Radiant energy – Source with recording detector – Using a stimulable phosphor
Reexamination Certificate
2000-03-31
2003-09-23
Mack, Ricky (Department: 2873)
Radiant energy
Source with recording detector
Using a stimulable phosphor
C250S587000
Reexamination Certificate
active
06624439
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an energy subtraction processing method and apparatus, wherein a subtraction process is performed on image signals representing radiation images of an object, which radiation images have been stored on stimulable phosphor sheets, and an image in which only an image pattern of a specific structure of the object, or the like, is thereby obtained.
2. Description of the Prior Art
It has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is recorded on a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet). The stimulable phosphor sheet, on which the radiation image has been stored, is then exposed to stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet, upon stimulation thereof, is photoelectrically detected and converted into an electric image signal. The image signal is then processed and used for the reproduction of the radiation image of the object as a visible image on a recording material.
Also, energy subtraction processing techniques for radiation images have heretofore been known. With the energy subtraction processing techniques, at least two stimulable phosphor sheets are superposed one upon the other with an energy separation filter, which absorbs low energy components of radiation, intervening therebetween. The stimulable phosphor sheets are then exposed simultaneously to radiation carrying image information of an object, which is composed of a plurality of structures having different radiation energy absorption characteristics. In this manner, two radiation images of the object are stored respectively on the stimulable phosphor sheets. Thereafter, a subtraction process is performed on a first image signal, which represents a first radiation image having been stored on a first stimulable phosphor sheet located on the side close to the object, and a second image signal, which represents a second radiation image having been stored on a second stimulable phosphor sheet located on the side remote from the object. Specifically, the image signal components of the first image signal and the second image signal, which image signal components represent corresponding pixels in the first and second radiation images, are subtracted from each other. An energy subtraction image signal representing an energy subtraction image, in which an image pattern of only a specific structure or part of the object is illustrated, is thereby obtained.
In the energy subtraction processing techniques described above, such characteristics are utilized that a plurality of structures of an object, e.g. a bone and a soft tissue of a human body, exhibit different levels of radiation absorptivity with respect to radiation with different energy distributions. By the utilization of such characteristics, a plurality of radiation images are formed with several kinds of radiation with different energy distributions. Thereafter, the image signals representing the plurality of the radiation images are weighted appropriately and subjected to a subtraction process in order to extract an image of a specific structure, e.g. an image of a bone or an image of a soft tissue. The energy subtraction processing techniques are proposed in, for example, U.S. Pat. Nos. 4,855,598 and 4,896,037.
However, with the energy subtraction processing techniques described above, the radiation having passed through the first stimulable phosphor sheet, which is located on the side close to aradiation source, and having then passed through the energy separation filter impinges upon the second stimulable phosphor sheet, which is located on the side remote from the radiation source. Therefore, a comparatively small amount of radiation impinges upon the second stimulable phosphor sheet. As a result, the second image signal having been detected from the second stimulable phosphor sheet has a low signal-to-noise ratio. In cases where the subtraction process is performed by utilizing the second image signal having a low signal-to-noise ratio, an energy subtraction image signal having a low signal-to-noise ratio is obtained from the subtraction process. Accordingly, the problems occur in that an energy subtraction image having good image quality cannot be obtained. The problems become worse particularly in cases where an image recording operation is to be performed with a restricted dose of radiation.
SUMMARY OF THE INVENTION
The primary object of the present invention is to provide an energy subtraction processing method for performing a subtraction process on image signals representing radiation images of an object, which radiation images have been stored on stimulable phosphor sheets, wherein problems with regard to a low signal-to-noise ratio of an image signal having been detected from a stimulable phosphor sheet, which is located on the side remote from a radiation source, are eliminated, and an energy subtraction image having good image quality is capable of being obtained.
Another object of the present invention is to provide an apparatus for carrying out the energy subtraction processing method.
The present invention provides an energy subtraction processing method, wherein at least two stimulable phosphor sheets are superposed one upon the other with an energy separation filter, which absorbs low energy components of radiation, intervening therebetween and are then exposed simultaneously to radiation carrying image information of an object, which is composed of a plurality of structures having different radiation energy absorption characteristics, radiation images of the object are thus stored respectively on the stimulable phosphor sheets, and a subtraction process is performed on a first image signal, which has been detected by reading out a first radiation image having been stored on a first stimulable phosphor sheet located on the side close to the object, and a second image signal, which has been detected by reading out a second radiation image having been stored on a second stimulable phosphor sheet located on the side remote from the object, an energy subtraction image signal being thereby obtained, the method comprising the steps of:
i) utilizing a stimulable phosphor sheet, which allows detection of two image signals from its opposite surfaces, as the second stimulable phosphor sheet,
ii) performing an addition process on a front surface side image signal, which has been detected by reading out the second radiation image from a front surface of the second stimulable phosphor sheet, and a back surface side image signal, which has been detected by reading out the second radiation image from a back surface of the second stimulable phosphor sheet, in order to obtain the second image signal, and
iii) performing the subtraction process on the first image signal and the thus obtained second image signal.
In the energy subtraction processing method in accordance with the present invention, the first stimulable phosphor sheet may be a stimulable phosphor sheet, which allows detection of an image signal from its one surface alone, and
the first image signal may be an image signal having been detected by reading out the first radiation image from the first stimulable phosphor sheet, which allows detection of an image signal from its one surface alone.
Alternatively, in the energy subtraction processing method in accordance with the present invention, the first stimulable phosphor sheet may be a stimulable phosphor sheet, which allows detection of two image signals from its opposite surfaces, and
the first image signal may be an image signal having been detected by reading out the first radiation image from the front surface of the stimulable phosphor sheet, which allows detection of two image signals from its opposite surfaces.
As a
Fuji Photo Film Co. , Ltd.
Harrington Alicia M
Mack Ricky
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