Correction method and apparatus for magnetic resonance diffusion weighted imaging image
In a correction method and apparatus for a magnetic resonance diffusion weighted imaging image, a diffusion weighted imaging image is corrected based on a launch site correction factor and/or a receiving field correction factor. The launch site correction factor is used for correcting inhomogeneity of a launch site, and the receiving field correction factor is used for correcting inhomogeneity of a receiving field. The imaging sequence of the diffusion weighted imaging image is thereby improved and the corresponding image reconstruction of the diffusion weighted imaging image, and the homogeneity of the diffusion weighted imaging image also can be improved, without measuring the intensity of the launch site, which significantly reduces the correction workload and is easy to automate.
1. A correction method for a magnetic resonance diffusion weighted imaging (DWI) image, comprising:
correcting a diffusion weighted imaging image based on a launch site correction factor and/or a receiving field correction factor,
wherein the launch site correction factor is used for correcting inhomogeneity of a launch site, and the receiving field correction factor is used for correcting inhomogeneity of a receiving field,
wherein the launch site correction factor and/or the receiving field correction factor are each calculated based upon a modification of an initial excitation pulse flip angle setting value to a modified excitation pulse flip angle setting value that are used as part of the same scanning repetition to perform DWI imaging in different scanning directions, and
wherein the modified excitation pulse flip angle setting value is used in accordance with the same scanning repetition to perform DWI imaging in the different scanning directions.
2. The correction method as claimed in claim 1 , comprising using said launch site correction factor to correct said diffusion weighted imaging image, and determining the launch site correction factor based on an excitation pulse flip angle actual value of the diffusion weighted imaging image and a refocusing pulse flip angle actual value corresponding thereto.
3. The correction method as claimed in claim 2 , comprising:
calculating the excitation pulse flip angle actual value and the refocusing pulse flip angle actual value based on the pulse flip angle correction factor.
4. The correction method as claimed in claim 2 , comprising:
calculating an excitation pulse flip angle actual value of a first diffusion weighted imaging image scanning according to an image signal intensity of the first and a second diffusion weighted imaging image scanning and a preset relationship between excitation pulse flip angle setting values of the first and second diffusion weighted imaging image scanning, and determining the pulse flip angle correction factor according to a ratio of the excitation pulse flip angle actual value of the first diffusion weighted imaging image scanning to the excitation pulse flip angle setting value of the first diffusion weighted imaging image scanning.
5. The correction method as claimed in claim 4 , wherein in that the preset relationship is that, for the same diffusion sensitive factor, the excitation pulse flip angle setting value of the second diffusion weighted imaging image scanning is N times the excitation pulse flip angle setting value of the first diffusion weighted imaging image scanning, where N is a positive number, the excitation pulse flip angle actual value α actual of the first diffusion weighted imaging image scanning is determined according to a first general formula, and the first general formula is
Sin
(
N
*
α
actual
)
Sin
α
actual
=
S
2
,
measured
S
1
,
measured
,
wherein S 1,measured denotes the image signal intensity of the first diffusion weighted imaging image scanning, and S 2,measured denotes the image signal intensity of the second diffusion weighted imaging image scanning.
6. The correction method as claimed in claim 5 , wherein N=2.
7. The correction method as claimed in claim 6 , wherein the excitation pulse flip angle setting value of the first diffusion weighted imaging image scanning is 60 degrees.
8. The correction method as claimed in claim 5 , wherein the diffusion sensitive factor is zero.
9. The correction method as claimed in claim 2 , comprising determining the launch site correction factor, based on an excitation pulse flip angle actual value and a refocusing pulse flip angle actual value corresponding thereto, according to a second general formula, wherein the second general formula is
C
+
=
sin
θ
1
,
nominal
sin
2
(
θ
2
,
nominal
/
2
)
sin
θ
1
,
actual
sin
2
(
θ
2
,
actual
/
2
)
,
wherein C + denotes the launch site correction factor, θ 1,actual denotes the excitation pulse flip angle actual value, θ 2,actual denotes the refocusing pulse flip angle actual value corresponding to θ 1,actual , θ 1,nominal denotes the excitation pulse flip angle setting value corresponding to θ 1,actual , and θ 2,nominal denotes the refocusing pulse flip angle actual value corresponding to θ 1,nominal .
10. The correction method as claimed in claim 9 , wherein the diffusion sensitive factor is zero.
11. The correction method as claimed in claim 1 comprising using said receiving field correction factor for correcting inhomogeneity of a receiving field, and calculating the receiving field correction factor based on a pulse flip angle correction factor.
