X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
2002-05-20
2004-03-16
Church, Craig E. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S901000
Reexamination Certificate
active
06707876
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an X-ray CT apparatus and method, and more particularly to an X-ray CT apparatus and method in which an X-ray tube and an X-ray detector (multi-row detector) are opposed to each other interposing a subject, which detector comprises a multiplicity of X-ray detector elements linearly arranged in the channel arrangement direction to form a plurality of rows in the subject body axis direction, for reconstructing a CT tomographic image of the subject based on detected signals from the X-ray detector.
In the X-ray CT apparatus of this type, since projection data can be simultaneously obtained from the plurality of rows of the multi-row detector in one scan, the speed of X-ray CT imaging can be increased. However, the apparatus cannot be flexibly adapted to imaging for various medical purposes because the scan (projection) data collecting scheme (i.e., a pattern of slices of the subject) is fixed, and improvement is desired.
FIG. 1
is a configuration diagram of the main portion of a conventional X-ray CT apparatus. The apparatus is generally comprised of a scan gantry section
30
for performing an axial/helical scan and reading on the subject by an X-ray fan beam XLFB, an imaging table
20
for supporting the subject
100
and moving the subject
100
in the body axis CLb direction, and an operating console section
10
remotely located for controlling the scan gantry section
30
and imaging table
20
, and being operated by, for example, a radiologist.
In the scan gantry section
30
, reference numeral
40
designates a rotary anode type X-ray tube,
150
a collimator for limiting the irradiation width of X-rays in the body axis direction,
50
A a collimator control section for controlling the slit width &ohgr; of the collimator
150
,
70
an X-ray detector (multi-row detector) in which a multiplicity (n~1,000) of X-ray detector elements are linearly arranged in the channel CH arrangement direction to form four rows L
1
-L
4
, for example, in the body axis direction,
80
′ a data collecting section (DAS) for generating projection data g(X, &thgr;) of the subject based on channel detected signals of the X-ray detector
70
and collecting the data, and
30
A a rotation control section for performing rotation control of the X-ray image capturing system (which will be sometimes referred to simply as a gantry hereinbelow).
FIG. 1
additionally shows the x-, y- and z-coordinate axes fixed with respect to the scan gantry section
30
, where the z-axis coincides with the body axis CLb direction.
In the operating console section
10
, reference numeral
11
designates a central processing apparatus for performing main control and processing of the X-ray CT apparatus (such as scan planning, scan control, CT tomographic image reconstruction processing, etc.),
13
a display device (CRT) for displaying the scan plan, the scanned/reconstructed CT tomographic image and the like,
14
a control interface for exchanging several kinds of control signals C
1
, C
2
and monitor signals between the central processing apparatus
11
and the scan gantry section
30
and imaging table
20
, and
15
a data collection buffer for accumulating the projection data from the data collecting section
80
′.
The operation will be now outlined. The X-ray fan beam XLFB from the X-ray tube
40
passes through the subject
100
and impinges upon all the detector rows L
1
-L
4
of the X-ray detector
70
. The data collecting section
80
′ generates corresponding projection data g
1
(X, &thgr;)-g
4
(X, &thgr;) by integrating and A/D converting channel detected signal currents of the detector rows L
1
-L
4
, and stores the projection data in the data collection buffer
15
. Next, similar projection is performed with the gantry slightly rotated to a view angle &thgr;, and so forth; thus collecting and accumulating the projection data for one rotation of the gantry.
Moreover, the imaging table
20
is intermittently/continuously moved in the body axis direction of the subject
100
according to an axial/helical scan scheme, and consequently, all the projection data of a required imaged region in the subject are collected and accumulated. The central processing apparatus
11
then reconstructs a CT tomographic image of the subject
100
based on the resulting projection data simultaneously with or after the scan operation, and displays the CT tomographic image on the display device
13
.
Inset (a) shows a planar view of the conventional collimator
150
. The collimator
150
has a structure such that two parallel slit plates
150
a
and
150
b
lying perpendicular to the z-axis are pivotally attached to two links
152
a
and
152
b
by pins
154
at the four corners to form a parallelogram, and the links
152
a
and
152
b
are pivotally supported by respective pivots
153
a
and
153
b
on a centerline CL of the links
152
a
and
152
b
. In this configuration, the slit width &ohgr; in the z-axis direction can be changed symmetrically with respect to the centerline CL by swiveling the pivot
153
b
of the link
152
b
right and left by a geared motor
155
. The centerline CL of the slit width &ohgr; corresponds in position to a centerline CLd of the X-ray detector rows.
The conventional data collecting section
80
′ comprises a switch unit (SWU)
81
′ that can combine (add) the channel detected signal currents across the detector rows, and a data collecting unit (DAS
1
-DAS
4
)
82
that can generate four series of projection data g
1
(X, &thgr;)-g
4
(X, &thgr;) by integrating and A/D converting channel combined currents output from the switch unit
81
′. By combining the channel detected signal currents across the detector rows corresponding to a required slice width, the data collecting section
80
′ can reconstruct CT tomographic images symmetric with respect to the centerline CLd of the X-ray detector rows and having different slice widths, as will be described below. A conventional scan (projection) data collecting scheme for providing the different slice widths will be particularly described below.
FIG. 2
is a diagram for explaining a conventional data collecting scheme. Specifically, FIG.
2
(A) shows a case in which channel detected signal currents i
1
-i
4
of the detector rows L
1
-L
4
are individually converted into projection data S
1
-S
4
having a small slice width by DAS
1
-DAS
4
, without combining the channel detected signal currents i
1
-i
4
across the detector rows. Thus, four CT tomographic images having a small slice width can be reconstructed in one scan. This data collecting scheme is suitable for imaging of minute tissues (in the head, lesion site, etc.) of the subject.
FIG.
2
(B) shows a case in which channel detected signal currents i
1
and i
2
of the detector rows L
1
and L
2
, and i
3
and i
4
of the detector rows L
3
and L
4
are added (combined) beforehand by the SWU
81
′, and then the combined signals are converted into projection data S
1
and S
2
having a relatively large slice width by, for example, DAS
1
and DAS
3
. Thus, two CT tomographic images having a relatively large slice width can be reconstructed in one scan. This data collecting scheme is suitable for rather minutely checking for the presence of disorder in a relatively large imaged region (thorax, abdomen, etc.) of the subject.
FIG.
2
(C) shows a case in which channel detected signal currents i
1
-i
4
of all the detector rows L
1
-L
4
are added (combined) beforehand by the SWU
81
′, and then the combined signal is converted into projection data S
1
having a large slice width by, for example, DAS
1
. Thus, one CT tomographic image having a large slice width can be reconstructed in one scan. This data collecting scheme is suitable for broadly checking for the presence of disorder in a large imaging region (thorax—abdomen, etc.) of the subject. In any case, imaging by the four detector rows can be achieved during one scan, and the speed of the X-ray CT imaging can be increased.
However, since th
Armstrong Teasdale LLP
Church Craig E.
GE Medical Systems Global Technology Company LLC
Horton Esq. Carl B.
Yun Jurie
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