Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
1999-08-25
2001-08-21
Oda, Christine (Department: 2862)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C324S309000
Reexamination Certificate
active
06278891
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to the field of Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) apparatus and methods. More specifically, the invention relates to methods and apparatus for using NMR for rapid, in-vivo determination of bone properties, such as Bone Mineral Density (BMD). The invention more particularly relates to NMR methods and apparatus for diagnosing diseases that affect bone, such as osteoporosis. In addition, the invention relates to methods and techniques of monitoring bone condition during progress of the disease, including the effect of different types of treatments on the disease.
2. Description of the Related Art
The description of the invention and its background are approached in the context of osteoporosis because osteoporosis is recognized as a significant public health problem, and NMR as well as other diagnostic techniques for bone studies have been widely applied and investigated. It is to be explicitly understood that the invention is not limited to the field of study, analysis and monitoring of osteoporosis.
a. Bone in a Human Skeleton
The skeleton serves to support the body, anchor muscles and protect vital organs. The human skeleton consists of approximately 80% of cortical (compact) bone and approximately 20% of trabecular (cancellous, or “spongy”) bone. The structure and composition of individual bones varies, and is generally related to the specific function performed by the particular bone. Generally, an anatomical bone consists of about 25% by volume of a specific bone tissue and about 75% by volume of bone marrow. Bone marrow consists of yellow and red bone marrow. Yellow bone marrow includes primarily fat cells (about 85% by volume), water (about 15% by volume) and a small fraction of protein (typically less than about 1% by volume). Red bone marrow mainly includes erythropoetic tissue elements, and its composition is approximately 40% water by volume, 40% fat by volume, and 20% protein by volume. The overall mass of red marrow typically decreases with age. The lost red marrow mass is replaced with yellow marrow. At any age, the proportion of red and yellow marrow varies with the skeletal site. Of the specific bone tissue weight in any particular bone, only about 20% is organic matter (mainly collagen), about 70% is mineralized phase (crystals of hydroxyapatite and amorphous calcium phosphate) and about 10% is water.
In the foregoing discussion and in the description of the invention to follow, these definitions will be used. An “anatomical bone” is a structural, functional part of the skeleton such as the tibia, the radius, the calcaneus, for example. The term “bone” in general refers to a part of any of the previously mentioned anatomical bones, including cross-sections of any anatomical bone. “Bone tissue” is the tissue composition of the cortical bone and trabecular bone making up any anatomical bone. “Specific bone tissue” represents the part of bone tissue excluding any microscopic cavities, blood vessels and the like. The microscopic cavities include osteocytes, lacunae, canliculae, Haversian canals, and Volkmann's canals. “Bone matrix” is the specific bone tissue excluding any chemically bound water. The bound water is also known in the literature as the hydration shell. Bone matrix consists of organic matter, 95 percent of which is in the form of collagen fibers, and inorganic matter referred to as bone mineral. The foregoing definitions have been provided to clarity of the description to follow, because reconciliation of the various terminologies for bones and their components has been difficult since no techniques have been developed to measure the bone matrix quantity in vivo.
Bone continuously undergoes remodeling or turnover during a person's life. Older bone tissue is replaced at anatomically discrete sites with newly formed tissue to avoid cumulative skeletal fatigue damage. Approximately 20% of bone tissue is replaced annually by this process, on a cyclical basis throughout the skeleton. There are five phases to bone remodeling: activation, resorption, reversal, formation and quiescence. The entire remodeling process occurs over approximately 4 to 8 months, with a range of 3 months to 2 years depending on the particular bone.
In bone growth, and during the remodeling process in a normal, healthy person, the organic matter remains a relatively constant fraction of the total specific bone tissue volume, while mineralization of bone occurs by replacement of water by the previously described mineral phase (crystals of bone mineral). Mineralization and crystal growth continue until there is no space left for further mineral expansion. Crystals form and grow within a fixed volume by displacement of water. The space between the crystals become smaller and smaller as the crystals grow, until eventually a state of maximum mineralization is achieved. For bone crystals to grow, mineral ions must diffuse in from fluid circulation. As the intercrystalline spaces become so small as to approach atomic dimensions, ions can no longer diffuse at appreciable rates. Specifically, polyvalent ions of calcium, which form a large part of bone mineral, are large and have high electric charge that prevents them, by electric repulsion, from entering narrow intercrystalline spaces. The same size spaces, however are accessible to univalent ions. Additional chemical evidence suggests that the water in calcified tissues is largely in chemically bound form.
b. Osteoporosis
Osteoporosis is a systematic skeletal disease characterized generally by low bone mass and microarchitectural deterioration of bone tissue, with a consequent increase in susceptibility to fracture. More specifically, in osteoporosis, the volume of the anatomical bones remains unchanged during progress of the disease, but the bones show cortical thickening and porosis, and the bones exhibit a specific bone tissue fraction and a bone mineral fraction of their total volumes which are less than the normal proportions of the anatomical bone volume. However, within the specific bone tissue, the ratio of mineral to organic matter and water remains relatively unchanged. The structural and chemical composition of the specific bone tissue in osteoporotic bone tissue is thus indistinguishable from that of normal bone. This has made analysis of osteoporotic bone difficult using methods known in the art for analyzing bone.
c. Radiologic Bone Densitometry
The National Osteoporosis Foundation has issued specific and aggressive recommendations for managing and preventing osteoporosis in, First guidelines for osteoporosis issues by National Osteoporosis Foundation in collaboration with multidisciplinary physician organizations (news release Nov. 5, 1998). These guidelines include the use of BMD as the single most reliable tool for assessing bone strength and osteoporosis risk. The rationale for using BMD as a monitoring and predictive tool is that there is a well-established relationship between BMD and the ability of bone to withstand compressive, torsional and bending forces. A strong correlation between BMD and the load necessary to induce skeletal failure has been shown, for example, by Johnston and Melton, Bone densitometry measurement and the management of osteoporosis, Primer on Metabolic Bone Diseases and Disorders of Mineral Metabolism, American Society for Bone and Mineral Research, Society Office, pp. 93-100 (1996). In-vivo radiologic bone densitometry methods for diagnosis and therapeutic follow-up include:
I. Conventional skeletal radiography.
This method is relatively insensitive and bone loss is apparent only when bone mass has decreased by about 30-50%.
II. Radiographic photodensitometry.
This method uses exposure to X-rays of a reference wedge alongside the area of interest in measuring the optical density of X-ray films of the bones in the area of interest.
III. Radiogrammetry.
This method relies on an expected linearity of measurements of X-ray films made of cortical bone taken under standardized co
Reiderman Arcady
Taicher Gersh (Zvi)
Echo Medical Systems, LLC
Oda Christine
Rosenthal & Osha LLP
Vargas Dixomara
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