Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2001-11-07
2004-07-20
Hannaher, Constantine (Department: 2878)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S584000
Reexamination Certificate
active
06765225
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for reading radiation image information. More specifically, the present invention relates to a radiation image information reading apparatus for reading radiation image information recorded on a stimulable phosphor sheet by using a plurality of line sensors.
2. Description of the Related Art
Radiation image recording and reproducing systems using stimulable phosphor (see Japanese Unexamined Patent Publication Nos. 55(1980)-12429, 55 (1980)-116340, and 56 (1981)-104645, for example) have been in wide use. The stimulable phosphor stores a portion of energy of radiation irradiated thereon and emits light in accordance with the radiation energy stored therein upon exposure to an excitation light such as visible light and a laser beam. In such a system, radiation image information of a subject such as a human body is recorded on a stimulable phosphor sheet comprising a stimulable phosphor layer over a base material. By irradiating the excitation light such as a laser beam on each of the pixels on the sheet, light is emitted from the pixels. The light is photoelectrically read by photoelectric reading means to obtain an image signal, and an erasing light is irradiated on the sheet after the reading to release the radiation energy still remaining in the sheet.
Image processing such as tone processing and frequency processing appropriate for observation is carried out on the image signal obtained in the above manner, and the image signal after the processing is recorded on a film as a visible diagnostic image (a final image) or displayed on a high-definition CRT for diagnosis. By irradiating the erasing light on the sheet to release the residual energy, the sheet can be used repeatedly for recording radiation image information.
In a radiation image information reading apparatus used in the radiation image recording and reproducing system described above, a linear light source is used for linearly irradiating the excitation light on the sheet, in order to reduce time for reading the light, to downsize the apparatus, and to reduce cost (see Japanese Unexamined Patent Publication Nos. 60(1985)-111568, 60(1985)-236354, and 1(1989)-101540, for example). As the photoelectric reading means, a line sensor having a plurality of photoelectric conversion devices arranged in a lengthwise direction of an area in the sheet on which the excitation light is irradiated from the linear light source (hereinafter called a main scan direction) is used. The reading apparatus also comprises scanning means for moving either a combination of the linear light source and the line sensor or the stimulable phosphor sheet relative to the other in a direction substantially perpendicular to the main scan direction (hereinafter called a vertical scan direction).
Each of the photoelectric conversion devices such as a CCD sensor and a MOS image sensor comprising the line sensor has a limit called a saturation charge in terms of an amount of an electric charge to be stored therein. It is difficult to produce the sensor with a large surface area, and the sensor cannot detect light having an amount larger than a predetermined amount. As a result, an accurate measurement result is not obtained for a range in which an amount of the radiation information is large (a high dose range) in the sheet, and a range of the amount of the light readable by the sensor (a dynamic range) is narrow.
Therefore, a width of each of the photoelectric conversion devices in the vertical scan direction has been conventionally set several times smaller than a width of one pixel in the vertical scan direction in a final image. Data from several consecutive photoelectric conversion devices are read sequentially in the vertical scan direction and added to obtain data for one pixel in the final image. In this manner, the dynamic range of the line sensor can be widened.
However, in the above method, in order to add the data in the vertical scan direction, it is necessary to store, at least for each reading, all outputs from all the photoelectric conversion devices arranged in the main scan direction. Since the line sensor has the photoelectric conversion devices arranged in the main scan direction, a large-scale storage device (a line memory) is necessary to store all the outputs from each of the photoelectric conversion devices, which increases the cost.
Therefore, a radiation image information reading apparatus for solving this problem has been proposed (see Japanese Patent Application No. 2000-178327 filed by the assignee). In this apparatus, outputs from several (n) photoelectric conversion devices arranged consecutively in a lengthwise direction (the main scan direction) of a line sensor are added to comprise one pixel in a final image (this method is called pixel density conversion), instead of addition in the vertical scan direction. Therefore, each of the photoelectric conversion devices detects data whose amount is 1
th of the amount of data for one pixel. In this manner, each of the photoelectric conversion devices can avoid reaching a saturation charge. By using such an apparatus, data can be read accurately in a range having high radiation energy stored on the sheet without using a large memory space, and a high-quality image can be obtained.
However, the length required for a line sensor used in the above radiation image information reading apparatus is approximately 35-43 cm, which is equivalent to the length of the stimulable phosphor sheet. However, due to a limitation in production, the length of the line sensor is several tens to 100 mm. Therefore, a plurality of line sensors are arranged in the direction of main scan to carry out reading. Since each of the line sensors are packaged, insensitive areas where the light is not received appear at joints of neighboring line sensors. Light emitted from an area in the sheet where the excitation light is irradiated is not detected in areas corresponding to the insensitive areas, and an artifact (false image) is created.
Therefore, a radiation image information reading apparatus for solving the above problem has been proposed (Japanese Patent Application No. 2000-217516 filed by the assignee). In this apparatus, a plurality of line sensors are arranged in the main scan direction and in the vertical scan direction, and the light emitted from the sheet is received by the photoelectric conversion devices of at least one of the line sensors. In this manner, the light can be received thoroughly.
Although an initial image comprising data each having a pixel size smaller than a pixel size of a final image is obtained by using the above apparatus, processing for converting the data is also necessary. In the processing, outputs from several lines of the line sensors in the vertical scan direction are converted into data for one line in the vertical scan direction, and pixel density conversion processing in accordance with the size of the final image is also carried out. When the processing for conversion into the data for one line is carried out on the outputs from the line sensors after the pixel density conversion processing is carried out thereon for each line in the vertical scan direction, the final image tends to become uneven. Therefore, a high quality final image cannot be obtained.
SUMMARY OF THE INVENTION
The present invention has been conceived based on consideration of the above problems. An object of the present invention is therefore to provide an apparatus enabling generation of a high quality image by preventing the image from becoming uneven. The apparatus has a plurality of line sensors arranged in a main scan direction and a vertical scan direction. The apparatus obtains an initial image comprising data having a pixel size smaller than a pixel size of a final image, and obtains the final image having the larger pixel size by processing the initial image data.
A radiation image information reading apparatus of the present invention comprises:
a linear light source for linea
Fuji Photo Film Co. , Ltd.
Hannaher Constantine
Moran Timothy J.
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