Electronically controllable groups of artificially structured unit cells providing localized B1 magnetic fields for MRI and NMR devices

Patent metadata

Field	Value
Publication number	US-9897669-B2
Application number	US-201414334424-A
Country	US
Kind code	B2
Filing date	Jul 17, 2014
Priority date	Jul 17, 2014
Publication date	Feb 20, 2018
Grant date	Feb 20, 2018

Abstract

Described embodiments include a system, apparatus, and method. A system includes an array of at least two groups of at least two artificially structured electromagnetic unit cells. Each group includes a controllable amplifier responsive to a B 1 localization control signal and configured to amplify a received pulse of radiofrequency electromagnetic waves. Each group includes an electromagnetic wave conducting structure configured to deliver an amplified pulse of radiofrequency electromagnetic waves to the at least two artificially structured electromagnetic unit cells. The at least two artificially structured electromagnetic unit cells are configured to transform the incident amplified pulse into a pulse of radiofrequency magnetic field B 1 orientated transverse to a segment of the z-axis. A control circuit selects an arbitrary examination segment transverse to the z-axis responsive to data indicative of a transverse slice selected for examination, and generates the B 1 localization control signal defining an amplification state assigned to each group.

First claim

What is claimed is:

1. A system comprising:
at least two groups of at least two artificially structured sub-wavelength electromagnetic unit cells, each group of the at least two groups configured to be sequentially positioned in a respective plane transverse to a z-axis of a bore of a magnetic resonant imaging or a nuclear magnetic resonant device,
each group of at least two groups includes an electronically controllable radiofrequency amplifier switchable between an off-state and an on-state in response to a received B 1 localization control signal, and configured in the on-state to amplify a received pulse of radiofrequency electromagnetic waves,
each group of at least two groups includes a respective radiofrequency electromagnetic wave conducting structure configured to deliver an amplified pulse of radiofrequency electromagnetic waves to the at least two artificially structured sub-wavelength electromagnetic unit cells of the group as an incident amplified pulse of radiofrequency electromagnetic waves,
the at least two artificially structured sub-wavelength electromagnetic unit cells of each group respectively configured to transform the incident amplified pulse of radiofrequency electromagnetic waves into a pulse of radiofrequency magnetic field B 1 orientated transverse to a segment of the z-axis (hereafter “transverse segment”) and spatially proximate to the group; and
a control circuit configured to select an arbitrary examination segment transverse to the z-axis in response to data indicative of a transverse slice selected for examination, and to generate the B 1 localization control signal defining an amplification state assigned to each group of the at least two groups, the amplification states collectively defining a pulse of radiofrequency magnetic field B 1 localized to the selected arbitrary examination segment and having a magnetic field intensity sufficient to excite a detectable magnetic resonance in magnetically active nuclei located within the selected arbitrary examination segment.

2. The system of claim 1 , wherein each radiofrequency amplifier of each group of the at least two groups is electronically switchable between an on-state and off-state.

3. The system of claim 1 , wherein each radiofrequency amplifier of each group of the at least two groups includes an electronically controllable variable gain amplifier.

4. The system of claim 3 , wherein the B 1 control signal includes an amplification parameter assigned to a group of the at least two groups.

5. The system of claim 1 , wherein each group of the at least two groups includes an electronically controllable radiofrequency amplifier and an electronically controllable phase shifter or variable phase delay lines.

6. The system of claim 1 , wherein the pulse of radiofrequency electromagnetic waves is received from a radiofrequency signal generator or synthesizer component of the magnetic resonant imaging or a nuclear magnetic resonant device.

7. The system of claim 1 , wherein the data includes data indicative of a location along the z-axis of the transverse slice selected for examination.

8. The system of claim 1 , wherein the defined pulse of radiofrequency magnetic field B 1 localized to the selected arbitrary examination segment includes a magnetic field intensity sufficient to excite a detectable magnetic resonance in magnetically active nuclei located within the selected arbitrary examination segment.

