable tracking with a high temporal resolution . an example of a rapid imaging technique is spiral acquisition which collects data in a rapid and efficient manner . the utility of this embodiment was investigated by acquiring phase patterns in the planes of interest using the same microcoil discussed above using a spiral acquisition ( fov = 8 cm , tr = 36 ms , te = 10 ms , fa = 45 deg , 3 4096 - point spiral interleaves in k - space with an additional acquisition for field map calculation , total acquisition time = 216 ms ). the phase patterns obtained from the microcoil using a spiral acquisition are shown in fig5 a and 5 c with reference to simulated phase patterns around microcoils in a similar orientation . in the axial phase pattern obtained without slice selection ( fig5 a ) radial lines of constant phase extending from the coil &# 39 ; s edges can clearly be seen , wherein the phase pattern resembles the simulations ( fig5 b ). the phase pattern in the oblique slice ( fig5 c ) consists of two regions of constant phase , wherein phase values in these regions are in agreement with the predicted values ( fig5 d ). the results of the simulation studies underscore several advantages of the phase sensitivity method of the present invention . unlike magnitude sensitivity methods disclosed in the prior art , phase patterns are unique to a microcoil &# 39 ; s position and orientation and yield accurate information about both localization parameters . according to the present invention , phase pattern information also provides a more robust localization algorithm , since phase patterns are more spatially varying than magnitude projections and yield clear position and orientation information over a circular area of at least 4 coil diameters . furthermore , since global two - dimensional correlations can be used to identify the phase patterns , low - resolution scans may be sufficient for locating the coil . as a result , localization using the phase pattern methods disclosed by this invention may prove particularly useful in real - time applications , wherein as one non - limiting example , if the coil were to be located within a 2 cm volume , a single spiral acquisition at sufficient resolution ( 2 cm fov , 1 . 05 mm resolution , 31 . 25 khz bandwidth , 1024 readout ) could be performed on a 1 . 5 t ge signa cv / i system in 16 ms . according to this application of the method of the invention , catheter position and orientation could be determined in under 100 ms even with extra acquisitions to correct for inhomogeneities . in another preferred embodiment of the present invention , active mr localization of the orientation and position of an interventional device may also be achieved by means of several microcoils positioned along the longitudinal axis of a catheter or other interventional device . particularly preferred are microcoils consisting of a circular loop of conductive material positioned around the functional parts of an interventional device , such as a drug delivery catheter . depending on the orientation of the coil with the magnetic b 0 , single microcoils may be used separately or may be constructed in an array . in order to reduce the thickness of the microcoil , the coil material may be sputter - coated onto the surface of the device . to provide information about angular twist of the device , the loop may be sputter - coated onto the side of the device rather than in a plane perpendicular to the longitudinal axis of the device . also preferred is a microcoil able to move and rotate inside a catheter sleeve attached to another component of the device . this could be used to provide position and / or orientation information about this component ( eg . shaft ) inside the catheter ). in another preferred embodiment , more than one microcoil may be present , wherein the distribution of microcoils along a length of the catheter defines the mr - visible region of the interventional device . in general , this embodiment of the invention is best practiced by employing an array of microcoils , such that an mr image is obtained for any orientation of the interventional device . according to the invention , where functional elements are combined into a single interventional device , the positioning and orientation of several microcoils may be tailored for a particular interventional procedure . in the method of the invention , one or more microcoils may be positioned near or at the distal end of the central catheter to assist in positioning the device at a target anatomical location . other configurations of microcoils , such as parallel alignment of the microcoils in a strip - like orientation , stacking of microcoils in rows and columns , or mixtures of these and other configurations may also be useful in the practice of the present invention . in another embodiment of the present invention , two microcoils are placed in orthogonal directions at the distal tip of the catheter , as shown in fig6 . in this configuration tracking is performed using both coils . advantages with this configuration include the ability to track the device with adequate signal regardless of device orientation . in this configuration there is also minimal inductive coupling between microcoils . furthermore , the configuration is well suited for acquiring high - resolution images of the anatomy immediately surrounding the device . other functional elements of interventional probes which may be localized using the method of the invention include thermal elements for providing heat , radiation carrying elements ( e . g ., ultraviolet radiation , visible radiation , infrared radiation ), optical fibers , detection elements ( e . g ., ph indicators , electronic activity indicators , pressure detectors , ion detectors , thermal detectors , etc . ), and any other sensing or detection element which would be useful during medical procedures . in accordance with the method of the invention , these individual elements would benefit from accurate directed placement of the functional tip of the device within the target site in a tissue . for example , in the treatment of neurological diseases and disorders , targeted drug delivery can significantly improve therapeutic efficacy while minimizing systemic side - effects of the drug therapy . image - guided placement of the tip of a drug delivery catheter directly into specific regions of the brain can initially produce maximal drug concentration close to the loci of tissue receptors following injection of the drug . high - resolution visual images denoting