System and method for simultaneous magnetic resonance elastography and water-fat imaging
Systems and methods for simultaneous water-fat magnetic resonance imaging (“MRI”) and magnetic resonance elastography (“MRE”) using an integrated data acquisition and reconstruction scheme are described. This integrated acquisition and reconstruction technique can mitigate motion misregistration and provide improved image SNR relative to existing multiparametric acquisition techniques that require multiple separate acquisitions.
1. A method for multiparametric magnetic resonance imaging (“MRI”) using an MRI system, the steps of the method comprising:
(a) acquiring motion-encoded data from a subject with the MRI system by sampling a plurality of different echo signals each formed at a different echo time in a single repetition time period, each echo signal being encoded for motion along at least one of a different motion-encoding direction or a different phase offset than the other echo signals by applying a different motion-encoding gradient before each echo signal is sampled;
(b) extracting motion-induced phase information from the acquired motion-encoded data;
(c) generating stiffness maps based on the extracted motion-induced phase information;
(d) producing phase-demodulated data by demodulating the motion-induced phase information from the acquired motion-encoded data; and
(e) generating from the phase-demodulated data, a water image that depicts water spins and a fat image that depicts fat spins.
2. The method as recited in claim 1 , wherein step (e) further includes generating a main magnetic field map from the phase-demodulated data.
3. The method as recited in claim 1 , wherein step (e) includes generating the water image and the fat image using a variable projection technique.
4. The method as recited in claim 1 , further comprising estimating auxiliary phase information resulting from concomitant field effects and demodulating the auxiliary phase information from the acquired motion-encoded data.
5. The method as recited in claim 4 , wherein the auxiliary phase information is demodulated from the acquired motion-encoded data before extracting the motion-induced phase information from the motion-encoded data.
6. The method as recited in claim 1 , wherein the motion-induced phase information is estimated in step (b) using a phase differencing technique.
7. The method as recited in claim 6 , wherein the phase differencing technique includes using graph cuts.
8. The method as recited in claim 6 , wherein the phase differencing technique includes using a region growing method.
9. The method as recited in claim 1 , wherein acquiring the motion-encoded data in step (a) includes each echo signal being encoded for motion along a same motion-encoding direction using a different phase offset for each echo signal.
10. The method as recited in claim 1 , wherein steps (c) and (e) can be performed simultaneously using a joint estimation of a displacement image and of a main magnetic field map.
11. The method as recited in claim 1 , wherein step (e) includes estimating a transverse relaxation parameter from the phase-demodulated data.
12. The method as recited in claim 11 , wherein the transverse relaxation parameter is an apparent transverse relaxation rate, and the apparent transverse relaxation rate.
13. The method as recited in claim 1 , wherein step (e) includes generating from the phase-demodulated data, at least one additional image that depicts spins associated with a chemical species.
14. The method as recited in claim 13 , wherein the chemical species is silicone.
15. The method as recited in claim 1 , wherein acquiring the motion-encoded data in step (a) includes sampling two different echo signals each formed at one of two different echo times in the single repetition time period.
16. The method as recited in claim 1 , wherein step (a) includes acquiring the motion-encoded data using at least three different motion-encoding phase offsets.