X-ray or gamma ray systems or devices – Specific application – Computerized tomography
Reexamination Certificate
1999-12-30
2001-11-27
Bruce, David V. (Department: 2882)
X-ray or gamma ray systems or devices
Specific application
Computerized tomography
C378S901000
Reexamination Certificate
active
06324247
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to computed tomography (CT) imaging methods and apparatus, and more particularly to methods and apparatus for reconstructing images of objects from partial scans.
In at least one known computed tomography (CT) imaging system configuration, an x-ray source projects a fan-shaped beam which is collimated to lie within an X-Y plane of a Cartesian coordinate system and generally referred to as the “imaging plane”. The x-ray beam passes through the object being imaged, such as a patient. The beam, after being attenuated by the object, impinges upon an array of radiation detectors. The intensity of the attenuated beam radiation received at the detector array is dependent upon the attenuation of the x-ray beam by the object. Each detector element of the array produces a separate electrical signal that is a measurement of the beam attenuation at the detector location. The attenuation measurements from all the detectors are acquired separately to produce a transmission profile.
In known third generation CT systems, the x-ray source and the detector array are rotated with a gantry within the imaging plane and around the object to be imaged so that the angle at which the x-ray beam intersects the object constantly changes. A group of x-ray attenuation measurements, i.e., projection data, from the detector array at one gantry angle is referred to as a “view”. A “scan” of the object comprises a set of views made at different gantry angles, or view angles, during one revolution of the x-ray source and detector. In an axial scan, the projection data is processed to construct an image that corresponds to a two dimensional slice taken through the object. One method for reconstructing an image from a set of projection data is referred to in the art as the filtered back projection technique. This process converts the attenuation measurements from a scan into integers called “CT numbers” or “Hounsfield units”, which are used to control the brightness of a corresponding pixel on a cathode ray tube display.
Ideally, in cardiac CT reconstruction, scanner speed would be matched to a heart rate of a patient so that as many contiguous (or slightly overlapped) sectors would be acquired as there are measuring rows in the imaging system. For a four-slice system, it is desirable to subdivide a range of source angles into four sectors that, when combined together, allow image reconstruction from data essentially acquired at the same cardiac phase. Although a minimum source angle span of 180+fan-angle (&pgr;+2&Ggr;) is sought for reasons of adequate temporal resolution, it is not always possible to achieve this minimum due to the limited number of scanner speeds and wide range of patient heart rates. It would therefore be desirable to provide means and apparatus to provide image quality optimization for a given time resolution with full utilization of patient dose.
Due to the continuous range of patient cardiac motion, and the fixed number of scanner rotation speeds, cardiac sector reconstruction, in practice, leads to a usable data set that encompass more views than a minimum number required for half-scan reconstruction. Patient dose and image noise considerations indicate that it would be desirable to provide means and apparatus for a partial scan reconstruction in which any helical pitch faster than a high-quality (HQ) mode could be directly reconstructed.
BRIEF SUMMARY OF THE INVENTION
There is therefore provided, in one embodiment, a method for reconstructing an image from a set of projection data acquired in a computed tomographic (CT) scan of an object. The method includes the steps of: selecting a pitch in a range between a zero pitch and a high-speed (HS) pitch; helically scanning the object with a CT imaging system having a multislice detector and a moving radiation source, at the selected pitch, to acquire projection data; helically interpolating the acquired projection data; to generate or synthesize projections in a plane of reconstruction for a source angle &bgr; spanning a partial scan angle; applying a partial scan weight W
PS
written as:
W
PS
(
β
,
γ
)
=
β
-
π
2
+
Γ
2
(
Γ
-
γ
)
β
inf
=
π
2
-
Γ
≤
β
≤
β
-
=
π
2
+
Γ
-
2
γ
W
PS
(
β
,
γ
)
=
1.0
β
-
≤
β
≤
β
+
=
3
π
2
-
Γ
-
2
γ
W
PS
(
β
,
γ
)
=
3
π
2
+
Γ
-
β
2
(
Γ
+
γ
)
β
+
≤
β
≤
β
sup
=
3
π
2
+
Γ
(
1
)
to the generated or synthesized projections in a plane of reconstruction, where &ggr; is a fan angle, &bgr; a source angle, and &Ggr; a maximum fan angle; and
filtering and backprojecting the weighted projections.
The above described embodiment permits full utilization of patient dose in a scan, such as a cardiac scan with different pitches, while optimizing image quality for a given time resolution. Reconstruction can be accomplished from any set of projection data larger or equal to a minimum required for half-scan reconstruction, up to a full rotation. In addition, partial scan weighting enables any helical pitch faster than HQ mode to be directly reconstructed, thus allowing continuous pitch selection in a given interval (which may be geometry dependent).
REFERENCES:
patent: 5606585 (1997-02-01), Hu
patent: 6118841 (2000-09-01), Lai
“Optimal short scan convolution reconstruction for fanbeam CT”, Dennis L. Parker, Med. Phys. 9(2), Mar./Apr. 1982.
“Optimization of short scan convolution reconstruction in fan beam CT, ” Dennis L. Parker, IEEE 1982.
“A general approach to the reconstruction of x-ray helical computed tomography,” Jiang Hsieh, Med. Phys. 23(2), Feb. 1996.
“New classes of helical weighting algorithms with applications to fast CT reconstruction,” Guy Besson, Med. Phys. 25(8), Aug. 1998.
“An Optimized Reconstruction Algorithm for Temporal Resolution Improvement in CT Fluoroscopy,” Jiang Hsieh, 1998.
Armstrong Teasdale LLP
Bruce David V.
Cabou Christian G.
GE Medical Systems Global Technology Company LLC
LandOfFree
Partial scan weighting for multislice CT imaging with... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Partial scan weighting for multislice CT imaging with..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Partial scan weighting for multislice CT imaging with... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2601284