the actual position of the drug delivery device within the brain are extremely useful to the clinician in maximizing the safety and efficacy of the procedure . in a particularly preferred embodiment , drug delivery devices , such as catheters , could be monitored by the mr phase tracking method of the present invention , thus making intra - operative verification of catheter location possible . the present invention also overcomes other limitations of the prior art . for example , the limited distribution of drug injected from a single catheter location can reduce the therapeutic efficacy of the intervention in cases of anatomically extensive neurological damage , such as , for example , with certain brain tumors and stroke . since the volume flow rate of drug delivery typically must be very low in order to avoid indiscriminate damage to brain cells and nerve fibers , delivery of a drug from a single point source limits the distribution of the drug by decreasing the effective radius of penetration of the drug agent into the surrounding tissue receptor population . another aspect of this invention is therefore to overcome these inherent limitations of single point source drug delivery by devising a catheter tracking method which provides the ability for accurately monitoring the placement of a catheter tip at several tissue locations in order to allow multiple drug release sources , which effectively disperse therapeutic drug agents over a brain region containing receptors for the drug , or over an anatomically extensive area of brain pathology . the availability of an mr - visible drug delivery device combined with clinically acceptable low - resolution imaging would make it possible to obtain near real - time information on drug delivery during interventional procedures in an intra - operative mr system , as well as for pre - operative and post - operative confirmation of the location of the drug delivery device . medical and surgical applications of the present invention would include vascular surgery and interventional radiology , cardiac surgery and cardiology , thoracic surgery and radiology , gastrointestinal surgery and radiology , obstetrics , gynecology , urology , orthopedics , neurosurgery and neurointerventional radiology , head and neck surgery and radiology , ent surgery and radiology , and oncology . in addition to direct tissue injection , the method of the invention applies to drug delivery via intraluminal , intracavitary , laparoscopic , endoscopic , intravenous , intraarterial applications . the present invention also provides clinical benefits for certain cardiovascular procedures , such as , for example , traversing chronic total occlusions , where an intravascular device is pushed through a chronic occlusion in an artery to re - establish blood flow . knowledge of the orientation and position of the device tip with respect to both the occlusion and vessel wall is extremely important because of significant risk of incidental surgical damage to the vessel wall ( fig7 a ). mri can now reliably differentiate vessel wall from surrounding tissue . the method of the present invention can be used to determine and image both the position and orientation of a device with respect to critical anatomic landmarks resulting in improved safety and procedural efficacy . in a preferred embodiment , device position and orientation would be imaged in real - time on an mr image thereby providing clinically beneficial guidance for the procedure ( fig7 b ). in a particularly preferred embodiment , the present invention can also be used for targeted delivery of stem cells in the myocardium . in order to achieve preferential migration of stem cells into infracted myocardium , injections must be made at the border between diseased and healthy tissue . mr can be used to identify such sites through delayed contrast - enhanced images , wherein the method of the present invention can be used to guide an injection device to appropriate target sites in the penumbra of the ischemic myocardium and to properly orient the injection needle for delivery of cells into region best suited for establishing functional improvement . it should be understood that the foregoing description is merely illustrative of the invention . various alternatives and modifications can be devised by those skilled in the art without departing from the scope or spirit of the invention . accordingly , the present invention is intended to embrace all such alternatives , modifications and variances which fall within the scope of the appended claims . as used herein , the terms “ comprises ”, “ comprising ”, “ including ” and “ includes ” are to be construed as being inclusive and open ended , and not exclusive . specifically , when used in this specification including claims , the terms “ comprises ”, “ comprising ”, “ including ” and “ includes ” and variations thereof mean the specified features , steps or components are included . these terms are not to be interpreted to exclude the presence of other features , steps or components . the foregoing description of the preferred embodiments of the invention has been presented to illustrate the principles of the invention and not to limit the invention to the particular embodiment illustrated . it is intended that the scope of the invention be defined by all of the embodiments encompassed within the following claims and their equivalents . 4827931 may , 1989 longmore 128 / 334 . 4984573 january , 1991 leunbach 128 / 653 . 4989608 february , 1991 ratner 128 / 653 . 5154179 october , 199 ratner 128 / 653 . 5155435 october , 1992 kaufman et al 324 / 309 . 5188111 february , 1993 yates et al . 128 / 657 . 5201314 april , 1993 bosley et al . 128 / 662 . 5211166 may , 1993 sepponen 128 / 653 . 5218964 june , 1993 sepponen 128 / 653 . 5262727 november , 1993 behbin et al . 324 / 318 . 5271400 december , 1993 dumoulin et al 128 / 653 . 5290266 march , 1994 rohling et al . 604 / 272 . 5318025 june , 1994 dumoulin et al . 128 / 653 . 5353795 october , 1994 souza et al . 128 / 653 . 5357958 october , 1994 kaufman 128 / 653 . 5409003 april , 1995 young 128 / 653 . 5419325 may , 1995 dumoulin et al . 128 / 653 . 5534778 july , 1996 loos et al . 324 / 318 . dick a j , guttman m a , raman v k , peters d c , pessanha b s , hill j m , smith s , scott g , mcveigh e r , lederman r j . “ magnetic resonance fluoroscopy allows targeted delivery of mesenchymal stem cells to infarct borders in swine .” circulation 108 ( 23 ): 2899 - 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