Method and apparatus for imaging artefact reduction

• US 6,341,179 B1
• Filed: 11/17/1998
• Issued: 01/22/2002
• Est. Priority Date: 07/09/1996
• Status: Expired due to Term

• Current Assignee: Siemens Healthcare GMBH (Siemens AG)
• Original Assignee: The secretary of state for defence in her Britannic Majesty's Government of the United Kingdom of Great Britain And Northern Ireland
• Inventors: Hill, Derek L G, Atkinson, David, Stoyle, Peter N R
• Primary Examiner(s): Lee, Thomas D.
• Assistant Examiner(s): BRINICH, STEPHEN M
• Application Number:
  US09/180,751
• Time in Patent Office: 1,162 Days
• Field of Search: 382/254-255, 396/76-82, 396/104
• US Class Current: 382/254
• CPC Class Codes: G06T 11/008 Specific post-processing after tomographic reconstruction, e.g. voxelisation, metal artifact correction
• CPC Class Codes: G06T 2211/412 Dynamic
• CPC Class Codes: G06T 2211/424 Iterative

Abstract

The invention relates to a method and apparatus for reducing imaging artifacts in physiological images, such as magnetic resonance imaging images. A model of a physical cause for the image artifact is modelled and the effects of perturbing this model on a focus criterion of the image analyzed so as to optimize the focus criterion. For an optimized focus criterion, the model should reflect the actual physical cause of the image artifact. A focus criterion is a measure of entropy of the image, with an optimized image having reduced entropy.

Claims

1. A method for generating a corrected image of an object by:

(i) employing scanning means (12) to scan an object and derive an image data set from signals received from the object, and

(i) manipulating the data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that manipulating the data set incorporates the steps of;

a) providing a focus criterion for the image data set prior to correction,

b) generating a trial artefact corresponding to a possible artefact cause,

c) producing a manipulated version of the image data set in which the trial artefact is counteracted and providing a focus criterion for this version,

d) varying the trial artefact and repeating the preceding step iteratively to produce a manipulated version of the image data set compensated for a version of the trial artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) producing corrected image data from a manipulated version of the image data set associated with optimisation of the focus criterion.

2. A method according to claim 1 characterised in that the said trial artefact is a first trial artefact, and after step (d), steps (b) to (d) are repeated for a second trial artefact.

3. A method according to claim 1 characterised in that the image is a physiological image and the unwanted artefact effects are associated with object motion during operation of the scanning means (12).

4. A method according to claim 3 characterised in that the scanning means is a magnetic resonance imaging (MRI) scanning means (12).

5. A method for generating a corrected image of an object by:

(i) employing scanning means (12) to scan an object and derive an image data set from signals received from the object, and

(i) manipulating the data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that manipulating the data set incorporates the steps of;

a) providing a focus criterion for the image data set prior to correction,

b) generating a modelled artefact corresponding to a possible artefact cause,

c) producing a manipulated version of the image data set in which the modelled artefact is counteracted and providing a focus criterion for this version,

d) varying the modelled artefact and repeating the preceding step iteratively to produce a manipulated version of the image data set compensated for a version of the modelled artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) producing corrected image data from a manipulated version of the image data set associated with optimisation of the focus criterion, wherein the image is a physiological image and the unwanted artefact effects are associated with object motion during operation of the scanning means (12), wherein the scanning means is a magnetic resonance imaging (MRI) scanning means (12), wherein the focus criterion is an image entropy criterion.

6. A method according to claim 5 characterised in that the artefact effects arise from object displacement and the step of producing a manipulated version of the image data set incorporates multiplying a plurality of the received signals by respective phase factors.

7. A method according to claim 6 characterised in that the MRI scanning means (12) defines a data readout direction, and to correct for a displacement m_x^j of an image data set point in this direction the phase factor is exp[−

K_x;

m_x^j], where K_x=2/FOV_x(u−

N_x/2), FOV_x is the field of view in the readout direction and u is an index number of the said image data set point in a line of such points extending in the readout direction and containing a number N_x of such points.

8. A method according to claim 6 characterised in that the MRI scanning means (12) defines a phase encode direction, the image data set is a set of lines of data points, and to correct for a displacement m_y^j of a line of index number j in the image data set, the phase factor is exp[−

K_y;

m_j^j], where K_y=2/FOV_y(u−

N_y/2), FOV_y is the field of view in the phase encode direction and N_y is the number of lines in the data set.

9. A method for generating a corrected image of an object by:

(i) employing scanning means (12) to scan an object and derive an image data set from signals received from the object, and

(i) manipulating the data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that manipulating the data set incorporates the steps of;

a) providing a focus criterion for the image data set prior to correction,

b) generating a modelled artefact corresponding to a possible artefact cause,

c) producing a manipulated version of the image data set in which the modelled artefact is counteracted and providing a focus criterion for this version,

d) varying the modelled artefact and repeating the preceding step iteratively to produce a manipulated version of the image data set compensated for a version of the modelled artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) producing corrected image data from a manipulated version of the image data set associated with optimisation of the focus criterion, wherein the focus criterion is an image entropy criterion determined from sub-divisions of an image which are identified as being non-dark.

