Electricity: measuring and testing – Particle precession resonance – Using a nuclear resonance spectrometer system
Reexamination Certificate
2001-09-26
2004-02-10
Gutierrez, Diego (Department: 2862)
Electricity: measuring and testing
Particle precession resonance
Using a nuclear resonance spectrometer system
C324S307000, C324S318000
Reexamination Certificate
active
06690166
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
Applicant's invention relates to magnetic resonance technology as applied to the non-invasive in-situ measurement of bone porosity, pore size distribution, and other bone properties including aging.
2. Background Information
Bone is a porous material in nature. In human bone, there are three major natural cavities or “voids”. Among them, Haversian and Volkmann's canals play a role in accommodating longitudinal and transverse vascular vessels to transport cells, nutrients, and proteins needed for metabolism inside the bone. Besides, they provide surfaces for bone resorption and formation of cells (osteoclasts and osteoplasts, respectively) to attach to during bone remodeling processes. The diameter of the canals is on the order of 50 microns, with a length of a few millimeters. Cohen, J. and Harris, W. H., “The Three Dimensional Anatomy of the Haversian System,” Journal of Bone & Joint surgery, 40-A: 419, 1958. In addition, bone has many small ellipsoidal cavities called lacunae that contain bone cells called osteocytes. Although the role of osteocytes is still not well understood, it has been known that these cells may greatly contribute to the initiation of the bone remodeling process by sensing changes in stress or strain fields around them. These quasi-spherical voids have a diameter of approximately 5 microns. Johnson, J. C., “The Kinetics of Skeletal Remodeling,” Birth Defects Original Article Series, 2: 66, 1966. Furthermore, these osteocytes are interconnected by small capillary channels (termed “canaliculi”) emanating from the vascular vessels. These canaliculi are about 0.5 micron in diameter, and are considered to be responsible for delivering nutrients and relaying signals between the cells. Johnson, J. C., “The Kinetics of Skeletal Remodeling,” Birth Defects Original Article Series, 2: 66, 1966. It is noteworthy that the vascular canals are one order greater in diameter than lacunae, and lacunae are one order greater in diameter than canaliculi.
Previous studies have shown the overall porosity of bone has a significant effect on the mechanical strength of bone. In a comprehensive review on porosity of bone, Martin described that small changes in porosity would lead to significant changes in the stiffness and strength of bone for both compact and spongy bone. Martin, R. B., “Porosity and Specific Surface of Bone,” CRC Critical Reviews in Biomedical Engineering, 10 (3):179, 1984. In a recent study, McCalden reported that the effect of age-related increase of bone porosity on bone properties is manifested in the decreased capacity of bone to absorb post-yield plastic energy. McCalden, R. W., McGeough, J. A., Barker, M. B., Court-Brown, C. M., “Age-related Changes in the Tensile Properties of Cortical Bone: The Relative Importance of Changes in Porosity, Mineralization, and Microstructure,” Journal of Bone & Joint Surgery (Am.), 75(8):1193, 1993. Since changes in numbers and sizes of these natural cavities are directly related to the remodeling processes and biomechanical properties of bone, a direct sensing technique to detect such changes in bone has been long wanted. However, particularly for compact bone, none of the current techniques can quantitatively assess the porosity and pore size distribution in a non-invasive manner.
Microgravity induced bone loss has been a major concern for the health of astronauts. Under weightless conditions, the mechanical stimuli to the skeleton is significantly reduced. Based upon the widely accepted theory of bone adaptation to a mechanical environment, such disuse may trigger the bone remodeling processes leading to the reduction of bone mass. However, the underlying mechanisms for such changes still remain unclear. In the past, biochemical assays were widely used to monitor the bone remodeling process in animal models and to study the mechanisms of such bone mass loss. Since all these assays can be performed in an indirect manner, only qualitative results can be obtained. Thus, it would provide great opportunities for researchers to investigate the mechanisms of bone mass loss if a non-invasive and direct monitoring of the bone remodeling process is available. In a sense, by monitoring changes in these natural voids, i.e. Haversian canals, lacunae, and canaliculi, in situ, one may assess the process of bone remodeling.
