CT imaging methods and systems

Patent metadata

Field	Value
Publication number	US-9702832-B2
Application number	US-201414304848-A
Country	US
Kind code	B2
Filing date	Jun 13, 2014
Priority date	Jun 14, 2013
Publication date	Jul 11, 2017
Grant date	Jul 11, 2017

Abstract

Disclosed is a CT imaging method and system. The method includes: CT scanning an object with a dual-energy CT system to obtain a first complete set of projection data in a first scan mode, and to obtain a second incomplete set of projection data in a second scan mode; reconstructing a first attenuation coefficient image of the object from the first set of projection data, and extracting, from the first attenuation coefficient image, prior structure information of the object indicating edge intensity; and reconstructing a second attenuation coefficient image of the object from the second incomplete set of projection data using the extracted prior structure information as a constraint. With the method using the prior structure information of the imaged object as a constraint in reconstruction, it is possible to dramatically reduce an amount of data required for reconstruction, and achieve satisfactory effects even with ill-conditioned problems of limited-angle and inner reconstruction.

First claim

The invention claimed is:

1. A CT imaging method, comprising:
CT scanning an object with a dual-energy CT system to obtain a first complete set of projection data at a first energy level, and to obtain a second incomplete set of projection data at a second energy level different from the first energy level;
reconstructing a first image of the object from the first set of projection data, and extracting, from the first image, prior structure information of the object indicating edge intensity, wherein the extracted prior structure information describes boundaries and details having obvious difference in the first image; and
reconstructing a second image of the object from the second incomplete set of projection data using the extracted prior structure information as a constraint.

2. The method according to claim 1 , wherein
the dual-energy CT system comprises multiple rows of low-energy detectors, and high-energy detectors disposed behind part of the rows of low-energy detectors;
said obtaining a first complete set of projection data in a first scan mode comprises performing a 360-degree circular or helical CT scan on the object with rays at a first energy level, to obtain the first complete set of projection data;
said obtaining a second incomplete set of projection data in a second scan mode comprises performing a limited-angle CT scan on the object with rays at a second energy level different from the first energy level, to obtain the second incomplete set of projection data.

3. The method according to claim 1 , wherein
the dual-energy CT system comprises multiple low-energy detectors, and multiple high-energy detectors disposed behind the low-energy detectors;
said obtaining a first complete set of projection data in a first scan mode comprises performing a 360-degree circular or helical CT scan on the object with rays at a first energy level, to obtain the first complete set of projection data;
said obtaining a second incomplete set of projection data in a second scan mode comprises performing a sparse-angle sampling CT scan on the object with rays at a second energy level different from the first energy level, to obtain the second incomplete set of projection data.

4. The method according to claim 1 , wherein
the dual-energy CT system comprises at least one row of low-energy detectors, and a plurality of high-energy detectors which are uniformly provided behind part of the low-energy detectors;
said obtaining a first complete set of projection data in a first scan mode comprises performing a 360-degree circular or helical CT scan on the object with rays at a first energy level, to obtain the first complete set of projection data;
said obtaining a second incomplete set of projection data in a second scan mode comprises performing a detector undersampling CT scan on the object with rays at a second energy level different from the first energy level, to obtain the second incomplete set of projection data.

5. The method according to claim 1 , wherein
the dual-energy CT system comprises at least one row of low-energy detectors, and a plurality of high-energy detectors which are concentrated and provided behind part of the low-energy detectors;
said obtaining a first complete set of projection data in a first scan mode comprises performing a 360-degree circular or helical CT scan on the object with rays at a first energy level, to obtain the first complete set of projection data;
said obtaining a second incomplete set of projection data in a second scan mode comprises performing an inner reconstruction CT scan on the object with rays at a second energy level different from the first energy level, to obtain the second incomplete set of projection data.

6. The method according to claim 1 , wherein said extracting prior structure information of the object from the first image comprises performing edge extraction on the first image to obtain the prior structure information.

7. The method according to claim 6 , wherein said reconstructing a second image of the object from the second incomplete set of projection data comprises:
calculating the second image f according to an equation

min
⁢



G
⁢

∇
f



1

+

λ
⁢



∇
f



1

=

min
⁢



(

G
+

λ
⁢

⁢
I

)

⁢

∇
f



1

s
.
t
.

⁢



Hf
-
p



W

≤
ɛ

wherein ε is a quantity related to an overall noise level in the second set of projection data, and λ is used to balance a prior structure information constraint and a Total Variation (TV) constraint; the prior structure information constraint is dominant when λ≦1, while minimization of the TV is a dominant constraint when λ>1; the second image is denoted as f={f 1 , f 2 , . . . , f n }, the second set of projection data obtained by the CT scan is denoted as p={p 1 , p 2 , . . . , p m }, a line integral projection process is denoted as

H
⁢

{

h

i
⁢

⁢
j

}

m
×
n

,

Assignees

• Nuctech Co Ltd

Inventors

• Shen Le
• Xing Yuxiang
• Zhang Li
• Chen Zhiqiang

Classifications

• G06T12/20 Primary

  Inverse problem, i.e. transformations from projection space into object space · CPC title

• G06T12/10

  Image preprocessing, e.g. calibration, positioning of sources or scatter correction · CPC title

• G06T2211/408

  Dual energy · CPC title

• A61B6/4241

  using energy resolving detectors, e.g. photon counting · CPC title

• A61B6/03

  Computed tomography [CT] · CPC title