Electricity: measuring and testing – Particle precession resonance – Spectrometer components
Reexamination Certificate
2002-09-20
2004-01-06
Gutierrez, Diego (Department: 2859)
Electricity: measuring and testing
Particle precession resonance
Spectrometer components
C324S322000
Reexamination Certificate
active
06674283
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus used in nuclear magnetic resonance (NMR) imaging, and more particularly, to a new and improved imager for use in a toroid cavity detector so that in situ magnetic resonance analysis can be accomplished of samples such as battery components, membranes and thin film materials.
2. Background of the Invention
Nuclear magnetic resonance (NMR) techniques have been used as a nondestructive assay (NDA) of various materials. One NMR technique that has been used involves a toroid cavity probe. This technique enables the determination of both the presence and quantity of individual elements as well as full chemical-shift resolution (i.e., chemical speciation). For example, the toroid cavity probe has been used to determine the presence of hydrogen in materials and as to whether hydrogen is bound with oxygen (water) or another element such as a salt. At the same time, protons in other forms, such as hydrides, hydrates and acids, also are detectable and quantifiable. The ability to make such determinations and the sensitivity of toroid-based NMR imaging makes this type of technique ideal for analyzing certain types of material particularly when the materials are in disposed in various types of packaging or containers.
In one type of toroid cavity detector, a sample to be analyzed is placed in the toroid cavity and the toroid cavity is placed in an externally applied static main homogeneous magnetic field (B
0
). The presence of the B
0
field causes the magnetic moments of a targeted class of nuclei in the sample to precess about the field's axis at a rate which is dependent on the magnetic field strength. Another magnetic field (B
1
) is produced that is perpendicular to the B
0
field and is alternately energized and de-energized within the cavity. In the case where the B
1
field is produced by a radio frequency (RF) transmitter pulse applied to a wire or rod (working electrode) extending along the central axis of the cavity, the net sample magnetization is caused to rotate about the B
1
field axis. Following the RF pulse, the response of the sample to the applied field is detected and in most applications, received signals from the energized nuclei serve as input signals for spectroscopic analysis of the sample.
One of the unique features of the toroid cavity detector compared to some other types of detectors is the full containment of the RF magnetic field flux that is generated when the working electrode is pulsed with an RF current. As a result, the RF magnetic field flux that emanates from a sample contained within the toroid cavity and subjected to an excitation pulse of electromagnetic radiation is completely captured (i.e., detected). This feature makes the toroid cavity detector two to four times more sensitive to weak nuclear resonance signals than conventional coil resonators and allows a quantitative measurement of the total number of NMR-active nuclear spins in the sample, not possible with other types of NMR detectors.
For samples placed in a magnetic field of sufficiently high homogeneity, it is possible to record different chemical species containing a common nucleus. Not only can a proton be distinguished from a uranium nucleus, but also protons in water molecules can be distinguished from protons in hydrogen gas molecules. In fact, protons in water molecules that are in different physical environments can be distinguished. The resolving capability of chemical shift makes the toroid cavity detector a useful device for analyzing and monitoring various types of radioactive materials from spent nuclear fuel to plutonium ash.
The toroid cavity detector also differs from other, more conventional electromagnetic detectors in that it produces a gradient in the generated RF magnetic field. This B
1
field gradient has a mathematically well-defined spatial distribution. This magnetic field gradient feature has two significant consequences. First, the sensitivity of the toroid cavity is radially distributed, with the greatest sensitivity near the central axis of the device or a principal detector element located in the toroid cavity along the central axis. This enables measurements on samples of limited quantity. Second, concentric annular regions of a sample contained in the toroid cavity exchange energy with the resonator circuit at different rates. Thus, analysis of energy transfer rates in a toroid cavity can yield a radial spatial mapping of the different nuclear constituents in a cylindrical sample container. The toroid cavity also has been proven to function with asymmetric conductors.
As is disclosed in U.S. Pat. Nos. 5,574,370 and 6,046,592, the toroid cavity of a toroid cavity detector can be a cylindrically shaped, hollow housing which is closed at both opposite ends and made for example of copper. A central conductor or working electrode (for example, an inner wire or rod in a Teflon outer jacket) extends through the base of the cylinder and is positioned coincident with the major, central axis of the cylinder. In the case of the toroid cavity disclosed in the ′370 patent, a fluid or gas sample to be analyzed by the toroidal cavity detector is simply introduced into the toroid cavity whereas in the case of the toroid cavity detector disclosed in the ′592 patent, the fluid or gas sample to be analyzed is introduced into an electrochemical cell compartment which is disposed within the toroid cavity. This electrochemical cell compartment consists of a cylindrically shaped glass container along the central axis of which extends the working electrode of the toroid cavity detector and into which a counter electrode is disposed. The counter electrode consists of a cylindrical solenoid coil that is positioned in the electrochemical cell compartment (either at the base of the compartment or expanded along the walls of the compartment) so that it is symmetrical about the centrally located working electrode. In operation, voltages are applied across the working electrode and the counter electrode by means of an external potentiostat resulting in the chemical composition of the sample being changed adjacent to the working electrode within the electrochemical cell compartment. A NMR spectrometer records the response of the sample to the applied magnetic field generated by the toroid cavity detector when a RF frequency signal is applied to the working electrode. The use of such an electrochemical cell compartment within the toroid cavity detector allows for the measurement of macroscopic transport properties, local dynamics, and chemistry of ions as a function of distance from the electrode.
In the toroid cavity detector of the type disclosed in the '370 and '592 patents, the B
1
field is completely confined within the cavity formed in the housing of the toroid cavity detector and is generated when an RF signal is transmitted along the central conductor. The B
1
field is strongest near the central conductor and drops off as the inverse of the distance toward the outer wall of the toroid cavity. Both sensitivity and distance resolution increase with the gradient in the B
1
field and consequently, the toroid cavity detector provides a means to image simultaneously both the chemical shift of the targeted nuclei as well as their radial distance from the center and is well suited for NMR microscopy of films that uniformly surround the central conductor. In this regard, the amount of energy that is absorbed or transmitted by a sample within the toroid cavity detector varies with the location of the sample within the toroidal cavity such that multiple distances within the NMR active sample can be resolved by varying the transmitter pulse length. Because a homogeneous B
0
field is used, the chemical shift information is not destroyed by the imaging process as happens in conventional magnetic resonance imaging (MRI) where transient inhomogeneous B
0
fields are required. In addition, such toroid cavity detectors appear to be useful for investigations of solids
Gerald, II Rex E.
Klingler Robert J.
Rathke Jerome W.
Gutierrez Diego
Pennington Joan
Shrivastav Brij B.
The University of Chicago
LandOfFree
Nuclear magnetic resonance imaging apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Nuclear magnetic resonance imaging apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nuclear magnetic resonance imaging apparatus will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3236619