Method and probe for compensating for magnetic noise fields in space volumes, particularly in magnetic resonance imaging apparatus

A magnetic resonance imaging apparatus comprising a cavity for accommodating a body under examination or a part thereof and means for generating a static field which permeates the cavity;

• a noise field compensation device inside the cavity wherein the body under examination or a part thereof is accommodated, and at least one probe for detecting the noise fields outside the cavity;
• means for determining the noise fields inside the cavity on the basis of external measurements by executing theoretically or empirically defined computation or correlation functions, means for generating compensation fields for compensating noise fields inside the cavity;
• wherein the means for generating a static field which permeates the cavity and the means for generating compensation fields for compensating noise fields inside the cavity are mounted rotatable together and for the same angular displacement;
• and the at least one probe assembly for detecting the noise fields outside the cavity is stationary and comprises two sensing elements each one being capable to measure the magnetic field along only one direction of measurement, the at least two sensing elements being oriented one with respect to the other so that the corresponding directions of measurements are oriented non parallel one with respect to the other, preferably orthogonally one with respect to the other.

A method for compensating in a space volume for a magnetic noise field outside the space volume, the method comprising:

• determining a strength of the magnetic noise field outside the space volume;
• defining, on a theoretical basis according to laws of electromagnetism, or on an empirical basis, a correlation between the noise field outside the space volume and a corresponding noise field inside the space volume, or calculating the noise field inside the space volume on the basis of the measurements of the magnetic field outside the space volume;
• from the inside magnetic field, as determined theoretically or empirically, generating a magnetic compensation field for neutralizing the noise field in the space volume;
• wherein the method includes the steps of generating, at least at some or at each of the noise field detection locations, a local magnetic field for at least partly compensating for the effect of the predetermined magnetic field in the space volume.