Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-07-29
2001-08-14
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S422000, C600S411000, C600S414000, C600S423000, C324S308000, C324S318000, C324S322000, C606S130000
Reexamination Certificate
active
06275722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to methods and apparatus for nuclear magnetic resonance (MR) imaging, in particular to MR methods and apparatus permitting reconstruction of MR images from signals received from an RF receiving coil which is swept over a region of interest during imaging.
2. Description of the Related Art
The clinical success of surgical tumor resection is often limited by residual tumor which remains at the completion of the procedure. This limitation is particularly common with brain tumors where access to the lesion is limited both by anatomic constraints (skull, etc.) and by the surgeon's desire to produce minimal morbidity. As a result, tumor may remain hidden from the surgeon and go undetected until post-operative imaging is performed.
Studies (see, e.g., Albert et al., 1994, Neurosurgery 34-1:45-60) have motivated the addition of intra-operative imaging modalities, including ultrasound, computed tomography (CT), and magnetic resonance (MR), in order to provide feedback to the surgeon on the status of the surgical procedure at a time when the surgeon can still react appropriately. In particular, such imaging can provide an assessment of the tissue along the border of the resection cavity that has been created by the surgical procedure and identify residual tumor.
Therefore, for this and other reasons, intra-cavity MR imaging is of particular interest. Intra-cavity RF coils for MR imaging have been proposed and developed for evaluation of the prostate (Martin et al., 1988, Inflatable surface coil for MR imaging of the prostate, Radiology 167:570-574), cervix (Baudouin at al., 1992, Magnetic resonance imaging of the uterine cervix using an intravaginal coil, Magnetic Resonance in Medicine 24:196-203), vascular wall (Hurst et al., 1992, Intravascular (catheter) NMR receiver probe: preliminary design analysis and application to canine iliofemoral imaging, Magnetic Resonance in Medicine 24:343-357; Martin et al., 1992, MR imaging of blood vessels with an intravascular coil, Journal of Magnetic Resonance Imaging 2:421-429), and esophagus. Such small internal coils offer substantial signal-to-noise (S/N) advantages over larger external coils, and thereby permit high resolution imaging of tissue in close proximity to the RF coil.
However, these intracavity coils are necessarily small, and, therefore, are necessarily limited because their region of sensitivity is thereby strictly localized. Tissue away from the RF coil is not efficiently detected with such intracavity coils. Unfortunately, an optimally large coil for intra-cavity imaging is unlikely to be available because the extent of the cavity is unique and may not be known a priori, and because access to the surgical cavity may be through an orifice of minimal diameter.
Citation of a reference herein, or throughout this specification, is not to be construed as an admission that such reference is prior art to the Applicant's invention of the invention subsequently claimed.
SUMMARY OF THE INVENTION
The objects of the present invention are to provide methods and apparatus which overcome the above identified problems in the current art, namely which provide for imaging other than a strictly localized region by use of intracavitary coils. In particular, according to one object of this invention, novel imaging methods are provided according to which an intracavitary coil is swept or moved around the periphery of a cavity during imaging in order to obtain high resolution images of a substantial region of the cavity boundary and adjacent tissue. According to another object of this invention, smaller RF coils are provided which may be introduced into surgical cavities and cooperate with these novel imaging methods. Finally, according to other objects, this invention provides MR apparatus for performing these methods and software for controlling an MR apparatus to perform these methods.
The methods and apparatus of this invention are routinely extendable to other imaging applications where movement of an RF coil during imaging is necessary or unavoidable. For example, they are extendable to imaging the exterior of a patient and adjacent tissues at high S/N ratio.
These objects are achieved by the following embodiments of this invention.
In a first embodiment, the invention includes a method for magnetic resonance (MR) imaging of a region of interest in an object to be examined by means of a moveable RF receiving coil assembly, the method comprising: exciting nuclear magnetization in the region of interest by applying radio-frequency (RF) pulses and magnetic field gradients according to a selected imaging protocol, sweeping the moveable RF receiving coil assembly near the region of interest, receiving RF imaging signals generated in an RF receiving coil by the excited nuclear magnetization, wherein the moveable RF receiving coil assembly comprises the RF receiving coil and means for repetitively determining a 3D position and a 3D orientation of the RF receiving coil, determining repetitively 3D positions and 3D orientations of the RF receiving coil during the period of receiving of RF imaging signals, reconstructing an MR image of the region of interest from the received MR imaging signals and from the determined 3D positions and 3D orientations of the RF receiving coil.
In a first aspect of the first embodiment, the means for repetitively determining a 3D position and a 3D orientation comprises at least three MR-active microcoils, and wherein the step of determining repetitively further comprises: exciting nuclear magnetization in the microcoils, receiving MR signals generated in the microcoils from the excited nuclear magnetization, determining the 3D spatial coordinates of the microcoils from the received MR signals, and determining the 3D position and the 3D orientation of the RF receiving coil from the 3D spatial coordinates of the microcoils.
In a second embodiment, the invention includes a moveable radio-frequency (RF) receiving coil assembly for receiving RF signals generated by nuclear magnetization excited by a magnetic resonance (MR) apparatus in a region of interest in an object to be examiner comprising: manipulation means for manipulating the moveable RF receiving coil assembly, an RF receiving coil for receiving RF imaging signals, at least three MR-active microcoils for receiving MR position signals from which the 3D spatial coordinates of the microcoils can be determined, wherein at least three of the microcoils are non-collinearly arranged, and signal lines for connecting the RF receiving coil and the microcoils to RF receivers in the MR apparatus.
In a third embodiment, the invention includes a magnetic resonance (MR) apparatus for MR imaging of a region of interest in an object to be examined comprising: a main field magnet for generating a steady magnetic field in the region of interest, a magnetic field gradient system for generating gradients in the steady magnetic field in the region of interest, a radio-frequency (RF) transmitter for transmitting RF pulses to the region of interest, an RF receiving coil assembly further comprising manipulation means for manipulating the RF receiving coil assembly, an RF receiving coil for receiving MR imaging signals from the region of interest, at least three MR-active microcoils for receiving MR position signals from which the 3D spatial coordinates of the microcoils can be determined, wherein at least three of the microcoils are non-collinearly arranged, and signal lines for connecting the RF receiving coil and the microcoils to the MR apparatus, means for detecting the received MR imaging signals and the received MR position signals, control means responsive to the detected MR imaging signals and the detected MR position signals for controlling the RF transmitter, the magnetic field gradient system, and the means for detecting to (i) excite nuclear magnetization in the region of interest by applying RF pulses and magnetic field gradients according to a selected imaging protocol and to detect MR im
Martin Alastair
Vaals Van Joop
Lateef Marvin M.
Lin Jeoyuh
Philips Electronics North America Corporation
Vodopia John F.
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