Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2001-04-05
2003-04-22
Lefkowitz, Edward (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S322000
Reexamination Certificate
active
06552544
ABSTRACT:
FIELD OF THE INVENTION
This invention is in the technical field of magnetic resonance imaging (MRI) using nuclear magnetic resonance (NMR) phenomenon and relates to a detunable coil assembly with a simplified design and capable of detuning both quadrature modes at the same time.
BACKGROUND OF THE INVENTION
It has been known for producing images by utilizing NMR to employ separate specially designed coils for producing a radio frequency (RF) excitation field and receiving the NMR signal. The excitation is commonly provided by a large-volume field coil (or a “volume coil”) capable of generating a homogeneous RF magnetic field throughout a relatively large region such as around the entire body of a subject to be imaged. For receiving the NMR signals from specified localized portions of the body, smaller coils (such as so-called “surface coils” which generally have excellent sensitivity and poorer B1 homogeneity) is used for detailed imaging. Since both the excitation coil and the receiving coil are tuned to resonate at the same frequency, they would interact, or couple, with each other and thereby cause non-uniformity in the excitation field.
In order to minimize such coupling, it has been known to build both the volume coil for excitation an the surface coil with an active detuning feature. While the excitation volume coil excites the sample, the surface coil is detuned to a different frequency. Immediately after the excitation phase, the volume coil is detuned to an off-resonance frequency and the surface coil is tuned back to the resonance frequency for detection. Throughout herein, therefore, “detuning” will mean a frequency shift by at least the sum of the half widths of the resonance peaks of the two coils. For the purpose of these detuning operations, it has also been knownto make use of pin diodes as switches because they must be carried out within a few microseconds.
Prior art apparatus and methods for actively detuning (or “disabling”) an NMR volume coil include those described in U.S. Pat. Nos. 4,833,409 (issued May 23, 1989 to M. G. Eash) and 4,763,076 (issued Aug. 9, 1988 to M. Arakawa, et al.). These prior art apparatus are characterized as having a pin diode-containing switching circuit electrically connected to the RF circuit of the field coil, and this makes it difficult to handle the currents and the problem of electrical noise becomes severe.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a detunable coil assembly with a simple design with which the detuning of a field coil for MRI can be accomplished.
It is another object of this invention to provide such a coil assembly with which frequencies of both quadrature modes of the field coil can be shifted at the same time.
It is still another object of this invention to provide a method of detuning an RF field coil for MRI with a detuning coil of a simple design.
It is a further object of this invention to provide a method of detuning a quadrature field coil for MRI from frequencies of both its quadrature modes.
A detunable coil assembly embodying this invention is characterized not only as comprising a main coil which resonates at a specified resonance frequency and a switchable detuning coil which, when switched on, becomes inductively coupled to the main coil so as to detune it from its resonance frequency but also wherein the detuning coil and the main coil are electrically insulated from each other. Because the main coil which serves as the field coil in an MRI application is physically separated from the low-frequency switching circuit for the detuning coil, the circuit design is much more simplified without adversely affecting the performance. The invention is applicable to situations where the main coil is a quadrature birdcage coil or a multiply tuned coil with a coil array and the main coil can be detuned from more than one of its resonance frequencies at the same time.
REFERENCES:
patent: 4638253 (1987-01-01), Jaskolski et al.
patent: 4717881 (1988-01-01), Flugan
patent: 4725779 (1988-02-01), Hyde et al.
patent: 4763076 (1988-08-01), Arakawa et al.
patent: 4812764 (1989-03-01), Bendall
patent: 4833409 (1989-05-01), Eash
patent: 5323113 (1994-06-01), Cory et al.
patent: 5445153 (1995-08-01), Sugie et al.
patent: 5453692 (1995-09-01), Takahashi et al.
patent: 5585721 (1996-12-01), Datsikas
patent: 5898306 (1999-04-01), Liu et al.
patent: 5903150 (1999-05-01), Roznitzky
patent: 6137291 (2000-10-01), Mitamura et al.
patent: 6198962 (2001-03-01), Su
patent: 6211677 (2001-04-01), Burl et al.
patent: 01094834 (1989-04-01), None
patent: 01213559 (1989-08-01), None
Stewart C. Bushong; Magnetic Resonance Imaging physical and biological principles; second edition; 1996, Chapter 12, pp. 144-158).*
Article by C.E. Hayes, et al., entitled “An Efficient, Highly Homogeneous Radiofrequency Coil for Whole-Body NMR Imaging at 1.5T” published inJournal of Magnetic Resonance, 63, pp. 622-628 (1985).
Yoda Kiyoshi, High Frequency Probe for NMR and NMR signal measuring method Jun. 10, 1987, Patent Abstract of Japan pp. 1-16.*
Yoda Kiyoshi, Probe for NMR and its adjusting method Feb. 23, 1988, Patent Abstract of Japan pp. 1-12.
Rath Alan R.
Wong Wai Ha
Berkowitz Edward H.
Fishman Bella
Lefkowitz Edward
Varges Dixomara
Varian Inc.
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