Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2001-01-29
2003-05-20
Porta, David (Department: 2878)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S584000
Reexamination Certificate
active
06566675
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of and apparatus for obtaining a radiation image in which a radiation image recorded on a radiation image conversion panel is obtained as a digital image signal.
2. Description of the Related Art
When certain kinds of phosphors are exposed to a radiation such as X-rays, &agr;-rays, &bgr;-rays, &ggr;-rays, cathode rays or ultraviolet rays, they store a part of energy of the radiation. Then when the phosphor which has been exposed to the radiation is exposed to stimulating rays such as visible light or a laser beam, light is emitted from the phosphor in proportion to the stored energy of the radiation. A phosphor exhibiting such properties is generally referred to as “a stimulable phosphor”. In this specification, the light emitted from the stimulable phosphor upon stimulation thereof will be referred to as “stimulated emission”. As a system alternative to the conventional radiography using photographic film and a sensitized screen, a radiation image recording system using such a stimulable phosphor has been put into practice. In this system, a radiation image conversion panel (sometimes called “stimulable phosphor sheet”) having thereon a stimulable phosphor layer is used. That is, when the radiation image conversion panel is exposed to a radiation passing through an object or emitted from an object, the stimulable phosphor layer absorbs a part of energy of the radiation and stores a radiation image of the object as a latent image. When the radiation image conversion panel is exposed to stimulating light such as visible light or infrared rays, the stimulable phosphor layer emits stimulated emission in proportion to the radiation energy stored thereon. The stimulated emission is photoelectrically converted into an electric image signal and a radiation image of the objected is reproduced as a visible image on the basis of the electric image signal. After the radiation image is read out the radiation image conversion panel is exposed to erasing light and is caused to release residual radiation energy so that the radiation image conversion panel can be used again.
It is preferred that the radiation image conversion panel be highly sensitive and can reproduce a high quality radiation image. Especially, in the diagnostic radiation image recording and reproducing system, which is a typical application of the radiation image recording system using the radiation image conversion panel, a high quality image is desired.
However, the stimulating light projected onto the stimulable phosphor layer of the radiation image conversion panel when the radiation image stored thereon is to be read diffuses in the stimulable phosphor layer and deteriorates resolution of the radiation image. That is, the latent radiation image stored on the stimulable phosphor layer of the radiation image conversion panel is read out by causing a beam of the stimulating light focused on the surface of the radiation image conversion panel to scan the radiation image conversion panel in both a main scanning direction and a sub-scanning direction and detecting the stimulated emission emitted in sequence from the parts of the radiation image conversion panel as the stimulating light beam scans the radiation image conversion panel. When the stimulating light two-dimensionally diffuses inside the phosphor layer, the stimulable phosphor outside the scanning spot is also stimulated to emit stimulated emission, which deteriorates the resolution of the radiation image.
In order to avoid such a phenomenon, it has been proposed to provide a partition wall impermeable to the stimulating light in the stimulable phosphor layer to linearly or two-dimensionally part the stimulable phosphor layer into a plurality of regularly arranged fine cells. In such an arrangement, stimulating light impinging upon one cell is prevented from diffusing to adjacent cells by the partition wall which is impermeable to the stimulating light, whereby a radiation image having a high resolution can be read out.
The partition wall impermeable to the stimulating light need not be perfectly impermeable to the stimulating light so long as it is less permeable to the stimulating light as compared with the stimulable phosphor in the cell.
However, the system provided with the partition wall impermeable to the stimulating light is disadvantageous in that each time the stimulating light beam passes the partition wall, the intensity of the stimulated emission becomes weak at regular intervals, and the analog image signal obtained by photoelectrically converting the stimulated emission into an electric signal comes to include periodic signals (e.g., signals which will generate moiré fringes) which represents that the stimulating light beam passes the partition wall. When the analog image signal is digitized into a digital image signal, aliasing noise can be generated to distort the image depending on the relation between the periodic signals generated when the stimulating light beam passes the partition wall and the sampling periods at which the analog image signal is sampled.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a method of and an apparatus for obtaining a digital radiation image which is free from aliasing noise which is generated when an analog image signal read out from a radiation image conversion panel provided with a partition wall is digitized and which can reproduce a high quality radiation image.
In accordance with a first aspect of the present invention, there is provided a method of obtaining a radiation image in which a radiation image conversion panel having a stimulable phosphor layer which is parted into a plurality of cells regularly arranged at least in a main scanning direction by a partition wall and has been exposed to a radiation bearing thereon a radiation image of an object is scanned by a stimulating light beam in the main scanning direction and a sub-scanning direction, stimulated emission emitted from the radiation image conversion panel upon stimulation by the stimulating light beam is photoelectrically detected to make up an analog image signal and a digital image signal representing a radiation image of the object is obtained by digitizing the analog image signal, wherein the improvement comprises that
the sampling intervals Ts (in seconds) for digitizing the analog image signal are set to satisfy formula
Ts≦Na/
2
v,
wherein Na represents the pitch (m) of the cells in the main scanning direction and v represents the scanning speed (m/sec).
It is preferred that the sampling intervals Ts be set to satisfy formula
Na/
40
v≦Ts≦Na/
2
v.
It is further preferred that the analog image signal be obtained through a low-pass filter whose cut-off frequency fc (Hz) satisfies formula
fc≦
0.5
/Ts.
In accordance with a second aspect of the present invention, there is provided a method of obtaining a radiation image in which a radiation image conversion panel having a stimulable phosphor layer which is parted into a plurality of cells regularly arranged at least in a sub-scanning direction by a partition wall and has been exposed to a radiation bearing thereon a radiation image of an object is scanned by a stimulating light beam in a main scanning direction and the sub-scanning direction, stimulated emission emitted from the radiation image conversion panel upon stimulation by the stimulating light beam is photoelectrically detected to make up an analog image signal and a digital image signal representing a radiation image of the object is obtained by digitizing the analog image signal, wherein the improvement comprises that
the scanning intervals L (m) in the sub-scanning direction are set to satisfy formula
L≦Nb/
2,
wherein Nb represents the pitch (m) of the cells in the sub-scanning direction.
It is preferred that the scanning intervals L be set to satisfy formula
Nb/
40≦
L≦Nb/
2.
When the radiation image conversion panel has a stimulable pho
Fuji Photo Film Co. , Ltd.
Sughrue & Mion, PLLC
Sung Christine
LandOfFree
Method of and apparatus for obtaining radiation image does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of and apparatus for obtaining radiation image, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of and apparatus for obtaining radiation image will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3059951