U.S. patent application number 14/606377 was filed with the patent office on 2015-07-30 for correction method and apparatus for magnetic resonance diffusion weighted imaging image.
This patent application is currently assigned to SIEMENS AKTIENGESELLSCHAFT. The applicant listed for this patent is SIEMENS AKTIENGESELLSCHAFT. Invention is credited to Wei Liu, Kun Zhou.
Application Number | 20150212181 14/606377 |
Document ID | / |
Family ID | 53678830 |
Filed Date | 2015-07-30 |
United States Patent
Application |
20150212181 |
Kind Code |
A1 |
Liu; Wei ; et al. |
July 30, 2015 |
CORRECTION METHOD AND APPARATUS FOR MAGNETIC RESONANCE DIFFUSION
WEIGHTED IMAGING IMAGE
Abstract
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.
Inventors: |
Liu; Wei; (Shenzhen, CN)
; Zhou; Kun; (Shenzhen, CN) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SIEMENS AKTIENGESELLSCHAFT |
Muenchen |
|
DE |
|
|
Assignee: |
SIEMENS AKTIENGESELLSCHAFT
Muenchen
DE
|
Family ID: |
53678830 |
Appl. No.: |
14/606377 |
Filed: |
January 27, 2015 |
Current U.S.
Class: |
324/307 |
Current CPC
Class: |
G01R 33/5659 20130101;
G01R 33/56341 20130101 |
International
Class: |
G01R 33/565 20060101
G01R033/565 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 27, 2014 |
CN |
201410041042.X |
Claims
1. A correction method for a magnetic resonance diffusion weighted
imaging 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.
2. The correction method as claimed in claim 1, comprising
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; and/or calculating the receiving field
correction factor based on a pulse flip angle correction
factor.
3. The correction method as claimed in claim 2, 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.
4. 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.
5. 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.
6. The correction method as claimed in claim 5, 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 .alpha..sub.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 * .alpha. actual ) Sin .alpha. actual = S 2 , measured S
1 , measured , ##EQU00019## wherein S.sub.1,measured denotes the
image signal intensity of the first diffusion weighted imaging
image scanning, and S.sub.2,measured denotes the image signal
intensity of the second diffusion weighted imaging image
scanning.
7. The correction method as claimed in claim 6, wherein N=2.
8. The correction method as claimed in claim 7, wherein the
excitation pulse flip angle setting value of the first diffusion
weighted imaging image scanning is 60 degrees.
9. The correction method as claimed in claim 6, wherein the
diffusion sensitive factor is zero.
10. 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 .theta. 1 , nominal sin 2 ( .theta. 2 , nominal / 2 ) sin
.theta. 1 , actual sin 2 ( .theta. 2 , actual / 2 ) , ##EQU00020##
wherein C.sup.+ denotes the launch site correction factor,
.alpha..sub.1,actual denotes the excitation pulse flip angle actual
value, .theta..sub.2,actual denotes the refocusing pulse flip angle
actual value corresponding to .theta..sub.1,actual,
.theta..sub.1,nominal denotes the excitation pulse flip angle
setting value corresponding to .theta..sub.1,actual, and
.theta..sub.2,nominal denotes the refocusing pulse flip angle
actual value corresponding to .theta..sub.1,nominal.
11. The correction method as claimed in claim 10, wherein the
diffusion sensitive factor is zero.
12. A correction apparatus for a magnetic resonance diffusion
weighted imaging 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.
13. The correction apparatus as claimed in claim 12, 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.
14. The correction apparatus as claimed in claim 12, wherein: the
correction factor acquisition unit is configured 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;
and/or calculate the receiving field correction factor based on a
pulse flip angle correction factor.
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 .alpha..sub.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 * .alpha. actual ) Sin .alpha. actual = S 2 , measured S
1 , measured ; ##EQU00021## wherein S.sub.1,measured denotes the
image signal intensity of the first diffusion weighted imaging
image scanning, and S.sub.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 .theta. 1 , nominal
sin 2 ( .theta. 2 , nominal / 2 ) sin .theta. 1 , actual sin 2 (
.theta. 2 , actual / 2 ) , ##EQU00022## wherein C.sup.+ denotes the
launch site correction factor, .theta..sub.1,actual denotes the
excitation pulse flip angle actual value, .theta..sub.2,actual
denotes the refocusing pulse flip angle actual value corresponding
to .theta..sub.1,actual, .theta..sub.1,nominal denotes the
excitation pulse flip angle setting value corresponding to
.theta..sub.1,actual, and .theta..sub.2,nominal denotes the
refocusing pulse flip angle actual value corresponding to
.theta..sub.1,nominal.
21. The correction apparatus as claimed in claim 17, wherein the
diffusion sensitive factor is zero.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to the field of medical
appliances, and in particular to a correction method and apparatus
for a magnetic resonance diffusion weighted imaging image.
[0003] 2. Description of the Prior Art
[0004] Magnetic resonance diffusion weighted imaging (DWI) can
detect water molecule diffusion motion in a viable tissue. The
water molecule diffusion state (freedom and direction) in the
tissue is detected by measuring the change in signal intensity of
the tissue before and after applying a diffusion sensitive gradient
field, and the detection result can indirectly reflect the tissue
microscopic structure characteristics and changes thereof.
