Method for magnetic resonance imaging
A method of magnetic resonance imaging based on rapid acquisition by sequential excitation and refocusing is provided. The method comprises turning on a first time-encoding gradient and applying an excitation pulse in the presence of the first time-encoding gradient. The excitation pulse excites magnetization sequentially along one spatial axis. Thereafter, a first refocusing pulse is applied. A second time-encoding gradient is turned on followed by a second refocusing pulse. A third time-encoding gradient is turned on and a signal is acquired in the presence of the third time-encoding gradient. The third time-encoding gradient sums to zero with the first time-encoding gradient and the second time-encoding gradient for sequential points in space.
1. A method of magnetic resonance imaging comprising:
applying a substantially static magnetic field to an object;
applying an excitation pulse to the object;
applying an acquisition gradient in a time-encoding direction during an acquisition window;
applying on an alternating frequency-encoding gradient in a frequency-encoding direction, the frequency-encoding direction different from the acquisition gradient;
acquiring a signal in the presence of the acquisition gradient and the alternating gradient, the signal being time-encoded, frequency-encoded, and being substantially contiguous; and
using the signal, and at least one processor, to create an image having at least two dimensions of the object.
2. The method of claim 1 , further comprising applying a selection gradient and wherein the excitation pulse is applied in the presence of the selection gradient.
3. The method of claim 2 , further comprising applying a first refocusing pulse, applying a refocusing gradient, and applying a second refocusing pulse.
4. The method of claim 3 , wherein the excitation pulse excites isochromats to precess in a transverse plane, wherein the excitation gradient causes each isochromat to experience a different amount of dephasing, and wherein the first and second refocusing pulses and the acquisition gradient rephase the isochromats sequentially.
5. The method of claim 3 , wherein the acquisition gradient sums to zero with the selection gradient and the refocusing gradient.
6. The method of claim 5 , further comprising applying a phase-encoding gradient after applying the excitation pulse and before applying the first refocusing pulse, wherein a plurality of slices are acquired.
7. The method of claim 6 , wherein the slices are overlapped.
8. The method of claim 6 , wherein the slices are spaced.
9. The method of claim 6 , wherein the time-encoding direction of the acquisition gradient is through-plane.
10. The method of claim 6 , wherein the phase-encoding gradient has a phase-encoding direction and further wherein using the signal includes performing a first Fourier transform in the frequency-encoding direction and performing a second Fourier transform in the phase-encoding direction.
11. The method of claim 5 , further comprising applying a first slice selection gradient approximately concurrently with the first refocusing pulse and applying a second slice selection gradient approximately concurrently with the second refocusing pulse.
12. The method of claim 11 , wherein the time-encoding direction of the acquisition gradient is through-plane.
13. The method of claim 5 , wherein the acquisition gradient is blipped.
14. The method of claim 5 , wherein the acquisition gradient is continuous.
15. The method of claim 3 , wherein applying the first refocusing pulse and applying the second refocusing pulse includes applying two 180 degree pulses.
16. The method of 1 , wherein the excitation pulse has varied frequency.
17. The method of claim 1 , wherein the excitation pulse has varied gradient.
18. The method of claim 1 , wherein the excitation pulse includes a chirp pulse.
19. The method of claim 1 , wherein the excitation pulse includes a hyperbolic secant pulse.
20. The method of claim 1 , wherein applying the excitation pulse includes applying a 90 degree pulse.
21. The method of claim 1 , wherein using the signal includes performing a Fourier transform.
22. The method of claim 1 , wherein using the signal includes performing a Fourier transform in the frequency-encoding direction.
23. A method of magnetic resonance imaging comprising:
applying a substantially static magnetic field to an object;
applying excitation to the object;
applying a time-encoding acquisition gradient in a time encoding direction and corresponding to the excitation;
applying an alternating frequency-encoding gradient in a direction different than the time encoding direction and corresponding to the excitation;
acquiring a signal encoded in time using the time-encoding acquisition gradient and encoded in frequency using the alternating frequency-encoding gradient; and
generating, using at least one processor, an image of the object using the signal.
24. The method of claim 23 wherein applying excitation includes applying a 90° frequency-swept pulse.
25. The method of claim 23 wherein applying excitation includes applying a frequency-swept pulse.
26. The method of claim 25 wherein applying the frequency-swept pulse includes applying an adiabatic pulse.
27. The method of claim 26 wherein applying the adiabatic pulse includes applying at least one of a hyperbolic secant pulse and a chirp pulse.
28. The method of claim 23 wherein applying excitation includes sequentially applying an excitation pulse and applying a refocusing pulse.
29. The method of claim 28 wherein applying the refocusing pulse includes applying a 180° pulse.
30. The method of claim 23 wherein applying excitation includes applying spiral excitation.
31. The method of claim 23 wherein applying excitation includes applying an excitation pulse having a constant frequency and a modulated gradient.
32. The method of claim 23 wherein generating the image includes generating a 3D image.
33. The method of claim 23 wherein generating the image includes calculating a Fourier transform using the signal.