Automatic motion map generation in helical CT
View Patent ↗As an illustration of generating a motion map, although the cardiac CT is described for selecting an optimal phase, the disclosure is not limited to the cardiac CT. For the cardiac CT, the cardiac phase map is efficiently generated based upon helical scan data, and the optimal phase is selected within a reasonable time. At the same time, the optimal phase is accurately determined based upon complementary rays as indexes for minimal movement so as to select the projection data for minimizing artifacts in reconstructed cardiac images. The helically scanned data reflect motion within the same cardiac cycle or over the continuous cardiac cycles. The application of the complementary ray technique to the helically scanned data is accomplished by three-dimensionally determining a pair of the complementary rays in order to take into account motion within the same cardiac cycle or over the continuous cardiac cycles. The absolute sum of the differences for the top ray and or the bottom ray is determined in order to determine the amount of cardiac motion.
1. A method of determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data, comprising the steps of:
helically scanning an object using a predetermined scanner;
determining, using a selection device, an absolute sum of differences in projection data between at least one pair of a direct view and a complementary view on at least one predetermined PI boundary, the absolute sum of differences indicating motion of the object;
filtering the absolute sum of differences by a predetermined function;
shifting the filtered absolute sum of differences; and
generating a motion map based upon the shifted and filtered absolute sum of differences.
2. The method of determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 1 wherein the object is an organ including the heart.
3. The method of determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 1 wherein a pitch is over 0.3 in said helical scanning step.
4. The method of determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 1 wherein said absolute sum of differences includes SAD top based upon direct rays and complementary rays when the direct rays are current rays and the complementary rays are subsequently sampled in said helical scanning step.
5. The method of determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 4 wherein said SAD top is defined in terms of a view and a channel as follows:
SAD
top
[
view
]
=
∑
ch
abs
(
direct
top
[
ch
,
view
]
-
comp
bot
[
ch
,
view
]
)
where direct top is projection data for the direct rays on a UP PI window while comp bot is projection data for the complementary rays on a DOWN PI window.
6. The method of determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 1 wherein said absolute sum of differences includes SAD top based upon direct rays and complementary rays when the direct rays are current rays and the complementary rays are subsequently sampled in said helical scanning step.
7. The method of determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 6 wherein said SAD bottom is defined in terms of a view and a channel as follows:
SAD
bottom
[
view
]
=
∑
ch
abs
(
direct
bot
[
ch
,
view
]
-
comp
top
[
ch
,
view
]
)
where direct bot is projection data for the direct rays on a DOWN PI window while comp top is projection data for the complementary rays on a UP PI window.
8. The method of determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 1 wherein said predetermined function in said filtering step includes an averaging function, a weighting function and a Gaussian weighting function.
9. The method of determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 1 wherein a filter length is approximately one half of a number of views per revolution in said filtering step.
10. The method of determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 1 wherein an amount of shift is approximately one quarter of a number of views per revolution in said shifting step.
11. A system for determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data, comprising:
a data acquisition unit for helically scanning an object using a predetermined scanner;
a selection unit operationally connected to said data acquisition unit for determining an absolute sum of differences in projection data between at least one pair of a direct view and a complementary view on at least one predetermined PI boundary, the absolute sum of differences indicating motion of the object, said selection unit filtering the absolute sum of differences by a predetermined function and shifting the filtered absolute sum of differences; and
a reconstruction unit connected to said selection unit for generating a motion map based upon the shifted and filtered absolute sum of differences.
12. The system for determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 11 wherein the object is an organ including the heart.
13. The system for determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 11 wherein a pitch is over 0.3 in said data acquisition unit.
14. The system for determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 11 wherein said absolute sum of differences includes SAD top based upon direct rays and complementary rays when the direct rays are current rays and the complementary rays are subsequently sampled in said helical scanning step.
15. The system for determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 14 wherein said SAD top is defined in terms of a view and a channel as follows:
SAD
top
[
view
]
=
∑
ch
abs
(
direct
top
[
ch
,
view
]
-
comp
bot
[
ch
,
view
]
)
where direct top is projection data for the direct rays on a UP PI window while comp bot is projection data for the complementary rays on a DOWN PI window.
16. The system for determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 11 wherein said absolute sum of differences includes SAD top based upon direct rays and complementary rays when the direct rays are current rays and the complementary rays are subsequently sampled in said helical scanning step.
17. The system for determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 16 wherein said SAD bottom is defined in terms of a view and a channel as follows:
SAD
bottom
[
view
]
=
∑
ch
abs
(
direct
bot
[
ch
,
view
]
-
comp
top
[
ch
,
view
]
)
where direct bot is projection data for the direct rays on a DOWN PI window while comp top is projection data for the complementary rays on a UP PI window.
18. The system for determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 11 wherein said predetermined function in said filtering step includes an averaging function, a weighting function and a Gaussian weighting function.
19. The system for determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 11 wherein a filter length is approximately one half of a number of views per revolution in said selection unit.
20. The system for determining the optimal phase for reconstructing a substantially motion-artifact free image from helical scan data according to claim 11 wherein an amount of shift is approximately one quarter of a number of views per revolution in said selection unit.