Reducing dead-time effect in MRI projection

1. A method for collecting data representative of a magnetic resonance image of a region-of-interest, the method comprising:

applying a first gradient field to the region-of-interest, the first gradient field having a first gradient;

while the first gradient field is applied, collecting, from the region-of-interest, a first data set having first time samples of a first free-induction decay stimulated by a first RF excitation pulse, the first time samples being separated from each other by a first time-sampling interval;

applying a second gradient field to the region-of-interest, the second gradient field having a second gradient differing from the first gradient; and

while the second gradient field is applied, collecting, from the region of interest, a second data set the second data set having second time samples of a second free-induction decay stimulated by a second RF excitation pulse, the second time samples being separated from each other by a second time-sampling interval.

2. The method of claim 1 , further comprising selecting at least one of the first and second time-sampling intervals on the basis of the ratio between the first and second gradients.

3. The method of claim 1 , further comprising selecting the first and second time-sampling intervals such that

first k-space samples corresponding to the first time samples and

second k-space samples corresponding to the second time samples are separated in k-space by the same selected k-space-sampling interval.

4. The method of claim 3 , further comprising beginning the collection of the second data set at a time selected such that

a k-space sample associated with a last time sample from the first data set and

a k-space sample associated with a first time sample from the second data set are separated in k-space by the selected k-space-sampling interval.

5. The method of claim 3 , further comprising selecting the first and second time-sampling intervals such that the k-space samples are located at integer multiples of the k-space sampling interval.

6. A magnetic resonance imaging system configured to execute the method recited in claim 1 .

7. A method for reducing data loss resulting from dead time in a magnetic resonance imaging system, the method comprising:

applying a first gradient field to a region-of-interest, the first gradient field having a first gradient;

applying a first radio frequency pulse to the region-of-interest, thereby stimulating a first free-induction decay;

after a dead time following application of the first radio frequency pulse, collecting a first set of time samples of the first free-induction decay from the region-of-interest;

applying a second gradient field to the region-of-interest, the second gradient field having a second gradient different from the first gradient;

applying a second radio frequency pulse to the region-of-interest, thereby stimulating a second free-induction decay; and

after a dead time following application of the second radio frequency pulse, collecting a second set of time samples of the second free-induction decay from the region-of-interest.

8. The method of claim 7 , wherein

collecting a first set of time samples comprises selecting a first time sampling interval between time samples, and

collecting a second set of time samples comprises selecting a second time sampling interval between time samples,

wherein at least one of the first and second time sampling intervals is selected on the basis of a ratio between the first and second gradients.

9. The method of claim 8 , wherein

collecting a first set of time samples comprises selecting a first time sampling interval between time samples, and

collecting a second set of time samples comprises selecting a second time sampling interval between time samples,

wherein at least one of the first and second time sampling intervals is selected such that

first k-space samples corresponding to the first time samples, and

second k-space samples corresponding to the second time samples are separated in k-space by the same selected k-space-sampling interval.

10. The method of claim 9 , further comprising beginning the collection of the second set of time samples at a time selected such that

a k-space sample associated with a last time sample from the first set of time samples, and

a k-space sample associated with a first time sample from the second set of time samples are separated in k-space by the selected k-space-sampling interval.

11. The method of claim 10 , further comprising selecting the first and second time sampling intervals such that the k-space samples are located at integer multiples of the selected k-space sampling interval.

12. A magnetic resonance imaging system configured to execute the method recited in claim 7 .

13. In a magnetic resonance imaging machine, a method of populating k-space with samples, the method comprising:

applying a first magnetic field to a region-of-interest;

collecting a first set of time samples of a first free-induction decay signal from the region-of-interest;

populating a first subset of k-space on the basis of the first set of time samples; and

applying a second magnetic field to the region-of-interest, the second magnetic field being different from the first magnetic field;

collecting a second set of time samples of a second free-induction decay signal from the region-of-interest; and

populating a second subset of k-space on the basis of the second set of time samples, the second subset including a portion of k-space excluded from the first subset.

14. The method of claim 13 , wherein applying a first magnetic field comprises applying a gradient field having a first gradient, and applying a second magnetic field comprises applying a gradient field having a second gradient that differs from the first gradient.

15. The method of claim 13 wherein collecting a first set of time samples comprises collecting time samples separated by a first time-sampling interval and collecting a second set of time samples comprises collecting time samples separated by a second time-sampling interval, wherein the first and second time-sampling intervals are selected on the basis of the first and second magnetic fields.

16. The method of claim 15 further comprising selecting the first and second time-sampling intervals to uniformly populate the k-space.

17. The method of claim 16 , further comprising selecting the first and second time-sampling intervals to generate k-space samples located at integer multiples of a k-space sampling interval.

18. A magnetic resonance imaging system configured to execute the method recited in claim 13 .

19. A computer-readable medium having encoded thereon software for collecting data representative of a magnetic resonance image of a region-of-interest, the software comprising instructions for causing a magnetic resonance imaging system to:

apply a first gradient field to the region-of-interest, the first gradient field having a first gradient;

while the first gradient field is applied, collect, from the region-of-interest, a first data set having first time samples of a first free-induction decay stimulated by a first RF excitation pulse, the first time samples being separated from each other by a first time-sampling interval;

apply a second gradient field to the region-of-interest, the second gradient field having a second gradient differing from the first gradient; and

while the second gradient field is applied, collect, from the region-of-interest, a second data set, the second data set having second time samples of a second free-induction decay stimulated by a second RF excitation pulse, the second time samples being separated from each other by a second time-sampling interval.

