Dual contrast vessel wall MRI using phase sensitive polarity maps

1. A method for using magnetic resonance imaging to identify high-risk features of atherosclerotic plaque in a single scan, the method comprising:

performing an inversion recovery gradient magnetic resonance imaging sequence by applying an inversion recovery (IR) pulse to a subject disposed in a magnetic field in an MR imaging machine;

obtaining an I 1 image which is T1 weighted by detecting a first magnetic resonance signal at a time TI 1 after the IR pulse and at an acquisition flip angle α;

obtaining an I 2 image which is proton-density weighted by detecting a second magnetic resonance signal at a time TI 2 after the IR pulse and at an acquisition flip angle θ;

obtaining a polarity map P(x,y) from the I 1 image and the I 2 image according to the equation

P

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=

I

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I

2

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I

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I

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;

and

obtaining an S 2 image by reconstructing, from the I 2 image and the polarity map, a polarity enhanced proton-density-weighted image according to the equation S 2 (x,y)=P(x,y)∥I 2 (x,y)∥;

wherein I 1 (x,y) is the I 1 image, I* 2 (x,y) is a complex conjugation of the I 2 image, ∥I 1 ∥ is a norm of the I 1 image, ∥I 2 ∥ is a norm of the I 2 image, ∥I 2 (x,y)∥ is the norm of the I 2 image, and S 2 (x,y) is the S 2 image.

2. The method of claim 1 , further comprising:

comparing the I 2 image and the S 2 image for identifying false potential regions of calcification; and

excluding the false positive potential regions of calcification using the comparing.

3. The method of claim 1 , further comprising:

determining a location of a vessel outerwall boundary using the S 2 image.

4. The method of claim 3 , further comprising:

obtaining an S 1 image by reconstructing, from the I 1 image and the polarity map, a T1-weighted corrected real image according to the equation S 1 (x,y)=P(x,y)∥I 1 (x,y)∥;

determining the location of a vessel lumen using the S 1 image; and

determining a plaque burden by comparing the location of the vessel lumen with the location of the vessel outerwall boundary;

wherein S 1 (x,y) is the S 1 image.

5. A method for using magnetic resonance imaging, the method comprising:

with I 1 and I 2 images obtained from an inversion recovery (IR) magnetic resonance imaging sequence, I 1 being T1-weighted and I 2 being proton-density weighted,

obtaining a polarity map P(x,y) from the I 1 image and the I 2 image, the polarity map corresponding to a polarity function indicating a positive or a negative direction of magnetization associated with each of a plurality of spatial locations in the I 1 and I 2 images;

obtaining an S 2 image by correcting the I 2 image with the polarity map, such that S 2 is a polarity enhanced proton-density-weighted image; and

outputting the S 2 image in a manner perceptible to a user, wherein the S 2 image is indicative of at least one of a calcification or a plaque burden.

6. The method of claim 5 further comprising:

obtaining the I 1 image and the I 2 image by performing an inversion recovery gradient magnetic resonance imaging sequence by applying an inversion recovery (IR) pulse to a subject disposed in a magnetic field, and detecting a first magnetic resonance signal at time TI 1 and a second magnetic resonance signal at a time TI 2 , respectively.

7. The method of claim 6 , wherein the time TI 1 is between 300 and 500 ms, and the time TI 2 is at least 1500 ms.

8. The method of claim 5 , wherein the polarity function is defined by

P

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I

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when I 1 (x,y)=∥I 1 (x,y)∥P(x,y)e −Ø(x,y) and I 2 (x,y)=∥I 2 (x,y)∥P(x,y)e Ø(x,y) ;

wherein Ø(x,y) denotes the total background phase; and

wherein I 1 (x,y) is the I 1 image, I * 2 (x,y) is a complex conjugation of the I 2 image, ∥I 1 ∥ is a norm of the I 1 image, ∥I 2 ∥ is a norm of the I 2 image, ∥I 1 (x,y)∥ is the norm of the I 1 image, ∥I 2 (x,y)∥ is the norm of the I 2 image, and S 2 (x,y) is the S 2 image.

9. The method of claim 5 , further comprising:

determining a vessel outerwall boundary using the S 2 image;

determining an inner lumen using the S 2 image; and

determining a plaque burden by comparing the vessel outerwall boundary and vessel inner lumen.

10. The method of claim 9 , further comprising:

identifying a region of calcification using the I 2 image.

11. The method of claim 10 , further comprising:

determining a juxtaluminal calcification by comparing the region of calcification to the inner lumen to determine whether the region of calcification is adjacent to the lumen.

12. The method of claim 5 , further comprising:

obtaining an S 1 image by correcting the I 1 image with the polarity map, such that S 1 is a T1-weighted corrected real image;

obtaining a bright-blood S 1 image by taking a negative part of the S 1 image; and

determining stenosis using the bright-blood S 1 image.

13. The method of claim 5 further comprising:

determining a region of intraplaque hemorrhage using the S 1 image by identifying a bright region in the S 1 image proximate to the lumen.

14. The method of claim 5 , further comprising:

determining stenosis using the S 2 image.

15. The method of claim 5 , further comprising:

displaying, in a manner perceptible to a user, the S 2 image.

16. The method of claim 5 , further comprising:

obtaining an S 1 image by correcting the I 1 image with the polarity map, such that S 1 is a T1-weighted corrected real image;

obtaining a bright-blood S 1 image by taking a negative part of the S 1 image; and

displaying, in a manner perceptible to a user, two or more of the S 1 image, bright-blood S 1 image, I 2 image, and S 2 image in a spatially proximate configuration for comparison.

17. The method of claim 16 wherein the spatially proximate configuration comprises superimposing a partial transparency of at least one image over at least one other image.

18. A magnetic resonance (MR) imaging system for acquiring a dual acquisition from an inversion-recovery (IR) pulse and using the dual acquisition to determine features of atherosclerotic plaque, the system comprising:

an MR imaging scanner having a static magnetic field, radio frequency (RF) emitter coils, and RF receiving coils configured for acquiring first and second MR resonance signals from a subject by applying an IR pulse; and

a computer unit having a processor and memory, and having stored executable instructions thereon configured to perform operations comprising:

reconstructing the first and second MR resonance signals into I 1 and I 2 images, respectively, the I 1 image being T1-weighted and the I 2 image being proton-density weighted;

obtaining a polarity map P(x,y) from the I 1 image and the I 2 image, the polarity map corresponding to a positive or negative polarity of each of a plurality of voxels associated with the I 1 and I 2 images; and

obtaining an S 2 image by correcting the I 2 image with the polarity map, such that S 2 is a polarity-enhanced proton-density-weighted image.

19. The system of claim 18 , further comprising a display unit configured to output one or more MR images in a manner perceptible to a user.

20. The system of claim 18 , wherein the operations further comprise:

obtaining an S 1 image by correcting the I 1 image with the polarity map, such that the S 1 image is a T1-weighted corrected real image.

21. The method of claim 1 , further comprising:

outputting the S 2 image to one of a nontransitory storage medium or a display for a user, wherein the S 2 image is indicative of at least one of a calcification or a plaque burden.