10. A method for generating a corrected image of an object by:

(i) employing scanning means (12) to scan an object and derive an image data set from signals received from the object, and

(i) manipulating the data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that manipulating the data set incorporates the steps of;

a) providing a focus criterion for the image data set prior to correction,

b) generating a modelled artefact corresponding to a possible artefact cause,

c) producing a manipulated version of the image data set in which the modelled artefact is counteracted and providing a focus criterion for this version,

d) varying the modelled artefact and repeating the preceding step iteratively to produce a manipulated version of the image data set compensated for a version of the modelled artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) producing corrected image data from a manipulated version of the image data set associated with optimisation of the focus criterion, wherein the scanning means is an MRI scanning means (12), characterised in that the modelled artefact is associated with object motion, the image data set is a set of lines of data points and the step of iteratively varying the modelled artefact is performed initially using a data segment incorporating a larger number of such lines relative to those of a data segment used later.

11. A method for generating a corrected image of an object by:

(i) employing scanning means (12) to scan an object and derive an image data set from signals received from the object, and

(i) manipulating the data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that manipulating the data set incorporates the steps of;

a) providing a focus criterion for the image data set prior to correction,

b) generating a modelled artefact corresponding to a possible artefact cause,

c) producing a manipulated version of the image data set in which the modelled artefact is counteracted and providing a focus criterion for this version,

d) varying the modelled artefact and repeating the preceding step iteratively to produce a manipulated version of the image data set compensated for a version of the modelled artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) producing corrected image data from a manipulated version of the image data set associated with optimisation of the focus criterion, wherein the scanning means comprises an MRI scanning means (12), characterised in that the modelled artefact is associated with object motion, and the step of iteratively varying the modelled artefact is performed initially using a smaller number of nodes relative to those used later.

12. A method for generating a corrected image of an object by:

(i) employing scanning means (12) to scan an object and derive an image data set from signals received from the object, and

(i) manipulating the data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that manipulating the data set incorporates the steps of;

a) providing a focus criterion for the image data set prior to correction,

b) generating a modelled artefact corresponding to a possible artefact cause,

c) producing a manipulated version of the image data set in which the modelled artefact is counteracted and providing a focus criterion for this version,

d) varying the modelled artefact and repeating the preceding step iteratively to produce a manipulated version of the image data set compensated for a version of the modelled artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) producing corrected image data from a manipulated version of the image data set associated with optimisation of the focus criterion, wherein the scanning means comprises an MRI scanning means (12), characterised in that the modelled artefact is associated with object motion, the MRI scanning means (12) is arranged to use a sub-set of the data set to obtain a sub-image, the step of iteratively varying the modelled artefact is performed over a region corresponding to the sub-set, and the sub-set is extended later in such iteration.

13. An imaging system incorporating:

(i) scanning means (12) for scanning an object and deriving an image data set from signals received from the object, and

(ii) processing means (38) for manipulating the image data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that the processing means (38) is arranged to execute the following functions;

a) provision of a focus criterion for the image data set prior to correction,

b) generation of a trial artefact corresponding to a possible artefact cause,

c) production of a manipulated version of the image data set in which the trial artefact is counteracted and provision of a further focus criterion for this version,

d) variation of the trial artefact and repetition of the preceding function iteratively to produce a manipulated version of the image data set compensated for a version of the trial artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) production of corrected image data from the manipulated version of the image data set associated with optimisation of the focus criterion.

14. An imaging system according to claim 13 characterised in that the said trial artefact is a first trial artefact and after function (d) the processing means (38) is arranged to repeat functions (b) to (d) for a second trial artefact.

15. An imaging system according to claim 13 characterised in that the image is a physiological image and the unwanted artefact effects are associated with object motion during operation of the scanning means (12).

16. An imaging system according to claim 15 characterised in that the scanning means is an MRI scanning means (12).

17. An imaging system incorporating:

(i) scanning means (12) for scanning an object and deriving an image data set from signals received from the object, and

(ii) processing means (38) for manipulating the image data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that the processing means (38) is arranged to execute the following functions;

a) provision of a focus criterion for the image data set prior to correction,

b) generation of a modelled artefact corresponding to a possible artefact cause,

c) production of a manipulated version of the image data set in which the modelled artefact is counteracted and provision of a further focus criterion for this version,

d) variation of the modelled artefact and repetition of the preceding function iteratively to produce a manipulated version of the image data set compensated for a version of the modelled artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) production of corrected image data from the manipulated version of the image data set associated with optimisation of the focus criterion, wherein the image is a physiological image and the unwanted artefact effects are associated with object motion during operation of the scanning means (12), wherein the scanning means is an MRI scanning means (12), wherein the focus criterion is an image entropy criterion.

