Method for creating images indicating material decomposition in dual energy, dual source helical computed tomography
View Patent ↗A system and method for the accurate quantitative evaluation of dual-energy computed tomography (CT) projection data that is acquired in a dual-source helical scan includes employing a dual-source z-axis helical interpolation method. The method includes transforming the two helical projection data sets, where corresponding projections of high- and low-energy data sets are shifted with respect to one another by 90 degrees or another angle, into corresponding non-helical projection data sets. A dual-source helical interpolation algorithm allows for projection space dual-energy processing by realigning the high- and low-energy datasets based on the z-axis interpolation. This algorithm may be implemented using a variety of interpolation schemes and can be extended from single slice to multi-slice data acquisitions. Subsequent to the registration of the non-helical projection data sets, projection space processing allows for accurate material quantification and virtual monochromatic images in which beam hardening artifacts have been substantially suppressed.
1. A method for producing an image with a computed tomography (CT) imaging system, the method comprising the steps of:
a) acquiring a first helical, projection data set using a first-energy x-ray source traversing a helical trajectory along a longitudinal axis of a subject;
b) acquiring a second helical, projection data set using a second-energy x-ray source traversing a helical trajectory along the longitudinal axis of the subject, wherein the first-energy x-ray source and the second-energy x-ray source deliver x-ray energy at differing energy levels;
c) transforming the first helical, projection data set into a first non-helical, projection data set;
d) transforming the second helical, projection data set into a second non-helical, projection data set;
e) registering the first non-helical, projection data set with the second non-helical, data set; and
f) reconstructing, from the registered first and second non-helical, projection data sets, at least one image indicative of a basis-material decomposition within the subject.
2. The method of claim 1 wherein the at least one image indicative of a basis-material decomposition includes bone.
3. The method of claim 1 wherein the at least one image indicative of a basis-material decomposition includes water.
4. The method of claim 1 wherein step f) includes performing a basis-material decomposition.
5. The method of claim 1 wherein the first projection data set and the second projection data set are related as:
I
k
=
∫
S
k
(
E
)
·
D
(
E
)
·
E
·
ⅇ
-
[
(
μ
ρ
)
1
(
E
)
·
L
1
+
(
μ
ρ
)
2
(
E
)
·
L
2
]
ⅆ
E
,
where S k (E) is an x-ray spectrum for the k th x-ray energy, D(E) is a detector response, L 1 =∫dl·ρ 1 (r) , and L 2 =∫dl·ρ 2 (r) , which represent a line integral of densities of two basis materials.
6. The method of claim 1 wherein the first non-helical, projection data set and the second non-helical, data set are circular fan-beam projection data sets.
7. The method of claim 1 wherein the first-energy x-ray source and the second-energy x-ray source are the same x-ray source.
8. The method of claim 1 wherein the first-energy x-ray source and the second-energy x-ray source are different x-ray sources.
9. The method of claim 1 wherein, prior to step f), projection space processing is performed for virtual monochromatic images to substantially suppress beam hardening artifacts in the at least one image.
10. A method of processing projection data acquired with a dual-source computed tomography (DSCT) imaging system, the method comprising the steps of:
a) acquiring a helical, high-energy projection data set using a high-energy x-ray source traversing a helical trajectory along a longitudinal axis of a subject;
b) acquiring a helical, low-energy projection data set using a low-energy x-ray source traversing a helical trajectory along the longitudinal axis of the subject;
c) transforming the helical high-energy projection data set into a non-helical high-energy projection data set;
d) transforming the helical low-energy projection data set into a non-helical low-energy projection data set;
e) registering the non-helical high-energy projection data set with the non-helical low-energy data set;
f) performing a basis-material decomposition on the registered projection data sets to create a decomposition data set; and
g) reconstructing, from the decomposition data set, an image indicative of a selected material within the subject.
11. The method of claim 10 wherein step f) includes reconstructing, from the decomposition data set, at least one image indicating multiple selected materials.
12. The method of claim 11 wherein the multiple selected materials include bone and water.
13. The method of claim 10 wherein the non-helical projection data sets are circular fan-beam projection data sets.
14. The method of claim 10 wherein the low-energy x-ray source and the high-energy x-ray source are different x-ray sources.
15. The method of claim 10 wherein, prior to step g) projection space processing is performed for virtual monochromatic images to substantially suppress beam hardening artifacts within the image indicative of the selected material within the subject.
16. The method of claim 10 wherein step a) includes using a first source of the DSCT imaging system and step b) includes using a first source of the DSCT imaging system and, wherein the first source and the second source are different sources.