Background field removal method for MRI using projection onto dipole fields

• US 9,448,289 B2
• Filed: 11/23/2011
• Issued: 09/20/2016
• Est. Priority Date: 11/23/2010
• Status: Active Grant

• Current Assignee: Cornell University
• Original Assignee: Cornell University
• Inventors: Wang, Yi, de Rochefort, Ludovic, Liu, Tian, Khalidov, Ildar
• Primary Examiner(s): Koziol, Stephen R
• Assistant Examiner(s): CHOI, TIMOTHY WING HO
• Application Number:
  US13/304,141
• Publication Number:
  US 20120141003A1
• Time in Patent Office: 1,763 Days
• US Class Current: 1/1
• CPC Class Codes: G01R 33/24 for measuring direction or magnitude of magnetic fields or magnetic flux
• CPC Class Codes: G01R 33/5608 Data processing and visualization specially adapted for MR, e.g. for feature analysis and pattern recognition on the basis of measured MR data, segmentation of measured MR data, edge contour detection on the basis of measured MR data, for enhancing measured MR data in terms of signal-to-noise ratio by means of noise filtering or apodization, for enhancing measured MR data in terms of resolution by means for deblurring, windowing, zero filling, or generation of gray-scaled images, colour-coded images or images displaying vectors instead of pixels image data processing or generation, in general G06T
• CPC Class Codes: G06T 2207/10088 Magnetic resonance imaging [MRI]

Abstract

For optimal image quality in susceptibility-weighted imaging and accurate quantification of susceptibility, it is necessary to isolate the local field generated by local magnetic sources (such as iron) from the background field that arises from imperfect shimming and variations in magnetic susceptibility of surrounding tissues (including air). We present a nonparametric background field removal method based on projection onto dipole fields in which the background field inside an ROI is decomposed into a field originating from dipoles outside the ROI using the projection theorem in Hilbert space.

Claims

1. A method for removing background field from a spatial region of interest in magnetic resonance imaging using magnetic susceptibility for contrast, comprising:

obtaining, from a magnetic resonance imaging system, magnetic resonance imaging data using magnetic susceptibility for contrast;

calculating, by a processing system, the background field by decomposing a field measured inside the spatial region of interest into a field generated by dipoles outside the spatial region of interest; and

generating and outputting, by the professing system, magnetic susceptibility maps with enhanced contrast based on removing the calculated background field, wherein removing the calculated background field comprises subtracting the calculated background field from a total measured field.

2. The method of claim 1 wherein said decomposing comprises projecting the field measured inside the spatial region of interest in Hilbert space to estimate a background susceptibility distribution outside of the spatial region of interest corresponding to the dipoles outside of the spatial region of interest.

3. The method of claim 1 wherein the total field measured inside the spatial region of interest is decomposed.

4. The method of claim 1 wherein the field measured inside the spatial region of interest is decomposed into all the dipoles.

5. The method of claim 1 wherein poor shimming is corrected prior to removing background.

6. The method of claim 1 further comprising correcting spatial variants of noise by normalizing the noise to a normal distribution.

13. The method of claim 2, wherein the background field is calculated from the background susceptibility distribution outside of the spatial region of interest.

7. A system for magnetic resonance imaging comprising a tangible, non-transitory computer-readable medium having computer-executable instructions thereon for removing background field from a spatial region of interest in magnetic resonance imaging using magnetic susceptibility for contrast, the computer-executable instructions, when executed, facilitating performance of the following:

obtaining, from a magnetic resonance imaging system, magnetic resonance imaging data using magnetic susceptibility for contrast;

calculating, by a processing system, the background field by decomposing a field measured inside the spatial region of interest into a field generated by dipoles outside the spatial region of interest; and

generating and outputting, by the processing system, magnetic susceptibility maps with enhanced contrast based on removing the calculated background field, wherein removing the calculated background field comprises subtracting the calculated background field from a total measured field.

8. The system of claim 7, wherein calculating the background field further comprises projecting the field measured inside the spatial region of interest in Hilbert space to estimate a background susceptibility distribution outside of the spatial region of interest corresponding to the dipoles outside of the spatial region of interest.

9. The system of claim 7, wherein calculating the background field further comprises decomposing the total field measured inside the spatial region of interest.

10. The system of claim 7, wherein calculating the background field further comprises decomposing the field measured inside the spatial region of interest into all the dipoles.

11. The system of claim 7, wherein the computer-executable instructions, when executed, further facilitate:

correcting poor shimming prior to removing background.

12. The system of claim 7, wherein the computer-executable instructions, when executed, further facilitate:

correcting spatial variants of noise by normalizing the noise to a normal distribution.

14. The system of claim 8, wherein the background field is calculated from the background susceptibility distribution outside of the spatial region of interest.