Magnetic resonance imaging concepts
A method for producing multiple temporal frames of a time-resolved contrast enhanced magnetic resonance angiogram from a subject using an MR contrast agent by repeatedly applying RF pulses and sampling data in the corresponding image k-space along spiral trajectories that start at the k-space center and spiral outward toward the k-space edge.
1. A method for producing a time-resolved, three-dimensional contrast enhanced magnetic resonance image, the method comprising:
enhancing contrast in a tissue;
applying a first radio frequency (RF) pulse over a scan time;
sampling a first plurality of resonance data along a first spiral trajectory in a corresponding image spatial frequency domain defined by a plurality of parallel planes, each parallel plane including at least one group of interleaves, the first spiral trajectory corresponding to a first of the plurality of parallel planes and within the group of interleaves, the first spiral trajectory originating at a first center in the first of the plurality of parallel planes and spiraling outward towards a first edge in the first of the plurality of parallel planes;
applying a second RF pulse over a scan time;
sampling a second plurality of resonance data along a second spiral trajectory in the corresponding image spatial frequency domain, the second spiral trajectory corresponding to a second of the plurality of parallel planes, the second spiral trajectory originating at a second center in the second of the plurality of parallel planes within the group of interleaves and spiraling outward towards a second edge in the second of the plurality of parallel planes; and
reconstructing the magnetic resonance image using at least the first plurality of resonance data and the second plurality of resonance data, with a frame reconstructed for each group of interleaves wherein for n groups of interleaves the frame time is 1/n th of the scan time; and
wherein:
the first spiral trajectory has a first sampling density at the first center and a second sampling density at the first edge that is less than the first sampling density;
the first spiral trajectory radius increases linearly with respect to azimuthal angle at the first center;
the second spiral trajectory has a third sampling density at the second center and a fourth sampling density at the second edge that is less than the third sampling density; and
wherein the first sampling density and the third sampling density are each a constant sampling density over a predetermined plurality of spatial frequencies,
the first sampling density decreases non-linearly to the second sampling density.
2. The method of claim 1 , wherein the first sampling density and the third sampling density are the same.
3. The method of claim 2 , wherein the second sampling density and the fourth sampling density are the same.
4. The method of claim 3 , wherein the second sampling density and the fourth sampling density are undersampled.
5. The method of claim 4 , wherein the second sampling density and the fourth sampling density are undersampled by 30%.
6. The method of claim 2 , wherein the first sampling density and the third sampling density are oversampled.
7. The method of claim 6 , wherein the first sampling density and the third sampling density are oversampled by 30%.
8. The method of claim 1 , wherein the group of n interleaves includes 4 interleaves, and the frame time is ¼ th of the scan time.
9. A method for producing a time-resolved, three-dimensional contrast enhanced magnetic resonance image, the method comprising:
enhancing contrast in a tissue;
applying a first radio frequency (RF) pulse over a scan time;
sampling a first plurality of resonance data along a first spiral trajectory in a corresponding image spatial frequency domain defined by a plurality of parallel planes, each parallel plane including at least one group of interleaves, the first spiral trajectory corresponding to a first of the plurality of parallel planes and within the group of interleaves, the first spiral trajectory originating at a first center in the first of the plurality of parallel planes and spiraling outward towards a first edge in the first of the plurality of parallel planes;
applying a second RF pulse over a scan time;
sampling a second plurality of resonance data along a second spiral trajectory in the corresponding image spatial frequency domain, the second spiral trajectory corresponding to a second of the plurality of parallel planes, the second spiral trajectory originating at a second center in the second of the plurality of parallel planes within the group of interleaves and spiraling outward towards a second edge in the second of the plurality of parallel planes; and
reconstructing the magnetic resonance image using at least the first plurality of resonance data and the second plurality of resonance data, with a frame reconstructed for each group of interleaves wherein for n groups of interleaves the frame time is 1/n th of the scan time; and
wherein:
the first spiral trajectory has a first sampling density at the first center and a second sampling density at the first edge that is less than the first sampling density;
the first spiral trajectory radius increases linearly with respect to azimuthal angle at the first center;
the second spiral trajectory has a third sampling density at the second center and a fourth sampling density at the second edge that is less than the third sampling density; and
wherein the first sampling density and the third sampling density are each a constant sampling density over a predetermined plurality of spatial frequencies,
the third sampling density decreases non-linearly to the fourth sampling density.
10. The method of claim 9 , wherein the first sampling density and the third sampling density are the same.
11. The method of claim 10 , wherein the second sampling density and the fourth sampling density are the same.
12. The method of claim 11 , wherein the second sampling density and the fourth sampling density are undersampled.
13. The method of claim 12 , wherein the second sampling density and the fourth sampling density are undersampled by 30%.
14. The method of claim 10 , wherein the first sampling density and the third sampling density are oversampled.
15. The method of claim 14 , wherein the first sampling density and the third sampling density are oversampled by 30%.
16. The method of claim 9 , wherein the group of n interleaves includes 4 interleaves, and the frame time is ¼ th of the scan time.