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  Method and system of tracking an intracorporeal device with mr imagingUSPTO Application #: 20080027310Title: Method and system of tracking an intracorporeal device with mr imaging Abstract: A system and method for tracking or otherwise determining positioning of an intracorporeal device is provided. The invention includes a device that may be inserted into a subject and tracked based on an imageable tag included with the device. The imageable tag is at least partially formed of a substance whose nuclei precess at a Larmor frequency different than the Larmor frequency of hydrogen when subjected to a polarizing magnetic field. MR data may be acquired from the imageable tag using an RF receiver tuned to the Larmor frequency of the substance and used to track movement of the device within the subject. (end of abstract) Agent: Ziolkowski Patent Solutions Group, Sc (gems) - Port Washington, WI, US Inventors: Eric R. Tamaroff, John M. Pile-Spellman, Lei Feng, Stephen M. Dashnaw, Robert L. DeLaPaz USPTO Applicaton #: 20080027310 - Class: 600420000 (USPTO) Related Patent Categories: Surgery, Diagnostic Testing, Detecting Nuclear, Electromagnetic, Or Ultrasonic Radiation, Magnetic Resonance Imaging Or Spectroscopy, Using Detectable Material Placed In Body The Patent Description & Claims data below is from USPTO Patent Application 20080027310. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS REFERENCE TO RELATED APPLICATIONS [0001] The present application is a divisional of and claims priority of U.S. Ser. No. 11/160,811 filed on Jul. 11, 2005, the disclosure of which is incorporated herein. BACKGROUND OF THE INVENTION [0002] The present invention relates generally to MR imaging and, more particularly, to a method and system of imaging devices having an imageable tag that includes nuclei that precess at a Larmor frequency different than that of hydrogen when subjected to a polarizing magnetic field. [0003] When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B.sub.0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B.sub.1) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or "longitudinal magnetization", M.sub.Z, may be rotated, or "tipped", into the x-y plane to produce a net transverse magnetic moment M.sub.t. A signal is emitted by the excited spins after the excitation signal B.sub.1 is terminated and this signal may be received and processed to form an image. [0004] When utilizing these signals to produce images, magnetic field gradients (G.sub.x, G.sub.y, and G.sub.z) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques. [0005] MR imaging is frequently used for tracking or otherwise determining the position of an intracorporeal device, such as an endovascular catheter. Hereinafter, the term "intracorporeal device" generally refers to any type of device that is navigable, moveable, or otherwise insertable in whole or in part within a body. To properly guide the device, a number of tracking techniques have been developed. These techniques generally fall into one of two categories: passive tracking or active tracking. [0006] Passive tracking utilizes signal voids or image artifacts for visualization of the medical device. Typically, the medical device is labeled with a paramagnetic marker. Paramagnetic markers are commonly used because the paramagnetic properties of the marker substance shorten its relaxation time. As such, with the appropriate pulse sequence parameters, a signal will not be collected from the marker resulting in a signal void in a reconstructed image. [0007] Other passive tracking techniques include use of susceptibility artifacts on metal wires connected to the medical device. In this regard, the artifacts in a reconstructed image reflect the presence of the medical device. In a further passive tracking technique, electrical current is induced in the electrical wires during signal acquisition so as to modify the intensity of the artifacts for improved device detectability. Additional passive tracking techniques include use of intravascular contrast agents or the passing of similar suitable fluids through a lumen. Passive tracking of devices, however, does have drawbacks. [0008] While passive tracking supports the simultaneous visualization of endovascular devices and subject physiology, such as blood vessels and surrounding tissue, the spatial and temporal resolutions are acquisition dependent and, as a result, the spatial and temporal resolution is inadequate to distinguish the endovascular device from subject anatomy. Further, since the markers used to tag the devices predominantly include hydrogen nuclei, it is difficult to distinguish between subject anatomy and the device with MR imaging of precessing hydrogen. [0009] Active device tracking techniques involve the placement of an RF receiver coil on the endovascular device or use of a guide wire as a linear receiver coil. In this regard, MR signals are acquired at the endovascular device and may be used to reconstruct tracking images. While active tracking techniques are commonly preferred because of the high signal-to-noise ratio (SNR) as well as higher spatial and temporal resolution it provides, electrical wires connect the RF receiver coil to the data acquisition system of the MR scanner. These electrical wires add to the complexity of the endovascular device and can be cumbersome when inserting and positioning the device in the subject. Additionally, it may not be desirable to have electrically conductive leads extending from a subject undergoing an MR scan. [0010] It would therefore be desirable to have a system and method capable of tracking a wireless intracorporeal device through a subject without sacrificing SNR as well as spatial and temporal resolution. BRIEF DESCRIPTION OF THE INVENTION [0011] The present invention provides a system and method for imaging, and in certain embodiment