18. An imaging system according to claim 17 characterised in that the artefact effects are associated with object displacement and the processing means (38) is arranged to implement the function of producing a manipulated version of the data set by multiplying a plurality of the received signals by respective phase factors.

19. An imaging system according to claim 18 characterised in that the MRI scanning means (12) defines a data readout direction, and to correct for a displacement m_x^j of an image data set point in this direction the phase factor is exp[−

K_x.m_x^j], where K_x=2/FOV_x(u−

N_x/2), FOV_x is the field of view in the readout direction and u is an index number of the said image data set point in a line of such points extending in the readout direction and containing a number N_x of such points.

20. An imaging system according to claim 17 characterised in that the MRI scanning means (12) defines a phase encode direction, the image data set is a set of lines of data points, and to correct for a displacement m_y^j of a line of index number j in the image data set the phase factor is exp[−

K_y.m_y^j], where K_y=2/FOV_y(u−

N_y/2), FOV_y is the field of view in the phase encode direction and N_y is the number of lines in the data set.

21. An imaging system incorporating:

(i) scanning means (12) for scanning an object and deriving an image data set from signals received from the object, and

(ii) processing means (38) for manipulating the image data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that the processing means (38) is arranged to execute the following functions;

a) provision of a focus criterion for the image data set prior to correction,

b) generation of a modelled artefact corresponding to a possible artefact cause,

c) production of a manipulated version of the image data set in which the modelled artefact is counteracted and provision of a further focus criterion for this version,

d) variation of the modelled artefact and repetition of the preceding function iteratively to produce a manipulated version of the image data set compensated for a version of the modelled artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) production of corrected image data from the manipulated version of the image data set associated with optimisation of the focus criterion, wherein the focus criterion is an image entropy criterion determined from sub-divisions of an image which are identified as being non-dark.

22. An imaging system incorporating:

(i) scanning means (12) for scanning an object and deriving an image data set from signals received from the object, and

(ii) processing means (38) for manipulating the image data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that the processing means (38) is arranged to execute the following functions;

a) provision of a focus criterion for the image data set prior to correction,

b) generation of a modelled artefact corresponding to a possible artefact cause,

c) production of a manipulated version of the image data set in which the modelled artefact is counteracted and provision of a further focus criterion for this version,

d) variation of the modelled artefact and repetition of the preceding function iteratively to produce a manipulated version of the image data set compensated for a version of the modelled artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) production of corrected image data from the manipulated version of the image data set associated with optimisation of the focus criterion, wherein the scanning means is an MRI scanning means (12), characterised in that the modelled artefact is associated with object motion, the image data set is a set of lines of data points and the processing means (38) is arranged to perform iterative variation of the modelled artefact using initially a data segment incorporating a larger number of such lines relative to those of a data segment used later in the iteration function.

23. An imaging system incorporating:

(i) scanning means (12) for scanning an object and deriving an image data set from signals received from the object, and

(ii) processing means (38) for manipulating the image data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that the processing means (38) is arranged to execute the following functions;

a) provision of a focus criterion for the image data set prior to correction,

b) generation of a modelled artefact corresponding to a possible artefact cause,

c) production of a manipulated version of the image data set in which the modelled artefact is counteracted and provision of a further focus criterion for this version,

d) variation of the modelled artefact and repetition of the preceding function iteratively to produce a manipulated version of the image data set compensated for a version of the modelled artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) production of corrected image data from the manipulated version of the image data set associated with optimisation of the focus criterion, wherein the scanning means is an MRI scanning means (12), characterised in that the modelled artefact is associated with object motion and the processing means (38) is arranged to perform iterative variation of the modelled artefact using initially a smaller number of nodes relative to those used later in the iteration function.

24. An imaging system incorporating:

(i) scanning means (12) for scanning an object and deriving an image data set from signals received from the object, and

(ii) processing means (38) for manipulating the image data set to reduce unwanted artefact effects associated with the object and produce corrected image data to yield an artefact-reduced image,

characterised in that the processing means (38) is arranged to execute the following functions;

a) provision of a focus criterion for the image data set prior to correction,

b) generation of a modelled artefact corresponding to a possible artefact cause,

c) production of a manipulated version of the image data set in which the modelled artefact is counteracted and provision of a further focus criterion for this version,

d) variation of the modelled artefact and repetition of the preceding function iteratively to produce a manipulated version of the image data set compensated for a version of the modelled artefact associated with optimisation of the focus criterion to the extent obtainable by iteration, and

e) production of corrected image data from the manipulated version of the image data set associated with optimisation of the focus criterion, wherein the scanning means is an MRI scanning means (12), characterised in that the modelled artefact is associated with object motion, the MRI scanning means (12) is arranged to use a sub-set of the data set to obtain a sub-image, the processing means (38) is arranged to perform iterative variation of the modelled artefact over a region corresponding to the sub-set and to extend the sub-set later in the iteration function.