[0005] DWI technology can be widely used for identifying infarction
and other pathological states. However, inhomogeneous rotating
magnetic field B1 causes inhomogeneous DWI image signal intensity,
thereby decreasing image quality and easily causing misdiagnosis,
and this defect is much more obvious in the case of a strong
magnetic field. Inhomogeneity of the signal intensity of a DWI
image is largely due to two factors. One factor is inhomogeneity of
a launch site B1+, which arises from an interaction between a radio
frequency (RF) field and the human body; the other factor is
inhomogeneity of a receiving field B1-, which corresponds to the
signal intensity that is introduced by a receiving coil and
normally varies with space.
[0006] Conventionally, in order to correct inhomogeneity of the DWI
image, it is generally required to measure the intensity of the
launch site B1+, and then correct the DWI image based on the
intensity of the launch site B1+.
[0007] However, measuring the intensity of the launch site B1+ will
entail heavy workload, and therefore this correction method is
difficult to implement and has a low degree of automation.
SUMMARY OF THE INVENTION
[0008] An object of the present invention is to provide a
correction method for a magnetic resonance diffusion weighted
imaging image, which can be implemented easily.
[0009] A further object of the present invention is to provide a
correction apparatus for a magnetic resonance diffusion weighted
imaging image, which can be operated easily to achieve the
correction.
[0010] A correction method for a magnetic resonance diffusion
weighted imaging image in accordance with the invention includes
correcting a DWI image based on a launch site (radiation site,
emission 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.
[0011] The method further includes determining the launch site
correction factor based on an excitation pulse flip angle actual
value of the DWI image and a refocusing pulse flip angle actual
value corresponding thereto, and/or calculating the receiving field
correction factor based on a pulse flip angle correction
factor.
[0012] The calculating of the receiving field correction factor
based on a pulse flip angle correction factor includes calculating
a reciprocal of the pulse flip angle correction factor, and
determining the reciprocal as the receiving field correction
factor.
[0013] The method further includes calculating the excitation pulse
flip angle actual value and the refocusing pulse flip angle actual
value based on the pulse flip angle correction factor.
[0014] The method further includes calculating an excitation pulse
flip angle actual value of a first DWI scanning according to an
image signal intensity of the first and a second DWI scanning and a
preset relationship between excitation pulse flip angle setting
values of the first and second DWI scanning, and determining the
pulse flip angle correction factor according to a ratio of the
excitation pulse flip angle actual value of the first DWI scanning
to the excitation pulse flip angle setting value of the first DWI
scanning.
[0015] The preset relationship is that, for the same diffusion
sensitive factor, the excitation pulse flip angle setting value of
the second DWI scanning is N times the excitation pulse flip angle
setting value of the first DWI scanning, where N is a positive
number. The excitation pulse flip angle actual value
.alpha..sub.actual of the first DWI scanning is determined
according to a first general formula, and the first general formula
is
Sin ( N * .alpha. actual ) Sin .alpha. actual = S 2 , measured S 1
, measured ; ##EQU00001##
wherein S.sub.1,measured denotes the image signal intensity of the
first DWI scanning, and S.sub.2,measured denotes the image signal
intensity of the second DWI scanning.
[0016] The value of N is 2.
[0017] The excitation pulse flip angle setting value of the first
DWI scanning is 60 degrees.
[0018] The launch site correction factor is determined, 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 .theta. 1 , nominal sin 2 ( .theta. 2 , nominal / 2 ) sin
.theta. 1 , actual sin 2 ( .theta. 2 , actual / 2 ) ;
##EQU00002##
wherein C.sup.+ denotes the launch site correction factor,
.theta..sub.1,actual denotes the excitation pulse flip angle actual
value, .theta..sub.2,actual denotes the refocusing pulse flip angle
actual value corresponding to .theta..sub.1,actual,
.theta..sub.1,nominal denotes the excitation pulse flip angle
setting value corresponding to .theta..sub.1,actual, and
.theta..sub.2,nominal denotes the refocusing pulse flip angle
actual value corresponding to .theta..sub.1,nominal.
[0019] The diffusion sensitive factor is zero.
[0020] A correction apparatus for a magnetic resonance diffusion
weighted imaging image has a correction factor acquisition unit and
a correction unit, wherein the correction factor acquisition unit
is designed (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. The correction unit
is designed to correct a DWI image based on the launch site
correction factor and/or the receiving field correction factor.
[0021] The correction factor acquisition unit is designed to
determine the launch site correction factor based on an excitation
pulse flip angle actual value of the DWI image and a refocusing
pulse flip angle actual value corresponding thereto, and/or to
calculate the receiving field correction factor based on a pulse
flip angle correction factor.
[0022] The correction factor acquisition unit is designed to
calculate a reciprocal of the pulse flip angle correction factor,
and determining the reciprocal as the receiving field correction
factor.
[0023] The correction factor acquisition unit is designed 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.
