X-ray or gamma ray systems or devices – Specific application – Mammography
Reexamination Certificate
2001-03-16
2002-11-19
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Mammography
C378S086000, C378S088000, C378S090000
Reexamination Certificate
active
06483891
ABSTRACT:
FIELD OF THE INVENTION
The proposed invention relates to devices for producing an object image using reduced-angle scattering of a penetrating radiation, namely—to mammography devices that determine changes in the tissue structure. The invention can be suitably used in medical application for diagnosing the cancer cases of mammary glands at an early stage of a disease.
PRIOR ART
The known mammography devices are generally based on the principle that different substances, being subjected to raying, exhibit different properties of absorbing the X-ray radiation. The intensity of a radiation passed through an object and forming its projection image is determined by absorption property (absorption coefficient) of the substances constituting the object and by their thickness in the raying direction. To provide a quality image, it is necessary that a whole object would have the same thickness in the raying direction. The known devices provide said feature by compressing mammary gland to desired (or allowable) size (U.S. Pat. No. 4,962,515, Sep. 10, 1996). However, such compression results in that a patient feels a pain and discomfort.
Another method of compensating a variable thickness of an object consists in placing mammary gland in a cylindrical vessel filled with an immersion liquid that has the same X-ray absorption coefficient as the gland. Such approach is used, for example, in mammary gland tomography (U.S. Pat. No. 3,973,126, Mar. 08, 1976). For producing one projection of mammary gland, a similar result can be attained by introducing plate-shaped attenuating filters (made of aluminium or other material) into the raying zone, in particular in cases of studying the subsurface subcutaneous areas of mammary gland (U.S. Pat. No. 4,969,174, Jun. 11, 1990). There is no need of any compression in the use of this approach for producing an image.
Another technique to obviate the need to compress mammary gland is provided when an image is produced by scanning of an object with a narrow X-ray beam. In the device of such approach (U.S. Pat No. 4,969,174, Jun. 11, 1990), an image is produced on a photographic film, under which film rows of X-ray detectors are arranged. The detectors determine the time required for exposing the photographic film for each of the raying beam position. A signal from the detector is supplied to a scanning system control unit, and allowance for various breast thickness was made for by different rates of the beam movement. In this system, scanning is performed along the breast axis.
In the devices based on principles of the conventional absorption X-raying, i.e. on registration of intensity distribution of the radiation passed through a rayed object, the scattered radiation is a parasitic phenomenon that creates a background and affects the image contrast. To overcome the scattered radiation, said radiation is registered separately using a collimating grid and a filter, and the registered signal is deducted as the background from the total signal produced when an object is rayed (U.S. Pat. No. 4,651,002). The scattering pattern is measured integrally, and a filter is implemented as a movable member, the scattered radiation being measured at large angles.
An essential index of performance of an X-ray mammography device is the irradiation dose absorbed by a patient during checking. A partial decrease of the irradiation dose is provided by a decreased thickness of the checked object (breast compression).
Another technique to reduce the irradiation dose is selection of the X-ray radiation parameters. For example, application of replaceable filters allows to select the radiation hardness for each patient (U.S. Pat. No. 4,969,174, Jun. 11, 1990).
When a patient's breast is scanned by an X-ray beam, the irradiation dose is decreased by monitoring of the passed radiation by detectors. Then the breast raying (scanning) is selected to be optimal so that to minimize the patient irradiation dose and produce a clear image.
In all above-discussed devices, a patient usually is positioned in the standing or inclined position, and mammary gland is fixed normally to the patient's body.
All above-discussed devices are based on the principle of producing images as the difference in absorption of the rays passing through a patient's mammary gland via different paths. As coefficients of absorption by the breast soft tissues have only a slight difference, so it is difficult to determine minor changes in tissues in early stages of a disease.
The mentioned drawbacks are avoided by using a method of registering the radiation coherently scattered by an object for producing an image. U.S. Pat. No. 4,751,722, G 01 N 23/22, 1988, describes a device, wherein the radiation passed through an object and the angular distribution of the coherently scattered radiation lying at angles of 1° to 12° in relation to the incident beam direction are registered simultaneously. As said patent discloses, the main portion of the elastically-scattered radiation is concentrated in the angles less than 12°, and the scattered radiation has a characteristic angular relationship having pronounced maxima, the location of which maxima is determined both by the irradiated substance itself and the incident radiation energy. As distribution of intensity of the coherently scattered radiation within small angles depends on the molecular structure of a substance, then different substances having the same absorptive capacity may differ regarding the distribution of intensity of the coherent radiation angular scattering being intrinsic to each substance. In case an object is heterogeneous, i.e. consists of different substances, then intensity of a radiation scattered at each particular angle is constituted by intensities of the rays scattered by different substances on the path of propagation of a penetrating radiation beam. This patent proposes to use a narrow collimated beam of a monochromatic or polychromatic radiation for irradiating an object. A detecting system has the resolution property both for energy and coordinate (scattering angle). Said device comprises an X-ray source having a diaphragm that forms a primary radiation beam such that said beam has a small cross-section in the plane normal to the beam propagation direction. Having passed through a tested object, the beam is registered by a row of detectors, one of which is positioned such that it registers the primary beam passed through an object (or the tested object area), the other detectors being positioned in the plane normal to the ray plane, or on a straight line in said plane, and oriented such that they register only the coherently scattered radiation. Further, each detector of said detector row registers the radiation that is scattered at a certain angle.
The above-described device has a relatively low sensitivity to the radiation scattered in immediate vicinity of the primary beam, because the primary beam radiation intensity considerably exceeds that of the scattered radiation and hinders the registration thereof. Further, the radiation intensity sharply falls when the scattering angle grows, thus the coherently scattered radiation intensity within the range of 1-12 degrees is low, hence the sufficiently high irradiation doses and a long exposure are required for testing an object.
DISCLOSURE OF THE INVENTION
The object of the invention is to provide devices that are more sensitive to registration of the coherent scattered radiation in ultra-small angles (tens of seconds to one degree), which will allow to reduce the radiation dose in testing of an object. Attainment of said object will allow to avoid compression of breast, i.e. avoid patient's pain and discomfort.
The main part of coherently scattered radiation is concentrated in the central diffraction peak that is situated in the scattering angles of 0 to 1 degree relative to the primary beam incidence direction. In this angular range concentrated is the radiation coherently scattered by heterogeneities of the object electronic structure, which heterogeneities have characteris
Komardin Oleg Valentinovich
Lazarev Pavel Ivanovich
Burns Doane Swecker & Mathis L.L.P.
Ho Allen C.
Porta David P.
Quanta Vision, Inc.
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