X-ray or gamma ray systems or devices – Accessory – Testing or calibration
Reexamination Certificate
1999-12-20
2001-10-16
Kim, Robert H. (Department: 2882)
X-ray or gamma ray systems or devices
Accessory
Testing or calibration
C378S018000
Reexamination Certificate
active
06302582
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not applicable
BACKGROUND OF THE INVENTION
The present invention relates to phantoms for x-ray machines and the like, and in particular, to a phantom providing calibration for dual energy x-ray equipment used in bone density measurement.
The absorption of x-rays by material is dependent on two independent atomic properties of the material, the Compton scattering of x-rays by the material and photoelectric absorption. The relative proportion of these two types of absorption is different for different materials and varies as a function of frequency. Accordingly, measurements of the material at two x-ray energies (generally corresponding to different x-ray frequencies) can reveal information about the properties of the material.
Dual energy measurements can be used to measure relative proportions of any two basis materials making up the material. A principal use of this phenomenon is in the measurement of the basis materials of bone and soft tissue to provide an in vivo measurement of 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.
In making bone density measurements, it is important that repeatable quantitative results be produced. For this reason, it is necessary that a machine be calibrated frequently to prevent drifting of the measurements over time. In the case where multiple machines may be used in a study, each machine must be cross-calibrated to identify inconsistencies among the machines. Critical too, for bone density measurements, is that a similar region of the bone be examined among patients or for an individual patient over different scans. Finally, when making calibrations for bone density, it is important that they show the same range of readings for different samples.
What is needed is a simple and accurate phantom that can be used with dual energy densitometers to monitor its calibration performance over time, as well as to provide cross-calibration of multiple densitometers, by simulating measurement of the irregular and inhomogeneous spine.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a phantom simulating a range of vertebra types and densities, curvature of the lateral vertebral walls, intervertebral cartilage, and the cortical and trabecular regions of the vertebra. Simplified construction of the phantom is made possible by equating the density variations in the three dimensionally complex and inhomogeneous spine as a set of easily machined flat surfaces of different thicknesses.
In particular, the present invention provides a spine phantom for calibrating a dual energy x-ray attenuation measurement device for measuring vertebral bone density. The spine phantom includes a vertebra-simulating body having a base surface extending in longitudinal and transverse directions to support the vertebra-simulating body substantially perpendicular to an x-ray beam of the measurement device. The vertebra-simulating body defines an intervertebral section, a composite bone section and cortical wall sections. These sections each extend to respective first, second and third planes of different heights from the base surface, so as to simulate the x-ray attenuation characteristics of cartilage, cortical and trabecular bone, and cortical bone wall regions of a human spine, respectively.
The spine phantom can include a plurality of such vertebra-simulating bodies, each having an intervertebral section, composite bone section and cortical wall sections. The vertebra-simulating bodies are aligned and joined at the intervertebral sections to define voids between the composite bone sections of each body. The composite bone sections and the cortical wall sections of each vertebra-simulating body extend to a different height from the base surface, such that each vertebral body has second and third planes at unique heights from the base surface. This variation in height between the vertebra-simulating bodies simulates various human vertebral bone density values, ranging from that of a healthy human spine to that of an osteoporotic spine. Additionally, the distance between the second and third planes is different for each vertebra-simulating body and the composite bone section of each body has a plateau surface at its second plane of a unique size, simulates vertebra of different overall bone masses. The spine phantom may also include one or more calibration blocks extending to a prescribed height above the base surface.
In one aspect of the invention, the vertebra-simulating bodies may be a homogeneous material, preferably, calcium hydroxyapatite. In another aspect, the cortical wall sections define concave outer surfaces. These surfaces provide a means for testing the edge detection algorithms of x-ray attenuation measurement devices and can be used by certain devices for locating a particular spinal region of interest.
In another aspect of the present invention, the spine phantom may include a preferably acrylic block into which the vertebral body is embedded. A sheet layer, preferably made of polyvinylchloride, can also be affixed to the block that attenuates x-rays differently than the block such that the sheet layer and block together have x-ray attenuation characteristics simulating human soft tissue. So that when a vertebra-simulating bodies are disposed in the block, the spine phantom simulates a human vertebra surrounded by soft tissue.
In yet another aspect, the spine phantom can be disposed in a suitable carrying case or bag for transport between x-ray attenuation devices needing calibration as well as for safe storage. Preferably, the carrying case is made of a suitable x-ray translucent material such that the spine phantom may be scanned without being removed from its case.
Thus, the present invention provides a calibration phantom simulating a human spine at various spinal regions and in various states of bone decay. The phantom is made from a homogenous material and has easily machinable surfaces. These and still other advantages of the present invention will be apparent from the description of the preferred embodiments which follow.
REFERENCES:
patent: 5235628 (1993-08-01), Kalender
patent: 5335260 (1994-08-01), Arnold
patent: 5481587 (1996-01-01), Mazess
Miller Colin G.
Nord Russell H.
Bio-Imaging Technologies, Inc.
Kim Robert H.
Quarles & Brady LLP
Thomas Courtney
LandOfFree
Spine phantom simulating cortical and trabecular bone for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Spine phantom simulating cortical and trabecular bone for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Spine phantom simulating cortical and trabecular bone for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2568621