[0024] The correction factor acquisition unit is designed to
calculate an excitation pulse flip angle actual value of a first
DWI scanning according to an image signal intensity of the first
and a second DWI scanning and a preset relationship between
excitation pulse flip angle setting values of the first and second
DWI scanning, and determining the pulse flip angle correction
factor according to a ratio of the excitation pulse flip angle
actual value of the first DWI scanning to the excitation pulse flip
angle setting value of the first DWI scanning.
[0025] The preset relationship is that, for the same diffusion
sensitive factor, the excitation pulse flip angle setting value of
the second DWI scanning is N times the excitation pulse flip angle
setting value of the first DWI scanning, wherein N is a positive
number, and the excitation pulse flip angle actual value
.alpha..sub.actual of the first DWI scanning is determined
according to a first general formula, and the first general formula
is expressed as
Sin ( N * .alpha. actual ) Sin .alpha. actual = S 2 , measured S 1
, measured ; ##EQU00003##
wherein S.sub.1,measured denotes the image signal intensity of the
first DWI scanning, and S.sub.2,measured denotes the image signal
intensity of the second DWI scanning.
[0026] The value of N is 2.
[0027] The excitation pulse flip angle setting value of the first
DWI scanning is 60 degrees.
[0028] The correction factor acquisition unit is designed 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 .theta. 1 , nominal sin 2 ( .theta. 2 , nominal / 2 ) sin
.theta. 1 , actual sin 2 ( .theta. 2 , actual / 2 ) ;
##EQU00004##
wherein C.sup.+ denotes the launch site correction factor,
.theta..sub.1,actual denotes the excitation pulse flip angle actual
value, .theta..sub.2,actual denotes the refocusing pulse flip angle
actual value corresponding to .theta..sub.1,actual,
.theta..sub.1,nominal denotes the excitation pulse flip angle
setting value corresponding to .theta..sub.1,actual, and
.theta..sub.2,nominal denotes the refocusing pulse flip angle
actual value corresponding to .theta..sub.1,nominal.
[0029] The diffusion sensitive factor is zero.
[0030] From the above, it can be seen that the correction method
for a magnetic resonance diffusion weighted imaging image includes
correcting a DWI 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. It can be seen that,
after applying the embodiments of the present invention, the DWI
sequence and the corresponding DWI image reconstruction are
improved, and the homogeneity of the DWI image can be improved
without measuring the intensity of the launch site B1.sup.+, which
significantly reduces the correction workload and which is easy to
automate.
BRIEF DESCRIPTION OF THE DRAWINGS
[0031] FIG. 1 is a flowchart of a correction method for a magnetic
resonance diffusion weighted imaging image according to an
embodiment of the present invention.
[0032] FIG. 2 is a schematic diagram of a radio frequency pulse
flip angle according to an embodiment of the present invention.
[0033] FIG. 3 is a schematic flowchart of a correction method for a
magnetic resonance diffusion weighted imaging image of an
embodiment of the present invention.
[0034] FIG. 4 is a structure diagram of a correction apparatus for
a magnetic resonance diffusion weighted imaging image of an
embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] In order to make the technical solution and advantages of
the present invention more apparent, the present invention will be
further described in detail in conjunction with the accompanying
drawings and embodiments. It should be understood that particular
embodiments described herein are merely used for illustrating the
present invention and not intended to limit the scope of protection
of the present invention.
[0036] In an embodiment of the present invention, the DWI sequence
of the corresponding DWI image reconstruction is improved, and the
homogeneity of the DWI image can be improved without measuring
intensity of the launch site B1.sub.+.
[0037] In a conventional DWI sequence, in a first scanning
(repetition 1), when a diffusion sensitive factor b=0, the
excitation pulse flip angle is set to 90 degrees, and for other
scanning with a b value, the excitation pulse flip angles are set
similarly to 90 degrees.
[0038] In a second scanning (repetition 2), when the diffusion
sensitive factor b=0, the excitation pulse flip angle is set to 90
degrees, and for other scanning with a b value, the excitation
pulse flip angles are set similarly to 90 degrees.
[0039] In the embodiment of the present invention, the conventional
DWI imaging sequence is improved. By setting a preset relationship
between the excitation pulse flip angle setting values of the first
and second DWI scanning, a launch site correction factor and/or a
receiving field correction factor for subsequent correction of DWI
images can be calculated according to the image signal intensity of
the first and second DWI scanning and the preset relationship. In
an embodiment of the present invention, a DWI image is corrected
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.
[0040] FIG. 1 is a flowchart of a correction method for a magnetic
resonance diffusion weighted imaging image according to an
embodiment of the present invention.
[0041] As shown in FIG. 1, the method includes Step 101, wherein a
pulse flip angle correction factor is acquired based on the preset
relationship between the excitation pulse flip angle setting values
of the first and second DWI scanning and the image signal intensity
of the first and second DWI scanning.
[0042] Here, the preset relationship between the excitation pulse
flip angle setting values of the first and second DWI scanning can
comprise: corresponding to a same diffusion sensitive factor, the
excitation pulse flip angle setting value of the second DWI
scanning is set to any multiple of the excitation pulse flip angle
setting value of the first DWI scanning. That is to say, only the
excitation pulse flip angle setting value of the first DWI scanning
and a multiple relationship between the excitation pulse flip angle
setting values of the first and second DWI scanning need to be
clear.
