Patent EP0212526A2 successfully refreshed from Google Patents.
EP0212526A2
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Method for reducing image artifacts due to periodic signal variations in NMR imaging
Assignee: General Electric Co
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Filing: 1986-08-11
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Granted: —
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Expires: 2006-08-11
Abstract
Abstract A method for reducing image artifacts due to periodic motion of a subject undergoing examination by nuclear magnetic resonance (NMR) techniques includes the acquisition of scan data for imaging the object. The scan data is composed of a number of views. The acquisition of each view includes the generation of an NMR signal and the application of a magnetic gradient along at least one dimensional axis of the object. The magnetic field gradient is characterized by a parameter value (e.g., amplitude or direction) adjustable from view to view to encode spatial information into the NMR signal. The method includes the step of selecting the value of the adjustable parameter value for each view. A view order is then selected so as to attempt to obtain a predetermined relationship between the object motion and the adjustable parameter of the magnetic field gradient. The relationship is chosen to minimize artifacts in the reconstructed image. The method is applicable to various NMR imaging techniques, including Fourier Transform and multiple angle projection reconstruction.
Inventors
- 👤 Norbert Joseph Pelc
- 👤 Gary Harold Glover
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-08 14:58
CPC Classifications
G; G01; G01R; G01R33/00; G01R33/20; G01R33/44; G01R33/48; G01R33/54; G01R33/56; G01R33/565; G01R33/56509; G01R33/561; G06; G06T; G06T5/00; G06T5/80; G06T2207/00; G06T2207/10; G06T2207/10072; G06T2207/10088
Claims Analysis
Total Claims: 37
Claim 1
Independent Claim
181 words
A method for reducing artifacts in a desired image due to substantially periodic signal variations while a portion of an object is being examined using nuclear magnetic resonance techniques, which techniques include measurement of imaging data about the object portion through the implementation of a plurality of views, each of which includes irradiation of the object portion by an RF excitation pulse at the Larmor frequency to produce an NMR signal, and application of a pulsed magnetic field gradient along at least one dimensional axis of the object, said magnetic field gradient having a parameter value adjustable from view to view so as to encode spatial information into the NMR signal, said method comprising: (a) determining the period T B of the signal variations; (b) selecting a view increment time T ; (c) selecting a predetermined relationship between the signal variation and the parameter value of said magnetic field gradient; and (d) selecting a temporal order of application of said gradient parameter value so as to approximate said predetermined relationship, said order being dependent on T B and T v .
Claim 2
Independent Claim
181 words
A method for reducing artifacts in a desired image due to substantially periodic signal variations while a portion of an object is being examined using nuclear magnetic resonance techniques, which techniques include measurement of imaging data about the object portion through the implementation of a plurality of views, each of which includes irradiation of the object portion by an RF excitation pulse at the Larmor frequency to produce an NMR signal, and application of a pulsed magnetic field gradient along at least one dimensional axis of the object, said magnetic field gradient having a parameter value adjustable from view to view so as to encode spatial information into the NMR signal, said method comprising: (a) determining the period T B of the signal variations; (b) selecting a view increment time T ; (c) selecting a predetermined relationship between the signal variation and the parameter value of said magnetic field gradient; and (d) selecting a temporal order of application of said gradient parameter value so as to approximate said predetermined relationship, said order being dependent on T B and T v .
Claim 3
Dependent Claim
18 words
The method of Claim 1 wherein said signal variations are due to motion of the object being studied.
Claim 4
Dependent Claim
32 words
The method of Claim 1 wherein said pulsed magnetic field gradient comprises a phase-encoding magnetic field gradient and wherein the adjustable parameter value comprises the time integral of the gradient pulse waveform.
Claim 5
Dependent Claim
20 words
The method of Claim 3 wherein said time integral is controlled by the amplitude of said phase-encoding magnetic field gradient.
Claim 6
Dependent Claim
82 words
The method of Claim 1, 3 or 4 wherein the temporal order of said gradient parameter value applied in the course of implementing said plurality of views is selected such that when measurements acquired ir: each view are rearranged in order of monotonically increasing parameter value, the signal variations as a function of gradient parameter value are of a lower frequency than the signal variations as a function of view number, thereby to decrease displacement of the artifacts from the desired image.
