Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2001-12-21
2004-02-03
Shaw, Shawna J. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C324S309000
Reexamination Certificate
active
06687530
ABSTRACT:
BACKGROUND OF INVENTION
The field of the invention is nuclear magnetic resonance imaging (MRI) methods and systems. More particularly, the invention relates to the tracking of small coils that can be incorporated into interventional devices and other external devices, using MRI methods.
During MR tracking procedures, MR signals are generated throughout the patient using a large transmit coil, but are detected with small receive coils. Locating these coils is accomplished by acquiring the MR signal in the presence of applied magnetic field gradient, Fourier transforming the signal and identifying the position of the most intense frequency-domain signal.
Frequently, tracking coils are almost fully immersed in MR signal generating fluids. This is particularly true for MR tracking catheters. Because the coils detect signals from their entire surroundings, localization of the MR signal can be difficult when the data's pixel size is smaller than that of the coil. Localization becomes even more difficult when the Signal-to-Noise Ratio (SNR) is relatively low. Under these conditions the measured location of the coil appears to hop around the true location of the coil since the local signal maximum varies both spatially and temporally.
One way to improve the precision of the location measurement is to increase the SNR of the acquisition. This can be done by 1) increasing the static magnetic field strength, 2) signal averaging, 3) using larger tracking coils and/or 4) changing the T1 of the MR signal source. Unfortunately, all of these remedies have implications for system cost, resolution (temporal and spatial), and clinical use.
What is needed is a method and system for locating a tracking coil which is insensitive to the location and orientation of the coil or similar tracking device. What is further needed is a method and system for locating a tracking coil with reduced artifacts.
SUMMARY OF INVENTION
In a first aspect, a method for tracking the location of a device within the field of view of a Magnetic Resonance Imaging (MRI) system is provided. The method comprises computing a centroid of signal intensity in a region centered about a location of maximum signal intensity, L
max
of acquired magnetic resonance (MR) signals corresponding to the device.
In a second aspect, a system for tracking the location of a device within the field of view of a MRI system is provided in which a locator sub-system is adapted to compute a centroid of signal intensity in a region centered about a location of maximum signal intensity.
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Liu et al. “Comparison of Navigator Echo and Centroid Corrections of Image Displacement Induced by Static Magnetic Field Drift on Echo Planar Functional MRI” (Jan. 16, 2001) Journal of Magnetic Resonance Imaging 13:308-312.
General Electric Company
Patnode Patrick K.
Shaw Shawna J.
Testa Jean K.
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