[0043] In fact, for the first and second DWI scanning, the values
of the diffusion sensitive factor b used by them can vary, as long
as the values of b used in the first and second DWI scanning are
the same. For example, for the first and second DWI scanning, in
the case of the diffusion sensitive factor b=0, a pulse flip angle
correction factor with a better correction effect can be
calculated.
[0044] Preferably, the excitation pulse flip angle setting value of
the second DWI scanning is twice the excitation pulse flip angle
setting value of the first DWI scanning. More preferably, the
excitation pulse flip angle setting value of the first DWI scanning
is set to 60 degrees, and the excitation pulse flip angle setting
value of the second DWI scanning is 120 degrees.
[0045] FIG. 2 is a schematic diagram of a radio frequency pulse
flip angle according to an embodiment of the present invention. In
FIG. 2, the diffusion mode is: three direction scanning, b=0, 1000
s/mm.sup.2.
[0046] As shown in FIG. 2, in the first scanning (Rep 1), for b=0,
the excitation pulse flip angle is set to 60 degrees, and the
refocusing pulse flip angle is set to 180 degrees. For a first
direction with b=1000, the excitation pulse flip angle is set to 90
degrees, and the refocusing pulse flip angle is set to 180 degrees.
For a second direction with b=0, the excitation pulse flip angle is
set to 90 degrees, and the refocusing pulse flip angle is set to
180 degrees. For a third direction with b=1000, the excitation
pulse flip angle is set to 90 degrees, and the refocusing pulse
flip angle is set to 180 degrees.
[0047] In the second scanning (Rep 2), for b=0, the excitation
pulse flip angle is set to 120 degrees, and the refocusing pulse
flip angle is set to 180 degrees. For a first direction with
b=1000, the excitation pulse flip angle is set to 90 degrees, and
the refocusing pulse flip angle is set to 180 degrees. For a second
direction with b=0, the excitation pulse flip angle is set to 90
degrees, and the refocusing pulse flip angle is set to 180 degrees.
For a third direction with b=1000, the excitation pulse flip angle
is set to 90 degrees, and the refocusing pulse flip angle is set to
180 degrees.
[0048] The preset relationship between the excitation pulse flip
angle setting values of the first and second DWI scanning is
described above in detail by examples. Those skilled in the art
will recognize that these examples are exemplary only, and not
intended to limit the protection scope of the embodiment of present
invention.
[0049] For a DWI image, its signal intensity S is as following:
S = M 0 sin .theta. 1 sin 2 ( .theta. 2 / 2 ) ( 1 + ( cos .theta. 2
- 1 ) - ( TR - TE / 2 ) / T 1 - cos .theta. 2 - TR / T 1 ) 1 - cos
.theta. 1 cos .theta. 2 - TR / T 1 .times. - TE / T 2 .times. - bD
; ##EQU00005##
wherein M.sub.0 is steady state magnetization intensity; TE is echo
time; TR is repetition time; T.sub.2 is transverse relaxation time;
T.sub.1 is longitudinal relaxation time; D is spreading factor;
.theta..sub.1 is excitation pulse flip angle; .theta..sub.2 is
refocusing pulse flip angle; and b is diffusion sensitive
factor.
[0050] When TR>>T1, it can be simplified as:
S=M.sub.0 sin .theta..sub.1
sin.sup.2(.theta..sub.2/2).times.e.sup.-TE/T.sup.2.times.e.sup.-bD.
[0051] Due to inhomogeneity of B1, an excitation pulse flip angle
actual value is not normally equal to the excitation pulse flip
angle setting value, and therefore an actually acquired image is
different from that calculated by theory and needs to be
corrected.
[0052] The pulse flip angle correction factor can be calculated
based on the image signal intensity of two DWI images obtained by
two scannings with the same diffusion sensitive factor and the
preset relationship between the excitation pulse flip angle setting
values of the first and second magnetic resonance diffusion
weighted imaging DWI scanning.
[0053] In an embodiment, an excitation pulse flip angle actual
value of the first DWI image scanning is calculated according to
the image signal intensity of the first and second DWI scanning and
the preset relationship between the excitation pulse flip angle
setting values of the first and second DWI scanning, and the pulse
flip angle correction factor is determined according to the
excitation pulse flip angle actual value of the first DWI scanning
and the excitation pulse flip angle setting value of the first DWI
scanning.
[0054] In an embodiment, an excitation pulse flip angle actual
value of the second DWI image scanning is calculated according to
the image signal intensity of the first and second DWI scanning and
the preset relationship between the excitation pulse flip angle
setting values of the first and second DWI scanning, and the pulse
flip angle correction factor is determined according to the
excitation pulse flip angle actual value of the second DWI scanning
and the excitation pulse flip angle setting value of the second DWI
scanning.
