B1 field-based regulation within a sequence for NMR
A B1 magnetic field may be regulated during a magnetic resonance tomography (MRT) imaging sequence.
1. A system comprising:
a magnetic resonance tomography (MRT) system configured to regulate a B1 magnetic field during an imaging sequence;
a measuring device configured to:
measure a reference variable during a reference pulse transmitted before one or more calibration pulses transmitted before or during at least one sequence segment of the imaging sequence, the reference variable representing at least an amount of a B1 magnetic field caused by the reference pulse, and
measure a calibration pulse variable during the one or more calibration pulses, the calibration pulse variable representing at least an amount of a B1 magnetic field caused by the one or more calibration pulses; and
a controller configured to regulate a voltage, a flip angle, or the voltage and the flip angle of high-frequency (HF) pulses of the imaging sequence following the calibration pulse using a ratio of the reference variable to the calibration pulse variable measured during the one or more calibration pulses.
2. The system as claimed in claim 1 , wherein the MRT system comprises one or more magnetic field probes configured to measure the reference variable representing at least the amount of the B1 magnetic field caused by the reference pulse, the calibration pulse variable representing at least the amount of the B1 magnetic field caused by the one or more calibration pulses, or the reference variable representing at least the amount of the B1 magnetic field caused by the reference pulse and the calibration pulse variable representing at least the amount of the B1 magnetic field caused by the one or more calibration pulses.
3. The system as claimed in claim 2 , wherein the one or more magnetic field probes comprise a plurality of pickup probes.
4. The system as claimed in claim 2 , wherein the MRT system comprises one or more voltage, current, or voltage and current measurement devices connected between a high-frequency (HF) transmit device and an HF transmit antenna, the one or more voltage, current, or voltage and current measurement devices configured to measure the reference variable representing at least the amount of the B1 magnetic field caused by the reference pulse, the calibration pulse variable representing at least the amount of the B1 magnetic field caused by the one or more calibration pulses, or the reference variable representing at least the amount of the B1 magnetic field caused by the reference pulse and the calibration pulse variable representing at least the amount of the B1 magnetic field caused by the one or more calibration pulses.
5. The system as claimed in claim 1 , wherein the measuring device comprises at least one direction coupler.
6. The system as claimed in claim 1 , wherein the MRT system is configured to measure at least one voltage value as the calibration pulse variable and is configured to measure at least one voltage value as the reference variable.
7. A method for magnetic resonance tomography (MRT) imaging, the method comprising:
regulating a B1 magnetic field within an imaging sequence;
measuring a reference variable during a reference pulse transmitted before one or more calibration pulses transmitted before or during at least one sequence segment of the imaging sequence, the reference variable representing at least an amount of a B1 magnetic field caused by the reference pulse;
measuring a calibration pulse variable during the transmission of the one or more calibration pulses, the calibration pulse variable representing at least an amount of a B1 magnetic field caused by the one or more calibration pulses; and
determining a ratio of the reference variable to the calibration pulse variable measured during the one or more calibration pulses,
wherein regulating the B1 magnetic field comprises generating high-frequency (HF) pulses of the imaging sequence, based on the determined ratio, following the transmission of the one or more calibration pulses.
8. The method as claimed in claim 7 , wherein regulating the B1 magnetic field further comprises measuring, via one or more magnetic field probes, the reference variable representing at least the amount of the B1 magnetic field caused by the reference pulse or the calibration pulse variable representing at least the amount of the B1 magnetic field caused by the one or more calibration pulses.
9. The method as claimed in claim 8 , wherein measuring the reference variable representing at least the amount of the B1 magnetic field caused by the reference pulse or the calibration pulse variable representing at least the amount of the B1 magnetic field caused by the one or more calibration pulses comprises measuring via a plurality of pickup probes.
10. The method as claimed in claim 7 , wherein regulating the B1 magnetic field further comprises measuring, via one or more voltage, current, or voltage and current measurement devices, the reference variable representing at least the amount of the B1 magnetic field caused by the reference pulse, the calibration pulse variable representing at least the amount of the B1 magnetic field caused by the one or more calibration pulses, or the reference variable representing at least the amount of the B1 magnetic field caused by the reference pulse and the calibration variable variable representing at least the amount of the B1 magnetic field caused by the one or more calibration pulses, the one or more voltage, current, or voltage and current measurement devices being connected between a high-frequency (HF) transmit device and a HF transmit antenna.
11. The method as claimed in claim 7 , wherein regulating the B1 magnetic field comprises:
measuring at least one voltage value as the calibration pulse variable; and
measuring at least one voltage value as the reference variable.