X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2000-05-09
2002-04-16
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S020000
Reexamination Certificate
active
06373916
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
This invention relates to cone beam type X-ray CT apparatus for performing CT (computerized tomography of selected sections) by irradiating an object under examination such as a patient or an article with X rays emitted in a diverging cone form. More particularly, the invention relates to a technique for accurately determining a reconstruct area in advance of CT imaging.
(2) Description of the Related Art
X-ray CT apparatus widely used in hospitals and the like include, as shown in
FIG. 1
, an X-ray tube
71
for emitting a fan-shaped X-ray beam FB, and an X-ray line detector
73
with X-ray detecting elements
72
arranged in a row or a plurality of rows along a spreading direction of the X-ray beam. The X-ray tube
71
and X-ray line detector
73
are constantly opposed to each other across a patient M, and constitute an X-ray image pickup unit
74
. In time of CT imaging, the X-ray tube
71
and X-ray line detector
73
revolve around the patient M, with the X-ray tube
71
emitting the fan-shaped X-ray beam FB, and the X-ray line detector
73
outputting transmitted X-ray detection data. A reconstruction process is performed to produce CT images based on the detection data. However, with X-ray CT apparatus shown in
FIG. 1
, since the fan-shaped X-ray beam FB has only a very small width, the X-ray image pickup unit
74
must be shifted along the body axis of patient M and revolved many times around the patient M in order to collect transmitted X-ray detection data necessary for a CT imaging covering a wide range. This inevitably consumes a long time in image pickup.
With this in view, an X-ray CT apparatus is being considered, which employs a wide conical X-ray beam instead of the fan-shaped X-ray beam FB, and a flat panel X-ray sensor (X-ray area sensor) instead of the X-ray line detector
73
, the flat panel X-ray sensor having a large detection surface with X-ray detecting elements arranged in a matrix form. While the conical X-ray beam irradiates a site of interest of an object under examination all at once, the flat panel X-ray sensor having the large detection surface detects X rays transmitted through the site of interest all at once. This cone beam type X-ray CT apparatus can acquire transmitted X-ray detection data covering a wide range, with one rotation about the patient M of the X-ray image pickup unit. This results in a substantial reduction in image pickup time.
However, compared with the fan beam type X-ray CT apparatus, the conical beam type X-ray CT apparatus has a disadvantage that it is difficult to determine a reconstruct area in advance of CT imaging.
With CT imaging, overlapping portions of all X-ray beams emitted from around the body axis of patient M provide a reconstruct area, i.e. an imaging range, for making CT images of selected sections. It is therefore necessary, before starting an image pickup operation, to determine a reconstruct area carefully and confirm that a site of interest to be imaged is included in the reconstruct area. With the conical beam type X-ray CT apparatus, however, since it is difficult to determine a reconstruct area beforehand, an inconvenience could occur after an image pickup operation that CT images acquired fail to show desired sections, with the site of interest excluded from the reconstruct area.
Further, in a conventional practice of acquiring sectional images of patient M, a so-called scanning plan is made for a particular site of interest by setting an imaging range, positions from which sectional images are to be picked up, and sectional image pickup intervals of 10 mm, for example, based on a fluoroscopic image of patient M acquired beforehand. Based on the scanning plan, a relative position between the patient M and the apparatus is determined to be suitable for an image pickup starting position, and then the apparatus is operated.
In the conventional practice, however, while the scanning plan is based on a fluoroscopic image of patient M, an actual image pickup starting position is determined with reference erence to the position of patient M at that time rather than the fluoroscopic image. Consequently, an error in the position of patient M relative to the apparatus would result in a deviation of the imaging range, making desired sectional images impossible.
Furthermore, depending on patients M, diverse sites of interest may have to be imaged. These sites include, for example, one having a large imaging range transversely of the body, such as the whole stomach or the whole abdomen, one having a small imaging range transversely of the body but a large imaging range along the body axis, such as the gullet or the vertebra, and one having small imaging ranges both transversely of the body and along the body axis, such as the liver.
To cope with the varied situations, the X-ray CT apparatus includes an aperture or the like for the X-ray source to vary the size of a reconstruct area of X rays irradiating the patient M.
Conventionally, however, a reconstruct area of X rays is determined unequivocally according to an image pickup site when making a scanning plan. Particularly where the reconstruct area is small, an error tends to occur in the relative position between the reconstruct area of X rays and the patient M in time of actual image pickup, making desired sectional images impossible to acquire.
SUMMARY OF THE INVENTION
This invention has been made having regard to the state of the art noted above, and its primary object is to provide a conical beam type X-ray CT apparatus for accurately determining a reconstruct area in advance of CT imaging.
Another object of this invention is to allow desired sectional images to be acquired properly by correctly setting, to an object under examination, an imaging range and positions of sectional images to be reconstructed, based on a fluoroscopic image picked up of the object in time of actual imaging.
To fulfill the above objects, this invention provides the following constructions:
(1) An X-ray CT apparatus for picking up sectional images of an object by irradiating the object with a conical X-ray beam from around a body axis of the object and detecting X rays transmitted through the object, the apparatus comprising:
an X-ray image pickup device including an X-ray tube for emitting the conical X-ray beam to the object placed on a top board, and a flat panel X-ray sensor with X-ray detecting elements arranged in a matrix form for detecting transmitted X rays;
a drive device for driving the X-ray image pickup device about the body axis of the object;
an image reconstruct device for reconstructing a sectional image of a designated section based on transmitted X-ray detection data outputted from the flat panel X-ray sensor of the X-ray image pickup device driven in a fluoroscopic imaging mode;
an image display device for displaying X-ray images;
a fluoroscopic imaging device for acquiring a fluoroscopic image based on the transmitted X-ray detection data outputted from the flat panel X-ray sensor of the X-ray image pickup device driven in the fluoroscopic imaging mode, and displaying the fluoroscopic image on the image display device; and
a reconstruct area superimposing device for displaying a reconstruct area for CT imaging as superimposed on the fluoroscopic image acquired by the fluoroscopic imaging device.
With the above apparatus according to the invention, a fluoroscopic imaging (simple X-ray imaging) operation is carried out first to acquire a fluoroscopic image for confirming a reconstruct area. That is, the X-ray image pickup device is set to an appropriate position for the fluoroscopic imaging mode, and the object is irradiated with a conical X-ray beam from the X-ray tube. The flat panel X-ray sensor detects a transmitted X-ray image. Based on the transmitted X-ray detection data outputted from the X-ray sensor, the fluoroscopic imaging device acquires a fluoroscopic image and displays it on the image display device. At this time, with the X-ray CT apparatus according to this invention, the reconstruct area
Inoue Yoshihiro
Morita Eiichi
Church Craig E.
Rader Fishman & Grauer
Shimadzu Corporation
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