Radio frequency field localization for magnetic resonance
Technology for controlling non-uniformity in the B 1 field includes selecting the phase, magnitude, frequency, time, or spatial relationship among various elements of a multi-channel excitation coil in order to control the radio frequency (RF) power emanating from the coil antenna elements. Non-uniformity can be used to steer a constructively interfering B 1 field node to spatially correlate with an anatomic region of interest. A convex (quadratically constrained quadratic problem) formulation of the B 1 localization problem can be used to select parameters for exciting the coil. Localization can be used in simulated Finite Difference Time Domain B 1 field human head distributions and human head phantom measurement.
1. A system comprising:
a magnetic resonance coil having a plurality of individually controllable segments;
a multi-channel driver, each channel of the driver coupled to a segment in one to one relation;
a processor coupled to the driver and configured to control the coil; and
a set of instructions executable by the processor, the set of instructions configured to execute a convex optimization algorithm, and further configured to obtain at least one of a minimized specific absorption rate (SAR), a localized SAR, a particular signal to noise ratio, and a particular contrast criterion.
2. The system of claim 1 wherein the algorithm is executed over a selected region.
3. The system of claim 1 wherein the algorithm includes a closed loop feedback iterative procedure.
4. The system of claim 1 wherein the processor provides time varying modulation of phase and magnitude using a convex optimization procedure.
5. A system comprising:
a magnetic resonance coil having a plurality of individually controllable segments;
a multi-channel driver, each channel of the driver coupled to a segment in one to one relation;
a processor coupled to the driver and configured to control the coil; and
a set of instructions executable by the processor, the set of instructions configured to execute a convex optimization algorithm, and further configured to obtain at least one of a uniform B1 field distribution, a localized B1 field distribution, a masked B1 field distribution, and a custom B1 field distribution.
6. The system of claim 5 wherein the algorithm is executed over a selected region.
7. The system of claim 6 wherein the selected region includes a three-dimensional surface or volume.
8. The system of claim 1 wherein the algorithm includes a closed loop feedback iterative procedure.
9. The system of claim 1 wherein the processor provides time varying modulation of phase and magnitude using a convex optimization procedure.
10. A method comprising:
receiving a target field distribution for a transverse magnetic field within a coil for use in magnetic resonance imaging (MRI);
executing a convex optimization algorithm to determine a solution corresponding to the target field distribution; and
selecting a drive signal for a current element of the coil based on the solution.
11. The method of claim 10 wherein selecting the drive signal includes selecting at least one of a phase, a magnitude, and a frequency.
12. The method of claim 10 wherein receiving the target field distribution includes receiving at least one of a uniform distribution, a localized distribution, and a masked distribution.
13. The method of claim 10 wherein executing the convex optimization algorithm includes executing a program on a computer.
14. The method of claim 10 wherein executing the convex optimization algorithm includes minimizing a specific absorption rate (SAR).
15. The method of claim 10 wherein executing the convex optimization algorithm includes achieving a localized specific absorption rate (SAR).
16. The method of claim 10 wherein receiving the target field distribution includes receiving a distribution for a three-dimensional surface.
17. The method of claim 10 wherein receiving the target field distribution includes receiving a distribution for a volume.
18. The method of claim 10 further including iteratively repeating the executing and selecting.
19. The method of claim 10 wherein selecting the drive signal includes selecting a time varying signal.
20. The method of claim 10 wherein selecting the drive signal includes selecting a spatial position for the current element.