Optimized spectral-spatial pulse

1. A computer implemented method for designing a spectral-spatial pulse for exciting at least one passband and minimally exciting at least one stopband for execution on a MRI system having a magnet system and a controller for controlling the magnet system and generating a desired pulse sequence, comprising:

a) generating in the controller a uniform shaped spectral envelope; and

b) generating in the controller for a plurality of k z ≠0, k z dependent weights for a spectral envelope that approximate a k z =0 envelope and provide the at least one passband and the at least one stopband for each of the plurality of k z ≠0;

c) generating through the magnetic system a spectral-spatial excitation pulse with the uniform shaped envelope and the plurality of k z dependent weights.

2. The computer implemented method, as recited in claim 1 , wherein the generating k z dependent weights for a spectral envelope further provides skew correction.

3. The computer implemented method, as recited in claim 2 , wherein the at least one passband and one stopband provide a selective excitation of a first species while suppressing a second species.

4. The computer implemented method, as recited in claim 3 , wherein the first species is water and the second species is fat.

5. The computer implemented method, as recited in claim 4 , wherein the spectral-spatial pulse has a zig-zag trajectory through excitation k-space.

6. The computer implemented method, as recited in claim 5 , wherein the generating for a plurality of k z ≠0, k z dependent weights comprises applying a weighted least squares formulation to solve for non-uniformly spaced r values with a Fourier transform that most closely matches a desired frequency response H according to an equation r=(A † WA) −1 A † WH, where A is a Fourier matrix modified to include sample delays and W is a diagonal matrix of weights and H is a column vector containing a desired frequency response defined by the at least one passband and one stopband.

7. The computer implemented method, as recited in claim 1 , wherein the generating for a plurality of k z ≠0, k z dependent weights comprises applying a weighted least squares formulation to solve for non-uniformly spaced r values with a Fourier transform that most closely matches a desired frequency response H according to an equation r=(A † WA) −1 A † WH, where A is a Fourier matrix modified to include sample delays and W is a diagonal matrix of weights and H is a column vector containing a desired frequency response defined by the at least one passband and one stopband.

8. A magnetic resonance imaging (MRI) method for selectively imaging a first species and suppressing a second species in a MRI system having a magnet system and a controller for controlling the magnet system, comprising:

a) generating in the controller a uniform shaped spectral envelope; and

b) generating in the controller for a dependent weights for a spectral envelope that approximate a k z =0 envelope and provide the at least one passband and the at least one stopband for each of the plurality of k Z ≠0;

c) providing a spectral-spatial excitation pulse with the weighted k z dependent spectral envelope for selectively exciting the first species and suppressing the second species through the magnet system;

d) acquiring a readout signal through the magnet system; and

e) generating an image from the readout signal through the controller.

9. The method, as recited in claim 8 , further comprising displaying the image from the readout signal through the controller.

10. The method, as recited in claim 9 , wherein the providing a spectral-spatial excitation pulse with a weighted k z dependent spectral envelope, provides an excitation at a k z ≠0, wherein weighting is provided to the spectral envelope to approximate a k z =0 envelope.

11. The method, as recited in claim 10 , wherein subpulses are weighted to provide the spectral-spatial excitation pulse with a weighted k z dependent spectral envelope.

12. The method, as recited in claim 11 , wherein the first species is water and the second species is fat.

13. The method, as recited in claim 8 , wherein the generating for a plurality of k z ≠0, k z dependent weights comprises applying a weighted least squares formulation to solve for non-uniformly spaced r values with a Fourier transform that most closely matches a desired frequency response H according to an equation r=(A † WA) −1 A † WH, where A is a Fourier matrix modified to include sample delays and W is a diagonal matrix of weights and H is a column vector containing a desired frequency response defined by the at least one passband and one stopband.

14. A magnetic resonance imaging (MRI) method for selectively imaging a first species and suppressing a second species in a MRI system having a magnet system and a controller for controlling the magnet system, comprising:

a) providing spectral-spatial excitation pulse with a weighted k z dependent spectral envelope for selectively exciting the first species and suppressing the second species through the magnet system, wherein the providing the spectral-spatial excitation provides a skew correction;

b) acquiring a readout signal through the magnet system; and

c) generating an image from the readout signal through the controller.

15. The method, as recited in claim 14 , wherein the acquiring the readout uses an echo planar-readout trajectory.

16. The method, as recited in claim 15 wherein the providing spectral-spatial excitation provides a zig-zag trajectory through excitation k-space.

17. The method, as recited in claim 16 , wherein the generating for a plurality of k z ≠0, k z dependent weights comprises applying a weighted least squares formulation to solve for non-uniformly spaced r values with a Fourier transform that most closely matches a desired frequency response H according to an equation r=(A † WA) −1 A † WH, where A is a Fourier matrix modified to include sample delays and W is a diagonal matrix of weights and H is a column vector containing a desired frequency response defined by the at least one passband and one stopband.

18. An apparatus for providing magnetic resonance imaging by selectively exciting a first species and suppressing a second species, comprising:

a magnetic resonance imaging excitation and detection system; and

a controller electrically connected to the magnetic resonance imaging excitation and detection system, comprising:

a display;

at least one processor; and

computer readable media, comprising:

computer readable code for providing a spectral-spatial excitation pulse with a weighted k z dependent spectral envelope for selectively exciting the first species and suppressing the second species, wherein the providing the spectral-spatial excitation provides a skew correction;

computer readable code for acquiring a readout signal;

computer readable code for generating an image from the readout signal; and

computer readable code for displaying the image from the readout signal on the display.

19. An apparatus, as recited in claim 18 , wherein the computer readable media further comprises:

computer readable code for generating a uniform shaped spectral envelope; and

computer readable code for generating for a plurality of k z ≠0, k z dependent weights for a spectral envelope that approximate a k z =0 envelope and provide the at least one passband and the at least one stopband for each of the plurality of k z ≠0.