Magnetic field sensor, method for operating the said magnetic field sensor and method and system for compensation magnetic noise caused by environmental noise

Patent metadata

Field	Value
Publication number	US-11204407-B2
Application number	US-202016779894-A
Country	US
Kind code	B2
Filing date	Feb 3, 2020
Priority date	Feb 4, 2019
Publication date	Dec 21, 2021
Grant date	Dec 21, 2021

Abstract

Magnetic field sensor, in particular for measuring magnetic noise fields caused by environmental magnetic noise in combination with MRI apparatus, the magnetic field sensor being further provided with field compensation coils assembly and with a compensation circuit driving the field compensation coils assembly to generate a magnetic field compensating the static magnetic field dissipating outside from the static magnetic field generator or from the gantry of the MRI apparatus at the position of the magnetic sensor. A method for operating the magnetic field sensor and a method and a system for compensation magnetic noise caused by environmental noise are also provided. An MRI apparatus is also disclosed comprising such a system and carrying out such a method for compensating magnetic noise fields.

First claim

The invention claimed is:

1. A magnetic field sensor for measuring magnetic noise fields caused by environmental magnetic noise in combination with an MRI apparatus, the said magnetic field sensor comprising:
a first field compensation coil assembly,
a second field compensation coil assembly, and
a compensation circuit configured to drive the said field compensation coil assemblies to generate a magnetic field compensating a static magnetic field dissipating outside from a static magnetic field generator or from a gantry of the MRI apparatus at a position of the magnetic field sensor,
wherein the first field compensation coil assembly is configured to carry out a raw compensation of the effects of the static magnetic field at the position of the sensor and the second compensation coil assembly is configured to carry out a fine compensation of the effects of the static magnetic fields at the position of the sensor,
each of the field compensation coil assemblies being driven by a respective compensation circuit, the respective compensation circuits being tuned respectively for causing a raw and a fine compensation of the effects of the static magnetic field at the sensor position.

2. Magnetic field sensor according to claim 1 in which the said magnetic sensor is a resistive sensor.

3. Magnetic field sensor according to claim 1 , in which the compensation circuits driving the compensation coils assembly is provided in combination with a static magnetic field sensor measuring the strength of the static magnetic field dissipating outside the static magnetic field generator or from the gantry of the MRI apparatus at the position of the magnetic sensor for the magnetic noise fields.

4. Magnetic field sensor according to claim 1 , in which both compensation circuits for respectively raw and fine compensation of the static magnetic field are connected to one or more common static magnetic field sensors or each of the said compensation circuits may be connected to at least some dedicated static magnetic field sensors.

5. A method for measuring a magnetic noise field in a presence of a static magnetic field having a strength saturating at least partially a magnetic noise field sensor, the method comprising:
placing a magnetic noise field sensor configured for measuring the magnetic noise field at a predetermined position;
measuring a strength of the static magnetic field at the predetermined position of the magnetic noise field sensor with a second sensor;
generating a magnetic compensation field of the magnetic static field at the predetermined position of the magnetic noise field sensor as a function of the measured strength of the static magnetic field;
the magnetic noise field sensor being placed in the compensation field, and
measuring the magnetic noise field by the magnetic noise field sensor placed inside the compensation field.

6. Method according to claim 5 , wherein there is provided at least one static magnetic field sensor and at least one compensation coils assembly generating a compensation field at the position of the magnetic noise field sensor.

7. Method according to claim 5 , in which the step of compensating the static magnetic field at the magnetic noise field sensor comprises a first step of a raw compensation and a second step of a fine compensation, two compensation coils assembly being provided.

8. Method according to claim 7 in which the raw and the fine compensation of the static magnetic field are carried out by generating a first raw and a further fine compensation field respectively as a function of the strength of the static magnetic field at the position of the magnetic noise field.

9. A method for compensating for magnetic noise fields in a spatial volume, the method comprising:
providing at least a magnetic noise field sensor at a certain position in space;
measuring a strength of a magnetic static field at the position of the at least one magnetic noise field sensor with a second sensor;
generating a magnetic compensation field of the static magnetic field as a function of the measured strength of the static magnetic field at the position of the magnetic noise field sensor;
the magnetic noise field sensor being placed in the magnetic compensation field;
measuring a strength or other characteristic parameters describing a magnetic noise field outside said spatial volume at least at one location surrounding said spatial volume;
determining by means of the measured characteristic parameters describing the magnetic noise field a compensation magnetic field to be generated outside the spatial volume and which permeates the space outside the spatial volume; and
determining, by means of the measured characteristic parameters describing the magnetic noise field a compensation magnetic field which permeates only the space inside the spatial volume.

10. Method according to claim 9 in which the step of generating a magnetic compensation field of the said static magnetic field as a function of the measured strength of the said static magnetic field at the position of the said magnetic noise field sensor comprises a first step of generating a compensation field for a raw compensation of the static magnetic field and a further step of generating a further compensation field for a fine compensation of the said static magnetic field.

11. Method according to claim 9 , in which the step of determining the compensation magnetic field which permeates only the space inside the spatial volume is carried out by:
calculating on a theoretical basis according to the laws of electromagnetism, or on an empirical basis, a correlation between the noise field outside the spatial volume and a corresponding noise field inside said spatial volume, or
calculating the noise field inside the spatial volume, from the measurement/s of the noise magnetic field outside the spatial volume; and
from the inside magnetic noise field, as determined theoretically or empirically, generating a magnetic compensation field, particularly for neutralizing the noise field in said spatial volume, said compensation magnetic field permeates the spatial volume.

12. A system for compensation magnetic noise caused by environmental noise applying the method according to claim 9 , the said system comprising:
at least a magnetic noise field sensor placed at a certain position in a space;
at least a static magnetic field sensor for measuring the strength of a static magnetic field at the position of the said at least one magnetic noise field sensor;
at least a compensation coils assembly for generating a compensation field of the static magnetic field at the position of the said magnetic noise field sensor;
a compensation circuit driving the said at least one compensation coils assembly and configured to generate a compensation field of the said static magnetic field at the position of the said magnetic noise field sensor, the said compensation field being determined as a function of the measured strength of the static magnetic field sensor the at least one static magnetic field sensor being connected to an input of the said compensation circuit;
an open loop magnetic noise field compensator comprising:
at least one magnetic noise compensation field generator generating a magnetic noise compensation field permeating the environment.

13. A system according to claim 12 , wherein it comprises a first compensation coils assembly and a second compensation coils assembly each one driven by a dedicated compensation circuit, the compensation circuit for the first compensation coils assembly being configured for generating a compensation field of raw compensation of the static f

Assignees

• Esaote Spa

Inventors

• Punzo Vincenzo
• Iaia Paolo
• Trequattrini Alessandro

Classifications

• G01R33/56563

  caused by a distortion of the main magnetic field B0, e.g. temporal variation of the magnitude or spatial inhomogeneity of B0 (G01R33/56509, G01R33/56518, G01R33/56536 take precedence) · CPC title

• G01R33/025

  Compensating stray fields {(G01R33/0017 takes precedence)} · CPC title

• G01R33/48

  NMR imaging systems · CPC title

• G01R33/387 Primary

  Compensation of inhomogeneities · CPC title

• G01R33/389 Primary

  Field stabilisation {, e.g. by field measurements and control means or indirectly by current stabilisation} · CPC title