X-ray or gamma ray systems or devices – Beam control – Filter
Reexamination Certificate
1998-10-28
2001-11-20
Porta, David P. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Filter
C378S159000, C378S018000, C250S515100
Reexamination Certificate
active
06320938
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a method of obtaining a diagnostic image using computer tomography.
BACKGROUND OF THE INVENTION
Diagnostic computer tomography (CT) is used to obtain a diagnostic image of a patient's internal organs. A CT scanner forms the image using x-rays. The patient is placed in the CT scanner between an x-ray source and an x-ray sensor so that x-rays pass through the patient's body and are detected by the x-ray sensor which then generates output signals based on the x-rays. A computer receives the signals and processes the signals to form parts of an image. The computer assembles the partial images from the scan to generate a desired cross section image of the body, including the organ or organs targeted for diagnosis.
A diagnostic CT examination commonly targets a specific body organ for diagnosis. For example, a thoracic CT scan typically obtains an image of the lungs or heart. Other organs commonly targeted for CT scans include the brain, spine and pelvis. The CT scan should return to the doctor a readable diagnostic image of the target organ.
During. a CT scan, an organ other than the target organ may be exposed to x-rays. X-rays pass through the entire cross section of the body, and the x-rays will pass through an organ adjacent the target organ. The adjacent, secondary organ is seldom the target of a diagnostic CT examination. The secondary organ is exposed to x-rays as an incidental by-product of the CT examination of the target organ.
An organ may be radiosensitive, that is, the organ may be susceptible to cancer induced by radiation (including x-rays). Common radiosensitive organs exposed to x-rays as an incidental by-product of a CT examination include the breasts, eyes, thyroid and scrotum.
Incidental exposure of a radiosensitive secondary organ to x-rays may increase the risk of cancer. For example, a thoracic CT examination typically exposes each breast to a radiation dose of 2.0-3.5 rads. Young women are especially sensitive to radiation-induced breast cancer. It is desirable to reduce incidental exposure of secondary organs to x-rays.
Thus, there is a need for an improved method of obtaining a diagnostic image using a CT scanner. The method should reduce x-ray exposure to a radiosensitive secondary organ during CT examination of a target organ. The method should not degrade the diagnostic portion of the image nor contain artifacts that extend into the diagnostic portion of the diagnostic image. The method should be usable with existing CT scanners and scanner protocols.
SUMMARY OF THE INVENTION
The present invention is directed to an improved method of obtaining a diagnostic image using a CT scanner. The improved method reduces x-ray exposure to a radiosensitive secondary organ during CT examination of a target organ. The improved method does not degrade the diagnostic portion of the image and does not generate artifacts extending into the diagnostic portion of the image. The improved method is usable with existing CT scanners and scanner protocols.
A method to obtain a diagnostic image with a CT scanner having features of the present invention includes the step of placing a shield on a patient's body over a secondary organ adjacent a target organ. The shield is partially transparent to x-ray radiation. A CT scan of the target organ is conducted according to conventional protocols and technical parameters. X-rays pass through the target organ, the shield and secondary organ. A sensor detects the x-rays and generates signals. A computer processes the signals to form an image. No artifacts are formed in the diagnostic portion of the image and there is no degradation of the diagnostic portion of the image. The shield reduces the radiation dose of the secondary organ about 40% to 60% as compared to the radiation dose received during the same CT scan made without the shield.
In a preferred version of the method, the shield is a thin layer of radioabsorbent material. The material overlies the secondary organ and absorbs some of the x-rays that otherwise would have passed through the secondary organ. The material is smoothed to eliminate folds or creases that may cause an artifact in the image. The material selectively protects the secondary organ without affecting the diagnostic image of the target organ.
Other objects and features of the invention will become apparent as the description proceeds, especially when taken in conjunction with the accompanying drawings illustrating the invention, of which there are three sheets and three embodiments.
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F & L Medical Products
Hooker, P.C. Thomas
Porta David P.
Yun Jurie
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