Method of reading a radiation image converting panel

Details Method of reading a radiation image converting panel Method of reading a radiation image converting panel

2000-09-08

2003-07-22

Hannaher, Constantine (Department: 2878)

Radiant energy

Source with recording detector

Using a stimulable phosphor

C250S585000, C250S586000

Reexamination Certificate

active

06597008

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to a method of reading a radiation image converting panel, and more particularly to a radiation image-converting panel reading method of a double focusing type that takes advantage of the photostimulated luminescence of a stimulatable fluorescent substance (BaFBr, Eu
2+
).
2. Description of the Related Art
A radiation image recording-reproducing method (radiation image converting method) employing a stimulatable fluorescent substance is known as a replacement method for radiography that employs a combination of radiographic film and a sensitizing screen. This method makes use of a radiation image converting panel that contains a stimulatable fluorescent substance (also stated as a stimulatable fluorescent substance sheet). In the method, radiation transmitted through or emitted from a subject is absorbed in the stimulatable fluorescent substance contained in the sheet. Then, an electromagnetic wave (excitation light), such as visible light, infrared radiation, etc., is irradiated to the stimulatable fluorescent substance to excite it. With the excitation, the radiation energy that has been stored in the stimulatable fluorescent substance is emitted as fluorescent light. This phenomenon is called photostimulated luminescence. The fluorescent light is photoelectrically read and converted to an electrical signal. Based on the electrical signal, the radiation image of the subject is reproduced as a visible image. After the radiation energy remaining in the stimulatable fluorescent substance has been erased, the radiation image converting panel that has finished the reading is repeatedly used by the same radiation recording-reproducing method.
The radiation image converting panel employed in the above-mentioned radiation image recording-reproducing method is normally provided on its lower surface with a supporting member and on its upper surface with a protective film. The stimulatable fluorescent layer of the radiation image converting panel is usually made up of stimulatable fluorescent particles and a bonding agent containing and supporting the fluorescent particles in a dispersed state. However, a stimulatable fluorescent layer consisting of an aggregate of a stimulatable fluorescent substance without a bonding agent formed by a deposition or sintering method, or a stimulatable fluorescent layer containing a high polymer in a gap in the above-mentioned aggregate, is also known. Radiation image converting panels employing these stimulatable fluorescent layers can all be used in the aforementioned radiation image recording-reproducing method.
Reading of radiation image information by the radiation recording-reproducing method is generally performed by irradiating excitation light to the upper surface of the radiation image converting panel, then reading out the fluorescent light emitted from the stimulatable fluorescent substance by a focusing guide provided on the side where the excitation light is irradiated, and converting the read fluorescent light to an electrical image signal (single focusing type). However, in the case where the fluorescent light emitted from the stimulatable fluorescent substance is read out as much as possible, or in the case where, for a latent image formed by radiation energy stored within the radiation image converting panel, an energy intensity change (intensity distribution) in the direction of depth of the sheet is obtained as radiation image information, a double focusing type that focuses the fluorescent light emitted from the upper and lower surfaces of the radiation image converting panel is utilized. A radiation image recording-reproducing method of this double focusing type is described, for example, in Japanese Unexamined Patent Publication No. 55(1980)-87970.
In the radiation image recording-reproducing method of the above-mentioned single focusing type or double focusing type, it is desirable that the radiation image converting panel have high sensitivity and be capable of reproducing a high-quality radiation image. Particularly, in the formation of a medical radiation image that employs X-rays, which is a representative use of the radiation image recording-reproducing method, it is desirable to obtain a radiation image having high quality (particularly, high sharpness related with high resolution), with a small exposure-dose of X-rays.
The diffusion of excitation light within the radiation image converting panel has a significant influence on the sharpness of a radiation image formed by the radiation image recording-reproducing method. This is for the following reason. The latent image of the radiation energy recorded on the radiation image converting panel is read out by moving a beam of excitation light to irradiate it to the panel surface in a time-series manner and then sequentially focusing the fluorescent light emitted from the panel surface by the irradiation of the excitation light. However, if the irradiated excitation light diffuses within the panel (particularly, in the plane direction), the excitation light will go beyond the irradiated region and excite the fluorescent particles outside the irradiated region that have radiation energy, and consequently, the radiation energy outside the irradiated region, as well as the radiation energy inside the irradiated region, will be read out as fluorescent light.
It is known that, in the radiation image converting panel employed in the radiation image recording-reproducing method of the single focusing type, excitation-light reflecting partitions for dividing the panel finely along the panel surface are provided in the stimulatable fluorescent layer of the panel to avoid diffusion of excitation light. For example, Japanese Unexamined Patent Publication No. 59(1984)-202100 discloses that a honeycomb structure consisting of cells divided by partitions is provided in a radiation image converting panel wherein a stimulatable fluorescent layer is provided on a supporting member and that each cell is filled with a stimulatable fluorescent substance. Japanese Unexamined Patent Publication No. 62(1987)-36599 discloses a radiation image converting panel wherein a large number of recesses (in which the ratio between the diameter and the depth is 1:3.5 or greater) are regularly provided on one surface of a supporting member and filled with a stimulatable fluorescent substance. Japanese Unexamined Patent Publication No. 2(1990)-129600 discloses a radiation image converting panel wherein a great number of holes formed in the direction of depth of a supporting plate are filled with a stimulatable fluorescent substance. Japanese Unexamined Patent Publication No. 2(1990)-280100 discloses a radiation image converting panel wherein a micro structure in the form of a honeycomb, formed on a supporting member, is filled with a fluorescent substance. PCT Japanese Publication No. 5(1993)-512636 discloses a method of fabricating phosphorescent pixels by the use of a metal mold.
The above-mentioned stimulatable fluorescent layer, in which a large number of recesses formed in the base or supporting member are filled with fluorescent particles, is effective in forming a radiation image with high quality (particularly high sharpness), because diffusion of excitation light is prevented by the supporting material which becomes partitions within the radiation image converting sheet. However, since the partitions occupy part of the stimulatable fluorescent layer, the problem of the fill amount of the fluorescent particles per unit volume being necessarily reduced will arise. A reduction in the amount of the fluorescent substance within the stimulatable fluorescent layer per unit volume reduces an absorption amount of X-rays and therefore gives rise to a reduction in the sensitivity of the radiation image converting panel. The sensitivity of the radiation image converting panel can be increased by increasing the thickness of the layer. An increase in the layer thickness, however, results in a reduction in the sharpness

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