Metamaterial liners for high-field-strength traveling-wave magnetic resonance imaging

Patent metadata

Field	Value
Publication number	US-9529062-B2
Application number	US-201313757459-A
Country	US
Kind code	B2
Filing date	Feb 1, 2013
Priority date	Feb 3, 2012
Publication date	Dec 27, 2016
Grant date	Dec 27, 2016

Abstract

A liner for a bore of a waveguide is provided. The liner as an aperture passing through it and is formed of a metamaterial that has a relative electrical permittivity that is negative and near zero. When the liner is installed in the waveguide, it lowers the cutoff frequency of the waveguide while allowing the waveguide to remain hollow. This liner can be used in the bore of an MRI machine to lower the cutoff frequency of the bore of the MRI machine to allow the MRI machine to operate using waves having a lower frequency that if the liner was not used.

First claim

The invention claimed is:

1. A liner for a bore of an MRI machine comprising:
a body having an annular shape and formed of a metamaterial having a relative electrical permittivity that is negative and near zero,
wherein, when the body is provided in the bore, the metamaterial increases uniformity of electric and magnetic fields in the bore and lowers a cutoff frequency for propagating waves in the bore.

2. The liner of claim 1 wherein the relative electrical permittivity of the metamaterial forming the body is substantially −0.1.

3. The liner of claim 2 wherein the relative electrical permittivity of the metamaterial forming the body approaches ε MAX but is less than ε MAX , wherein

ɛ
MAX

=

1
-

b
2

/

a
2

1
+

b
2

/

a
2

,

and wherein a is the inner diameter of the liner and b is the outer diameter of the liner.

4. The liner of claim 3 wherein the relative electrical permittivity of the metamaterial forming the body is between 4.3465ε MAX and ε MAX .

5. The liner of claim 1 wherein the body has an outer diameter having a size that is substantially the same as an inner diameter of the bore of the MM machine.

6. The liner of claim 5 wherein the liner is sized to fit within the bore of the MRI machine and adjacent to an inside surface of the bore of the MM machine.

7. The liner of claim 1 wherein the metamaterial is a negative-refractive-index transmission-line (NRI-TL) metamaterial.

8. The liner of claim 7 wherein the liner is formed of stacks of planar NRI-TL metamaterial layers.

9. The liner of claim 8 wherein the stacks are oriented radially and arranged azimuthally in periodic fashion in the liner and each stack extends a length of the bore.

10. The liner of claim 1 wherein the thickness of the liner decreases a diameter of the bore of the MM machine by 10% or less.

11. The liner of claim 1 wherein the liner is sized to fit within the bore of the MRI machine and adjacent to an inside surface of the bore of the MM machine.

12. A liner for a bore of a waveguide comprising:
a body having an aperture defined therein and formed of a metamaterial having a relative electrical permittivity that is negative and near zero,
wherein, for propagating waves in the bore, the metamaterial decreases a cutoff frequency of the bore relative to the cutoff frequency of the bore without the liner.

13. The liner of claim 12 wherein the relative electrical permittivity of the metamaterial forming the body is substantially −0.1.

14. The liner of claim 12 wherein the relative electrical permittivity of the metamaterial forming the body approaches ε MAX but is less than ε MAX , wherein

ɛ
MAX

=

1
-

b
2

/

a
2

1
+

b
2

/

a
2

,

and wherein a is the inner diameter of the liner and b is the outer diameter of the liner.

15. The liner of claim 14 wherein the relative electrical permittivity of the metamaterial forming the body is between 4.3465ε MAX and ε MAX .

16. The liner of claim 12 wherein the body has an annular shape with an outer diameter having substantially the same size as an inner diameter of the bore of the waveguide.

17. A method of lowering the cutoff frequency of a waveguide having a bore to a reduced cutoff frequency, the method comprising:
selecting the reduced cutoff frequency for the waveguide, the reduced cut off frequency being less than the natural cutoff frequency of the waveguide;
selecting a size of a liner to be used in the bore of the waveguide, the liner formed of a metamaterial;
using the equation,

f
c

=

2
⁢
c

π
⁢

⁢
a

⁢

1
-

(

ɛ
TARGET

/

ɛ
MAX

)

1
-

3
⁢

(

ɛ
TARGET

/

ɛ
MAX

)

determining ε TARGET , wherein f c is the reduced cutoff frequency, a is the inner diameter of the liner and c is the speed of light in vacuum and ε MAX is determined using the equation,

ɛ
MAX

Assignees

• Univ Alberta
• Alberta Health Services

Inventors

• Iyer Ashwin
• Pollock Justin
• De Zanche Nicola

Classifications

• G01R33/4802 Primary

  Travelling-wave MR · CPC title

• Y10T29/49016

  Antenna or wave energy "plumbing" making · CPC title

• H01P11/00

  Apparatus or processes specially adapted for manufacturing waveguides or resonators, lines, or other devices of the waveguide type · CPC title

• G01R33/28 Primary

  Details of apparatus provided for in groups G01R33/44 - G01R33/64 · CPC title