20. The computer-readable medium of claim 19 , wherein the software further comprises instructions for causing the magnetic resonance imaging system to select at least one of the first and second time-sampling intervals on the basis of the ratio between the first and second gradients.

21. The computer-readable medium of claim 19 , wherein the software further comprises instructions for causing the magnetic resonance imaging system to select the first and second time-sampling intervals such that

first k-space samples corresponding to the first time samples, and

second k-space samples corresponding to the second time samples are separated in k-space by the same selected k-space-sampling interval.

22. The computer-readable medium of claim 21 , wherein the software further comprises instructions for causing the magnetic resonance imaging system to begin the collection of the second data set at a time selected such that

a k-space sample associated with a last time sample from the first data set and

a k-space sample associated with a first time sample from the second data set are separated in k-space by the selected k-space-sampling interval.

23. The computer-readable medium of claim 21 , wherein the software further comprises instructions for causing the magnetic resonance imaging system to select the first and second time-sampling intervals such that the k-space samples are located at integer multiples of the k-space sampling interval.

24. A magnetic resonance imaging system comprising a computer-readable medium as recited in claim 19 .

25. A computer-readable medium having encoded thereon software for reducing data loss resulting from dead time in a magnetic resonance imaging system, the software comprising instructions for causing a magnetic resonance imaging system to:

apply a first gradient field to a region-of-interest, the first gradient field having a first gradient;

apply a first radio frequency pulse to the region-of-interest, thereby stimulating a first free-induction decay;

after a dead time following application of the first radio frequency pulse, collect a first set of time samples of the first free-induction decay from the region-of-interest;

apply a second gradient field to the region-of-interest, the second gradient field having a second gradient different from the first gradient;

apply a second radio frequency pulse to the region-of-interest, thereby stimulating a second free-induction decay; and

after a dead time following application of the second radio frequency pulse, collect a second set of time samples of the second free-induction decay from the region-of-interest.

26. The computer-readable medium of claim 25 , wherein

the instructions for causing the magnetic resonance imaging system to collect a first set of time samples comprise instructions for causing the magnetic resonance imaging system to select a first time sampling interval between time samples, and

the instructions for causing the magnetic resonance imaging system to collect a second set of time samples comprise instructions for causing the magnetic resonance imaging system to select a second time sampling interval between time samples,

wherein at least one of the first and second time sampling intervals is selected on the basis of a ratio between the first and second gradients.

27. The computer-readable medium of claim 26 , wherein

the instructions for causing the magnetic resonance imaging system to collect a first set of time samples comprise instructions for causing the magnetic resonance imaging system to select a first time sampling interval between time samples, and

the instructions for causing the magnetic resonance imaging system to collect a second set of time samples comprise instructions for causing the magnetic resonance imaging system to select a second time sampling interval between time samples,

wherein at least one of the first and second time sampling intervals is selected such that

first k-space samples corresponding to the first time samples, and

second k-space samples corresponding to the second time samples are separated in k-space by the same selected k-space-sampling interval.

28. The computer-readable medium of claim 27 , wherein the software further comprises instructions for causing the magnetic resonance imaging system to begin the collection of the second set of time samples at a time selected such that

a k-space sample associated with a last time sample from the first set of time samples, and

a k-space sample associated with a first time sample from the second set of time samples are separated in k-space by the selected k-space-sampling interval.

29. The computer-readable medium of claim 28 , wherein the software further comprises instructions for causing the magnetic resonance imaging system to select the first and second time sampling intervals such that the k-space samples are located at integer multiples of the selected k-space sampling interval.

30. A magnetic resonance imaging system comprising a computer-readable medium as recited in claim 25 .

31. A computer-readable medium having encoded thereon instructions for causing a magnetic resonance imaging system to populate k-space with samples, the software comprising instructions for causing the magnetic resonance imaging system to:

apply a first magnetic field to a region-of-interest;

collect a first set of time samples of a first free-induction decay signal from the region-of-interest;

populate a first subset of k-space on the basis of the first set of time samples; and

apply a second magnetic field to the region-of-interest, the second magnetic field being different from the first magnetic field;

collect a second set of time samples of a second free-induction decay signal from the region-of-interest; and

populate a second subset of k-space on the basis of the second set of time samples, the second subset including a portion of k-space excluded from the first subset.

32. The computer-readable medium of claim 31 , wherein

the instructions for causing the magnetic resonance imaging system to apply a first magnetic field comprise instructions for causing the magnetic resonance imaging system to apply a gradient field having a first gradient, and

the instructions for causing the magnetic resonance imaging system to apply a second magnetic field comprise instructions for causing the magnetic resonance imaging system to apply a gradient field having a second gradient that differs from the first gradient.

33. The computer-readable medium of claim 31 , wherein

the instructions for causing the magnetic resonance imaging system to collect a first set of time samples comprise instructions for causing the magnetic resonance imaging system to collect time samples separated by a first time-sampling interval, and

the instructions for causing the magnetic resonance imaging system to collect a second set of time samples comprise instructions for causing the magnetic resonance imaging system to collect time samples separated by a second time-sampling interval,

wherein the first and second time-sampling intervals are selected on the basis of the first and second magnetic fields.

34. The computer-readable medium of claim 33 wherein the software further comprises instructions for causing the magnetic resonance imaging system to select the first and second time-sampling intervals to uniformly populate the k-space.

35. The computer-readable medium of claim 34 , wherein the software further comprises instructions for causing the magnetic resonance imaging system to select the first and second time-sampling intervals to generate k-space samples located at integer multiples of a k-space sampling interval.

36. A magnetic resonance imaging system comprising a computer-readable medium as recited in claim 31 .