Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2001-02-13
2003-12-23
Hannaher, Constantine (Department: 2878)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S581000, C250S589000
Reexamination Certificate
active
06667488
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a radiation image acquisition method and apparatus, and more particularly to a radiation image acquisition method and apparatus wherein a radiation image recorded on a radiation image conversion panel is obtained as a digital image signal, further comprising a cell interval detection method and apparatus therefor.
2. Description of the Related Art
The use of a stimulable phosphor in recording radiation images as an alternative to the method of recording radiation images employing conventional photographic film and a sensitized screen is well known. In this method, an radiation image conversion panel (also called a stimulable phosphor sheet) having on the surface thereof a stimulable phosphor layer (herein after referred to as a phosphor layer) containing stimulable phosphor, absorbs energy from radiation passing through the body of a subject or emitted by a subject to record a latent image representing a radiation image. Afterwards, the stimulable phosphor is exposed to stimulating electromagnetic energy such as visible or infrared light, causing the energy from the radiation accumulated thereon to be emitted as light. In this specification, the light emitted from the stimulable phosphor upon stimulation thereof will be referred to as “stimulated emission”. This stimulated emission is then read out as photoelectrical signals and reproduced as a visible image. After the radiation image has been read out from the phosphor layer, the energy stored thereon is erased and the radiation image conversion panel is reused for recording and reproducing radiation images in the same way.
It is preferable that the radiation image conversion panel described above be highly sensitive and capable of reproducing high-image quality radiation images. In particular, the ability to reproduce high-resolution X-ray images, which are the representative diagnostic-use radiation image, is desirable.
However, the stimulating light employed for reading out the radiation image stored in the phosphor layer of the radiation image conversion panel is dispersed within the phosphor layer, causing a degradation in image resolution. That is to say, the beam of stimulating light focused on the inner surface of the phosphor layer is scanned in the main and a sub-scanning directions, and the stimulated emission caused thereby to be emitted from the phosphor sheet is sequentially focused and read out; however, if the stimulating light irradiating the phosphor layer is dispersed horizontally therein, the stimulable phosphor on the periphery of the irradiation range (the scan spot) of the stimulating light are also stimulated as a result, causing the stimulable phosphor outside of the irradiation range of the stimulating light to emit stimulated emission, which is then detected as stimulated emission from within the irradiation range of the stimulating light, and the resolution of the image data of the latent image stored in the phosphor layer is deteriorated.
In order to avoid this phenomenon, a method is known wherein partition walls composed of a material impermeable to the stimulating light are disposed so as to partition the phosphor layer into a one- or two-dimensional fine grid along the plane of the panel, and the plurality of small compartments (hereinafter referred to as cells) formed by these partition walls are filled in with stimulable phosphor, forming columns or belts (as in for example, Japanese Unexamined Patent Publication No. 62(1986)-36600). In a phosphor layer having these cells arranged in the horizontal orientation thereof//spread across the plane thereof, the stimulating light is limited by the impermeable material of which the cell partition walls are formed and is not dispersed outside of a cell it enters, and the emission of stimulated emission outside of the irradiation range of the stimulating light can thereby be prevented. Therefore, the quantity of stimulated emission emitted from each cell corresponds to a value of one pixel of when the radiation image described above is to be reproduced, and when the image is read out from the phosphor layer, the radiation image reproduced has a high resolution, which is beneficial.
Note that aforementioned “material impermeable to stimulating light” is not limited to a material which cuts off the stimulating light completely, but refers to a material for which it is relatively difficult, compared to the stimulable phosphor packed within the cells, for the stimulating light to penetrate (preferably, substantially difficult for the stimulating light to penetrate).
However, although the cells forming the phosphor layer have a cyclical structure, the pitch of each cell is uneven. When stimulating light is irradiated onto the phosphor sheet having cells with an uneven construction, the quantity of stimulated emission from each cell corresponds to a value of one pixel when the radiation image described above is to be reproduced, and when the image is read out from the phosphor layer, aside from the change in the quantity of stimulated emission emitted in proportion to the quantity of radiation energy accumulated on the phosphor sheet, the quantity of stimulated emission changes depending on the unevenness of the pitch of the cells, and this causes a degradation in the image quality of the reproduced radiation image. For example, even if every region of the phosphor sheet is exposed to a strong beam of stimulating light of a uniform intensity, a fixed quantity of stimulated emission will not be emitted from each cell, and if a value of one pixel is assigned corresponding to the light emitted from each cell, a blurred image will be reproduced.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary objective of the present invention is to provide a radiation image acquisition method and apparatus in which even if the pitch of the cells of the phosphor layer are uneven, the quantity of stimulated emission emitted from each cell can be acquired precisely as a digital image signal. The second objective of the present invention is to provide a cell interval detection method for aforementioned radiation image acquisition method and apparatus capable of precise detection of the interval between the multiple cells arranged in the phosphor layer.
In the radiation image acquisition method according to the present invention, the phosphor layer formed of a plurality of cells, arranged in at least the main scanning direction, filled with stimulable phosphor bearing thereon a radiation image is scanned in the main and a sub-scanning direction with a stimulating light beam and the stimulated emission emitted by the phosphor layer due to said scanning is photoelectrically detected as an analog image signal, and said analog image signal is digitized to obtain a digital image signal representing the radiation image; the signal component representing the cell partition walls included in the analog image signal is recognized, and the digital image signal is obtained from the component of the analog signal obtained between the recognized signal components of the cell partition walls.
Note that the expression “arranged in at least the main scanning direction” refers not to a matrix in which cells are lined up in the main and sub-scanning//vertical and horizontal directions, but to the long straight stripe-shaped cells disposed in the horizontal orientation.
In the radiation image acquisition method according to the present invention, a phosphor having light conversion characteristics different from the stimulable phosphor is mixed with either the cell partition walls or the stimulable phosphor contained therebetween, and the fluorescent light emitted from the phosphor material in the phosphor layer due to aforementioned scanning is detected and the signal component representing the partition walls included in the detected signal can be recognized in this way.
In addition, the signal component representing the partition walls included in the signal obtained b
Kohda Katsuhiro
Tazaki Seiji
Fuji Photo Film Co. , Ltd.
Hannaher Constantine
Moran Timothy
Sughrue & Mion, PLLC
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