Apparatus and method for increasing the sensitivity of a nuclear magnetic resonance probe
First Claim
1. A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising:
- a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen;
a tuning circuit element connected to the sample coil, the sample coil and tuning circuit element substantially forming a resonant circuit tuned to a selected Larmor frequency; and
a balanced impedance circuit means connected to the sample coil and tuning circuit element for controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground.
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Accused Products
Abstract
The discovery has been made that coil-to-ground parasitic losses substantially reduce the sensitivity of a nuclear magnetic resonance probe used in nuclear magnetic resonance analyses of lossy dielectic (i.e., relatively conductive) samples, such as biological tissue. A probe circuit is disclosed in which a balancing impedance is inserted for substantially reducing the influence of coil-to-ground parasitics. The probe circuit resulting from the insertion of the balancing impedance markedly increases sensitivity. Concomittantly, the quality factor of the probe circuit and the signal-to-noise ratio of nuclear magnetic resonance signals are substantially improved. The disclosed probe circuit can be incorporated in nuclear magnetic resonance analysis systems where the sample coil is either implanted or placed on the surface of a sample; where the sample coil forms a portion of a large-scale imaging system; or the sample coil is used in a traditional analytical mode with a sample contained in a glass tube.
112 Citations
45 Claims
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1. A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising:
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a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen; a tuning circuit element connected to the sample coil, the sample coil and tuning circuit element substantially forming a resonant circuit tuned to a selected Larmor frequency; and a balanced impedance circuit means connected to the sample coil and tuning circuit element for controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground. - View Dependent Claims (2, 3, 4)
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5. A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising:
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a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen; a tuning capacitor connected to the sample coil, the sample coil and tuning capacitor substantially forming a resonant circuit tuned to a selected Larmor frequency; a first impedance matching capacitor connected between the sample coil and an ungrounded output terminal; and a second impedance matching capacitor connected between the sample coil and a grounded output terminal; the sample coil being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals; the first and second impedance matching capacitors controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16)
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17. A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising:
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a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen, the sample coil being connected between a first node and a second node; a tuning capacitor connected between the first and second nodes, the sample coil and tuning capacitor substantially forming a parallel resonant circuit resonant at a selected Larmor frequency; a first impedance matching capacitor connected between the first node and an underground output terminal; and a second impedance matching capacitor connected between the second node and a grounded output terminal; the parallel resonant circuit formed substantially by the sample coil and tuning capacitor being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals; the first and second impedance matching capacitors controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground. - View Dependent Claims (18, 19, 20, 21, 22, 23)
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24. A nuclear magnetic resonance probe circuit having an improved quality factor in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen, comprising:
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a sample coil having a nominal inductance, the sample coil being positioned in close proximity to the specimen, the sample coil being connected between a first node and a second node; a tuning capacitor connected between the first node and a grounded output terminal, the sample coil and tuning capacitor substantially forming a parallel resonant circuit resonant at a selected Larmor frequency; a first impedance matching capacitor connected between the first node and an ungrounded output terminal; and a second impedance matching capacitor connected between the second node and the grounded output terminal; the sample coil being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals; the first and second impedance matching capacitors controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, thereby reducing the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground. - View Dependent Claims (25, 26, 27, 28, 29, 30, 31)
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32. A method for improving the signal-to-noise ratio of nuclear magnetic resonance signals detected in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen by a probe circuit having a sample coil and a tuning circuit element, the sample coil and tuning circuit element substantially forming a resonant circuit across an ungrounded output terminal and a grounded output terminal, the resonant circuit being tuned to a selected Larmor frequency, comprising the steps of:
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positioning the sample coil in close proximity to the specimen; and inserting a balanced impedance circuit means connected to the sample coil and tuning circuit element for controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, whereby the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground is reduced. - View Dependent Claims (33, 34, 35)
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36. A method for improving the signal-to-noise ratio of nuclear magnetic resonance signals detected in the presence of coil-to-ground parasitics encountered in nuclear magnetic resonance analysis of a specimen by a probe circuit having a sample coil and a tuning capacitor, the sample coil and the tuning capacitor substantially forming a resonant circuit across an ungrounded output terminal and a grounded output terminal, the resonant circuit being tuned to a selected Larmor frequency, and further having a first impedance matching capacitor between the sample coil and the ungrounded output terminal, comprising the steps of:
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positioning the sample coil in close proximity to the specimen; and inserting a second impedance matching capacitor between the sample coil and the grounded output terminal; the sample coil being connected in series circuit between the first and second impedance matching capacitors across the ungrounded and grounded output terminals; the first and second impedance matching capacitors controlling the voltage across the sample coil in the presence of leakage current from the sample coil through the specimen to ground in a manner to balance the leakage currents as seen from the ends of the sample coil, whereby the influence of coil-to-ground parasitics additional to any coil-to-ground parasitic attributable solely to leakage current directly from the sample coil to ground is reduced. - View Dependent Claims (37, 38, 39, 40, 41, 42, 43, 44, 45)
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Specification