[0055] Preferably, the preset relationship is that, for the same
diffusion sensitive factor, the excitation pulse flip angle setting
value of the second DWI scanning is N times the excitation pulse
flip angle setting value of the first DWI scanning, wherein N is a
positive number, and at this point the excitation pulse flip angle
actual value .alpha..sub.actual of the first DWI scanning is
determined according to the following general formula, wherein:
Sin ( N * .alpha. actual ) Sin .alpha. actual = S 2 , measured S 1
, measured ; ##EQU00006##
where S.sub.1,measured denotes the image signal intensity of the
first DWI scanning, and S.sub.2,measured denotes the image signal
intensity of the second DWI scanning.
[0056] Preferably, when N is 2, .alpha..sub.actual can be
calculated easily by a transformation of triangle function. More
preferably, the excitation pulse flip angle setting value of the
first DWI scanning is 60 degrees, and the excitation pulse flip
angle setting value of the second DWI scanning is 120 degrees,
thereby acquiring a better correction result.
[0057] For example, in the first scanning (repetition 1), when an
image is scanned with b=0, the excitation pulse flip angle is set
to 60 degrees (namely .alpha..sub.nominal is 60 degrees); while for
other scannings with b, the excitation pulse flip angles are still
set to 90 degrees. The image signal intensity obtained from the
scanning is denoted by S.sub.1,measured, and the expression is:
S.sub.1,measured=M.sub.0 sin .alpha..sub.actual
sin.sup.2(.beta..sub.actual/2).times.e.sup.-TE/T.sup.2.times.e.sup.-bD;
where .alpha..sub.actual is actual excitation pulse flip angle; due
to the inhomogeneity of B1 field, and normally .alpha..sub.actual
is not equal to the set excitation pulse flip angle
.alpha..sub.nominal, the acquired actual image is different from
that acquired by theory; .beta..sub.actual is refocusing pulse flip
angle actual value.
[0058] In the second scanning (repetition 2), when an image is
scanned with b=0, the excitation pulse flip angle is set to 120
degrees (namely twice 60.degree.); while for other scannings with b
value, the excitation pulse flip angles are still set to 90
degrees. The image signal intensity obtained from the scanning is
denoted by S.sub.2,measured, and the expression is:
S.sub.2,measured=M.sub.0 sin 2.alpha..sub.actual
sin.sup.2(.beta..sub.actual/2).times.e.sup.-TE/T.sup.2.times.e.sup.-bD.
[0059] By a transformation of triangle function, the following
equation can be calculated:
.alpha. actual = arccos ( 1 2 S 2 , measured S 1 , measured ) ;
.alpha. actual .alpha. nominal ##EQU00007##
is the ratio of the actual excitation pulse flip angle to the set
excitation pulse flip angle, which can reflect the case of
inhomogeneity of B1 field, and therefore it can act as a pulse flip
angle correction factor to participate in the correction process of
a DWI image to be corrected.
[0060] In Step 102, a DWI image is corrected based on the pulse
flip angle correction factor.
[0061] In an embodiment, based on the pulse flip angle correction
factor, the excitation pulse flip angle actual value and the
refocusing pulse flip angle actual value of DWI scanning
corresponding to the DWI image to be corrected are calculated;
based on the excitation pulse flip angle actual value and the
refocusing pulse flip angle actual value calculated, a launch site
correction factor is determined, and the DWI image to be corrected
is corrected according to the launch site factor. Here, the launch
site factor can be determined based on the excitation pulse flip
angle correction factor, and then the DWI image to be corrected is
corrected according to the launch site factor, thereby improving
the DWI image which has poor imaging quality due to inhomogeneity
of the launch site.
[0062] According to the pulse flip angle correction factor
determined in step 101, the excitation pulse flip angle actual
value .theta..sub.1,actual and the refocusing pulse flip angle
actual value .theta..sub.2,actual of the DWI scanning corresponding
to the DWI image to be corrected can be calculated respectively
as:
.theta. 1 , actual = .theta. 1 , norminal .alpha. actual .alpha.
norminal ; .theta. 2 , actual = .theta. 2 , norminal .alpha. actual
.alpha. norminal , ##EQU00008##
wherein .theta..sub.1,nominal is the excitation pulse flip angle
setting value of DWI scanning corresponding to the DWI image to be
corrected; and .theta..sub.2,nominal is the refocusing pulse flip
angle value of DWI scanning corresponding to the DWI image to be
corrected.
[0063] Therefore, the launch site correction factor C.sup.+ for
correcting the inhomogeneity of the launch site B1.sup.+ is:
C + = sin .theta. 1 , norminal sin 2 ( .theta. 2 , norminal / 2 )
sin .theta. 1 , actual sin 2 ( .theta. 2 , actual / 2 ) .
##EQU00009##
[0064] Accordingly, the image to be corrected can be corrected
homogeneously to acquire a corrected image S.sub.corrected as
follows:
S.sub.corrected=S.sub.measuredC.sup.+.
[0065] Thus the inhomogeneity correction of an image to be
corrected is realized with respect to the launch site.
[0066] In an embodiment, a receiving field correction factor is
calculated based on the pulse flip angle correction factor, and the
DWI image to be corrected is corrected according to the receiving
field correction factor. Here, the receiving field correction
factor can be determined based on the pulse flip angle correction
factor, and then the DWI image to be corrected is corrected
according to the receiving field factor, thereby improving the DWI
image which has poor imaging quality due to inhomogeneity of the
receiving field.
