Method to correct magnetic field/phase variations in proton resonance frequency shift thermometry in magnetic resonance imaging

• US 7,359,745 B2
• Filed: 05/14/2003
• Issued: 04/15/2008
• Est. Priority Date: 05/15/2002
• Status: Active Grant

• Current Assignee: Case Western Reserve University
• Original Assignee: Case Western Reserve University
• Inventors: Barkauskas, Kestutis J., Lewin, Jonathan S., Duerk, Jeffrey L.
• Primary Examiner(s): Casler; Brian L.
• Assistant Examiner(s): Ramirez; John F.
• Application Number:
  US10/437,662
• Publication Number:
  US 20040041563A1
• Time in Patent Office: 1,798 Days
• Field of Search: 324/318, 324/320, 128/653.2, 600407-423
• US Class Current: 600/410
• CPC Class Codes: G01R 33/022 Measuring gradient
• CPC Class Codes: G01R 33/4804 Spatially selective measurement of temperature or pH
• CPC Class Codes: G01R 33/565 Correction of image distortions, e.g. due to magnetic field inhomogeneities
• CPC Class Codes: G01R 33/56563 caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0 G01R33/56509, G01R33/56518, G01R33/56536 take precedence

Abstract

PRF shift MRI data is acquired. The PRF shift MRI data may include signals affected by both a desired PRF shift and an undesired PRF shift. Thus, example systems and methods describe manipulating the PRF shift MR! data to make it substantially free of the effects of the undesired PRF shift, which facilitates displaying certain MRI images based on the desired PRF shift.

Claims

1. A method, comprising:

centering a point of interest of an object to be imaged in a field of view;

receiving a first MRI data of the object;

establishing a reference image from the first MRI data;

receiving one or more second MRI data of the object, where the object has been subjected to one or more proton resonance frequency altering actions;

determining a maximum k-space amplitude location in one or more of the second MRI data;

manipulating the first MRI data to align the maximum k-space amplitude locations with an assumed k-space center to within a tolerance;

phase correcting the first MRI data;

determining a wrap free phase change from the reference image on an element-by-element basis; and

producing a display data that can be displayed, where the display data facilitates displaying the results of a desired phase shift event on the object to be imaged.

2. The method of claim 1, where determining a maximum k-space amplitude location comprises iteratively bisecting a given search space about an initial guess where one or more linear phase offsets in an image domain are employed to selectively interpolate midpoints between one or more known k-space amplitudes.

3. The method of claim 1, where phase correcting the first MRI data comprises employing the phase of a low resolution image of an N×

M mask of low-frequency Fourier co-efficients as a phase correction map, where N and M refer to the respective number of rows and columns of data contained within the mask, M and N being integers.

5. The method of claim 3, where N and M are related to one or more of the FOV and the size of the expected site of phase variation.

8. The method of claim 1, where the element is a pixel.

4. A method, comprising:

centering a point of interest of an object to be imaged in a field of view;

receiving a first MRI data of the object;

establishing a reference image from the first MRI data;

receiving one or more second MRI data of the object, where the object has been subjected to one or more proton resonance frequency altering actions;

determining a maximum k-space amplitude location in one or more of the second MRI data;

manipulating the first MRI data to align the maximum k-space amplitude locations with an assumed k-space center to within a tolerance;

phase correcting the first MRI data;

determining a wrap free phase change from the reference image on an element-by-element basis; and

producing a display data that can be displayed, where the display data facilitates displaying the results of a desired phase shift event on the object to be imaged,

where phase correcting the first MRI data comprises employing the phase of a low resolution image of an N×

M mask of low-frequency Fourier co-efficients as a phase correction map, where N and M refer to the respective number of rows and columns of data contained within the mask, M and N being integers, and

where N is less than 5 and where M is less than 5.

6. A method, comprising:

centering a point of interest of an object to be imaged in a field of view;

receiving a first MRI data of the object;

establishing a reference image from the first MRI data;

receiving one or more second MRI data of the object, where the object has been subjected to one or more proton resonance frequency altering actions;

determining a maximum k-space amplitude location in one or more of the second MRI data;

manipulating the first MRI data to align the maximum k-space amplitude locations with an assumed k-space center to within a tolerance;

phase correcting the first MRI data;

determining a wrap free phase change from the reference image on an element-by-element basis; and

producing a display data that can be displayed, where the display data facilitates displaying the results of a desired phase shift event on the object to be imaged,

where the tolerance is about 1/128th of a cycle/FOV.

7. A method, comprising:

centering a point of interest of an object to be imaged in a field of view;

receiving a first MRI data of the object;

establishing a reference image from the first MRI data;

receiving one or more second MRI data of the object, where the object has been subjected to one or more proton resonance frequency altering actions;

determining a maximum k-space amplitude location in one or more of the second MRI data;

manipulating the first MRI data to align the maximum k-space amplitude locations with an assumed k-space center to within a tolerance;

phase correcting the first MRI data;

determining a wrap free phase change from the reference image on an element-by-element basis; and

producing a display data that can be displayed, where the display data facilitates displaying the results of a desired phase shift event on the object to be imaged,

where determining the wrap free phase change comprises examining one or more relationships between two phasors over the range 0 to 2π

.