9. The system of claim 1 , wherein the localized pulse of the radiofrequency magnetic field B 1 includes a first electric field intensity in the selected arbitrary examination segment and includes a second electric field intensity in another arbitrary transverse segment of the examination region, the second electric field intensity less than the first electric field intensity.

10. The system of claim 9 , wherein the other arbitrary transverse segment abuts the selected arbitrary examination segment.

11. The system of claim 1 , wherein the localized pulse of the radiofrequency magnetic field B 1 includes (i) a first radiofrequency electric field intensity in the selected arbitrary examination segment, (ii) a second radiofrequency electric field intensity in a second arbitrary transverse segment of the examination region abutting the selected arbitrary transverse segment, and (iii) a third radiofrequency electric field intensity in a third arbitrary transverse segment of the examination region abutting the selected arbitrary transverse segment and positioned opposite to the second arbitrary transverse segment, the second and third radiofrequency electric field intensities each less than the first radiofrequency electric field intensity.

12. The system of claim 1 , wherein the localized pulse of the radiofrequency magnetic field B 1 is configured to produce a first specific absorption rate (SAR) in the selected arbitrary examination segment and to produce a second SAR in another arbitrary transverse segment of the examination region, the second SAR less than the first SAR.

13. The system of claim 1 , wherein the amplification state includes an on-state or an off-state.

14. The system of claim 1 , wherein the amplification state includes an off-state for at least one of the two groups.

15. The system of claim 1 , wherein the B 1 localization control signal defines an amplification state and an amplification parameter assigned to each group of the at least two groups.

16. The system of claim 15 , wherein the amplification parameter includes an amplitude or a phase assigned to each group of the at least two groups.

17. The system of claim 1 , wherein the B 1 localization control signal defines a respective power distribution and phase delays (including zero and non-zero phase delays) of a particular incident pulse of radiofrequency electromagnetic waves to each group of the at least two groups.

18. The system of claim 1 , wherein the control circuit includes a control circuit configured to (i) select an arbitrary examination segment transverse to the z-axis responsive to data indicative of a transverse slice selected for examination, (ii) select at least one group of the at least two groups to deliver a localized pulse of radiofrequency magnetic field B 1 to the selected arbitrary examination segment, (iii) define a pulse of radiofrequency magnetic field B 1 localized to the selected arbitrary examination segment and having a magnetic field intensity sufficient to excite a detectable magnetic resonance in magnetically active nuclei located within the selected arbitrary segment, and in response thereto (iv) generate the B 1 localization control signal defining an amplification state assigned to each group of the at least two groups.

19. The system of claim 18 , wherein the (iii) define includes define an optimized pulse of radiofrequency magnetic field Bilocalized to the selected arbitrary examination segment.

20. The system of claim 1 , wherein a first group of the at least two groups includes at least two artificially structured sub-wavelength electromagnetic unit cells configured to generate a magnetic field-dominant radiofrequency near-field with magnetic and electric field intensities with (B 1 c)/E 1 >1, and a second group of the at least two groups includes at least two artificially structured sub-wavelength electromagnetic unit cells configured to generate an electric field E counteracting a non-vanishing electric field component generated by the first group of artificially structured sub-wavelength electromagnetic unit cells.

Assignees

• Elwha Llc

Inventors

• Driscoll Tom
• Smith David R
• Urzhumov Yaroslav A

Classifications

• G01R33/36

  Electrical details, e.g. matching or coupling of the coil to the receiver · CPC title

• G01R33/3621

  NMR receivers or demodulators, e.g. preamplifiers, means for frequency modulation of the MR signal using a digital down converter, means for analog to digital conversion [ADC] or for filtering or processing of the MR signal such as bandpass filtering, resampling, decimation or interpolation · CPC title

• G01R33/3415

  comprising arrays of sub-coils {, i.e. phased-array coils with flexible receiver channels} · CPC title

• G01R33/345

  of waveguide type (G01R33/343 takes precedence) · CPC title

• G01R33/3607 Primary

  RF waveform generators, e.g. frequency generators, amplitude-, frequency- or phase modulators or shifters, pulse programmers, digital to analog converters for the RF signal, means for filtering or attenuating of the RF signal · CPC title