Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2001-09-12
2004-05-25
Gagliardi, Albert (Department: 2878)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S586000
Reexamination Certificate
active
06740898
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image information read-out method and apparatus, wherein a technique for detecting light emitted from opposite surfaces of a stimulable phosphor sheet and thereby detecting two image signals from the opposite surfaces of the stimulable phosphor sheet is employed, and an operation-processed image signal is obtained from the two image signals.
2. Description of the Related Art
In various fields, such as the medical field, techniques for reading out a radiation image of an object, which has been recorded on a stimulable phosphor sheet, to obtain an image signal, performing predetermined image processing on the image signal, and thereafter displaying a visible image, which is reproduced from the processed image signal, on an image display device, such as a cathode ray tube (CRT) display device, or outputting the visible image on film with a printer, such as a laser printer (LP), have heretofore been utilized. As apparatuses for reading out the radiation image, for example, computed radiography (CR) apparatuses, in which digital image processing techniques utilizing computers are employed, have heretofore been utilized.
The CR apparatuses are radiation image recording and read-out apparatuses. With the radiation image recording and read-out apparatuses, a radiation image of an object, such as a human body, is recorded on a sheet provided with a layer of a stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet). The stimulable phosphor sheet, on which the radiation image has been stored, is then exposed to stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal with photoelectric read-out means, such as a photomultiplier. Recently, the CR apparatuses are widely used in practice.
As techniques for photoelectrically detecting light is emitted by a stimulable phosphor sheet, the applicant proposed techniques for detecting light emitted from opposite surfaces of a stimulable phosphor sheet and thereby detecting two image signals from the opposite surfaces of the stimulable phosphor sheet in, for example, U.S. Pat. No. 4,346,295 and Japanese Unexamined Patent Publication No. 8(1996)-116435. With the proposed techniques, two photoelectric read-out means are located respectively on opposite surface sides of the stimulable phosphor sheet. Also, stimulating rays are irradiated to the two surfaces or only to one surface of the stimulable phosphor sheet, and the light, which is emitted by the stimulable phosphor sheet when it is exposed to the stimulating rays, is photoelectrically detected on the opposite surface sides of the stimulable phosphor sheet.
Specifically, with the techniques for detecting light emitted from opposite surfaces of a stimulable phosphor sheet and thereby detecting two image signals from the opposite surfaces of the stimulable phosphor sheet, a stimulable phosphor sheet is formed by overlaying a stimulable phosphor layer on a surface of a transparent substrate, and a radiation image is stored on the stimulable phosphor sheet. The stimulable phosphor sheet, on which the radiation image has been stored, is fitted on a transparent holder, and two photoelectric read-out means are located respectively above and below the holder. In this state, the light, which is emitted from one surface side of the stimulable phosphor sheet when the stimulable phosphor sheet is exposed to the stimulating rays, is detected by the photoelectric read-out means located above the holder, and an image signal (a one surface side image signal) is thereby detected. Also, the light, which is emitted from the other surface side of the stimulable phosphor sheet when the stimulable phosphor sheet is exposed to the stimulating rays, is detected by the photoelectric read-out means located below the holder, and an image signal (an other surface side image signal) is thereby detected.
Thereafter, an addition operation is performed on the image signal components of the two image signals having been detected from the opposite surfaces of the stimulable phosphor sheet (i.e., the one surface side image signal and the other surface side image signal), which image signal components represent corresponding pixels on the one surface and the other surface of the stimulable phosphor sheet, and an addition image signal (a superposition image signal) is thereby obtained. With the addition operation, high frequency noise occurring at random in each of the one surface side image signal and the other surface side image signal can be smoothed. Also, since the emitted light is collected from the two surfaces of the stimulable phosphor sheet, the light collecting efficiency can be enhanced. As a result, a superposition image, which has good image quality with an enhanced signal-to-noise ratio, can be reproduced from the addition image signal.
Also, as techniques for obtaining radiation image information by utilizing stimulable phosphor sheets, or the like, subtraction processing (subtraction operation) techniques have heretofore been known. With the subtraction processing techniques, a plurality of radiation images are recorded under different conditions and are then read out to obtain a plurality of image signals. Thereafter, a subtraction operation is performed on the plurality of the image signals, and a subtraction image signal is thereby obtained. In this manner, a subtraction image corresponding to the difference between the plurality of the radiation images, i.e. a subtraction image in which only a pattern of a specific object part (hereinbelow referred to also as a pattern of a tissue, a structure, or the like) in the radiation images has been enhanced or extracted, is obtained. Basically, the subtraction processing techniques may be classified into a temporal (time difference) subtraction processing technique and an energy subtraction processing technique. The applicant proposed various energy subtraction processing techniques utilizing stimulable phosphor sheets in, for example, U.S. Pat. Nos. 4,855,598 and 4,896,037. In order for the plurality of the image signals for the subtraction processing to be obtained, it is also considered to utilize the aforesaid technique for detecting light emitted from opposite surfaces of a stimulable phosphor sheet and thereby detecting two image signals from the opposite surfaces of the stimulable phosphor sheet.
Also, in order for a signal-to-noise ratio to be enhanced over the entire frequency band of an image obtained from the addition operation or the subtraction processing, the applicant proposed a technique for performing masking processing on the image signal obtained from each of the opposite surfaces of a stimulable phosphor sheet, such that a parameter (a weight factor) appropriate for each of the opposite surfaces of the stimulable phosphor sheet and each of frequency bands is capable of being utilized, as disclosed in, for example, Japanese Unexamined Patent Publication No. 7(1995)-319092.
When the image signal is to be obtained from each of the opposite surfaces of the stimulable phosphor sheet, read-out conditions (read-out modes) are set, and thereafter the operation for reading out the radiation image information is performed. Examples of the read-out conditions include a level of stimulation energy (i.e., an intensity of the stimulating rays irradiated to the stimulable phosphor sheet), an image signal gathering range (i.e., a range of a radiation dose, over which the image signal is capable of being detected), a read-out pixel density, and a pixel sampling frequency. (The image signal gathering range is also referred to as the read-out gain.) The read-out conditions are set in accordance with the performance required of the image to be obtained. The image signal gathering ranges with respect to the op
Fuji Photo Film Company Limited
Gagliardi Albert
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