[0067] Here, since the inhomogeneity of an image will also be
affected by the receiving field,
(.alpha..sub.norminal/.alpha..sub.actual) is used as an
inhomogeneity correction factor C.sup.- of the receiving field
B1.sup.-.
[0068] The image to be corrected can be corrected homogeneously to
acquire a corrected image S.sub.corrected as follows:
S.sub.corrected=S.sub.measuredC.sup.-.
[0069] Thus the inhomogeneity correction of an image to be
corrected is realized with respect to the receiving field.
[0070] In an embodiment, based on the pulse flip angle correction
factor, the excitation pulse flip angle actual value and the
refocusing pulse flip angle actual value of DWI scanning
corresponding to the DWI image to be corrected are calculated,
based on the excitation pulse flip angle actual value and the
refocusing pulse flip angle actual value calculated, a launch site
correction factor is determined, and based on the pulse flip angle
correction factor, a receiving field correction factor is
calculated; and the DWI image to be corrected is corrected
according to the receiving field correction factor and the launch
site factor. Here, the launch site correction factor and the
receiving field correction factor can be determined based on the
pulse flip angle correction factor, and then the DWI image to be
corrected is corrected according to both the launch site correction
factor and the receiving field factor, thereby improving the DWI
image which has poor imaging quality due to inhomogeneity of the
launch site and inhomogeneity of the receiving field.
[0071] Here, according to the pulse flip angle correction factor
determined in step 101, the excitation pulse flip angle actual
value .theta..sub.1,actual and the refocusing pulse flip angle
actual value .theta..sub.2,actual of DWI scanning corresponding to
the DWI image to be corrected can be calculated respectively
as:
.theta. 1 , actual = .theta. 1 , normina .alpha. actual .alpha.
norminal ; .theta. 2 , actual = .theta. 2 , normina .alpha. actual
.alpha. norminal , ##EQU00010##
wherein .theta..sub.1,norminal is the excitation pulse flip angle
setting value of DWI scanning corresponding to the DWI image to be
corrected; and .theta..sub.2,norminal is the refocusing pulse flip
angle value of DWI scanning corresponding to the DWI image to be
corrected.
[0072] Therefore, the correction factor C.sup.+ for correcting the
inhomogeneity of the launch site B1.sup.+ can be calculated as:
C + = sin .theta. 1 , norminal sin 2 ( .theta. 2 , norminal / 2 )
sin .theta. 1 , actual sin 2 ( .theta. 2 , actual / 2 ) .
##EQU00011##
[0073] Moreover, a reciprocal of the pulse flip angle correction
factor is calculated, and the reciprocal is determined as the
receiving field correction factor, namely employing
(.alpha..sub.norminal/.alpha..sub.actual) as the correction factor
C.sup.- of inhomogeneity of the receiving field.
[0074] Accordingly, the inhomogeneity correction of an image to be
corrected is corrected homogeneously with respect to the launch
site B1.sup.+ and the receiving field to acquire a following
corrected image S.sub.corrected:
S.sub.corrected=S.sub.measuredC.sup.+C.sup.-.
[0075] An embodiment of the present invention is described below in
more detail with an example in which, in the first scanning, for
b=0, the excitation pulse flip angle is set to 60 degrees; and in
the second scanning, for b=0, the excitation pulse flip angle is
set to 120 degrees.
[0076] FIG. 3 is a schematic flowchart of a correction method for a
magnetic resonance diffusion weighted imaging image of an
embodiment of the present invention.
[0077] As shown in FIG. 3, in Step S301, in the first scanning
(repetition 1), when an image is scanned with b=0, the excitation
pulse flip angle is set to 60 degrees; while for the other scanning
with b value, the excitation pulse flip angles are still set to 90
(in accordance with the traditional DWI sequence). The image signal
intensity obtained from the scanning is denoted by
S.sub.1,measured, and the expression is:
S.sub.1,measured=M.sub.0 sin .alpha..sub.actual
sin.sup.2(.beta..sub.actual/2).times.e.sup.-TE/T.sup.2.times.e.sup.-bD;
wherein .alpha..sub.actual is actual excitation pulse flip angle of
the first scanning; .beta..sub.actual is refocusing pulse flip
angle actual value of the first scanning.
[0078] In Step S302, in the second scanning (repetition 2), when an
image is scanned with b=0, the excitation pulse flip angle is set
to 120 degrees (twice 60 degrees); and for the other scanning with
b value, the excitation pulse flip angles are still set to 90
degrees (in accordance with the traditional DWI sequence), and the
image signal intensity obtained in the scanning is denoted by
S.sub.2,measured which is expressed as:
S.sub.2,measured=M.sub.0 sin 2.alpha..sub.actual
sin.sup.2(.beta..sub.actual/2).times.e.sup.-TE/T.sup.2.times.e.sup.-bD.
[0079] In Step S303, the pulse flip angle correction factor is
calculated according to the images of two scannings with b=0.
