Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2000-08-01
2002-06-11
Williams, Hezron (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S307000, C324S320000
Reexamination Certificate
active
06404197
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the field of nuclear magnetic resonance (NMR) spectroscopic devices, and more particularly to a small scale NMR spectroscopic apparatus, and a method of spectroscopy such as measurement of a patient's body fluid glucose levels.
Nuclear magnetic resonance (NMR) spectroscopy is an analytical and diagnostic technique that can be used for structural and quantitative analysis of a compound in a mixture. NMR is based on the nuclear magnetic properties of certain elements and isotopes of those elements. It is a fundamental law of quantum mechanics that nuclei with a nonzero spin will have a magnetic dipole and will thus interact with electromagnetic radiation. The presence or absence of a spin and the nature of the spin is expressed in terms of the spin quantum number (I) of the nucleus, which may be either 0, ½, or integer multiples of ½. The most important group analytically, because it includes
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H present in many compounds of interest, has a nuclear spin quantum number of ½.
In a uniform magnetic field, a nucleus having a spin quantum number of ½ may assume two orientations relative to the applied magnetic field. The two orientations have different energies, so that it is possible to induce a nuclear transition, analogous to flipping a bar magnet in a magnetic field, by applying electromagnetic radiation of the appropriate frequency. This nuclear transition, known as resonance, is thus brought on when the correct combination of magnetic field strength and exciting frequency characteristic of the nuclei of interest are applied. After resonance is achieved, the NMR instrument detects a signal, the signal being a function of the nature and amount of a compound in the test sample as well as nuclear magnetic relaxation considerations. Because all nuclei have unique resonances, e.g. approximately 60 megahertz in a 14 kiloGause (1.4 Tesla) field for protons,
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H NMR will only detect compounds having protons. Moreover, because the exact frequency at which a proton resonates within this range is related to its chemical environment, the
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H NMR signal of protons of one compound can generally be distinguished from another, and the integrated intensity of the signal is directly proportional to the amount of the compound of interest. The position of the resonance signal is characterized by its frequency, i.e., the chemical shift, which is usually expressed on a ppm scale relative to the resonance frequency of some standard compound.
A NMR spectrometer generally comprises one or more magnets producing a strong homogenous magnetic field within a test region, a coil to apply the excitation frequency (the transmitter coil), a coil to generate a signal when the nuclei of the test sample resonate (the receiver coil), and a radiofrequency (RF) oscillator to supply A/C current through the transmitter coil. One coil may act as both the transmitter coil and receiver coil if the current is appropriately gated. A transition occurs in the test sample when the RF frequency applied matches the resonance frequency of the nuclei of the compound of interest.
The size and complexity of NMR spectrometers are largely a function of the magnetic field requirements. A typical NMR magnet used for analytical or chemical structural analysis purposes can weigh from a few hundred to as many as 500 kilograms. However, because the strength of the detected resonance signal is proportional to the magnetic field strength raised to the 3/2 power in the test region, it is very important to provide a magnet with the highest field possible as the magnet is scaled down in size. On the other hand, providing a strong magnetic field generally requires larger, higher weight magnets, which typically increases the cost of the spectrometer depending on the type and the weight of materials used. The most expensive, by far, is the permanent magnet material. Thus, the competing factors of spectrometer field strength and magnet cost must be balanced so that the desired signal strength and cost requirements are met. Moreover, the magnetic field produced must be stable and homogeneous within the test region. The magnetic field strength within the test region, and resulting magnet weight, is a function of a number of variables including the type of magnetic materials used, the extent of the suppression of leakage fields, the size of the test area between the magnets and the configuration of the field flux shaping and conducting components.
Diabetes is a disorder of metabolism characterized by lack of insulin effect. One of the pathologies of diabetes is the inability of glucose to enter the body's cells and be utilized. Due to the severe effects of excessively high or low blood glucose levels, insulin dependent diabetics should measure their blood glucose levels several times a day. However, the most widely used method requires obtaining a blood sample by finger pricking, which is painful and thus may often be neglected by the patient.
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H NMR is a suitable technique for measuring a patient's glucose level. However, the in vivo
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H NMR spectroscopic analysis of glucose is complicated by the intense signals generated by water and other compounds in the patient's blood and tissue. A hand held NMR device has been suggested for in vivo measurement of a patient's blood glucose levels in U.S. Pat. No. 4,875,486 (Rapoport et al.). However, the device described by Rapoport apparently has never been commercialized. It is believed that the device described could not effectively suppress the large signal of water in the body fluid as required for a clinically suitable device.
Therefore, what has been needed is a small NMR spectrometer and method which allows for the measurement of the concentration of a compound, such as glucose, in a patient. The present invention satisfies these and other needs.
SUMMARY OF THE INVENTION
The invention is directed to a relatively small, light weight NMR apparatus and a method for the spectroscopic analysis of a compound in a fluid, such as a patient's body fluid, and particularly the measuring of a patient's body fluid component, such as glucose, using a radiofrequency (RF) pulse sequence specific for the detection of such component. The term “body fluid” should be understood to include intracellular and extracellular fluids.
The NMR spectroscopic system of the invention includes a magnet assembly suitable for developing a strong uniform magnetic field across a test region and an RF emission system for the application of a variable exciting frequency normal to the uniform field. The magnet assembly generally comprises two permanent magnets facing one another so that the facing surfaces have opposite polarities, a pole cap tapering inwardly on each of the two facing surfaces of the permanent magnets, and a plurality of radially polarized canceling magnets disposed about the permanent magnets and pole caps. A test region and a coil are located in an air gap between the pole cap facing surfaces.
The permanent magnets are formed from high energy material such as neodymium-iron-boron alloy, so that relatively small, light weight magnets can be used which will generate a strong field in the test region. However, the same high energy magnetic potential generating the high magnetic field in the test region also will exist in all parts of the pole caps. This magnetic potential will, therefore, generate extraneous magnetic fields outside the test region that contribute nothing to the NMR signal. These extraneous fields are called leakage fields. If nothing is done to reduce these leakage fields, the size of the high energy permanent magnetic material must be increased to carry them or their effectiveness will be reduced resulting in reduced magnetic field strength. The principal unchecked leakage fields will form barrel shaped patterns from the sides of one pole cap to the other pole cap and lateral fan shaped patterns from both pole caps to the outer housing. Conventional methods of mitigating the effect of su
Anderson Marvin H.
John Boban K.
Schleich Thomas W.
Shoolery James N.
Fetzner Tiffany A.
Heller Ehrman White & McAuliffe LLP
Magnetic Diagnostic, Inc.
Williams Hezron
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