Systems and methods for reducing artifacts in MRI images

1. A system, comprising:

one or more storage devices storing a set of instructions; and

one or more processors configured to communicate with the storage device, wherein when executing the set of instructions, the system is caused to:

obtain a designed time-domain waveform wherein the designed time-domain waveform is a scanning sequence;

direct a radio frequency power amplifier (RFPA) of a magnetic resonance imaging (MRI) scanner to generate an output RF pulse based on the designed time-domain waveform;

measure an output time-domain waveform of the output RF pulse;

determine, based on the designed time-domain waveform and the output time-domain waveform, a modified time-domain waveform corresponding to an excitation RF pulse wherein the modified time-domain waveform including a compensation time-domain waveform; and

direct the MRI scanner to generate, using a waveform generator and the RFPA and based on the modified time-domain waveform, the excitation RF pulse to excite one or more slices of an object in an MRI scan;

wherein to determine the modified time-domain waveform corresponding to the excitation RF pulse based on the designed time-domain waveform and the output time-domain waveform, the system is caused to:

transform the designed time-domain waveform into a designed frequency-domain waveform with one or more excitation bands;

transform the output time-domain waveform into the output frequency-domain waveform;

determine the one or more frequency-domain sidebands in the output frequency-domain waveform by comparing the designed frequency-domain waveform with the output frequency-domain waveform;

select a portion of the output frequency-domain waveform, the portion of the output frequency-domain waveform including the one or more frequency-domain sidebands but not the one or more excitation bands;

determine a compensation frequency-domain waveform based on the selected portion of the output frequency-domain waveform;

transform the compensation frequency-domain waveform into a compensation time-domain waveform; and

determine the modified time-domain waveform based on the compensation time-domain waveform and the designed time-domain waveform.

2. The system of claim 1 , wherein the modified time-domain waveform is closer to satisfying an execution capability criterion than the designed time-domain waveform, the execution capability criterion embodying a criterion for a refocusing flip angle of the designed RF pulse.

3. The system of claim 1 , wherein a phase difference between the selected portion of the output frequency-domain waveform and the compensation frequency-domain waveform is 180°.

4. The system of claim 1 , wherein to determine the modified time-domain waveform corresponding to the excitation RF pulse, the system is caused to:

repeatedly determine an updated time-domain waveform in an iteration process including a plurality of successive iterations until a termination criterion is satisfied, wherein the updated time-domain waveform determined at the end of the iteration process is the modified time-domain waveform.

5. The system of claim 4 , at least one of the plurality of iterations including:

determining the updated time-domain waveform based on the designed time-domain waveform and a previous output time-domain waveform, the previous time-domain waveform corresponding to the designed time-domain waveform in a first iteration of the iteration process or a previously updated time-domain waveform determined in a previous iteration, the updated time-domain waveform corresponding to an updated RF pulse;

directing the RFPA of the MRI scanner to generate the updated RF pulse; and

measuring an output time-domain waveform of the updated RF pulse.

6. The system of claim 5 , wherein at feast one of the plurality of iterations further includes:

determining an iteration count of iterations that have been performed;

determining that the iteration count is equal to or greater than a first threshold; and

terminating, based on the determination that the iteration count is equal to or greater than the first threshold, the iteration process.

7. The system of claim 5 , wherein at least one of the plurality of iterations further includes:

displaying, to a user, a frequency-domain waveform of an RF pulse generated by the RFPA based on the modified time-domain waveform updated in the at least one of the plurality of iterations;

receiving, from the user, an instruction related to the updated time-domain waveform determined in the at least one of the plurality of iterations; and

terminating, based on the received instruction, the iteration process.

8. The system of claim 7 , wherein the received instruction includes that the updated RF pulse generated by the RFPA based on the updated time-domain waveform generated in the at least one of the plurality of iterations is acceptable.

9. A method implemented on a computing device having one or more processors and one or more storage devices, the method comprising:

obtaining a designed time-domain waveform wherein the designed time-domain waveform is a scanning sequence;

directing a radio frequency power amplifier (RFPA) of a magnetic resonance imaging (MRI) scanner to generate an output RF pulse based on the designed time-domain waveform;

measuring an output time-domain waveform of the output RF pulse;

determining, based on the designed time-domain waveform and the output time-domain waveform, a modified time-domain waveform corresponding to an excitation RF pulse wherein the modified time-domain waveform including a compensation time-domain waveform; and

directing the MRI scanner to generate, using a waveform generator and the RFPA and based on the modified time-domain waveform, the excitation RF pulse to excite one or more slices of an object in an MRI scan;

wherein determining the modified time-domain waveform corresponding to the excitation RF pulse based on the designed time-domain waveform and the output time-domain waveform comprises:

transforming the designed time-domain waveform into a designed frequency-domain waveform with one or more excitation bands;

transforming the output time-domain waveform into an output frequency-domain waveform;

determining one or more frequency-domain sidebands in the output frequency-domain waveform by comparing the designed frequency-domain waveform with the output frequency-domain waveform;

selecting a portion of the output frequency-domain waveform, the portion of the output frequency-domain waveform including the one or more frequency-domain sidebands but not the one or more excitation bands;

determining a compensation frequency-domain waveform based on the selected portion of the output frequency-domain waveform;

transforming the compensation frequency-domain waveform into a compensation time-domain waveform; and

determining the modified time-domain waveform based on the compensation time-domain waveform and the designed time-domain waveform.

10. The method of claim 9 , wherein the modified time-domain waveform is closer to satisfying an execution capability criterion than the designed time-domain waveform, the execution capability criterion embodying a criterion for a refocusing flip angle of the designed RF pulse.

11. The method of claim 9 , wherein a phase difference between the selected portion of the output frequency-domain waveform and the compensation frequency-domain waveform is 180°.

12. The method of claim 9 , wherein determining the modified time-domain waveform corresponding to the excitation RF pulse comprises:

repeatedly determine an updated time-domain waveform in an iteration process including a plurality of successive iterations until a termination criterion is satisfied, wherein the updated time-domain waveform determined at the end of the iteration process is the modified time-domain waveform.

13. The method of claim 12 , at least one of the plurality of iterations including:

determining the updated time-domain waveform based on the designed time-domain waveform and a previous output time-domain waveform, the previous output time-domain waveform corresponding to the designed time-domain waveform in a first iteration of the iteration process or a previously updated time-domain waveform determined in a previous iteration, the updated time-domain waveform corresponding to an updated RF pulse;

directing the RFPA of the MRI scanner to generate the updated RF pulse; and

measuring an output time-domain waveform of the updated RF pulse.

14. The method of claim 13 , wherein at least one of the plurality of iterations further includes:

determining an iteration count of iterations that have been performed;

determining that the iteration count is equal to or greater than a first threshold; and

terminating, based on the determination that the iteration count is equal to or greater than the first threshold, the iteration process.

15. The method of claim 13 , wherein at least one of the plurality of iterations further includes:

displaying, to a user, a frequency-domain waveform of an RF pulse generated by the RFPA based on the modified time-domain waveform updated in the at least one of the plurality of iterations;

receiving, from the user, an instruction related to the updated time-domain waveform determined in the at least one of the plurality of iterations; and

terminating, based on the received instruction, the iteration process.

16. The method of claim 15 , wherein the received instruction includes that the updated RF pulse generated by the RFPA based on the updated time-domain waveform generated in the at least one of the plurality of iterations is acceptable.