Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2001-02-26
2004-11-16
Hannaher, Constantine (Department: 2878)
Radiant energy
Source with recording detector
Using a stimulable phosphor
Reexamination Certificate
active
06818913
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of and apparatus for reading image information by the use of a stimulable phosphor sheet, and a solid-state image detector used therefor.
2. Description of the Related Art
It has been well known in the art to read out image information using a stimulable phosphor sheet. The stimulable phosphor stores part of radiation energy when exposed to radiation, and exhibits photostimulated luminescence (PSL) according to the stored energy when exposed to stimulating light, such as visible light, etc. The radiation image information of a subject, such as a human body, etc., is temporarily recorded on a stimulable phosphor sheet. The stimulable phosphor sheet is scanned with a stimulating light beam such as a laser beam, and is caused to emit photostimulated luminescence light. The photostimulated luminescence light is photoelectrically detected and converted to an image signal carrying the radiation image information. As the image information reading apparatus, a wide variety of apparatus varying in manner of scanning and in the form of the photoelectric conversion means have been proposed.
For example, Japanese Unexamined Patent Publication Nos. 55(1980)-12492, 56(1981)-11395, etc. (hereinafter referred to as Reference 1), disclose an image reading method and apparatus, which is equipped with a stimulating light source for emitting a light spot, such as a laser beam, etc., as stimulating light; a photomultiplier (zero-dimensional photoelectric converter) with an electron doubling function of converting the photostimulated luminescence light, emitted from a sheet by irradiation of the light spot, to an electrical signal; and a stimulating-light scanning optical system for irradiating the light spot onto the sheet in a horizontal-scanning direction and, at the same time, moving the stimulating light and the photomultiplier (including an optical guide) relative to the sheet on the sheet surface in the vertical-scanning direction approximately perpendicular to the horizontal-scanning direction. In the image reading apparatus, the photostimulated luminescence light, emitted from the sheet when scanned with the light spot, is sequencially read by the photomultiplier.
The photomultiplier as a photoelectric converter has a high sensitivity to the wavelength of photostimulated luminescence light ranging from about 300 to 500 nm (blue light band) and a low sensitivity to the wavelength of stimulating light ranging from about 600 to 700 nm (red light band). The photomultiplier amplifies a micro signal resulting from feeble photostimulated luminescence light, by the external photoelectric effect so that it is not influenced by electrical noise.
The photomultiplier may have a circular or polygonal photomultiplier and may be used along with a focusing guide in the form of a dustpan, or may be employed as a long photomultiplier which has a photomultiplier having approximately the same length as the sheet width (width in the horizontal-scanning direction). In either case the photomultiplier is used as a zero-dimensional detector.
The apparatus employing the photomultiplier, however, has the following problems:
1) The photomultiplier has low shock resistance, because it is constructed of a hollow glass tube.
2) The photomultiplier is fairly difficult to be made in a thin form, as it uses a complex multistage dynode to double photons. The cost of manufacturing a long photomultiplier which has a width of 17 inches would be unduly high.
3) The quantum efficiency of the photocathode utilizing external photoelectric effect is low. The quantum efficiency with respect to photostimulated luminescence light of wavelengths 300 to 500 nm (blue light band) is normally as low as about 10 to 20%, whereas the quantum efficiency with respect to photostimulated luminescence light of wavelengths 600 to 700 nm (red light band) is relatively great and normally about 0.1 to 2%. For this reason, a special stimulating light cut filter becomes necessary to obtain a satisfactory signal-to-noise ratio (S/N) and results in an increase in the manufacturing cost.
4) Since the photomultiplier uses a complex multistage dynode, it is difficult for the photomultiplier to constitute a long one-dimensional detector (line sensor) of 17 inches in width which has a small pixel size of about 100 &mgr;m.
Japanese Unexamined Patent Publication No. 60(1985)-111568 (hereinafter referred to as Reference 2) has proposed an image reading method and apparatus to reduce the time for reading photostimulated luminescence light, make the apparatus compact in size, and reduce the cost. This apparatus is equipped with a linear light source (stimulating light source such as a fluorescent lamp, a cold cathode type fluorescent lamp, a light-emitting diode array, etc.) for irradiating stimulating light in a form of a line onto an image recording sheet having a stimulable phosphor layer; a line sensor (photoelectric converter) having a large number of solid photoelectric conversion elements arrayed along a line on the image recording sheet irradiated with linear light (stimulating light) by the linear light source, and scanning means for moving the linear light source and the line sensor relative to the sheet on the sheet surface in the vertical-scanning direction approximately perpendicular to the length-wise direction of the irradiated line. The photostimulated luminescence light, emitted from the sheet when scanned with the stimulating light, is sequencially read by the line sensor.
The Reference 2 discloses photoconductors as solid photoelectric conversion elements which constitute a line sensor used herein. Solid photoelectric conversion elements with bandgap E greater than the photon energy hc/&lgr; of stimulating light wavelength &lgr; (E>hc/&lgr;), and solid photoelectric conversion elements with bandgap E smaller than hc/&lgr; (E<hc/&lgr;), are both used. As examples of substance having E>hc/&lgr;, there are ZnS, ZnSe, CdS, TiO
2
, ZnO, etc. As examples of substances having E<hc/&lgr;, there are &agr;-SiH, CdS(Cu), ZnS(Al), CdSe, PbO, etc. Note that the Greek letter “&agr;” in “&agr;-SiH” means “amorphous.” Reference 2 also proposes use of a line sensor composed of silicon photodiodes.
The apparatus that uses a line sensor employing a plurlity of substances mentioned above, however, has problems as follows. That is, as photostimulated luminescence light is feeble, a photoconductor to be used is required to have extremely high dark resistance. However, the disclosed photoconductors are all low in dark resistance. Since reading is performed under a relatively large electric field, the dark current increases and it is fairly difficult to obtain a satisfactory S/N ratio. Particularly, when the bandgap E is small (E<hc/&lgr;), the dark current resulting from thermal excitation is large and therefore it is extremely difficult to obtain a satisfactory S/N ratio.
In addition, in order to facilitate manufacture, a substance, which can be manufactured at a low substrate temperature and become, even in a large area, uniform in characteristic, is preferred. However, the aforementioned substance must be manufactured at a high substrate temperature of 100 ° C. or greater. Because each substance is composed basically of two kinds of elements, a film, which stabilizes the composition and is uniform, even in a large area, in characteristic, is made and therefore results in an increase the in the manufacturing cost.
Japanese Unexamined Patent Publication No. 60(1985)-236354 (hereinafter referred to as Reference 3) proposes an image reading method and apparatus, which is equipped with a stimulating light source for emitting a light spot, such as a laser beam, as stimulating light; and a stimulating-light scanning optical system for irradiating a sheet with the light spot in a horizontal-scanning direction and, at the same time, moving the stimulating light and a line sensor relatively to the sheet on the surface of the sheet in the vertical-scanning direction
Imai Shinji
Yasuda Hiroaki
Fuji Photo Film Co. , Ltd.
Hannaher Constantine
LandOfFree
Method and apparatus for reading image information by use of... 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 and apparatus for reading image information by use of..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for reading image information by use of... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3330255