Magnetic resonance imaging system with a rotatable magnet

1. A magnetic resonance imaging (MRI) system comprising:

an image acquisition region;

a radiofrequency system including at least one radiofrequency antenna, the radiofrequency system being configured to emit a radiofrequency excitation pulse into the image acquisition region and receive magnetic resonance signals from the image acquisition region; and

a magnetic field generator that includes:

at least one magnet configured to generate a magnetic field in the image acquisition region;

a magnet holder configured to carry the at least one magnet; and

a rotation system configured to position the magnet holder along a rotation trajectory.

2. The MRI system according to claim 1 , wherein the at least one magnet is configured to generate an inhomogeneous magnetic field in the image acquisition region, the inhomogeneous magnetic field including a magnetic field gradient along a radial direction of the rotation trajectory.

3. The MRI system according to claim 2 , further comprising a controller configured to perform a spatial encoding of magnetic resonance signals acquired from the image acquisition region based on the magnetic field gradient along the radial direction of the rotation trajectory.

4. The MRI system according to claim 1 , wherein the rotation system comprises a mechanical guiding rail configured to guide the magnet holder along the rotation trajectory around a rotation center.

5. The MRI system according to claim 1 , wherein the rotation trajectory comprises a rotation angle in the range of 120° to 270°.

6. The MRI system according to claim 1 , wherein the magnetic field generator comprises:

a first magnet of the at least one magnet configured to generate a first magnetic field inside the image acquisition region; and

a second magnet of the at least one magnet configured to generate a second magnetic field inside the image acquisition region.

7. The MRI system according to claim 6 , wherein the rotation system is configured to:

move the first magnet from a first end position on the rotation trajectory to a predefined position on the rotation trajectory; and

move the second magnet from the predefined position to a second end position on the rotation trajectory.

8. The MRI system according to claim 1 , wherein the magnetic field generator comprises a magnetic field gradient system including at least one gradient coil configured to provide a magnetic gradient field in the image acquisition region, the at least one gradient coil being carried by the magnet holder.

9. The MRI system according to claim 4 , wherein:

the magnetic field generator comprises a magnetic field gradient system including at least one gradient coil configured to provide a magnetic gradient field in the image acquisition region; and

the rotation system comprises a gradient coil holder configured to carry the at least one gradient coil, the mechanical guiding rail being configured to guide the gradient coil holder along the rotation trajectory.

10. The MRI system according to claim 8 , wherein the magnetic gradient field generated by the at least one magnet is oriented at an angle of at least 50° to the magnetic gradient field generated by the at least one gradient coil.

11. The MRI system according to claim 8 , further comprising a controller configured to perform spatial encoding of magnetic resonance signals acquired from the image acquisition region based on a change of the magnetic field induced by the positioning of the at least one magnet along the rotation trajectory and the magnetic gradient field of the at least one gradient coil.

12. The MRI system according to claim 1 , wherein:

a contour of the rotation trajectory corresponds to a contour of a body region of a patient; and

the rotation system is configured to position the magnet holder along the contour of the body region of the patient.

13. The MRI system according to claim 12 , wherein the contour of the rotation trajectory corresponds to a contour of a jaw region of the patient, the magnetic resonance imaging system being configured to acquire magnetic resonance signals of a tooth and/or a jaw of the patient.

14. The MRI system according to claim 12 , wherein the magnetic field generator comprises an adjustment mechanism configured to adjust a position, a shape, and/or an orientation of the rotation system to accommodate for a geometry of the body region of the patient.

15. The MRI system according to claim 12 , wherein the magnetic field generator further comprises a distance adapter configured to adjust a spacing between the magnet holder and a surface of the patient.

16. The MRI system according to claim 15 , wherein the distance adapter comprises a sensor configured to determine a distance value between the magnet holder and the surface of the patient, the distance adapter being configured to adjust a spacing between the magnet holder and the surface of the patient based on the distance value.

17. The MRI system according to claim 15 , wherein:

the radiofrequency system is configured to acquire magnetic resonance navigator data from the image acquisition region;

the MRI system further comprises a controller configured to determine a distance value between the magnet holder and the surface of the patient based on the magnetic resonance navigator data; and

the distance adapter is configured to adjust a spacing between the magnet holder and the surface of the patient based on the distance value.

18. The MRI system according to claim 6 , wherein:

the first magnet is configured to generate a pulsed first magnetic field and the second magnet is configured to generate a homogenous second magnetic field, and

the magnetic resonance imaging system further comprises a controller configured to:

control the first magnet to generate the pulsed first magnetic field to pre-polarize nuclear spins inside an imaging volume and switch off the first magnet when the second magnet is switched on; and

control the second magnet to generate the homogeneous second magnetic field inside the imaging volume during a radiofrequency excitation of the pre-polarized spins and during an acquisition of magnetic resonance signals from the imaging volume.