Surgery – Diagnostic testing – Detecting nuclear – electromagnetic – or ultrasonic radiation
Reexamination Certificate
2002-02-19
2003-07-08
Lateef, Marvin M. (Department: 3737)
Surgery
Diagnostic testing
Detecting nuclear, electromagnetic, or ultrasonic radiation
C600S442000, C600S443000, C073S592000, C073S597000
Reexamination Certificate
active
06589178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and an apparatus for estimating a Bone Mineral Density (hereinafter referred to as “BMD”), and in particular, to a method and an apparatus for estimating a Bone Mineral Density utilizing an ultrasound and a bioelectrical impedance.
2. Prior Art
With age, human bones tend to become more brittle, the ratio of fractures caused by falls etc. tends to increase, and it tends to take much more time to recover after such a fracture. For example, if an elderly person fractures a leg, the time period during which it is difficult to walk tends to become longer, and such a person may thus be requested to stay in bed. As a result, this person's everyday life is significantly effected, and further asthenia tends to progressively advance since it is impossible for this person to move and for other reasons.
Thus, as one of the means for judging the brittleness of human bones, a method and an apparatus for measuring BMD, which is one of the indexes of the degree of bone health, have been developed and are used at hospitals or the like. The term “BMD” herein refers to Bone Mineral Calcium (hereinafter referred to as “BMC”) contained per unit area of the bone. Although a bone includes a bone radical component (fiber component) and a component of calcification, bone mass is referred to as the Bone Mineral Calcium, since, at the present time, when measuring the bone mass, calcification mass thereof is measured.
In consequence of the measurements made at hospitals etc. utilizing the above measuring method, we have learned that, among elderly people, there are a great many whose bones are in condition in which they easily fracture, that is, osteoporosis, and moreover, half of females more than 65 years old and half of males more than 80 years old are diagnosed as having osteoporosis, and thus this matter is becoming a very significant problem. Also, in recent years, not only among elderly people but also among youths, people who are diagnosed as having osteoporosis have been increasing due to the effects of a lack of exercise, an unbalanced diet, excessive dieting or the like. Also, invalids tend to get osteoporosis for reasons similar to the above given ones, and also expectant mothers are often said to easily get osteoporosis since a large amount of calcium in their bodies is consumed because of giving birth and breast feeding. Thus, it is possible to say that the risk of getting osteoporosis has become very high.
Consequently, various methods and apparatuses for determining the degree of bone health have been developed so as to prevent osteoporosis, and they can be categorized as follows:
(1) Simple X-ray Image
The determination of the degree of bone health will be made, based on an X-ray picture of a bone, by judging the degree of reduction of a calcium fiber, that is, calcification mass in a vertebra or a transcervical.
(2) Second Metacarpus Atrophy Degree Measurement Method (MD Method, DIP Method)
This is a method in which, by utilizing a computer, an X-ray picture of a bone is analyzed and then an atrophy degree of a bone is indicated by a numeral. In the MD method (Micro-Densitometry Method), a picture of a second metacarpus is taken using an X-ray and analyzed, while, in the DIP method (Digital Image Processing Method), an X-ray picture is transmitted to a high resolution processing equipment via a television camera for instrumentation, so that the bone mass can be estimated.
(3) Dual Energy X-ray Absorptiometry (DEXA Method)
This is a method in which, by utilizing two X-rays of different wavelengths, the bones of the umbar spine front, back and side, transcervical or the like are measured and analyzed. In this method, both a cortical bone and a cancellous bone are measured.
(4) QTC Method
This is a method in which an X-ray absorbed dose is estimated without a picture and the bone mass is estimated by a computer process. In this method, only a petrous cancellous bone of a spine can be measured in ring sections thereof without the effects of a bone deformation and a pool of calcium.
(5) Ultrasonography
This is a method in which an ultrasound signal is transmitted to a heel or the like and a stiffness of a bone is estimated based on a traveling speed of the ultrasound etc.
Now, a principle of the ultrasonography will be described below.
FIG. 6
is a diagram illustrating a principle of the ultrasonography. This figure shows a sectional view of a heel portion when the ultrasound has passed through a calcaneus. “
30
” indicates a heel, “
31
” indicates the calcaneus, “
33
” indicates a cortical bone which is a peripheral part of a bone and “
32
” indicates respective cancellous bones which are an inner part of a bone. “
34
” indicates a cutis and “
35
” indicates an ankle. “
27
a
” indicates an ultrasound transmitter for transmitting the ultrasound and “
27
b
” indicates an ultrasound receiver for receiving the ultrasound which has passed through the calcaneus.
Even if a bone is thin, if the cortical bone
33
thereof is thick and the cancellous bones
32
thereof are densified, such a bone is resistant to fracture. On the contrary, even if a bone is thick, if the cortical bone
33
thereof is thin and the cancellous bones
32
thereof each have a space therein (loose condition), such a bone is brittle and thus easy to fracture. Thus, it is necessary to comprehensively judge both the thickness of the cortical bone
33
and the condition of the cancellous bones.
A cell such as a cutis has almost the same acoustic character as that of water, and a sound can be transmitted therethrough at a speed of 1500 m/s, an attenuation thereof caused by such transmission being small. Compared to an ordinary cell, a bone is very hard, a speed of sound transmitted therethrough is fast and an attenuation thereof caused by such transmission becomes great. When osteoporosis occurs, the cortical bone
33
is decreased in width, a medullary cavity is increased, and in each of the cancellous bones
32
, a trabeculae thereof is decreased and rarified. Since most parts of the rarified medullary cavity are filled with bone marrow liquid, the acoustic character of such a rarified bone becomes more similar to that of water in comparison with that of a healthy bone. That is, as compared to the healthy bone, the speed of sound transmitted through the rarified bone is slow and the attenuation thereof becomes small. Thus, an ultrasound is inputted into the bone from one side thereof and the time it takes for the ultrasound to reach the other side thereof is calculated, so that the calculated speed of sound should reflect the bone mineral density thereof.
As the calcaneus is relatively large and the side shape thereof is almost planar, it is easy to measure the length thereof and such a calcaneus can resist the effect of the sound wave diffracted from the cortical bone. Also, as it is clear that ninety percent of the content in the calcaneus are the cancellous bones, the calcaneus can be adequately measured by the ultrasound measuring method and is often measured by this method. Further, since the flesh portion covering the calcaneus is thin, if this measurement is made from the top of the cutis, any possible error in this measurement is not great.
Now, a method of obtaining a sound of speed SOS in the heel will be described. The time “T” that elapsed before the ultrasound, which is transmitted from the ultrasound transmitter
27
a
, has passed through the calcaneus
31
and reached the ultrasound receiver
27
b
, is measured. Assuming the distance between the transmitter and the receiver is “Lt”, the equation:
SOS=Lt÷T
(equation 1)
is satisfied.
Now, the method of obtaining the bone mineral density from the SOS will be described. For a number of subjects, their bone mineral densities BMDs are measured by utilizing the highly accurate DEXA method, and their SOSs are measured by means of the ultrasonography to obtain a regression equation between the BMDs and the SOSs. By utilizing such a correlation
McDermott & Will & Emery
Tanita Corporation
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