Frequency swept excitation for magnetic resonance
A method of magnetic resonance is provided that uses a frequency swept excitation wherein the acquired signal is a time domain signal is provided. In one embodiment, the method comprises, applying a sweeping frequency excitation and acquiring a time domain signal. The sweeping frequency excitation has a duration and is configured to sequentially excite isochromats having different resonant frequencies. Acquisition of the time domain signal is done during the duration of the sweeping frequency excitation. The time domain signal is based on evolution of the isochromats.
1. A method comprising:
using a magnetic resonance scanner to excite a specimen with a sweeping frequency excitation having a plurality of alternating excitation segments and quiescent segments, the excitation segments modulated according to at least one of a phase modulation function and a frequency modulation function;
applying at least one functional pulse;
acquiring a time domain signal from the specimen based on resonance during a plurality of the quiescent segments; and
processing the acquired time domain signal.
2. The method of claim 1 , wherein the at least one functional pulse is applied before exciting a specimen with a sweeping frequency excitation.
3. The method of claim 1 , wherein effects of the functional pulse are localized in one or more spatial dimensions in the presence of a field gradient.
4. The method of claim 1 , wherein the at least one functional pulse is applied after exciting a specimen with a sweeping frequency excitation.
5. The method of claim 1 , wherein the at least one functional pulse establishes a steady or oscillating spatial magnetization state.
6. The method of claim 1 , further comprising applying a gradient during the at least one functional pulse.
7. The method of claim 6 , wherein a subset of gradients is used during the at least one functional pulse.
8. The method of claim 1 , wherein the at least one functional pulse prepares magnetization.
9. The method of claim 1 , wherein the at least one functional pulse spoils magnetization.
10. The method of claim 1 , wherein the at least one functional pulse restores magnetization.
11. The method of claim 1 , wherein the at least one functional pulse suppresses or enhances magnetization based on T2, T1, T1ρ, T2ρ, or diffusion.
12. The method of claim 1 , wherein processing comprises performing conjugate multiplication of a Fourier transform of the time domain signal and a Fourier transform of the frequency excitation.
13. The method of claim 12 , wherein at least one of the Fourier transformed signal and Fourier transformed excitation are windowed or filtered before processing and wherein processing comprises conjugate multiplication.
14. The method of claim 1 , further comprising applying a field gradient to create an image.
15. The method of claim 14 , further comprising reconstructing the image based on the time domain signal.
16. The method of claim 15 , further comprising adjusting the time domain signal with a constant, linearly, quadratic, or higher order phase correction prior to reconstructing the image.
17. The method of claim 15 , further comprising deleting pulse contamination during reconstruction.
18. The method of claim 1 , wherein the acquired time domain signal has a poor quality segment and or edges, and further comprising eliminating the poor quality segment or edges before correlation or deconvolution.
19. The method of claim 1 , wherein processing the acquired time domain signal comprises applying a phase consistency algorithm.
20. The method of claim 1 , wherein processing the acquired time domain signal comprises processing complex phased projections.
21. The method of claim 1 , wherein processing the acquired time domain signal comprises processing real phased projections.
22. The method of claim 1 , wherein processing the acquired time domain signal comprises applying a cone beam resampling algorithm to correct between expected angles of projections and actual projections by estimating new projections from different measured projections.
23. The method of claim 1 , wherein the sweeping frequency excitation is located in a radiofrequency spectrum.
24. The method in claim 1 , wherein the sweeping frequency excitation is in an optical spectrum.