Claim 7
Dependent Claim
56 words
The method of Claim 5 wherein the temporal order of said gradient parameter applied in the course of implementing said plurality of views is selected such that when the measurements acquired in each view are rearranged in order of monotonically increasing parameter value the signal variations will appear to go through no more than one cycle.
Claim 8
Dependent Claim
77 words
The method of Claim 1, 3 or 4 wherein said step of selecting the temporal order of said gradient parameter value comprises: (a) calculating for each of said plurality of views a relative phase of signal variation; (b) assigning a different rank, RAHK L (j), to each view in monotonic order of relative phase of signal variation; and (c) assigning a different value of said gradient parameter to each view in proportion to the rank assigned thereto.
Claim 9
Dependent Claim
45 words
The method of Claim 7 wherein the relative phase of signal variation, P(j), is calculated using the equation in which HOD (x,y) is the smallest positive number such that y = kx + MOD (x,y) for an interger k, and T o is any number.
Claim 10
Dependent Claim
49 words
The method of Claim 7 wherein said adjustable parameter comprises the amplitude of said phase-encoding magnetic field gradient, and wherein the amplitude, A(j), implemented in each view is calculated using the equation in which A is the maximum phase-encoding amplitude; and N is the total number of views. v
Claim 11
Dependent Claim
67 words
The method of Claim 1 wherein said step of selecting a temporal order includes (a) selecting an integer N such that N is approximately equal to T B /T v ; and (b) assigning gradient parameter values to temporally adjacent ones of said plurality of views such that the parameter value assigned to each view differs from that assigned to a temporally adjacent view by approximately N.
Claim 12
Dependent Claim
80 words
The method of Claim 1, 3 or 4 wherein the temporal order of said gradient parameter applied in the course of implementing said plurality of views is selected such that when measurements acquired in each view are rearranged in order of monotonically increasing parameter value, the signal variations as a function of gradient parameter value are of a higher frequency than the variations as a function of view number, thereby to increase displacement of the artifacts from the desired image.
Claim 13
Dependent Claim
69 words
The method of Claim 11 wherein the temporal order of said gradient parameter applied in the course of implementing said plurality of views is selected such that when the measurements acquired in each view are rearranged in order of monotonically incrasing parameter value the signal variations will appear to go through N v /2 cycles, where N is equal to the number of views comprising said plurality of views.
Claim 14
Dependent Claim
100 words
The method of Claim 1, 3 or 4 wherein said step of selecting the temporal order of said gradient parameter value comprises: (a) calculating for each of said plurality of views a relative phase of signal variation; (b) assigning a different rank, RANK L (j), to each view in monotonic order of relative phase of signal variation; and (c) assigning a different rank, RANK H (j), to each view wherein RANK H (j) is determined by: - and (d) asigning a different value of said gradient parameter to each view in proportion to the value of R H assigned thereto.
Claim 15
Dependent Claim
33 words
The method of Claim 13 wherein the phase-encoding amplitude for the j'th view, A(j), is calculated using where A is the maximum phase-encoding amplitude and N v is the total number of views.
Claim 16
Dependent Claim
94 words
The method of Claim 1, 3 or 4 wherein said step of selecting the temporal order of said gradient parameter value comprises: (a) calculating for each of said plurality of views a relative phase of signal variation; (b) assigning a different rank, RANK L (j). to each view in monotonic order of relative phase of signal variation; and (c) assigning a different rank, RANK H (j), to each view wherein RANK H (j) is determined (d) assigning a different value of said gradient parameter to each view in proportion to the rank assigned thereto.
Claim 17
Dependent Claim
32 words
The method of Claim 15 wherein the phase-encoding amplitude for the j'th view, A(j), is calculated using where A is the maximum phase-encoding amplitude and N is the total number of views.
