X-ray or gamma ray systems or devices – Specific application – Absorption
Reexamination Certificate
2001-11-09
2002-12-03
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Absorption
Reexamination Certificate
active
06490339
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method and apparatus for measuring bone mineral density and may be used for osteoporosis screening. More specifically, the invention relates to a method and apparatus for measuring bone mineral density using electromagnetic wave radiation and storage layer radiation screens.
2. Description of Related Art
Osteoporosis is a bone disease in which bones become thinner and more porous, commonly resulting in fractures of the bones. More than 1.5 million osteoporosis-related fractures occur each year in the United States, usually in the spine, hip and wrist. Osteoporosis is most common in older women and about 25% of women older than 60 years have osteoporosis.
Bone density testing, which measures bone mineral content, is used to diagnose osteoporosis. A low bone density may indicate a risk for fractures in the future. The test can also be used to determine a rate of bone mineral loss in those not receiving treatment, and a rate of bone gain in those being treated.
Several different methods and apparatuses have been developed for measuring bone mineral density. These different methods and apparatuses can be broadly divided based on whether they are single or dual energy X-ray systems.
Mineral loss in a person's bones can be estimated from a single X-ray image of a body part. One potential difficulty associated with single X-ray images is that it is difficult to determine how much of the X-ray image is due to hard tissue (e.g., bones) and how much is due to soft tissue (skin, muscle, ligaments, etc.).
Dual-energy x-ray absorptometry (DXA) is a technique which has been developed which uses two x-ray images obtained using x-rays of different energy levels to compensate for the fact that hard tissue is surrounded by soft tissue that also contributes to an x-ray image. Dual energy systems use two images to obtain a set of two simultaneous equations for each pixel in the images and then solve those equations to determine the amount of x-rays that was absorbed by the bone. Shimura (U.S. Pat. No. 5,187,731) describes a method for quantifying bone mineral using a dual energy radiation system.
The two x-ray images are obtained using x-rays with different energy levels to compensate for tissue variations in quantifying bone mass in an x-ray image. Typically, existing DXA systems rely on known x-ray absorption characteristics of hard tissue and soft tissue to both high-energy and low-energy radiation. Some systems use an x-ray image of a wedge of material with bone-like x-ray attenuation properties (e.g., aluminum) to calibrate the system, where the thickness and density of each part of the wedge is known in advance.
Existing DXA measurements generally require expensive equipment that is usually available only in specialized facilities. This equipment is typically complex, and the test results must be interpreted by a skilled person (e.g., a radiographer), resulting in significant cost of labor. In addition, because the test results must be interpreted by humans, existing tests are not highly repeatable. It would be advantageous to remove human variations and determine more accurately the progression of osteoporotic condition over a period of time, such as one year intervals, to determine the progression of bone loss. The need for the interpretation of test results also makes it more difficult to return these results to the patient instantly.
U.S. Pat. Nos. 5,150,394 and 5,465,284 describe systems which measure bone density using x-ray radiation at two different energy levels. In these patents, x-ray radiation of two intensity levels is transmitted through a portion of the patients body to a scintillator which converts the x-rays into visible light. The visible light emitted by the scintillator is provided to a charge-coupled device (CCD), which in turn converts the visible light into an electrical signal. The system then forms an image of the body from the electrical signal, and determines the density the patient's bone from the image.
U.S. Pat. Nos. 5,852,647 and 5,898,753 also describe dual energy level systems. In U.S. Pat. No. 5,898,753, a system is described which uses CMOS wafers instead of CCD wafers which allows larger sensors to be manufactured more readily.
SUMMARY OF THE INVENTION
The present invention relates to apparatuses and methods for forming and reading a radiation image of an object.
In one embodiment, an apparatus is provided for forming and reading a radiation image of an object which comprises: a platform adjacent to which may be placed an object of which a radiation image is to be taken; a cylindrically shaped rotatable drum; a storage layer radiation screen mounted adjacent a surface of the rotatable drum; an electromagnetic wave radiation source positioned relative to the storage layer radiation screen and the platform such that radiation from the electromagnetic wave radiation source which traverses the platform and the object adjacent the platform is absorbed by the storage layer radiation screen; an image acquisition optical system positioned adjacent the drum, the image acquisition optical system including an excitation system for directing an excitation beam in the direction of the drum, the excitation beam causing energy to be emitted from portions of the screen which are contacted with the excitation beam as the drum is rotated, and an emission collecting system for collecting the energy emitted from the screen; an optics driver for moving the image acquisition optical system in a direction parallel to the rotational axis of the drum as the drum is rotated; and a drum drive mechanism which causes the rotatable drum to rotate. The system may further include embedded software for controlling system functions. Functions which the software may perform include, but are not limited to: interfacing with the system operator in accepting patient data, providing system status information, automatic image processing and analysis, and presentation of exam results.
In one variation, the apparatus may further include a screen erasing mechanism for erasing the storage layer radiation screen. According to this variation, the apparatus is able to be reused without having to remove the screen between scans. The screen erasing mechanism may be positioned adjacent the rotatable drum and used to release any radiation energy remaining stored on the screen after the screen has been read.
The screen erasing mechanism may also be positioned within the image acquisition optical system and moved by a same mechanism as the image acquisition optical system. The screen erasing mechanism may be designed to erase the screen as the screen is rotated without having to move the screen erasing mechanism. The screen erasing mechanism may be designed to provide energy over a sufficiently large area that the screen may be erased without either the erasing mechanism or the screen being moved.
In another embodiment, an apparatus is provided for forming and reading a radiation image of an object which comprises: a platform adjacent to which may be placed an object of which a radiation image is to be taken; a rotatable platter; a storage layer radiation screen mounted adjacent a surface of the rotatable platter; an electromagnetic wave radiation source positioned relative to the storage layer radiation screen and the platform such that radiation from the electromagnetic wave radiation source which traverses the platform and the object adjacent the platform is absorbed by the storage layer radiation screen; an image acquisition optical system positioned adjacent the platter, the image acquisition optical system including an excitation system for directing an excitation beam in the direction of the drum, the excitation beam causing energy to be emitted from portions of the screen which are contacted with the excitation beam as the platter is rotated, and an emission collecting system for collecting the energy emitted from the screens; an optics driver for moving the image acquisition optical system in a direction ra
Donlon Edward P.
Mitchell Christopher R.
Rimsa Joseph R.
Sprehn Gregory A.
Alara, Inc.
Davis Paul
Heller Ehrman White & McAuliffe
Porta David P.
Thomas Courtney
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