Optimised pulse sequences for evaluating spatial frequency content of a selectively excited internal volume
In a structural analysis using NMR techniques, a method for gathering k-value data from frequency encoded spin echoes generated from internal volumes selectively excited by intersecting 90° and 180° slice selective and refocusing RF pulses and subjected to a read gradient for the purpose of quantifying the spatial frequency content of the selected internal volume without contamination by a FID signal, comprising: acquiring spin echo data such that the FID signal generated by imperfections in the 180° slice selective refocusing RF pulse is attenuated by the read gradient such that any remaining FID signal is spatially encoded with higher k-values than the frequency encoded k-values being recorded for subsequent structural analysis while simultaneously providing for t2 t2* and t1 contrast. Other aspects of the invention are disclosed.
1. In a structural analysis using NMR techniques, a method for gathering k-value data from frequency encoded spin echoes generated from internal volumes selectively excited by intersecting 90° and 180° slice selective and refocusing RF pulses and subjected to a read gradient for the purpose of quantifying the spatial frequency content of the selected internal volume without contamination by a FID signal, comprising: acquiring spin echo data such that the FID signal generated by imperfections in the 180° slice selective refocusing RF pulse is attenuated by the read gradient such that any remaining FID signal is spatially encoded with higher k-values than the frequency encoded k-values being recorded for subsequent structural analysis while simultaneously providing for t2 t2* and t1 contrast.
2. The method of claim 1 wherein the frequency encoded spin echoes are Fourier symmetric spin echoes with T1 contrast further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
3. The method of claim 2 wherein the Fourier symmetric spin echoes are refocused using a refocusing gradient and further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max in the gradient refocused echo, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
4. The method of claim 2 wherein the Fourier symmetric spin echoes are refocused using a 180° slice selective and refocusing RF pulse and further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max in the echo generated, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
5. The method of claim 1 wherein the frequency encoded spin echoes are partial Fourier symmetric spin echoes with T 1 contrast further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 and further permitting shortening the spin echo time by as much as two times the time difference between a leading portion of a full Fourier symmetric echo acquisition and a leading portion of the partial Fourier echo acquisition.
6. The method of claim 5 wherein the partial Fourier symmetric spin echoes are refocused using a refocusing gradient and further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max in the gradient refocused echo, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
7. The method of claim 5 wherein the partial Fourier symmetric spin echoes are refocused using a 180° slice selective and refocusing RF pulse and further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max in the echo generated, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
8. The method of claim 1 wherein the frequency encoded spin echoes are Fourier symmetric spin echoes with T 2 contrast further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
9. The method of claim 8 wherein the Fourier symmetric spin echoes are refocused using a refocusing gradient and further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max in the gradient refocused echo, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
10. The method of claim 8 wherein the Fourier symmetric spin echoes are refocused using a 180° slice selective and refocusing RF pulse and further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max in the echo generated, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
11. The method of claim 1 wherein the frequency encoded spin echoes are Fourier asymmetric spin echoes with T 2 * contrast further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
12. The method of claim 11 wherein the Fourier asymmetric spin echoes are refocused using a refocusing gradient and further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max in the gradient refocused echo, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
13. The method of claim 11 wherein the Fourier asymmetric spin echoes are refocused using a 180° slice selective and refocusing RF pulse and further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max in the echo generated, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
14. The method of claim 1 wherein the frequency encoded spin echoes are partial Fourier asymmetric spin echoes with T 2 * contrast further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 and further permitting shortening the spin echo time by as much as two times the time difference between a leading portion of a full Fourier symmetric echo acquisition and a leading portion of the partial Fourier echo acquisition.
15. The method of claim 14 wherein the partial Fourier asymmetric spin echoes are refocused using a refocusing gradient and further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max in the gradient refocused echo, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .
16. The method of claim 14 wherein the partial Fourier asymmetric spin echoes are refocused using a 180° slice selective and refocusing RF pulse and further comprising gathering k-value data for subsequent structural analysis of a portion of the k-value data acquired from k 0 to k-max in the echo generated, thereby avoiding the potentially FID contaminated portion of the spin echo prior to k 0 .