Establishing changes in a B0 field from reflected waves

Patent metadata

Field	Value
Publication number	US-11357418-B2
Application number	US-201816171932-A
Country	US
Kind code	B2
Filing date	Oct 26, 2018
Priority date	Oct 27, 2017
Publication date	Jun 14, 2022
Grant date	Jun 14, 2022

Abstract

A control device establishes a change in a main magnetic field expected for a respective time instant and based on the established expected change in the main magnetic field, correctively adjusts the main magnetic field and/or a nominal receive frequency of the RF receive coil and/or a transmit frequency for subsequent RF transmit pulses and/or takes the expected change in the main magnetic field into account in the evaluation of the received MR signals. At least for some of the RF transmit pulses, the control device acquires, via a sensor device, a portion of the respective radiofrequency wave supplied to the RF transmit coil. The controller extracts therefrom an oscillation corresponding to a respiratory motion of the patient and based on the variation with time of the extracted oscillation, establishes the change in the main magnetic field expected for the respective time instant.

First claim

The invention claimed is:

1. An operating method for a magnetic resonance system comprising a main magnet configured to generate a main magnetic field that is static with respect to time and substantially homogeneous with respect to space in an examination zone of the magnetic resonance system, the operating method comprising:
exciting a patient located in the examination zone into emitting magnetic resonance signals, wherein the exciting of the patient comprises supplying, by a controller of the magnetic resonance system, a plurality of radiofrequency waves to a radiofrequency transmit coil, such that the radiofrequency transmit coil applies radiofrequency transmit pulses to the patient;
receiving, by a radiofrequency receive coil, the magnetic resonance signals emitted by the patient and supplying the magnetic resonance signals received by the radiofrequency receive coil to the controller;
evaluating, by the controller, the magnetic resonance signals supplied to the controller;
compensating for an effect of a change in the main magnetic field varying with a respiratory motion of the patient, wherein the compensating for the effect of the change in the main magnetic field comprises establishing, by the controller, a change in the main magnetic field expected for a respective time instant and, based on the change in the main magnetic field expected for the respective time instant, correctively adjusting the main magnetic field, correctively adjusting a nominal receive frequency of the radiofrequency receive coil, correctively adjusting a transmit frequency for subsequent radiofrequency transmit pulses, taking the change expected for the respective time instant in the main magnetic field into account in evaluating the magnetic resonance signals supplied to the controller, or any combination thereof;
acquiring, by the controller, via a sensor device, a portion of a respective radiofrequency wave of the plurality of radiofrequency waves supplied to the radiofrequency transmit coil for at least some of the radiofrequency transmit pulses, the portion of the respective radiofrequency wave being reflected by the radiofrequency transmit coil; and
extracting, by the controller, an oscillation corresponding to the respiratory motion of the patient from the portions of the respective radiofrequency waves reflected by the radiofrequency transmit coil,
wherein establishing the change in the main magnetic field expected for the respective time instant comprises establishing, by the controller, the change in the main magnetic field expected for the respective time instant based on a variation with time of the oscillation corresponding to the respiratory motion of the patient.

2. The operating method of claim 1 , wherein establishing the change in the main magnetic field expected for the respective time instant comprises establishing, by the controller, the change expected for the respective time instant in the main magnetic field based on the variation with time of the oscillation corresponding to the respiratory motion of the patient in conjunction with a function already predefined before the patient is arranged in the examination zone, the function placing the change expected for the respective time instant in the main magnetic field in relation to a current elongation of the oscillation.

3. The operating method of claim 1 , further comprising initially performing, by the controller, test measurements once the patient has been arranged in the examination zone, wherein initially performing the test measurements comprises:
supplying a radiofrequency wave to the radiofrequency transmit coil in each case, such that a radiofrequency sample pulse is applied to the radiofrequency transmit coil in each case;
acquiring in each case during the radiofrequency sample pulses, via the sensor device, a portion of the respective radiofrequency wave supplied to the radiofrequency transmit coil, the portion of the respective radiofrequency wave being reflected by the radiofrequency transmit coil;
additionally acquiring, via a further sensor device, a measured variable that is different from the portion reflected by the radiofrequency transmit coil and is characteristic of the change in the main magnetic field during the radiofrequency sample pulses;
establishing, by the controller, the change in the main magnetic field during the radiofrequency sample pulses based on the measured variable that is different from the portion reflected by the radiofrequency transmit coil;
determining, by the controller, a function that places the change expected for the respective time instant in the main magnetic field in relation to a current elongation of the oscillation based on the portions reflected by the radiofrequency transmit coil during the radiofrequency sample pulses and the change in the main magnetic field; and
establishing, by the controller, the change expected for the respective time instant in the main magnetic field based on the variation with time of the oscillation in conjunction with the function determined by the controller.

4. The operating method of claim 1 , wherein establishing the change in the main magnetic field expected for the respective time instant comprises establishing, by the controller, the change expected for the respective time instant in the main magnetic field within the examination zone in a spatially resolved manner.

5. In a non-transitory computer-readable storage medium that stores instructions executable by a controller of a magnetic resonance system to operate the magnetic resonance system, the magnetic resonance system comprising a main magnet configured to generate a main magnetic field that is static with respect to time and substantially homogeneous with respect to space in an examination zone of the magnetic resonance system, the instructions comprising:
exciting a patient located in the examination zone into emitting magnetic resonance signals, wherein the exciting of the patient comprises supplying, by a controller of the magnetic resonance system, a plurality of radiofrequency waves to a radiofrequency transmit coil, such that the radiofrequency transmit coil applies radiofrequency transmit pulses to the patient;
receiving, by a radiofrequency receive coil, the magnetic resonance signals and supplying the magnetic resonance signals received by the radiofrequency receive coil to the controller;
evaluating, by the controller, the magnetic resonance signals supplied to the controller;
compensating for an effect of a change in the main magnetic field varying with a respiratory motion of the patient, wherein the compensating for the effect of the change in the main magnetic field comprises establishing, by the controller, a change in the main magnetic field expected for a respective time instant and based on the change expected for the respective time instant in the main magnetic field, correctively adjusting the main magnetic field, correctively adjusting a nominal receive frequency of the radiofrequency receive coil, correctively adjusting a transmit frequency for subsequent radiofrequency transmit pulses, taking the change expected for the respective time instant in the main magnetic field into account in evaluating the magnetic resonance signals supplied to the controller, or any combination thereof;
acquiring, by the controller, via a sensor device, a portion of a respective radiofrequency wave of the plurality of radiofrequency waves supplied to the radiofrequency transmit coil for at least some of the radiofrequency transmit pulses, the portion of the respective radiofrequency wave being reflected by the radiofrequency transmit coil; and
extracting, by the controller, an oscillation corresponding to the respiratory motion of the patient from the portions of the respective radiofrequency waves reflected by

Assignees

• Siemens Healthcare Gmbh

Inventors

• Bildhauer Petra
• Carinci Flavio
• Köhler Michael

Classifications

• A61B5/704

  Tables · CPC title

• A61B5/055 Primary

  involving electronic [EMR] or nuclear [NMR] magnetic resonance, e.g. magnetic resonance imaging · CPC title

• G01R33/56509 Primary

  due to motion, displacement or flow, e.g. gradient moment nulling (G01R33/567 takes precedence) · CPC title

• A61B5/113

  occurring during breathing · CPC title

• A61B5/7285

  for synchronizing or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal · CPC title