Driven equilibrium and fast-spin echo scanning
An NMR imaging process includes subjecting an imaging object to a uniform polarizing magnetic field. Orthogonal magnetic field gradients are applied to the imaging object. RF energy is applied to the imaging object. The RF energy includes a plurality of angular precession frequencies simultaneously applied to correspond to a respective plurality of selected slices of the imaging object. A corresponding plurality of nuclear magnetic resonance signals emitted by the imaging object are simultaneously detected. The nuclear magnetic resonance signals are processed to provide diagnostic information related to individual ones of the plurality of selected slices. In this way, multiple slices are excited and sampled simultaneously. The RF energy can be applied by applying RF energy to the imaging object according to a fast-spin echo technique and subsequently applying RF energy to the imaging object according to a driven equilibrium technique.
1. An NMR imaging process, comprising:
subjecting an imaging object to a uniform polarizing magnetic field;
applying orthogonal magnetic field gradients to the imaging object;
applying RF energy to the imaging object such that the RF energy includes a plurality of angular precession frequencies simultaneously applied to correspond to a respective plurality of selected slices of the imaging object;
simultaneously detecting a corresponding plurality of nuclear magnetic resonance signals emitted by the imaging object; and
processing the nuclear magnetic resonance signals to provide diagnostic information related to individual ones of the plurality of selected slices.
2. The process of claim 1 , wherein detecting the corresponding plurality of nuclear magnetic resonance signals emitted by the imaging object includes sampling the plurality of nuclear magnetic resonance signals simultaneously.
3. The process of claim 2 , further comprising separating the diagnostic information corresponding to the individual ones of the plurality of selected slices.
4. The process of claim 3 , wherein detecting a corresponding plurality of nuclear magnetic resonance signals emitted by the imaging object includes applying a number of phase-encoding gradient steps proportional to the degree of resolution of desired imaging information.
5. The process of claim 4 , wherein separating the diagnostic information includes using RF phase cycling.
6. The process of claim 5 , wherein the RF phase cycling includes stepping the phase of each said individual one of the plurality of selected slices during RF excitation.
7. The process of claim 6 , wherein the phase of each said individual one of the plurality of selected slices is stepped according to RF phase=(2s−1) πl/n, wherein s is the slice number, n is the total number of selected slices, and l is a phase-encoding level number.
8. The process of claim 1 , wherein applying RF energy to the imaging object includes:
applying RF energy to the imaging object according to a fast-spin echo technique;
subsequently applying RF energy to the imaging object according to a driven equilibrium technique.
9. The process of claim 8 , wherein the fast-spin echo technique includes application of a multi-echo NMR imaging sequence.
10. The process of claim 9 , wherein the multi-echo NMR imaging sequence includes a plurality of different echoes, and wherein each of the plurality of different echoes is encoded differently.
11. The process of claim 9 , wherein the multi-echo NMR imaging sequence includes a plurality of different echoes, and wherein at least one of the plurality of different echoes is encoded differently than another one of the plurality of different echoes.
12. The process of claim 9 , further comprising applying a 90-degree RF pulse at the center of any of the plurality of different echoes.
13. The process of claim 12 , wherein the applied 90-degree RF pulse has a phase such that magnetization of the imaging object is forced in the direction of the uniform polarizing magnetic field.
14. The process of claim 9 , wherein the multi-echo NMR imaging sequence includes a first 90-degree RF pulse followed by a series of 180-degree RF pulses.
15. The process of claim 14 , wherein the series of 180-degree RF pulses includes m 180-degree pulses, which are followed by m echoes.
16. The process of claim 15 , further comprising applying a second 90-degree RF pulse at a center of the mth echo, such that magnetization of the imaging object is oriented in the direction of the uniform polarizing magnetic field.
17. The process of claim 1 , wherein the diagnostic information is imaging data.
18. The process of claim 17 , further comprising providing the diagnostic information to a presentation device such that a visual image corresponding to the imaging object can be viewed by an operator.
19. The process of claim 1 , wherein the imaging object is a human being, and the uniform polarizing magnetic field is produced by a magnetic resonance imaging system, wherein the human being is oriented upright within the uniform polarizing magnetic field.