[0080] According to the images of two scannings with b=0, an actual
flip angle .alpha..sub.actual is calculated as follows:
.alpha. actual = arccos ( 1 2 S 2 , measured S 1 , measured ) ,
##EQU00012##
wherein .alpha..sub.norminal is the set flip angle of an excitation
pulse of the first scanning;
.alpha. actual .alpha. norminal ##EQU00013##
is the ratio of the actual flip angle to the set flip angle and can
reflect the case of inhomogeneity of the B1 field, and therefore it
can act as an pulse flip angle correction factor to participate in
the correction process of the DWI image to be corrected.
[0081] In Step S304, the image to be corrected is corrected
homogeneously by employing the pulse flip angle correction
factor.
[0082] In general, a signal formula of a DWI image to be corrected
can be expressed as:
S=M.sub.0 sin .theta..sub.1
sin.sup.2(.theta..sub.2/2).times.e.sup.-TE/T.sup.2.times.e.sup.-bD;
.theta..sub.1 and .theta..sub.2 are flip angles of the excitation
pulse and the refocusing pulse of DWI scanning corresponding to the
DWI image to be corrected respectively.
[0083] According to
.alpha. actual .alpha. norminal ##EQU00014##
calculated in the previous step, the actual angles of the
excitation pulse and refocusing pulse can be calculated
respectively:
.theta. 1 , actual = .theta. 1 , normina .alpha. actual .alpha.
norminal ; .theta. 2 , actual = .theta. 2 , normina .alpha. actual
.alpha. norminal ; ##EQU00015##
.theta..sub.1,norminal is the excitation pulse flip angle setting
value of DWI scanning corresponding to the DWI image to be
corrected; and .theta..sub.2,norminal is the refocusing pulse flip
angle setting value of DWI scanning corresponding to the DWI image
to be corrected.
[0084] Accordingly, the correction factor for correcting
inhomogeneity of the field B1 can be calculated:
C + = sin .theta. 1 , norminal sin 2 ( .theta. 2 , norminal / 2 )
sin .theta. 1 , actual sin 2 ( .theta. 2 , actual / 2 ) ; C - =
.alpha. norminal / .alpha. actual ; ##EQU00016##
[0085] The image to be corrected is corrected homogeneously with
respect to the launch site B1.sup.+ and the receiving field
B1.sup.- as following:
S.sub.corrected=S.sub.measuredC.sup.+C.sup.-.
[0086] In Step S305, the subsequent image processing steps are
executed. For example, the images acquired in two scannings are
averaged, so as to acquire a final result.
[0087] Various embodiments are described above in detail, in which
an excitation pulse flip angle actual value of the first DWI image
scanning is calculated based on the image signal intensity of the
first and second DWI scanning and the preset relationship between
the excitation pulse flip angle setting values of the first and
second DWI scanning, and the launch site correction factor and/or
the receiving field correction factor is determined according to
the excitation pulse flip angle actual value.
[0088] In practice, the excitation pulse flip angle actual value of
DWI scanning can also be determined by other any method (such as
measurement), and the pulse flip angle correction factor is
determined based on the determined ratio of the excitation pulse
flip angle actual value to the excitation pulse flip angle setting
value. For example, the excitation pulse flip angle actual value of
a certain DWI scanning can be measured, and the ratio of the
excitation pulse flip angle actual value of the DWI scanning to the
excitation pulse flip angle setting value of the DWI scanning is
used as the pulse flip angle correction factor. Or, multiple DWI
scanning can be executed, so as to measure the excitation pulse
flip angle actual value of each DWI scanning, and the ratio of the
actual excitation pulse flip angle measurement value of each DWI
scanning to the excitation pulse flip angle setting value of the
DWI scanning is calculated to obtain multiple candidate pulse flip
angle correction factors from which one candidate pulse flip angle
correction factor is then selected as the final pulse flip angle
correction factor, or the final pulse flip angle correction factor
is weighted by these candidate pulse flip angle correction factors
according to a weighted algorithm.
[0089] The embodiment of calculating the pulse flip angle
correction factor is exemplarily described above, and the person
skilled in the art may recognize that the description is exemplary
only and not intended to limit the protection scope of the present
invention.
[0090] Based on the above analysis, the embodiments of the present
invention disclose a correction apparatus for a magnetic resonance
diffusion weighted imaging image.
[0091] FIG. 4 is a block diagram of a correction apparatus for, a
magnetic resonance diffusion weighted imaging image of an
embodiment of the present invention.
[0092] As shown in FIG. 4, the correction apparatus 400 for a
magnetic resonance diffusion weighted imaging image has a
correction factor acquisition unit 401 and a correction unit
402.
[0093] The correction factor acquisition unit 401 is designed 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.
[0094] The correction unit 402 is designed to correct a DWI image
based on the launch site correction factor and/or the receiving
field correction factor.
[0095] In an embodiment, the correction factor acquisition unit 401
is designed to determine the launch site correction factor based on
an excitation pulse flip angle actual value of the DWI image and a
refocusing pulse flip angle actual value corresponding thereto;
and/or calculating the receiving field correction factor based on a
pulse flip angle correction factor.
[0096] In an embodiment, the correction factor acquisition unit 401
is designed 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.
