Magnetic resonance imaging apparatus and apparatus for measuring radio frequency output for the same
An apparatus for measuring radio frequency output for a magnetic resonance imaging apparatus includes a plurality of directional couplers, a comparator, a switcher and a converter. The plurality of directional couplers are different in degree of coupling from each other, and attenuate an RF signal which is generated in an RF signal generator and amplified in an RF power amplifier. The comparator compares input-level information of a signal inputted into the RF power amplifier with a threshold value. The switcher switches to any one of the plurality of the directional couplers based on a result of the comparison so as to output an RF signal by the one directional coupler. The converter performs a digital conversion of the RF signal from the one directional coupler so as to output a digital signal.
1. An apparatus for measuring radio frequency output for a magnetic resonance imaging apparatus, comprising:
a plurality of directional couplers different in degree of coupling from each other, and configured to attenuate a radio frequency signal which is generated in a radio frequency signal generator and amplified in a radio frequency power amplifier;
a comparator configured to compare input-level information of a signal inputted into the radio frequency power amplifier with a threshold value;
a switcher configured to switch to any one of the plurality of the directional couplers based on a result of the comparison so as to output a radio frequency signal by the one directional coupler; and
a converter configured to perform a digital conversion of the radio frequency signal from the one directional coupler so as to output a digital signal.
2. A magnetic resonance imaging apparatus, comprising:
a static magnetic field magnet configured to generate a static magnetic field;
a gradient coil configured to generate a gradient magnetic field where intensity of a magnetic field varies,
a transmission coil which is a radio frequency coil configured to generate a radio frequency magnetic field;
a radio frequency power amplifier configured to amplify a radio frequency signal generated in a radio frequency signal generator and to provide the amplified radio frequency signal to the transmission coil;
a plurality of directional couplers different in degree of coupling from each other, and configured to attenuate the radio frequency signal amplified in the radio frequency power amplifier;
a comparator configured to compare input-level information of the signal inputted into the radio frequency power amplifier with a threshold value;
a switcher configured to switch to any one of the plurality of the directional couplers based on a result of the comparison so as to output a radio frequency signal by the one directional coupler;
a converter configured to perform a digital conversion of the radio frequency signal from the one directional coupler so as to output a digital signal; and
a calculator configured to calculate a specific absorbed fraction based on the radio frequency signal outputted from the converter.
3. The magnetic resonance imaging apparatus according to claim 2 , wherein
the input-level information is predicted based on a radio frequency level which is a radio frequency signal output in a case of an excitation pulse having a flip angle used as a reference.
4. The magnetic resonance imaging apparatus according to claim 3 , wherein
the radio frequency level is measured in each object and in each imaging region.
5. The magnetic resonance imaging apparatus according to claim 3 , wherein
the input-level information is set for each radio frequency pulse included in a pulse sequence based on the radio frequency level.
6. The magnetic resonance imaging apparatus according to claim 5 , wherein
the radio frequency pulse included in the pulse sequence includes a pre-pulse and an excitation pulse.