tracking, an intracorporeal device or any other device that may be disposed within a subject, which is tagged with an imageable marker distinguishable from the subject anatomy or an object that overcomes some or all of the aforementioned drawbacks. [0012] A system and method for tracking or otherwise determining positioning of an intracorporeal device is provided. The invention includes a device that may be inserted into a subject and tracked based on an imageable tag included with the device. The imageable tag is at least partially formed of a substance whose nuclei precess at a Larmor frequency different than the Larmor frequency of hydrogen when subjected to a polarizing magnetic field. MR data may be acquired from the imageable tag using an RF receiver tuned to the Larmor frequency of the substance and used to track movement of the device within the subject. [0013] Therefore, in accordance with one aspect of the present invention, a method of MR imaging is provided. The method includes impressing a polarizing magnetic field on a region-of-interest (ROI) having a device disposed therein. The device includes an imageable tag formed of at least a substance distinguishably present in the ROI and that precesses at a first Larmor frequency when subjected to the polarizing magnetic field. The method further includes subjecting the ROI to an excitation field at the first Larmor frequency and acquiring MR data from the ROI with a receiver tuned to the first Larmor frequency. The method also includes the step determining a position of the device within the ROI from the MR data. [0014] In accordance with another aspect, the present invention includes an MRI apparatus having a magnetic resonance imaging (MRI) system that has a plurality of gradient coils positioned about a bore of a magnet to impress a polarizing magnetic field. The MRI system also has an RF transceiver system and an RF switch controlled by a pulse module to transmit RF signals to an RF coil assembly to acquire MR images from precessing hydrogen nuclei in an ROI. The MRI system further includes a computer readable storage medium having stored thereon a computer program comprising instructions, which when executed by a computer, cause the computer to cause excitation of hydrogen nuclei in the ROI. The computer is further caused to cause excitation of nuclei of at least a hydrogen-absent substance having been introduced to the ROI. Nuclei of the hydrogen-absent substance precess at a Larmor frequency different than that of hydrogen nuclei. The computer is also caused to acquire MR data from at least the ROI and reconstruct an image of the ROI that includes contrast between the substance and other structures within the ROI. [0015] According to another aspect of the present invention, a method of MR imaging includes inserting a medical device into a subject. The medical device includes an imageable tag that precesses at a Larmor frequency different than that of hydrogen. The method further includes exciting the subject with a B.sub.1 field at the Larmor frequency of hydrogen and acquiring MR data from at least nuclei in the subject precessing at the Larmor frequency of hydrogen. The method also includes reconstructing tracking images showing movement of the medical device within the subject. [0016] In accordance with a further aspect, the present invention includes a medical device insertable into a subject. The device has a body and at least one sealed chamber connected to the body. An imageable substance including non-hydrogen nuclei is disposed in the at least one sealed chamber. [0017] According to yet another aspect of the present invention, a medical device insertable into a subject is provided. The medical device has a body and one or more cavities formed in at least a portion of an outer surface of the tubular body. An imageable substance predominantly devoid of hydrogen at least partially fills the one or more cavities. [0018] In accordance with yet a further aspect, a method of MR imaging includes placing a fluorinated substance into a restricted portion of a subject. A medical device is inserted into the restricted portion. The medical device is constructed substantially free of the fluorinated substance placed in the restricted portion. MR data is acquired from the restricted portion with a receiver coil at least tuned to acquire RF signals at the Larmor frequency of the fluorinated substance. The method further includes reconstructing an image of the restricted portion from the MR data and determining relative positioning of the medical device within the intracorporeal cavity from the image. [0019] According to yet another aspect, the present invention includes a navigable MR imaging device constructed of a substance to precess at a Larmor frequency of approximately 60 MHz when subjected to an approximately 1.5 T substantially uniform magnetic field. [0020] In accordance with yet a further aspect, the present invention includes an imaging technique having means for impressing a substantially uniform magnetic field about a subject to be imaged and means for translating a navigable device within the subject. The navigable device is constructed to have a detectable tag comprised of a substance whose nuclei precess at a Larmor frequency other than that of hydrogen nuclei. The imaging technique further has means for exciting nuclei of the substance to precess at the Larmor frequency other than that of hydrogen nuclei and means for acquiring MR data from nuclei precessing at the Larmor frequency other than that of hydrogen nuclei. Means for actively tracking displacement of the navigable device within the subject is also provided. [0021] Various other features, objects, and advantages of the present invention will be made apparent from the following detailed description and the drawings. Continue reading... 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