Radiation image read-out apparatus

Details Radiation image read-out apparatus Radiation image read-out apparatus

2001-04-03

2003-01-14

Hannaher, Constantine (Department: 2873)

Radiant energy

Source with recording detector

Using a stimulable phosphor

C250S585000

Reexamination Certificate

active

06507040

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a radiation image read-out apparatus which reads out a radiation image stored on a stimulable phosphor sheet by the use of a line sensor.
2. Description of the Related Art
When certain kinds of phosphor are exposed to a radiation, 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. There has been known a radiation image read-out apparatus in which a stimulating light beam such as a laser beam is caused to scan a stimulable phosphor sheet (a sheet provided with a layer of the stimulable phosphor) which has been exposed to a radiation passing through an object such as a human body to have a radiation image of the object stored on the stimulable phosphor sheet, the stimulated emission emitted from the stimulable phosphor sheet pixel by pixel is photoelectrically detected, thereby obtaining an image signal (a radiation image signal), and then the stimulable phosphor sheet is exposed to erasing light after the image signal is obtained from the stimulable phosphor sheet so that the residual energy of the radiation is fully released from the stimulable phosphor sheet. See, for instance, Japanese Unexamined Patent Publication Nos. 55(1980)-12429, 55(1980)-116340 and 56(1981)-104645.
The radiation image signal thus obtained is subjected to image processing such as gradation processing and/or frequency processing and a radiation image of the object is reproduced as a visible image on the basis of the processed radiation image signal on a recording medium such as a photographic film or a display such as a CRT. When the stimulable phosphor sheet is exposed to erasing light, the residual energy of the radiation is fully released from the stimulable phosphor sheet and the stimulable phosphor sheet comes to be able to store a radiation image again, whereby the stimulable phosphor sheet can be repeatedly used.
In the radiation image read-out apparatus, a line light source which projects a line beam onto the stimulable phosphor sheet is used as a stimulating light source and a line sensor having a linear array of photoelectric convertor elements is used as a means for photoelectrically reading out the stimulated emission. The line beam is moved relative to the stimulable phosphor sheet and the line sensor in the direction perpendicular to the longitudinal direction of the line beam by a scanning means. The longitudinal direction of the line beam is referred to as “the main scanning direction” and the direction perpendicular to the longitudinal direction of the line beam is referred to as “the sub-scanning direction”. By the use of a line beam and a line sensor, the reading time is shortened, the overall size of the apparatus can be reduced and the cost can be reduced. See, for instance, Japanese Unexamined Patent Publication Nos. 60(1985)-111568, 60(1985)-236354, and 1(1989)-101540.
In the case of a transparent stimulable phosphor sheet
50
, a stimulable phosphor layer
50
a
is supported by a support sheet
50
b
transparent to stimulated emission M and the line beam L is projected onto the stimulable layer side of the stimulable phosphor sheet
50
while the line sensor
21
is disposed on the support sheet side of the same to detect the stimulated emission M passing through the support sheet
50
b
as shown in FIG.
21
. In such a transparent stimulable phosphor sheet
50
, as well as in a reflective stimulable phosphor sheet where the line beam and the line sensor are disposed on the same side of the stimulable phosphor sheet, there is a problem that since the stimulating light L is scattered inside the sheet
50
and stimulating emission emitted from the phosphor layer
50
a
upon exposure to the stimulating light L is also scattered inside the sheet
50
, the width d
M
of the stimulated emission M passing through the support sheet
50
b
becomes larger than the width d
L
of the line beam L.
As can be understood from
FIG. 21
, when the width d
P
of the line sensor
21
is smaller than the width d
M
of the stimulated emission M passing through the support sheet
50
b
, a substantial part of the stimulated emission M misses the line sensor
21
, that is, the stimulated emission accumulating efficiency of the line sensor
21
is poor, and accordingly, a high quality image cannot be obtained.
It is important to minimize the amount of stimulated emission M which misses the line sensor in order to obtain a high quality image.
In Japanese Unexamined Patent Publication No. 2000-66316, we have proposed a radiation image read-out apparatus in which stimulated emission M emitted from a part of the stimulable phosphor sheet exposed to a line stimulating beams is detected by a line sensor comprising a two-dimensional array of photoelectric convertor elements (that is, the line sensor has a plurality of photoelectric convertor elements in both the main scanning direction and the sub-scanning direction) in which the sum of the widths of the photoelectric convertor elements in the sub-scanning direction is substantially equivalent to the width d
M
of the stimulated emission M passing through the support sheet
50
b
as measured on the plane of the light receiving face of the line sensor, and the output of each photoelectric convertor element for each scanning position is processed with respect to the portion of the stimulable phosphor sheet, thereby increasing the stimulated emission accumulating efficiency.
As shown in
FIG. 22
, the intensity of stimulated emission M is the most high at the portion corresponding to the width d
L
of the stimulating light beam and lowers outward. When a plurality of photoelectric convertor elements are arranged in the sub-scanning direction so that the sum of the widths of the photoelectric convertor elements in the sub-scanning direction is substantially equivalent to the width d
M
of the stimulated emission M passing through the support sheet as measured on the plane of the light receiving face of the line sensor, substantially the whole stimulated emission M can be accumulated. However, as light becomes weaker, noise becomes relatively stronger, and accordingly, noise becomes stronger relatively to the accumulated stimulated emission. From the viewpoint of cost, it is not preferred to arrange an excessive number of photoelectric convertor elements in the direction of width of the stimulated emission M.
In our Japanese Patent Application No. 2000-217516, there is disclosed a radiation image read-out apparatus using a detecting system comprising a plurality of line sensors arranged in the sub-scanning direction. In the patent application, the width of the detecting system is not mentioned to. When the width of the detecting system is substantially equivalent to the width d
M
of the stimulated emission M passing through the support sheet
50
b
as measured on the plane of the light receiving face of the line sensor, the same problem as in the radiation image read-out apparatus disclosed in Japanese Unexamined Patent Publication No. 2000-66316 arises.
SUMMARY OF THE INVENTION
In view of the foregoing observations and description, the primary object of the present invention is to provide a radiation image read-out apparatus in which the stimulated emission accumulating efficiency is improved and a high quality image is obtained without increasing noise and without substantially adding to the cost.
In accordance with the present invention, there is provided a radiation image read-out apparatus comprising a line stimulating light beam source which projects a line stimulating beam extending in a main scanning direction onto a stimulable phosphor she

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