Eddy-current artifact reduction in balanced steady-state free precession magnetic resonance imaging
Magnetic resonance imaging techniques are described that utilize bSSFP sequences in which two or more gradient waveforms are interleaved in a “groupwise” fashion, i.e., each waveform is executed consecutively two or more times before switching to the other waveform, where “N” counts the number of times each waveform is executed consecutively. As a result, embodiments of the present disclosure can mitigate steady-state signal distortions or artifacts in interleaved balanced steady-state free precession (bSSFP) caused by slightly unbalanced eddy-current fields. Related MRI systems are also described.
1. A method of artifact reduction using gradient waveform grouping for balanced SSFP imaging, the method comprising:
with a MRI system, providing a balanced steady state free precession (SSFP) pulse sequence of RF pulses and balanced gradient pulses to an object;
interleaving two different gradient waveforms of the SSFP pulse sequence;
switching between from a first of the two different gradient waveforms to the second gradient waveform after a number of N repetitions, where N>2; and
imaging the object with the MRI system.
2. The method of claim 1 , wherein the repetition time (TR) is 8.0 ms.
3. The method of claim 1 , wherein providing a balanced steady state free precession pulse sequence comprises providing a plurality of phase encoding steps, wherein each phase encoding step comprises a slice selection gracient, a phase encoding gradient, and a readout gradient.
4. The method of claim 1 , wherein a flip angle is 40°.
5. The method of claim 4 , wherein 180° phase cycling occurs every TR.
6. The method of claim 1 , wherein N=4.
7. The method of claim 1 , wherein N=6.
8. The method of claim 1 , wherein imaging an object comprises CINE imaging.
9. The method of claim 8 , wherein the SSFP pulse sequence comprises a single-slice 2DFT pulse sequence.
10. The method of claim 8 , wherein the flip angle is about 50°.
11. The method of claim 1 , wherein a velocity-encoding value (VENC) is about 4.6 m/s.
12. The method of claim 1 , wherein imaging the object comprises transient imaging.
13. A MRI system for generating MRI images of an object, the MRI system comprising:
a static field generator configured to generate a static magnetic field B 0 ;
a gradient field generator configured to generate a time-varying gradient field G(r), parallel to B 0 ; and
an RF excitation pulse generator configured to generate an RF excitation field B 1 and apply the field B 1 to the object so that nuclear spins in the object flip at a flip angle; and
a balanced SSFP pulse sequence of RF and gradient pulses, wherein the SSFP pulse sequence includes two interleaved different gradient waveforms that are alternated after a number of N repetitions, where N>2; and
an image processing system configured and arranged to display images of the object.
14. The system of claim 13 , wherein the SSFP pulse sequence comprises a single-slice 2DFT pulse sequence.
15. The system of claim 13 , wherein the VENC is about 4.6 m/s.
16. The system of claim 13 , wherein N=6.
17. An MRI controller system for a magnetic resonance imaging (MRI) system, the system comprising:
a controller configured and arranged to (i) control an RF excitation pulse generator and gradient field generator to produce a balanced steady state free precession (SSFP) pulse sequence, (ii) interleave two different gradient waveforms of the SSFP pulse sequence, (iii) switch between a first of the two different gradient waveforms to the second gradient waveform after a number of N repetitions, where N >2, (iv) image an object with the MRI system.