12. The correction method as claimed in claim 11 , comprising calculating the receiving field correction factor based on a pulse flip angle correction factor by:
calculating a reciprocal of the pulse flip angle correction factor, and determining the reciprocal as the receiving field correction factor.
13. A correction apparatus for a magnetic resonance diffusion weighted imaging (DWI) image, comprising a correction factor acquisition unit and a correction unit, wherein:
the correction factor acquisition unit is configured to acquire a launch site correction factor and/or a receiving field correction factor, wherein the launch site correction factor is used for correcting inhomogeneity of a launch site, and the receiving field correction factor is used for correcting inhomogeneity of a receiving field; and
the correction unit is configured to correct a diffusion weighted imaging image based on the launch site correction factor and/or the receiving field correction factor,
wherein the correction factor acquisition unit is configured to calculate the launch site correction factor and/or the receiving field correction factor based upon a modification of an initial excitation pulse flip angle setting value to a modified excitation pulse flip angle setting value that are used as part of the same scanning repetition to perform DWI imaging in different scanning directions, and
wherein the modified excitation pulse flip angle setting value is used in accordance with the same scanning repetition to perform DWI imaging in the different scanning directions.
14. The correction apparatus as claimed in claim 13 , wherein:
the correction factor acquisition unit is configured to use said launch site correction factor to correct said diffusion weighted imaging image, and to determine the launch site correction factor based on an excitation pulse flip angle actual value of the diffusion weighted imaging image and a refocusing pulse flip angle actual value corresponding thereto.
15. The correction apparatus as claimed in claim 14 , wherein the correction factor acquisition unit is configured to calculate the excitation pulse flip angle actual value and the refocusing pulse flip angle actual value based on the pulse flip angle correction factor.
16. The correction apparatus as claimed in claim 14 , wherein the correction factor acquisition unit is configured to calculate an excitation pulse flip angle actual value of a first diffusion weighted imaging image scanning according to an image signal intensity of the first and a second diffusion weighted imaging image scanning and a preset relationship between excitation pulse flip angle setting values of the first and second diffusion weighted imaging image scanning, and determine the pulse flip angle correction factor according to a ratio of the excitation pulse flip angle actual value of the first diffusion weighted imaging image scanning to the excitation pulse flip angle setting value of the first diffusion weighted imaging image scanning.
17. The correction apparatus as claimed in claim 16 , wherein the preset relationship is that, for the same diffusion sensitive factor, the excitation pulse flip angle setting value of the second diffusion weighted imaging image scanning is N times the excitation pulse flip angle setting value of the first diffusion weighted imaging image scanning, where N is a positive number, the excitation pulse flip angle actual value α actual of the first diffusion weighted imaging image scanning is determined according to a first general formula, and the first general formula is
Sin
(
N
*
α
actual
)
Sin
α
actual
=
S
2
,
measured
S
1
,
measured
;
wherein S 1,measured denotes the image signal intensity of the first diffusion weighted imaging image scanning, and S 2,measured denotes the image signal intensity of the second diffusion weighted imaging image scanning.
18. The correction apparatus as claimed in claim 17 , wherein N=2.
19. The correction apparatus as claimed in claim 18 , wherein the excitation pulse flip angle setting value of the first diffusion weighted imaging image scanning is 60 degrees.
20. The correction apparatus as claimed in claim 19 , wherein the correction factor acquisition unit is configured to determine the launch site correction factor, based on an excitation pulse flip angle actual value and a refocusing pulse flip angle actual value corresponding thereto, according to a second general formula, wherein the second general formula is
C
+
=
sin
θ
1
,
nominal
sin
2
(
θ
2
,
nominal
/
2
)
sin
θ
1
,
actual
sin
2
(
θ
2
,
actual
/
2
)
,
wherein C + denotes the launch site correction factor, θ 1,actual denotes the excitation pulse flip angle actual value, θ 2,actual denotes the refocusing pulse flip angle actual value corresponding to θ 1,actual , θ 1,nominal denotes the excitation pulse flip angle setting value corresponding to θ 1,actual , and θ 2,nominal denotes the refocusing pulse flip angle actual value corresponding to θ 1,nominal .
21. The correction apparatus as claimed in claim 17 , wherein the diffusion sensitive factor is zero.
22. The correction apparatus as claimed in claim 13 wherein said correction factor acquisition unit is configured to use said receiving field correction factor to correct said diffusion weighted imaging image, and to calculate the receiving field correction factor based on a pulse flip angle correction factor.
23. The correction apparatus as claimed in claim 22 , wherein:
the correction factor acquisition unit is configured to calculate a reciprocal of the pulse flip angle correction factor, and to determine the reciprocal as the receiving field correction factor.