Magnetic resonance (MR) imaging (MRI) techniques have been used to study soft tissue and the gross skeletal structure. Recently high resolution MR imaging has been used to resolve the larger porosity cavities in trabecular bone structure in vitro at high magnetic field strengths, and in vivo using clinical scanners at fields of 1.5 T. Chung, H., Wehrli, F. W., Williams, J. L., Kugelmass, S. D., “Relationship between NMR Transverse Relaxation, Trabecular Bone Architecture and Strength,” Proc. Nat'l. Acad. Sci, USA 90:10250, 1993; Hipp, J. A., Jansujwicz, A., Simmons, C. A., Snyder, B., “Trabecular Bone Morphology Using Micromagnetic Resonance Imaging,” J. Bone Mineral Res. 11:286, 1996, Majumdar, S., Gies, A., jergas, M., Grampp, S., Genant, H., “Quantitative Measurement of trabecular Bone Structure Using High Resolution Gradient Echo Imaging of the Distal Radius,” Proceeding of the Society of Magnetic Resonance in Medicine, New York, P455, 1993; Jara, H., Wehrli, F. W., Chung, H., Ford, J. C., “High-resolution Variable Flip Angle 3D MR Imaging of Trabecular Microstructure in Vivo,” Magnet Reson Med 29:528, 1993. However, this MR imaging technique is not suitable for resolving the smaller pores and voids in compact bone. Compact bone does not generate any detectable MR images of the porosity structure. On the other hand, nuclear magnetic resonance (NMR) spin-spin (T
2
) or spin-lattice relaxation time (T
1
) measurements and analyses have been used to determine the porosity and pore size distribution in different porous media. Gallegos, D. P., Munn, K., Smith, D. M., and Stermer, D. L., J. Colloid Interface Sci. 119:127, 1987; Glaves, C. L., and Smith, D. M., J. Membr. Sci. 46:167, 1989; Howard, J. J., and Kenyon, W. E., Mar. pet. Geol. 9:139, 1992; Kenyon, W. E., “Petrophysical Principles of Applications of NMR Logging,” The Log Analyst, Mar.-Apr. p21, 1997. For instance, the low field NMR well logging technique uses a similar principle to detect the porosity, pore size distribution and permeability in oil reservoirs where the fluids (oil and water) are in pores in the rock structure-ranging from submicron to submillimeter. This MR technique is based upon the fact that proton relaxation time of fluid (water, oil, etc.) in porous media is shorter than that of pure fluid itself and is a function of the pore size. The enhanced relaxation rate (1/T
1
or 1/T
2
) of fluid in a heterogenous system is accounted for by the presence of a relaxation “sink” at the surface of the pores. Owing to the interactions between the fluid molecules and the solid surface of the pore walls, protons near these surfaces relax faster than in the bulk. The fluid in large pores tends to relax slower (longer relaxation time T
1
or T
2
) than fluid in small pores because of the different relative amounts of surface area compared to the volume of bulk fluid. Thus, the measured relaxation profile provides information about pore size distribution, or more precisely, the pore volume to pore surface area ratio distribution while the total amplitude of the pore fluid signal provides a measure of the porosity.
It has been known that water makes up a major portion of the fluid in the bone natural cavities or pores which is similar to water saturated in a rock. Therefore, the amplitude of the T
2
relaxation time data can be used to determine the porosity of the bone, and its inversion T
2
relaxation distribution can be transformed to the pore size distribution if the surface relaxivity constant is known. NMR T
2
relaxation rate (1/T
2
)is known to depend on a surface-to-volume ratio with the proportionality of the surface relaxivity constant. Since bone has chemical, molecular, and
King James D.
Ni Qingwen
Wang Xiaodu
Evans Michelle
Gunn, Lee & Hann
Gutierrez Diego
Shrivastav Brij B.
Southwest Research Institute
LandOfFree
Nuclear magnetic resonance technology for non-invasive... 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 technology for non-invasive..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Nuclear magnetic resonance technology for non-invasive... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3323237