X-ray or gamma ray systems or devices – Accessory – Testing or calibration
Reexamination Certificate
1999-12-20
2001-11-13
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Accessory
Testing or calibration
C378S018000, C378S051000, C378S053000, C378S056000, C378S098900
Reexamination Certificate
active
06315447
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
BACKGROUND OF THE INVENTION
The present invention relates to calibration phantoms for x-ray machines and the like and, in particular, to a phantom providing calibration of dual energy x-ray equipment for percent body fat measurements.
The absorption of x-rays by material is dependent on two independent absorption mechanisms: Compton scattering and the photoelectric absorption. Each of these absorption mechanisms differs in relative contribution for different materials. Further, the amount of absorption by each of these mechanisms is dependent on the energy of the x-rays. Measurements of the attenuation of a body at two x-ray energies (generally corresponding to different x-ray frequencies) can therefore reveal information about the relative contribution of Compton scattering and the photoelectric absorption by materials of the body and thus can reveal information about the constituent materials of the body.
One important use of dual energy measurement is in determining relative proportions of bone and soft tissue in a patient providing information about the patients bone mass. Lunar Corporation, the assignee of the present application, manufactures a number of dual energy x-ray machines suitable for this purpose as described in the following U.S. patents hereby incorporated by reference: U.S. Pat. Nos. 5,253,282; 5,228,068; 5,287,546; 5,291,537; 5,305,368; 5,306,306; 5,408,439; 5,485,492; 5,509,042; 5,533,080; 5,533,084; 5,577,089 and 5,673,298.
If the basis materials are chosen to be tissue and fat instead of tissue and bone, the same techniques may be used to provide a measurement of percentage body fat as may be useful in the investigation of drugs and in the study of wasting diseases.
In either of these applications, it is important that repeatable quantitative results be produced. For this reason, the entire patient may be scanned so as to eliminate variation caused by change in measurement regions for different patients or the location of the measurement region between measurements of a single patient. Further, the machine must be calibrated both to prevent drifting of the measurements of a single machine over time and, in the case where multiple machines are used in a study, to ensure consistency among results. Critical to this calibration is that the machines produce identical readings for the same patient at a given time regardless of the patient's body fat. Given that a total body scan will typically be used, it is preferable that the calibration process reflect measurements over a substantial area on the machine.
What is needed is a simple and reliable phantom that allows accurate calibration of dual energy equipment for body fat measurement under these constraints.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a simple yet accurate phantom for calibrating dual energy x-ray equipment for body fat measurements. In particular, the present invention provides a limited number of standard plates of materials simulating different body fat percentages. By combining the plates, a range of body fat percentages may be precisely obtained. The plates may be of arbitrary size to provide a simulation over a broad area and may include a high density end cap for triggering an automatic region of interest detection for certain scanner systems.
In particular, the present invention is a modular body fat phantom for calibrating body fat percentage measurements made by a dual energy x-ray attenuation measurement device. The body fat phantom includes a first calibrated plate made of a first basis material having a first high energy x-ray attenuation value and a first low energy x-ray attenuation value. The phantom also includes a second calibrated plate made of a second basis material having a second high energy x-ray attenuation value and a second low energy x-ray attenuation value. The second set of x-ray attenuation values is different from the second set of x-ray attenuation values. The two plates may be stacked together to define a known simulated body fat composition.
Preferably, stacking the first and second calibrated plates together defines a simulated body fat composition less than that of the first calibrated plate alone.
In one aspect of the invention, the body fat phantom can also include a third calibrated plate made of a third basis material having a third set of high and low energy x-ray attention values different from both the first and second sets x-ray attenuation values. The calibrated plates may be stacked together to define a second known simulated body fat composition. Preferably, stacking the first, second and third calibrated plates together defines a simulated body fat composition less than that of the first and second calibrated plates.
In another aspect, the body fat phantom has a plurality of first, second and third calibrated plates stackable in different combinations to define various known simulated body fat compositions.
In another aspect, the modular body fat phantom includes a high density end cap positionable next to a first end of the calibrated plates. The end cap is used for for triggering an automatic region of interest detection in certain known attenuation measurement devices.
Thus, the present invention provides a modular body fat phantom comprised of a number of calibrated plates of various materials simulating different percentages of body fat when scanned by dual energy x-ray measurement equipment. The plates can be configured into various stacks having different combinations of plates to provide a phantom of variable simulated body fat compositions for calibrating dual energy x-ray equipment at various attenuation levels.
These and still other advantages of the present invention will be apparent from the description of the preferred embodiments which follow.
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Miller Colin G.
Nord Russell H.
Bio-Imaging Technologies, Inc.
Ho Allen C.
Kim Robert H.
Quarles & Brady LLP
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