X-ray or gamma ray systems or devices – Beam control – Antiscatter grid
Reexamination Certificate
2001-03-29
2004-08-24
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Beam control
Antiscatter grid
C378S154000, C378S098800
Reexamination Certificate
active
06782077
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an imaging apparatus, imaging system, imaging control method, and computer-readable storage medium which stores processing steps in executing the method, which are used for, e.g., an apparatus or system for performing radiation imaging of an object using a grid.
BACKGROUND OF THE INVENTION
Conventionally, a radiation method may involve irradiating an object with radiation such as X-rays and detecting the intensity distribution of the radiation transmitted through the object to acquire the radiation image of the object. This method is widely used in the field of industrial non-destructive inspection or medical diagnosis.
In the most popular radiation imaging method, a combination of a so-called “phosphor plate” (or “sensitized paper”) which emits fluorescent light by radiation and a silver halide film is used.
In the above radiation imaging method, first, an object is irradiated with radiation. The radiation transmitted through the object is converted into visible light by the phosphor plate to form a latent image on the silver halide film. After that, the silver halide film is chemically processed to acquire a visible image.
A thus obtained film image (radiation image) is a so-called analog picture and is used for medical diagnosis or inspection.
A computed radiography apparatus (referred to as a “CR apparatus” hereinafter) which acquires a radiation image using an imaging plate (referred to as an “IP” hereinafter) coated with a stimulable phosphor as a phosphor is also being put into practice.
When an IP primarily excited by radiation irradiation is secondarily excited by visible light such as a red laser beam, light called stimulable fluorescent light is emitted. The CR apparatus detects this light emission using a photosensor such as a photomultiplier to acquire a radiation image and outputs a visible image to a photosensitive material or CRT on the basis of the radiation image data.
Although the CR apparatus is a digital imaging apparatus, it is regarded as an indirect digital imaging apparatus because the image formation process, reading by secondary excitation, is necessary. The reason for “indirect” is that the apparatus cannot instantaneously display the radiation image, like the above-described apparatus (referred to as an “analog imaging apparatus” hereinafter) which acquires an analog radiation image such as an analog picture.
In recent years, a technique has been developed, which acquires a digital radiation image using a photoelectric conversion device in which pixels formed from small photoelectric conversion elements or switching elements are arrayed in a matrix as an image detection means for acquiring a radiation image from radiation through an object.
Examples of a radiation imaging apparatus employing the above technique, i.e., having phosphors stacked on a sensor such as a CCD or amorphous silicon two-dimensional image sensing element are disclosed in U.S. Pat. Nos. 5,418,377, 5,396,072, 5,381,014, 5,132,539, and 4,810,881.
Such a radiation imaging apparatus can instantaneously display acquired radiation image data and is therefore regarded as a direct digital imaging apparatus.
As advantages of the indirect or direct digital imaging apparatus over the analog imaging apparatus, it becomes possible to provide a filmless system, an increase in acquired information by image processing, and database construction.
An advantage of the direct digital imaging apparatus over the indirect digital imaging apparatus is instantaneity. The direct digital imaging apparatus can be effectively used on, e.g., a medical scene with urgent need because a radiation image obtained by imaging can be immediately displayed at that place.
When the radiation imaging apparatus described above is used as a medical apparatus to detect the radiation transmission density of a patient as an object to be examined, a scattering ray removing member called a “grid” is normally inserted between the patient and a radiation transmission density detector (also simply referred to as a “detector” hereinafter) to reduce the influence of scattering rays generated when radiation is transmitted through the person to be examined.
A grid is formed by alternately arranging a thin foil of a material such as lead which hardly passes radiation and that of a material such as aluminum which readily passes radiation perpendicularly to the irradiation direction of radiation.
With this structure, radiation components such as scattering rays in the patient, which are generated when the patient is irradiated with radiation and have angles with respect to the axis of irradiation, are absorbed by the lead foil in the grid before they reach the detector. For this reason, a high-contrast image can be obtained.
If the grid stands still during imaging, the radiation reaching the lead in the grid is wholly absorbed including both the scattering rays and the primary rays of radiation. Since a density difference distribution corresponding to the array in the grid is formed at the detection section, a striped radiation image is detected, resulting in inconvenience in reading at the time of image diagnosis or the like.
A radiation imaging apparatus having a mechanism for moving the grid during imaging has already been placed on the market.
However, since the above-described conventional digital radiation imaging apparatus is designed to execute discrete sampling, interference called “moire” may take place for a periodical image such as stripes of the grid (this phenomenon will be referred to as “grid stripe image formation on the object” hereinafter).
Especially when a reduced radiation image is displayed, the period of moire changes in various ways depending on the reduction magnification and adversely affects reading at the time of image diagnosis or the like.
To avoid the problem of grid stripe image formation on the object as described above, the grid stripe image formation on the object must be sufficiently reduced by more strictly managing grid movement than in the analog imaging apparatus.
More specifically, a radiation generator generally has a delay time of several ten to several hundred ms from a radiation irradiation instruction (instruction by pressing the imaging button and also referred to as an “imaging request” hereinafter) from the user to actual radiation irradiation (also referred to as “actual irradiation” hereinafter). This delay time changes between radiation tubes and between devices (radiation generators) for generating radiation by the radiation tubes.
Hence, to avoid the problem of grid stripe image formation on the object, the position and speed of the grid must be controlled in consideration of the delay time corresponding to the radiation tube and radiation generator used for radiation imaging. Neither an apparatus nor system that implements such control are conventionally available.
Additionally, in radiation imaging aiming at, e.g., image diagnosis, since the positional relationship between internal organs represented by lungs and diaphragm largely contributes to the image diagnostic performance, the imaging timing is very important.
For this reason, the user must issue an imaging request while observing the movement of the object and control the radiation imaging apparatus as soon as possible for the imaging request. However, after the imaging request, the sensor such as a two-dimensional solid-state image sensing element and the grid must be initialized. Each initialization takes several ten to several hundred ms.
Although the time delay from the imaging request to actual irradiation is preferably shortened by parallelly performing control of the radiation imaging apparatus and initialization of the sensor and grid, neither an apparatus nor system that implements such control are conventionally available.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above problems, and has as its object to provide an imaging apparatus, imaging system, imaging control method, and computer-readable storage medium which stores pro
Barber Therese
Church Craig E.
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