Systems and methods for suppressing Nyquist ghost for diffusion weighted magnetic resonance imaging

1. A method for suppressing Nyquist ghost for diffusion weighted magnetic resonance imaging, the method performed by a magnetic resonance imaging (MRI) system including gradient coils, a radio frequency (RF) coil, and a processor connected to the gradient coils and the RF coil, the method comprising:

applying, by the MRI system, multiple sets of diffusion weighted imaging pulse sequences;

acquiring, by the MRI system, multiple k-space data sets using the multiple sets of diffusion weighted imaging pulse sequences;

reconstructing a magnetic resonance image from each of the multiple k-space data sets respectively;

averaging magnitudes of the magnetic resonance images; and

suppressing Nyquist ghost by generating an average magnitude magnetic resonance image based on the averaged magnitudes.

2. The method of claim 1 , wherein acquiring multiple k-space data sets further comprises:

applying, by the MRI system, a first set of diffusion weighted imaging pulse sequences;

acquiring, by the MRI system, a first k-space data set using the first set of diffusion weighted imaging pulse sequence;

applying, by the MRI system, a second set of diffusion weighted imaging pulse sequences; and

acquiring, by the MRI system, a second k-space data set using the second set of diffusion weighted imaging pulse sequence; and

wherein odd- and even-numbered echoes in the second k-space data set are swapped with respect to the first k-space data set.

3. The method of claim 1 , wherein each of the multiple sets of diffusion weighted imaging pulse sequences includes a pulsed gradient spin echo (PGSE) portion and an echo-planar imaging (EPI) sequence following the PGSE portion.

4. The method of claim 3 , wherein the PGSE portion comprises a diffusion gradient pair, one dephasing and one exactly opposite rephasing gradient.

5. The method of claim 3 , wherein the EPI sequence comprises a blipped EPI sequence, wherein a phase-encoding gradient blip is placed at each frequency-encoding gradient reversal.

6. The method of claim 5 , wherein acquiring multiple k-space data sets further comprises:

acquiring a first k-space data set using a first set of diffusion weighted imaging pulse sequence which comprises a first blipped EPI sequence; and

acquiring a second k-space data set using a second set of diffusion weighted imaging pulse sequence which comprises a second blipped EPI sequence; and

wherein odd- and even-numbered echoes of the second blipped EPI sequence are swapped with respect to the first blipped EPI sequence.

7. The method of claim 6 , wherein acquiring multiple k-space data sets further comprises:

acquiring a third k-space data set using a third set of diffusion weighted imaging pulse sequence which comprises a third blipped EPI sequence; and

acquiring a fourth k-space data set using a fourth set of diffusion weighted imaging pulse sequence which comprises a fourth blipped EPI sequence; and

wherein odd- and even-numbered echoes of the third blipped EPI sequence are swapped with respect to the second blipped EPI sequence, and wherein odd- and even-numbered echoes of the fourth blipped EPI sequence are swapped with respect to the third blipped EPI sequence.

8. A magnetic resonance imaging (MRI) system comprising:

gradient coils configured to generate encoding gradients;

a radio frequency (RF) coil configured to generate RF pulses; and

a processor connected to the gradient coils and the RF coil, the processor being configured to:

instruct the gradient coils and the RF coil to generate multiple sets of diffusion weighted imaging pulse sequences to acquire multiple k-space data sets;

reconstruct a magnetic resonance image from each of the multiple k-space data sets respectively;

average magnitudes of the magnetic resonance images; and

suppress Nyquist ghost by generating an average magnitude magnetic resonance image based on the averaged magnitudes.

9. The MRI system of claim 8 , wherein acquiring multiple k-space data sets further comprises:

acquiring a first k-space data set using a first set of diffusion weighted imaging pulse sequence; and

acquiring a second k-space data set using a second set of diffusion weighted imaging pulse sequence; and

wherein odd- and even-numbered echoes in the second k-space data set are swapped with respect to the first k-space data set.

10. The MRI system of claim 8 , wherein each of the multiple sets of diffusion weighted imaging pulse sequences includes a PGSE portion and an EPI sequence following the PGSE portion.

11. The MRI system of claim 10 , wherein the PGSE portion comprises a diffusion gradient pair, one dephasing and one exactly opposite rephasing gradient.

12. The MRI system of claim 10 , wherein the EPI sequence comprises a blipped EPI sequence, wherein a phase-encoding gradient blip is placed at each frequency-encoding gradient reversal.

13. The MRI system of claim 8 , wherein acquiring multiple k-space data sets further comprises:

acquiring a first k-space data set using a first set of diffusion weighted imaging pulse sequence which comprises a first blipped EPI sequence; and

acquiring a second k-space data set using a second set of diffusion weighted imaging pulse sequence which comprises a second blipped EPI sequence; and

wherein odd- and even-numbered echoes of the second blipped EPI sequence are swapped with respect to the first blipped EPI sequence.

14. The MRI system of claim 13 , wherein acquiring multiple k-space data sets further comprises:

acquiring a third k-space data set using a third set of diffusion weighted imaging pulse sequence which comprises a third blipped EPI sequence; and

acquiring a fourth k-space data set using a fourth set of diffusion weighted imaging pulse sequence which comprises a fourth blipped EPI sequence; and

wherein odd- and even-numbered echoes of the third blipped EPI sequence are swapped with respect to the second blipped EPI sequence, and wherein odd- and even-numbered echoes of the fourth blipped EPI sequence are swapped with respect to the third blipped EPI sequence.

15. A method for suppressing Nyquist ghost in magnetic resonance imaging, the method performed by a magnetic resonance imaging (MRI) system including gradient coils, a radio frequency (RF) coil, and a processor connected to the gradient coils and the RF coil, the method comprising:

applying, by the MRI system, a first set of imaging pulse sequences;

acquiring, by the MRI system, a first k-space data set using the first set of imaging pulse sequences;

applying, by the MRI system, a second sets of imaging pulse sequences;

acquiring, by the MRI system, a second k-space data set using the second set of imaging pulse sequences, wherein odd- and even-numbered echoes of the second first k-space data set are swapped with respect to the first k-space data set;

reconstructing a first magnetic resonance image from the first k-space data set;

reconstructing a second magnetic resonance image from the second k-space data set; and

averaging magnitudes of the first and second magnetic resonance images to generate an average magnitude magnetic resonance image.

16. The method of claim 15 , wherein the first and second sets of imaging pulse sequences are diffusion weighted and each includes a PGSE portion and an EPI sequence following the PGSE portion.

17. The method of claim 16 , wherein the PGSE portion comprises a diffusion gradient pair, one dephasing and one exactly opposite rephasing gradient.

18. The method of claim 16 , wherein the EPI sequence comprises a blipped EPI sequence, wherein a phase-encoding gradient blip is placed at each frequency-encoding gradient reversal.

19. The method of claim 18 , wherein odd- and even-numbered echoes of the blipped EPI sequence of the second set of imaging pulse sequences are swapped with respect to the blipped EPI sequence of the first set of imaging pulse sequences.