Phase correction for echo-planar imaging
Systems and methods include conversion of a first frame of k-space data acquired using a first initial readout polarity to first hybrid (k x , y)-space data, conversion of a second frame of k-space data acquired using a second initial readout polarity to second hybrid (k x , y)-space data, determination of a relationship between phase difference and y-position based on phase differences between a plurality of pixels located at k x =a of first hybrid (k x , y)-space data and a plurality of pixels at k x =b of second hybrid (k x , y)-space data, where a and b are constants, modification of the second hybrid (k x , y)-space data based on the relationship, conversion of the modified second hybrid (k x , y)-space data to a modified second frame of k-space data, generation of two single-polarity readout k-space frames based on the first frame of k-space data and the modified second frame of k-space data, and correction of a third frame of EPI image data based on the two single-readout polarity k-space frames.
1. A system comprising:
a chassis defining a bore;
a main magnet to generate a polarizing magnetic field within the bore;
a gradient system to apply a gradient magnetic field to the polarizing magnetic field;
a radio frequency system to transmit RF pulses to an object disposed within the bore and to receive signals from the object; and
a computing system to execute program code to:
acquire a first frame of k-space data using a first initial readout polarity;
acquire a second frame of k-space data using a second initial readout polarity opposite to the first initial readout polarity;
convert the first frame of k-space data to first hybrid (k x , y)-space data;
convert the second frame of k-space data to second hybrid (k x , y)-space data;
determine a relationship between phase difference and y-position based on phase differences between a plurality of pixels located at k x =a of first hybrid (k x , y)-space data and a plurality of pixels at k x =b of second hybrid (k x , y)-space data, where a and b are constants;
modify the second hybrid (k x , y)-space data based on the relationship;
convert the modified second hybrid (k x , y)-space data to a modified second frame of k-space data; and
generate two single-polarity readout k-space frames based on the first frame of k-space data and the modified second frame of k-space data.
2. A system according to claim 1 , wherein determination of the relationship comprises:
identification of a plurality of pairs of hybrid (k x , y)-space pixels, where each pair includes a pixel of the first hybrid (k x , y)-space data and a pixel of the second hybrid (k x , y)-space data located at a same y-position; and
determination of a phase difference between the pixels of each pair of the plurality of pairs.
3. A system according to claim 2 , wherein a=b=0.
4. A system according to claim 2 , wherein a does not equal b.
5. A system according to claim 1 , wherein modifying the second hybrid (k x , y)-space data based on the relationship comprises:
determining a phase correction associated with each pixel of the second hybrid (k x , y)-space data based on the relationship and the y-position of the pixel; and
for each pixel of the second hybrid (k x , y)-space data, applying the associated phase correction to the pixel to generate corrected second hybrid (k x , y)-space data.
6. A system according to claim 1 , the computing system to execute program code to:
correct a third frame of EPI image data based on the two single-readout polarity k-space frames.
7. A system according to claim 1 , the computing system to execute program code to:
phase-correct the first frame of k-space data and the second frame of k-space data in the k x -direction.
8. A method comprising:
acquiring a first frame of k-space data using a first initial readout polarity;
acquiring a second frame of k-space data using a second initial readout polarity opposite to the first initial readout polarity;
converting the first frame of k-space data to first hybrid (k x , y)-space data;
converting the second frame of k-space data to second hybrid (k x , y)-space data;
determining a relationship between phase difference and y-position based on phase differences between a plurality of pixels located at k x =a of first hybrid (k x , y)-space data and a plurality of pixels at k x =b of second hybrid (k x , y)-space data, where a and b are constants;
modifying the second hybrid (k x , y)-space data based on the relationship;
converting the modified second hybrid (k x , y)-space data to a modified second frame of k-space data; and
generating two single-polarity readout k-space frames based on the first frame of k-space data and the modified second frame of k-space data.
9. A method according to claim 8 , wherein determining the relationship comprises:
identifying a plurality of pairs of hybrid (k x , y)-space pixels, where each pair includes a pixel of the first hybrid (k x , y)-space data and a pixel of the second hybrid (k x , y)-space data located at a same y-position; and
determining a phase difference between the pixels of each pair of the plurality of pairs.
10. A method according to claim 9 , wherein a=b=0.
11. A method according to claim 9 , wherein a does not equal b.
12. A method according to claim 8 , wherein modifying the second hybrid (k x , y)-space data based on the relationship comprises:
determining a phase correction associated with each pixel of the second hybrid (k x , y)-space data based on the relationship and the y-position of the pixel; and
for each pixel of the second hybrid (k x , y)-space data, applying the associated phase correction to the pixel to generate corrected second hybrid (k x , y)-space data.
13. A method according to claim 8 , further comprising:
correcting a third frame of EPI image data based on the two single-readout polarity k-space frames.
14. A method according to claim 8 , further comprising:
phase-correcting the first frame of k-space data and the second frame of k-space data in the k x -direction.
15. A computing system comprising:
a memory storing processor-executable program code; and
one or more processors to execute the program code to:
convert a first frame of k-space data acquired using a first initial readout polarity to first hybrid (k x , y)-space data;
convert a second frame of k-space data acquired using a second initial readout polarity to second hybrid (k x , y)-space data;
determine a relationship between phase difference and y-position based on phase differences between a plurality of pixels located at k x =a of first hybrid (k x , y)-space data and a plurality of pixels at k x =b of second hybrid (k x , y)-space data, where a and b are constants;
modify the second hybrid (k x , y)-space data based on the relationship;
convert the modified second hybrid (k x , y)-space data to a modified second frame of k-space data;
generate two single-polarity readout k-space frames based on the first frame of k-space data and the modified second frame of k-space data; and
correct a third frame of EPI image data based on the two single-readout polarity k-space frames.
16. A computing system according to claim 15 , wherein determination of the relationship comprises:
identification of a plurality of pairs of hybrid (k x , y)-space pixels, where each pair includes a pixel of the first hybrid (k x , y)-space data and a pixel of the second hybrid (k x , y)-space data located at a same y-position; and
determination of a phase difference between the pixels of each pair of the plurality of pairs.
17. A computing system according to claim 16 , wherein a=b=0.
18. A computing system according to claim 16 , wherein a does not equal b.
19. A computing system according to claim 15 , wherein modification of the second hybrid (k x , y)-space data based on the relationship comprises:
determination of a phase correction associated with each pixel of the second hybrid (k x , y)-space data based on the relationship and the y-position of the pixel; and
for each pixel of the second hybrid (k x , y)-space data, application of the associated phase correction to the pixel to generate corrected second hybrid (k x , y)-space data.
20. A computing system according to claim 15 , the one or more processors to execute the program code to:
phase-correct the first frame of k-space data and the second frame of k-space data in the k x -direction.