Enhanced spectral selectivity for steady-state free precession imaging
View Patent ↗A method of collecting image data with selective spectral suppression for at least two species is provided. A sequence of RF excitation pulses is repeatedly applied, whereby a repeated sequence of at least two substantially different spectrally selective steady-state magnetizations is established. Magnetic gradients are applied between said RF pulses. A plurality of magnetic resonance image (MRI) signals is acquired. The plurality of MRI signals is combined using a weighted combination where the weights depend on a control parameter that adjusts a trade-off between selective spectral suppression and signal-to-noise ratio (SNR).
1. A method of providing selective spectral suppression in steady-state free procession (SSFP) magnetic resonance imaging, comprising:
a) acquiring a plurality of SSFP images with different RF phase increments of an object to be imaged; and
b) combining the plurality of SSFP images using a weighted combination in which the weights depend on a control parameter that adjusts a trade-off between selective spectral suppression and signal-to-noise ratio (SNR).
2. The method, as recited in claim 1 , wherein the combining the plurality of SSFP images uses a weighted combination of complex-valued SSFP images in which the weighting is based on the SSFP images themselves and which a power of the weight is a function of the control parameter.
3. The method, as recited in claim 1 , wherein the combining of the plurality of SSFP images uses a weighting according to the equations
Y
1
=
D
0
-
0
p
D
0
-
0
+
i
D
0
-
180
p
D
0
-
180
1
1
+
p
Y
2
=
D
0
-
0
p
D
0
-
0
-
i
D
0
-
180
p
D
0
-
180
1
1
+
p
wherein Y 1 is an image for a first species and Y 2 is an image for a second species, D 0-0 is a data set of consecutive RF pulses that are all in phase and D 0-180 is a data set of consecutive RF pulses that are all out of phase and p is a real number in the range (−1, 0), where p is a control parameter.
4. The method, as recited in claim 3 , further comprising displaying the combined plurality of SSFP images.
5. The method, as recited in claim 4 , wherein the first species is water and the second species is fat.
6. The method, as recited in claim 5 , further comprising repeatedly applying a sequence of RF excitation pulses with a phase progression which provides an SSFP image in which a spectrally dependent steady-state magnetization is established.
7. The method, as recited in claim 6 , further comprising applying magnetic gradients between said RF excitation pulses.
8. The method, as recited in claim 1 , further comprising displaying the combined plurality of SSFP images.
9. The method, as recited in claim 8 , further comprising repeatedly applying a sequence of RF excitation pulses with a phase progression which provides an SSFP image in which a spectrally dependent steady-state magnetization is established.
10. The method, as recited in claim 9 , further comprising applying magnetic gradients between said RF excitation pulses.
11. The method, as recited in claim 1 , wherein the combining the plurality of SSFP images uses a weighted combination of complex-valued SSFP images in which the weighting is based on the SSFP images themselves and which a power of the weight is a function of the control parameter and further comprising displaying the combined plurality of SSFP images.
12. The method, as recited in claim 11 , further comprising repeatedly applying a sequence of RF excitation pulses with a phase progression, which provides an SSFP image in which a spectrally dependent steady-state magnetization is established.
13. The method, as recited in claim 12 , further comprising applying magnetic gradients between said RF excitation pulses.
14. A method, comprising:
a) repeatedly applying a sequence of RF excitation pulses with a phase progression, which provides an SSFP image in which a spectrally dependent steady-state magnetization is established;
b) applying magnetic gradients between said RF excitation pulses;
c) acquiring a plurality of suppression in steady-state free procession SSFP images with different RF phase increments of an object to be imaged; and
d) combining the plurality of SSFP images using a weighted combination using a weighting according to the equations
Y
1
=
D
0
-
0
p
D
0
-
0
+
i
D
0
-
180
p
D
0
-
180
1
1
+
p
Y
2
=
D
0
-
0
p
D
0
-
0
-
i
D
0
-
180
p
D
0
-
180
1
1
+
p
wherein Y 1 is an image for a first species and Y 2 is an image for a second species, D 0-0 data set based on consecutive RF pulses that are all in phase and D 0-180 is a data set based on consecutive RF pulses that are all out of phase and p is a real number in the range (−1, 0), where p is a control parameter;
e) displaying the combined plurality of SSFP images.
15. The method, as recited in claim 14 , wherein the first species is water and the second species is fat.
16. An apparatus, comprising:
a magnet system;
a controller electrically connected to the magnet system, comprising:
a display;
at least one processor; and
computer readable media, comprising:
computer readable code for acquiring a plurality of SSFP images with different RF phase increments of an object to be imaged; and
computer readable code for combining the plurality of SSFP images using a weighted combination in which the weights depend on a control parameter that adjusts a trade-off between selective spectral suppression and signal-to-noise ratio (SNR).
17. The apparatus, as recited in claim 16 , wherein the computer readable code for combining the plurality of SSFP images uses a weighted combination of complex-valued SSFP images in which the weighting is based on the SSFP images themselves and which a power of the weight is a function of the control parameter p.
18. The apparatus, as recited in claim 16 , wherein the computer readable code for combining of the plurality of SSFP images uses a weighting according to the equations
Y
1
=
D
0
-
0
p
D
0
-
0
+
i
D
0
-
180
p
D
0
-
180
1
1
+
p
Y
2
=
D
0
-
0
p
D
0
-
0
-
i
D
0
-
180
p
D
0
-
180
1
1
+
p
wherein Y 1 is an image for a first species and Y 2 is an image for a second species, D 0-0 is a data set of consecutive RF pulses that are all in phase and D 0-180 is a data set of consecutive RF pulses that are all out of phase and p is a real number in the range (−1, 0), where p is a control parameter.
19. The apparatus, as recited in claim 18 , further comprising computer readable code for displaying the combined plurality of SSFP images.