Radiant energy – Calibration or standardization methods
Reexamination Certificate
1999-05-14
2002-03-26
Hannaher, Constantine (Department: 2878)
Radiant energy
Calibration or standardization methods
C378S207000
Reexamination Certificate
active
06362471
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to surrogate structures, or phantoms, that exhibit radiological properties of bone, muscle, and other soft tissue. Specifically, this invention relates to phantoms which have been designed to accurately exhibit anthropometric and radiological properties of human bone and soft tissue for use in calibrating the response of spectroscopic instruments that enable in vivo measurement of the levels of contamination from stable metals and radioactive material.
BACKGROUND OF THE INVENTION
The hazards of exposure to heavy metal contamination, examples of which arsenic, beryllium, lead, cadmium, chromium, nickel, zinc, mercury and barium, and the radioactive substances which deposit in human bone, examples of which are uranium, plutonium, and americium, are very serious and are well known to scientific and medical professionals.
Since lead is a prevalent metal contaminant which deposits in human bone, and its effects are quite hazardous, especially to young children, the focus of this disclosure will be on methods of detecting lead exposure. While it is possible to detect the level of lead in the body through the use of a blood test, the relevancy of such tests is limited, since the risk to humans from lead exposure is related to the amount of lead deposited in the bones of the exposed person and not, necessarily, the amount in the blood. Moreover, drawing blood causes some discomfort on the part of the person being tested, which is especially difficult with small children, who are particularly at risk to lead exposure due to various environmental factors Accordingly, an alternative method, the indirect measure of the level of cumulative lead exposure in the bones of a person by use of x-ray fluorescence, is often employed.
By way of example, by directing a source of radiation, such as gamma rays from a
109
Cd source, through a portion of the human body, such as the midshaft of the tibia, a suitable detector is capable of providing a calcium to lead ratio in the bone by comparing the intensity of the Pb x-rays caused by the interaction with the
109
Cd photons to the intensity of the back scattered photons caused by the interactions of the
109
Cd photons with the calcium atoms in the bone.
The accuracy of the lead measurements given by this method, especially when the levels of lead exposure are low, is questionable for two reasons: first, because it relies on an assumed calcium content in the particular bone, which may or may not be accurate in individual cases, and second, since there is a wide diversity in skeletal size in humans, as well as differences in the amount of tissue surrounding the bone that the x-rays must pass through and be partially absorbed by, these differences have to be taken into account for the x-ray source to be calibrated correctly.
While cadaver samples are the most realistic calibration structures to use, limitations on availability generally require the use of surrogate structures, or phantoms, in making calibration measurements. Currently, such phantoms are 4″ long, cylindrical structures made of either Plaster of Paris or polyacrylamide. Neither of these materials is an acceptable, realistic substitute for human bone. Moreover, these conventional phantoms do not account for the x-ray attenuation caused by the layers of tissue overlying the bone being tested by this method. These concerns also hold for the other metal contaminants, such as mercury, that would be tested for by means of x-ray fluorescence.
It is well-known by those skilled in the art that, when testing to determine the amount of a radioactive contaminant that has been deposited in bone, gamma spectrometry is the usual analytical tool. Since the above-mentioned prior art phantom is also used in gamma spectrometry measurements, the same concerns apply.
There is, therefore, a substantial need for an improved phantom representative of tissue-covered human bone containing lead in a long-term, stable format, and a low cost method of quantifying human bone lead content which is fast, accurate, reproducible, and widely available.
BRIEF SUMMARY OF THE INVENTION
Pursuant to the present invention, a method of making anthropomorphically correct phantom structures will be provided.
Also pursuant to the present invention, a method of using these anthropomorphically correct phantom structures will be provided.
It is an object of the present invention to provide a phantom allowing direct measurement of the amount of radioactive or heavy metal contaminants deposited in a particular human bone.
It is another object of the present invention to provide an anthropomorphically correct phantom structure that is designed from commonly available materials, is easily reproducible, and is capable of widespread availability and usage.
Additional objects, advantages, and novel features of the present invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
REFERENCES:
patent: 4577338 (1986-03-01), Takahashi et al.
patent: 4663772 (1987-05-01), Mattson et al.
patent: 4845729 (1989-07-01), Rosen et al.
patent: 4873707 (1989-10-01), Robertson
Hu et al, Effect of Repeated Occupational Exposure to Lead, Cessation of Exposure, and Chelation on Levels of Lead in Bone, American Journal of Industrial Medicine, 20:723-735 (1991).
Richard P. Wedeen, In Vivo Tibial XFR Measurement of Bone Lead, Archives of Environmental Health, 43: 69-71 (1990).
Andrew C. Todd et al, Workshop on the X-Ray Fluorescence of Lead in Bone: Conclusions, Recommendations and Summary, Neuro Toxicology 14: 145-154 (1993).
Howard Hu et al, X-Ray Fluorescence Measurements of Lead Burden in Subjects with Low-Level Community Lead Exposure, Archives of Environmental Health, 45: 335-341 (1990).
Howard Hu et al, The Use of K X-Ray Fluorescence for Measuring Lead Burden in Epidemiological Studies: High and Low Lead Burdens and Measurement Uncertainty, Environmental Health Perspectives, 94: 107-110 (1991).
Jane A. Hoppin et al, In Vivo Bone Lead Measurement in Suburban Teenagers, Pediatrics, 100: 365-370 (1997).
D.R. Chettle et al, Lead in Bone: Sampling and Quantitation Using K X-Rays Excited by109Cd, Environmental Health Perspectives, 91: 49-55 (1991).
Hirokastsu Watanabe et al, Correlates of Bone and Blood Leads Levels in Carpenters, American Journal of Industrial Medicine, 26: 255-264 (1994).
Lillian J. Somervaille et al, In Vivo Measurement of Lead in Bone Using X-Ray Fluorescence, Phys. Med. Biol., 10: 929-943 (1985).
Mauricio Hernandez-Avila et al, The Influence of Bone and Blood Lead on Plasma Lead Levels in Environmentally Exposed Adults, Environmental Health Perspectives, 106: 473-477 (1998).
A C A Aro et al, Improvements in the Calibration of109Cd K X-Ray Fluorescence Systems for Measuring Bone Lead in Vivo, Phys. Med. Biol., 39:2263-2271 (1994).
Andrew Christian Todd et al, In Vivo X-Ray Fluorescence of Lead in Bone, Environmental Research, 59: 326-335 (1992).
D.R. White, Tissue Substitutes in Experimental Radiation Physics, Med. Phys., 5: 467-479 (1978).
A.J. Stacey et al, A New Phantom Material Employing Depolymerised Natural Rubber, 34: 510-515 (1961).
John H. Harris, Jr., et al, The Development of a Chest Phantom For Use in Radiologic Dosimetry, Radiology, 67: 805-813(1956).
R.V. Griffith et al, Fabrication of a Tissue-Equivalent Torso Phantom for Intercalibration of In-Vivo Transuranic-Nuclide Counting Facilities, presented at Symposium on Advances on Radiation Protection Monitoring, Stockholm, 1978.
Bornschein Robert
Jenkins Mark
Lodwick Jeffrey
Spitz Henry B.
Frost Brown Todd LLC
Hannaher Constantine
University of Cincinnati
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