Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Utility Patent
1997-12-01
2001-01-02
Oda, Christine K. (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S309000
Utility Patent
active
06169399
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a multiple resonance superconducting probe for detecting multiple nuclei. The probe can be used, for example, to produce high quality magnetic resonance images.
BACKGROUND OF THE INVENTION
Magnetic loop probes have previously been used to detect signals within a single selected frequency range in a number of applications such as magnetic resonance imaging. Conventional receiving loops typically used today are made from copper wire.
Magnetic resonance imaging (“MRI”) is used in the medical field to produce images of various parts of the body for examination and diagnosis by measuring the response of selected nuclei in the body when subjected to a magnetic field. The MRI probe is configured to have a resonance frequency equal to the resonance frequency of the selected nuclei. An example of a MRI performed is a mammography, which detects lumps in a woman's breast. A probe in the form of a coil is placed around the breast being examined and a MRI “picture” is taken. The MRI picture is based on the detection of a particular nuclei in the tissue by a coil with the same resonance frequency as the particular nuclei being imaged. Another example of an MRI application is of a human head for the detection of a tumor or cancer. There are two commonly used MRI probes: a body coil and a surface coil. The body coil is large enough to enclose a part of a human or animal body such as a head coil. The surface coil is in a shape of a plane or of a local surface of a body organ. The surface coil is placed in close proximity to the imaging area, thus has a small field of view (“FOV”) which gives a high resolution image of a local region of interest. Conventionally, the wire coils used for an MRI are not made from superconducting materials.
Recently, superconducting probes have been used in MRI, microscopy (MRM), and spectroscopy (MRS) to improve the signal-to-noise ratio (SNR) of the probe over the conventional copper wire probes. These superconducting probes can provide substantial SNR gains by lowering the noise contribution of the receiving coil. This is due to the fact that the resistance of a superconductor at RF frequency (1-500 MHz) and cryogenic temperature is about three orders of magnitude lower than that of metal. Lower resistance of a superconductor leads to a higher quality factor (Q) of a coil made from a superconductor, which in turn, increases the SNR of the probe since the SNR is proportional to the square root of Q. As a comparison, a thin film coil made of high temperature superconductor (“HTS”) material has a Q of over 10,000 at 33.7 MHz and 77 K, while a similar thin film coil image using the metal Ag has a Q of 10 at the same frequency and temperature.
Because the Q value of a thin metal film coil is so low in practice, metal wires (mainly Cu) are used to make both conventional body coils and surface coils. In general, the coils made of Cu wires have Q values of 100-500. The low resistance nature of the superconductor allows the realization of a thin film coil to a have a Q value even higher than the wire coil.
Magnetic loop probes have been developed to produce an MRI picture based on the presence of sodium 23 (
23
Na), a nuclei that is very useful for medical imaging. A probe made with superconducting materials can achieve a signal-to-noise ratio (“SNR”) at least a factor of 10 higher than that of a copper coil that creates a large amplitude of noise due to its high internal resistance. Such SNR gains are of critical importance to in vivo
23
Na MRI which generally suffers from a poor SNR as a result of the low overall sensitivity of
23
Na. Another major practical difficulty associated with a
23
Na MRI is to correctly localize the probe with respect to the area of interest to be imaged.
It would therefore be beneficial to detect two or more resonating nuclei at the same time which have different resonance frequencies. It would be desirable to detect the multiple resonances with a single probe in order to properly localize and focus on the desired area to be scanned. However, if multiple receiver coils are located in close proximity, the mutual inductance created between the two coils must be taken into account in order for the probe to be properly tuned.
SUMMARY OF THE INVENTION
The present invention is a multiple resonance superconductor probe which can be used in MRI, MRM and MRS applications, among others. The multiple resonance probe has a plurality of coils created from superconducting thin film disposed on a substrate. Each coil preferably consists of a spiral inductor with interdigited fingers between the inner and outer loops. The coils in the preferred embodiment are concentric around a common point to increase the overall field of view of the probe for the plurality of receiving coils. The probe is constructed to take into account the effect of the mutual inductance between the individual receiving coils on the substrate and can be further finely tuned for each coil configuration by changing the number of fingers attached to a particular coil. The multiple resonance probe allows for improved imaging of a desired subject from the additional data obtained from the added resonance frequencies. The multiple resonance probe can be made by depositing a superconducting film on a substrate, creating the proper coil configuration to account for mutual inductance and finely tuning the individual coils.
The multiple resonance probe can also be constructed using separate layers for each receiving coil, where a buffer layer is placed in between any two adjacent coil layers. The multi-layered configuration allows for using coils with an equal diameter to increase the mutual field of view for all the receiving coils.
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Withers et al., “Thin-Film HTS Probe Coils for Magnetic-Resonance Imaging,”IEEE Transactions on Applied Superconductivity, vol. 3, No. 1, p. 2450-2453, Mar. 1993.
Penn et al., “Design of RF Receiver Coils Fabricated from High Temperature Superconductor for Use in Whole Body Imaging Equipment,”World Congress of Superconductivity, vol. 1, Nos. 10-12, pp. 1855-1861, 1993.
Hill, “A High-Sensivity NMR Spectroscope Probe Using Superconductive Coils,”Magnetic Moments, vol. 8, No. 1, p. 1, 4-6, 1996.
Ma Qiyuan
Miller Jason R.
Mun Ki
Zhang Kuan
Baker & Botts LLP
Oda Christine K.
Shrivastav Brij B.
The Trustees of Columbia University in the City of New York
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