[0097] In an embodiment, the correction factor acquisition unit 401
is designed to calculate, according to the image signal intensity
of a first and a second DWI scanning and a preset relationship
between the excitation pulse flip angle setting value of the first
and second DWI scanning, an excitation pulse flip angle actual
value of the first DWI scanning, and, according to a ratio of the
excitation pulse flip angle actual value of the first DWI scanning
to the excitation pulse flip angle setting value of the first DWI
scanning, determine the pulse flip angle correction factor.
[0098] Preferably, the preset relationship is: corresponding to the
same diffusion sensitive factor, the excitation pulse flip angle
setting value of the second DWI scanning is N times the excitation
pulse flip angle setting value of the first DWI scanning, wherein N
is a positive number, and the excitation pulse flip angle actual
value .alpha..sub.actual of the first DWI scanning is determined
according to the following general formula, wherein:
Sin ( N * .alpha. actual ) Sin .alpha. actual = S 2 , measured S 1
, measured ) ; ##EQU00017##
wherein S.sub.1,measured denotes the image signal intensity of the
first DWI scanning, and S.sub.2,measured denotes the image signal
intensity of the second DWI scanning.
[0099] Preferably, the value of N is 2. More preferably, the
excitation pulse flip angle setting value of the first DWI scanning
is 60 degrees, and the excitation pulse flip angle setting value of
the second DWI scanning is 120 degrees.
[0100] In an embodiment, the correction factor acquisition unit 401
is designed 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
the following general formula:
C + = sin .theta. 1 , nominal sin 2 ( .theta. 2 , nominal / 2 ) sin
.theta. 1 , actual sin 2 ( .theta. 2 , actual / 2 ) ,
##EQU00018##
wherein C.sup.+ denotes the launch site correction factor,
.theta..sub.1,actual denotes the excitation pulse flip angle actual
value, .theta..sub.2,actual denotes the refocusing pulse flip angle
actual value corresponding to .theta..sub.1,actual,
.theta..sub.1,nominal denotes the excitation pulse flip angle
setting value corresponding to .theta..sub.1,actual, and
.theta..sub.2,nominal denotes the refocusing pulse flip angle
actual value corresponding to .theta..sub.1,nominal.
[0101] In an embodiment, the diffusion sensitive factor is
zero.
[0102] It should be noted that not all of the steps and modules in
each of the above-mentioned flows and structural schematic diagrams
are necessary, and it is possible to ignore certain steps or
modules according to actual needs. The execution sequence of each
step is not fixed and can be adjusted as needed. The division of
various modules is merely a division in functions adopted for the
purpose of facilitating description, and in actual implementation,
one module may be respectively implemented by a plurality of
modules, and the functions of the plurality of modules may also be
implemented by the same module, and these modules may be located in
the same device and may also be located in different devices.
[0103] The hardware modules in various embodiments can be realized
either mechanically or electronically. For example, a hardware
module may comprise a specially designed permanent circuit or logic
device (e.g., a dedicated processor, such as FPGA or ASIC) for
completing a specific operation. The hardware module may also
comprise a programmable logic device or circuit (e.g., comprising a
general-purpose processor or other programmable processors) which
is configured by software temporarily for carrying out a specific
operation. It can be determined, according to the considerations of
cost and time, whether to implement the hardware module
specifically adopting the mechanical manner, or adopting a
dedicated permanent circuit, or adopting a circuit which is
temporarily configured (e.g., configured by software).
[0104] The present invention also provides a machine-readable
storage medium which stores instructions for making a machine
perform the method as described herein. Particularly, a system or a
device with a storage medium can be provided, on which storage
medium there are stored software program codes for implementing the
functions of any of the abovementioned embodiments, and a computer
(or CPU or MPU) of the system or device is enabled to read and
execute the program codes stored in the storage medium. In
addition, some or all of the actual operations can be performed by
an operating system executed on a computer with instructions based
on program codes. The program codes read from the storage medium
can also be written into a memory provided in an extension board
inserted inside the computer or into a memory provided in an
extension unit connected to the computer, subsequently the
instructions based on the program codes cause the CPU mounted on
the extension board or the extension unit to carry out part of or
all of the practical operations, thereby realizing the function of
any one of the above-mentioned embodiments.
[0105] The embodiments of the storage medium for providing program
codes include a floppy disk, a hard disk, a magnetic optical disk,
an optical disk (such as CD-ROM, CD-R, CD-RW, DVD-ROM, DVD-RAM,
DVD-RW, and DVD+RW), a magnetic tape, a non-volatility storage
card, and a ROM. Selectively, the program codes can be downloaded
from a server computer via a communication network.
[0106] In summary, the correction method for a magnetic resonance
diffusion weighted imaging image of the present invention
comprises: correcting a DWI 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. It can be seen
that, after applying the embodiments of the present invention, the
DWI sequence and the corresponding DWI image reconstruction are
improved, and the homogeneity of the DWI image can be improved
without measuring intensity of the launch site B1.sup.+, which
significantly reduces the correction workload and is easy to
automate.
[0107] Although modifications and changes may be suggested by those
skilled in the art, it is the intention of the inventors to embody
within the patent warranted hereon all changes and modifications as
reasonably and properly come within the scope of their contribution
to the art.
* * * * *