X-ray or gamma ray systems or devices – Source support – Including object support or positioning
Reexamination Certificate
2003-03-27
2004-12-28
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Source support
Including object support or positioning
C378S197000
Reexamination Certificate
active
06834994
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2002-100757, filed on Apr. 3, 2002; the entire contents of which are incorporated herein by reference.
TECHNICAL FIELD
The present invention relates to an X-ray imaging apparatus for collecting a subtraction image by photographing a mask image and a contrast image while an arm for oppositely supporting an X-ray tube and an X-ray detector with a subject between is reciprocated and rotated over the range of a predetermined angle around the subject.
BACKGROUND OF THE INVENTION
A DSA (Digital Subtraction Angiography) image is collected when a blood vessel system, the blood vessels of internal organs, etc. are diagnosed. In a procedure for collecting this DSA image, the mask image is first photographed and is once stored to a memory before a contrast medium is injected. Next, the contrast medium is injected into the subject, and the contrast image is photographed and is also stored to the memory. Then, the mask image and the contrast image in the same position of the subject are read from the memory and both the images are subtraction-processed. Thus, the background such as bones, etc. is removed so that the DSA image left with respect to only a blood vessel image injecting the contrast medium thereinto is obtained.
The digital subtraction rotational angiography is known as a technique for obtaining a solid DSA image of the region of interest as well as the DSA image of a planar shape. In this technique, for example, the X-ray tube and the X-ray detector are oppositely supported at both ends of the arm formed in an arc shape or a C-shape, and an X-ray image is continuously photographed by rotating the arm around the subject rested between this X-ray tube and the X-ray detector. In such rotation photographing, the mask image before the injection of the contrast medium, and the contrast image after the injection of the contrast medium are photographed at the same angle, and a contrast blood vessel, etc. are displayed by subtraction-processing both the images. Thus, an image suitable for the diagnosis can be provided by easily grasping a solid shape.
The schematic construction of a conventional X-ray imaging apparatus for performing such digital subtraction rotational angiography is shown by a systematic view in FIG.
1
.
As shown in
FIG. 1
, the conventional X-ray imaging apparatus has an X-ray tube
1
as an X-ray generator for irradiating an X-ray, an X-ray detector
2
for detecting this X-ray, an arm
3
for oppositely supporting the X-ray tube
1
and the X-ray detector
2
and formed in e.g., a C-shape, an arm driving unit
4
for holding the arm
3
and rotating this arm
3
with its holding axis as a center, and an angle detector
5
for detecting the rotation angle of the arm
3
. Further, the conventional X-ray imaging apparatus has an A/D converter
6
for converting an image signal output from the X-ray detector
2
to a digital signal. The apparatus further includes an image memory
7
for recording the image signal converted to the digital signal through the A/D converter
6
and a subtraction module
8
for subtraction-processing plural image signals read from the image memory
7
. The apparatus also has a D/A converter
9
for converting the image signal obtained by the subtraction processing in the subtraction module
8
to an analog signal, a display unit
10
for displaying an output of the D/A converter
9
, a main controller
11
, and an input device
12
. The main controller
11
has an central processing unit (CPU) and a memory for controlling the irradiation of the X-ray from the X-ray tube
1
, rotation control of the arm
3
using the arm driving unit
4
, fetch of the image signal to the image memory
7
and reading of this image signal, subtraction processing of the image signal in the subtraction module
8
, etc. The input device
12
has a keyboard, a mouse, a track ball, etc. for suitably inputting a set value, etc. to the main controller
11
by an operator. Further, the conventional X-ray imaging apparatus has a bed
13
for locating the subject placed on a tabletop between the X-ray tube
1
and the X-ray detector
2
.
The X-ray detector
2
generally uses a type in which the X-ray image is converted to a visible light image by an image intensifier (hereinafter briefly called I.I.) and this visible light image is photographed by a television camera through an optical system for controlling the transmitting amount of the visible light image formed on the output fluorescent screen of the I.I. However, the X-ray detector
2
may be also constructed by a flat panel detector (hereinafter briefly called FPD) recently practically used and formed by a semiconductor array in which a switching element and a capacitor formed on e.g., a glass substrate are covered with a photoelectrically conductive film, etc. for converting the X-ray to an electric charge, etc. Since the output of this FPD is a digital signal, no A/D converter
6
is required when the FPD is used.
The procedure for executing the digital subtraction rotational angiography by such an X-ray imaging apparatus is as follows.
First, while the arm
3
is rotated over the angle range registered in advance around the subject lying on the bed
13
by giving the instructions of a photographing start from an operator through the input device
12
, the X-ray is irradiated from the X-ray tube
1
and an X-ray photograph is taken. Thus, the image detected by the X-ray detector
2
is stored to the image memory
7
. At this time, the above image is collected in the same angle range of the arm
3
before and after the contrast medium is injected. As a result, the mask image and the contrast image are obtained every angular position.
Next, in the subtraction module
8
, the contrast image and the mask image collected at the same angle as this contrast image are subtraction-processed. This processing is continuously performed at each angle, and its result is displayed in the display unit
10
so that the regeneration of a rotation DSA image is realized.
An image collecting pattern is divided into four kinds of typical patterns as shown in
FIG. 2
by the combination of rotating directions of the arm
3
at the collecting time of the mask image and the contrast image.
Namely, FIG.
2
(A) shows a pattern in which the mask image is collected by a mask sequence from a rotation start position of the arm
3
to a rotation end position, and the arm
3
is subsequently returned from the rotation end position to the rotation start position and the contrast image is collected by a contrast sequence during this return. This pattern is called an MC mode.
FIG.
2
(B) shows a pattern in which the mask image is collected by the mask sequence from the rotation start position of the arm
3
to the rotation end position, and a return operation for returning the arm
3
from the rotation end position to the rotation start position is then performed, and no X-ray is irradiated (no photographing operation is performed) during this return operation, and the arm
3
is subsequently again returned from the rotation start position, and the contrast image is collected by the contrast sequence while the arm
3
reaches the rotation end position from the rotation start position. This pattern is called an MRC mode.
In such MC and MRC modes, the X-ray is irradiated every predetermined angle in the predetermined rotation range of the arm
3
, and the mask image and the contrast image are collected. The rotation DSA image is obtained by subtraction-processing both the mask and contrast images respectively photographed in the same angle position.
In contrast to this, similar to the MC mode, FIG.
2
(C) shows a pattern in which the mask image is collected by the mask sequence from the rotation start position of the arm
3
to the rotation end position, and the contrast image is subsequently collected by the contrast sequence (a first contrast sequence) during the return of the arm
3
from the
Ozawa Masahiro
Shiraishi Kunio
Church Craig E.
Yun Jurie
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