Claim 18
Dependent Claim
67 words
The method of Claim 1 wherein said step of selecting a temporal order includes (a) selecting an integer N such that N is approximately equal to T B /T v ; and (b) assigning gradient parameter values to temporally adjacent ones of said plurality of views such that the parameter value assigned to each view differs from that assigned to a temporally adjacent view by approximately 2N.
Claim 19
Dependent Claim
29 words
The method of Claim 1 wherein said magnetic field gradient comprises a read-out magnetic field gradient and wherein the adjustable parameter value comprises the direction of said read-out gradient.
Claim 20
Dependent Claim
79 words
The method of Claim 18 wherein the temporal order of said gradient parameter value applied in the course of implementing said plurality of views is selected such that when measurements acquired in each view are rearranged in order of monotonically increasing parameter value, the signal variations as a function of gradient parameter value are of a slower frequency than the signal variations as a function of view number, thereby to decrease displacement of the artifacts from the desired image.
Claim 21
Dependent Claim
56 words
The method of Claim 19 wherein the temporal order of said gradient parameter applied in the course of implementing said plurality of views is selected such that when the measurements acquired in each view are rearranged in order of monotonically increasing parameter value the signal variations will appear to go through no more than one cycle.
Claim 22
Dependent Claim
74 words
The method of Claim 18 wherein said step of selecting the temporal order of said gradient parameter value comprises: (a) calculating for each of said plurality of views a relative phase of signal variation; (b) assigning a different rank, RAYK L (j), to each view in monotonic order of relative phase of signal variation; and (c) assigning a different value of said gradient parameter to each view in proportion to the rank assigned thereto.
Claim 23
Dependent Claim
44 words
The method of Claim 21 wherein the relative phase of signal variation, P(j), is calculated using the equation in which MOD (x,y) is the smallest positive number such that y = kx + MOD (x,y) for an interger k, and T is any number.
Claim 24
Dependent Claim
67 words
The method of Claim 18 wherein said step of selecting a temporal order includes (a) selecting an integer N such that N is approximately equal to T B /T v ; and (b) assigning gradient parameter values to temporally adjacent ones of said plurality of views such that the parameter value assigned to each view differs from that assigned to a temporally adjacent view by approximately N.
Claim 25
Independent Claim
176 words
A method for reducing artifacts in a desired image due to substantially periodic signal variations while a portion of an object is being examined using nuclear magnetic resonance techniques, which techniques include measurement of imaging data about the object portion through the implementation of a plurality of views, each of which includes irradiation of the object portion by an RF excitation pulse at the Larmor frequency to produce an NMR signal, and application of a pulsed magnetic field gradient along at least one dimensional axis of the object, said magnetic field gradient having a parameter value adjustable from view to view so as to encode spatial information into the NMR signal, said method comprising: (a) Selecting a predetermined relationship between the signal variations and the parameter value of said magnetic field gradient, such that the signal variations as a function of gradient parameter value are of a lower frequency than the variations as a function of view number; and (b) selecting a temporal order of application of said parameter so as to approximate said predetermined relationship.
Claim 26
Independent Claim
176 words
A method for reducing artifacts in a desired image due to substantially periodic signal variations while a portion of an object is being examined using nuclear magnetic resonance techniques, which techniques include measurement of imaging data about the object portion through the implementation of a plurality of views, each of which includes irradiation of the object portion by an RF excitation pulse at the Larmor frequency to produce an NMR signal, and application of a pulsed magnetic field gradient along at least one dimensional axis of the object, said magnetic field gradient having a parameter value adjustable from view to view so as to encode spatial information into the NMR signal, said method comprising: (a) Selecting a predetermined relationship between the signal variations and the parameter value of said magnetic field gradient, such that the signal variations as a function of gradient parameter value are of a lower frequency than the variations as a function of view number; and (b) selecting a temporal order of application of said parameter so as to approximate said predetermined relationship.
Claim 27
Dependent Claim
32 words
The method of Claim 24 wherein said pulsed magnetic field gradient comprises a phase-encoding magnetic field gradient and wherein the adjustable parameter value comprises the time integral of the gradient pulse waveform.
Claim 28
Dependent Claim
20 words
The method of Claim 25 wherein said time integral is controlled by the amplitude of said phase-encoding magnetic field gradient.
