MRI-compatible magnet apparatus and associated methods

1. A magnet apparatus, comprising:

a case defining a central axis;

a magnet frame within the case and rotatable about the central axis of the case; and

a plurality of elongate diametrically magnetized magnets that are located in the magnet frame, the magnets each defining a respective longitudinal axis that is perpendicular to the central axis, a respective N-S direction that is perpendicular to the longitudinal axis, and a respective N-S rotational orientation, the magnets each being freely rotatable about its respective longitudinal axis relative to the magnet frame, and the magnets being configured to be magnetically attracted to one another in a manner that, absent the presence of a dominant magnetic field and in the presence of a headpiece magnet, the N-S rotational orientation of the magnets is perpendicular to the central axis of the case.

2. A magnet apparatus as claimed in claim 1 , wherein

the magnets each define a length in the direction of the longitudinal axis, a thickness, and a width; and

the length is greater than the width and the thickness.

3. A magnet apparatus as claimed in claim 2 , wherein

the width is greater than the thickness.

4. A magnet apparatus as claimed in claim 3 , wherein

the width extends in the N-S direction.

5. A magnet apparatus as claimed in claim 2 , wherein

the magnets each define a cross-section, including first and second curved surfaces that are connected to one another by first and second flat surfaces, in a plane perpendicular to the longitudinal axis;

the curved surfaces are separated from one another in the N-S direction; and

the flat surfaces are separated from one another in a direction perpendicular to the N-S direction.

6. A magnet apparatus as claimed in claim 2 , wherein

the magnet frame defines a thickness; and

the thickness of the magnets is less than the thickness of the magnet frame.

7. A magnet apparatus as claimed in claim 6 , wherein

the magnet frame includes a plurality of magnet recesses, defining recess lengths and recess widths, in which the plurality of magnets are located;

the magnet recess lengths are substantially equal to the magnet lengths; and

the magnet recess widths are substantially equal to the magnet widths.

8. A magnet apparatus as claimed in claim 2 , wherein

at least one of the magnets is longer than an adjacent magnet.

9. A magnet apparatus as claimed in claim 1 , wherein

the magnets each define a non-circular cross-section in a plane perpendicular to the longitudinal axis.

10. A magnet apparatus as claimed in claim 1 , wherein

the longitudinal axes of the magnets are parallel to one another.

11. A magnet apparatus as claimed in claim 1 , further comprising:

lubricious material between the case and the magnet frame.

12. A magnet apparatus as claimed in claim 1 , further comprising:

lubricious material between the magnets and the magnet frame.

13. A magnet apparatus as claimed in claim 1 , wherein

the magnets are located within respective tubes formed from lubricious material.

14. A magnet apparatus in claim 1 , wherein

the magnet frame includes a single magnet recess in which all of the plurality of magnets are located with no portion of the magnet frame located between adjacent magnets.

15. A magnet apparatus as claimed in claim 14 , wherein

the single magnet recess includes a first portion and second and third portions that are shorter than the first portion.

16. A magnet apparatus as claimed in claim 1 , wherein

the magnet frame includes a lubricious outer layer.

17. A magnet apparatus as claimed in claim 16 , wherein

the case defines an inner surface that does not include a lubricious layer.

18. A magnet apparatus as claimed in claim 16 , wherein

the magnets define respective outer surfaces; and

at least a portion of the outer surfaces of the magnets is covered by lubricious material.

19. A magnet apparatus, comprising:

a case defining a central axis;

a magnet frame within the case and rotatable about the central axis of the case;

a plurality of elongate diametrically magnetized perpendicular magnets that are located in the magnet frame, the perpendicular magnets each defining a respective longitudinal axis that is perpendicular to the central axis, a respective N-S direction that is perpendicular to the longitudinal axis, and a respective N-S rotational orientation, the perpendicular magnets each being freely rotatable about its respective longitudinal axis relative to the magnet frame; and

a plurality of elongate diametrically magnetized non-perpendicular magnets that are located in the magnet frame, the non-perpendicular magnets each defining a respective longitudinal axis that is not perpendicular to the central axis, a respective N-S direction that is perpendicular to the longitudinal axis, and a respective N-S rotational orientation, the non-perpendicular magnets each being freely rotatable about its respective longitudinal axis relative to the magnet frame;

the perpendicular magnets and non-perpendicular magnets being configured to be magnetically attracted to one another in a manner that, absent the presence of a dominant magnetic field and in the presence of a headpiece magnet, the N-S rotational orientation of the perpendicular magnets and non-perpendicular magnets is perpendicular to the central axis of the case.

20. A magnet apparatus as claimed in claim 19 , wherein

two non-perpendicular magnets include longitudinal ends and are positioned end-to-end with adjacent ends near the central axis; and

the adjacent ends are connected to one another with a connector that is configured to prevent rotation of the two non-perpendicular magnets about their respective longitudinal axes relative to the connector in the absence of an MRI magnetic field and to permit rotation of the two non-perpendicular magnets about their respective longitudinal axes relative to the connector in the presence of an MRI magnetic field.

21. A magnet apparatus as claimed in claim 19 , wherein

the longitudinal axis of one or more of the non-perpendicular magnets is offset from perpendicular to the central axis by 5 degrees or less.