Method and device for monitoring radio-frequency exposure in a magnetic resonance measurement

A radio-frequency monitoring device for monitoring a physiologically effective radio-frequency exposure in a defined volume of an examination subject in a magnetic resonance data acquisition sequence in a magnetic resonance system, said magnetic resonance system comprising a radio-frequency antenna structure having a plurality of individually controllable radio-frequency signal channels that collectively generate a radio-frequency field distribution in an examination volume in which the examination subject is disposed in said sequence, each of said radio-frequency channels having a radio-frequency signal associated therewith selected from the group consisting of a radio-frequency signal emitted by that radio-frequency channel in said sequence and a radio-frequency signal to be emitted by that radio-frequency signal channel in said sequence, said radio-frequency monitoring device comprising:

• a detection arrangement that, for each of said radio-frequency signal channels, detects an amplitude value and a phase value of the radio-frequency signal associated therewith at a plurality of known acquisition points in time;
• and
• a processor that, for each of said known acquisition points in time for each of said radio-frequency signal channels, automatically determines respective local exposure values from the respective amplitude and phase values, the local exposure values respectively representing a physiological exposure caused by the radio-frequency signal at a known location in the examination volume, and that, for each of said radio-frequency signal channels, automatically forms exposure control values from the local exposure values, and that compares the respective exposure control values with respective predetermined exposure limit values, and that generates a control signal that alters at least one of said radio-frequency signals if an exposure limit value is met or exceeded.

A magnetic resonance system comprising:

• a magnetic resonance data acquisition unit configured to receive an examination subject in an examination volume therein;
• a system controller that operates said data acquisition unit to acquire magnetic resonance data from a defined volume of the examination subject in the examination volume of the data acquisition unit;
• said magnetic resonance data acquisition unit comprising a radio-frequency antenna structure having a plurality of individually controllable radio-frequency signal channels that collectively generate a radio-frequency field distribution in the examination volume in which the examination subject is disposed in said sequence, each of said radio-frequency channels having a radio-frequency signal associated therewith selected from the group consisting of a radio-frequency signal emitted by that radio-frequency channel in said sequence;
• and
• for each of said radio-frequency signal channels, detecting an amplitude value and a phase value of the radio-frequency signal associated therewith at a plurality of known acquisition points in time;
• for each of said known acquisitions points in time for each of said radio-frequency signal channels, automatically electronically determining respective local exposure values from the respective amplitude and phrase values, the local exposure values respectively representing a physiological exposure caused by the radio-frequency signal at a known location in the examination volume;
• for each of said radio-frequency signal channels, automatically electronically forming exposure control values from the local exposure values;
• comparing the respective exposure control values with respective predetermined exposure limit values;
• and
• generating a control signal that alters at least one of said radio-frequency signals if an exposure limit value is met or exceeded.