Claim 29
Dependent Claim
56 words
The method of Claim 24 wherein the temporal order of said gradient parameter applied in the course of implementing said plurality of views is selected such that when the measurements acquired in each view are rearranged in order of monotonically increasing parameter value the signal variations will appear to go through no more than one cycle.
Claim 30
Dependent Claim
77 words
The method of Claim 24, 25 or 26 wherein said step of selecting the temporal order of said gradient parameter value comprises: (a) calculating for each of said plurality of views a relative phase of signal variation; (b) assigning a different rank, RANK L (j), to each view in monotonic order of relative phase of signal variation; and (c) assigning a different value of said gradient parameter to each view in proportion to the rank assigned thereto.
Claim 31
Independent Claim
176 words
A method for reducing artifacts in a desired image due to substantially periodic signal variations while a portion of an object is being examined using nuclear magnetic resonance techniques, which techniques include measurement of imaging data about the object portion through the implementation of a plurality of views, each of which includes irradiation of the object portion by an RF excitation pulse at the Larmor frequency to produce an NMR signal, and application of a pulsed magnetic field gradient along at least one dimensional axis of the object, said magnetic field gradient having a parameter value adjustable from view to view so as to encode spatial information into the NMR signal, said method comprising: (a) Selecting a predetermined relationship between the signal variations and the parameter value of said magnetic field gradient, such that the signal variations as a function of gradient parameter value are of a higher frequency than the variations as a function of view number; and (b) selecting a temporal order of application of said parameter so as to approximate said predetermined relationship.
Claim 32
Independent Claim
176 words
A method for reducing artifacts in a desired image due to substantially periodic signal variations while a portion of an object is being examined using nuclear magnetic resonance techniques, which techniques include measurement of imaging data about the object portion through the implementation of a plurality of views, each of which includes irradiation of the object portion by an RF excitation pulse at the Larmor frequency to produce an NMR signal, and application of a pulsed magnetic field gradient along at least one dimensional axis of the object, said magnetic field gradient having a parameter value adjustable from view to view so as to encode spatial information into the NMR signal, said method comprising: (a) Selecting a predetermined relationship between the signal variations and the parameter value of said magnetic field gradient, such that the signal variations as a function of gradient parameter value are of a higher frequency than the variations as a function of view number; and (b) selecting a temporal order of application of said parameter so as to approximate said predetermined relationship.
Claim 33
Dependent Claim
32 words
The method of Claim 29 wherein said pulsed magnetic field gradient comprises a phase-encoding magnetic field gradient and wherein the adjustable parameter value comprises the time integral of the gradient pulse waveform.
Claim 34
Dependent Claim
20 words
The method of Claim 30 wherein said time integral is controlled by the amplitude of said phase-encoding magnetic field gradient.
Claim 35
Dependent Claim
69 words
The method of Claim 29 wherein the temporal order of said gradient parameter applied in the course of implementing said plurality of views is selected such that when the measurements acquired in each view are rearranged in order of monotonically incrasing parameter value the signal variations will appear to go through N v /2 cycles, where N is equal to the number of views comprising said plurality of views.
Claim 36
Dependent Claim
76 words
The method of Claim 29, 30, or 31 wherein said step of selecting the temporal order of said gradient parameter value comprises: (a) calculating for each of said plurality of views a relative phase of signal variation; (b) assigning a different rank, RANK L (j), to each view in monotonic order of relative phase of signal variation; and (c) assigning a different rank, RANK H (j), to each view wherein RANK H (j) is determined by:
Claim 37
Dependent Claim
92 words
The method of Claim 29, 30, or 31 wherein said step of selecting the temporal order of said gradient parameter value comprises: (a) calculating for each of said plurality of views a relative phase of signal variation; (b) assigning a different rank, RANK L (j), to each view in monotonic order of relative phase of signal variation; and (c) assigning a different rank, RANK,(j), to each view wherein RANK H (j) is determined (d) assigning a different value of said gradient parameter to each view in proportion to the rank assigned thereto.
References Cited (Backward Citations)
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